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NATIONAL BUREAU OF STANDARDS REPORT

19^^-

INVESTIGATION OF FIRE RESISTANCE

OF AIRCRAFT FUSELAGES

Rrs Re, i, idg° zS „ -. A252

Washington, ac. 20234

ervices

by

A.

J.

C. Hutton

and

V . Ryan

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Charles Sawyer, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Aslin, Director THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards is suggested in the following listing of

the divisions and sections engaged in technical work. In general, each section is engaged in specialized research, development, and engineering in the field indicated by its title. A brief description

of the activities, and of the resultant reports and publications, appears on the inside of the back

cover of this report.

Electricity. Resistance Measurements. Inductance and Capacitance. Electrical Instruments. Magnetic Measurements. Apphed Electricity. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Optical Instnunents. Photographic

Technology. Length. Gage.

Heat and Power. Temperature Measurements. Thermodynamics. Cryogenics. Engines and

Lubrication. Engine Fuels. Cryogenic Engineering.

Atomic and Radiation Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid State

Physics. Electron Physics. Atomic Physics. Neutron Measurements. Infrared Spectroscopy.

Nuclear Physics. Radioactivity. X-Rays. Betatron. Nucleonic Instrumentation. Radiological Equipment. Atomic Energy Commission Instruments Branch.

Chemistry. Organic Coatings. Sinface Chemistry. Organic Chemistry. Analytical Chemistry.

Inorganic Chemistry. Electrodeposition. Gas Chemistry. Physical Chemistry. Thermochemistry. Spectrochemistry. Pme Substances.

Mechanics. Sound. Mechanical Instruments. Aerodynamics. Engineering Mechanics. Hydraulics. Mass. Capacity, Density, and Fluid Meters. Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifi- cations. Polymer Structure. Organic Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion.

Mineral Products. Porcelain and Pottery. Glass. Refractories. Enameled Metals. Concreting Materials. Constitution and Microstructure. Chemistry of Mineral Products.

Building Technology. Structural Engineering. Fire Protection. Heating and Air Conditioning. Floor, Roof, and Wall Coverings. Codes and Specifications.

Applied Mathematics. Nmnerical Analysis. Computation. Statistical Engineering. Machine

Development.

Electronics. Engineering Electronics. Electron Tubes. Electronic Computers. Electronic

Instrumentation.

Radio Propagation. Upper Atmosphere Research. Ionospheric Research. Regidar Propagation Services. Frequency Utilization Research. Tropospheric Propagation Research. High

Frequency Standards. Microwave Standards.

Ordnance Development. These three divisions are engaged in a broad program of research

Electromechanical Ordnance, and development in advanced ordnance. Activities include

Electronic Ordnance. basic and applied research, engineering, pilot production, field testing, and evaluation of a wide variety of ordnance materiel. Special skills and facilities of other

NBS divisions also contribute to this program. The activity is sponsored by the Department of

Defense.

Missile Development. Missile research and development: engineering, dynamics, intelligence,

instrumentation, evaluation. Combustion in jet engines. These activities are sponsored by the

Department of Defense. • Office of Basie Instrumentation • Office of Weights and Measures.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

1002-40-^700 September 23, 1952

NBS REPORT

1944

INVESTIGATION OF FIRE RESISTANCE

OF AIRCRAFT FUSELAGES

by

Ao C. Hutton

and

J . Vo Ryan

The publication, reprinting, or leproductionlof this!report In any'form, either in wholelor In part. Is prohibited

unless permission is obtained In writing from theOffice of the Director, National Bureau of Standards, Washington

25, D, C. Such permission Is not needed, however, by a Government agency for which a report has been specifically prepared If that agency wishes to'reproduce additional copies of that particular report for Its own use,

IITVESTIGATION OF FIRE RESISTANCE

OF AIRCRAFT FUSELAGES

ABSTRACT

A group of fire resistance tests

have been performed on small panels representative of sections of aircraft

fuselages. The methods of insulating

and painting of the various sections were

varied in an attempt to improve the fire

resistance performance of aircraft fuselages exposed to fires during crash

landings. It is shown that the use of

ordinary paints on the exterior of the

fuselage is not desirable. The tests

confirm that further work of this nature

should be directed towards study of improved methods of insulating the aluminum

skin from the flames, consideration of

heat absorbing coatings to reduce skin

temperature^ and study of possible changes

in fuselage skin construction to provide a

more fire retardant barrier.

1, INTRODUCTION

An investigation being conducted by the National Advisory

Committee for Aeronautics on simulated full-scale airplane

crashes of such severity that a majority of the occupants

might be considered to have survived, and from actual crashes

in commercial airlines, indicates that present fuselage construction provides only a relatively short period of protection to the passengers from oil and gasoline fires likely to

develop from the crash.

The simulated crash fires involved full scale aircraft

fuselages and during these tests control of all the variables

was not possible. Therefore, the NACA requested that the

National Bureau of Standards conduct small scale tests, which

could be better controlled, to investigate the relative fire

- 2

resistance of the various fuselage constructions used in the

larger tests, and to explore designs that offer promise of

greater fire resistance than the present conventional structures o The NACA submitted for test typical sections cut from

the aircrafts used in their crash testso These specimens were

supplemented by simulated fuselage sections having various

combinations of coatings and insulationso Following five

pilot tests, a total of fourteen sections were tested.

2. TEST SPECIMENS

Two distinct types of specimens were employed in these

tests. The first specimens were taken from the fuselages of

C82 type aircraft and were provided by the NACA. The others

were simulated sections of aircraft fuselages constructed at

the National Bureau of Standards by regularly employed skilled

craftsmen. Nine of the latter group and five of the former

were tested.

2.1 Specimens from Aircraft Fuselages

These test specimens, cut from fuselages of the C82 type

aircraft, may be considered as typical of current aircraft,

both as to materials and workmanship. They consisted of an

aluminum skin, longitudinal members, and transverse or bulkhead members. They were submitted with a white paint on the

outside and an olive green paint on the inside. Some of the

specimens had an interior insulating protection. The specimens were approximately 30 in. square, with an essentially

flat skin of .032 in. clad aluminum. The longitudinal members

were spaced 7 in. o.c. and Joined to the skin by 1/8- in.

rivets 1-in. o.c. The two transverse members, one 3 in. and

the other 8 in. high, were similarly riveted.

In preparation for tests, all four edges of some of the

specimens were bent up to form a box 2k in. square, while only

two opposite edges of others were so bent, forming a 2k in.

wide channel. Three thermocouples were riveted to the inner

side of the skin of each specimen, one at the center and the

others 8 in. from the center towards opposite sides. A fourth

thermocouple was mounted on one longitudinal member. The

paint was removed from the exterior surface of one of the

specimens in order to make a comparative evaluation.

The specimens submitted with insulation had a combination of two layers of 1-in. thick glass-fiber blanket, each

of which weighed .05 ~ »06 Ib/ft^, held in place by a cover

» 3

-

layer weighing ol2 Ib/ft^ and consisting of l/^-in<, glassfiber blanket with a cotton fabric facing c This is believed to

be the standard insulation in the C82 type aircraft used in

the NACA crash tests » Several of the uninsulated specimens

were modified by the addition of heat and flame barriers of

two other types. The first was a single stainless steel

layer , 002-in, thick and weighing ,07 Ib/ft^ and the second a

3A6-in, thick insulation -weighing ,28 Ib/ft^ and consisting

of two layers of felted refractory fibers with a supporting

glass-fiber mesh cemented between. The melting points of refractory and glass fibers, such as used in the insulations,

are reported to be approximately 1700°and 600°C respectively,

2,2 Simulated Construction

These specimens were in the form of a box 2h-in, square

and 5“ in, deep with a 1-in^ lip turned in to the otherwise

open top. They were made by cutting the pattern from a

single sheet of ,032- in, 2h-ST clad aluminum, bending it into

shape, and securing with rivets, or by cutting the bottom

piece from a separate ' sheet and riveting it to the sides of

previously used box sections. Two longitudinal members were

simulated, each consisting of a 2- in, wide strip of the same

thickness aluminum sheet bent along its length to form a 1-in, angle piece, and riveted to the inner surface of the

skin, each one along a line perpendicular to one side and

through its third points. The 1/8- in, rivets were spaced

1-in, OoCo Three thermocouples were riveted to the skin and

one to a longitudinal member in the same locations described

for the C82 specimens.

The exterior surfaces of the test specimen skins were

left the bright aluminum in some cases and painted in others.

This protective coating consisted of a wash primer, two

layers of an intumescent paint which made up the major bulk

of the coating, and a weather-resistant finish coat. Two

specimens were given an interior coat of a standard zincchromate primer. The insulation applied to the inner.*-, sides

of four of the specimens consisted of a single layer of the

1-in, thick glass-fiber blanket previously described, which

was held in place by a plastic leatherette material weighing

oil Ib/ft^-o This plastic material was attached to the sides

of the specimen.

The combinations of paint and insulation used on the iidividual test specimens are given in table 1,

- 4 -

3 o TEST METHOD

The tests were conducted with a furnace in the form of a

box with a 22 1/2-in. square opening in the top over which the

test specimen was placed, with the outer surface of the fuselage skin downo Heat was provided by the combustion of premixed gas and air in the chamber of the furnace o The walls

were of sufficient thickness and mass to make the maintenance

of stable temperatures possible o Measurements were made of

the temperatures in the combustion space of the furnace and at

the locations previously described on the unexposed surface of

the skin and the longitudinals. Measurements were made with a

radiation pyrometer at a point 6-ino from the upper surface of

the skin, from which the radiation intensity at that surface

was determined.

In the pilot tests, the procedures described in the

Standard Methods of Fire Tests of Building Construction and

Materials of the American Society for Testing Materials (ASTM

E119“50) were followed. As this method was not found adaptable for tests of such short duration, a modified test procedure

was adopted. With a light steel sheet over the furnace opening,

the flames were regulated to obtain a steady furnace temperature

of approximately 860°C (arbitrarily ^ected); the steel sheet

was removed and the test specimen immediately placed over the

opening, at which time the test observations were started, • Observations of temperatures and the condition of the specin^n

were continued as long as deemed of value and the test specimen

was then removed and replaced by the steel sheet. Any flaming

of the test specimen was extinguished by a stream of water

from a hand- pumped fire extinguisher.

ho RESULTS

The particular physical changes observed and the times at

which they occurred varied from test to test and were dependent on the presence or absence of the various paints and insulations, The behavior of the intumescent paint ranged from

good to very poor, with a froth or foam layer as thick as 2- in,

produced in some tests while in others, such as No, lA, the

paint fell off early in the test. The aluminum skin was observed to melt, gradually producing a hole- through. Eventually,

flames appeared at the upper surface of many of the test specimens and considerable smoke was produced. The conditions pf

twelve ofythe specimens after test are shown in figures 1 and 2.
-• .. ^

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The times at which certain phenomena were observed are given

in table 1, along with the intensity of radiation at the time

when the specimen ceased to be an adequate barrier to the

fire or at the end of the test, whichever was earlier. Graphs

of the radiation and observed temperatures are given in figures

3 through 7» The more important observations are indicated at

the appropriate times on these graphs.

5o DISCUSSION

The establishment of one or more criteria for failure is

very difficult in tests such as these. The chief aim is the

determination of the time during which the test specimen would

continue as an effective safeguard to the lives of aircraft

occupants. However, much is yet to be learned of the ability

of the human body to withstand the types of exposure encountered, Each of the recorded phenomena -- melting and

perforation of the aircraft skin, melting of the longitudinal

members, the condition of the insulation, and radiation intensity - could be a criterion for failure in some cases and of

little concern in others. For example, the melting of the

longitudinal members is of little importance if flames have

already entered the occupied space through perforated skin,

but is of great importance if those longitudinal members support an interior flame barrier such as incombustible insulationo Consequently , the failure times listed in table 1 are

based on different physical phenomena in different tests but

always with a view to life safety.

The inconsistent behavior of the intumescent paint

coatings was disappointing, and added to the difficulty of

evaluating other variables in the performance of the specimens, However, the paint coatings in general appeared to

cause certain effects. In tests No. l4 and No. 10, which

differed only in having the exposed surface unpainted and

painted respectively, the painted specimen failed earlier

than the unpainted specimen. This indicated that the unpainted

aluminum skin absorbed heat at a lov;er rate than that with a

paint coating, an effect to be expected from considerations

of the emissivity of the tv;o surfaces. The effect of paint

on the interior surface is shown by comparing test No. 2A

(also 3A) with No. 4-, Here the coating retarded failure of

the skin due to the ability of the painted interior surface

to more readily dissipate heat by radiation. This naturally

resulted in higher radiation levels from the unexposed surface

of the specimen which corresponded to the interior of a fuselage ,

6

The various insulations inereased the overall resisbance

in most cases, as determined by flames or radlatioi, bub

hastened the melting of the skin and longitudinal jiieinbers.

This latter effect could be quite important v/lien the insulation is supported from those members, especially on bhe

-oping and arched overhead of most

Pin ical considerations of aircraft desig^i, co;i ana operation, place

i n b r o dneed into tests.

limitations o^i the variables

rue oion,

It is necessary tha

uhich may be

rnits of aircraft be proteebed from the low temperatures encounb.ered at

flight altitudes by insulation. Therefore, further tests

without insulation would be of questionable value. Additional

work should be directed towards the development of barriers of

high melting point, good reflection of radiation, and some

strength. It vjould also appear desirable to stiidy the possible

use o; energy absorbing material v/hic'i would delay developmeii'

The material, or

materials in a combination barrier, should be inco mb ;s t.I ble

and should not give off acrid or toxic vapors or smoke.

The tests reported give evidence of the possibility of

modifying the fire resistance of airccaft fuselages by changes

in the finish and insulation of the aluminira skin. Eo’uever,

the differences acJiieved as yet, do not appear of sufficient

value to justify adoption of any of the structures studied

v:itnout furblier exnerimental work.

A research program for the purpose of studying avdultlonal

insulations , heat absorbing iiiethods, and flame or radiation

barrier 3 would seem advisable. ' Tne test method and specimen

size employed in the present series is satis facbory and should

be continued. In addition, a few tests with larger specimens

in positions other than horizontal would be of value in de~

, par

;insu-^atio:i. Such larger tests should

evaluation of promising assetiblies.

ter ailing the effect of larger failure areas, par t Iciilarly on

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THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act

of Congress, March 3, 1901, as amended by Congress in Public Law 619, 1950.

These include the development and maintenance of the national standards of

measurement and the provision of means and methods for making measurements

consistent with these standards; the determination of physical constants and

properties of materials; the development of methods and instruments for testing

materials, devices, and structures; advisory services to Government Agencies on

scientific and technical problems; invention and development of devices to serve

special needs of the Government; and the development of standard practices,

codes, and specifications. The work includes basic and applied research, development, engineering, instrumentation, testing, evaluation, calibration services

and various consultation and information services. A major portion of the

Bureau’s work is performed for other Government Agencies, particularly the

Department of Defense and the Atomic Energy Commission. The scope of activities is suggested by the listing of divisions and sections on the inside of the

front cover. Reports and Publications

The results of the Bmeau’s work take the form of either actual equipment and

devices or published papers and reports. Reports are issued to the sponsoring

agency of a particular project or program. Published papers appear either in the

Bureau’s own series of publications or in the journals of professional and scientific

societies. The Bureau itself publishes three monthly periodicals, available from

the Government Printing Office: The Journal of Research, which presents complete papers reporting technical investigations; the Technical News Bulletin, which

presents summary and preliminary reports on work in progress; and Basic Radio

Propagation Predictions, which provides data for determining the best frequencies

to use for radio communications throughout the world. There are also five series

of nonperiodical publications: The Applied Mathematics Series, Circulars, Handbooks, Building Materials and Structures Reports, and Miscellaneous Publications.

Information on the Bureau’s publications can be foimd in NBS Circular 460,

Publications of the National Bmeau of Standards ($1.00). Information on cali- bration services and fees can be found in NBS Circular 483, Testing by the National

Bureau of Standards (25 cents). Both are available from the Government Printing Office. Inquiries regarding the Bureau’s reports and publications should be

addressed to the Office of Scientific Pubhcations, National Bureau of Standards,

Washington 25, D. C.
I