GFA Basic Sailplane Engineering, AIRW-M005

THE GLIDING FEDERATION OF AUSTRALIA INC(ABN 82 433 264 489)
C4/1-13 The Gateway, Broadmeadows Victoria 3047
Phone: (03) 9359 1613; Fax: (03) 9359 9865

GFA Basic Sailplane Engineering
PART 3
Airworthiness
UNCONTROLLED WHEN PRINTED
Revision 24.1
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GFA Basic Sailplane Engineering, AIRW-M005
REVISION RECORD
Prepared

Approved

VersionDate

VariousCAD

24.1

24/05/23

Précis of changes
Correction of minor errors throughout. Additions to Chapter 20 Electrical Systems and Chapter 11 Flutter.
Inclusion of Chapter 27 Radios, Antennae and Avionics and Chapter 28 L’Hottelier Connectors.
Mandatory policy of release springs moved to MOSP 3 Section 13.3 and 23.
VariousCAD

24

08/09/17

Précis of changes
Correction of minor errors throughout. Many chapters have been extensively updated. Mainly with a view
to incorporating AD and AN requirements and referencing MOSP 3 V7.
Sean Jorgensen-Day

Vice-President

23

10/4/16

Précis of changes
Create electronic version and modernisation of all sections to cover current practices.

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GFA Basic Sailplane Engineering, AIRW-M005
TABLE OF CONTENTREVISION RECORD ...................................................................................................... 2
TABLE OF CONTENT .................................................................................................... 3
1.

2.

3.

INTRODUCTION .................................................................................................. 23
1.1

ACKOWLEDGEMENT....................................................................................................... 23

1.2

AMENDMENTS TO THIS MANUAL .................................................................................. 23

1.3

PRIORITY OF PROCEDURES ......................................................................................... 23

1.4

DEFINITIONS .................................................................................................................... 24

1.5

DOCUMENT CHANGE PROPOSAL ................................................................................ 25

TERMINOLOGY ................................................................................................... 26
2.1

SAILPLANE COMPONENTS ............................................................................................ 26

2.2

SAILPLANE GEOMETRY ................................................................................................. 27

2.3

HORIZONTAL STABILISER. ............................................................................................ 27

2.4

WOODEN STRUCTURES. ............................................................................................... 28

2.5

METAL STRUCTURES. .................................................................................................... 31

2.6

FIBRE REINFORCED PLASTIC (FRP) CONSTRUCTION. ............................................. 32

2.7

STEEL TUBE CONSTRUCTION. ..................................................................................... 34

INSPECTIONS ..................................................................................................... 35
3.1

THE INSPECTION REGIME ............................................................................................. 35

3.2

SYSTEMIC AND HUMAN FACTORS ............................................................................... 36

3.2.1

CLUB STRUCTURE .......................................................................................................... 36

3.2.2

FINANCE ........................................................................................................................... 36

3.2.3

WORKLOAD ...................................................................................................................... 36

3.2.4

COMPETENCY OF HELPERS ......................................................................................... 36

3.2.5

INSPECTOR SUITABILITY ............................................................................................... 36

3.2.6

LACK OF TECHNICAL INFORMATION ........................................................................... 37

3.3

THE ANNUAL INSPECTION PROCESS .......................................................................... 37

3.3.1

PREPARATIONS .............................................................................................................. 37

3.3.1.1

DETERMINING WHEN TO CONDUCT THE INSPECTION ............................................. 37

3.3.1.2

LEVEL OF INSPECTION .................................................................................................. 38

3.3.2

PRE-INSPECTION REVIEW OF DOCUMENTATION...................................................... 38

3.3.2.1

ADS, ANS, AND AWAS..................................................................................................... 39

3.3.3

AIRCRAFT OVERVIEW .................................................................................................... 39

3.3.4

FUNCTIONAL CHECKS.................................................................................................... 40

3.3.4.1

WING FREQUENCY CHECK ........................................................................................... 40

3.3.4.2

CONTROL SURFACE FREEPLAY CHECK ..................................................................... 40

3.3.4.3

CONTROL SURFACE DEFLECTION CHECK ................................................................. 40

3.3.4.4

FLIGHT CONTROL SYSTEM STOPS .............................................................................. 41

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4.

3.3.4.5

ASI AND ALTIMETER CALIBRATION .............................................................................. 41

3.3.4.6

HARNESS INSPECTION .................................................................................................. 41

3.3.4.7

FATIGUE LIFE .................................................................................................................. 41

3.3.4.8

LOAN EQUIPMENT .......................................................................................................... 41

3.3.4.9

INSPECT AND RECTIFY .................................................................................................. 41

3.3.5

CHECKS AFTER RIGGING THE SAILPLANE ................................................................. 42

3.4

DOCUMENTING THE INSPECTION OUTCOME ............................................................ 42

3.4.1

THE LOGBOOK ENTRY ................................................................................................... 42

3.4.2

OTHER SECTIONS OF THE LOGBOOK ......................................................................... 43

3.4.2.1

WHITE PAGES.................................................................................................................. 43

3.4.2.2

GREEN AND YELLOW PAGES........................................................................................ 43

3.4.3

OTHER GUIDANCE .......................................................................................................... 44

3.5

EVALUATION FLYING ...................................................................................................... 44

3.5.1

EVALUATION PILOT AUTHORISATION.......................................................................... 44

3.5.2

PREFLIGHT PROCEDURES ............................................................................................ 44

3.5.3

FLIGHT PROCEDURES ................................................................................................... 45

3.5.4

LAUNCH ............................................................................................................................ 45

3.5.5

FUNCTIONAL CHECK ...................................................................................................... 45

3.5.6

GENERAL HANDLING ...................................................................................................... 46

3.5.7

RUN TO VNE ...................................................................................................................... 46

3.5.8

STALL - STRAIGHT AND LEVEL ..................................................................................... 46

3.5.9

STALL - TURNING ............................................................................................................ 46

3.5.10PITCH STABILITY ............................................................................................................. 47

3.5.11TURN STABILITY.............................................................................................................. 47

PITOT-STATIC SYSTEMS ................................................................................... 48
4.1

GENERAL ......................................................................................................................... 48

4.2

INSPECTION AND TESTING REQUIREMENTS ............................................................. 48

4.3

DEFINITION OF TERMS................................................................................................... 48

4.4

PITOT-STATIC SYSTEM COMPONENTS ....................................................................... 49

4.4.1

MINIMUM EQUIPMENT AND UNITS ............................................................................... 49

4.4.2

GENERAL SYSTEM LAYOUTS........................................................................................ 49

4.4.3

PORTS OR VENTS ........................................................................................................... 50

4.4.4

TUBING ............................................................................................................................. 51

4.5

AIRSPEED ........................................................................................................................ 51

4.5.1

AIRSPEED INDICATOR (ASI) .......................................................................................... 51

4.5.2

LIMITING AIRSPEEDS ..................................................................................................... 52

4.5.3

POSITION ERROR ........................................................................................................... 53

4.5.4

INSTRUMENT ERROR ..................................................................................................... 53

4.5.5

REDUCING VNE WITH ALTITUDE .................................................................................... 53

4.6

ALTIMETER ...................................................................................................................... 54

4.6.1

ALTIMETER ERRORS ...................................................................................................... 55

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4.6.2

ALTIMETER ADJUSTMENT ............................................................................................. 56

4.7

INSPECTION PROCEDURES .......................................................................................... 56

4.7.1

ANNUAL INSPECTION REQUIREMENTS ....................................................................... 56

4.7.1.1

ANNUAL INSPECTION REQUIREMENTS: ...................................................................... 56

4.7.1.2

BIENNIAL (EVERY SECOND YEAR) INSPECTION REQUIREMENTS: ......................... 56

4.7.2

PITOT-STATIC SYSTEMS ................................................................................................ 57

4.7.2.1

PITOT-STATIC SYSTEM INSTALLATION AND MAINTENANCE ................................... 57

4.7.2.2

PITOT-STATIC SYSTEM LEAK TESTING ....................................................................... 57

4.7.2.3

LEAKAGE TOLERANCES IN GFA AIRCRAFT ................................................................ 58

4.7.3

AIRSPEED INDICATOR.................................................................................................... 58

4.7.3.1

THE WATER-TUBE MANOMETER .................................................................................. 58

4.7.3.2

TESTING AN ASI .............................................................................................................. 60

4.7.3.3

CALIBRATION CHART ..................................................................................................... 60

4.7.4

ALTIMETER CALIBRATION ............................................................................................. 61

4.7.5

ALTIMETER TESTING PROCEDURE.............................................................................. 62

4.7.5.1

COMPARISON .................................................................................................................. 62

4.7.5.2

SUB-SCALE TESTING...................................................................................................... 62

APPENDIX A GFA ALTIMETER & ASI TEST KIT INSTRUCTIONS ........................... 63
APPENDIX B ALTIMETER CALIBRATION INSTRUCTIONS ..................................... 70
5.

NUTS, BOLTS AND HARDWARE....................................................................... 78
5.1

INTRODUCTION ............................................................................................................... 78

5.2

TYPES OF BOLTS ............................................................................................................ 78

5.2.1

DIN STANDARD................................................................................................................ 78

5.2.2

ONL STANDARD (FITTED TO BLANIKS) ........................................................................ 79

5.2.3

EUROPEAN AIRCRAFT STANDARD BOLT .................................................................... 81

5.2.4

AN (ARMY NAVY) OR MS (MILITARY SPECIFICATION) ............................................... 81

5.2.5

BSF (BRITISH STANDARD FINE) .................................................................................... 83

5.2.6

BA (BRITISH ASSOCIATED) ............................................................................................ 83

5.2.7

AUSTRALIAN COMMERCIAL BOLTS.............................................................................. 84

5.3

INSPECTION OF BOLTS .................................................................................................. 84

5.4

BOLTING PRACTICE........................................................................................................ 84

5.4.1

BOLTING WOODEN STRUCTURES ............................................................................... 85

5.4.2

BOLT TORQUES .............................................................................................................. 86

5.5

SAFETYING OF BOLTS ................................................................................................... 86

5.5.1

ELASTIC LOCK NUTS ...................................................................................................... 86

5.5.2

OTHER LOCK NUTS ........................................................................................................ 86

5.5.3

REDUCED HEIGHT LOCK NUTS .................................................................................... 87

5.5.4

CASTELLATED NUTS ...................................................................................................... 87

5.5.4.1

SPLIT PINS ....................................................................................................................... 87

5.5.5

SAFETY WIRING .............................................................................................................. 88

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6.

7.

5.5.6

JAM NUTS ......................................................................................................................... 88

5.5.7

PUNCH LOCKING............................................................................................................. 89

5.5.8

LOCTITE ........................................................................................................................... 89

5.5.9

TAB WASHERS ................................................................................................................ 89

5.6

WASHERS ........................................................................................................................ 89

5.7

CLEVIS PINS .................................................................................................................... 90

5.8

ROLL PINS ........................................................................................................................ 90

5.9

TORQUE ........................................................................................................................... 90

5.9.1

NUT FRICTION AND TORQUE ........................................................................................ 91

5.9.2

SPANNER LENGTH.......................................................................................................... 91

5.10

REPLACING HARDWARE ................................................................................................ 91

5.11

REFERENCE AND FURTHER READING ........................................................................ 92

CABLE SYSTEMS ............................................................................................... 93
6.1

INTRODUCTION ............................................................................................................... 93

6.2

CABLE TYPES .................................................................................................................. 93

6.2.1

AMERICAN CABLES ........................................................................................................ 93

6.2.1.1

NICOPRESS SWAGE ....................................................................................................... 94

6.2.2

BRITISH CABLES ............................................................................................................. 95

6.2.2.1

TALURIT SWAGE ............................................................................................................. 95

6.2.3

OTHER CABLE SYSTEMS ............................................................................................... 96

6.3

CABLE INSPECTION ........................................................................................................ 96

6.4

CABLE LIFE ...................................................................................................................... 97

6.5

CABLE CARE .................................................................................................................... 97

6.6

PULLEYS .......................................................................................................................... 97

6.7

CABLE TENSION .............................................................................................................. 98

6.8

TURNBUCKLE LOCK WIRING SCHEMES ...................................................................... 98

6.9

MAKING A NEW CABLE ................................................................................................... 99

6.9.1

PROOF TESTING ........................................................................................................... 100

CANOPIES ......................................................................................................... 101
7.1

INTRODUCTION ............................................................................................................. 101

7.2

ROUTINE CARE ............................................................................................................. 101

7.2.1

DAILY CARE ................................................................................................................... 101

7.2.2

PERIODIC CARE ............................................................................................................ 101

7.2.3

CANOPY COVERS ......................................................................................................... 101

7.2.4

HANDLING OF CANOPIES ............................................................................................ 102

7.3

REPAIR OF PERSPEX ................................................................................................... 102

7.3.1

CUTTING PERSPEX....................................................................................................... 102

7.3.2

CRACKS IN PERSPEX ................................................................................................... 102

7.3.3

DRILLING PERSPEX ...................................................................................................... 102

7.3.4

PERMANENT REPAIRS ................................................................................................. 103

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8.

7.3.4.1

SOLVENT CEMENTS ..................................................................................................... 103

7.3.4.2

REPAIR OF CRACKS ..................................................................................................... 104

7.3.5

WARNING - DAMAGED CANOPIES .............................................................................. 105

7.4

FINISHING-POLISHING.................................................................................................. 105

7.5

MECHANICAL ATTACHMENT OF PERSPEX ............................................................... 105

7.6

CANOPY JETTISON MECHANISMS ............................................................................. 106

7.7

CLEARVIEW PANELS .................................................................................................... 106

SAILPLANE SEAT HARNESS .......................................................................... 107
8.1

INTRODUCTION ............................................................................................................. 107

8.2

HARNESS FUNCTIONAL PERFORMANCE .................................................................. 108

8.3

HARNESS WEBBING ..................................................................................................... 108

8.3.1

WEBBING CONDITION: ................................................................................................. 109

8.3.2

WEBBING CLEANING .................................................................................................... 109

8.4

HARNESS LIFE LIMITS .................................................................................................. 110

8.4.1

AGING OF WEBBING ..................................................................................................... 110

8.5

BUCKLES AND STRAP END FITTINGS ........................................................................ 110

8.5.1

QUICK RELEASE BUCKLE ............................................................................................ 111

8.6

LENGTH ADJUSTERS.................................................................................................... 111
H ...................................................................................................................................... 113

9.

8.7

ARNESS INSTALLATION ............................................................................................... 113

8.7.1

HARNESS ATTACHMENT TO FUSELAGE ................................................................... 113

8.8

HARNESS REPLACEMENT AND REWEBBING ........................................................... 114

8.8.1

HARNESS REPLACEMENT AFTER ACCIDENTS ........................................................ 116

8.9

CUSHIONS...................................................................................................................... 116

8.10

ANNUAL INSPECTION ................................................................................................... 117

8.11

REFERENCES ................................................................................................................ 118

OPTIONAL EQUIPMENT ................................................................................... 119
9.1

GENERAL ....................................................................................................................... 119

9.2

CHANGE IN WEIGHT AND BALANCE........................................................................... 119

9.3

EQUIPMENT CHANGES - PLACARDS.......................................................................... 120

9.4

INTERFERENCE WITH FLIGHT CONTROL SYSTEMS ............................................... 120

9.5

PILOT INJURY PREVENTION ........................................................................................ 120

9.5.1

EQUIPMENT RESTRAINT .............................................................................................. 120

9.5.2

JUSTIFYING THE STRENGTH OF A RESTRAINT ....................................................... 121

9.6

OTHER CONSIDERATIONS .......................................................................................... 122

10. FATIGUE ............................................................................................................ 123
10.1

GENERAL ....................................................................................................................... 123

10.2

FATIGUING LOADS ........................................................................................................ 123

10.3

DAY TO DAY FATIGUE .................................................................................................. 123

10.4

POOR WORKMANSHIP - INDUCING FATIGUE ........................................................... 124

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10.5

BEHAVIOR OF MATERIALS .......................................................................................... 124

10.5.1WOOD ............................................................................................................................. 124

10.5.2

FIBRE REINFORCED PLASTIC ..................................................................................... 125

10.5.3METAL ............................................................................................................................. 125

11. FLUTTER ........................................................................................................... 127
11.1

WHAT IS FLUTTER ........................................................................................................ 127

11.2

FACTORS AFFECTING FLUTTER................................................................................. 128

11.3

CONTROL SURFACE FLUTTER ................................................................................... 128

11.3.1

INCORRECT CONTROL SURFACE BALANCE ............................................................ 129

11.3.2EXCESS FREE PLAY ..................................................................................................... 130

11.3.3

REDUCED CONTROL CIRCUIT STIFFNESS................................................................ 130

11.3.4

FRICTION ........................................................................................................................ 130

11.3.5

REDUCED STRUCTURAL STIFFNESS FROM DAMAGE ............................................ 130

11.3.6

WATER BALLAST ........................................................................................................... 130

11.3.7GAP SEALING TAPE ...................................................................................................... 131

11.3.8SPEED ............................................................................................................................ 131

11.4

WING FLUTTER AND WINGLETS ................................................................................. 132

11.5

FLUTTER PREVENTION ................................................................................................ 132

11.5.1MEASURING CONTROL SURFACE BALANCE AND MASS ........................................ 132

11.5.2

RECTIFICATION OF CONTROL SURFACES WHICH ARE OUTSIDE THE MANUFACTURER’S
LIMITS ............................................................................................................................. 133

11.6

DUSTER'S DEMISE - A FLUTTER CASE HISTORY ..................................................... 133

11.7

REFERENCES ................................................................................................................ 134

12. LOADS ON SAILPLANES ................................................................................. 135
12.1

GENERAL ....................................................................................................................... 135

12.2

MANOEUVRING LOADS ................................................................................................ 135

12.2.1SYMMETRICAL LOADS ................................................................................................. 135

12.2.2LOADS IN THE SAILPLANE (SYMMETRICAL MANOEUVRING) ................................. 136

12.2.3ASYMMETRIC LOADS ................................................................................................... 137

12.3

GUST LOADS ................................................................................................................. 137

12.4

LAUNCHING LOADS ...................................................................................................... 138

12.4.1

WINCH LAUNCHING LOADS ......................................................................................... 138

12.5

HEAVY LANDING AND GROUND LOOP LOADS ......................................................... 138

13. CONTROL CIRCUIT RIGGING .......................................................................... 139
13.1

GENERAL ....................................................................................................................... 139

13.2

CONTROL SURFACE TRAVEL ...................................................................................... 139

13.2.1CHECKING TRAVEL....................................................................................................... 139

13.2.2ELEVATOR TRAVEL ...................................................................................................... 139

13.2.3RUDDER TRAVEL .......................................................................................................... 140

13.2.4AILERON TRAVEL .......................................................................................................... 140

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13.2.5

TRIM TAB TRAVEL ......................................................................................................... 140

13.3

SETTING UP A CONTROL SYSTEM ............................................................................. 140

13.4

CONTROL SYSTEM STOPS .......................................................................................... 140

13.5

CONTROL SYSTEM FREEPLAY ................................................................................... 141

13.6

CONTROL SYSTEM FRICTION ..................................................................................... 142

13.7

ENDFLOAT OF CONTROL SURFACES ........................................................................ 142

13.8

CONTROL SYSTEM STIFFNESS .................................................................................. 142

13.9

GAP SEALS .................................................................................................................... 143

13.10

PUSH ROD RIGGING ..................................................................................................... 144

13.10.1 ROD END SAFETY ......................................................................................................... 144
13.10.2 ROD END ALIGNMENT .................................................................................................. 144
13.11

AIRCRAFT GEOMETRY ................................................................................................. 145

13.11.1 CHECKING RIGGING ANGLES ..................................................................................... 145
13.11.2 WING-TAILPLANE ANGLE ............................................................................................. 146
13.11.3 DIHEDRAL ...................................................................................................................... 146
13.11.4 WASHOUT ...................................................................................................................... 146
13.11.5 WING TO FUSELAGE..................................................................................................... 146
13.11.6 TAILPLANE TO FUSELAGE ........................................................................................... 146
13.11.7 FIN ANGLE...................................................................................................................... 146
13.12

STRUCTURAL FREEPLAY ............................................................................................ 146

13.12.1 TANGENTIAL PLAY OF WINGS .................................................................................... 147
13.12.1.1 SHIMS ............................................................................................................................. 147
13.12.1.2 TAILPLANE ..................................................................................................................... 147
13.13

CONTROL CIRCUIT FLUTTER ...................................................................................... 147

13.14

REFERENCES ................................................................................................................ 147

14. WORKSHOP PRACTICE ................................................................................... 148
14.1

GENERAL ....................................................................................................................... 148

14.2

SAFETY ........................................................................................................................... 148

14.2.1CHEMICALS.................................................................................................................... 148

14.2.2MANUAL HANDLING ...................................................................................................... 148

14.2.3

SLINGING AND SUPPORTS .......................................................................................... 148

14.2.4

HOUSEKEEPING ............................................................................................................ 149

14.2.5

WORKSHOP FACILITIES ............................................................................................... 149

14.3

EQUIPMENT ................................................................................................................... 149

14.3.1

WORKSHOP EQUIPMENT ............................................................................................. 149

14.3.2

HAND TOOLS ................................................................................................................. 149

14.4

DISASSEMBLY ............................................................................................................... 150

14.5

STORAGE OF PARTS .................................................................................................... 150

14.6

FOREIGN OBJECTS....................................................................................................... 150

14.6.1

TOOL CONTROL ............................................................................................................ 150

14.7

REASSEMBLY ................................................................................................................ 151

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15. SAILPLANE MATERIALS ................................................................................. 152
15.1

GENERAL ....................................................................................................................... 152

15.2

MATERIALS .................................................................................................................... 152

15.3

FRP CONSTRUCTION ................................................................................................... 152

15.3.1

GENERAL COMPOSITE INSPECTION TECHNIQUES ................................................. 153

15.3.2GLASS REINFORCED PLASTIC .................................................................................... 153

15.3.3

CARBON FIBRE AND KEVLAR REINFORCED PLASTIC (CFRP AND KRP) .............. 153

15.3.4

DELAMINATION.............................................................................................................. 153

15.3.5

CRACKING ...................................................................................................................... 154

15.3.6FAILURE OF SANDWICH MATERIALS ......................................................................... 154

15.3.7

GELCOAT CRACKS ....................................................................................................... 154

15.4

WOOD CONSTRUCTION ............................................................................................... 154

15.4.1COMPRESSION SHAKES .............................................................................................. 154

15.4.2DRY ROT ........................................................................................................................ 155

15.4.3

GLUE FAILURE............................................................................................................... 155

15.4.3.1 THE FINGERNAIL TEST................................................................................................. 155
15.4.4FAILURE OF FABRIC COVERINGS .............................................................................. 156

15.5

METAL CONSTRUCTION............................................................................................... 156

15.5.1RIVET FAILURE .............................................................................................................. 156

15.5.2

FATIGUE CRACKING ..................................................................................................... 157

15.5.3BUCKLING ...................................................................................................................... 158

15.5.4INTER-RIVET BUCKLING............................................................................................... 158

15.5.5CORROSION .................................................................................................................. 158

15.5.5.1 STEEL ............................................................................................................................. 158
15.5.5.2 ALUMINIUM .................................................................................................................... 158
15.5.6FAILURE OF STEEL TUBES .......................................................................................... 159

15.6

METAL FITTINGS ........................................................................................................... 159

15.7

REFERENCES ................................................................................................................ 159

16. TOW RELEASE MAINTENANCE ...................................................................... 160
16.1

INTRODUCTION ............................................................................................................. 160

16.1.1TERMINOLOGY .............................................................................................................. 161

16.1.2

WHO MAY INSPECT, MAINTAIN AND TEST TOW RELEASE MECHANISMS ........... 161

16.1.3PURPOSE OF THE TOW RELEASE SYSTEM .............................................................. 161

16.1.4

MANUFACTURERS OF RELEASES .............................................................................. 162

16.1.5AIRCRAFT FITTED WITH TWO RELEASES ................................................................. 163

16.2

RELEASE PRINCIPLES: OVER-CENTRE & CAGED .................................................... 163

16.2.1

OVER-CENTRE .............................................................................................................. 163

16.2.2

CAGED ............................................................................................................................ 164

16.3

RELEASE CONTROL CIRCUIT ...................................................................................... 165

16.3.1COMMON RELEASE CONTROL CIRCUIT ISSUES ..................................................... 165

16.3.2

INSPECTION AND MAINTENANCE OF RELEASE CONTROL CIRCUIT .................... 166

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16.4

TOW RELEASE CLEANING, SERVICING AND OVERHAUL........................................ 167

16.4.1REGULAR CLEANING WHILST INSTALLED ................................................................ 167

16.4.2

ANNUAL SERVICE ......................................................................................................... 167

16.4.3

OVERHAUL ..................................................................................................................... 170

16.4.3.1 REASSEMBLING TOST RELEASES ............................................................................. 170
16.4.4

REPLACEMENT OF THE TOW RELEASE ASSEMBLY................................................ 171

16.4.5AIRCRAFT NEW TO THE AUSTRALIAN REGISTER .................................................... 171

16.5

RELEASE TROUBLESHOOTING GUIDE ...................................................................... 172

16.6

SPRING REPLACEMENT ............................................................................................... 173

16.6.1TOST MAIN SPRING REPLACEMENT IN SAILPLANES .............................................. 173

16.6.2TOST MAIN SPRING REPLACEMENT IN TOW PLANES............................................. 173

16.6.3

NON-TOST SPRING REPLACEMENT ........................................................................... 173

16.7

TESTING RELEASES ..................................................................................................... 173

16.7.1BACKGROUND TO TESTING ACTUATION UNDER HIGH TOW FORCES................. 174

16.7.2

THE GFA TOW RELEASE TESTS ................................................................................. 175

16.7.3

SUMMARY OF WHEN TESTS ARE CONDUCTED AND SPRINGS REPLACED ........ 176

16.7.4LOGBOOK AND MAINTENANCE RELEASE ENTRIES ................................................ 176

16.8

CONDUCTING THE TESTS ........................................................................................... 177

16.8.1NOMENCLATURE .......................................................................................................... 177

16.8.2NON-STANDARD LEVER ARM - CONVERSION OF FORCE READINGS .................. 178

16.8.3

CALIBRATION OF SPRING BALANCES ....................................................................... 178

16.9

TEST 1: OVER-CENTRE ................................................................................................ 179

16.9.1TEST 1 PROCEDURE .................................................................................................... 180

16.9.2TEST 1 CHART ............................................................................................................... 181

16.9.3

INTERPRETATION OF TEST 1 RESULTS .................................................................... 181

16.9.4

WORKED EXAMPLE OF TEST 1 CHART...................................................................... 182

16.9.5ADJUSTING THE OVER-CENTRE................................................................................. 182

16.9.5.1 RELEASES WITH ADJUSTING SCREWS. .................................................................... 182
16.9.5.2 RELEASES WITH SUNKEN ADJUSTING SCREW. ...................................................... 182
16.9.5.3 RELEASES WITHOUT ADJUSTING SCREWS. ............................................................ 183
16.10

TEST 2: MAIN SPRING TENSION ................................................................................. 183

16.11

TEST 3: PILOT ACTUATION FORCE ............................................................................ 184

16.12

TEST 4: BACK-RELEASE ............................................................................................... 185

APPENDIX C GFA 450 RELEASE TESTER.............................................................. 186
APPENDIX D TOW RELEASE TEST SHEET ............................................................ 188
APPENDIX E TOST RELEASE REASSEMBLY AIDS. ............................................. 189
17. OXYGEN ............................................................................................................ 191
17.1

GFA RECOMMENDATIONS AND REQUIREMENTS .................................................... 191

17.2

OXYGEN SPECIFICATIONS .......................................................................................... 191

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17.3

SAFETY PRECAUTIONS WHEN WORKING WITH OXYGEN ...................................... 192

17.3.1

CLEANLINESS ................................................................................................................ 192

17.3.2

WORK PRACTICES ........................................................................................................ 192

17.4

UNDERSTANDING OXYGEN SYSTEMS ...................................................................... 193

17.4.1TYPES OF INSTALLATION ............................................................................................ 193

17.4.2SYSTEM COMPONENTS ............................................................................................... 193

17.4.3SYSTEM CONFIGURATIONS ........................................................................................ 193

17.4.4CYLINDERS .................................................................................................................... 195

17.4.5SYSTEM TYPES AND THEIR CONTROLLERS ............................................................ 195

17.4.5.1 CONSTANT FLOW ......................................................................................................... 195
17.4.5.2 DILUTER DEMAND CONTROLLER ............................................................................... 196
17.4.5.3 PRESSURE DEMAND CONTROLLER .......................................................................... 196
17.4.5.4 ELECTRONIC (PULSE) DEMAND CONTROLLER........................................................ 196
17.4.6FLEXIBLE LOW PRESSURE HOSES ............................................................................ 197

17.4.7

CANNULAS AND MASKS ............................................................................................... 197

17.4.7.1 NASAL CANNULAS ........................................................................................................ 197
17.4.7.2 MASKS ............................................................................................................................ 197
17.4.8SYSTEM MANUFACTURERS ........................................................................................ 198

17.4.9BASIC REQUIREMENTS FOR ALL OXYGEN SYSTEMS IN SAILPLANES ................. 198

17.5

CYLINDER INSTALLATION AND RESTRAINT ............................................................. 199

17.6

PERMANENT PLUMBING INSTALLATIONS ................................................................. 199

17.6.1TERMINOLOGY .............................................................................................................. 199

17.6.2

SECURITY ...................................................................................................................... 200

17.6.3

HIGH PRESSURE PLUMBING ....................................................................................... 200

17.6.3.1 Copper Tubing ................................................................................................................. 200
17.6.3.2 Flexible Hose ................................................................................................................... 200
17.6.4LOW PRESSURE PLUMBING ........................................................................................ 200

17.6.5COMPONENT CLEANING .............................................................................................. 200

17.6.6SEALING PLUMBING AND FITTINGS ........................................................................... 201

17.7

WEIGHT AND BALANCE ................................................................................................ 201

17.8

SYSTEM TESTING ......................................................................................................... 201

17.8.1CYLINDER TESTING ...................................................................................................... 201

17.8.2LEAK TESTING ............................................................................................................... 202

17.8.3

FLOW CHECK ................................................................................................................. 202

17.8.3.1 CONTINUOUS FLOW REGULATORS ........................................................................... 202
17.8.3.2 DEMAND REGULATORS ............................................................................................... 202
17.8.4

DORMANT OXYGEN SYSTEMS .................................................................................... 203

17.9

PLACARDING ................................................................................................................. 203

17.9.1

INDICATED AIRSPEEDS................................................................................................ 203

17.9.2SYSTEM SAFE HEIGHT LIMITS .................................................................................... 203

17.9.3CYLINDER MOUNTING BRACKET ................................................................................ 203

17.9.4FILLING INSTRUCTIONS FOR PERMANENT INSTALLATIONS ................................. 203

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17.10

AIRWORTHINESS CERTIFICATION ............................................................................. 204

17.10.1 INITIAL INSTALLATION .................................................................................................. 204
17.10.2 ANNUAL INSPECTIONS................................................................................................. 204
17.10.2.1 PORTABLE OXYGEN SYSTEMS................................................................................... 204
17.10.2.2 PERMANENTLY INSTALLED OXYGEN SYSTEMS ...................................................... 204
17.10.3 RETURN TO SERVICE INSPECTION............................................................................ 204
17.10.4 DAILY INSPECTIONS ..................................................................................................... 204
17.11

DECANTING ................................................................................................................... 205

17.11.1 FILLING PRESSURES .................................................................................................... 205
17.12

REFERENCES ................................................................................................................ 206

18. FLIGHT OVERLOAD ......................................................................................... 208
18.1

GENERAL ....................................................................................................................... 208

18.1.1

WINCH LAUNCHING ...................................................................................................... 209

18.2

WHEN CAN OVERLOAD OCCUR?................................................................................ 209

18.3

FLIGHT OVERLOAD INSPECTION................................................................................ 210

18.4

FRP OVERLOAD INDICATION ...................................................................................... 211

18.5

OTHER INSPECTION TECHNIQUES ............................................................................ 211

18.5.1

SOUND ............................................................................................................................ 211

18.5.2

FEEL ................................................................................................................................ 211

18.5.3

SIGHT .............................................................................................................................. 211

18.6

GELCOAT CRACKS ....................................................................................................... 211

18.7

CARBON REINFORCED PLASTIC ................................................................................ 212

18.8

INTERNAL INSPECTION TOOLS .................................................................................. 212

18.9

WING LIFT PINS ............................................................................................................. 212

18.10

MAINSPAR PINS AND BEARINGS ................................................................................ 212

18.11

CRACKS IN WING FITTINGS ......................................................................................... 213

19. EXAMINING DAILY INSPECTOR CANDIDATES ............................................. 214
19.1

GENERAL ....................................................................................................................... 214

19.2

DOCUMENTATION ......................................................................................................... 214

19.3

CANDIDATE PREREQUISITES ..................................................................................... 214

19.4

TRAINING ....................................................................................................................... 214

19.5

DAILY INSPECTOR SYLLABUS .................................................................................... 215

19.5.1TESTING ......................................................................................................................... 215

19.5.2

ORAL TEST QUESTIONS .............................................................................................. 215

19.5.3

PRACTICAL TESTS ........................................................................................................ 216

19.5.4

NOTIFICATION OF AUTHORISATION .......................................................................... 216

19.6

POWERED SAILPLANES ............................................................................................... 216

20. ELECTRICAL SYSTEMS ................................................................................... 217
20.1

GENERAL ....................................................................................................................... 217

20.2

TYPICAL SAILPLANE INSTALLATION .......................................................................... 217

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20.2.1CIRCUIT DIAGRAM ........................................................................................................ 218

20.2.2SINGLE LINE CIRCUIT DIAGRAMS .............................................................................. 219

20.3

THE BATTERY ................................................................................................................ 219

20.3.1REMOVABLE BATTERIES ............................................................................................. 220

20.3.2

DUAL BATTERY (SELECTABLE) INSTALLATIONS ..................................................... 223

20.4

THE MASTER SWITCH .................................................................................................. 223

20.5

CIRCUIT PROTECTION ................................................................................................. 225

20.5.1

FUSE/CIRCUIT BREAKER RATINGS ............................................................................ 226

20.5.1.1 FUSES RATING AND MARKING ................................................................................... 226
20.5.1.2 TYPE OF FUSES ............................................................................................................ 227
20.7

WIRES AND CABLES ..................................................................................................... 229

20.7.1DEFINITIONS .................................................................................................................. 229

20.7.2AIRCRAFT GRADE WIRE .............................................................................................. 230

20.7.3

AUTOMOTIVE AND MARINE CABLE ............................................................................ 232

20.7.4WIRES AND CABLES IN SAILPLANES ......................................................................... 232

20.7.5WIRE COLOUR CODING ............................................................................................... 233

20.7.6WIRE SECURITY ............................................................................................................ 233

20.8

JOINS AND TERMINATIONS ......................................................................................... 233

20.8.1SOLDERING ................................................................................................................... 234

20.8.2CRIMPED JOINS AND TERMINALS .............................................................................. 234

20.8.3TERMINAL BLOCKS ....................................................................................................... 235

20.8.5CONNECTORS ............................................................................................................... 237

20.10.1 PERMENANTLY INSTALLED POWER CONVERTERS ................................................ 238
20.13

PLACARDS ..................................................................................................................... 240

20.14

UNDERCARRIAGE WARNING SYSTEMS .................................................................... 240

20.15

MOTOR GLIDERS .......................................................................................................... 242

20.17

ANNUAL INSPECTION ................................................................................................... 242

20.18

EXAMPLES OF FAULTS AND CONCERNS .................................................................. 243

20.19

REFERENCES ................................................................................................................ 244

21. LUBRICATION ................................................................................................... 245
21.1

GENERAL ....................................................................................................................... 245

21.2

LUBRICANT REQUIREMENTS ...................................................................................... 245

21.3

TYPES OF LUBRICANTS ............................................................................................... 246

21.3.1

OIL ................................................................................................................................... 246

21.3.2

GREASE .......................................................................................................................... 246

21.3.3

SOLID FILM..................................................................................................................... 246

21.3.4

SILICONE ........................................................................................................................ 246

21.4

RECOMMENDED LUBRICANTS .................................................................................... 246

21.5

SHELF LIFE OF LUBRICANTS ...................................................................................... 246

21.6

LUBRICATION TECHNIQUES ........................................................................................ 247

21.6.1SIMPLE GREASE GUN .................................................................................................. 247

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21.6.2

GREASE NIPPLES ......................................................................................................... 248

21.6.3

PRESSURE PACK LUBRICANT WARNING .................................................................. 248

21.7

GREASING FREQUENCY - UNDERCARRIAGE ........................................................... 249

21.8

REFERENCES ................................................................................................................ 249

22. WOODEN CONSTRUCTION INSPECTION AND REPAIR ............................... 250
22.1

WOOD ............................................................................................................................. 250

22.1.1

GENERAL ....................................................................................................................... 250

22.1.2CHARACTERISTICS OF WOOD .................................................................................... 250

22.1.2.1 GROWTH RINGS ............................................................................................................ 250
22.1.2.2 SAWING OF TIMBER ..................................................................................................... 250
22.1.2.3 MOISTURE CONTENT ................................................................................................... 250
22.1.2.4 GRAIN EFFECTS ............................................................................................................ 251
22.1.3

DEFECTS IN TIMBER..................................................................................................... 252

22.1.3.1 COMPRESSION FAILURES ........................................................................................... 252
22.1.3.2 KNOTS ............................................................................................................................ 253
22.1.3.3 DOTE ............................................................................................................................... 253
22.1.3.4 PITCH POCKETS............................................................................................................ 253
22.1.4

SELECTING AIRCRAFT TIMBER .................................................................................. 253

22.1.5AIRCRAFT TIMBERS...................................................................................................... 254

22.1.5.1 SPRUCE .......................................................................................................................... 254
22.1.5.2 KIEFER ............................................................................................................................ 254
22.1.5.3 DOUGLAS FIR ................................................................................................................ 255
22.1.5.4 ASH ................................................................................................................................. 255
22.1.5.5 BEECH ............................................................................................................................ 255
22.1.5.6 BIRCH ............................................................................................................................. 255
22.1.5.7 BALSA ............................................................................................................................. 255
22.1.5.8 KLINKI ............................................................................................................................. 255
22.1.5.9 MAHOGANY.................................................................................................................... 255
22.1.5.10 IMPROVED WOOD ......................................................................................................... 255
22.1.6AIRCRAFT PLYWOODS ................................................................................................. 255

22.1.6.1 BIRCH PLY ...................................................................................................................... 256
22.1.6.2 DOUGLAS FIR ................................................................................................................ 256
22.1.6.3 KLINKI PLY ..................................................................................................................... 256
22.1.6.4 GABOON PLY ................................................................................................................. 256
22.1.6.5 MAHOGANY.................................................................................................................... 256
22.1.6.6 COACHWOOD ................................................................................................................ 256
22.1.6.7 HOOP PINE..................................................................................................................... 256
22.2

ADHESIVES .................................................................................................................... 256

22.2.1

GENERAL ....................................................................................................................... 256

22.2.2LEGACY AIRCRAFT ADHESIVES ................................................................................. 257

22.2.2.1 CASEIN ........................................................................................................................... 257
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22.2.2.2 UREA GLUE .................................................................................................................... 257
22.2.2.3 RESORCINOL ................................................................................................................. 257
22.2.3AIRCRAFT EPOXY GLUES ............................................................................................ 257

22.2.4

GLUING PROCEDURES ................................................................................................ 258

22.2.4.1 TEST SAMPLES ............................................................................................................. 258
22.2.4.2 SURFACE PREPARATION ............................................................................................ 259
22.2.4.3 GLUING CONDITIONS ................................................................................................... 259
22.2.4.4 GLUING PREPARATION ................................................................................................ 259
22.2.4.5 CLAMPING REQUIREMENTS ........................................................................................ 259
22.3

WOOD REPAIR............................................................................................................... 260

22.3.1

GENERAL ....................................................................................................................... 260

22.3.1.1 MATERIALS .................................................................................................................... 260
22.3.1.2 JIGGING .......................................................................................................................... 260
22.3.1.3 REPAIR SCHEMES ........................................................................................................ 260
22.3.1.4 GRAIN DIRECTION ........................................................................................................ 260
22.3.1.5 VENTILATION/DRAINAGE ............................................................................................. 260
22.3.1.6 INTERIOR SEALING ....................................................................................................... 260
22.3.2SPLICING ........................................................................................................................ 260

22.3.2.1 STANDARDS FOR SCARF ANGLES ............................................................................. 261
22.3.2.2 SPLICING QUALITY ....................................................................................................... 261
22.3.2.3 AMERICAN SPLICE METHOD ....................................................................................... 261
22.3.2.4 SUPPORTING PLYWOOD SKIN SPLICES.................................................................... 262
22.3.3‘D’ NOSE REPAIR ........................................................................................................... 262

22.3.4

DESIGN OF REPAIRS .................................................................................................... 262

23. SAILPLANE FABRIC INSPECTION AND REPAIR........................................... 263
23.1

GENERAL ....................................................................................................................... 263

23.1.1EXTENT OF USE ............................................................................................................ 263

23.1.2

FUNCTION OF FABRIC AND ASSOCIATED FINISHING MATERIALS ........................ 263

23.1.3

CONDITION OF STRUCTURE UNDER FABRIC ........................................................... 263

23.2

LEGACY FABRICS AND DOPES ................................................................................... 263

23.2.1LEGACY FABRICS ......................................................................................................... 263

23.2.2LEGACY DOPES AND FINISHES .................................................................................. 263

23.2.2.1 DOPES ............................................................................................................................ 263
23.2.2.2 FILLERS .......................................................................................................................... 263
23.2.2.3 PAINTS ............................................................................................................................ 263
23.3

CURRENT FABRICS ...................................................................................................... 264

23.3.1

TYPE OF FABRIC ........................................................................................................... 264

23.3.1.1 CECONITE / POLYFIBER ............................................................................................... 264
23.3.1.2 ORATEX .......................................................................................................................... 264
23.3.2

CARE OF FABRIC PRIOR TO APPLICATION ............................................................... 264

23.4

CURRENT ADHESIVE AND COATING PRODUCTS .................................................... 265

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23.4.1

CECONITE (RANDOLPH) NITRATE / BUTYRATE DOPE SYSTEM ............................ 265

23.4.2OTHER NITRATE / BUTYRATE DOPE SYSTEMS ........................................................ 266

23.4.3

POLY-FIBER VINYL COATING SYSTEM ...................................................................... 266

23.4.4

ORATEX SYSTEM .......................................................................................................... 268

23.5

FABRICING OF WINGS .................................................................................................. 268

23.5.1FABRIC LAYOUT ............................................................................................................ 268

23.5.2FABRIC DETAIL .............................................................................................................. 269

23.5.3

RIB STITCHING .............................................................................................................. 270

23.6

FABRICING OF FUSELAGES ........................................................................................ 270

23.6.1FABRIC LAYOUT – WOODEN FUSELAGE ................................................................... 270

23.6.2FABRIC LAYOUT – STEEL TUBE FUSELAGE ............................................................. 270

23.6.3

FABRIC DETAIL .............................................................................................................. 271

23.7

FABRICING OF TAILPLANES ........................................................................................ 271

23.7.1FABRIC LAYOUT ............................................................................................................ 271

23.7.2FABRIC DETAIL .............................................................................................................. 271

23.8

WEIGHT AND BALANCE AND LOGBOOK ENTRY....................................................... 271

23.8.1

WEIGHT AND BALANCE REQUIREMENT .................................................................... 271

23.8.2

LIKELY WEIGHT OUTCOME ......................................................................................... 271

23.8.3LOGBOOK ENTRIES ...................................................................................................... 271

23.9

REMOVAL OF OLD FABRICS AND DOPES.................................................................. 271

23.9.1

NECESSITY .................................................................................................................... 271

23.9.2REMOVAL TECHNIQUES .............................................................................................. 271

23.10

FABRIC REPAIRS AND INSPECTION ........................................................................... 272

23.10.1 TYPES OF DAMAGE ...................................................................................................... 272
23.10.2 REPAIR MATERIALS ...................................................................................................... 272
23.10.3 REPAIR FUNDAMENTALS ............................................................................................. 272
23.10.4 REPAIR TECHNIQUES................................................................................................... 272
23.10.5 FABRIC INSPECTION .................................................................................................... 273
23.11

REFERENCES ................................................................................................................ 273

24. SAILPLANE UNDERCARRIAGE ...................................................................... 274
24.1

GENERAL ....................................................................................................................... 274

24.2

MAIN UNDERCARRIAGE ARRANGEMENTS ............................................................... 274

24.2.1SKID ................................................................................................................................ 274

24.2.2

MONOWHEEL ................................................................................................................. 274

24.2.3

TAILDRAGGER ............................................................................................................... 274

24.2.4TRICYCLE ....................................................................................................................... 274

24.2.5OTHER ............................................................................................................................ 274

24.3

SUPPLEMENTARY UNDERCARRIAGE ARRANGEMENTS ........................................ 274

24.3.1SKID – NOSE OR TAIL ................................................................................................... 274

24.3.2WHEEL – NOSE OR TAIL .............................................................................................. 275

24.3.3

OUTRIGGERS ................................................................................................................ 275

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24.3.4

WINGTIPS ....................................................................................................................... 275

24.3.5

DOLLIES AND WiNG WALKERS ................................................................................... 275

24.4

TYRES ............................................................................................................................. 275

24.4.1

GENERAL ....................................................................................................................... 275

24.4.2PARTS OF THE TYRE .................................................................................................... 276

24.4.3

TYRE MARKINGS ........................................................................................................... 276

24.4.4

RATINGS ......................................................................................................................... 277

24.4.5PLIES............................................................................................................................... 277

24.4.6

SIZE NOMENCLATURE ................................................................................................. 277

24.4.7

INSPECTION................................................................................................................... 277

24.4.8

STORAGE ....................................................................................................................... 278

24.5

TUBES ............................................................................................................................. 279

24.5.1

GENERAL ....................................................................................................................... 279

24.5.2VALVES ........................................................................................................................... 279

24.6

BRAKES .......................................................................................................................... 280

24.6.1DRUM .............................................................................................................................. 281

24.6.2

DISC ................................................................................................................................ 282

24.6.3HYDRAULIC BRAKING SYSTEMS ................................................................................ 283

24.6.4HYDRAULIC LINES ........................................................................................................ 284

24.6.5HYDRAULIC/BRAKE FLUIDS ......................................................................................... 284

24.6.6

DIFFERENTIAL BRAKING .............................................................................................. 285

24.6.7

DIRECT MECHANICAL BRAKING ................................................................................. 285

24.6.8PARACHUTE ASSISTANCE .......................................................................................... 285

24.7

SUSPENSION ................................................................................................................. 285

24.7.1

GENERAL ....................................................................................................................... 285

24.7.2

RIGID ............................................................................................................................... 285

24.7.3SIMPLE SPRINGING ...................................................................................................... 285

24.7.4

OLEOS/ SHOCK STRUTS .............................................................................................. 286

24.7.5

RUBBER OR SYNTHETIC SUSPENSION ..................................................................... 287

24.8

RETRACTION SYSTEMS ............................................................................................... 287

24.8.1

DIRECT MECHANICAL................................................................................................... 287

24.8.2STORED ENERGY ......................................................................................................... 287

24.8.3

RETRACT SPRINGS/DAMPERS ................................................................................... 287

24.9

OTHER ITEMS ................................................................................................................ 288

24.9.1DOORS ........................................................................................................................... 288

24.9.2SPATS AND FAIRINGS .................................................................................................. 288

24.9.3

MUDGUARDS ................................................................................................................. 288

24.10

MAINTENANCE AWARENESS ...................................................................................... 288

24.10.1 HARD LANDINGS ........................................................................................................... 288
24.10.2 TYRE SIZE DISCREPANCIES ....................................................................................... 288
24.10.3 RIM CONDITION ............................................................................................................. 289
24.10.4 MOUNTINGS................................................................................................................... 289
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24.10.5 CORROSION .................................................................................................................. 289
24.11

GUIDELINE FOR ANNUAL INSPECTION ...................................................................... 289

24.11.1 DISSASSEMBLY ............................................................................................................. 289
24.11.2 CLEANING ...................................................................................................................... 289
24.11.3 INSPECTION................................................................................................................... 290
24.11.4 REGREASE..................................................................................................................... 290
24.11.5 REASSEMBLY ................................................................................................................ 290
24.12

REFERENCES ................................................................................................................ 290

25. INSPECTION AFTER HARD LANDINGS .......................................................... 291
25.1

GENERAL ....................................................................................................................... 291

25.2

THE MECHANICS OF HEAVY LANDINGS .................................................................... 291

25.2.1TAIL FIRST...................................................................................................................... 291

25.2.2

MAIN WHEEL FLY ON .................................................................................................... 292

25.2.3NOSE FIRST ................................................................................................................... 292

25.2.4NOSE FIRST – MAIN WHEEL BEHIND CoG ................................................................. 293

25.2.5OVERBRAKING ON THE GROUND ROLL .................................................................... 294

25.2.6GROUND LOOPS ........................................................................................................... 294

25.3

THE PILOT ...................................................................................................................... 295

25.4

STRUCTURAL DAMAGE ................................................................................................ 295

25.4.1

ALL TYPES ..................................................................................................................... 295

25.4.2

FRP.................................................................................................................................. 295

25.4.3

WOOD ............................................................................................................................. 296

25.4.4METAL ............................................................................................................................. 296

25.4.5STEEL TUBE................................................................................................................... 297

25.4.6MOTOR GLIDERS .......................................................................................................... 297

25.5

CASE STUDIES .............................................................................................................. 297

25.6

REFERENCES ................................................................................................................ 297

26. NON DESTRUCTIVE INSPECTION .................................................................. 298
26.1

GENERAL ....................................................................................................................... 298

26.2

TYPES OF NON DESTRUCTIVE INSPECTION ............................................................ 298

26.2.1LIQUID PENETRANT TESTING (PT) ............................................................................. 298

26.2.1.1 RED DYE PENETRANT .................................................................................................. 298
26.2.1.2 FLUORESCENT DYE PENETRANT .............................................................................. 298
26.2.2MAGNETIC PARTICLE (MT) .......................................................................................... 299

26.2.3EDDY CURRENT TESTING (ET) ................................................................................... 299

26.2.4ULTRASONIC (UT) ......................................................................................................... 300

26.2.5

RADIOGRAPHIC (RT)..................................................................................................... 301

26.3

PROCEDURES FOR FLUORESCENT DYE PENETRANT ........................................... 301

26.3.1INITIAL CLEANING ......................................................................................................... 301

26.3.2

PRE-CLEANING.............................................................................................................. 302

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26.4

PENETRANT APPLICATION .......................................................................................... 302

26.5

DWELL TIME................................................................................................................... 302

26.6

PENETRANT REMOVAL ................................................................................................ 302

26.7

DEVELOPING ................................................................................................................. 303

26.8

INDICATION INTERPRETATION ................................................................................... 303

26.9

CLEANING ...................................................................................................................... 304

26.10

REFERENCES ................................................................................................................ 304

27. RADIO, ANTENNAE, FLARM AND AVIONICS................................................. 305
27.1

INTRODUCTION ............................................................................................................. 305

27.2

RADIO BASICS ............................................................................................................... 305

27.2.1

RADIO WAVES ............................................................................................................... 305

27.2.2WAVELENGTH AND FREQUENCY ............................................................................... 306

27.2.3HOW FREQUENCY AND WAVELENGTH ARE RELATED ........................................... 306

27.2.4

USING RADIO WAVES ................................................................................................... 307

27.2.5

MODULATION................................................................................................................. 307

27.3

VHF COM RADIOS ......................................................................................................... 308

27.3.1

GOLDEN RULES - WARNING!....................................................................................... 308

27.3.2

THE VHF COM RADIO ................................................................................................... 308

27.3.3

MICROPHONE AND PTT ............................................................................................... 309

27.3.4LOUDSPEAKERS ........................................................................................................... 310

27.3.5

RADIO WIRING HARNESS ............................................................................................ 311

27.4.1ANTENNA BASICS ......................................................................................................... 312

27.4.2ANTENNA POLARISATION ............................................................................................ 313

27.4.3

TYPES OF AIRCRAFT ANTENNA ................................................................................. 313

27.4.4

WHIP ANTENNAE........................................................................................................... 314

27.4.5CONNECTING THE RADIO TO THE ANTENNA ........................................................... 315

27.4.6

COAXIAL CABLE ............................................................................................................ 315

27.4.7

VHF COM RADIO ANTENNA CONNECTORS .............................................................. 317

27.4.8

MAKING A COAX PLUG CRIMP CONNECTION ............................................................... 318

27.4.9ANTENNA PERFORMANCE .......................................................................................... 318

27.4.10 THE EFFECT OF ANTENNA DIAMETER/WIDTH ON PERFORMANCE ...................... 319
27.4.11 USING A SWR METER ................................................................................................... 320
27.4.12 HOW TO TUNE ANTENNAE .......................................................................................... 321
27.5.1AVIONICS INTRODUCTION ........................................................................................... 321

27.5.2IGC STANDARDS FOR DOWNLOADING FLIGHT DATA ............................................. 322

27.5.3

INTERCONNECTION OF AVIONICS ............................................................................. 323

27.5.4DATA SIGNAL INTERCONNECTION............................................................................. 325

27.5.5

RS-232 (TRUE AND TTL) ............................................................................................... 326

27.5.6

USB – DIFFERENTIAL SIGNALLING ............................................................................. 326

27.5.7

CAN-BUS ........................................................................................................................ 327

27.5.8CONNECTORS ............................................................................................................... 327

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27.5.8.1 SUB MINIATURE D-CONNECTORS .............................................................................. 327
27.5.8.2 RJ12 AND RJ45 CONNECTORS ................................................................................... 328
27.5.8.3 USB CONNECTORS....................................................................................................... 329
27.5.8.4 OTHER CONNECTORS ................................................................................................. 330
27.6.1

FLARM INTRODUCTION ................................................................................................ 330

27.6.2

GPS ANTENNA ............................................................................................................... 332

27.6.3DATA ANTENNA ............................................................................................................. 332

27.6.4

FLARM REMOTE DISPLAYS AND INTERCONNECTION TO OTHER DEVICES ........ 333

27.6.5REVIEWING FLARM PERFORMANCE.......................................................................... 334

27.6.6

FLARM MAINTENANCE/FAULT CHECKLIST ............................................................... 334

27.7

MODIFYING INSTRUMENT PANELS ............................................................................ 335

27.7.1PANEL STANDARD INSTRUMENT SIZE CIRCULAR HOLES ..................................... 336

27.7.2

INSTRUMENT FASTENERS .......................................................................................... 336

27.7.2.1 FASTENER MATERIAL AND COLOUR ......................................................................... 336
27.7.2.2 FASTENER THREAD STANDARD, HEAD TYPE AND DRIVE TYPE ........................... 337
27.7.3

INSTRUMENTS WITH UNTHREADED ATTACHMENT LUGS...................................... 339

27.7.4BLANKING OR DOWNSIZING AN EXISTING INSTRUMENT HOLE ............................ 339

27.7.5

ADDING OR ENLARGING HOLES IN INSTRUMENT PANELS .................................... 339

27.7.6

INSTRUMENT PANEL LABELLING ............................................................................... 341

27.8

VHF COM RADIO FAULT FINDING GUIDE ................................................................... 342

28. L’HOTELLIER CONNECTORS.......................................................................... 344
28.1

BACKGROUND ............................................................................................................... 344

28.2

DESCRIPTION OF L’HOTELLIER MECHANISM ........................................................... 344

28.3

SAFETY INCIDENTS INVOLVING L’HOTELLIER CONNECTORS ............................... 346

28.4

SAFETY LOCKING ......................................................................................................... 346

28.4.1SAFETY LOCKING PINS ................................................................................................ 347

28.4.2SCHEMPP-HIRTH SAFETY SPRINGS .......................................................................... 347

28.4.3

UERLING TYPE SLEEVES ............................................................................................. 348

28.4.4

WEDEKIND SAFETY SLEEVES ..................................................................................... 349

28.4.5LS SAFETY SLEEVES .................................................................................................... 350

28.5

INSPECTIONS AND PERIODIC MAINTENANCE REQUIREMENTS ........................... 351

28.6

DAILY INSPECTION ....................................................................................................... 351

28.7

PERIODIC LUBRICATION .............................................................................................. 353

28.8

ANNUAL INSPECTION AND PERIODIC MAINTENANCE ............................................ 353

28.8.1SAFETY LOCKING ......................................................................................................... 353

28.8.2

BALL WEAR .................................................................................................................... 354

28.8.3

COUPLING CLEARANCE AND WEAR .......................................................................... 354

28.8.4LATCH SPRING CHECK (TYPE 41) .............................................................................. 355

28.91000 / 3000 HRS TTIS PERIODIC MAINTENANCE ...................................................... 355

28.10

ANNUAL INSPECTION DOCUMENTATION .................................................................. 355

28.10.1 LOGBOOK ENTRY ......................................................................................................... 355
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28.10.2 MAINTENANCE RELEASE DOCUMENTATION ............................................................ 355
28.11

MAINTENANCE ACTIONS ............................................................................................. 356

28.11.1 TYPE 41 SOCKETS (WITH WEDGE LOCK) SAFETY HOLE ........................................ 356
28.11.2 TYPE 45 SOCKETS (WITH CAM LOCK) SAFETY HOLE ............................................. 356
28.11.3 INSTALLATION OF BALLS WITH REDESIGNED THREADS ....................................... 357
28.12

EXTRACTS FROM L’HOTELLIER PRODUCT GUIDE .................................................. 358

28.13

HISTORY OF AIRWORTHINESS REQUIREMENTS REGARDING L’HOTELLIER CONNECTIONS......................................................................................................................................... 361

28.13.1 GFA AIRWORTHINESS DIRECTIVES ........................................................................... 361
28.13.2 OTHER REFERENCES .................................................................................................. 361

29. GLOSSARY OF ABBREVIATIONS AND TERMS............................................. 362

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1.

INTRODUCTION
This manual sets down some of the technical standards and procedures and is the book of knowledge for
GFA authorised Annual Inspectors when studying, inspecting, repairing and weighing sailplanes. It also
serves as a standard reference of technical standards and procedures for all persons involved in themaintenance of GFA registered sailplanes so as to ensure a consistent, correct, high standard is achieved.
The GFA Manual of Standard Procedures (MOSP) Part 3 - Airworthiness sets down the GFA procedures
such as; the GFA Maintenance system which fills the place of CAR Part 4 and 4A to which GFA hold an
exemption, sailplane registration and certification, minimum equipment and placarding, inspection and repair
requirements and the authorisation of inspectors and their responsibilities. It also details the requirements foramateur built sailplanes. It is intended to be a simpler and clearer guide to the airworthiness rules/
regulations that apply to gliding than the Australian Regulations and is mandatory to all GFA members.
All gliding inspectors and persons interested in airworthiness work should reference the latest version of theManual of Standard Procedures Part 3 - Airworthiness. But read the simpler and plain English guide; MOSPPart 3 Registered Operator’s Handbook, to get the basics of being a sailplane owner. And they must use thisBasic Sailplane Engineering (BSE) manual as the primary reference on how to perform the GFA Standard
System of Maintenance.
BSE provides background and guidance as well as procedures on how to carry out inspections and the workrequired to maintain sailplanes. Note that for LSA gliders you must use the manufacturer’s procedures anddocumentation but you can use MOSP and BSE for guidance. There are Chapters of BSE which now havethe status of ADs and take precedence.

1.1

ACKOWLEDGEMENT
We acknowledge the few hard working GFA Inspectors who have helped review and update this version.
You know who you are and you can be proud. Thank you for all the enthusiastic volunteer work.

1.2

AMENDMENTS TO THIS MANUAL
It is GFA policy to amend this manual annually in November to ensure that the latest knowledge andexperience is available to all inspectors. This 2023 version has two new sections covering L’hottelier
connectors, and radios and avionics.
As part of the ongoing need to maintain quality and standards, a process that enables GFA members tomake recommendations for improvements and inclusions has been included. A document change proposal
form is outlined in this chapter. This form should be forwarded to the GFA office, where it will be added to
the review documentation and forwarded to the person conducting the review at the start of November eachyear. Due to the high workload of our volunteers and staff, it is essential that suggestions have strong detailand reasoning or they may not be acted upon.
Amendments will be completed by reissuing the entire affected section and renumbering it to a different
version. These will be notified in the Soaring Australia magazine and on the GFA webpage. It is the
responsibility of each sailplane inspector to ensure he or she is working from the latest version of thismanual.

1.3

PRIORITY OF PROCEDURES
These standards and procedures are to be followed when the manufacturer’s manuals are lacking on thesubject. The information contained herein is also intended to provide additional information and knowledge
to assist inspectors in learning and performing the required tasks in an efficient manner.
The sailplane manufacturer’s documentation remains the overriding authoritative data in any case where
they differ from any information in this manual. There are Chapters of BSE which have replaced ADs. The
mandatory component of the AD will be added to MOSP 3 and the informative component is in this manual.
A lot of this manual was originally taken from FAA AC43.13. The latest version, 1B/2B or later available
online, should be referred to for more information. In case of conflicting data BSE takes precedent or you
should ask the CTO for advice. It is possible that BSE provides differing advice to suit Australian gliding.

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1.4

DEFINITIONS
Throughout this manual every attempt has been made to be consistent with respect to common terms andabbreviations. However, over time the usage of some terms has changed and inspectors should attempt toassess the context of any abbreviations as to their meanings.
There is a specific chapter in this manual which defines the terminology used. However, the terms ‘glider’,‘powered sailplane’ and ‘sailplane’ are often used interchangeably. Strictly in Australian regulations LSA are
defined as gliders whereas sailplane is used for all others. BSE is being converted to use the term sailplane
instead of glider where possible.
The specific terminology may differ from the common glider pilot usage, but an airworthiness inspector
needs to be able to relate technical names to common glider pilot jargon.

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1.5

DOCUMENT CHANGE PROPOSAL
Tracking Details (Office use only)

Document Title:
GFA Basic Sailplane Engineering

Number:Date Received:

Phone:GFA Number:

Name of person submitting change:
Email Address:
Affected Section(s):Reason for Change:

Source for supporting data or details that may assist the review:

Suggested change (please add extra pages if it is substantial):

NB: In order to take appropriate action on a change request please ensure a:clear description of the issue has been given;

supporting data, if available, has be identified; andsuggested change has been provided.

This form may be sent to the GFA by any of the following means:
Email:Fax:
Mail:

returns@glidingaustralia.org(03)9359 9865
The Gliding Federation of Australia
C4/1-13 The Gateway,
Broadmeadows, Vic.,3047

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2.

TERMINOLOGY
Inspecting and repairing of sailplanes is highly technical and the ability to communicate with other inspectors
is vital. Throughout this manual, specific terms will be defined as needed however it is important that
inspectors are familiar with some of the more general terms.

2.1

SAILPLANE COMPONENTS

Figure 2-1

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2.2

SAILPLANE GEOMETRY

Figure 2-2

2.3

Geometry

HORIZONTAL STABILISER.
There are five basic horizontal stabiliser configurations. They are the conventional tail such as found on theBlanik, the cruciform tail such as on the Libelle, the T tail, the V tail such as on the Salto and the canard
where the stabiliser is mounted forward of the wings.
Each configuration will consist of either an all moving control surface or a fixed tailplane and elevator.

Figure 2-3

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2.4

WOODEN STRUCTURES.
Wooden structures are usually constructed with a structural skin supported by internal structure (semimonocoque). Individual components are glued together as this provides that highest possible strength for agiven weight. Almost all modern repairs are done using epoxy glues. The front of the wings are usually
covered with sheet plywood and the rear of the wings are covered with fabric which is shrunk onto thestructure to make it taut.

Figure 2-4

Figure 2-5

Figure 2-6

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Plywood rib with lightening holes

Pratt Truss rib with tension diagonals

Pratt Truss rib with compression diagonals

Figure 2-7

Solid Spar

Figure 2-8

Routed Spar

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Figure 2-9

Box SparFigure 2-10

Figure 2-11

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Figure 2-12

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2.5

METAL STRUCTURES.
Metal structures are usually semi-monocoque, however some types are constructed so that the skin carries
all of the loads (such as the rear fuselage of the IS-28B2). Most of the metal components are constructedfrom sheet metal by cutting the metal to shape and then bending it to produce the necessary flanges.

Figure 2-13 Metal Wing Components

Figure 2-14 Main Spar

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Figure 2-15 Pressed Aluminium Rib

Figure 2-16 Foam Rib

Figure 2-17 Stiffener
Most metal structures are held together by rivets. These come in many types some of which are shown
below:

Figure 2-18 Rivet Types

2.6

FIBRE REINFORCED PLASTIC (FRP) CONSTRUCTION.
FRP structures (also known as composites) are manufactured by embedding fibres in a matrix material. In
sailplanes the fibres may be woven together as a cloth or grouped in unidirectional bundles called rovings.
The fibres may be manufactured from glass, carbon fibre or aramid (trade name - Kevlar). The matrix used isan epoxy resin.

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A composite laminate which is strong enough for many sailplane applications is actually quite thin andtherefore flexible. To improve the stiffness of the laminate it is often ‘sandwiched’ around a layer of foam or,on older types, balsa wood. Sandwich construction increases the stiffness considerably for only a small
increase in weight.

Figure 2-19 Typical Twill Cloth (two over, one under)

Figure 2-20 Roving

Figure 2-21 Composite Wing

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Figure 2-22

2.7

Composite Wing Components

STEEL TUBE CONSTRUCTION.
Some older sailplanes use a frame work of steel tubes as the fuselage structure. These tubes are joined intoa truss by welding.

Figure 2-23

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3.

INSPECTIONS
Sailplanes are subjected to a comprehensive regime of inspection designed to ensure the sailplane isairworthy and thus safe to fly. In this chapter, an overview of the regime is provided and then themethodology for Annual Inspections is explained.
Depending on how your aircraft is certificated (CoA, EC, amateur built, LSA) varies how you may maintainyour aircraft and the Registration Holder may elect some variations. A Logbook Statement is the method of
conveying the system and the owners decisions to the Inspectors, refer to MOSP 3 and various advisory
documents. A major difference of LSA is that you must follow the manufacturer’s maintenance directions,
you may not do the GFA Form 2 as an alternative.
For every sailplane you must submit a Form 2 return for every Maintenance Release you issue.

3.1

THE INSPECTION REGIME
The airworthiness of a sailplane is assured through the regime of inspections as follows:
Type ofinspection

Purpose

When

Who

Daily
Inspection

To establish that the sailplane is fit for
flight for that day’s flying operations
and certify that in the MaintenanceRelease.

Before the first flight each day

DI Note 1

Independent
control check

A double check that all controls havebeen correctly reconnected.

Following reconnection ofcontrols eg after a Form 2 or rerig

DI Note 1

AnnualInspection(Form 2)To ensure that the sailplane is in asound condition and that, provided it
can still pass a daily inspection, it willremain airworthy for 1 year.

Annually, survey, or following amajor repair or modification

AI Note 2

First
inspection

Brings the sailplane into the GFA
airworthiness system

On import or local constructionof a sailplane

AI Note 2

Periodic
inspections

To ensure the airworthiness of
sailplanes, or components of, which
may be subject to time (usually hours
flown) based deterioration factors.

As required by the manufacturer
or a specific AD for the sailplane
type or component (eg TOST
release).

AI Note 2

Post incident
inspections

To ensure no damage has occurredthat renders the sailplane unairworthy.

Following any abnormal incident
which may have damaged thesailplane eg heavy landing or
ground loop

AI Note 2

Life
Inspections

To extend the life beyond a timebounded age (eg 10 years) or numberof hours limit.

As required by the TC holder ora specific AD for the type. Many
sailplanes are subject
to these.

AI Note 3

Surveys

A detailed inspection, including partsof the sailplane which are notnormally or may not have been
recently inspected.

As required by the TC holder ordirected by MOSP 3 Chapter 14.
Same purpose as life extension
and covers all sailplanes.

AI Note 3

Weight &Balance

To ensure the sailplanes centre ofgravity and empty weight are within
the Type Certification.

After major repairs/
modifications. If equipmentcausing significant mass or
moment is added or removed. At
least at time of surveys.

AI Note 4

Table 3.1 The Inspection Regime
Notes:
1.
DI authorisation is by classification FRP, Wood, Metal
2.
AI authorisation is by classification FRP, Wood, Metal
3.
Surveys and Life Extensions may only be certified by specially authorised AIs

4.
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Details of who can perform which inspection are shown in MOSP 3.
Information regarding the conduct of Daily Inspections is shown in the GFA Gliding DI Handbooks. Details
regarding training and examining AI candidates are in a later chapter of BSE.
The order of precedence of documents is confusing and more so now because some parts of MOSP 3 andBSE have taken over from ADs and have the status of an AD. GFA make it clear which have the status of an
AD and take precedence over manufacturer’s documents. Refer to MOSP 3 for details.

3.2

SYSTEMIC AND HUMAN FACTORS
Before describing the inspection process, it is important to consider the systemic (ie organisational) andpeople related problems that may affect the quality of an Annual Inspectors work.

3.2.1

CLUB STRUCTURE
In modern accident investigation, increasing emphasis is being placed on the overall responsibility of theorganisation to provide a working environment which is conducive to safety.
If an inspector fails to tighten
a bolt because he or she is under pressure to have the aircraft finished then the club officer who has set an
unreasonable work schedule or failed to provide adequate facilities for the job must bear some of the
responsibility.

3.2.2

FINANCE
Airworthiness standards cannot be compromised for any reason. An inspector cannot stand up in court andsay “we couldn’t afford to put a new one in so I let it go”. If the money is not available and the problem isserious enough, the sailplane should be grounded.

3.2.3

WORKLOAD
Overloaded inspectors are more likely to rush and may make mistakes. Inspectors should make a point of
having as many helpers as is necessary (but not so many that the inspector loses track of what they are
doing). This has a double advantage as there is someone to help lift heavy objects and you may be training
someone who can ease the workload in the future.
Teaching potential new inspectors and the spreading of airworthiness knowledge are very important.
Inspectors who lock themselves away alone, deny themselves the chance of a second opinion.
Club management must also bear some responsibility for the workload of its inspectors.

3.2.4

COMPETENCY OF HELPERS
As well as dealing with the technical aspects of inspecting sailplanes, inspectors must deal with helpers and“experts”. When working with helpers it is important to keep a close eye on their work. The word of unknown
experts must be treated with caution. If technical assistance is required, seek out a recognised source of
information. Be prepared to ask a disruptive person to leave the workshop. After all, it is the inspector’s final
signature that says a sailplane is safe to fly.

3.2.5

INSPECTOR SUITABILITY
The person who is to inspect and signoff the sailplane must be fit to perform the task. This fitness includes
having the relevant approvals, knowledge of the sailplane (or the ability to find and use information) and theability to physically perform the inspection tasks.
The following attributes of physical ability are required:a.

Good vision. If glasses are required then they must be used. Good lighting is important. To assist in
this area there are various scoping devices that are useful and relatively cheap, they can assist in thevisual assessment of dark and hard to get to areas.

b.

Good hearing. Movement of damaged or poorly supported parts usually results in sound and theability to hear this is important. A workshop with low ambient noise levels often assists with thesetypes of assessments.

c.

Sufficient movement so that access to the relevant parts can be gained. Removal of parts such as
releases often requires considerable dexterity. It is often the case that specialist tools can be
made/adjusted to minimise physical load.

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3.2.6

LACK OF TECHNICAL INFORMATION
Inspectors are often faced with inadequate manufacturers’ manuals when inspecting sailplanes, especiallyfor older types. BSE is intended to fill in the gaps; however sometimes an inspector will encounter a problem
which is not covered by any documentation and which they have not experienced before.
Inspectors who cannot solve a problem on their own should seek the advice of a more experienced
inspector. We don’t have to know everything but we do need to make certain we use the correct approved
data. If the problem still cannot be solved the inspector should contact their RTO-A or the CTO. Inspectors
should never “guess” the solution to a problem.
Be self regulating. If you don’t know enough about a task, get help or learn how. Just because you have arating does not mean you can, have to or should do everything.

3.3

THE ANNUAL INSPECTION PROCESS
Conducting an annual inspection of a sailplane is an involved and complex task. If it is not handled in aclear, systematic, logical way it is possible for faults to be missed and for sailplanes to be reassembled
incorrectly. There are eight main steps for performing an inspection:

3.3.1

a.

Preparationsb.

Pre-inspection review of documentationc.

Aircraft overviewd.

Functional checkse.

Rectify and Inspectf.

Checks after rigging

g.

Documenting the inspection outcomeh.

Evaluation flight

PREPARATIONSIn good time before the planned inspection action the following:a.

Request an Annual Inspection Kit from the GFA in good time.

b.

Determine the best dates to conduct the inspection.

c.

Arrange for access to a suitable workshop or hangar.

d.

Arrange for suitable helpers.

e.

Arrange any expert help needed for repairs or particular elements of the inspection.

f.

Acquire any necessary special tools and consumables.

g.

Or instead of c. to f. send it to a GFA Approved Maintenance Organisation (AMO). You can greatly
reduce their charges by having your paperwork in order.

3.3.1.1 DETERMINING WHEN TO CONDUCT THE INSPECTION
A sailplane must not fly once the Maintenance Release (MR) has expired. An Annual Inspection may be
conducted before expiry of the MR. Therefore, when determining the date of the inspection, consider:a.

How long will the annual inspection take? This depends on the sailplane, the inspector’s experience,
availability of help? Is there a repair that needs to be sent away or a part required and if so what is
the lead time?

b.

When will expert help be available for a repair or planned modification (eg installation of oxygen)?

c.

Is the sailplane required to be available for use up to the date of expiry of the MR? Plan an inspection
period after this date.

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d.

Is the sailplane required for a special event (eg competition or wave camp)? Will the MR expire
before or during the required period? In which case plan the annual inspection to commence at adate that will comfortably ensure it is completed before the special event.

3.3.1.2 LEVEL OF INSPECTION
The level of inspection required varies with a number of factors. These factors include:a.

The sailplane’s usage in the past 12 months. High usage may have caused more wear or
deterioration. Low hours may mean underlying issues have not yet become apparent.

b.

Storage or operational conditions. An inspector may need to be more cautious if the sailplane has
been stored in a damp or leaking trailer, compared with if it has been stored in a dry hangar. Or flown
near the sea.

c.

The Inspector’s familiarity with the specific aircraft. If an inspector has never seen a particular
sailplane before, the level of inspection will obviously be more in depth than if the inspector has
worked on that particular sailplane over the past few years and knows the history. For example, if theInspector lubricated the elevator circuit last year, then he might decide a visual inspection will beadequate this year.

d.

It is wise that every few years the sailplane is inspected by another AI. This will apply anotherperspective and set of expertise.

Ultimately, the inspector must conduct a level of inspection that will satisfy them that all ADs have been
complied with and the aircraft is airworthy.

3.3.2

PRE-INSPECTION REVIEW OF DOCUMENTATION
The documentation trail of a sailplane will usually show areas that need to be reviewed, specific actions thatneed rectification, and historical problems that keep arising and therefore require further understanding.
The documents that should be assembled and consulted include the following:a.

GFA Annual Inspection Kit for the specific sailplane. This is provided by GFA Secretariat on request
and payment of a fee. The kit provides a wealth of information intended to help the Annual Inspector
perform his duty fully.

b.

Aircraft logbook. This will give a complete history of the sailplane, and is very useful for understanding
previous work undertaken on the sailplane. It is also required for the recording of the results of thecurrent inspection.

c.

Previous Maintenance Release. This will show the amount of flying, any Major or Minor defects andany periodic maintenance activities undertaken in the last year. All minor defects except Permissible
Unserviceabilities must be corrected at an annual inspection.

d.

Certificate of Airworthiness and Certificate of Registration will show the current legal situation of the
sailplane. Note, if the registered operator or his email recorded on the Certificate of Registration is notcorrect then Airworthiness Directives will not be sent to the person(s) who need them. These must be
checked annually for validity and currency.

e.

Current flight and service manuals from the manufacturer or equipment/parts supplier (eg a radio
manual), will often give advice on servicing cycles and replacement schedules.

f.

Airworthiness Directives (ADs), technical notes and Airworthiness Advice Notices (ANs) will all assist
the understanding of the current and future needs of the sailplane. Airworthiness Alerts will provide
updates and warnings.

A good understanding of these matters prior to commencing the inspection should allow a plan of actions
and requirements to be created.

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3.3.2.1 ADS, ANS, AND AWAS
The Form 2 kit will include a list of known general and type specific ADs and ANs for sailplane to beinspected. This can be used as the basis of a checklist of applicable ADs and ANs, but must not be regarded
as definitive. An example is shown in the following figure:

Figure 3-1

Example of a Form 2 Kit Type Specific AD List

It is the Registered Operator and Annual Inspector’s role to find all applicable ADs and technical notes. GFA
will help with the above registers of what we know may be applicable to your aircraft.
An inspector can also check the GFA General Registers of ADs and ANs on the GFA website where asearchable list is provided. This is required if the Form 2 kit is old and the registers may have been updated.
Be aware that the complexity of modern sailplanes has made it almost impossible for GFA to find all ADs. A
motor glider for example may have ADs on the airframe, various instruments, propeller, generators andmany other items. The other factor that adds complexity to the AD situation is that many different
organisations issue ADs, eg CASA, EASA, FAA, and other state-of-design authorities as well as GFA.
If you find an AD that has not been identified by GFA, please advise the GFA which will then put it in theregisters where applicable. Manufacturer’s Technical Notes (TN) or Service Bulletins(SB) are not on theirown mandatory but they are good advice and usually provide the background to an AD that makes them
mandatory if necessary.
We have moved a number of ADs into MOSP 3 and BSE so in future just refer to those sections, they aremandatory. We will cancel the ADs and list the MOSP sections in the Registers. Generally no change iscaused by this but the reason is ADs are not meant to provide the standard system of maintenance but are
rather there to address risks to flight. It is the modern way.

3.3.3

AIRCRAFT OVERVIEWWhen inspecting a sailplane the next step, regardless of the type of inspection, is to assess the entire
aircraft. This overview should include an assessment of the overall condition of the sailplane, is it tatty, clean
etc. Obvious damage will be easily spotted but if you have never seen a particular sailplane before you
have to start by identifying all obvious damage.
Items which should be identified in the overview inspection include, but are not limited to: Damaged skin,cracked canopies, flat tyres, badly aligned controls, controls working in the incorrect sense etc. Every
inspection of a sailplane, including the pre-flight walk around, should detect these items.

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If a sailplane appears to be complete and undamaged then the inspection should progress to the function
stage. If there is damage, then obviously it must be repaired before the functional check can be conducted.
Up to here and even the Functional Checks should be done weeks before you take it out the air so you knowwhat needs doing and thereby allowing some pre-planning to be done. Obviously it is better to know before
you start that the ASI needs overhauling, rather than finding out after the rest of the inspection is completed
and the sailplane is about to be put back in service. Or to get a few bearings so you can replace them.

3.3.4

FUNCTIONAL CHECKS
During this part of the inspection each part should be examined to ensure it is in a suitable condition to
perform the task it was designed for. The inspector should use the GFA Form 2 as the basic checklist
together with any additional inspection requirements from the manufacturer’s manuals. Alternatively theowner can elect (in a logbook statement) to follow the manufacturer’s or another approved maintenancesystem. Inspectors should also ensure that all ADs have been complied with by checking the logbook
entries.
It is best to start with a rigged sailplane so that all faults can be found as follows. The function check should
ensure that the structure is undamaged, has no unacceptable cracks and is assembled correctly. The control
systems should be checked for correct operation, damaged parts, free-play, attachment to the structure,cleanliness, adequate lubrication etc.
As a general rule this is the best time to conduct deflection and wing frequency checks (see below). A wing
frequency check may also indicate if there have been structural changes since the last sailplane inspection.
This philosophy of inspecting for correct function and condition of each sub-system should be continued until
the entire sailplane has been inspected. If defects are found or it is necessary to dissemble the system tocomplete the inspection, the operation of the system should be re-inspected after re-assembly.
Details of the inspections required for the tow release mechanism are contained in a separate dedicatedchapter of this manual.
Details of the inspections required for oxygen systems, if fitted, are contained in a separate dedicatedchapter of this manual.

3.3.4.1 WING FREQUENCY CHECK
A wing frequency check is conducted as follows:a.

The aircraft documentation will have the wing frequency, both initial and historical; this is the natural
vibration of the wings. It is generally conducted on the main undercarriage, with the tire at the correctpressure, but each manufacturer has their own ideas and you must follow the manufacturer’s
instructions.

b.

A drinking glass will ‘ring’ when tapped, but if it is cracked it will be ‘dead’. Similarly a sailplanestructure will respond to internal damage, loose wing fittings, etc by changing the frequency at which it
wants to naturally vibrate.

c.

Therefore it is important to know the frequency and monitor it to ensure any sudden changes are
known and the reason investigated.

d.

The manner of conducting a wing frequency check is to set the aircraft up as described above, on asolid surface with the wings level, gently shake the wings up and down until the wings flex at a steadyrate. Maintain the gentle shaking and, using a suitable watch or someone else counting, determine thetotal number of wing flexes in a period (up and down is a count of one). Confirm the rate iscomparable with previous checks and the sailplane specification.

3.3.4.2 CONTROL SURFACE FREEPLAY CHECKFree play in excess of the maker's (or BSE) limits may indicate bearing wear, loose control horns, or othercontrol system defects that may not be readily found once the sailplane is de-rigged.

3.3.4.3 CONTROL SURFACE DEFLECTION CHECK
Incorrect control surface deflection may indicate control system damage, incorrect pushrod/ cableadjustment or control stop problems and could explain adverse handling characteristics.
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3.3.4.4 FLIGHT CONTROL SYSTEM STOPS
Incorrectly adjusted or damaged control stops can lead to system damage (bent pushrods, damaged
bellcranks and control surface hinges etc.

3.3.4.5 ASI AND ALTIMETER CALIBRATION
If the ASI or Altimeter calibration is out, the instrument will need to be sent away for overhaul and this takes
time. Check any colour coding against the cockpit placard; differences could indicate that the instrument
may have been swapped from another aircraft. The ASI need not be colour coded unless the Flight Manual
requires it but if there is colour coding on an instrument it must accurately reflect the limits for the particular
sailplane.

3.3.4.6 HARNESS INSPECTION
Is there an Airworthiness Directive out on the harness? How old is it? Webbing damage or age deterioration
may require the harness to be replaced or re-webbed. It is common to find harnesses still in service wellbeyond their approved service life. Re-web or replace such harnesses and if the harness is of the “pull down
to tighten” variety, take the opportunity to convert it to “pull up to tighten”.

3.3.4.7 FATIGUE LIFE
As time goes by sailplanes may be kept flying by cannibalising parts. Many of these parts will have fatigue
life limits. Check for components that may have exceeded their life limit or will do so during the next 12months (exchanged component life must be listed in the Logbook). The whole airframe may also be close to
its certified fatigue life limit.

3.3.4.8 LOAN EQUIPMENT
GFA and the State Associations have a number of specialised tools available for loan to inspectors. If you
will need to borrow any of these items, book them in advance through your RTO-A or State Association.
Loan equipment includes:a.

Electronic weighing scalesb.

Tow release testing toolc.

Endoscope (Boroscope)d.

Cable swaging tools (not all states)e.

Fluoro crack detection equipment (not all states)f.

Altimeter and ASI tester (new equipment coming soon)

3.3.4.9 INSPECT AND RECTIFY
The above functional checks before you derig tell you what needs addressing. You now derig and resolve allthese issues.
The inspector then carries out the inspection using the Form 2 (or a manufacturer’s schedule) as a checklist.
It is good policy to inspect the sailplane together with all ancillary equipment such as radio, oxygen system,tie-down, battery etc. The Inspector should review these items for function, security and their influence on
weight and balance.
To complete each area ensure that all parts have the correct safety locking. Since a sailplane cannot “pullover to the side of the road”, all nuts and bolts, turnbuckles, pins etc. must have two factors which prevent
them from undoing. The primary securing method for nuts and bolts is the friction generated when the bolt istightened. The secondary securing method, referred to as “safetying”, may be the elasticity of a Nyloc nut or
mechanical securing such as split pins, safety wiring etc.
The inspection schedule is designed to be used as a checklist. At the end of each major component group
there is provision for recording a dual inspection by an independent inspector of DI or higher authorisation(See items 16, 20 and 45). This is to verify the integrity of critical internal items & controls which would not
be visible once the structure is closed up.

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The Form 2 is setup so that the inspector can sign it out before re-rigging and independent control checks.
He only does this if he knows he has done the rigged checks already and he made no changes. The
Independent check and rerig can then be done later at the airfield by a DI inspector.
Otherwise it is re-rigged so control surface deflections can be re-measured to ensure they are within thespecified tolerances. If extensive fabric replacement, painting or repairs have been done or extensivechanges made to the aircraft equipment or ballast, then the sailplane must be reweighed.
Once he has completed the Logbook certification (see Section 3.4.1 below), the Annual Inspector signs &dates the “Inspectors Certification” on the bottom of Form 2 Page 2 and fills out the Maintenance Release.
The MR can be issued for any period up to a maximum of 12 months, at the inspector's discretion, but notbeyond due Survey or life extension programs. Any scheduled maintenance required by the manufacturer,
the GFA, or the inspector which may fall due before the next Annual Inspection must be entered in Part 1 of
the MR. The date of issue of the MR is on or prior to the evaluation flight.
For powered sailplanes; the main Annual Inspector may not have an engine rating. The AI arranges anengine rated inspector signs off the engine and then he can sign out the whole aircraft.
The Inspector completes the Inspection Report (and a copy of Appendix A/ Manufacturer’s schedule if theaircraft is a powered sailplane) and forwards it to the GFA secretariat.

3.3.5

CHECKS AFTER RIGGING THE SAILPLANE
The sailplane may now be rigged in preparation for the evaluation flight. At this point the Independent
Control Check must be performed. Check the pitot system is working. Once the inspection is completed an
Independent Control Check is performed by the holder of a Daily Inspection or higher airworthinessauthorisation. This person must check that all parts are correctly attached, that all controls are correctly
connected and safety locks in place, that there is full and free movement and that the controls move in thecorrect sense. Concealed controls, which have already been checked and signed out at Form 2 items 16, 20& 45 in the inspection schedule, need not be re-inspected for safety locking.
Check the documentation is complete:a.

The Maintenance Release has been issued.

b.

The Logbook certified.

c.

A Daily Inspection and independent inspection has been performed and recorded in the DI section of
the MR and signed off on the bottom of the Form 2.

The sailplane may now undergo an Evaluation Flight in accordance with the procedures in Section 3.5.
Please submit your Form 2c return with hours and landings to date to the GFA office every time you issue a
MR.

3.4

DOCUMENTING THE INSPECTION OUTCOME

3.4.1

THE LOGBOOK ENTRY
No inspection is complete without a logbook entry to show that the inspection has been completed and torecord all rectifications which were necessary. A short and concise entry must be made in the Maintenance
Log (white pages) of the logbook of everything that was done during the inspection. Write your entries so theperson reading it in the future understands exactly what has been done. Make sure you record everythingthat you did so it is clear. The most common fault is to say “All ADs complied with” this does not tell anyone
which or what you did.
The RO may fill in lists and hours in the Logbook, neatly, but only an Annual Inspector may make acertification entry in the front part of the Logbook certifying the maintenance was correctly performed and the
Logbook is correct.
The following is an example of a logbook entry and should be used as a guide:

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At TTIS = xxx hours, Landings = xxx an annual inspection in accordance with GFA
Form 2 and the Maintenance Manual was completed during which the following
rectifications were carried out:a. New left front rudder cable fitted.
b. New nose release spring fitted.
c. New bearings fitted to right hand aileron wing root bell crank.
d. GFA ADs XX issue 1, ZZ issue 3 complied with.
Wing frequency = xxx.
Maintenance Release No 0001 issued.
Name: ________________ Signed: ________________ M________ Date: ________
Please do similar for engine and propellers. Some of these have their own logbook so if they are changed itgoes with them – keep it up to date as well as the airframe logbook.

3.4.2

OTHER SECTIONS OF THE LOGBOOK
There are some differences in logbooks dependent on their age. Please amend your logbook to make itcompatible. This helps ensure entries and format for all types are similar, makes it clearer, and easier toensure the continued maintenance of your sailplane and makes the next inspector’s job easier. It is worth
getting the above right now and then it will be correct and easier thereafter.
Please see MOSP 3 for requirements on Logbooks.
What is essential in a logbook is as follows;

3.4.2.1 WHITE PAGESWhite pages:a.

Annual updates are permissible but monthly totals of hours and landings are transferred from themaintenance release (Form 1) at the Annual. Except where a maintenance activity has been
performed requiring a logbook entry during the year; in which case hours and landings must be
updated at that date. It is worth double checking all MR records and arithmetic as errors are very
common after a day flying.

b.

The Maintenance Log is exactly that, it is the only legal record and must contain a certification(signature, name, GFA number (new M-xxxxx) and date for each entry, bulk entries at an Inspection
may have one certification). Maintenance activities that require a logbook entry are; each AD when
first performed or a listing for recurring ADs each year, ANs, repairs, modifications, test results, lifed
component changes, scheduled maintenance and any other significant activity. (Cleaning andpolishing are not significant but installing a new radio is.)c.

Inspection entries in the Maintenance Log should be opposite the corresponding years, hours andlanding record. Pages should be ruled off at the annual so that it is very clear where the entry starts
and finishes for that year, do not leave blank lines/spaces in your certification statement.

3.4.2.2 GREEN AND YELLOW PAGESGreen and yellow pages:a.

The Modification Record is a complete list of authorised modifications and the date of incorporation {*}b.

The Repair Record contains records of all (significant, usually structural) repairs carried out {*}c.

The AD Record is a complete list of ADs and the incorporation date. For convenience this can beseparated into General and Specific ADs and into non-recurring and recurring ADs, ie a number ofpages but easier to check off. {*}d.

The Lifed Structural Component Record is a complete list of any component that requires changing at
a defined interval (if any) and details of the life limit and date of changes. Look in the Maintenance
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e.

Weight and Balance Record records the weight and balance data and any changes since the last
weight and balance.

Note: Green and Yellow pages are not certifications, all work must be certified in the Maintenance Log, i.e.
the front part of the logbook; therefore all ADs will have two entries; one in the AD Record and one in the
Maintenance Log. The neatest way to tie all of these together is to record the page number of thecertification against the record entry e.g. (P14). Make sure the certification is there or an Annual Inspector
adds one once he has confirmed the AD was completed. Then complete the AD Record so you don’t have tosearch for all of them every year.
The Lists marked {*} above will make your life easier next year. Please add them if your Logbook does nothave them.
Remember you are responsible for all work you certify even after you sell the aircraft. An honest mistake is
one thing but if it kills someone be sure you did your work properly at all times. You have liability insurance
under GFA if you are a paid up member at the time of the certification and the sailplane is GFA registeredand you have followed the regulations and GFA procedures.

3.4.3

OTHER GUIDANCE
If you type up certification statements then glue and staple them into the logbook. And make a shortsummary statement that you certify in pen in the logbook in case the page goes missing. Make sure you
write everything you did. And be clear, “All ADs complied with” tells the coroner nothing. Whereas “Thefollowing ADs were checked and complied with; GFA AD 123, EASA AD 231, CASA AD/Eng/2.” says
exactly.
a.

The Weight and Balance sheet must be recorded as an entry on the W&B pages then put in the
pocket in the back of the logbook.

b.

All other entries must be neatly handwritten in pen or printed.

c.

Errors are to be neatly crossed out and the correct entry made adjacent to it; liquid paper or white
out is not to be used.

The logbook is a valuable and legal part of the sailplane. Without it or poorly completed and the future ownershould realise he is taking a chance and expect a large reduction in price. Look after the logbook; store it so
it is safe from fire or accidents.

3.5

EVALUATION FLYINGThe annual inspection is completed when the sailplane logbook is signed. The evaluation flight is not part of
the annual inspection. However, an evaluation flight must be performed to ensure that the sailplane’s
handling characteristics are normal for the type. The inspector should provide the evaluation pilot with theinformation in this section. The completion of a satisfactory evaluation flight may require multiple launches.
Any defects found are to be recorded under Major or Minor Defects in the Maintenance Release as
appropriate. Any Major Defect will mean that the sailplane cannot be flown again until the defect is rectified
and signed out by an Annual Inspector. Minor Defects mean the sailplane may continue to be flown but thedefect must be checked at each Daily Inspection or interval as listed in the MR.
If the flight is satisfactory the Evaluation Flight Report in the Maintenance Release is signed by the pilot andthe sailplane can be returned to service. If you do a run to VNE then tick the box. Otherwise write the speed
you went to so that future pilots know.

3.5.1

EVALUATION PILOT AUTHORISATION.
Pilots must be experienced and authorised in accordance with the GFA Manual of Standard Procedures Part
2-Operations.

3.5.2

PREFLIGHT PROCEDURES
Once the annual inspection is completed and the maintenance release has been issued, a daily inspection
should be performed and certified in the new maintenance release. The DI will normally be performed by theevaluation pilot (would you let anyone else do it for you?).

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The sailplane will potentially have had control systems disconnected and reconnected, it is a requirement to
conduct and document an independent control system check prior to flight.
An airworthy parachute must be worn.
The pilot should visually check that the canopy jettison system appears to be operational.
The pilot must also be aware of things which can go wrong on the flight. A pilot who is prepared for an
emergency has a much greater chance of dealing with it. Things which have gone wrong during evaluationflights include:

3.5.3

a.

Control system reversal.

b.

A primary flight control not connected.

c.

Premature release due to incorrect release maintenance.

d.

Vibration and or flutter caused by slack cable control systems, loose hinges, loose bolts, incorrect
control surface balance etc.

e.

Poor control effectiveness due to incorrect control deflections or missing gap tapes or loose cables.

f.

No ASI indication due to covers left on, plumbing incorrectly fitted, holes drilled through plumbing etc.,g.

No altimeter readings due to covers or plugs.

h.

The sailplane does not fly straight due to miss-rigged controls, bad repairs (twisted tailplane or wings)
etc.

i.

Lack of stability due to errors in the weight and balance calculations (CG too far aft).

j.

Inability to flare due to errors in the weight and balance calculations (CG too far forward).

k.

Structural failure due to defects missed during the inspection.

FLIGHT PROCEDURES
The following procedures should be followed during evaluation flights. The order of these tests is important
as discovering a flutter problem part way through a spin recovery would be very unpleasant. The pilot should
assess that the sailplane is functioning correctly, especially the ASI, before attempting the VNE run.
Multiple launches may be required to complete the entire programme.

3.5.4

LAUNCH
Under some circumstances, depending on the work done on the sailplane, an aero tow is the only way togain enough altitude. In most cases winch launching is satisfactory however two or three flights may benecessary to fully check the sailplane.

3.5.5

FUNCTIONAL CHECK
Once airborne, the first step is to ensure that the sailplane is functioning correctly. The following items
should be checked:a.

You can even abort before takeoff. In a motorglider make sure you achieve static or normal RPM, youachieve the normal acceleration, etc. Check braking before moving.

b.

Aircraft controllable.

c.

Instruments operating correctly.

d.

Undercarriage operation.

e.

Flap operation (if fitted).

f.

Spoilers or dive brake operation.

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3.5.6

GENERAL HANDLING
Examine the handling characteristics by flying straight and observing for:a.

Slip or skid.

b.

Uncommanded roll or turn.

Gently turn in both directions paying attention to control coordination and controllability.

3.5.7

RUN TO VNE
Increase the speed in 10 knot intervals up to the manoeuvring speed, then in 5 knot intervals up to VNE. At
each speed check the handling. If turbulence (thunderstorms, rotor) is evident do not exceed the maximum
rough airspeed limit. Do NOT use full controls above maximum rough airspeed limit, this can overstressthe aircraft.
Observe the following:a.

Vibration or snatching of controls.

b.

Excessive control movements or forces.

c.

Oscillations in yaw or pitch.

d.

Any abnormal structural deformation or movement

If any problems are encountered, slow down immediately. Flutter becomes worse with increasing speed.
If unable/ unwilling to complete the run to VNE, write the speed attained next to the high speed tick box inPart 1 of the Maintenance Release.

3.5.8

STALL - STRAIGHT AND LEVEL
The sailplane should be flown at its minimum sink speed with the wings level and no slip. The control column
is pulled back gently to lower the speed by 1 knot per second until either a minimum speed or stall is
produced. Recover in the normal way.
Observe the following:

3.5.9

a.

The indicated minimum or stall speedb.

Aileron control through the stallc.

Stall buffetd.

Wing drop and tendency to spine.

Difficulty recoveringf.

Height lost

STALL - TURNING
Only perform this manoeuvre on sailplanes approved for intentional spinning.
For an effective way to enter a spin (having first done a pre-aerobatic check of course):a.

Enter a turn at normal circling speed but stop the bank at about 10º.

b.

Smoothly apply an increasing amount of rudder, at the same time maintaining a constant nose attitude
by progressive back stick movement.

c.

Allow the bank to increase due to secondary effect of rudder - do not “hold off bank” by crossing thecontrols.

d.

The spin will occur from about 40º bank angle.

Provided the sailplane is capable of spinning (i.e. it is correctly rigged and within its CG limits), the above
method is always successful. Crossing controls at spin entry will usually cause unpleasant effects, such as
pitch oscillations, and will often inhibit spin development when it would otherwise be possible.
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Recover from the incipient spin after ¼ of a turn using the standard procedure.
Observe the following:

3.5.10e.

The motion of the sailplane during entry and recoveryf.

The maximum speed during recoveryg.

The height lost (estimate)

PITCH STABILITY
Trim the sailplane at 1.4 times the stall speed. If there is no trimmer fitted note the trim speed. Gently
increase this speed by 20% and slowly relax the pressure on the control column. Note the speed thesailplane returns to. Repeat only this time decrease the speed by 20%.
Function the trimmer to achieve the maximum and minimum trim speeds.
On easing the pressure on the control column the speed should immediately return towards the trim speed.
On some types the speed will oscillate around the trim speed pitching nose up and nose down every 20 - 30
seconds. Provided this can be easily controlled, it is not a problem.

3.5.11TURN STABILITY
Fly the sailplane in both left and right hand turns at 30° angle of bank. Reduce the speed gently until theminimum flying speed is reached. Complete several full orbits.
Observe the following:a.

Minimum speed for a steady turn.

b.

Any control difficultyc.

Any abnormal control forces, particularly reversald.

Position of controls during the turne.

Response to small control movements

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4.

PITOT-STATIC SYSTEMS

4.1

GENERAL
The pitot-static system is a combined system that uses the static air pressure, and the dynamic pressure
due to the motion of the aircraft through the air. These combined pressures are used for the operation of the
Air Speed Indicator (ASI), altimeters, Vertical Speed Indicator (VSI) and gliding computers.
The correct operation of this system is of vital importance to the safe operation of the sailplane. Leaks in thesystem may cause errors in Indicated Airspeed reading of 10 knots or more. Errors may result in incorrect
reporting to other aircraft and ATC infringements can be a danger to other aircraft.

WARNINGA GFA Annual Inspector or a CASA approved instrumentation technician is required
to check and certify in the logbook after any work on the Pitot- Static system.

4.2

INSPECTION AND TESTING REQUIREMENTS
MOSP 3 Section 13.6 defines the mandatory GFA procedures for the Pitot-Static system. BSE Chapter 4
provides the GFA System of Maintenance for Pitot-Static systems replacing the regulations to which GFA
has exemptions, ie CAO 100.5. This chapter provides training and guidance on how to perform the required
testing and is to be followed unless manufacturer’s data dictates otherwise. Refer to Section 4.7 below for
details.
AN 169 has been incorporated into this chapter of BSE, the standard GFA system of maintenance, and so iscancelled.

4.3

DEFINITION OF TERMS
Static Pressure

The static pressure is the ambient air pressure surrounding the
sailplane. This pressure reduces with increasing height. Most
instruments use it as a reference pressure.

Dynamic Pressure

The dynamic pressure is the pressure that the air flow exerts due
to its kinetic energy impacting a surface.

Total Pressure

The total pressure of an airflow is the pressure that would be
generated if the flow were brought to a complete stop against aflat wall or a pitot tube.

(Ram Air or stagnation P)
Position Error

The static ports are affected by the airflow around the sailplane. If
the altitude is constant and the angle of attack changes, the flow
over the static port changes and the static pressure measured will
be different even though the air pressure has not changed. Flight
manuals often have a position error correction chart to allow
calculation of Calibrated Airspeed (CAS).

True Airspeed (TAS)(knots = kn)

This is the speed of a sailplane relative to the airmass in which it isflying (only equals the speed over the ground in nil windconditions).

Indicated Airspeed(IAS)

This is the speed shown on the airspeed indicator. IAS only shows
true airspeed at standard sea level pressure and temperature.

Calibrated Airspeed(CAS)

This is the speed of the aeroplane after density and temperature
affects have been allowed for. Calibrated airspeed equals
Indicated Airspeed when instrument error and position error are
zero. See below.

Cabin pressure

In sailplanes this is usually below static pressure. Sailplane
cockpits usually leak air out around the top of the canopy where
the pressure is reduced. This lowers the pressure in the cockpit
slightly. In a very well sealed sailplane, it may be possible to haveslightly higher pressure in the cockpit if the air vent is open forcing

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air into the cockpit. Cabin pressure is not to be used as a sourceof static pressure for ASI, VSI or gliding computers. Altimeters are
not significantly affected and can use cabin pressure as a sourceof static pressure.
hPa = mbars

The units of hPa and millibars are the same. The sub-scale ofaltimeters must be in the unit of hPa and mbars.

QNH

The aviation Q code for the sub-scale setting, ie the barometricpressure scale, so the altimeter reads height above sea level. The
standard barometric pressure is 1013mBar which should be used
above 10,000ft to report altitude in flight levels. It is reset to QNH
on decent below 10,000ft. The sub-scale is important to be correct
if flying above 10,000ft.

Table 4-1 Definitions of Terms

4.4

PITOT-STATIC SYSTEM COMPONENTS

4.4.1

MINIMUM EQUIPMENT AND UNITSMOSP 3 v7.3 states in Section 8.1.1; Each sailplane must have certain minimum equipment, and that
equipment must meet appropriate standards. The minimum equipment for all Australian registeredsailplanes, except LSA, is:a.

One Air Speed Indicator (ASI). The instrument must be able to indicate at least 5% above the
manufacturer's Maximum Allowable Speed in Smooth Air (VNE). The ASI must be in full view of thepilot in command.

b.

One altimeter, displaying height in feet and with its sub-scale calibrated in Hectopascals (same as
millibars)c.

Magnetic compassd.

A time piece (This requirement may be met by a pilot wearing a watch)

For LSA the minimum equipment is specified by the manufacturer and only the manufacturer may authorise
other equipment.
The placards must be in the same units as the instruments.

4.4.2

GENERAL SYSTEM LAYOUTS
There are three basic layouts of pitot-static systems found in sailplanes:a.

Separate pitot and static ports (the most common type).

b.

Separate pitot and static probes found on many older sailplanes.

c.

Combined pitot/static probes. These probes are usually mounted on the tailfin or nose of the sailplaneattempting to measure undisturbed airflow.

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Figure 4-1

4.4.3

Typical pitot-static system layouts

PORTS OR VENTS
The ports or vents are special holes in the sailplane connected to the pressure tubing which are used tomeasure the Total and Static Pressures.
The Total Pressure, also known as “ram air” (i.e. air that is stopped against a moving aperture), is measured
through a pitot tube which is an open tube facing directly into the airflow.
The Static Pressure is measured through a “static port” which is a hole usually in the side of the fuselage ata point where the manufacturer has determined that the pressure over the fuselage at that point is as close
as possible to the true static pressure. There are usually static ports on both sides of the fuselage to reduce
sensitivity to yaw. They don’t measure the pressure due to movement and attempt to measure the airmasspressure as if the sailplane was not there. Many Flight Manuals will have Pressure Error Correction Chart tocorrect for static errors due to the location of the static ports.
It is very important that the correct static ports are connected to the ASI. Many sailplanes have 2 sets ofports; one for the ASI and one for the variometer (vertical speed) system. It is vital that the correct ports areused or the ASI may read incorrectly.

Figure 4-2 Typical Vent Locations

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4.4.4

TUBING
Each port is connected to a length of tubing which transmits the pressure to the instruments. This tubing is
usually 5mm PVC tubing although the softer, more expensive silicone tubing is sometimes used. PVC tubing
hardens over time and it is recommended that the tube is replaced every few years and connections
checked annually and trimmed if they leak. Once the tubing has gone hard it is very likely to leak if
reinstalled.
Throughout the pitot-static system there will be a number of connectors and T-junctions necessary toprovide the correct system layout. Wherever a junction exists, there is the possibility of a leak and so theyshould be kept to a minimum.
A correctly installed junction should need no extra sealing other than the fit of the tube onto the barbed
fitting. The need to install elastic castrator rings or cable ties to remove leaks indicates that the tubing is
faulty and should either have the hardened end removed or a new piece of tubing fitted.

4.5

AIRSPEEDIn line with the International Civil Aviation Organisation (ICAO) agreement, the airspeed of all Australian civil
aviation aircraft, including sailplanes, is usually measured in knots.
A knot is defined as 1 nautical mile per hour. This is slightly faster than a mile per hour and not quite 2
kilometres per hour. Table 4-2 gives the conversion of knots to the most common speed units.

1 knot (kn)1.688 ft/s

1.1508 mph

1.852 km/h

0.5144 m/s

Table 4-2 Speed Conversion Factors

4.5.1

AIRSPEED INDICATOR (ASI)
The ASI is a primary flight instrument which displays Indicated Air Speed to the pilot(s). It is a mandatory
item specified in MOSP 3 Section 8.1.1. For certified sailplanes, the ASI must be certified to a standard eg
FAA TSO-C2d or ETSO C2d.
All ASI’s are essentially a differential pressure gauge. Airspeed is derived from the difference between theram air pressure from the pitot tube, or stagnation pressure, and the static pressure. The dynamic airpressure is a function of airspeed and air density. As altitude increases the air density decreases, thiscauses the ram pressure in the diaphragm to be lower and the resultant indicated airspeed to be lower thantrue airspeed.
Traditional analogue ASIs have ram air pressure from the aircraft’s pitot tube directed into a diaphragm in an
instrument case. Static air pressure from the aircraft static vent(s) is directed into the case surrounding thediaphragm. As the speed of the aircraft varies, the ram air pressure varies, expanding or contracting thediaphragm. Linkages attached to the diaphragm cause a pointer to move over the instrument face, which iscalibrated in knots.
There are other factors that must be considered in measuring airspeed throughout all phases of flight. These
can cause inaccurate readings or indications that are not useful to the pilot in a particular situation. In
analogue airspeed indicators, the factors are often compensated for with ingenious mechanisms inside thecase and on the instrument dial face.
Analogue ASIs can have a calibration chart to correct for instrument errors found when it is calibrated.
Sailplanes will often have a position error chart in the Flight Manual that allows correction of indicatedairspeed to calibrated airspeed.

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Figure 4-3 Airspeed Indicator Cutaway
Digital ASIs have ram air pressure from the aircraft’s pitot tube being measured by a pressure transducer.
Similarly, the static air pressure from the aircraft static vent(s) is measured by another pressure transducer
and the airspeed is digitally calculated. Some digital ASIs may have a position error correction table built
into the firmware for the sailplane type it is fitted to and be able to display Calibrated Airspeed. Some digital
ASIs can also calculate True Airspeed and, if connected to a GPS, ground speed and wind speed as well.
Whilst this is an advantage, digital ASIs rely on battery power and may not function if there is an electricalproblem, whereas analogue ASIs would continue to function. At present, many digital ASIs available on themarket are not certified.

Figure 4-4 Example Digital Airspeed Indicator Display

4.5.2

LIMITING AIRSPEEDS
Every sailplane has speeds which must not be exceeded in given circumstances. These are referred to bystandard “V” designations as follows:

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VNE

Never Exceed Speed. This is the maximum speed the aircraft may be
flown at. At this speed only 1/3 of the maximum control deflection may
be used. The aircraft can be overstressed by the pilot using excessive
control deflections.

VRA

Rough Air Speed. In most modern sailplanes this is the speed atwhich the aircraft will withstand gusts of ± 15 m/s. Some older aircraft
such as the Standard Libelle and the Hornet were designed to an
earlier standard which had no rough airspeed. Instead they wererequired to withstand a gust of ± 10 m/s at VNE.

VA

Manoeuvring Speed. This is the maximum speed at which full control
surface deflections cannot cause overstress. Below this speed thewing stalls before maximum "g" is reached. Above this speed thestructure can be overloaded before the wing stalls ie the pilot canoverstress the aircraft.

VFE

Maximum Flap Extended Speed . The maximum speed for each flap
setting. Each type may have several flap speeds.

VW

Maximum Winch Launching Speed.

VT

Maximum Aerotow Speed.

VLO

Maximum Landing gear operating speed. This is the maximum speed
at which the landing gear may be extended or retracted.

VY

The Best Rate of Climb Speed for powered sailplanes.

VS1

The Stall Speed of the sailplane at maximum weight with wing flaps
neutral and air brakes retracted.

VS0

The Stall Speed at maximum weight with landing gear extended, wing
flaps in the landing position and the air brakes in the position which
gives the lowest stall speed.

Table 4-3 Air Speed Definitions

4.5.3

POSITION ERROR
The pressure distribution over the sailplane is very complex and changes with factors such as speed, flap
position and airbrake deployment. As a consequence it is not possible to find a point on the aircraft which
gives true Static Pressure at all speeds and configurations.
When a sailplane type is certified the position error is determined at each speed and a chart of this error isprepared. When the placarded limits are prepared for a sailplane this error is taken into account.

4.5.4

INSTRUMENT ERRORThis is the error inherent in the instrument either due to its design or because a defect has developed. This
must be within given limits to ensure that the sailplane is being flown within its design limits and at thealtitude displayed.

4.5.5

REDUCING VNE WITH ALTITUDE
As we fly higher, the density of the surrounding air decreases. This means that for a wing to produce thesame amount of lift at a constant angle of attack and balance the sailplane’s weight, the wing must movethrough the air at a faster true airspeed. For example, if a sailplane is at the stalling angle of attack at 35kn
TAS at sea level then the same sailplane at the same weight will stall at 40.7kn TAS at 10,000 feet.
Fortunately the reduction in air density which reduces the ability of the wing to produce lift also reduces theability of the airflow to deflect the needle in the ASI in exactly the same proportion and so the stall speed
shown on the ASI is constant regardless of height.
The structural loads on the sailplane are also proportional to the Calibrated Airspeed, which with a few small
adjustments translates to Indicated Air Speed. So flying at at height with the IAS kept within the placarded
IAS limits does lead to the True Airspeed being higher, but you cannot overstress the sailplane frommanoeuvre or gust loads. Unfortunately flutter is dependent on True Airspeed and not Calibrated Airspeed
and as you fly higher VNE in IAS is closer to the critical flutter speed of the sailplane.

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During the certification of each new type, the manufacturer tests the saiplane to VNE at the maximum height
for which VNE will be valid. This gives a VNE as a single figure limit for lower level flying. Above this heightVNE must be reduced to prevent flutter.
MOSP3 Section 8.3.11 states whenever a sailplane is fitted with an oxygen system a placard of reducing
VNE with altitude must be fitted. This placard is normally available from the flight manual. A typical placard
showing the reduction of VNE with altitude is as below.
Some older types don't have this placard in the flight manual and if they are fitted with an oxygen systemthen a placard must be determined by calculating the True Airspeed for VNE at 10,000 ft and then using thatvalue as the maximum True Air Speed above 10,000 ft leading to the corresponding IAS reducing withheight. This calculation can be done by the CTOA on request.
Altitude (ft)VNE IAS (kn)

0

135

5,000

135

10,000135

12,000130

14,000126

16,000122

18,000118

20,000110

24,000106

26,000103

28,00099

30,00095

Table 4-4 Example VNE Reduction Placard

4.6

ALTIMETER
An altimeter is an instrument that is used to indicate the height of the aircraft above a predetermined level,such as sea level or the terrain beneath the aircraft.
Altimeters that measure the aircraft’s altitude by measuring the pressure of the atmospheric air are known aspressure altimeters. A pressure altimeter is made to measure the ambient air pressure at any given location
and altitude. In aircraft, it is often connected to the static vent(s) via tubing in the pitot-static system. The
relationship between the measured pressure and the altitude is indicated on the instrument face, which iscalibrated in feet. These devices are direct-reading instruments that measure absolute pressure.
A sealed diaphragm (the aneroid) is at the core of the pressure altimeter’s inner workings. Attached to thisdiaphragm are the linkages and gears that connect it to the indicating pointer.
Static air pressure enters the airtight instrument case and surrounds the diaphragm. At sea level, thealtimeter indicates zero when this pressure is exerted by the ambient air on the aneroid. As air pressure is
reduced by moving the altimeter higher in the atmosphere, the diaphragm expands and displays altitude on
the instrument by rotating the pointer. As the altimeter is lowered in the atmosphere, the air pressure aroundthe diaphragm increases and the pointer moves in the opposite direction.
The face, or dial, of an analogue altimeter is read similarly to a clock. As the longest pointer moves aroundthe dial, it is registering the altitude in hundreds of feet. One complete revolution of this pointer indicates
1,000 feet of altitude.

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The second-longest pointer moves more slowly. Each time it reaches a numeral, it indicates 1,000 feet of
altitude. Once around the dial for this pointer is equal to 10,000 feet. When the longest pointer travels
completely around the dial one time, the second-longest point moves only the distance between two
numerals—indicating 1,000 feet of altitude has been climbed. If so equipped, a third, shortest or thinnest
pointer registers altitude in 10,000 foot increments. When this pointer reaches a numeral, 10,000 feet of
altitude has been attained. Sometimes a black-and-white or red-and-white cross-hatched area is shown on
the face on the instrument until the 10,000 foot level has been reached.

Figure 4-5 Altimeter Mechanism
The altimeter setting knob sets the sub-scale or barometric pressure scale (labelled the Altimeter setting
window above).

4.6.1

ALTIMETER ERRORS
There are several sources of error in an altimeter. The two main errors are Instrument Error (IE) and Position
Error (PE).
Instrument error mainly arises from wear in the internal gearing or distortion of the capsule (the capsule that
inflates and deflates as air pressure changes). In addition, an altimeter may become sticky; in other words,
changing pressure does not result in a corresponding movement of the pointers on the instrument's face.
This problem is more prevalent on altimeters fitted to sailplanes that are not frequently flown. Usually, agood few hours flying will resolve stickiness and the problem will go away. However, if it persists, servicing
the altimeter by a certified instrument repairer may be required. Do not attempt this repair yourself.
Position Error derives from the location of the static ports and from disturbance the aircraft introduces to the
air that it is sensing. PE changes with speed and selection of flaps, airbrakes, or yaw of the aircraft. The jobof a sailplane design engineer is to find a position on the airframe to place the static ports, such that the PE
is minimised over the whole flight envelope. The PE is then measured during prototype test flying to ensurethat the PE is within acceptable limits.
In sailplanes the altimeter can be simply left vented to cockpit pressure, with no plumbing connected. While
this arrangement will work, it is not good engineering practice as it introduces unwanted PE. Further, there
will be minor pressure differences between the pressure caused by the mass flow of air though the cockpit(open vents, etc.) and that measured at the static ports. To minimise these errors, the altimeter should beconnected to the static plumbing.

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However, in sailplanes the cabin pressure should not cause a significant error and because blockages intubes and leaks in altimeter cases are more likely to cause significant error, altimeters are best leftconnected to cabin air and not the static. Ask the pilot to check and connect to static if required. If notconnected to static, then leaks do not matter except to the calibration process and the test procedure canaccommodate some leakage, but beware.

4.6.2

ALTIMETER ADJUSTMENT
The altimeter barometric pressure scale setting occasionally needs to be adjusted so that the relationshipbetween the indicated altitude and the barometric pressure scale is correct. With the altimeter pointersdisplaying the correct ground elevation at the location, the value indicated on the barometric pressure scale
shall be adjusted to correctly match the current value of the QNH for that location.

CAUTION
Altimeters are complex delicate instruments built like a mechanical watch. They areeasily damaged by rough handling and even by putting them down roughly on a hardsurface. Be careful or it will require expensive repair. Altimeters are safer remaining in theaircraft. Be careful taking them out and transport in a padded box.
IF YOU DROP IT – RECALIBRATE IT!
Altimeter model specific information is provided at Appendix B . If the specific model is not detailed in thisAppendix, it may point to possible ways adjustment may be achieved with that particular altimeter design.
Before proceeding to testing the altimeter scale accuracy across low, medium and high altitudes, thebarometric pressure scale setting is checked for correct adjustment. With the known elevation at the test
location displayed on the altimeter pointers to within +/- 20ft, the barometric pressure scale indicated value
shall match the current local QNH value in hectopascals. Current QNH information for a locality may beobtained from the Bureau of Meteorology (BOM) website www.bom.gov.au looking at the observation pages listingdata either state-wide or for the state capital city and immediate surrounds. The automated weather stations
supply information to the BOM every ten minutes or half-hour depending on location. Airport weather stations are
particularly useful sources. Be aware that in changeable weather circumstances the local QNH may vary quickly
such that testing the altimeter during a slower moving pressure system should be considered.
The adjustments are more easily performed with the altimeter on a soft bench top and away from the instrument
panel. Putting an altimeter down on a hard surface jolts the fine internal bearings (jewels) and can cause impact
damage (dents) on the bearing surface. Adjustments are made using small “jewelers” screwdrivers which are
typically flat bladed.

4.7

INSPECTION PROCEDURES

4.7.1

ANNUAL INSPECTION REQUIREMENTS
The current requirements for sailplane maintenance are given in MOSP 3 Section 13.6 and must be
performed by a trained annual inspector or CASA authorised technician. And this work must be certified bythem in the logbook.

4.7.1.1 ANNUAL INSPECTION REQUIREMENTS:a.

Check each pneumatic system for leaks and rectify leaksb.

Ensure that the ASI is connected to the correct static sourcec.

Check the ASI colour coding is correctd.

Check for VNE reduction with altitude placard if an oxygen system may be used

(The above is simple and quicker than before.)

4.7.1.2 BIENNIAL (EVERY SECOND YEAR) INSPECTION REQUIREMENTS:
a.
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4.7.2

b.

Calibrate each altimeter. An accurate altimeter is required to advise other aircraft of your altitude. If
not calibrated you may use a permissible unserviceability if you remain out of controlled airspace.
Make sure they all read the same at the same barometric pressure scale, including the transponder (ifit gives a readout) or placard the calibration errors for the pilot's information.

c.

The transponder and its altitude encoder must be calibrated by a CASA authorised technician. If notcalibrated within 24 months you may not turn it on (as ruled by CASA). The reason given is it may
mislead other aircraft.

PITOT-STATIC SYSTEMS

4.7.2.1 PITOT-STATIC SYSTEM INSTALLATION AND MAINTENANCE
When replacing the tubing of a pitot-static system (or installing a new system in an amateur built sailplane),
there are certain aspects of the installation which will protect the instruments from the effects of both waterand dust.
All plumbing must be installed so that water tends to run out of the ports. The best way to achieve this is toinstall the tubing so that the first direction the tubing runs is up.
Some sailplanes also have purpose designed water traps in their pitot-static systems. These water traps
have a drain tap which allows them to be periodically drained.
To prevent dust and other foreign objects reaching the instruments it is good policy to install filters in thesystem. The best filters are small automotive or motorcycle fuel filters which can be installed in the lines.
Whenever a sailplane is not being flown covers should be fitted to all pitot and static vents to prevent the
ingress of dust and to prevent wasps building nests in the holes. This is particularly important as wasps inAustralia have been known to build a nest sufficient to block the standard vents within a few hours.

4.7.2.2 PITOT-STATIC SYSTEM LEAK TESTING
One of the most important aspects of a correctly maintained pitot-static system is that any leaks are within
specification. A leak in the pitot and to a lesser extent the static can influence the pressures in the tubing andresult in significant errors. Eg. A likely serious error is in the ASI near Vne – the pitot pressure is highest, it
will leak the most, the flow rate in the small pitot entry and through a filter reduces pressure which makes the
ASI under-read Vne. This is serious when you are doing Vne IAS as actually you will exceed Vne and you
risk flutter!
When testing pitot-static systems, the following points should be noted:a.

The instruments can be damaged and you must not cause pressures in them that will cause
damage. If you are unskilled do not do this testing – it requires care and finesse – get someone who isprepared to take the time to do it carefully.

CAUTION
Ensure that all instruments are disconnected before commencing to purge.
b.

If purging is necessary, use compressed air or blowing to remove foreign matter which may haveaccumulated in the tubing.

c.

Purge disconnected Pitot and Static lines outwards, from the instrument panel end towards the pitot
tube and static vents.

d.

Many systems have multiple vents, and it is necessary to seal all vents.

e.

It is best to connect to the pitot and the static vents without disturbing the tubing. This is not always
possible and care with reconnection is required.

f.

Be aware of any capillary leaks through the variometer or stall warning system. Static systems which
are connected to a capillary type variometer should be separate from those connected to the ASI.

g.

Do not use silicon sealers to fix leaks in pitot-static systems. Many silicon sealers produce acetic acidas they cure and this acid can cause damage to the instrument’s internal mechanisms. While there

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are silicones which do not produce acetic acid, they should not be used as future inspectors cannot
tell which type of silicon has been used.
h.

The best way to prevent leaks is to use fresh tubing over the correct sized barbed fitting. The need touse elastrator rings or lock wire wrapped around the fitting is a sign that either the tubing should be
replaced or the connection is of a poor design. Where an installation, such as a plain tube, ispermanently installed in the sailplane then the best way of sealing the system is to wrap locking wire
twice around the joint and twist the ends together to form a clamp.

i.

A good way to apply a small vacuum to the static or pressure to the pitot systems is with a 20ml
syringe. WITH CARE.

j.

Test as below. Fix the leaks.

k.

Ensure all temporary seals are removed after testing.

4.7.2.3 LEAKAGE TOLERANCES IN GFA AIRCRAFT
Leakage tolerances in GFA aircraft:a.

Static system; evacuate the static system to a pressure differential of approximately 1,000ft on thealtimeter, above the aircraft’s elevation. Without additional pumping for a period of 1 minute, the lossof indicated altitude must not exceed 100 feet on the altimeter.

b.

The pitot system is tested for leaks by applying pressure at the pitot head sufficient to cause theairspeed indicator to read about 120 knots.

c.

There must be no discernible lag in the movement of the airspeed indicator pointer with theapplication of the pressure, as such a lag indicates restrictions in the piping.

d.

There must be no decrease in the reading when the system is sealed for at least 10 seconds.

The above is tighter than before and is the same as required by CAO 100.5. Our previously wide tolerances
may have resulted in sailplanes unknowingly exceeding Vne.

4.7.3

AIRSPEED INDICATOR

4.7.3.1 THE WATER-TUBE MANOMETER
In order to calibrate an ASI, it is necessary to have an accurate and controllable source of low-pressure air.
The most practical way of providing this air pressure is with a water-tube manometer. You can construct thisas below, and it can be accurate enough. You do not require this for testing for leaks as above.
GFA is arranging an electronic calibrated test kit you may borrow from the regional equipment officer mainly
for altimeters, but it will also test ASI.
A suitable water-tube manometer is shown in Figure 4-6Error! Reference source not found.. However, any
manometer is suitable, provided it has the following characteristics:a.

The manometer must be vertical when in operation unless it has been designed to operate at a set
angle. If the manometer is designed to operate other than vertical, then it must be at the design angle,
and the scale will have to be altered (during manufacture) so that the vertical heights are as per Table
4-5.

b.

The scale must be adjustable up and down to allow for changes in water level. There must be ameans of locking the scale while the manometer is in use.

c.

The manometer should be mounted to provide a degree of robustness.

d.

Both tubes must have identical internal diameters. This is particularly important should a tube need tobe replaced. Glass tubes are best, but a uniform plastic tube can work if held straight over the test
length.

e.

The manometer must be checked for leaks before it is used.

f.

The water must be clean. It can have a very small amount of dishwashing soap added to reduce theviscosity and colourant to make it visible. But these must be slight as they affect the readings. There

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must be no air bubbles.
g.

The markings on the scale must be as per Table 4-5. The figures shown are the full height of thewater column (from meniscus to meniscus), so the distance from the zero (ambient pressure) is half
the height as shown in the figure below:
Speed (kn)

mm of water

30

15.0

40

26.5

50

41.5

60

59.5

70

81.5

80

106.0

90

134.0

100

165.5

110

200.5

120

239.0

130

280.0

140

325.0

150

373.0

160

424.5

Table 4-5 Scale Dimensions

CAUTION: Figure above is not toscale. Do not photocopy and use it.

Figure 4-6 The Water-Tube Manometer

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4.7.3.2 TESTING AN ASI
The basic procedure for testing an ASI is as follows:a.

Open the bleed valve and move the syringe plunger to the most extended position.

b.

Connect the free tube from the manometer or calibration gauge to the pitot connection of the ASI(normally the connection in the centre of the instrument. But it is best to connect to the pitot as you
then check the whole system).

c.

Close the bleed valve. At this point both the menisci should be level with one another.

d.

Adjust the scale until the zero coincides with the menisci.

e.

Gently push the plunger in until the manometer reads 30kn. Record the ASI reading in a calibrationtable as shown in Table 4-6 below.

f.

Continue to increase the manometer readings in 10kn intervals recording the ASI readings at eachinterval until a speed about 10kn above VNE is reached. If a stop is missed (the manometer overreads), do not reverse the movement to obtain the intended manometer reading.

g.

Once VNE is reached, reduce the pressure in 10kn intervals back to zero recording the ASI readings
as you go. Again do not reverse the direction of movement, record the manometer reading and theerror from it.

h.

Using the recorded readings, for each 10kn interval, determine the instrument error by subtracting the
manometer reading from the ASI indication.

i.

The allowable error is 4knots at all readings. (We used to require better accuracy near the stall but
there is no good reason for this.)j.

Open the bleed valve before disconnecting the ASI.

Notes:
1.

The ASI is extremely sensitive and can be easily damaged.

2.

Do not apply negative pressure with the ASI at zero.

3.

Apply the pressure very carefully as sudden movements can damage the ASI mechanism.

4.

Don’t apply vibration or tap the ASI. It must read correctly when gliding and we don’t tap it then.

5.

The manometer has water in it and ASIs do not like water. Keep the ASI above the manometer andensure the tubing from the manometer to the ASI is dry and at least 1 m long.

6.

Calibration is best done with two people. One operating the manometer valve and calling out the
manometer steps; the other reading the ASI and writing down the reading in the calibration table.

7.

Obviously, calibration with the new GFA tester is preferred, but you may use the manometer if you are
sure it is correct.

4.7.3.3 CALIBRATION CHART
PRESSURE INCREASING
Manometer(kn)

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ASI
(kn)

Error
(kn)

PRESSURE DECREASING
Manometer
(kn)

30

30

40

40

50

50

60

60

70

70

80

80
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(kn)

Error
(kn)

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90

90

100

100

110

110

120

120

130

130

140

140

150

150

160

160
Table 4-6 Calibration Table

4.7.4

ALTIMETER CALIBRATION
Calibration means recording the error over a suitable range relative to an accurate instrument anddetermining if this is acceptable.
GFA has in the past not required altimeter testing other than checking sub-scale on the basis that sailplanes
bob up and down with the thermals and we cannot maintain altitude. To fit in safely with other aircraft this is
not entirely satisfactory although it has not been a contributing factor in incidents. But these days we need tobe more responsive to the expectations of others, and we have to avoid incursions into controlled airspace.
So we now require calibration of altimeters, but we provide a reasonable alternative; you can use apermissible unserviceability as long as you will stay well clear of controlled airspace to allow for errors.
Obviously, when you report to other aircraft, you must be suitably clear that your altitude will vary, eg.
”currently at about 3,000ft AGL, descending”. If the sailplane is used competitively or is a motorglider, thenyou should calibrate the altimeters if you may go near controlled airspace.
We are exempt to CAO 100.5 which details the testing required in other aircraft. We need to be reasonably
similar. So we have developed a test rig and procedures that are somewhat easier for GFA to apply
ourselves. The principle is as follows:a.

It is a risk to remove instruments and transport them for testing. It is better, quicker and easier to test
them in place. It is a big cost to the whole fleet to test most altimeters every other year. So it is betterthat we test them ourselves, installed.

b.

Contrary to past practices of testing in a vacuum box it is quite safe to test the altimeters by applying avacuum to the instrument. But then the instrument must not leak . It is, therefore an easy procedure toconnect a calibration instrument to the altimeter static connection with a plastic tube and test it in situ.
Testing has shown we can actually test to 30,000ft this way although for most 20,000ft or even
10,000ft may be satisfactory. You only have to test to the expected maximum operating altitude.

c.

We must test against a calibrated
and reliable calibration instrument. To do this we must havequality control on it. We have therefore developed and tested a kit which we will make available to all
regions to buy. Or they can make their own or clubs or AMOs have or can make their own.

d.

Whatever instrument is used must be check calibrated each year and proven to be accurate. If theregions hold the kits, then the Regional Equipment Officer (REO) must check them annually, andcontrol on which sailplane it is used and contact the owner if it may be in error when the calibration isfound to be out. In reality, the first person to use a faulty calibration instrument will find out, and it will
be corrected.

e.

The plan is the REO will mail them out to each club once a year. Each club has two trained inspectors
who then test half the sailplanes over two weekends. Then mail it back to the REO. The equipment isrobust enough to mail. Large clubs may wish to have their own.

f.

The clubs must choose suitably minded inspectors to be trained. When the equipment is first shippedto them, they will be given a manual and training by phone. It is not hard – it only requires care,patience and understanding. This will mean we are compliant. ,and will save each sailplane ownerabout $100 pa and it works easier and safer. It will take longer initially, but the altimeter can be tested
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in 30 minutes. And the ASI can also be tested in about 20 minutes with the same kit.

4.7.5

g.

If an instrument is faulty, it will have to be sent for repair to a professional instrument workshop. But
they are hardly ever faulty. The risk is that initially, we may find many that are as we have old
instruments that have hardly been checked. We are generally not capable or qualified to correct errors
except the sub-scale setting. If your club has a trained instrument technician (there are many Airforce
and commercial people in GFA who are capable), it is permissible for them to fix instruments.

h.

Obviously, this is a hassle and extra work. If you do not need to go near controlled airspace, then we
have put in place permissible unserviceability to allow you to continue easily as you have in the past.
See AIRW-M15 Schedule of Permissible Unserviceabilities.

ALTIMETER TESTING PROCEDURE

4.7.5.1 COMPARISON
The kit manual is attached as Appendix 1. In summary:a.

The altimeter sub-scale is tested and reset if necessary. This is easy and safe if you have been
trained.

b.

The calibration instrument is connected via flexible tubing to the altimeter under test. The air pressureis gradually lowered by hand vacuum pump on tubing connected to both altimeters. The altimeter
usually remains in the sailplane but is disconnected from the static system.

c.

The altimeter's reading at each specified altitude is compared against the reading on the calibration
instrument, and the error noted. There is a hand vacuum pump to apply vacuum. The calibration
instrument is very accurate however ignore slight variations that can be caused by temperature. It isalso robust and so should not get damaged but look after it, it is costly to replace or repair.

d.

It is necessary to test the altimeters readings on the way up (increasing altitude) and down
(decreasing altitude). The altimeter should be tested to an altitude of at least 20,000 ft. But the owner
may specify less and it can then be placarded to that height.

e.

You may tap alongside the altimeter as sailplane pilots tend to do this to reduce stickiness. (Especiallyin weak thermals it helps to climb!)f.

On the way down, stickiness and hysteresis is also calibrated.

g.

The procedure defines the acceptable errors.

h.

The altimeter is reconnected to the static system if it needs to be and the system is checked for leaks
as above.

4.7.5.2 SUB-SCALE TESTING
The altimeter sub-scale is probably best corrected using the new calibration instrument.
To otherwise perform a sub-scale test, it is necessary to obtain an accurate QNH at your location. This canbe easily obtained by either using a recently calibrated altimeter, or by reference to the Bureau of
Meteorology (BoM). In this latter case, wait until there is a large pressure system over your location; that is,
the pressure system shows isobars (lines of equal pressure) wide apart over your area. Then lookup the
QNH for your location on the BoM website. If you are at an airfield for which a Terminal Area Forecast (TAF)
is issued, the QNH shown on the TAF is considered sufficiently accurate.
Set the QNH obtained above on the sub-scale of the altimeter. Then compare the altimeter's indicatedaltitude with the known altitude of your location. If the error is greater than 50 ft, the altimeter should beconsidered out-of-tolerance and a trained person can reset it.
Check each altimeter in use in the sailplane, including readouts on the transponder are within 100ft when at
the same QNH setting, usually the standard 1013mbars. Note errors and have the offending instruments
repaired.

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Appendix A GFA ALTIMETER & ASI TEST KIT INSTRUCTIONS

A.1 ALTIMETER & ASI TEST KIT INSTRUCTIONSGeneral Notes:a.

The objective of this kit was to enable compliance testing in a quick, simple, lower risk method.
Instruments can be tested outside the aircraft system but the system will require a separate leak test
after re-installation. Instruments are at risk of being dropped etc. If removed they need to betransported safely to a workshop and back. If they can be calibrated without removal this testing takes
30 minutes for an altimeter and saves you hundreds of dollars every 2 years. If the altimeter leaks you
will have to remove it, test it in a vacuum chamber or send it for repair. This kit can work with avacuum chamber, but it is not supplied. We may add this if it becomes necessary.

b.

It is likely that initially we are going to find many leaky or faulty altimeters but they usually go for
decades once overhauled and are then quick and cheap to test.

c.

Tests required are laid out in BSE Chapter 4 “Pitot Static Systems”. This replaces the CASA CAO
100.5 appendix 1 requirements for GA aircraft. These procedures form part of the GFA standard
system of maintenance as required by MOSP 3 Section 13.6.

d.

The test kit consists of a Meriam M203 Altimeter/ ASI Calibrator, a fine control mechanical pump, test
fittings and hoses all packed in a padded carry casee.

The Meriam calibrator, in particular, is a precision instrument and needs to be treated as such.
However, it was chosen as an electronic robust calibration unit that can survive postage in its paddedbox. But it will be used by many in an important function and must be treated with care and itself
calibrated biennially.

f.

The Meriam calibrator can measure in many different units and functions; however, for our purposes,
it has been locked by pin number to only Altimeter/ ASI calibration and leak testing.

g.

The kit is not required for leak testing and ASI calibration can be done by manometer to save using
the kit excessively, eg if it is too busyh.

These tests may all be done by an annual inspector but only if trained and capable in this testing.
Care is required in all this testing and instruments can be damaged and caused to read incorrectly.
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This is mainly a risk for infringing airspace or exceeding Vne, ie serious risks.
i.

Problems, damage or missing components should be reported to the Regional Equipment Officer orthe RTO in your region as soon as possible as it could mean the previous sailplanes were incorrectly
calibrated.

j.

Please fill in the kits logbook of altimeters tested so you may be contacted if calibrator errors arise.

k.

Please ensure all kit items are returned promptly and safely to the equipment officer.

A.2 CALIBRATION TESTING
Pitot and Static system tests required by MOSP 3 are as follows:a.

Pitot/Static system leak test, annually and whenever the plumbing is disturbed. Can be done using
only a 20ml disposable syringe and the aircraft instruments as given in BSE.

b.

Full altimeter calibration, biennially using this test kit or another calibrated calibration system andincludes the following sub-tests:c.

First; Altimeter barometric scale. Set sub-scale, see BSE and this manual
i.

ii.

d.

On rising altitude:
1.

Friction

2.

Scale error

3.

Case leakOn falling altitude:
1.

Hysteresis

2.

After effect3.

Sub-scale readings – check range of settings.

4.

Refer to the Altimeter Test Results sheet that summarises and is used to record results.

Full ASI calibration, biennially. Can be done at any time using a manometer as in the past or with thiskit.

A.3 UNPACKING AND SETUP
Unpack and setup as per the attached photograph
Wherever possible the calibration test needs to be conducted on the installed system however if amechanical variometer or a flask are fitted to the static system then they will need to be disconnected or
isolated.
Instruments can be tested outside the aircraft system, but the system will require a separate leak test after
re-installation.
Keep the test equipment tubing as short as possible, do not use silicon tubing.

A.4 ALTIMETER TESTING
You may test all altimeters including the transponder altitude encoder with this kit. However, you are only
required to test the primary altimeter and to list the others as un-calibrated in the minor defects of theMaintenance Release. eg a gliding computer need not be calibrated. Although you can check thetransponder, it has to be calibrated anyway by a qualified technician who checks signals and other factors
important to reliable data communications.
The Meriam calibrator operation is:a.
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to prevent inadvertent or other adjustments
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GFA Basic Sailplane Engineering, AIRW-M005b.

To change from “Altimeter” to “ASI” calibration press “Tare”; to change back press “Tare” againc.

It has been locked at sub-scale setting = 1013hPa. i.e. the whole altimeter calibration is done at
1013hPa

Test and set Sub-scale; Set the aircraft altimeter sub-scale to 1013hPa. (all testing is done with reference to1013hPa not QNH or QFE). Ensure that the shut-off needle valve is open. The altimeter should read thesame altitude as the Meriam; if not you have a sub-scale error that needs adjusting (see separate instruction
on adjusting the sub-scale for your type of altimeter, there are differences in each type)
If you do the tests in the order suggested by the test sheet and below you will save time going up and down.
ie you can with practice calibrate an altimeter in 30 minutes by going up to 20,000ft and back down once. On
the way up you do a leak test and the friction and scale error tests, on the way down you do the hysteresis
test in comparison to Test 2 and an after effect test once complete. Then you adjust the sub-scale to eachvalue given and record the error from the altitude it should read at that sub-scale.
Although in unpressurized aircraft such as sailplanes the altimeter can be left disconnected from the staticand so avoid the influence of case leaks, it is not possible to do the tests this simple way if the case leaks
significantly. Often it is the sub-scale knob that leaks. But it should be quite cheap and simple to get the leakfixed for many years of simpler testing. Alternatively, you must use a vacuum chamber and must not connect
the altimeter to the static. Then the altimeter does not have to pass the leak test.
If there are any errors, then you will have to have a qualified technician overhaul it.

A.4.1

ALTIMETER SCALE ERROR AND FRICTION TEST
Proceed as follows:a.

Ensure that the shut off needle valve is openb.

Wind the coarse pump handle fully inc.

Close the shut off needle valve to start testingd.

The Meriam calibrator and the Altimeter must read the same within 20ft or set the sub-scale again as
above

e.

Wind out the coarse adjusting handle stopping at the test points specified in the attached Altimeter
Test Results sheet. Try to only go up in altitude, ie decrease vacuum, because allowing the vacuum tooscillate at the reading will induce errors. This is hard to do.

f.

Test 1 is the Friction test; record the change on the altimeter caused by tapping as soon as you get toeach altitude on the Meriam.

g.

Test 2 is the actual scale error test; record the altitude error of the altimeter from the Meriam after
holding the vacuum and tapping the altimeter case to get rid of friction. If the altimeter drops in altitude
then allow it to drop a few hundred feet and try again to pause at the required altitude on the Meriam
or close to it. A bit of practice will allow you to do this well enough. The important point is to estimate
the error to within 10ft caused by friction and scale. Do not get distracted by the precision of the
Meriam – it is super sensitive and will show variations and is therefore influenced by temperaturechanges and small leaks.

h.

If the case or the plumbing is leaking, you will find it hard to carry out the test procedure accurately.
Fix the leaks.

i.

GFA have set wider tolerances than GA aircraft as it is usually impossible to maintain accurate altitudein a sailplane and the important factor is to have an altimeter that is accurate to about 100ft so thatyou can advise other aircraft of your altitude and avoid infringing airspace.

A.4.2 ALTIMETER CASE LEAK TEST
Proceed as follows:a.

At 1,000ft and any other altitude you desire perform a case leak test by;b.

Stop pumping and isolate the altimeter using the shutoff valve.

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c.

It should not reduce in altitude by more than 100ft in 1 minute. This is much more onerous thanpreviously specified by GFA but is the norm. As per the note above strictly, this may not matter tounpressurized aircraft, but it would make this calibration hard to do. And if connected to your static
system it could induce errors in variometers and gliding computers.

d.

In other aircraft, CASA specify the test is carried out at 18,000ft. In un-pressurized aircraft, this does
not make sense, and so we do the test at 1,000ft AGL.

A.4.3 TESTING TO HIGHER ALTITUDE
You must test to an altitude above that at which the aircraft may be flown. Usually, GFA calibrates to
20,000ft but if the pilot plans wave flying then 25,000 or even 30,000ft is possible using this kit. Record thelimiting altitude in the logbook and maintenance release. It will save time and may avoid workshop repair if
you test to 10,000ft or even 5,000ft and that is sufficient.
The vacuum pump may not have sufficient capacity to reach a high altitude in one go. This varies with leaks
and case volume. To continue testing above this altitude, you must:a.

Close the isolating valve on the altimeter to lock in the altitude gainedb.

Open the hand pump shut off valvec.

Wind the coarse adjusting handle fully ind.

Operate the hand pump to climb back to the previous altitude. This pumps the crank pump and the
Meriam back to the altitudee.

Close the hand pump isolation valve and open the valve to the altimeterf.

Continue testing as previouslyg.

Repeat to get higher and higher. But leaks will get worse and may prevent accurate testing at somepoint. Placard the altimeter to limit altitude or get it repaired.

A.4.4 HYSTERESIS TEST, TEST 4This is done at 2 altitudes on the way down.
It is the error from the altitude on the way up. ie the difference between the altitude when rising and falling.

A.4.5 AFTER EFFECT TEST, TEST 5This is the error from when you started.

A.4.6 SUB-SCALE ERROR TEST, TEST 6
Set the Meriam to 0ft by applying slight pressure with the pump.
You adjust the sub-scale on the altimeter to each value given and record the error of thealtitude reading
while maintaining the Meriam at 0ft.

A.5 ASI CALIBRATION
You may calibrate the ASI using this kit but a manometer can be as accurate. See BSE Chapter 4 fordetails.

A.5.1 ASI SCALE ERROR TEST
Proceed as follows:a.

Connect the ASI pitot, in place of the altimeter static, to the kitb.

Ensure that the bleed needle valve is openc.

Wind the coarse adjustment handle fully outd.

Close the bleed needle valvee.

Change the screen from “Altimeter” to “Airspeed” by pressing “Tare”

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f.

Wind the coarse adjusting handle in stopping at the primary scale markings up to the aircraft VNE.
Record each ASI errorg.

Wind the coarse adjusting handle out stopping at the primary scale markings down to below stall
speed, record each errorh.

Tolerance required is ± 4 kn. (We have increased this as it is not practical or useful to have an ASI
more accurate near stall. ie the pilot should not be fixated on the ASI at that point. In any case the stall
speed varies with load.)

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GFA Basic Sailplane Engineering, AIRW-M005
Ref: MOSP 3 & BSE Ch 4

Altimeter Test Results
Aircraft Registration:
Test Date:
Altitude 1. Friction
Set
0AGL Subscale
0
1,000
2,000
5,000
8,000
10,00015,00020,000Tests:

Up
Up
Up
Down
Down

Altimeter Sno:
Tested By:20

2. Scale Tol+/Test, After
tap

70
70
70
70
70
80
90
100

50
50
50
50
60
80
110
130

Tol +/-

Test Kit Sno:
Signature:
3. CaseLeak

14/09/2017

Calibration Due:Membership No:

Tol +/- 4. Hysteresis Tol +/- 5. A/Effect Tol +/- 6. S/scale Alt Diff Altitude Error
50
100

75
75

A. Static systems leak test. Fix all to give less than 100ft over 1 minute at 1000ft AGL.
B. Pitot system leak test. Fix all to give no discernable drop over 10 seconds at 120kn.

Easiest is to hold Meriam at 0ft.
952
965
982
999
1013
1033
1046
1049

-1727
-1340
-863
-392
0
531
893
974

Tap the case.
Don't tap

C. Altimeter Test. Don't do the greyed cells. Approach the test value on the reference altimeter carefully, try not to overshoot.
Write down the error or movement in ft at the given altitude while holding the reference altimeter constant with the pump.
1. Friction test: Measure change due to tapping case.
Note before and after tapping
2. Up Scale test: Measure error after tapping case.
3. Case Leak: Leak in 1 minute at 1,000ft AGL.
Always tap the case for each reading.
4. Hysteresis: Measure difference between up and down reading.
Always tap the case for each reading.
5. After effect of up and down. Error after returning to AGL.
Always tap the case for each reading.
6. Subscale test. Alt diff is the altitude you should get at constant pressure. Error can be +/- 50 ft. Fill in 'Altitude' reading.

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Ref: BSE, Ch 4

Airspeed Indicator Test Results
Aircraft Registration:
Test Date:

Airspeed
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Version 24.1

Altimeter S.no:

Test Kit S.no:

Calibration Due:

Tested By:

Signature:Membership No:

Tolerance+/4 Kt.
4 Kt.
4 Kt.
4 Kt.
4 Kt.
4 Kt.
4 Kt.
4 Kt.
4 Kt.
4 Kt.
4 Kt.
4 Kt.
4 Kt.
4 Kt.
4 Kt.
4 Kt.
4 Kt.
4 Kt.
4 Kt.
4 Kt.

Measured Rising

Measured Falling

Complies Y/NDon't tap the case.
Write down the error

4 Kt.
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Appendix B ALTIMETER CALIBRATION INSTRUCTIONS
B.1

KOLLSMAN SENSITIVE ALTIMETERS
MODEL: Late Model Kollsman Altimeter Variant with Screws Front and Side Facilitating BarometricPressure Scale Adjustment.
Source: www.mrkent.com/flying/altimeter/

1.

Before starting, obtain an accurate barometric pressure reading from a local weather service, and knowwhat your exact altitude is as you make the adjustment. Set the altimeter to the exact altitude of yourlocation.

2.

You will find a small screw (Screw #1) near the main adjusting knob, just to the left and a little above, on
the instrument bezel (see Figure A1 below). Remove this screw. Its purpose is to lock another "apparent"
screw (Screw #2) in position.

Screw #1

Figure B-1: Locking Screw #1
3.

You may not be able to see the "apparent" screw (screw #2) as it is positioned on the side of the bezel
rather than on the front. Although it has a screw head, it has no threads. It simply slides in and out of thehole it occupies. By removing screw #1, located on the front of the bezel, you will release the "fixed"
condition of this side screw (screw #2).

Screw #2

Figure B-2: Apparent Screw #2
4.

Once you have removed screw #1, you will be able to see what is shown in Figure A3. It displays thethreaded hole through the shaft of screw #2. Use a paper clip or piece of safety wire to slide the screw #2
slightly "up", or out of it’s hole (only 1.5 mm or so).

Threadedhole

Figure B-3: Threaded hole through Screw #2
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5.

Once screw #2 has been moved up as shown in Figure A4, the altitude mechanism is disengaged fromthe adjusting knob. Pull the adjusting knob out and turn it to change the barometric reading in the window
without changing the altitude setting.

Figure B-4: Screw #2 moved outwards to disengage altitude mechanism
6.

Determine the current barometric pressure reading from the BOM observations website or otherreputable source.

7.

Pull out on the adjusting knob and set the barometric pressure to the correct amount in the window. You
may have to try this a couple of times because when you release the adjusting knob it must mesh withthe gears. As it snaps into place it may move the setting slightly.

8.

Once the adjustment has been completed, use safety wire or paper clip to slide screw #2 back into its
original position. You may have to re-align it with the viewing hole in order to re-position screw #1.

9.

Replace screw #1 and tighten.

MODEL: Early Model Kollsman Altimeter Variants with Central Adjusting Knob and Separate Plate.
1.

Before starting obtain an accurate barometric pressure reading from a local weather service, and knowwhat your exact altitude is as you make the adjustment. Set the altimeter to the exact altitude of yourlocation.

2.

The barometric pressure scale adjusting knob is at the 6 o’clock position. The small plate underneath theknob is secured with a small screw left and right of the knob. Remove the screws on the left and right ofthe plate.

Removescrew

Removescrew
Figure B-5: Early Kollsman Altimeter with Removable Plate

3.

Pull the adjustment knob out gently to disengage the altimeter mechanism.

4.

Determine the current barometric pressure reading from the BOM observations website or otherreputable source. Reset the barometric pressure scale s to the current local QNH without disturbing thealtimeter hands.

5.

Gently push the adjustment knob in to mesh the gear teeth again and secure the plate in position using
the two screws.

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MODEL: Early Model Kollsman Altimeter Variants with Central Adjusting Knob and Integral Plate.
1.

Before starting obtain an accurate barometric pressure reading from a local weather service, and knowwhat your exact altitude is as you make the adjustment. Set the altimeter to the exact altitude of yourlocation.

Removescrew

Figure B-6: Early Kollsman altimeter with integral plate
2.

Remove the small screw underneath the adjusting knob.

3.

Determine the current barometric pressure reading from the BOM observations website or otherreputable source.

4.

Pull out the adjusting knob to disengage the altimeter mechanism.

5.

Hold the knob out and adjust the barometric pressure scale.

6.

Once satisfactory gently push the adjusting knob in.

7.

Replace the small screw and tighten.

B.2 WINTER ALTIMETERS
MODEL: 4 FGH 20 Article Numbers 4220 and 4440, and 4 FGH 10 Article Number 4110
Source: Winter website 2020
1.

Before starting obtain an accurate barometric pressure reading from a local weather service, and knowwhat your exact altitude is as you make the adjustment. Set the altimeter to the exact altitude of yourlocation.

2.

Remove the adjusting knob.

Adjusting knob
Lock nut underneath
Figure B-7: Winter Altimeter3.

Using the special tool, unwind the locking nut for 1.5 to 2 turns.

4.

Reinstall the adjusting knob.

5.

Determine the current barometric pressure reading from the BOM observations website or otherreputable source.

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6.

Lift up the adjusting knob and turn to adjust the barometric pressure scale.

7.

Once adjustment complete, remove the adjusting knob and tighten the locking nut using the special tool.
Pay attention to the torque of the lock nut.

8.

Reinstall the adjusting knob.

MODEL: 4 FGH 40 Article Number 4550, and 4 FGH 10 Article Number 4320
Source: Winter website 2020
1.

Before starting, obtain an accurate barometric pressure reading from a local weather service, and knowwhat your exact altitude is as you make the adjustment. Set the altimeter to the exact altitude of yourlocation.

2.

Remove sealing compound and wind out ‘special screw no.1’ shown in Figure B-8 for 3 turns.

Figure B-8: Winter Altimeter 4 FGH 10 Article Number 4110
3.

Determine the current barometric pressure reading from the BOM observations website or otherreputable source.

4.

Lift up adjusting knob 2 to 3 mm higher than normal to disconnect altimeter mechanism and turn thesubscale.

5.

Once adjustment is complete, lower the adjusting knob. Return ‘special screw no.1’ to its original
location. Do not over tighten this screw.

6.

Replace sealing compound over ‘special screw no.1’.

B.3 FALCON GAUGE ALTIMETERS
MODEL:
Source: Wultrad Inc website
1.

Before starting obtain an accurate barometric pressure reading from a local weather service, and knowwhat your exact altitude is as you make the adjustment. Set the altimeter to the exact altitude of yourlocation.

2.

Locate the screw near the main adjusting knob, just to the left and a little above on the adjustment knob
as shown in Figure C1. Remove the screw using a screwdriver.

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Removescrew

Figure B-9: Falcon Gauge Altimeter3.

If in the aircraft: Separate the gear Part No.1 shown at Figure B-10 from the shaft by using a small
tweezers or screwdriver (care needs to be taken, only use the tool small enough to get into the screwhole).

Figure B-10: Cross Section of Adjusting Mechanism
1.
4.

If out of the aircraft: Hold the altimeter in your hand and turn 90 degrees to the left. Pat the back area of
the instrument to have part no. 1 shown at Figure B-10 separate from the main gear.
Determine the current barometric pressure reading from the BOM observations website or otherreputable source.

5.

Pull out on the adjustment knob and turn it to change the barometric reading in the window withoutchanging the altitude setting. You may have to try this a couple of times because when you release theadjusting knob it must fit between some gears as it snaps into place it may move the setting slightly.

6.

If in the aircraft: Use the small tweezers or screwdriver to slide part no. 1 back into its original position.
You may have to re-align it with the viewing hole, in order to reposition the screw.

2.

If out of the aircraft: Turn the altimeter 180 degrees so that it is now 90 degrees to the right and pat theback of the altimeter to let part No. 1 move back to its original position.
Replace and tighten the screw.

7.

MODEL: UI MODEL 5934 SERIES
Source: United Instruments Maintenance Manual TM-5934, 2017
1.

Before starting obtain an accurate barometric pressure reading from a local weather service, and knowwhat your exact altitude is as you make the adjustment. While gently tapping the altimeter with a finger,
set the altimeter to the exact altitude of your location.

2.

Remove the locking stud screw beside the adjustment knob using a screwdriver as shown in Figure D1.

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Figure B-11: Locking Stud Screw Removal
3.

Slide the locking stud away from the knob to unlock the knob shaft as shown in Figure B-12.

Figure B-12: Unlocking The Adjustment Knob
4.

Determine the current barometric pressure reading from the BOM observations website or otherreputable source.

5.

Pull the knob out gently until it stops and has disengaged the knob shaft from the altimeter mechanism.
Turn the knob to move the barometric pressure scale independently from the pointers and set the local
QNH.

6.

Keeping the local indicated altitude matched to the local QNH on the barometric pressure scale, push in
the knob and turn slightly so that all gears engage.

7.

Slide the locking stud back towards the knob shaft, and tighten the locking stud screw. Ensure that thescrew is perpendicular in the hole when tightening. As it is tightened, the turning force (torque) required
will increase if it is properly aligned. When properly aligned and tightened, the screw will not move toeither side when pressed.

8.

Check security of the locking screw by pulling on the knob while turning it. The pointers and thebarometric dial shall rotate simultaneously.

MODEL:
Source: Sloley and Coulthard “Aircraft Engineer’s Handbook No. 4 Instruments” 5th edition 1953
1.

Before starting obtain an accurate barometric pressure reading from a local weather service, and knowwhat your exact altitude is as you make the adjustment. Set the altimeter to the exact altitude of yourlocation.

2.

Locate the screw to the left of the adjusting knob, as shown in Figure B-13. Remove the screw using ascrewdriver. The adjusting knob may need to be removed first.

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Removescrew

Figure B-13: Smith altimeter with drum counter style barometric pressure scale
3.

Determine the current barometric pressure reading from the BOM observations website or otherreputable source.

4.

Rotate the adjustment knob to change the barometric reading in the window without changing thealtitude setting.

5.

Replace and tighten the screw.

MODEL:
Source: From G.E.Irvin “Aircraft Instruments” 1st Edition 1941 McGraw-Hill page 321

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5.

NUTS, BOLTS AND HARDWARE

5.1

INTRODUCTION
The correct installation of the general hardware found in sailplanes is vital to the safe operation of the
sailplane and also to a long life for the sailplane. The use of an incorrect bolt may result in an under-strength
joint, excessive wear or a joint which is liable to undo.
Nuts and bolts primary function is to hold components together.
A bolt is always used with a nut; sometimes these are ‘captive’ nuts which are fixed in the aircraft and notplaced on the bolt by the operator. Nuts and bolts serve as a fundamental component in many structures as
they provide strong bonds that do not break even under great amounts of pressure. Nuts and bolts can haveseveral different styles and types, each suited to match the needs of a particular application or need of thejob.
Many steel structures, including buildings, are designed to be simply bolted together. The Eiffel Tower inParis, for example was originally a temporary structure and after twenty years it was to be dismantled. As aresult it was built with bolts, and has lasted a long time.
The nut is always used opposite a mating bolt and features a threaded hole which is the same as the threadon the bolt. When secured, the nut and the bolt are able to stay together without dropping apart due to thefriction that is generated by their thread, compression of the parts, and a slight stretch of the bolt.
There can be application where vibrations and rotation may cause the nut and bolt to come loose, in thiscircumstance a locking system using the nut itself (self-locking nuts), or a separate locking system such as
lock washers, split pin or lockwire are used.

5.2

TYPES OF BOLTS
Because different sailplane manufacturers use different types of nuts and bolts it is very important to be able
to identify each type to avoid mixing bolt types with the possibility of damage to the fastener and loss ofstrength of the assembly. It is important to note that some types of bolts are metric and others are imperial.
A screw pitch gauge and a micrometer are useful for this task especially with bolts of similar size e.g. 3/16"
BSF, 10-32 AN and 2 BA.

5.2.1

DIN STANDARD
The DIN standard are a metric bolt. DIN stands for Deutsche Industrie-Norm which basically translates as
German Industrial Standard. All German and some other European sailplanes use bolts which have been
manufactured to a DIN specification. Table 9 shows the specifications for the most common bolt DIN 931.
DIN specifications are used for almost everything in Germany including split pins and spanners!

b1
k1

s1

l1

Figure 5-1 Bolt Specifications

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b1

d

e1

k1

s1

l1

From

Available in lengths
from

To

to

M4

14

7.74

2.8

7

22

70

M5

16

22

8.87

3.5

8

30

80

M6

18

24

11.05

4

10

30

90

M8

22

28

14.38

5.3

13

35

110

M 10

26

32

18.9

6.4

17

40

150

M 12

30

36

21.1

7.5

19

45

180

M 16

38

44

26.75

10

24

55

200

M 20

46

52

33.53

12.5

30

65

220

M 24

54

60

39.98

15

36

75

220

Table 5-1 DIN 931 Bolt Specifications
Each type of DIN specification bolt is available in a number of strength grades and the grade is usually
embossed on the head of the bolt.
Typical grades and the strength they represent are shown in Table 5-2. As can be seen from the table, DIN
bolts are very strong compared to the typical loads in a sailplane control system however whenever a bolt is
replaced it should be replaced with one of the same grade or higher. DIN specification bolts are available
from most specialist bolt suppliers.
Property class

3.6

4.6

4.8

5.6

5.8

6.8

8.8

10.9

12.9

Minimum
Tensilestrength
N/mm2

330

400

420

500

520

600

800

1040

1220

Tensile load tobreak an M 6bolt (kgf)

676

819

860

1024

1065

1229

1639

2130

2500

Table 5-2 Property Classes
There are 4 basic types of DIN nuts: the normal nut DIN 934, the thin check nut (about 60% of the thicknessof the normal nut) DIN 439, the self-locking nut (nyloc) DIN 985 and the castellated nut DIN 935.
The advantage of the DIN standard bolts is that they are readily available and cheap. The disadvantages arethat they will have a slightly looser fit in a hole or bearing (which may allow a small amount of free play incontrol connections), have a relatively long threaded section of the bolt (which may need to cut down to size)
and tend to come in length increments of 5mm. The 5mm increments in length may result in one bolt having
a shank that is 1mm too short and the next length of bolt having a shank 4mm too long resulting in excess
washers being needed.

5.2.2

ONL STANDARD (FITTED TO BLANIKS)
The ONL standard are a metric bolt. The ONL standard originated in Czechoslovakia (now the Czech
Republic) and is used on the Blanik L13 and any other aircraft originating from that country. Because thesebolts have metric dimensions, they have often been used as replacements when DIN bolts have not been
available. However care must be taken to ensure that understrength bolts are not installed and they must not
be loaded in tension due to the small size of the head.

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Grade

8E

8G

10G

10K

12K

Tensile Strength
N/mm2

800-950

800-100

1100-1300

1000-1200

1200-1400

Shear Strength
N/mm2

65

64

90

90

108

Identification
marking

Table 5-3 ONL bolt identification

b1
s1

l1

k1

d

e

k

s

Split pin size

M5

9.2

2.5

8

1.2 x 10

M6

10.4

2.5

9

1.6 x 12

M8

13.8

2.5

12

2.0 x 16

M 10

16.2

3

14

2.5 x 18

Table 5-4 ONL 3120 calibrated bolts with hexagonal head (Standard 10G material)

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d

D

k

Split pin size

M5

9

3

1.2 x 10

M6

11

4

1.6 x 12

M8

14

5

2.0 x 16

M 10

17

6

2.5 x 18

Table 5-5 ONL 3125 Calibrated Bolts With Slotted Head (Standard 8e Material)

5.2.3

EUROPEAN AIRCRAFT STANDARD BOLT
Similar to the DIN and ONL standards, these are a metric bolt. There are a wide variety of speciallyapproved aircraft bolts available from Europe eg LN 9037 or EN 2859 and have many similarities with the
AN and MS bolts described below. They are available in a variety of strengths, head styles and are available
with drilled heads or threads for lock wire or split pins.
All European aircraft approved bolts will have the standard number either stamped or embossed on the headof the bolt. The head of the bolt will also have a number for its diameter and a number for the length of thebolt e.g. 9037 06 044 on the head of the bolt will be a LN9037 bolt with a 6mm diameter and a 44mm length.
Note that some older standards will have the ‘length’ as the total length of the bolt, while newer standards
will have the ‘length’ as the length of the shank.
The advantages of European aircraft approved bolts are that the fit of the bolt is slightly tighter (close
tolerance) than the DIN standard (resulting in reduced free play) and the lengths come in 1mm or 2mmincrements meaning that you can almost always get the exact shank length you need without needingexcess washers. The disadvantage is that they are not widely available in Australia and can be costly.

5.2.4

AN (ARMY NAVY) OR MS (MILITARY SPECIFICATION)
The AN specification bolts are imperial sizes. They are the preferred fasteners for all general aviation aircraft
manufactured in the US and are also used extensively on airliners. Because these are specially approved
aircraft bolts, their quality is assured and they come cadmium plated for excellent corrosion prevention. The
cadmium plating give the bolts a yellow or silver colour depending on the process used to plate the bolts.

WARNINGAN hardware should not be welded as the cadmium plating gives off highly
toxic fumes.
AN bolts are certified to a minimum tensile strength of 125000 psi (860 N/mm2).
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AN fasteners are only available in imperial sizes and can be purchased from your local LAME in small
quantities or from an aircraft parts supplier
Sailplane inspectors will find AN fasteners on American built sailplanes as well as the Pilatus. AN fasteners
are the preferred choice for amateur built sailplanes and are often used as replacements for BSF on British
and Australian sailplanes.

Standard Bolt Head

Drilled Hexagonal HeadCountersunk HeadInternal Hexagonal Head

Eyebolt

Clevis Bolt
Figure 5-2 Some AN Bolt Types

To aid the identification of AN bolts, the head of each bolt has an embossed symbol which represents thetype of bolt and the material it is manufactured from. Because these bolts are manufactured by a number ofsources, the exact markings can vary between manufacturers. However, all AN standard steel bolts will havestandard markings as per
Figure 5-3 and may also have markings identifying the manufacturer.

Figure 5-3 AN bolt identification
To fully Identify an AN bolt, it is necessary to know its nominal diameter in 1/16” and its length. An AN 4 bolt
is 4/16” in diameter = 0.25”. Likewise an AN 5 bolt is 5/16” in diameter = 0.3125”.

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The length of the bolt from under the head of the bolt to the end of the shank and is expressed as a dashnumber. An AN 4-10 bolt is 0.25” diameter and is 1.03” long. Each dash number specifies a different lengthfor different bolt diameters. You must refer to a size chart or AN bolt gauge to find the correct dash number.
If AN bolts are being purchased, a catalogue should be consulted to ensure that the correct bolts areordered.
AN No

DiameterThreadSpanner size A/F

AN 3

3/16”

10-32 UNF-3A

3/8”

AN 4

1/4”

1/4-28 UNF-3A

7/16”

AN 5

5/16”

5/16-24 UNF-3A

1/2”

AN 6

3/8”

3/8-24 UNF-3A

9/16”

AN 7

7/16”

7/16-20 UNF-3A

5/8”

AN 8

1/2”

1/2-20 UNF-3A

3/4”

Table 5-6 AN Bolt Specification

5.2.5

BSF (BRITISH STANDARD FINE)
BSF are an imperial bolt. They are the standard fastener on older British and Australian production
sailplanes although care must be taken with Australian sailplanes as bolt installation was heavily driven by
supply of WWII surplus bolts. The best way to tell if BSF fasteners are fitted to a sailplane is by trying to fit anormal spanner. BSF bolts larger than 1/4” require special spanners such as 17/32 A/F.
Because BSF hardware is no longer readily available in Australia whenever a bolt becomes unserviceable itshould be replaced with an AN specification bolt.

Nominal SizeThreads per inch

Spanner size A/F

1/4”

26

7/16”

5/16

22

17/32”

3/8

20

39/64”

7/16

18

91/128”

Table 5-7 BSF Specifications

5.2.6

BA (BRITISH ASSOCIATED)The BA standard are an imperial bolt. As the BSF series of bolts only goes down to 1/4” nominal diameter, asecond standard exists for smaller sized bolts. As for BSF, BA is the standard fastener on older British andAustralian sailplanes for 3/16” and smaller.
The usual sizes for BA fasteners are 2BA and 4BA (said “Four B A”) and like gauge sizes the higher thenumber the smaller the bolt. Other sizes from 0BA to 10BA are available although, like BSF, they are very
difficult to find in Australia. BA fasteners also use special spanner and drill sizes.
BA Number

Shank Diameter

Width acrossflats

Threads per inch

2BA

0.185” = 3/16”

41/128”31.4

4BA

0.142” = 9/16”

1/4”

38.5

Table 5-8 BA Specifications

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5.2.7

AUSTRALIAN COMMERCIAL BOLTS
When bolts are no longer serviceable it is sometimes possible to use commercial bolts in lieu of the original
specification bolts. Whenever a bolt is replaced the inspector must be sure that the replacement part is ofequivalent or higher strength than the original and if a close tolerance bolt has been used then the new bolt
must be of an equivalent tolerance. Replacement bolts should be purchased from a reputable supplier who
is able to provide traceability of the bolt. This traceability should include the bolt manufacturer, the bolt batch
number and the heat treatment that has been applied to the bolt. Bunnings will not be able to provide thisinformation. However, suppliers like Konnect (Coventry Fasteners) or United Fasteners should be able tosupply this information when you request it for your records.
When replacing DIN specification bolts, equivalent grade bolts may be used as most Australian metrichardware standards are based on DIN specifications.
If replacing a bolt that is directly in contact with aluminium structure, only cadmium plated bolts are to be
used as the cadmium plating will corrode in preference to the aluminium.
Where AN bolts were originally fitted then only AN bolts may be used as a replacement.
When replacing BSF bolts, AN bolts should be used. However, if commercial imperial bolts can be shown tohave equivalent strength then they may be used provided they have a UNF thread. Bolts with UNC of
Whitworth thread may not be used as replacement bolts in sailplanes.

5.3

INSPECTION OF BOLTS
Whenever a bolt is removed it should be inspected for general condition and should be replaced if it has anyof the following faults:

5.4

a.

Corrosion. Only bolts with light corrosion may be re-used and the corrosion should be removed andsteps taken to prevent it recurring.

b.

Cracks. Any sign of a crack is cause for immediate replacement and investigation into why the crack
occurred.

c.

Rounded head. If the head of the bolt is at all rounded due to slipping spanners (the spanner used
was too big) the bolt must be replaced. Even if it is possible to reinstall the bolt to the correct torque,
you may never remove it again!

d.

Worn threads. Normal threads are not designed to be undone and done up forever. Each time the nut
is torqued the thread wears and the nut becomes looser on the thread. A bolt which is twenty years
old and has been removed at each annual inspection may have threads worn beyond acceptable
limits.

BOLTING PRACTICE
Generally, bolts which carry any significant load in sailplane structures or control circuits are loaded in shear.
Consequently the plain "shank" of the bolt carries the load and the thread is used only to clamp thecomponents together. Bolts should be selected to ensure that only the shank is within the components.
Because only a limited number of bolt lengths are available, a bolt will sometimes have to be used which isslightly too long in the shank and washers will be needed to stop the nut becoming "thread bound" i.e. being
tightened on the thread run out rather than clamping the components together. The washers should be
added to the threaded end of the bolt to ensure that the shank is fully in contact with the bearing surface.

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INCORRECTCORRECT

Thread inShear
No thread in Shearor Bearing

WasherThread in
Bearing
Figure 5-4

The Right and Wrong Way to Assemble a Bolt - Non-moving Parts.

Whenever a bolt has excess thread length, the end of the bolt should be shortened so that no more than 3threads protrude beyond the end of the nut to prevent the bolt catching on other parts of the sailplane or if
the bolt is external, the possibility of a tow rope catching the bolt. If the bolt is plated, the cut end of the bolt
should be painted with primer to prevent corrosion.
In a push rod assembly joint or a bearing assembly the nut should always be tightened so that the
movement takes place in the bearing rather than between the bolt and the mounting hole.
Bush
Bolt

Pulley Bracket

PulleyFigure 5-5

5.4.1

Correct Bush Assembly

BOLTING WOODEN STRUCTURES
Correct bolting practice when installing bolts in wooden structures is vital to ensure the joint is strong enoughand that it will not degrade over time. Because timber changes size with varying moisture content, if the bolt
is installed in the middle of winter the moisture content of the timber is likely to be high, six months later insummer the timber may have dried out and shrunk therefor allowing the bolt to be loose. If the bolt istightened at this point then as the timber swells again next time it is wet the fibres may be crushed anddamaged.
In this situation the inspector has a difficult decision in deciding the correct tightening of the bolt as the bolt
cannot be loose or it will work and damage the timber but over torqueing can easily cause fibre damage inthe timber. In general bolts should be tightened until they are just snug. About 1/2 a washer depth of fibrecrushing seems to be about right.

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To alleviate this problem, most designers place a “penny washer” at both ends of the bolt (one under thehead and another under the nut) to spread the load over a much larger area and thus reduce the problem ofdamaging the timber and the bolt periodically loosening. Penny washers should be used wherever a bolt
bears on wood, provided there is room.

5.4.2

BOLT TORQUES
Whenever a bolt is installed it is important that the tightening torque is correct.
Because the spanner length increases in proportion to bolt size it is usually possible for an experienced
inspector to tension a normal steel bolt by applying a firm torque with the correct sized spanner until the bolt
is snug. Where a bolt is unusual or the inspector is inexperienced, the manufacturer’s recommended torqueshould be obtained and a torque wrench used.
Wherever possible, the nut should be rotated and the bolt held still as the friction of the bolt rotating in thehole will significantly affect the torque of the assembly.

5.5

SAFETYING OF BOLTS
The primary forces which prevent the nut unscrewing from the bolt is the friction force developed between
the thread of the bolt and the thread of the nut and, as experience on many types of machines has shown, if
the bolt is correctly torqued the nut is very unlikely to come undone. It is for this reason that all threads
should be free from oil or grease before being assembled unless the manufacturer explicitly says to lubricate
the thread.
Because of the consequences of a bolt coming undone in flight every bolt in a sailplane (in every aircraft forthat matter) must have a second method of preventing the nut from coming undone.

5.5.1

ELASTIC LOCK NUTS
The most common method of safetying bolts in sailplanes is to use an elastic lock nut. These nuts have aplastic or fibre insert in one end which is cut into by the bolt thread as the nut is wound onto the bolt.
Because of the elastic nature of the insert, it provides a high friction force on the thread which is independentof the tightening torque and so is acceptable as a safetying device.
When using elastic lock nuts the following points should be noted:

5.5.2

a.

The bolt is in safety when one full thread is showing through the elastic insert.

b.

The nuts may be reused until they can be wound on with the fingers. The nut may not be salvaged bytapping the end of the nut with a hammer to tighten insert.

c.

The nuts may be used over bolts which have been drilled to accept split pins provided there are noburrs on the bolt.

d.

The nuts may be used over bolts which have had the excess thread removed provided the thread at
the cut end of the bolt has been filed to prevent the sharp edge from cutting the plastic insert.

e.

The nuts must be torqued sufficiently to prevent the bolt rotating in the joint. In some designs it is notpossible to tighten a rotating joint and maintain movement and in these installations elastic stop nuts
must not be usedf.

Most elastic lock nuts are not heat resistant and so should not be used in the engine compartments ofpowered sailplanes.

g.

Elastic lock nuts must not be used on rotating components like rudder hinges as the frequent rotation
may cause it to loosen. Split pins must be used for such application and castellated nuts must not be
replaced by elastic nuts.

OTHER LOCK NUTS
When an elastic stop nut cannot be used because of the possibility of fire an all metal lock nut must be used.
These nuts come in a number of varieties and have generally been deformed in some way so they provide a
metal to metal interference fit. Whenever an all metal locknut is disassembled both the bolt and nut must be
replaced as the threads are permanently damaged when the nut is wound onto the bolt.

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5.5.3

REDUCED HEIGHT LOCK NUTS
In some applications where there is limited clearance eg air brake blades, some release installations,
reduced height lock nuts are sometimes used. As these nuts are thinner than the full size nuts, they will have
reduced tensile strength as their load transfer to the bolt thread is reduced. These must only be used where
the bolt is loaded in shear.

Figure 5-6 Reduced Height Lock Nut
Bossard Australia have BN19175 reduced height lock nuts in a range of styles available at their online store:
https://uat9.bossard.com/au-en/. The maximum torque for M6 BN19175 is 4 Nm.

5.5.4

CASTELLATED NUTS
On older types constructed before elastic stop nuts became readily available the primary means of safetyingbolts is to install a castellated nut and a split pin through a hole in the bolt. This method of safetying may be
used where it is not possible to correctly torque the bolt because the required rotation will be lost.
When installing castellated nuts the nut should be torqued until the slot in the nut aligns with the hole in thebolt. If it is not possible to align the hole and the slot using a reasonable torque then different thicknesses of
washers should be used so the correct alignment can be obtained.

5.5.4.1 SPLIT PINS
The usual way to safety the castellated nut is using a split pin. It is important that the pin be the correct size
as if a pin the wrong size is used it may not be strong enough to adequately retain the nut. As shown in
Figure 5-5-7 there are two possible ways to install a split pin.
Optional

PreferredFigure 5-5-7 Split Pin Installation
When installing a split pin the following rules should apply:a.

The prong over the end of the bolt should be trimmed so that it doesn’t extend beyond the bolt
diameter.

b.

The prong bent down should be trimmed so that it doesn’t touch the washer.

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5.5.5

c.

If the optional wrap around method is used the prongs should be trimmed so they do not extend past
the nut.

d.

Reasonable bend radii should be used as tight bends are prone to breakage.

e.

Split pins should never be reused.

SAFETY WIRING
Whenever a bolt is installed in a captive nut or where a number of bolts form a cluster, it is usual to safety
these bolts using lock wire.

Figure 5-8 Safety Wiring
When safety wiring is used the following points should be noted:a.

Only use aircraft grade safety wire. It is cheap and readily available with a little planning.

b.

All lock wiring must be installed so that the tension in the wires tends to tighten the bolts.

c.

Proper aircraft lock wire pliers make the task of lock wiring much easier. See Figure 5.8.

Figure 5-9 Lock Wire Twisters

5.5.6

JAM NUTS
The use of jam nuts on ordinary nut and bolt installation is not recommended on sailplanes because themethod is poorly understood. When the outer nut is tightened against the inner nut it experiences muchhigher loads than the inner nut and so the thick nut should be to the outside.

Incorrect

Correct

Figure 5-10 Jam Nut Assembly
The only place on a sailplane that jam nuts are commonly used is to secure the rod ends into the pushrods.
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5.5.7

PUNCH LOCKING
Sailplane manufacturers sometimes use punch locking to secure a nut when there is not enough space for aself-locking nut or castellated nut. This method has been used in the past for reasons of economy where it
was intended that the nut would be seldom, if ever undone.
To remove the bolt, the deformed end must first be filed or ground back to the nut. The nut may now be
unscrewed but any remaining burrs on the end of the bolt should be removed before an attempt is made toremove the bolt from its hole.
A new bolt must be fitted each time a bolt secured by punch marking is removed. The new bolt must havethe correct length of shank with the thread trimmed off to allow approximately half a millimetre to extend
beyond the nut.
After the nut has been tightened, the bolt head should be supported with a dolly while the punch marks are
made.

Figure 5-11 Punch Locking

5.5.8

LOCTITE
Sometimes, especially when vibration is high such as in powered sailplanes, Loctite or a similar product isused to secure the bolt. These products set in the absence of oxygen and so only harden between thethreads. The advantage of the Loctite is that all other products are excluded and so the chances of corrosion
are greatly reduced.
Special care must be taken to select the correct Loctite grade. Most manufacturers specify the grade to use
and this must be adhered to. Where the manufacturer hasn’t specified the grade then the Loctite publishedguides should be used when selecting the correct grade to use.

5.5.9

TAB WASHERS
A tab washer is a special washer which is bent up after the nut has been tightened and provides amechanical safetying of the fastener.

Figure 5-12 Typical Tab Washer
Any tab washer which has been used should not be used again.

5.6

WASHERS
Whenever a nut and bolt is used, a washer should be installed between the nut and the fitting to adjust theposition of the nut to prevent thread binding. When bolting steel, the washer may be omitted so the nut iswithin safety.

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If aluminium or magnesium structures are being bolted then a cadmium plated steel washer should be usedas the cadmium will corrode rather than the alloy structure.
As noted in Section 5.4.1, “penny” washers should be used wherever wooden structures are bolted.

5.7

CLEVIS PINS
Clevis pins are used in cable systems and in secondary control systems. They consist of a steel pin with ahead at one end and a hole drilled at the other end to accept a split pin.

Figure 5-13 Typical Clevis Pin
Whenever a clevis pin is installed, a washer should be placed between the split pin and the parts to preventthe part being worn by the split pin.

5.8

ROLL PINS
Roll pins are a convenient method for sailplane manufactures to use for securing parts, especially the pins
used as hinges of control surfaces on some Grob and Schempp-Hirth sailplanes.
During maintenance, roll pins can cause a few problems. They rely on expansion to provide the friction
which locks them in place. Because of the likelihood of damage to the roll pin during fitting and removal, theyshould be only used once.
The end of the roll pin should be checked for burrs before any attempt is made to remove it. If there areburrs or the pin has been flared out during installation, it is necessary to file the end of the pin flat so it willpass through the hole.
Removal should be done using some form of extractor or pressing tool to avoid damage to the sailplanestructure. If the use of a hammer and punch cannot be avoided, the structure should be supported with adolly. The punch used must be slightly smaller than the hole and have a flat end.
Components are usually drilled by hand at assembly e.g. aileron hinge pins on Grob Astirs’. The parts will
only go together with the original pin in the original hinge so care must be taken not to mix the pins.

5.9

TORQUE
Nuts are tightened onto a bolt by applying a twisting force (torque) to the nut. Torque is measured as Force(kg, N or pounds) times a lever length. Typically, Newton-meters or foot-pounds are used, but sometimes anunusual unit such as a kg-cm is used.
It is very important that the correct torque be applied. In particular, over-torqueing must be avoided because
it can cause failure of the bolt. Under-torqueing can cause wear by allowing movement where none should
exist.
A correctly torqued bolt will have the correct amount of tensile stress and the correct amount of bolt stretch,thus allowing the bolt to exert the proper clamping force.
For example, a 6mm diameter bolt carrying 288 kg of tensile load has a tensile stress of 99.8 n/mm2 andhas stretched .057mm. (See below for details of this calculation)
For most sailplane work, it is not necessary to use a torque wrench, but it is necessary that the sailplane
engineer calibrate themselves to find out how much force they need to apply with the spanners they areusing. Where the torque is critical for particular bolts, the bolt torque will be specified in the aircraft
maintenance manual.

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Below is a table of the correct torques for commonly-used bolts. The figures are based on turning the NUT
and not rotating the whole bolt while holding the nut still.
Bolt type
Cadmium plated unlubricated AN(Army-Navy) aircraft bolts

Metric DIN (Deutsche Industrie-Norm, as used on most German
sailplanes)
Property Class 12.9 (this is thehighest property class andequivalent in strength to AN bolts).

Size

Correct Torque

1/4"

11 N-m

5/16"

34 N-m

3/8"

40 N-m1/4", into wood with penny washers

9.5 N-m

M5

8 N-m maximum

M6

14 N-m maximum

M8

35 N-m maximum

M12

121 N-m maximum

Table 5-9 Recommended Bolt Torques
A cautionary case example: On a Jabiru undercarriage, a high-tensile bolt from a hardware shop was
substituted for an AN bolt. The person doing this substitution thought he was doing a good thing. Well thebolt failed very early from fatigue, luckily as the aircraft was being wheeled out the hangar. In this case, thehardware shop bolt was defective in toughness, as measured by "elongation to failure" in comparison to the
AN bolt. It may well have had other property defects too.

5.9.1

NUT FRICTION AND TORQUE
In order to apply the correct tensile stress to a bolt by means of tightening a nut, it is important that thefriction between the nut and bolt be known. It has been estimated that only 10% of the applied torque goes
into tensile stress in the bolt. 50% is spent overcoming nut friction and 40% overcoming thread friction. So
the nature of the surfaces involved in producing this friction becomes important. Lubricated nuts require lesstorque than dry nuts.
A cautionary case study: An automotive manufacturer changed to a different bolt supplier, with no otherchanges intended. Suddenly the factory suffered a spate of bolt tensile failures. It turned out that the newbolts had a lower coefficient of friction and applying the same torque was overloading them.
On some torque wrenches, you will see that an alternative method of achieving the correct tensile stress iscatered for... the nut is turned a calculated amount after contacting the surface to be clamped.
Thus in the 6mm example bolt referred to previously, where 0.057 mm of stretch is to be applied to achieve
the stress of 99.8 N/mm2 , this corresponds to 20.5 degrees of rotation of a 1 mm thread pitch nut. (Thiscalculation uses 210,000 N/mm2 as the Young's Modulus for steel)

5.9.2

SPANNER LENGTH
Remembering that Torque = Force x Distance, it follows that doubling the length of your spanner will double
the torque applied by a given hand force.
This fact has caused some manufacturers to deliberately cut down the length of spanners used in production
so that nuts are less likely to be over-torqued.

5.10

REPLACING HARDWARE
If you cannot obtain the correct replacement and you are not sure of the correct replacement based on theabove guidelines then you must apply for engineering help from the GFA. We can arrange an engineeringorder to specify a replacement.

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5.11

REFERENCE AND FURTHER READING
1)

EA-AC 65-9A Airframe & Power plant Mechanics General Handbook. IAP Inc. Casper, Wyoming.

2)

AC 43.13-1A Change 3. Acceptable Methods, Techniques and Practices. IAP Inc. Casper, Wyoming.

3)

Ajax Fasteners. Fastener Handbook, Bolt Products. Ajax Fasteners, Richmond, Victoria, 1985.

4)

Machinery’s Handbook, 24th Edition. Industrial Press Inc., New York, 1992.

5)

Ray C. Stafford-Allen. Glider Maintenance Manual. British Gliding Association, London, 1959.

6)

Sailplane Overhaul Manual (Wooden Construction) General Part. Warsaw, 1967

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6.

CABLE SYSTEMS

6.1

INTRODUCTION
Steel cables are used extensively in sailplanes as part of the control system and in some vintage sailplanes
as external bracing as part of the structure. Each cable assembly consists of the cable itself and some formof end terminal. The terminal is usually a looped end which is held in shape by a thimble and a sleeve whichis swaged into place. The cable assembly may also contain a turnbuckle for adjusting cable tension and may
pass around a number of pulleys and through fairleads (a device to guide a cable around an object).
Some older sailplanes may contain hand woven splices rather than swaged endings. Teaching of hand
woven cable splicing is beyond the scope of this book and the local club expert (if there is one) should be
consulted before attempting a woven splice. The expert may be identified by his great age and gnarledfingers!
All hand woven cables must be in accordance with the procedures in AC 43.13 1B Chapter 7.

Figure 6-1

Typical Cable End

The steel cable used in aircraft is available in galvanised steel or in stainless steel. The stainless steel cable
is more expensive than the galvanised cable and in most applications wears more quickly. Only inenvironments where corrosion is a real problem should the use of stainless steel cable be considered.

6.2

CABLE TYPES
All cables consist of a series of wires which are wound together to produce a strand. The strands are thenwound together around a central strand to form the cable. Cable designation is set down as:
Number of
strands x Number of wires per strand. Most cables used in Australia are either:7 x 7 flexible cable or

7 x 19 extra flexible

Figure 6-2

6.2.1

Cable construction

AMERICAN CABLES
The main cable type is the American system which designates its cables by the outside diameter of thecable. This is the cable system used on almost all GA aircraft and is readily available, at a price, from any
LAME workshop in the country.
Almost all cables found in sailplanes in Australia will be either 3/32" or 1/8" with a small amount of 5/32"
cable.

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CAUTION
You cannot mix imperial and metric cable components even if they look right.
Available cable sizes are:Diameter(Inches)

Construction

Breaking Strength(lb.)

Approx. weight per
100' (lb)

1/16"

7x7

480

0.75

3/32"

7x7

920

1.60

3/32"

7 x 19

1000

1.70

1/8"

7 x 19

2000

2.90

5/32"

7 x 19

2800

4.50

3/16"

7 x 19

4200

6.50

1/4"

7 x 19

7000

11.00

Table 6-1 Available American cables sizes

6.2.1.1 NICOPRESS SWAGE
American cables must be terminated with a Nicopress swage. The process must be done using the correct
sleeve and the correct thimble in the special Nicopress tool, the finished joint is then stronger than the cable
itself. There are two types of tool, a hand squeezer which resembles a set of bolt cutters or the lessexpensive clamp squeezer both of which are genuine Nicopress tools and the only tools which may be used
to swage American aircraft cables.

Figure 6-3

Figure 6-4

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Swaging Sequence for 1/8” Cable

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Cable

SleeveAN 100ThimbleThimbledimensions

Size

Stock No.

Dash No.

A

B

C

1/16"

18-1-C

-3

0.35

0.7

3/32

3/32"

18-2-G

-4

0.35

0.7

9/64

1/8"

18-3-M

-4

0.35

0.7

9/64

5/32"

18-4-P

-5

0.4

0.8

11/64

3/16"

10-6-X

-6

0.5

1.0

13/64

Table 6-2 Sleeve and Thimble Dimensions for American Cable
After the Nicopress splice is completed, it must be inspected to the following criteria:

6.2.2

a.

Sufficient "tail" extending from the sleeve (2 to 3 mm).

b.

Thimble gripped firmly but with tips not distorted or buried in the sleeve.

c.

On the 1/8 inch cable splice, the three compressions must be evenly spaced with no overlap or
bending of the sleeve.

d.

Check each compression for size with the appropriate gauge.

e.

Proof load to 60% of cable breaking strength (or proof load sample).

BRITISH CABLES
The British system is found in a number of older designs and the cables are designated by the minimum
breaking strain which the cable should sustain in hundredweight (cwt.) (one hundredweight is equal to 112
lb. or 50.8 kg). The most common sized cable used in sailplanes is the 10 cwt.

6.2.2.1 TALURIT SWAGE
Manufacturing of a Talurit swage is similar to producing a Nicopress swage. When using the Talurit system,
only genuine Talurit ferrules, thimbles and compressing tools may be used. After the Talurit swage has been
completed, the flash may be removed carefully with a file provided the diameter of the ferule is not reduced.
Inspection must include:a.

Check for correct diameter of ferrule after compression.

b.

Sufficient "tail" extending from the sleeve (2 to 3 mm).

c.

Thimble gripped firmly but with tips not distorted or buried in the sleeve.

d.

Check ferrule for cracks with 5X magnifiere.

Proof load to 60% of cable breaking strength (or proof load sample).

Figure 6-5 Sectioned Talurit Sleeve

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6.2.3

OTHER CABLE SYSTEMSThe other systems which may be encountered are:a.

Metric DIN specification cable. The metric system is a direct equivalent for the American system as
the sizes of the cable have been chosen to match the American system. The most common size cable
is 3.2 mm diameter. But you cannot use a metric swage on a very similar imperial cable, etc, they may
slip, and it would be illegal.

b.

Hemp cored cable. This was used in eastern European countries but has been banned fromsailplanes in Australia for many years.

As well as the Nicopress swages some sailplanes use cable terminal ends. Installation of these terminal
ends is a specialist job and requires the use of a rotary swaging tool. If you have to replace a cable whichuses these type of terminals the job should be entrusted to your local LAME. Note if stainless steel thenfollow CASA AD/GEN/87 (must be replaced every 15 years.)

Figure 6-6 Typical Cable Terminals

6.3

CABLE INSPECTION

Figure 6-7 Individual Outer Wires Worn Less Than 40% (Worn Areas Individually Distinguishable)
The most common reason for replacing a control cable is wear, which will occur at every point at which thecable makes contact with any other part of the sailplane. Worn cable will show itself by bright areas on thecable (provided the cable has been in recent service) and the individual strands of the cable must be
inspected under magnification for excessive wear. Cable wear patterns should be compared to thediagrams. Cables as per Figure 6-7 may continue in service. Cables in which the outer strands are morethan half worn must be replaced.

Figure 6-8 Individual Wires Worn 40 - 50 % (Note Blending Of Worn Areas)

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Figure 6-9 Individual Wires Worn More Than 50 %Fatigue will show itself in the form of broken wires at any point where the cable changes direction. Small
diameter pulleys and fairleads which force a change of direction are likely areas to look. Running a rag along
the cable should detect any broken wires or the cable can be bent and any broken wires will stand out.

Figure 6-10 Cable Inspection TechniqueCorrosion should be looked for anywhere the cable is likely to get wet, either from water, sweat or battery
fumes. Hemp cored control cable, which was banned in Australia many years ago, was very susceptible tocorrosion. To check for the presence of a hemp core, twist the cable against its direction of "lay" and observe
the core strand. If the Inspector does not have the strength to execute the foregoing method, a two-inch nailcan be inserted between the strands without damage to the cable and the core inspected.
Note: Some cables may have a thin coloured cotton thread, which is acceptable, as distinct from a hemp
core which will be brown in colour.

6.4

CABLE LIFE
Cable life may be limited by 3 factors:

6.5

a.

The requirements of an Airworthiness Directive.

b.

There may be specific instructions contained in the sailplane’s maintenance manual.

c.

Where cable life is not limited by a) or b) above, the cables must be replaced on condition.

CABLE CARE
In order to obtain maximum cable life the cable should be protected by a light coating of graphite grease or
general purpose low temperature oil. If over time a heavy accumulation of the corrosion preventative
compounds occurs then it should be removed and fresh protector applied. When cleaning the cable do not
use MEK or other solvents as this will remove the internal lubricant in the cable.
Special care should be taken when handling cables to prevent kinking. Once a cable is kinked it is ruined
and must not be used in aircraft.

6.6

PULLEYS
Pulleys should be checked for any roughness of operation and condition of bearings. These pulleys are also
known to seize and instead of rotating the cable slides over the pulley. This causes excessive control circuit
friction and wear to both pulley and cable.

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Figure 6-11 Pulley Wear Patterns
The wear pattern which appears on the pulley can be a good guide to the health of the cable system.

6.7

CABLE TENSION
The turnbuckle is used to alter the length of the control cable for the purpose of adjusting the control position
and adjusting cable tension.
On sailplanes with closed type control cable systems, the cable tension determines the amount of control
free play and control circuit stiffness. It is critical the correct cable tension is maintained and this can bechecked with a cable tensiometer. The correct tension for a closed circuit control cable should be provided in
the aircraft’s Maintenance Manual.

Figure 6-12 Typical Tensiometer

6.8

TURNBUCKLE LOCK WIRING SCHEMESWhen locking a turnbuckle, it must meet the following specifications:a.

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showing.
b.

Safety wiring should be done neatly with no loose ends which can catch on adjacent structure or
another turnbuckle.

c.

Safety wire must not be reused. The minimum size of the safety wire and the minimum strength of thelock wire material varies depending on the size of the cable (the correct sized turnbuckle must also beused) and is shown in the following table:
Cable Size

Type of wrap

Diameter of safety
wire

Material(annealed condition)

1/16”

Single0.040

Copper, Brass.1

3/32”

Single0.040

Copper, Brass.1

1/8”

Single0.040

Stainless Steel, Moneland “K” Monel.

1/8”

Double0.040

Copper, Brass.1

1/8”

Single0.057 min.

Copper, Brass.1

5/32” and greater

Double0.040

Stainless Steel, Moneland “K” Monel.

5/32” and greater

Single0.057 min.

Stainless Steel, Moneland “K” Monel.

5/32” and greater

Double0.0512

Copper, Brass.1

1

Galvanised or tinned steel or soft iron wires are also acceptable.

2

The safety wire holes in 5/32” diameter and larger turnbuckles may be drilled sufficiently toaccommodate the double 0.051” copper or brass wires when used.
d.

Turnbuckles must not be lubricated.

e.

There are 4 ways of lock wiring a turnbuckle however only two of these commonly are used on
sailplanes. They are the single wrap and the double wrap as shown in shown below. Both methods
are acceptable.

Figure 6-13 Single Wrap

Figure 6-14 Double Wrapf.

6.9

Whenever the safety wire is wrapped around the turnbuckle (position A in Figure 6-13 and Figure6-14), it must pass around at least 4 times.

MAKING A NEW CABLE
The most important part of making and installing new cables is to ensure the length of the cable is correct.
Incorrect cable lengths can cause uneven rudder pedals and loss of full control movement. Most FRP
sailplanes which use cables in the rudder system have no turnbuckles to adjust out the slight inaccuracies ofcable construction and so special care must be taken to ensure correct cable length.

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If an old cable is being copied it is important to check the operation of the control in all positions prior to
beginning. Available turnbuckle adjustment should also be checked.
Cables stretch when loaded for the first time as the cables bed in. It is therefore advisable the cables be
preloaded to 50% of their breaking load prior to being fabricated into cable assemblies. When stretching thecables special care must be taken by placing a guard over cable to prevent injury in the event of a cablebreak.
If it is not possible to manufacture the cable and then install it in the sailplane then the cable must be madeup in situ. One end of the cable (the end which is most difficult to access in the sailplane) should be made up
and cable then fitted to the sailplane. The length of the cable should be adjusted and the second end
swaged. Construction of the cable may be made easier by the use of a splicing clamp as shown in Figure
6-15.

Figure 6-15

6.9.1

Cable Swaging Clamp

PROOF TESTING
Each cable manufactured must be proof tested to 60% of its breaking strain where the cable can beremoved from the sailplane. If it is not practical to proof load the finished cable in the sailplanes a sample
cable may be tested provided it is made using the same materials and process as the ones fitted to thesailplane.
Testing the cables can be performed by using a leverage assembly, say 10 to 1, and a spring balance tomeasure the load. When loading the cable precautions, such as guards over the cable, must be taken toprevent injury if the cable should fail.
Sample calculation:
Assume testing in a rig with 10:1 leverage and 1/8 cable.
Load on Lever =Version 24.1

𝑩𝒓𝒆𝒂𝒌𝒊𝒏𝒈 𝑺𝒕𝒓𝒂𝒊𝒏 𝒙 𝟎.𝟔
𝟏𝟎=𝟐𝟎𝟎𝟎∗𝟎.𝟔
𝟏𝟎= 120 lb

54 kg

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7.

CANOPIES

7.1

INTRODUCTION
The canopy is one of the most expensive and vulnerable parts of the sailplane with some canopy bubbles
costing over $8000. The condition of the canopy also has several significant airworthiness considerations.
Most canopies are made of Polymethyl methacrylate (PMMA), also known as acrylic or acrylic glass as well
as by the trade names Plexiglas, Acrylite, Lucite, and Perspex. In the rest of this chapter “Perspex” (atrademark belonging to ICI) is used to generically describe the canopy material.
If Perspex is not cared for properly it will, over time, develop cracks, pitting and discolouration whichsignificantly reduce the optical qualities of the canopy. This leads to a significant reduction in safety especiallywhen the sun is low on the horizon and when conditions are hazy. If the pilot’s vision through the canopy issignificantly impaired then it must be considered un-airworthy.
As the canopy also doubles as the point of entry and exit on almost all sailplanes, the correct operation of the
opening mechanism and the canopy jettison system are also vital.

7.2

ROUTINE CARE

7.2.1

DAILY CARE
Cleaning of the canopy should be performed at each Daily Inspection to ensure that the pilot can see throughit. Clean the plastic by washing it with plenty of clean water and mild soap, using a clean, soft, grit-free cloth,
sponge, or bare hands. It is important to thoroughly dry the canopy with a clean chamois as any small beads
of water will leave a dirt mark when they dry.
The canopy can be polished using a specific Perspex polish. The regular use of a Perspex polish will reducethe build-up of a static electricity charge.
Do not use gasoline, alcohol, benzene, acetone, carbon tetrachloride, fire extinguisher or de-icing fluids,
lacquer thinners, or window cleaning sprays. These substances can be dangerous to handle and use and may
soften the plastic and cause crazing.
Static electricity builds up when the Perspex is rubbed by a dry material. This can be a dry cloth, the air overthe canopy or even normal handling. The static electricity causes dust particles to stick to the canopy which
can reduce pilot vision.
The use of silicon based cleaners is not recommended on FRP or fabric covered aircraft as the silicon willinterfere with the glues and dopes which may be used during any repairs.

7.2.2

PERIODIC CAREAt least annually after removing dirt and grease and if no great amount of scratching is visible, finish the plastic
with a good quality grade of commercial Perspex polish such as Maguires or Mothers. Apply the polish as
directed on the bottle and bring to a high polish by rubbing lightly with a soft clean cloth.
Friction created by buffing or polishing too long in one spot can generate sufficient heat to soften the surface.
This condition produces visual distortion and should be avoided.
These specialised polishes contain chemicals which are designed to rejuvenate the acrylic material and reduce
the effects of static electricity.
Annually you are required to test the emergency exit, see MOSP 3 Section 13.8 Emergency Exits. This means
ejecting the canopy, carefully, making sure it works and reinstalling it. During the DI you must check the canopy
mechanisms are visually correct for hinges, release mechanisms, and that they appear they can be ejected if
required.

7.2.3

CANOPY COVERSThe use of a good quality, clean, flannelette lined canopy cover will have a triple benefit by reducing thechances of minor scrapes and scratches, lowering the internal cockpit temperatures and reducing the Ultra
Violet light in the cockpit. Reducing the amount of UV light will have a positive effect on harness life and reducefading of cockpit linings.

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A poor quality or dirty cover can reduce the life of a canopy. An ill-fitting cover will rub on the canopy when thewind blows causing a build-up of static electricity. The static electricity then attracts dust which acts as agrinding compound between the canopy and the cover resulting in scratches. Lycra stretch fit covers work
well. But grit can get under it and movement then scratches the canopy. Other composite covers work or todifferent degrees. Take care and care of your cover.

7.2.4

HANDLING OF CANOPIESThe correct handling of canopies is vital to their life span. Canopies must NEVER be lifted by the clear viewpanel as this places stress on the Perspex in an area where there are significant stress raisers.
Where the manufacturer has not provided obvious handles, it is recommended that these be installed so thatpilots and passengers do not have to lift the canopy on the Perspex.

7.3

REPAIR OF PERSPEXThe concept of repairing Perspex is quite straight forward however even simple repairs take a significant
amount of time and if the inspector does not take special care at each step then a poor repair will result. If the
optical qualities of the repair are not good enough then the canopy will need to be replaced.

7.3.1

CUTTING PERSPEX
Before cutting Perspex it should be warmed to at least 20°C. This will soften it enough to reduce the chanceof the Perspex chipping or cracking.
The saw should have at least 14 teeth per inch, finer saws should be used on very thin layers, and the Perspex
should be held firmly to prevent vibrations which can cause cracking. The saw should be worked through thematerial allowing the saw to cut the Perspex at its own pace. Do not try and force the pace by pressing hard.
The cut surface should be polished smooth to remove all notches which may cause cracks.

7.3.2

CRACKS IN PERSPEXThe brittle nature of Perspex makes it very susceptible to cracks. If cracks are left unattended they will growin a very short time to the point where the canopy will have to be replaced. Once a crack is identified the endof the cracks should be stop drilled immediately.

Figure 7-1

7.3.3

Stop Drilling

DRILLING PERSPEX
Stop drilling eliminates the stress concentration effect at the end of the crack and, if done properly, should
prevent further crack growth provided the overall strength of the canopy bubble is not compromised. The area
just in front of the visible crack will be affected by the crack and so the hole should be drilled just past the endof the crack. For all but the smallest cracks the hole should be about 3mm diameter. The hole must be drilledwith a specially sharpened drill or else the drill will chip the hole, creating stress risers which cause morecracks to form, often in several new directions.
Before drilling Perspex the drill must be specially sharpened so that it scrapes away the material rather thancutting it. This achieved by regrinding the tip with a zero rake angle as shown in the picture below. Or an easier
way is to dull the sharp cutting edges or use old drills to SCRAPE, not cut.

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Before drilling the canopy perform some test drills on scrap Perspex to ensure the correct technique is being
used. Like all drilling, a light pressure should be used allowing the drill to do the work. Pushing hard on the
drill is likely to result in cracked or broken Perspex.
Refer to: AC 43.13-1B Change 1. Acceptable Methods, Techniques and Practices Aircraft

Figure 7-2

Correct Sharpening Of Drill For Perspex

Ref: http://www.plasticsmag.com/features.asp?fIssue=sep/oct-01
Clamping a piece of wood to the Perspex material and drilling through into the wood can eliminate chippingon the backside of drilled holes. Start drilling the warmed Perspex with slow speeds and light pressure.
Increase speeds and pressures as you progress. As the drill bit starts to go through the canopy, reduce thespeed and pressure so that the drill bit penetrates through slowly. It is important to deburr both sides of theholes lightly with a machine countersink. No hole should have a sharp corner. (source vansaircraft.com)
There are many other views on drill bit sharpening. Consider these but in any case test, practice, and takecare. A canopy is a precious item that is hard to repair and is expensive.

7.3.4

PERMANENT REPAIRS
Stop drilling a small crack will stop its growth for a while however if the crack is left for long enough it will
inevitable begin to grow again. If the crack is large enough to allow relative movement between the sides thenthe crack should be repaired immediately as stop drilling will not stop the crack growing.
Regardless of the size of the crack the first step is to drill the end. This will redistribute the stresses and help
the repair last longer. The hole should then be plugged. This is done by gluing a small length of Perspex rod
into the hole. The hole should be drilled the same size as the stock rod and the end of the rod is then dippedin a Perspex solvent. The rod is then pushed into the hole and left until it sets. The rod is cut to length andblended in during steps g and h of Section 7.3.4.2

7.3.4.1 SOLVENT CEMENTS
As a solvent the following materials should be used or a proprietary Perspex solvent obtained from your
Perspex supplier.
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CAUTION
Perspex solvents may be toxic and dangerous to use. Follow safety direction on the solvent container. Use
only in a well ventilated area and wear gloves and safety glasses as a minimum.

7.3.4.2 REPAIR OF CRACKSTo repair a small fine crack a small amount of solvent should be placed on the crack and allowed to move into
the crack by capillary action. Larger cracks should be repaired by using Acrifix 92.
The canopy can be repaired as follows:a.

Cut out a 60° vee in the affected area as shown in the figure below with a chisel or similar tool using ascraping action, leaving a small-gap at the bottom of the vee. Keep your fingers, dirt and grease awayfrom the vee. A wipe with methyl dichloride will help clean the joint.

Figure 7-3 Vee Cut into Perspexb.

Using multiple layers of tape or other suitable damming material, build up each side of the vee toretain the cement.

c.

Tape along the underside of the vee covering the gap which need only be 0.5mm, no more.

d.

Apply the Acrifix 92 to the vee, filling the vee and dam completely. Be careful to not trap air under the
cement as you lay it in.

Figure 7-4 Gluing Techniquee.

Acrifix 92 cures under UV light so it must be left to cure in sunlight or under a UV light source.

f.

If during curing the natural shrinkage reduces the cement to a lower level than the top of the vee, refill
with Acrifix 92 to the top of the dam.

g.

After 24 hours of curing, using a scraper reduce the build-up to the level of the Perspex.

h.

Polish starting with 600 grit paper and ending up with a fine polish. To achieve the best results use theMicro-mesh method to polish the canopy (see the section below Finishing Polishing).

i.

Acrifix cures clear, and the only evidence of the repair is usually the bubbles you couldn’t get out.

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7.3.5

WARNING - DAMAGED CANOPIESWARNING
Canopies can generate high air loads. If a repair is extensive and its failure in-flight could influence the pilot's
safety then a new canopy should be fitted. We have had canopy failure blamed for accidents in the past.

7.4

FINISHING-POLISHING
Canopies which have a small amount of scratching may be rejuvenated by using a canopy scratch remover.
This is a slightly abrasive polishing compound which grinds away the surrounding material until the scratches
are gone. Special care should be taken when using these polishes as excessive pressure may cause the
Perspex to locally overheat and warp out of shape.
Canopies which have significant scratching or which have been repaired require more work. The best method
is to use the ‘Micro-mesh’ system to actually sand the surface to remove deeper scratches. The system begins
with 1500 grit paper (sailplane wings are normally finished to 1200 grit) and finishes at 2000 grit.

Mechanical polishing of canopies may be performed by experienced persons however inspectors who havelittle experience should carefully weigh up the cost of a new canopy with the potential time saved. A mechanicalpolisher will quickly overheat the Perspex if left in the one place for even a few seconds.

7.5

MECHANICAL ATTACHMENT OF PERSPEXThe fitment of canopy bubbles to the canopy frames is outside the scope of normal inspection work. Fitmentof any canopy bubble to a frame (metal or composite) requires a repair authorised person. The sailplaneinspector’s role is to ensure that the canopy bubble is airworthy and securely attached to its frame.
On metal frames such as IS sailplanes and Blaniks, check that the Perspex is securely attached to the frame.
Check for looseness of the securing screws and/or rattling of the Perspex in its frame. Gently tighten any loose
screws or bolts being sure not to over-tighten any screws or bolts as the pressure can easily crack the Perspex.
On composite frames, check for cracks in the frame that may indicate that the Perspex is de-bonding from theframe. Check for voids or gaps between the frame and the Perspex that may indicate that the Perspex is delaminating or separating from the frame

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7.6

CANOPY JETTISON MECHANISMS
A correctly functioning canopy jettison mechanism is vital to the airworthiness of the sailplane even if it isintended that the sailplane will never be flown with a parachute. Even in a relatively minor accident the ability
to jettison the canopy to access an injured pilot could be vital.
For this reason the jettison mechanism must be functioned at each Annual Inspection. Any moving parts mustbe lubricated (unless they are designed not to be lubricated) and the mechanism must be rearmed. The
maintenance manual for each type should be consulted for specific details.
To reduce the risk of inadvertent operation without precluding intentional operation then a method of using aclear worded placard, a cover, or other protection is permissible. If using a lock-wire then soft wire, such as
fuse wire, should be used. The person installing the wire must perform a function test to ensure that the locking
wire can be easily broken. Alternatively, a placard that is breakable could be used to seal the control but notprevent easy operation.

7.7

CLEARVIEW PANELSThe clear view panel (it is a lot more than an air vent) is required to be fitted to each sailplane in a responseto certain conditions which can cause instant and complete fogging of the canopy during the early stages of
the climb. This occurs when the sailplane has sat overnight in very cold air and the airframe has ‘cold soaked’.
As the sailplane climbs through the inversion into a warmer and moister layer of air the moisture instantly
condenses out and blocks all vision. The only way for the pilot to see is to look through the clear vision panel.
The sailplane inspector must therefore ensure that a clear vision panel is fitted and functions properly.

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8.

SAILPLANE SEAT HARNESS

8.1

INTRODUCTION
This section presents information on pilot seat harnesses and their applicable inspection procedures. MOSP
3 Section 13.2 defines the mandatory maintenance requirements.
The two main functions of the seat harness are:a.

To firmly restrain the pilot in the sailplane under normal flight loads resulting from both manoeuvringand gusts, andb.

The “once in a lifetime” function to restrain the pilot during ground impact in an accident.

To be able to deliver these functional requirements the harness must:a.

Be readily adjustable by the pilot in flight without excessive hand forces,b.

Not have the harness adjustment slip or the buckle attachments detach under load, andc.

Always be in top condition.

For each seat, safety belt, and harness, its attachment to the structure must be shown, by analysis, tests, orboth, to be able to withstand the inertia forces prescribed in the standard that the sailplane is designed to.
For CS 22 (CS 22.561) these design loads are:a.

Upward 7.5 gb.

Forward 15.0 gc.

Sideward 6.0 g

d.

Downward 9.0 g

This mean that a human body weighing 110 kg loads the webbing and seats to the equivalent of 1650 kg in
the forward direction. All components of the harness must withstand these loads. Fittings attaching
webbing to structure have additional factors of safety applied. For CS 22 (CS22.625), the design loads are
multiplied by a fitting factor of 1.33 and the harness attachments are loaded to the equivalent of 2195 kg in
the forward direction.
To ensure this level of strength the inspection procedures on harnesses will need to be adhered to very
closely.
Research studies suggest that higher loading is within the capacity of most people to survive and so future
requirements may dictate that harnesses should be strong enough to withstand loads up to 25 g such aswith aircraft used for agricultural use. To ensure this level of strength the inspection procedures onharnesses will need to be adhered to very closely.

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WARNING
The harness is an essential part of occupant protection during a sailplane crash event. It
must be in good condition and properly maintained so that during a crash it does its job
perfectly, otherwise the pilot may be severely injured. Re-webbers are closely controlled
by CASA. We must use CASA approved re-webbers who use approved parts, approved
procedures, and do the job correctly. Refer Section Error! Reference source not found.
below for more details.
In recent years, changes in webbing have occurred and this may not be compatible withold fittings. Testing showed some slipped at half the load required. You may be able to use
your old buckles but you may need to change the length adjustment fittings. Also sailplane
harnesses often require shorter stitch patterns which need special testing. GFA has
arranged testing and approval of this. Please contact the CTO for details and approvals
that your rewebber can use. Ensure the rewebber knows and follows approved procedures
and is not doing you a cheap job!
ADs exist on harnesses, usually buckle defects. You must find these and resolve them.

8.2

HARNESS FUNCTIONAL PERFORMANCE
There are many factors affecting how well people are restrained in a sailplane. These include:

8.3

a.

The design of the webbing straps (webbing material, stitching patterns etc),b.

The condition of the webbing,c.

The condition and functionality of the buckles, and fittings,d.

The ease in length adjustment and the holding against slippage,e.

The correct installation of the harness in the sailplane, andf.

The type of cushions used.

HARNESS WEBBING
Like any woven material, harness webbing has threads running along the strap and threads running acrossthe strap, these are called the warp and weft directions respectively. The warp threads provide the strengthof the strap and the weft threads hold the strap together.
When webbing is loaded the load tends to concentrate towards the edge of the material as shown in Figure8-1. This is why frayed edges on the webbing are so detrimental to the strength of the webbing and webbing
with frayed edges must be replaced.

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Figure 8-1 Load Distribution in Webbing
The harness must distribute the acceleration loads as evenly as possible on the body. To do this theharness needs the maximum area of contact with the body and to achieve this some manufactures installlarge abdominal pads on the lap strapss of their harnesses. Where these have been fitted they should be ingood condition without losing their stiffness and any worn or soft pads should be replaced.

8.3.1

WEBBING CONDITION:
The condition of the webbing is critical to the performance of the harness.
In contrast to a low total hours per annum private sailplane, a high utilisation training sailplane will havemuch higher hours and cycles leading to more UV exposure, and webbing surface wear at metal fittings andattachment points.
Chafing on the metal fittings causes surface fibre damage, which decreases the strength of the harness.
This should be repaired by rewebbing either immediately,or within a short time according to circumstance.
Fraying at the edges is particularly critical. Where the harness chafes on the sailplane’s structure, consider
fitting sacrificial rubbing sleeves over the straps.
Due to the harsh ultraviolet (UV) light environment and/or high sailplane utilisation, the harness may
deteriorate or wear quicker and require more frequent webbing replacement. Webbing life limits must becomplied with. Prematurely worn, faded or deteriorated webbing shall be replaced when found.
You must check that the adjustment of the harness length works without high hand forces. As an illustration,
one defect report stated the harness webbing had to be scrapped having failed this requirement after 6
years installation. The use of slightly thicker webbing when rewebbing the harness, together with the narrowslot in the webbing length adjuster clip, led to the webbing surface furring up and blocking the slot. The
harness adjustment was very difficult and beyond what a crew person could reasonably manage in flight.
Webbing in sailplanes with a rear canopy half which stands erect when open (eg. Hornet, ASK-21) can havethe sun’s rays concentrated by the erect rear canopy onto a small area such as a shoulder harness strap
leading to damage due to excess heating of webbing fibres or even burn marks.

8.3.2

WEBBING CLEANING
Maintain the webbing in good condition by keeping it free of harmful contaminants. Therefore, at each ‘Form
2’ inspection consider if the harness webbing needs washing to remove contaminants. Refer to the harness
manufacturer’s instructions regarding safe washing practice. In the absence of such instructions thefollowing advice applies.

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Clean the webbing only when there is sound reason to do so, such as to remove excessive dust & dirt, salts
from sweating, mould, oils or greases and occasionally vomit (acids). The important protective finish on thesurface of webbing fibres can be adversely impacted by excessive washing with inappropriate cleaningproducts and/or excessive mechanical abrasion. Carelessly conducted washing is counterproductive byreducing strength and harness life, increasing wear, and can adversely impact the way the harness performs
under load.
If washing is required, use a sponge together with clean luke-warm water (never hot) and ordinary mild soap
so that the water is neutral pH, ie. neither acidic or alkaline. Note that nylon materials respond adversely to
any acidic substances, whereas with polyester, alkalis have an adverse effect.
Do not use a bristle brush in order to avoid mechanical damage to fibres. Following washing, rinse withclean water, and leave the webbing to air dry without heat. Avoid exposing metal fittings to water as muchas possible. The central buckle must not become wet with cleaning media (water/soap) at any stage.
Reinstall only when all parts are completely dry. If the metal fittings need cleaning, then use a cloth with isopropyl alcohol and apply this ONLY to the metal fittings.

8.4

HARNESS LIFE LIMITSThe life of a harness is specified in MOSP 3 Section 13.2.

8.4.1

AGING OF WEBBING
In the early 1970's experiments began to establish the effect of aging on harnesses. The effect of ultraviolet(UV) light, as well as some other environmental factors was established. Experiments show that the main
environmental causes of the decline in the strength of synthetic webbing are UV light, temperature, humidity
and the oxygen content of the atmosphere. Of these, UV light is the major factor.
In Australia, harnesses in sailplanes are subjected to high levels of UV light. A case study was carried out at
ARL on an 11 year old harness with the following results:
Harness type

Early model Gadringer

Sailplane type

AS-K 13Time in service

11 years, 2000 hours.

Strap

Breaking load

Right shoulder

550 kgLeft shoulder

500 kgRight lap1122 kg

Left lap1428 kg

Original webbing strength

2000 kg

Table 8-1 Harness Breaking Load With Age.
The shoulder straps have a larger reduction in strength due to the high exposure to sunlight compared withthe lap straps. Webbing used in light aircraft suffers from UV during long term outside storage, whereas withsailplanes the webbing suffers from UV exposure under bubble canopies. So consider what factors are atwork increasing UV exposure in each case and replace webbing when inspection reveals this as necessary .

8.5

BUCKLES AND STRAP END FITTINGS
The strap metal end fittings engaging in the buckles must be stronger than the webbing, be in sound
functional condition and be subject to close inspection for wear, corrosion, deformation and loss of surface
finish such as chrome plating.

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Damage to the chrome plating is particularly dangerous as the flaking chrome is sharp and may cut the
webbing. Harness fittings which have been re-plated must be viewed with suspicion unless they have been
re-plated by an approved organisation and have a release note stating that the components have been replated to an approved procedure. There is the danger of hydrogen embrittlement which cannot be detectedusing non-destructive techniques and can potentially result in strength loss sufficient to cause metalcomponents to shatter when dropped onto a very hard surface. If faced with plating issues, then it isstrongly recommended to replace the fitting(s) with new because this is relatively cheap and certainly
effective.

8.5.1

QUICK RELEASE BUCKLE
All harnesses must have a central quick release feature where one action releases at once all the straps end
fittings inserted into the central buckle, or as interleaved centrally together in the case of early harnesses.
Quick release buckles shall be checked for correct operation and demonstrate:a.

Positive locking. Of particular importance for some quick release buckles is that the correct webbing
end lug is inserted to the corresponding location around the buckle periphery.

b.

Immediate and clean release of all the strap end fittings when the control knob or quick releasemechanism is activated. However, the quick release should require positive force to activate and not
be on a “hair trigger”. At least one accident is suspected to have been caused by a quick release
being activated unintentionally by the pilot because it required too little force to open.

c.

No inadvertent release of any webbing strap ends.

d.

Smoothness of operation without any signs of jamming.

e.

Any springs to return the control knob to the closed position.

f.

No evidence of significant wear.

g.

The release control for separate disengagement of the shoulder straps (if fitted) shall function
correctly.

Best practice is to carry out a function test with a person actually sitting in the seat to ensure the quick
release unit functions correctly in fastening and unfastening modes.
Failure of the central buckle on any of these points requires that the harness be replaced before further flightwith a serviceable harness. Then the buckle can be replaced or repaired before returning the harness toservice. Repair, if practical, must be carried out by an approved service organisation or the manufacturer.
Please report such defects via an SDR to the CTO because such problems can have broad implications.
Some modern harness quick release buckles have the facility to release the shoulder harness independentof the lap straps. It is highly recommended, particularly for aerobatic sailplanes, that this facility be disabled
if the harness release manufacturer or GFA has approved data for this action. For Gadringer-Gurte
harnesses, refer instruction 38 dated 9 June 2015, or later edition, on their website.
If the quick release buckle incorporates a separate release control for releasing only the shoulder straps,
then that release control must be checked for operation. It must not release on a ‘hair trigger’ action but bepositive in operation and must not release the lap straps either on shoulder strap disengagement or when
the shoulder strap ends are re-engaged.

8.6

LENGTH ADJUSTERS
Length adjusters typically operate by the webbing wrapping over a sliding cross bar (slider). The tension in
the webbing pulls down on the slider which then clamps down on the tail / free end of the webbing. Whilst
the clamping provides a significant amount of the grip of the length adjuster on the webbing that prevents
slippage, a portion comes from friction of the webbing wrapping around the slider under tension. Quite often
there is a thin wire spring that provides pressure to the slider to keep it in the clamped position if there isinsufficient tension in the webbing.
On occasion, the thin wire spring has become dislodged from the adjuster assembly. This has allowed the
webbing to slip in flight. In one case a harness lap strap came loose during a high speed final glide and thepilot struck their head on the canopy during turbulence.

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Figure 8-2 Wire Spring on Length Adjuster Slider of a Gadringer Harness. The Two Images on the
Right Show Displaced Springs
It has been found that some length adjusters have been disassembled for cleaning and then incorrectly
reassembled. In some cases the slider has been installed upside down.

Figure 8-3 Length Adjuster Slider Installed Upside Down in a Gadringer Harness
The slider bar also has a specific cross section which is important for maintaining harness tension. Incorrectorientation can cause “micro-slippage” where the webbing eventually becomes loose over time despite
appearing to hold load over a short time. The curved face must be where the webbing wraps around theslider and the sloping face must be towards where the slider clamps onto the webbing.

Straight face

Straight face

Figure 8-4 Incorrect and Correct Orientation of Slider on Gadringer Harness

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8.7

HARNESS INSTALLATION
The installation of the harness can have a significant impact on its ability to function properly, particularly in acrash. Beware of assumptions when inspecting the installation or when installing harnesses. The central
buckle always has one lap strap permanently installed in a specific receptacle location around the buckle
periphery. While in most cases the harness will be supplied with that lap strap orientated for the port sideanchor point, beware as orientation to the starboard side is found occasionally. The buckle has an uprightorientation and must not to be installed upside down.
The installer may falsely assume that this fixed lap strap always goes to the port side anchor point. If a fixed
lap strap orientated for the starboard anchor point is installed to the port side, then the buckle will be upside
down. This can lead to the three remaining belts being fitted by the pilot to the wrong insertion points aroundthe buckle periphery thus reducing or negating safe harness performance.
This is an issue with harnesses with a circular periphery to the buckle, such as with Schroth. If a club fleet
has these harnesses widely installed and a mixture of port and starboard attachments, it is recommended tostandardise on port side attachment. There is a procedure for changing over starboard to port in the Schrothharness manual.
On some harnesses it is not immediately clear which strap is for the shoulders and which strap is for the lap.
However, the fittings that connect to the buckle will differ and may affect the performance of the harness
under load if the wrong fitting is inserted into the wrong slot of the buckle. In one example during a Daily
Inspection on a club two seat sailplane, it was discovered that the rear seat left hand lap strap would
disengage from the rotary buckle under applied load. The shoulder strap end tangs were of a different
shape to the lap strap end tangs. The shoulder strap ends will not successfully engage the buckle if used in
the lap strap location. Note that the harness manufacturer’s manual specifically states a WARNING relating
to the positioning requirements. It was clear that the straps from both seats had been shuffled around after
cleaning during an annual inspection.

Figure 8-5 A Two Seat Sailplane With Incorrect Harness Installation

8.7.1

HARNESS ATTACHMENT TO FUSELAGE
Correct wrapping of webbing around the fuselage attachment points is critical and the attachments must be
serviceable by examination for wear, damage, distortion, delamination or structural cracking.
With some sailplanes it is possible to attach the harness incorrectly such that the attachment might fail in an
emergency. Figure 8-6 shows how this is possible with the shoulder straps of an Astir. The correct method
is to loop the webbing around the crossbar. The thin wire prevents the webbing sliding along the crossbar, it
is not the attachment point! Similarly, Figure 8-7 shows a crotch strap from a 5 point harness fitted to an
ASK-21 where the strap has been attached to the thin sheet metal intended to prevent the strap from sliding
along the structural tube.

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Figure 8-6 Example of Harness Attachment Error
Note in Figure 8-6 that the doubling back of the strap tail through the three-bar clip, if it can be achieved, isan effective way of reducing slippage.

Figure 8-7 ASK-21 Crotch Strap (from 5 point harness) Wrapped Around Locator Rather Than Main
Structural Tube

8.8

HARNESS REPLACEMENT AND REWEBBING
Safety harnesses may only be rewebbed in accordance with MOSP 3 Section 13.2. All replacement
harnesses, whether rewebbed or new, must have a release note from the approved organisation performing
the rewebbing work (CASA Form 1) or, if new, from the manufacturer (usually an EASA Form 1). This
release note goes into the sailplane’s maintenance records and must be kept with the logbook records
folder. The release note reference & number is entered in the logbook entry together with the inspector’scertification for harness installation.
It is mandatory that sailplanes manufactured after 30 August 1980 are fitted with ‘pull up to tighten’ lap
straps. It is very strongly recommended that all sailplanes are similarly fitted with ‘pull up to tighten’ lap
straps when the harness is next replaced or rewebbed.

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Like new harness webbing, all rewebbed straps must have a label identifying:a.

the company performing the rewebbing or repair work,b.

the part number if there is such identification in their document system,c.

the webbing serial number, job number or rewebbing work order number, andd.

the date of manufacture (DOM) and/or the date of webbing life expiry.

The CASA standard may also be listed, but it is not always found.
This information shall be printed in waterproof ink onto a cloth patch and stitched to the strap in a durable
manner, possibly including a clear flexible plastic cover. If the harness does not have this identification anddoes not have a logbook entry as to when it was fitted, then the webbing should be rejected as it is notpossible to know its history.
When putting a harness out to a reweb organisation, it is recommended to make a photo record, and:a.

prior to sending, record the webbing thickness (undamaged), width and lengths, and specify that the
new webbing be like for like so that it is compatible with the hardware,b.

ask the reweb organisation if they need to see the whole harness with all its hardware, even if It isonly a single shoulder or lap belt needing attention,c.

ensure that the webbing lengths are fit for purpose and communicate the length specifications
clearly to the rewebbing organisation or manufacturer. Copying the old harness may be valid but it
is very worthwhile considering whether the old harness lengths were indeed suitable, andd.

require the lap straps be sewn with ‘pull up to adjust’ operation if that is not already the case, ande.

specify that the webbing free ends are not simply cut with a hot knife but instead folded back onthemselves and sewn so as to make the ends bulky.

Later check the work when the harness is received back and prior to reinstallation:a.

Thin webbing or more slippery material may slip through the fittings and not tighten properly as has
been found occasionally with newly rewebbed harnesses.

b.

Thicker webbing may be supplied with insufficient consideration of the narrow gap in the length
adjuster such as with Schroth harnesses.

c.

Other mistakes in rewebbing have occurred such as locking tabs sewed on the wrong side.

Quite a bit of variation, particularly in length can be found between harness used in the same sailplane type.
Figure 8-8 shows the differences between harnesses from 2 different Grob Astirs.

Figure 8-8 Variations in Harness Lengths for the Same Type of Sailplane
The harness with the red tabs was a newly manufactured harness which had been fitted to an Astir. After a
few flights, the lap straps detached from the attachment points during pilot strapping in. Investigation foundthat the lap strap tails were so short that there was insufficient material to fold the tail back on itself andpermanently stitch it. The thin webbing tail was able to slip through the three-bar clip at the attachment tostructure.

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Also, the shoulder straps had insufficient length to adjust for large pilots such that on strapping in the buckle
was pulled up and would not allow the lap straps to sit low on the hips as required. Even for an average size
pilot, there was not enough shoulder webbing length to grip to pull down for tightening. When the new straps
were compared with those from another Astir, the difference in dimensions was very noticeable.

8.8.1

HARNESS REPLACEMENT AFTER ACCIDENTS
It is not permitted to re-use any harness that has been recovered from a serious accident where it is likelythat it has been loaded over the rated strength or the residual strength following years of use. The harness
is a fundamental piece of safety equipment, and it must be treated as such. All harnesses recovered froman accident should be destroyed unless it can be established beyond doubt that the harness is serviceable,
such that the inspector is completely satisfied that the harness or seat belt was not subject to any abnormalloads. If the sailplane is being rebuilt following an accident, it is strongly recommended that new harness(s)are fitted.

8.9

CUSHIONS
The cushions used with the harness also have a large influence on harness performance. Seats withexcessively soft cushions are compressed under acceleration. As the foam is compressed the webbing
comes loose and the body "submarines" under the belt. When the acceleration stops, the foam thenrebounds as shown in Figure 8-9, resulting in possible injury to the abdomen, internal organs and spine.

Figure 8-9 Pelvis Rotation and Submarining
Energy-absorbing seats, seat cushions or seat mountings constitute another means of improving safety by
reducing the load on the occupants’ head and spine in a crash and /or landing with retracted wheels (Refer
to CS 22.561(c)). Two commercially available materials which are known to be effective in sailplane
cockpits are Confor (CF45/CF47) and Dynafoam.
Tests in England (refer to Doctor A Segal) have indicated that substantial reductions in spinal g loading canbe achieved by the use of the correct foam while the g experienced by the spine is actually increased by theuse of soft foam compared to a bare seat. The best results were found by combining 25 mm of hard grade
low resilience foam with 12 mm of medium grade low resilience foam for comfort. The medium foam isplaced above the hard foam and the sandwich is upholstered to prevent damage by UV light and abrasion.
It is recommended that the foam cushion be as thin as possible as this reduces the loosening of the harness
under acceleration and therefore reduces submarining.

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1.1.0

WEBBING CONDITION:
The condition of the webbing is critical to the performance of the harness. As stated previously, the load in
the webbing is concentrated at the edges and so fraying is critical to the strength of the webbing.
Webbing also wears where it chaffs on the metal fittings. Webbing damage decreases the strength of theharness and should be repaired within a short time of being noticed. Where the harness chaffs on theaircraft's structure, rubbing sleeves should be fitted over the straps.
In order to maintain the webbing in good condition it must be kept free of harmful contaminates e.g. dirt, rust,salt and especially grease. It is therefore important to wash the harness webbing at each Form 2 inspection
with mild soap and warm water, rinse and then allow to dry completely before re-installing.

1.1.0

FITTINGS
One predominant fact arising from gliding accidents in recent years has been the high proportion of harness
fitting failures in comparison to harness webbing failures. The metal fittings must be stronger than the
webbing and so the continued inspection of the fittings is important.
The fittings must be inspected for wear, corrosion, deformation and loss of surface finish such as chrome
plating. Damage to the chrome plating is particularly dangerous as the flaking chrome is sharp and may cut
the webbing. Also, the fittings may in time allow the webbing to slip and therefore prevent the harness frombeing correctly tightened.
Harness fittings which have been re-plated must be viewed with suspicion unless they have been re-plated
in an approved organisation and have a release note saying that the components have been re-plated to an
approved procedure. The reason for this is the danger of hydrogen embrittlement. Hydrogen embrittlement
cannot be detected using non-destructive techniques and can result in strength loss sufficient to cause
components to shatter when dropped onto a hard floor from a height of a few feet.
The release mechanism of the harness must be of the quick release type. If the buckle will not releaseproperly, it is unserviceable and should be replaced or repaired before further flight.
A release that has the ability to release the shoulder harness separately must have that ability disabled.

1.1.0

AGING
In the early 70's experiments began to establish the effect of aging on harnesses. The effect of ultraviolet(UV) radiation, as well as some other environmental factors was established. The experiments show that themain causes of the decline in the strength of synthetic webbing are UV light, temperature, humidity and theoxygen content of the atmosphere. Of these UV light is the major factor.
In Australia, harnesses in sailplanes are subjected to high levels of UV light. A case study was carried out onan 11 year old harness with the following results:
Table 8-1 Harness Breaking Load With Age.
The shoulder straps have a larger reduction in strength due to the high exposure to sunlight compared withthe lap straps. Webbing made for aircraft probably was not expected to get the UV exposure we give them insailplanes. So we need to expect more frequent deterioration and replace them more often.

1.1

LIFE OF A HARNESS:
The life of a harness is specified by the manufacturer or by MOSP 3 Airworthiness, whichever is shorter.

8.10

ANNUAL INSPECTION
At the annual inspection, the harness shall be inspected to determine if it is satisfactory to continue inservice ‘on condition’ for the coming 12 months, or if any repair or replacement actions are now necessary:a.

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A readable manufacturer’s label shall be present on all webbing components and show that the
webbing will continue to be within life limits for the next 12 months. If less than 12 months, but say 3
to 11 months usefully remains, then the required rewebbing action with latest action date must be
written into the Maintenance Release Part 1.
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Assess for significant webbing colour fade caused by ultra-violet light. Compare suspect areas toareas which rarely see sunlight.

c.

Fraying. Any frayed webbing will cause a reduction in strength. It may also point to a defect in theharness end fittings, length adjusters or attachment to structure.

d.

Consider if the harness webbing has reached the stage where washing is needed to remove
contaminants such as mould, grit/dirt, oil, grease, etc. Refer to Section 8.3.2 on cleaning.

e.

Stitching condition.

f.

Stains on stitching or webbing may indicate chemical contamination and the need for cleaning.

g.

Length adjusters. Check for ease of operation, locking facility (incl. springs) and no slippage when
under tension. Look for wear, corrosion, contamination and incorrect reassembly.

h.

Central buckle. Check for ease of operation, locking facility (incl. springs) and no release when
under tension. Look for wear, corrosion, contamination and incorrect reassembly.

i.

Installation. Check that the harness is installed securely to the correct structure attachment points.
The webbing must not have any possibility of inadvertently coming detached. Check for structuralissues at attachment points, such as cracking, FRP delamination, glue failure in timber, etc.

j.

Webbing width mismatch. Webbing which is too wide for adjusters and fittings will bunch and notwork correctly. Webbing too narrow may allow tilting and slippage of the adjuster.

k.

Consider if the webbing lengths are functionally satisfactory for the range of occupants. Do any
pairs of straps, lap or shoulder, need lengthening?

l.

Pull up straps are present?

m.

Seat cushions. They should be made from energy absorbing foam with minimal rebound. They
should be anchored so that they cannot move and must not restrict control movement.

Following inspection, test the harness for function on buckling up and releasing with an occupant seated in
the sailplane.

8.11

REFERENCES
Flying Safety Information. Harness - Safety through Knowledge. Braunschweig, 27-3-87.
CAA UK Safety Notice SN-2019/003 re Harness Integrity
British Gliding Association, AMP Part 4, Leaflet 4-8“Is Pilot Insecurity a Problem at Your Club?”, Anthony Smith GFA CAD, Gliding Australia September 2020
via GFA website.
“Energy Absorbing Seat Cushions for Use in Gliders”, Dr Antony M Segal, Technical Soaring Vol. 32 No. 1/2
Jan/April 2008
British Gliding Association booklet, “Why you should fly with an energy absorbing safety cushion” 12 pages,
second edition March 2017.
“Safety In The Cockpit, Cushions and Harnesses” by Len Diekman of GFA. - Via GFA website
Amsafe - Webbing Service Life Guidelines - April 2014
The Aircraft Crash Survival Design Guide.

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9.

OPTIONAL EQUIPMENT

9.1

GENERAL
Most of our sailplanes have equipment fitted and removed at regular intervals and provided care is taken thisshould not present any problems. Optional equipment is defined to be any item that can be added or
removed from the aircraft without the need for tools. In more general terms equipment that you carry withyou to the aircraft and place in the cockpit just before flight would fall under the optional category. Examples
would be oxygen bottles in special enclosures found on DG aircraft, flight computers or mobile devices fixedwith velcro in the cockpit or a tie down kit. Changing of a radio or flight computer that is normallypermanently fixed into the instrument panel is not considered optional equipment. However, in some cases
oxygen systems are semi-permanently installed and so would be classified as non-optional equipment.
Removal of such an item could thus change the weight and balance.
There are no hard and fast rules about when a weight and balance calculation should be performed due toequipment change, so the following guides should be used to inform your decision.
Flight safety can be maintained if the following three areas of concern are given proper consideration:a.

Change in sailplane Weight and Balance.

b.

Interference with Flight Control Systems.

c.

Pilot Accident Protection

These three topics will be taken one at a time and their implications considered.
We are restricted by law in what and how we can alter an aircraft. Certified aircraft may only be modified withan Engineering Approval, Experimental aircraft may be changed but the GFA may need to be advised, andLight Sport Aircraft (LSA) may only be changed with manufacture’s approval. This is obviously restrictive andwe need to be sensible. GFA have therefore created some new rules to help you free this up and make surewhat you do and how you do it is safe and correct. So refer to MOSP 3 Clause 18.7 “Minor Changes Not
Requiring Approval” and related sections on what you can and cannot do. Another set of rules allowingchanges are given in MOSP Part 3 AIRW-M15 “Permissible Unserviceabilities”. These allow you to do what
is sensible and restrict or guide you on what is risky. Be sensible.
If in doubt get an engineer to approve it. GFA has engineers to assist you.

9.2

CHANGE IN WEIGHT AND BALANCE
Fitting of non-optional equipment is a matter for an Annual Inspector, but may require additional signoff froma Weight and Balance certified inspector. Typically these equipment changes will be for instruments. So longas the instrument weight change is kept under the 1kg mark, typical weight and balance should not beaffected enough to warrant needing a recalculation of W&B.
When considering changing equipment, the following must be looked for:a.

C.G. movement too far rearward.

b.

C.G. movement too far forward.

c.

Reduction/increase of maximum allowable pilot weight.

d.

Increase/reduction of minimum allowable pilot weight.

e.

Decrease/increase of weight of non-flying parts.

See rules in MOSP 3 Clause 20.2.3 –Definition of significant change in weight and balance.
Some sailplanes use batteries and radio equipment mounted either well rearward or well forward as fixedballast to control the Centre of Gravity travel. Removal of these items can result in a pilot accidentally flying
outside of his allowable limits. In cases like this, the sailplane MUST be PLACARDED "Not to be flown
without tail battery", etc.

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The logbook maintains the history of the weight and balance, and should be consulted and updated eachtime changes are made. The record will include all the fittings at the time, including instruments etc. When
you consider that in some cases over 30kg of additional weight is accumulated between instruments, oxygen
systems, tie down kits and so forth, keeping track of equipment fitted and removed plus weighing after repainting or repairing, is extremely important.
Be absolutely certain you understand the situation. For instance most sailplanes have the pilot forward of the
CoG and so a minimum pilot is critical to spin recovery. But in very few the pilot is behind the CoG and so
the max pilots are the critical case. Likewise fuel may allow it to take off but as the fuel runs out the CoGchanges. Don’t chance it.

9.3

EQUIPMENT CHANGES - PLACARDS
Where it is intended to fly with and without particular equipment, for instance oxygen, (a system could beshared by several aircraft) then there must be two sets of placards in the cockpit to cover allowable pilot
weights in both cases.

9.4

INTERFERENCE WITH FLIGHT CONTROL SYSTEMS
It is of the utmost importance that optional equipment does not interfere with flight control systems, and twocases must be considered:a.

Simple interference by being fitted into the wrong position.

b.

Displacement during loading generated by extreme flight manoeuvres, or ground impact.

A case history "A sailplane went through a Certificate of Airworthiness Inspection at the completion of which a dual control
inspection was carried out prior to the pilot accepting it for test flying.
As part of the cockpit check the pilot felt the need to check rudder travel with the ADJUSTABLE pedals first
fully back, then fully forward. In the fully forward position he applied FULL RIGHT RUDDER and found it
impossible to bring the rudder back to the central position.
The rudder pedal was caught on a RADIO installed through the instrument panel".

9.5

PILOT INJURY PREVENTION
When fitting optional equipment, safety of the pilot should be the utmost consideration. Gliding operates in aturbulent atmosphere, by nature, so poorly secured equipment can become internal missiles very quickly.
Almost all sailplanes will have something stored behind the pilot’s head - batteries, water bottles and tie
down kits are typical examples. A hammer and pegs in a tie down kit can be fatal if it breaks loose in flight.
Even a rapid shift can temporarily daze the pilot if hit in the wrong place - leading to potentially fatal
consequences.
The following section will enable you to calculate the design strength and the test loads of the restraint
required.

9.5.1

EQUIPMENT RESTRAINT
Restraint of equipment must be designed such that under maximum flight or emergency landing loads theequipment will not move or break free of its restraints. Consider these cases:a.

Equipment in the front panel and nose ie ahead of the pilot (s): This equipment must be restrained tomaximum flight load factor the sailplane is certified to (these flight limit "G" values are shown in the
Flight Manual and refer to Section Error! Reference source not found. for flight envelope) multipliedby 1.5. For example: if a type is certified as “Aerobatic” under CS-22 then the equipment must be
designed to not move under: Positive (downward) = 7G x 1.5 = 10.5G, Negative (upward) = 5G x 1.5= 7.5G.

h.

Equipment behind the pilot(s): This equipment must be restrained as above, but because it could
strike the pilot(s) in the event of ground impact it must be designed to be restrained for 15G loading
forward.

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b.

9.5.2

All equipment should be designed to withstand 6G loading sideways and 9G rearward.

JUSTIFYING THE STRENGTH OF A RESTRAINT
The justification of the strength of a restraint for a piece of equipment in many cases can be achieved bydesign calculations. However, it is often more practical to test the restraint by applying proof loads to theitem. The proof loads are 2/3 of the design load.
Direction

Proof Load

UPWARD5G

DOWNWARD: Utility category
Aerobatic category

6G
7G

FORWARD

10G

REARWARD

6G

SIDEWAYS

4G
Table 9-1 Equipment Proof Loads

All proof loads must be applied through the CG of the restrained equipment. The proof loads must be held
for at least 3 seconds. The restraints and surrounding structure must be inspected afterwards and must notshow any signs of damage or deformation.
Any damage found in the sailplane supporting structure after the proof load must be repaired and isconsidered a failure of the design. Damage or deformation of the restraint structure is also a failure, and thedesign needs to be reconsidered.
The REARWARDS load may be difficult to apply in some situations and can be validated by comparison if
the FORWARD test was successful and the restraint design is symmetrical in the fore-aft direction ie thedesign is such that it does not matter if it faces forwards or backward. Similar applies to the SIDEWAYS test.
If the design is symmetrical in the port-stbd direction, the SIDEWAYS test only needs to be applied in one
direction.
Once the restraint design has been proven, the Annual Inspector shall record and sign for the conduct of thetests, the proof loads applied and the outcome in the sailplane logbook.
Example: An item located behind the seat of a “Utility” category sailplane.
Item = 3kg.
By reference to the above, the item restraint will have to withstand these proof loads UP

3X5= 15 kg

DOWN

3X6=18 kgFORWARD3 X 10 = 30 kg

BACK

3X6

= 18 kg.

SIDE

3X4

= 12 kg

Note: If proof loading with the item in situ and the loads are applied to the item, the weight of the item must
be considered in the above loads. The UP proof load will be 15 kg + 3 kg = 18 kg. The DOWN proof load
will be 18 kg – 3 kg = 15 kg. If the proof load is applied directly to the restraints ie the item is not fitted, theweight of the item does not need to be considered.
By using a 50 kg spring balance (or a digital load cell) with suitable straps, the item can be loaded UP,
SIDESWAYS and FORWARD to the PROOF loads determined and held for at least 3 seconds. To verify
the DOWNWARD load capacity, 15 kg of ballast blocks can be loaded onto the item (total weight is then
18kg) to press it down.
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If the restraint capacity is difficult to determine or it is difficult to apply proof loads, seek the assistance ofyour RTO-A or CTO.
Any items over 10 kg must be treated as a modification.

9.6

OTHER CONSIDERATIONS
The installed optional equipment must not impede the pilot(s) visibility of the instruments or the controls. An
example that happened: a pilot had mounted a PDA on the right hand side of the canopy of a DG-400 with asuction cap mount. This obscured the pilots vision of the air vent knob and the canopy jettison knob on the
stbd side of the cockpit. During the flight the pilot tried to open the air vent but inadvertently pulled the
canopy jettison knob, despite these knobs being a different shape and feel. The partially jettisoned canopy
has held in place by hand and the aircraft landed safely.
The installed optional equipment should not impede the egress of the pilot(s) in an emergency. An example
that happened: A pilot had installed a flight computer on the canopy. The thin power wire was routed via thefront hinge of the canopy to the instrument panel. When the pilot tried to bail out the thin wire prevented the
canopy lifting to jettison. The pilot was found dead in the crash with their parachute ready.

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10.

FATIGUE

10.1

GENERAL
Like any human or animal, if you work a structure long enough and hard enough, it will become "tired", andloses its ability to carry load, it becomes "fatigued".
It is common to hear the comment "wood doesn't fatigue", or “fibreglass doesn't fatigue". The unfortunate
thing is that all aircraft structural materials will fatigue, given the right circumstances.
An Inspector is interested in fatigue from two points of view:a.

Total fatigue life set by the manufacturer, for the complete airframe or major components.

b.

In service, individual component fatigue life dealt with on a day to day basis.

Fatigue is primarily controlled by the manufacturer setting life limits on airframes and components. Some ofthese may be extended “on condition”. For recreational aircraft in Australia some flexibility is allowed but
sensible care must be taken. Life limits of airframes and items specified in Airworthiness Directives andsome other items may not be exceeded, refer MOSP 3 for the regulations and the sailplane Logbook
Statement. But for instance the TBO of an engine or prop may be extended by the Registration Holder. This
does take on extra risk and it must be decided sensibly and taking into account the manufacturer’s good
advice. Do not just take a chance, increase inspections and know what to look for.

10.2

FATIGUING LOADS
Under normal operations, sailplanes and powered sailplanes experience flight and ground loads that varywith the state of flight:a.

Take-offb.

Landingc.

Winch launchd.

Aero towe.

Soaring flightf.

Aerobatics

By using a full instrumented sailplane, the range of loads for each of the above areas of flight can berecorded. Then a sample structure can be put into a test rig and the flight loading simulated, continuously,
until evidence of structural breakdown occurs.
Recording of this flight load information is difficult and expensive, and the results will vary from country tocountry, area to area, pilot to pilot, which means that the load values used for fatigue test programmes areusually a compromise to achieve an "average" result.
WARNING
Ground handling can generate loads and vibrations that are quite destructive to tail wheels, tail wheel
mounts, rudder hinges, elevator hinges, rear fuselages, etc.

10.3

DAY TO DAY FATIGUE
By far our biggest problem as Inspectors is the deterioration of minor structural and mechanical parts, during
the safe life of the primary structure.
We have classic cases of local fatigue damage:a.

Rear Fuselage frames in the Blanik fuselage.

b.

Blanik tailplane and fin tip rib cracking

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c.

Twin Astir undercarriage castings.

d.

Slingsby T61 rear spar to fuselage attachment cracks.

e.

ES 60 dive brake system bell cranks - cracks.

f.

And many more.

Australia has the highest sailplane/powered sailplane utilisation in the world. This means that we are most
likely to find a defect before anyone else including the manufacturer, so we must be very careful and must
report them so everyone can learn and correct.
Detail design of airframe and system parts can be heavily cost oriented, with the possibility of design
mistakes or errors which can develop into problems in service.
Inspection of a Pik 20 D revealed cracks in the bend zone of the lower rudder hinge attached to the fin post.
It is suspected that flapping of the rudder in the wind while the sailplane was tied down may have been acontributing factor, but also the fact that in the subject fitting it appears that the bend was made along the"grain" of the material.

10.4

POOR WORKMANSHIP - INDUCING FATIGUE
In the past, a tailplane fell off a Blanik following a ground handling incident. Some 7 years previously the
tailplane front attachment plate and channel was damaged and replaced with new parts. The repair riveting
standard was such that only half of the rivets put back carried load the way the designer intended. Thisoverloaded the other rivets and the local structure; fatigue cracks started, resulting in total failure under very
minor loading conditions.
This incident, and others, points to a requirement for repairs to be periodically checked to ensure that they
are sound and the structure around them is sound.
Typical things to look for are:

10.5

a.

Badly driven or loose rivets, holes oversize.

b.

Sharp bend radiic.

Bolts in oversize holesd.

Delamination in FRP - air pocketse.

Incorrect glue mix - in timberf.

Incorrect mating of spliced jointsg.

Incorrect materialsh.

Original shape not reproduced.

BEHAVIOR OF MATERIALS
To be able to find premature fatigue the inspector must have some idea of the behaviour of different types ofmaterial, subject to fatiguing load cycles.

10.5.1WOOD
To all intents and purposes, timber has an indefinite fatigue life in sailplane and powered sailplane structuresdesigned to accepted airworthiness standards.
However defects can occur due to reasons discussed in this section, so the Inspector must be aware of:a.

Splitting in solid timber components.

b.

Glue failure causing delamination.

c.

Attachment of steel and alloy parts, looseness resulting in oversize holes, etc.

d.

Plywood splitting, an example being at the top of the fuselage, behind the wing on Kookaburras,

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resulting from repeated landings on rough ground or one heavy landing.

10.5.2

FIBRE REINFORCED PLASTIC
From testing carried out by Slingsby sailplanes and other European bodies, plus knowledge of the physicalbuild-up of a Fibre Reinforced Plastic (FRP) structural element, the manner in which FRP shows fatigue isclear. Taking a wing as an example:a.

Bending loads are resisted by the wing spar:b.

The critical section is usually at the root end which is built with bundles of rovings at the top andbottom, running span wisec.

On the compression side, the epoxy resists the load, with little support from the thin glass fibres,
buckling under loadd.

On the tension side the glass strands resist the load, not the epoxy.

e.

Signs of fatigue will show up first on the compression side in the form of hairline cracks in the directionof the glass fibres, with the epoxy tending to turn opaquef.

The second stage is marked by cracking at 90 degrees to the glass strands; the structure is becoming
unsafe.

g.

It has been shown that when this evidence first becomes visible, the structure will still support
maximum design load, obviously there must then be a slide in strength as the cracking develops.

Summarising:
FRP structure is fatigue sensitive in those parts of the structure subject to compression loading, with the firstvisual evidence being breakdown of the epoxy resin. Development of inspection methods should allow FRP.
structures to be life extended on the same basis as timber, with "condition” to be established by inspection.
FRP is now a well developed material and has shown very long life resulting in repeated life extensions
being allowed. FRP fatigue relates to:

10.5.3a.

Manufacturing techniques such as resin types and cure procedures.

b.

Natural ageing.

c.

Exposure to UV and extremes of hot and cold.

d.

Repairs.

METAL
Experience shows, most if not all of our fatigue and premature fatigue problems have been in metalcomponents, which means that the practical serviceability of wooden and FRP structures is controlled by the
behaviour of their metal parts.
We are able to predict with reasonable accuracy the load cycle capability of most metals used in aircraft
construction. In turn, if we know the exact load cycle on a component, then the service life of the component
can be predicted.
Metals however can be totally unpredictable in their behaviours if:a.

The component is exposed to excessive vibration.

b.

The environment causes component corrosion.

c.

The component heat treatment is not correct.

d.

The machining or fabricating technique is at fault.

e.

Incorrect plating proceduresf.

Actual loading higher than the designer thought.

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Installation is incorrect.

h.

Notch sensitivity

i.

Pre-stressing due to manufacturing process.

The detection of premature failure of components depends on sound inspection techniques and inspector
awareness.

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11.

FLUTTER
Flutter is mentioned in many sections of this manual. Flutter is a complex subject and this section isintended to give a basic overview of what flutter is and the preventative measures.

11.1

WHAT IS FLUTTER
Flutter is, by definition, an aero elastic phenomenon. An aero elastic phenomenon is one in which the
aerodynamics and structure of the aircraft combine to cause the structure to oscillate. In many cases thisoscillation can cause catastrophic structural failure within one second of onset.

Figure 11-1 Damage to Tail Boom from Suspected Rudder Flutter
When designing a sailplane, it is the designer's responsibility to prove that it is free of flutter at all the speeds
below the Design Maximum Speed, a speed well above VNE. To maintain freedom from flutter, the inspector
must ensure the sailplane is within the limits for control surface balance and free play. The sailplanestructure must be in good condition and free from structural damage.
Flutter is a very important subject that used to kill many sailplane pilots. Over time, flutter prevention
knowledge has improved and procedures and practices were implemented to reduce the risks. The numberof flutter incidents has reduced until now it is almost unheard of. But it is still possible and even likely if
inspections are not performed correctly.
Flutter is caused and influenced by many factors; design, maintenance, various control surface or systemaspects, over-speeding (and therefore instruments), and then pilot understanding and operation such as
reducing VNE with altitude and how indicated airspeed works, and poor speed control. Be sure you
understand and address all the factors involved as it could be caused due to many different factors which
are discussed in several Chapters.
The simplest and therefore most likely forms of flutter are control surface flutter: rudder, aileron, flap,
elevator and even trim tab. Slightly more complicated is flutter of a control surface driven by a trim tab.
More complicated forms are: wing twisting and bending driven by the ailerons, fuselage vertical bending
driven by the elevator, and fuselage lateral bending and twisting driven by the rudder.
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Flutter requires some sort of input to start, often merely a tap on the controls or a minor bump from theairflow. Once it starts, the flutter will continue until the airspeed is reduced. Even when the airspeed isreduced it may take some seconds for the oscillations to completely die out.

11.2

FACTORS AFFECTING FLUTTER
There are many factors that contribute to the flutter characteristics of a sailplane. The designer controls
these factors and through design calculations and testing, proves sufficient safety margins against flutter innormal flight. These design factors are: stiffness of the each structural component eg the wing, or control
surface, the mass distribution of each structural component, and stiffness of the control systems. Many very
high aspect ratio sailplanes have their structure determined by stiffness requirements to avoid flutter rather
than simply strength.
The designer will also put a lot of flutter related information into the flight and maintenance manuals.
However, this information is often distributed throughout the manuals and will not be found under a ‘flutter
avoidance’ heading.
Inspectors must pay attention to a wide range of maintenance factors when inspecting a sailplane to ensurethat it will remain free of flutter including:a.

Control surface centre of gravity and mass balance. Refer to Section 11.3.

b.

Control surface drain holes are clear to prevent a build up of water shifting the centre of gravity.

c.

Control surface hinge wear and hinge cracking / debonding.

d.

Trim tab freeplay and control stiffness.

e.

Control system freeplay from worn control system bearings. Refer to Section Error! Reference
source not found..

f.

Control system cable tension.

g.

Maintenance of control system dampers (if fitted).

h.

Structural damage which changes system stiffness eg debonding ribs that support control systemhinges. Hidden wing structural damage may be detected with a wing frequency check – refer to
Section Error! Reference source not found..

i.

ASI calibration. Refer to Section Error! Reference source not found..

j.

Pitot-static system integrity and leak checks. Refer to Section Error! Reference source not found..

k.

Airspeed placards are installed and readable.

l.

Mounting pin and bearing freeplay for wings and tailplanes.

m.
Fore-aft wingtip freeplay.
Inspectors teaching or examining Daily Inspector candidates must ensure that the member knows how tocarry out control surface freeplay checks, pitot-static system checks and tailplane mounting checks as these
are important safeguards against flutter.
Pilots have a critical role in avoiding flutter by:

11.3

a.

Avoid flying beyond VNE either through inattention to airspeed or poor understanding of VNE reduction
with height at higher altitudes,b.

Performing competent daily inspections, andc.

Arranging for inspections after hard landings, ground loops or flight overloads.

CONTROL SURFACE FLUTTER
With sailplanes the parts most likely to flutter are the control surfaces especially the ailerons, flaps, rudder
and elevators or all flying tailplane. The most common form of flutter and the easiest to visualise is flutter ofhinged control surfaces.
The following figure shows a typical wing or tailplane with a hinged control surface and the basic sequenceof events involved in 1 cycle of flutter. The dotted lines show the original position of the structure.

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Figure 11-2 Flutter Sequence
The flutter sequence is, from left to right:

11.3.1a.

The initial condition showing the available range of control surface travel and the centre of gravity ofthe surface behind the hinge line.

i.

Deflection “downward” of the structure from its initial position by some factor such as a gust or
manoeuvring. Note that the control surface is “left behind” due to its own inertia. The upward
deflected control surface causes an increase in the air loads, particularly torsion on the wing /tailplane.

b.

This has two effects; deflection of the structure further away from its initial position and rotation of thestructure. This is the ‘aero’ part of aero elastic. The twisting of the structure increases the air loads
trying to return the structure to its original position.

c.

The structure then springs back to its original position and, because of the energy stored in the
structure, it overshoots. This is the ‘elastic’ part of aero elastic. Note that the control surface now lagsin the other direction due to its own inertia.

d.

The control surface again rotates from the torsion applied by the control surface and increases theloads trying to deflect the structure.

e.

If the process continues and the oscillations increase, the structure risks being deflected too far and it
will fail. Alternatively the control surface will repeatedly hit it’s deflection limits and it will fail.

INCORRECT CONTROL SURFACE BALANCE
As shown above, the centre of gravity position of a control surface relative to the hinge line has a significant
effect on the flutter of a control surface. The further aft the CG is from the hinge line, the more inertia thecontrol surface will build up when moving. The greater inertia causes the control surface to deflect further
and cause greater loads on the structure. The easy solution is to design the surface so that its centre ofgravity is on or in front of the hinge line by adding mass balance weights. This can take the form of weights
attached to the forward portions of the control surface, bob weights which protrude from the control surface(Foka) or weights attached to pushrods etc in the control circuit (G109). This solution adds a considerable
mass to the control surface. Often a sailplane designer will validate a compromise where the control surface
center of gravity is allowed to be located within a short range of distance behind the hinge line. These limits
are published in the maintenance manual, either as a CG position relative to the hingle line, or as a hinge
moment.
Every change in the mass of a control surface requires checking of its mass and balance to ensure it iswithin limits.
Many older types, especially wood and fabric types, have no manufacturer set limits. They fly relatively
slowly and the mass and balance of the control surfaces varies only slightly as repairs and re-fabricing
should return the surface to its original condition.
Modern sailplanes with high VNE require more care especially as repairs and refinishing can have asignificant effect on the balance of the control surfaces. Where the manufacturer has set down limits for thecontrol surface balance, they must remain within those limits.

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Best practice is to check the control surface weight and balance before and after repair, refabricing or
refinishing. That ensures that there is awareness of potential issues before work commences and reducesrisks of a surprise after the work is completed. Common practice on large powered aircraft is to write theweight and balance of the control surface on its leading edge (where it is typically hidden from direct view)along with the date. Again this is done to ensure that there is awareness of potential issues before workcommences. It is recommended that the weight and balance and the date is written on the leading edge ofthe control surface in marker pen as well as recorded separately in the logbook.

11.3.2EXCESS FREE PLAY
If the freeplay of the control surface is beyond that allowed by the manufacturer or the limits set down in
Section 13.5 (in the case that the manufacturer has not set limits), then the control surface may flutter.
Under dynamic loading the extra freeplay causes the surface to lag and this increases the possibility offlutter.

11.3.3

REDUCED CONTROL CIRCUIT STIFFNESSA fault in a control system, such as a damaged bell crank mount, may reduce the stiffness of the system.
This will allow the control surface to deflect further under a given disturbance. Obviously the increased
control deflections will increase the possibility of flutter.
In sailplanes with control cables the tension in the cables directly affects the stiffness of that control system.
It is therefore vital that the tension in the control cables be adjusted to the manufacturer’s specifications.

11.3.4

FRICTION
Friction tends to increase the damping of the control system. This absorbs the energy of flutter and reduces
its chances. Inspectors need to be careful with any maintenance which reduces control system friction. This
will have little impact on push rod systems but may be significant in cable systems.
Like control circuit stiffness, control cable tension has a significant effect on system friction and therefore
flutter. There have been numerous instances of loose control cables causing flutter - even at speeds below
stall speed and all inspectors should ensure that cable tensions are as per specification.
Inspectors should also be aware that the cable tension varies considerably with temperature due to thedifferential expansion of steel and timber. For this reason a periodic re-tensioning schedule should beconsidered to ensure that cable tension is correct in summer (cables too slack causing flutter) and winter(cables too tight causing structural damage).

11.3.5

REDUCED STRUCTURAL STIFFNESS FROM DAMAGE
Damage such as glue failure, delamination, cracks, etc. that reduces the stiffness of the structure will allow
the forces that drive flutter to deflect the structure further than would normally occur. In particular, reduced
torsion stiffness will lead to increased air loads further deflecting the structure. Any reduction in stiffness ofthe structure, especially the torsional stiffness, can alter the frequency of the structures natural oscillationand may cause flutter at an airspeed lower than VNE. A change in structural stiffness may also bring thefrequency of the structure closer to the frequency of other structural components. This could lead tooscillation of one component setting up an oscillation in a separate component causing a feedback loop withpotentially catastrophic consequences.
Ground loops can cause disbonding of interior structure in the lower fin which can lead to reduced structural
stiffness and flutter. A video showing this damage is here:
https://www.youtube.com/watch?v=ZXjTaGjS3j0&t=97s Inspectors may be assisted by comparing thestiffness of the sailplane to others of the same type. The video demonstrates flexing of the fin and listening
for noises from the disbonded structure and watching for bulges in the skin.

11.3.6

WATER BALLAST
The addition of water ballast changes the mass distribution of the wing and this affects the way the wing
oscillates. As an experiment perform a wing frequency check on a wing with and without water ballast. The
wing will oscillate at a lower frequency with the water ballast. The wing will have a range of resonant
frequencies between full and empty of water ballast.

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11.3.7GAP SEALING TAPEAs discussed above, flutter requires some form of initial disturbance to start. The initial disturbance is usuallya gust or an input from the pilot. So a sailplane may fly many times before an adverse input appears (or ismade) and flutter occurs.
Flutter may also start on a control surface, which would not normally flutter, if a vibrational input is started
and maintained. This can occur when a gap tape sticks-up into the airflow. The airflow can form rollingeddies as the flow breaks away behind the tape. These eddies have a low pressure and roll downstream
with the airflow. The cascade of fluctuating pressures can excite the control surface causing it to vibrate andmay lead to flutter. The gap tape needs to be flush with the surface.

Figure 11-3 Gap Seal Tape
Flutter can also be caused by airflow asymmetry on a symmetrical airfoil. An unusual example occurred ona Twin Astir. During an annual inspection, the gap seal on the rudder was replaced. Unfortunately, themaintainers only had sufficient tape to do one side. They instead used plain gap seal tape to complete one
side of the rudder and used combination gap seal tape with built in zig zag turbulator on the other side. Bytripping the boundary flow on one side of the rudder and not the other, the sailplane encountered rudder
flutter at relatively modest speed. Fortunately it was able to land safely.

11.3.8SPEED
Any control surface not balanced around its hinge line will flutter if flown fast enough. When the designer
sets the VNE, the sailplane is proven to be free of flutter up to that speed with a small safety margin. It
therefore follows that exceeding VNE may cause flutter.
If a sailplane’s pitot-static system is not functioning correctly then the pilot may exceed VNE unintentionally.
Under reading of the ASI may be caused by problems in both the pitot and static systems. A leaking or
blocked pitot tube or a kinked line to the instrument may affect the pitot system.
The static system is affected by leaks in the static system. If the static pressure in the cockpit is slightly
higher that the surrounding air (normal when the ventilation system is open) and the static system is open tothis higher pressure, then instruments connected to the system will under read. Only a small leak in thestatic system is needed to cause a significant under reading of the ASI. Blocked static ports will cause the
ASI to indicate lower airspeed as altitude is increased.
Because the flutter airspeed is strongly dependent on true airspeed (TAS), flying at high altitude brings the
sailplane closer to its flutter speed at indicated airspeeds which are less than it’s sea level VNE. For thisreason, a reducing indicated airspeed VNE with altitude placard is required for sailplanes which have an
oxygen system fitted. Refer to Section Error! Reference source not found. on oxygen for the full details of
this requirement.
It is therefore vital that the pitot-static system is functioning correctly in accordance with Section Error!
Reference source not found. on the Pitot Static system.

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11.4

WING FLUTTER AND WINGLETS
Encountering wing flutter in sailplanes is very rare. If mass is added to the wingtip of a sailplane wing, it will
resonate at a noticeably lower frequency. This lower frequency will correspond to a lower wing flutter speed.
Adding winglets to older sailplanes will increase the mass at the wingtip and reduce the flutter speed. For
this reason, many sailplanes that have had winglets retro-fitted have had their VNE reduced as a result. One
fatal in flight breakup in Japan was blamed on the retro-fitting of winglets to an older FRP sailplane.
All fitment of winglets to older FRP sailplanes need to have a modification order or approval from the
manufacturer.

11.5

FLUTTER PREVENTION
The large number of factors that affect the flutter characteristics of a particular sailplane requires theinspector to be especially vigilant.
Often flutter is discussed with single modes of flutter in isolation. Whilst this simplifies the discussion, it
obscures the fact that the entire sailplane is involved in a flutter event. At annual inspection, the inspector
needs to consider all the factors connected to flutter and resist signing out a sailplane with myriad small
deficiencies where each is just within the acceptable limit. These multiple factors can combine to produce
flutter.
Ongoing preventative maintenance and not letting small deficiencies accumulate over the years is the bestpractice to avoid flutter.

11.5.1MEASURING CONTROL SURFACE BALANCE AND MASS
The balance and mass of control surfaces can have a major effect on both the handling characteristics andflutter properties of any sailplane.
When measuring the balance of a control surface, use the following procedure unless there are specificprocedures in the Maintenance Manual for the sailplane:j.

Remove the control surface from the sailplane. Unless the control surface is off the sailplane you
cannot be sure that there is no friction due to seals, control systems, etc.

k.

Mount the control surface so it can rotate freely around its hinge line. The normal procedure is toclamp supports to a work bench and balance the control surface on the supports. Other options
include suspending the control surface from overhead supports. The critical aspect in all mounts isthat the control surface is free to rotate about its hinge line. Take special care when measuring
rudders from Glasflugel types. Support them using part of the gimbals mechanism that mounts in therudder.

l.

Position an accurate set of scales under the trailing edge of the control surface (accurate means
within ± 2 g) so that the surface is horizontal. Mark a point on the control surface where the scales areto touch. Ensure that the load on the scales is through a single point and not distributed over an area.
Take the reading from the scales and measure the perpendicular distance from the hinge line to thepoint of contact of the scales.

M

Figure 11-4 Mass Balance Measurement

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Determine the balance of the control surface (the residual moment) by multiplying the reading from thescales by the distance from the hinge line to the scales. Take special care with units to ensure that thecalculated value is in the correct units.
Measure the mass of the control surface as this can have an effect on the flutter of the surface it is attached
to and the loads on the hinges. When measuring the mass of the control surface the scales should be
accurate to within 25g and take care to ensure that the surface is not touching any other objects.
Mass balance weights are located in particular positions by the designer and this sometimes reflects
complex considerations. For example: the rudders of the Janus, Duo Discus and Arcus all have a large bobweight at the bottom and a small weight towards the top of the rudder The bob weight is close to thefuselage tail boom axis where there is no movement when the fuselage is twisting about the longitudinalaxis, but significant movement occurs in large side to side fuselage tail end swinging. As a contrast theweight at the top participates in all the various flutter motions. Respect that the designer knows theunderlying reasons.

11.5.2

RECTIFICATION OF CONTROL SURFACES WHICH ARE OUTSIDE THE MANUFACTURER’S
LIMITS
If a control surface is outside the manufacturer’s limits, it is necessary to bring it back inside those limits
before the sailplane flies again. This is because the manufacturer has proven the sailplane is free from flutter
provided the surfaces are within balance, the control system is within the freeplay limits and the aircraft is ingood condition. Flutter may not occur, even though the surface is out of balance, for many flights because
just the right combination of speed and vibration (from atmospheric turbulence) has not occurred. The only
way to guarantee that flutter will not occur is for the sailplane to fully meet the manufacturer’s specification.
If a surface is out of limits with regard to balance but is under the maximum permitted mass then bring thesurface back into balance by adding mass balance in front of the hinge line.
Attach the mass balance in accordance with the Maintenance Manual. If there are no instructions in the
Maintenance Manual then inspect the attachment of mass balancing lead elsewhere in the sailplane fordetails such as type of fastener, spacing, the use of glues, etc. When installing this balance mass takespecial care to ensure that the new mass does not foul with any other part of the sailplane and attach it
securely. Mass balance weight attachment must sustain 24 G due to the potential violence of flutter. If in
doubt, seek RTOA advice.
If you cannot balance the surface without exceeding the maximum permitted mass then the only option is tomake the surface lighter. This will usually require the removal of finishing coats such as gel coat from theunderside and if necessary from the upper side. In severe cases it may be necessary to remove all gel coatand apply a thin layer of paint (probably polyurethane) to protect the surface. In extreme cases seek advice
from the RTOA or from the sailplane manufacturer.
If you still cannot bring the surface back into tolerance, then replacing it is the only option.

11.6

DUSTER'S DEMISE - A FLUTTER CASE HISTORY
Saturday, April 24th, was a good soaring day at Orient Airfield in South Africa, and I had been flying my new
home built Duster in the vicinity of the airfield for some 4 hours. The time was 17:00 hours and I felt that the
air was calm enough to conduct the high speed test to red-line which is 206 km/h . I decided to pass over the
airfield at circuit height at right angles to the runway in use to enable me to complete a proper landing
approach.
I manoeuvred myself into a position some three kilometres out and radioed my intentions to the tower who
gave me the all clear. I started the run from a height of 400 m and was surprised at how rapidly the Duster
built up speed. In a very short period I had 200 km/h indicated and eased back on the stick to maintain thatspeed. I then passed through some mild ‘bubbly’ turbulence and immediately afterwards felt a violent highfrequency vibration from the rear of the fuselage. I have read a lot about flutter and knew straight away what
had happened.
The sequence of events thereafter (according to the wreckage recovered) was that the rudder broke awayfrom its spar first, followed shortly afterwards by the fin. The rudder oscillations probably caused the twoelevator halves to oscillate in opposite frequency because although they stayed with the aircraft the main
spar joining the two halves sheared leaving the sailplane without elevator control.

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The Duster began diving and, when I felt no response to the stick, I realised immediately that I would have tobail. I released the canopy and seat belts with remarkable efficiency (having practiced this manoeuvre a few
times before), and the negative g from the steepening dive (combined with the slipstream) got me out of the
cockpit as effectively as any ejector seat would have done.
The official inquiry into the accident found that it was probably caused by flying the sailplane beyond its VNE
which in turn was probably cause by the ASI under-reading due to; a) the pressure altitude on the day being
8000 feet and b) the ASI being connected to cockpit static which may have caused it to under read.
There are several points which should be noted from this report. Firstly, the pilot began the VNE run at 400
m  1200 ft. This is very low and leaves no margin if something goes wrong. In this case the pilot was lucky
as very few pilots who experience difficulties under 1500 ft. are able to bail out in time.
Secondly, the flutter did not occur until the sailplane hit turbulence. Something was required to start the
flutter.

11.7

REFERENCES
Basic Glider Criteria Handbook. Federal Aviation Administration, Flight Standards Service, Washington DC,
1962
DG Flugzeugbau website - Flutter resistance of the DG1000
Australian Gliding July – August 1998 p.18-22, “Flutter” by Mike Burns
OSTIV Volume 18 No 4 1994, “Possibilities of Hight Altitude Flutter During Wave Flights", by Walter Stender,
Germany, Fritz Kiessling, Germany, Joachim P Kuettner, USA

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12.

LOADS ON SAILPLANES

12.1

GENERAL
When inspecting a sailplane a good knowledge of the loads it is likely to be subject to is required. The loads
which are imposed on the sailplane structure during normal operations fall into four broad categories:
Manoeuvring loads, gust loads, launching loads and landing loads. Additionally, powered sailplanes
are subject to engine and propeller loads.
The load cases and numbers presented here apply to sailplanes which have been certified to JAR 22
introduced in 1980. Older sailplanes are certified to earlier standards and the numbers and meanings ofsome terms when applied to these sailplanes are slightly different. Since 2002, most European sailplanes
have been certified to CS22. Other standards may be adopted but the differences are not likely to be sosignificant that this text, BSE, is made invalid.
When inspecting a specific sailplane, the information contained in the Type Certificate Data Sheet (TCDS) is
primary, or a GFA Data Sheet if no TCDS, and the manufacturer’s Flight and Maintenance Manual isauthoritative. The latest versions apply for the life of the sailplane.

12.2

MANOEUVRING LOADS
Manoeuvring loads are those imposed on the structure when the pilot moves the control column, the rudder
pedals, the dive brake handle or the flap lever.

12.2.1SYMMETRICAL LOADS
Symmetrical loads are primarily generated by moving the elevator although changing flap settings andopening the dive brakes can significantly affect the load distribution over the wings. When the sailplane isdesigned it must be proven to be strong enough throughout the Manoeuvring Envelope.

Figure 12-1 Manoeuvring Envelope ( JAR 22 Utility Category G Loading )The manoeuvring envelope is a plot of normal force as a ratio of the normal force necessary for steady level
flight (the ‘g’ loading) versus speed. The sailplane must be able to withstand the forces inside the envelope
and it may fail if it is taken outside the envelope.
The region from zero up to the stall speed is only of academic interest as the sailplane cannot maintainsteady flight. From the positive stall speed up to the manoeuvring speed (VA) it is not possible for the
sailplane to be flown outside the envelope because the wing stalls. The designer has to prove the sailplaneis strong enough to withstand the maximum g loading. Above VA it is possible for the pilot to damage thesailplane by careless use of the controls.
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The negative case is similar (except the g loads are negative of course) and the differences can be
explained as follows: The aerofoil is less able to generate negative g load so the -1g stall speed is fasterthan the +1g stall speed (if the section was symmetrical then the stall speeds would be the same) and thesailplane is not required to be as strong in negative g.
The table below shows the limit g loading for a Utility Category sailplane certified to JAR 22 and CS-22.

n1

at VM

+5.3 gn2

at VNE+4.0 gn3

at VNE-1.5 gn4

at VM-2.65 g

The table below shows the limit g loading for an Aerobatic Category sailplane certified to CS-22.

12.2.2n1

at VM+7.0 gn2

at VNE+7.0 gn3

at VNE-5.0 gn4

at VM-5.0 gLOADS IN THE SAILPLANE (SYMMETRICAL MANOEUVRING)
When a sailplane is manoeuvred, the wings generate the increased lift to accelerate the sailplane. In
addition, the tailplane loads change because an increased force is required to rotate the aircraft to increase
the angle of attack and hence the wing lift

Air load distribution at 5 g

Air load
Wing deflection at 5 g
Air load distribution at 1g
Wing deflection
at 1 gFigure 12-2 Spanwise Load Distribution
This increase in wing lift bends the wing upward as shown above and results in compressive stresses in the
top spar cap and tensile stresses in the lower cap. The up load on the wing combined with the tail down loadin the fuselage and the increased ‘apparent’ weight of the pilot(s) results in stresses in the fuselage asshown below

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Lift
Balancing Tail Load
Effective
pilot weight
Resultant Tension

Resultant Compression

Figure 12-3 Loads in the Fuselage During Positive Manoeuvres
In the positive load case there is also a distributed down load over the tailplane which is of similar shape tothe wing loads but reversed. This results in compressive loads on the underside of the tailplane and tensileloads in the top surface.
Because the angle of attack is increased to provide the extra lift the induced drag on the sailplane wings also
increases. This extra drag acts on the wings and tends to pull them backwards. This will place the rear wing
pick-ups into compression and, depending on their design, will place the forward pick-ups into tension.
During negative manoeuvres the concept of the loads is similar but they are reversed.

12.2.3ASYMMETRIC LOADS
If a pilot applies aileron or rudder, the resultant loads on one side of the aircraft are different from the otherside.
The application of aileron causes an increase in lift on the side with the down going aileron and less lift on
the side of the up going aileron. Application of rudder will cause side loads on the fin and the secondary
effect of rudder (roll) results in asymmetric loads on the wing. The diagram below gives a conceptual idea ofthe loads and deflections on a sailplane during a typical asymmetric manoeuvre.

Figure 12-4 Combined Loads During a Rolling Pull Up

12.3

GUST LOADS
When a sailplane flies through air with varying up and down velocities, the angle of attack on the wingchanges. This results in changing loads on the sailplane. The designer is required to prove the sailplane isstrong enough to withstand the maximum gust strength the sailplane is likely to experience.

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Sailplanes which have been certified under JAR 22 are required to be strong enough to withstand a verticalgust of ±15 m/s ( 30 kts) at the rough air speed and a gust of ±7.5 m/s ( 15 kts) at the design dive speed.
Some older sailplanes are required to withstand a ±10 m/s gust at the design dive speed and so do not havea rough airspeed as such. The actual strength of the wing and fuselage which is required to meet theserequirements is similar.
If a sailplane has a Maximum Rough Airspeed and it is being flown below that speed then the wing will stall
before the structure is overstressed.

Figure 12-5 Gust Flight Envelope

12.4

LAUNCHING LOADS
During launching additional loads are imposed on the sailplane. These are quite simple during aerotow as
the sailplane is flying normally and the only addition is the pull on the aerotow release. This pull is a
maximum during the initial acceleration. During the steady climb (with no gusts or pilot inputs) the cableloads are low and may be estimated as per the following example:

L
 30
D
L = Weight (for steady flight) = 400 kg
D = cable load (or the sailplane would accelerate or decelerate) = 400/30 = 13.3 kg of cabletension.

12.4.1

WINCH LAUNCHING LOADS
When a sailplane is winch launched, the loads imposed on the structure by the launch method aresubstantial. The pull on the cable can be thought of as extra payload in the fuselage. Because the stresses
due to this are high, the wing is not able to withstand the manoeuvring loads (5.3 g) during the launch. For
this reason the maximum speed which is permissible during the winch launch is reduced so the wing stalls
or the weak link breaks before the sailplane structure is overstressed.

12.5

HEAVY LANDING AND GROUND LOOP LOADS
When a sailplane is subject to a heavy landing or a ground loop the inspector must understand the loads
which the sailplane is likely to have been subjected to so that the inspection can cover the likely damage
points.
Refer to BSE Chapter 25.

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13.

CONTROL CIRCUIT RIGGING

13.1

GENERAL
A correctly rigged sailplane has its control system travels, freeplays and their geometry within the
manufacturer's specifications. Correct rigging is vital to the handling and operational characteristics of the
sailplane.
Check the control systems travels at each annual inspection and after any major repairs that could affect the
sailplane’s geometry, such as a broken fuselage or a heavy landing. Metal gilders, either aluminium or steel
tube, are susceptible to gradual bending of components and therefore the geometry of the sailplane is more
likely to change with time and heavy landings. Wood and FRP structures are more likely to fracture whenoverloaded and so damage to sailplanes constructed of these materials is more noticeable.

13.2

CONTROL SURFACE TRAVEL
Incorrect control surface travel can result in unsafe flying characteristics, unpleasant handling andunnecessary drag.

13.2.1CHECKING TRAVELThe Flight or Maintenance Manual for each type contains the specifications for the control surface
deflections. Most manuals give the deflections as either an angular deflection or as a distance from theneutral position at a specified point.
Where deflections are given as an angular deflection it is often helpful to use an inclinometer.

X

DISTANCE: The deflection
X is shown as the distance
moved by the trailing edge,
at a fixed position along thecontrol surface, from theneutral position.



ANGLE:The deflection 
is shown in degrees of
movement from the neutral
position.

Figure 13-1 Distance Vs Angle

13.2.2ELEVATOR TRAVELThis is the most critical control surface for correct travel as it has a primary influence in the stall and spin
entry characteristics of a sailplane:a.

Insufficient up travel: The sailplane may be unable to stall or flare properly during landing.

b.

Insufficient down travel: The sailplane may be unable to recover from a spin or the pilot may beunable to prevent nose pitch up at the start of a winch launch or in a towplane upset.

c.

Excessive up travel: Sailplanes designed as unspinable, e.g. ASK 21 and Grob 103 Twin II, may

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stall/spin and the load on the control surface may exceed that allowable.
d.

13.2.3

Excessive down travel: The tailplane may stall during launch ground run, particularly all flying tails,
and the surface may be overloaded.

RUDDER TRAVEL
The rudder travel can also be critical as the rudder plays an important role in recovering from a spin.

13.2.4a.

Insufficient travel: The sailplane may not recover from a spin and may have reduced turncoordination.

b.

Excessive travel: The rudder and fuselage structure may be overloaded or the fin may stall.

AILERON TRAVEL
Incorrect aileron travel may reduce the roll response, reduce turn coordination, increase aileron drag andincrease total drag. Increased travel may cause a sailplane to become more susceptible to spinning at low
speeds. Incorrect up/ down differential movement can make the handling poor.

13.2.5

TRIM TAB TRAVEL
The minimum and maximum trim speeds will alter handling and speed control of the sailplane. Makes it
harder to fly at stable airspeeds.

13.3

SETTING UP A CONTROL SYSTEM
Follow these basic steps when setting up a control system:

13.4

a.

Set the control column up in the neutral position. This may be with the stick vertical or a distance froma datum as shown in the aircraft’s manuals. Clamp the stick in place. Be aware that some sailplanes
mix controls e.g. the elevator fore/aft position and aileron droop.

b.

Work through the control system from the stick to the control surface ensuring that each component isin safety and set as per the aircraft data. For flaps and ailerons ensure the system is symmetrical fromone side to the other. At the end of this step ensure fairing of the control surface with the supporting
structure. Note: On some types the correct neutral point is with the controls unfaired. Check the
manuals for details.

c.

Remove the clamps and check the control surface deflections. Adjust the stops so that the control
deflections are correct.

CONTROL SYSTEM STOPSManufacturers design control stops to serve the dual purpose of limiting the force a pilot can apply to thecontrol circuits and also to ensure that the mechanisms of the control circuit themselves cannot be damagedby moving further than they were intended to.

Figure 13-2 Control System Stops
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At each annual inspection, check the control stops for correct functioning. If the stops are not operatingcorrectly, the end of travel will be spongy rather than exhibiting a crisp stopping action. The control surface
movement must be limited by the stop only and this sponginess indicates the control circuit binding or
rubbing somewhere other than at the stops. Long term binding and rubbing in the control circuit will lead todamage. Take care to check that the stops operate properly through the full range of control stick
movement, e.g. do the aileron stops work correctly at both full up and full down elevator?
Some control systems also provide stops at the control surface to absorb loads due to wind action on amoored sailplane. Where there are stops at each end of the system, the stop near the control should contact
first and the stop near the surface should be about to contact.

13.5

CONTROL SYSTEM FREEPLAY
Excessive control system freeplay can cause flutter. All freeplays must be within the manufacturer's
specifications where these are available. Where manufacturer's freeplay limits are not available, the freeplay
must be less than 2.5% of control surface chord.
From the US FAA Basic Glider Criteria Handbook.

CAUTION
Flutter may occur if, when the cockpit control is blocked in the central position andfinger pressure is applied at the trailing edge causing the control surface to rotate,
the trailing edge moves in excess of 2.5 percent of the control surface chord.

Figure 13-3 Control Surface Freeplay
For example: If an aileron has a chord (C) of 250 mm then the maximum freeplay (P) at the trailing edge is
6.25 mm, from the calculation:

250 

2.5
 6.25 mm
100

If freeplay is excessive, check for the following defects:a.

Slack cables.

b.

Worn hinges.

c.

Worn pivot pins and holes.

d.

Worn bearings (of all types).

e.

Movement in bell crank mounting points.

f.

Loose bolts.

Excessive freeplay beyond the manufacturer’s limits, or (if there are no manufacturer’s limits) beyond 2.5%of the control surface chord, requires rectification before the sailplane flies again.
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13.6

CONTROL SYSTEM FRICTION
Mechanical systems always contain friction which tends to inhibit movement. A small amount of friction isbeneficial because it tends to damp out vibrations which could cause flutter but if the friction is excessive it
leads to stiff and heavy controls.
If there is too much friction in the flight control systems then it can make the sailplane difficult to control. E.g.
As the pilot tries to move the control, friction prevents its movement. The pilot increases the force until thesystem ‘breaks out’ and starts to move. As the sliding friction is often less than the static friction, the control
system ‘jumps’ past the desired position leading to over control of the sailplane.
Friction in other control systems such as the undercarriage retraction mechanism or trimmer, causes them tobe heavy to move, may overstress the components and may be beyond the physical strength of some pilots(e.g. juniors, females) to operate.
There are three possible reasons why a control system may have excessive friction:a.

Lack of maintenance. This is usually a lack of lubrication.

b.

Improper maintenance. If the geometry of the system is not set up correctly parts may bind, causing
friction.

c.

Damage. If parts are damaged they may be rubbing on other parts, misaligned etc. causing extra
friction.

The maximum friction which is acceptable varies from type to type and information may be contained in theaircraft’s Maintenance Manual. Measuring control system friction should be done at the normal place thepilot grips the control. The friction is the force required to just make the system move. If the Maintenance
Manual does not contain any limits, the following values should be used as a guide:Control System

Typical Maximum Friction

Elevator

15 N (1.5 kgf)

Aileron

10 N (1.0 kgf)

Rudder

50 N (5.0 kgf)

Tow Release75N (7.5 kgf) Unloaded cable load.
Or <170N (17kgf) for two releases.

Trim

15 N (1.5 kgf)

Flaps

50 N (5.0 kgf)

Table 13-1 Control Friction Limits
If friction is above these values then further investigation of the system is warranted.

13.7

ENDFLOAT OF CONTROL SURFACES
All control surfaces should be free to move along their hinge line. This is important because the control
surface and the mounting structure will expand and contract differently with changing temperature. This
could cause failure of the hinges if there is no possibility of the hinges sliding endways.
A similar effect occurs as the wing flexes. This may also load the hinges axially unless there is sufficient end
float.

13.8

CONTROL SYSTEM STIFFNESSThe manufacturer sets the stiffness of the control system during the design phase and does stiffness
measurements during type certification. Inspectors must check for any obvious reduction in the stiffness of acontrol system.
Reduced stiffness may be caused by damage to the control system, damaged control system mounts orincorrect system rigging. Possible causes of reduced control system stiffness include:a.

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13.9

b.

Slack control cables.

c.

Buckled pushrods.

d.

Incorrect control system geometry.

GAP SEALS
The majority of sailplanes have tape sealing the control surface gaps. Gap seals reduce drag and improve
control effectiveness. Note the following points when reinstalling gap seals:a.

Some types have specifically approved types of gap seal and only these may be used.

b.

The use of incorrect tape has caused control system buzz. This may be a prelude to flutter.

c.

Restricted control surface travel is possible if the control surface is not fully deflected in the direction of
maximum tape stretch when fitting gap tape. Recheck the control surface travel after fitting gap tape.
Some tapes shrink after installation and they must be loose enough.

d.

Tape that is not secure, either because of incomplete removal of the old adhesive or the newadhesive is faulty, may work loose and jam the flight controls. Note: Skin oils from the fingers may
affect the adhesive.

e.

The tape may work loose from the leading edge and then “stand up” in flight. This may reduce control
effectiveness to the point where it is impossible to maintain flying speed. In one incident the pilot has
to use more than 3/4 forward stick to maintain 55 knots.

f.

Note some types have fowler type flaps or even ailerons and are not meant to have gap seals.

Figure 13-4 Typical Sealing For Side Hinged Control Surface

Figure 13-5 Older Style Seal

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Figure 13-6 Internal ‘U’ Seal

13.10

PUSH ROD RIGGING
The flight control systems in most modern sailplanes use pushrods and bell cranks. The design of pushrods
takes into account both tension and compression loads. For most pushrods the critical loading iscompression because of pushrod buckling. Any damage to the pushrod such as dents or bends canseriously reduce the compression strength of the pushrod and the control system stiffness. This may reduce
control effectiveness and possibly cause flutter.

13.10.1 ROD END SAFETY
Most pushrods have an adjustable rod end at one end to allow adjustment for manufacturing tolerances in
the control system. When installing a rod end, screw it in past the witness hole. Test for correct safety byinserting a piece of wire through the witness hole. It should be possible to detect the rod end with the pieceof wire. Inspectors should be careful as on some designs it is possible to push the wire past the rod end
even though it is correctly in safety.

Figure 13-7 Rod End Safetying
Where there is no witness hole, the length of thread engagement must be at least 1.3 times the outside
diameter of the rod end thread for steel in steel fittings.

13.10.2 ROD END ALIGNMENT
When reinstalling rod ends on a pushrod, the relative alignment of the rod ends must be correct or the rod
ends will bind. When installing pushrods, ensure they do not bind throughout their travel.

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Figure 13-8 Pushrod Rotation

13.11

AIRCRAFT GEOMETRY
Check the aircraft geometry after any repairs if there is a possibility for the wings, tailplane or fuselage tohave moved relative to each other.

13.11.1 CHECKING RIGGING ANGLES
The usual way to check rigging angles is with a water tube manometer. This consists of a length of clear
plastic tubing filled with water. To make the water level more obvious use food dye to colour the water. It isalso helpful to add a small amount of dish washing liquid to the water as this lowers the surface tension of
the water and gives a more accurate reading. Be careful not to shake the tube as the froth will makeaccurate readings impossible.
L

Typical set-up for measuring wing incidence

H

Figure 13-9 Water Tube Manometer
h/l = tangent of angle of incidence.
if h/l is less than 0.15 then the angle of incidence in degrees equals h/l x 57.24.
Dimension l is best measured using two plumb bobs, one at the leading edge and one at the trailing edge
and measuring between the two.
Checking of aircraft geometry using laser levels is becoming more common as the price has fallen.
Incidence boards and survey dumpy levels are also possible tools. However the water tube manometerremains as a simple and accurate tool.
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When measuring the geometry of a sailplane that has undergone substantial repairs, use a good steel tapemeasure to measure distances to ensure the aircraft is symmetrical.

13.11.2 WING-TAILPLANE ANGLE
This is the angle between the tailplane and the wing and is very important to the stability and handling of the
sailplane. Verify this angle after any repairs to the rear fuselage, wing mounts, tailplane, etc. In metal aircraft(aluminium or steel tube) this angle may slowly change with a succession of heavy landings.

Figure 13-10 Wing Tailplane Angle

13.11.3 DIHEDRAL
The dihedral angle is the angle of the wing relative to the horizon when viewed from the front. It is normal tocheck this angle only after a major repair or if the inspector is suspicious that something is wrong.

13.11.4 WASHOUT
The washout of a wing is the twist of the wing along the span. This must be the same in both wings to within½° at each span wise station. Incorrect washout can produce unpleasant stalling characteristics and atendency for the aircraft to fly one wing low.

13.11.5 WING TO FUSELAGE
The wing to fuselage angle is important when checking if the level reference is still valid.

13.11.6 TAILPLANE TO FUSELAGE
The tailplane to fuselage angle is important when checking if the level reference is still valid.

13.11.7 FIN ANGLE
Changes in the fin geometry will noticeably affect the handling of the sailplane. All T-tail sailplanes,
particularly those of metal construction, are vulnerable to changes in the fin geometry due to heavy landings
and ground loops.
Displacement of the vertical fin as shown or twisting in plan view, are possible. Either defect will be evident
by the need to fly with crossed controls.

Figure 13-11 Fin Misalignment

13.12

STRUCTURAL FREEPLAY
Excessive freeplay between the different components of a sailplane such as wings to fuselage or tailplane tofuselage can cause flutter, excessive wear of rigging pins and premature fatigue due to the movement of thepins in the bushes.

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13.12.1 TANGENTIAL PLAY OF WINGSOne of the most common forms of structural freeplay is tangential play of the wings on FRP sailplanes. The
main cause of freeplay is wear on the main pins or in the main pin holes that prevents the wings from pullingup tight on the drag fittings. Typically the maximum fore and aft play measured at the wing tip of a 15 m
sailplane is 20 mm.
To remove this play use any of the following methods:a.

Provided there is sufficient material left in the bushes, assemble the wings and line bore the hole until
it is round and obtain an oversize pin. Take special care to ensure that the bush thickness is not below
the minimum allowable.

b.

Install shims on the drag pick-ups as detailed below.

c.

Other methods exist; however, these are not covered by BSE.

13.12.1.1

SHIMS

Most manufacturers specify the correct method for installing shims to remove wing freeplay. If the
manufacturer does not specify how to install shims, use the following method:a.

The shims are simply custom made washers. Manufacture them so that the inside diameter is justlarger that the pin and the outside diameter should be large enough to cover the part of the structurethat transfers the loads.

b.

Thoroughly clean the pin and the shim using a solvent such as acetone. Be careful not to spill any on
the paint or the canopy.

c.

Gently roughen the surface of the shim and the flange of the lift pin and glue the shim in place using
suitable glue such as contact adhesive.

d.

Record the location and thickness of each shim in the log book. It is also advisable to permanently
write the shim thickness on the wing or fuselage next to each pin.

13.12.1.2

TAILPLANE

Play in the tailplane fittings is possible on most types of sailplanes. Removal of this play usually requires remanufacturing of the pins or purchasing new pins from the manufacturer. Typically the maximum playpermitted at the tailplane tip is 5 mm. This freeplay is critical in all flying tailplane designs as flutter has
occurred due to excessive tailplane freeplay.

13.13

CONTROL CIRCUIT FLUTTER
Flutter is a very important subject that used to kill many sailplane pilots. When it was realised andprocedures and practices were implemented, largely promoted by the GFA worldwide, the number of flutter
incidents has reduced until now it is almost unheard of. But it is still possible and even likely if things aredone wrong.
Flutter is caused and influenced by many factors; design, maintenance, various control surface or systemaspects, overspeeding and therefore instruments, and then pilot understanding and operation such as
reducing Vne with altitude and how indicated airspeed works, and poor speed control.
So flutter is in a chapter on its own, Chapter 11. Be sure you understand and address all the factors involved
as it could be caused due to many different Chapter subjects. And maintenance and modifications all have apart to play!

13.14

REFERENCES
Basic Glider Criteria Handbook. Federal Aviation Administration, Flight Standards Service, Washington DC,
1962

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14.

WORKSHOP PRACTICE

14.1

GENERAL
Before an inspection can be performed, certain facilities and equipment are required. Without an adequate
workshop or the correct tools it is not possible to perform the tests which are required, make any
rectifications or to disassemble the sailplane.

14.2

SAFETY

14.2.1CHEMICALS
Minor maintenance which often involves cleaning with solvents, finish touch up and lubrication ofcomponents is usually associated with most inspections.
Solvents, greases, paints, resins and other chemicals can enter the body when a person breathes in theirvapour, through skin contact, or through the mouth from contact with food or fingers. Vapour can beconcentrated in enclosed spaces, such as inside a sailplane fuselage, so good ventilation should beavailable. Some chemicals can impair memory and cause headaches, dizziness, fatigue, mood changes ornausea and exposure to high levels can cause liver damage, unconsciousness, death and cancers.
Solvents can also be flammable so care must be taken to keep them away from sources of ignition, such aslead lights. A battery powered torch is safer in these situations.
All chemicals used when working on sailplanes should only be used as recommended by the manufacturer
and detailed in their Safety Data Sheet (SDS) - previously called a Material Safety Data Sheet (MSDS). Thisis a document that provides information on the properties of hazardous chemicals and how they affect healthand safety in the workplace. For example an SDS usually includes information on:a.

The identity of the chemical,b.

Health and physicochemical hazards,c.

Safe handling and storage procedures,d.

Emergency procedures, ande.

Disposal considerations.

The SDS should always be referred to when assessing risks in the workplace. A file of relevant SDSs should
be maintained and kept in the workshop for reference.

14.2.2MANUAL HANDLING
Lifting and moving equipment and materials as well as working in awkward postures are part of mostinspection tasks.
Work tasks may involve bending and stretching as well as twisting sideways which increase the risk ofmanual handling injury. It is possible to control risks associated with manual handling by:a.

Organising the work to reduce the number of manual handling tasks involvedb.

Providing mechanical lifting devices such as trolleys, hoists and jacks where appropriatec.

Taking regular resting breaks from awkward tasksd.

Making sure the workplace layout allows enough space to move and work safely and comfortably.

If lifting equipment or other aids are not available, the job may require more than one person to achieve.

14.2.3

SLINGING AND SUPPORTS
During inspection and other work, the sailplane will be derigged and the major pieces worked on separately.
They can be supported on trestles or in purpose built cradles. Parts such as the fuselage which can support
their own weight may be steadied by slings, ropes or ratchet tie downs. In all cases thought should be given
to the risk of damage if the sailplane part should fall off the trestle or slings loosen. Clamping wing spars totrestles and using multiple slings for fuselages will reduce the likelihood of accidental damage.

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Extra care should be taken both when working underneath major sailplane parts such as when changing
wheels etc. and when working alone. People have been killed when the fuselage has rolled on top of themand no one was able to assist to lift it off.

14.2.4

HOUSEKEEPING
A slip or fall can cause injury to the arms, legs, back, neck or head. Neck and head injuries can cause
damage to the spinal cord and nervous system. Many people have suffered permanent disabling injuries asa result of a fall. Poor ‘housekeeping' in the workshop leads to slips, trips and falls. Oil spills, parts, extension
cords and hoses left on the workshop floor can all result in preventable accidents. Bins should also be
provided for disposal items such as old rags, empty containers, paper and other rubbish. These should not
be allowed to overflow.

14.2.5

WORKSHOP FACILITIESIt is almost impossible to perform a complete and thorough inspection without a place to work that is out of
the weather. If an inspector is trying to work outdoors then allowance must be made when scheduling workfor delays due to rain. Any workshop used should have excellent light as many cracks are impossible todetect in dim light.

14.3

EQUIPMENT

14.3.1

WORKSHOP EQUIPMENT
The following workshop equipment is likely to be required by the inspector and so should be readily
available:

14.3.2a.

Trestles or other supports.

b.

Bench with vice.

c.

Equipment for slinging

d.

Mobile lighting

HAND TOOLS
Inspectors require the correct tools for the job. Each inspector should own a basic tool kit which consists of:a.

Spanner and socket set (1/4” drive sockets are recommended).

b.

Screwdriver set (Phillips and chisel).

c.

Inspection mirror.

d.

Good torch with batteries.

e.

Bearing cleaning and greasing equipment.

f.

Steel ruler.

As an inspector gains experience the following tools, among many others, should be gradually added to theirtool kit:g.

Inclinometer (incidence measuring tool).

h.

Magnet on a stick.

i.

Magnifying glass or loupe.

j.

Spring balance or electronic luggage scalesk.

Micrometer or digital callipers.

l.

Lock wire pliersm.

Water tube manometer for ASI checking.

n.

A pair of small diameter brass tubes for rope release re-assembly.

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o.

Various short lengths of non-ferrous rod for drifts and hole alignment tools.

p.

Artery clamps for split pins and other small parts.

q.

Torque spanner for propellers and spark plugs.

r.

Centre punches for bearing peening.

s.

Files for minor smoothing.

t.

Drill and bits for perspex relief holes etc.

u.

Boroscope.

Inspectors should also consider purchasing a cheap set of spanners which can be “modified” to fit difficult toreach nuts and bolts.

14.4

DISASSEMBLY
When disassembling a sailplane, particularly if you are not very familiar with it, it is recommended that asketch be made of how all the parts fit together. The sketch need not be very complicated but it needs toshow all of the relevant details necessary to reassemble the parts. Instead of a sketch, often a photographon a mobile phone may assist later reassembly.
If possible, the parts themselves should be marked to show the correct reassembly. Care needs to be
exercised here because any scratches or dents can form stress raisers that may lead to fatigue cracking.
Also if the part is repainted then pen markings will be lost.

14.5

STORAGE OF PARTS
As parts are removed from the sailplane, small parts should be placed in a sealable container which has
been clearly marked as to where the parts are from. Suggested containers are plastic bags with the zip
closing mechanisms. These bags often have a printed area which can be written on using a normal pen thus
making labelling of the parts easier.
Larger parts must be stored so they are not damaged and are protected from the elements. Parts that are
carefully greased each time the sailplane is rigged may have the grease removed during maintenance,
which makes them susceptible to corrosion, so protection is needed during storage.

14.6

FOREIGN OBJECTSThe introduction of foreign objects during maintenance is a problem which is as old as aviation itself.
Spanners, nuts, bolts, off cuts and personal items such as coins or keys have caused fatal accidents,
sometimes months or years after the maintenance has been completed. These foreign objects slowly work
their way through the structure until they jam the flight controls leaving the pilot with no hope of recovery.
Before closing any compartment, either during a repair or when reinstalling a seat pan or inspection panel, acareful inspection, preferably by an independent person, is required to ensure no foreign objects are left
behind. All tools should be accounted for and tools should never be placed in the sailplane. Use a separate
bench, preferably a mobile one, so that tools are accessible but are not in the sailplane.
Each part which is removed from the sailplane should be placed in a storage place so that it is not lost andcan be accounted for.

14.6.1

TOOL CONTROL
Some ideas to reduce the chances of leaving items inside the sailplane are:a.

Keep socket sets in the original case and spanners in tool rolls for quick identification of missing
items. Make a dedicated tool holder for other items.

b.

Purchase or paint tools a bright colour to be more easily spotted.

c.

Use a small table to store the tools on prior to use. Using masking tape identify the tools that are
being used by writing the tool name and sticking the tape to the table. Remove the tape when thetools are returned to the table.

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14.7

d.

Use a tool trolley and cultivate the habit of putting tools down on the trolley.

e.

Do not use tool sets belonging to more than one person.

f.

Place all tools away at the completion of each job or at the end of each working period.

REASSEMBLY
It is preferable that the person reassembling the parts is the person who disassembled it but sometimes thisis unavoidable.
When assembling a sailplane following maintenance it is important to ensure that:a.

Parts are reassembled correctly. Now is the time that sketches and photographs made during thedisassembly are useful. When unsure of how a part goes back together the inspector must rely on
the manufacturer’s manuals and if necessary contact the RTOA or CTOA for guidance.

b.

All parts are accounted for. If parts are missing the manufacturer will need to be contacted for a
replacement and the possibility that the part is located in the sailplane waiting to jam a control must
be considered. Even nuts and bolts which are replaced should be accounted for. Excess parts are
obviously a problem

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15.

SAILPLANE MATERIALS

15.1

GENERAL
The inspection of sailplanes requires knowledge of the properties of the different materials that sailplanes
are constructed from. The inspector must know the failure modes the material is likely to exhibit whenoverloaded and the signs which are exhibited once failure has occurred.

15.2

MATERIALS
Sailplanes can be constructed from a number of different materials and it is important for inspectors to know
the tell-tale signs of damage in each. Materials can be broadly classified into two classes according to theirfailure mode; brittle and ductile. Brittle materials fail by catastrophic cracking and usually show little sign ofdamage prior to failure. Ductile materials permanently deform steadily above the limit load and can carrysignificant loads up to ultimate failure.

Figure 15-1 Ductile And Brittle Materials
Thin materials loaded in compression or shear can also fail by buckling. Most buckling failures arecatastrophic because the material deforms and the new shape is only able to carry less load. It is possible
for structures loaded in shear to undergo elastic buckling during which the sheet continues to carry load andreturns to its original shape when the load is removed. This type of buckling is usually found on the top
surface of wings during flight and is regarded as normal behaviour of the structure. If a buckled shape ispresent after the load is removed then a repair is required.

15.3

FRP CONSTRUCTION
Composite materials are constructed by wetting out layers of cloth, one on top of the next, using a liquid
resin which then sets binding the fibres together so they are strong and stiff. This ‘mixing’ of materials
produces a composite material which is better than the original components. The fibres increase thetoughness of the resin and the resin holds the fibres in place so they can hold the load better and prevents
the individual fibres from buckling under compression loads.
This laminating of the material allows the strength of the part to be tailored to provide strength where it isneeded. This is done by orientating most of the fibres in the direction which has the largest load. Examplesof this are the orientation of the fibres at ±45° to the flight directions in the wing skins as this is the directionof highest load due to wing torsion.

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The only exception to laminating of layers is when the loads are simple compression or tension. The clothmaterial is replaced by long strands of fibres called rovings. These are very good at carrying pure tension orcompression and so are used in the spar caps to provide maximum strength in the required direction.
The epoxy resin and the fibres are brittle, with carbon being extremely brittle. Therefore composites arebrittle in their failure mode.

15.3.1

GENERAL COMPOSITE INSPECTION TECHNIQUESTechniques which can detect damage in all composite materials are as follows:

15.3.2a.

The exterior surface may be deformed showing buckles or waviness where the skin is no longer
attached to the internal stiffeners.

b.

An actual fracture surface which can be seen or felt. Be careful as sharp fracture surfaces easily cut
skin.

c.

The gelcoat surface will show cracks. Paint materials are more flexible than the composites they coverand so an impact which cracks the matrix will not necessarily crack the paint. Painted sailplanes
require very careful inspection.

d.

A strong light shone along the surface (at a very flat angle) will high-light defects by casting a shadow.

e.

A light placed inside the structure will allow any cracks or defects to be seen as they will tend to show
up as dark shadow lines. This test requires a fairly dark workshop and a strong light. It will not workthrough sandwich construction.

f.

The tap test, where a coin or similar round edged, hard object, is tapped over the surface is a reliable
method of finding damage in FRP sailplanes. If the part is damaged the sound will be dull comparedwith undamaged structure.

g.

Placing a stethoscope on the structure and then deflecting it may find damage because any fracturesurfaces will rub against each other as the structure is deflected.

h.

Ultrasonic inspection is becoming normal practice for composite inspection of airliners. While thismethod is not yet used with sailplanes, this it may well change in the future.

i.

Inspection cameras on cables, typically attaching to a computer's USB port, are now cheap and they
enable internal inspections which were previously very difficult.

GLASS REINFORCED PLASTIC
The inspection of Glass Reinforced Plastic (GRP) is relatively easy because damaged areas turn white. Thischange of colour is marked and provides a reliable guide to presence of damage.
A problem area with GRP is where it is subjected to crushing loads, such as occurs under screw or bolt
heads. In time, the hole enlarges and the component may become unserviceable until repaired.

15.3.3

CARBON FIBRE AND KEVLAR REINFORCED PLASTIC (CFRP AND KRP)
When the fibre reinforcement is Carbon or Kevlar, the detection of damage is much more difficult. Unlike
GRP, damaged CFRP and KRP do not change colour when damaged. Parts must therefore be examined
more closely and other techniques used to detect damage. Be aware that CFRP in particular can transmit
overloads through the entire structure and damage may exist well away from the point of impact.

15.3.4

DELAMINATION
One of the most common failure modes of composite materials is delamination. This is the separation of thelayers of fibres caused by failure of the matrix material.
When the components are laid up in one cure cycle, chemical bonds form throughout the part anddelamination is unlikely in normal situations.

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Delamination is most likely to occur where parts have been manufactured and then joined together by someform of glue or else when the original layer has been allowed to cure before more layers are added.
Failure in these locations is more likely because the bond on the surface is mechanical, ie thebonding resin only flows into the tiny sanding marks in the surface of the part being joined to. Despite this aproperly prepared surface can give a mechanical bond which is as strong as a wet layup one.
When preparing a part for a wet-on-dry layup, it is a good idea to blow the part clean and look for shiny spots
which indicate insufficient sanding.

15.3.5

CRACKING
When a composite structure is overloaded it is common for the structure to be deflected and damaged andthen to spring back to the original shape. The consequences of this are that the structure may look largely
intact with only a small fracture in the finish but the damage can be very serious with delaminated bulkheads
and shattered skins.
Other cracks can be the result of fatigue. Like sailplanes constructed of other materials, these often formaround the corners of the dive brake boxes, especially on the lower surfaces which are subject to tension.
Fatigue cracks in sailplanes of composite construction can also grow in parts subject to compression. Oncesome small damage has occurred, the crushing of the damaged matrix material causes the damaged area togrow.

15.3.6FAILURE OF SANDWICH MATERIALS
There are two primary failures which occur to sandwich materials; the outer layers of fibreglass can separate
from the foam or balsa core and the core material itself can be crushed or damaged. Delamination can best
be detected by the tap test and because the separated laminate tends to bubble up from the core creating abulge. Crushed core material is normally detected because the surface is dented or pushed in.

15.3.7

GELCOAT CRACKS
Cracks in gelcoat are caused by deflection of the underlying structure taking the gelcoat past its limits, thismay or may not damage the underlying structure, or by failure of the gelcoat itself. Gelcoat failure is usually
the result of exposure to ultra violet light, water and the presence of microscopic scratches which are
introduced during the final sanding of the gelcoat.
Impact cracks are usually identified as they seem to originate from a point and radiate out or they follow thestress lines of the sailplane. Gelcoat failure cracks tend to be fine, close together lines which run fore-aft on
the wings except for the leading edges where they run span wise following the sanding marks along themould line.

15.4

WOOD CONSTRUCTION
Sailplanes constructed from wood are in many ways similar to inspect to FRP because timber fails in a brittle
manner. The inspection techniques in Section 15.3.1, except for shining a light through the structure, areeffective on wooden structures. In addition, wood structures have failure modes which are specific to timber
construction and these must be inspected for.

15.4.1COMPRESSION SHAKESPerhaps the most insidious failure that can occur in a sailplane is the compression shake. A compression
shake occurs when timber is subject to a shock compression load. Shakes leave the timber almost
unmarked with no deformation or change in shape but the strength of the material is reduced to almost zero.
Compression shakes are microscopic buckling of the cellulose fibres in the timber. These buckles effectively
sever the fibres which provide the timber’s strength. Only the most careful inspection will detect shakes andoften the only sign is damage to varnish across the shake.

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Figure 15-2 Compression shakes

15.4.2DRY ROT
Dry rot is a fungal growth in timber which eats away at the strength of the part. Despite its name, dry rot only
begins in the presence of water and it can be detected by a bluish discolouration which looks something likewater ‘tide’ marks.
As the fungus is eating away the cellulose, the strength of the timber reduces very rapidly from the onset ofdry rot and this is why wooden sailplanes should never be allowed to get wet.

15.4.3

GLUE FAILURE
Repairs to older wooden sailplanes and newly constructed amateur built wooden sailplanes use, almost
universally, epoxy glues to join the timber. The epoxy is many times stronger than the timber being joined
and because it is inert, once set, it is immune to the effects of water and fungus. Unfortunately many of theolder glues are not so stable.
Resorcinol is a black glue which also shows as black lines between the various components. Like epoxy,
resorcinol is very resistant to water damage and fungal attack but it requires high precision in the fit of one
part to another. For this reason careful inspection is required as components which have gaps between
them are unlikely to have a full bond.
Older glues such as casein are very susceptible to water damage. Sailplanes constructed from casein are
best inspected by nose!
If casein is wet it gives off a strong, unpleasant smell and reduces to zerostrength almost immediately. Another type of glue which has shown a tendency to failure when wet is kaurit.
Kaurit was used on older German types such as the K7. Kaurit is a pink glue and sailplanes which havebeen wet or have resided in a tropical climate are very likely to have failure of this type of glue.

15.4.3.1 THE FINGERNAIL TESTIn several regions of the sailplane small gussets should be given "The Fingernail Test" to determine thequality of the glue joint. The fingernail test is performed by inserting a fingernail behind the gusset andapplying pressure until it feels uncomfortable. Note: If small gussets cannot be broken off using reasonable
finger pressure then the glue is considered to be satisfactory. If the gusset breaks off the surfaces must be
inspected and interpreted as follows:a.

Failure in the timber, shown by wood fibres attached to the glue, indicates that the glue is in goodcondition. Gussets must be glued back on by appropriately rated persons.

b.

Failure of the glue, no wood fibres attached to the glue, indicates that the glue is in poor condition andfurther investigation must be undertaken to determine the extent of the substandard glue and repairs
made as necessary.

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Wherever there are signs of water having entered the structure the fingernail test must be performed.

15.4.4FAILURE OF FABRIC COVERINGS
Most sailplanes constructed from timber and the control surfaces of many FRP and aluminium sailplanes arecovered by fabric to give the aerodynamic surface. All fabric is a lifed component and will, due to exposure
to heat, dust, moisture and especially UV light, gradually weaken until it can no longer be consideredairworthy.
Fabric can be divided into two classes. The older cotton fabric which is tensioned on the airframe by the useof tautening dopes (dopes which contract as they dry removing the slack from the fabric) and the more
modern polyester fabrics which shrink onto the airframe after heating. Cotton in regular use has a life of 7 to
10 years, whereas the heat-shrink fabrics seem to last at least twice as long.
Inspecting fabric requires significant experience to determine whether the strength has degraded to the point
where the fabric requires replacement. Signs that the fabric is nearing the end of its life include:

15.5

a.

Loss of tension.

b.

Permanent dimples introduced by a solid push with the thumb.

c.

Cracks in the paint surface.

d.

A slight tearing sound when the fabric is loaded with the thumb.

METAL CONSTRUCTION
Sailplanes constructed from metallic materials exhibit different failure modes than those constructed from
FRP or wood. This is because metals tend to exhibit ductile failure. Materials which have ductile failuremodes have a limit load and if the loads in the part are less than this it returns to its original shape but if it isloaded to more than its limit load if takes on a deformation which remains after the load is removed.

15.5.1RIVET FAILURE
When a sailplane constructed from sheet aluminium is overloaded, it is common for the rivets that attach onepart to another, to fail. If the load is high enough, the rivet will fail completely and fall out of its hole. If theload is less than that required to completely fail the rivet, the heads of the rivet will remain in place but the
rivet may be damaged such that its strength is significantly reduced. This can take the form of tilting of therivet head or partial shearing through the shank.

Figure 15-3

Tilting Of Rivet Head

Figure 15-4 Partially sheared rivet
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In addition to overloading, rivets may loosen and move in their holes. This is known as a working rivet.
Because the rivet moves in the hole the internal surfaces rub against each other which continuously
removes the protective oxide coating. The removal of the coating allows corrosion to occur and the corrosion
products form a black ring around the rivet head.
A certain number of working rivets is allowed but the actual number varies from type to type and with theposition of the rivets on the sailplane. For this reason the sailplane’s Maintenance Manual should be
consulted to determine the maximum number of working rivets allowable at any location.

15.5.2

FATIGUE CRACKING
Metallic materials, much more than other materials, are prone to fatigue cracking. These cracks are a resultof repeated loading of the part and are most likely to occur at holes and cut outs as these increase local
stresses to many times what the material would experience if the discontinuity was not there. Fatigue cracks
are usually very fine and the non-destructive testing methods of Section 1.22 are well proven methods offinding these cracks.

Figure 15-5 Fatigue Cracks Initial Stages

Figure 15-6 Final Stages Of Fatigue Cracking
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15.5.3BUCKLING
All thin materials can fail by buckling, however aluminium based materials are more likely to take on apermanent set after buckling because they are ductile. The change of shape after a structure has nonelastically buckled causes a significant reduction in the strength of the part as it is no longer correctly aligned
to take the load. Aluminium structures must be carefully inspected for creases and wrinkles which may havebeen caused by buckling. If buckling is detected the internal structure requires careful inspection as frames,
ribs, bulkheads or stiffeners may have been damaged.

15.5.4INTER-RIVET BUCKLING
Buckling on a small scale can occur between rivets causing corrugations in the metal.

Figure 15-7 Inter-Rivet Buckling15.5.5CORROSION
Metallic materials are susceptible to corrosion however the degree of susceptibility and the type of corrosion
depends on the type of metal and the alloying elements which have been added to produce the desired
material properties.

15.5.5.1 STEEL
Steel is an alloy of iron and carbon. When it corrodes, the iron combines with oxygen in the presence ofwater to form iron oxide which is the familiar red powder seen on rusted steel. Iron oxide is a crumbly,
porous material which retains water and allows the corrosion process to continue.
Small surface corrosion of steel can be tolerated provided the surface is repaired. The old paint should be
removed and the rust treated with a rust converter (phosphoric acid). The paint must be renewed toprevent the rust returning. Large areas of corrosion require replacement of the component.

15.5.5.2 ALUMINIUM
The most common aluminium used in aircraft structures is an alloy of pure aluminium and copper.
Aluminium is very easily corroded forming aluminium oxide. Fortunately, aluminium oxide bonds very well tothe underlying metal and provides a protective coating which prevents further corrosion.
Pure aluminium produces the best oxide coating therefore aluminium alloys corrode more readily than purealuminium. To take advantage of this many aircraft are manufactured from Alclad where a thin layer of purealuminium is coated onto the stronger alloyed aluminium so providing improved corrosion resistance.
The most common form of corrosion seen on aluminium sailplane skins is pitting corrosion which starts witha small defect, often a stone chip, which disrupts the protective coating and allows corrosion to start. The
newly formed surface layer will be imperfect and so corrosion can grow at this spot.
While aluminium and copper (plus a few extra trace elements) is the most common alloy for sheet metal, thelarger aluminium parts such as spar caps and fittings are manufactured from different alloys. These parts areoften extruded and need to be stronger, because of the concentrated loads, than the copper alloys. Typicalalloying materials are magnesium and silicon.
These alloying elements and the extrusion process which is commonly used to manufacture the part, results
in a susceptibility to exfoliation corrosion. Exfoliation is corrosion between the grains of the material and ischaracterised by swelling of the material as corrosion products form a white powdery dust.
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15.5.6FAILURE OF STEEL TUBES
Steel tube structures fail in a number of ways. They can gradually deform over time which changes the angle
between the wings and the tailplane. This can have a significant effect on the controllability of the sailplaneand may make the level reference used for weighing invalid.
Steel tubes subject to high compression loads can fail by forming a bulge adjacent to a cluster joint. Thesebulges require special inspection, especially following heavy landing as they are difficult for the untrained
eye to spot. The tubes appear to be normal to a casual inspection and only careful inspection of eachjunction will reveal their presence.

15.6

METAL FITTINGS
The inspection techniques for metal fittings do not differ significantly from the techniques for other metal
airframes except that the area where metal fittings attach to timber or FRP structures are often a weak point.
Points to look for include whitening of the surrounding FRP, loose bolts, crushed timber and cracking of thefittings.
Spigot pins are constructed with a taper to aid in assembly of the parts and these can be damaged by
misaligned bearings during the assembly process. When next assembled the damage marks on the pins cancatch on the bearings, knocking them out of alignment and making rigging difficult. Any ridges or burrs on
the pins should be dressed out with a fine file and emery cloth paying special attention to ensuring thesurfaces the bearings normally bear on are not damaged. The use of extreme pressure grease isrecommended.
Spigot pins are subject to wear, especially if play is excessive. Check for this by noting the fore and aftwingtip play on the assembled sailplane. Be prepared to replace worn spigot pins when necessary.

15.7

REFERENCES
ANC 18. Design of Wood Aircraft Structures. Aircraft Committee Munitions Board, 1951.
Acceptable Methods, Techniques, and Practices, Aircraft Inspection, Repair & Alterations, U.S. Departmentof Transportation, FAA, 1998.
Military Standardization Handbook. Metallic Materials and Elements for Aerospace Vehicle Structures.
Department of Defence, Washington DC. 1983.

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16.

TOW RELEASE MAINTENANCE

16.1

INTRODUCTION
This chapter specifies the GFA Standard System of Maintenance for tow releases in sailplanes andtowplanes. MOSP 3 Sections 13.3 and 23, and this section of BSE replaces previous GFA ADs 277 and293. It takes precedent over release manufacturer’s manuals. It does not take precedence over the aircraft
Maintenance Manual or all other applicable ADs – these cover the specific installation which may requiredifferences. However, the servicing and overhaul of the releases must be done according to this procedure
for Australian sailplanes and towplanes.
Sections Error! Reference source not found. to Error! Reference source not found. are backgroundabout releases. Sections Error! Reference source not found. onwards are the test procedures previously
specified in AD 277 and AD 293. But note there are slight differences.
Significant changes in this version from the ADs and previous BSE:a.

Common testing regime for Tost and Tost-like releases. GFA has decided to use the same testing
regime for all releases. Because TOST is the most common and best developed, we have decided touse TOST documentation and added consideration for the dusty Australian conditions.

b.

Mandatory requirement to change Tost main springs in releases is now defined in MOSP 3 Section
13.3.

c.

Revised acceptable value criteria for tests 2 and 3. We have changed to the current TOST manual
specifications and made them more logical.

d.

Revised Test 4, now tests the back-release operates within a specified angle range when under agiven tow load. Previously in AD277 it measured the force of the load required to activate the backrelease at a given angle – this was not what TOST intended.

e.

GFA has confirmed TOST specification values and changed to these. There were slight variations
which new TOST components may not have met.

This chapter does not apply to the following release types:f.

Blanik: Blanik sailplanes usually have Blanik branded releases which are to be maintained according
to the manufacturer’s documentation. See GFA AD 015 which still applies.

g.

Schweizer: Schweizer sailplanes usually have Schweizer branded releases which are to be
maintained according to the manufacturer’s documentation.

Other types of releases not able to comply with the procedures described in this chapter must request
approval from the GFA CTO for their use and their maintenance regime.

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16.1.1TERMINOLOGYThis chapter uses the following terms extensively:

16.1.2

Actuation force

The force, when applied directly to the release lever arm
attachment point, that is required to activate the release.

Pilot actuation force

The force that the pilot exerts in the cockpit to activate therelease. It includes any force required to overcome friction in
the release control circuit.

Tow load or force

The force exerted on the beak of the tow release by the tow
or test ring.

Units

A multitude of units are used. BSE uses kgf (kg force ie theforce exerted by 1 kg mass subject to gravity).
CAO 100.5 uses N (Newton is a force unit ~ 0.1kgf.) and kN
which is ~ 100kgf.
TOST uses daN which is 10N ~ 1kgf.
These are approximate as the unit of gravity relates to themand is not exactly 10 m/s2, it is 9.8 m/s2. But for our uses, 10
m/s2 is good enough.

±A range of values is specified X±Y. this means any value
from and including X-Y to X+Y. eg, 7.5±1.5 is 6.0 to 9.0 or+83o±7o is 76 to 90o. Y is the tolerance.

WHO MAY INSPECT, MAINTAIN AND TEST TOW RELEASE MECHANISMS
Daily Inspectors must inspect releases installed in aircraft prior to the first flight of the day.
Testing and servicing of tow releases and associated control circuits shall only be conducted by, or under
the direct supervision of, persons with a GFA Annual Inspector maintenance authorisation.
The GFA has approval from the manufacturer to carry out maintenance on Tost releases, as long as their
supplied parts are used, thus meeting their requirements without having to send the releases to Germany.
GFA Annual Inspectors are authorised by CASA to overhaul towplane releases. Tow pilots are authorized as
detailed in CAAP 42ZC, Schedule 8 to remove and replace sailplane tow hooks. However any maintenanceof the release mounting or release control circuit must be undertaken by a certified LAME. Note that themaintenance and operation of the towplane releases must be in accordance with CAO 100.5 Appendix 1
Clause 12 as most towplanes do not have an exemption to CAO 100.5. (Only GFA registered sailplanes
currently have an exemption in total to CAO 100.5). By following this maintenance schedule CAO 100.5 will
be complied with.

16.1.3PURPOSE OF THE TOW RELEASE SYSTEM
The tow release system attaches the sailplane to a launching force that may be aero-tow, winch or auto-tow.
It transmits the launch force from the tow cable to the airframe. It enables the pilot to release the tow
rope/cable at his command.
The tow release system comprises the tow cable ring assembly, the tow release and the release control
circuit. To reliably operate, all components of the release system need to be of sound design, properly
cleaned, maintained in serviceable condition, inspected regularly and tested.
Releases designed specifically for winch launching (some time referred to as centre of gravity or C of G
releases) include an automatic back-release function to ensure the sailplane does not inadvertently progressbeyond the normal top of climb with the cable attached.

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16.1.4

MANUFACTURERS OF RELEASES
By far the most common tow release device used on sailplanes in Australia is the Tost release, of which
there are several models.

Tost E85 aero tow release assembly

Tost Winch launch release assembly withback-release.

Figure 16-1 Tost Releases
The 2nd most common release is the Ottfur OM100 series, which was original equipment in many older
British sailplanes. The Ottfur was originally manufactured by Vickers in the UK and then from 1990 until
2005 by Cair Aviation also in the UK. The mechanisms are very similar to Tost.

Ottfur OM100 Type D

Ottfur OM100 Type E

Figure 16-2 Ottfur Releases
Other makes of release sometimes found on older sailplane types are:a.

Blanik - Blanik sailplanes were manufactured with a Blanik specific release.

b.

Davies - Small numbers possibly still in use. Similar to Tost.

c.

Bennet - Small numbers possibly still in use. Similar to Tost.

d.

Schweizer - These releases use a very different method of capturing the tow ring, locking andtriggering release compared with Tost like releases.

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Schweizer release on a sailplane

Schweizer release on a tow plane

Figure 16-3 Scweizer Releases
Fitting a release of a different type to that specified by the sailplane’s manufacturer is considered amodification and approval must be obtained from the GFA CTO who can arrange an Engineering Order.

16.1.5AIRCRAFT FITTED WITH TWO RELEASES
Many sailplanes are fitted with both nose and belly releases. As they are connected by a common control
circuit, a malfunction in one may affect the operation of the other.
At annual and periodic inspections, if both releases are connected in the circuit then both releases must be
serviced/overhauled, even if one has not been used for launching since last overhaul. This is because theunused release is still considered as in service and its performance may be degraded by dirt, use andoperation of the release control circuit will actuate the release and fatigue the spring.
In some cases, it may be decided to remove a release that is not being used and alter the control circuitaccordingly. In which case AIRW-15 Schedule of Permissible Unserviceabilities must be complied with.

16.2

RELEASE PRINCIPLES: OVER-CENTRE & CAGED
It is important to understand the two main design principles that make these releases function: over-centre
and caged.

16.2.1

OVER-CENTRE
The hook locking action and unlocking action is described and shown in diagrams below:

LockedIn the locked position, (C) has
gone "over-centre", ie it has"crossed over" the straight line
between A and B.
In this configuration, the cable
can be pulled as hard as isdesired and the mechanism
will not "unlock" because thecable load locks themechanism harder against thestop.
The location of the stop
determines the "degree ofover-centre". This is adjustableusing a screw in somereleases.

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Open
To open the release, the pilot
rotates the mechanism fromthe "over-centre" position,
through "centre", to "open".
Once past "centre" the tow
cable load will continue theopening action assisting thepilot.

The mechanism is pushed into an over-centre locked state initially by the release mechanism’s main spring.
Then when subjected to a tow load on the beak, a resulting force further acts to maintain the over-centre
position.
The pilot actuation force (as required by the pilot in the cockpit) to unlock the mechanism is thus proportional
to the tow cable/towrope load and the amount of “over-centre”, plus the main-spring tension and friction in
the release control circuit.
It is important to understand how the position of the stop affects the pilot actuation force required:

16.2.2a.

Too much over-centre: This will result in a high pilot actuation force being required to achieve
release, especially at high tow cable loads. The pilot actuation force must be reasonable and suchthat a low strength pilot can operate the release up to the maximum tow cable load (as determined by
the weak link used).

b.

Too little over-centre:
This can result in a "hair trigger" release which requires little pilot actuation
force and can make the release sensitive to dirt and main spring tension. This has resulted innumerous uncommanded releases whilst under tow.

c.

Correct over-centre:
tow cable load.

This creates a reasonable level of pilot actuation force even with a maximum

CAGED
The purpose of the cage is to ensure the force on the beak during a tow is always longitudinal to thesailplane. Ie no sideways pull is experienced by the beak.
Some older sailplanes are not fitted with a cage built into the release but rely instead on two angle pieces
located on the skin of the sailplane to act as a cage. These can become worn down because of wheel up
landings. The angle pieces must be installed to the dimension shown in the manufacturer’s documentationand parallel to each other for proper release function.
In most releases designed for aero-tow, slots in the side plates of the mechanism body form jaws on eitherside of the beak to position the ring in the correct position for the beak to hook over.
With an automatic back-release as used for winch launching, the jaws are usually part of the moving cage.
As the sailplane is towed aloft, the angle of the rope relative to the fuselage longitudinal axis increases,
causing the cage and jaws to rotate. At a designed angle and minimum load, unless a commanded releasehas already occurred, the ring is effectively swept off the beak by the moving jaws and the ring is released.

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Figure 16-4

16.3

Release Components (belly release with automatic back-release)

RELEASE CONTROL CIRCUIT
The release control circuit consist of cables, Bowden cables (ie cables in tubes/sleeves) and sometimes
rods, pulleys or U-tubes to transfer the pulling force of the pilot to the release lever. Some sailplane
manufacturers vary the release operating lever length so as to change the operating force. Or include pulley
returns etc. The problem is the extra friction and lever arm that may prevent the release closing properly.
In some instances the sailplane manufacturer may have included in the control circuit an additional spring toensure the mechanism always returns from the release state to locked state properly.
The release control circuit must allow full travel of the release mechanism. In the closed position, the releasemust lock (over-centre) and in the open position the hook beak must fully retract into the casing. The releasecircuit must therefore have some ‘dead movement’ to ensure it does not hold open the release.
The release control circuit must not introduce too much friction. Excessive friction can stop a release closing
properly or cause it to be inoperable under high tow load. The level of friction can change whilst in service
due to loss of lubrication or dirt ingress, and therefore regular maintenance checks are necessary.

16.3.1COMMON RELEASE CONTROL CIRCUIT ISSUES
Faults in the release control circuit can cause the release not to fully lock. The most common issues are:a.

Control cable too short preventing the release mechanism from going fully over-centre and locking.

b.

Bad guidance of control cables (particularly Bowden cables) casing excessive friction that the main
spring cannot overcome and thus the release fails to close and lock.

c.

Too little return (pull-back) force due to worn out or broken release main spring. Perhaps even thewrong spring.

d.

Binding in the control mechanism, eg. a bolt being used as a pivot point has been over-tightened
causing a clamping action on a component that should swivel or a cable has come off a pulley.

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Example issue (Ref Airworthiness Alert 2015-2)

Multiple uncommanded releases experienced
on a nose hook installation fitted to a new ASK
21 Mi sailplane.
It was found that the bolt with nyloc nut
attaching the pulley system to the Tost lever(shown in photo) was too tight causing binding
just prior to the release fully closed position.

Figure 16-5 Example of a Release Issue
A few other examples of other issues that have occurred:e.

A jammed open belly release, full of dirt, allowed a shackle on the slack operating cable to swing overand the thimble to catch. This in turn limited the operating movement on the nose release preventing itfrom opening fully.

f.

A yellow release knob on a cable that was too long became jammed in the control column in the rear
cockpit seriously reducing aileron movement.

Example issue (Ref AWA 2007-2)
Duo Discus release control cable damaged
at exit of Tee-handle.
The failure was not easy to detect as thebroken wires were effectively shielded fromeasy view by the protruding steel swage atthe base of the release handle.

Figure 16-6

16.3.2

Example of Release Knob Issue

INSPECTION AND MAINTENANCE OF RELEASE CONTROL CIRCUIT
During Annual Inspection and following any maintenance of the control circuit:a.

Inspect cables for corrosion, wear and fatigue.

b.

Check pulleys for signs of jamming, bearing condition and correct caging.

c.

Cleaned and lubricated cables, rods and levers at their connecting points and pivots.

d.

Check the entire circuit is reasonably free of friction. Check for misalignment of pulleys, displaced
fairleads and rods or levers fouling on other structures.

e.

Adjust the release control circuit to allow full travel of the release mechanism. Cables must have atleast 10mm of freeplay when the release is locked.

f.

Check the pull knob or handle is securely attached to the control cable and is clearly yellow in colour.

g.

Where two releases are fitted and operational, make sure they both lock properly and that both hooks
retract fully.

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When replacing cables, make sure that cable joining sleeves, turnbuckles and shackles do not foul or cause
other problems.
Some operating circuits are quite complex. A sailplane fitted with two releases and having two controls (onefor each seat) will need careful checking and adjustment and should be tested in all operating positions.

16.4

TOW RELEASE CLEANING, SERVICING AND OVERHAUL

16.4.1REGULAR CLEANING WHILST INSTALLED
During operation, the release is often exposed to dirt, especially if operating from gravel runways and duringout-landings. Because Australia is dry and dusty compared to European grass runways, it is necessary toclean and check our releases more frequently than European manufacturers specify.
The best method of cleaning the release whilst fitted in the aircraft is with compressed air and a brush, while
operating both the hook and the back-release mechanism.
Be very certain that a sluggish back-release action is actually dirt and not due to a deteriorating return springor other mechanical binding. This is a very common mistake.
Excessive lubrication may create a build-up of dirt which may cause excessive friction or prevent full travel ofcomponents. Dust may combine with the lubricant to form a grinding paste which makes wear more rapid.
It may be necessary to use suitable solvents if there is an accumulation of oily dirt and then relubricate
sparingly. TOST recommend WD-40.

16.4.2

ANNUAL SERVICE
Servicing of tow releases consists of cleaning, inspection, lubrication and testing. It can often be
accomplished without having to remove the release from the aircraft and does not always require stripping
the assembly.
If an AD requires maintenance action or faults/suspicions arise from the service, then the release will need
to be removed from the aircraft and overhauled as detailed in the next section.
At each Annual Inspection, or every 250-Hour Inspection for high use sailplanes, if more than 200 launches
have been completed since the last service, then the following servicing must be completed:a.

Check the GFA, the sailplane manufacturer’s and the release manufacturer’s or National Aviation
Authority websites for any ADs relating to the type of release being serviced – they are mandatory.
Service Bulletins may give useful advice.

b.

Clean the release as described above. Consider removing the release from the airframe anddisassembly to allow deep cleaning which may prolong life. If friction continues to inhibit operation
then disassembly is required.

c.

Operate the release to feel if the main spring is broken or feels weak. In most cases the main spring
has to return the control circuit as well as lock the release and therefore is a relatively firm spring.
Release spring performance is affected by breakage, wear, loss of tension, corrosion and dirt
contamination. Perform the tests as detailed later in this chapter.

d.

Inspect the hook beak.

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i.

Tow cable rings tend to wear the hook beak and jaws which can become grooved or burred.
This can make it difficult to operate the release under load, or else the tip can become roundedoff causing premature release.

ii.

The profile of the hook beak must be such that as the hook rotates it will enable the towing ring
to move out of the release.

iii.

On some types of release the original profile can be returned by careful filing or grinding
providing sufficient material remains. However, if the hook is case hardened and the hardened
surface is worn through, the part is no longer serviceable.

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Figure 16-7

Figure 16-8

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Figure 16-9e.

Beak Profile Diagram – Casing Type Ring Retention

Check the jaws have not become excessively worn by the ring with repeated use (see picture below).
Excessive wear of the jaws can mean the ring is not held in the correct position so the beak may notengage the ring fully. With extreme wear, or use of undersize rings, the ring may slip out causing an
uncommanded release. In some cases it may be possible to build up with weld and file to the original
dimension; but usually a replacement release or new part will need to be obtained.

Figure 16-10 Jaw Wear Inspectionf.
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16.4.3

OVERHAUL
Tost releases require the main spring to be replaced at intervals described later on. When the spring is to be
replaced, the release must be given an overhaul.
Non-tost releases do not require spring replacement at overhaul unless it fails the tests. However, 2,000
launches is a recommended interval to replace the spring and give it an overhaul.
Overhaul involves: removal from the aircraft, testing, disassembly, cleaning, inspection, repair or
replacement of worn or faulty components, lubrication, re-assembly, testing and refitting in the aircraft.
With TOST, these days, it is probably better to obtain a new exchange release from TOST if the beak, jaws
or cage are excessively worn. GFA only keep the common replacement parts, springs, because GFA is the
only approved maintenance organisation. TOST suppliers in Australia keep exchange releases and someparts.
Procedure:a.

Some types of release have multiple mounting holes and use different length bolts in specific holes.
To ensure correct refitting to the aircraft, mark the mounting position before removing the release.

b.

Before dismantling, mark the parts first and/or take photographs to aid reassembly. On many releases
the toggle link and bell crank are reversible and as the limit stop usually contacts one of thesecomponents, a potential problem arises if incorrectly reassembled. It is often best to remove thelinkage mechanism from the casing and clean and lubricate the pivots with the hook, toggle link andbell crank left attached to each other.

c.

If the release includes a back-release mechanism, it can be removed and cleaned separately.

d.

Wash all components in solvent to clean them. Check all components, especially pivots and bearings
not normally visible, for wear. Excessively worn parts will need to be replaced.

e.

Lubricate the mechanism components lightly before reassembly. TOST recommend WD-40. Somereleases can be tricky to re-assemble and any extra lubrication will quickly get on your hands and allover the release making the job even more of a challenge.

f.

After any overhaul activity involving disassembly, the over-centre locking and main spring tension
must be tested and in accordance with Tests 1 and 2 described later, plus Test 4 if it has a backrelease.

g.

Most GFA approved releases rely on over-centre locking and on some types the amount of overcentre can change through incorrect assembly. Examine your pre-dismantling notes and photographs
and conduct the required tests – get it right!

16.4.3.1 REASSEMBLING TOST RELEASES
Reassembling Tost releases requires a few tools such as spanners, screwdrivers etc plus a vice with soft
jaws (aluminium pieces between the vice jaws and the release to protect the casing) to securely hold the
body of the release. A small amount of wire is also useful to make loops to hold the spring ends.
There are a number of different techniques for installing the main spring. Many inspectors who do a lot of
inspections make up specialised tools to make the reassembling of the release easy. Australian Gliding
magazine published details of such specialised tools in September-October 1998. These are republished at
Appendix C.
The following method has been used successfully and has the advantage that no special tools arenecessary:a.

Assemble the release up to the main spring and bell crank fitting stage, leaving the hook pivot bolt out.

b.

Grip the casing in a vice (be careful not to crush it) so that the hook pivot hole is accessible.

c.

Manoeuvre the mechanism (through the hook pivot hole) so that the bell crank can be lined up with its
pivot hole - try a dry run without the main spring.

d.

Mount the main spring on the bell crank and slip a loop of lock wire around both ends of the spring.

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Hook a screw driver under the loop and lever the spring ends up as the bell crank is pushed into thecase.
When installed correctly, actuating the mechanism tightens the main release spring. It is possible to get it
wrong, so take care. The correct orientation is depicted in a diagram earlier in this chapter.

16.4.4

REPLACEMENT OF THE TOW RELEASE ASSEMBLY
If a new or reconditioned release is to be fitted to the sailplane, it should be inspected and tested before
being installed and adjusted if necessary.

16.4.5AIRCRAFT NEW TO THE AUSTRALIAN REGISTER
During the first GFA survey inspection, used release assemblies (ie >200 launches) are to be tested inaccordance with the maintenance requirement for the type fitted. New releases need not be tested if they
arrive with a Release Note (RN) from the manufacturer, in which case the RN number is to be recorded in
the inspection documentation.

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16.5

RELEASE TROUBLESHOOTING GUIDESYMPTOM
Uncommanded
releasePROBLEMPOSSIBLE CAUSE
Dirt in release

Clean release

Excessive friction in
operating circuit

Inspect and overhaul ifnecessary

Operating circuit
restricting releaseclosureCheck for control cables longenough, catchingsleeves/turnbuckles, seizedpulleys, etc. Adjust if
necessary

Main spring weak or
brokenReplace main spring

Release not set overcentre

Overhaul, load test andadjust if necessary

Ring thickness not to
specification

Replace with new ring

Worn jaws and/or cage

Replace release mechanism

Hook beak tip worn

Repair or replace

Back-release spring
weak or broken

Replace back-release spring

Hook beak tip worn

File or grind hook beak tocorrect profile or replace
hook

Under tow load,
the release did notrelease eventhough knob pull
to stop'False stop' encounteredbecause of wear in jaws
and grooving in hookbeak preventing beaksliding over ring

File or grind hook to correct
profile or replace hook. Build
up worn areas of jaws andfile to original shape orreplace component

Pilot unable toapply enoughforce to operate
release

Release set too far
over-centre

Conduct over-centre test
and adjust as necessary

Excessive friction inrelease circuit

Inspect, repair and lubricate
circuitInsufficient leverage inoperating circuit

Modify system - Consult
RTOA/CTO

Release notlocking

Ring pulls out
whilst release islockedBack-release (iffitted) not holding

Hang up underload

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16.6

SPRING REPLACEMENT

16.6.1TOST MAIN SPRING REPLACEMENT IN SAILPLANES
Tost Technical Notice No TM 1-2001, removed the requirement for 4-yearly overhaul and mainspring
replacement of its releases and instead based the replacement requirement on 10,000 actuations. Since
each launch usually involves multiple actuations, the overhaul interval for sailplanes is specified by Tost as a
maximum number of launches. Since sailplanes used for training typically use more actuations per launch,
Tost has specified a lesser interval for training sailplanes.
Tost releases shall be overhauled and the main spring replaced at the following interval after a new main
spring is fitted:
1,250 launches

All sailplanes used mainly for training (ie most two-seat sailplanes)

2,000 launches

All other sailplanes

Contact GFA Office for details of how to obtain replacement springs.

16.6.2TOST MAIN SPRING REPLACEMENT IN TOW PLANES
Tost has not provided a specification for tow planes other than the 10,000 actuations limit. Therefore
towplane registered operators should make their own determination of the time until next replacement based
upon the aircraft’s frequency of use for towing operations. If the use cannot be estimated, the spring is to be
replaced at the next annual inspection.
A typical example of consideration of the time until next spring replacement is:
Towplane is flown for 100 weekend days plus 10 day camp/course per annum = 110 days.
Assuming 5 release actuations per day gives 550 actuations per year.
Time to complete 10,000 actuations limit = 18.2 years.
As this is a rough estimate then halve the time to be careful.
Details of how the main spring life was determined should be recorded on the GFA form “Towplane Release
AIR F010” along with the test results to inform the LAME of the actions you have taken.

16.6.3

NON-TOST SPRING REPLACEMENT
For springs other than Tost main springs there is usually no guidance from the release manufacturer as tothe spring’s service life. Therefore it is acceptable to replace them depending on condition and notdepending on number of launches, actuations or hours. In other words, if a non-Tost spring is broken or fails
a test, then replace it with a suitable new spring. However this strategy does risk uncommanded releases
and thus owners are recommended to replace springs periodically. For uniformity, GFA recommends all
springs are replaced every 2,000 launches.

16.7

TESTING RELEASES
Prior to this version of BSE, the testing procedures for Tost and Non-Tost releases were different anddetailed in GFA AD277 and GFA AD293 respectively. With effect from 2017, the test procedure andacceptability criteria have been standardised in BSE, resulting in some subtle differences compared to pastpractices.
To maintain flight safety, tow releases used for all types of launching procedures must:a.

Be able to sustain the forces experienced during towing operations.

b.

Not be prone to uncommanded release.

c.

Release when commanded by the pilot, requiring a level of pilot actuation force that is within thecapability of all pilots likely to fly the aircraft for up to the maximum tow load the sailplane may
experience.

To meet these 3 requirements, each release assembly and control circuit must be properly designed,
installed, maintained and regularly tested.

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It is recognised that many of the "Ottfur", "Davies'' and other releases in-service, have historically had alarge amount of over-centre in their mechanical function, requiring significant pilot pull force to operate. Thatfeature can lead to the pilot having insufficient strength to operate the release under high towrope loads.
Compliance with these test procedure and the standards of acceptability will ensure ‘over-centre' travel isreduced and enhance pilot safety under high tow rope loads.

16.7.1BACKGROUND TO TESTING ACTUATION UNDER HIGH TOW FORCES
For safety reasons, the most important test for a tow release is proving that the pilot can activate a releaseof the tow rope using reasonable physical effort whilst the release has the maximum tow force applied.
Historically the test requirement has been specified in a number of different ways:
GFA AD277 specification for
Tost releases:

No specification for maximum pilot actuation force but:

Tost manufacturer’s operating
manualWhen the release hook is under a load of approx. 150 daN(150 kgf) you should still be able to operate the manual
release lever in the cockpit with the same force, ie, 7.5 ± 1.5
daN (7.5 ± 1.5 kgf.). (ref Tost E85 )GFA AD293 specification for
non-Tost releases:

20 kgf maximum hand load with a tow load equal to thesailplanes rated weak-link, or 450 kgf if not stated.

CAO 100.5“Pilot effort must be tested to ensure that it is less than 200N
(20 kg force) with a 4.5kN (450 kg force) load applied to therelease anywhere in a 30 degree cone.”(24 December 2015)
specification for tow planes:

6.75 kgf maximum actuation force at 450 kgf tow force (fromChart 1 of AD277). Note this is with release removed fromaircraft and no main spring which adds about 4kgf and so
effectively the force installed would be 10.75 kgf.

When one considers that the average human, when standing and leaning back, can typically only pull ahorizontal force of 30-40kgf and that this is enough to move a sailplane, then applying higher tow forces andanchoring aircraft is fraught with difficulty and risk. But by using tools and levers this can be done safely. Be
careful and do it correctly.
In practice it is impractical and unsafe to conduct a test with the release installed in the aircraft and with tow
loads of 450kgf, or even 150kgf, applied by pulling against the aircraft.
High tow load testing of sailplane Tost releases in Australia has for a long time been conducted with therelease removed from the airframe and utilising the purpose designed GFA 450 Release Tester (newhydraulic or the older spring tester). This is a safe and practical means of testing a release’s integrity (ability
to survive without damage the applied load) and the over-centre setting.When combined with thoroughinspection of condition (wear and cleanliness) of the release and the control circuit, this method has proved
to be effective.
GFA has thus adopted the strategy that high tow load testing is to be conducted with the release removed
from the aircraft and installed in a suitable test rig (such as the GFA 450 Release Tester).
However, some actuation force testing is wise to ensure friction and actuation system errors are found andcorrected. This mainly occurs during design of aircraft but GFA have added a small amount of this testing as
below.

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16.7.2

THE GFA TOW RELEASE TESTSThe tow release test regime for all sailplanes and tow planes comprises using the following tests at various
times of maintenance:a.

Test 1: Over-centre. This test measures the actuation force required to activate the release at various
levels of tow load. When graphed, the data provides an indication of the level of over-centre in themechanism. The test also proves that release of the ring is achieved when commanded and that therelease’s beak can sustain a straight line pull of up to 450kgf without premature release. The test isalways conducted with the release removed from the aircraft and with the main spring removed fromthe release. The GFA 450 Release Tester (new Hydraulic release tester or the older Steel Stallion)
enables testing up to 450kgf which is sufficient to simulate the maximum tow load experienced bymost modern sailplanes.

b.

Test 2: Main Spring Stiffness. This test is to determine that the main spring is strong enough to return
the actuating mechanism to the closed position and exerts sufficient force to hold the mechanism
over-centre and thus locked at all times so as to avoid uncommanded release. (As required for tow
planes by CAO 100.5 Appendix 1 Clause 12.4c).

c.

Test 3: Pilot actuation. This test ensures the pilot is easily able to operate the release. It measures thepilot actuation force required to operate the release with no tow load force. (This is a Tost test
requirement). It also checks that with a small, humanly possible tow load that the pilot effort has notincreased significantly as it might if there was wear or excessive over-centre.

d.

Test 4: Back-release. This test confirms that the automatic back-release mechanism (if fitted)
activates within the specified angle range.

e.

Test 5: Pilot actuation force with release actuation force as for 450 kgf tow load. This test is for tow
planes only, to satisfy CAO 100.5, and ensures that there is not excessive friction in the control circuit.
When used with the results from Test 1, it tests that the pilot actuation effort does not exceed 20kgf
when the tow load is 450kgf (as required for towplanes by CAO 100.5 Appendix 1; 12.6

Details of how tests are performed and result acceptability criteria are described in later sections.

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16.7.3

SUMMARY OF WHEN TESTS ARE CONDUCTED AND SPRINGS REPLACED
A summary of when the tests are to be performed is shown below. Details of the tests are provided in later
sections.

Aircraft

Maintenance Intervals

Sailplanes

All releases: Annual Inspection when >200
launches since previous testing.

Tests 2 and 3

Non-tost releases: At every 2,000 launches
following last main spring
replacement.

Tests 1 and 2 to determine if main
spring ok- Remove release from sailplane,
overhaul and test.
- Replace main spring if faulty or fails
tests.
Tost releases: Following the stated numberof launches since last main spring
replacement,Trainers



Non-trainers 2,000 launches

Tests Required

Test 4 if back-release typeIf main spring replaced, repeat Tests 1
and 2
Test 3
Test 4 (if back-release)
Tests 1, 2, 3 and 4 (if back-release)1,250 launches- Overhaul the release, including
replacement of the main spring irrespectiveof condition.
Tow planes

Daily inspection

Test 2

Reoccurring maintenance at whichever ofthe following happens first:

Tests 1, 2 and 3(a) every 1,000 hours time-in-service;(b) every 12 months.
- Remove release from tow plane, perform
annual service and tests.
Tost release only:
Replacement of
release main spring at interval asdetermined by the Registered Operator inaccordance with 16.6.2 above.

Tests 1, 2 and 3- Remove release from tow plane, perform
overhaul, replace spring and test.

16.7.4LOGBOOK AND MAINTENANCE RELEASE ENTRIESWhen certifying compliance with the requirements of this chapter, the logbook entry should state:a.

“Release check as per BSE Chapter 16 version xx”, where “xx” is the version of BSE Chapter 16 used
as reference.

b.

“Tests 1, 2, 3, 4 completed”, as applicable.
i.

c.
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Next service due at next Annual Inspection if greater than XX launches” (where “XX” is the last
service launch count + 200).

If the main spring has been replaced, record:
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d.

i.

The source and tracking data (batch number etc) of the replacement spring.

ii.

The number of recorded launches at which main spring replacement is next due.

Any other action taken.

For example:“Release check as per BSE version 24. Tests 1, 2 and 3 completed. Next service due at next Annual
Inspection after xxxx launches. Main spring replaced, sourced from GFA, batch XYZ. Main spring due next
replacement at yyyy launches”.
The future required maintenance that may be required during the year is to be recorded in the MaintenanceRelease. For example:

Item
No.

Recurring Maintenance Items

Due dateor time inservice1

Release main spring due next
replacement at

yyyy
launches

Maintenancecertified byDatecompleted

The spring replacement requirement is before 10,000 actuations and therefore may be required before thenext annual inspection. At Annual Inspection it is wise to consider if the spring may expire before next
annual and replace it early to avoid hassles. It is a low cost item.

16.8

CONDUCTING THE TESTS
Always check to see if a new AD has been issued on the topic before commencing tests.
The following procedures are derived from both manufacturers’ specifications and local research. There may
therefore be variations if direct comparison is made with manufacturers’ publications.
Use the form at Appendix B to record the test results. A completed copy of the form should be retained withthe sailplane maintenance records.
Before commencing any of the tests:

16.8.1a.

The tow rings used for the test must be dimensionally the same as serviceable genuine rings as
specified by the release manufacturer.

b.

The release must be cleaned, inspected for wear (especially beak and jaws) and lubricated.

NOMENCLATURE
Throughout this chapter the following terms and names are used:Term
X axisDirection of flight

Y axisSpanwise direction

Z axis

90° to the direction of flight (up)P

Actuating Force on lever (kgf)P

Spring return force (kgf) to close it again

Q

Load applied to beak (kgf)lLever arm (standard arm has 68 mm lever distance but varies from35 to 120 mm on different sailplane types).

R

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Figure 16-11 Typical Aerotow Release

Figure 16-12 Typical Winch Release

16.8.2NON-STANDARD LEVER ARM - CONVERSION OF FORCE READINGSThe interpretation of the data assumes that the lever arm is 68mm, which is the most common length. If thelever arm of the release, or the total effective lever length created by an attachment specific to sailplane
type, extends the lever then a conversion to the equivalent force must be made. The calculation is madeusing the following formula:
Equivalent force = measured force x (lever length / 68)
Example: A 3.3 kgf spring balance reading on a 140mm lever is equivalent to:Equivalent force = 3.3 x (140 / 68) = 6.8 kgf on a standard 68 mm lever.

16.8.3

CALIBRATION OF SPRING BALANCES
Spring balances used for tow release tests must be checked and adjusted for accuracy before being used
for any tests. They are calibrated by adjusting the scale to read the correct mass of a known object such as.
a.

The GFA 450 Release Tester has its weight stamped on it (around 5 kg).

b.

For the lower end of the scale, a plastic bucket with a couple of measured litres of water can be used.
Noting that 1 litre of water has a mass of 1kg.

Since Force = Mass x Acceleration, then the force exerted by the acceleration due to gravity on 1 kg is 1x
9.8 kgf or 9.8 Newtons (which is 0.98 daN) and is correctly termed 1kgf (kg force).

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16.9

TEST 1: OVER-CENTRE
This test measures the actuation force required to activate the release at various levels of tow load. Whengraphed, the data provides an indication of the level of over-centre in the mechanism. The test also provesthat release of the ring can be achieved when commanded and that the release’s beak can sustain a straightline pull of up to 450kgf without premature release.
This test is performed with the release removed from the aircraft and with the main spring removed. The
spring is removed to avoid variability of the spring and the release has to be dismantled anyway to replace
the spring and possibly adjust the over-centre.
The test is intended to be performed using a GFA 450 Release Tester (either the new Hydraulic releasetester or the older Steel Stallion) which is a GFA purpose designed device for holding the release andapplying a calibrated tow load up to 450kgf. These are available in large clubs or on loan from RTO-As.
Annex A to this chapter details how to use the GFA 450 Release Tester and how the GFA 450 Release
Tester is calibrated.

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16.9.1TEST 1 PROCEDURE
Step

Actiona.

Remove the release from the aircraft. Disassemble, clean, inspect and lubricate the release.
Re-assemble, ensure all body nuts/bolts are tight and only the main spring has been
removed. Secure the GFA 450 Release Tester in a bench vice.

b.

Check that the mechanism has some over-centre otherwise the release may open when theload is applied. To test, pull on the beak with the fingers and move the lever arm. The levershould move about 5 mm before the release can be opened by the beak.

c.

Install the release in the GFA 450 Release Tester and apply a load Q of 200 kgf to the beak.

d.

Measure the actuation force “P” required to open the release using a spring balance attachedby cord and acting at an angle of 90° to the actuating lever.

e.

If the actuating lever is not the standard 68 mm lever, then determine the “equivalent force”
using the formula and plot the result on release test Chart 1 using the equivalent force.

f.

Repeat steps 3, 4 and 5 using a Q of 300 and 400 kgf. The actuation force “P” required
should increase with load.

g.

On Chart 1, plot the three test result points and draw a straight line of best fit through them. If
the results are not close to a straight line the release should be carefully inspected for otherfaults.

h.

The line of best fit should remain within the unshaded area on Chart 1 within the Q range of200-400 kgf. If necessary adjust the over-centre and repeat the test until acceptable results
are achieved.

Note: On the hydraulic tester 100kg load = 1,000kPa on the hydraulic gauge. It has been manufactured togive this 10:1 ratio and convert the units.

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16.9.2TEST 1 CHART

Tow Release Test Chart 1 (no spring fitted)
9.0

Actuation force on 68mm lever (kgf)

8.5
8.0

Too much over‐centre

7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5

Too little over‐centre

2.0
1.5
100

200

300

400

500

600

700

Load on beak Q (kgf)
16.9.3

INTERPRETATION OF TEST 1 RESULTS
ResultReasonRelease opens immediately when the load
Q is applied

The release is not over-centre.

No increase in P as the load Q isincreased(ie the line of best fit on the graph ishorizontal or slopes down to the right)

The mechanism is on the centre-line but not over-centre
and therefore has “hair trigger” behaviour. The release isentirely dependent on the main spring for locking and isvulnerable to other factors, such as wear and vibrationthat may cause it to release. ** The amount of overcentre must be increased **Load P increases but is still below theminimum line on Chart 1

The release is over-centre but not enough to allow forpossible future wear.

Load P is above the maximum line onChart 1

Too much over-centre and the pilot may not be able tooperate the release in an emergency.

Note: If the beak has a groove the actuation force P will be high. If the tip of the beak is worn it will require alower actuation force P.

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16.9.4

WORKED EXAMPLE OF TEST 1 CHART

Tow Release Test Chart 1 (no spring fitted)
9.0

Actuation force on 68mm lever (kgf)

8.5

Too much over‐centre

8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5

Too little over‐centre

2.0
1.5
100

200

300

400

500

600

700

Load on beak Q (kgf)
Theoretically the lines would go through the zero point without a main spring installed but may be curved.
Don’t be concerned what may happen below 200kgf beak load. Reduce over-centre if the projection to
700kgf goes far above the line. The lines should be fairly straight, if not this may produce odd projections
and there may be other wear factors at play.

16.9.5ADJUSTING THE OVER-CENTRE
See Figure 16-4 which illustrates the internal construction of a typical release.

16.9.5.1 RELEASES WITH ADJUSTING SCREWS.
Unlock the locknut. Turn the adjusting screw with an 'Allen' key anticlockwise to increase over-centre andclockwise to decrease over-centre. The adjuster is fairly sensitive, half a turn being the difference between acorrectly adjusted release and one that is not.
If difficulty is experienced getting enough over-centre, check that the bell crank is not contacting the casing.
It may be necessary to relieve the bell crank in this area to utilise the adjusting screw.
Tighten the lock nut before retesting otherwise the screw may turn during the testing. Once testing iscomplete punch lock the screw to prevent it moving in service.

16.9.5.2 RELEASES WITH SUNKEN ADJUSTING SCREW.
To gain access to the screw it may be necessary to remove a cover plate. This can be done with a hammer
and a small chisel or punch. A special spanner will be needed for the sunken locknut. This can be madefrom a tube spanner cut down and a handle welded to it. Proceed as above.
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16.9.5.3 RELEASES WITHOUT ADJUSTING SCREWS.
To increase the over-centre on this model, remove metal from the bell crank where it contacts the casing. To
decrease the over-centre the bell crank must be built up with weld and filed or ground to suit. Be careful, it'seasier to remove metal than put it back on.

16.10

TEST 2: MAIN SPRING TENSIONThis test is to determine that the main spring is in good condition which means:a.

Strong enough to return the actuating mechanism to the closed position and exerts sufficient force tohold the mechanism over-centre and thus locked at all times so as to avoid uncommanded release.

b.

Not too strong, so as not to burden the pilot with excessive effort required to overcome it.

This test may be conducted with the release remaining in the airframe if access and space permits.
Step

Action1.

With the release in the aircraft or else removed and secured in a GFA 450 Tester or a bench
mounted vice. If the control circuit does not impede the test or affect the reading, it may
remain attached.

2.

Attach a spring balance via a cord to the actuating arm at the normal point of connection withthe release control circuit.

3.

With no load applied to the beak, apply a force P at right angles to the actuating arm to fully
rotate the lever through its arc. The spring force should increase as the actuating arm
rotates.
Check and record whether the spring force increases as the actuating arm rotates.
Gently relax and allow the arm to pull the spring balance until the release is closed.

4.

Measure and record force PR just before the release is fully closed.
The allowable PR is 2.5 to 5.0 kgf.

A force below the allowable may indicate a weak or broken spring is installed or that the spring is fitted
incorrectly.
A force above the allowable may indicate that a non-standard spring, which is too strong, has been fitted or
there is excessive friction in the release.

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16.11

TEST 3: PILOT ACTUATION FORCE
This test ensures the release fully closes and locks, and that the pilot is able to operate the release without
excessive effort. It measures the pilot actuation force required to operate the release with no tow load force
and confirms that with a light tow load, pulling through the normal operational arc, the release will let go of
the ring.
Step

Action1.

With the release fully assembled, fitted in the aircraft and fully connected with the normal
release control circuit:2.

Attach a spring balance via a cord to the cockpit tow release knob/handle
With no load applied to the beak, apply a force to the release knob in the cockpit until therelease activates, ie the ring will drop out

3.

Measure and record the maximum force that was required for the activation.
The allowable force is 6 to 9 kgf .

4.

If the sailplane has 2 tow releases connected, the maximum pilot actuation force to achieve a
release with the tow rope in either release must not exceed 17 kgf for any tow load.
If there is doubt repeat the test at Step 3 with an assistant applying a tow load of approx 25,
150, or 450 kgf (use a lever and spring balance to multiply the load or the GFA release tester
as described in Appendix A).
** Caution – warn your assistant the rope is about to be released. Setup the test with care to
avoid damage to personnel and aircraft – there is a lot of force involved at 150 or 450kgf. ** .

5.

Apply the spring balance pull to the release knob until the release activates. Measure andrecord the maximum force that was required for the activation.
Repeat the above with tow load pulls at 30 degrees either side of the centreline. This helps
check the condition of the beak and cage.
The allowable force in all situations is again 6 to 9 kgf.
Pull the release knob to its extreme limit of travel and gently allow the knob to retract under
the spring tension.

6.

Check and record that the knob does not foul with any of the controls and that it easily fully
retracts.
Measure the force at 68mm lever length at the release (or adjust to 68mm) at the point ofclosure while the knob is slowly released. It must exceed 1.5kgf as per TOST to safely close
the release. This test may be impractical in certain sailplanes and then a best assessmentthat there is more than 1.5kgf closure force is satisfactory.

7.

If the sailplane has 2 seats and two release knobs/handles, then repeat this test from thesecond pilot seat.

If the pilot actuation force with 25 kgf tow load is significantly different (>0.5 kgf) to that with zero tow load,then suspect that beak, jaws or cage are excessively worn. Or else that there is a fault with the control circuitor there is excessive over-centre.

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16.12

TEST 4: BACK-RELEASE
The purpose of this test is to ensure the release will automatically let go of the winch rope should thesailplane fly too far overhead the winch.
This test can usually be performed with the release installed in the sailplane but may be performed with it outof the airframe.

Figure 16-13 Back-Release Test Setup

Step

Action1.

Check that the cage is able to pivot and that there is sufficient spring force from the backrelease spring to hold the cage in the forward position.

2.

Apply a Load Q of 20kgf using a spring balance. Start initially with the load at a small angle to
the X-axis and then progressively increase the angle.

3.

Measure and record the angle at which the back release activates.
It must activate at an angle of

83 ± 7° ie 76 to 90°

Failure of the back-release to automatically operate in the specified angle range indicates a fault which couldbe:a.

A high level of friction or jamming due to dirt, insufficient lubrication of pivots or possibly overtightening of the release securing bolts.

b.

Wear of the beak, jaws or cage.

c.

An over-strength back-release spring

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Appendix C GFA 450 RELEASE TESTERThe GFA 450 Release Tester is a device designed to load tow releases to simulate a range of towing forces
for testing purposes. It is used with a spring balance, which measures release actuation forces.

Figure 16-14 GFA 450 Release Tester, new Hydraulic version
Dean Hill made the first hydraulic tester after the stallion was being used and because it was so violent due
to the big spring. Dean agreed GFA could make it.
Also still in service and acceptable for these tests, is the earlier GFA spring tester usually called a “Steel
Stallion.

Figure 16-15 GFA 450 Release Tester, old Steel Stallion
Articles are available from GFA comparing these and showing them compatible. Both can test releases in orout of the aircraft. These days we consider the new hydraulic version is better in all ways.
The Steel Stallion can test releases in situ in most cases. The front adapter is unbolted and the end of thetester bears on the TOST release ring. By propping it up it can test moving or unmovable cage releases. But
beware it jolts the sailplane/ towplane and is violent at high loads.
A new front adapter would be required for the hydraulic version to test in the same way in situ.

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C.1

WARNING OF DANGER
Forces of up to 450 kgf can be applied when using the GFA 450 Release Tester so it is essential that safety
precautions are taken.
When using the tester in a bench vice, it is not necessary to touch the tester when the release is operated so KEEP CLEAR.
Avoid physical contact with the end of the tester as injury could result.

C.2

BENCH TESTING RELEASES
Grip the GFA 450 Release Tester in a bench vice. Attach an adapter appropriate for the release to betested. Mount the release in the adaptor in appropriate set of holes and tighten bolts. Because ofinterference with the adaptor it may be necessary to relocate the release operating arm or fit another arm forthe test.
Fit tester ring to release and make sure the release mechanism has gone over-centre before applying test
load. Tighten the nut until desired load is reached.
To measure operating force, apply spring balance to operating arm and pull gently at right angles to arm.
NOTE: - This kind of work is fairly hard on the spring balance. If a 150 mm piece of wire or cord is fitted
between the spring balance and the operating arm the spring balance won’t be knocked around as much.
Where a back-release is fitted, it will need to be locked in some way. Use a block or wedge to lock it during
the test.

C.3

CALIBRATION OF GFA 450 RELEASE TESTER
Regional GFA 450 Release Testers are to be calibrated by the GFA Regional Equipment Officers at least
every two years by comparing test readings for a calibrated tow release that is borrowed from GFA and onlyused for calibration. If the readings are within 2% of the calibrated values, the Regional Tester is deemed to
be within calibration.
The GFA Regional Equipment Officers are responsible for maintaining a testing logbook of the aircraft
registrations on which the GFA 450 Release Tester has been used during inspection.
Should a GFA Release Tester be found to be out of calibration, then the RTO-A will consider whether it isnecessary for all releases tested by the tester since last calibration to be retested. He should first consider if
the standard release may be at fault. The Release Tester logbook will be used to contact owners who may
have had suspect test results.
This is important quality control and so the RTO-A is responsible for ensuring this happens and to receive areport every two years on the aircraft tested, the results of the calibration, and the rectification undertaken.
Luckily the testers hardly every go out without it being noticed and fixed.

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Appendix D TOW RELEASE TEST SHEETAPPENDIX B : TOW RELEASE TEST RESULTS
Release type: ____________(for all release types) July 17

Position: Nose  Belly 

S/N: ___________Aircraft: VH‐ ______

Launches to date: ____________
Release testing tool employed for test:

Release due replacement (launches):____________


GFA 450 Tester, S/No.______

Other _________________



Spring balance calibration method: ______________________________
Release actuating arm lever length:Either (a) Standard Arm = 68 mm
Use Chart 1 directlyOR (b) Actual arm length = ____mm
Use conversion equation below:
Converted force = Measured force x (Arm ____ mm) / 68

TEST 1: Over-centre test
Tow Load

Allowable Force

(kgf)

(kgf)

(release removed from aircraft, main spring removed)

Actuating forces measured at arm length as above
Measured Priorstndrd
1 Adjustment 2 Adjustment 3 Adjustment
to Adjustment

Chart 1 with Arm
=68mm
200

2.2 to 4.8

(kgf)

(kgf)

(kgf)

(kgf)

Mea s ured
Converted

300

2.9 to 5.6

Mea s ured
Converted

400

3.6 to 6.4

Mea s ured
Converted

Note: Convert measured force to equivalent force at standard arm (68mm) only when release arm length is not 68mm

Plot above 3 data points on Chart 1 and project results to 450 kgf tow load:

Satisfactory  Unsatisfactory Confirm actuation force increases with tow load

Yes 
Satisfactory without adjustment 

Result:Measured

Allowable

TEST 2: Main Spring Tension

No 

Satisfactory after adjustment 
Unsatisfactory after adjustment 
Acceptable(measured at release actuating arm)

Force just before release fully closed________ kgf

Yes 

No 

Main spring action taken.
TEST 3: Pilot Actuation

New main spring installed? Yes No 

P1 seatP2 seatPull force with nil tow load________ kgf________ kgf

6 to 9 kgf *

Yes 

No 

Pull force with 150 kgf tow load ________ kgf________ kgf

6 to 9 kgf *

Yes 

No 

Residual Pull force with nil
tow load at 68mm lever________ kgf>1.5 kgf

Yes 

No 

Yes 

No 

________ kgf

2.5 to 5 kgf(mea s ured a t cockpi t rel ea s e knob)

Release knob retracts under spring tension and release locks* If two operational releases then max allowable is 17 kgf.

+/‐ 30 deg 

For Tow Planes CAO 100.5 allows <20kgf @ 450kN tow load.

TEST 4: Back release spring (Belly release only)
Angle of activation with 20 kgf tow force_____ degrees

Yes 

No 

TEST RESULT:

Tow Release fit for purpose? Yes No 

83 +/‐ 7Notes following test:
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Appendix E TOST RELEASE REASSEMBLY AIDS.
It was at a sailplane maintenance school at Kingaroy several years ago that I observed a tost spring
replacement tool used. It was designed by Craig Tuit from Brisbane, and made the task so easy it wasalmost enjoyable. Not enjoying doing things the hard way I decided to invent a kit to make overhaulingreleases more rewarding.
Tool no. 1 is used for replacing the main return spring.
Tool no. 2 is used to hold the release spring back out of the way when replacing cage in to releaseassembly. These tools are made using 3mm thick FMS about 30mm wide, length about 200mm. Dimensions
provided in the diagram are accurate enough but it is handy to have a release on hand to allow fine tuning
for a neat fit.
Tool no. 3 is a pilot to replace the parrot beak/back release cage pivot bush. There is sometimes a problemaligning shim washers in this mechanism and this tool makes it easy. The tool can be made out of any roundbar and lathed to size, a 6mm nut can be fixed to some type of handle and when the bush is fitted to the pilot
it can be screwed on behind it to push into the assembly.
Tool no. 4 is a general alignment tool also made out of round bar. Dimensions shown are accurate enough,length is not critical and a handle is also fitted. Plastic file handles are good.
Tool no. 5 is used to hold the release while working on it. The release is bolted into the holder which is thenclamped in a vice, this stops damage to the release cage. It is made by welding two side plates of 75 x 50 x
3mm flat plate to a length of 25 x 25mm RHS. Holes are pre-drilled to suit the release. Drill holes slightly
oversize to make fitting the release easier.
Full size plans are available from the Grafton Gliding Club.

Figure 16-16 Release Test Tools
Copied from Australian Gliding Sep/Oct 98

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Many people develop tools like this to help.

Figure 16-17 This is a very simple tool that is effective once you perfect its use.

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17.

OXYGEN
This chapter of Basic Sailplane Engineering covers the installation, maintenance and inspection of gaseous
oxygen systems, providing guidelines for both inspectors and operators. These guidelines are compiled fromgeneral aviation practice, CIG recommendations, Australian Standards and CASA requirements and tailoredto suit our needs.
Operational guidelines for the use of oxygen may be found in the relevant section the GFA MOSP Part 2
Operations.
Australian regulations differ from other regulatory bodies, such as FAA and EASA. Please only use CASA
regulations when operating in Australia. CAO 108.26 - System specification - Oxygen systems, applies to
GFA sailplanes and LSA gliders. Compliance with MOSP 3 and BSE should guide compliance with CAO
108.26 but it retains precedence.
Note: GFA AD348 Oxygen Systems was cancelled on 02 March 2016 and superseded by MOSP 3 and
BSE.

17.1

GFA RECOMMENDATIONS AND REQUIREMENTS
Since circa 2005, portable light weight oxygen systems with sophisticated flow control devices specificallydesigned for sailplanes and sports aviation have emerged and become popular due to their higher duration
per kg load, relative simplicity of use and safety features. These have rendered older permanently installedsystems undesirable and largely obsolete.
GFA recommends when choosing a new oxygen system for use in a sailplane:a.

Choose a portable oxygen system designed and manufactured by a reputable manufacturer
specifically for aviation use.

b.

The oxygen regulator should be mounted directly to the oxygen cylinder with no high pressure
plumbing involved.

c.

Permanently installed high or low pressure plumbing, rigid or flexible, is best avoided.

The new permanent installation of any system, including ex-military systems, requires GFA approval foreach individual installation.

CAUTION
For sailplanes with an existing permanent oxygen system, due to the high maintenance requirement andinherent safety risks, GFA recommends the removal from sailplanes of any oxygen system that has highpressure plumbing and/or rigid fitted low pressure plumbing. If installed it must be properly approved andmaintained.
Annual Inspectors and Replacement of Component inspectors are expected to be trained and receive arating to perform inspections of oxygen installations and to remove systems. But extra expertise is required
to design, produce and install permanent systems. If you have this expertise and the necessary design
approvals then you may install permanent oxygen systems but most people are best to leave this high risk
activity to experts.

17.2

OXYGEN SPECIFICATIONS
The type of oxygen used in sailplanes must be “Aviators Dry Breathing Oxygen” (ADBO).
CAO 108.26 (2/11/2007) states the specifications of ADBO:

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Code 430 oxygen is usually described by suppliers as “Oxygen, Dry Breathing, Extra High Pressure,Compressed” and is readily available in Australia. Code 420 is similar to Code 430 but supplied at a lower
pressure and is rarely available in Australia.
There is considerable debate as to whether there is any significant difference, other than price, between thevarious grades of oxygen such as; industrial, food, medical and dry breathing. Whilst the method of
producing the oxygen may be identical, the subsequent storage and protection/testing for impurities doesvary. In particular, industrial and food (processing) grades of oxygen are not intended for humanconsumption and thus contamination from cylinders and lines may cause a health hazard.
It is normally stated that medical grade oxygen (eg Gas code 400) is unsuitable for aviation use because it
may contain more moisture than ADBO and thus may cause a freezing hazard at low temperatures. Sceptics
pointed out that medical oxygen is so dry that for pro-longed consumption it is usually humidified andwarmed by a bedside device (because breathing compressed gas causes drying, and may cause damage
to, the tracheal mucosa). However medical oxygen is not intended for use at the -30C temperatures that
sailplane pilots might experience at altitude.
Whatever the merits of the arguments, the use of medical
grade oxygen in aviation oxygen systems is not approved by CASA and thus it must not be used insailplanes.

CAUTION"Aviators Dry Breathing Oxygen" is expected to have moisture content less than 0.005 milligrams of water
vapour per litre of oxygen at a temperature of 15°C and a pressure of 760 millimetres of mercury. "Medical"
oxygen may not meet the moisture requirements for “Aviators Dry Breathing Oxygen”.
Operators responsible for the filling of oxygen cylinders, either at a recognised re-filling station or bydecanting in the field, must be absolutely sure that the gas being used is oxygen and the correct grade ofoxygen.

17.3

SAFETY PRECAUTIONS WHEN WORKING WITH OXYGENWARNING
When high pressure oxygen comes in contact with grease, oil, or any form of hydrocarbon, instant fire and/or
explosion will occur. Total working cleanliness is absolutely imperative for sailplane and pilot safety.

17.3.1

CLEANLINESSThe importance of absolute cleanliness during installation, use and maintenance procedures for oxygen
equipment cannot be over emphasised. The inspector, pilot and operator must at all times respect the factthat oxygen and malfunction are potentially lethal.

17.3.2

WORK PRACTICESGood work practices when working with oxygen include:a.

Always turn the gas valves on and off slowly to prevent heating of system components, possible
internal combustion or rupture of oxygen lines.

b.

Always work with tools that have been degreased.

c.

Hands and clothing must be free of oils and greases. Note: Beware of suntan oils and creams.

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d.

Do not use lubricants on oxygen system components unless they are oxygen compatible and comply
with manufacturer’s specifications.

17.4

UNDERSTANDING OXYGEN SYSTEMS

17.4.1TYPES OF INSTALLATION
Oxygen systems may be permanently installed in a sailplane or be portable:a.

Permanently installed oxygen systems - have all, or some, of the components permanently installed in
the sailplane. The installed components may be plumbing, valves and cylinder. The cylinder may be
refilled in situ via a refilling port or removed to a refilling station.

b.

Portable oxygen systems - all components of the system are removable from the sailplane, exceptthat the cylinder mounting bracket may remain. GFA requires that the oxygen regulator must be
mounted directly to the oxygen cylinder with no high pressure plumbing involved.

Portable systems are considered optional equipment and count as part of the cockpit baggage load and thus
are part of the pilot’s responsibility, not the Annual Inspector’s. However, portable system components
should still be secured and restraint tested using the same considerations as fixed systems, as all aircraft
will experience turbulence and a badly secured bottle could become a potentially fatal missile.
The installation of permanent systems, including ex-military equipment, requires engineering approval via
GFA (MOSP 3 Section 18.7.1)

17.4.2SYSTEM COMPONENTS
All oxygen systems have the following main components:a.

The cylinder which stores the oxygen under high pressure.

b.

An on/off valve fitted to the cylinder.

c.

A high pressure gauge which shows the pressure within the cylinder and thus indicates the quantity ofoxygen. In modern portable systems, the gauge and on/off value are often an integrated fitting (withthe gauge sited before the on/off valve) and permanently fitted to the cylinder. Often the gauge is partof the regulator and removable, ie after the valve.

d.

A regulator which converts the stored high pressure oxygen to the delivery low pressure. Regulators
may have one or more low pressure ports (outlets).

e.

The low pressure plumbing or flexible hose which is used to transport the oxygen from the regulator,
via a controller, to the pilot.

f.

The flow or demand controller which meters out the correct amount of oxygen according to either thepilot chosen setting or automatically, depending on the type of controller. Some demand controllers
are designed to supply two users simultaneously.

g.

The mask or cannula that interfaces the oxygen system to the pilot.

It is normal practice to refill a cylinder by removing the regulator and connecting the charging tube to theon/off valve. However a permanently installed cylinder that is refilled in situ, may additionally have a filling
port and an on/off or non-return valve.
Older permanent installations may have high pressure plumbing to enable the high pressure gauge and asecondary on/off valve to be located more conveniently for the pilot to see and operate.

17.4.3SYSTEM CONFIGURATIONS
The following diagrams illustrate some common system configurations. The first diagram shows the modern
and most common portable single user system.

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Figure 17-1 Common oxygen system configurations

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17.4.4CYLINDERS
Oxygen cylinders used to all be made of steel, but modern cylinders used in sailplanes are now usuallyaluminium and sometimes Kevlar or a composite. They are available in a wide variety of sizes, the mostpopular being in the range 160- 250 litres. Aluminium cylinders have a maximum working pressure of 20002200 psi ie 140 to 150 bar and steel cylinders are often 3000 psi ie 200 bar.
All cylinders are stamped with the date of the last inspection and pressure test, the cylinders maximum
allowable working pressure, together with a stamp identifying the organisation certifying the cylinder.
The cylinders are pressure vessels and therefore are subject to the Australian Standards on testing andserviceability. Further information on cylinder testing is provided later in this chapter.

WARNING
Under no circumstances should a cylinder that does not have a current pressure vessel certification, be
used. No cylinder is to be filled to a pressure beyond its certified working pressure.

17.4.5SYSTEM TYPES AND THEIR CONTROLLERS
There are two types of oxygen systems generally used in sailplanes:a.

b.

Demand systems:
Oxygen is mixed with air and is only delivered to the mask as the pilot
inhales. This system is the most precise and gives the most economical consumption and thus
duration. There are three types of controller available:i.

Diluter Demand Controllerii.

Pressure Demand Controlleriii.

Electronic or Pulse Demand Controller. This is the most commonly used controller in sailplanes.

Continuous flow systems:
Oxygen is delivered continuously to the cannula/mask at a constantflow rate. This type uses more oxygen than Demand systems and thus larger cylinders are required
for a similar endurance. There are two forms of controller available:i.

Pre-set constant flowii.

Pilot adjustable flow to match the operating altitude.

Oxygen generators, automatic emergency systems and portable therapeutic sets are not used in sailplanes
and are not covered by this document.

17.4.5.1 CONSTANT FLOWThis type of system delivers a fixed rate and continuous flow of oxygen from the storage container. It is arelatively low cost solution as it doesn’t need complicated masks or controllers to function. But it is also very
wasteful—the flow of oxygen is constant whether you’re inhaling, exhaling, or pausing in between breaths. It
uses a bag on the mask to store the oxygen between breaths and reduce wastage.
An improvement on a pre-set rate continuous flow is the pilot adjustable controller. This again is relatively
simple – the pilot sets the flow rate according to the altitude he is flying. However soaring rarely involves
flight at a constant altitude so multiple adjustments of the controller are necessary and there is a risk of pilot
mismanagement.
The constant flow system is limited to a maximum height of FL250 feet with a mask but only FL180 with acannula. MH3 useable to FL180 MH4 useable to FL250 (with a mask)

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Figure 17-2 Examples of Pilot Adjustable Continuous Flow Controllers From Mountain High17.4.5.2 DILUTER DEMAND CONTROLLER
A diluter demand regulator supplies oxygen only in response to the pilot’s breathing. The oxygen is
automatically diluted with air according to the height at which the system is operating. So at 10,000 feet thepilot only breaths a small amount of supplemental oxygen whereas at 35,000 feet the pilot is breathing pureoxygen. This is the maximum height for use of this type of controller.

17.4.5.3 PRESSURE DEMAND CONTROLLER
The pressure demand regulator works in a similar way to the diluter demand regulator but above 35,000 feetit supplies oxygen at a pressure slightly over the ambient pressure at the operating altitude. Thispressurisation enables the lungs to absorb sufficient oxygen for safe operation at heights up to 42,000 feet.

17.4.5.4 ELECTRONIC (PULSE) DEMAND CONTROLLER
The electronic pulse demand controller monitors micro-pressure changes during the breathing cycle anddelivers a precise pulse of oxygen at the very beginning of each breathing cycle. Delivery of the oxygen to
the pilot is via a cannula or face mask.
These systems feature lower oxygen consumption rates compared with other demand systems, but do
require electronics to function correctly. Power loss due to flat batteries will cause the system to fail tooperate.
The maximum altitude of use is specified by the manufacturer but will be circa 25,000 feet.

Figure 17-3 The Mountain High EDS O2D1 pulse demand controller

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Figure 17-4 MH regulator and gauge

17.4.6FLEXIBLE LOW PRESSURE HOSES
Some systems use low pressure small bore flexible hoses from a permanently installed oxygen outlet andothers use it throughout such as in modern portable systems. These hoses should be of the type specified
for use with oxygen. Depending on the design of the system, it may use either made up hoses or cut lengths
of hose with push connectors.
Flexible hose will be non-kink in normal usage and may be colour coded. Do not use general purpose
flexible hose purchased from the DIY stores, as this may not be compatible for use with oxygen.

17.4.7

CANNULAS AND MASKS

17.4.7.1 NASAL CANNULAS
Nasal cannulas have become increasingly popular alternatives to face masks. Cannulas free the pilot to talk,eat, or drink without the hassle of a conventional facemask. In short, they're more comfortable.
They are restricted by Australian CAO 108.26 to a maximum of FL180 altitude because of the risk of
reducing blood-oxygen saturation levels if one breathes through the mouth or talks too much.

CAO 108.26 (including Amendment Order Nbr 1 2007)
5.1.3

Every unit (individual dispensing unit) provided in an aircraft operating above flight level 180
must be designed to cover the nose and mouth.

You can keep them clean by using mild water and soap. Then disinfect them. They should be considered apersonal use item rather than shared.

17.4.7.2 MASKS
The partial rebreather mask is the most common mask used with a constant flow system and usually has anexternal plastic bag that inflates each time you exhale. The purpose of the bag is to store any unused
oxygen, so that it can be inhaled with the next breath and increase system efficiency. These masks work
fairly well up to 25,000 feet — as long as the mask seals well against the face.
Masks designed for altitudes higher than 25,000 feet will be sturdier, better forming to the face and of course
more expensive.
Excessive sun exposure and normal wear and tear can make a mask less effective at altitude. The heat of abaking cabin can deform the face seal of any mask, as well as bring on cracks in the re-breather bag.

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Beards and moustaches don't go well with oxygen masks as they may prevent the mask sealing properly tothe face. For this reason, some manufacturers suggest that bearded pilots fly no higher than 18,000 feet on
oxygen. Above that altitude, the risk of oxygen leakage is too great.
Masks can be ordered with built-in microphones. This spares the pilot of the bother and risk of removing andreplacing the mask every time a radio transmission is made. The down side is that the masks can impart an
odd muffled sound to transmissions, sometimes making them nearly undecipherable.
The Aerox 4110-711 Series continuous flow oxygen mask.
Intended for use of crew and passengers in the general aviationindustry up to a maximum altitude of 25,000 feet.

The Mountain High ALPS Mask
For use with Mountain High continuous flow or EDS systems.

The Aerox Diluter Demand Mask
This 4110-725 series mask is intended to be used by crew andpassengers in the general aviation industry up to an altitude of
40,000 feet MSL.

Figure 17-5 Examples of aviator oxygen masks

17.4.8SYSTEM MANUFACTURERS
Below are details of some manufacturers of aviation oxygen systems whose products are frequently used insailplanes:a.

Mountain High

http://www.mhoxygen.com/

b.

Aerox

https://aerox.com/

c.

Precise Flighthttps://www.preciseflight.com/

d.

Delta Oxygen Systems

http://www.deltaoxygensystems.com/index.html

Note: Inclusion in the above list does not constitute a recommendation or endorsement by GFA.

17.4.9BASIC REQUIREMENTS FOR ALL OXYGEN SYSTEMS IN SAILPLANES
The basic requirements for any oxygen system used in a sailplane are:a.

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There must be an "on/off" valve located as close to the cylinder/s as possible to which a pilot hasaccess in flight. In a tandem two seat sailplane this may be difficult and must be solved. This valve isanalogous to the master switch in an electrical circuit and is there in case something goes wrong withthe regulator, mask etc. If the cylinder valve is inaccessible in flight, a separate on/off valve must be
installed.
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b.

The pilot, or one of the pilots in a tandem two seater, must have visual and physical access to theregulator and be able to see the pressure gauge and the flow (a mirror is acceptable).

c.

A mask or cannula, compatible with the regulator, must be provided for each seat.

d.

Cylinders, lines, regulators, flow meters and pressure gauges must be compatible with; each other,
the function of the system and the range of pressures for which the system is designed.

The four specific requirements above, combined with the guidelines in the following text, will allow Annual
Inspectors to certify the airworthiness of new and existing installations by logbook entry.

17.5

CYLINDER INSTALLATION AND RESTRAINT
Irrespective of whether the oxygen system is portable or permanent, the oxygen cylinder must be adequately
secured to the sailplane during flight.
Oxygen cylinders come in all shapes and sizes and can be difficult to site due to their bulk and weight. The
weight of the cylinder for assembly should be calculated as the sum of weight of: empty cylinder, full oxygengas fill, on/off valve, gauge, regulator and mounting bracket.
When determining the mounting location for an oxygen cylinder the vital points to consider are:a.

Effect on weight and balance.

b.

Possible interference with flight control systems.

c.

Ease of re-filling or removal for re-filling.

d.

Restraint under crash and flight loads.

e.

Remote from oil, grease and heat (powered sailplanes).

The cylinder and all other components must be installed and restrained in accordance with Installation of
Optional Equipment Chapter of this manual. In particular, if the oxygen cylinder is located behind the pilot, it
must be restrained to the 15g crash load case.
Most modern composite sailplanes feature a built-in oxygen cylinder mounting point that satisfies theappropriate Type Certification standards in the country of origin. When a sailplane type is issued a
Certificate of Type Acceptance in Australia, the mounting point will be checked against CASA relevant
standards and thus comply with this restraint requirement. It may be necessary to purchase an approved
specific mounting plate or clamps from the oxygen system supplier to secure the cylinder.
Where a mounting plate must be custom fabricated, then it must be engineered so as to withstand the gforce loads specified in the Optional Equipment Chapter and must be approved by an Annual Inspector.
If the sailplane does not have suitable built-in oxygen mounting points, then consult with the RTOA regarding
previous solutions or a new design and new engineering order. A logbook entry will be required for an
approved modification (see MOSP 3).

17.6

PERMANENT PLUMBING INSTALLATIONS

17.6.1TERMINOLOGY

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"Low Pressure"Pressures below 2750 kPa (400 psi)

"High Pressure"Pressures up to 25000 kPa (3650 psi) (250 bar)

"Working Pressure"

Maximum pressure the component will experience in normal service.

"Burst Pressure"Pressure at or in excess of which failure of the component is expected.

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17.6.2

SECURITY
All plumbing, high pressure and low pressure, must be located and secured through the airframe such that
there is no possibility of touching or jamming flight controls or causing abrasion to the plumbing itself. If
plumbing is not properly secured and can vibrate, it will eventually fatigue causing cracking and gas leakage.
Clearance of 15 mm from pushrods and bellcranks and 50 mm from cables will usually ensure no abrasionin service.
Plastic or cord ties are better than wire or metal brackets (unless the metal brackets are lined with a soft
material to stop abrasion).
Where rigid lines are used, it is important to provide sufficient flexibility at each end to prevent cracking orwork hardening due to repeated connection and disconnection.
Particularly where vibration is present (powered sailplane), plumbing should be secured at intervals of no
more than 350 mm.

17.6.3

HIGH PRESSURE PLUMBING
High pressure plumbing extends from the cylinder to the regulator. It must have a safety factor of not lessthan 3 between maximum allowable working pressure and calculated burst pressure. (BS 3N 100:1985).

17.6.3.1 Copper Tubing
Some older systems have used copper tubing for high pressure oxygen plumbing. These are fraught withpotential dangers due to fatigue cracking. GFA recommends removal of old copper plumbing andreplacement with flexible hose, or a simpler low pressure system.
If copper systems are installed, theymust conform to FAA AC 43.13.

17.6.3.2 Flexible HoseIf a flexible hose is to be used for high pressure plumbing, it must be very clearly approved for Aviators Dry
Breathing Oxygen. Many hoses rated for oxygen are only intended for industrial oxygen and must not be
used for breathing oxygen.

WARNING
Teflon in pure or "virgin" form is safe in oxygen systems. However most teflon hose linings etc are not pureand can, in systems over 600 psi, cause combustion in combination with any foreign matter. It is strongly
recommended not to use Teflon in any components in a sailplane oxygen system. Teflon seals in regulators
etc must be viewed with caution.

17.6.4LOW PRESSURE PLUMBING
Permanently installed low pressure plumbing is now unusual but may sometimes be found in two-seat
sailplanes where low pressure lines may extend from the regulator to separate oxygen outlet sockets foreach pilot. Both aluminium alloy and copper tubing are acceptable for low pressure lines, with either flarelessor flared fittings.

17.6.5COMPONENT CLEANINGThe cleaning process prior to and during assembly of a system is a most important part of installation. Alllines and fittings must be degreased internally and externally to remove all traces of oils, greases, dust,
swarf etc. If silver soldered fittings have been used, all traces of flux must be removed from the inside oflines and fittings.
The recommended practice is to degrease using a vapour degreaser or sonic cleaner followed by flushingwith stabilised trichloroethylene, acetone or similar non oily solvent.
Parts can be immersed and cleaned in trichlorotrifluoroethane ("fluorosil" is an acceptable product for thispurpose). Any brushes used should have 100% nylon bristles.

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CAUTION
Fats and oils can be deposited by fingers. This means that care should be taken while handling parts
between cleaning and final assembly.
"Carbon Tetrachloride" is now illegal to use and "Methylated spirits" is not recommended as degreasing
agents.
Following degreasing, the lines and parts must be dried by either:a.

Heating to 70°C for half an hourb.

Blowing dry with dry, clean air or nitrogen.

WARNING
Air from a compressor will be wet and most likely have significant oil content from the compressor lubricant.
It therefore must not be used in a sailplane.

17.6.6SEALING PLUMBING AND FITTINGS
The aim of all plumbing systems is to not have to use any form of sealing compound. However, if a leakoccurs in a joint made by a threaded tapered male fitting that locates into a female threaded fitting, then theleak will be around the thread and either of the following sealants can be used, (keeping the sealant off thefirst one or two threads):a.

"Oxy Tape". Pure Teflon tape marketed in a dispenser preventing finger contact. (MIL T 27730).

b.

Loctite 520. A white paste which, unlike other "Loctites", will set in the presence of oxygen.

Leaks in flared fittings, "Swagelocks" etc. will be due to damage to metal to metal seats. The best cure is not
to use a sealing compound but to remake the joint.
Note: At no time must sealing material be allowed to enter the plumbing system.

17.7

WEIGHT AND BALANCE
After a new installation or major change to an oxygen system has been completed, the changes to thesailplane’s weight and balance must be considered. The sailplane should be weighed or a calculated change
in weight and balance completed. New pilot weight limits or ballast requirements may need to be set andcockpit placards amended. Many sailplanes fitted with oxygen are extremely limited in pilot weightallowance.
In many sailplanes it will be necessary to placard load limits for two separate configurations:a.

With oxygen fitted; andb.

With the oxygen system removed.

The sailplane must not be flown with the centre of gravity, the maximum gross weight or the maximum
weight of non-lifting parts outside of the manufacturer’s limits.

17.8

SYSTEM TESTING
Following the installation of a new system or the breakdown of a system for component maintenance,cylinder refilling etc., the system must be tested.

17.8.1CYLINDER TESTING
Testing and inspection of pressure vessels is very important as a rupture failure could have very serious or
fatal consequences. Testing can be arranged through a number of organisations approved for this class ofwork.
In many cases imported oxygen cylinders are made to overseas standards not recognised/approved inAustralia. This makes it difficult to have them pressure tested, inspected and recertified since theorganisation doing that work can only certify cylinders made to recognised standards. You may have toprovide the cylinder manufacturer’s specification documentation to the testing organisation in order to havethe cylinder accepted.

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Individual Australian State laws on pressure vessels have been applied in the past to some sailplane oxygen
cylinders resulting in the derating of those cylinders to lower maximum working pressures
Oxygen cylinders must be inspected and hydrostatically tested at the intervals as specified by the cylinder
manufacturer but not greater that the interval specified in MOSP 3.

MOSP 3 makes CASA CAO 100.5 Appendix 1 Section 15 mandatory for GFA registeredaircraft which states:
15.11 Subject to subclauses 15.12 and 15.13, inspection and testing of cylinders under thisclause must be carried out at intervals not exceeding every 5 years after
manufacture.
15.12 For 3HT cylinders, inspection and testing under this clause must be carried out atintervals not exceeding every 3 years after manufacture.
15.13 For DOT-E type cylinders, inspection and testing under this subclause must be
carried out:(a)at the intervals mentioned in the latest revision of the applicable DOTSpecial Permit; or(b)

at intervals not exceeding every 3 years after manufacture.

The test interval makes no differentiation between in-use and storage.
Cylinder manufacturers often specify a service life specified by years from manufacture or the number ofrefill charges and CAO 100.5 imposes maximums. Both limits must be adhered to.
Reputable gas suppliers have a responsibility for statutory testing and will refuse to refill any cylinder that isout of test date. Some cylinders will have a limited service life, others have unlimited service lives. Due tothe complexity of different types, the testing inspector or manufacturer will be able to advise on the service
life.

17.8.2LEAK TESTING
All joints should be tested with the system at full pressure, by applying soapy water to all joints and watchingfor bubbles. Observation of pressure drop over time can also be used for leak detection, the effects oftemperature change must be considered in any observed change.
Some items of equipment have small leaks inherent in their design, those leak rates should be specified by
the manufacturer.
If a leak is found, relieve the pressure before attempting to rectify the problem.
If any gas other than Dry Breathing oxygen is used for system leak testing, then the system must be flushed
out with Dry Breathing oxygen before use.

17.8.3

FLOW CHECK
Once the system is verified as leak free, its ability to flow at or more than the minimum required rate must be
confirmed. In a two seat sailplane installation, both outlets must be tested individually and together.

17.8.3.1 CONTINUOUS FLOW REGULATORSThe minimum flow rate should comply with the chart (labelled Appendix II) published in CASA CAO 108.26
which is based on low efficiency masks. Note that cannula manufactured under the name “Oxymizer” arepermitted at lower flow rate due to their better efficiency. Flow rate can be checked using a "rotameter".

17.8.3.2 DEMAND REGULATORSThis includes diluter, pressure demand and electronic regulators. The regulator must meet the
manufacturer’s gas flow specifications, which requires testing by an approved laboratory. This testing should
be done in accordance with the manufacturer’s schedules.
When installing or inspecting this equipment, the Annual Inspector only need do a functional check asdetailed in the regulator manufacturer’s handbook.

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17.8.4

DORMANT OXYGEN SYSTEMS
Most oxygen systems can lay dormant for long periods and in many cases components are changed fromsailplane to sailplane. This aspect of oxygen systems presents a number of safety considerations:

17.9

a.

If a cylinder is kept disused at a pressure less than 350 kPa (50 psi), there is a strong chance thatinternal corrosion will be found in the cylinder. The presence of moisture can often be detected by apungent odour in the oxygen remaining in the cylinder. If the Inspector has any doubts, the cylinder
should be sent away for inspection and hydrostatic test.

b.

Where cylinders or other components are removed and plumbing left in place, the plumbing must be
sealed with a proper plug or cap - not a piece of rag or masking tape.

c.

Before returning an old system back to service, all of the procedures applicable to a new systemshould be followed to ensure system cleanliness and safety.

d.

If there is any suspicion of fatigue cracks in existing copper or alloy lines, the lines should be renewed

PLACARDING
The placarding requirements are specified in MOSP 3 Section 8.3.11.

17.9.1

INDICATED AIRSPEEDS
With gain of height comes reduction in air density. The lowering of air density causes an increase in true
airspeed at constant indicated airspeed and while this does not affect the structural loads applied to theaircraft at constant indicated airspeed, the aircraft is being flown closer to its flutter limit as this is related totrue airspeed.
The reduction of Vne with gain of altitude must therefore be placarded. Refer to Section 4.5.5 for an
example.

17.9.2SYSTEM SAFE HEIGHT LIMITS
Each type of oxygen system has its own operating height limitations and some individual equipment items,
due to their design or quality, are height restricted. To ensure pilot awareness of system limits, themanufacturer’s system limits must be placarded. This is usually incorporated in the Vne placard as shown
above.
If the system used is portable, there is probably no placarding in the sailplane. The pilots are responsible toensure they operate to the manuals. Placards are recommended.
GFA members must follow the manufacturer’s safe height limits for the equipment in use.

17.9.3CYLINDER MOUNTING BRACKET
Because the bracket is likely to be specific to a manufacturer or bottle size, the bracket or mounting shouldbe placarded with the type and size of bottles for which it has been tested. Eg
Tested for use with Mountain High
AL-180 oxygen cylinders only.

17.9.4FILLING INSTRUCTIONS FOR PERMANENT INSTALLATIONS
Where an installation is permanent and the cylinder will be filled whilst fitted in the sailplane, a placard
stating the maximum filling pressure and a caution about keeping the surroundings clean and free from oil
and grease must be fitted adjacent to the filling valve. An example is shown below:

DANGER OXYGENMAXIMUM PRESSURE 12,400 kPa (1,800 psi)
KEEP OIL AND GREASE AWAY FROM THIS FILLING POINT

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17.10

AIRWORTHINESS CERTIFICATION

17.10.1 INITIAL INSTALLATIONA GFA authorised Annual Inspector (of any category) must supervise or carry out the installation of apermanent oxygen system or the mounting plate/straps of a portable system. This enables the
documentation of compliance with this Chapter of BSE to be recorded by logbook entry. If necessary, design
approval of the cylinder restraint and any modifications to original structure and systems should be soughtfrom the GFA. Weight and balance must be checked by an appropriately authorised W&B Inspector.

17.10.2 ANNUAL INSPECTIONS
17.10.2.1

PORTABLE OXYGEN SYSTEMSThe Annual Inspector should check the following:a. The cylinder mounts for corrosion, cracks, general condition and security.
b. No significant change to weight and balance causes by changes to the portable oxygen system used in
the sailplanec.

Placards present and correct.

The pilot is responsible for checking the portable oxygen equipment before use for: correct gas, gas content,
serviceability, non-interference with controls, operating limits and restraint.

17.10.2.2

PERMANENTLY INSTALLED OXYGEN SYSTEMSThe annual inspection may be handled one of two ways by an Annual Inspector:
The Inspector may confirm that the cylinder and all other components are securely mounted and notinterfering with flight controls or other systems but not carry out any inspection or checking to confirm theserviceability of the system. In this case the Inspector should endorse the Maintenance Release "Oxygen
system to be inspected for serviceability before use". This is the preferred procedure if the oxygen system is
not to be going into service soon after the Annual Inspection.
Alternatively the Inspector may fully inspect and functionally check the system in accordance with this
Chapter of BSE plus any particular check or inspection required by the equipment manufacturer. That willallow the system to go straight into service. That should include:a.

Confirmation that all components that have pressure testing or overhaul requirements (cylinder,
regulator etc.) are not out of date or will not exceed their overhaul period during the life of the new
Maintenance Release. Where an item of equipment will exceed its overhaul period that fact must be
written into the sailplane's Maintenance Release.

b.

Check the cylinder, cylinder mounts, for corrosion, cracks, general condition and security.

c.

Check plumbing for damaged, corroded, squashed tubing and regulator and flow meter for conditionand security.

d.

Check the system for function and carry out a leak check. This will require the system to be fully
charged.

e.

Placards and weight and balance correct.

17.10.3 RETURN TO SERVICE INSPECTION
Where a permanent system has been dormant for some time, a full inspection should be carried out by an
Annual Inspector, following the guidelines above. It should be recorded by a logbook entry and cancel any
restrictions on the Maintenance Release.

17.10.4 DAILY INSPECTIONS
Security of the cylinder, plus security and condition of the other visible components is considered part of anormal Daily Inspection. Gas type, gas content and system function are not a Daily Inspector’s responsibility.

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17.11

DECANTING
Decanting is the act of filling one container from another at a higher pressure. In gliding, this means filling an
empty or partly empty cylinder from a high pressure cylinder. This can be done in two ways:a.

The empty cylinder may be left in the sailplane and the higher pressure cylinder brought to it. For apermanently installed system, this is the preferred method so as to avoid breaking plumbing
connections that will need to be leak checked when the cylinder is replaced.

b.

The empty cylinder can be taken out of the sailplane to the high-pressure cylinder.

Irrespective of which way it is done, this process is potentially very dangerous and requires due care as
follows:c.

If decanting into the sailplane the filling point and the area around it should be thoroughly cleaned
before connecting the plumbing from the external cylinder and that plumbing must be clean.

d.

The plumbing to the external cylinder must be long enough and flexible enough to not risk fracture ordamage while being used.

e.

There must be a pressure regulator or pressure limiting valve fitted at the external cylinder set suchthat the sailplane system cannot be over-pressurisedf.

Before connecting the line from the external cylinder the line must be carefully purged with oxygenfrom the cylinder to remove air, moisture or any foreign objects.

g.

The filling procedure must be carried out slowly to prevent the generation of excessive heat in thesystem and the sailplane cylinder.

h.

Accurate filling is subject to oxygen temperature so the following chart of pressure versus temperature
should be used to control the filling procedure. Both oxygen cylinders should be kept out of direct
sunlight.

i.

On completion, all joints disturbed for the filling process must be leak checked with detergent andwater or by noting any pressure drop.

17.11.1 FILLING PRESSURESThe following tables give the correct filling pressures for a given pre-fill cylinder temperature.
TO OBTAIN 3600 PSI AT 15°C
TEMP °C

PSI

kPa

0

3318

22890

5

2420

23590

10

3522

24300

15

3625

25000

20

3727

25710

25

3829

26410

30

3931

27120

35

4034

27820

40

4136

28530

Table 17-1 3600 PSI

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TO OBTAIN 2000 PSI AT 15°C
TEMP °C

PSI

kPa

0

1836

12670

5

1886

13010

10

1936

13360

15

1986

13700

20

2036

14040

25

2086

14390

30

2135

14730

35

2185

15070

40

2235

15420

Table 17-2 2000 PSI
TO OBTAIN 1850 PSI AT 21°C
TEMP °C

PSI

kPa

-1

1775

12200

4

1825

12600

10

1875

12900

16

1925

13300

21

1975

13600

27

2000

13800

32

2050

14100

38

2100

14500

43

2150

14800

Table 17-3 1850 PSI
Table 17-1, Table 17-2 & Table 17-3, assume a 14°C rise in temperature due to the heat of compression
and they assume that the cylinders are being filled at their maximum rate. These values are approximations
and must not be used if the filling information of a specific system gives different values.

17.12

REFERENCES
References in the following list are recommended however, where any differences between this Chapter ofthe BSE and any reference is noted, this Chapter is authoritative.
a.

FAA AC 43.13-1B. Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair,
1998.

b.

FAA AC 65-15A Airframe & Powerplant mechanics - Airframe Handbook.

c.

CAO 100.5 General requirements in respect of maintenance of Australian aircraft. Section 15
Compressed gas cylinders.

d.

CAO 108.26 System Specification - Oxygen Systems - Amendment Order (No. 1) 2007e.

British Standard BS 4N 100-1:1999 Oxygen Systemsf.

AS 2030.1-2009 Gas Cylinders - General Requirementsg.

AS 2030.5-2009/Amdt 1-2015 Gas cylinders - Filling, inspection and testing of refillable cylinders

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h.

BOC Gas Agents Manual 2009i.

Ian Robertson. Stirling Range Wave Camp Manual. Beverley Soaring Society. Nov 1994.

j.

FAA FAR 91.21

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18.

FLIGHT OVERLOAD

18.1

GENERAL
The design strength of a sailplane is described in this chapter using the manoeuvre and gust envelopes as
illustrated in this chapter with diagrams. Please refer to these as you study the following. (Getting a printoutof the relevant pages may help).
Remember that safe flight is within the envelope.

Figure 18-1 Flight envelope
The manoeuvre envelope shows the design limits of a sailplane flying in still air. You will notice that at VA, it
is possible to reach the design limit of 5.3 g (at which a 100 kg pilot is effectively a 530 kg pilot) byapplication of the elevator alone, provided the elevator is sufficiently powerful to stall the wing at this speed.
But we don't usually fly in still air, so the next envelope (the gust envelope) is important. On this diagram,please note VB, the rough air speed. This corresponds to the loading produced by an up-gust of 15m/s (30knots)

Figure 18-2 Gust loading
But look more carefully and compare this diagram with the previous manoeuvre envelope. See how the top
left-hand corner shows that flying close to the rough air speed and using coarse elevator control can lead toflight outside the envelope, and therefore outside the design strength of the sailplane.
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Next, consider weight. As we saw with the 100 kg pilot, the loads carried by the structure depend on the gforce multiplied by the weight carried. This is why the cockpit weight allowance is placarded, and why the"weight of the non-lifting parts" is an important airworthiness measurement.
Now look at the high-speed limits. The top right corner corresponds to 4g and an up-gust of 7.5m/s at VD, thedesign dive-speed. What is the risk here?
The answer is “flutter”. Before this was understood, a lot ofpilots in fast aircraft suffered a terrible surprise as their aircraft disintegrated around them. It is a very real
result of flying faster than the design of the aircraft allows. Sailplanes have suffered from flutter, FRP is more
flexible than metal, and therefore flutter is a real possibility. For this reason, it is critically important that
control surface weight and balance limits be adhered to and control surface free-play be kept withinallowable limits.
Especially with low-drag modern sailplanes, it is possible that some aerobatic situations will result in flightoutside the design envelope. Dives and negative “g” manoeuvres are examples of this.

18.1.1

WINCH LAUNCHING
There is an exception to saying that "flight within the envelope is safe" and that is when the sailplane has a
big additional load applied which is not considered in the envelopes. That load is the launch cable or towrope.
The additional load of this cable or rope makes it necessary to specify a new and lower maximum speed
during launching to ensure that the wing will stall before its design loading is exceeded.
In addition, a weak link is included in the cable assembly (or is inherent in the rope used) which is designed
to protect the sailplane from overloading due to pilot error. Please refer to the GFA "Winch Launch Manual".
Note that impact loads due to rigid cables can result in much higher loads. The normal spring wire is heavy
and hangs in a loop; this provides give which reduces loads. However modern dyneema and other light
synthetic winch cables or even tow ropes are very rigid and hang straighter so they have less give. Ifchanging cables be aware and if you feel more shock loads in the sailplane or have more weak link failures
you may need to include a ‘spring’ to absorb shock. Rather use proven technology.

18.2

WHEN CAN OVERLOAD OCCUR?
Aerodynamic overload, other than flutter, will only occur if the sailplane is flown outside its placarded speeds
and weights and then subjected to pilot-induced or atmospheric loading.
The following list covers most overload possibilities:
a.

b.

c.

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Aerobatics:i.

Executing manoeuvre and aerobatics the airframe was not designed for.

ii.

Applying full control deflection at speeds higher than the placarded maximum manoeuvre
speed.

High speed flight:i.

Flying faster than the placarded max rough airspeed and encountering turbulence.

ii.

Flying faster than the max manoeuvre speed and applying coarse control surface deflectioniii.

Coarse use of dive-brakes at high speed. This can cause an overload due to the rearward force
transmitted through the wings to the spars and attachment points, as well as overstressing thedive-brake mechanism itself. It is not unknown for dive-brakes to "suck open" by themselves asa result of high-speed flight and incorrect adjustment of the dive-brake mechanism.

iv.

Coarse use of flaps at high speed. Positive flap increases the wing lift at any speed, andtherefore increases the loading produced by gust or control inputs.

Winch launching:i.

Exceeding the maximum winch speed and encountering a strong vertical gust.

ii.

Exceeding the maximum winch speed and applying coarse control inputs.
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d.

Aero-towing:i.

e.

Flying overweight:
i.

f.

Exceeding the maximum placarded speed and encountering severe turbulence.

Flight in excess of placarded limits. Each limit is specified to correspond to a design strength.

Non-airborne overload:i.

Ground Loops. These occur when a wingtip digs into the ground and the sailplane rotatesaround this wingtip. The tail can slam onto and dig into the ground while the fuselage is rotating
at high speed. The sideways momentum of the sailplane tail-end can then twist the fuselage
into a torsional failure.

ii.

Tail Slam. Some 2 seaters sit nose-down with a front pilot and tail-down with none. Serious
damage can occur if the tail is allowed to slam down onto a hard surface. But even singleseaters can suffer tail-slam, for example as the result of heavy braking.

iii.

Heavy Landings. The vertical speed of the sailplane is greater than designed for when it
contacts the ground.

The sailplane design contains energy absorbing features such as the deflection of the tyre, the deflection of
the entire structure including the wings, and maybe features such as energy-absorbing undercarriage struts.
If the downwards kinetic energy of the sailplane arrival exceeds the sum of the energy-absorbing features,
then damage can result.

18.3

FLIGHT OVERLOAD INSPECTION
As with heavy landings, damage can be expected anywhere and not be obvious. Here is a checklist. All
these things have happened in practice:a.

Equipment dislodgedb.

Critical fuselage areas (in front of the fin, near the wing leading edge and trailing edge, near the main
wheel, near the tail wheel or skid, near the wing /fuselage connection pins)c.

Rudder and rudder stopsd.

Wing root area, especially near the lift-pins and the main spar.

e.

All flight control-runs. Rods can be buckled, cables can be stretched and fittings can be distorted.

f.

Water ballast tanks can be damaged causing leaks.

g.

The wing leading edge itself may be damaged, especially along the join-line, where the wing upper
shell joins the wing lower shell.

h.

Dive-brake/wing box damaged.

i.

Torsional damage to wingj.

Bending damage to wing. In positive g loading, the upper side of the wing will have compression
damage (buckling, delamination and creasing) while the underside will show tension damage,especially cracking.

k.

Bending damage to tailplane. A little-known effect of over-speeding can be that the tailplane isdamaged in downwards bending. Why downwards?
Because the faster the forward speed, themore downwards force the tailplane must provide to counter the nose-down pitching moment of thewing. Thus the compression damage will be in the tailplane underside.

l.

All flight control hinges and stops strained or otherwise damaged, (flaps, ailerons, elevator andrudder).

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18.4

FRP OVERLOAD INDICATION
Fibre Reinforced Plastic (FRP) is a wonderful material as far as overload inspection is concerned if it can beseen properly.
Here's why: The plastic, that is the epoxy resin, is translucent and it stays that way with normal loading. But
in an overload, the resin is less elastic than the glass fibres. It then fails in the form of millions of tiny cracks.
These have the effect of making the translucent resin appear opaque white.
So white around stressed areas is a good indication of overload. Further, the white areas do not transmit
light, and so a light inside the fuselage at night will enable overstressed areas to be seen. Unfortunately, thislight trick doesn't work with wings because the foam sandwich material is impervious to light.

18.5

OTHER INSPECTION TECHNIQUES

18.5.1

SOUND
Sound can be a useful inspection technique when used as follows:

18.5.2a.

Tapping the area being investigated (an object like a coin is used) can reveal information about theunderlying structure. For example, it is easy to tell where the main spar is located, in particular, any
delamination or loss of bonding between the FRP and the sandwich core will show a distinctly
different tap sound.

b.

Listening, with an ear on the surface or with a stethoscope, while an assistant applies loads, canenable internal movements to be heard.

c.

Ultrasonic inspection machines are already in use for airliners, and it is expected that they will soon beavailable for sailplane inspections.

FEEL
The hand is quite sensitive to ripples in a smooth surface and sometimes a defect can be felt before it isseen.

18.5.3SIGHT
Sight is a useful and most common inspection techniques, such as:

18.6

a.

The use of a strong light, placed very low on the surface, can reveal defects not obvious in normal
light. As with the interior light test, this is best done at night.

b.

Sighting up the whole sailplane is an often overlooked check. Although composite structures have astrong tendency to spring back into shape, they may not do so completely.

c.

Is the tailplane still true with respect to the wings?

d.

Are the wings still straight with respect to the fuselage? Measuring from each wingtip to the fin willshow this.

e.

Are the wing and tailplane incidence still the same?
incidence of each wing and the tailplane.

Sighting from the front or rear will show this.

A water-filled tube can be used to check the

GELCOAT CRACKS
Gelcoat, generally polyester resin with white pigment added, is less elastic than the underlying FRP. Thismeans that cracks in the gelcoat may or may not be an indication of underlying damage.
Interpreting gelcoat cracks takes a lot of experience, so don't be shy about asking for help from senior
people in the GFA. It is not at all unusual for experienced inspectors to carefully remove gelcoat along a
crack to see if the crack continues into the underlying FRP.
The need for care cannot be overstated. The glass/epoxy layer is eggshell-thin, and it can easily bedamaged by sanding. Here are a few techniques which do not involve sanding:a.

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Mark the end of the crack and then apply loading and flexing to see if any movement can be seen or
any growth of the crack occurs, or any sound can be heard.
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18.7

b.

Use your internal light source if possible for a fuselage.

c.

Use an internal camera or borescope for a wing, looking for damage to the inner skin in the vicinity ofthe outer crack. The internal control-fittings in the wings can also be examined, looking for distortions
or damage to the structure where they are fixed.

CARBON REINFORCED PLASTIC
Carbon fibres are much stiffer than glass fibres and they are opaque black. There is good and bad resulting
from this:

18.8

a.

A good feature is that gelcoat cracks are less likely to occur in the absence of underlying damage.
Compared with FRP, CRP is brittle.

b.

A bad feature of CRP is that the structure can transmit forces such that damage can occur well awayfrom the point of impact. While this possibility cannot be overlooked with glass, it is much more so withcarbon.

INTERNAL INSPECTION TOOLS
Years ago, inspectors were limited to lights and mirrors to see inside closed areas such as wings. Thenaffordable borescopes became available and more recently small USB cameras that plug into a laptop
computer. They are quite cheap and great for taking photos. They enable the inspector to examine, forexample, the inner skin of a wing and the leading edge joint from the inside. But don’t be misled as most do
not have the resolution to see fine cracks and the old optical borescope works better.

18.9

WING LIFT PINS
These are the connection between the wing and the fuselage. There are 4 lift-pins and they carry all the nonlifting parts. Even the tailplane is a non-lifting part, as we discussed when considering lift-pins in the overload
possibility from over-speed.
In most sailplanes (Astirs are an exception) the pins are free to move in and out of the bearings. They do thisin flight in response to yawing forces. The effect of this movement and the steel-to -steel contact is that wear
can occur quite rapidly.
The wear on these pins is therefore an important maintenance check and their replacement must be
regarded as a standard procedure. Excessive wear will cause the wings to have unwanted free-play, with areduction in the flutter threshold.
When inspecting these pins after a heavy landing or suspected flight overload, the first procedure is visual: isthere any evidence of distortion of the pins themselves or in the structure which holds them?
Is there any
sign of overload in the epoxy in the vicinity of the pins? Can a camera or borescope be used to inspect the
inner wing root?
The second procedure carries the risk that damage may be caused from the investigation when none
existed to begin with. A tube is put over the pin to enable more force to be applied than is possible with thehand. This obviously requires care and experience, the aim being to apply enough force to detect adamaged embedment without applying enough force to damage a good one.
In this and the other overload inspections, the most important attributes for a good inspector are thediligence to be thorough and the willingness to seek out help. The great advantage we have in maintenanceis that instant decisions are not needed since we generally have the time to research what is the rightdecision.

18.10

MAINSPAR PINS AND BEARINGS
Most of the preceding discussion applies to the mainspar fittings, with the exception that there is not usually
any movement between the pins and their bearings, and therefore no wear. But an overload event cancertainly cause damage here. One clue to look for or ask about is whether or not the sailplane de-rigged
normally afterwards.

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18.11

CRACKS IN WING FITTINGS
Sailplane manufacturers have generally used mild steel for wing fittings. This material is not prone to
cracking, but the possibility exists, especially in the vicinity of a weld. A weld has an associated zone where
the weld-steel and the "parent metal" intermingle, and degradation of the steel properties can occur. For
example, "hydrogen embrittlement" has caused failures to occur.
Most cracks occur as the result of cyclic loading slowly enlarging a tiny flaw, but the possibility of a crack
resulting from an overload event should not be ignored. Crack detection is not easy, but the inspector needs
to be wary enough to avoid allowing a suspect fitting to be flown. Again, seek advice if unsure! It may be an
option to send a suspect part away for testing.
The most common ways of testing for cracks are dye penetrant and magnetic flux. Dye penetrant test kits
are readily available and should be part of an inspector’s equipment and there have been AirworthinessDirectives which have specified that this test be used. See the later Chapter on non-destructive testing.

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19.

EXAMINING DAILY INSPECTOR CANDIDATES

19.1

GENERAL
This chapter gives guidance on the technique to be followed when training and authorising Daily Inspectors.
Authorising Daily Inspectors is extremely important as this is for most people the first introduction to the GFA
airworthiness systems. A favourable impression during the training for the DI qualification may kindle an
ongoing interest in airworthiness.
The Examiner must ensure that each candidate who is authorised meets the minimum standard and iscompetent to certify a Daily Inspection. This is the last and most frequent inspection that should find faults or
deterioration to prevent failure in flight. Since a sailplane may fly many times on the basis of the Daily
Inspection, including the carriage of passengers and the general public, a responsibility rests with the
Examiner to ensure the candidate has the skills and knowledge necessary to certify a sailplane is safe for a
day’s flying.

19.2

DOCUMENTATIONThe GFA maintains several documents relevant to the training of Daily Inspectors. These can be found on
the GFA’s website. Relevant to the training is:a.

Daily Inspector’s Handbook Sailplanes (AIRW-M03)b.

Daily Inspector’s Handbook Powered Sailplanes (AIRW-M04)

c.

GFA MOSP 3 Section 10.7 (AIRW-M01)d.

Flight/Maintenance Manual(s) for the appropriate sailplanes

Persons who are authorised as a Daily Inspector Examiner may authorise persons as Daily Inspectors forthat particular field of expertise. GFA MOSP 3, Section 10.18 outlines how to become a Daily Inspector
Examiner. But all Annual Inspectors are trained and authorized to be a Daily Inspector Examiner.
The DI authority is a pilot logbook entry and GFA does not keep a record. The DI Authority is often for a
specific type first and additional Field(s) of Expertise are added.

19.3

CANDIDATE PREREQUISITES
Persons wishing to be Daily Inspectors should obtain the Daily Inspector’s Handbook from the GFA Website.
This handbook provides the basic technical reference to be used when checking inspectors against thesyllabus.
The candidate must meet the requirements of MOSP 3 Section 10.7.
In addition to the formal requirements, the candidate must have good vision and hearing. Many of the clues
to problems are very small cracks and damaged structures often creak and groan as they are moved.
It is also desirable that the candidate be a near solo pilot as this will ensure they have been involved ingliding long enough to have a feel for what is considered normal. However there will be exceptions and thecandidate's previous experience should be taken into account.

19.4

TRAINING
The training of daily inspectors can be performed by an authorised Daily Inspector. The best method of
training is for the candidate to assist on as many daily inspections as possible.
Candidates should work with as many Daily Inspectors, on as many types as possible. This will give thecandidate a broad range of experience and knowledge of specific items such as L’Hotellier couplings, wingattachment designs and tailplane attachment designs.

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19.5

DAILY INSPECTOR SYLLABUS
While all aspects of the DI Handbook are testable, an Examiner must make sure that the candidate is
specifically tested for knowledge of the following areas:

19.5.1a.

Why a DI is important and the extent of authority and responsibility for the safety of the sailplane forthe day. Note that GFA liability insurance covers DI inspectors if they are qualified and follow theprocedures.

b.

When a Daily Inspection is requiredc.

Why a Daily Inspection is requiredd.

The significance of a Major Defect and where to record ite.

The significance of a Minor Defect and where to record itf.

Maintenance procedures that a DI may sign off and record new entries forg.

How to certify a Daily Inspection and Independent Control Checksh.

How to determine that nuts, bolts and turnbuckles are correctly safety lockedi.

How to determine that control cable is serviceablej.

Checking control systems for movement in the correct sensek.

Various types of control couplings and how each type is safety lockedl.

Various types of wing and tailplane attachments and how each is held in safetym.

How to measure available free play and assess whether there is too muchn.

Specific features of each construction type being authorisedo.

Where to go for further information

TESTING
When testing potential daily inspectors, the DI Examiner must ensure that the candidate fully understands allof the items in the syllabus. This understanding should be in place before testing begins. If a candidate has
not understood the syllabus, as demonstrated by the need to review the handbook for the answers to almost
all questions, then the testing should be halted.

19.5.2

ORAL TEST QUESTIONS
While candidates will have had access to the questions and answers contained in the DI Handbook, aneffective testing technique will be to work through the questions only allowing the candidate access to thehandbook to demonstrate why a particular answer is incorrect.
It is also desirable to include a few questions which are not directly from Self-Test Questionnaires in thehandbook as this will confirm the candidate’s understanding of the topic.

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19.5.3

PRACTICAL TESTS
Because daily inspection is a practical function, the candidate must demonstrate the ability to perform aninspection of a sailplane.
The practical tests should be completed on as many sailplanes as are required to demonstrate a fullunderstanding of the necessary skills. It is desirable to perform the test on a type which the candidate is not
fully familiar with. This will allow the candidate’s ability to think through a problem to be demonstrated rather
than the ability to remember the peculiarities of a particular sailplane or type.

WARNING
The intentional introduction of defects into sailplanes is dangerous and is strictly PROHIBITED. The
Examiner is responsible to ensure all defects are corrected before the DI is signed for the day.
All sailplanes are imperfect and so will have a variety of defects and imperfections which the candidate
should be able to find. A good time to test a candidate is during maintenance or rigging while some items areincompletely assembled. It is desirable to perform DI tests on older sailplanes as they are more likely tohave minor defects and they are also more likely to contain unusual design features.

19.5.4

NOTIFICATION OF AUTHORISATION
Upon successful completion of the DI examination, the DI Examiner should make an appropriate entry in thelogbook of the pilot, indicating which Field(s) of Expertise they are authorised to perform Daily Inspections,and be signed, dated and the Examiner’s membership number recorded. The GFA is not required to be
notified of the authorisation(s) obtained.

19.6

POWERED SAILPLANES
The process for authorising Powered Sailplane Daily Inspection Authorisations is similar to that for a
sailplane however the powered sailplane’s Flight Manual will need to be used as the reference. Most
manuals contain a specific section on how to complete a DI on the type and the candidate should
demonstrate a detailed knowledge of all specific DI requirements on the type.
Depending on the specific requirements for the particular powered sailplane type, Daily Inspector candidates
must demonstrate knowledge of:a.

How to check for water in the fuel system.

b.

How to check the oil level.

c.

How to check the coolant level.

d.

How to examine the exhaust system (for security, cracks and tight bolts).

e.

How to ensure the propeller is correctly mounted and the bolts correctly lock wired.

f.

The allowable damage to a propeller.

g.

All specific requirements related to the type.

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20.

ELECTRICAL SYSTEMS

20.1

GENERAL
Nearly all sailplanes have electrical systems, either installed by the manufacturer or added by owners since
manufacture. Electrical systems include:a.

Devices that make piloting easier eg electronic variometers, GPS nav, glide computers, IGC
tracking.

b.

Devices that improve safety eg radios, FLARM, wheel-up warning systemsc.

Portable electronics devices eg mobile phones, personal computers (eg Oudie) which may bephysically connected to the installed electrical system, connect via Bluetooth or else be independent.

d.

In motorgliders, electrical systems may also be used for starting, ignition, fuel control or in very
recent designs, as the energy source for propulsion.

It is worth remembering that sailplanes fundamentally do not require an electrical system to fly and thathaving an electrical system creates safety hazards that would otherwise not exist. Hazards introduced byelectrical systems include:a.

Battery as a projectile: if not secured to the crashworthiness standard, a lose battery has sufficientmass to cause major injury in a crash.

b.

Battery thermal runaway: rapid discharge causing smoke, fire, or explosion.

c.

Wiring short circuits or overload: causing heat, smoke or fire.

d.

Portable devices charging inflight: risk of device batteries overheating.

e.

Entanglement of pilot’s limbs or control linkages due to lose wires.

It is vital to safety that where electrical systems are installed, they are fitted correctly, inspected regularly andfaults are properly remedied by competent persons.
This chapter of Basic Sailplane Engineering explains typical sailplane electrical systems, provides guidance
for Annual Inspectors in the inspection of electrical systems in sailplanes (excluding electrical systems
specific to motorgliders) and has information to aid building battery packs and making basic electricalrepairs.
Design and installation of sailplane electrical systems requires significantly more knowledge than is
contained in this chapter. See also the related Chapter 27 RADIO, ANTENNAE, FLARM AND AVIONICS.
All repairs and alterations to sailplane electrical systems must be inspected and approved by an Annual
Inspector and recorded in the sailplane’s logbook.

20.2

TYPICAL SAILPLANE INSTALLATION
Practically every sailplane electrical system is unique because of changing manufacturers’ options during
the production life and owners’ subsequent customisation. However, all installations comprise of thefollowing elements:m.

Battery. Stores electrical energy which it delivers on demand from the sailplanes electrical system,
until it is depleted and needs recharging. Usually, the battery is removeable for charging.

n.

Primary fuse (sometimes referred to as the master or battery fuse). Located at the battery to protect
all cabling downstream, from overcurrent.

o.

Master switch. Connects and disconnects all electrical equipment loads from the system.

p.

Cabling. A network of insulated wires that connect elements in the system. These include:

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i.

Power cables distributing the supply (usually 12V) to the equipment.

ii.

Power cables distributing the supply to the equipment.

iii.

Control circuits e.g. microphone press to talk, and electric variometer cruise/climb switch.
These carry a relatively small current.
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20.2.1

iv.

Audio cables e.g. microphone and loudspeakers.

v.

Data cables connecting electronic devices such as components of a GPS/electronicvariometer system. These carry a relatively small current.

vi.

Combined power and data, as in a USB cable.

vii.

Radio frequency cables connecting radios, Flarm, GPS to their antennas. These arenormally braded coaxial.

q.

Connecting blocks/busbars. If the system has little electrical equipment, these might be simply a multiwire crimp connector or not present at all. When there are more than 3 equipment devices installed,there are usually connector blocks.

r.

Equipment circuits. Equipment is divided onto a number of independently protected circuits. Devices
with a relatively high current draw (eg radios) usually have a dedicated circuit. Other equipment may
be grouped logically and/or considering redundancy ie if two GPS devices are fitted it may be best to
put each on a different circuit so that a fault causing a secondary fuse to blow only results in the lossof one GPS.

s.

Secondary fuses. Each equipment circuit is protected from current overload by its own fuse.

t.

Circuit switches. These allow the pilot to electrically isolate (switch off) selected equipment. Circuit
switches may be omitted if the fuses or circuit breakers are accessible to the pilot in flight (egpositioned on the instrument panel) and thus provide a means of isolation.

u.

Equipment and devices such as radio, electronic variometer, Flarm.

v.

An auxiliary DC power converter for a portable device such as a flight computer.

CIRCUIT DIAGRAM
Every sailplane should have a circuit diagram showing the configuration of its elements and the fuse values
that should be fitted. In addition, it is suggested that a set of photographs of the cabling in the control panel
and backs of equipment is a useful reference, maintenance aid and record.
A circuit diagram of a typical dual battery (selectable) installation for a sailplane is shown below:

Figure 20-1 Typical dual battery sailplane electrical circuit diagram
Points to note:a.

The primary fuse is positioned in the +ve line at the battery.

b.

The wiring gauge (size) from the battery is maintained all the way to the secondary fuses, and until
and throughout the negative busbar.

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c.

In a dual battery selectable system, the selector switch is electrically located before the master switch.
In a single battery installation, the selector switch is omitted.

d.

Secondary fuses are positioned before equipment switches and as close to the positive bus bar as
possible. Secondary fuses protect the wiring to the electrical equipment.

e.

All equipment devices, including the auxiliary DC output are protected by secondary fuses.

f.

Switches S1-S3 and wiring on the device side of the secondary fuses can be a lower current rating
than the cables from the batteries. The current rating of the cable and switch must be appropriate to
the expected current and secondary fuse rating.

g.

Switch S1 is frequently omitted as most radios have an inbuilt on/off switch.

h.

The radio is usually the device with the highest current draw which occurs during transmission. For
this reason, the radio is normally given its own dedicated fuse.

The battery negative terminal (marked “-“ and/or coloured black) must electrically connected to all devices
requiring electrical power. In a metal sailplane (as with motor vehicles) it is possible for the metal fuselage
to be used as the negative conductor and all devices are connected, referred to as “grounded”, to thefuselage. In wood and FRP sailplanes, wire cables are provided as the negative conductors which must be
the same quality and gauge as their corresponding positive conductors.

20.2.2SINGLE LINE CIRCUIT DIAGRAMS
For simplicity on circuit diagrams, details of the negative wiring are sometimes omitted and single line
diagrams drawn. A symbol (often an electrical earth symbol) is used to show the devices connect to“ground”, whereas in fact there is a network of negative conductors running alongside the positive
conductors (except for aluminium sailplanes where the hull may be used as the negative conductor).

Figure 20-2 Single Line Circuit diagram example (only +ve connections shown)

20.3

THE BATTERY
The battery stores and provides electrical energy to drive the equipment. Sailplanes usually use a nominal
12-volt system where the actual voltage may vary between fully charged 13.5V and a minimum usefulvoltage of 11.5V. (Note: The maximum charged voltage depends on the chemistry of the battery type andalso its condition).
There are numerous different chemistries of batteries. For many years the standard sailplane battery was a
Lead Acid but with the issue of MTAR1/2017, GFA authorised the use of specific Lithium batteries. Check
with GFA to establish the current status of battery types, brands and models permitted for use in Australianregistered sailplanes.

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The most common size battery for a single seat sailplane is 151 x 65 x 95mm. Battery capacity is usuallyreferred to in terms of Amp-Hours (Ah) eg A battery of 5 Ah is capable of delivering a current of 1 amp for aperiod of 5 hours or 2.5 amps for a period of 2 hours.
Lithium batteries have become popular because they have two clear advantages:a.

A higher charge/weight density. Example: a same standard size Lead Acid 12V is rated 7Ah
whereas the same physical size lithium-ion battery is rated as 12Ah.

b.

A significantly more useful discharge profile in that Lithium-ion batteries maintain a near constantvoltage before rapidly decaying at around 90% discharge, whereas a lead acid battery may havefallen below 12V when only 40% discharged.

Figure 20-3 Discharge Curves for Different Battery Chemistries
Lithium batteries have gained an unfortunate reputation for thermal runway. During a short circuit situation,
the battery rapidly discharges and generates of a lot of heat within the battery. When it gets hot enough, theheat causes the break down of the electrolyte in the battery and the expanding gases within the case canrupture the battery case. The gasses are very flammable and if ignition occurs, the resulting fire is very
difficult to extinguish until the battery is completely discharged.
Lithium batteries now usually contain voltage and current control circuitry designed to prevent overcurrent ina short circuit situation external to the battery. However, a damaged battery (eg from being dropped) may
experience an internal short circuit which the control circuitry is unable to protect, therefore it is vital that allbatteries are handled with care and carefully inspected for damaged prior to use in a sailplane. IF THERE
IS ANY DOUBT ABOUT THE SERVICEABILITY OF A BATTERY, DO NOT USE IT.
Battery performance (ie discharge voltage vs time) will degrade with age, number of charge cycles, depth ofdischarge and storage temperature. Using a multi-meter across a battery’s terminals will indicate thevoltage at that instant which serves only to show whether the battery is dead (ie no charge) or charged. To
test a battery’s performance, the simplest test method is to measure and then graphically plot the voltage atregular intervals (say every 10 minutes) as the battery discharges into a known resistance (often a light bulb
is used) selected to imitate the discharge current that the battery will experience in the sailplane.
A sailplane owner can determine the electrical load imposed on the battery by auditing the device
manufactures specifications and tabulating/summing the current draw. Alternatively, and probably moreaccurately, an ammeter can be used in-line at the battery positive terminal. Consider the normal load (alldevices switched on, radio in receive mode) and the intermittent load when the radio is on transmit.

20.3.1REMOVABLE BATTERIES
Most sailplanes use a removable battery pack comprising the battery, a fuse or circuit breaker, short leadand connector plug. The pack is often located on the parcel shelf behind the pilot and sometimes either in
the nose or in the tail fin.

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Sailplane owners will from time to time need to have replacement battery packs built. A person competentwith electrical hand tools may construct a battery pack but an Annual Inspector must approve it before it isused.
There are numerous designs of battery packs in use in Australia and few examples are shown below.
Gliding Australia does not mandate any specific design, however the important features to be achieved are:a.

There must be an inline fuse or circuit breaker located not more than 175mm from the battery’s
positive terminal (marked “+” and/or coloured red). This is the primary fuse and should be thehighest rated fuse in the installation.

b.

The battery to sailplane connector should have a ‘key’ function’ that only fits one way with thematching connector in the sailplane. This is to ensure the correct polarity is always achieved onconnection.

c.

The connector must have a locking function so that the battery cannot unintentionally disconnect
from the aircraft electrical system whilst in flight.

d.

For club sailplanes where batteries may be swapped between different aircraft, it is important that acommon standard of wiring for all battery, sailplane and charger plugs and sockets is used so as toensure compatibility and correct polarity.

e.

There should be strain relief for the terminal connectors so they don’t pull off the terminals. With thecommon battery style shown in Figure 20-6, a good quality tape wrapped around the battery willusually give support to the sometimes flimsy battery terminal connections

f.

Battery terminals must be electrically insulated. The use of insulated Faston connectors is
recommended. Heatshrink can be added for extra insulation. Insulation tape wrapped aroundbattery terminals is not acceptableg.

Be wary that the method of restraint of the battery in the sailplane does not pose a risk of shortcircuit to the terminals and electrically unprotected short length of cable. Metal clamps, metal
buckles on fabric straps and metal containers pose considerable risk if they can be wrongly
positioned or the battery moves and makes contact.

Battery terminals are usually designed to connect with Faston connectors which lock on to the terminal lugs.
Crimp Faston connectors are available in straight or ‘flag’ 90° format. The flag format is less prone to being
pulled off the battery terminal lugs.
Soldering cables onto the battery lugs is not recommended as a lot of heat is required and much of it will be
conducted to within the battery case, potentially damaging the voltage/current protective circuitry (if present).

Special crimpers are required for Flag
terminals

Insulated Flag 90° Faston vs insulated inline
Faston crimp connectors

Figure 20-4 Types of Faston Crimp Connectors for Battery Terminals

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Many sailplanes use XLR inline
plugs/sockets. The female socket is fitted tothe battery (think house wall socket, don’t
want protruding pins on the power supply).

CAUTION: The pin wiring shown above is by no means
standard in Australia. Clubs should publish theirstandard and owners are recommended to use thestandard set by their local club.

Figure 20-5 XLR Inline Plugs and Sockets Often Used For Battery Packs

A typical removable sailplane battery

Battery connector using flag Faston connectors andautomotive in-line fuses (mini and micro shown) andXLR socket

Commercial battery cap with inbuilt 10A circuit breaker

Figure 20-6 Examples of Removable Sailplane Battery
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Inline Fuses: There are several different typesof inline fuse that can be used on the battery
connector cable. The most commonly fuse is an
automotive inline blade fuse or mini-blade fuse.
These are available from Altronics and Jaycar
and are usually of large format (physical size
and thick wire). Smaller format inline fuses areavailable from various online suppliers.
Fuses are usually supplied with a 250-300mm
loop of wire connected which is cut in the middle
to give two wire ends. This is sufficient length formost connectors.

If a longer cable is needed, then it isrecommended to use an inline insulated crimp
butt connector to extend the positive wire andcut the negative wire to the length required.

Figure 20-7 Inline Fuse

20.3.2

DUAL BATTERY (SELECTABLE) INSTALLATIONSWhen a standard size lithium battery in good condition is used with modern radios and avionics, the battery
is usually capable of supporting flights of 6 or even more hours. The biggest drain on the battery is the radio
when transmitting which normally has a low duty cycle (ie the proportion of flight time spent transmitting isvery small).
Where Lead Acid batteries are used or flights longer than 6 hrs flight duration are planned or a back-up isrequired, then sailplanes may be equipped with two batteries and a battery changeover/selector switch. The
selector switch must not have a centre off position and need only switch the positive supply.
Switching between batteries with the selector switch will cause a momentary loss of power to the supplied
electrical devices which may cause them to reset, render then useless for a short period and/or loose data.
It is possible to bridge the changeover without loss of continuity of supply by using a suitable capacitor butthat is beyond the scope of this Chapter.
Without careful consideration of fusing and current flow protection, sailplane batteries should not be installed
in a parallel arrangement where both batteries simultaneously supply power with the intention of increasing
power duration or current available. There is a risk if one battery suffers and an internal short circuit that theother battery will rapidly discharge due to the short-circuit across its terminals causing the inter-battery wiring
to overheat.

20.4

THE MASTER SWITCH
The master switch is a very important item in the electrical system because it enables the pilot to quickly
disconnect the power from all electrical equipment after the master switch. This is a key safety action if thepilot senses an acrid smell, smoke or fire.
However, a short circuit could still occur in the cabling from the battery to the master switch. As the battery
is often located behind the pilot, the cable from battery to master switch frequently runs under the pilot’s seat– this is not a place you want an overheating cable or fire! This is why a primary (master) fuse is locatedvery close to the battery terminals.
The master switch must have sufficient capacity to carry the peak current loads to which it will be subjected.
The capacity of the switch should be greater than the capacity of the primary fuse/circuit breaker. The
master switch need only switch the positive feed from the battery. It is not required to switch both thenegative and positive feeds, in fact having both wired to the same 2-pole switch increases the risk of shortcircuit.

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What do SPST, SPDT, DPST, and DPDT mean when describing switches?
SP and DP refer to Single Pole and Double Pole: Pole refers to the number of circuits
controlled by the switch: SP switches control only one electrical circuit. DP switches
control two independent circuits (and act like two identical switches that are mechanicallylinked). Do not confuse ‘pole’ with ‘terminal’. The DPST switch, for example, has four
terminals, but it is a DP, not a 4P switch.
ST and DT refer to single throw and double throw: Throw refers to the extreme positionof the actuator: ST switches close a circuit at only one position. The other position of thehandle is Off. DT switches close a circuit in the Up position, as well as the Down position(On-On). A DT switch can also have a centre position (frequently On-Off-On). A throw
position may also be ‘momentary’ ie needs to be physically held in the position.
All master switches must be wired as single throw ON-OFF with no centre position. A Double Throw (DT)switch may be used provided the terminal at one end of the throw is not used.
For most applications in a sailplane, only a SPDT switch is needed. However, acommonly available switch format is the Double Pole, Double Throw DPDT ON-ON
switch (which has 6 terminals). A DPDT switch can easily be used as SPDT by
ignoring one of the poles. The circuit symbol for a DPDT switch is shown right.
It is usual for the master switch to be a toggle switch (rather than a rocker, push button or rotary switch)
because they provide a more affirmative feel and indication of the off position in an emergency. The aviation
standard for switch installation is toggle UP or forward for ON.
Dual battery (selectable) installations must have a single ON-OFF master switch in addition to a battery
selector switch. The battery selector switch should be a Double Throw (DT) switch with ON-ON capability.
DT switches of the ON-OFF-ON type shall not be used as a combined master switch and battery selector fordual battery installations due to the risk of passing through the OFF position in an emergency andunintentionally selecting the alternate battery.
There are hundreds of different switch types available from suppliers such as Element14 and RS. You are
not limited to just the products sold in automotive shops or electronics shops such as Jaycar and Altronics.
The characteristics to consider when selecting a switch include:a.

Switch action. It is recommended use only toggle switches because they give a clear visible andtactile indication of switch status.

b.

Current/voltage rating. It is best to use a switch rated at 24V or 12V Direct Current (DC) and at least
the desired max current eg 7.5A. However, many switches are only rated in Voltage Alternating
Current (VAC). As a rule of thumb, a product rated as 10A at 120VAC is usually suitable for 10A at
12V DC.

c.

Number of poles and throws. Select SPST or DPDT. Do not use On-Off-On switches.

d.

Dust proof.

e.

Physical size. The switch does not have to be big to handle the current, see figure below.

f.

Panel hole diameter. If replacing a switch, it is important that the switch diameter matches.

g.

Terminal connections. The options are: soldered, screws, Faston. Soldered is most commonly
used.

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Figure 20-8 Example of Different Size DPDT On-On toggle switches Rated at 7.5A - all are suitable as
Master or Battery Selector
Annual Inspectors may come across DPDT Master switches that have been wired in several ways other thanas a Single Pole switch. Often this is with the intent of ‘sharing the load’ across two poles so that a lower
rated switch DPDT switch can be used. These are some of the configurations that might be found:Figure 20-9 Examples of Alternative DPDT Wiring

20.5

CIRCUIT PROTECTION
Circuit protection is provided by either fuses, circuit breakers (CBs) or a combination of both.
The purpose of a fuse/CB is to prevent a current flow in excess of the capability of the wiring system or
equipment item. A fuse/CB is the “weakest link” in the circuit, the part that fails first, (fuse “blows” and CBs“pop”), and thus prevents the cabling or equipment overheating and at worst catching fire.
In a sailplane, the circuit protection comprises:a.

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The primary fuse (also known as master fuse or battery fuse). There must be one located as close to
the positive terminal possible (not more than 175mm) for each battery. This has to be large enough to
supply the current required by all the equipment loads operating at the same time (worst case) but
must be less than the rating for the cable supplying the secondary fuses. A 5A fuse is usually suitable
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in single seat sailplanes.
b.

Secondary fuses (also known as equipment or circuit fuses). So that a fault can be isolated and notaffect the entire system, the equipment is divided into circuits with each circuit having its own overload
protection. As the current flow from the battery is divided between the circuits, the individual
equipment circuits wiring current will be lower than the battery current and the secondary fuses will
have a lower rating than the primary fuse. The circuit switch rating and circuit cable gauge may besmaller thus saving weight, space and making the installation easier to install. However thesecondary fuse must always be rated lower than the following switch and cable that it protects.

In the past fuses have been used almost exclusively due to cost and the bulk of CBs but now small andinexpensive circuit breakers have become available from aircraft equipment suppliers. The Klixon 7277
series is an example of one type of miniature circuit breaker.
Whilst circuit breakers are very useful solution in certain applications, it should be noted that a good quality
fuse will ultimately be more reliable (there are no moving parts) so should be considered first. Where
sensitive electronic equipment is involved a circuit breaker is not recommended because the time taken forthe circuit breaker to operate can be longer than it would take a traditional fuse to blow, potentially exposing
the equipment to damaging overload currents for longer.
Overcurrent protection should be checked on an annual basis ie check the fuses or CBs match the
manufacturer’s specification or circuit diagram and appear appropriately rated. Particularly in club
sailplanes, blown fuses have often been replaced with a fuse that was at hand rather than a fuse of thecorrect rating.

20.5.1

FUSE/CIRCUIT BREAKER RATINGS
Each fuse or circuit breaker used in the electrical system must be correctly rated for the circuit it has toprotect. The rating of each fuse should be slightly greater than the equipment manufacturer’s specified
maximum current draw (but the same as their recommended fuse rating) and lower than the cables it
protects.

Figure 20-10 Two Klixon Circuit Breakers Being Prepared for Installation.
Voltage drop in long cables (due to the cable’s resistance) must be considered when sizing overcurrent
protection as a voltage drop will cause a current increase for the same power draw by the equipment load.
When installing fuses/CBs, the correct values should be taken from the manufacturer’s published data forthe equipment. Where this data is not available, Table 11-3 in FAA AC 43.1B provides some limited
guidance.

20.5.1.1 FUSES RATING AND MARKING
Fuses are rated and marked with the following:

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a.

Continuous Rating:Fuses are marked with the current that they will continuously pass (at astandard temperature) without blowing, known as the continuous rating. It is good practice not to allow
the continuous current to exceed 75% of the fuse's rated value to accommodate momentary current
surges that might cause the fuse to fatigue over time or blow unnecessarily (nuisance blow).

b.

Blow Rating:In simplified terms this is the current rating at which the fuse will blow. Most fuses
have a blow rating around twice that of the marked continuous rating. A 5A continuously rated fusewill have a blow rating of approximately 10A. Some older style fuses may still be marked with the blow
rating rather than the continuous rating so care should be taken when replacing an older style fusewith a modern one that the ratings are understood and the correct fuse used.

c.

Voltage Rating: Fuses are marked with the maximum voltage they can be operated up to. It is normal
to find 230V rated fuses in a sailplane’s 12V system.

20.5.1.2 TYPE OF FUSES
The most common fuse types found in sailplanes are:a.

3AG. These measure length of 1-1/4 inches and 1/4 inch diameter. ‘3AG’ means Size 3 Automotive
Glass. Sometimes call ‘the American Fuse’.

b.

M205. These measure 20m x 5mm diameter. Sometimes called the ‘European Fuse’.

c.

Automotive standard, mini and micro blade fuses.

Fuse holders for each fuse type are available as in-line or panel mount. For secondary fuses, it isrecommended they be panel mounted so as to be easily accessible to replace or remove (to isolate acircuit). Also, the 3AG and M205 fuse in-line holders that are generally available are often of poor electricalquality.

M205 panel fuse holder. This type isrecommended.

5A 3AG Inline Fuse Holder. This type ofholder is not recommended for battery
packs or behind panels.

20A 3AG In-line Fuse Holder. This type is
not recommended behind instrument
panels.

Automotive blade fuses panel-mounted in
an Astir, (the 2 black items on the left).
Not often seen but nothing wrong withusing them.
Fuses should be marked with a device
description and current rating. Eg Radio
3A.
Also shows a double USB socket bottom
left.
Figure 20-11 Examples of Fuses
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20.6

VOLTAGE DROP
All components, including cable and connectors, in an electrical circuit have a level of resistance to the flowof the electrical current and thus a potential difference is established across the component according toOhms Law V=IR. This potential difference is known as the component’s voltage drop. The bigger thecurrent, the large the voltage drop across each component. The resistance to current flow causes heat to begenerated.
In sailplane electrical system, the battery provides a potential difference (measured as voltage) that drives
current around the circuit to reach a target device eg the radio. Since all components in the circuit have a
voltage drop, the voltage available at the target device is less than the voltage at the battery. If too muchvoltage is ‘dropped’ across the circuit components, then there may be not enough voltage remaining tooperate the device.
Radios on transmit mode may fail to transmit properly when the voltage at the radio drops below 12 volts but
will usually continue to receive provided the supply voltage in excess of 10 volts. Modern avionics are
relatively tolerant of voltage drop because they have voltage regulators that convert the presented supply
voltage down to 6 volts for the electronic circuits. 12 volts, as measured at the radio, is thus considered theminimum useful voltage.
Voltage drop is much more an issue with systems using Lead Acid batteries because the battery voltage
diminishes significantly and early during the discharge cycle, so the threshold of useful voltage at the radio isreached sooner. Lithium batteries discharge at a near constant voltage so the threshold of minimum voltage
at the device will not be met until near the end of the discharge cycle. However, voltage drop is always an‘enemy’ because it is a parasitic drain on the battery charge and thus is best minimised.
Major causes of voltage drop in sailplane electrical circuits and strategies to minimise it are:

CAUSE

MITIGATION STRATEGY

Battery voltage drop with discharge

Use lithium battery

Small gauge battery feed cableUse minimum 18AWG tinned stranded copper.

High resistance joints and connectors

Minimise joints and connectors
Use ferrules to avoid loose strands and ensure
max contact with screw terminals
Screw terminals tight but not over tight.
Use crimps rather than solder

Circuit breakers have a high resistance,
especially low Amp rated CBs.

Use fuses.

The smaller the CB rating the higher thevoltage drop.

Use the highest safe value of circuit breaker.

Cable has resistance

Minimise cable lengths, increase cable diameter(ie reduce gauge)

Switch internal resistance – dust penetration,
contact degradation due to age or use beyond
specification

Use good quality dust proof switches of suitable
ratingRadio draws a high current so all components
in radio circuit have bigger voltage dropRadio must have own dedicated sub-circuit

Table 20-1 Voltage Drop Cause and Mitigation

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20.7

WIRES AND CABLES

20.7.1DEFINITIONS
A wire is described as a single, solid conductor, or as a stranded conductor covered with an insulating
material. Because of in-flight vibration and flexing, all aviation wire should be stranded to minimize fatigue
breakage.
The most common conductor material is copper but occasionally aluminium may also be found in sailplanes.
The copper wire strands are usually coated or ‘tinned’ with tin or silver to stop oxidation of the copper
surface and hence improves conductivity.
Wires are insulated with a non-conductive sheath to prevent short circuits. Insulation is usually a single wall
but double wall insulated wire is available.
The most common forms or cable insulation found in sailplanes are:a.

PVC: Relatively soft and flexible. Most automotive grade cable is PVC. A fingernail will usuallydent insulation and then it restores.

b.

ETFE (often called Tefzel wire): Hard and relatively inflexible. A fingernail will not dent insulation.
Good quality wire strippers are needed to work with this type of cable.

c.

Rubber/silicon: Very flexible and feels spongy. Not as common as PVC and ETFE.

In aviation, wire is considered to be either:a.

Hook-up wire (for use behind a panel) - single wall insulated.

b.

Airframe wire (for use in exposed situations) - double wall insulated.

See AC 43-13 Chapter 11 for details on this topic. Sailplanes usually only use ‘hook-up’ wire.
Where two wires (each individually insulated) are together covered with a sheath of insulation, it is referred
to as ‘jacketed’.
The term “cable,” as used in aircraft electrical installations, includes:a.

Two or more separately insulated conductors in the same jacket.

b.

Two or more separately insulated conductors twisted together (twisted pair).

c.

One or more insulated conductors covered with a metallic braided shield (shielded cable).

d.

A single insulated centre conductor with a metallic braided outer conductor (radio frequency cable).

The term “wire harness” is used when an array of insulated conductors are bound together by lacing cord,
metal bands, or other binding in an arrangement suitable for use only in specific equipment for which theharness was designed; it may include plug/socket terminations. Wire harnesses are often supplied withradios and flight computers to connect with other electrical components.

Figure 20-12 Example of Wiring Harness
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All wire has resistance to current flow and therefore will consume power and under high current will heat up.
A wire will fail if it becomes so hot that the wire melts or the insulation melts/burns. A thicker diameter wire
has less resistance and therefore can conduct more current but has bigger weight and costs more.
Therefore, in general, we seek to use the minimum diameter wire that can carry the circuit maximum current
plus a safety margin so that neither the wire or insulation melts.
Wire is rated for the maximum current (plus a safety margin) it can pass without melting the wire or insulation
when used in free air. If used in bundles or in conduits, the safe current capacity must be down rated but
this is rarely required in sailplanes.
Most wire and cables have specification codes printed on the outer insulation at regular intervals. This canbe difficult to read (a magnifying glass or mobile phone camera is useful) and may be missing on shortlengths. The outside diameter of the insulation is not a valid indication of the diameter of the conductor wireor the wire’s rating.

20.7.2AIRCRAFT GRADE WIRE
There are a bewildering number of standards that apply to wire. Reference to “aircraft grade wire” isnormally taken to mean wire than conforms to SAE AS22759 standards (also seen written as MIL-W-22759
or M22759). This is an old standard from which the military and commercial aircraft manufacturers have
moved on to newer standards. However, M22759 is still widely cited and available.
The product coding system for M22759 is shown below.

Figure 20-13 M22759 Coding System
The most commonly used single insulated wire is M22759/16 which is unshielded multi-strand copper wirewith each strand usually coated with tin or silver) with extruded EFTE (ethylene-tetrafluoroethylene)
insulation. ETFE insulation has fire resistance properties well suited to the aviation environment. It ispreferred by many sailplane owner/operators and is compliant with CASA motorglider engine system wiring
requirements.
There is also M22759/32 which is also ETFE but much thinner insulation than /16.
M22759/16-20-0 (black) and M22759/16-20-2 (red) wire is probably the best option if you want a generalpurpose good quality hook-up wire. This is available from Australian suppliers such as Cambridge
Technologies or various specialist auto racing supply companies, usually in 30m rolls.
The most common brands of aircraft grade cables historically have been:a.

Tefzel®. Tefzel is a brand name belonging to Dupont and describes the insulation material which isa modified ETFE fluoropolymer known for its mechanical toughness and outstanding chemical
inertness.

b.

Spec 55 and Spec 44. These are brand names owned by Raychem - TE Connectivity and describes
a range of cable products insulated with modified radiation cross-linked ETFE polymer andcompliant with the AS22759. Spec 55 has its own part numbering system as shown below.

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Figure 20-14 Specification of Type 55 Wire and Cables
Another common specification for cables is MIL-C-27500. This is a specification of screened / shieldedcables often used for sailplane microphones.

As a general guide for aircraft grade wire current ratings, the following table based up AC43-13 (Table 11.3),
Tefzel wire manufacturer’s information, AN standards and common practice may be useful:

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Wire
Gauge
AWG

Cable

CB

Fuse

Max
Amps

Max Amps

Max Amps

Core
Diametermm

Core crosssectionAC43-13AC43-13

24

3.5

N/A

N/A

0.51

0.20

Very thin, light duty only.
Microphones (when shielded)

22

7.0

5

5

0.65

0.33

Adequate for most panel work
but not radio power supply.
Fiddly to work with.

20

11

7.5

5

0.81

0.52

Good for most panel work,
easy to work with

18

16

10

10

1.02

0.82

Battery feed

16

22

15

10

1.29

1.31

Battery feed

mm2

Use and comments

Note: All of the above current ratings are conservative (ie below the theoretical maximum for situations likely
in a sailplane).

20.7.3

AUTOMOTIVE AND MARINE CABLE
Automotive and marine cable is often insulated with PVC which does not perform as well under heat as
Tefzel and is a softer material.
Automotive and marine cable is usually sold in nominal sizes of “2.5mm”, “3mm”, “4mm” etc. Note thedimension is often neither the conductor diameter or conductor cross-section area.
The cable manufacturer will normally specify a current rating at an ambient temperature of say 30⁰C for asingle cable. It will then give tables of “derating factors” for situations of cables being bundled and/or
operating at higher ambient temperature.
For example: A leading Australian manufacturer of automotive cable states: “3mm” (1.13mm2 cross-section)
cable rated at 20A at 30⁰C. When used bundled with a second similar cable apply factor of 0.8. When usedin an ambient temperature of 50⁰C apply factor of 0.76.”
So in a typical sailplane application it would be advisable to regard this manufacturer’s 3mm cable maximum
current capacity as:
20A x 0.8 x 0.76 = 12A
Note that retailers of automotive cable may have already applied the derating factors to their products by thetime they appear packaged and on the shelf. So it is common to see automotive cables labelled as “2.5mm(0.64mm2) 5A” and “3mm (1.13mm2) 10A”. You need to read the specification to see that it has beenderated sufficiently to match the sailplane environment but it is likely that the retailers have beenconservative in the current rating they state.

20.7.4WIRES AND CABLES IN SAILPLANESa.

All wire must be multiple-strand for maximum flexibility and of sufficient gauge to carry the maximum
expected current load for that circuit. Do not use 230V house electrical cable.

b.

All wire around engines and engine systems (including charging systems to batteries) must be ofaircraft-grade wire according to CASA specifications. All other wire should be at least high-quality
automotive/marine cable.

In practice, the main cabling elements in sailplanes are:a.

The power feed from the battery connector to the distribution busbars or secondary fuses. As this isoften 1.5m or more long, it should be at 18AWG or thicker so as to reduce voltage drop. Preferably
it should be jacketed 2-core automotive/marine cable or at least aircraft grade single wall insulated
to offer a good level of physical protection.

b.

Device wiring harnesses. It is common practice for the manufacturer of complex devices to provide
a harness with a plug at one end that matches a socket on the device and lose wires at the otherend to be terminated in connector blocks or joined to other wires. The harness may not use aircraft
grade wire but it can be assumed the manufacturer has been diligent in the design and constructionof the harness. In many cases the harness installer will not have shortened the harness wires andVersion 24.1

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thus left a coil/bundle of wires behind the panel which can include numerous unused wires. A skilled
technician may be able remove excess wire length and neaten the installation.

20.7.5c.

Link wires. These are relatively small wire lengths linking devices and creating busbars. 20AWG
wire is recommended as it has ample current capacity for in sailplanes and is easy to work with.

d.

Microphone cables. Cabling should be 22AWG or 24AWG 2-core aircraft-grade screened cable toreduce the possibility of interference noise.

e.

Speaker cables. Usually figure-8 general purpose 22 AWG or 20AWG copper speaker cable isadequate. The cable described above for microphones is also suitable.

f.

Radio antenna cable. Radio antenna cables (including Flarm and GPS aerials) should be goodquality 50Ω coaxial antenna cable with good quality fittings. Poor radio performance is frequently
due to antenna cabling issues.

g.

Data cable Where data cables are used, such as between flight computers, GPS, FLARMs etc, anycommercially manufactured cable for the appropriate data type that conforms to the relevant
communications standard.

WIRE COLOUR CODING
In accordance with normal electrical practice, red wire is normally used between the positive terminal of abattery through to the devices, and black is used for all negative (ground) wires.
The use of a different coloured wire for the positive of different sub-circuits can aid clarity, especially if thisinformation is recorded on the circuit diagram.
Commercial and military aircraft often use exclusively white wire/cable. This is acceptable in sailplanes but it
must be well labelled to enable easy maintenance in the future.

20.7.6WIRE SECURITY
All electrical wire must be secured to prevent movement. Wires should be secured to the aircraft structureand not to items such as control systems etc. Securing the wires will reduce abrasion, fatigue and generalwear and tear on the wires. Special care must be taken with securing wires in metal aircraft as abradedinsulation may result in a short circuit to the metal structure.
Use proper cable clips or else nylon/plastic cable ties. Do not use insulation table to secure cables as thisdries out and comes undone.
When installing electrical wires it is important that they are not stretched too tight. The correct amount ofslack is shown in the figure below. If there is more than about 12 mm slack in a wiring loom, then extra
supports will be required.

Figure 20-15 Slack between supports
Wires and cables that supply movable devices (eg PTT, cruise/climb buttons in control columns) must be
specifically selected for this task and sufficient allowance for full travel movement should be made for thisapplication.

20.8

JOINS AND TERMINATIONS
Wherever an electrical system is installed, joins between wires and terminations with equipment will need tobe made. The most effective ways to achieve these are:a.

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Joining multiple wires - Terminal blocks (screwed, spade/Faston or stud/ring)c.

Common earthing point for multiple negative terminals - Single stud using crimped ring terminatorsd.

Plug/socket connectors – with soldered or crimped terminals

It is not acceptable to rely on mechanically twisting wires together or wrapping wires around pins/studs tomake joints and terminations.
The connector types shown below in Figure 20-16 are not to be used as they have questionable reliability ina sailplane environment.

Figure 20-16 Connectors That Should Not Be Used In Sailplanes
Heatshrink tubing is often used when making joins and terminations to add a layer of insulation and/or formof basic labelling. A heat gun or back of a soldering iron is used to apply heat. Beware of damaging heatblowing/conducting to other components such as the fuselage and canopy!
Insulating tape does not provide an effective long-term joint insulating solution as the adhesive is prone to
failure with age and heat.

20.8.1SOLDERING
Soldering involves using a lead-free metal alloy wire with rosin flux core that melts at relatively low
temperature when heated with an electric powered soldering iron.
There are numerous videos available on YouTube that demonstrate soldering techniques such as butt joints,
wrap joints, tinning etc. It is best to practice on spare wire before attempting on a sailplane electricalsystem. Beware of using large soldering irons which can rapidly transfer high temperature heat that candamage insulation and devices.
It is usual to cover soldered joints with heatshrink tubing. It is important to consider when to place theunshrunk heatshrink on the cable as it may not be possible to position it after the soldering has been done.
When inspecting soldered terminals and joints an inspector should check for:a.

Damage caused by corrosive flux that may have been used causing the joint to deteriorate over
time.

b.

Fatigue (ie bending) failure. Wire strands are stiffened by the solder and can become susceptible tofailure.

c.

Wire insulation charred and/or shrunk back during the soldering process, exposing wires. This isoften a problem with PVC insulated wire.

d.

Stray strands or sharp solder protrusions puncturing the heatshrink.

Heatshrink covered low temperature solder butt
connectors are available. The solder is meltedwith the heatshrink in place using a heat gun or
soldering iron. It takes practice to use theseeffectively!

20.8.2CRIMPED JOINS AND TERMINALS
Crimping involves squashing a metal tube around the wire. It is, electrically and mechanically, a very
effective way of joining cables or attaching a lug to a cable. The most important tip for achieving a firm
conductive crimp is invest in good quality crimpers which match the crimps you are going to use. Do not try
and crimp with normal pliers or a cheap automotive crimp tool as they rarely achieve a secure result.

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Figure 20-17 Types of crimp terminals

Figure 20-18 Commonly used types of crimp terminals in sailplanes
Crimp terminals are colour coded for wire size (gauge). The correct size of crimp terminal must be used forthe wire that is to be connected. Red (20-24 AWG ) is the most commonly used terminal colour in
sailplanes.
When using ring terminals, the ring internal diameter should be matched to the diameter of the bolt or stud it
is to attached to. 3.5mm diameter rings are used with switches and CBs. 4mm or 5mm diameter rings areused with terminal studs.
Spade terminals must not be used as they are prone to becoming detached.
Heatshrink pre-covered terminals are available.
Faulty crimps should be replaced by a competent person using the correct crimp tool.
Where crimp terminals have been used, the inspector should ensure that the crimps are secure by gently
pulling on the wire to see if it will pull free of the crimp.

20.8.3TERMINAL BLOCKS

20.8.4

Terminal blocks are a convenient way of joining multiple wires. There are numerous types including studs,
spade blocks and screw terminal blocks.

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Stud block

Screw terminal block

Faston blade terminal blockTwo types of screw block are available

Figure 20-19 Examples of terminal blocks
Screw terminal blocks are commonly used in sailplanes for power, data and control wiring. The following
points should be observed:a.

Use a good quality block that is correctly current rated and securely fixed to an appropriate part ofthe sailplane. Usually a 6A rated block is suitable. Higher current rated blocks are designed forlarger wire and may not securely grip small wires used in sailplanes.

w.

No more than 3 wires per screw clamp.

x.

If inserting more than one wire under a screw, twist the wires together before inserting under thescrew and tightening the screw firmly. Two wires may be crimped together in a ferrule before
inserting under the screw.

y.

There must be no mechanical load on the wires (ie force that might pull the wire out from under thescrew.

z.

Ensure minimum exposure of bare wire and no lose strands. Insulated ferrules (sometimes referred
to as ‘boot lace’ terminals) prevent this.

aa.

It is recommended not to mix power supply connections with other connections (eg speaker,
microphone or data connections) on the same connector block. This reduces the risk of inadvertently
feeding power where it might cause damage.

bb.

Stud blocks must be well insulated if used for positive connections.

Terminal module blocks should be securely mounted and provided with adequate electrical clearances orinsulation strips between mounting hardware and conductive parts, (not necessary when the terminal blockis used only for grounding purposes). (ref AC43-13A).
Where multiple connections are required, a terminal block is best configured as a ‘busbar’ as shown below
for a screw terminal block. Note the same gauge wire as used from the Master Switch, is used for allconnections along the top of the terminal in the diagram.

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Figure 20-20 Screw Terminal Block Configured as a Busbar
Rather than constructing positive and negative buses, some technicians prefer to interleave the positive andnegative terminals as pairs. This is not wrong but does mean there is an increased possibility of short circuit
between positive and negative wires.
A single lone threaded stud (usually 4 or 5mm diameter) secured to the instrument panel frame can be used
as a common ‘earthing point’ for negative wires in a sailplane. It is not necessary to insulate an earthing
point provided positive wires are secured well away and insulated.

Figure 20-21 Single Threaded Stud as a Common ‘Earthing’ Point and Connector Blocks

20.8.5CONNECTORS
Wherever there is a need to disassemble a wiring loom for maintenance, such as to remove an instrument
panel, it is recommended that a multi-pin connector be installed. Use connectors with suitable current
ratings.
Other places where electrical connectors can be used are; for all wires entering or leaving the instrument
panel, the wires for the press-to-talk switch on the control column and where several wires go into the one
instrument such as the radio.

20.9

RADIO PRESS TO TALK (PTT) SWITCHES
The radio press to talk switch is probably the most used switches in a sailplane. Whilst it appears to be justa simple spring return OFF-ON (Momentary) switch there are other characteristics that need to beconsidered:a.

Size - small enough to fit in the end of the control stickb.

Reliable – must work consistentlyc.

Tactile – ideally the switch should have a feeling of a ‘click’ as it makes contact

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d.

Positive contact – when pressed it makes a good contact, no need to keep pressing harde.

Sealed – protected against dust and body sweatf.

Current rating – not usually a factor as little current passes through

There are numerous cheap options available at Jaycar, Altronics and online. However, it is probably worth
buying a higher quality but more expensive switch such as shown below.

Figure 20-22 Example Push to Talk Button

20.10

AUXILLARY DC POWER OUTPUTS
Many pilots choose to use portable electronic devices for navigation, soaring performance data orcommunication. They often wish to power these devices from the sailplane power system but until recently
this facility was rarely provided by sailplane manufacturers. Thus, the addition of a DC power outlet or lead
is a common modification which needs careful consideration and implementation.
Many of the portable devices use the USB standard voltage of 5V DC. Since the sailplane system voltage isnominally 12V, a 12V DC to 5V DC power converter is required. Some panel fitted variometer or GPS
devices offer a 5V power output suitable for USB.
If a voltage convertor is required, it must be decided if the converter is to be permanently wired into thesailplane system or else a 12V DC outlet connector provided so a portable converter can be connected.

CAUTION
It has been found that many cheap 12V to 5V converters cause radio interference.

20.10.1 PERMENANTLY INSTALLED POWER CONVERTERS
Some sailplane specific portable devices are supplied with their own 12V power converters. As an example,
the Naviter Oudie is supplied with a 12V to 5V mini-USB power converter and also includes prewiring of themini USB with a data connection via a RJ45 plug with standard IGC pin-out.
For a smart phone or PDA device running a soaring application such as XCSoar, a USB socket may bedesired to extend battery life. Commercially manufactured DC converters for permanent installation areavailable relatively cheaply and normally provide a 5V output of up to 3A shared usually by 2 pre-wired
sockets or leads with female jacks. For such a unit, the input current would be approx. 1.5A at max output
load.

Typical 12V/5V converter with USB sockets“Oudie 2” power lead and converter

Figure 20-23 A typical DC power convertor
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Most USB connected devices do not draw much current but consideration must be given to the worst case ofconnecting a device with a flat battery which will draw a charging current as well as an operating current.
Also consider if multiple USB devices will be connected.
Whilst a converter will usually have inbuilt protection for output short-circuiting and over current, there is noprotection for the input supply cables and malfunction of the converter. Therefore, it must be connected sothat it is protected by the secondary fusing of a circuit.
The point of connection to the sailplane’s 12V system should either be to:a.

An existing circuit, but not the radio circuit. Connect after the circuit fuse and switch (if fitted).
Check that the fuse rating is suitable for the now changed maximum current load possible in thecircuit. Check that the fuse rating is lower than any of the wiring used in the existing circuit and theadded wiring to the converter.

cc.

A new circuit. This requires a new secondary fuse to be added and connected to the positive busbar.
The fuse should be rated slightly higher than the expected current draw by connected devices but
must be rated lower than the cabling used.

It is dangerous to connect an auxiliary output socket or lead to the positive busbar without a secondary fuse.
In the event of a short-circuit in the relatively thin wire used on these sockets and leads, without a suitablefuse, the wire may overheat and burn.

20.11

RADIO INTERFERENCE
Radio systems are prone to interference from other components or Radio Frequency (RF) feedback due topoor antenna matching. The interference may manifest as unwanted noise on receive and distorted
transmissions. Using shielded cables or twisted wires on microphone leads and good quality antenna leads
can help.
RF feedback can be reduced by positioning RF filters, known as ferrites, on cables. Ferrites are metal beads
made from a specially formulated ferrite powder. These are occasionally seen as bulges on printer and USB
cables. It’s important to ensure they are suitable for the VHF frequency range used by sailplanes. Slip onand clip on versions are available.

Figure 20-24 Examples of RF ferrites and where to use them (MGL products)
There is a good explanation of the causes and possible solutions to radio interference at this URL:
http://www.mglavionics.co.za/Docs/EMI%20suppressor%20for%20VHF%20frequencies.pdf

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20.12

ELECTRICAL BONDING
Sailplanes with metal or conductive parts (eg carbon fibre) may be fitted with electrical bonding – wires
joining all conductive parts together to create an equipotential structure. This bonding prevents static
electricity build-up that can interfere with radio and navigational equipment. Bonding also provides lightning
protection by allowing the current to pass through the airframe with minimum arcing.
Bonding wire is usually multi-strand fine
braided with crimped lugs and uninsulated.
In motorised sailplanes, bonding is used tominimise the risk of dangerous static
discharges in aircraft fuel tanks and hoses.

20.13

PLACARDS
Sailplanes fitted with electrical systems must be placarded to allow safe operation. Specifically:

20.14

a.

The master switch must be labelled MASTER and at least the ON position identified. It must be
positioned to operate ON in the UP orientation.

b.

The battery selector switch must be labelled for the different batteries eg BATT1 – BATT2.

c.

All fuses and CBs must be labelled as to which circuit they protect. Fuses should additionally belabelled as to fuse rating to be used e.g. 2A.

d.

Any circuit (power) switches for individual equipment must be labelled for ON and OFF and theequipment operated by the switch e.g. RADIO, AVIONICS, AUX.

e.

Control switches should be labelled with their function e.g. CRUISE/CLIMB.

UNDERCARRIAGE WARNING SYSTEMS
Many sailplane owners choose to install an undercarriage warning system to alert the pilot that theundercarriage is not down when the airbrakes are deployed. Such systems reduce the risk of landing“wheel up” by sounding a buzzer and/or illuminating a warning LED when on final.
The system usually uses two sensing switches; one that closes the circuit when the undercarriage lever is
moved from the wheel-down and locked position and one that closes the circuit when the airbrake (divebrake) lever is moved from the retracted (in and locked) position. The basic system is shown in Figure20-26.
The switches may be operated mechanically by physical contact (usually called a micro-switch) or by else by
sensing a magnet in close proximity (usually called a reed or proximity switch). These switches usually haveconnections for Normally Open (NO), Normally Closed (NC) and Common (COM). Normally Open means
an electrical current passes if a microswitch is not in physical contact or a reed switch is not in proximity witha magnet.
With a magnetic reed switch, it is usual for the switch to be fixed to the airframe and the magnet to be
attached to the control rod to avoid wires moving when the rod is activated.
Warning system switches, magnets and wiring must be secure and not interfere with the movement ofcontrols.

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Figure 20-25 Magnetic Reed Switch Principle of Operation

CAUTION
Some undercarriage warning systems include a “Test” function. In most cases this ismerely a test that the battery is fitted and switched on, and that buzzer makes a noisethat can be heard by the pilot. The Test function does not confirm that the mircoswitches are correctly sensing the positions of the undercarriage and airbrakes.
Therefore, when inspecting the undercarriage warning system, it may be necessary to lift
the glider so that the wheel is clear of the ground and cycle the system to ensure that it isoperating correctly.

Figure 20-26 Undercarriage Warning System
A slightly more advanced version has the test switch wired to short just the undercarriage switch. Thus, on
the ground with the test switch pressed (simulating the wheel up), operating the divebrake should cause thebuzzer/LED to operate.
For 2-seater aircraft, test switches and warning LEDs can be sited in both cockpits by adding a 2nd test
switch in parallel with 1st test switch, and 2nd LED in parallel with 1st LED.

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20.15

MOTOR GLIDERS
The engine electrical system must be maintained in accordance with the information supplied by the
manufacturer.
If an electrical system for driving the avionics is added to a motor glider, it must be completely independentof the engine electrical system unless the design is approved by the motor glider’s manufacturer or GFA.
Electrical systems in a motor glider have the additional effects of vibration and heat to be considered. This
usually restricts the use of soldered connections unless the joint is supported and protected by heat shrink
tubing.
Further information regarding electrical systems in motor gliders can be found in the GFA “BSE – Engines”
publication.

20.16

INSTALLATION OF EQUIPMENT
Most electrical systems installed in sailplanes are modifications to the manufacturer’s original TypeApproved sailplane. These modifications, like all modifications, must be in accordance with the standard
procedures set down here in BSE and MOSP3.
When inspecting systems such as radios, variometers, undercarriage warning systems etc. these systems
must be checked for physical interference with flight controls when these controls are deflected to theirmaximum travels with the sailplane rigged and derigged.
When fitting electrical components, it is vital that all components are is properly restrained. The installation
should be done in accordance with BSE. In particular, when a battery or other component is installed
directly behind the pilot, the crash load case of at least 15G forward must be used. See Sections 9.5.1
EQUIPMENT RESTRAINT and 9.5.2JUSTIFYING THE STRENGTH OF A RESTRAINT.
If a battery (or any other equipment) is installed in a position where it has a significant effect on the weightand balance characteristics of the sailplane, the changes to the aircraft weight and balance must be
determined by persons authorised for weight and balance work.

20.17

ANNUAL INSPECTION
At each Annual Inspection, the electrical system must be checked to ensure that it is still in airworthy
condition. If the manufacturer installed an electrical system in the sailplane, it must be maintained inaccordance with the manufacturer’s instructions.
All electrical equipment should be kept free of dust, dirt and grime.
When inspecting an electrical system, the inspector should ensure that the system has safe operating
characteristics with respect to master switches, fuses, wiring quality etc. as described in the previous
sections.
During the inspection, the following should be examined:a.

All batteries that are normally used in the sailplane for the presence of a primary (master) fuse (or CB)
in the positive lead, a suitably rated fuse is in use and that the battery terminal connections are secureand insulated to prevent short circuit.

b.

The battery mounting/securing device. The battery must be secured so as to remain in position if
subjected to a force of 15G in the longitudinal plane.

c.

The Master Switch isolates all devices and has the correct orientation (On is up or forward).

d.

The following for damage or overheating:

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v.

20.18

Insulatione.

Electrical bonding integrity. However, if bonding was not fitted by the manufacturer there is no needto fit it.

f.

No dirty equipment or connections.

g.

Cables are adequately supported and secure so that no risk of cables causing limb or controls
entanglement.

h.

Connectors and terminals for:i.

Loose connections.

ii.

Poor crimps

iii.

Excessive number of wires in the same terminal screw-down hole or stud.

iv.

Excessive exposure of wire at terminals due to too much insulation cutback or shrinkage.

v.

Stray wire strands (not contained in the connector/terminal) that might cause a short circuit.

vi.

‘Orphan’ wires that go nowhere and are not terminated with an insulator.

i.

Check there is sufficient clearance between exposed current carrying wires/parts and ground/negative(especially where a metal airframe is used as the current return), e.g. at the +ve busbars.

j.

Circuit protection fuses and/or circuit breakers for appropriate rating.

k.

Placards on switches, fuses and CBs.

l.

Functionality of undercarriage warning system, if fitted.

m.

Condition of tail battery, if fitted. Check for leakage and potential damage to components below thebattery.

EXAMPLES OF FAULTS AND CONCERNS

Concern: Soldered connections tobattery – not recommended. Clear
heatshrink in placed but has notbeen shrunk!
Risk: Increased risk of short circuiton battery side of fuse where there isno fuse protection

Fault: 30A fuse holder has exposed
wire on battery side of fuse holder
and insulation is splitting.
Risk: Increased risk of short circuiton battery side of fuse where there isno fuse protection

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Battery changeover switch withpositive and negative wires bothswitched at a small profile DPDT
switch.
The heat shrink has been wellapplied. It is not possible to checkthe soldering without damaging theheatshrink.
Concern: It is not required to switch
both positive and negative wires.
Risk: Unnecessary risk of shortcircuit due to +ve and -ve wires from
2 batteries in close proximity.

ASK21 Master Switch pitted after
20+ years in service.
Concern: General deterioration of
the switch, possible dust ingression.
Risk: Unable to switch off system.
Note: Switch failed in service approx
2 months after photo taken!
Fault: Insulation cutback too far or
screw terminal lose.
Risk: Wire could depart fromterminal, short circuit.

20.19

REFERENCES
AC 43.13-1A Change 3. Acceptable Methods, Techniques and Practices. IAP Inc., Casper, Wyoming, 1988.
Tony Bingelis. Sportplane Construction Techniques. Sportplane Builder Publications, Austin, Texas, 1986.

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21.

LUBRICATION

21.1

GENERAL
Lubrication is a wide subject, with a seemingly endless variety of greases and oils available, each with its
own particular properties.
To be able to choose suitable lubricants, proper account must be made of the way the lubricants will be
expected to work in the sailplane/powered sailplane and the types of bearings to be serviced.

21.2

LUBRICANT REQUIREMENTS
Many factors influence the choice of lubricant. While you should endeavour to use the recommended or
required types according to your aircraft maintenance manual, sometimes nothing is specified.
Consideration of the following factors will help the selection of an appropriate type in the absence of specificguidance from the manufacturer:
a.

b.

c.

d.

e.

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Environment:i.

Heat Range,ii.

Moisture, and

iii.

Dust;

Load carrying ability:i.

Impact,ii.

Speed (high or low), andiii.

Cyclic;Material compatibility:i.

Bronze,

ii.

PTFE,

iii.

Steel,

iv.

Aluminium, andv.

Nylon;

Seal type (rubber, nylon etc):i.

Serviceability,ii.

Access for lubrication, andiii.

Maintenance intervals;

Bearing type:i.

Slide,

ii.

Plain rotary,iii.

Ball rotary,iv.

Roller rotary, andv.

Sealed rotary.

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21.3

TYPES OF LUBRICANTS
There are four main types of lubricants that can be used in a sailplane:

21.3.1

a.

Oil

b.

Greasec.

Solid filmd.

SiliconeOIL
Oil is a liquid at room temperature and comes in both organic and synthetic forms. It is not normally used insailplane applications, except where used in motors and hydraulic systems (e.g. wheel brakes, oleo struts).
Oils suffer from evaporative losses so have a shorter service interval compared to other forms. They do tend
to attract dust and dirt, and can wick into unprotected composite fibre structures if used excessively.

21.3.2

GREASE
Grease is just oil with a thickener added to make it semi-solid at the appropriate working temperature. Threemain classes of thickeners are used; metal soaps, organic (urea) or inorganic. The thickeners contribute
greatly to the properties of the lubrication, such as the temperature range that it will lubricate at (both low
and high temperatures), but the actual lubrication is still performed by the contained oil. The thickeners also
contribute other useful properties, such as anti-oxidant, rust prevention, and ability to work under extreme
pressures.

21.3.3

SOLID FILM
These are non-oil-based methods of coating a surface to help prevent sticking and interference. They are
typically used in situations where oil and grease would not survive for any reasonable length of time, such assuspension and gas struts. Typical soft examples are graphite, PTFE (Teflon) and hard examples Titanium
Carbide/Nitride (TiC/TiN) and Chrome. These lubricants, apart from graphite, will not be applied by an
Annual Inspector. If wear is found in surfaces with these lubricants then the item should be checked with anappropriately authorised professional service.

21.3.4

SILICONE
Silicone is a synthetic lubricant that is particularly good where rubber may be used in sliding applications anddirt pickup is not desirable. It typically comes in a pressure pack.
It is not good for rubber seals around water dump systems (standard grease is better here), but the sliding
rails on clearview panels can benefit from silicone if they are sticky.
Silicone can be very problematic around paint and fibreglass, making it impossible to paint or repair areas. It
must be very carefully applied if being used, to ensure that none gets on the main structures of the aircraft.

21.4

RECOMMENDED LUBRICANTS
It is not GFA policy to specify commercial products, particularly lubricants as there is such a wide range
available, and applicable to different roles, as the previous checklist outlines. Use of a Molydenum DiSulphide grease in one application, would be incorrect in another application. When in doubt, first check theaircraft’s Maintenance Manual for requirements.
Use aircraft low temperature grease on control linkages to avoid freezing at high altitude.
Don’t use copper slip in aluminium head spark plug threads. Use Nickel Anti-Seize.

21.5

SHELF LIFE OF LUBRICANTS
Oils and greases are generally quite stable and do not deteriorate over time if left in the original container,
unopened. Some special purpose oils, such as hydraulic (brake) fluid, will have a very limited shelf life as
they will accumulate water if left in an open container, so it is important to be aware of the type of fluid andstorage requirements. Check the packaging for storage requirements.

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As a general rule, synthetic oils and greases will last for 10 or more years with no discernible impact on
performance. Greases can appear to separate so that you get standing liquid and the thickener. Typically aquick mix of the two together will restore the grease to a workable solution.

21.6

LUBRICATION TECHNIQUES
Applying lubricants to various surfaces always should start with a thorough cleaning. Solvents may be used,
but first check as some solvents have a habit of destroying rubber seals and other essential components inthe system being lubricated. Most of the time, a good wipe with a clean rag will be sufficient cleaning before
applying the new lubricant.
Once cleaned, exposed items like spar pins should also be checked for deterioration in the underlying item.
Spar end pins have a tendency to get a light amount of rust due to water from the trailer or being left outside
tied down during a storm – clean and polish it off. Undercarriage and control surface hinges will gather a lotof dust, which can cause scoring or excessive wear. Where possible, a quick test fit should be done without
lubricant applied to ensure that there is not too much freeplay in the system. Lubricants, particularly grease,should not be used to compensate for out of tolerance play.
Don't lubricate a bearing without understanding how the bearing is made and how the manufacturer
considers it should be serviced. The sailplane/powered sailplane manufacturer will also provide somedirections for lubrication maintenance; those recommendations should be adhered to wherever possible.
Some bearings, such as plastic linear control rod bearings must not be lubricated.

21.6.1SIMPLE GREASE GUN
While many greasing tasks can be performed with just the use of a finger and rag, sometimes a grease gun
will be better to lubricate bearings. Several commercial options are available from the local auto parts store
and will work sufficiently well. Alternatively, a homemade grease gun can be fashioned from a simple bolt
and piece of hose.
To use it, fill the hose up with grease using your finger and then press the open end of the hose to the target
bearing. Press on the bolt head until the clean grease starts to appear on the other side of the bearing. See
the following figure.
A cut off disposable syringe also works well and come in various sizes from the chemist.

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Figure 21-1

21.6.2

Simple Grease Gun

GREASE NIPPLESThe Blanik L13 and other European sailplanes and powered sailplanes are manufactured with greasenipples that are not compatible with Australian hand grease guns. In these cases the grease nipples may bereplaced with a local type to allow grease guns to connect properly.
It is not uncommon to see older metal sailplanes still in service with the European nipples, which usuallymeans those parts, in particular the undercarriage, may never have been properly greased. This usually
results in rapid wear of undercarriage mechanisms.
Newer sailplanes should have had these replaced as part of their initial issue of the Certificate of
Airworthiness checks when they are brought into the country, so an Annual Inspector should not need tocheck this often. If nipples have been replaced, an appropriate entry should be found in the logbook.

21.6.3

PRESSURE PACK LUBRICANT WARNING
Most spray can (pressure-can) "Freeing Agents”, such as WD40, are not true long term lubricants, as thefollowing article warns:

Control Lever Rod End Wear
In the process of monitoring an increase in replacements of control lever cable rod ends due to excessive
wear service engineers have made a surprising discovery: some rod end bearings are being lubricated todeath. A review of operator maintenance practices reveals that a significant portion of the failures arebeing induced by over lubrication through improper procedures.
The Heim F34-14 bearing has a split outer race and an SAE 52100 steel element. The bearing is pregreased upon assembly and a small reservoir to hold the operating grease is built into the rod end.
A review of operator maintenance techniques has revealed that operations with the highest frequency of
F34-14 bearing failures are those who are lubricating them with pressure-can lubricants such as LPS or
WD4O. While affording some benefit immediately after application, the method of application of theselubricants may actually contribute to the failure of the bearing.

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Application of pressure-can lubricants, through the use of the extended application tubes furnished withthe can, delivers the lubricant with such force that it actually washes the manufacturer's lubricant out of
the rod end removing its protection and contributing to the failure.
Few of the pressure-can lubricants are effective in high temperature areas such as the engine installation
due to accelerated evaporation of the lubricant carrier. It is felt that elimination of direct application ofpressure-can lubricants will contribute to the life of the F34-14 bearing. If the operator determines thatlubrication is required, it is recommended that the ball element be hand packed with MIL~G-81322, themoisture and temperature resistant grease used in the landing gear wheel bearings.

21.7

GREASING FREQUENCY - UNDERCARRIAGEIn club trainers, experience shows that 50 hour lubrication periods result in extended undercarriage life. GFA
strongly recommends, even where the sailplane/powered sailplane manufacturer does not request it, that aregular "grease and oil change" be adopted as a maintenance policy. This could be hour or number of flights
based.

21.8

REFERENCES
AIR5433A Lubricating Characteristics and Typical Properties of Lubricants Used in Aviation Propulsion andDrive Systems
AeroShell Listing of US Aviation Lubrication Standards
https://www.shell.com/content/dam/shell/static/aviation/downloads/AeroShell-Book/aeroshell-book10busspecs.pdf

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22.

WOODEN CONSTRUCTION INSPECTION AND REPAIR

22.1

WOOD

22.1.1

GENERAL
While wooden sailplanes are no longer being commercially manufactured there are many vintage wooden
aircraft still flying. There are a significant number still in regular club service. Some wooden aircraft continue
to be amateur built from plans.
This chapter provides information on inspection, maintenance, repair and construction of wooden sailplanes.

22.1.2CHARACTERISTICS OF WOOD

22.1.2.1 GROWTH RINGS
Each stage in the growth of a tree is visible by a dark ring formed during the latter part of the growing
season, when the fibres have somewhat heavier walls. For timber grown in temperate climates these rings
represent yearly growth.
For any one species of timber, wood density is indicated by closeness of the growth rings. Widely spaced
growth rings indicate faster grown, less dense and consequently weaker timber.
Aircraft specifications always call up a minimum permitted number of growth rings per unit of radial
dimension of the timber. This is necessary to ensure that minimum strength properties used in design areachieved in practice. For most timbers the growth rings should not be less than six per 25mm, whenmeasured at right angles to the growth rings.

22.1.2.2 SAWING OF TIMBER
A log may be cut in three distinct planes with respect to the annual rings:a.

Cross wise, exposing the transverse or end grain surface.

b.

Lengthwise along any of the radii of the annual rings, exposing the radial, or so called full quarter
sawn, or edge grain surface.

c.

Lengthwise at a tangent to any of the annual rings, exposing the tangential or so called full back sawn
or flat grain surface.

The annual rings often run diagonally across the end of the timber, so that it cannot be said to be either fullback sawn or full quarter sawn. These methods of sawing are illustrated below:

Figure 22-1 Growth Rings

22.1.2.3 MOISTURE CONTENT
Wood will continually give off or take in moisture in accordance with the relative humidity and temperature of
the surrounding atmosphere. The strength is directly related to the moisture content, the higher the moisture
content, the lower the strength.
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After felling, green timber is cut, seasoned and kiln dried to a moisture content of about 15%. In service,moisture content of wood in a typical sailplane will vary from almost zero in Central Australia up to 12% near
the coast. Moisture content will also vary between summer and winter seasons.
When wood loses its moisture, it shrinks. This shrinkage is greatest across the grain in the direction along
the growth rings (tangentially), about half to two thirds as much across these rings (radially) and relatively
little along the grain (longitudinally).
Shrinkage and associated distortion in wooden sailplanes is often a problem, not only because the resulting“starved horse” effect reduces performance, but also large internal stresses may be set up and metal fittingsloosen as the wood shrinks.

Figure 22-2

Shrinkage

Quarter sawn timber shrinks less in width than back sawn timber and is less likely to twist and develop
checks during seasoning. On the other hand, back sawn timber is cheaper and any knots present will be
round or oval, instead of long spike knots.

22.1.2.4 GRAIN EFFECTS
Timber is a complex structural material consisting of large numbers of hollow fibres cemented together. The
individual fibres are relatively strong in tension, but depend on collective restraint against buckling for theircompressive strength. Timber is strongest when loaded in the direction of the grain.
The compressive strength of timber is about half of the tensile strength and this fact governs the design ofmajor parts such as wing spars.
Because the individual hollow fibres are also comparatively weak across the grain, the orientation of thegrain in a piece of timber is of vital importance.

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22.1.2.4.1

MEASUREMENT OF SLOPE OF GRAIN

Slope of grain is expressed as the number of units in which a deviation of one unit occurs. A slope of 1 in 15
means that in a distance of 150mm along the longitudinal axis of the piece, a given fibre has deviated by
10mm. The grain direction on a radial surface is clearly indicated by the darker bands of summer wood
which appear as lines along the length of the piece. On a tangential or near tangential surface, however, theindication of fibre direction is much less clear, the principal indications being checks, pores, resin ducts andwood rays. A clear indication of the fibre direction on a tangential surface may be obtained by drawing a
sharp steel scriber along the surface in the direction in which the grain seems to run.

22.1.2.4.2

CROSS GRAIN

Cross grain in wood means that the fibres are not parallel to the major axis of the piece.
Cross grain is objectionable because it reduces strength, may cause warping in drying and makes it difficult
to surface wood smoothly when planing against the grain.
Cross grain may be of two major types, namely; diagonal grain or spiral grain, or a combination of both.
Diagonal grain is a deviation of the plane of the annular rings from parallel with the longitudinal axis of apiece of wood. It is due to such natural causes as crook, bulges, butt swell, pitch and bark pockets, blistergrain, some types of curly grain, healing over of knots and injuries, and to the common practice of sawing
tapered logs parallel to the pith instead of to the bark.
The fibres in some trees are not vertical, but follow a spiral course similar to the stripes on a barber’s pole.
Spiral grain in peeled posts, poles or tree trunks is evidenced by inclined rather than vertical season checks.
Ordinarily the steepness of the spiral decreases from the bark towards the pith of the tree, however this is
not universally true. Also the slope of the spiral sometimes fluctuates, especially near the butt of the tree.
When spiral grain is present, the principal evidence on a radial surface of a piece is the tendency for thesurface to be chipped in planing, and for a splinter raised by a knife point to run into the piece, instead oftearing out to a uniform depth.

22.1.3

DEFECTS IN TIMBER
Some of the common timber defects are:a.

Checks, splits and shakesb.

A check is a longitudinal crack in wood generally in the radial direction, or across the annual rings.
Checks are due to uneven shrinkage in seasoning. Thick stock is more susceptible to checks than thinstock and aircraft veneer is too thin to be subject to checking.

c.

A split is a longitudinal crack extending through the thickness of the piece from side to side regardlessof whether the piece is edge grained. A split is caused by rough handling or other artificially induced
stress, and veneer, because of its greater fragility, splits much more readily than heavier stock.

d.

A shake is separation between adjoining layers of wood, due initially to causes other than drying.
Shakes may become accentuated during seasoning.

e.

A longitudinal shake is one running parallel with the length of the fibres, and usually exceeds half ametre in length, as compared with checks which are likely to be less than 100mm in length. A
transverse shake is one running across the fibres. A ring shake is one occurring between two
adjoining annual rings. A heart shake is one extending radially from the pith of the tree, and a starshake is a number of heart shakes arranged more or less in the form of a star. A falling shake is alongitudinal or transverse shake caused during felling of a tree.

Checks, splits and shakes may seriously weaken wood members in longitudinal shear, and timber
containing them should be rejected.

22.1.3.1 COMPRESSION FAILURES
Compression failures are deformations of the fibres due to excessive compression along the grain either indirect end compression or in bending. The deformations range from well-defined buckling of the fibres,
visible to the unaided eye as wrinkles across the face of the piece, to slight crinkling of the fibre walls visible
only with a high power microscope.
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Compression failures can best be detected under a concentrated light, placed so that it shines along thefibres at an angle of about 200. When viewed at an angle of about 450 to the grain, from the side on which
the light is located, the compression failure will show up as an irregular line extending across the grain.

Figure 22-3

Compression Shake22.1.3.2 KNOTS
A knot is the base of a limb embedded in the tree trunk. The only type of knot permitted in aircraft is a sound,tight knot, solid across its face, and so fixed by growth or position that it will firmly retain its place in thepiece. Intergrown knots are always tight in the sizes permitted in aircraft stock, but encased knots are
frequently loose.
Knots are objectionable because of the distortion, and in encased knots, the discontinuity of grain which they
produce, thus weakening the wood, causing irregular shrinkage and making machining more difficult.

22.1.3.3 DOTE
Dote is a disease which, when present in spruce, renders the timber useless for aircraft use. Advanced
stages are easily detected as obviously decayed timber, but in the early stages it is present in the form ofyellowish or brownish spots. However small the evidence may be, the timber must be rejected because thedecay, once present, will spread.

22.1.3.4 PITCH POCKETS
Pitch pockets are approximately plano-convex lens shaped openings within annual rings, usually longer thanthey are wide. As a rule, they contain resin and occasionally bark. They occur frequently in spruce, pine anddouglas fir. They may weaken small members, and resin may exude from them, especially when the wood
becomes warm. In quarter sliced veneer, pitch pockets appear as narrow slits.

22.1.3.4.1

BARK POCKETS

A bark pocket is a patch of bark partially or wholly enclosed in the wood. There is usually some separation
involved which has a weakening effect. They are occasionally found in most aircraft woods, particularly in
spruce, and are considered equal in damaging effect to pitch pockets of similar size, which they superficiallyresemble, the main difference being that they lack pitch.

22.1.3.4.2

PITCH STREAKS

These are defined infiltrations of resin in the fibres in the form of streaks, usually extending a greater
distance along than across the grain. They occur mainly in spruce, pine and douglas fir, and in the better
grades of timber are quite small.

22.1.4

SELECTING AIRCRAFT TIMBER
Aircraft specification timber should be free from rot, dote and all forms of incipient decay or discolouration,
deleterious shakes, knots, resin pockets and reaction or compression wood.
There shall be no grain disturbances which may constitute a weakness and the maximum inclination of thegrain to the length of the piece shall not exceed 1 in 15. The timber shall be free from brittleness.

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The detection of spiral grain in finished spruce is rather difficult, and if present, it is detected by examining
the flower side or figured surface of a piece of timber. It is important to note that grain direction coincides
with that of the gross stripe pattern only on quartered or near quartered faces. The most reliable test is to cut
off a short piece and split it with a chisel at right angles to the growth rings. The maximum limit of spiral grain
is also 1 in 15.
Although wood with small resin pockets is acceptable, wood with resin veins should always be rejected. Avein, as distinct from a pocket, runs with the grain in the form of a streak embracing one or more growthrings, and can be detected by discolouration.
Moisture content should be in the range of 12-15%.
Density must be within the range specified for the type of timber being inspected.
The number of growth rings must comply with the specification, or not less than 6 rings per 25mm radialmeasurement.
Where possible structural timber should be bought from a recognised aircraft timber supplier, certified that itcomplies with the relevant standard. Where the inspector/repairer has to select his own material, compliancewith the relevant specification will allow the material to be used.
A copy of British Standard BS 2V 37:1968 Sitka spruce as finished timber is attached at the end of thissection.

22.1.5AIRCRAFT TIMBERS
Not all timbers are suitable for use in aircraft. A good strength to weight ratio is required and the species oftrees used should grow to a good length with straight grained timber, free from faults.
Species used in sailplanes include:a.

Spruceb.

Kieferc.

Douglas Fir

d.

Ash

e.

Beech

f.

Birch

g.

Balsa

h.

Klinki

i.

Mahoganyj.

Improved Wood

22.1.5.1 SPRUCE
Spruce is a light reddish brown coloured wood grown in Canada and northern USA. Most Australian andBritish sailplanes were built from spruce which is particularly easy to work. When broken, good spruce
breaks with a fibrous fracture and all along the broken surfaces will be found tiny whiskers of grain that havepulled up. Bad, dry spruce breaks “short” or snaps like a carrot and the whiskers are absent. Sub-species
are Red Spruce and Sitka Spruce. Sitka Spruce is superior and is generally specified for spars (e.g.
Kookaburra, Arrow, and Skylark).

22.1.5.2 KIEFER“Kieferholz” is literally German for pine wood, also known as Baltic Pine, Polish Pine or Red Deal.
Slightly more yellow in colour than Spruce, it is also more fibrous, the fracture being less “short grained”.
First grade Kiefer is slightly heavier and stronger than Spruce and repairs to Polish and German sailplanes
should only be made with the correct material. (E.g. Schleicher Ka2, Ka6, Ka7 etc., Mucha, Bocian andspars for Australian built ESKa6).
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22.1.5.3 DOUGLAS FIR
Douglas fir or Oregon, is also heavier and stronger than Spruce. The growth rings are very pronounced andthe timber is prone to split. It has been used as a substitute for Kiefer (e.g. ES49 spars built in Australia, also
BG12).

22.1.5.4 ASH
A white hardwood with characteristic flecks in the grain. Its great merit is that it has good resistance tobending and is therefore used for skids and occasionally for the keel of sailplanes. Australian mountain ash
and alpine ash have been used also.

22.1.5.5 BEECH
A hardwood used for re-enforcing blocks in certain places. In colour it is a whitish wood, darker than Ash andcontains short flecks in the grain.

22.1.5.6 BIRCH
A hardwood used mainly in the manufacture of plywood but used on its own in certain applications. It faintly
resembles Beech but is of a darker colour. It is used for re-enforcing blocks, tailskid spring carrying
members and in many aircraft where the fittings of the wings are attached to the spars.
Birch veneers are sliced and glued to make TBU-7, having seven veneers per millimetre and TBU-11 having
11 veneers/mm. TBU-7 is used in the spars of the ES60 series sailplanes.

22.1.5.7 BALSA
Balsa is a very light wood used as a non-structural former and as a core material in early glass fibre aircraft(e.g. Early Libelle).

22.1.5.8 KLINKI
Klinki pine is grown in New Guinea. It is light in colour and selected grades are as strong as spruce. It has avery “green stick” fracture and is difficult to cut cleanly with an edged tool, the wood tearing. It is generally
used only in plywood and for laminating (e.g. Kookaburra and Boomerang bulkheads).

22.1.5.9 MAHOGANY
This is a generic term for a whole family of timbers. It is a dark timber which comes from various places in
the world (Honduras, Africa and other places). It varies in hardness but it has great resistance to shock,hence its use in places like wheel boxes and propellers.

22.1.5.10

IMPROVED WOOD

Various grades of Improved Wood or “Pregwood” are made from Spruce and Beech (e.g. Lo150).
The most commonly used type is known as “Compreg” which is made by assembling resin treated veneers
under pressure greater than normally required for a good adhesive joint, the pressure being accompanied byheating. The resulting product is quite hard with a specific gravity of 1 to 2 compared with 0.3 to 0.5 fornormal wood. The strength is entirely dependent upon the amount of impregnation and compression. The
material has a definite fatigue strength which is much lower than that for untreated timber of the same
variety. Care must be taken to ensure a roughened surface for gluing.

22.1.6AIRCRAFT PLYWOODS“Three Ply” is constructed of three veneers of wood glued together with a thermosetting synthetic type resin
while under pressure. The grain of the outer veneers runs parallel with the length of the sheet, while thegrain of the middle veneer (or core) runs at right angles to that of the outer veneers, or across the sheet.
With “Diagonal Ply” the grain directions are set at 450 to the length of the sheet. Diagonal ply has become
difficult to obtain in recent years. Where more than three veneers are used, the material is termed “multi-ply”
or “five-ply” or “seven-ply” as the case may be. Five-ply is commonly used in sailplane wings.
The range of plywoods includes:a.

Birch Plyb.

Klinki Ply

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Gaboon Plyd.

Mahoganye.

Coachwoodf.

Hoop Pine

22.1.6.1 BIRCH PLY
Birch ply is the most commonly used plywood for sailplanes. Metric sizes are sourced out of Europe. Three
ply with thicknesses from 0.8 to 1.5mm and 5 ply from 1.5 to 2.5mm thick are commonly used. Standard
sheet size is normally 1.2m square. This ply is available in GL1 and GL2 grades. GL2 specification allows
more defects per unit of area than GL1.

22.1.6.2 DOUGLAS FIR
Marine grade plywood manufactured in USA.

22.1.6.3 KLINKI PLY
Klinki ply is available in marine grades and is used as a substitute for American marine ply specified in somedesigns for homebuilding (e.g. BG-12 and Cherokee). It was also used to make thick bulkheads for local
designs (e.g. Kookaburra, Arrow, and Boomerang).

22.1.6.4 GABOON PLY
Gaboon or African mahogany plywood is less dense and more stable than Birch and was extensively used
to cover wing leading edge torsion boxes (e.g. Ka6, Dart, and Skylark). Gaboon is not as strong as Birch andtherefore should not be used as a substitute for birch plywood. It is light in colour with less “grain” showing
than birch.

22.1.6.5 MAHOGANY
American Mahogany plywood is lighter and almost as strong as birch. The Mahogany is red-brown in colour.
It is sometimes used with a core veneer of another wood such as birch. American three ply may have theusual construction of three equal veneers, but some are of 1:2:1 construction. That is the core veneer is
twice the thickness of the facing veneers. This plywood is equal in strength in the two major directions,unlike normal aircraft plywoods which are designed to take higher load in one direction.

22.1.6.6 COACHWOOD
Locally made in Australia. It is heavier than most other plywoods, so its use should include consideration ofhigher structural weight.

22.1.6.7 HOOP PINE
Locally made in Australia in marine grade. It is lighter than coachwood, but more brittle.

22.2

ADHESIVES

22.2.1

GENERAL
This section covers glues used in wooden aircraft construction.
For all glues the surfaces to be glued are covered with liquid adhesive. It is necessary for the adhesive to‘wet’ the surface and penetrate the microscopic pores and hollows of the wood.
Surfaces to be glued must be free from any traces of oil or grease. Therefore the gluing surface should not
be touched.
The liquid adhesive can be transformed into a solid by heat, chemical reaction or the evaporation ofsolvents.
Both the wetting and transformation processes need to be well managed by the operator to ensure a
successful outcome.

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22.2.2LEGACY AIRCRAFT ADHESIVES
While it is unlikely that a new wooden aircraft build or repair would be carried out with any glue other than an
epoxy, a knowledge of legacy wood adhesives is essential since most of our sailplanes were built and had
previous repairs using the legacy glues.
Legacy glues were “water resistant”. Some were more resistant than others. None took kindly to continuing
damp conditions. Many glue failures in the wooden sailplane fleet can be traced to moisture exposure.
The following glues were commonly used in sailplane construction:a.

Caseinb.

Urea Gluec.

Resorcinol

22.2.2.1 CASEIN
Casein was derived from milk proteins and supplied in powder form. This was mixed with water to form aliquid glue. With proper care Casein built sailplanes will remain airworthy for very long periods.
Most sailplanes built by Edmund Schneider were glued with Casein.
Casein is highly susceptible to fungal attack if water is present. Fungal attack gives off a tell-tale smell likesour milk.

22.2.2.2 UREA GLUE
Urea formaldehyde glue was generally used by applying the glue to one surface and the hardener to theother before the surfaces were brought together.
Urea was commonly used on British built sailplanes (e.g. Slingsby T31, Gull4, Skylark 2, and Olympia 2).
Kaurit was a German Urea glue commonly used on Schleicher Ka 1, Ka 2, Ka 2B, Ka 3, Rhönlercher II (Ka4), Ka 6 series, K7, K7 conversions, K8 series, K10, ASK 13 series, ASK 14, ASK 16, ASK 18 series aircraft.
This glue has shown some problems with age. It is suspected that the problems are moisture induced. The
BGA has issued an ongoing detailed inspection schedule for these aircraft.

22.2.2.3 RESORCINOL
Resorcinol was mixed from a liquid resin and a powder hardener. The resulting glue is a dark reddish brown
colour.
Resistance to hot, wet conditions and fungal attack is good.
Resorcinol was used extensively on German aircraft and later British designs. The main spar of the ESKa6
is built of Resorcinol, but the remainder of the structure used Casein.

22.2.3AIRCRAFT EPOXY GLUES
A range of 2 part epoxy glues is available for wooden aircraft construction and repair. It is recommended thatepoxy glues be used for repairs.
Manufacturers publish full data sheets on their resin systems, including recommendations for surface
preparation, mixing and curing.
In general:a.

Ratios must be accurateb.

Mixing must be thoroughc.

Temperature and humidity must be within specified limitsd.

Higher temperature will reduce glue viscosity and reduce pot life.

Epoxy resins may have an adverse effect on skin. The relevant MSDS should be obtained and health andsafety recommendations followed.
The following epoxy glues have been successfully utilised on wooden sailplanes and GA aircraft in Australia:
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e.

Huntsman Araldite 106f.

Huntsman Araldite 134g.

Huntsman Araldite 2011h.

International Epiglue

Other epoxy glues are likely to be acceptable. In selecting a suitable glue consideration needs to be given to
the following issues:i.

Suitability for gluing woodj.

Glue strengthk.

Cure timel.

Pot lifem.

Working temperature and humidity rangen.

Shelf life

Epoxy resins and associated hardeners have reasonable shelf life if stored in good airtight containers. They
should be stored away from extremes of heat and cold. In particular freezing conditions will substantiallyreduce shelf life.

22.2.4

GLUING PROCEDURES

22.2.4.1 TEST SAMPLES
It is a wise precaution to make test glue joints for destructive testing with each batch of glue mixed. The
main benefit of test samples will be identification of erroneous resin/hardener ratio being used.
The following diagram shows a test sample made for destructive testing:Figure 22-4 Test Sample
Reduction of the test piece to half the above dimensions is satisfactory.
The test piece should be clamped. It should also be marked with the date and time the glue batch was
mixed.
Following destructive testing the glue faces should contain embedded timber.
With epoxy resins the residual glue in the mixing cup should cure to a brittle plastic. If the residual is tooplastic to shatter with a hammer blow it is likely the mixture ratio was incorrect.

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22.2.4.2 SURFACE PREPARATIONThe essential points to be observed when gluing are as follow:a.

The surfaces must be clean. The faces should not be handled after final sanding.

b.

The surfaces must fit accurately. The fit must be over the whole area to be glued.

c.

Plywood has a surface condition called “case hardening” which prevents proper wetting. Accordingly it
should be lightly sanded on all glue faces with 220 grit paper.

d.

If repairing existing structure the original glue must be removed totally to allow the new glue to wet thetimber.

22.2.4.3 GLUING CONDITIONS
Ensure gluing is carried out within the temperature and humidity ranges recommended by the data sheet.
If gluing in cold conditions and heating equipment is used, remember to pre warm the two components. It is
the temperature at the glue face that is important.
Establish before you start, the time you have available from finished mixing to joint closed (pot life). This
governs how much work can be done in one operation and how many helpers are required.
Keep glue faces and general area free of dust and moisture.

22.2.4.4 GLUING PREPARATION
Make a “dry run” without glue to check the assembly time and to make sure there are sufficient clamps andblocks available.
Mixing ratios specified in the data sheet must be carefully observed.
Use good quality scales if mixing by weight.
Use clean mixing pots and stirrers. Disposable plastic cups can be used, however do not use polystyrene
cups.
Stir to achieve a thorough mix. Allow air bubbles to release before use.
Do not use glue which is beginning to gel.
When mixing an additional batch of glue use a fresh container.

22.2.4.5 CLAMPING REQUIREMENTS‘G’ clamps should be used with softwood blocks to spread the load. Tighten by feel - don’t crush.
Brad strips are used over plywood. Brad length and ply strips are selected to give adequate pressure anddistribution. Use packing blocks sufficient to back up the brad strips. Do not leave brads in the timber.
A staple gun can be used as an alternative to brads provided the job is reasonably solid. For best results use
a strip of cloth to obtain full pressure from the staples. This also facilitates removal of the staples.
Wedges, special blocks and tourniquets are useful.
Small spring clamps are useful on small repairs.
Weights often won’t provide sufficient pressure.
Clamping must provide an even pressure over the area to be glued. Clamps should not be too far apart or
too close to the edge.
Sequence of clamp tightening should start from the centre and work outwards.
A uniform squeeze out should show along the glue joint. Where possible wipe squeeze out off before theglue gels.
Clamps may be removed when the squeeze out is hard.
In cold conditions heat the job till the glue has cured. Do not allow the structure to be overheated.

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All clamps, brad strips and other devices should be wrapped with glad wrap or similar material to prevent
bonding to the work piece.
Curing of epoxy resins is an exothermic reaction. A larger amount of mixed resin in a cup will warm up andsignificantly reduce pot life. Residual mixed resin in a cup should not be left on a wing or other aircraftcomponent due to the risk of excessive temperature rise as the resin cures.

22.3

WOOD REPAIR

22.3.1

GENERAL
There are a number of basic rules to be observed in structural timber and ply repairs:a.

Materialsb.

Jiggingc.

Repair Schemesd.

Grain Directione.

Ventilation/Drainagef.

Interior Sealing

22.3.1.1 MATERIALS
Always use materials used in the original structure or as recommended in this manual, or specified by thetype certificate holder. Where other alternatives are to be used modification design approval will be required.

22.3.1.2 JIGGING
Aerodynamic shape and structural alignment must be maintained. Inadequately jigged repairs will lead topoor flying characteristics. Take particular care to maintain subtle shape changes like wing tip washout etc.

22.3.1.3 REPAIR SCHEMES
Use repair schemes provided by the type certificate holder or shown in this manual. Where alternative
schemes are to be used modification design approval will be required.

22.3.1.4 GRAIN DIRECTION
Original grain directions are critical and must not be varied, particularly 450 plywood skinning and sparmaterial grain. In some cases continual in service cracking can be traced to the manufacturer selecting thewrong grain direction, or wrong cut, producing cracking, loosening of fittings etc. In these cases, a change in
grain direction is desirable.

22.3.1.5 VENTILATION/DRAINAGE
Ensure the finished repair has vent and drainage holes re-instated and not blocked with glue.

22.3.1.6 INTERIOR SEALING
Use shellac, epoxy or marine varnish on all interior surfaces to moisture proof timber surfaces. Take care toensure the moisture proofing coat does not infringe on the gluing faces.

22.3.2SPLICING
Aircraft wooden structures depend on glued joints for their integrity. When loaded to ultimate loading thetimber adjacent to the glue should fail before the glue. To achieve this joints must always be loaded in shear
or compression in the glue line, never tension. Scarfed joints are used in splices to achieve shear loading
rather than tension.
a.

Standards for Scarf Anglesb.

Splicing Qualityc.

American Splice Method

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Supporting Plywood Skin Splices

22.3.2.1 STANDARDS FOR SCARF ANGLESMinimum scarf angles for splices on sailplanes should be:a.

For plywood with supported edge:

W/T = 12b.

For plywood with unsupported edge:

W/T = 15c.

For structural timber (spars, ribs etc.):

W/T = 15

Unsupported edge plywood repairs should only be used for smaller damage areas on relatively flat ply
surfaces.

Figure 22-5 Splice22.3.2.2 SPLICING QUALITY
Cutting, fitting and gluing splices is not easy. The following sketches show the common defects that must be
avoided.

Figure 22-6 Splice Quality

22.3.2.3 AMERICAN SPLICE METHOD
AC43 shows a method of cutting a low splice angle and using side plates to support it. This method is notconsidered suitable on the light, highly flexible structures found in sailplanes since the plates tend to causechanges in local stiffness which changes stress distribution.
A longer unsupported splice is required to maintain original structure flexibility.

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22.3.2.4 SUPPORTING PLYWOOD SKIN SPLICESTo enable ply skin to be properly spliced and the joint clamped correctly with a tacking strip the minimum
support shown below must be provided. The support block should be installed and its glue cured before
gluing in the patch.

Figure 22-7 Splice Support Block22.3.3‘D’ NOSE REPAIR
Older wooden sailplanes generally had a plywood ‘D’ nose with ply grain running at 450. A repair requires
steaming and forming of ply to bend around the leading edge. Following bending the ply must be allowed tothoroughly dry before final cutting, scarfing and gluing.
It is much easier to achieve a satisfactory repair if the span wise scarf line is a bit further back away from thetightly bent leading edge. Splice angles and backing should follow the requirements shown in 22.3.2 above.
Later wooden sailplanes with Wortman profiles (e.g. ES60 series, Bergfalke IV) had a significantly different‘D’ nose structure. The plywood was generally thicker (5 ply) with the grain running along the wing. The
plywood was not wrapped around the leading edge. A leading edge timber or plywood face carried the wing
torsional load. Generally ‘D’ nose repairs are simpler with this arrangement since there is no requirement totightly bend the plywood.

22.3.4

DESIGN OF REPAIRS
Before commencing work on a repair, sit back and consider all aspects of the repair design. Rash cuttingback of the damage area can lead to the job becoming substantially larger than it needed to be.
Design considerations should consider material specifications and quantities, scarf locations, backing timber
locations and final surface re-instatement.

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23.

SAILPLANE FABRIC INSPECTION AND REPAIR

23.1

GENERAL

23.1.1EXTENT OF USE
Aircraft fabrics have been used to surface aircraft since the days of the Wright brothers.
Most wooden aircraft have fabric covered ribs and control surfaces, some have fabric covered steel tube
fuselages. They also commonly had fabric covering over ply surfaces.
Many metal and some composite sailplanes also have fabric covered control surfaces.

23.1.2

FUNCTION OF FABRIC AND ASSOCIATED FINISHING MATERIALS
Fabric covering on aircraft together with associated finishing materials serve the following functions:23.1.3a.

Provide the aerodynamic surface over open rib areasb.

Provide a lightweight skinc.

Prevent moisture ingress to the internal structured.

Block damaging UV rays from reaching the fabric and structure

CONDITION OF STRUCTURE UNDER FABRIC
With modern fabrics lasting 10 to 15 years in service it is important to carefully inspect and repair any
structures before applying new fabric. Particular care needs to be taken to identify corrosion, glue
deterioration or wood failures since they will be covered up for a prolonged period.

23.2

LEGACY FABRICS AND DOPES

23.2.1LEGACY FABRICS
Traditionally wooden aircraft were covered with linen and then later cotton fabrics. These were heavier andgenerally had a shorter service life than a modern polyester fabric.

23.2.2LEGACY DOPES AND FINISHES

23.2.2.1 DOPES
A taughtening dope was utilised with the legacy fabrics. The earliest dopes were nitrate based and areconsidered more flammable than later butyrate dopes. The dope had multiple functions:a.

It glued the fabric to the structureb.

It caused the fabric to shrink and tightenc.

It provided an air and water proofing function.

23.2.2.2 FILLERS
Some types of fillers were used with the legacy fabrics for UV protection and weave filling. The mostcommon one was “red oxide” which is an anti-fungal and moderate UV blocker. In a thick mix it was also
used as a filler for small gaps and bumps.

23.2.2.3 PAINTS
Following application of fabric and dope, the surfaces were painted. A wide range of paint types were
utilised, some were better than others. Problems encountered with the paints were:a.

Commonly they were not very effective at excluding UV radiation. This lead to early deterioration of
the underlying fabric.

b.

Generally they were not flexible enough to match the in-service deflections of the aircraft structure.
This lead to early paint cracking. During maintenance additional paint coats were added to cover thecracks. This lead to overweight aircraft.

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23.3

CURRENT FABRICS

23.3.1

TYPE OF FABRIC
All currently utilised aircraft fabrics used on sailplanes are woven from polyester thread. Polyester is subject
to shrinking when heated. Normal non-aircraft fabric is pre-shrunk as part of the manufacturing process.
Aircraft fabrics are woven from unshrunken fibre, allowing them to be heat shrunk after installation on theaircraft. Currently available fabrics include the following:

23.3.1.1 CECONITE / POLYFIBER
Ceconite and Poly-Fiber fabrics are manufactured in USA and are now both owned by Consolidated Aircraft
Coatings. Each type has 3 weights of fabric. While they are labelled differently they are in fact identical. The
3 fabric weights are as follow:

Ceconite Label

Poly-Fiber Label

Uncertified Light

Uncertified Light

Ceconite 102

MediumCeconite 101

Heavy-Duty

Ceconite 101 / Poly-Fiber Heavy Duty are not normally used on sailplanes.
Ceconite 102 / Poly-Fiber Medium is required on aircraft with wing loadings over 44kg/m2. Wing loadings on
all our wooden sailplanes are substantially below this value.
Uncertified Light is generally acceptable for use on sailplanes, however consideration should be given tousing Ceconite 102 / Poly-Fiber Medium on areas subject to unusual loads. This would include undersides offuselages subject to launch cable and loose stone impact and areas subject to excessive prop wash on
motorgliders.

23.3.1.2 ORATEX
Oratex fabrics are manufactured in Germany by Lanitz-Prena Folien Factory GmbH. They produce 2 weights
of fabric as follow:a.

Oratex 6000

b.

Oratex 600

Oratex 6000 is the heavier fabric and is recommended for use on sailplanes subject to heavy use, such as
for training. Oratex 600 may be acceptable on sailplanes which fly less frequently or carry less weight. If in
doubt information can be found in the Oratex application manual or a factory “application request” can besought.
Oratex fabric differs from the Ceconite / Poly-Fiber range by being precoated. It is available in a range ofcolours.

23.3.2

CARE OF FABRIC PRIOR TO APPLICATION
All fabrics should be kept clean and free of dust, oils and any other contaminants which may affect the glues
or paints which will be used in the covering application. They also should be kept dry and not exposed toharsh light.
Folding polyester based fabrics (Ceconite and Oratex) should be avoided as it may introduce “white breaks”
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Before beginning, check the whole fabric roll for blemishes, such as weaving mistakes or minor cuts, which
may spoil the final finish. The blemishes may be able to be worked around if found early enough, but once
cutting the fabric has begun, late discovery will be harder to work around.

23.4

CURRENT ADHESIVE AND COATING PRODUCTS

23.4.1

CECONITE (RANDOLPH) NITRATE / BUTYRATE DOPE SYSTEM
Ceconite fabric is utilised with a series of nitrate and butyrate coatings and associated materials to provide acomplete finishing scheme. The following basic products are utilised to complete the scheme:a.

Fabric is attached to the airframe using “New Super Seam” cement.

b.

Following heat taughtening with a calibrated iron the whole surface is covered with a brush coat of“Rand-O-Proof” nitrate dope. Rand-O-Proof provides the basic water proofing of the structure. Over
closed plywood areas like the ‘D’ nose Rand-O-Proof is applied to the surface and allowed to dry
before the fabric is installed. The brush coat through the fabric re livens this earlier coating and bonds
the fabric to the plywood. Rand-O-Proof is thinned down with Nitrate thinner before application. This
coat must be applied by brush. Spraying will not penetrate the fabric properly. Rand-O-Proof is usuallytinted green but tan tinted and clear are available. These two types differ from the green tint foraesthetic reasons only. Typically they are used in places where the inside of the fabric is visible (eg incockpit areas) or for non-painted schemes.

c.

Additional coat(s) of Rand-O-Proof are sprayed on to ensure water tightness of the surface.

d.

Non-taughtening clear butyrate dope can now be sprayed on to fill the fabric weave. With theuncertified light fabric this may not be necessary. Elimination of this stage will reduce weight of thefinished job.

e.

Silver coloured Rand-O-Fill non taughtening butyrate dope is then applied. This dope carries
aluminium flakes in suspension and provides critical UV protection for the fabric and underlying
structure. Sufficient Rand-O-Fill coats should be sprayed on so that light cannot be seen through thefabric.

f.

Finish colour can be achieved by use of either coloured butyrate dope or Ranthane polyurethane
paint. Ranthane gives a shinier finish, however it has 2 significant disadvantages:i.

Future fabric repairs will be much more difficult due to the need to sand the polyurethane off theedges of the old fabric without damaging the underlying fabric.

ii.

The spray mist during application is extremely toxic and requires careful use of a good quality
fresh air respirator.

The following notes are applicable to the Ceconite / Nitrate / Butyrate process:g.

The spray mist from all the products is harmful. MSDS sheets for each product should be studied
before use. Ranthane is especially toxic.

h.

The spray mists are also highly inflammable. Ignition sources including electrical sparking should be
eliminated.

i.

Butyrate dopes were developed to be less flammable and more flexible than nitrate dopes but they do
not adhere as well to the fabric fibres or other surfaces. They should not be used as first coats.

j.

For detailed information on the Ceconite / Randolph products refer to the Ceconite Procedure Manual
101. It should be recognised that this manual has been written for heavier GA aircraft and some of therequirements and suggestions are inappropriate for sailplanes which have much lighter wing loadings,
lower maximum airspeeds and significantly more rigorous aerodynamic requirements.

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Colored Non - Tautening Butyrate Dope

Ranthane Polyurethane

EV-400 Epoxy Varnish

A-1690 Non - Tautening Butyrate (clear)Y

G-6303 Rand-O-Fill (silver)

W-8350 Non - Tautening Butyrate (tan)23.4.2YYYYCeconite Tapes, precoat and 1st coat
Ceconite 2nd coat and fill
Ceconite UV protection coat(s) after fill
Varnish/Undercoat for wood
Colour top coat
286 Nitrate thinner
9703 Butyrate thinner

E-4964 Non -Tautening Nitrate (clear)Y

W-7868 Non -Tautening Nitrate (blue)NP

G-6302 Rand -O-Proof (green)

Organic fabrics till shrunk
Organic fabrics fill after shrinking
Organic fabrics UV protection after fill9701 Tautening Butyrate Dope (clear)“Y”, Correct Application“NP”, Non Preferred Application

210 Tautening Nitrate Dope (clear)

Randolph Dopes
Application Matrix

Y

Y

Y
Y

Y
Y
Y

Y

Y

Y

Y

Y
Y

Y

Y

Y

OTHER NITRATE / BUTYRATE DOPE SYSTEMS
A number of other manufacturers provide Nitrate and Butyrate dopes for aircraft use. The use of theseproducts is similar to the Randolph system described above.

23.4.3

POLY-FIBER VINYL COATING SYSTEM
Poly-Fiber fabric is utilised with a series of vinyl coatings and associated materials to provide a complete
finishing scheme. The following basic products are utilised to complete the scheme:a.

Fabric is attached to the airframe using “Poly Tak” cement.

b.

Following heat taughtening with a calibrated iron the whole surface is covered with a brush coat of“Poly-Brush” vinyl coating. Poly-Brush provides the basic water proofing of the structure. Over closed
plywood areas like the ‘D’ nose Poly-Brush is applied to the surface and allowed to dry before thefabric is installed. The brush coat through the fabric re livens this earlier coating and bonds the fabricto the plywood. Poly-Brush is thinned down with the appropriate Poly-Brush Reducer before
application. This coat must be applied by brush. Spraying will not penetrate the fabric properly. PolyBrush is usually tinted pink.

c.

Additional coat(s) of Poly-Brush are sprayed on to ensure water tightness of the surface.

d.

Thinned silver coloured Poly-Spray vinyl coating is then applied. This product carries aluminium flakes
in suspension and provides critical UV protection for the fabric and underlying structure. Sufficient
Poly-Spray coats should be sprayed on so that light cannot be seen through the fabric.

e.

Finish colour can be achieved by use of either Coloured Poly-Tone or Aero-Thane polyurethane paint.
Aero-Thane gives a shinier finish, however it has 2 significant disadvantages:

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i.

Future fabric repairs will be much more difficult due to the need to sand the polyurethane off theedges of the old fabric without damaging the underlying fabric.

ii.

The spray mist during application is extremely toxic and requires careful use of a good quality
fresh air respirator.

The following notes are applicable to the Poly-Fiber process:a. The spray mist from all the products is harmful. MSDS sheets for each product should be studied before use.
Aero-Thane is especially toxic.
b. The spray mists are also highly inflammable. Ignition sources including electrical sparking should be
eliminated.
c.

For detailed information on the Poly-Fiber products refer to the Poly-Fiber Aircraft Coatings manual. It
should be recognised that this manual has been written for heavier GA aircraft and some of therequirements and suggestions are inappropriate for sailplanes which have much lighter wing loadings,
lower maximum airspeeds and significantly more rigorous aerodynamic requirements.

EP-420 Epoxy Primer (green or white)

EV-400 Epoxy Varnish

UV-550 Urethane Varnish

AO-l00 Clear Aero-Thane

Aero-Thane

EnamelRanthane Polyurethane

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Poly-Tone Finish

R 65-75 Reducer (65-75 Deg. F)
RR 8500 Reducer Retarder (85+ Deg. F)
BR-8600 Blush Retarder
RJ 1200 Rejuvenator
G-4200 Ranthane Reducer
D-7201 Ranthane Accelerator
UE-820 Urethane Reducer
UR-826 Urethane Retarder
E-500 Epoxy Reducer
EX-501 Epoxy Accelerator
Enamel Reducer
Ultra Violet Blocker
Flattener

Poly--Spray

Fabric cement for seams/main attachment
1st & 2nd coat and tapes etc.
UV protection coats
Fabric colour topcoats
Metal/FRP colour topcoats
Metal primer
Aluminum varnish
Wood varnish

Poly--Brush“Y”, Correct Application“UL”, For weak UV protection. Poly-Fibersuggest for Ultralights only.

Poly--Tak Fabric Cement

Poly-Fiber System
Application Matrix

Y
Y
Y

UL
Y
Y

Y
Y

Y

Y
Y
Y
Y
Y

Y
Y
Y

Y
Y
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Y
Y
Y
Y

Y

Y
Y
Y
Y
Y

Y
Y

Y
Y
Y

Y
Y

Y
Y
Y

Y

Y

Y
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23.4.4

ORATEX SYSTEM
Oratex fabric is delivered completely pre finished with polyurethane. It is available in a range of colours. The
following process is used to complete the job:a.

Fabric is attached to the airframe using “Oratex Dispersion Hotmelt Adhesive”. The adhesive ispainted on to the structure and the fabric and allowed to completely dry. This is a water based productand is best left 24 hours. Once dry, the surfaces are brought together and tacked using a calibrated
hot air gun at 500C. Once tacked a final setting pass is made with an iron at 900C. The following points
should be noted in relation to this process:b.

A piece of stiff felt is used to impart pressure to the joint in the first (hot air gun) pass. The iron is used
to impart pressure to the joint in the second pass. Heat and pressure need to be applied for about 10
seconds.

c.

The fabric can still be moved slightly during the first lower temperature pass. The second higher
temperature pass fully hardens the adhesive. The fabric cannot be moved during this pass.

d.

To prevent iron marks on the fabric a Silicon Release Paper is placed between the iron and the fabric.

e.

Following attachment to the surface the fabric is heat shrunk. Unlike the Ceconite and Poly-Fiberprocesses, shrinking is carried out with a calibrated hot air gun. Shrinking commences at 1000C. Each
100C the fabric shrinks approximately 1% biaxially. Recommended maximum stretching temperature
over wood structures is 1800C. Temperatures above 2000C will damage the fabric. During fabricinstallation it should be hand stretched as much as possible to ensure a satisfactory final tension
without exceeding the recommended temperatures.

The following notes are applicable to the Oratex process:a.

For detailed information on the Oratex process refer to the Oratex Application Manual. It should berecognised that this manual has been written for heavier GA aircraft and some of the requirements
and suggestions are inappropriate for sailplanes which have much lighter wing loadings, lower
maximum airspeeds and significantly more rigorous aerodynamic requirements.

b.

Because the Oratex products don’t contain organic solvents they can be air freighted.

c.

While Oratex does use water based adhesives, water must not be used to thin the adhesive.

d.

Oratex utilises modern chemical UV blockers rather than an aluminium layer. Accordingly light can beseen through the fabric (see detail comments, 1.5.2).

e.

Because temperature control is critical to the process it is recommended that Oratex supplied iron andhot air gun be used. It is also strongly recommended by the factory that the shrinking takes place withmultiple steps of small temperature increases, rather than one big attempt at shrinking.

f.

When using the Oratex system on refurbished steel tube structures the factory recommend using a
two pack paint as they have found some older and single pack paints do not adhere to the steel wellenough for the Oratex adhesives to have a secure bond. If in doubt, a small patch can be glued in an
unobtrusive spot and a peel test carried out.

g.

Spot shrinking of wrinkles etc, should not be carried out until the whole structure is covered as there isa small chance that the fabric could be pulled out of position.

23.5

FABRICING OF WINGS

23.5.1FABRIC LAYOUT
Wooden powered aircraft, especially those of US origin, traditionally were covered with a length of fabricapplied along the top surface with a separate length along the underside. This resulted in joints at theleading and trailing edges. The leading edge joint was taped.

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Figure 23-1

Typical Powered Aircraft Wing Fabric Layout

Wooden sailplanes were covered with a length of fabric wrapped around the trailing edge and bonded to the
top and bottom surfaces around the spar line. Commonly European built sailplanes did not have fabric overthe leading edge. Sailplanes built by Schneider in Australia had a leading edge fabric which was bonded
over the trailing edge fabric. These lap joints should not be taped.

Figure 23-2 Typical Sailplane Wing Fabric Layout
Generally paint over plywood without fabric failed prematurely in Australian conditions. It is recommended
that plywood be fabric covered in any resurfacing.
Handbooks published by fabric/dope manufacturers follow the traditional powered aircraft fabric layout.
Since jointing/taping at the leading edge will degrade a sailplane’s aerodynamic performance, it isrecommended that traditional sailplane fabric layout be followed. This is critically important for later wooden
aircraft like the ES60 Boomerang and Scheibe Bergfalke IV which utilise early Wortmann laminar flow
profiles.

23.5.2FABRIC DETAIL
While we do our best to keep our aircraft protected from the elements we must accept that they will becaught in the rain from time to time. Accordingly fabric needs to completely cover all wooden surfaces
including root ribs, inside aileron cut outs and preferably under metal fittings bolted to the surface (aileron
hinges etc). It is generally better to apply fabric in these areas before laying down the main fabric. This way
the main fabric can be lapped over the detail material.
Fabric should also be folded down into and bonded at airbrake cut outs etc.

Figure 23-3 Fabric Detail in Aileron Cut Out
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When using fabrics which require no further coatings, such as Oratex, colour differences in the substrate
may show through where the fabric is in direct contact with the substrate. A light coloured fibreglass nose
fairing with dark repair patches may cause a “blotchy” finish. Where this happens the substrate should begiven a light coat of a consistent colour. This is most noticeable on lighter coloured schemes and is lessnoticeable if the different coloured areas are some distance apart, for instance, the nose and turtle deck.
This has no effect on the strength or airworthiness of the finish but it can make an otherwise acceptablefinish less aesthetically pleasing.
Polyester fabric schemes should only be shrunk as much as is needed rather than as much as possible, toavoid damage to the underlying aircraft structure.

23.5.3

RIB STITCHING
Traditionally powered aircraft were rib stitched. Sailplanes, with their lower wing loadings and slower speeds,
were not.
With cotton fabric and nitrate dope, the dope penetrated the cotton thread and acted as both the bonding
agent and the taughtening agent. With polyester fabric the fabric cement does not penetrate the fabricthreads, but is dependent on encapsulating the fabric weave. If the rib is not stitched it is critical to ensure
thorough encapsulation to effect a satisfactory bond.
With nitrate/butyrate and Poly-Fiber vinyl schemes the fabric is heat shrunk after bonding to the structure,but before application of any dopes. The dopes utilise identical solvents to the fabric cement. On concave
surfaces (underside ribs) initial brush coats of dope are likely to temporarily soften the fabric cement to theextent that the taught fabric pulls clear of the ribs. This is difficult to repair, so care should be taken when
applying the brush coat if rib stitching is not utilised. Oratex fabric is precoated so this problem will not be
encountered.
If rib stitching is used, either a propriety stitching thread or a good quality linen thread can be used.

23.6

FABRICING OF FUSELAGES

23.6.1FABRIC LAYOUT – WOODEN FUSELAGE
Fuselages vary in shape and size. It will be necessary to consider the fabric layout before commencing eachjob. The following issues should be taken into consideration:

23.6.2a.

Width of fabricb.

Location of lap jointsc.

Complexity of shape and associated difficulty applying large sections. The nose cone area canprovide a challenge which may be best handled with a separate piece of fabric.

d.

If laps are required at right angles to the airflow the leading fabric should be lapped over the trailingfabricFABRIC LAYOUT – STEEL TUBE FUSELAGE
The issues shown in 23.6.1 above are also relevant to steel tube fuselages. The following issues also need
to be taken into consideration:a.

Fabric can only be jointed at a tube. The first piece of fabric applied is wrapped around the tube andthe second piece is lapped over the first.

b.

The underside fabric around the wheel and release is commonly subject to damage in service. It isbest if the fabric layout provides a separate piece of fabric in this area which is installed last. This
allows easy replacement of damaged fabric during maintenance. This final piece of fabric can also beof a heavier grade to resist damage.

c.

Fins are bolted to the steel tube fuselage. It is best to fabric the steel tube fuselage and the fin
separately. Once the fin is bolted on a bridging tape or fabric section can be applied. This allows
relatively easy fin removal during later maintenance/survey.

d.

Where fabric bends around a longeron it is subject to wear and handling damage. Placing a tape overthe bend provides a wear surface and is relatively easy to replace if it is damaged. This is particularly

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the case with lower longerons where the fabric is subject to grass/stone damage.

23.6.3

FABRIC DETAIL
Fabric detail considerations should be similar to those for wings (see 23.5.2 above).

23.7

FABRICING OF TAILPLANES

23.7.1FABRIC LAYOUT
Fabric width is sufficient to cover a tailplane without joints except at the trailing edge. Where a tailplaneleading edge is tapered it will be necessary to have a fore/aft lapped joint at the centreline of the tailplane.

23.7.2FABRIC DETAIL
Fabric detail considerations should be similar to those for wings (see 23.5.2 above).

23.8

WEIGHT AND BALANCE AND LOGBOOK ENTRY

23.8.1

WEIGHT AND BALANCE REQUIREMENT
If the whole aircraft or any significant section is refabriced the aircraft must be reweighed and pilot weights
recalculated by an inspector holding the necessary authorisation.

23.8.2

LIKELY WEIGHT OUTCOME
Generally aircraft requiring new fabric have had paint added over time during maintenance so they are likely
to lose weight when refabriced. The potential outcomes of this are as follow:

23.8.3a.

Total empty weight will reduce. A higher allowable maximum pilot weight is possibleb.

Total weight of non-lifting parts will reduce (assuming tailplane/fuselage have been refabriced). A
higher allowable maximum pilot weight is possible.

c.

Empty centre of gravity will move forward (assuming tailplane/fuselage have been refabriced). This
will allow a lower minimum pilot weight to be placarded. In a few aircraft (e.g. Motorfalke) this may
incur a reduction in maximum pilot weight due to forward centre of gravity limit consideration.

LOGBOOK ENTRIESThe logbook entry for the refabric work must accurately describe the aircraft components refabriced anddetails of the scheme utilised including the final topcoat colour. This will make life much easier for future
fabric maintenance.
Following reweigh, the weight and balance records must be updated in the logbook and the pilot weightplacard updated in the cockpit.

23.9

REMOVAL OF OLD FABRICS AND DOPES

23.9.1

NECESSITY
It is critical that all remnants of previous coverings be removed before commencing new fabric work. It is
likely new materials will not be compatible with previously used schemes.

23.9.2REMOVAL TECHNIQUES
Often fabric can be carefully pulled away from the surface complete with its topcoats. Care should be taken
to not damage underlying structure while pulling the fabric.
Old degraded cotton fabric with many layers of paint is likely to disintegrate when pulled. It will then benecessary to remove the paint and dopes layer by layer. Paints and dopes will generally respond to
appropriate strippers and solvents. Polyurethane top coats are especially difficult and will need to be sanded
off. Caustic paint strippers should be thoroughly cleaned off plywood surfaces with a solvent to prevent
damage to the plywood.

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Following removal of fabric, residual dope must be removed from the surface. This is best done by laying a
rag soaked with the relevant solvent on the surface for 10 minutes, then scraping. Solvent soaked steel wool
rubbed along the timber grain does a good job of final clean up.

23.10

FABRIC REPAIRS AND INSPECTION

23.10.1 TYPES OF DAMAGE
Fabric damage is likely to take one of the following formats:a.

Large damage area associated with structural damageb.

Smaller fabric penetrations due to hangar/trailer rash or access holes cut for inspection/maintenancec.

Fabric “dents” in open structure areasd.

Surface coating degradation and cracking

23.10.2 REPAIR MATERIALS
Since dopes and paints are not compatible across schemes, fabric repairs should be made using the same
products as the original.

23.10.3 REPAIR FUNDAMENTALSFabric repairs should be carried out as follows:a.

Be generous with the lap widthb.

For solvent based fabric cements existing surfaces have to be stripped back to the bare fabric before
the patch is glued on.

c.

With Nitrate/Butyrate and Poly-Fiber schemes a significant dent on open panel areas will need to be
cut out and patched. With Oratex fabric the dent is likely able to be stretched out with the hot air gun.

23.10.4 REPAIR TECHNIQUESThe following techniques are useful:a.

When repairing damage in the middle of an open panel it may be easier to cut back and repair to apoint where the fabric is solidly supportedb.

When solvent removing dope etc around the edge of the damage area it is best to support the insideof the fabric by holding a small piece of plywood or sheet metal behind the fabric. This will minimise
the amount of stretching of the fabric. Alternatively, not cutting the fabric repair to its final size until
after the dope has been removed can also avoid unwanted stretching of the remaining fabric.

c.

Polyurethane top coats will not respond to any solvents or dopes. Where the fabric lap is overplywood it can be carefully sanded back using 280 grit paper. Once through the polyurethane
remaining dope layers can be removed with solvents. In open fabric areas where access to the rear of
the fabric is available through the hole, soaking the rear with appropriate solvent will allow thecomplete surface coatings to be prised away from the fabric.

d.

Pinking the edges of a patch will help to get the edges to sit down neatly.

e.

Finishing and top coats should be identical to the original.

f.

Sprayed Butyrate or Poly-Tone top coats will be easy to blend in with the original surface. With
Polyurethane top coats it is likely the complete panel will need to be sprayed over to achieve a blend.

g.

With Oratex don’t leave any cement on the surface beyond the limit of the joint. It will be difficult toremove later.

h.

Rejuvenators are available to bring degraded/cracked Butyrate and Poly-Tone top coats back to life.
Polyurethane surfaces weather better, but cannot be rejuvenated. If a top coat is cracking and it is notcaused by an underlying structural fault, it may indicate that the original coatings were too thick.

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23.10.5 FABRIC INSPECTION
The sailplane inspection regime must include the fabric and associated coatings. With polyester fabrics the
fabric will last a long time provided the surface UV protection is effective.
If there is any doubt about the integrity of the fabric, the only true test is to remove a sample and subject it totensile test. AC 43.13.1B allows minimum tensile strength to degrade to 35 pound per inch before the fabricmust be replaced (sailplanes). The test is easy to conduct. A one inch wide strip of fabric with coatings
removed needs to be carefully clamped at each end and pulled with a spring balance to failure. If it exceeds
35 pound the fabric is still airworthy.
At any time fabric damage occurs and a repair is necessary it is worth considering removal of a sample fortesting. The additional size of the ensuing repair does not add much time to the job.
Cotton fabric tears very easily once it has a hole. Minimum tear strength of brand new cotton for sailplanes
was only 3 lb (AC 43.13.1B). Accordingly tear strength is a poor indication of fabric condition. While
polyester fabrics have better tear strengths, tensile testing is still the only reliable test for integrity.

23.11

REFERENCES
AC 43.13-1A Change 3. Acceptable Methods, Techniques and Practices. IAP Inc., Casper, Wyoming, 1988.
(Chapter 2)
Aviation Maintenance Technician Handbook–Airframe, Volume 1, 2012. (Chapter 3)Standard Repairs to Gliders (Section 2), British Gliding Association.
Ceconite Procedure Manual 101, June 2008.
Polyfiber Procedure Manual 1, “How to Cover an Aircraft Using the Poly-Fiber System”, Revision 21.
Oratex Application Manual ADxC-51-001-AMM Edition 5.4
Stewart Systems Fabric Covering and Finishing Manual 21, Second Edition, March 2009

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24.

SAILPLANE UNDERCARRIAGE

24.1

GENERAL
The undercarriage supports the sailplane when it is on the ground. It allows the sailplane to move withminimal friction when landing, taking off or moving on the ground. The undercarriage also provides somedegree of suspension when moving over rough surfaces or during landing. In some types, the undercarriage
can be retracted, in part or totally, into the sailplane to reduce drag. It also carries the brakes and provides
braking. And influences ground handling and balance on the ground dependent on configuration (but has
little influence in the air).

24.2

MAIN UNDERCARRIAGE ARRANGEMENTS
The main undercarriage supports all of, or a major part of, the weight of the sailplane. There are a number ofdifferent ways this can be achieved:

24.2.1SKID
The most basic and earliest form of undercarriage is the skid where a solid structural member slides along
the ground. It is not usual to find any sailplanes now with a skid alone, a main skid is more normally used in
combination with a main wheel located behind the centre of gravity. Typically found on older training
sailplanes such as Bergfalkes and Schleicher K7/8/13.

24.2.2

MONOWHEEL
A single large wheel located near the sailplane centre of gravity is by far the most common form ofundercarriage and is the type commonly found on non-powered sailplanes. It can be either fixed or
retractable.

24.2.3

TAILDRAGGER
A “conventional” undercarriage arrangement consists of two main wheels located forward of the centre ofgravity. This arrangement is common on touring motorgliders such as the Grob 109, Dimona H36 and somelater Motorfalkes. Retractable versions can be found on the Stemme S10, Ximango and IS28M2.

24.2.4TRICYCLE
A tricycle undercarriage consists of two main wheels located behind the centre of gravity and one other main
wheel located under the nose. The nose wheel is usually the same size as the mains but it may be slightly
smaller than the other two. Examples are the Super Dimona and Valentin Taifun.

24.2.5OTHER
Other types of undercarriage, such as skis for snow or floats for water do exist and have been used on
sailplanes. However, as these would not practically be used in Australia they will not be addressed in thismanual.

24.3

SUPPLEMENTARY UNDERCARRIAGE ARRANGEMENTS
In addition to the main undercarriage located somewhere near the centre of gravity, there are often
supplementary parts of the undercarriage at the extremities of the aircraft which support a minor portion of
the aircraft weight, are used for balance and/or are located to reduce shocks to the airframe when it ismoving.

24.3.1SKID – NOSE OR TAIL
A skid is used for its simplicity. It has no moving parts, so is easier to maintain than a wheel. It has more
friction than a wheel which can assist in the braking of a sailplane when landing. This was helpful in older
sailplanes which had poor or non-existent wheel braking systems, however this causes wear on the skid
structure itself. To reduce wear, the skid usually has a wear plate of metal or tough plastic.
Most monowheel sailplanes of the 1960s to 1980s with wheels forward of the centre of gravity were
produced with tailskids. Tailskids can be found on virtually all wooden sailplanes, Blaniks, LS and Schleicher
sailplanes, Schempp Hirth Standard Cirrus, Nimbus and Ventus as well as Grob Single and Twin Astirs.
Many of these tailskids were subsequently modified to tail wheels.

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Some sailplanes, notably the Blanik, may have a small nose skid or bumper to prevent damage to theunderside of the nose if the aircraft is upset by too severe braking or sudden stopping.
Where the main wheel is located behind the centre of gravity the sailplane will rest on its nose when loaded
for flight. In this case the skid is normally substantial as it is subject to large forces on badly handled
landings and really forms part of the main undercarriage (see 24.2.1).

24.3.2WHEEL – NOSE OR TAIL
Instead of a skid it is more common on modern aircraft to find a tail wheel or nose wheel and on sometrainers depending on the location of the main wheel with respect to the centre of gravity. In cases where theempty sailplane tail rests on the ground, but the loaded sailplane nose rests on the ground, both a nose andtail wheel might be found on the one aircraft. The nose wheel for takeoff and landing, the tail wheel forground handling.
The balance varies from one extreme to the other. Eg the PW-6 is strongly nose heavy on the ground and so
acts as a nose-wheel aircraft. Whereas IS-28 and many self-launchers have heavy tailwheel balance and act
as tailwheelers. Others like the DG-505 or some DG-1000 are neutrally balanced – this makes for easy
ground handling. They all fly the same but on the ground act differently, and in a botched landing may whip
lash from front to rear in different ways and so must be inspected for damage accordingly.
While a small wheel arguably is more complex than a simple skid, wheels give better directional stability on
the ground and less rolling resistance during takeoff. A nose wheel used in place of a skid is substantiallylighter.
In a few cases, such as the SF27M, the tail wheel may be steerable, self-launchers need a steerable wheel– nose or tail. Eg the ASK21Mi has a front steerable nose wheel.

24.3.3

OUTRIGGERS
Outriggers are smaller supplementary wheels mounted on long stalks under the wings in approximately thehalf span position. They are used to keep the wings level during low speed taxiing on mono-wheel
motorgliders. This arrangement is seen on the Motorfalke, Fourniers and the Europa.

24.3.4

WINGTIPS
The wingtips may also carry a supplementary device to prevent damage to the under surface of the wingtips. These can be small skids, wheels or wire loops. Sometimes these items also serve as the tie down
attachment point. They should not be overlooked when maintaining the whole undercarriage. And deserve
inspection at every daily inspection as they often suffer.

24.3.5

DOLLIES AND WiNG WALKERS
Wing walkers and tail dollies are used when ground handling. They are not a part of the aircraft when it isflying, so strictly are not covered by any certification or other rules. They can be supplied by the
manufacturer or locally made to suit the aircraft.
They should be examined carefully to ensure that they will not cause inadvertent damage to the sailplane.
They should be maintained just as well as the other parts of the sailplane undercarriage.
They have often caused damage to sailplanes mainly by poor installation and handling. Check they aresuitable and are handled carefully.

24.4

TYRES

24.4.1

GENERAL
An aircraft tyre must withstand a wide range of operational conditions. While on the ground, it must support
the weight of the aircraft. During movement, it must provide a stable, cushioned ride while resisting shockloads, rotational stresses, abrasion, and wear. The tyre is a composite of a number of different rubbercompounds, fabric material and steel. Each component serves a specific purpose in the performance of thetyre.
Two different and distinct aircraft tyre constructions are available.
a.

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b.

The Radial tyre, this type is not usually seen on pure sailplanes.

Figure 24-1

24.4.2Tyre Construction. Cross Ply (Left), Radial (Right)

PARTS OF THE TYRE
Tread: The tread refers to the part of the tyre that comes in contact with the ground. The tread rubbercompound is formulated to resist wear, abrasion, cutting, cracking, etc. It prolongs the life of the casing byprotecting the underlying tyre structure. The tread may contain grooves or patterns which act as a visualindicator of tread wear and provide a mechanism to channel water from between the tyre and runway
surface.
Casing Ply: The ply consists of fabric cords between two layers of rubber. They give the tyre its primarystrength and are anchored around the bead wires. Multiple layers of plies are bonded together, as
necessary, to form the casing and give the tyre the capability to hold the inflation pressure.
Casing: The combination of all the parts of the tyre except the tread zone.
Bead The bead contains wires or synthetic rope which anchor the tyre to the wheel and transfer the load to
the wheel.
Sidewall: A layer of rubber covering the outside of the casing. Its purpose is to protect the casing and it can
carry surface markings.

Figure 24-2

24.4.3

Parts of a Tyre

TYRE MARKINGS
Information is moulded into the rubber of tyres. It will include the manufacturer and tyre size and may include
other information such as plies and various rating.

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24.4.4

RATINGS
The speed rating of a tyre (for example, 225 mph) is its maximum rated ground speed (approved after
completion of tests on the tyre at that speed).
The Ply Rating (PR), (for example, 22 PR), is an index which can identify the maximum rated static load thatcan be applied to the tyre when it is inflated to a specified pressure and is used in specified conditions ofoperation. It is not the number of plies.

The Load Rating (LR) is the maximum static working load that is permitted.
24.4.5PLIES
The number and type of plies affect the tyre rigidity, load capacity and resistance to penetration. Plies are
the layers of reinforcement as shown in Figure 24-1 above. They can be steel, canvas or synthetic fabric. In
aircraft tyres they are often synthetic for lightness.

24.4.6

SIZE NOMENCLATURE
Two-part tyre size specification: N – D
N = nominal width of the tyre at the widest point, indicated in inches
D = nominal diameter of the tyre seat, in inches, corresponds to the wheel rim size
Example:5.00-5 = tyre width 5"or 127 mm and tyre seat 5"4.00-6 = tyre width 4"or 102 mm and tyre seat 6"
Two-part tyre size specification: M x N
M = nominal outside diameter of the tyre, expressed in millimetres or inches
N = Nominal tyre width in the widest point, expressed in millimetres or inches
Example:210x65 = outer diameter 210mm, tyre width 65mm
Three part specification of tyre size: M x N – D
M = nominal outside diameter of the tyre, expressed in millimetres or inches
N = Nominal tyre width in the widest point, expressed in millimetres or inches
D = nominal diameter of the tyre seat, in inches, corresponds to the wheel rim size
Example:380x150-5 = Outside diameter tyre 380 mm, widest place 150 mm, tyre seat 5"or 127 mm
15x6.00-5 = Outside diameter tyre 15"/ 380 mm, widest place 6" / 150 mm, tyre seat 5 "If the “‐“ is replaced by the letter “R” the tyre is of radial construction.
24.4.7

INSPECTION
The surface condition of a tyre can be inspected with the tyre on the aircraft. The tread should be checked
for abnormal wear. If the tread is worn in the centre of the tyre but not on the edges, this indicates thatthe tyre is over‐inflated and the operational air pressure should be reduced. On the other hand, a tyreworn on the edges, but not in the centre, indicates under‐inflation. These indications are shown in thefollowing figure. Wear is relative to the design shape, ie should it be flat or rounded.

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Figure 24-3 Tread Wear Patterns
The following guidelines should be used for tyre inspection:

24.4.8a.

Tread Wear. Inspect the tyres visually for remaining tread. Tyres should be removed when tread hasworn to the base of any groove at any spot, or to a minimum depth as specified by the tyre or aircraft
manufacturer. Tyres worn to fabric in the tread area should be removed regardless of the amount oftread remaining.

b.

Uneven Wear: If tread wear is excessive on one side, the tyre may be dismounted and turned
around, providing there is no exposed fabric. However, this may indicate some form of gear
misalignment which should be investigated. But due to splayed gear and deflection due to load andlanding on one wheel it is very common for dual gear tyres to wear and need turning.

c.

Tread Cuts: Inspect tread for cuts and other foreign object damage, and mark with crayon or chalk.
Remove tyres that have the following:i.

Any cuts into the carcass ply.

ii.

Cuts extending more than half of the width of a rib and deeper than 50 percent of the remaining
groove depth.

iii.

Weather checking, cracking, cuts, and snags extending down to the carcass ply in the sidewall
and bead areas.

iv.

Bulges in any part of tyre tread, sidewall, or bead areas that indicate a separation or damaged
tyre.

v.

Cracking in a groove that exposes fabric or if cracking undercuts tread ribs.

d.

Flat Spots: Generally speaking, tyres need not be removed because of flat spots due to skid burns
unless fabric is exposed. If an objectionable unbalance results from the flat spot, then remove the tyrefrom service.

e.

Beads: Inspect bead areas next to wheel flanges for damage, especially if brake drag or severe
braking has been reported during ground towing (taxiing for motorgliders), takeoff or landing.

f.

Tyre Clearance: Look for marks on tyres, the gear, and in the wheel wells that might indicate rubbing
due to inadequate clearance.

STORAGEFor long term storage, tyres and tubes should be kept in a cool, dry and reasonably dark location, free fromair currents and dirt.

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Avoid sunlight as UV rays will damage the rubber.
Avoid contact with hydrocarbon-based contaminants such as oil, petrol and grease as hydrocarbon
contaminants will deteriorate rubber.
Don’t store at temperatures greater than 35oC for extended periods.

24.5

TUBES

24.5.1

GENERAL
Aircraft tyre tubes are made of a natural rubber compound. They contain the inflation air with minimal
leakage. Tubes come in a wide range of sizes to match tyre sizes. Only the tube specified for the applicabletyre size must be used. Tubes that are too small stress the tube construction.
There is no mandatory age limit for an aircraft tyre tube. It should be elastic without cracks or creases inorder to be consider serviceable. The valve area is prone to damage and should be inspected thoroughly.
Bend the valve to ensure there are no cracks at the base where it is bonded to the tyre or in the area where
it passes through the hole in the wheel rim. Inspect the valve core to ensure it is tight and that it does notleak.

24.5.2VALVESThe valve used in nearly all vehicle tyres is known as the Schrader valve. It consists of an externallythreaded hollow cylindrical metal tube, typically of brass. In the center of the exterior end is a metal pin
pointing along the axis of the tube; the pin's end is approximately flush with the end of the valve body.

Figure 24-4 Valve Construction
Valve (stem) length and orientation is often a problem in sailplanes and must be checked and fixed so thevalve does not rub on the U/C. Some valve stems need a small spacer to hold them in the correct spot – thisis often a small length of plastic tube over the stem inside the rim. Tubes are available with a variety ofstems and the correct one must be obtained.

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Figure 24-5

Close Up Of Valve Spacer Sleeve To Stop Valve Protruding Too Much

Figure 24-6

24.6

Valve Spacer Sleeve To Stop Valve Protruding Too Much

BRAKES
Most braking systems in sailplanes rely on a direct mechanical connection to the brake on the wheel. This is
usually through a Bowden cable. Operation of the wheel brake lever in the cockpit causes the brake pads tobe pressed against some part of the wheel to provide friction to slow the sailplane.

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24.6.1DRUM

Figure 24-7 Drum Brake Mechanism
The drum brake consists of two brake shoes (pads) inside the hub (drum) of the wheel. The brake shoes aremounted on a fixed portion of the hub which does not rotate with the rest of the wheel. The fixed portion is
known as the backing or torque plate. When a cam between the shoes rotates the brake shoes are forced
against the inside surfaces of the wheel hub/drum which provides friction and slows the aircraft.
A return spring provides the mechanical force to allow the shoes to clear the drum when the cam is returnedto the non-braking position.
With time, the friction lining material on the shoes wear and must be replaced. Caution should be used as
asbestos was used in some older lining materials. If so don’t blow out with compressed air.
Sailplane drum brakes are most commonly operated mechanically by Bowden cables, however some may
have hydraulic cylinders in place of the cam. It should be noted that many early FRP sailplanes were
designed to a standard where the brake is defined as an emergency brake only

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24.6.2

DISC

Figure 24-8 Hydraulic Disc Brake Mechanism
Disc brakes are usually hydraulically operated. They consist of a hard steel or iron disc (rotor) which is
attached to the wheel. A calliper contains disc pads of friction material which are forced to rub on the brakedisc to provide stopping friction. The disc calliper is attached to the airframe. However, where a calliper
contains a fixed pad and a pad operated by a cylinder (as shown in Figure 24-7) the calliper may not be
fixed solidly, it may float a little along the length of its mounting bolts to allow the pressure of both pads
bearing on the rotor to equalise during braking.

Figure 24-9 Jantar type disc brake mechanism
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The Jantar is a mechanical disc brake system. It has two fixed steel discs which brake the hub on which aring of brake pad material is bonded. It is sometimes troublesome. The main problems are:a.

Sideways movement on the axle is only prevented by the disc brake. If towed down a long sloped
surface like a cambered runway then the brake is slightly on which builds up heat and damage occurs.

b.

The mechanical movement method is a screw. Probably after overheating this distorts and jams andso while braking it tends to jam on bringing the sailplane to an abrupt stop.

Hints: Careful adjustment helps. Avoid overheating while towing behind a car. Finesse in using the brake isrequired. Car brake repairers can bond on new brake pads but remove the plastic shelled bearing as theyuse heat that damages the bearings.

24.6.3HYDRAULIC BRAKING SYSTEMS
Instead of a direct mechanical connection to the wheel brake, a hydraulic system may be installed. This
generally works better because it has less losses than a cable/mechanical system. It will consist ofcomponents shown in the following schematic of TOST systems. TOST and others supply kits to convert
many sailplanes to hydraulic or mixed cable-hydraulic systems. These greatly improve braking both inbraking force and fine control. The hydraulic system will use a master cylinder connected to the rudder
pedals or brake lever (or both) to convert mechanical force to hydraulic pressure. The hydraulic pressure isthen applied to the brake cylinder(s).

Figure 24-10 Simple Hydraulic System Schematic

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Figure 24-11 Master Cylinder Mechanism

24.6.4HYDRAULIC LINES

Figure 24-12 Hydraulic Hose Installations
Ensure hoses are not twisted, abrade on bulkheads, and do not have sharp radius bends. This can reducethe cross section of the hoses, and possibly reduce braking effects. It will also reduce the service life of thehoses. Twisted hoses may also loosen in service.

24.6.5HYDRAULIC/BRAKE FLUIDS
To transfer pressure from the master cylinder to the brake cylinder(s) an incompressible fluid must be used.
The fluid must also have a number of other characteristics:a.

High boiling point to prevent the heat of braking vapourising the fluid in the system. Vapour bubbles in
the fluid would prevent the pressure transfer and the brakes would fail.

b.

Low viscosity to allow the fluid to flow freely. The viscosity must stay constant over wide temperature
ranges too.

c.

Non-corrosive so that the metal components of the braking system do not deteriorate over time.

There are two types of fluids used in sailplane braking systems.
d.
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type of fluid used in sailplanes. Don’t use DOT 5 or any other.
e.

Hydraulic Fluid (MIL-H-5606 or similar)“Hydraulic” fluids originate from industrial uses and are commonly used in general aviation aircraft
where the hydraulic system may extend beyond braking to include controls, suspension and othersystems. This type of fluid is mineral oil based.

Note that these two types of fluids are not interchangeable. The seals, hoses and other non-metal parts ofthe sailplane braking system may be damaged by use of the wrong type of fluid. When seals and hoses arebeing replaced they must be positively identified as being the appropriate material type.
The appearance of the hydraulic system components is also no guide as (for instance) Cleveland
components which normally use 5606 fluid in GA aircraft may be remanufactured by Tost to use DOT 4
brake fluids for sailplane use. The only reliable indication of the correct fluid to use is from the aircraft
manual.
Automotive type brake fluids absorb moisture and may become corrosive over time. This is not as serious
for steel parts but the old fluid may attack alloy components in the braking system. If the aircraft
maintenance manual does not give a recommended maintenance cycle, the brake fluid should be changed
and the components cleaned every 2 or 3 years. BEWARE! The rubbers may need changing every 5 years.
Hydraulic and brake fluids may have damaging effects on plastics and paint. Spills and leaks should be
avoided or at least cleaned up as soon as possible. Brake fluid is water soluble, whereas hydraulic fluid ishydrocarbon soluble.

24.6.6

DIFFERENTIAL BRAKING
A system of differential braking is found in some motorgliders with dual main wheels. The brakes on the left
and right main wheels can be individually operated to assist in ground steering. Usually this differential
braking system is operated by use of the rudder pedals.

24.6.7

DIRECT MECHANICAL BRAKING
Some early types of sailplane have a rudimentary band braking system consisting of a metal plate/band
which can apply friction directly to the tyre.

24.6.8PARACHUTE ASSISTANCE
While not strictly part of the undercarriage some sailplanes use a tail parachute as a supplementary braking
device. A detailed description of these systems is not included in this manual.

24.7

SUSPENSION

24.7.1

GENERAL
In addition to supporting the aircraft for taxi, the forces of impact on an aircraft during landing must be
controlled by the landing gear. This also reduces the impact of rough taxi surfaces. This is done in two ways:

24.7.2a.

the shock energy is altered and transferred throughout the airframe at a different rate and time than
the single strong pulse of impact, andb.

the shock is absorbed by converting the energy into heat energy

RIGID
The most common sailplane undercarriage design is a rigid landing gear where the wheel axle is attachedeither directly to the airframe or via a rigid metal frame which is part of the retract system. Shock loads
transfer directly to the airframe with this design. Only the use of correctly inflated pneumatic tyres aids insoftening the impact loads.

24.7.3SIMPLE SPRINGING
Some sailplanes utilise flexible spring steel, aluminium, or composite gear legs to receive the impact oflanding and return it to the airframe to dissipate at a rate that is not harmful to the airframe or occupants.
The gear flexes initially and forces are transferred as it returns to its original position.

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24.7.4

OLEOS/ SHOCK STRUTS
A typical pneumatic/hydraulic shock strut uses compressed air or nitrogen combined with hydraulic fluid toabsorb and dissipate shock loads. It is sometimes referred to as an air/oil or oleo strut or shock absorber.
A typical aviation type shock strut is constructed of two telescoping cylinders or tubes that are closed on theexternal ends. The upper cylinder is fixed to the aircraft and does not move. The lower cylinder is called thepiston and is free to slide in and out of the upper cylinder. Two chambers are formed. The lower chamber isalways filled with hydraulic fluid and the upper chamber is filled with compressed air or nitrogen. An orificelocated between the two cylinders provides a passage for the fluid from the bottom chamber to enter the top
cylinder chamber when the strut is compressed. As the oleo is compressed the incompressible hydraulicfluid remains as a constant volume and flows through the orifice into the top chamber. The gas in the top
chamber is compressed to a smaller volume at a higher pressure and acts like a spring.
In some cases a tapered pin is attached to the lower cylinder and protrudes through the orifice. As the strut
compresses the movement of the pin reduces the orifice size to vary the rate of oil flow.

Figure 24-13 Typical Oleo Cross Section

Figure 24-14 East European Type Oleo
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In some east European sailplanes the gas space and the oil space are physically separated by a sub piston
or cup as shown in the figure above.
The extension of the strut should be checked to see that it conforms to the distance specified by the
manufacturer. If an air-oil strut “bottoms”, the gas charge has been lost from the air chamber. This isprobably due to a loose or defective air valve or to defective O-ring seals.

CAUTION
Before an air-oil strut is removed or disassembled, the air valve should be opened to make sure that all airpressure is removed. Severe injury and/or damage can occur as the result of disassembling a strut wheneven a small amount of air pressure is still in the air chamber.

24.7.5

RUBBER OR SYNTHETIC SUSPENSION
Many modern sailplanes use compressible rubber or synthetic donuts or rods to act as springs and shock
absorbers. These often specify replacement on a time basis as they do change characteristics. The correctelements need to be changed as specified. See the specific manuals, eg PW-6 and Stemme S10.

24.8

RETRACTION SYSTEMS

Figure 24-15 Simple Retract Mechanism With Overcentre
Retract systems in sailplanes rely on an overcentre mechanism to lock in the down position. This overcentre
is usually found in the arrangement of the gear legs (see Figure 24-14). In this example, increasing weighton the wheel causes the rear leg pivot point to lock in the down position.
If the gear geometry does not achieve an overcentre when it is extended it may collapse at any time whenon the ground.

24.8.1

DIRECT MECHANICAL
Nearly all sailplane undercarriage retraction systems rely on direct mechanical linkages to allow the pilot tolift the wheel. Through mechanical advantage of the retract system, the pilot extends and retracts the landing
gear by operating a lever in the cockpit.

24.8.2STORED ENERGY
Some more sophisticated aircraft, generally touring type motorgliders, may use stored energy to provide thedriving force for their retraction systems. The most common system is electric, using the aircraft battery as
the energy source and geared electric motors as the drive mechanism. A detailed description of thesesystems is not included in this manual and the particular aircraft manual should be referred to.

24.8.3

RETRACT SPRINGS/DAMPERS
Springs or dampers may be found in the undercarriage retraction system to assist the effort of the pilot to lift
the weight of the wheel.

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24.9

OTHER ITEMS

24.9.1DOORS
Retract systems often use doors which close automatically after a wheel has been retracted. The door may
be attached to the undercarriage leg itself as on the IS28 M2, but usually the door is hinged on the fuselage
and held closed by springs or rubber shock cord. The door is displaced by the undercarriage mechanism
itself.
Weak shock cord or broken/missing springs can lead to incomplete closing of the doors which can introduce
a flutter issue.
In some cases the doors are connected to the undercarriage mechanism by solid linkages. This reduces theneed for maintaining the door close spring tensions, but it can be difficult to set up the door closing/retract
geometry precisely.

24.9.2SPATS AND FAIRINGS
Where the undercarriage does not retract the parasite drag caused by the landing gear can be reduced bybuilding the gear as aerodynamically as possible and by adding fairings or wheel pants to streamline theairflow past the protruding assemblies. A small, smooth profile to the oncoming wind greatly reduces landing
gear parasite drag.

24.9.3

MUDGUARDS
Where a mudguard is fitted to the undercarriage the clearances to the tyre are closer than normal. Incorrect
tyre size or excessive dried mud can cause the wheel to bind and may lead to damage of the tyre.

24.10

MAINTENANCE AWARENESS
The undercarriage is located in a place that makes inspecting it for normal wear and tear and damage more
awkward than many other parts of the sailplane. When carrying out annual inspections or other routine
maintenance the opportunity to have an especially careful inspection of the undercarriage should be taken.

24.10.1 HARD LANDINGS
Mishandled and hard landings are a common form of damage to all aircraft undercarriage systems. The
undercarriage itself and the mounting structure it attaches to are designed to resist and transfer only certain
mechanical loads. Where that level is exceeded some damage will result. This damage will show up in theweakest part of the wheel/undercarriage/fuselage which may not be the immediately expected location. The
shock loads themselves may also damage other parts of the sailplane not directly related to theundercarriage.
Obvious results of hard landings:a.

cracked rimb.

bent axlec.

bent undercarriage legs/tubingd.

cracked welds

e.

damaged mounting points in the fuselage

Non-obvious areas of damage possible after a hard landing are very diverse, depending on many factors,
such as the type of construction of the sailplane, specifics of the impact and many more. For a full
discussion of hard landings see BSE Chapter 25.

24.10.2 TYRE SIZE DISCREPANCIES
Tyres can vary slightly in their dimensions, depending on brand, retreads etc. While this does not pose a
problem on fixed landing gear aircraft with open wheel arrangements, it may present a serious problem
when installed on sailplanes with retractable landing gear or tightly confined wheels, either in a fuselage tube
cage structure or in a spat.

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If a different brand or type of tyre is installed on an aircraft with close tolerances in its landing gear,
consideration should be given to possible tyre expansion. This can be due to high ambient temperature, heatgenerated from taxi and take-off, repeated landings, or heavy braking. Ensure the tyre will not expand to thepoint that it could rub excessively or become wedged.

24.10.3 RIM CONDITION
Rims used on sailplane main wheels are usually aluminium but some types, particularly amateur-builts, canbe pressed steel. Older cast aluminium hubs are brittle, so any damage, such as from hitting a rock on
landing, may crack them or break pieces off. Pressed steel is more malleable and in the same situation will
dent and deform.
Tailwheel rims may also be plastic which is tougher than aluminium, so less likely to crack when new.
However aging can make some plastics more brittle and plastic tail wheels should be checked for cracking
and general deterioration as well. These can also be an intentional weakness and if replaced future hardlandings may damage the sailplane structure.
Most sailplane rims are split types to make the changing of tyres easier, however the tyre must always bedeflated before attempting to disassemble the wheel rims.

24.10.4 MOUNTINGS
The main undercarriage structure is tied directly to the structure of the fuselage to transfer landing loads tothe sailplane as a whole. In a fixed wheel sailplane this may be as simple as the wheel axle passing througha suitably reinforced part of the fuselage structure. More complex arrangements, particularly where thewheel is retractable, may be through a tube structure or cast metal frame attached to the fuselage. This
attachment is achieved by using bolts, or in the case of some FRP sailplanes, by bonding.
As these mounting points are virtually continuously subject to high loads when normally carrying the resting
weight of the sailplane, and to impact loads when in motion on the ground these areas should be checked
carefully for any stress related wear.

24.10.5 CORROSION
The main wheel is always in contact with the earth’s surface when on the ground and will pick up and spreadmud, plant matter, dust and other material. This means the undercarriage is the area of the sailplane most
likely to be subject to contaminants and most likely to have corrosion issues.
See BSE Section 15.5.5 for specific information on corrosion.

24.11

GUIDELINE FOR ANNUAL INSPECTION
As a guide, when maintaining a sailplane undercarriage at an annual inspection the following process can befollowed:

24.11.1 DISSASSEMBLY
During disassembly, to assist with later re-assembly :a.

Beware of turning over the sailplane; manage risks it is heavy, beware hydraulic systems may ingest
air.

b.

Draw a diagram/ take photosc.

Secure items in labelled bagsd.

Mark the axle and other components as required (up/down left/right etc)e.

Often distortion and corrosion make disassembly difficult. Use thought, lubricants/ penetrants andgentle persuasion. Don’t cause more damage.

24.11.2 CLEANING
Clean the undercarriage components removing dirt and grease as required.
Do you need to replace the brake fluid and / or clean/ fix leaks that may be causing corrosion?
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24.11.3 INSPECTION
Inspection for:a.

Tyre and tube conditionb.

Bent mechanical componentsc.

Brake lining and pads residual lifed.

Over-centre locking mechanism correct adjustmente.

OLEO/gas strut conditionf.

Leaks in the hydraulic systemg.

Wear or fraying on brake Bowden cables

24.11.4 REGREASE
Regrease any axles, bearings or pivots with the correct type and grade of grease.
Take care to avoid contaminating the brake linings or pads
Replenish any hydraulic fluids if needed

24.11.5 REASSEMBLY
During reassembly check for:

24.12

a.

Correct adjustment of the wheel brake(s)b.

Undercarriage locking correctly (up and down positions). Over-centre works correctly.

c.

Safety locking of axle/nuts/bolts/pins is completed.

Wheel doors do not jam. On each other or on the undercarriage itselfe.

Wheel doors close completely with sufficient holding force.

f.

Undercarriage alarm, where fitted, operates as expected.

g.

Tyre valve is accessible and not likely to bind on any other structure.

h.

Bleed hydraulic brakes until they have no problem air and they work well.

REFERENCES
Michelin Aircraft Tire Care and Service Manual, MAT-CSM 32-45-01, Revision E January 2016.
(Dunlop) Abbreviated Component Maintenance Manual Aircraft Tyres And Tubes, DM1172, Revision 3
February 2016.
(TOST GmbH) Betriebshandbuch Flugzeugräder, Revision 2 July 2013 (Operators Handbook for Aircraft
Wheels)(TOST GmbH) Produktkatalog, September 2013
AC 43.13-1A Change 3. Acceptable Methods, Techniques and Practices. IAP Inc., Casper, Wyoming, 1988.
(Chapter 9, Section 1)
Aviation Maintenance Technician Handbook–Airframe, Volume 2, 2012. (Chapter 13)

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25.

INSPECTION AFTER HARD LANDINGS

25.1

GENERAL
Aircraft are designed to withstand flight and landing loads within specified limits. If the design limits are
exceeded the structural integrity of the aircraft may be jeopardised and safety could be impaired. Any reportor evidence on the aircraft which suggests that the design limits have been exceeded should be followed bya careful inspection appropriate to the nature of the occurrence. An Annual Inspector or higher is authorized
to perform the inspection and sign it out.
The following advice is provided as guidance for this situation. It is not possible to provide precise details ofinspections to be adopted after every type of incident due to the varying nature of the stress that may occur.
Many forms of signs of distress and many degrees of damage occur. Hard landings happen in many ways
and sometimes the pilots reaction to the situation influence the results, e.g. the pilot jerks back on the stickat the last second and smashes the tailwheel into the ground. So be open minded and look for everything.

25.2

THE MECHANICS OF HEAVY LANDINGS
There are many different methods of inspection possible and areas where those inspections may be applied
to a sailplane. To assist with understanding what is most appropriate, an understanding of the forces applied
to the aircraft in question is useful.

25.2.1TAIL FIRST

Figure 25-1

Tail First Landing

The aircraft touches down tail first which causes the aircraft to rotate around the rear contact point andimpact the ground with the main undercarriage at a higher rate than normal. This can lead to:a.

Heavy impact on the mainwheel and associated structure.

b.

Heavy loading at the wing roots due to wings tending to bend down.

c.

Recoil of the wings upward can cause damage to the wing structure.

d.

Aileron mass balances are heavily loaded both at impact, and possibly higher during recoil.

e.

The pilot experiences high ‘g' loading, higher than the ‘g' load on the aircraft.

f.

Highest ‘g' load will be on equipment or mass balance weights fitted into nose.

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25.2.2

MAIN WHEEL FLY ON

Figure 25-2

Main Wheel First Impact

The aircraft touches down on the main wheel at much higher than normal speed. This causes the aircraft todecelerate heavily with large inertia forces. This can lead to:25.2.3a.

Heavy impact on wheel and structure with high loading rearward.

b.

Heavy loading at wing root with wings tending to move forward under deceleration, as well as down.

c.

Inertia of the tail leads to the fuselage bending down.

NOSE FIRST

Figure 25-3

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The aircraft touches down nose first. The initial contact can vary from a simple rub on the ground to full
destruction of the front cockpit. Rapid loss of airspeed causes the aircraft to fall first on the mainundercarriage, then subsequently on the tail. This can lead to:25.2.4a.

Initial contact putting high forward loading on pilot, and all fixed equipment.

b.

Wings try to keep going forward, putting their trailing edge into tension, then recoiling, putting thetrailing edge into compression.

c.

High forward loading on all mass balances.

d.

The main wheel impact can be mild to destructive with high vertical loads on the wheel and associatedstructure.

e.

Heavy loading at the wing root due to wings tending to bend down during main wheel impact.

f.

Final impact on the tail can put high 'g' forces into the tailwheel assembly and tend to break thehorizontal tailplane.

g.

High loads on the rudder attachments, the elevators and elevator hinges.

NOSE FIRST – MAIN WHEEL BEHIND CoG

Figure 25-4

Nose First Impact – Main Wheel Behind COG

The aircraft touches down nose first similar to 25.2.3. The initial contact can vary from a simple rub on the
ground to full destruction of the front cockpit. Rapid loss of airspeed causes the aircraft to fall first on themain undercarriage, but may not rotate to the extent that the tail impacts the ground. This is typical of types
such as the ASK 13, Grob G 103, K7 and Kookaburra. This leads to:a.

Initial contact putting high forward and vertical loading on pilot/s and fixed equipment.

b.

Wings tending to bend down and forward, then flick back.

c.

Impact loads on the main wheel and its structure. High vertical ‘g' loading on fixed equipment aroundwheel area.

d.

The tail assembly suffers high ‘g' loading without touching the ground. This causes severe stress in
the rear fuselage, typically buckling the bottom rear fuselage structure.

e.

High loading on horizontal tailplane tending to bend both halves down.

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25.2.5OVERBRAKING ON THE GROUND ROLL

Figure 25-5

Over Braking on Ground Roll

The aircraft touches down on the main wheel, usually at higher than normal speed. The pilot then uses
strong braking to intentionally decelerate the aircraft, which causes the sailplane to tip onto its nose. This iscommon with Blaniks, other sailplanes with heavy pilots and aircraft with good braking systems such as
Jantars or older sailplanes with nose skids. The situation then becomes very like the fast fly on 25.2.2
leading to:25.2.6a.

Heavy loading at wing root with wings tending to move forward under deceleration.

b.

Inertia of the tail bends the fuselage down.

c.

The aircraft stops and the tail drops. Sometimes up to 2 metres, severely loading the; tailwheel;rudder and hinges; rear fuselage; horizontal tail; elevators and elevator control system.

GROUND LOOPS
In a heavy landing the pilot knows the aircraft has been highly loaded.
But during a ground loop, even though it may be very severe, the pilot may not realise the aircraft has been
overloaded.
A ground loop usually follows a pattern.
a.

The wing drops into an object, ground, bush, grass etc.

b.

The sailplane rotates around that tip out of control, tail up.

c.

Somewhere between the start and the finish of the event, the tailwheel strikes the ground.

d.

This can lead to:

Version 24.1i.

Extreme damage in the wing root area, dive brake box area, root end of aileron area and in thewing that strikes the ground.

ii.

The weight of the tail, especially a “T” tail, can cause the rear fuselage to “wind up”, due to therear fuselage hitting the ground sideways. This can cause considerable damage at the base of
the fin, and the tailplane to fin attachment.

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25.3

THE PILOT
The thing most likely to be damaged, without necessarily a large amount of airframe damage, is the pilot.
Some sailplanes/powered sailplanes are far more dangerous in this respect than others, but all are so lightin construction that any reasonable impact will be felt by the pilot.
For these reasons any pilots involved in heavy impacts or heavy landings, without apparent injury, but who
subsequently experience pains or discomfort in the back should seek medical attention.
Statistics show that over 50% of persons injured in sailplanes and powered sailplanes sustain a fracture of
the spine.

25.4

STRUCTURAL DAMAGE
Following any of the incidents described in 25.2, damage is likely to be found ranging from very severe toalmost undetectable. The types of construction we deal with behave in different ways.

25.4.1

ALL TYPES
There are common areas of damage which should be checked for on all aircraft types after a heavy landing:a.

damage to main wing attachmentsb.

damage to tailplane mounting bolts/brackets

c.

undercarriage wheel, gear, mounting damaged.

loosened or damaged hinges on all control surfacese.

damage to the pilots’ seat pan and harness attachmentsf.

instrumentsg.

battery mounting arrangements

There are also items which can be indicative of hidden damage after a heavy landing and should be
examined further if found:25.4.2h.

distortions which make canopies or hatches fit poorly or not latch properlyi.

a change in control feel or full/free movementj.

general damage to the extremities of the aircraft (tips, nose and tail)k.

hydraulic leaks

FRP
Indications found in or damage specific to fibre reinforced plastic airframes include:a.

(a) A change of material colour around mounting pin holes, the FRP turning white which indicates
failure of the resin.

b.

(b) Shell structures often suffer internal delamination which is not visible from the outside.

c.

(c) Internal frames become debonded from the outside shell, particularly in tailcones.

d.

(d) FRP can fracture internally and return to shape without external evidence which means carefulinspection is required. In FRP construction gel coat cracks can act as "tell tale", however, this property
is lost if the sailplane has been repainted.

Look for:e.

delamination of wing internal skinsf.

wing leading edge splitsg.

spar web wrinkles and debonding

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25.4.3h.

dive brake box damagei.

cracking at the inboard end of ailerons

j.

trailing edge de-bondingk.

main wing attachment damagel.

general fuselage shell damagem.

fracture and debonding, especially at the ends of the fuselage tail boom

WOOD
Indications found in or damage specific to wooden airframes include:a.

Ply wood skins usually buckle diagonally similarly to metal panels, and stay buckled if over loaded bytearing fibres.

b.

Glued joints can fail internally, ply can debond from ribs and frames.

c.

Timber spar caps, longerons, ribs etc. are usually weak in compression, bending and splintering underoverload.

d.

edge failure is common, caused by "springback" of the wing structure following substantial downward
and forward loading.

Look for:25.4.4e.

split plywood, especially in the fuselage behind the wing rootf.

damaged fuselage framesg.

fin post damageh.

wrinkles in the ply on the fuselage or wingsi.

main skid damagej.

damage in the dive brake areak.

buckled/split wing trailing edgesl.

fractured wing ribsm.

ply/spar delamination in the wing

METAL
Indications found in or damage specific to metal airframes include:a.

Mild damage often shows up as "tilted” or partly sheared rivetsb.

Skin buckles between rivets indicate excessive compression loading has occurred.

c.

Once metal is buckled, it stays buckled. There is no "spring back" and the torsional strength andbending strength of the structure is lost.

Look for:d.

buckling of complete panels, usually diagonally;e.

buckling of frames;f.

kinking of stiffeners.

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25.4.5STEEL TUBE
On a steel tube aircraft the wings are usually wooden and should be inspected for the same damage as
detailed in 25.4.3 above.
The fuselage tubes should be inspected for bowing or buckling. Sometimes this may be subtle and using astraight edge or comparing symmetrical parts of the frame can assist. Wrinkles in the fabric surface may also
indicate distortion in the fuselage tube structure.

25.4.6MOTOR GLIDERS
As all items in the motor glider are subject to shock loads during a heavy landing it follows that items withlarge mass are affected the most. Consequently, undercarriage, motor mounts and firewalls should receive aparticularly careful examination after any hard landing.

25.5

CASE STUDIESGFA AD 231
An ASW 15 elevator actuating bell crank failed in flight. An inspection of the bell crank showed that an older
crack most likely caused by a hard landing some years previously resulted in fatigue failure of the bell crank.
Due to the inaccessible location of the bell crank the original hard landing damage was not detected before it
ultimately failed.

25.6

REFERENCES
GFA AD 231
CAAP 42L-1. Inspection of Aircraft after abnormal flight loads, heavy landing or lightning strike. CASA May
2000

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26.

NON DESTRUCTIVE INSPECTION

26.1

GENERAL
Non Destructive Inspection (NDI) or Non Destructive Testing (NDT) is an inspection process that allows anexperienced inspector to check a part for cracks and other defects without damaging the component.
Trained sailplane inspectors holding an authorization may perform inspections using the fluorescent dye
penetrant inspection. If the inspector is uncertain there is or is-not a crack experts should be called in. Other
inspection processes must be performed by persons holding the appropriate authorisations.
GFA can arrange special training to increase your understanding. GFA have fluoro kits to borrow in mostregions. And GFA holds some special test probes for specific ADs.
CASA authorized NDT inspectors/ technicians may perform NDT inspections and approvals for GFA
sailplanes.

26.2

TYPES OF NON DESTRUCTIVE INSPECTION
There are six common NDT techniques used in aviation:a.

Visual/ optical Inspection is the most common and obvious using good light and a lens.

b.

Liquid penetrant (PT)c.

Magnetic particle (MT)d.

Eddy current (ET)e.

Ultrasonic (UT)f.

Radiography (RT)A brief description of each special method is given below for the general knowledge of inspectors. You needto know about these rather than be able to perform them. There are other methods available.

26.2.1LIQUID PENETRANT TESTING (PT)PT can be divided into two types: Visible Dye Inspection and the more sensitive Fluorescent Dye Penetrant
Inspection.

26.2.1.1 RED DYE PENETRANT
Previously it was acceptable for sailplane inspectors to perform a Visible Dye Inspection using a Red Dye
Penetrant. This method has a relatively low sensitivity to the fine defects possible in aircraft structures and is
no longer considered a suitable inspection method.

WARNING
Because red dye penetrants stop fluorescent penetrants, fluorescent inspection must not be performed onparts which may have been previously inspected using red dye penetrant.
If inspection of a component previously inspected with red dye penetrant is required, contact your local RTOA for advice.

26.2.1.2 FLUORESCENT DYE PENETRANT
Fluorescent dye penetrant differs from red dye penetrant in that the dye used is fluorescent under ultra violet(UV) light. The advantage of this method is that because the dye is radiating light, it is much easier to detectthan the red dye. This factor alone accounts for a significant improvement in crack detection ability
especially when the defects are small.
This type of penetrant comes in a variety of sensitivities from medium to ultra-high.
Because there is a requirement for a UV light source (a Black Light) and a darkened environment for
fluorescent dye penetrant, this method is only useful on parts which have been brought into a suitableviewing area. The need to purchase a black light also increases the capital costs and the setup required.
However the increased sensitivity makes this the preferred method for General Aviation workshops.
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Figure 26-1 Fluorescent Dye Penetrant

26.2.2MAGNETIC PARTICLE (MT)Magnetic particle inspection can only be performed on magnetic materials. A magnetic field is induced in thecomponent and wherever there is a defect the flow of the magnetic field is disrupted and a small stray field isformed. This field is detected by small magnetic particles spread over the component which then accumulate
at the defect. The magnetic particles usually take the form of iron filings which may be applied dry orsuspended in a light oil.
This method is the most sensitive available for ferro-magnetic materials.

Figure 26-2 Magnetic Particle Inspection

26.2.3EDDY CURRENT TESTING (ET)
Eddy current NDI uses an induced electrical current to detect defects. Cracks in the sample produce eddies
in the basic material which can be detected by a sensitive electronic probe.
Expensive equipment and a qualified NDI technician are required to use eddy current NDI and it is only usedon sailplanes at fatigue sensitive spots, such as the wing root area of the Blanik to support life extension
programs.

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Figure 26-3 Eddy Current Testing

26.2.4ULTRASONIC (UT)
Ultrasonic inspection involves passing high frequency sound waves (of the order 2-10 MHz) through the partand detecting the return waves which are reflected off any defects in a similar way to radar detecting anaircraft. In order to pass the sound waves into the structure, the “speaker” must be in intimate contact withthe part which is usually achieved with a water bridge or a gel between the part and the speaker.
It is also possible to pass the sound waves completely through the test piece and detect the attenuation of
the sound through a microphone on the other side of the part. If there is a defect within the part, there will beless sound transmitted through and the reduced sound can be used to detect the damage.

Figure 26-4 Ultrasonic Testing
Ultrasound is the prime means of NDI on composite parts during the manufacturing phase as it is lesssusceptible to background noise from small insignificant defects but is well suited to finding large areas ofdelamination which is the prime type of defect found in composites. Unfortunately ultrasound is expensive to
set up and so is of little use when inspecting FRP sailplane components in the field.
The main use of ultrasound in sailplane inspection is the detection of fatigue cracks in buried items such as
the root end of spar spigot pins.

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26.2.5

RADIOGRAPHIC (RT)Radiographic inspection consists of exposing one side of a part to an X-ray source and placing aphotographic film on the other side. After the correct exposure time, the film is developed and the exposureon each part of the film is dependent on the density and thickness of the material in front of it. Defects
effectively change the local density of the material and therefore show up on the film.
Interpretation of X-ray inspection results is very difficult and requires a skilled interpretation not to mention
the health and safety requirements which must be applied.

Figure 26-5 Radiographic Inspection

26.3

PROCEDURES FOR FLUORESCENT DYE PENETRANT
The procedure for performing a fluorescent dye penetrant inspection is quite simple but must be followed
very closely. When testing components using fluorescent dye penetrant a positive crack indication showsthat a crack is present. But if there is no indication, a crack may be present but not show up because of
faulty procedures.
The following procedure is based on a commercially available fluorescent dye penetrant system. Only
products from one supplier’s system may be used together. The instructions on all packaging should be readthoroughly and followed explicitly. If there are any differences between the following and the instructions on
the packaging, the instructions on the packaging must be followed except where noted below.

26.3.1INITIAL CLEANING
Initial cleaning is required to remove the bulk dirt and contaminants which may affect the detection of cracks.
Any paint on the area of interest must be removed at this stage. Water based paint stripper that iscompatible with the sub-straight may be used, but take care to prevent contamination of the aircraft structurearound the inspection area. The area shall be through cleaned at the completion of the stripper process.
Mechanical processes, such as sand blasting and machine grinding / sanding, must not be used as theaction may smear / peen over the surface of the crack making the crack harder or perhaps impossible todetect. But plastic bead blasting may be acceptable.
Initial cleaning is usually performed using a basic degreaser such as petrol and then paint is removed usingchemical removers. Basic cleaning may also be performed using soapy water.

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26.3.2

PRE-CLEANING
Pre-cleaning is the first true step of the fluorescent dye penetrant inspection.
Spray the pre-cleaner onto the surface in question and wait approximately 10 to 30 seconds to allow any
contaminants to dissolve. Wipe the component dry with clean towelling before the cleaner fully evaporates.
Repeat the process until the part is clean.
Allow the part to stand for a few minutes to allow any excess cleaner to evaporate.
In a commercial environment, other cleaning methods such as vapour degreasing or ultrasonic cleaning may
be available. Note: vapour degreasing is being phased out due to the ozone destroying properties of thevapour, trichloroethylene and its incompatibility with some materials. If these processes are available theyshould be used in conjunction with the spray cleaner to ensure the cleanest possible part.

Figure 26-6 Cleaned surface

26.4

PENETRANT APPLICATION
Check the test specimen temperature. Normal operation may be considered to be in the temperature range
15 to 40°C.
Shake the can well (any can with a stirring marble, the rattle in the can, should be shaken before use) andspray the penetrant onto the surface from a distance of 80 to 120 mm until an even but light wet coating is
obtained. The part should then be allowed to stand for the appropriate dwell time.

Figure 26-7 Fluorescent dye penetrant seeps into continuity

26.5

DWELL TIME
The minimum dwell time shall be 20 minutes. If the test is under adverse conditions such as low test
specimen temperature or where particularly small or tight cracks (fatigue cracks are very tight cracks) are
expected then the dwell time should be doubled. The fluorescent dye penetrant should not be allowed to dry
out on the part undergoing inspection.

26.6

PENETRANT REMOVALExcess or surface penetrant must be removed. The penetrant is removed by lightly moistening (not soaking)a clean cloth or paper towel with remover/cleaner and wiping the surface. After each wipe the cloth should
be folded over to present a fresh surface to the part. This is the most critical step in the process as
excessive cleaning can easily remove the dye from any cracks making them impossible to detect.
CAUTION
The cleaner must not be sprayed directly onto the surface.

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Figure 26-8 Excess penetrant removed
If you have not cleaned it well enough you will see this in the next step and you can repeat the penetrant
removal from the surfaces.

26.7

DEVELOPING
Shake the can well. Test spray the developer away from the job then spray the developer on to the test
piece. The developer is correctly applied when there is an even, light and slightly wet coating. Excessive useof developer can mask small defects. The metal surface should still be seen through the light powder
coating.
Large defects will be found almost instantly however the item should be allowed to sit for 10 minutes before
a final interpretation is performed. On extremely critical inspections the developing time should be extended
to equal the fluorescent dye penetrant dwell time. Continuously check the part for new developing
indications.

Figure 26-9 Developer applied drawing penetrant to the surface

26.8

INDICATION INTERPRETATION
The most difficult part of fluorescent dye penetrant inspection is interpreting the indications to determine if
the dye which is seen represents a true defect, is caused by a fault in the fluorescent dye penetrant process
or by a section of the part which holds penetrant. A press fitted plug may cause an indication but not
represent a fault. Interpretation shall be done in a darkened environment, with all white light eliminated and asuitable UV light source used for illumination of the subject part.
The intensity of the indication can be used as a guide to the size of the defect. A wide crack will contain a lotof penetrant and so produce a very strong indication while a narrow or tight crack will contain only a small
amount of penetrant and so only produce a very fine indication. If a crack has been peened over during a
manufacturing or cleaning process it may show as a series of small defects in a line rather than as acontinuous line. Porosity in items such as castings will show up as scattered dots.

Figure 26-10 Large Crack or Opening

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Figure 26-11 Fine Crack

Figure 26-12 Crack Partly Closed Over

Figure 26-13 Pits or Porosity
To confirm defects the indication can be wiped off with a clean cloth lightly moistened with pre-cleaner andthe part resprayed with developer. A crack will be revealed slowly whereas a scratch will not reappear. Do
not repeat more than once.
The use of a different system is not permitted as different systems sometimes have incompatible chemicals
which react together and destroy any indication.
It should also be noted that as inspections are repeated any defects fill with the remnants of earlier tests andindications tend to fade.

26.9

CLEANING
Once the part has been found to be defect-free the part must be thoroughly cleaned and any corrosion
protection (such as paint) reapplied. Inadequate removal of the penetrant system can prevent paint adhesion
and lead to future corrosion.

26.10

REFERENCES
Aircraft Reciprocating Engines. IAP Inc., Casper, Wyoming, 1993
AC43.13-1A Change 3. Acceptable Methods, Techniques and Practices. IAP Inc., Casper, Wyoming, 1988.
CAO 108.10 Process Control - Dye Penetrant Inspection. Issue 1. Civil Aviation Authority, 7 September
1971.
Lecture notes from the dye penetrant inspection courses run by Aviation and Industrial N.D.T. Supplies.
NDI Familiarisation Course-GFA, Aerospace NDI Pty Ltd, 10/11/2016.

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27.

RADIO, ANTENNAE, FLARM AND AVIONICS

27.1

INTRODUCTION
Modern sailplanes invariably have 2-way VHF radios and ever increasingly sophisticated avionics such as
FLARM, electric variometers, glide and navigation computers and flight data loggers. This equipment needs
to be properly installed, tested and maintained since it provides considerable safety benefits as well asaiding the pilot’s soaring performance. This chapter aims to give the basic theory and useful knowledge toenable an Annual Inspector to undertake these tasks.
This chapter should be read in conjunction with the BSE Electrics Chapter.
There are no specific inspection requirements during the Annual Inspection, other than testing theequipment is; securely installed, without risk of electrical overheating, suitably fused and is operatingcorrectly. If FLARM is installed, the firmware and obstacle files should be checked at the Annual Inspection
to ensure they are the current versions.
In this Chapter:a.

Basic radio theory is explained;b.

The characteristics of a modern VHF com radio are discussed;c.

Antennae are explained and demystified. Poor antenna connection or tuning are frequent causes ofpoor radio performance so best practice detail is provided;d.

A look at avionic devices in general, including information to assist installation and inter-connection.

e.

FLARM, its installation and maintenance are discussed as they are an important safety aid to see andavoid other similarly equipped aircraft.

Throughout this chapter the term “VHF Com radio” means the 2-way VHF aircraft band communications
radio, elsewhere sometimes referred to as Com, Radio or Transceiver. The term “Antenna” (plural =“Antennae”) is the receiving and/or transmitting element attached to a radio, elsewhere sometimes referred
to as an aerial.
Acknowledgement: The Antenna section contains content modified from the “XCOM Dummies guide toaircraft antennae 2007”.

27.2

RADIO BASICS

27.2.1

RADIO WAVESRadio waves are a type of electromagnetic radiation. Electromagnetic radiation is transmitted in waves ofparticles in a broad range of wavelengths and frequencies known as the electromagnetic (EM) spectrum.
The spectrum is generally divided into seven regions in order of decreasing wavelength and increasingenergy and frequency. The common designations are: radio waves, microwaves, infrared (IR), visible light,
ultraviolet (UV), X-rays and gamma-rays.
The radio wave region of the spectrum is divided into 9 bands as follows:

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Table 27-1 Radio Band Frequencies
Band

Frequency Range

Wavelength Range

Extremely Low Frequency (ELF)<3 kHz>100 km

Very Low Frequency (VLF)

3 to 30 kHz

10 to 100 km

Low Frequency (LF)

30 to 300 kHz

1 m to 10 km

Medium Frequency (MF)

300 kHz to 3 MHz

100 m to 1 km

High Frequency (HF)

3 to 30 MHz

10 to 100 m

Very High Frequency (VHF)

30 to 300 MHz

1 to 10 m

Ultra-High Frequency (UHF)300 MHz to 3 GHz

10 cm to 1 m

Super High Frequency (SHF)

3 to 30 GHz

1 to 1 cm

Extremely High Frequency (EHF)

30 to 300 GHz

1 mm to 1 cm

The frequency band allocated internationally for aircraft communications, and used by sailplanes, is referred
to as the “Airband”. It lies in the VHF band and is specified as 118.000 MHz to 136.975 MHz.
Commercial and general aviation aircraft flying in remote areas will likely also be fitted with HF radio which
has longer range than VHF.

27.2.2WAVELENGTH AND FREQUENCY
The wavelength is the distance between peaks or troughs within a single oscillation of a transmission.
Imagine a wave moving across the water - as each wave hits the shore, the water rises and falls, and there
are the peaks and troughs in the height of the water. A radio signal travels in the same way and thewavelength is simply the distance between two consecutive peaks or troughs.
Frequency is simply the number of waves emitted per second. A frequency of 118.000 MegaHertz (MHz)means that 118 million waves are emitted each second. Now, if more waves are emitted each second, thenthey must be closer together, so this means that the higher the frequency the shorter the wavelength.

27.2.3HOW FREQUENCY AND WAVELENGTH ARE RELATEDElectromagnetic waves always travel at the speed of light (299,792 km per second). This is one of theirdefining characteristics. In the electromagnetic spectrum there are many different types of waves withvarying frequencies and wavelengths. They are all related by one important equation: Any electromagnetic
wave's frequency, multiplied by its wavelength, equals the speed of light.
Frequency of oscillation x Wavelength = speed of light
We can use this relationship to figure out the wavelength or frequency of any electromagnetic wave if wehave the other measurement. Just divide the speed of light by whichever measurement you have and thenyou've got the other.

Figure 27-1 Radio Wave and Frequency Equations
Since the frequency range for the aircraft band is from 118.000 MHz to 136.975 MHz, then the aircraft bandwavelength is approximately 2.2 metres. This wavelength is an important dimension as it dictates the size ofantenna required, though fortunately a full wavelength is not needed.

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27.2.4

USING RADIO WAVES
It is a basic fact of physics that when electrons move as an electric current in a wire, an electromagnetic fieldis created around that wire thus radiating energy in many directions. Similarly, if a wire is placed in anelectromagnetic field of waves, the field will cause electrons to flow in the wire.
Wikipedia has an excellent animated representation of how electromagnetic waves cause a current to flow inan antenna. See: https://en.wikipedia.org/wiki/Radio_wave
A screen shot of this is shown below at Figure 27-2

Figure 27-2 Half-Wave Dipole Antenna
So to communicate with radio waves we start by using a crystal-oscillator controlled frequency synthesiser toaccurately create electric current waves at the desired frequency within the Airband. This is referred to as
the carrier wave. Signal information (eg a voice message) is then added to the carrier wave by modulation(see next section). The radio frequency electric current waves are transferred by special screened
connecting cable (which minimises the escape of energy as electromagnetic waves) to a carefully tuned
antenna which maximises the conversion of the electric current waves into electromagnetic waves of thedesired frequency. The transmitted electromagnetic field travels from the antenna in many directions and at
the speed of light.
If another antenna is placed in the electromagnetic field, then a small electric current will be generated in theantenna wire at a frequency corresponding to the transmitted wavelength. The signal electric current
produced is very small but can be maximised by tuning the length of the antenna to the wavelength of theelectromagnetic wave and also matching the antenna polarisation (see later section) with the transmitterpolarisation. The radio frequency electric current is conveyed by screened cable (which minimises theescape of energy as electromagnetic waves and introduction of interference) to the radio. At the radio, theradio frequency signal is amplified and processed (demodulated) by the radio to leave only the signal
information (eg voice message) as an output.

27.2.5

MODULATION
A “carrier” wave, as discussed in the previous section, does not contain any message information. The
simplest way to convey a message is to key on/off the carrier wave, eg Morse Code, but this is inconvenientand inefficient. However, this is still the way that pilots can turn on runway lights at some airfields just by
keying their VHF com radio a few times in regular succession.
In order to convey a message by radio, the carrier wave at the transmitter needs to be combined, referred toas “modulated”, with the analogue voice or digital data message signal. Then at the receiver, the carrier
wave needs to be “demodulated” (eg a low pass filter) to recover the message signal.

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The two most common ways to modulate the carrier wave with a message signal are:
Amplitude modulation (AM). The power, or amplitude, of the signal is varied, or modulated, at a rate
corresponding to the frequencies of an audible signal such as voice or music. AM radio has a longrange, particularly at night, but it is subject to interference that affects the sound quality. When asignal is partially blocked, the volume of the sound is reduced accordingly. Aircraft band voicecommunications uses AM.
Frequency modulation (FM). The amplitude of the signal remains constant while the frequency of thecarrier wave is varied slightly higher or lower at a rate and magnitude corresponding to the audio ordata signal. This results in better signal quality than AM because environmental factors do not affectthe frequency the way they affect amplitude, and the receiver ignores variations in amplitude as longas the signal remains above a minimum threshold.

27.3

VHF COM RADIOSA VHF Com Radio is a combined Airband radio transmitter and receiver in one package with a single
antenna. It operates in half-duplex mode in that it is either receiving or transmitting but not both at the sametime. By default, the radio is in receive status unless the operator activates transmit.
There are numerous brands of aircraft radios on the market. Since they all must communicate with eachother, they must carefully comply with international technical standards. Over time, the physical form,
technical features and methods of operating the different brands of radios commonly used in sailplanes havebecome very similar but are still different so the manufacturer’s user/installation manual is the primarysource of information.
Hand-held VHF Airband com radios are readily available but their range is usually far less than a wellinstalled radio and, as a loose object in the cockpit, they may be an inflight hazard.
An installed VHF com radio system usually comprises the following components and these are discussed in
the following text:

27.3.1a.

VHF com radio unitb.

Microphone and Press To Talk (PTT) switchc.

Loudspeakerd.

Antennae.

Antenna-Radio cablef.

Wiring harness (to connect the above components)

GOLDEN RULES - WARNING!
Before going any further, there are a few Golden Rules when working with radios that need to be observed:a.

DO NOT transmit without an antenna connected that is suitable for the radio’s frequency operating
range.

b.

DO NOT transmit with a damaged coax cable.

c.

DO NOT transmit with a disconnected coax cabled.

DO NOT transmit when the antenna is grossly out of tune i.e. SWR greater than 3:1

Failing to comply with any of the above may cause the reflected power (ie power normally radiated by theantenna) to severely damage the radio.

27.3.2

THE VHF COM RADIO
Most countries divide the 19 MHz of the Airband into 760 channels of 25kHz bandwidth and use amplitude
modulation voice transmissions, on frequencies from 118–136.975 MHz, in steps of 25 kHz. Hence theproduct name of many VHF com radios includes the number “760”.

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In Europe, to create more available channels each ‘760 channel’ has been further divide into three channelsof 8.33 kHz bandwidth, thus permitting 2,280 channels. These 8.33kHz radios are compatible with 25kHz
spaced frequencies. At the time of editing, Australia has no published plan to use the new channels createdby 8.33kHz bandwidth.
Aircraft VHF radio communications worldwide uses amplitude modulation. A typical sailplane radio has an
output of 5-10 watts Radio Frequency (RF) output.
The usual physical form of modern VHF com radio found in sailplanes is a rectangular box typically 60 x 60 x
200mm. They are designed to be installed in a standard 57mm (2 ¼”) circular instrument panel hole (frombehind the panel) and secured using 4x mounting screws through the panel.

Figure 27-3 Example VHF Com Radio Panel Mounted
Some manufacturers offer a remote-controlled version which allows the controller “head” to be installed in
instruments panels lacking depth whilst the main box is installed elsewhere. Eg Becker RT6512.

Figure 27-4 Remote VHF Com Radio and Controller Head
It is best practice to install the radio with its own dedicated fuse/circuit breaker. The manufacturers’
recommended value is often 3A but check with radio’s user/installation manual.
The radio case is usually metal and often has its own grounding connection which is important to minimise
interference.
In a 2-seat tandem sailplane, the VHF com radio should be fitted in the panel of the cockpit used for solo
flight, usually the front cockpit. This has the unfortunate disadvantage that an instructor in the rear seat is
unable to adjust the radio frequency/volume in flight. If this is an important issue, then a rear seat ‘remoteradio head’ which connects to the main radio may be a suitable solution (Eg Trig TY91).

27.3.3

MICROPHONE AND PTT
A microphone, colloquially called a mic or mike, is a transducer that converts sound into an electrical signal.
There are two types of microphone commonly used in aviation and many radios can be set to accommodate
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 The dynamic microphone. A coil is glued to the rear of a membrane, and there is a strong magnet
surrounding this coil. When sound waves hit the microphone, the membrane moves to the rhythm of thesound waves, and the coil on its back moves along with it. The relative movement of the coil within thestationary magnetic field induces a small signal voltage in the coil. (This is effectively a loudspeaker inreverse). The output signal level is low. Some brands of VHF com radios have a special input
connection and internal amplification for this type of mic. Other brands require an add-on mic amplifier tobe used or deem this type not suitable.
 The electret microphone (a statically pre-charged form of condenser microphone). This uses a vibrating
diaphragm as a capacitor plate that varies the capacitance in sympathy with the sound wave. This isprobably the most common microphone type in use in aviation. They are small in size and can have noise
cancelling capability. They are a high signal device and thus do not normally require amplification. It is
important to wire an electret microphone with the correct polarity as it must have a voltage bias applied to
it by the radio.
Any mismatch in the antenna tuning can set up standing waves currents along the outside of the antennacoax which are capable of electromagnetically inducing unwanted signals into microphone wires. This is thecause of many of oscillation and feedback problems. To protect against interference:

Do not run the microphone cable alongside the antenna coax, keep them separated as much as
possible, and;

Use screened cable between microphones and the radio should be via screened cable where the screen
is grounded on one end only.

It is normal for the microphone to be mounted on the end of a flexible gooseneck and to activate it with a
PTT (Press To Talk) button switch on the control stick. This means the pilot can position the microphonenear his mouth, has both hands available to fly the aircraft and can activate the radio via the PTT without
letting go of the control stick. The PTT cable where it enters or is attached to the control stick should bechecked at each Annual Inspection as it may be subject to fatigue as the stick is moved.
It can be convenient for maintenance to connect the microphone/gooseneck to the in-fuselage wiring via agood quality connector, such as a miniature DIN 3-pin, maintaining the screening through the connector.
This enables easy disconnection and removal for maintenance.
In two seat sailplanes with a single radio, the radio usually has separate input pins for each microphone andeach PTT. When two microphones are used, some radios require the microphones to be of the same typeie matched, whilst some radios have different inputs and/or internal software configuration to allow unmatched microphone pairs. Read the installation manual carefully to ensure a valid configuration.

27.3.4LOUDSPEAKERS
Loudspeakers convert electrical energy into sound waves using an electro-magnet to excite and vibrate adiaphragm. A speaker is described by its impedance (usually 4 ohms or 8 ohms), power handling capability(typically 5 watts) and its physical size. The speaker’s impedance must match and the power rating matchor exceed the radio/device’s specification.
Note: Impedance = resistance + reactance (due to capacitance and induction created by alternating current
signals).
Adding a second speaker in series or parallel will result in a different impedance to the individual speakers(in accordance with resistive network theory) and is best avoided. In a two-seat tandem sailplane with asingle speaker, it is usually best to mount the speaker in or on the rear instrument panel so as to position it
between the two pilots where both can similarly hear a reasonable volume setting.
Do not ground wires feeding loudspeakers unless the radio installation instructions state this is required.
Do not connect speakers to headphone outputs or headphones to speaker outputs.
You cannot simply connect multiple input sources to the same speaker. Whilst there are electronic
mixer/amplifiers that can combine multiple input sources into one output, this is done at low signal levels
prior to the main amplification. It is thus normal in sailplanes to have separate speakers for the radio andelectronic variometer(s).

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All speakers contain a powerful magnet that can affect a magnetic compass. It is best to mount it as far
away as practical from the compass to avoid erroneous compass readings. After a new radio installation,
you should re-swing your compass, including radio transmit and receive operation, to confirm the compass is
not unduly affected.

27.3.5

RADIO WIRING HARNESSConnections to modern radios are usually via a male sub-miniature D socket (often 15 or 25 pin) on the rearof the radio. This socket usually provides all connections except the antenna and a case/chassis ground.
This enables the radio to be easily disconnected and removed from the sailplane in the event of requiring
service.
Some manufacturers provide a matching female D plug with pre-soldered wires as a wiring harness. Other
manufacturers provide a wiring diagram and perhaps an unwired male socket for the installer to solder wires
to.
There is no common standard shared by manufacturers for the wiring of the connectors used in radio wiring
harness. If you replace a radio with a different model or brand, even if the new radio looks like it will simply
plug into the existing harness, you must read the installation manual and ensure the correct wiring is
configured at the connector pins or you may damage the radio.
An example of a VHF com radio wiring harness and it’s wiring diagram are shown below at Figure 27-5 andFigure 27-6 (acknowledgement to Microair):Figure 27-5 VHF Com Wiring Harness

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Figure 27-6 VHF Com Example D-Plug Wiring Diagram

27.4

ANTENNAE

27.4.1ANTENNA BASICS
An antenna is a transducer that enables:a. Transmission by converting radio frequency electric current into electromagnetic waves
that are then radiated into space, orb.

Reception by converting electromagnetic waves into radio frequency electric current

An antenna consists of an active/driven element and a ground plane element. In physical form, antennae
are either a dipole antenna (two conducting elements are clearly visible) or a monopole antenna (one active
element is visible and the other, the ground plane, is not so obvious).

Figure 27-7 Forms of Antennae
The physical length of the antenna’s active element needs to be matched/tuned to the frequency range ofuse. Antenna lengths of 1, ½, ¼ or 1/8 of the wavelength of the mid frequency of the required band are all
suitable. Generally, the longer the length of antenna, the greater output strength. For practical reasons, theoptimum length of a sailplane antenna’s active element should match one quarter of the wavelength of thefrequency being used.
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The ground plane element of an antenna should be of similar equivalent electrical size to the active element.
Where the two elements are physically aligned as a ’dipole’, they are usually described as half-wave dipoles
as each element is ¼ of a wavelength. Monopole antennae, such as a whip antenna, are usually describedas ¼-wave whip but must still have an equivalent ground plane.
The ground plane (sometimes referred to as the counterpoise) is simply the 'grounded' side of the antenna.
All antennae require a suitable ground plane but there are several different ways of achieving this for amonopole antenna, such as:

27.4.2a.

Use the aircraft skin (on metal aircraft)b.

Use a foil or aluminium sheet inside the aircraftc.

Use wires radiating from the base of the antennad.

Use a tuned coil of wire built into the base of the antenna

ANTENNA POLARISATION
The term “Polarisation” simply refers to the orientation of the electromagnetic radio wave being transmitted
from the antenna. A vertical antenna radiates a vertically polarised signal and a horizontal antenna radiates
a horizontally polarised signal. For good communication, the transmitting and receiving antennae need tohave the same orientation.

Figure 27-8 Antennae Polarisation
For aircraft band frequencies, vertical polarisation is the standard. Thus, a sailplane’s antennae radiating
element should be mounted so as to as near vertical as possible with the sailplane in a straight and level
flight.
An Airband radio with a vertical antenna is omni-directional in that theoretically it transmits/receives equallyin all horizontal directions. However, the structure of the sailplane may degrade the signals in somedirections eg a tail-mounted antenna may have a weak zone in the forward direction.

27.4.3

TYPES OF AIRCRAFT ANTENNA
There are several different types of antenna available for aircraft. Some are expensive, some are cheap,
some are designed to be used externally and others are designed to be used internally ie inside the aircraft
structure. All Airband antennae have a designed input impedance of 50 ohms
For practical reasons, most modern GRP sailplanes have a vertical half-wave dipole built into the verticalstabiliser during construction. Accessing such an antenna or the point of connection of the cable to theantenna is likely to be very difficult, however such antenna installations are generally very reliable. To
prolong the life of a tail antenna, do not pull or strain the antenna cable.

There are hundreds of antennae on the market with many different features but they can be split into the fmajor groups shown in the table below:

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Table 27-2 Antennae Groups
Internal dipole antennae - The mostcommon dipole is the half wavelength
dipole antenna which has two 1/4
wave 'elements' placed end to end withthe connection point at the centre.

Fibreglass or stainless-steel whip
antennae —these are 1/4 wave
antennae most suited to ultralightaircraft, sailplanes, sport aircraft, etc.
Fibreglass rigid antennae - more
expensive 1/4 wave antennae like the
Comant 121 model which offer
extremely good SWR readings acrossthe entire aviation band and offer
excellent performance. Often seen on
GA aircraft.
Base station antennae - usually longer
in length than standard 1/4 wave
antennae, most base station antennaeare 1/2 wavelengths being
approximately 1.2 m long plus a basesection. They are normally 'groundplane independent' (meaning that the
ground plane is 'in-built') and aremounted vertically on towers or theside of buildings. Due to their bulk
they are not suitable for sailplanes.

27.4.4

WHIP ANTENNAE
In metal aircraft, a whip antenna can be grounded through the antenna mounting screws into the airframe.
In which case, it is important to obtain a good electrical bond where the antenna is mounted by ensuring thearea is free of paint and debris. With many antennae, a backing plate is placed in the aircraft interior withthe antenna connected by mounting screws through the aircraft skin. The backing plate must obtain a goodelectrical ground to the aircraft skin by removing the paint. The electrical ground can be checked by placing
a multi-meter between the antenna mounting screw and the aircraft skin. The reading should be no greaterthan 0.003 ohm
Wood/fabric sailplanes and modern GRP sailplanes lack a metal frame or body and thus create challenges
when trying to ground a whip antenna. To ensure good communications, care must be taken to provide anadequate ground plane. For best performance the ground plane should be horizontal and have a radius of atleast one quarter wavelength of the antennae operating frequency, or as large as practical.
Internal antennae and ground planes will not work inside sailplanes with carbon fibre reinforcement in thefuselage. Such sailplanes usually deliberately have no carbon fibre in the stabiliser and/or rudder so that adipole antenna can be installed there.
The location of an antenna on any aircraft is very important. VHF transmissions are line of sight and any
object in the transmission path like the tail plane, other antennae, people or carbon fibre reinforcement will
reduce the performance of the antenna in the direction of the interrupted line of sight. In a perfect
installation the antenna would be located on a flat surface centrally located in the middle of a ground plane.
Unfortunately, this is not always possible and the best position must be a compromise for each individual
aircraft type.
On powered sailplanes, antennae should not be mounted anywhere near an engine exhaust.

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27.4.5CONNECTING THE RADIO TO THE ANTENNA
You cannot use normal parallel-pair wire cable to connect a radio with the antenna – you must use a coaxial
cable, often referred to as 'coax', where one conductor forms a concentric “shield” around a central core
conductor. This cable provides a pathway for the transmission signal and needs to have physical properties
that provide the best possible performance regarding low loss of signal and exclusion of interference.
In most cases, newly constructed sailplanes come ready installed with an antenna and connecting coax
cable or a purchased antenna comes with a coax cable deemed suitable by the antenna manufacturer or
supplier. However, there may be times when a coax cable must be replaced or extended, so the following
text is provided to aid understanding and selection of suitable cable.

27.4.6

COAXIAL CABLE
Coax cable has a centre wire, a dielectric/insulation layer, a concentric outer braid/foil shield and an outer
protective jacket (see diagrams below). The centre wire carries the signal to/from the antenna and the outershield cancels any electromagnetic radiation and suppresses external interference that might degrade thetransmission signal quality.
Every coax cable exhibits capacitance between the centre wire and the braid, and also inductance along thelength of the cable. For coax cables at radio frequencies, the capacitance typically dominates the
impedance value and is thus often stated in a cable’s specification.

Understanding Impedance
In direct current circuits the relationship of current (I), voltage (V) and resistance (R) is defined by
Ohm’s Law V = I x R. However, with alternating current (such as radio frequency signal fluctuations)in circuits, there is further opposition to the current changes due to the effects of capacitance andinduction known as reactance.
So in alternating current circuits, the relationship equation becomes V = I x Z where Z is called
Impedance and measured in ohms (symbol is Ω). Impedance is the resistance plus the reactance(due to capacitance and induction). The value of reactance depends on the frequency of the signal aswell as the value of the capacitance and induction.

Coax cable is classified by its “characteristic impedance”. The characteristic impedance of a uniform
transmission line is defined as its input impedance when its length is infinite. Characteristic impedance isdetermined by the geometry and materials of the transmission line and, for a uniform line, is not dependent
on its length. The importance of this for radio communications is that for maximum power transfer the radio
output impedance, coax cable characteristic impedance and antenna impedance must all match. VHF com
radio coax cables must have a characteristic impedance of 50 ohms. Do not use TV coax, which has acharacteristic impedance of 75 ohms, in sailplanes.
Aside from the characteristic impedance, the most important electrical parameter of coax is probably thesignal loss (sometimes referred to as “attenuation”) per metre. Signal loss in the cable means that a fractionof the radio’s output fails to reach the antenna or else that the received signal at the antenna is diminishedby the time it reaches the radio. Ideally, we want to choose a cable with low loss. Signal loss is usually
expressed as decibels (dB) per 100m. Decibels is an exponential scale, not a linear scale, so for example a
3dB loss is equivalent to a reduction to 50% of the input signal level and a 10db loss is equivalent to a
reduction to 10%.
There are several factors that influence the signal loss in a coax cable, the key ones being:a.

Cross section area and number of stands in centre wire. The bigger the diameter the better the
conductivity but heavier the weight per metre. Theoretically a solid core centre wire has greater crosssection than a stranded core and so less loss. Stranded cores however are more flexible so lessinclined to break.

b.

Dielectric/Insulator thickness and material.

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c.

Quality of braiding shield. The fewer gaps in the braiding the less loss of signal and possibility ofinterference. This is often specified as the percentage of coverage – the higher the percentage thebetter. Copper braid may be further improved by coating with silver. Two layers of braid aresometimes used as it results in fewer gaps. Foil is an alternative to braid and has no gaps but isrelatively fragile. Composite shields comprising a layer of foil covered in a layer of braid are available.

For sailplanes, the length of run of the coax cable is relatively short (so the length related loss is usually
fairly small), the RF transmit power is relatively low (4-10W), we need to minimise the weight and choose adurable flexible cable which will have a long life. In practice this means we are seeking a good quality 50ohm low loss coax of approx 5mm outside diameter. There is a bewildering choice in the market!
At first glance there appears to be a standard for coax cables (originating from the US military in the 1950s),
all commencing with the designation “RG”. For example, RG58 is a 50 ohm (Ω) coax with an outside
diameter of approx 5mm. But the RG standards are no longer officially maintained and have beensuperseded in the US by MIL-C-17. Manufacturers may also put to market products that do not match
precisely these standards but may be fit for sailplane use.
The following table summarises a number of appropriate RG specifications for 50 ohm coax and a couple ofmanufacturers’ products that might be considered for sailplanes:

Table 27-3 Typical Specifications of Suitable CoaxType
Single shield

Code orbrandname
RG58/URG58A/URG58C/U

Double shield
Low lossd.

RG8X (Mini 8)
RG142U
RG400
LMR195Hyperflex 5
Airborne 5Centre conductor /ShieldSolid / Braid
Stranded / Braid
Stranded / Braid (noncontaminating jacket”)
Stranded / Braid
Solid / double Braid
Stranded / double Braid
Solid /Foil + braid
Stranded /Foil + braid
Stranded /Foil + braid

Typical Loss/100m
OD mm@ 100MHz
15.0
5.0
17.0
5.0
17.0

5.0

10.1
10.8
10.8
12.0
8.2
9.4

6.1
5.0
5.0
5.0
5.0
5.0

“Non-contaminating jacket” meaning: Over time, exacerbated by UV and heat, the migration ofplasticiser from a PVC jacket into the polyethylene core of a coaxial cable causes contamination
which can significantly alter the high-frequency transmission characteristics of the cable. A noncontaminating jacket is less prone to deteriorate in performance overtime.

When comparing signal loss factors, it is important to use consistent units of measure and ensure thefrequency at which the attenuation is measured is close to the Airband range.
Coax cable similar to RG58 is available with an aluminium foil shield instead of a wire braid. Theoreticallyfoil, having 100% coverage compared to braid having gaps between the braids, has less loss and istherefore superior. However, foil alone cannot be soldered and if crimped the foil may be damaged bybending. There are also double shielded cables, that have a braid shield and also a foil shield, which offer
excellent shielding and practicality.
For motor sailplanes with unshielded ignition systems, it is preferable to use RG400 or RG142/U which is adouble shielded coax, or a branded low loss coax, since the extra shielding will reduce interference noisedue to the ignition system.

Figure 27-9

Shielded Coax

If choosing a coax to connect a base station with an antenna over 8m away, you might consider a thicker
coax cable, say 10mm outside diameter so as to minimise the losses and because size/weight is not an
issue.
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It is good practice and gives the best performance if the coax cable is kept as short as possible. Avoid sharp
bends, do not coil the coax cable to create loops and do not run the VHF antenna coax alongside atransponder coax to avoid interference problems.
Once the coax is installed, it generally lasts the life of the aircraft so skimping on a few dollars during
installation does not make good sense. You should purchase the best quality coax and connectors that you
can afford and ensure that they are correct for your avionics installation.
If it is required to extend an existing coax cable, do not attempt to solder or crimp an add-on length to theexisting cable as such a joint would most likely be a cause of signal loss. It is best to have male BNC plugson the ends of the cables to be joined and use a female-female inline connector to join them.

Figure 27-10 Female-Female Coax Connector
Potential suppliers of suitable coax cable and connectors in Australia are:27.4.7a.

Altronicsb.

Jaycarc.

radioparts.com.aud.

rfsolutions.com.au

e.

zcg.com.auf.

commswestdistribution.co.au

VHF COM RADIO ANTENNA CONNECTORS
When a coax cable needs to be connected to either the antenna or to the radio, it is usually done with a BNC(bayonet) connector or occasionally a TNC (threaded) connector. These connectors are light, mechanicallystrong and reasonably weatherproof. There are numerous manufacturers to choose from. Right angled
versions are available which can be useful where there is a depth issue behind the panel. They areavailable in crimped or soldered versions. There are also solderless/crimp-less versions but these are notgood enough for radio frequency use.
If using coax other than standard RG58, then check that the connector matches the coax diameter else thecrimp or securing gland (on a soldered connected) may be the wrong size.

Figure 27-11 RG58
BNC bayonet(crimp) 50 ohms

Figure 27-12 RG58
TNC screw on(crimp) 50 ohms

Figure 27-13 RG58
BNC bayonet(crimp) right-angle
50 ohms

Notes: BNC = Bayonet Neill–Concelman. It features two bayonet lugs on the female connector; mating is fully achieved with a quarter
turn of the coupling nut.
TNC = Threaded Neill–Concelman. This has a screwed coupling nut.
RG59 connectors are designed for 75 ohm cables and should not be use with VHF com radios.

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27.4.8

MAKING A COAX PLUG CRIMP CONNECTION
It is a common error to apply too much heat when soldering and this can damage both the plug and thecable, therefore a crimped connection is usually the best solution. Properly made crimped connections arevery reliable and strong, offering years of service in the field.
Crimped connections need to be performed with the correct size and profile crimping tool. An example isshown in the figure right. The table below describes the process steps.

Figure 27-14 Typical Ratchet Crimpers
Table 27-4 The steps for making a crimp connection on a BNC or TNC connector
Step 1. Layout all the parts required for acrimped connection.

Step 2. Strip back the outer cable shield to
expose the braid and also strip back the
dielectric/insulator to expose the cable core.
Experimentation on a practice piece may berequired to establish how much strip back.
Step 3. Slide the ferrule over the cable, out of
the way for now. Position the contact pin on the
exposed cable core and then crimp the contact
pin in place.
Step 4. Insert the cable into the rear of the BNC
connector until you hear the contact pin click
into position.
Step 5. Slide the ferrule back down the cableuntil it is firmly seated on the base of the BNC
and crimp into position using an appropriate
size crimping tool.

Finally, check the coax cable and BNC fitting for physical security and electrical continuity to make sure theconnection has been completed correctly.

27.4.9ANTENNA PERFORMANCEThe Voltage Standing Wave Ratio (VSWR), or SWR for short, of an antenna is a measure of how efficiently
the radio is radiating the energy it produces when it transmits. It is represented as a ratio and is generally,
all though not accurately, referred to as the ratio of emitted power to reflected power within an antenna.
You don't need to know what it actually is in order to measure it; you just need an SWR meter to get three
simple readings.

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Every new antenna installation in an aircraft, regardless of the quality of the antenna, should be checkedwith a SWR meter before first flight. For existing antenna installations, if faults are suspected with the radioor antenna then a SWR test may help verify the issue.
SWR meters are readily available in electronics shops and on the internet. Make sure the meter covers the
Airband frequency range and comes with the appropriate connectors.
Here is what you need to know:a.

The scale on a SWR meter reads from 1 to infinity. The smaller the number, the better the SWR
reading and the antenna will perform. The scale is not linear, it is logarithmic. From 1 to 3 covers
more than half of the scale on a SWR meter. The remainder covers 3 to infinity.

b.

The ideal number to aim for on the SWR meter is 1:1 (pronounced 1 to 1) but this is rarely achieved.
This means all the energy is being radiated and none being 'reflected' back into the radio. Less than
1.5:1 is very good. A SWR of 2:1 or less is OK. It is generally regarded that a SWR reading of lessthan 2.5:1 is acceptable for aviation use, but the intention is to get the SWR as low as possible.

c.

A SWR reading of more than 3 may be hazardous to a radio. This is often marked in red on the SWR
scale. Because of the logarithmic scale, you don't have to be far into the red before you are into the
big numbers!

d.

The Airband covers a very wide range from 118.000 MHz up to 136.975 MHz. For any given
frequency there is a corresponding wavelength and one ideal length of antenna. Because we arechanging frequencies often, it stands to reason that the actual length of our antenna must be acompromise since we can't keep changing the length of the antenna every time we change frequency.
Most aircraft antennae are tuned in the middle of the Airband frequency (usually 127 MHz) and we
accept a compromise of the SWR reading at frequencies above and below this middle frequency.

e.

In practice the size and shape of the antenna's ground plane can also affect the SWR of an antenna.
(no ground plane = high SWR)f.

ATC radio transmissions are vertically polarised, as described earlier. This means that your aircraft
antenna should be installed so as to be more vertical than horizontal for best performance.

27.4.10 THE EFFECT OF ANTENNA DIAMETER/WIDTH ON PERFORMANCE
Generally, a larger diameter/width antenna will give a broader band performance. That is, an antenna that islarge in diameter or flat and wide like the internal dipoles, will give a much better broadband performance
than a thin stainless-steel whip antenna. When a thin stainless-steel antenna is tuned to 127 MHz (roughly
the middle of the aircraft band) the maximum broadband performance it can give is around 5 MHz (ie2.5MHz either side of 127 MHz) whereas larger diameter antennae can give broadband performance over
10 MHz range.
The following two graphs are a good indication of how a wider diameter antenna can generally provide better
performance. The graph on the left-hand side shows a performance chart for a Mobile 1 base station
antenna.
Reading the graph at 118 MHz shows a SWR of less than 1.6:1, at 126 MHz it is 1:1 and 136 MHz it isaround 1.7:1 making this a fantastically performing antenna across the entire Airband range.
The graph on the right however shows a stainless-steel whip type antenna which is tuned to 124 MHz where
it has a SWR reading of around 1.1:1 which is great. Unfortunately, at 129 MHz the antenna is alreadyabove our upper limit of 3:1 SWR and the same at the lower frequency of around 121 MHz. What thismeans is the stainless-steel whip type antenna will perform really well at around 124 MHz but its
performance drops off quickly when the radio is moved off this frequency. This antenna should not be used
for any frequencies lower than 121 MHz or higher than 129 MHz because of the risk of radio damage.

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Figure 27-15 Example SWR Results Graphs

27.4.11 USING A SWR METER
Connect the antenna BNC plug to the side of the SWR meter marked antenna. Connect the radio to theside of the SWR meter marked transmitter. In other words, the SWR meter is connected between the radio
and the antenna.

Figure 27-16 SWR Meter Between Radio and Antenna
Rig the aircraft and move it well away from hangars. Conducting SWR tests inside a hanger is a complete
waste of time because the meter will measure the signal bouncing off the metal from the hangar and give ahigh reading!
Firstly, set the first frequency to 118.000 MHz and calibrate the SWR meter by doing a brief transmission on
the calibrate setting and adjust the power needle to the 'set' position (100% full scale deflection) using theknob on the front of the meter. Make sure the frequencies you use are not in use at your location.
If you have the most common SWR meter which is a single dial meter, you will have to switch between
calibrate and SWR operations and note the readings.
Note: You don't need to talk to anyone; in fact you don't even need your headset plugged in. You are justmeasuring the efficiency of the 'carrier wave', not the modulation (voice signal).
Then repeat the operation above on 127.000 MHz and again on 136.975 MHz. This will give us three SWR
readings across the entire aircraft band. One reading is at 118.000 MHz, the second reading at 127.000
MHz and a final reading at 136.975 MHz.
A typical example set of SWR readings follows:
118.000 MHz = 2.3 :1
127.000 MHz = 1.5 :1
136.975 MHZ = 2.8 :1

From these three readings we can see that the antenna is best at 127 MHz, it is not too bad at 118 MHz but
the SWR readings get high at 136 MHz. This tells you that the antenna is going to perform better in thecentral and lower frequencies than it is at the top of the frequency range.
In this example the antenna is not perfect especially at 136 MHz but it will do the job.
We would like to get a better reading and to do this ideally you would tune the antenna. However, many
sailplane antennae are built-in during manufacture, are inaccessible and thus untuneable. We should takecomfort that the antenna was carefully selected by the sailplane manufacturer to be suitable and provided
the Airband frequency range has not changed, it should be adequately tuned.
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If a SWR test suggests that an installed antenna is poorly tuned, then the most likely cause is the connecting
cable or the deterioration of the connection (eg strain induced disconnect or corrosion) of the coax to theantenna. Accessing the latter may be challenging.

27.4.12 HOW TO TUNE ANTENNAE
Many of the more expensive add-on antennae come pre-tuned and it is pretty much impossible to maketuning changes to the antenna. Some of the cheaper antennae however have the ability and therequirement to be tuned in each installation. The procedure for tuning is:a.

If it is a whip antenna, screw the antenna onto the antenna base as far as it will go and ensure you
have a suitable ground plane with good electrical contact. A poor ground plane will cause yourantenna to be grossly out of tune and cannot be remedied by tuning the whip as described below.

b.

Note the SWR readings at the three frequencies 118.000, 127.000 and 136.975 MHz. To get correct
readings, keep people and metallic items away from the antenna.

c.

The higher the frequency, the shorter the required antenna length. You should try to adjust towards
the frequency with the higher SWR, so in the previous example we need to adjust towards the higher
frequency (136.975). This means we need a shorter antenna, so we can trim one or two millimetres
off the top of the antenna and recheck the SWR.

d.

If the SWR is higher on the lower frequency, then (the lower the frequency the longer the antenna) weneed to lengthen the antenna.

e.

Take care - it may not be possible to get 'flat line' in all cases. If the SWR reading starts to increaseagain before reaching 1:1, then you have gone too far, so stop cuttingf.

When you have the best SWR reading you can, remove the meter and reconnect the coax directly tothe radio. Go for a fly and get a proper radio check

27.5

AVIONICS

27.5.1AVIONICS INTRODUCTION
Aside from VHF com radios, modern sailplanes frequently have an array of avionics installed in the
instrument panel such as:a.

FLARM – other aircraft detection, relative location display and collision hazard warningb.

Electric variometerc.

GPS navigationd.

Map displaye.

Flight computersf.

Track and height logging

All these devices require power, some require antennae or sensors and often they also requireinterconnection to transfer data.
Pilots may choose to supplement the installed avionics with portable/temporarily fitted personal devices (egOudie) running flight computer software and flight loggers (eg Nano). Whilst these can often function
independently, pilots may wish to connect them to the sailplane’s power system and exchange data withinstalled avionics.
Whilst there are trends towards devices with integrated multiple functions, and Bluetooth radio is sometimes
a connection option, it looks likely that sailplane cockpits will continue to require the physical interconnectionof multiple devices for many years.
Fortunately there are some standards and conventions in use and manufacturers usually provide good
documentation. However, unless well planned, installed and recorded in the Maintenance Logbook, thisavionics interconnectivity can mean a “spaghetti” of wiring which is difficult to understand and fault find.

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Transmitting (more than 1-2 sec for test purposes) without an antenna connected or with an antenna grossly
out of tune could damage the radio. The energy produced by the radio when in transmit mode needs toradiate (and hence dissipate heat). If it is unable to do so (for whatever reason) it will be reflected back into
the radio and likely damage the power amplifier circuit.

27.5.2IGC STANDARDS FOR DOWNLOADING FLIGHT DATA
A number of years ago, the International Gliding Commission (IGC) devised standards for the connectors
and fittings for downloading flight data. These are published as “Technical Specification for GNSS Flight
Recorders”. Extracts from the Second Edition with Amendment 4a - 10 April 2016 follow below.
Whilst this IGC standardisation has been helpful, unfortunately the IGC appears to have deviated from theconventional RJ45 plug/socket numbering convention which can cause confusion. The key relevant parts of
the IGC Standard are shown in the Figure below:
6.4 Connectors and Fittings for downloading Flight Data. IGC-approved types of connectors fordownloading flight data are listed in Appendix F. Where a PC is used for downloading, either the RJ45 or
USB connector is recommended because standard wiring to these types includes both power and data
download facilities. The IGC standard connections for the RJ45 are given in Appendix F and the USB
connections are to the international standard.

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Figure 27-17 Figure 27-1 Extracts from IGC standards

27.5.3

INTERCONNECTION OF AVIONICS
Avionics interconnection can comprise:a.

Power: May be 12V (nominal aircraft battery voltage), 5V (ie USB voltage level) or 3.3V (data logic
and LED display voltage level)b.

Data exchange: Signal inputs/outputs. Several different formats exist.

c.

Sensors (eg outside air temperature, airbrake status): These could be digital or analogued.

Antennaee.

Pneumatic ie Pitot, static, TE. This is not covered in this chapter.

Whilst there is an IGC standard for cable and connectors used with Flight Loggers and Personal Digital
Assistants (PDAs) such as Oudie, Kobo and Nano, these standards are not always universally applied andsome manufacturers may occasionally use their own variations. Some of these are made for other uses andmodified to carry out a sailplane function.
The interconnection of avionic devices is relatively simple if you follow manufacturers’ suggested installation
configurations and use the purpose made cables and connectors available from the suppliers. If you choose
to implement an unpublished configuration, make your own cables, repair cables or want to incorporate
existing legacy equipment, then proceed carefully with caution as you can easily damage avionics if
incorrectly connected.
There are numerous different standards for how digital signals are passed along cable and, clearly,
compatibility is essential. Therefore, if you are attempting a non-standard configuration, the interconnectionof data may require more than just a simple plug/socket cable converter, eg the data signal may need to beconverted to different signal levels or format.
It can be difficult to shorten many types of pre-made connectors because of the tools, parts and skills
required to re-terminate the cable’s cut end. Therefore, it is best to buy the appropriate length of pre-madecable. Some cables may be available in customed lengths from specialist suppliers. If a cable isunavoidably too long, then carefully coil and tie-wrap the surplus. But be aware that coiled or even close
parallel cables act as antenna and may transfer/receive spurious signals. Be wary of what you cable tie
together and where you create coils. As a general rule, keep all cables away from the radio antenna coax,
some multiplexed data cables and engine ignition wiring.
Beware of voltage compatibility between devices and do not wire two supplies of different or even the same
voltage to one device unless the device explicitly requires it. For example: The PowerFLARM may besupplied with 12V via its D-connector or via its RJ12 socket. If you connect the PowerFLARM to a LXNAVS100 via the RJ12 socket you will connect the required 12V and you should not connect the power leads via
the D-connector. However, if you want to fuse the PowerFLARM separately to the S100, then you should
power it via the D-connector but must modify the RJ12 lead such that the 12V pin is not connected.
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You need to carefully consider socket and plug pinout details. Only the USB connector international
standards have compliance from most manufacturers. For example; compare the published LXNav S100
RJ45 socket (labelled PDA) pinouts with the IGC standard for the RG45 connection cable to flight recording
devices as shown below. Clearly these are not directly compatible. A special cable from LXNav is available
to convert the LXNav RJ45 PDA socket to a fully standard compliant mini-USB-A plug.

Figure 27-18 IGC standard RJ45

Figure 27-19 LXNav S100 PDA RJ45
If you buy pre-made RJ45 to RJ45 cables, be careful that you buy “straight through” cables unless you haveidentified that you specifically need “crossover” data cables.
Bluetooth radio is becoming more common as a means of connecting PDAs to FLARM and navigation
avionics. Refer to the device manuals for set up instructions.
To aid future maintenance, it is strongly recommended that details of the avionics interconnection is included
on the sailplane’s electrical wiring diagram. An example follows:

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Connector‐
7.5A

Main Battery
+

‐
5.0A

Tail Battery+

MasterOn/OffBattery selector
On/On

3A (Flarm)
Brown

3A (S100)

Blue

Red

White

4A (Radio)

Connector

Blue

Brown

Blue

1

2

3

4

5

6

7

8

9

10

11

12

‐

+

‐

+

‐

+

‐
Chassis

+

‐

+

‐

+

Connector block

Ant

Spare

Radio

Mike
Speaker
PTT

Oudie
Power/Data
12V

Pitot pressure
switch

S100
PDA

GPS

data

VDO/Hobbs
data & power

12V power wires cut atconnectors

USB to OUDIE

ChassisSplitter

Notes:
S100 GPS socket output = 12V
S100 PDA output = 5V

VH-XXX LS4 #9999

data

data

ELECTRICAL SCHEMATIC

PowerFlarm

GPS ant
TX antRX antButterfly Dsiplay

AS AT 15 OCT 2018

Figure 27-20 Electrical Schematic with Data Interconnection Shown

27.5.4DATA SIGNAL INTERCONNECTION
Computer equipment and modern avionics pass information and instructions between devices in a timeseries of digital bits (ie a binary logic format comprising “1” and “0”). Information is arranged into packets
which are framed to identify the beginning and end of the data and usually includes an error check.
The transfer of digital data between devices basically (this is a greatly simplified explanation!) requires twothings to be shared at the sending and receiving nodes:a.

A common language - the way that the information is encoded and structured into packets of data. A
good example frequently used in sailplane avionics is the National Marine Electronics Association(NEMA) protocol for encoding GPS data. Avionic manufacturers may incorporate such international
standard formats within their own message packets or create their own unique protocols.

b.

A common interface – including the physical way the data is represented, the rate of data transfer andthe physical interconnection of the sending and receiving nodes. Examples commonly used insailplanes are: RS-232, TTL, USB, CAN-Bus and Bluetooth.

The rate at which information is transferred in a communication channel is known as the baud rate. In theserial port context, as an example "9600 baud" means that the serial port can transfer a maximum of 9600
bits per second. The most commonly used baud are 1200, 2400, 4800, 9600 and 19200, up to 128,000.
Obviously, the connected devices must be able to operate at the same rate and sometimes they need to be
set to a specific rate for compatibility. The higher the baud rate, the more sensitive the equipment is to thequality of the cable and installation.

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The following sub-sections explain a few of the different ways that data can be represented on wired
connections. Unless devices use the same format for data, they cannot directly communicate with eachother and an interface/converter (with active circuits rather than just a cable) may be required.

27.5.5

RS-232 (TRUE AND TTL)
RS-232 originated in the 1960s but is still one of the most widely used interface standards and is often foundin avionic devices. The RS-232 standard defines how data is transmitted in a serial stream but does notdescribe the content. It defines the framing and the timing. It also defines the signal voltage levels.
The RS-232 standard defined numerous roles for connecting wires which originally required a 25-pin
connector but for most purposes a 9-pin connector was found satisfactory and for many years was astandard port on personal computers.
RS-232 uses single-ended signalling in that the transmitter generates a voltage on a single wire that thereceiver compares with a fixed reference voltage relative to a common ground connection shared by bothends. Two-way communication requires two wires and ground. A minimal "3-wire" RS-232 connection
therefore consists only of transmit data (Tx), receive data (Rx) and ground and is commonly used when thefull facilities of RS-232 are not required. Note the Tx to Rx cross-over.

Device A

Device B

TX

TX

RX

RX

GRD

GRD

Figure 27-21 Tx to Rx Cross-OverBecause RS-232 has its origins in the 1960s, the signal voltage levels required were relatively high so as topower electromechanical devices. Thus the “True” RS-232 standard defines logic ‘1’ as a low level -3V to 15V, while high level +3V to +15V is defined as logic ‘0’. The dead area between +3V and -3V is designed
to absorb line noise. However, with that development of transistors and integrated circuits, which typicallyoperate at 3.3-5V, the True RS-232 signal voltages became unnecessary and unavailable and thus “TTL
RS-232” evolved.
TTL RS-232 means that data is transmitted using the framing and timing of RS-232 but uses voltage levels
compatible with TTL logic chips. The reason for doing this is that it eliminates the requirement to uplift thesignal voltages between devices which would add cost and offer no benefit over short distance connections
between TTL devices. TTL RS-232 signal levels always remain between the limits of 0V and Vcc (usually 5V
or 3.3V). A logic high ('1') is represented by Vcc, while a logic low ('0') is 0V. This was the format used on
personal computers up until USB sockets became dominant.

27.5.6

USB – DIFFERENTIAL SIGNALLINGThe Universal Serial Bus (USB) standard dates from 1996 and has evolved since into a widely used
standard. There are numerous types of USB connectors, the most common one used in avionics as themeans of communicating with PDAs is the mini-USB-B, illustrated later.
USB uses Differential Signalling which is a method for electrically transmitting information using twocomplementary signals, labelled D+ and D-. This technique sends the same electrical signal as a differential
pair of signals, each in its own conductor. The pair of conductors is usually twisted together to reduce
interference. The receiving circuit responds to the electrical difference between the two signals, rather thanthe difference between a single wire and ground. In this way any interference/noise induced in the cable iseffectively eliminated.
Transmitted signal levels are 0.0–0.3V for logic “0”, and 2.8–3.6V for logic”1”. Note that the communication
over D+ and D- is half-duplex, in other words it is either send or receive on the same pair of wires with thedevices at either end managing the data flow.

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27.5.7

CAN-BUSA CAN (Controller Area Network) Bus is a standardised means of interconnecting power and data between anumber of intelligent controller devices along a cable defined as the bus. In practice it can look like a “daisy
chain” in/out topology but, in reality, devices “T” off the bus, ie one pair of wires goes from one to the next
device and can include many devices, and more can be added later. Each intelligent controller device
monitors the bus for any coded messages intended for it and can also send encoded messages to otherspecified controllers. It is used extensively in modern automotive vehicles and an enhanced version is usedin aviation.
In the sailplane world at the time of writing, LXNav uses a CAN-Bus to connect an S80x/S10x to a
S8xD/S10xD second cockpit repeater. Physically the connection is a general purpose, multi-core cable withsub DE-9 connectors (male one end, female the other end). Two wires are used for data, one wire forground and usually a wire providing power for the devices connected to the bus (obviously one device must
be the source of the power). Loops of ground or power wires must be avoided to avoid electromagnetic
interference and variations in signal levels.
The type of signalling used is complex and beyond the scope of this document.
With CAN-Bus it is important that the far end of the bus is correctly terminated to ensure the integrity of thedata signal. Termination is a resistor but is often plugged on the end connector for convenience. The
LXNav CAN-Bus terminator looks like a blank D-plug but contains the required bleed resisters on the datalines.

27.5.8CONNECTORS

27.5.8.1 SUB MINIATURE D-CONNECTORSThe D-sub connector contains two or more parallel rows of pins or sockets usually surrounded by a Dshaped metal shield that provides mechanical support and ensures correct orientation.
These connectors are often used for VHF com radio connection.

Figure 27-22 Male DE-9 Connector (often called a DB-9)
Strictly, the part-numbering system uses D as the prefix for the whole series, followed by one of A, B, C, D,
or E denoting the shell size, followed by the number of pins.
Each shell size usually corresponds to a certain number of pins or sockets: A with 15, B with 25, C with 37,
D with 50, and E with 9. For example, DB-25 denotes a D-sub with a 25-position shell size and a 25-position
contact configuration. However, “high density” configurations are also available such as the DE-15 (often
called a VGA connector) which has the same physical size as the DE-9 but has 15 pins arranged in 3 rowsof pins rather than 9 pins in 2 rows.
In practice, the original naming pattern is not always followed due to an ignorance of the factthat B represented a shell size and also historic mislabelling. Hence it is now common to see DE-9
connectors sold as DB-9 connectors. So “DB-9” nearly always refers to a 9-pin connector with an E sizeshell.
The DE-9 is sometimes called a “RS-232 serial” connector. The LXNAV CAN-BUS uses DE-9 connectors.
When making soldered connections to D-connectors it is easiest to “tin” the wire and “tin” the connector’s pin
cups with solder before soldering them together. Best practice is to slip a piece of heat shrink on the wire
before soldering and then shrink it over the soldered joint. See illustration below (from Microair M760 Userand Installation Manual):

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Figure 27-23 Soldering a Connector

27.5.8.2 RJ12 AND RJ45 CONNECTORSRJ12 and RJ45 plugs and sockets are a common way of connecting both data and power between avionicdevices. RJ stands for Register Jack. The most frequently seen types are:Table 27-5

RJ Connector Types

RJ11 = 6 pins but only 4 pins connected
RJ12 = 6 pins and 6 pins connected.
(Sometimes called RJ25
Both have the same size plug/socket (9 x 6mm) and six pins but the difference is thenumber of connected pins.
They are commonly used for telephones anddata.
Unfortunately, the locking tab is prone tobreaking off resulting in it either not locking or
being difficult to unlock.

RJ45 (8-pin connector)
The physical size (not including the tab) is 12 x
6mm.
This is also commonly used for Cat 6 Ethernet
where it has 4 pairs of twisted wires.

Fitting RJ12 and RJ45 male plugs onto cable is relatively straight-forward but requires care. Special
crimpers are needed and are readily available from good electronics shops or on the internet. It is not
generally necessary to make up leads with inline female sockets. If one is needed, it is easiest to crimp on amale plug and use a female-female connector.
According to the original ACTA standard, the pins on a socket are numbered 1-8 with the tab key
underneath. But note that the IGC standard does not comply with the ACTA numbering standard as shown
below. So be very careful.

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Figure 27-24 ACTA numbering
standard

Figure 27-25 IGC standard for RJ45 pins

It is usually possible for a RJ12 plug to fit into a RJ45 socket but it is not recommended. Often the tab key
will centrally locate the RJ12 plug pins 1-6 over the RJ45 socket pins 2–7. And in many uses of the RJ45,
wiring diagrams show that the two outer pins (pins 1-2 and 7-8) are shorted to each other on both sides ofthe socket/plug, so the outer pins 1 and 8 are redundant. But this cannot be relied upon and the RJ12 plugcasing may damage pins 1 and 8 of the RJ45 socket.
See PowerFLARM Core (RJ45) and FLARMmouse (RJ12) example below which shows how pins 2-7 of the
RJ45 connector match pins 1-6 of the RJ12 connector.

Figure 27-26 PowerFLARM Core RJ45

Figure 27-27 FLARMMouse RJ12

27.5.8.3 USB CONNECTORSThe IGC standard recognises the USB- A and mini-USB-B connectors. USB-A is found on most PCs andnotebook computers. Mini-USB-B sockets are used on Oudie, Nano and many other Personal Digital
Assistant (PDA) devices because of its small size. This type of connector is easily identified by its bentsides.

Figure 27-28 Mini-USB - B Plug
The standard pinout for the Mini-USB-B is:

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Table 27-6 Mini-USB-B Pinout
Pin

Name

Description

Colour

1

VCC+5 VDCRed

2

D-

Data -

White

3

D+

Data+

Green

X

ID

May be N/C GND or used as an attached device
presence indicator (shorted to GND with resister)

4

GND

GroundBlack

Note that according to the USB standard, pins 2 and 3 (Data- and Data +) are both used for a single channelbi-directional differential signalling. (This is not one wire for data out and the other for data in).
Pin X is usually unconnected or grounded. However some manufacturers of devices have designed theirdevice’s USB port to adopt a “secret” RS-232 mode when a voltage Vcc (eg 5V) is applied to the socket’s X
pin. The USB port will still operate to the USB standard if the X pin is not connected or at Ground. Thisavoids the need for an external RS-232 to USB converter. In other words:
When pin X=”0” : device USB port is in standard USB mode where pin 2 is D- and pin 3 is D+
When pin X=”1” : device USB port is in duplex TTL RS-232 mode where pin 2 is Tx and Pin 3 is Rx.
There are several other types of USB connectors defined by the international standards. Interconnecting
plugs/cables are generally easily available.
The USB-mini-B is not a strong plug. The wires in the device are often broken off and are hard to fix as it issurface mount technology. If the device becomes intermittent then this is likely the problem. It is best to
support the connector to avoid bending and tugging.

27.5.8.4 OTHER CONNECTORS
There are numerous other types of connectors such as SMA and MCX in use by avionics manufacturers. A
good guide to cables and connectors can be found at: www.telcoantennas.com.au.
Serial connections and connectors is a rapidly evolving system as it is commonly used on modern devices
such as smartphones. New connectors are available for Apple and Android devices that are stronger andcan be inserted either way. Eg. USB-C is a smarter connector that can serve more functions at higher
speed. If you come across other devices/connectors then they will likely be documented on the internet. A
converter plug or cable can connect a B to a C but it will only operate at the B capabilities.

27.6

FLARM

27.6.1 FLARM INTRODUCTION
FLARM is an electronic system for sailplanes used to selectively alert pilots to potential collisions between
other aircraft similarly equipped with FLARM. It is becoming increasingly popular in Australia and worldwide.
FLARM is a portmanteau of "flight" and "alarm". FLARM is a Swiss company that has licensed othermanufacturers to use its technology. FLARM devices have low power consumption and are relatively
inexpensive to purchase and simple to install.
FLARM obtains its position and altitude readings from an internal GPS and a barometric sensor and thenbroadcasts this together with forecast data about the future 3-dimensional flight track. At the same time, itsreceiver listens for other FLARM devices within range and processes the information received. Advanced
motion prediction algorithms, optimised for sailplanes (eg whilst in thermal ‘gaggles’), predict potential
conflicts for up to 50 other aircraft and alert the pilot using visual and aural warnings.
During the initial installation of a Flarm, the device setup with the aircraft’s details so that the identity of the
sailplane is transmitted to other users.
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In areas where the Open Glider Network ground receiving stations have been set up, it is possible to monitor
Flarm based sailplanes via the internet on the live.glidernet.org website and other sites such as
flightradar24.com. If the sailplane information has been correctly setup in the FLARM and registered with
OGN, the registration code and aircraft type will be displayed anyone with internet access. This is aconvenient way to check a FLARM GPS and data transmit functions.
Most FLARM devices automatically record sufficient flight data to satisfy the requirements of a Position
Recorder, storing data files in the required IGC format. Some are IGC approved Flight Recorders. Consult
the device user manual to discover how to extract the IGC file.
The main limitation of FLARM is it only ‘sees’ other FLARM equipped aircraft and so non-equipped GA
aircraft and sailplanes are not seen. Most GA aircraft do not and will not install FLARM because they aremandated to use similar purpose but expensive higher power devices like transponders and ADS-B.
FLARM has developed a version which also includes ADS-B and transponder detection but nottransmission. A Mode-S transponder with ADS-B capability is an international standard broadcast
surveillance system in which an aircraft automatically transmits to a ground station and other air traffic its
identity, precise location, altitude, velocity and other information. In Australia (as at Dec 18), ADS-B isrequired only for aircraft operating under instrument flight rules (IFR) but offers substantial benefits for visualflight rules (VFR) pilots as it provides in-cockpit visibility of all transponder equipped aircraft. Use in
sailplanes is currently low but as the cost of this equipment falls it will likely become more common in
sailplanes, especially those flying at or near GA airfields. Further information is on the CASA and Air
Services Australia web sites.
All FLARM devices can be connected to dedicated FLARM displays or compatible navigation devices to givevisual and aural warnings and also show the relative bearing and altitude of conflicting traffic. Some show
position using a simple pattern of LEDs and others use a map format. Licensed manufacturers produce a
range of integrated FLARM devices, dedicated displays and display integration into their avionic products.
Eg FLARM data may be supplied to and displayed by other devices such as: Oudie and LXNav S80/S100.
Most FLARM displays also have a ‘Nearest mode’ which displays the closest sailplane equipped with
FLARM. This is not a warning of potential conflict but is an aid to situational awareness. Nearest mode canbe switched off if not wanted.
The range of FLARM devices on the market changes rapidly. Note that FLARM frequency ranges are thesame in USA and Australia but different in Europe. For illustration purposes, some popular products inAustralia as at December 2018 are:PowerFLARM core

LX Nav FLARMMouse

LX Nav FLARMBat

Air Avionics Butterfly FLARM
display

LX Nav FLARMLED
display

Aboba V4+M display

Figure 27-29 Example Flarm Devices

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27.6.2

GPS ANTENNAFLARM has an internal GPS receiver to know where you are and a computer to determine expected future
track. Timing signals are picked up from a network of geostatic satellites by the GPS antenna and computed
to determine position and altitude.
The GPS antenna is usually internal to the device case or an external small square block connected with acable to the FLARM device. Do not share/split an antenna output with another device.
If using an internal GPS antenna, then the whole top of the unit must have a clear view of the sky. If using an
external GPS antenna, then the top of the antenna must have a clear view of the sky and remember to set
the internal DIP switches if required in the manual.

Figure 27-30 GPS External Antenna
If the GPS antenna is buried behind the instruments or has fallen on its side, the FLARM systems
knowledge of your position and course will not be accurate and collision prediction warnings may be
impaired.
The FLARM unit has a GPS status LED that will be green (or off on some old units) when good signals arereceived from the satellites and the position is calculated. When the unit is first turned on it will be red but
after a minute or so, and before you take off, it needs to be green (possibly off but not red).

27.6.3DATA ANTENNAFLARM uses a very low powered radio data link to communicate with other FLARM’s, so it’s important thatthe corresponding data antenna is set up correctly. The data antenna can be either a small pole antenna or
a loop antenna (now discontinued) stuck on the inside of the canopy.
In Australia, FLARM uses a data communication frequency in the range 917.0 MHz – 926.6 MHz. So the
mid-band wavelength is approx 0.325m. A half-wave dipole antenna is thus approx 180mm tall.
Orientation of this antenna is important as all antennae are directional to some degree. The pole typeantenna must be vertical to communicate in the directions of interest. If it has fallen over or bent forward,
then there might be blind spots in your coverage and reduced range. There should also be no metal or
carbon obstructions blocking the “view” of the data antenna to the other sailplanes. This usually means thebest position for the data antenna is again on top of the instrument panel.

Figure 27-31 Flarm Antenna on Top
The data antenna may not be very robust and numerous faults have been found to be caused by broken
antennae. Regularly give the antenna a visible inspection and replace it if damaged in any way. Also
replace it if you are not receiving anybody or others claim they cannot see you. The half-wave antennae are
better than the short stubby ones. The stick-on loop antennae were prone tend to break the tracks near theconnector.

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As FLARM transmitted signals are very weak, it is easy for external interference to affect the performance.
The frequencies used by phones and the FLARM are close enough in the spectrum to cause some blocking
in the FLARM (850MHz and 900MHz compared to the 921MHz for FLARM). Mobile phones in close
proximity will likely degrade the sensitivity of FLARM and pilots should thus turn theirs off when in the air.
The sailplane’s VHF radio may also interfere when transmitting but the frequency is further away and thus
less prone to interfere. Also, you can control when transmit on the radio but a mobile phone transmits
automatically and frequently to the network.
The data link frequency for Australia is different to Europe and if set to the wrong frequency the FLARM will
be useless. Visiting pilots with FLARM that has been used overseas should check the frequency. The
FLARM tool software can be used to check and change all the settings including the frequency. This issoftware that runs on a PC and plugs into the power/data port. The latest FLARM versions have automatic
frequency setting according to the location determined by the device’s GPS.
Early FLARMs were thought to have an issue with static electricity destroying the receiver front end. For asmall cost, the unit could be returned to the manufacturer for additional cost protection to be installed.
The data receive green LED on the FLARM will indicate when it is receiving a signal from another FLARM.
Before take-off, it’s a good idea to check the light is on if there is a sailplane or tug with FLARM in thevicinity.
FLARM requires regular software updates otherwise a unit may become incompatible with other FLARMs
and collision detection may be ineffective. The updates are free and are easy to do if your FLARM has a SD
card. If no SD card, then there should be a method of upgrade via connection to a PC, consult the manual.
The software should be checked at every Annual Inspection.

27.6.4

FLARM REMOTE DISPLAYS AND INTERCONNECTION TO OTHER DEVICESA FLARM device transmitter/receiver device may have an inbuilt display and/or provide data to one or more
remote display (eg FLARM Butterfly), navigation equipment (eg LXNav S100) or PDA (eg Oudie) devices fordisplay. These display devices may present information slightly differently, but the basic alarm status
warnings should trigger simultaneously as the collision vector analysis is done by the FLARM.
Correct connection and configuration of the FLARM with displays or/or other devices is essential. Once you
have a working setup, it is good practice to record the details in the aircraft’s logbook for future reference.
Key things to consider are:a. Data physical connection. Serial data communication between FLARM devices isachieved via data/power cables with RJ12 sockets or Bluetooth on some devices. Avoid
unnecessarily long cables.
b.

Multiple displays connect to one FLARM. Where two or more FLARM displays/devices are to be
driven by cables from a single FLARM, then care must be taken to avoid data collision issues (ie only
one display should be in control of the FLARM).

ooSome displays have a Master/Slave software setting (only one display should be set to Master).
Some equipment may need a special RJ45 ‘Y-splitter’ that has one port that allows data in both
directions between the FLARM and display and the 2nd port only sends data from the FLARM to
the other display.

c.

Power connection. All devices involved need to be powered and this is achieved either by a
dedicated power connection or via the data/power cable. Some devices can operate from 3V via one
socket or 12V from another socket, however inputting power via both may damage the unit.
Sometimes special data/power leads will be required which have been assembled without thestandard power connection. Take care to read the user manuals.

d.

Device configuration. Some devices require hardware ‘dip’ switches or software settings to be
configured to match the devices they connect with. Devices are often supplied with default settings,
such as data baud rate, which may not always be compatible. Consult the appropriate user manuals
and look for compatible settings. Some devices may revert to the default settings if a key sequence isaccidentally pressed or the device is subjected to power spikes. If faults appear, check the settings
are still compatible.

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27.6.5REVIEWING FLARM PERFORMANCE
Valid collision warning alerts are only generated if FLARMs in all equipped aircraft are working properly.
Unfortunately, there is no simple test a pilot can do to verify his/her aircraft’s FLARM is working properly
before takeoff. The status indicator lights only give some of the status and are not an end to end check.
If the sailplane is equipped with a Flarm display device that provides a map plot and you can physically see
sailplanes that you know have FLARMs, then they should show on the plot. If you are with multiple
sailplanes turning in a thermal, then you may get a warning from one of them. If you don’t get indications or
warnings when you would normally expect to get them, then check your equipment is functioning correctly.
There is a FLARM web page (http://www.flarm.com/support/analyze) where you can upload a FLARM IGC
data file and get an analysis of the received range information for a flight. Flights to be analysed must haveat least a duration of 30 minutes and contact with 5+ other FLARM equipped aircraft during the flight toenable a valid analysis.
The radio range analysis below shows poor performance later traced to a broken data antenna:

Figure 27-32 Flarm Range Analysis Diagram
Remember FLARM only detects other FLARM equipped aircraft so it’s important that owners of all FLARM
equipped aircraft maintain and check their installations regularly.

27.6.6

FLARM MAINTENANCE/FAULT CHECKLISTThe following check list will help ensure FLARMs are operational:a.

Check the GPS antenna is facing the sky and clear of everything.

b.

Check the data antenna is vertical and clear of everything.

c.

Check the data antenna is not damaged in any way.

d.

Check the software is up to date.

e.

Check the frequency is set up for Australia if the FLARM has come from overseas.

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27.7

f.

Check your display is set up correctly. (Sequentially flashing status lights means it is not getting
messages from the FLARM and possibly a wrong data baud rate setting)g.

Check the GPS status light goes green before takeoff.

h.

Check the receive light occasionally goes green when another FLARM is nearby.

i.

In the air, check you are receiving other FLARMs by staying in nearest mode for a while.

j.

In the air turn off your mobile phone to avoid interference with the FLARM.

k.

Upload the FLARM IGC file to the FLARM web site if you have had lots of FLARM traffic during a
recent flight and see what range you are getting.

l.

Have all the other sailplanes flying at your location completed the above checklist and haveoperational FLARMS?

MODIFYING INSTRUMENT PANELS
A well designed and constructed instrument panel is a delight to see and use. The configuration and layoutof a sailplane’s instrument panel should be an aspect of careful consideration by the purchaser of a new
sailplane and an owner contemplating modification.
Inevitably during the life of the sailplane, the availability of new avionic devices and pilot choices will meanthat additions and modifications are made to the instrument panels. This can be more challenging thanstarting from a totally blank panel since a new instrument may be a different size compared to what it
replaced and sailplane instrument panels have numerous physical and electrical constraints.
MOSP3 allows owners to modify instrument panels with due care and subject to approval by an Annual
Inspector (refer Section 18.7). Obviously, there are minimum instruments requirements (as specified by the
manufacturer) and all critical instruments like the altimeter and ASI must be serviceable. Be wary of
introducing structural changes, weight and balance change and crashworthiness. You must document allchanges in the maintenance logbook and have then signed off by a qualified and competent Annual
Inspector.
Instrument panels are usually made of aluminium or glass fibre. Do not use steel or wood (unless the
sailplane is a wooden sailplane) when constructing or modifying an instrument panel. Instruments panels
are usually coloured flat black or flat dark grey because this provides the best background contrast for the
instruments to be seen and avoids light reflections.

Figure 27-33 New Aluminium
Panel Cutting Design

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Figure 27-34 Instruments Being
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27.7.1PANEL STANDARD INSTRUMENT SIZE CIRCULAR HOLES
Most sailplane radio, avionics and pitot/static instruments are designed to be installed in aviation instrument
standard 57mm (2¼”) or 80mm (3⅛”) diameter holes with a standard x4 securing screws layout as shown
below (not to scale):

57mm (2¼”)

80mm (3⅛”)

Figure 27-35 Standard Aircraft Instrument Panel Hole Templates
Instrument securing screws are typically 4mm diameter but some manufacturers use other small metric or
imperial (eg UNC) sizes. Some instruments may require one or more of the securing screw holes to belarger for control knob spindles. Some instrument panels use countersunk ‘flat’ screws to give a flush panel
appearance.

27.7.2

INSTRUMENT FASTENERS
Many modern avionic instruments have pre-tapped holes in their bodies, so the manufacturer supplied or
specified screws should be used. Note that often there is stated a maximum length of screw penetration into
the instrument body – do not use overly long screws as you risk damaging the instrument.

27.7.2.1 FASTENER MATERIAL AND COLOUR
Aircraft instrument panel screws and the accompanying washers and nuts have historically been made fromnon-ferrous materials such as brass, aluminium or plastic (eg nylon) which are not magnetically susceptible
and thus do not interfere with the aircraft compass. One downside of non-magnetically susceptible
fastenings is that you obviously cannot use a magnet-on-a-stick to pickup any dropped washers or nuts
under the panel.
Steel screws (especially if they have become magnetised) that are in close proximity to a compass, may
disturb the earth’s natural magnetic flux sufficiently to cause the compass to misread. The amount of error isdifficult to predict, is unlikely be constant on all bearings and may not be significant. Since sailplane pilots
rarely use their aircraft compass for dead reckoning navigation over long distances, a small amount ofcompass inaccuracy is usually acceptable.
If magnetically attractive (eg steel) screws are added or removed from a panel, then the compass accuracy
should be checked before the sailplane returns to service. Significant compass errors attributed to steelscrews may require their replacement with non-magnetically susceptible screws.
Brass, aluminium and plastic screws are prone to the threads or drive heads stripping as the materials are
relatively soft. Stainless steel has become more commonly used for instrument fasteners because of its
strength and is considered to have low magnetic attraction.
Note that ‘300 series’ (ie 304 and 316) stainless steel is naturally not susceptible to magnetism but may
become somewhat attractive to magnetic during cold forming manufacturing processes involving
compression such as rolling, bending and stamping which changes the crystalline structure of the material.
304 (often referred to as A2) stainless steel is more prone to this than 316 (often referred to as A4 or marine
grade). In general then, stainless steel small screws, nuts and washers are not usually magneticallyattractive.

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Panel screws are usually black to match the most common panel colour. Depending on the material, theblack surface colour is created by annodisation (eg passivated black zinc-nickel), chemical staining orprocesses causing a surface coating of black oxide. Note that black oxide is usually coated with oil or wax
to prevent brown rust forming, thus steel and sometimes 304 grade stainless steel screws may show rust.
Of course, it is possible to DIY paint natural colour screws to the desired colour but the coating may not lastlong. A light sanding of the head and degreasing will prolong the paint adhesion.
Where an instrument has non-threaded lugs for fixing to the panel, then screws with washers and some formof locked nut (eg locking washer and plain nut or else an elastic nut) must be used. Brass elastic nuts insizes suitable for instrument screws are rare. It is common practice to use stainless steel elastic nuts withbrass screws. There is little risk of galvanic corrosion as the two metals are relatively close together on theanodic index.

27.7.2.2 FASTENER THREAD STANDARD, HEAD TYPE AND DRIVE TYPE
Historically many American made aircraft and aircraft instruments have used small diameter American UNF
and UNC standard screws and thus such screws are readily available from most aviation parts suppliers,
including in Australia. However most modern sailplanes and sailplane instruments are now manufactured
using metric fasteners. Unfortunately, the two screw standards are not compatible as can be seen in thetable of specifications of commonly used instrument panel screws shown in the Table below:

Table 27-7 Specifications of common UNC and Metric instrument screws
Size

Description

Major diameter (mm)Threads per inch

4-40

#4 gauge, UNC 40 TPI

2.845

40

M3

3mm x 0.5 pitch (coarse)

3.0

50.8

M3.5

3.5mm x 0.6 pitch (coarse)

3.5

42.3

6-32

#6 gauge, UNC 32 TPI

3.505

32

M4

4mm x 0.7 pitch (coarse)

4.0

36.3

8-32

#8 gauge, UNC 32 TPI

4.166

32

M3.5 screws at first sight look to be the same as 6-32 but they have different thread pitch/TPI. M3.5 screws
are not widely available in Australia. Australian mains 230V electrical general-purpose outlets (ie electricwall sockets) use screws described by some manufacturers as ‘M3.5 x 0.8 pitch’. Since 0.8 pitch isequivalent to 32 threads per inch, then you’ll see that in fact they are UNC 6-32 screws.
Screws come in a range of head types (shown below) and drive types eg slotted, cross drive (Philips/Pozi),
hexagonal socket. The most common form used on instrument panels is pan head cross drive, thoughpanhead with internal hexagonal socket drive is gaining popularity due increasing availability.

Figure 27-36 Screw Head Types
Flat head screws, often referred to as countersunk screws, give a flush finish. If considering this type ofhead, note:
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a.

UNF/UNC flat head screws usually have a head angle of 100 degrees, as is normal for most aviation
rivets. Metric flat head screws to DIN standard have a head angle of 90 degrees. Nearly all
Australian DIY and tool store sourced counter sink drills are 90-degree, which does not provide agood seating for screw heads with 100-degree angle.

b.

It can be difficult to control the depth/width and concentricity of the countersink drilling using ahandheld drill. If you wish to use this style, you may need to source a combined pilot
hole/countersunk drill and some form of drill depth control. The right tools, experimentation,
consistency and practice will be needed to get a good result. Pan head screws are much easier!

UNC/UNF instrument screws are often listed under their ‘MS’ designation or the now superseded AN
designation. The following table shows some of the commonly used standards:

Table 27-8 UNC/UNF Screw Standards
MS

AN
AN 515B

Black Brass, Round head, slot or crossMS 35214MS 24693-BB

Description

Black Brass, Pan head (#4, #6, #8 screws)
AN 507B

Black brass flat head, crossMetric screws are often listed under their DIN or ISO designation as follows:

Table 27-9 Metric Screw Standards
DIN

ISO

Description

963

2009

Slot drive, flat head

965

7046

Cross drive, flat head

85

1580

Slot drive, pan head

7985

7045

Cross drive, pan head

7380

7380

Hex internal socket drive, pan head

Winter Instruments products are now supplied with 4mm black aluminium and previously M4 black brassscrews. These screws may be available from the Aircraft Spruce or the Australian Winter agent,
MrSoaring.com.
Black metric stainless steel screws are usually 304 (A2) grade with black oxide. They can be difficult tosource in pan head cross drive but are readily available on the web with hex internal drive.
If not magnetically attracted fasteners are essential for the installation, then probably the ultimate choice isblack metric 316 (A4) grade pan head cross drive stainless steel but there are few suppliers in the world. At
the time of writing, there is no known stockist in Australia but Accu.co.uk had these available.
Many Australian fastener companies supply M4 steel (magnetically attractive) screws with black oxide finish
with slot, cross and hex internal socket. The quality of finish can vary greatly between suppliers andmanufacturers.
Steel (magnetic) pan head cross drive screws with zinc-nickel black passivated finish are available from a
few sources such as: RS, Element14, BoltandNut.com.au. The quality of the blackening varies.
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27.7.3

INSTRUMENTS WITH UNTHREADED ATTACHMENT LUGS
Some instruments, particularly older instruments, have lugs with holes rather than pre-threaded holes. In
this case there is some freedom of choice of imperial/metric and fastener size. In most cases a washer will
be required at the nut end of the screw to spread the load. A locking washer and nut, or else an elastic nut,
should be used. When installing or removing this sort of hardware, consider how you can stop items
dropping down inside or under the control panel. Placing a cloth to catch dropped items may save many
minutes of frantic searching!
With this style of instrument, the installation can be made much easier by using a ‘nut ring’ which is frame(aluminium or plastic) with rivnuts. This eliminates the washers, locking rings and washers – so less risk ofdropping hardware into the bowels of the instrument panel. They are readily available for 4-32 screws but
none were found in M4 at the time of writing. It would be relatively easy, but time consuming, to DIY
fabricate one with basic hand tools.
Some instruments can be converted to screwed lugs by inserting stainless steel helicoils. These spring-likefitments are usually used to repair damaged threads and low cost kits are available on the internet. The lughole must be drilled to a special size (eg 4.2mm for an M4 x0.7 pitch thread) and then a screw thread cut
with the corresponding special size/pitch tap. The helicoil is then screwed in with a special tool. After thisprocess has been completed, the inside of the helicoil acts as the thread for a standard (eg M4) instrument
securing screw.

Figure 27-37 Helicoils

27.7.4

Figure 27-38 Nut Ring (example from
Wings & Wheels USA)BLANKING OR DOWNSIZING AN EXISTING INSTRUMENT HOLE
Pre-cut, drilled/punched and painted blanking plates and downsizing plates are readily available from avionicsuppliers made from aluminium or plastic. Alternatively, they can easily be fabricated from aluminium sheet
or even 3-D plastic printed. Do not use steel as it is heavy and magnetically attractive.
Small unwanted holes can often be covered up with a label or placard (eg local radio frequencies).
Unwanted holes in GRP panels can be blanked out by careful adhering a thin mat of glass fibre behind thepanel and filling the hole with resin/beads.

27.7.5

ADDING OR ENLARGING HOLES IN INSTRUMENT PANELS
Large circular holes for radios and instruments may be cut by using several methods:a.

Water jet or laser jet cutting or CNC routing. This will give a very accurate cut precisely as wasplanned on the CAD (Computer Aided Drawing) file you agreed with the specialist workshop. It
requires the panel to be stripped and taken to a specialist workshop.

b.

Die/punch cutter. These work by shearing the material, they do not rotate. They make an accurate
and neat hole. They can be used with a panel partially dismantled in a cockpit and create little mess.
They are readily available in USA but the sizes are uncommon in Australia. You may find a LAME, or
aircraft home builder has a set and can provide a service or loan/rental of this tool.

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Figure 27-39 Reversible cutter for 21/4" and 3-1/8" panel holesc.

Figure 27-40 Single size punches

The correct sizes are available in good tool stores and on the internet, sometimes listed under theimperial size. Beware of the course cut (few teeth per inch) models and cheap versions which may
not form a complete circle of teeth or be truly circular. Hole saws require a central pilot hole and aslow drilling speed. Very even and gentle pressure perpendicular to the panel face is needed to avoid
the teeth “grabbing”. Trial and practice are recommended on scrap material first as it is easy to messup a hole which may ruin the entire panel. You have been warned!

Figure 27-41 Fine cut (many TPI),
continuous circle cutter(pilot drill not shown fitted)d.

Figure 27-42 Course cut (few TPI) cutter

Routing or hole drilling, finished by hand filing. This method, when performed with care and patience,
can achieve good results at minimum cost. It may be the only option when enlarging an existing hole.

oooCareful marking out and accurate initial centre punching of the hole is critical. Scribed circles
directly onto the material with dividers is generally more precise than pencil/compass onto the bareface or masking tape.
Remove the bulk of the material by drilling chains of small holes and using a hacksaw. With GRP,a rotary burr can be used. Use a vacuum cleaner to collect the dust as you cut.
Finish to dimension using a half-round smooth grade file. (Note: Files are usually classified by cut
grades: 1st cut = Bastard, 2nd cut = Second or Medium, 3rd cut = Smooth).

Enlarging a 57mm hole to 80mm can be challenging to mark-out and cut. To assist with marking out, screw
an old blanking plate (or piece of aluminium sheet) in position. To establish the centre position of the oldhole, draw bisecting lines through the mounting hole centres. If the new 80mm hole is not concentric withthe old 57mm hole, carefully consider the position of the existing mounting screw holes to ensure they arewithin the 80mm hole.
Be careful not to remove too much material from the panel such that its structural integrity is compromised.
The small mounting holes for instruments (usually approx 4mm) need to be carefully positioned. Either
carefully mark out and centre punch the locations or else use a proven template. A strategy for a precision
fit of the securing screws is to drill the holes undersize, say 3mm, place the avionic device in the opening
and observe how the securing holes align. Then open out the sides of the securing holes to match thelocation of the instrument’s holes using a needle file.
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Before cutting a new or enlarged instrument hole:a.

Check there is enough space for the intended radio or instrument behind the panel. Carefully
consider the full volume of the radio/instrument (ie width, length, corners, space for connectors).
Check that there is not interference when the panel cover/cowling is replaced.

b.

Carefully mark out the position of the hole and screw holes. Measure twice, cut once!

c.

If cutting by hand, consider making an aluminium sheet template to use as a guide for cutting
accuracy. Making the template is good practice at marking out and cutting.

d.

Remove other instruments or carefully protect them from vibration, dust and swarf. If cutting
fibreglass, use a vacuum cleaner to remove the dust as you cut.

e.

After cutting a hole, consider if the raw edge of the cut material will be visible. If so, then it is best to
paint (or use a permanent marker pen) the edge before fitting the instrument.

Even using computer drawn plans and computer-controlled cutting does not guarantee perfect results firsttime. Consider making a prototype from a cheap panel of clear Perspex. Fit all the instruments. Make surethe layout suits you. Identify clashes and fix these. Eg the edges of instruments touch or interfere on theedge, or a screw does not fit. Some types of instrument (eg altimeters) require special cut-out shapes –match yours exactly. Adjust the CAD drawing until perfect. Then get the final panel cut.
Holes for switches and fuses are often in the range 10-16mm diameter which are difficult to cut in thinmaterial using conventional twist drills. Clamping a block of wood behind the area being drilled will improve
results and remember that the bigger the drill, the slower the RPM needed.
Good results in sheet materials can be achieved using a slotted/spiral cone drill, or else careful use of around file starting from a small hole.

Figure 27-43 Cone Drills

27.7.6

INSTRUMENT PANEL LABELLING
Sailplane manufacturers may specify mandatory placard and labelling requirements in the pilot handbook.
This may include full size pictures of what is required.
Don’t forget that a fireproof (brass or stainless) engraved placard showing the aircraft registration is
mandatory (ref GFA AN 84) inside the cockpit and preferably in sight of the pilot. This is normally attachedto the instrument panel. At the time of writing, engraved brass plates are available from the GFA shop.
There are several methods of labelling instrument panels, including:a.

DIY computer printed adhesive labels. This method may be used to easily reproduce manufacturers’
placards and pictorial labels. Depending on the label material and/or ink permanency, a transparent
covering may be required.

b.

Transfers/decals. Either standard sets or custom made. Professional builders of instrument panels
often use this technique. A coat of clear matt varnish/lacquer is often applied on top to add protection.

c.

Pre-printed stick on labels. Sets of printed labels are available for common general aviation aircraft
and also generic sailplane pictorial labels (eg release, airbrake).

d.

Engraving or laser etching. Either directly onto the panel or placards which are stuck on the panel.
This requires specialist equipment or finding a competent service provider. It may be worth
considering if building a new panel.

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e.

Stick-on thermally printed tape. Relatively inexpensive handheld thermal label printers are available(eg models by Brother and Dymo) that print text, numbers and symbols onto special adhesive backed
tapes. They can be used to create custom labels in a variety of print sizes with a choice of several
tape widths. White print on black tape, with works well on black instrument panels. The appearance
can be enhanced by trimming excess blank tape from the top, bottom and ends of the label. Takecare to make sure they are straight – identify and align with a valid horizontal or vertical datum line on
the panel.

Thermal printers are also available with the capability of printing text and numbers on heat shrink which is agood way of labelling wires and cables. So if thinking of buying a thermal label printer, consider spending alittle more to gain this capability.

Figure 27-44 Example of Stick on
Labels27.8

Figure 27-45 Example Thermal Label
Printer

VHF COM RADIO FAULT FINDING GUIDEThe following table is a general aid for fault finding. The user/installation manual for the installed radio islikely to have a section on fault finding and should be referred to.

Table 27-10 Radio Fault Finding Guide
Symptom

Possible causes

Radio shows no
indication operatingwhen the master switch
is switched on

No power to radio

No TX indicated onradio when PTT pressed

PTT cable not connected to radio or
PTT switch failing to make a closed
circuit.

Check: battery present and charged, mainbattery fuse ok, radio external fuse ok, radio
internal fuse/breaker ok
Use a multi-meter to check voltage at radio.

Battery voltage low, voltage drop or no
power connected to radio.
Radio indicates TX but
other stations do notappear to receive.

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ChecksTransmitting on wrong frequency or outof range.
Your radio volume is turned down (youare transmitting, other stations are

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Check connections of power and PTT.
Check PTT switch is functional
Check battery charged. Check voltage atradio when in transmit mode.
Check correct frequency set
Turn volume up to fullCheck connections. Try using a known goodmic.
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receiving but you are not hearing theother stations’ responses)
Microphone faulty or poor connection.
Antenna poor connection or antenna nottuned.

Check connections. SWR test.
Check all power supply connections.
Measure voltage at radio when in transmit
mode. Consider if power cable cross section
is sufficient.

Excessive voltage-drop when transmit
power required due to small cablecross-section or high resistanceconnections.
Carrier wave only
received by otherstations or weak signal

Microphone faulty or poor connection.

Check connections

Microphone type not set up properly inradio or incompatible.

Check microphone is compatible with theradio, connected to correct input and radio
software settings correct.

Poor microphone use technique.
Voltage low due to battery or voltage
drop

Try microphone close to mouth and speak
directly into it.
As above

Speaker output is notworking

Speaker not connected or not
impedance matched to radio output.

Check speaker connected and volume turnedup

The radio’s speaker function is notturned on or volume is turned down.
“Hot mike”, ie prolonged
transmissions,

Receiver noise is always
present.

PTT sticking or short circuit in PTT
circuit.

Check PTT switch function and circuit
integrity.

Pilot tense.

Pilot needs to relax.

The noise suppression function(squelch) of the noise is not set properlyor is not working.

Try to suppress the interference by adjusting
the squelch to a higher value. Note, that ahigher value causes a reduced sensitivity.

Some avionic or portable device isproducing a relatively high level ofelectromagnetic interference.

Remove mobile phones, portable devices
and power charges to identify and eliminate
interference source.
Reduce the interference emitted by theavionics near the radio and antenna byimproving: shielding, distance, grounding or
use of ferrite suppression cores.

The Antenna SWR
exceeds 3:1.

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Possibly caused by a defective or
insufficient ground plane for theantenna.

Check for sufficient size of the ground planeand make sure there is no mechanical defecton the antenna.

The impedance of the antenna cabledeviates significantly from 50 ohm.

Make sure the used antenna cable has 50 Ω
impedance and the cable is not pinched or
kinked on its way from the radio to theantenna.

Possibly caused by a fault on the BNC
connectors of the radio-antenna cable.

Check for proper crimp/solder work on the
BNC connectors

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28.

L’HOTELLIER CONNECTORS
L’Hotellier connectors are used in a wide range of sailplanes as a flexible joint and means of quickconnection / disconnection of flight control systems for rigging and de-rigging purposes. This Chapter details
the essential daily checks, periodic inspection and maintenance requirements for L’Hotellier connections that
ensure the integrity of the control system and thus the safety of the sailplane and pilot.
This BSE chapter was first published in November 2021 and supersedes GFA AD177 Issue 7 and AD178
which were then cancelled.

28.1

BACKGROUND
L’Hotellier is a French manufacturing company based in Anthony, France. As at the date of creation of thisdocument, L’Hotellier is part of Collins Aerospace and there is no appointed company agent in Australia forpurchase of parts and no product information posted on the internet.
Orders for components placed directly with L’Hotellier are subject to large minimum order quantities andlong lead times. Some L’Hotellier component stock is held in Australia by Morgy's Sailplane Works(Waikerie SA) and Maddog Composites (Dinmore QLD). Otherwise, L’Hotellier components can usually beobtained via the sailplane’s manufacturer or their Australian agent.

28.2

DESCRIPTION OF L’HOTELLIER MECHANISM
L’Hotellier connectors enable linear (push/pull) forces to be transmitted but not rotary forces. They arecommonly found connecting aileron, elevator and airbrake control linkages in sailplanes built between
approx 1975-2000.
L’Hotellier connectors comprise a ball and a matching spherical socket into which the ball is inserted andheld by a plunger. The plunger is locked into position by a spring-loaded wedge tab or else a spring-loaded
cam. Depressing the wedge or cam enables the plunger to slide and thus the socket opens to allow the ball
to be insert or removed from the socket.

Figure 28-1 L’Hotellier Mechanism (standard 90⁰ Type 41 connector)
There are 3 types of connection:a.

‘Standard’ 90-degree swivel joint. The axis of the ball shaft is at approximately 90 degrees to theaxis of the socket shaft. Eg this is the configuration used to connect an Astir elevator.

b.

‘Z’ swivel joint. This has the axis of the ball shaft and socket shafts approximately inline. Eg this is
the configuration used for Astir ailerons and dive brakes.

c.

“W” swivel joint. There are no known applications of this in sailplanes in Australia.

There are 2 types of socket lock mechanism:

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a.

Type 41 with a sliding wedge lock mechanism. This is the most common type found in sailplanes inAustralia.

b.

Type 45 with a rotating cam lock mechanism. There is a small number of these in sailplanes inAustralia.
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Figure 28-2 Types of L’Hotellier Connectors
NOTE
GFA AD178 10/06/1980 identified that some sailplanes in Australia had erroneously had ‘Z’
inline swivel sockets installed in 90-degree joints. In this case the coupling is subjected tomore rapid wear due to the reduced bearing surface at the open end of the socket which
can lead to a wear pattern that grips the ball, restricts flexibility and could cause failure of
the ball shank. Immediate inspection and, if necessary, replacement was required.
L’Hotellier ball variants are available with a spigot on top of the ball which require a special socket with aslot. These are only used in the ‘Standard’ (90 degree) configuration. Eg connecting the elevator of an
Astir. Do not use these anywhere other than specifically where the sailplane manufacturer has designed forthem to be used.
L’Hotellier sockets are available with several types of shaft:a.

Type K or M: Fixed length, for tube – These are attached to control rods directly with rivets, glue or
both.

b.

Type N: Adjustable length, for threaded rod - not known to be used in sailplanesc.

Type RK or RM: Adjustable length (with lock nut), for tube – These are attached to control rods
directly with rivets, glue or both.

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Figure 28-3 Various L’Hotellier Fittings

28.3

SAFETY INCIDENTS INVOLVING L’HOTELLIER CONNECTORS
Since 1980 there has been a steady run of incidents and accidents, including fatalities, caused byunintended disconnection of L’Hotellier coupling. The couplings have been found to disconnect for thefollowing reasons:a.

Incorrect assembly during rigging. Either not connected at all or only partly engaged resulting inseparation of the control linkage whilst in flight.

b.

Disconnection in flight of controls which have been correctly connected. In most cases this has
been due to weak latch springs. The use of an approved form of safety locking device, such as asafety pin, is now mandatory to prevent this.

c.

Fracture of the ball coupling at the top of the threaded section at the neck immediately under theball.

The frequency of incidents and adverse outcomes has lowered over time as a result of better knowledge andimproved maintenance procedures with these connectors.

28.4

SAFETY LOCKING
It is mandatory that all L’Hotellier couplings in sailplanes on the Australia register must have a means ofsafety locking the wedge or cam. The manufacturers approved safety locking methods will normally beshown in the Flight/Maintenance Manual or manufacturer’s Technical Note or an EASA AirworthinessDirective.

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28.4.1SAFETY LOCKING PINS
In the absence of a sailplane manufacturer’s specified safety method for the L’Hotellier couplings, the GFA
approved safety locking method is to use safety pins or safety wire through a small hole in the wedge/cam
as shown in Figures 28-4 and 28-5.
It is recommended that each safety pin be tied to part of the fitting by thin nylon cord or similar to avoid loss.

Figure 28-4 Safety Pin Hole Locations

Figure 28-5 Types of Safety Pin
There are other safety locking methods, suitable for wedge locks (Type 41 connectors), fitted by somemanufacturers and / or approved by some sailplane manufacturers for retrofit.
Whilst it may be possible to retrofit the above safety locking mechanisms, they are significantly bulkier thansafety pins/wires. Therefore, unless approved by the sailplane manufacturer, each locking method must be
specifically approved by GFA for use in a particular aircraft type.
Should a sailplane equipped with L’Hotellier connections be found not to have one of the above methods ofsafety locking or an alternative method approved by GFA for the specific sailplane, then the sailplane isdeemed unairworthy and is to be grounded immediately. This is a Major Defect which shall be entered into
the Maintenance Release and requires rectification before further flight.

28.4.2SCHEMPP-HIRTH SAFETY SPRINGS
These springs are fixed to the socket body using an existing hole. One end of the spring aligns with and isinserted into the safety hole in the wedge when it is locked. Left and right hand versions are available.

CAUTION
The Schempp-Hirth safety springs rely on positive spring force to keep the end of thespring in the wedge safety hole. If the spring is overextended to unlock the connector, it
can permanently bend the spring such that it wants to remain open. In thesecircumstances vibration and movement could cause the spring to open in flight.

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Figure 28-6 Schempp-Hirth Safety Locking Spring

28.4.3

UERLING TYPE SLEEVES
These ‘add-on’ sleeves are designed to stop the ball being removed from the socket by physicallyobstructing any disconnect motion. They are only suitable for Type 41 inline (Z-swivel) connectors.
For installation, the sleeves must be slid axially onto the L’Hotellier socket shaft - they must not be installedby clipping radially onto the socket shaft. Radial clipping requires excessive opening of the sleeve and maylead to cracks and ruptures due to over stressing such that the sleeve cannot function properly anymore.
Early Uerling sleeves, as fitted to LS3 sailplanes, were a red colour, fairly flimsy and required replacement
every two years. It was mandated by LS (ref TM3049) that these be replaced with thicker, white colour,
sleeves. There should be no red Uerling Type sleeves currently in use in Australian sailplanes.
More modern LS ‘Uerling type’ sleeves are made from white nylon / plastic and are much more solid than
the red ones, see Figure 28-8. These do not have to be replaced after fixed life period, but must be
inspected annually for deterioration and functionality.
In some old Grob documentation there is reference to ‘Securing Sockets S26’ which it is believed were an
Uerling type sleeve. However, these are not now available for purchase from Linder.

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Figure 28-7 Uerling Type Safety Sleeves in Operation

Figure 28-8 LS White ‘Uerling Type’ Sleeve

28.4.4

WEDEKIND SAFETY SLEEVES
Wedekind safety sleeves are permanently fitted onto Type 41 inline (Z-swivel) socket shafts. They are
sprung loaded and function by preventing the wedge from moving out from the locked position.
The ball must be fully inserted into the housing to allow the plunger and wedge to function correctly and lockthe ball in position. The securing sleeve must then cover the wedge lock plate for a minimum of 3mm (refGrob TM306-32).

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Figure 28-9 Wedekind Safety Sleeve Cross-Section

Figure 28-10 Wedekind Safety Sleeves Shown In Retracted And Wedge Secured States

28.4.5LS SAFETY SLEEVES
These sleeves are permanently fixed on the ball side of the coupler. They are sprung loaded but needed tobe screw-twisted over the joint so as to prevent the ball from leaving the socket. They are only suitable forType 41 inline (Z-swivel) connections. Eg as used on the LS4.

Figure 28-11 Control Rod With L’hotellier Ball and LS Safety Sleeve

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Figure 28-12 Diagrams of LS Safety Sleeve Operation
NOTE
The twist motion to secure is anti-clockwise when looking at the end of the rod with the ball.
Therefore, when checking a sailplane, the left-wing connector may appear to twist in the opposite
direction to the right-wing connector.

Figure 28-13 Aileron Connectors Direction of Twist of LS Safety Sleeves (Viewed Looking Aft)

28.5

INSPECTIONS AND PERIODIC MAINTENANCE REQUIREMENTS
The mandatory inspections and mandatory periodic maintenance are specified in MOSP 3 Section 13.4.

28.6

DAILY INSPECTION
Daily inspection and the connection / disconnection of L’Hotellier couplings, fitting safety pins and lubricationof the coupling must be performed by qualified Daily Inspectors who are familiar with the type of L’Hotellier
and safety method fitted.

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In most sailplanes it is difficult to see the L’Hotellier connectors in their normal locations as they are often
hidden from view behind spars. Touch / feel is often the sense used to make the connection and establish it
is locked together and the safety mechanism has been applied. Torches, mirrors, smartphone cameras andendoscopes may be useful tools to assist visual inspection. Inspectors should thoroughly familiarise
themselves with how the connectors look and feel whilst the sailplane is derigged.
The actions to be taken during the Daily Inspection of the L’Hotellier connectors are:Action A: Check Maintenance Release for Periodic Maintenance Requirements. Part 1 of the
sailplane’s Maintenance Release (MR) must be checked for the periodic maintenance requirements
applicable by Total Time In Service (TTIS) or date. Any required maintenance due by virtue of the stated
TTIS or date must be completed prior to the next flight.
Action B: Ball and Socket Installation Integrity. Inspect and check for defects such as looseness ofballs, loose locking nuts, broken tab washers, worn threads etc. Any of these defects will allow the
L’Hotellier connectors to wind out or loosen. Any looseness can cause bending failure and cracking of theshank at the underside of the flange. This sort of defect is significant and must be treated as a Major Defectand the sailplane not be flown until evaluated and rectified by an Annual Inspector.
Action C: Ball Correctly Engaged in Socket. The correct and incorrect assembly of the couplings must
be pointed out by Daily Inspector Examiners and understood by Daily Inspectors. This is shown in Figure28-14.

Figure 28-14 Correctly and Incorrectly Assembled Couplings
Daily Inspectors must be aware that it is possible to connect these couplings incorrectly. The ball may not be
fully seated as shown in Figure 28-15.
Method: The inspector should physically try to pull the ball from the socket to ensure it is fully inserted andheld by the plunger.

Figure 28-15 Incorrectly Assembled Coupling
Action D: Safety Locking. The presence and effectiveness of the safety locking must be checked at each
Daily Inspection.
Method: Visually or by touch, establish that the safety locking is present and has been correctly applied.
Where possible, the cam/slide should be pushed to ensure it is impossible to move the cam/slide enough toopen the coupling.

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Action E: Positive Control Check. Positive control checks should be carried out every time a sailplane issubject to a Daily Inspection. It is also essential for positive control checks to be carried out every time asailplane is rigged (assembled for flight). This is advised even if there is automatic control connection.
Method: Taking care not to apply excessive force, each control surface should be restrained while anattempt is made to move the control, and the direction of motion checked. It only takes a couple of minutes
for a helper to advise the Daily Inspector whether movement of the cockpit controls generates the correct
responses at the control surface. A positive control check can reveal connections that have only partiallybeen engaged.

28.7

PERIODIC LUBRICATION
The lubrication intervals are specified in MOSP 3 Section 13.4.
The locking wedge should be cleaned but not lubricated.
Where periodic lubrication is impractical due the aircraft’s construction, alternative arrangements may beapproved by the CTO/A on written application by the Registered Operator.
Lubrication may be undertaken and signed-off in Part 1 of the Maintenance Release by a Daily Inspector.
Because the control linkage has been disconnected to enable the lubrication, a duplicate inspection andsignature by another Daily Inspector is required regarding the reconnection,
On completion of lubrication, it shall be recorded and signed off in the Maintenance Release and the next
due date / TTIS for lubrication shall be calculated entered in the Maintenance Release by the inspector
actioning the lubrication.
A high-quality grease may be used for flight in non-freezing conditions. Flight in sub-zero temperatures (e.g.
high altitude wave flying) requires the use of low temperature aviation greases such as Aeroshell 7 or
Mobilgrease 28.

28.8

ANNUAL INSPECTION AND PERIODIC MAINTENANCE
L’Hotellier couplers may be subjected to ball wear and ball stem/thread fracture due to incorrect adjustments
elsewhere in the control linkages. Annual Inspectors must check for:a.

Excessive pilot effort to lock / unlock airbrake systems.

b.

Proper out-travel stops close to the pilot in the airbrake systems so as to prevent ball stems bending
and cracking when the airbrake is fully functioned during pre-flight cockpit checks.

c.

Free play within manufacturer’s limits

Annual inspection and periodic maintenance (other than lubrication) of L’Hotellier connectors may only be
performed by qualified and current Annual Inspectors. In addition to the daily inspection checks (Actions AE above) and periodic lubrication requirements, the following actions are required:

28.8.1SAFETY LOCKING
Check there are safety locking mechanisms present and functional for all L’Hotellier connections fitted on the
sailplane. If the sailplane manufacturer’s operating manual does not describe a L’Hotellier safety locking
mechanism, then the safety pin method described in this chapter must be applied or else an alternative
method fitted as approved by GFA for the specific sailplane under inspection.

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28.8.2

BALL WEAR
All balls must be checked for wear, as per
Figure 28-16, at 500-hour intervals and during
Annual Inspections, whichever comes first.
The maximum out-of-round dimension A minus
B or B minus A is 0.1 mm
Also check the ball thread (no damage is
acceptable) and the base of the ball for cracks.

Figure 28-16 Ball Wear
Measurements
The fit of the ball in the fitting can be checked by unbolting the ball from the control system and installing it in
the coupling and attempting to rotate it. Any variation in the torque needed to rotate the ball is an indicationof wear and ball replacement should be considered.
The collar of the ball must be perfectly set on its base. See Figure 28-17 below.

Figure 28-17 L’Hotellier Ball Collar Installation Requirement

28.8.3

COUPLING CLEARANCE AND WEAR
At each Annual Inspection, the projection of the Type 41 wedge locking plate must be checked as per Figure28-18. This measurement is an indication of the combined wear of the ball and socket. If replacing the balldoes not bring the extension back into tolerance, then the socket is excessively worn and must be replaced.

Figure 28-18 Locking Plate Extension

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Some sailplane types were originally fitted with aluminium alloy socket fittings. These must be checked ateach Annual Inspection for socket wear and when replaced, replacement is to be with a steel alloy
assembly.

28.8.4LATCH SPRING CHECK (TYPE 41)
At each Annual Inspection, clean the coupling and measure the force required to initially move the sliding
latch (pre-load) and the maximum force just before the latch reaches its natural stop.
The pre-load should be approximately 600g and the force when the latch is fully out is approximately 1000g.
Significant variance to these figures indicates a weak spring which may not secure the coupling and thus
replacement of the socket unit is required.
Note: Faulty latches have been found with zero pre-load and a maximum load of 300g.

28.91000 / 3000 HRS TTIS PERIODIC MAINTENANCE
The replacement intervals are specified in MOSP 3 Section 13.4.
Balls and sockets removed due to time in service or not to specification, must be deliberately made unusableand disposed of to prevent accidental further use.
Replacement of balls and/or sockets shall be recorded in the sailplane’s logbook including:

28.10

a.

Details of the part number, description, supplier source and any manufacturer batch information
providedb.

The next due TTIS or date of required maintenance or replacement.

c.

The date of replacement, the signature and GFA number of the Annual Inspector approving thework.

ANNUAL INSPECTION DOCUMENTATION

28.10.1 LOGBOOK ENTRY
The sailplane’s logbook entry for the Annual Inspection is to record that the inspection requirements of thischapter have been completed and any remedial action taken. The entry must also detail the future periodic
maintenance requirements as follows:a.

The next 50-hour lubrication is required by Total Time in Service (TTIS).

b.

The TTIS by which a 500-hour wear inspection must be completed.

c.

The TTIS by which L’Hotellier balls must be replaced. Note there may be more than one such entry
if more than one size of ball is installed and/or similar size balls are installed in different control
circuits and have been changed at different times.

A record of ball measurements and latch spring tensions should be added to the sailplane’s support
documentation.

28.10.2 MAINTENANCE RELEASE DOCUMENTATIONThe Reoccurring Maintenance Items page of the Maintenance Release of a sailplane equipped with
L’Hotellier couplings must be endorsed with the periodic maintenance requirements identified at the Annual
Inspection documentation as detailed above.

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Figure 28-19 Example of Entries in Maintenance Release Part 1
Since these actions may be completed before the stated due date / TTIS, the subsequent check / action
date / TTIS is best not written into the MR in advance. When the action is completed, the inspector should
enter when the next periodic maintenance action is due.

28.11

MAINTENANCE ACTIONS

28.11.1 TYPE 41 SOCKETS (WITH WEDGE LOCK) SAFETY HOLE
Type 41 sockets were originally manufactured with a 1.0 mm  ‘witness’ hole that visually confirmed thecoupler was locked. L’Hotellier later changed this to a 1.2 mm  hole for inserting a safety pin. Sockets
with witness holes of only 1.0 mm  may be redrilled to 1.2 mm .

28.11.2 TYPE 45 SOCKETS (WITH CAM LOCK) SAFETY HOLE
All cam style L’Hotellier sockets are to have a hole for a safety pin. Safety pins must be inserted before
flight. Early manufactured cam style couplings did not have a safety hole, but GFA AD177 Issue 5 dated 12
May 1998 required that all such couplings be inspected and modified by 31 July 1998.
If a cam style coupling is found without a safety hole, it is to be modified by drilling a hole as shown in Figure28-20 using the following procedures:a.

Remove the connector from the aircraft.

b.

Fit a coupling ball so that the coupling is in the connected state.

c.

Drill a 1.3 mm  hole as show in the Figure below. Clean the coupling and ensure no swarf
remains.

d.

Reinstall the couplings. Ensure that any locknuts are tight.

e.

Check the control surface deflections and freeplay of all control circuits which have been disturbed.

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Figure 28-20 Drilling Safety Pin Hole in a Type 45 Cam Locking Socket
Once the holes have been drilled, safety pins or lock wire must be fitted. When fitting the pins for the firsttime, clearance around the fitting must be checked as some designs do not permit the installation of thesafety pins due to fouling with the adjacent structure and in these instances locking wire must be used.
Each safety pin installation must be checked for clearance from the surrounding structure and control
systems through the full travel of each control system.

28.11.3 INSTALLATION OF BALLS WITH REDESIGNED THREADSGFA AD177 Issue 6 identified that L’Hotellier had redesigned some of the balls to remove the undercut
thread and introduce a small length of shank. Figure 28-21 shows the original and the replacement designs.
The part number designation of the balls with redesigned threads is believed to be 961S-150-150.

Figure 28-21 L’Hotellier Ball Redesigned Thread
Because of the redesigned thread, the mounting brackets must be modified to accept the new thread. Where
the ball is mounted at 90° as shown in Figure 22 below and there is a nut on the ball, then the plate may be
drilled out to accept the 961S ball.

Figure 28-22 Modified Mounting for 961S-150-150.L3 Ball
The ball may be installed in push rod end fittings by installing 2.5 mm of washers under the ball flange.
Because this changes the geometry of the control system the control deflections or dive brake locking forcesmust be checked and adjusted to bring them back into tolerance.
The installation of 961S-150-150.L3 balls in any other designs requires formal design approval from GFA.

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28.12

EXTRACTS FROM L’HOTELLIER PRODUCT GUIDE

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28.13

HISTORY OF AIRWORTHINESS REQUIREMENTS REGARDING L’HOTELLIERCONNECTIONS

28.13.1 GFA AIRWORTHINESS DIRECTIVES
AD177 Issue 2, 24/5/1983. Combined all known inspection, replacement and maintenance actions required
to ensure safe operations of L’Hotellier couplings.
AD177 Issue 3, 18/4/1990. Represented the experience generated since 1983 from the application of Issue
2 requirements.
a.

Correct lubrication prevents ball wear. Correct installation will help to prevent fracturing of thethreaded part of the ball.

b.

Excessive pilot effort to lock/unlock airbrake systems is a major contributor to ball wear and ballstem/thread fracture. When rigging an airbrake system, the sailplane manufacturer's recommended
procedure, including freeplay limits, must be followed.

c.

Lack of proper out-travel stops close to the pilot in airbrake systems can cause ball stems to bend
and crack when the airbrake is fully functioned during pre-flight cockpit checks.

d.

Balls with threaded shanks larger than 6mm diameter need not be replaced at intervals less than3000 hours, as recommended by the L’Hotellier coupling manufacturer.

AD177 Issue 4, 30/10/1991. Added an additional check on the condition of the springs.
AD177 Issue 5, 12/5/1998. Required Type 45 couplings with a locking cam to have safety pins installed andthe maintenance requirements updated to reflect the latest information from L’Hotellier.
AD177 Issue 6, 25/1/2001. Changes the requirements for lubrication of the couplings.
AD177 Issue 7, 9/5/2001. Corrects an erroneous part number for replacement L’Hotellier coupling balls.
Superseded by chapter in BSE.
AD178 Issue 1, 10/6/1980. Check for and remedy incorrect type of L’Hotellier socket fitted (inline socket
incorrectly used for 90-degree joint).

28.13.2 OTHER REFERENCES
Glasser-Dirks Technical note No. 826/24.
LBA ADs 1993-001/3 and 1994-001/2
Grob Service Bulletin TM306-32 & TM315-57 regarding use of Wedekind sleeves and Securing Socket S26
in G102 and G103 sailplanes
L’Hotellier Maintenance Instructions 10.01 dated 03/94.

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29.

GLOSSARY OF ABBREVIATIONS AND TERMS

AAF

Airworthiness Administration Fee – the fee payable to GFA for the issue of the Annual Inspection Kit ,the documentation that supports a sailplane’s annual "Form 2" inspection.

AC

Aerodynamic Centre - the point on a wing aerofoil where the pitching moment produced by the
aerodynamic forces is constant with angle of attack.

AD

Airworthiness Directive – a document detailing mandatory actions for the continuing airworthiness ofthe sailplane usually generated in response to some technical issue such as a serious defectrequiring rectification advice from manufacturer

AI

Annual Inspection. Often referred to as a “Form 2 Inspection”

AN

Airworthiness Advice Notice - a GFA document providing non-mandatory airworthiness advice.

AN bolts

Army Navy bolts – A specification system for bolts originating in America.

AIP

Aeronautical Information Publication - as issued by Airservices Australia.

ASI

Air Speed Indicator

ATSB

Australian Transport Safety Bureau - the national body responsible for civil aircraft accident
investigation being an independent Commonwealth Government statutory agency.

BA bolts

British Associate bolts - A specification system for bolts originating in Britain

BCAR

British Civil Airworthiness Requirements - the standard to which many British and some Australian
sailplanes have been certificated. Now largely superseded by EASA and OSTIV standards.

Boom

The upper & lower spanwise beams of a sailplane main spar which carry the main bending loads
acting on the wing. Also called a spar cap.

Box sparA spar constructed of two booms top and bottom joined together by shear webs on both the front andrear of the booms thus forming a box in cross section.

BS

British Standard – a system of standards now mostly replaced by international or European standards

BSE

The GFA publication Basic Sailplane Engineering

CS-22

Certification Specifications for Sailplanes and Powered Sailplanes CS-22 issued by EASA.

CASA

Civil Aviation Safety Authority.

CAR

Civil Aviation Regulation.

CAO

Civil Aviation Order.

CFRP

Carbon Fibre Reinforced Plastic

Chord

The distance between the leading and trailing edges of a flying surface such as a wing or tailplane etc

C of A

Certificate of Airworthiness.

Control circuit

The friction present in a control circuit resulting from the cumulative friction of all the components inthe circuit.

frictionControl circuit
stiffness

The stiffness of a control circuit resulting from components deforming or stretching under load. Higher
stiffness = less deflection/deformation/stretching = less flexibility.

CG

The point on the aircraft through which the total weight acts with the line of action at right angles tothe earth's surface.

CP

Centre of Pressure - the position on the wing where all of the aerodynamic pressure field may be
represented by a single force vector with no moment.

CRP

Carbon Reinforced Plastic.

CTOA

Chief Technical Officer Airworthiness. The officer appointed by the GFA to supervise theairworthiness functions of the GFA and who holds delegated authority from CASA.

DI

Daily Inspection.

DIN

Deutsche Industrie-Norm. A set of standards originating in Germany.

D-noseFor earlier sailplanes with little or not much structure aft of the main spar, the D shaped front sectionof a wing, forward of the main spar and consisting of a load-bearing skin and numerous internal ribs.
Resists the torsional or twisting loads exerted on a wing

DoITRD

Department of Infrastructure, Transport, Regional Development & Local Government

EASA

European Aviation Safety Agency - implements Europe wide aviation regulation.

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EC

Experimental Certificate

FAA

Federal Aviation Authority

Form 2The GFA form used during an Annual Inspection as a checklist and record

Freeplay

Slack in the control systems. eg the amount of movement required of the control stick before theelevator moves

FRP

Fibre Reinforced Plastic - a generic term for all forms of fibre reinforced plastic structures.

g

The acceleration due to gravity, equal to 9.81 m/s2

Gelcoat

The smooth, hard polyester resin surface coating of a fibreglass structure

GFA

Gliding Federation of Australia.

GFA Ops Regs

The GFA Operational Regulations

GRP

Glass Reinforced Plastic.

“I" sparA spar constructed of two booms (top and bottom) joined together by a single shear web usuallyequidistant between the front and rear of the booms

JARs

Joint Airworthiness Requirements - a European standard - Section 22 re sailplanes and powered
sailplanes now superseded by CS-22 issued by EASA.

KRPKevlar Reinforced Plastic

LAME

Licensed Aircraft Maintenance Engineer

LE

Leading Edge

LSA

Light Sport Aircraft

MAC

Mean Aerodynamic Chord - the average chord of a flying surface taking into account geometric taperand other characteristics of the wing profile and geometry.

Major Defect

A significant defect, recorded in the Maintenance Release, which renders the sailplane un-airworthy
until it is cleared by an appropriately authorised person.

MAR

Mandatory Airworthiness Requirements. A set of GFA requirements for new sailplane types.

Minor DefectA defect, recorded in the Maintenance Release, which does not render the sailplane un-airworthy but
needs to be monitored at subsequent DIs (in case it hasgot worse) and pilots should be aware of. It
may be cleared by an appropriately authorised person.

MOSP

The GFA Manual of Standard Procedures.

MR

Maintenance Release. The document providing the legal records of the maintenance status of the
sailplane and informing of the actions required of a Daily Inspector seeking to release the sailplane forflight operations on a particular day. Must be kept with the aircraft at all times.

N

Newtons – The unit measure for Force.

NDI

Non Destructive Inspection

NDT

Non Destructive Testing

ONL

A standard for bolt specification originating from Czech Republic

OSTIV

An acronym in French which translates as "International Scientific and Technical Organisation for
Gliding". A body of people interested in these aspects of gliding.

OSTIVAS

Airworthiness standards according to OSTIV

PSI

Pounds Square Inch – A unit of pressure

PTT

Press To Talk –RFRadio Frequency

RTOA

Regional Technical Officer Airworthiness

SDS

Safety Data Sheet – information provided by the manufacturers of materials and chemicals

Shear

A load tending to deform a structure by sliding one section against or over another.

Shear webThe vertical facing used to join together the top and bottom booms of a sailplane spar and carrying
shear loads when the spar is deflected up and down.

STOA

Senior Technical Officer Airworthiness – a GFA appointed role

TBO

Time Between Overhauls

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TC

Type Certificate

Torque tube

A metal tube which transmits control forces to a control surface (e.g. flaps) by means oftorque/twist/torsion applied to the tube.

Torsion box

Structure designed to resist torsional (twisting) loads.

TOST

A manufacturer of launch cable releases and undercarriage components

TTIS

Total Time In Service

UV

Ultra Violet – a form of light

VA

Maximum manoeuvring speed (the speed beyond which full deflection of the controls may create
forces that could cause structural damage)

VB

Design speed for maximum gust intensity

VD

Design diving speed, the highest speed planned to be achieved in testing

VNE

Never Exceed airspeed

W&B

Weight & Balance

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