Autogenous welding in airplane construction


Material Information

Autogenous welding in airplane construction
Series Title:
Physical Description:
9 p. : ill ; 27 cm.
Kuchel, Ludwig
United States -- National Advisory Committee for Aeronautics
Place of Publication:
Washington, D.C
Publication Date:


Subjects / Keywords:
Aerodynamics   ( lcsh )
Airplanes -- Design and construction   ( lcsh )
Oxyacetylene welding and cutting   ( lcsh )
federal government publication   ( marcgt )
technical report   ( marcgt )
non-fiction   ( marcgt )


Sponsored by National Advisory Committee for Aeronautics
Statement of Responsibility:
by Ludwig Kuchel.
General Note:
"Report date July 1929."
General Note:
"Translation of "Die autogene Schweissung im Flugzeugbau," from Schweissen, Schneiden und Metallspritzen mittels Acetylen, 1927, pp.27-33."

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 003874350
oclc - 156929988
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By Ludwig Kuchel.

In the original manufacture of airplanes from wood, the

warping of the structural parts through the influence of the

elements could not be entirely prevented, despite the careful

selection of the wood. An improvement was made by using plywood

for covering the fuselage and wings. Plywood was used in Ger-

many during the war on most of the military airplanes.

The increased requirements of airplanes, especially in mod-

ern air traffic, called for a homogeneous building material of

greater strength and reliability than wood, which is so easily

affected by external conditions.

The advantages of steel for highly stressed parts, as dis-

covered in engine building, led, in airplane construction, to

the use of steel tubing, which also offers less obstacles to

future structural development. Autogenous acetylene-oxygen

welding was found to be the only practical way to join the steel


Lightness is an essential characteristic of the structural

parts of an airplane. All the structural requirements which

must be satisfied by the building materials must therefore be

adequate without being excessive. While military airplanes are
*"Die autogene Schweissung im Flugzeugbau," from Schweissen,
Schneiden und Metallspritzen mittels Acetylen, 1927, pp. 27-33.

N.A.C.A. Technical Memorandum No. 523

not subject to considerations of economy, but only to those of

maximum efficiency, commercial airplanes must be governed by

both of these factors.

The structural parts of an airplane are the fuselage, wings,

tail surfaces, engine mount and landing gear.

Figure 1 is the picture of a twin-engine Albatros commer-

cial airplane. It has a full load of 3800 kg (8378 lb.) and an

engine power of 430 HP.

Fuselage.- The steel-tube framework of a twin-engine Alba-

tros commercial airplane (Fig. 2) for eight passengers and two

pilots has a framework of approximately square cross section

in the form of a lattice girder. The front part has K braces.

The rear fields are crossed by brace wires with the exception.

of the next to the last field, in which there are welded diago-

nal tubes for withstanding the stresses produced by the tail

skid in landing. The fuselage framework weighs 224 kg (494 lb.Y.

The joints are autogenously welded in all the structural parts.

The longerons consist of telescoped steel tubes of 40 mm (1.57

in.) diameter at the front end and tapering to 25 rm (0.98 in.)

at the rear end. The ends of the tubes are joined by sloping

welds. The requisite reinforcement is effected by muffs, which
are driven on and welded. The attachment joints of the wings

and landing gear, which are subject to great tensile or com-

pressive stresses, are reinforced by strips of sheet metal driven

IN.A.C.A. Technical Memorandum No. 523 3

into slots in the ends of the tubes and completely welded. The

eyelets required for attaching the brace wires are formed by

welded-in. tubular loops. No tube in the whole fuselage has a

wall thicker than 1 mm (0.04 in.), but the required safety fac-

tor of eight for the airplane is nevertheless exceeded.

Wings.- Figure 3 shows the whole wing structure, consist-

ing of a middle section and two lateral sections. Figure 4

shows a wing in process of construction. The spars are full-

walled box girders with open duralumin members. The fitted-irr

steel ribs have the form of lattice girders. The open spaces

in the front part of the wings are intended for the reception

of the fuel tanks.

The welded steel-tubing engine supports, which also serve

as wing struts, are installed between the upper and lower wings

on each side of the fuselage.

Figure 5 shows two of the ribs. The upper and lower

flanges are made of steel tubing 6 x 0.5 mm (0.24 x 0.02 in.),

while the welded-in lattices are made of steel tubing 5 x 0.5 mm

(0.2 x 0.02 in.). A span of 19 m (62.33 ft.) requires 65 such

ribs for each wing. These ribs are produced in quantity and

are welded with the aid of former.

Figure 6 shows the tail structures. The horizontal tail

structures, consisting of the stabilizer and elevator, have

welded frames with diagonal braces made from steel tubing of

N.A.C.A. Technical Memorandum No. 523

5 to 25 mm (0.2 to 1 in.). The stabilizer is adjustable, and

the elevator is hinged to it. The vertical tail structures,

consisting of the finmr and rudder, are likewise made of autoge-

nously welded steel tubing.

The ailerons are likewise made of welded steel tubing with

diagonal bracing. The hinge supports are made of steel tubing

with triangular bracing and are autogenously welded to the wing


Power plant.- Figure 8 shows the engine mount on a one-

engine commercial airplane. The autogenously welded steel-'

tubing engine mount is attached to the steel-tubing fuselage

at four points, so that the whole can be detached by removing

four bolts. The joints are reinforced by sheet metal, because

of the great stresses to which they are subjected. The weight

of the 220 HP. engine, with all its accessories, is 295 kg

(650 lb.). It is separated from.the pilot room by a fire wall.

Landing gear.- The streamlined struts are autogenously

welded (Fig. 9). The landing shock is absorbed by the telescop-

ing struts. The shock absorbers operate by compression of air,

sealed and regulated by oil. In this way the kinetic energy of

the airplane is converted into friction and heat, and the un-

avoidable springing in landing with rubber shock absorbers is

eliminated. With a stroke of about 24 cm (9.44 in.), an energy

absorption of about 45% of the total weight is attainable. The

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N.A.C.A. Technical Lamorandum No. 523 5

absorbed energy corresponds to a free fall of about 0.5 m (1.64

ft.) of the fully loaded airpl-'.ne. The unabsorbed forces are

transmitted to the fuselage.

Aside from the main structural parts, whose joints al-

most exclusively welded, the gas-welding process is used to ad-

vantage in all kinds of fittings, connections, levers, etc.

Properly welded parts satisfactorily replace parts cut out or

forged in one piece. The welding process is simpler, quicker,

and cheaper cnd saves much weight, which is a very important

consideration in airplane construction.

For the different materials available for welding in air-

craft construction, adaptations of the welding wire have been

discovered, which render the welds, as improved by after-treat-

ment, very nearly as strong as the unwelded tubes. The excel-

lence of the weld depends largely on the skill of the welder,

who should have some understanding of the physical process in-

volved. In training welders, their individual qualifications

must be considered first of all. The inspectors must be able

to tell the difference between a good weld and one that simply

adheres or is burned.

For testing the welds, portions are taken from the completed

structures, from which samples are prepared for tensile and

bending tests. A bending test is made of the finished part, in

order to determine its buckling strength. This is a very good

test of the excellence of the welds and exposes any defects in

the welds.

N.A.C.A. Technical Memorandum No. 523 6

It is generally assumed that the excellence of a welded

structure depends on the strength of the weld seam, since this

is ordinarily the weakest point. I cannot accept this assump-

tion unconditionally, however, since the weld seam may 'e the

strongest part of the structure under certain conditions. I

will omit the discussion of the welding wire to be used, as be-

ing too far reaching. I will only mention that it is important

to test the welding wire thoroughly for the different uses.

Autogenous welding has now become very important in airplane con-

struction. It facilitates the construction and shortens the

time required.

The new industries of aircraft construction and autogenous

welding constitute a timely coincidence. In 1903 the first

flights were made with engine-propelled airplanes, and in the

same year the first burners for acetylene-oxygen welding were

put on the market.

Although the laws of statics are fundamental for construc-

tion, progress is nade through the properties of the materials

used, as determined by experience. The type of girder used for

withstanding bending and buckling stresses in aircraft is al-

ready regarded with increased respect in other lines of construc-

tionr The autogenous welding industry is one of the few indus-

tries which can increase its usefulness through the discovery

and appropriation of new fields of application. There are many

such fields not yet aware of the fact that production ccn be
cheapened by the use of autogenous welding.

N.A.C.A. Technical Memorandum No. 523

D i s c u s s i on

Mr. Herz.- I only wish to ask whether autogenously welded

or seamless drawn tubes were used:

Dr. Kuchel.- Seamless drawn steel tubes, as obtainable in

the market, are generally used in airplane construction. There

is no need of producing them in the aircraft factory, because

every kind of tube can be bought ready made in the market.

Mr. Herz.- My question was meant somewhat differently. In

recent years quite an extensive industry has developed in the man-

ufacture of well-made autogenously welded tubes for all purposes.

Have these tubes yet been used in aircraft construction? I un-

derstand that such tubes were investigated in Italy in 1923 or

1924. I do not know, however, what the outcome was.

Dr. Kuchel.- I do not know of autogenously welded tubes

being used in aircraft construction either in Germany or else-

where. In a tour of investigation in the spring through France

and England, I found, however, that this kind of welding is done

with no such precision in either of these countries as in Germany.

Mr. Butz.- In the welding of thin-walled tubes, are there

any data available on the effect of the purity of the welding


Dr. Kuchel.- The welding section generally uses apparatus

in which the gas is purified in the ordinary way. It is endeav-

ored to keep the gas as cool as possible, to have it well washed

N.A.C.A. Technical Memorandum To. 523 8

and to have the purifying rateri:Ls renewed often enough.

Mr. Butz.- I recently ascertained the effect of the purity

of the oxygen in a large welding factory which produces thin-

walled tubes and bicycle frames in large quantities. This fac-

tory undertook to use high percentage oxygen. The rejections

were 30% greater than with oxygen under 98% pure. The demands

on the skill of the welder increase with the purity of the oxy-

gon, especially for thin-walled tubes.

Mr. Pothmann.- We found that the purer the gas, the rore

sensitive the flane was when wrongly adjusted. We also found

that oxidation occurred much more readily with very pure gas.

In ordinary welding poorer results were obtained with very pure

gas (93.5o).

Dr. Streb.- According to our experiments, nitrogen up to

5% has no harmful effect on the quality of the weld. We have

not yet determined whether a smaller amount of nitrogen has an

actually favorable effect on the quality of the weld. There

were some indications in other experiments that the presence of

a small quantity of nitrogen in the oxygen prevented or substan-

tially reduced the carbonization of the weld, when a slight ex-

cess of acetylene was used.

Dr. Vogel (the presiding officer).- It seems that the ex-

perimental results do not yet justify their adoption. in practice.

This remark applies also to the results thus far obtained by

Dr. Streb.

Translation by Dwight M. Miner,
National Advisory Committee for Aeronautics.

N.A.C.A. Technical Memorandum No.523 Figs.1,2,3,4,5,6,7,8,9





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