NASA Contractor Report 3916

i NASA-CR-3916 19850025820

Design and Testing of an

Energy-Absorbing Crewseat

for the F/FB-111 Aircraft

Volume I--Final Report

S. JosephShane : : i_;_" i_ ! Po_ €

CONTRACT NAS1-17387 z : ! c,-;,

AUGUST 1985

fiJ/A

https://ntrs.nasa.gov/search.jsp?R=19850025820 2018-07-18T17:39:18+00:00Z

NASA Contractor Report 3916

Design and Testing of an

Energy-Absorbing Crewseat

for the F/FB-111 Aircraft

Volume 1--Final Report

S. Joseph Shane

Simula Inc.

Phoenix, Arizona

Prepared for

Langley Research Center

under Contract NAS1-17387

N/

Nationa

L

l Aeronautics

S/X

and Space Administration

Scientific and Technical

Information Branch

1985

PREFACE

This report was prepared by Simula Inc. under Contract No. NAS1-17387 for the

National Aeronautics and Space Administration, Langley Research Center, Hampton, Virginia. Mr. Claude B. Castle served as the Technical Monitor.

Several other organizations made contributions to this work. The effort of

the Federa| Aviation Administration was managed by Mr. Richard F. Chand|er,

Chief of the Protection and Survival Laboratory, Civil Aeromedical Institute.

Contributions of the U.S. Army Applied Technology Laboratories (AVSCOM)were

managed by Mr. Kent Smith. Efforts of the U.S. Air Force were supervised by

Mr. Patrick Santucci, Sacramento Air Logistics Center (SM-ALC), McLellan Air

Force Base.
TABLE OF CONTENTS

Page

1.0 INTRODUCTION ........................ 1

1.1 BACKGROUND........................ 1

1.1.1 System Description................ 1

1.1.2 AccelerationEnvironment............. 3

1.1.3 InjuryRecord................... 7

1.2 PROGRAM OBJECTIVES.................... 9

2.0 ENERGY-ABSORBINGSEAT DESIGN ................. 12

2.1 OPERATIONALF-111 SEAT.................. 12

2.1.1 General...................... 12

2.1.2 Restraint..................... 14

2.1.3 Cushions ..................... 16

2.2 DESIGN GUIDELINES.................... 16

2.2.1 Energy-AbsorbingFunction............. 16

2.2.2 Other Seat Requirements.............. 18

2.3 TEST SEAT ........................ 19

2.4 SEAT PAN LOAD CELLS ................... 24

2.4.1 Modified OperationalSeat Pan........... 24

2.4.2 Modified Energy-AbsorbingSeat Pan ........ 24

3.0 SEAT TESTING ......................... 28

3.1 TEST OBJECTIVES..................... 28

3.2 CONDUCT OF TESTING.................... 28

3.2.1 Test Facility................... 28

3.2.2 Test Methods ................... 28

3.2.3 Test Matrix.................... 31

3.2.4 AccelerationPulse Characteristics........ 34

ii
TABLE OF CONTENTS (CONTD)

Page

3.3 PERFORMANCEOF THE ENERGY-ABSORBINGSEAT......... 36

3.3.1 AccelerationLevels................ 37

3.3.2 Energy-AbsorbingStroke.............. 45

3.3.3 StructuralIntegrity............... 45

3.3.4 Conclusions.................... 46

3.4 COMPARISONOF OPERATIONALAND ENERGY-ABSORBING

F-111 SEATS ....................... 47

3.4.1 AccelerationLevels................. 48

3.4.2 Spinal Loads ................... 56

3.4.3 Seat Pan Loads .................. 58

3.4.4 Conclusions.................... 64

4.0 CAPSULE TESTING........................ 73

4.1 TEST OBJECTIVES..................... 73

4.2 CONDUCT OF TESTING.................... 73

4.2.1 Test Facility................... 73

4.2.2 Test Methods ................... 75

4.2.3 Test Matrix.................... 90

4.3 RESULTS OF CAPSULETESTING................ 95

4.3.1 Test Conditions.................. 95

4.3.2 OccupantAccelerationLevels ........... 99

4.3.3 Seat Pan Loads ................. 105

4.3.4 VerticalStroking................. 108

4.3.5 StructuralIntegrity............... 114

4.4 CONCLUSIONS....................... 115

iii
TABLE OF CONTENTS (CONTD)

Pag____ee

5.0 RETROFIT SEAT......................... 116

5.1 DESIGN GUIDELINES.................... 116

5.2 SEAT DESCRIPTION..................... 118

5.2.1 Overall Description................ 118

5.2.2 BulkheadAttachment................ 122

6.0 CONCLUSIONS................... • • • • . . . 128

6.1 DISCUSSION........................ 128

6.2 CONCLUSIONS.......... ............. 132

6.3 RECOMMENDATIONS..................... 133

7.0 REFERENCES .......................... 135

IV
LIST OF ILLUSTRATIONS

Figure Page

1 F-111 crew module (courtesyU.S. Air Force).......... 2

2 Vertical seat pan accelerationsduringejection

phase of F-111 escape sequenceat 64.2 KEAS

eooelo 4

(courtesyU.S. Air Force).............

3 Vertical seat pan accelerationsduring ejection

phase of F-111 escape sequenceat 302.8 KEAS

(courtesyU.S. Air Force)................... 4

4 Dynamic Response Index during ejectionphase of

F-111 escape sequence(Reference1).............. 5

5 CorrelationbetweenDynamic Response Index and

spinal injury rate for ejection seats (Reference2)...... 5

6 Module verticalaccelerationsduring ground impact

(courtesyU.S. Air Force)................... 6

7 Values of Dynamic ResponseIndex for ground impacts

calculatedduring qualificationtesting of F-111

crew module (Reference3)................... 6

8 F-111 seat and occupant after shoulderstrap

haul-backwith harness yoke properlypositioned

(Reference3)......................... 10

9 F-111 seat and occupantafter shoulderstrap haul-back

with harnessyoke improperlypositioned(Reference3)..... 10

10 OperationalF-111 crewseat (Reference3) ........... 13

11 F-111 crewseatadjustmentgeometry .............. 14

12 F-111 crewseat restraintsystem (Reference3)......... 15

• . 20 13 Energy-absorbingtest seat ................

14 Front view of energy-absorbingtest seat ........... 21

15 Side view of energy-absorbingtest seat............ 21

22 16 Back view of energy-absorbingtest seat............

17 Operationalseat pan modified to incorporateseat

pan load cells (Reference3) ................. 25

18 Modificationof test seat to incorporateseat pan

load cells .......................... 26

v
LIST OF ILLUSTRATIONS(CONTD)

Figure Page

19 Seat pan from test seat that incorporatesseat

pan load cells

........................ 27

20 CAMI wire-bendingdeceleratormechanism(Reference

12)"'''''eeeeeeeeeeeeee,eeeeeeee. 29

21 Test fixture used in dynamic seat testingat CAMI....... 30

22 Energy-absorbingseat prior to CAMI test ........... 32

23 Energy-absorbingseat after CAMI test............. 33

24 Definitionof notationused in test pulse

description.e°oeeeeeeeeeeeeaeeeeeeee. 36

25 Seat pan vertical acceleration trace from CAMI

test of energy-absorbing seat ........ • • • • • • • . . 40

26 Acceptable duration-magnitude curve for seat pan

acceleration levels (Reference 14) .............. 42

27 Seat pan acceleration measured during

qualificationto MIL-S-58095(AV)............... 44

28 Seat pan accelerationand correspondingDRI for

energy-absorbingseat. .................... 46

29 Dynamic ResponseIndex as a functionof energyabsorberlimit loadeeeo°eeeeeeeeeoeeeeeee 47

30 Dynamic Response Indexmeasurementsfrom energyabsorbingseat tests at CAMI "'eeeoeeeeeeeeee. 48

31 Pretest photographfrom CAMI Test No. A83-101......... 49

32 Bearing assembly,roller, and bolt from energyabsorbingseat ........................ 51

33 Seat pan z-axis accelerationlevels from energyabsorbingand operationalseat tests at CAMI ......... 52

34 Peak accelerationlevelsalong the seat back

tangent line for energy-absorbingand operational

seat tests at CAMI eeeeeeeleeeeeeeeeeeeee 53

35 Dummy pelvis z-axis peak accelerationlevels from

energy-absorbingand operationalseat tests

at CAMI............................ 54

vi
LISTOF ILLUSTRATIONS(CONTD)

Figure Page

36 Dummy chest z-axis peak accelerationlevels from

energy-absorbingand operationalseat tests at

CAMI ............................. 55

37 Seat pan z-axis accelerationsfor energyabsorbingand operationalseats in similar tests

correspondingto NASA Test No. 5 ............... 56

38 Seat pan z-axis accelerationsfor energy-absorbing

operationalseats in similar tests corresponding

to NASA Test No. 6 ...................... 57

39 Seat pan z-axis accelerationsfor energy-absorbing

and operationalseats in similar tests corresponding

to NASA Test No. 8 ....................... 58

40 Dynamic Response Index determinedfrom seat pan z-axis

accelerationsin CAMI tests.................. 60

41 Dynamic Response Index determinedfrom seat back

tangent line accelerationsin CAMI tests ........... 61

42 Dynamic Response Index determinedfrom dummy

pelvis z-axis accelerationsin CAMI tests........... 62

43 Seat pan z-axis accelerationsand spinal compression

loads for CAMI tests correspondingto NASA Test No. 5..... 65

44 Seat pan z-axis accelerationsand spinalcompression

loads for CAMI tests correspondingto NASA Test No. 6..... 66

45 Seat pan z-axisaccelerationsand spinalcompression

loadsfor CAMItestscorrespondingto NASATestNo. 8..... 67

46 Dummy spinal compressionand center seat pan vertical

loads in CAMI tests correspondingto NASA Test No. 5 ..... 69

47 Seat pan z-axis accelerationsand spinalcompression

loads for CAMI tests correspondingto NASA Test No. 6..... 70

48 Seat pan z-axis accelerationsand spinalcompression

loads in CAMI tests correspondingto NASA Test No. 8 ..... 71

49 Impact DynamicsResearchFacility at NASA Langley

ResearchCenter (Reference17) ................ 74

50 Drop tower of ImpactDynamicsResearchFacilityat

NASA Langley ResearchCenter ................. 76

vii
LIST OF ILLUSTRATIONS(CONTD)

Figure Pag___ee

51 Structureat front of crew module added for

attachmentof attitudecontrol cables............. 77

52 Structureat rear of crew module added for

attachmentof attitudecontrolcables............. 78

53 Swing test set-upat NASA impact dynamicsresearch

facility ........................... 80

54 Diagram of NASA ImpactDynamicsResearchFacility

(Reference17) ........................ 81

55 Crew module immediatelyprior to swing test at

NASA Impact DynamicsResearchFacility ............ 82

56 Bulkheadaccelerometermountingsfor crew module

tests.... • ......................... 84

57 Capsule center of gravity accelerometermounting

for crew module tests..................... 85

58 Seat pan accelerometerattachmenton energyabsorbingseat in crew module tests.............. 86

59 Seat pan accelerometermounting on energy-absorbing

seat with seat pan load cells used in crew module

tests............................. 86

60 Modificationused to mount energy-absorbingseat in

crewseatmodule tests..................... 88

61 Doubler placed in air ventilationduct ............ 88

62 Modificationto capsule bulkhead .............. 89

63 Lower bearing fittingfor energy-absorbingseat........ 90

64 Occupantposition in energy-absorbingseat during

crew module tests....................... 91

65 Occupant positionin operationalseat duringcrew

module tests ......................... 92

66 Effect of parachuteoscillationson crew module

horizontaland verticalvelocities(courtesyof

U.S. Air Force)........................ 94

67 Bulkheadz-axis accelerationfrom NASA Test No. 5....... 98

viii
LIST OF ILLUSTRATIONS(CONTD)

Figure Page

68 Seat pan verticalaccelerationfrom right seat

in NASA Test No. 2 (data filteredwith class

180 filter).......................... 101

69 Peak seat pan verticalaccelerationsin crew module

drop tests .......................... 102

70 Peak accelerationlevels along the seat back tangent

line in crew module drop tests ................ 103

71 Peak dummy pelvis z-axis accelerationlevels in crew

module drop tests....................... 104

72 Seat pan z-axis Dynamic Response Index (DRI)

measurementsfrom module drop tests............... 107

73 Seat back tangent line Dynamic Response Index (DRI) 108 measurementsin module drop tests...............

74 Dynamic ResponseIndex (DRI)measurementsfrom

pelvis z-axis accelerationsin module drop tests ....... 109

75 Comparisonof total seat pan loads in module drop 111 tests.............................

76 Seat pan z-axis accelerationand center seat pan

vertical load for NASA Test No. 8 (32 ft/sec

• 112 drop test) .........................

77 Seat pan z-axis accelerationand center seat pan

verticalload for NASA Test No. 9 (25 ft/sec

drop test) .......................... 113

78 Conceptualdesign of energy-absorbingretrofitseat 119 for F-111 crew module.....................

79 Hardwarebehind pilot's seat in some F-111 aircraft...... 124

80 Upper bearing attachmenton pilot outboardside

during crew module tests ................... 125

81 Upper bearing attachmenton WSO inboard side during

crew module tests....................... 126

82 Inflatablebody and head restraint(Reference10)....... 129

83 Vertical stroke versus energy absorberlimit load

(Reference10) ........................ 131

ix
LIST OF TABLES

Table Pag____ee

i F/FB-111Major Injuries,October 1967 -

December1978 (Reference6)................. 8

2 VertebralFracturesAmong F/FB-111Ejectors

(Reference8)........................ 8

3 Velocity at EjectionFrom F-111 Aircraft .......... 17

4 Weight of Test Seat..................... 23

5 Seat Test Matrix ..................... 35

6 Test AccelerationPulse Description............. 35

7 Input AccelerationPulses for Dynamic Seat

Testing........................... 37

8 Peak VerticalAccelerationsMeasuredon Seat

Pan During Energy-AbsorbingSeat Testing at

CAMI ............................ 38

9 Eiband and Dynamic ResponseIndex Evaluation

of Energy-AbsorbingSeat Testing at CAMI .......... 45

10 Stroke Measured in CAMI Seat Tests ............. 50

11 Comparisonof Peak AccelerationsMeasuredon

Operational(F-111)and Energy-Absorbing(E/A)

Seats in CAMI Tests..................... 51

12 Comparisonof Dynamic ResponseIndex Measurements

for Operational(F-111)and Energy-Absorbing(E/A)

Seats in CAMI Tests..................... 59

13 Comparisonof EibandMeasurementsfor Operational

(F-111)and Energy-Absorbing(E/A) Seats in CAMI

Tests............................ 63

14 LumbarLoad Cell Measurementsfor Operational

(F-111)and Energy-Absorbing(E/A) Seats in

CAMI Tests ......................... 64

15 Seat Pan Load Cell Measurementsfor Operational

(F-111)and Energy AbsorbingSeats (E/A) .......... 68

16 Peak Vertical FootrestLoads Measured in CAMI Tests..... 68

17 Crew Module Test Matrix................... 93

X
LISTOF TABLES(CONTD)

Table Page

18 Crew Module Swing Test Conditions.............. 96

19 Velocity Change and Peak AccelerationMeasured

Along a VerticalAxis on Capsule Bulkhead.......... 97

20 Peak Vertical AccelerationsMeasured in Crew

Module Tests ........................ 100

21 Durationabove 23 G of Seat Pan Accelerations

Measured in Crew Module Tests................ 105

22 Dynamic Response Index (DRI) Measurementsfrom

Crew Module Tests...................... 106

23 Peak Seat Pan Loads RecordedDuring Module Tests ....... 110

24 VerticalStrokeMeasured During Crew Module Tests...... 114

xi

1.0 INTRODUCTIOI_

1.1 BACKGROUND

1.1.1 System Description

The F/FB-111aircraftuses a crew module escape systemdevelopedbetween 1963

and 1967. In this system, the crew remains inside the aircraftcockpit during

tileejectionsequence,which consistsof two main phases. The first phase, or

ejection,severs the module from the aircraftand rockets it away from the aircraft. The second phase, or descent,consistsof a controlledparachutedescent of the module and the inevitableground impact.

Under normal conditions,the crew module is an integralpart of the forward

fuselage. When the ejectionhandlesare pulledand the sequence is initiated,

gas-poweredinertia reels retractthe shou|derstraps, pulling the occupant

back into the seat. Shaped charges then fire, separatingthe module from the

aircraftas the module is liftedaway by the thrust from a rocketmotor. While

the rocketmotor is firing, a stabilization-brakeparachuteis deployed. Stabilizationf]aps are at the fore and aft ends of the module. However,none of

these items are controlledby the crew; the flight path of the module is determined by aerodynamicforces on the module and brake parachute,as well as the

directionof the rocket thrust.

The rocketmotor thrustcan be directedthrough two differentducts, depending

predominantlyon the aircraftspeed at ejection. In the low-speedmode, below

approximately300 KEAS (KnotsEquivalentAir Speed),most of the rocket thrust

is directed toward ]iftingthe module up from the aircraft. In the high-speed

mode however, it was anticipatedthat the forward portionof the module (shown

in Figure 1) would providesignificantaerodynamiclift,and thereforemore of

the exhaust gases would be ducted to the exit port in the aft bulkhead. This

preventsa severe pitching-upof the module in the high-speedejectionmode.

After rocketmotor burnout,which occurs between one and two seconds after the

ejection sequenceis initiated,the descent phase starts and the recoverychute

is deployed. A recentmoaificationto the escape systemalso cuts away the

stabilizationbrake parachuteat the same moment. This preventsentanglement

of the two chutes, which could prevent the recoverychute from opening.

After the recoverychute lines have stretched,the impactattenuationbag (IAB)

is filled from high-pressurenitrogengas bottles locatedbehind the pilot seat.

This bag, designed to cushion the module landing,has blow-out plugs to allow

the control|edrelease of the nitrogengas. The IAB has been designedfor both

ground ana water impacts.

While the IAB is filling,the parachutereaches the fully open conditionwith

the capsule repositionedto a descent attitudeof two degrees nose-up. The

IAB becomes fully inflated,and the capsule ready for ground impact, between

7 and 16 sec (dependingon speed and temperature)after initiationof the escape sequence.
STABILIZATION-BRAKE

PARACHUTE

AIRCRAFT COMMANDER._

PILOT'S INSTRUMENT

DISPLAY ca

_D

O

aO

O

PITCH FLAP

_FT FLOTATION BAG

Po

ROCKET MOTOR

.IARY

FLOTATION BAG

STABILIZATION

FLAP IMPACT ATTENUATION BAG

• PRE-EJECTION CONFIGURATION

(EXCEPT FOR DEPLOYED STABILIZATION FLAP)

• 95TH~ PERCENTILE OCCUPANT

• SEAT ADJUSTED FULL DOWN AND AFT

• RUDDER PEDALS ADJUSTED FULL FORWARD

Figure I. F-111 crew module (courtesy U.S. Air Force).
1.1.2 Acceleration Environment

The F-Ill crew module was developed to contend with a hazard inherent in all

open-seat ejection systems: windblast. While the module has been successful

in this respect, it has had other problems that involve the high accelerations

to which the occupants are subjected.

1.1.2.1 Ejection. The acceleration environment in the crew module was studied

during initial qualification testing of the escape system. It was shown that

during the modu|e separation from the aircraft, the amplitude and duration of

the vertical accelerations to which the occupants are subjected increase as

the aircraft velocity increases. This is shown in Figures 2 and 3, which present vertica] acceleration measurements from recent tests of the F-Ill crew

module.

The results of the increased acceleration levels are illustrated in Figure 4,

which shows the Dynamic Response Index (DRI) for the ejection pulse plotted as

a function of airspeed. The DRI value is the result of a simple lumped parameter mathematical model of humanresponse to vertical accelerations. The model has been correlatea with the probability of vertebral fracture in operational

U.S. Air Force ejection seats. The relationship in ejection seats between DRI

and spinal injury is shown in Figure 5.

In examining Figure 5, one can see that a DRI value of 18 corresponds to a spinal injury rate of 5 percent. Figure 4 thus shows that the expected spinal

injury rate would remain below 5 percent through an ejection airspeed of 450

KEAS. Above 450 KEAS, the DRI, and thus the expected spinal injury rate, climb

very steeply.

1.1.2.2 Ground Impact. As the capsule descends to the earth, it is supported

by a single recovery parachute with a nominal vertical descent rate of 32 ft/sec.

The capsule is designed for proper operation within the following maximumvalues for the given impact parameters:

• 20-knot wind

• Capsule swing under the parachute of I0 degrees

• Landing surface slope of 5 degrees.

The combination of a 20-knot wina and a capsule swing of i0 degrees can allow

the horizontal velocity of the capsule to reach a very severe 43 ft/sec.

Shown in Figure 6 is a typical ground impact pulse for a sled test series conducted at Holloman Air Force Base, NewMexico. Since these tests were only

conducted under conditions of low wind speed and with a level landing area,

the ground impact pulse shown is a relatively mild one. Changes in the wind

speed, aircraft attitude, and landing surface could all have some effect on

the magnitude and shape of the ground impact pulse.

Figure 7 shows the DRI for various ground impacts during the initial testing

of the F-111 crew module. Conclusions at the time were that under the most

like]y landing conditions, the spinal injury rate was going to be higher than

5 percent but probably less than 20 percent (Reference 3).
24 i = = ,

20

0

64.2 KEAS oo0

v o

Z 16 ,v

_o =

p.

W

-J

o

M

I'-- 4

W

_ 0

"r

,.1

-4

-_.6 8:8 9'.o 9.2' 91, 916 9.8' ,o.o',o.2' 1L4 ,0.6

TIME (SEC)

Figure 2. Vertica]seat pan acce|erationsduring ejectionphase of F-111

escape sequenceat 64.2 KEAS (courtesyU.S. Air Force).

TIME (SEC)

Figure 3. Vertica]seat pan acce]erationsduring ejectionphase of F-111

escape sequenceat 302.8 KEAS (courtesyU.S. Air Force).

4
40

o

0

X o

ILl

r_ 30 '€a_

z

° f

z

0

D.

03uj20 /

o

_ •

<

z 10

0

0 100 200 300 400 500 600 700 800

AIRSPEED AT EJECTION, KEAS

Figure 4. Dynamic ResponseIndex during ejectionphase of

F-111 escape sequence (Reference1).

50 OPERATIONAL DATA / /

40 -- CADAVER DATA / // m

F- 30 ///"

Z

UJ o

0 20 o

= /? °

&l.! o

0. 10 co

///

F- ®A

< 5

rr>'n" 2 _F_/GC

_z

_ 0.5

_z 0.2

O.

I I I I I I I

10 12 14 16 18 20 22 24

DYNAMIC RESPONSE INDEX

Figure 5. Correlationbetween Dynamic Response Index and spinal injury

rate for ejectionseats (Reference2).
-8

17.2 17.4 17.6 17.8 18.0 18.2 18.4 18.6 18.8 19.0 19.2

TIME (SEC)

Figure 6. Module vertica|accelerationsduringground impact

(courtesyU.S. Air Force).

28

J _ •J

26

o

x 24 • o

uJ • • o

a 22 • •

O0 • oo Z 20

zU) 18

0 16

m 14

12

_ 10

z>- 8 • Attenuator qualification tests

o 6 • Sled tests

• Air drop tests 4

2

I I I

2800 2900 3000 3100 3200

CREW MODULE EJECTED WEIGHT (LB)

Figure 7. Valuesof Dynamic ResponseIndex for ground impactscalculated

during qualificationtesting of F-111 crew module (Reference3).
1.1.3 Injury Record

Severa] examinations of injuries sustained during use of the F-111 escape module have been made (References 4, 5, 6, 7, and 8). All evaluations consider

three main factors: ejection forces, the restraint system, and ground impact

fo rce s.

Kazarian (References 4 and 5) studied the first 39 F-111 ejections (October

19, 1967 to June 30, 1977), 31 of which were considered sucessful (the ejection

occurred in the design envelope and the ejection system functioned properly).

During these successful ejections, 27 occupants suffered two types of back injuries, resulting in a total back injury rate of 43.5 percent. Negative shoulder

strap angles, reduced back support, and the position of the headrest were described as causes of hyperextension injuries during the power haul-back of the

occupant by the inertia ree|. Also, the high vertical ground impact forces

had resulted in hyperflexion injuries to the spine.

Slightly after Kazarian's evaluation, another examination of the F-111 injury

record by Harrison included 43 ejections that occurred between October 1967

and December 1978 (Reference 6). During the 35 successful ejections, only 24

occupants suffered a total of 33 major injuries. Somere-evaluation must have

been comp|eted by this time. Kazarian had listed 27 occupants as suffering

spina] injuries in the first 31 successful ejections, but Harrison lists only

24 occupants suffering spinal injury in the first 35 successful ejections.

Harrison categorizes the injuries as shown in Tab|e i, and cites "the position

of the restraint system, namely the shoulder harness, along with the forces of

ejection . ." as responsible for four of the injuries. The ejection forces

or landing forces are listed as the causes of the other injuries.

The Air Force Aerospace Medical Research Laboratory (AFAMRL)has more recently

re-evaluated the injury history of the F-Ill. Hearon (References 7, 8) reports on the first 50 ejections, of which 39 were nonfatal with proper module

functions. This analysis included re-examination of selected x-rays by several

orthopedic and radiologic consultants. The results of this analysis are shown

in Table 2. Retraction and ejection injuries are listed together because Hearon

found it impossib|e to distinguish between the two.

Brink|ey (Reference 3) and Hearon (Reference 1) also tested a proposed modification to the F-111 restraint system. The modification was based on the recommendations of Kazarian. The major points of the modification (which was never

incorporated) were to raise the anchor point for the reflected shoulder straps

and to raise the height of the support provided by the seat back. Their testing

of the modification, examination of the ejection and ground impact accelerations,

and subsequent analysis of the spinal injuries that have occurred during use

of the F-Ill escape module, resulted in several important conclusions. Some

of these conclusions are as follows:

• The accelerations imposed on the crewmen are sufficient, both at highspeed ejection and ground impact, to cause a significant spinal injury rate (Reference 3).

• There is no evidence to indicate a hyperextension injury mechanism

during retraction of the inertia ree] straps (Reference 8). However,

significant spinal flexion is possible during the retraction-ejection

phase (Reference 7).
TABLE 1. F/FB-111MAJOR INJURIES

OCTOBER 1967- DECEMBER 1978

(REFERENCE6)

Number of

Injuries Cause Injury

15 EjectionForce Vertebra]Fracture

13 Fiodu]eLanding Force Vertebra]Fracture

4 Restraints VertebralFracture

1 Struck Cockpit Rib Fracture

33

TABLE 2. VERTEBRALFRACTURESAMONG

F/FB-111EJECTEES

(REFERENCE8)

Number

SurvivedEjectees 78

No Vertebra]Fracture 55

VertebralFracture 23

Retraction- Ejection 9

Landing Impact 11

UnknownCause 3
• Future design changes in the ejection system should address reducing

the high grouna impact accelerations (References 1, 3, 7, and 8).

• Future proposed restraint system modifications should address all

the unconventional design features of the present system (Reference I).

Kazarian had identified some of the problems to which this last conclusion refers. However, a major problem identified by Brinkley is illustrated in Figures 8 and 9. It is possible to adjust the shoulder harness yoke in such a

way that when the inertia reel retracts, a vertical load is applied to the spine.

Figures 8 and 9 show an occupant after shoulder strap haul-back with the yoke

properly and then improperly positioned. Putting a compression load on the

spine in this manner would increase the chance of spinal injury when other upward vertical loads are applied, such as during ejection or ground impact.

1.2 PROGRAMOBJECTIVES

In recent years an increasing amount of effort has been directed toward the

survival aspects of aviation crash safety. Good examples are the U.S. Army's

Black Hawk and Apache helicopters. From the initial aircraft design, consideration was given to factors that affect survivability during a crash, such as:

maintaining the living space around the occupants; preventing any cargo, equipment, or structure from breaking loose; delethalizing the area in close proximity to the occupants, minimizing the threat of postcrash hazards (fire,

drowning, exposure, etc.), and reducing the intensity and duration of accelerations experienced by the occupant. The purpose of this program was to determine if this crashworthy technology could be used to reduce the injury potential

of F-Ill capsule ejections.

More specifically, since acceleration levels in the F-111 ejection sequence

have been targeted as the primary cause of the spinal injury rate, the program

objective was to determine if the technology used to reduce the severity of the

acceleration levels experienced by occupants of an aircraft in a crash was applicable to the environment inside the F-Ill capsule during an ejection sequence.

Whenan aircraft is designed with crash survivability in mind from the beginning,

three items are intended to absorb a substantial amount of the crash energy and

thus reduce the severity of the environment experienced by the occupant. These

items are the landing gear, the aircraft fuselage structure, and the seat. Each

of these items absorbs energy by applying a force through a distance. The landing gear is designed to deform according to a particular load-versus-deflection

curve. After the landing gear has reached its maximumdesign deflection, it

will no longer serve as an efficient energy absorber. Also, the fuselage structure will crush, applying a force through a distance to the aircraft structure

above it. Similarly, the energy-absorbing seat is designed to deform, allowing

the occupant to move towards the floor at a predetermined load and thus absorb

more of the crash energy.

In the F-111 capsule the situation is somewhat different. During the ejection

phase, there are no items designed to absorb energy and thus reduce the severity

of the acceleration levels to which the occupant is subjected. The occupant

sits in his rigid seat in a non-deforming capsule and escapes injury when the

1oaas to which he is subjected are below injurious levels. Conversely, he is

injured when the environment is too severe. During ground impact, the IAB
Figure _. F-111 seat and occupantafter shoulderstrap haul-backwith

harnessyoke properlypositioned(Reference3).

Figure9. F-111 seat and occupantafter shoulderstrap haul-backwith

harnessyoke improperlypositioned(Reference3).

10
does provide an energy-absorbing function. Whenthe IAB hits the ground, the

force of the capsule on top of it raises the pressure in the bag until the blowout plugs release. Then the nitrogen gas is forced through the resulting holes.

During this time, the IAB is applying an upward force on the capsule, absorbing

energy as the capsule pushes its way to the ground. However, when the capsule

hits the ground, there is no more energy absorption. There is only a sheet

metal floor above the IAB, and the seat is rigidly mounted to the bulkhead.

Efforts have been consiaered to modify the IAB to determine if it could absorb

more energy; there are two ways in which the IAB could be changed. One would

be to increase the load at which the energy is being absorbed. This could be

done by reducing the size of the ports, which would raise the bag pressure

during impact, and thus raise the load applied to the capsule. This assumes

however, that the loads presently applied by the IAB produce loads inside the

capsule that are below the threshold of injury for the occupants. Since the

injury rate in F-Ill ejections is already unacceptably high, this may not be

the case. The second method of increasing the energy absorbed by the bag would

be to increase the distance over which the bag absorbs energy. However, an IAB

with a longer energy-absorbing stroke may require a larger space in which to be

contained. The probability of capsule rollover may also be increased. Thus

while changing the IAB is a possible method of reducing the severity of the environment to which the occupants are subjected, there are many questions that

need to be answered.

It was not within the scope of this program to examine changes to the IAB. The

main purpose of this program was to adapt an energy-absorbing seat to the F-Ill

capsule and determine over what performance envelope the seat could absorb the

energy required to reduce the intensity and duration of the accelerations experienced by the occupants to non-injurious levels.

Towards this goal, the program was divided into two phases. During the first

phase, Simula Inc., with monitoring by Sacramento Air Logistics Center and

NASALangley Research Center, examined the existing seat design in detail.

Hany possible concepts for incorporating an energy-absorbing seat into the

F-Ill crew module were examined.

The concept that would be the most appropriate for a retrofit seat was used

in designing a test seat that was subjected to a thorough dynamic test series

by the FAA Civil Aeromedical Institute (CAHI).

The second phase of the project mounted the test seat inside the crew module,

which was then subjected to a series of swing and drop tests. This testing

was conducted at the Impact Dynamics Research Facility at NASALangley Research Center by NASAand the U.S. Army Applied Technology Laboratories (AVSCOM).

Volume I provides a discussion of the program, including the design of the test

seat, eva]uation of the data from the test series, a description of a concept

for a retrofit seat, and the overall conclusions of the program. Volume II presents the data from the dynamic seat testing conducted at CAMI. Data from the

crew module test series at NASALangley is in Volume III.

Ii
2.0 ENERGY-ABSORBINGSEAT DESIGN

The test seat designed for this program used many parts from the operational

F-Ill seat. This chapter will first present the operational F-111 seat, outline guidelines used in the design of the energy-absorbing test seat, and then

present the test seat.

2.1 OPERATIONALF-Ill SEAT

2.1.1 General

The operational F-111 seat is shown in Figure 10. It consists of three major

assemblies: the carriage assembly, the seat pan/back assembly, and the headrest assembly. The seat carriage is an aluminum frame enclosed by sheet metal.

The carriage has four sets of claws that enable it to slide up and down the

bulkhead on two sets of tracks. Vertical support of the carriage comes from

the seat adjustment actuator, an electromechanical device that can move the

carriage, guided by the tracks, along the bulkhead over an adjustment range of

5 in. The top of the seat adjustment actuator is pinned to a fixed clevis on

the bulkhead while the bottom of the actuator is pinned to a clevis on the carriage.

The seat pan has an aluminum base with grooved slots on each side that mate

with slots in the carriage, allowing the seat pan to s|ide horizontally inside

the carriage. The horizontal adjustment is actuated by a handle in front of

the seat pan and the position is fixed by pins extending out from the seat pan

into holes on both sides of the carriage. The horizontal adjustment range is

5 in. Proper adjustment for leg comfort is provided for not only in the seat

pan but in the 6 in. fore and aft adjustment of the rudder pedals. The top of

the seat pan is covered by fiberglass over a foam core, the shape of which is

contoured to provide for thigh support and comfort.

The seat back is a box-like structure with an aluminum honeycomb core. Rectangular aluminum tubes, open at the top, run along the sides of the back. At

the bottom of each tube is a fitting that is used to attach the seat back to

the seat pan with two bolts. This method of attachment allows the seat back

to rotate around the pitch axis relative to the seat pan. Rotation is necessary since as the seat pan slides forward, the bottom of the seat back moves

forward with it.

The headrest is supported by structure rigidly mounted to the bulkhead. While

the headrest can be adjusted horizontally over a range of 6 in., it remains at

the same vertical position for all seat adjustments. As the seat carriage is

moved up and down, rectangular tubes hanging from the headrest assembly slide

inside tubes that are part of the seat back. Conversely, when the headrest is

adjusted, these same tubes pull the top of the seat back with the headrest,

pivoting the seat back around the bolts that connect it to the seat pan.

One can see that with provisions for horizontal adjustment of both seat pan

and headrest, as well as vertical adjustment of the seat pan, various angles

of the seat back are possible. Figure 11 is a side view showing the geometry

of the described adjustments. The headrest support surface remains vertical

12
POWERED

INERTIA-LOCK

HEADREST REEL

HEADREST

TMENT

LEVER

SEAT BACK

CUSHION'--_

HEADREST

SEAT ADJUSTMENT __ ADJUSTMENT

ACTUATOR _ CONTROL

INERTIA REEL

CONTROL HANDLE

SEAT FORE AND SEAT TRACK

AFT ADJUSTMENT

HANDLE

SEAT PAN _j

CARRIAGE

Figure 10. Operational F-111 crewseat (Reference 3).

and is in front of the back tangent line. As the seat is tilted back, the

head support point remains in front of the seat back tangent line by an amount

that depends on the seat adjustment position and the seated height of the occupant. The headrest support plane can be as much as 2-1/4 in. in front of the

seat back tangent line. This does not conform to MIL-C-25969, "General Requirements for Capsule Energy Escape Systems" (Reference 9), which calls for the head

support to be 1 in. aft of the seat back tangent line. Pushing the head forward

13
Backrest

, !

Vertical J

adjustment

Horizontal adjustment

Figure 11. F-111 crewseatadjustmentgeometry.

as the F-111 headrestdoes leads to downwardand forward rotationof the head

and chest during a verticalimpact (Reference10). The loads associatedwith

this movement increasethe risk of injuryduring ejectionand ground impact.

2.1.2 Restraint

The restraintsystem for the operationalF-111 seat, shown in Figure 12, has a

|ap be]t, two shoulderstraps,and a crotch strap, sometimesreferredto as a

negative-Gstrap. The lap belts and crotch strap are connectedto the seat

pan. Operationof the single-pointrelease box knob, attached to the top of

the crotch strap, releasesthe four buckles of the lap belts and shou]derstraps. Adjustmentis providedin the shoulderand lap belts.

14
"IA LOCK REEL

RIGHT REFLECTION

LEFT REFLECTION STRAP STRAI

u_

It}

REFLECTION

;RAP LINK o

co

o

SEAT BACK TRACK

BUCKLE ROLLER GUIDE

SHOULDER STRAP

ELASTIC YOKE

KEEPER

EST STRAP

OXYGEN "RAINT STRAP

REGULATOR WEDGE

MTG. PLATE LUGS (4)

3.25 )WER RESTRAINT

HARNESS PAD

k

, r'<'--'-ADJUSTABLE LAP

STRAP

FIXED LAP STRAP

SEAT ATTACHMENT LUG

ESS RELEASE BOX

RELEASE BOX KNOB

SEAT PAN CUSHION SUPPORT

ANCHOR STRA! SEAT CUSHION

(CROTCH STRAP)

Figure 12. F-111 crewseat module restraint system (Reference 3).

Both shoulder straps attach to a yoke that sits like a "horse collar" on the

crewman's shoulders. Straps from the inertia reel, which is fixed in one position on the bulkhead, also attach to the yoke by passing around a roller and

15
then attachingto the seat back on the oppositeside at a point 24.09 in. above

the seat referencepoint. This arrangementusing the yoke and reflectedinertia reel straps provideslateral restraintfor the torso of the crewman.

However,the attachmentpoint of the reflectedstraps on the seat back is at

or below the mid-shouldersitting heightof approximately90 percent of the

flying population(Reference3). Therefore,in many cases power haul-back

loads in these strapswill apply compressionloads on the spine (Reference11).

While several investigationshave been done (References1, 3, 10, and 12), a

suitablen_odificationto alleviatethis problem has not yet been found.

2.1.3 Cushions

Cushionsare providedfor the headrest,seat back, and seat pan.

The headrest is covered with three cushions. The cushionsare 7/16-in.thick,

made from a closed-cellEnsolitefoam, and are covered with leatherbefore they

are bonded to the headrest.

The back cushion is a single layerof polyurethanefoam and is 1-1/2 in. thick.

The cushion has a fabric cover and is held in place by Velcrostrips. Because

of the short height of the seat back, the cushion is only 21 in. high, providing supportto a height of 23 in. above the seat referencepoint.

The seat pan cushion is made of two layersof foam bonded together. The top

layer of foam is I/2-in.-thickpolyethylene. The lower layer is a 1-1/2-in.-

thick pad of the same polyurethanefoam used in the seat back. Crewmen have

been Known to remove the cushion from its stretchablefabriccover and invert

the foam so that the polyurethaneis on top.

2.2 DESIGN GUIDELINES

As stated earlier,the main objectiveof the programwas to examine how crashworthy technologycould be used to reduce the injury potentialin F-111aircraft ejections. In oraer to do this, an energy-absorbingtest seat was designed. The seat designedwas not meant to be a retrofitseat. A retrofit

seat would nleetall the flight requirementsof the aircraft,while the test

seat was designedonly for use in the tests conductedduring this program.

To minimizecost, it was built using as much of the existingseat hardwareas

possible. Because of this, the test seat is heavier than an energy-absorbing

retrofitseat would be, yet still demonstratesthe capabilitiesof an energy- absorbingseat.

2.2.1 Energy-Absorbin9 Function

Previousevaluationsof the F-111 ejectionsequencediscussedin Section 1.0

have identifiedthe verticalinertialloads applied to the occupantas the primary cause of the high spinal injuryrate. Horizontalloads in both the forward and lateraldirectionsare below levelsthat would be injuriousto the

occupant. Therefore,an energy-absorbingretrofitseat should absorb energy

only in the verticaldirection. However,Section 1.0 identifiedboth the vertical accelerationson module ejectionand ground impactas capable of causing

spinal injury (Reference3). Therefore,it would be most desirableto have an

energy-absorbingseat that would be preparedto operate both during ejection

16
and ground impact. Because of the limiteddistanceavailablefor energyabsorbingstroke, such a systemmay need to "reset" itselfafter the ejection

and prior to ground impact. This systemwould operate by first allowingany

stroke necessaryduring the ejectionsequence. During the parachutedescent

the occupantwould then be liftedback up through any energy-absorbingstroke

that had occurred,or possiblyto the full-up seat position. Such a system

would providemaximum protectionduring both the ejectionand ground impact

phases. However,this systemwould also be more complex to build than one

that operatedduring either ejectionor ground impact. Therefore,the injury

potentialin each phase of the ejectionsequencemust be examined.

Table 3 shows a listingof the first 67 ejectionsfrom F-111 aircraftdivided

in terms of aircraftvelocityat ejection. Figure 4 shows that at a 450 KEAS

ejection velocitythe accelerationpulse to which the occupantwas subjected

has a DRI of 18. The U.S. Air Force considersthe DRI of 18 to be acceptable

for ejection seats. Figure 5 shows that for an ejectionseat, this DRI corresponds to an injury rate of 5 percent. While the accelerationenvironment

in a capsule ejectionmay be slightlydifferentfrom an ejection seat, and this

would affect the accuracyof the injury rate prediction,the DRI does give a

good understandingof how the severityof the environmentincreasesas the aircraft velocityat ejectionincreases. Therefore,Table 3 uses the 450 KEAS

ejectionvelocityas a dividing line to show that a relativelylow percentage

of ejectionsoccur at the higher velocities.

TABLE3. VELOCITYAT EJECTION

FROMF-111AIRCRAFT

Velocity Velocityat or Velocity

Below 450 KEAS Above 450 KEAS Unknown

Numberof

Ejections 59 5 3

Percentage

of Ejections 88.1 7.5 4.5

On the other hand, every ejectionhas the potentialfor injuryfrom ground impact. The qualificationtest data (Figure7) show that the injury rate on

ground impactwou]d probablybe too high. Also, several studies from the Air

Force AerospaceMedical ResearchLaboratory(References1, 3, 7, and 8) state

the need for reducinghigh ground-impactaccelerations.

There are several factors that influencethe potentialfor injuryduring ground

impact. The wind velocity,magnitudeof parachuteoscillations,slope and hardness of the landing surface,and the module attitudeat impactall affect the

risk of injury. While the pilot may be able to slow the aircraftand thus minimize the injury risk during ejection,he has littleor no control over the factors affectingthe injuryrisk at ground impact. For these reasons,the Air

Force was interestedin examiningthe use of the energy-absorbingseat to reduce high ground-impactaccelerations.

17
At tnis time, it appears that the difficultiesinvolvedin allowing the occupant to stroke during ejectionand then liftinghi_Jback up during module descent,and providingstroke again during ground impact, outweighthe benefits

that cou]d be gained by providingprotectionneeded only in a certain percentage of ejections. Therefore,the seat design and testing have concentratedon

the ground impact problem.

2.2.2 Other Seat Requirements

Altiloughthe test seat is not a retrofitseat, it was necessaryto choose a

aesignconcept for a retrofitseat before buildingthe test seat. This was a

requirementfor two reasons. First, the conceptsto be used for absorbingenergy

and guiding the strokingseat in a retrofitseat should also be used in the

test seats. Doing so he]ps to uncover any interferenceor performanceprob]ems

particularto a design concept. Second,a retrofitseat should be installed

with minimum ntodificationto the aircraft. Only Dy examiningthe conceptsto

be used for the retrofitseat can the requiredaircraftmodificationsbe deterF,_ined.The extent of the necessarymodificationscan then be used as criteria

in evaluatingseat designs. A]so, some specificaircraftmodificationsare

not acceptab]e,and will e|iminatesome designconcepts.

Since a specificationfor an energy-absorbingretrofitseat for the F-111 does

not exist at this tir_le,it was necessaryto establishcertain design guidelines. A discussionof these guide]ines,as well as the final design chosen

after the eva|uationof many possibleconcepts,are presentedin Section 5.0.

The retrofitseat wou|d use four bearingassembliesfixed to the bu|khead.

TuDes pass throughthese bearings,guiding the seat as it performs its energyabsorbingstroke. Inversion-tubeenergy absorbersare used. The test seat is

aesigned to perform in the same manner as the retrofitseat.

Variable-]oadenergy absorberswould be a requirementon the retrofitseat. A

variab|e-]oadenergy absorber is adjustedby the occupantto provide the proper

attenuating|oad for his individua]weight. This load should be set as high as

possible,but be]ow the thresholdof injury, since a higher load can absorb more

verticalenergy as the seat strokes. Experiencewith Simu]aenergy-absorbing

seats in the U.S. Amy's UH-60 B]ack Hawk helicopterhas demonstratedthe effectivenessof verticalenergy absorberloaas correspondingto acceleration |evelsof 14.5 G.

The energy absorbersin Simu]a B|ack Hawk seats are fixed-loadenergy absorbers, and are set at loads correspondingto 14.5-Gacceleration]evelsfor the

50th-percentileoccupant. Thus, a heavieroccupantexperiencesa lower deceleration level when the seat strokes,but requiresa correspondinglylongerstroking

distance. The lighteroccupantexperiencesa higherdeceleration|evel and a

shorterstrokingdistance. Variable-loadenergy absorbersal|ow the load to correspond to a decelerdtion]evel of 14.5 G for all occupants;therefore,all occupants require approximatelythe same strokingdistancefor a given crash pulse.

This systemmakes the most efficientuse of the space avai]ableand is therefore

needed in the F-111capsule becauseof the short availablestrokingdistance.

18
The reliabilityof Simula'svariable-loadenergy absorberswas demonstrated

under U.S. Naval Air DevelopmentCenter ContractNo. N62269-79-C-0241;they

would be suitablefor use on a retrofitF-111 seat. In order to simplifythe

seat design and the testing required,variable-loadenergy absorberswere not

used on the test seat. Instead,the energy absorberswere sized for the

50th-percentileoccupant,and all testing was done with a 50th-percentile

anthropomorphicdummy. Since variable-loadenergy absorberswould be used in

the retrofitseat, the vertical strokingdistancesmeasured in the tests apply

to all occupantsizes.

Some other design constraintswere typical to both the retrofitseat and the

test seat:

• In the presentconfiguration,the headrestremains at a constant

waterline(horizontalposition),and moves fore and aft with the

seat. The seat back angle is adjustable,moving with the headrest.

The power haul-backinertiareel is mounted to the bulkhead. The

retrofitseat need not incorporatethese design features.

• The seat back should providea 13-degreeback angle, either as a

fixed back or as one of the adjustmentpositions.

2.3 TEST SEAT

A drawing of the test seat is providedin Figure 13. Figures 14, 15, and 16

show front,side, and rear views of the test seat. It is a bulkhead-mounted

seat with the roller bearingassembliesmounted on the bulkhead. The seat

consists of a seat back and seat pan assemblyconnectedby diagonaltubes and

mounted on guide tubes. A headrestis mounted on the top of the seat back,

and the power haul-backinertia reel is mounted betweenthe tops of the guide

tubes. The attenuatorsare mounted between the clevison the bulkheadand the

seat pan assembly.

Since this seat is designedonly for testing,adjustmentin the verticaland

horizontaldirectionsis not provided. The heightof the headrestis designed

for a 50th-percentileoccupant,and the seat referencepoint is approximately

in the middle of the fore-and-aftadjustmentrange providedon the existing

seat. The seat is in the full-up positionto provide for measurementof the

maximum energy-absorbingstroke.

The seat pan assemblyuses the existingF-111 seat pan with only minor modifications. Along both sides of the seat pan are machined aluminumangles, which

grip the seat pan in the same manner that the seat-pancarriagedoes on the

existing F-111 seat. The seat-pancarriagewas not used because it reduces

the availablestrokingdistance. Underneaththe seat pan, three 1/4-in.-thick

aluminumstraps connect the ]eft and right tray supports.

The seat back from the existing F-111 seat is used and is fixed at a 13-degree

angle. The headrest is mounted at the top of the seat back and adjustedto

the proper height for a 50th-percentileoccupant. Parts of the headrestpreviously needed for adjustmenthave been removed. Also, since only a 50thpercentileoccupantwas used, the range of support providedby the headrest

could be reduced in the verticaldirection. As in the existingseat, the headrest is still mounted to the seat back with a sliding rectangulartube-in-tube

19
HEADR_

INERTIA

SEAT BACK_,_

TUBES

SECTION Z- Z

;y

ABSORBERS

s

I

SEAT PAN

ASSEMBLY

r--] .......

:Q:

' I

Figure 13. Energy-absorbing test seat.

20
Figure 14. Front view of energy-absorbingtest seat.

Figure15. Side view of energy-absorbingtest seat.

21
Figure 16. Back view of energy-absorbingtest seat.

arrangement. The heightof the headrestis fixed by a bo]t througheach set

of tubes. Rotationa]movementof the headrestis preventedby an aluminum

bracket. The headrest surfaceis fixea parallelto, and is 1-1/4 in. in front

of, the seat back tangent line.

The seat pan and seat back assembliesare mounted to the heat-treated4130

steel guide tubes. At the bottomof the seat, an aluminumfittingconnects

the guide tubes to the seat pan and seat pan tray. Another fitting,located

about halfway up each of the guide tubes, joins the guide tubes to the seat

back. Behindthe seat back, an a|uminumtube runs across the seat and is riveted to each of these fittings,definingthe distancebetween the guide tubes.

Also, from each fitting,a tube runs diagonallyforwardand down to a point

approximately1 in. in front of the buttocksreferencepoint. The upper fitting on the diagonal tube supportsa rod end to re]ease the top of this tube

from benaing loads. The bottom of the diagonaltube is riveted to a fitting

that is bo]ted throughboth the seat pan and the seat pan carriage. The triangular truss formed by the diagona]tube, seat pan carriage,and the guide

tube supportthe loads applied to the seat pan by the occupant.

22
The power haul-back inertia reel is mounted to the top of the guide tubes.

With the inertia reel cantilevered at the top of the guide tubes, the guide

tubes are subjected to high bending moments. The guide tubes serve as races

for the four linear roller bearing assemblies. Each bearing assembly contains

four contoured rollers located at 90-degree increments to surround the guide

tube. This assembly minimizes friction during the vertical energy-absorbing

stroke while still transferring loads to the bulkhead.

Two energy absorbers, which restrain the seat bucket in its vertical position,

are attached to fittings at the rear of the seat pan. The top of the attenuators are connected by a fitting that attaches to the clevis provided on the

bulkhead for the existing F-Ill seat vertical adjustment mechanism. The

test seat uses energy absorbers sized for the 50th-percentile occupant.

The cushions presently used on the F-111 seat are also used on the test seat.

Someof the headrest cushions are cut to fit the modified headrest; however,

the cushioning effect for the occupant's head is the same.

The restraint system on the test seat is that presently used on the F-Ill aircraft. It was described in Section 2.1.2, and has a five-point rotor-release

buckle with tiedown strap, lap belt, and shoulder straps. The shoulder straps

attach to a yoke that sits around the back of the occupant's neck. Straps from

the inertia reel pass through fittings on the yoke and back to the upper guide

tube fittings on the opposite side, not to the points on the seat back that are

used by the operational seat. Since the inertia reel and the reflection strap

anchor points are mounted to the upper guide tube fittings, the restraint system

moves with the occupant during the energy-absorbing stroke of the seat.

The weights of the various seat parts are listed in Table 4. Since the test

seat was made using as much of the existing seat as possible, it is much heavier than a retrofitseat would be.

TABLE4. WEIGHTOF TEST SEAT

Item Weight Ilb)

Seat Pan Assembly 19.2

DiagonalStrut Assembly 1.0

Seat Back 6.2

Guide Tubes 10.1

Headrest 4.7

Mid-Cross-TubeAssembly 1.5

InertiaReel Fittings 2.6

InertiaReel 7.4

RestraintSystem 4.0

Cushions 2.0

Roller Bearings 2.4

AttenuatorAssembly 1.9

TOTAL 63.0

23
2.4 SEATPANLOADCELLS

During the time that the concepts for a retrofit seat were being examined, it

was decided to also conduct some of the planned tests with the operational

F-Ill seat. The seat pruvided by the Air Force was an operational F-Ill seat

modified to incorporate seat pan load cells. In order to provide corresponding data during testing, one of the energy-absorbing test seats was also

modified to incorporate seat pan load cells.

2.4.1 Nodified Operational Seat Pan

Figure 17 shows a picture of the modified operational F-Ill seat pan. The majority of the seat pan material between the side rails has been cut away. At

the back of the seat pan, the seat back and lap belts are still attached in

the same manner. At the front of the seat pan, the crotch strap is attached

in the same manner as on tne operational F-111 seat. Horizontal and vertical

adjustment has not been changed by the modification.

The modified seat pan assembly is divided into upper and lower portions. The

lower portion, really the seat pan support, has two aluminum plates running

between the side rails. The rear plate has mounting provisions for one vertical load cell and two strain-gaged load links, which measure horizontal loads.

The front plate has mounting points for two vertical load cells and one load

link. The other end of each of the three load links is attached to the upper

portion of the new seat pan assembly. This upper part has really become the

new seat pan, and has the same foam core fiberglass-covered contour as all

operational F-Ill seats. However, the bottom consists of a I/2-in.-thick aluminum plate. The load links attach to fittings that are threaded into holes

in this plate.

When ass_ib]ed, the seat pan sits on the three load buttons of the vertical

load cells mounted in the seat pan support. Hard points have been added to

the bottom of the seat pan to reduce wear. The load links were used _n the

assembly, since they prevent the seat pan from sliding off the vertical load

cells; however, they were not used during the program to measure horizontal

loads. The weight of the seat pan sitting on the load cells is 12.45 lb.

2.4.2 Modified Enerqy-Absorbin_ Seat Pan

An energy-absorbing test seat was modified in much the same way as the operational seat. Figure 18 shows how the same material between the side rails

was ren_ovedand replaced with two machined plates. The crotch strap is attached in the same manner as on the operational seat. As is the case with the

other test seats, horizontal adjustment of the seat pan is not provided.

With respect to the seat reference point, positions of the vertical load cells

in the test seat are the same as in the modified Air Force seat. Since horizontal loads were not required, simpler load links were used. Other changes

included provisions for accelerometers on the rear plate and different load

buttons to provide easier adjustment and assembly.

24
Figure 17. Operationalseat pan modified to incorporateseat

pan load cells (Reference3.)

Figure 19 shows bottom and top views of the seat pan. The 5/16-in.-thickaluminum p|ate is bonded to the bottom of the F-111 contouredfoam and fiberglass

seat pan. The three fittings in the bottom view are the attachmentpoints for

25
Figure 18. Modificationof test seat to incorporateseat pan load ce||s.

the load links. Fittingsto reduce surfacewear were not needed at the points

of contactwith the load cell buttons because of the limiteduse of this seat.

This modificationto the seat, includingthe weight of the load cells, increased the total weight of the test seat by 13.4 lb. The seat pan sitting on

the load cells weighs 9.10 lb.

26
a. Bottom view

b. Top view

Figure 19. Seat pan from test seat that incorporates

seat pan load cells.

27
3.0 SEATTESTING

Dynamic testing of the Simula energy-absorbingseat and the operationalF-111

seat was conductedat the FAA Civil AeromedicalInstitute(CAMI) in December

1983and March, 1984.

3.1 TEST OBJECTIVES

The primary objectiveof the dynamic testing done at CAMI was to demonstrate

the energy-absorbingcapabilityand structuralintegrityof the seat when subjected to ]oads within the design envelopeof the possib]eground impactconditions. The decisionto study ground impactconditionswas based on the discussion in Section 2.2.1 of the injurypotentia]during ejectionand ground impact.

The second objective of these tests was to provide data for a comparison of

the existing F-Ill seat and an energy-absorbing seat. Three tests were conaucted in which the operational F-Ill seat was subjected to the same acceleration pulses as the energy-absorbing seat.

3.2 CONDUCTOF TESTING

3.2.1 Test Faci]ity

The CAMI test facility uses a sled guided along a set of horizontal rails while

being accelerated by a cable attached to a falling weight. The load from the

failing weight is removed, leaving the sled traveling at an essentially constant velocity just prior to the sled being decelerated by a wire bending mechanism. As shown in Figure 20, the wires are stretched across the track and

pulled through dies when impacted by the sled. The number and location of the

wires is varied to produce the proper pulse shape.

3.2.2 Test Methods

The fixture mounted on the sled in Figure 21 was provided by the Air Force.

Two standard (without seat pan |oad cells) energy-absorbing seats were provided

for the test series, but only one was used. A third energy-absorbing seat, modified to incorporate seat pan load cells, was used only in the tests where the

vertical seat pan loads _#ere recorded. Modifications to the fixture, necessary

for mounting the energy-absorbing seat, were provided by Simula and incorporated by CAMI personnel.

For each test, the fixture was oriented on the sled to provide the proper velocity change in all three axes of the seat. Just prior to each test, the inertia reel straps were pre]oaded to between i0 and 15 ]b. The arms were placed

in the position presently recommended by the U.S. Air Force: extended with

the hands on the knees. Input velocity was determined from the time it took

the sled to break successive light beams in a velocity trap placed just before

the wire-bending mechanism. Accelerometers on the sled measured the shape and

peak of the deceleration pulse.

28
(a) Sled and wires prior to test

(b) Wires followingtest

Figure 20. CAMI wire-bendingdeceleratormechanism.

29
Figure 21. Test fixture used in dynamic seat testing at CAMI.
The seat performance was monitored by various instruments:

• Accelerometers

- Seat pan, triaxial and a|ong back tangent line, four

channels

- Dummy

-- Pelvis, triaxial, three channels

-- Chest, triaxial, three channels

-- Head, triaxial, three channels

- Test fixture, triaxial (seat axes), three channels

- Sled, forwara (parallel to velocity vector), two channels

• Load Cel I s

- Restraint system webbing tensiometers, lap belts and inertia

reel straps, four channels

- Restraint system strain-gaged end fittings, inertia reel

straps, two channels

- Seat pan, vertical, three channels

- Dummyspine, triaxial, six channe|s

- Footrest, triaxial, three channels

• String Potenti ometer

- Seat stroke along guide tubes, one channel

Still photographs (Figures 22 and 23) were taken to document the pre- and posttest conditions of the test items, while high-speed motion pictures recorded

the dynamic response of the test artic|es.

3.2.3 Test Iv_atrix

Botll the seat testing conducted at CAMI, and the capsule testing conducted

later at NASALangley Research Center, were designed to evaluate the performance of the energy-absorbing seat over the ful| design envelope of ground impact conaitions. Therefore, both test matrices considered the following variables for the ground impact conditions:

• Wind velocity (0-20 knots)

• Wind direction (+180 degrees)

31
Figure 22. Energy-absorbing seat prior to CAMI test.
w

~)

Figure 23. Energy-absorbing seat after CAMI test.
• Parachuteoscillations(±10 degrees)

• Landing surfaceslope (±5 degrees).

The verticaldescent rate was always 32 ft/sec.

Eight tests were defined for the capsule series using the previousparameters,

and are discussedin detail in Section 4.2.3. During seat testing at CAMI,

seven of these eight impactconditionswere simulated. The conditionswere

simu]atedby placing the seat on the test sled at CAMI with the same orientation to the velocityvector that the seat would have in the corresponding

NASA capsule test. In this orientationthe seat was subjectedto an estimate

of the accelerationpulse in the correspondingcapsule test. Thus, the variables for the seat testingwere the seat (whetherthe operationalF-111 seat

or the energy-absorbingseat), the seat orientationto the velocityvector,

and the accelerationpulse. Table 5 presentsthe test matrix for the 13 dynamic tests conducted. For convenience(or comparison),column one lists the

NASA test numbers presentedin Section4.0. TileCANI tests in column two were

designedto be as similar as possibletothe NASA tests listed in column one.

Table 5 also lists the seat orientationsfor each test. Although the orientationof the seat and occupantto the velocityvector is basicallythe same

in correspondingCAMI aridNASA tests,some roundingoff in seat orientation

measurementswas permittedto reduce the number of test fixturesrequired.

However,even with these simplifications,velocitycomponentsalong the major

axes of the seat were always within 5 percent of the correspondingideal cap- sule test.

The characteristicsof the test accelerationpulses are given in Table 6, and

the notation used is defined in Figure24. The accelerationpulses were designed to be as similaras possibleto the module bulkheadaccelerationpulses

expectedduring actual ground impacts. Estimateswere made using Air Force

data from capsule ejection tests conductedat HollomanAFB in New Mexico. Tests

such as these are normallyconductedonly under low wind conditions. Indeed,

films of the tests show the capsule landingunder relativelymild conditions

with respect to previouslylistedparameters. In spite of this, the data was

the best available,and was thereforeused as a startingpoint in estimating

the bulkheadaccelerationpulseseven for the extremeconditionsthat were being

tested. The velocitychanges in the test pulseswere the same as the impact

velocitiesto be used in the crew module tests. This was done since no module

reboundwas evident in the referencedata. The onset rates and peak accelerations were also similar to the referencedata. The differencein pulsesthree

and four was a judgementbased on expectedchanges in IAB efficiencywith changes in aircraftattitude.

3.2.4 AccelerationPulse Characteristics

Table 7 presentsa comparisonof the measuredtest pulsesto the test pulse

descriptionin Table 5. Ratherthan tabulatethe values of T_ and T_, the

range of onset rates defined by T and T_ is listed in columni4of T_ble 7.

The onset rate for the n_easuredp_Ise wa_ determinedusing an approximation

techniquedescribedin Reference11.

34
TABLE 5. SEAT TEST FIATRIX

NASA CAMI

Test Test Pulse Seat Orientation(deg)

Number Number Seat(1) Number Pitch Ro|! Yaw

1 A83-110 E/A 3 40 0 30

2 A83-106 E/A 4 0 30 90

4 A83-108 E/A 3 60 0 45

5 A83-111 F-111 4 70 0 30

A83-109 E/A 4 70 0 30

A84-83 E/A 4 70 0 30

6 A83-113 F-111 2 40 0 0

A83-103 E/A 2 40 0 0

A84-81 E/A 2 40 0 0

7 A83-I04 E/A 2 -30 0 180

8 A83-112 F-111 1 90 0 0

A83-101 E/A 1 90 0 0

A84-82 E/A 1 90 0 0

(1) E/A refers to energy-absorbingseat, F-111 refers to operationa]seat.

TABLE 6. TEST ACCELERATIONPULSE DESCRIPTION

Pulse _v T1 T2

Number (ft/sec) (sec) (sec) GMin GMax

i 32 .040 .046 16 18

2 53.6 .053 .061 23 25

3 46.7 .043 .048 23 25

4 46.7 .049 .056 22 24

35
TIME (SEC)

Figure24. Definitionof notationused in test pulse description.

Despite the sma]l rangesdefined for onset rate and peak accelerationin the

definitionsof the test pulse, the largemajority of the test pulse characteristicsfell within the specifiedvalues. The most importantparameter,the

velocitychange, was held within 1 ft/sec of the specifiedvalue in every test

except A84-81. Peak accelerationswere within or slightlyabove the specified

ranges. Some variationsin the onset rates (TestsA83-112,A83-113,and A84-81)

are noticeable. However,the test pulseswere defined based on the available

data, obtainedunder conditionsdifferentfrom that which was being simulated.

Therefore,the measured test pulseswere certainlywithin the precisionnecessary to providean estimateof the capsule environment.

3.3 PERFO_4ANCEOF THE ENERGY-ABSORBINGSEAT

Three main factors are involvedin eva|uatingthe performanceof the energyabsorbingseat: accelerationlevels,strokingdistance,and structuralinteg- rity.

36
TABLE7. INPUT ACCELERATIONPULSESFORDYNAMICSEATTESTING(I)

NASA CAMI Ideal Pulse Measured Pulse

Test Test _v Onset Rate Peak _v Onset Rate Peak

Number Number I Ft/sec) (G/sec) (G) (Ft/sec) (G/sec) (G)

1 A83-110 46.7 480-580 23-25 47.1 567 25.1

2 A83-I06 46.7 390-490 22-24 46.4 486 23.0

4 A83-108 46.7 480-580 23-25 45.9 556 24.6

5 A83-111 46.7 390-490 22-24 46.9 455 25.7

A83-I09 46.7 390-490 22-24 46.8 473 26.2

A84-83 46.7 390-490 22-24 46.7 433 23.5

6 A83-I13 53.6 380-470 23-25 54.5 329 27.6

A83-103 53.6 380-470 23-25 54.4 478 26.9

A84-81 53.6 380-470 23-25 54.8 514 25.7

7 A83-I04 53.6 380-470 23-25 53.1 449 26.7

8 A83-I12 32 350-450 16-18 31.9 521 17.7

A83-I01 32 350-450 16-18 32.3 415 19,5

A84-82 32 350-450 16-18 32.3 401 17.7

(I) Data filtered with class 60 filter per SAE RecommendedPractice SAE J211b.

3.3.1 AccelerationLevels

Table 8 presentsfour of the peak accelerationsmeasuredduring each test of

the energy-absorbingseat. Both the seat-pan-zand seat-back-zaccelerometers

were mounted on the bottom of the seat pan. The seat-pan-zaccelerometermeasures pure verticalaccelerationswhile the seat-back-zaccelerometermeasures

accelerationsalong the seat back tangent line. The pelvis and chest accelerometers are mounted inside the dummy.

The seat pan accelerations,both verticaland along the seat back tangent line,

are the most commonly used measurementsfor evaluatingseat performance. These

peak accelerationvalues, ranging from 16.8 to 27.3 G, are well within the

37
TABLE8. PEAKVERTICALACCELERATIONSMEASUREDONSEAT PANDURING

ENERGY-ABSORBINGSEATTESTINGAT CAMItl)

NASA CAMI Accel erometer Orientation

Test Test Seat Back

Number Number Seat Pan z (G1 Tangent Line Pelvis z (G) Chest z (G)

i A83-II0 21.7 23.9 21.7 22.1

2 A83-i06 21. I 20.9 15.4 15.8

m _ Q m B

4 A83-I08 21.8 23.6 27,1 25.5

co

5 A83-I09 22.2 24.3 25.8 24.0

A84-83 22.9 23.4 27.5 27. i

6 A83-I03 24.6 27. i 24.4 24.4

A84-81 20.6 27.3 27.1 23.1

7 A83-I04 21.1 16.8 18.1 16.3

8 A83-101 21.3 22.0 23.7 23.3

A84-82 21.3 19.9 26.3 22.5

(1) Data filteredwith c|ass 180 filter per SAE RecommendedPracticeJ211b.
range of values that would be expected with an energy-absorbing seat. The pelvis and chest accelerations tend to be slightly higher due to the dynamic amplification effects of the dumn_ as it compresses into the seat pan during the test.

A typical seat pan acceleration trace from the test series is shown in Figure 25.

The shape of the seat pan acceleration curve is most easily explained under

the conditions when the seat and occupant are being subjected to a purely vertical crash test. Initially,the seat and occupantare travelingdownwardat

the same constantvelocitywith littleor no loads being transferredbetween

the occupantand the seat. The cushion,fleshy parts of the buttocksand torso, and the spine are uncompressed. When the aircraftstrikes the ground, an

upward accelerationis applied through the floor and seat structureto the seat

pan. This is shown by the increasingaccelerationbetween 20 and 40 msec.

At the time the accelerationsstart to increase,the occupant is not applying

a significantload to the seat pan. However,the cushion and fleshy parts of

the buttocks,as well as the torso and spine, start compressingas the accelerations continue to increase. The greater the compressionof these elements,

the higher is the load applied to the seat by the occupant. Thus, the seat

pan is now being acted upon by two forces: the upward loads,or accelerative

forces transferredthrough the seat structure,and the downward loads applied

by the occupant. However,the upward loads are transferredthrough the energy

absorbersand are thereforelimited in magnitude.

One can see in Figure 25 that after the initial peak is reached,there is a

small notch in the accelerationpulse around 50 msec. This is caused by a significant downward load applied to the seat pan by the pelvis. The cushion and

fleshy part of the buttocksare compressedand the pelvis starts experiencing

essentiallythe same decelerationas the seat pan. At this time the spine and

torso have not yet fully compressed. In this case the added load from the pelvis is not enough to start strokingthe seat. The accelerationsdrop for a

short time, but the applied accelerationscontinueto increaseand again start

driving the accelerationsupward.

This notch after the initial spike will not occur in all tests or with all

seats. The three main factors influencingthe shape of the pulse in this area

are the strokingweight of the seat, the peak accelerationlevel,and the rate

of onset of the accelerationpulse. For instance,if the strokingweight of

the seat is heavy, such as with an armored bucket, and the onset rate of the applied pulse is steep enough, accelerationlevelson the bucketwill get high

enough to stroke the seat before the occupanthas fully compressedthe cushion.

Obviously,other factors such as the cushion stiffness,seat pan stiffness,

and anthropomorphicdummy propertiesare continuouslyinfluencingthe shape of

the pulse.

Figure 25 shows another peak around 60 msec followedby a sharp drop in the

accelerations. It is at about the time of this peak that strokingstarts.

The energy absorbersare limitingthe load applied throughthe floor to the

seat structurewhile the spine continuesto compress,applyingmore and more

downward load to the seat pan. This increasingload applied by the occupant

drives the seat pan accelerationsdownward. Eventuallythe accelerations

drop to what is called the initial notch (70 msec). At this point the load

applied to the seat by the occupant is the greatest. It is also around this

39
0 i I I I I

o

<D

A83-101

32 _

o

o

24

z

0

_ 8

w

"' _ ,IL _ L. ,_ h ,. __

N

Z -8

a.

< -16 -

-24 -

-32 i , , I i

0 50 100 150 200 250 300

TIME (MSEC)

Figure 25. Seat pan vertical acceleration trace from

CAMItest of energy-absorbing seat.
time that the compression on the spine reaches its first maximum. The exact

time of maximumspinal load depends on the phase relationship between the head,

torso, and pelvis. The dynamics of the pulse, as well as the application of

loads in directions other than vertical, may cause the loads in different

parts of the dummyto peak at different times.

After the initial notch the acceleration starts rising again. This is due to

the rebound of the occupant off the seat pan. Up until this point in the crash

the body has been compressed down towards the seat pan. Now some of the body

is acting like a spriny, such as a ball thrown against the ground acts, and is

pushing up away from the seat pan. As the occupant rebounds, the downward load

he applies to the seat decreases and the steady load applied through the energy

absorbers causes the accelerations to rise to the secondary spike. After the

secondary spike the spine ana buttocks again start to compress and apply more

downward load to the seat pan, causing the accelerations to drop.

If the applied pulse were severeenougllto continuestroking,one would see

the accelerationlevelcontinueto oscillatewith decreasingmagnitudeuntil

it steadiedout at the energy absorberlimit load. In this case however,the

test input is not that severe. Strokingstops after approximately110 msec

and the accelerationsdrop down to O.

Accelerationsalony the seat back tangent line will have a shape similar to

the seat pan z-axis acceleration. However,dependingon the directionof the

applied load, the magnitudesof the accelerationsalong the back tangentwill

be differentfrom the pure verticalaccelerations. In most of the tests presented in Table 8, the seat orientationwas such that the load vectorwas more

in line with the seat back tangent line than with pure vertical. Thus the magnitudes of the accelerationsseen along the seat back tangent line are greater

than the accelerationsalong the seat pan z-axis.

Qualitatively,the accelerationtrace shows the seat to be performingin the

expectedmanner. As a more quantitativeevaluation,the seat pan accelerations

will be compared to the U.S. Army requirements for crashworthy crewseats presented in MIL-S-58095(AV) (Reference 14). Figure 26 shows the maximumacceptable duration-magnitude curve reprinted from FIIL-S-58095(AV). This curve is

based on data gathered by Eiband (Reference 15). Violations of the curve into

the area of injury occur when the acceleration levels are at least 23 G for

greater than .006 sec.

There are several deficiencies with this current criterion. One problem is

that the flexion of the upper torso, which can be a major contributor to spinal

injury, is not considered when examining the seat pan accelerations. However,

occupants of the F-Ill are pulled back into their seats by power-haul back inertia reels before the crew module blasts away from the aircraft. The upper

torso flexion would be much less in the F-Ill than in, for example, a helicopter pilot who was bent over the cyclic or collectivesticks tryingto maneuver

the aircraftwhen it crashed.

A major problem _ith the Eiband curve is simply that it uses only the maximum

seat pan accelerations as a measure of injury potential. From the discussion

of the seat pan acceleration plot in Figure 25, the maximumaccelerations do

not occur when the load on the spine is the highest, but when the lowest loads

are transmitted by the occupant to the seat. Therefore, the Eiband curves can

at best be considered an empirical tool.

41
!!jj!i!!i !IIIi!,

'''Ji f!i! 0 80,

0

40 OF I U I IJ

<_. I \lllll lil

U

"'

23O AREAl,l I OFII,J ] ACCEPTABLE MAXIMUM ' II ilJ! ACCEPTABLEPULSE DURATION-MAG NITUDE J

.<

DURATION-MAG NITUDE CURVE "" I0 O

-_ ,, I J

_ 8 [ II

6 _ .' i Jill ,

0 !

' ' MAGNITUDE u.I I

IIl'I

_ 2 j , Q

1

.001 .002 .004 .006 .01 .02 .04 .06 .I .2 .4 .6 .8 I 2 4 6 8 I0

DURATION OF UNIFORM ACCELERATION - SEC

Figure 26. Acceptable duration-magnitude curve for seat pan

acceleration levels (Reference 14).
Finally, problemshave occurredin the interpretationof the Eiband curves.

Figure 27 shows a seat pan verticalaccelerationmeasuredduring qualification

testing to MIL-S-58095(AV)of an energy-absorbingseat. These multiple spikes

obviouslyraise the average accelerationabove 23 G for more than .006sec.

The natural frequencyof the human body is too low to respond to each of these

inoividualspikes. It would respond,however,to the average of these spikes,

which is obviouslyover 23 G for more than .006 sec. However,this seat would

be judged to be in accordancewith MIL-S-58095(AV)since none of the individual

spikes violatesthe criterion. This interpretationimpairsthe use of Eiband's

work even as an empiricaltool.

With these factors in mind, Table 9 presentsthe durationsduring which the

seat pan verticaland seat back tangent lineaccelerationswere above 23 G.

The maximum time above 23 G, detemined using average accelerationsas well as

individualpeaks,was recorded. Since only the verticalaccelerationsare

used in MIL-S-58095(AV),this seat would easilymeet the criterion. Because

of the seat orientationsduring the testing,accelerationsalong the back tangent line tended to be higher. In only one case, A84-81, Eiband'scriterion

was violatedas the accelerationlevel remainedabove 23 G for .017 sec.

Also presentedin Table 9 are the values of the Dynamic ResponseIndex (DRI).

The DRI uses a single lumpedmass, damped spring systemto model the human body.

The accelerationcurve for which a DRI is being detemined is used as input to

the model. The maximum deflectionof the spring,multipliedby a factor, is

used as the DRI for that curve. The deflectionof the spring is related to

the deflectionof the spine; thus, the higher the DRI is, the greater the potential is for injury. A typical DRI measurementfor the energy-absorbing

seat is presentedalong with a seat pan accelerationused as input in Figure 28.

Presentedearlier in Figure 5 is the correlationmade for ejectionseats between the DRI and the spinal injuryrate. Differencesin pulse duration,onset rate, and the seat motion make the environmentin an energy-absorbingseat

differentfrom the environmentin an ejectionseat. At this time no data correlating DRI to spinal injuryrate in an energy-absorbingseat are available.

Figure 29 is reprintedfrom Reference13 to show what magnitudeof DRI values

can be expectedfrom an energy-absorbingseat. The change in DRI with respect

to a change in energy absorber load is not very steep. An energy absorber

load of 14.5 G correspondsto a DRI of approximately20.

Table 9 shows that the DRI's measured along the seat pan verticalaxis are all

less than 20. Valuesof the DRI along tileseat back tangent line are, as would

be expected from the seat orientations,slightlyhigher than the verticalDRI's.

However, all but one is in the expectedrange. The pelvis DRI's, as were the

pelvis peak accelerations,tend to be higher than the values measuredon the

seat pan.

The DRI tends to smooth out the sharp peaks that can cause inconsistentdifferences between the peak measurementsof seat pan and pelvisaccelerations.

The result is pelvisDRI's that are consistentlya few points higher than the

seat pan bRI's. This is best seen by examiningFigure 30. The pelvis DRI's

show the greatestdifferencefrom the seat pan DRI's in Test Numbers A83-I01

and A84-82. That is becausethe seat was lying on its back (Figure31) for

this test and the dummy was not preloadingthe cushion as well as in other

tests. Because of this the dynamic amplificationeffects noticeablyraise the

43
-30 ! ! ! !

0 .040 .080 .120 .160 .200

TIME (SEC)

Figure27. Seat pan accelerationmeasuredduring qualificationto MIL-S-58095.

pelvis acce]eration|eveland the resultingDRI value. One DRI va]ue is inconsistent with the other valuesmeasuredduring testing. The seat back tangent

line DRI test for A84-81 is higherthan would be expected. However,this DRI is

inconsistentwith seat pan and pelvisDRI values from the same test, as well

as the pattern of measurementsin other tests. At this time it is not clear why

this va]ue is so much higher than the correspondingvalue in Test NumberA83-103,

where the test conditionswere the same.

44
TABLE9. EIBANDAND DYNAMICRESPONSEINDEXEVALUATION

OF ENERGY-ABSORBINGSEATTESTINGAT CAMI

DurationAbove

NASA CAMI 23 G (secI Dynamic ResponseIndex

Test Test Seat Seat Back Seat Seat Back

Number Number Pan z Tangent Line Pan z TangentLine Pelvis z (G1

1 A83-110 0 0.002 14.9 19.7 23.4

2 A83-106 0 0 18.9 17.3 14.8

4 A83-108 0 0.001 16.3 19.5 22.3

5 A83-109 0 0.004 18.2 20.7 24.6

A84-83 0 0.002 18.1 19.9 22.5

6 A83-103 0.002 0.006 17.6 21.6 24.9

A84-81 0 0.017 17.0 26.1 24.5

7 A83-104 0 0 16.0 10.6 13.4

8 A83-101 0 0 18.6 18.4 24.2

A84-82 0 0 17.2 16.2 23.7

3.3.2 Energy-AbsorbingStroke

Tab]e 10 lists the verticalenergy-absorbingstrokemeasured in each of the

seat tests. The measuredstroke was the verticalmovementof the seat reference point. Preliminarylayoutshave shown that a retrofitseat would have an

availablestrokingdistanceof 6 to 11 in., dependingon vertical seat

position. In all cases the strokemeasuredwas less than the minimum stroke

that would be availab|e.

If the requiredstroke is more than the availablestrokingdistance,the seat

will hit the floor before the impactenergy has been dissipated. This will

mean an increasein the |oads to which the occupantis subjectedand producea

spike on the seat pan accelerationplots. If significantenergy is remaining

in the impact pulse, the loads created by "bottomingout" can be injurious.

3.3.3 StructuralInteBrity

No structuralfailuresof any seat parts occurredduring the test series.

45
0 . s !

A

(_

Z

0 32 A84-083

oO

G: o

LU ,_

"LU_ 24 ACCELERATION

N 16

z

Q.

_- 8

ILl

o_

0

!

nr_ 8

16 I I |

0 50 100 150 200

TIME (MSEC}

Figure 28. Seat pan accelerationand correspondingDRI for energy-absorbing seat.

Periodicmaintenanceof the seats during testing consistedof replacingstroked

energy absorbers,and also roller bearingsand bearing bolts (Figure32) when

necessary. Dependingon the directionof the applied loads, the roller bearings

may be subjectedto very high loads in bearingagainst the guide tubes. Even

while supportingthese loads,they must roll freely so that the seat strokes

with a minimum of frictionalresistingforce. After a few tests there is a

tendencyfor a roller to turn less smoothlydue to minor damage to the roller

or the bolt that supportsit. In either case, the part was replaced. This

type of wear would cause no trouble in the field since it only occurs under

very high loads such as during a ground impactafter ejection.

3.3.4 Conclusions

Certain conclusionscan be reached based only on the performanceof the energy- absorbingseat.

• The seat pan verticalaccelerationlevels and the correspondingDRI's

show the energy-absorbingseat to be functioningproperly.

46
15

I

n.-

10

Least-Squares Approximation

5 AV=45 FT/SEC DRI=0.403 LL+13.9

Gp=40 G R= 0.736

0 I I I I I

6 8 10 12 14 16 18

EFFECTIVE LIMIT LOAD FACTOR, L L (G)

Figure29. Dynamic ResponseIndex as a function

of energy absorberlimit load.

• It has been estimatedthat if an energy-absorbingretrofitseat is

placed in the F-111 capsule,the availablestrokingdistancewill

range from 6 to 11 in., dependingon vertical seat position. In

every seat test the measuredstroke was less than the minimum available stroke.

• The seat sufferedno structuraldamage. Therefore,it was reasonable

to assume that the seat is suitablefor capsule testingat NASA Langley ResearchCenter.

3.4 COMPARISONOF OPERATIONALANDENERGY-ABSORBINGF-111 SEATS

Three of the test conditions were run with both the operational F-Ill seat and

the energy-absorbing test seat. In each case two tests were conducted with

the energy-absorbing seat and one test with the operational seat. The second

set of energy-absorbing seat tests, A84-81, -82, and -83, were conducted after

seat pan load cells had been incorporated into the design.

Three major factors will be used in comparing the two seats. First, the vertical acceleration levels, including seat pan, seat back, pelvis, and chest,

will be examined. Secondly, vertical loads measured by load cells placed under

the seat pan will be compared. Finally, spinal load and moment measurements

from a load cell placed inside the dummywill be presented.

47
CAMI TEST NO.O" A83-110 A83-106 A83-108 A83-109 A83-103 A83-104 A83-I01

A84-83 A84-81 A84-82

NASA TEST NO. 1 2 4 5 6 7 8

0 • SEAT PAN Z-AXIS

A A SEAT BACK TANGENT LINE

[] [] PELVIS Z-AXIS

VALUES OF DYNAMIC RESPONSE If'!DEX RECORDED DURING CAMI TEST SERIES.

Figure 30. Dynamic Response Index measurements from

energy-absorbing seat tests at CAHI.

3.4.1 Acce|eration Levels

The first comparisons between the seats was done using the same measurements

that were used to evaluate the performance of the energy-absorbing seat: peak

acceleration levels in the vertical direction.

Table ii presents the peak accelerations for the seat pan z-axis, seat back

tangent line, pelvis z-axis, and chest z-axis. Figures 33 through 36 present

the same information in graphical form. One can see that the peak accelerations

for the energy-absorbing seat were below those for the operational seat in

every case but one. This one case is the seat back tangent line for Tests

A_3-112 and -101, where both accelerations peaked at 22.0 G. In some cases

the differences were not great, but they were significant and consistent.

The shape of the seat pan z-axis acceleration traces for both the energyabsorbing seat and the operational seat in similar tests are shown in Figures 37

through 39. Both traces follow the same path, rising steadily, for the first

30 to 40 msec. Whenthe energy-absorbing seat starts to stroke, its seat pan

acceleration drops off rapidly. However, the operational seat pan accelerations

continue to rise slightly and then level off. After remaining at this level

for 35 to 45 sec., the operational seat pan accelerations drop back to O.

48
Figure 31. Pretest photograph from CAMI Test No. A83-101.
TABLE10. STROKEMEASUREDIN CAMI SEATTESTS

NASA CAMI Stroking

Test Test Distance

Number Number . (in. 1

i A83-II0 2.1

2 A83-I06 0

_ _

4 A83-108 1.8

5 A83-109 5.1

A84-83 5.4

6 A83-103 4.35

A84-81 3.95

7 A83-104 0

8 A83-101 2.9

A84-82 2.9

In the other case, after the energy-absorbing seat pan acceleration drops to

zero, it rises again to a value equal to or slightly higher than the initial

peak. As discussed earlier in Section 3.3.1, the acceleration levels will now

oscillate while steadi]y decreasing to the energy absorber limit load. However, before much oscillation occurs in this case, the acceleration drops back

to O.

One can see that while the peak levelsfor the energy-absorbingseat are lower,

it is on|y by a matter of 2 to 4 G. What is more significantis that the energyabsorbingseat spreads the accelerationsout over a longer time period. The

area under these curves representsthe total velocitychange seen by the seat

and occupant,and since the input conditionsfor these two tests were the same,

the area under tilecurvesmust be equal. The accelerationtrace for the energyabsorbingseat satisfiesthis requirementby lastinga longer time. The energyabsorbingseat subjectsthe occupantto the velocitychange over a .015to .020

sec longertime periodthan the operationalseat. This lengtheningof the

pu|se reduced the loads seen by the occupantand is reflectedin the differences in the DRI's recordedfor the two seats. Table 12 presents the DRI's

for the seat pan and pelvis accelerations. The seat pan accelerationsproduce

DRI's that are 6 to 11 points lower for the occupantof the energy-absorbing

seat.

50
{D

3

0

_0

0

oO

Figure 32. Bearing assembly,rol]er,and bolt from energy-absorbingseat.

TABLE 11. COMPARISONOF PEAKACCELERATIONSMEASUREDON OPERATIONAL(F-111)

AND ENERGY-ABSORBING(E/A) SEATS IN CAMI TESTS

NASA CAMI Peak Acceleration(G)

Test Test Seat Seat Back

Number Number Seat Pan z Tanqent Line Pelvis z Chest z

5 A83-111 F-111 26.9 28.2 34.4 33.4

A83-109 E/A 22.2 24.3 25.8 24.0

A84-83 E/A 22.9 23.4 27.5 27.1

6 A83-113 F-111 27.3 30.6 30.1 32.2

A83-103 E/A 24.6 27.1 24.4 24.4

A84-81 E/A 20.6 27.3 27.1 23.1

8 A83-112 F-111 23.1 22.0 32.6 30.6

A83-101 E/A 21.3 22.0 23.7 23.3

A84-82 E/A 21.3 19.9 26.3 22.5

51
0 • ENERGY-ABSORBING SEAT

OPERATIONAL SEAT

,---,.,, AVERAGE OF TWO ENERGY-ABSORBING SEAT TESTS

1) CORRESPONDS TO NASA TEST NO. 5

2) CORRESPONDS TO NASA TEST NO. 6

3) CORRESPONDS TO NASA TEST NO. 8

40

o

o

,_ 30 - _

Z

0 "

LU

-- (

0

u

< () --...

< """_)0

UJ q

" 20 -

10

CAMI TEST NO _ A83-111(1) A83-113(2) A83-112(3)

O A83-109 A83-103 A83-101

• A84-83 A84-81 A84-82

Figure 33. Seat pan z-axis accelerationlevels from energy-absorbing

and operationalseat tests at CAF)I.

52
0 • ENERGY-ABSORBING SEAT

OPERATIONAL SEAT

AVERAGE OF TWO ENERGY-ABSORBING SEAT TESTS

1) CORRESPONDS TO NASA TEST NO. 5

2) CORRESPONDS TO NASA TEST NO. 6

a) CORRESPONDS TO NASA TEST NO. 8

40 _

t'N

o

o

10

CAMI TEST NO. _ A88-111 (1) A83-113 (2) A83-112 (3)

0 A83-109 A83-103 A83-101

• A84-83 A84-81 A84-82

Figure 34. Peak acceleration levels along the seat back tangent line

for energy-absorbing and operationa] seat tests at CAMI.

53
0 • ENERGY-ABSORBING SEAT

Z_ OPERATIONAL SEAT

AVERAGE OF TWO ENERGY-ABSORBING SEAT TESTS

1) CORRESPONDS TO NASA TEST NO. 5

2) CORRESPONDS TO NASA TEST NO. 6

3) CORRESPONDS TO NASA TEST NO. 8

40

o

o

30 - ------- "

z

o

!11

W

0

o )

< _

v,

W

n 20

10

CAMI TEST NO. /'k A83-111(1) A83-113(2) A83-1 2(3)

0 A83-109 A83-103 A83-101

• A84-83 A84-81 A84-101

Figure 35. Dummy pelvis z-axispeak accelerationlevels from energyabsorbingand operationalseat tests at CAMI.

54
0 • ENERGY-ABSORBING SEAT

,/_ OPERATIONAL SEAT

AVERAGE OF TWO ENERGY-ABSORBING SEAT TESTS

1) CORRESPONDS TO NASA TEST NO. 5

2) CORRESPONDS TO NASA TEST NO. 6

3) CORRESPONDS TO NASA TEST NO. 8

4O

0,1

o

o

10

CAMI TEST NO. _ A83-111(1) A83-113(2) A83-112(3)

0 A83-109 A83-103 A83-101

• A84-83 A84-81 A84-82

Figure 36. Dummy chest z-axis peak accelerationlevels from energy-absorbing

and operationalseat tests at CAMI.

55
40 I I I I I -

o

.... ENERGY-ABSORBING SEAT (A83-109)

o

32 - OPERATIONAL SEAT (A83-111) 00O

24 -

16

Z

o

< Ill LU

,,, 0

o

o

< I I !

:.N -8 II t

0. I iE

I- _'16 i <_

i

-24 -1

-32 -40 I I I I I 1

0 50 100 150 200 250 300

TIME(MSEC)

Figure 37. Seat pan z-axisaccelerationsfor energy-absorbingand

operationalseats in similar tests correspondingto

NASA Test No. 5.

The differencesin the DRI are representedin Figures40 through 42. Again,

the DRI along the seat back tangent line in Test NumberA84-81 is significantly

higher than would be expected. The seat pan verticaland pelvisDRI's for the

same test are consistentwith the resultsof Test NumberA83-103,which was

conductedunder the same conditions.

The durationsspent above 23 G for the seat pan accelerationmeasurementsare

presentedin Table 13. The only violationof the Eiband criterionis by the

energy-absorbingseat in A84-81. However,the overallmeasurementsare inconc]usive in showing any differencesbetween the two seats. Although these

pulseswere only an estimateof the capsule environment,it is interestingto

note that the operationalseat did not violate the Eibandcriterion,although

experiencewith the F-111 capsule shows the environmentto be severeenough to

cause spinal injuries.

3.4.2 Spinal Loads

The anthropomorphicdummy used in these tests had been previouslymodified to

incorporatea six-axis load cell at the base of the lumbar spine. The installationof this load cell is describedin Reference16. The data gathered

56
40 ! I i I i

__ __ __ ENERGY-ABSORBING SEAT (A83-103)

32 -- OPERATIONAL SEAT (A83-113) _0°°

o

24

-40 I I I I

0 50 100 150 200 250 300

TIME (MSEC)

Figure 38. Seat pan z-axis accelerationsfor energy-absorbingand

operationalseats in similar tests correspondingto

NASA Test No. 6.

through this dummy have not yet been correlatedwith an injurypotential. However, the data gatheredduring this test series was consistentand reasonable.

It is thereforebeing used as a comparativetool in examiningdifferencesbetween the energy-absorbingand operationalseats. If the spinal loads and moments can be accuratelyand preciselymeasured,these values would be the best

predictorsof spinal injury potential.

Table 14 presents the lumbarmeasurementsof both the z-axis peak load and the

peak moment about the y-axis. These measurementswere taken both during the

original test series and after seat pan load cells had been added to the energyabsorbingseat. The spinal compressionloads are consistentlymuch less for

the energy-absorbingseat: 1300 to 1500 ]b when comparedto 2000 to 2100 ]b

for the operationalseat. Differencesin the pitch-axismoments are not as

dramatic,with a significantdifferenceonly being shown for the three CAMI

tests with pure vertical loading,which correspondsto NASA Test Number8.

The CANI tests which correspondto NASA Test Number 6 resultedin the seat being

orientedon the sled in a pitch-up40-degreecondition. This combinedforward

and downward loading,as would be expected,producedthe highest bendingmoments on the spine, but these peak moments did not occur at the same time as

the peak compressionloads. Figures43a through 45a show the seat pan z-axis

accelerationand the spinal z-forcefor the operationalseat in all three tests.

57
4O

I I I i I

_ _ ENERGY-ABSORBING SEAT (A83-I01)

o

32 _ OPERATIONAL SEAT (A83-112) • oCO

0

24 -

-32 -

-40 I I I I I

0 50 100 150 200 250 300

TIME (MSEC)

Figure 39. Seat pan z-axis accelerations for energy-absorbing and

operationa] seats in similar tests corresponding to NASATest No. 8.

One can see how the spinal loads continue to climb even after the vertical accelerations have leveled off around their peak value. Figures 43b and c

through 45b ana c show similar p]ots with the energy-absorbing seat. One can

see that the spinal loads peak after the seat has started stroking, during the

initia] notch when the acceleration levels have dropped down to about zero.

However, the stroking of the seat prevents the spinal compression loads from

rising to as high a value as they did in the operational seat.

These traces also emphasize a point made earlier about problems with Eiband

evaluation traces. The peaks in spinal load occur at minimum values of seat

pan acceleration, while the Eiband evaluation uses the acceleration peaks to

detenT_ine the severity of the pulse.

3.4.3 Seat Pan Loads

The modification that added seat pan load ceils to the operational seat and

energy-absorbing seat is described in Section 2.4. The load cells measured

only the vertical loads applied downward from the bottom of the seat pan. The

maximummeasurements recorded from each load cell, as well as the maximumsummation of the three load cells at one time, are ]isted in Table 15. Total

loads for the energy-absorbing seat were mucll less than the operational seat

by amounts ranging from 1000 to 2200 lb.

58
TABLE 12. COMPARISONOF DYNAMICRESPONSEINDEX MEASUREMENTSFOR

OPERATIONAL(F-Ill) AND ENERGY-ABSORBING(E/A) SEATS

IN CAMI TESTS

NASA CAMI Dynamic Response Index

Test Test Seat Back

Number Number Seat Seat Pan z Tangent Line Pelvis z

5 A83-111 F-111 29.1 30.4 37.3

A83-109 E/A 18.2 20.7 24.6

A84-83 E/A 18.1 19.9 22.5

6 A83-I13 F-Ill 23.4 28.1 35.1

A83-103 E/A 17.6 21.6 24.9

A84-81 E/A 17.0 26.1 24.5

8 A83-I12 F-Ill 26.5 25.9 34.0

A83-101 E/A 18.6 18.4 24.2

A84-82 E/A 17.2 16.2 23.7

_o things should be noted while evaluating these data. First, no tare tests

were conducted. Such a test would have sent the seat down the track without

an occupant, and due to the inertial loading of the seat pan, the load cell

readings could have been recorded. These values could then have been subtracted from the readings taken during a test with the occupant. The result

would have been the load applied to the seat pan by the occupant. This would

be somewhat less than the loads listed in Table 15, which were measured at the

bottom of the seat pan. Secondly, as presented in Section 2.4, there was some

difference in the weights of the operational F-111 and the energy-absorbing

seat pans. This 3.35-Ib difference wi]] affect the loads measured at the bottom of the seat pans. Thus, if tare tests had been conducted, there would have

been a difference in the seat pan inertial loads recorded for the two seats.

Due to its higher weight, the operational seat would record higher inertial

loads. However, since the maximumaccelerations measured were on the order of

30 G, the maximumdifference in the inertial loads can be estimated to be approximately i00 lb. Even using this value as an adjustment to the loads measured, the data still show that the vertical loads experienced by the occupant

in the operational seat were much higher than those experienced in the energyabsorbing seat during a similar test.

The difference in the total loads recorded while simulating NASATest Number 6

is not as great as in the other two test conditions. The loads applied to the

seat pan are a function of both the test pulse and the seat orientation.

59
0 • ENERGY-ABSORBINGSEAT

A OPERATIONAL SEAT

AVERAGEOF TWO ENERGY-ABSORBING SEAT TESTS

1) CORRESPONDS TO NASA TEST NO. 5

2) CORRESPONDS TO NASA TEST NO. 6

3) CORRESPONDS TO NASA TEST NO. 8

4O

O0

O4

o

o

x 30 -

u.I

zm

z Z_

o _ _

= f o

<:

Z

>-

Q 20 -

10

CAMI TEST NO. A A83-111(1) A83-113_) A83-112(3)

0 A83-109 A83-103 A83-101

Q A84-83 A84-81 A84-82

Figure 40. Dynamic Response Index detemined from seat pan

z-axis accelerations in CAMI tests.

60
0 • ENERGY-ABSORBINGSEAT

/_ OPERATIONAL SEAT

AVERAGE OF TWO ENERGY-ABSORBING SEAT TESTS

1) CORRESPONDS TO NASA TEST NO. 5

2) CORRESPONDS TO NASA TEST NO. 6

3) CORRESPONDS TO NASA TEST NO. 8

4O

_D

04

o

o0

o

o0

x 30 - _

uJ _-

a

z

u.I

z

0 _ k

o..

o'_

ILl

nO

-

<

z

_- (

r_ 20- 1

10

CAMI TEST NO. A A83-111 (1) A83-113 (2) A83-112 (3)

0 A83-109 A83-103 A83-101

• A84-83 A84-81 A84-82

Figure 41. Dynamic Response Index determined from seat back

tangent line accelerations in CAMI tests.

61
© t ENERGY-ABSORBING SEAT

OPERATIONAL SEAT

AVERAGE OF TWO ENERGY-ABSORBING SEAT TESTS

1) CORRESPONDS TO NASA TEST NO. 5

2) CORRESPONDS TO NASA TEST NO. 6

3) CORRESPONDS TO NASA TEST NO. 8

40

tO

oO

x 30 -

LU

t_

z

LLI

co

z

0

a.

co

i.u -I _ )

n"

0

<

z

,'_ 20 -

10

CAMI TEST NO. A A83-111(1) A83-113(2) A83-112(3)

O A83-109 A83-103 A83-101

Q A84-83 A84-81 A84-82

Figure 42. Dynamic Response Index determined from dummypelvis

z-axis accelerations in CAMI tests.

62
TABLE13. COMPARISONOF EIBANDMEASUREMENTSFOROPERATIONAL

(F-111)AND ENERGY-ABSORBING(E/A)SEATSIN CAMI

TESTS

NASA CAMI DurationAbove 23 G (sec)

Test Test Seat Back

Number Number Seat Seat Pan z Tangent Line

5 A83-III F-Ill .005(I) .005(2)

A83-10g E/A 0 .004

A84-83 E/A 0 .002

6 A83-113 F-111 .002 .003(2)

A83-I03 E/A .002 .006

A84-81 E/A 0 .017

8 A83-I12 F-Ill 0 0

A83-I01 E/A 0 0

A84-82 E/A 0 0

(I) Longest duration of three spikes over 23 G.

(2) Longest duration of several spikes over 23 G.

In CAMI tests A83-113and A84-81 that simulatedNASA Test Number 6, the seat

was pitched up on the sled only 40 degrees,as shown previouslyin Figure22.

In this orientationa significantinertialload is carried through the legs

into the footreststructure. The peak footrestz-axis loads for all six tests

of interestare presentedin Table 16. With the energy-absorbingseat, the

seat pan loads are limited independentof the footrestloads. Thus, the total

inertialloads measuredon the seat pan in CAMI tests that simulatedNASA

Test Number 6 are not very differentfrom those measured in tests simulating

NASA Test Numbers5 and 8, where the seat was pitched 70 and 90 degrees,respectively. However,since the operationalseat does not limit the loads applied to the seat pan, the seat pan loads are dependenton the proportionof

the total load carried by the footrest. Therefore,under test conditions

where a high percentageof the vertical load is supportedby the footrest,the

differencebetween seat pan loads measuredon an energy-absorbingseat and an

operationalseat will not be as great as under seat orientationswhere the

fuotrestcarries less load. Of course, the test conditionsmust be severe

enough to cause seat stroke for there to be any differencein the seat pan

loads.

Figures46 through 48 show plots of the center seat pan load cell force and

the spinal z-axis force on the same plot. Whi]e there is some phase difference, which should be expected,the seat pan force and spinal force show the

63
TABLE14. LUMBARLOADCELLMEASUREMENTSFOROPERATIONAL

(F-111)AND ENERGY-ABSORBING(E/A)SEATSIN

CAMITESTS

Maximum Spinal Load Cel!

NASA CAMI Measurements

Test Test Test Z-Axis Load Y-AxisMoment

Number Number Seat (lb) (in.-lb)

5 A83-111 F-111 2162 979

A83-109 E/A 1436 1000

A84-83 E/A 1527 560

6 A83-113 F-111 1992 1870(1)

A83-103 E/A 1476 1795(1)

A84-81 E/A 1365 1916(1)

8 A83-I12 F-111 2049 951

A83-101 E/A 1364 631

A84-82 E/A 1240 333

(1) Peak moment occurredsignificantlyafter peak axial load.

same characteristics. While on the operationalseat the loads climb to a sing]e high value, with the energy-absorbingseat there are two smaller peaks.

The first peak occurs after the seat starts strokingand when the seat pan

accelerationsdrop to approximatelyO, the initial notch. The secondpeak

load occurs after the secondarypeak on the seat pan accelerations. During

the same time, loads in the dummy and seat pan of the operationalseat climb

to a much higher single peak. This illustrateshow an energy-absorbingseat

limitsthe loads experiencedby the occupant.

3.4.4 Conclusions

Severa] conclusionscan be made from the presenteddata:

• In every case, peak accelerationlevelsmeasured for the seat pan,

pe|vis, and chest z-axes, as wel] as seat pan accelerationsalong

the seat back tangent line,were lower on the energy-absorbingseat.

• DRI values for the energy-absorbingseat were consistently6 to 10

points lower than for the operationalseat.

64
2000. f _ 2000. ] I I I I I _ I I I I

OPERATIONAL SEAT (A83-111) °_ ENERGY-ABSORBING SEAT (A83-109) °e i i

e

1600, \ ---- SPINAL Z FORCE 1600. --_ SPINAL Z FORCE

\ --SEAT PAN Z ACCELERATION _ _ SEAT PAN Z ACCELERATION

1200. \ _) 1200. I \ 11"*'\\

_ ,.,, _ /\,,; ",,

- 800 _ - 800. / ,, . _ _ I

400. I '\ 400. / \\

L. _''1 a n ' / %

o '_I,A' T'_ '_,v,_,'T '_" _"-

-8. _ -8.

P- _ -18.

< -16. ,--I,

.J

W <

0 -24. 0 -24. N

N

Z -32. _ -32

,_ -4°-0. 8•" ,'0. 180. ' 200. ' 250. ' 300• -40., •O. 100. , 150. , 200. , 250. , 300.

TIME (MSEC) TIME (MSEC)

a. Operational seat b. Energy-absorbing seat

(,1"1 2000. I n u u I __

ENERGY-ABSORBING SEAT (A04-003)

o

1600. ------SPINAL Z FORCE o

t"_ --SEAT PAN Z ACCELERATION ..,

1200. / \\ // "\

800. / \./1 I

i '

- / '\

400.

/

I %',

w -16.

< -24.

N

Z

_< -32.

_4O.o. 50. n 100. i 150l . 200. i 250. I 300.

TIME (MSEC)

c. Energy-absorbing seat

Figure 43. Seat pan z-axis accelerations and spinal compression loads

for CAMI tests corresponding to NASATest Number 5.
2000.

' /"\ _ I _ I _ 20OO. I I I ; I

I _ OPERATIONAL SEAT (A83-113)

' t _ ENERGY-ABSORBING SEAT (A83-103) 1600. I I ------SPINAL Z FORCE _ 1600 .... SPINAL Z FORCE

I t --SEAT PAN Z ACCELERATION o m

I I ,_ --SEAT PAN Z ACCELERATION

O. <_ 1200. Ill I_\ I"_ _(_ 1200, / ///\\\\\\

.j 800. I I I

z eBB. / \ <

I \ - I

I

tt

I _

/ 400. //

. _-, ,, , _...... _,_ _._--:-_

N N

Z

O.

,_ -32. ._ -32.

O. SO. 100. 160. I 200. I 25I0. 300. -40"0. 5I0. 10I 0. 150. I 200. I 250. I 300.

TIME (MBEC) TIME (MSEC)

a. Operational seat b. Energy-absorbing seat

(_

o

ENERGY-ABSORBING SEAT (A84-081)

02

.1200.

u.

N 800.

so. ,;o. ,;0. 2_0. 2_0. _oo.

TIME (MSEC)

c. Energy-absorbing seat

Figure 44. Seat pan z-axis accelerations and spinal compression loads

for CAMI tests corresponding to NASATest Number 6.
2o0o. /\ , , _ © 2000. , , _ , ,

OPERATIONAL SEAT (A83-112) o ENERGY-ABSORBING SEAT [A83-101)

o

1600, ------SPINAL Z FORCE 1600. ------SPINAL Z FORCE o

--SEAT PAN Z ACCELERATION _ --SEAT PAN Z ACCELERATION

,_ 1200 '_ 1200. / \

a: a: I

o , o , \I_

500. ' _ BOO. / ',

, _ , \

400. / 400. /

i

i -16. -16.

N -24, N -24,

,_ -32. _ -32

-4% , , , • , -4o , , , , , 5 . 100. 1 0. 20. 250. 300. O. 50, 100. 160. 200. 250. SOO.

TIME (MSEC) TIME (MSEC)

a. Operational seat b. Energy-absorbing seat

c_

2000, I I I I ]

ENERGY-^BSSEA ORmNG CA84 T -082_

,600. ------SP,NAL ZFORCE

--SEAT PANz ACCELERAT,ON =-

_, 12oo. /_

OCt N / \\_///"_I

= BOO. l

4OO. /

/ t

o. _ .... "'

/ , _ /_JAh._,-v'_,_._ J,l.__ __

i -16

N -24

Z

_ -32

I I f I I

-4O'o. 50. 100. 150. 200. 250. 300.

TIME (MBEC)

c. Energy-absorbing seat

Figure 45. Seat pan z-axis accelerations and spinal compression loads

for CAMItests corresponding to NASATest Number 8.
TABLE 15. SEAT PANLOADCELL MEASUREMENTSFOROPERATIONAL

(F-IZl) AND E/A SEATS(E/A)

NASA CAMI MaximumSeat Pan Load Ce]]

Test Test Measurements (1b)

Number .Number Seat Center Left Right Summation

5 A83-III F-Ill 2319 229 2822 4830

A84-83 E/A 1121 320 1408 2626

6 A83-I13 F-Ill 1600 922 1355 3650

A84-81 E/A 1272 675 802 2611

8 A83-112 F-111 1995 1164 1647 4750

A84-82 E/A 1229 965 1029 2892

TABLE 16. PEAKVERTICALFOOTRESTLOADS

MEASUREDIN C_41 TESTS

NASA CAMI

Test Test Footrest

Number Number Seat Peak Load (]b)

5 A83-111 F-111 1573

A83-I09 E/A 1969

A84-83 E/A 1221

6 A83-113 F-Ill 2647

A83-I03 E/A 2661

A84-81 E/A 2687

8 A83-I12 F-111 1020

A83-I01 E/A 1528

A84-82 E/A 852

68
3000 I I I I i

OPERATIONAL SEAT (A83-111)

CENTER SEAT PAN FORCE o

__ ____ SPINAL Z-AXIS FORCE o

2400

1800

u.O 1200 I

_1 I \\

6oo \

\

\

0 --- I I _ _-- _

-300 I l I I I ,,,

0 50 100 150 200 250 300

TIME (MSEC)

2000 i I I I 1

ENERGY-ABSORBING SEAT (A84-083)

CENTER SEAT PAN FORCE oo

__ __ __ SPINAL Z-AXIS FORCE _o

1600

I I I \_,

12oo I / \

I

"' I L)

n- 800 0

U.

400

0

-200 I I I I I

0 50 100 150 200 250 300

TIME (MSEC)

Figure46. Dummy spinal compressionand center seat pan vertical loads

in CAMI tests correspondingto NASA Test Number 5.

69
3OO0

I I I I I

OPERATIONALSEAT (A83-113)

__ CENTER SEAT PAN FORCE o0

0o

___ __ SPINALZ-AXIS FORCE o

2400

1800 /

/ I

/I

o 1200

nO II

\

\

\

o ] \ I

\ i

-300 t t I I t

0 50 100 150 200 250 300

TIME OASEC)

2000 r i i t i

ENERGY-ABSORBING SEAT (A84-081)

-- CENTER SEAT PAN FORCE

o

__ __ __ SPINALZ AXIS FORCE =o

1600

40O

o } I I /

J

/

-200 I _ .t / I

0 50 100 150 200 250 300

TIME OvlSEC)

Figure 47. Dummy spinalcompressionloads and center seat pan vertical loads

in CAMI tests correspondingto NASA Test No. 6.

70
3000 I I i i i

OPERATIONALSEAT (A83-112)

CENTER SEATPAN FORCE °o

__ ___ SPINALZ-AXIS FORCE _0

o

_,4oo

1800 - _

_ 1200 -

0

u.

0--___- ,, , J.__... __

\ ,.. /

-300 , i _ r _'._ ./ I ,

o ,oo 200 250

TIME OvISEC)

2000 i 1 I | I

ENERGY-ABSORBING SEAT(A84-082)

__CENTER SEAT PAN FORCE o

__ __ _ SPINAL Z-AXIS FORCE ©o

16oo

1200

/

ILl

o 8O0

o

LL

400

o I I

I / _"" _-.

-200

0 50 100 150 \ / 200 250 300

TIME (MSEC)

Figure48. Dummy spinalcompressionloads and center seat pan vertical loads

in CAMI tests correspondingto NASA Test No. 8.

71
• The accelerationpulses did not cause the operationalseat to violate the Eibandcriterion,even though the tests attemptedto simulate an environmentthat field experiencehas proven to be severe.

• The average z-axis spinal loadmeasured for the operationalseat was

2070 lb; for the energy-absorbingseat it was 1400 lb (32 percent

less).

• Using the equation:

LOADE/A+ 100

% = 1 - LOAD X 100 percent,

Oper

The tota| seat pan vertica| loads for the energy-absorbingseat were

25 to 44 percent lower than for the operationalseat.

The i00 lb is simply a factorto take into account the differencein the seat

pan weights for the operationaland energy-absorbingseats. Since the 100 lb

is based on the maximum values of the accelerationmeasured,and the loads

actuallypeak at lower accelerationva|ues, the actual factor is less than

100 lb. Accordingly,the differencesin the energy-absorbingand operational

seat pan loads would be slightly largerthan calculatedin the above equation,

but not as large as the differencescalculatedif no adjustmentfactorwere

used.

72
4.0 CAPSULETESTING

Dynamic testing of the Simula energy-absorbing seat and the operational F-111

seat in an F-Ill capsule was conducted in April and May 1984 at NASALangley

Research Center, Hampton, Virginia.

4.1 TESTOBJECTIVES

The primary objectiveof this test serieswas to evaluate the performanceof

the energy-absorbingseat over the full range of ground impactconditions.

Thus, it was necessaryto make three main determinations:

e Determine the environment to which the occupant is subjected in the

energy-absorbing seat. Accelerometers were placed at various locations on the capsule, on the seat, and in the anthropomorphic dummy.

• Determine if there was enough room for the vertical energy-absorbing

stroke necessary to limit the spinal loads to non-injurious levels.

For this purpose, the stroke was measured in each of the tests.

• Determine if the capsule bulkhead structure was strong enough to withstand the loads imposed by the energy-absorbing seat. Overall, the

loads applied to the bulkhead by the energy-absorbing seat would be

|ess than the ]oads applied by the operational seat. However, the

energy-absorbing seat is attached to the bulkhead in a different location. Therefore, the bulkhead modification used to attach the test

seat carried the loads to the same structure that the retrofit seat

would carry the loads.

To satisfy all these objectives, testing was required over the full range

of design ground impact conditions.

There were some other secondary objectives to be examined during the test

series. This included gaining some additional comparative information on the

operationa] and energy-absorbing seats. Seat pan load cell measurements, as

well as the previously mentioned accelerometer measurements, were also used at

NASAfor this purpose. Another objective concerned reducing the severity of

the ground impact environment by reducing the vertica] descent rate of the capsule. The U.S. Air Force is presently considering replacing the existing parachute with one that would reduce the vertical descent rate from 32 to 25 ft/sec.

In order to briefly examine the performance of the energy-absorbing seat under

these conditions, some pure vertical tests were conducted at a reduced vertical ve|ocity.

4.2 CONDUCT OF TESTING

4.2.1 Test Faci]ity

AI] capsule testing in the programwas conductedat the NASA Langley Impact

DynamicsResearchFacility. Capsule swing tests requiringboth horizontal

and verticalvelocitieswere conductedunder the gantry shown in Figure 49.

The gantry is 240 ft high, 400 ft long, and has a movable bridge that can

traverse the |engthof the gantry at the 217-ft height. A|so visible in

73
Figure 49. Impact Dynamics Research Facility at NASA

Langley Research Center (Reference 17).
the figure,under the southwestquadrantof the gantry, is the control room,

from which all operationsare directedduring tests. Along the centerlinebeneath the gantry is a strip of reinforcedconcrete. During the F-111 capsule

testingthe landingarea on this concretewas covered with soil. Visiblejust

north of the concreterunway is the photographicbackboardthat was painted

with a 1-meterreferencegrid.

Pure verticaltests were conductedat the drop tower shown in Figure 50. This

is locatedat the northwestcorner of the gantry.

4.2.2 Test Methods

4.2.2.1 Test Procedure. All capsule testing startedwith proper outfitting

of the capsule. This includedfour main items: IAB, various instrumentation

devices,capsule hard points, and seats with anthropomorphicdummies.

A new IAB was used for each test. For the drops with a verticaldescent rate

of 32 ft/sec, the IAB that is presentlyinstalledon all F-111 aircraftwas

used. For the pure verticaltests at 25 ft/sec, special IAB's,modifiedto

account for the reduceddescent rate, were used.

During the capsule outfitting,certain preparationsfor the instrumentation

were made. This includedinstallationof a new power supply, examinationof

the accelerometermounts on the bulkheadand seat, and electroniccheckoutof

any instrumentationsuspectedof improperfunctioning. A complete list of the

instrumentationused is in Section 4.2.2.2.

Relocatingsome structurethat providedcapsule hard pointswas necessary

prior to most of the swing tests. These capsule hard pointswere used to support the capsule fr_n cables that controlledthe aircraft'spitch, roll, and

yaw orientationsduring a test. Some of the hardwareused is visible in Figures 51 and 52.

Prior to each test the seats were examinedfor any damage and preparedfor the

next test. This preparationincludedexaminationof the roller bearingassemblies; in some cases, bolts that had been scoredand or the rollersthemselves

were replacedto insurethat the energy-absorbingsystem loads were consistent

for a]l tests. Energyabsorbersthat showed any strokewere replacedprior

to the next test.

Four energy-absorbingseats were providedfor the test series,only one of which

was equippedwith seat pan ]oad cells. Both seats that had been used at CAMI

were used again at NASA. The operationalseat used (alsoequippedwith seat

pan load ceils) was the same seat used in testing at CAMI.

After the seats were installedin the aircraft,the anthropomorphicdummies

were placed in the capsule. In all tests, two 50th-percentilePart 572 dummies (the same type of dummy used in the seat tests at CAMI), were uti|ized.

These dummies however,were not equippedwith the spina| load cells.

After the capsule was fully preparedit was taken to the test area. At this

time the attitudecontrol cables were attached. The attitudecontrol cables

75
Figure 50. Drop tower of ImpactDynamicsResearchFacility

at NASA LangleyResearchCenter.

76
Figure 51. Structure at front of crew module added for

attachment of attitude control cables.
Figure 52. Structure at rear of crew module added for

attachment of attitude control cables.
were adjustedprior to each test to provide the properpitch, roll, and yaw of

the capsule. A typical set-up for a swing test is shown in Figure53. Attitude control cables for a drop test are visible in Figure50.

Figure54 is a diagram showingthe systems used in performinga swing test.

Platformsat the west end of the gantry support the winches and pulleys used

to control the lengthof the swing cables. The lengthof the swing cables is

adjustedto provide the proper impactangle and correct ratio of horizontal

and verticalvelocities. The pull-backplatformis attachedto the underside

of the movable bridge,where the winch and pulley system controlsthe length

of the pull-backcable. The aircraftis pulledup to the height requiredto

obtain the proper horizontaland verticalvelocitiesat impact.

For tests requiringonly a verticalvelocity,the drop tower was used. The

capsule was again supportedby cables attachingit to the test fixture,which

was then liftedto the height requiredto obtain the proper verticalvelocity.

The fixture is guidedalong rails during descent.

Final preparationfor either a swing test or a pure verticaldrop test started

after the attitude cablesare properlypositioned. The instrumentationumbilica] cord was attachedand the instrumentationwas once again checked for continuity. A final inspectionwas made of the seats,dummies, and restraintsystem.

The shoulderbelts are given their final tightening. Although in this case belt

tensionwas not being measured,the tighteningprocedureproducedapproximately

the same amount of tautnessindicatedin the CAMI test series.

During preparationfor a swing test, pyrotechnicwire cutterswere attachedto

the attitudecontrol cables. These are guillotine-typewirecutters that operate just before the capsule hits the ground. Thus, at ground impactthe capsule was not being subjectedto any loads from the cables. Another pyrotechnic device is attachedto the umbilicalcord fitting. This device released

the umbilicalcord but was delayed so that operationoccurredafter the important ground impactdata was transmitted. Releasingthe umbilicalcord reduced

the chances of damage from the capsule rolling during the ground impactsequence. In a verticaldrop test, these pyrotechnicdevices are not necessary.

The IAB was then inflatedfrom a nitrogengas bottle that remainedon the

ground. Pressurewas regulatedby the regulatorinside the capsule. With the

inflationof the IAB, the capsule was ready for the test. Pull-backcables

liftedthe capsule into the proper position,which was checked using surveying

equipment. Figure 55 shows the capsule in positionjust prior to a swing test.

For both the swing and the verticaldrop tests the landingarea was covered

with an 18-in.-deeplayer of soil.

Still photographswere also taken beforeand after each test. All accelerometerand loadcell data from the test were recordedon tape for analysis.

Severa] channelsfrom each test were then displayedon oscillographpaper for

immediateuse. NASA filteredall channelsof data per the Society of Automotive EngineersRecommendedPracticeJ211b, and determinedthe DRI values required for the evaluationof the test results.

79
00

C)

Figure 53. Swing test setup at NASA Impact Dynamics Research Facility.
MOVABLE BRIDGE AND

AUXILIARY UMBILICAL PULLBACK PLATFORM

PLATFORM

UMBILICAL PLATFORM MOVABLE CAMERA TH p,.

WITH CAMERA MOUNTS _,

o

o0

o

€o

PIVOT-POINT

PLATFORMS

I i

DATA TRANSFER

HARD WIRE

_CT SURFACE

MOVABLE PHOTOGRAPHIC FCONTROL

BACKBOARD

__N..-CAMERA

_CAMERAS

Figure 54. Diagram of NASAImpact Dynamics Research Facility (Reference 17).
ex>

N

'\

\

\

Figure 55. Crew module immediately prior to swing test

at Nasa Impact Dynamics Research Facility.
4.2.2.2 Instrumentation.Camera coveragefor each test was quite extensive.

The followingis a list of the motion picture cameras used.

e Cameras

- Normal speed, 16-mmcolor, hand held, one

- High speed, 16-mmcolor, 400 frames/sec, five minimum:

I - side view

1 - front view

i - top view

2 - in capsule (one each seat).

In most cases seven to nine cameras were used. Camera vie_s added included a

hand-held high-speed view, a close-up view from the side, and a close-up view

from the top.

Accelerometers, load cells, striny potentiometers, and pressure transducers

occupied up to 50 channels of data during the test series. The same acceleronteter measurements were taken for all tests. The load cell channels were utilized whenever seats with seat pan load cells were tested. String potentiometers were used to measure the stroke of the energy-absorbing seat. The

pressure transducer channels were only used with the modified IAB during the

vertical drop tests at the reduced descent rate.

• Accelerometers

- Aircraftbulkhead,left side, triaxial,three channels

- Aircraft bulkhead,right side, triaxial,three channels

- Aircraftcenter of gravity,triaxial,three channels

- Left seat pan, triaxialand along back tangent line, four

channels

- Right seat pan, triaxialand along back tangent line, four

channels

- Left dummy

-- pelvis, triaxia],three channels

-- chest, triaxial,three channels

-- head, triaxial,three channels

- Right dummy

-- pelvis, triaxial, three channels

-- chest, triaxial, three channels

-- head, triaxial, three channels

The bulkhead accelerometers for the right side are visible in Figure 56.

A similar location was used on the left side. The accelerometers mounted at

the capsule center of gravity are visible in Figure 57. Typical seat pan

accelerometer mountings are shown in Figures 58 and 59.

83
Figure 56. Bulkhead accelerometer mountings for crew module tests.
00

en

Figure 57. Capsule center of gravity accelerometer mounting for crew module tests.
Figure 58. Seat pan accelerometerattachmenton energy-absorbing

seat in crew module tests.

Figure59. Seat pan acce]erometermountingon energy-absorbingseat

with seat pan |oad ce]]s used in crew modu]e tests.

86
• Load CelIs

- Left seat pan, vertical,three channels

- Right seat pan, vertical,three channels

The load-cell-equippedseats were only used in certain tests. Mountingof

these load cells was describedin Section 2.4.

• Strin_ Potentiometers

- Left seat, along guide tubes, one channel

- Right seat, along guide tubes,one channel

The string potentiometerfor the right seat is visible in Figure56. These

were only used in tests requiringmeasurementof energy-absorbingstroke.

• PressureTransducers

- Modified IAB, exit holes, six channels

These transducerswere only used in the drop tests at a reduced descent rate.

• Radar Gun

- Horizontalorientationalong flight path, one channel

The radar gun was mounted to measure the horizontalvelocityof the capsule at

impact. The data was ana|yzedimmediatelyafter the test and recordedas a

velocity.

4.2.2.3 Seat Installation. Some modificationsto the aircraftbulkheadwere

necessaryto mount the energy-absorbingseat. Figure60 is a view of the modificationto the pilot side of the aircraft,which is similar to the modification on the weapons systemofficer (WSO)side of the aircraft.

The upper and lower bearingassembliesare attached by bolts to the appropriate fittings (labeledin Figure60). The top of the energy absorber

assembly is a rod end bearing that is also attachedby a bolt to the vertical

adjustmentclevis. These five pointsare the only seat attachmentsto the bulkhead.

The modificationused in the test series is not the same modificationthat

would be used in a retrofitapplication. The bulkheadmodificationused does

carry the loads to the same aircraftstructurethat would carry the loads from

a retrofitseat. The bulkheadmodificationalso positionsthe seat reference

point within the present|ydefined adjustmentenvelope.

Figure 61 shows the doubler placed in the bottom of the air ventilationduct.

In order to maintain access to the storageareas behind the crew, stringers

running across to connect the main verticalmembers were not used. Thus, torsional loadsmust be carriedup to strongerstructure. This doubler helps transfer torsionalloads from the main verticalmember to the strong structurerunning across the capsule.

87
VERTICAL

ADJUSTMENT

CLEVIS

BEARING

FITTINGS

BEARING

FITTINGS

Figure60. Modificationused to mount energy-absorbingseat in

crewseatmodu]e tests.

IBLER

Figure61. Doublerplaced in air ventilationduct.

88
Figure 62 is a side view showing the added main verticalmember. It is

attachedto the existingbulkheadstructure,an L-sectionrunning up and down

the bulkhead. Doublersprevent this L-sectionfrom opening up when forward

loadsare applied.

ADDED

STRUCTURE

KHEAD REFERENCE LINE

Figure62. Modificationto capsule bulkhead.

A closer view of the lower bearing fitting is shown in Figure63. In the F-111

capsule, two sets of tracksare used to guide the operationalseat. The lower

bearingattachmentfittingsuse the upper set of existingtracks to carry some

of the |oad.

89
Figure 63. Lower bearing fitting for energy-absorbingseat.

Figure64 is a side view showing the outline of a 50th-percentileoccupant in

the test seat when installedin the aircraft. No cushion is shown since the

occupantcompressedit during the impact. The seat is in approximatelythe

ful|-up positionto providethe maximum room for seat stroke. The seat reference point is approximately4 in. forwardof the full-backposition. This is

forward of neutral,but it allowed the seat to stroke to the floor without hitting the bottom set of tracks. The foot pedalsare in the full-backposition,

and remainedin this locationbecause no adjustmentwas possiblein the capsule

used.

Figure 65 is a side view of the operationalseat installedin the aircraft.

The height is about 3/4 in. below the midpointof the verticaladjustmentrange.

The seat pan is 3 in. forwardof the full-backposition. Again, the foot pedals

are in the ful]-backposition.

The differencein these two positionswill have some effecton various data

measuredduring the test series. The thigh angle differencesin the two figures show that the operationalseat will transfermore load to the foot pedals, and the energy-absorbingseat will transfermore load to the seat pan

through the thighs. This wil] change in cases where the energy-absorbingseat

strokes downwardtowards the floor. However,in cases where there is little

or no stroke the effects on the data will be noticeab]e.

4.2.3 Test Matrix

The capsule tests conductedconsistedof two groups. The first group was the

swing tests that were conductedunder the large gantry. These were NASA Test

90
t

°i2 ADJUSTMEN_

RANGE

WL

i 166.62

"_ r--- 3.96

STA

261.40

Figure 64. Occupant position in energy-absorbing

seat during crew module tests.

Numbers 1 through 7; the tests includedlarge horizontalvelocities. The primary objectiveof this test series was to determinethe performanceof the

energy-absorbingseat over the full range of ground impact conditionsdefined

by the origina|design envelopeof the capsule. The swing tests examinedconditions at the edges of the design envelope. The seconagroup of tests was

the pure verticaltests conductedusing the drop tower. These tests examined

the ideal ground impact conditionswith the capsule descendingin the designed

2-degreenose-up attitudeunder the parachuteand landingon a flat surface.

Hultipletests were conductedto examine the differencesin ground impactsat

32 and 25 ft/sec for the energy-absorbingand the operationalF-111 seats.

The CAMI test series did not examine the pure vertical25 ft/sec ground impact

because the decisionto includethis conditionin the analysiswas made after

the CAMI tests were concluded.

91
Fo

co

o

co

J

8.43

ADJUSTMENT

RANGE

WL

165.62

3.79

STA

281.40

Figure 65. Occupantpositionin operationalseat

during crew module tests.

The test matrix was suppliedby the Air Force and is shown in Table 17. The

tests consideredthe followingvariab]esfor the capsule impactconditions:

e Wind velocity(0-34 ft/sec)

• Wind direction(+180degrees)

• Parachuteoscillations(-+10degrees)

• Landing surface s]ope (+5 degrees)

• Verticaldescent rate (32 or 25 ft/sec).

The effect of wind velocityon the ground impact is obvious. The capsu|e,descendingunder the support of a parachute,will be carried along by the existing

wind. This both increasesthe magnitudeof the impactvelocityand changes

the directionof the velocityvector. Since the primary objectiveof this test

series was to examine the performanceof the energy-absorbingseat over the

92
TABLE17. CREWr_ODULETEST MATRIX

NASA Horizontal Vertical

Test Velocity Velocity Pitch (I) Rol| (2) Yaw(3) Left Right

Number Ift/sec I (ft/sec) (degrees I (degrees I (degrees I Seat Seat

i 34 32 -13 0 45 E/A E/A

2 34 32 0 15 90 E/A E/A

3 34 32 17 0 90 E/A E/A

4 34 32 -13 0 75 E/A E/A

5 34 32 17 0 45 E/A E/A

6 43 32 2 0 0 E/A E/A

7 43 32 7 0 180 E/A E/A

8 0 32 2 0 0 F-Ill E/A

9 0 25 2 0 0 F-Ill E/A

I0 0 25 2 0 0 F-Ill E/A

ii 0 25 2 0 0 F-Ill E/A

12 0 32 2 0 0 F-Ill E/A

(1) Positivepitch is nose up.

121 Positive Positive yaw roll isis nose rightright. wing down.

full design envelopeof the capsule,all the swing tests used conditionssimulatingthe maximum wind velocityof 32 ft/sec. For the verticaltests the simulated wind velocitywas O.

The effect of wind directionwas taken into account by yawing the capsule. Various yaw angles between 0 and 180 degrees were used.

The effect of the parachuteoscil|ationsis shown in Figure66. In all swing

tests (Test Numbers 1 through 7) maximum parachuteoscillationsof 10 degrees

were used as test conditions. In Test Numbers 1 through 5 the capsulewas

modeled as being at the outer edges of a lO-degreeswing. Therefore,the

pitch or ro|l attitudewas changed 10 degrees from the normal capsule descent

position,which is a nose-up pitch of 2 degrees. In Test Numbers 6 and 7 the

capsule conditionsimulatedwas the bottom of the pendulumswingingaction under

the parachute. Thus no adjustmentsin aircraftattitudewere made; however,

the horizontalvelocitywas increasedfrom 32 to 43 ft/sec. The verticaldrops

in Tests 8 through 12 simulatedconditionsunder which no parachuteoscillations

occurred.

93
NOTE: V and V are V's due to chute

X

oscillation and must be added to

system sink velocity, winds, etc.

Table below gives sign of Vx and

V during various phases of

m_tion. ©

g

o

0 0 Vx Vz ©o

+ + + -

+ - _ +

- + + -

10

° -'--.!.

o"' °

"

6 _ \< \

o

o 4

+Vx

2 _. +6

+0 Vz_-',,,_,,

0 _

0 2 4 6 8 10

OSCILLATION ANGLE - 0 DEG.

Figure66. Effectof parachuteoscillationson crew module horizontal

and verticalvelocities(courtesyU.S. Air Force).

Design parameters of the capsule were configured under the consideration that

the landing slope could vary by 5 degrees. Impact conditions in Test Numbers

i through 5, and 7 simulate a 5-degree slope on the landing surface by varying

the capsule pitch or roll by 5 degrees. Test Number 6, and all the vertical

tests, simulatea level landingarea.

94
Two verticaldescent rates were used. Thirty-twoft/sec is the descent velocity of the Qperationalescape systemand was used in all the swing tests and

some of the verticaltests. The verticaldescent rate of 25 ft/sec, based on

an estimate of a new parachutesystem presentlyunder consideration,was used

in only some of the verticaltests.

In all swing tests, the energy-absorbingseat was used on both sides of the

aircraft. In the verticaltests it was expectedthat the environmenton both

sides of the aircraftwould be similar. Therefore,it was possibleto use the

energy-absorbingseat in the right seat and the operationalF-111 seat in the

left seat to obtain comparativedata.

4.3 RESULTS OF CAPSULE TESTING

Test results from the capsule test serieswill be evaluatedwith respect to

three major concerns:

• The accelerationlevels to which the capsuleand the occupantare

subjected

• The seat pan loadsmeasuredmain|y as a comparativetool between the

operationaland energy-absorbingseats

• The vertica]strokingdistance used by the energy-absorbingseat

under variousconditions.

4.3.1 Test Conditions

The test conditionsmeasuredduring the swing tests are presentedin Table 18.

The verticalvelocitywas calculatedfrom the measured horizontalvelocityand

the angle of the capsule f|ightpath at impact,which was measured from the

high-speedfilms. Pitch,roll, and yaw measurementswere also taken from the

high-speedfilm data.

The roll in NASA Test Number 2 is defined as a 15-degree,right-wing-downconfiguration. Inadvertantly,this roll directionwas oppositeto that used in

CAFIITest NumberA83-106. However,the test conditionsin NASA Test Number 2

still representa data point at the edge of the designenvelope for the capsu|e.

For the verticaltests,a direct measurementof the velocitywas not made.

Analysisof the film data showed the drops to be within 2 ft/sec of the ideal

conditionslistedin Table 17. Althoughnormal camera angles for the measurement of pitch and yaw at ground impactwere not possibleon the drop tower,

the camera angles used did not show a noticeabledifferencefrom the planned

test conditions.

Accelerometersmounted on the bulkheadbehind both the left and right seats

gave the best indicationof the environmentto which each seat had been subjected. Table 19 presentsboth the velocitychange determinedby integrating

the bulkheadz-axis accelerationmeasuredon each side of the aircraftand the

peak value of the accelerationcurve.

95
TABLE 18. CREWMODULESWINGTEST CONDITIONS

Ideal Test Conditions MeasuredTest Conditions

llorizontalVertical(5)

NASA Test Horizontal Velocity Vertical Velocity Pitch(1) Ro|](2) Yaw(3) Velocity Velocity Pitch(1) Ro|l(2) Yaw(3)

Number (ft/sec) (ft/sec)(degrees)(degrees)(degrees).Xft/sec) (ft/sec) (degrees)(degrees)(degrees)

1 34 32 -13 0 45 33.3 32.7 -12 4 35

2 34 32 0 15 90 34.3 35.5 -10 21 85

3 34 32 17 0 90 33.5 31.2 8 2 82

4 34 32 -13 0 75 35(4) 35 -18 8 67

5 34 32 17 0 45 32.9 31.8 11 9 36

6 43 32 2 0 0 42.2 33.0 3 -3 2

7 43 32 7 0 180 40.6 32.9 7 -1 176

(1) Positivepitch is nose up.

2) 3 Positive Positive yaw roll isis nose rightright. wing down.

(4) Cable interference with radar gun, estimated to be within 2.2 ft/sec.

(5) Calculated from radar gun analysis of horizontal velocity and impact angle from fi|ms.
TABLE19. VELOCITYCHANGEAND PEAKACCELERATIONMEASURED

ALONGA VERTICALAXIS ONCAPSULEBULKHEAD

Left Seat(1) Right Seat _2j__

NASA V'eloci ty Peak(3) Ve|oci ty Peak(3)

Test Change Accel erati on Change Acce]erati on

Number Ift/sec) (G) (ft/sec) (G)

i 29.0 15.5 37.0 21.8

2 19.5 14.9 44.5 35.3

3 36.0 15.5 4_.0 25.8

4 22.0 18.2 32.0 27.4

5 29.0 18.6 51.5 33.4

6 40.5 19.1 41.0 21.1

7 35.0 21.3 33.5 16.0

8 31.5 15.7 29.5 15.5

9 24.0 10.7 26.5 11.0

10 23.5 11.6 23.0 10.9

11 24.5 10.8 26.0 10.5

12 30.5 16.6 29.5 16.2

(i) Pilot seat.

,ea ons AI| peak values measuredfrom plots of data reducedwith a class 60 filter

per SAE RecommendedPracticeJ211b.

Effects of the aircraftattitude in swing Test Numbers 1 through 7 are evident.

The yaw present in Test Numbers 1 through 5 created very differentacceleration traces on the |eft and right sides of the aircraft. Figure67 shows the

bu|kheadz-axis accelerationplots for Test Number 5; while the basic shapes

of the curves are similar,there is a |arge differencein magnitude. The orientations for Test Numbers6 and 7 could be expectedto create similar environments on the left and right sides of the aircraft. Table 19 shows that this

is indeedthe case, as the velocitychangesand peak accelerationmeasurements

are much closer than those measured in earlier swing tests.

Overall,the capsule swing test conditionsat NASA were more severe than those

at CAMI. At CANI, the seat was simply orientedproperlywith respectto the

velocityvector and subjectedto the impactvelocityand a designatedpeak acce|eration. This was done based on previoustest data that showedmild impacts

97
5

_ _

-lo

-15

< -20

0 .04 .08 .12 .16 .20 .24

TIME (SEC)

a. Left side

B

0

_5

Z

o -Io -- 0

< _15_ o

-20 --

0 -25 --

-30

-35-

I,,,,,,,,,I1,,,,,,,,I,,,,,,,,,I,,,,,,,,,I,,,,,,,,,I,,,,,,,,,I,,,,,,,,,

0 .04 .08 .12 .16 .20 .24

TIME (SEC)

b. Right side

Figure 67. Bulkhead z-axis acce]eration from NASATest Number 5.

98
under which there was littlereboundof the capsule. During the tests at NASA

the capsuleimpacted with various amountsof pitch, roll, and yaw. Under these

conditionsthe capsule does not uniformlyload the IAB, and thus the efficiency

of the IAB can be severelyreduced. When the capsule impactswith an orientation

which is yawed with respect to the velocityvector, occupantson oppositesides

of the capsule are subjectedto differentenvironmentswith differentamountsof

rebound. Even when the capsule is not yawed or rolled,a significanthorizontal

velocitywill increasethe severityof the impactfor both occupants. In most of

the swing tests conductedthere was a certainamount of yaw, and the capsule rolled between 90 and 360 degreesafter the initialground impact. Thus, the NASA

tests were more severe for two reasons. The capsule attitudesat impactreduced

the efficiencyof the IAB and the energy of the ground impact was not evenly

distributedbetweenthe two seats. While these problemswere anticipatedprior

to the CAMI test series, the data needed to make suitableadjustmentsin the

CAMI test pulseswere not available.

As would be expected for the drop tests, Table 19 shows similar velocityand

accelerationvalues for the leftand right sides in Test Numbers 8 through 12.

4.3.2 _cupant AccelerationLevels

This section includesthe evaluationof the accelerationmeasurementstaken in

the dummies and on the seat pan during all of the tests. Analysiscenterson

the verticalaccelerations,since they are most directly relatedto the spinal

injury potential. The peak verticalaccelerationsmeasured in all of the tests

are listed in Table 20.

Lookingat the performanceof the energy-absorbingseat, one can see that in

the swing tests the accelerationsmeasuredon the seat pan, both pure vertical

and along the back tangent line, varied from 17.2 to 22.1 G, excludingTest Number 2. In Test Number2 the seat used all of the availablestrokingdistance

and bottomedout for approximately.010 seconds. The vertical seat pan acceleration measured in this case is shown in Figure68. Even though the seat bottomed for a short time, the accelerationlevels did not climb to extremelyhigh

values; measurementsof 26 to 27 G were recordedon the seat pan.

Seat pan accelerationsfor the energy-absorbingseat in the vertical tests were

lower than those measured in the swing tests. Measurementsat the 32-ft/sec

descent rate ranged from 15 to 19 G, while at the 25-ft/secdescent rate the

seat pan accelerationswere all between 12 and 13 G.

Dynamic amplificationresultedin pelvis and chest accelerationsslightlyhigher

than the seat pan accelerations. In the swing tests the valuesmeasured ranged

mostly from 20 to 25 G. One data point, the chest z-axis accelerationin Test

Number 5, was not in accordancewith any other test data from either that test

or any other test. Pelvis and chest accelerationsin the verticaltests were

also slightlyhigher than the correspondingseat pan accelerations. Peaks of 19

to 21G for drops at 32 ft/sec, and 15 through 17 G for drops at 25 ft/secwere

recoraed. These valuesare all in accordancewith proper operationof the energyabsorbingseat.

Peak accelerationvalues can also be used to compare the operationaland energyabsorbingseats during the verticaltests. Figures 69 through 71 show plots

99
TABLE20. PEAKVERTICALACCELERATIONSMEASUREDIN CREWMODULETESTS (1)

Left Seat (2) Right Seat

NASA Seat Seat

Test Pan z Seat Back Pelvisz Chest z Pan z Seat Back Pelvis z Chest z

Number (G) TangentLine (G) (G) (G) TangentLine (G) (G)

1 17.2 18.7 22.6 22.1 18.0 19.2 21.3 21.8

2 19.6 19.9 24.6 23.6 26.6 26.4 25.6 23.2

3 21.2 17.8 19.8 20.2 20.1 19.8 21.6 20.9

4 21.1 20.7 25.6 24.8 19.2 21.9 25.5 24.9

5 19.5 19.5 23.8 22.6 20.4 22.1 21.1 43.3

6 19.3 19.5 21.2 22.4 19.2 19.7 24.1 23.7

o

7 18.1 16.1 16.8 18.8 18.3 16.8 18.6 18.9

8 23.1 21.8 25.0 19,4 15.0 18.6 19.4 19.6

g 12.6 11.6 17.7 16.3 13.0 12.7 15.0 15.8

10 12.8 12.7 17.6 16.9 12.5 12.3 15.6 16.5

11 11.9 12.2 17.4 16.7 12.5 12.4 14.9 15.7

12 22.1 21.1 26.4 25.7 16.5 16.0 21.0 20.7

(1) A|I peak va|ues measured from plots of data reduced with a class 180 filter per SAE recommended

practise J211b.

(2) Operational F-Ill seat used for left seat in test numbers 8 through 12.
-30 I , , I

0 .04 .08 .12 .16 .20

TIME (SEC)

Figure 68. Seat pan verticalaccelerationfrom right seat in NASA Test

Number2 (data filteredwith Class 180 filter).

of the peak accelerationlevelsmeasuredon the seat pan and in the dummy pelvis for both the operationaland energy-absorbingseats. All three plots show

an improvementwith the energy-absorbingseat in Test Numbers 8 and 12, conducted at 32 ft/sec. There is no significantdifferencein the seat pan peak

accelerationsmeasured in the 25 ft/sec tests. In Figure 71, there is a significant differencein pelvis z-axisaccelerationpeaks. However,this is believed to be due to the slightlydifferentpositionsof the occupantsin the

two seats rather than any differencein seat performance.

Another criterionused in evaluatingseat pan accelerationdata is the Eiband

criterion,previouslyexplainedin Section 3.3.1. Table 21 shows that in only

one case was the Eibandcriterionviolated;in the second test, the right seat

bottomedout and the acceleration|evelson the seat pan, both verticaland

a|ong the seat back tangent line, were above 23 G for more than .006 sec. In

other cases, the seat pan accelerationsdid not exceed 23 G.

The accelerationdurationsabove 23 G contain no informationuseful in comparing the energy-absorbingseat to the operationalseat in the drop tests.

The fact that some differenceswere visible in the earlier plots but neither

seat producedpan acce]erationsabove 23 G, shows the mild nature of these

tests.

i01
30 I I I I

o

o

co

o

eo

0 I I I I

NASATEST NO. 8 9 10 11 12

0 ENERGY-ABSORBING SEAT (RIGHT SEAT)

OPERATIONAL SEAT (LEFT SEAT)

Figure 69. Peak seat pan verticalaccelerations

in crew moduledrop tests.

Three accelerationplots (seat pan z-axis, seat pan along the back tangent line,

and pe|vis z-axis)were evaluatedto determinethe Dynamic ResponseIndex (DRI),

and the resu|ts are presentedin Table 22. In the swing tests, the seat pan

DRI's ranged from 19 to 23, with the average being around 21. This excludes

the one test where the seat bottomedout and the DRI climbed to between 24

and 25. Overall,the DRI's in the swing tests are higher than the DRI's measured in previoustestingat CAMI. The main reason for this is that the NASA

102
30 I I I ! ,,=.

o

o

0 I I I I

NASA TEST NO. 8 9 10 11 12

0 ENERGY-ABSORBINGSEAT (RIGHT SEAT)

A OPERATIONAL SEAT (LEFT SEAT)

Figure 70. Peak accelerationlevelsalong the seat back tangent

line in crew module drop tests.

test conditionswere on the averagemore severe than those at CAMI. The vertical velocitychanges and peak accelerationsmeasuredon one side of the bulkhead in the NASA tests were sometimesas large as the total velocitychange

and peak accelerationin the correspondingCAMI test. However,DRI values in

the range of 21 to 22 are still within the range that should be expectedfor

an energy-absorbingseat with energy absorber limit loads of 14.5 G. Also,

the test conditionsswing the capsule in a way that closely simulatesa free

103
o I I I I

NASA TEST NO. 8 9 10 11 12

0 ENERGY-ABSORBING SEAT (RIGHT SEAT)

/_ OPERATIONAL SEAT (LEFT SEAT)

Figure 71. Peak dummy pelvis z-axis accelerationlevels

in crew modu|edrop tests.

fal|. Under actual capsule descent,the body would be under a I-G preload.

With such a pre]oad,the dynamic amplificationeffects are reduced and the accelerationsmeasured on the seat pan and in the pe]vis can be expectedto be

slightlylower than in a free fall. The DRI values measuredwould also be lower.

Sled test conditionssuch as those at CAMI may providesome gravity preload

to the verticalaxis of the seat system,dependingon the orientationof the

seat on the sled.

104
TABLE21. DURATIONABOVE23 G OFSEAT PANACCELERATIONS

MEASUREDIN CREWMODULETESTS

NASA Left Seat (2) Riqht Seat

Test Seat Pan Seat Back Seat Pan Seat Back

Number Isec) Isec) Isec) Isec)

1 0 0 0 0

2 0 0 0.008(1) 0.010(I)

3 0 0 0 0

4 0 0 0 0

5 0 0 0 0

6 0 0 0 0

7 0 0 0 0

8 0.001 0 0 O

9 0 0 0 0

I0 0 0 0 0

ii 0 0 0 0

12 0 O 0 0

(i) Seat used all available vertical stroke and bottomed out.

(2) Operational F-Ill seat used for ]eft seat in Test Numbers 8 through 12.

The DRI's for the verticaltests are shown in Figures 72 through 74, as well

as in Table 22. Basically,the energy-absorbingseat shows a slight improvement over the operationalseat at 32 ft/sec, but no differenceat 25 ft/sec.

4.3.3 Seat Pan Loads

The energy-absorbingseat equippedwith seat pan load cells was used in some

of the capsule swing tests and in all of the drop tests. However,some of the

data channelsfrom the swing tests were lost. The limiteddata from these swing

tests are not meaningfu|,and are thereforenot presented. Individualchannels

that were recordedare presentedin Volume Ill. In the verticaltests, both

the operationalseat and the energy-absorbingseat were equippedwith seat pan

load cells. The peak values recordedare presentedas a comparativetool in

Table 23 and Figure 75.

I05
TABLE22. DYNAMICRESPONSEINDEX (DRI) MEASUREMENTS

FROMCREWMODULETESTS

Left Seat (I) Right Seat

NASA

Test Seat Seat Back Seat Seat Back

Number Pan Tangent Line Pelvis Pan Tangent Line Pe]vis

i 19.1 20.2 23.4 21.0 22.7 23.9

2 23.3 22.0 24.2 24.9 24.6 24.5

3 20.7 18.7 21.8 22.5 21.6 22.4

4 20.5 20.7 23.2 21.7 21.9 23.8

5 22.5 21.5 26.9 22.9 24.5 23.4

6 21.0 20.2 21.8 21.4 21.8 22.4

7 22.3 18.5 19.0 21.6 19.0 21.1

8 23.9 22.8 24.6 18.7 23.6 22.4

9 14.6 13.6 18.3 14.3 13.9 16.3

10 15.3 14.7 18.9 15.6 15.4 17.5

ii 14.2 14.0 18.0 14.7 14.4 15.6

12 24.9 23.9 29.6 20.9 20.4 19.8

(i) Operational F-Ill seat used for ]eft seat in test numbers 8 through 12.

One can see that in the 25-ft/sec tests (Test Numbers 10 and 11), the total

loads on the operational seat were less than those for the energy-absorbing

seat. This is related to the difference in occupant position in the two seats.

The energy-absorbing seat was in the fu]l-up position for all testing, whi]e

the operational seat was in a more neutral position. As explained in Section

4.2.2.3, the thigh loads for the energy-absorbing seat will be higher than for

the operational seat. Tests 9 through ii demonstrate this, as the difference in

the tota] seat pan load is due to the load under the dummy's thigh. The center load cells, more in line with the spine, show little difference between the

two seats.

In the 32-ft/sectests, the energy-absorbingseat shows some improvementover

the operationalseat. Despite the differencein seat positions,the total

load on the seat pan is noticeablyless on the energy-absorbingseat. Figures 76 and 77 show the centerseat pan load cells plottedalong with the seat

106
30 I I I I

o

o

x 20 IJJ

z_ o,, /

',' \

z \

o \

a. \

<

10 -

0 I I I I

NASA TEST NO. 8 9 10 11 12

O ENERGY-ABSORBING SEAT (RIQHT SEAT)

A OPERATIONAL SEAT (LEFT SEAT)

Figure 72. Seat pan z-axisDynamic Response Index (DRI)

measurementsfrom module drop tests.

pan z-axisaccelerations. The center ]oad cel]s show performanceimprovement

in the energy-absorbingseat at 32 ft/sec, but no differencein performanceat

25 ft/sec.

The va|ues presentedin Table 23 have not been adjusted for the slightweight

differencein the seat pans on the two seats. This weight differenceis discussed in Section 3.4.3. The weight differencewou]d have only a slighteffect on the numbers presented,and no effecton the conclusionsreachedusing

these numbers.

107
30 I I I I

g

o

o

0 I I I I

NASA TEST NO. 8 9 10 11 12

O ENERGY-ABSORBING SEAT (RIGHT SEAT)

A OPERATIONAL SEAT (LEFT SEAT)

Figure 73. Seat back tangentline DynamicResponse Index (DRI)

measurementsin moduledrop tests.

4.3.4 VerticalStrokin9

The vertical strokemeasured in each of the 12 tests is listed in Table 24.

As would be expected,the higherstrokingdistanceswere recordedin the more

severe swing tests. The maximum strokewas recordedin Test Number 2, where

the right seat bottomedout after 7.75 in. of stroke. Dependingon the seat

position,6 to 11 in. of verticalstrokewould be availablewith a retrofit

108
o I I I I

NASA TEST NO. 8 9 10 11 12

0 ENERGY-ABSORBINGSEAT (RIGHT SEAT)

A OPERATIONALSEAT (LEFT SEAT)

Figure 74. Dynamic Response Index (DRI) measurements from pelvis z-axis

accelerations in module drop tests.

seat. Because of the test seat pan configuration, less stroke was available

with the test seat in the full-up position than would be available with a retrofit seat in the full-up position. The retrofit seat would need to have been

in the top half of the adjustment range to provide room enough to prevent bottoming out in Test Number 2. Other tests where the seat would need to have

been above the minimum position are Test Number 5 (the right seat) and Test

109
TABLE23. PEAKSEATPANLOADSRECORDEDDURINGMODULETESTS

Operational F-Ill Seat Energy-Absorbing Test Seat

NASA ILeftSide) (RightSide)

Test Left {;enter Right Total(1) Left Center Right TotaI(1)

Number (Ib) (lb) (Ib) (Ib) (]b) (lb) (Ib) (lb)

8 400 2481 213 (2) 3079 339 1578 326 2239

9 270 1357 85 1708 (3) 1334(2) 397 -

10 265 1413 131 1790 533 1194 322 2031

i i 242 1319 i i i 1665 282 1334 342 1950

12 386 2166 211 2750 333 1595 411 2339

(i) Total is maximumsummation of all load cells at one time.

(2) Raw data used to obtain load.

(3) Lost data channel,
6000 I I I I

o

o

o

4000 -

A

m

.J

o

0

.J

.s

2000 - 0-_ -.-- _ I._..0____

0 I I I I

NASA TEST NO. 8 9 10 11 12

0 ENERGY-ABSORBINGSEAT (RIGHT SEAT)

/_ OPERATIONALSEAT (LEFT SEAT)

Figure 75. Comparisonof total seat pan ]oads in module drop tests.

Number6 (both seats),measuring7.72, 6.45, and 6.00 in. of stroke, respectively. However,it must be rememberedthat these swing test conditionsrepresent the outer edges of the design envelope. Even in these cases, the

majority of occupantsrequiredbetween 1 and 6 in. of stroke. Under typical

capsule operation,enough stroke would most likelybe providedeven at the

lowest seat adjustmentposition.

111
50 e t t 2000

OJ PEAK AT 2480 '_

45 - 1800

co

o

'ql"

40 - 1600 _

\

35- _.,_ _ _ - 1400

30 '_ ii 1200 !•

25 1000

\

z 20 - 800 <

Q.

< 15 ,_ 600

10 400

5 \ 200

o I o

-5 I -200

0 40 80 120 160 200

TIME(MSEC)

OPERATIONALSEAT (LEFT)

ENERGY-ABSORBING SEAT (RIGHT)

Figure 76. Seat pan z-axis acceleration and center seat pan vertical

load for NASATest Number 8 (32-ft/sec drop test).

Stroking distances for the vertical tests are also shown in Table 24. The highve|ocity drops required about 2 in. of stroke, while the low-velocity drops

required little or no stroke. This is consistent with the previous acceleration and seat pan load data that has already been presented. In the lowvelocity drops, the energy-absorbing capability of the test seat was not required. Thus, there is not a noticeab]e difference in the performance of the

112
50 i = i i 2000

45 - 1800 oo

o

40 - - 1600 _

-5 I -200

0 40 80 120 160 200

TIME (MSEC)

OPERATIONAL SEAT (LEFT)

__ n ENERGY-ABSORBING SEAT (RIGHT)

Figure 77. Seat pan z-axis accelerationand center seat pan vertical

load for NASA Test _umber9 (25-ft/secdrop test).

energy-absorbingand operationalseats. When the descent velocity is increased,

the energy-absorbingcharacteristicof the test seat is needed. At this time,

the differencesin the two seats Decome apparent. Accelerationlevels and seat

pan loads both show the performanceof the energy-absorbingseat to be an improvementover that of the operationalseat.

113
TABLE24. VERTICALSTROKENEASUREDURINGCREWMODULETESTS

NASA

Test Left Seat Vertical Stroke Right Seat Vertical Stroke

Number (in.) (in.)

i 1.5 2.25

2 3.1 7.78(1)

3 1.25 5,25

4 3.15 5.30

5 3.15 7.70

6 6,00 6.45

7 0.75 1.25

8 -(2) 1.75

-(2) 0

10 -(2) 0.15

11 -(2) 0.05

12 -(2) 2.30

(i) Seat bottomed out.

(2) Operational F-Ill seat.

The ideal descent of the capsule, pure vertical with no wind, required 2 in.

of energy-absorbing stroke. Ground impacts under conditions on the edges of

the design envelope required from i to 8 in. of stroke. The very low stroke

was required when the capsule landed at an attitude yawed 180 degrees to the

ve]ocity vector. Thus, the energy-absorbing seat wou]d be beneficial in the

]arge majority, if not a11, of the ground impacts. The chances of an occupant

having his seat below the mid-height position and landing in an impact severe

enough to require more than the avai]able stroke, appear to be sma]l. A study

of the recorded impacts would have to be made to determine actual statistical

relationships.

4.3.5 Structural Integrity

Maintenance of the seat during the capsule test series consisted of the planned replacement of stroked energy absorbers, and the replacement when necessary

of rollers and bolts from the bearing assemblies. None of the four energyabsorbing test seats used suffered any structural damage during the test series.

114
The bulkheadmodificationused to mount the test seat is not the same modification that would be used for a retrofitseat. However,this modificationcarried loads up into the sill stiffenerthat runs across the capsule behind the

seat. In a retrofitseat this same sill stiffenerwould be requiredto carry

loads from the retrofitseat. Neitherthe sill stiffener,nor any of the bulkhead mountingpoints for the roller bearings,showed signs of deformationor

any loss of structuralintegrityduring the test series.

4.4 CONCLUSIONS

The NASAdata provide justifications for the following conclusions:

• On the average, module test conditions at NASAresulted in more

severe bulkhead accelerations than were simulated in corresponding

tests conducted at CAMI.

• The present IAB is very efficientin pure verticaldrops. Under

conditionssimulatinghigh-winddrift and capsule swing,the efficiency of the bag decreasessignificantlyfor one or both occupants.

• l_inddrift and capsule swing can cause the ground impactdeceleration pulse experiencedby one occupantto be much more severe than

that experiencedby the other occupant.

• The Eiband criterion does not show a hazardous condition in either

the 25 or 32-ft/sec pure vertical impact conditions.

• Peak accelerationlevelsfor the energy-absorbingseat were consistent with other successfulenergy-absorbingseats.

• DRI measurementsfrom seat pan accelerationsfor the energy-absorbing

seat in the swing tests were consistentlybetween 20 and 23. These

are higher than the values recordedat CAMI, but are still consistent

with properoperationof an energy-absorbingseat load limited to

14.5 G.

• Peak acceleration]evels,DRI, and seat pan loads show an improvement with the energy-absorbingseat for pure verticaldrops at

32 ft/sec, but no significantdifferencesin pure verticaldrops at

25 ft/sec.

• The maximumvertical stroke required was approximately 8 in. Since

between 6 and 11 in. of stroke would be provided in a retrofit seat,

a retrofit seat would need to have been in the top half of the vertical adjustment range to provide this much stroke.

• Neither the seat nor the module bulkheadsufferedany structural

damageduring the testing.

115
5.0 RETROFITSEAT

Before a seat was designed for the dynamic tests conducted at CAMI and NASA,

various concepts were considered for a retrofit energy-absorbing seat. The

concepts considered such options as:

• Whether or not the existing tracks could be used

• Where the inertia reel should De mounted

m How the vertical adjustment mechanism would be attached to allow

space for the energy absorbers

• _nether the bearings should be on the seat, the bulkhead, or another

structure between the seat and bulkhead

m How the headrest and seat pan adjustments would be provided.

Several ideas for how to provide the energy-absorbing stroke were also examined. These included guiding the seat vertically using round tubes, square

tubes, or l-beams. Rotating links guiding the seat as it moved along an arc

were also examined.

After a thorough examination of these and other factors, a concept for a retrofit seat was chosen. Based on this concept, the test seat described in Section 2.3 was designed and built. The guidelines for the design of the retrofit

seat are discussed in Section 5.1, while Section 5.2 presents a more detailed

description of the concept for a retrofit seat.

The design described in Section 5.2 is not a carefully refined design. It does

present the best concept for a retrofit seat based on the space and weight limitations of the existing seat and the requirement to provide some of the same

characteristics that exist in the present operational seat. If a retrofit seat

were to be developed, a specification for this seat would be required. Then

the conceptual design could be examined and changed when necessary, various

parts could be sized, and a proposal for a retrofit seat could be initiated.

5.1 DESIGNGUIDELINES

Three seats are discussed in this report: the operational seat, the energy,

absorbing test seat, and an energy-absorbing retrofit seat conceptual design.

Although the design guidelines for both the test and retrofit seats were based

on the operational seat, there are some differences between the requirements

for the two seats. Therefore, the design guidelines for the retrofit seat are

discussed before the conceptual design is presented.

As mentioned earlier, there is no specification for the design of an energyabsorbing seat for the F-Ill aircraft. The design guidelines presented here

come from evaluations of both the hardware and specifications currently used.

The operational seat was examined for characteristics that have proven worthwhile and should be maintained in a retrofit seat. The F-111 crew module was

thoroughly scrutinized to define the space limitations inherent in the design

of a retrofit seat. Specifications for ejection seats (MIL-S-g479, Reference

116
18) and escapemodules (MIL-C-25969)were also inspectedfor requirementsthat

might be imposedon a new seat.

The requirementsconsideredwere of a general nature: anthropometricrequirements for the seat back angle, headrest,etc. Know]edgeof these facts was

necessaryto analyze the space availablein the crew module. Strengthrequirements of the seat under specificloadingconditionswere not rigorouslydefined.

The resultingdesign guidelinesfor a retrofitseat include the followingrequirementsfor the seat adjustmentsystem:

• Five inchesof vertical (alongthe bulkheadreferenceline)adjustment

• Five inchesof fore and aft adjustmentof the seat pan

• A power screw verticaladjustmentmechanism.

The 5 in. of verticaladjustmentis necessaryto allow pilots to properly

positionthe seat with respect to the design eye point. Since the rudder pedal

adjustmentis limited,the horizontaladjustmentin the seat pan is necessary

to properlypositionthe rudder pedals for pilots.

In the present configurationof the operationalseat in the F-111 capsule,the

headrestremainsat a constantheight,and is adjustablein the fore and aft

directions. As discussedin Section 2.1, moving the headrestalso adjusts the

seat back angle. Behindthe headrest,the power haul-backinertiareel is

mounted to the bulkhead. Since these design featuresdid not have any inherent

advantages,the design guidelinesfor the retrofitseat did not require them.

Rather, the design guidelinesrequiredthat:

• The headrestbe attachedto the bulkheador the seat; however,proper head suppportat all adjustmentlocationsand throughoutany vertical energy-absorbingstrokemust be provided.

• The inertiareel may be mounted on the bulkheador the seat; however, proper restraintat all adjustmentlocationsand throughout

any verticalenergy-absorbingstrokemust be provided.

• The seat back should providea 13-degreeback angle, either as a

fixed back or as one of the adjustmentpositions.

Other designguidelinesconcernedthe entire escape system:

• The seat designmust allow access to survivalgear stored behindit.

e Aircraftmodificationsare to be kept to a minimum.

If access to the survivalgear was not required,the overall performanceof

the escape system would be degraded,and the retrofitseat design would be unacceptable. Any other modificationsto the aircraftthat are necessaryto install the seat but degrade overallcapsule performancewould also be unacceptable. Keeping the aircraftmodificationsto a minimum also keeps retrofit

costs to a minimum.

117
5.2 SEATDESCRIPTION

5.2.1 Overall Description

A layout of the conceptualdesign for the retrofitseat is presentedin Figure 78. The same seat would be used in both the pilot and weapons system officer positions. The seat consistsof four major subassemblies:

• Linear bearings

• Energy absorbers

• Carriage and guide tubes

• Seat pan and back.

The linearbearings providean interfacebetween the seat and bulkhead. The

energy absorberswould be attachedto the verticaladjustmentmechanismand

support the seat in the verticaldirectionduring normal flight. The carriage

and guide tubes would provide both the basic load-carryingstructurein the

seat and the means for horizontaladjustmentof the seat pan and headrest.

The guide tubes slide inside the linearbearingsduring verticaladjustment

and energy-absorbingstroke. The seat pan and back assemblywould provide the

structurethat comfortablysupportsthe occupantduring flight. One can see

that the retrofitseat would use the same guidedstroke concept and would interface with the bulkheadin the same way as the test seat.

The |inearbearingsthat would be used on a retrofitseat are not the roller

bearingsthat were used on the test seat and describedin Section 2.3. The

retrofitbearingswould have a Teflon-impregnatedlinermounted in an aluminum

housing. The liner providesa smooth sliding surface for the guide tube during

verticalseat adjustmentand energy-absorbingstroke. These bearingsrequire

much less room and are lighterthan the roller bearingsused on the test seat.

The small size of these bearingsallowsthe retrofitseat to be mounted much

closer to the bu|kheadthan the test seat.

The |inearbearingassemblieswould be attachedto the bulkheadin the same

four locationsused by the test seat. Prior to seat installation,fittings

would De bolted to the bulkheadat each attachmentpoint. The linearbearings

would already be on the seat, so that when the seat was placed in the aircraft

a single pin would attach the bearing to the fitting on the bulkhead. Hardware mounted on the bulkheadis discussedfurther in Section 5.2.2.

The back view of the seat in Figure78 shows the variable-loadenergy absorber

syst_1 supported by the vertical adjustment mechanism. The power screw mechanism shown attached to the bulkhead is the one presently used on the seat, but

the energy absorber subassembly could be designed to incorporate a different

mechanism.

In order to provide the best protectionin the most severe ground impacts,the

criterionfor determiningthe loadat which the verticalenergy-absorbingsystem should stroke was establishedas the maximum load tolerableby the occupant. The maximum load was selectedso that the system could absorb the maximum amount of energy within the limitedstroke distance. Based on experience

118
1. INERTIA REEL

2, GUIDE TUBES i

3. SLIDING BEARINGS

4. VENTILATION DUCT _ - _--

6. ENERGY ABSORBERS

6. VERTICAL ADJUSTMENT

MECHANISM

_'_'"--i _' _=_

/ °o

o

F----l{ I!oooooo_/

/

Figure 78. Conceptual design of energy-absorbing

retrofit seat for F-Ill crew module.

with seats for severalmilitaryhelicopters,includingSikorsky'sUH-60A Black

Hawk, a 14.5-G |oad factor was used in the test seat. In the retrofitseat,

the variab|e-loadadjustmentmechanismwould enable all occupantsfrom the

5th- to the 95th-weightpercentileto adjust the system to providethe 14.5-G

load factor.

119
In the retrofitseat for the F-111 aircraft,the variable-loadinverted-tubetype energy absorbersare installedbetween the verticaladjustmentmechanism

and the guided seat pan carriage. These energy absorbersfunction in the same

manner as on the test seat: the tubes elongatewhen the inertialloads from

the movable part of the seat and the effectivemass of the occupant reach the

load factor of the energy absorbers. The seat strokes until the inertia|loads

decreaseor the seat hits the floor. Decelerationspikeswill exceed 14.5 G

because of the dynamic responseof the occupant/seatsystem. Unlikethe test

seat, a pin would be incorporatedinto the bottom end of each energy absorber

of the retrofitseat. Tilepin would remain in place, preventingseat stroke

during the first phase of the escape sequence,when the rockets carry the capsule away from the aircraft. The pin would then be removed beforeground impact.

Thus, the energy-absorbingstroke would be availableto protect the occupant

during the ground impact phase. The pin could be removed pyrotechnicallyor

manually. A pin puller could be connectedto the existingpyrotechnicsystem

on the aircraft,enablingthe pin to be removed automatically. Manual removal

of the pin could be used either as the primarymethod of removal,or as a secondary safety measure. Since no final decisionon these requirementshas been

made, the pin is not shown in the layout.

The seat carriageand guide tube assemblyprovidemost of the major loadcarrying structureof the seat. The carriagewould consist of identical

aluminumforgingsfor the leftand right side, joined by sheet metal along the

bottom to form a "pan", and heavier structureincludinghard points for the

mounting of the energy absorbersalong the back of this pan. Holes in each

side of the carriagewill be providedfor horizontaladjustmentof the seat

pan. Each of the left- and right-sideforgingsattachesto a guide tube in

two places: at the bottom and at a point almostmidway up the tube.

The guide tubes will be heat-treatedsteel. The tubes are plated for protection from corrosionand coated to provide a smooth surface for the bearings.

The tubularshape is needed to supportthe high bending loads from the inertia

reel and the carriage. At the top of each guide tube an aluminum fitting

would be providedfor mounting the power haul-backinertia reel. The inertia

reel presentlyused with the operationalseat is shown in the layout;however,

the upper guide tube fittingscould be modifiedto use a differentreel. These

fittingsalso have slots for horizontaladjustmentof the headrest. S]ots are

necessaryinstead of holes because the headrestis adjusted independentlyof

the seat pan.

The mounting points for the reflectedstraps could be on the upper guide tube

fittingsor the top of the seat back. The guide tube mounting providesa more

direct load path; if the strapswere connectedto the top of the seat back,

the loads would go through the headrestadjustmentmechanism. However,mounting the straps to the seat back may provide better restraintover the full

range of seat positions. Some layouts,with the seat in various positions,

would be done to Oeterminethe best attachmentpoint for the reflectedstraps.

In either case, the inertiareel loadsand the headrestloads would be carried

to the guide tubes through the upper guide tube fittings.

The seat pan and back assembly providesthe interfacebetween the occupantand

the seat. This assemblywould consistof the seat pan and seat back, hinged

togetherby two pins, with the headrestmounted on top of the seat back.

120
The seat pan could be either aluminum,a fabric-reinforcedlaminate,or a combinationof the two types of materials. Horizontaladjustmentand attachment

of the tiedown strap would be similar to the operationalseat. There are two

options for the top of the seat pan. It could be flat and covered with strips

of Velcro tape. In this case, the contour requiredto provide maximum comfort

to the pilots would be formed in a hard foam in the bottom of the seat pan cushion. The alternateoption could have a comfort contourmolded into foam and

bondedto the top of the seat pan, as is done on the operationalseat. In either

case, the seat pan cushionwould be designed for both maximum comfort and protectionduring ground impact.

The seat back would be hinged to the seat pan in the same manner as the operational seat. Aluminumtubes would be supportedabove each of the hinge points,

and a contouredaluminumsheet would join the tubes to form the seat back. The

seat back cushion would be similar to that in the operationalseat, but the

cushion shape would be contouredto match the seat back. Support along the seat

back will be providedto the maximum height possible. Layoutswill have to be

made to determinethe optimum height of the inertia reel, positionsand of the

reflectedstraps, and supportheight of the seat back for the wide range of seat

positionsand occupant sizes. Improvementsover the operationalsystem,which

has low reflected-strapattachmentand seat back supportheights,would be made.

The headrestwould be attachedto the top of the seat back at a fixed height

above the seat referencepoint. To providemaximum visibility,the shape of

the support surfaceon the operationalseat would be retained. The length of

the headrestwould be that necessaryto provide supportfor the specifiedrange

of occupantsizes. Cushioningsuch as that on the operationalseat should be

proviaed. Headrestadjustmentwould be accomplishedby a lever beside the headrest; movementof the headrestis on an arc around the hinge point between the

seat back and pan.

Positionof the headrestcontact surfacewould be approximatelyI-1/2 in. in

front of the seat back tangent line. This is further forward than the requirements of References9 and 18, which place the headrestcontact surface 1 in.

aft of the seat back tangent line. However, further movementaft of the headrest is prevented by the inertia reel. If a smaller inertia reel could be used,

the headrest could be moved back to a preferred position. However, this headrest position is not unlike the position in the operational seat.

In comparing the operational seat to the retrofit seat, one can see that the

operational seat pan carriage has been replaced by a lighter version; the same

applies to the seat back and headrest assemblies. The structure on the bulkhead supporting the headrest and inertia reel has been completely removed. On

the other hand, the retrofit seat adds guide tubes with fittings, energy absorbers, and linear bearings. If the inertia reel and power screw mechanism

were replaced by lighter versions, then the retrofit seat could use steel guide

tubes and be bui]t at approximatelythe same weight as the presentoperational

system. If the presentinertia reel and power screw mechanismsare to be used,

the guide tubes would be made out of aluminumwith internalstiffeningstructure. This is a lighteralbeit more expensivemethod of producingthe guide

tubes.

121
This section has presented an interpretation of tile retrofit seat, and has presented improvements that would be made to the operational seat's restraint system and general occupant interface. The configuration shown in Figure 78 satisfies the design guidelines and provides the vertical energy-absorbing feature

for ground impacts. Obviously, the prototype design process would examine the

system in more detail. A new seat pan cushion could provide better protection

at ground impact with no sacrifice in comfort. Further layouts would be needed

to define the inertia reel/seat back interface, the headrest adjustment mechanism, and the energy absurber release mechanism, as well as many other items.

These layouts would show where further improvements could be made. If possible, the inertia reel and power screw mechanism should be replaced by newer

versions.

5.2.2 BulkheadAttachment

Obviously,implementationof the retrofitseat would require some modifications

to the capsu|e bulkhead. The modificationswould be made to the same portions

of the bulkheadthat were modifiedfor the capsule test series. However,the

modificationsnecessaryfor a retrofitseat would be considerablydifferent

than those made for the test series. The modificationsfor the test series

were conservativelydesignedfor several reasons. There was not enough time

in the program to rigorouslyanalyze the load-carryingabilitiesof the capsu|e bulkhead. Also, the modificationhardwarewas manufacturedwith cost in

mind. Extra machiningoperationsthat could have reduced the weight were eliminated in favor of Keepingcosts to a minimum. Finally,the guide tubes on

the test seat were farther from the bulkheadthan they would be on the retrofit seat. The guide tubes were positionedin this manner for two reasons.

Firstly, the configurationof the test seat, using the operationalseat back

and large roller bearing assemblies,requiredthe bearingsto be further from

the bu|khead. The retrofitseat wou|d use a contouredseat back and sliding

bearings. Secondly,the test seriesat NASA requiredthat the modifications

to the aircraft not destroy the capabilityof mounting the operationalseat in

the capsule. Thus, the tracks could not be removed. In order to allow the

seat to stroke to the floor without hittingthe seat tracks, the guide tubes

were pushedout slightlyfurther from the bulkhead. The retrofitseat is not

limitedby these requirements;thus, the guide tubes wil| be mounted much closer

to the bulkhead.

Moving the guide tubes closer to the bulkheadrequiresthe removalof some structure. First,the lower sets of tracksneed to be removed in each seat location.

These tracks interferewith the seat strokingfully to the floor. Also, with

a retrofitseat, the tracks serve no function;they are thereforeunnecessary

weight. Second, the front portion of the air vent behindeach seat position

must be removed,as they were for the capsule test series. The parts are formed

sheet metal held in place by screws,and could easily be replacedby a flat

piece of sheet metal, with a minimaleffect on the efficiencyof the system.

The four |ower bearingswould be mounted in the same positionsas the test seat

bearingswere mounted. A large part of the material in the upper set of tracks

could be removed,leaving only enough track to assist in attachingthe fitting.

The structurearound the upper track supportsa large portion of the loads from

the operationalseat. Thus, it is strongenough to support the lower bearing

|oads on the retrofitseat with no additionalstiffeningstructure.

122
The upper bearingswould be more difficultto mount becauseof the pyrotechnic

tubes,wire bundles,and other items that are mounted on the bulkheadin this

area. Eachof the four upper bearingattachmentsis discussedseparately.

Figure 79 shows a sketch of some of the typicalhardwarebehind the pilot's

seat in an F-111 aircraft. Obviously,in order to mount the bearingson the

bulkhead,some changeswill need to be made. Item 1 in Figure 79 is the chaff

dispenser. At the present time this is not being used; it may be possibleto

remove it. If not, a small change in tubing could move the switch slightly

down on the bulkheadto clear the area for mountingthe bearing,and slightly

inboard to allow the pilot access to the switch by reachingaround the guide

tube. The plate runningacross the opening (Item 2 in Figure 79) serves as a

support for both pyrotechnictubingand a box-shapedclamp (Item 6). It would

be necessaryto redesignthis supportso that the clamp could be moved to allow

for mounting of the bearingfitting and to interfacewith additionalstructure

added behind the bulkheadextrusions(Items3 and 4). The same support now given

the pyrotechnictubes could be provided. The large tube (Item 5) visible on the

inboard side would need to be reroutedslightlyso that it passeseither above or

below the bearingfitting.

Figure 80 is a view of the outboardupper bearing attachmentthat was used in

the test serieson the pilot side. For the retrofitseat, the bearing position would be much closerto the bulkhead. The stiffenerwould be a square

aluminumtube travelingfrom the bearing up to the stiff structureat the bottom of the lateralvent. Some grindingat the ends of the channels that support the nitrogen bottleswould be necessary,but the functionof the channels

would not be impaired. The existingrivetswould be removedand replacedwith

blind rivets,joining the existingbulkheadextrusionand the bottle supports

to the added stiffeningstructure. The area below the vent is free of pyrotechnic tubing. Thus, a fitting could be added in the area just below the vent and

in front of the bulkheadreferenceline to join the added tubingand the bulkhead extrusionto the strong vent structure.

It is more awkward to add structureto support the upper inboard bearingon

the pilot side; fortunately,less structureis needed. Figure60 shows a

front view of the pilot-sidemodificationsfor tiletest series. The bulkhead

extrusionon the inboardside is already tied in to the box structurein the

middle of the capsule. Thus, the inboardstructureis already stiffer than

the outboardstructure. The triangularstiffenersused in the test series,

shown in Figure80, would be suitablefor adding to this bulkheadextrusion.

Severalof these would provide the stiffnessnecessaryto carry the loads. At

the point where the bulkheadextrusionand the vent structuremeet, some pyrotechnic tubes pass in front of the bulkheadreferenceline. Therefore,it is

best to keep in mind two possiblemethods of addinga fitting that strengthens

the attachmentbetweenthe bulkheadextrusionand the vent. One option would

be a fitting in front of the bulkheadreferenceline in the crotch formed between the two parts. If this is not possible,the fitting could sit behind

the bulkheadreferenceline (at Item 3 in Figure 79) and extend towards the

clevis (Item 7 in Figure 79) at the seat centerline. Where appropriate,it

would extend in front of the bulkheadreferenceline and be attachedto the

vent structure.

123
l

!

i ___. 2. PLATE

3. BULKHEAD EXTRUSION

l 1 ; J, _ _ 4. BULKHEAD EXTRUSION

6. BOX CLAMP

7, CLEVIS

°

,' . . 0

r_

Figure 79. Hardware behind pilot's seat in some F-Ill aircraft.
VENT

STRUCTURE

CHANNEL

SUPPORTS FOR

NITROGEN

BOTTLES

TRIANGULAR

STIFFENERS

STRUCTURE

Figure 80. Upper bearingattachmenton pilot outboard

side during crew module tests.

Figure62 shows a view of the outboardstructureused on the weapons system

officer (WSO) side of the aircraftduring the capsule tests. The stiffener

placed behind the bulkheadextrusionin this positionwould be similar to that

used on the pilot outboardside. If necessary,a channel stiffenerrunning

from the bulkheadextrusionto structureat the back of the compartmentcould

also be added. This would carry loads in the same manner as the alreadyexisting bott|e supportson the pilot side. A tube runs across the area in the

crotch of the bulkheadextrusionand the vent. Therefore,the top fitting

must be behind the bulkheadreferenceline. However,on this side of the aircraft, the top of the compartmentbehind the seat is open. Thus, the fitting

can remain behind the bulkhead referenceline and still attach to the lower

vent structure.

The inboardstiffeneron the WSO side used for the capsule test is shown in

Figure81. This would be replacedby the diagonalstiffenersalso used on the

pilot side. One can see that there is already a stiffeningstructurerunning

to the back bulkheadof the capsule. At the top, the fitting would also need

to remainbehind the bulkheadreferenceline, similar to the outboard fitting.

125
EXISTING

STIFFENER

ADDED

STRUCTURE

Figure 81. Upper bearingattachmenton WSO inboard

side during crew module tests.

In the area needed for mounting the upper inboardbearing on the WSO side, severa| pyrotechnictubes run in front of the bulkheadreferenceline. Couplings

exist in these |ines very close to the bearing attachmentpoint. It would be

necessaryto modify these tubes to provide room for the bearingfitting.

The two compartmentsbehind the weapons system officer are used to store survival gear. The modificationsdescribedhere would occur only in the corners

of the compartments,and would not restrictaccess to, or noticeablychange

the volume of, the storage space. However,the upper compartmentcover would

have to be redesignedto a]|ow clearancefor the bearing fittings. Modification to the lowercompartmentcover may or may not be necessary.

The modificationsdiscussedare conceptsbased on pre|iminaryevaluationof

the aircraftand experiencegained in the test series. The estimatedweight

126
of these modificationsis approximately2 lb. A more detaileddefinitionof

the modificationscould be made after the following:

e Detailedstructuralanalysisof the capsule

• Statictests on actual bulkheadsto verify strengths

• Discussionswith the Air Force to determinewhat modificationsare

the most cost effectiveand practical.

127
6.0 CONCLUSIONS

6.1 DISCUSSION

The majority of the effort put forth in this program was to conduct extensive

testing. The seat tests at CAMI used estimates of the ground impact conditions to demonstrate:

e The proper operation of the energy-absorbing seat both in limiting

loads and maintaining structural integrity

e Superior performance of the energy-absorbing seat when compared to

the operational seat

e Adequate room for the required energy-absorbing stroke.

Even though the actual pulses at NASAwere more severe than expected, the CAMI

tests are still very important: they served as preparation for the NASAtests

and provide excellent comparative data on the performance of the two seats.

The NASAtests provided more information supporting conclusions that the seat

was operating properly ana that there was enough room for the needed energyabsorbing stroke in even the more severe conditions.

The severity of the present ground impact conditions was demonstrated throughout the NASAtests. With the current parachute and IAB and under the ideal

impact conditions of the pure vertical drop tests, the energy-absorbing seat

stroked 2 in. Under the swing test conditions, up to 8 in. of stroke was required by one of the occupants. Therefore, it is reasonable to assume that

the large majority of the current ground impacts have capsule environments severe enough to require stroking of an energy-absorbing seat with 14.5-G energy

absorbers. Conditions that might not require stroke are those where the capsule has a nose-up attitude and is facing aftward of any horizontal velocity

vector. Both of these orientation factors would reduce the vertical component

of the ground impact pulse.

The testing at NASAdemonstrated that under conditions not severe enough to

cause the energy-absorbing seat to stroke, the performance of the energyabsorbing and operational seats was approximately the same. However, when the

conditions did require seat stroke, the improved performance of the energyabsorbing seat was evident in all cases. The CAMItests showed lower seat pan

and dumn_ acceleration levels, DRI values, seat pan loads, and dummylumbar

spinal loads with the energy-absorbing seat. The 32-ft/sec vertical drop tests

at NASAshowed similar results. In the NASAswing tests, the more severe environment resulted in slightly higher DRI measurements for the energy-absorbing seat

than were recorded at CAMI. However, based on the pattern established in the

other tests, one wou|d expect that the DRI values for the operational seat under

swing test conditions at NASAwould be higher than those measured for the energyabsorbing seat.

Since the completion of the testing required for this program, additional swing

tests were conducted at NASAto evaluate an inflatable body and head restraint

systml (IBAHRS). A drawing of one of the configurations of the IBAHRSsystem

is show in Figure 82. Four swing tests featuring essentially the same test

procedure used in the F-111 program were conducted. The results of one test,

128
I!

tk)

_D

Normal Inflated

Figure 82. Inflatable body and head restraint (Reference 11).
conducted with one operational seat and one energy-absorbing seat in the capsule, are presented in Volume III, The test was conducted with the following

conditions:

• Horizontalvelocity: 34 ft/sec

o Vertica]velocity: 32 ft/sec

e Capsule attitude

Pitch: nose up 2 degrees

RolI: 0 aegrees

Yaw: 0 degrees.

Unaer these conditions,the input pulse for both seats was essentiallythe same.

However,the energy-absorbingseat again showed lower seat pan and dummy accelerationlevels. The DR| values for tlleenergy-absorbingseat were also much

lower, with a value of 22.3 measuredalong the seat pan z-axis,compared to

29.6 for the operationalseat.

Tnus, the energy-absorbingseat featuringenergy absorberswith 14.5-G load

capabi]ityhas shown improvedperformanceover the operationalseat under all

conditionsthat require the seat to stroke. Also, with this energy-absorbing

load there is enough space under the seat to providethe stroke requiredover

the full design envelopeof the F-111 escape systemground impactconditions.

Yet a maximum DR| of 18 is requiredin MIL-C-25969and could conceivablybe

imposed on an energy-absorbingretrofitseat as part of the specification.

There are two reasons that this shouldnot be done. First,there is no correlationof injurypotentialto DRI for an energy-absorbingseat that justifies a particularDR| value. For energy-absorbingseats the DR| is presently

useful as a comparativetoo|, not an absolutemeasure. Second, in order to

lower the DR| va|ue for an energy-absorbingseat, the limit load of the energy

absorberswould have to be reduced (see Figure 29). This increasesthe stroke

requiredto absorb the energy in any particularground impact pulse (as shown

in Figure83), and this raisesthe chances of bottomingout in the more severe

impacts. If the seat strokes to the floor and bottomsout, there will be a

decelerationspike applied to the seat. The severityof the effect of this

spike will depend on the velocityof the seat relativeto the floor when it

makes contact. The velocitywill vary with the severityof the ground impact

and the amount of energy absorbedby the IAB.

Some effort was also made to evaluatethe effects of a parachutereplacement

that would reduce the verticaldescent rate from 32 to 25 ft/sec. Obviously,

this would reduce the severityof the ground impactenvironment. However,the

aecrease in the efficiencyof the IAB at some aircraftattitudesand horizontal velocitieswould sti|| occur. In order to evaluatethe benefitsof an energyabsorbingseat in this system, one would have to examine the ground impactconditions over the fu|l design envelopeof the escape system. The originaldesign

envelopemay be used, or perhapsmore recent informationon the actual conditions

during previousejectionsfrom the aircraftwould be used to define a new design envelope. Cautionmust be exercisedin not placing too much importance

on previousejectionexperience,gatheredmainly during peacetime,to evaluate

a systemthat must perform in wartime.

130
16

o

o

14- - 00

12-

,,_ 10 -

uJ

0

nP" 8-

U.I

0

uJ

e." 6-

4-

25G

ACCELERATION PULSE 2 - FROM NASA TEST -

I "120 ISEC NO.3, RIGHTSEAT

0 I I I I I

10 11 12 13 14 5

ENERGY-ABSORBER LIMIT LOAD (G)

Figure 83. Verticalstroke versusenergy absorber limit ]oad

(as calculatedby method presentedin Reference11).

131
With this new and less severe environmentdefined, the benefitsof an energyabsorbingseat could be evaluated. In this case, the possibilityof reducing

the energy absorber limit load and still having the requiredstrokingdistance

becomesan option that could be considered. If the Air Force fee]s that the

14.5-Gload factor is not the most efficientfor the controlledground impact

of the capsule, the load factorcan be easily changed in the design phase of

the retrofitseat or even after seats are installedin aircraft.

6.2 CONCLUSIONS

The first conclusions concern the primary objective of the testing conducted:

to aetermine the performance of the energy-absorbing seat over the ground impact design envelope of the F-Ill escape capsule.

• The seat pan accelerations,dummy accelerations,and DRI values measured for the energy-absorbingseat are reasonablefor an energy absorber limit load of 14.5 G, and thereforeshow the seat to be functioningproperly.

• With the present escape system parachute and IAB an energy-absorbing

seat, with energy absorbers limited to stroke at 14.5 G, would stroke

for one or both occupants in the large majority of ground impacts.

• With a retrofitseat in the full-up positionand variable-loadenergy

absorbersset at 14.5 G, enough stroke is availableto prevent bottoming out within the aesignenvelope of ground impactconditions.

In comparingthe energy-absorbingseat to the operationalseat, the following

conclusionscan be made:

• Under conditionssevereenough to cause the energy-absorbingseat to

stroke, the seat pan accelerations,dummy accelerations,and DR|

values show that the energy-absorbingseatwith energy absorbersset

for 14.5 G providesa significantlyless severeenvironmentthan the

operationalseat.

• The seat pan loadsmeasuredat CAMI and NASA, and the dummy lumbar

spinal loadsmeasuredat CAM|, all show that the energy-absorbing

seat reduces the spinal loads experiencedby the occupantwhen the

ground impactis severeenough to cause seat stroke. The more severe

the environmentis, the greater the improvementwith the energyabsorbingseat.

• Under milder conditionsthat would not cause seat stroke, the performanceof the operationaland energy-absorbingseats was approximately the same.

• The results of evaluatingthe data using the Eibandcriterionare

inconclusive. They do not show differencesin performancebetween

the operationaland energy-absorbingseats that are shown by DRI,

seat pan loads,and lumbar spinal loads.

132
Reducingthe verticaldescent rate to 25 ft/sec by using a new parachutewill

reduce the severityof the ground impactenvironment. However,bag efficiency

wil] still decreaseas the effects of wind velocityand direction,as well as

capsule swing, becomemore pronounced.

6.3 RECOMMENDATIONS

Recommendations are divided into two groups, depending on whether or not the

parachute is changed to a design that would reduce the descent rate. If the

parachute remains the same, then the primary conc]usions of this report, which

illustrate the improved performance with an energy-absorbing seat, indicate

that the operationalseat should be rep|acedas quickly as possible. Therefore,

the followingsteps should be taken:

• Preparea specificationfor an energy-absorbingretrofitseat. Incluae the following:

- Requirementsfor variab|e-loadenergy absorberswith a 14.5-G

limit load

- Requirements for a pin that fixes the position of the seat

during ejection but a]lows energy-absorbing stroke during ground

impact

- Definition of the required static and dynamic testing of the

prototype seat

- A definition of other seat improvements where possible, such as

position of headrest and reflected strap attachment points.

• Design,fabricate,and test a prototyperetrofitseat.

If the parachuteis modified,then the reduced descent rate will lessenthe

severityof the ground impact environment. However,the extent of this change

is not known. Therefore,the followingsteps should be taken:

• Examinethe history of F-111 escape capsu|esto obtain statistica]

distributionsof ground impactconditionssuch as wind velocity,

wind direction,capsule attitude,and landingsurface.

• Based on escape system history (mostly during peacetime) and the

performance requirements of the F-Ill aircraft in a wartime situation, define the new design envelope for the improved escape system.

• Using the reduceddescent rate and the varying efficiencyof a new

IAB,determinethe ground impactenvironmentover the new design envelope.

• Eva|uatethe benefitsof an energy-absorbingseat over the full design envelope,consideringthe severityof the environment,the available strokingdistance,and a suitablerange of energy absorberlimit

loads.

133
One must remember that all the tests conducted in this program with the energyadsorbing seat used energy absorber limit loads of 14.5 G. Using this seat,

the ground impact environment in an F-Ill ejection is severe enough to cause

the seat to stroke in almost every case. Also, whenever the environment is

severe enough to cause the seat to stroke, the performance of the energyabsorbing seat is superior to that of the operational seat. That is, the vertical loads that the occupant experiences in the energy-absorbing seat are less

than experienced in the operational seat. However, even in the most severe

ground impact cases at the edge of the design envelope, if the seat starts in

the top half of the vertical adjustment range, there is enough room for the

seat to stroke vertically without bottoming out. Thus, an energy-absorbing seat

with a 14.5-G limit load provides improved protection for the occupants of the

F-Ill capsule over the entire design envelope of the ground impact conditions.

If the severity of the ground impact environment is reduced, then the energyabsorbing test seat might not use all of the available stroking distance even

at the edges of the design envelope. In this case, the difference in performance between the energy-absorbing seat and the operational seat could be made

even greater by lowering the energy absorber limit load, since this would lower

the seat pan acceleration, DRI's, seat pan loads, and dummyspinal loads measured with the energy-absorbing seat. However, the occupant must not be subjected to an injurious load from bottoming out. Care must be taken not to use

all the available stroking distance and subject the occupant to an injurious

load from hitting the floor before the energy in the impact has been dissipated.

134
7.0 REFERENCES

1. Hearon, B. F., Comparative Vertical Impact Testing of the F/FB-111 Crew

Restraint System and a Proposed Modification, AFAMRL-TR-82-13, March 1982.

2. Laananen, D. H., Aircraft Crash Survival Design Guide, Volume II, Aircraft

Crash Environment and HumanTolerance, Simula Inc.; USARTL-TR-79-22B, Applied Technology Laboratory, U.S. Army Research and Technology Laboratories

(AVRADCOM),Fort Eustis, Virginia, January 1980.

3. Brinkley, J. W., et al, Evaluation of a Proposed, Modified F/FB-III Crew

Seat and kestraint System, AFAMRL-TR-80-52, Aerospace Medical Research

Laboratory, Wright-Patterson Air Force Base, Ohio, November 1981.

4. Kazarian, L. E., et al, Spinal Injury Mechanism Assessment, AMRL-77-60,

Aerospace Medical Research Laboratory, Wright-Patterson Air Force Base,

Ohio, October 1977.

5. Kazarian, L. E., eta], Spinal Injuries in the F/FB-III Crew Escape System,

Aviation, Space, and Environmental Medicine, Volume 50, No. 9, September

1979, p. 948-957.

6. Ejection Experience in F/FB-III Aircraft, 1967-197L_, Proceedings of the

17th Annual SAFESymposium, December 2 - 6, 1979.

7. Hearon, B. F., F/FB-Ill Ejection Experience (1967 - 19801 Part I - Evaluation and Recommendations, AFAMRL-TR-81-113, November 1981.

8. Hearon, B. F., Mechanisms of Vertebral Fracture in the F/FB-Ill Ejection

Experience, Aviation, Space, and Environmental Medicine, May 1982.

9. Military Specification, Capsule Emergency Escape System, General Requirements for, MIL-C-25969 (USAF).

i0. Brinkley, J. N., et al, Vertical Impact Tests of a Modified F/FB-III Crewseat to Evaluate Headrest Position and Restraint Configuration Effects,

AFAMRL-TR-82-51, Air Force Aerospace Medical Research Laboratory, _JrightPatterson Air Force Base, Ohio, August 1982.

Ii. Desjardins, S. P., Laananen, D. H., et al, Aircraft Crash Survival Design

Guide, Volume IV, - Aircraft Seats, Restraints, Litters, and Padding, Simula, Inc., Tempe, Arizona; USARTL-TR-79-22D, Applied Technology Laboratory,

U.S. Army Research and Technology Laboratories (AVRADCOM),Fort Eustis,

Virginia, 1980.

12. Hearon, B. F., et al, Vertical Impact Evaluation of the F/FB-I11 Crew Restraint Confi(}uration, Headrest Position, and Upper Extremity Bracing

Technique, Aviation, Space, and Environmental Medicine, Volume 54, Number

Ii, November 1983, p. 977- 987.

13. Coltman, J. W., Design and Test Criteria for Increased Energy-Absorbing

Seat Effectiveness, USAAVRADCDM-TR-82-D-42,Applied Techno|ogy Laboratory,

U.S. Army Research and Technology Laboratories (AVRADCOM),Fort Eustis,

Virginia, March 1983.

135
14. Military Specification, MIL-S-58095(AV), Seat System: Crashworthy, NonEjection, Aircrew, General Specification for, Department of Defense,

Washington, D.C., August 27, 1971.

15. Eiband, A. M., HumanTolerance to Rapidly Applied Accelerations: A Summary

of the Literature, NASAMemorandum5-19-59E, Lewis Research Center, Cleve]and,

Ohio, June 1959.

16. Laananen,D. H., and Coltman,J. W., Measurementof Spinal Loads in Two

ModifiedAnthropomorphicDummies,TR-82405,Simula Inc., Tempe, Arizona;

ContractDAMD17-81-C-1175,Final Report, U.S. Army AeromedicalResearch

Laboratory,Fort Rucker,Alabama,May 5, 1982.

17. Vaughn, V. L., and A]faro-Bou, E., Impact Dynamics Research Facility for

Full-Scale Aircraft Crash Testing, NASA Technical Note D-8179, Langley

Research Center, Hampton, Virginia, April 1976.

18. MilitarySpecification,MIL-S-9479,Seat System, Upward Ejection,Aircraft,

General Specificationfor, Departmentof Defense,Washington,D.C.

136

TechnicalReport DocumentPage

I. ReportNo. 2. GovernmentAccessionNo. 3. Reclpient'sCatalogl#o.

NASA CR-3916

4. Tltleand Subtitle 5. ReportDate

Design and Testing of an Energy-Absorbing Crewseat August 1985

for the F/FB-IIIAircraft. Volume I--FinalReport 6. Perfoming OrganizationCode

8. PerfonqingOrganizationReportNo.

7. Author(s) TR-84428

S. Joseph Shane

IO. Work Unit No. (IRAIS)

9. Perfoming OrganizationName and Address

Simula Inc. Ii Contractor GrantNo.

10016 S. 51st Street NASI-17387

Phoenix,Arizona 85044 13. Type of Reportand PeriodCovered

12. SponsoringAgency Name and Address Final Report

National Aeronautics and Space Administration May 1983 - May 1985 Washington, D.C. 20546

14. SponsoringAgency Code

15. SupplementaryNotes

LangleyTechnicalMonitor: Claude B. Castle

NASA CR-3917 - Volume II--DataFrom Seat Testing

NASA CR-3918 - Volume III--DataFrom Crew ModuleTesting

16. Abstract

Over the past years, several papers and reports have documented the unacceptably high injury rate during the escape sequence (including the ejection

and ground impact) of the crew module for F/FB-111 aircraft. This report

documents a program to determine if the injury potential could be reduced by

replacingthe existingcrewseatswith energy-absorbingcrewseats. An energyabsorbingtest seat was designedusing much of the existingseat hardware.

An extensivedynamic seat test series,designedto duplicatevarious crew

module ground impactconditions,was conductedat a sled test facility. Comparative tests with operationalF-111 crewseatswere also conducted. After

successfuldynamic testingof the seat, more testing was conductedwith the

seats mounted in an F-111 crew module. Both swing tests and verticaldrop

tests were conducted. The vertica|drop tests were used to obtaincomparative data between the energy-absorbingand operationalseats. Volume I describes the energy-absorbingtest seat and testingconducted,and evaluates

the data from both test series. Volume II presentsthe data obtainedduring

the seat test series, while Volume Ill presentsthe data from the crew module

test series.

17. Key Words 18. DistributionStatement

Seat ImpactProtection

Crew Module RestraintSystems Unclassified- Unlimited Crashworthiness ImpactTests

Escape Systems Subject Category05

19. Security Classtf. (of this report) 20. Security Classtf. (of this page) 21. No. of Pages 2Z. Price

Unclassified Unclassified 150 A07

.._os ForsalebytheNationTalechnicIanlformatSioernvicSe,pringfieVi ldrg, inia22161

NASA-Langley, 1985

National Aeronautics and

Space Administration BULKRATE

Washington, D.C. POSTAGE& FEES PAID

20546 NASA Washington,DC

Permit No. G-27

Official Business

Penalty for Private Use, $300

POSTMASTER: If Undeliverable (Section 158 Postal Manual) Do Not Return