NBSIR 75-709'^)

Design and Fabrication of an

Integrally Illuminated Runway

Distance Marker Using Subminiature

Incandescent Lamps

M. R. Freund, W. F. Mullis

Illuminating Engineering Group

Optical Radiation Section

Heat Division

Institute for Basic Standards

National Bureau of Standards

May 1975

Final Report

Prepared for Ships Installation Division

Naval Air Systems Command

Department of the Navy

Washington, D. C. 20360

NBSIR 75-709

DESIGN AND FABRICATION OF AN

INTEGRALLY ILLUMINATED RUNWAY

DISTANCE MARKER USING SUSNIINIATURE

INCANDESCENT LAMPS

M. R. Freund, W. F. Mullis

Illuminating Engineering Group

Optical Radiation Section

Heat Division

institute for Basic Standards

National Bureau of Standards

May 1975

Final Report

Prepared for Ships Installation Division

Naval Air Systems Command

Department of the Navy

Washington, D. C. 20360

U.S. DEPARTMENT OF COMMERCE, Rogers C.B. Morton. Secretary

NATIONAL BUREAU OF STANDARDS. Richard W. Roberts. Director

PREFACE

At the request of the Naval Air Systems Command, Department

of the Navy, the National Bureau of Standards designed and

fabricated an integrally illuminated runway distance-to-go

marker using subminiature incandescent lan^ss. The work was initiated in an effort to improve the f>erformance of the markers

over existing units in terms of conspicuity, energy saving,

extent of maintenance required, and in regard to their in^jact mass. The prototype model fabricated is not considered a final

engineered design but is described primarily to illustrate the

design concept. The opinions, findings, and conclusions in this

report are those of the authors and are not necessarily those

of the Naval Air Systems Command.

1
CONTENTS

Page

1. INTRODUCTION 3

2. PROTOTYPE MARKER DESIGN 4

2.1 Mechanical 4

2.2 Electrical 5

3. DISCUSSION 7

4. APPENDIX 10

4.1 Introduction lo

4.2 Alternate Construction 10

5. REFERENCES 12

ILLUSTRATIONS

1 Daylight and Night Photographs of NBS Prototype

Integrally Illuminated Runway Distance Marker 13

2 Detail of Runway Distance Marker Construction 14

Al Cross-sectional Sketch of Al ternati ve Method #1 of

Constructing Integrally Illuminated Runway Distance

Marker Using Subminiature Incandescent Lamps 15

A2 Cross-sectional Sketch of Al ternati ve Method #2 of

Constructing Integrally Illuminated Runway Distance

Marker Using Subminiature Incandescent Lamps le

TABLES

1 Load-Voltage Characteristics of Existing Transformers 6

2 Estimated Number of Lamps and Power Required Per

Numeral 7

2
1. INTRODUCTION

Two typ^s of distance-to-go markers are currently in use at

military and joint-use (civil and military) airports to indicate

the runway-remaining distance. The two typ>es can be classified as externally illuminated and internally illuminated units. The markers

are spaced at 1000 foot intervals and indicate the distance to the

end of the runway in thousands of feet. The externally illuminated

marker was the first type to be used and consists basically of a "billboard" type sign painted orange with a white numeral. It is

illuminated at night with two 75-watt, 120-volt, PAR 38, floodlights,

one located adjacent to each side of the sign, (see MBS Report 5466,

dated September 1957) . The internally illuminated marker is the type

presently prescribed as the Navy Standard (NAEC Airfield Visual Aids

Bulletin #1, dated 16 Nov. 1970) and consists of an aluminum housing

with translucent plastic side panels and internally mounted incandescent

lamps. A transparent yellow numeral is displayed on a black opaque

background. Six 75-watt, 120-volt lamps are used to illuminate the

numerals of the sign. (NBS Report 6904, dated July 1960).

Although the present markers have proved fairly satisfactory,

concern has recently been voiced in regard to the extent of maintenance required for the units, and in regard to their weight or impact mass. Also, with advances in technology, the question has

been raised as to whether the niarkers might be improved in regard to

legibility and power requirements. Further, it has been suggested that

the painted surface type be replaced with an internally illuminated

type, either of the present design or of a new design.

Because of these factors, the National Bureau of Standards was requested to design and fabricate a marker that would effectively

alleviate as many of the above concerns as possible. The marker

thus produced has been evaluated at the Naval Air Test Center,

Patuxent River, Md. along with existing markers. Results of their

evaluation is contained in NATC Report FT-73R-74 and indicates that

the design concept of the marker is promising. The purpose of this

report, therefore, is to describe the construction of the NBS-designed

prototype marker. The prototype unit was not intended to be a final

engineered design but was constructed to test the lighting concept

and durability features. Alternative methods of construction for

reducing the impact mass of the marker while maintaining the design

concept are described in the appendix.

3
PROTOTYPE MARKER DESIGN

2.1 MECHANICAL

Except for the mounting hardware, (e.g., poles)

lamps, and wiring, the sign is constructed of plastic

materials. It consists of an integrally illuminated white

plastic (acrylic) numeral laminated to an aviation orangecolored acrylic background panel which in turn is bonded

to an opaque fiberglass panel. (See Figures 1 and 2).

Two such signs are mounted back-to-back on poles having

frangible couplings. The signs display a numeral or

nimverals on each side indicating the distcmce (in thousands

of feet) to the respective ends of the pavement. Ttie

dimensions of each side of the prototype sign were 4 feet

in height, 3 feet in width, and 11/16 inch in thickness.

The numerals of the sign were 40 inches high and 5 inches

wide. A plastic adaptor is used to fasten the signs to

the poles and to enclose the space between panels. The

adaptor also serves to stiffen the plastic panels. The

numeral is illuminated by sui miniature incandescent lamps.

The number of lan^js for a particular pemel depends on the

numeral being displayed. Foi excuiple, an "8" may take as many as 85-90 lamps, whereas a "1" may take only 40-45

lan5)s. The lan^s are designated with the trade number

715. They have a T-1/8 bulb, pigtail leads, and are rated

at 5 volts, 0.11 ampere, with 50,000 hour's life. The

dimensions of the sign amd tJie numerals were made in

accordance with the requiremt;nts of Technical Manual,

NAVAIR 51-50AAA-2, "Visual L^mding Aids Design Standards

Installations", dated 1 April 1966, except that the

width of the background panel was 3 feet instead of the

4 feet specified. The width was limited to the width of

the plastic sheets avail2±>le at the time of fabrication.

The weight of the prototype i wo-sided sign was approximately

60 pounds exclusive of the p<>les and mounting hardware.

Specific details of the marker construction are shown

in Figure 2. The lan^js are nounted in the white numeral

portion of the sign, approxinately 1 inch from each edge

in holes drilled both through the orange background sheet

and to a depth of 11/32 of aii inch into the numeral. The

numeral is translucent and is 1/8 inch thick, whereas the

background is essentially opaque and is 1/4 inch thick.

The holes for receiving the lamps are 1/8 inch in dicimeter.

Wiring for the leut^js is attached to the rear surface of the

background panel with small screws and is soldered to the

4
lainp leads (pigtails) at each hole location. The launps are placed at 2 inch intervals (although sharp curves may require closer spacing) amd thus outline the shape

of the numeral. Bare 20-gage copper wire was used for the

prototype model although flat-printed or ribbon circuitry

would be preferable. The wiring is protected by a 1/16

inch thick protective fiberglass sheet bonded to the

background panel by use of a 1/4 x 2 inch plastic spacer

strip bonded around the periphery of the sign. The spacer

was used in order to provide clearance for the wiring.

(If flat conductors are used the protective panel can be

bonded directly to the background pemel.)

2.2 ELECTRICAL

The electrical load requirements for the various marker

panels differ as each numeral displayed requires a different

number of lamps. The lan^^s are connected in parallel so that the current to the panel is directly proportional to

the number of lamps required. For excunple, if an "8" is

displayed containing 87 lamps, the current drawn at rated

voltage (5 volts) would be 9.57 anperes or 47.9 watts of

power, whereas, if a "1" is displayed requiring only 42

laiT^s, the current drawn under similar conditions, would

be 4.5 amperes or 23 watts of power. Power for the distcince

markers is usually obtained from the edge-lighting or other

series circuits. Since the current requiren>ents for signs

differ, a simple series/series isolating transformer can

not be used in its conventional unsaturated mode. In

addition, some dimming of the marker lights is desired as

the runway lights are dimmed. However, for optimum performance, the rcinge of dimming for the distance marker

lights should not be as great as the dimming of the runway

lights. Fortunately, some of the series transformers

presently used for the runway lights have appropriate

characteristics for powering the marker 1 ights through cin auxiliary step-down type transformer to obtain the re- quired 5 volts. From NBS Report No. 6337, dated March

1959, "Output Characteristics of Three 200-watt Seriesseries Transformers with Multiple Lcunps as Load", it is

evident that all of the three 200-watt 6.6A/S.6A series/

series, 5000-volt transformers described in that report

and used to power the airport runway edge lights Cein also

be used to power the marker lights. These transformers,

manufactured by three different con5)anies (Jefferson

Electric, Line Material, and AGA) have essentially the same shaped load-voltage characteristic curves, but differ

slightly in the magnitude of their secondary voltage. An

5
example of the differences are listed in Table I for

step 5 (maximuir current step) of the current regulator.

The differences are essentially proportional for the

other four dimming steps.

TAELE I Load-Voltage Characteristics of Existing Transformers

Output Voltage on Intensity Step 5 Transformer Load Line Material Jefferson Electric

(Watts) Company AGA Compcuiy

0 85 90 105

50 72.5 82.5 90

100 70 86 93

From these data, it is evident that step-down transformers having a ratio of about 15/1 would be satisfactory

for powering the marker signs from the Line Material transformer. However, trcinsformers having ratios of about 16/1

and 18/1 would be required to give the 5 volts required

from the transformer manufactured by AGA and the Jefferson

Electric Company respectively. A tapped step-down transformer would accommodate the variations in transformers

manufactured by the different con?>anies.

Calculations indicate that eui average distance marJcer

having a 75-watt load and operated from any of the above

mentioned transformers, would be dimned to about 60 to 70

percent of full current intensity, depending upon the type

of transformer used, when the intensity setting is changed

from step 5 to step 1; whereas the runway edge lights would

be dimmed to 0.2% of full current intensity (data from NBS

Report 6337)

A rough estimate of the quantity of lamps required

for each numeral and the electrical load of the numeral is

given in Table II.

6
TABLE II

Estimated Number of Laitps and Power Required per Numeral

Numeral Displayed

Quantity of Lan5)S

Required

Power Consumed

(Watts)

0

1

2

3

4

5

6

7

8

9

96

42

90

88

74

96

90

67

87

90

53

23

50

48

41

52

50

37

48

50

A combination of two or more numerals would constitute

the load on the power transformer at a given station along

the runway. From these data it is seen that the minimum load

for a single station would be of the order of 46 watts (2-ones)

to a maximum of cdxjut 104 watts {2-fives) . The load variations

are of the same wattage rainge as given for the tramsformers

in Table I. The secondary voltages of the transformers vary

less than 5% with a load change from 50 to 100 watts. A

5% voltage variation to the different marker signs would result

in an intensity difference of about 16%, which for practical

purposes is visually indistinguishable.

The design and construction of the marker described is simple, uses less electrical power than existing units, provides a high degree

of legibility for both day and night operations, offers reduced maintenance features, and is compatible with existing airport runway electrical

systems. From the standpoint of maintenauice , the all-plastic construction

should require little or no cleaning. Furthermore, the plastic was deemed to be durable because during the two years the prototype unit

was installed at the Naval Air Test Center at Patuxent River, Md. , no discoloration, fading, or other deterioration was detected. Also, from

the standpoint of lamp life, the 50,000-hour life represents almost

6 years of continuous burning. If average operating time is 10-12

hours per day, life of the marker, barring physical abuse, should be

well over 10 years.

3. DISCUSSION

7
As for night conspicuity in service, pilots judged the prototype

as a considerable improvement over the existing meurker and with a greater

readability range. In clear weather resolution of the numeral is

limited primarily by its size.

As for the daylight conspicuity, the NATC tests indicated that

the NBS marker "did not demonstrate any inprovement over the present

marker". The pilots pointed out that all the markers tended to blend

into the background. They further suggested that daylight contrast

might be improved by adding a black border eiround the white nvuneral or perhaps placing the white numeral on a black panel.

Two basic questions arise from these suggestions. The first

deals with detection range and distinguishing the whole sign from its

surroundings while the second deals with recognition of the numeral

displayed. As regards the first question, Judd and Yonemura-^ studied

the conspicuity of targets painted with international orange and with

black against various backgrounds. They concluded that international

orange is more conspicuous against a dark-foliage background; and

black is more conspicuous tham international orange for a lightfoliage background. For average foliage international orange is

more conspicuous at large angular subtense (greater than 10 minutes

of arc); and black is more conspicuous at small subtense. They stated

that "the virtue of international orange is that it is fairly con- spicuous against all foliage backgrounds". The question then is under

what background conditions and viewing angles are the signs used. The

background runs the gaimut in color from white to dark green to brcwn

and all shades and hues between (snov,, grass, forest, water, etc.).

In addition, the angular subtense of the numerals displayed (stroke

width 5 inches) can be considered as fairly small (about 1.5 minutes

of arc at 1000 feet and 3 minutes at 500 feet) . With this in mind,

and if the background Ccin be considered as "average foliage" then it

would appear that international orange might maintain a slight

superiority ever black for detection of the sign from the standpoint

of background whereas black would be the superior finish from the

standpoint of size (angular subtense) . Bear in mind that the differences

in question for practical purposes are small.

On the other hand, the purpose ot the sign is to convey information.

Therefore, legibility of the numeral is as inportant as detection of

the sign. Legibility is a function of the contrast between the

nuireral and its iiranediate surround. Usually, the greater the contrast,

the easier. the numeral is to read. Since the greatest contrast exists

between black and white ar.d since a white letter is used, this would

suggest that the surrounding panel should be tlack. Consequently,

there appears to be a conflict between optimum detection of the sign

and legibility of the numeral. Either background appears to be

adequate for the visibility ranges intended.

8
The 60 pounds of weight of the prototype marker is probably

comparable to existing signs and is considered greater than necessary

or desired from the standpoint of impact mass. Therefore, following

the fabrication and installation at Patuxent cf the prototype,

alternate designs which signi f icaritly reduce the weight of the unit were evolved. Entails of the lighter units are given in the appendix.

Based upon the potential improvement of marker signs using the

all plastic construction and the integrally illuminated concept with

respect tc lower maintenance, power consun^tion, and weight reduction,

it is recommended that a sufficient number of these signs be fabricated to equip a full runway for further evaluation. The design

concept should also be extended to taxiway and apron guidcince signs.

9
APPENDIX

ALTERNATIVE METHODS OF CONSTRUCTION OF THE INTEGRALLY

ILLUMINATED RUNWAY DISTANCE MARKER

4.1 INTRODUCTION

In the preceding report the prototype integrally

illuminated rianway distance rrarker was described. The

lighting concept as well as the durability of the sign

appears sound, based upon the field evaluation at the Naval

Air Test Center, Patuxent River, Md. However, as was pointed out in the report, the weight of the unit is of

the order of 60 pounds. This weight is considered

greater than needed or desirable. To reduce damage

to aircraft when they collide with signs of this type,

it is imperative that the mass of the signs be small eaid

that their center of gravity be as near to the ground as possible. Consequently, alternative methods of constructing

the NBS designed marker to reduce its impact mass and to

lower its center of gravity follow. Using this method of

construction, a sign of less than 40 pounds should be easily

achieved.

4.2 ALTERNATIVE CONSTRUCTION

The alternate method of construction consists of using

1/8, or 1/6 inch, thick orange background panels instead of

the 1/4 inch panels used in the prototype. The pamels are spaced parallel approximately 1 inch apart as shown in

sketch, A-1 or tapered slightly as shown in sketch A-2. The

space between the panels is filled with a light-weight foam

or honeycomb material for obtaining the necessary rigidity.

The filler material should be of a type that bonds to

the panels. The acrylic material for the numeral is increased to about 1/4 to 5/16 inch in thickness to accommodate

the installation of the wiring and sub-miniature Icinps. The

numeral and background panels are then laminated together as previously described or the numeral is attached mechanically

to the background if it is desirable to remove or replace

numerals. A light-weight perforated aluminum U-shaped

frame installed along the bottom edge of the panels coirpletes

the marker assembly. The U-frame carrying a pipe flange

attaches to the poles having fremgible couplings in the

usual manner. This method of mounting keeps all of the

relatively heavy structural members of the sign near the

ground (12 to 16 inches) and thereby should result in less

damage to an aircraft upon impact. Further, the all-plastic

10
construction above the mounting should result in a fixture that shatters nvore readily than existing signs.

Wiring for the marker sign is accomplished as described

for the prototype unit except that if removable numerals

are desired, appropriate electrical connectors are added

where the numerals are attached to the panels.

- 11 -
5. REFERENCES

1. Judd, D.B. and Yonemura, G.T., Target Conspicuity and Its

Dependence on Color and Angular Sibtense for Gray cind Foliage

Surrounds, NBS Report 10-120, Novitnber 1969.

12
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14
Figure A-1. Cross-sectional Sketch of Alternative Method #1 of

Constructing Integrally Illuminated Runway Distance

Marker Using Subminiature Incandescent Lamps.

NBSIR 75-709

USCOMM NBS DC

15
Background Panel Honeycomb or Foam Filler

Mounting Bracket

Figure A-2. Cross-sectional Sketch of Alternate Method //2 of

Constructing Integrally Illuminated Runway Distance

Marker Using Subminiature Incandescent Lamps.

NBSIR 75-709 16

NBS.n4A IREV. 7.73)

U.S. DEPT. OF COMM. 1. pcHLK ATION OR.RI'PORT NO. 2. Gov't Accessu.n BiDLIUuKArnIC UAIA INDoIK /b~/U9

SHEET

3. Recipient's Accession No.

4. TFTLF: and SUHTITIJ-: Design and Fabrication of an Integrally Illuminated

Runway Distance Marker Using Subminiature

Incandescent Lamps

5. Publication Date May 1975

6. Performing Organization Code

221.12

7 AUTHOR(S)

M~ R. Freund and W. F. Mull is

8. Performing Organ. Report No. NBSIR 75-709

9. PERFORMING OR(.ANIZA HON NAMI. AND ADDRKSS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and < omplt-lc- Address (Street, City, State, ZIP)

Ships Installation Division

Naval Air Systems Conmand

Department of the Navy

Washington, D. C. 20360

13. Type of Report & Period Covered

Final, May, 1975

14. Spon s or ing Agency CI ode

15. SUPPLKMKNTARY NO I hS

16. AHSTRA( 1' (A 200-word or less (actual nummary ot most si^tficant information. If document includes a significant

bibliography or literature survey, mention it here.)

A prototype integrally illuminated runway distance-to-go marker

was developed using embedded subminiature incandescent lamps. The all-plastic

construction of the marker offers improved performance over existing markers

in respect to conspicuity, energy saving, reduced maintenance, and in regard

to reduced impact mass. The marker is compatible with existing airport

electrical systems. The unit was evaluated over a 2 year period at the

Naval Air Test Center, Patuxent River, Md. and was selected as the most

promising of those tested.

17. KHY WORDS (six to twelve entrins; alphabetical order, capitalize only the first letter of the first key word unless a proper name; separated by semic olons ) Runway distance-to-go marker; airport conspicuity; contrast; readability ranqe- legibility; color. ^

'

18. AVAILABILITY i Unl imited 19. SH( IJRITY CLASS

'THIS RKPORT)

21. NO. OF PAGES

[2 For Official Distribution. Do Not Release to N I LS UN( L ASSIFIED

r ] Order T rom Sup. of Doc, U.S.

Washin>;ii.n, D.( . 20 U)2, SD ( (jovernment

at. No. ( 1 3

I'rinting OKiCe 20. Sf ( URITY CLASS

( l ifLS PA(.E)

22. Price

^ Order 1 rom National lechnica

Springticid, Virginia 221'il

1 Informanon Service (N1 ISl l'N( LASSIMED

USCOMM-DC 29042-P74