Since lightness is desirable in airplane construction, greater stresses must be tolerated than in other kinds of construction. It is therefore necessary to have a more accurate knowledge of the greatest stresses that may occur and of the actual properties of the materials used. The Aeronautic Research Laboratories took the limit of elasticity as the basis of the strength calculations. Many tests were made of different steels, woods, aluminum alloys, and fabrics

Van Ewijk, L J G

Wolff, E B

English

NASA Technical Reports Server

.-
./””TECHN1CAL MEMORANDUMS
NATIONAL ADVISORY CCMMITTEE FOR AERONAUTICS
~?O. 448
MECHANICAL PROPERTIES OF SOtiEMATERIALS tJSED
IN AIR?LANE CONSTBUCTIOIT
By E, B,’Wolff and L. J. G. Van Ewijk
l’rcm Report M 219
of the “lZijks-Studiedienst voor de Luchtvaart,” Amsterdam
Reprint from “De Ingenieur,ll of August ?; 1926
,,
Washington
i January, 1928%p>
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.—
NAT IONAL ADVISOR-f COMMITTEE
>. .. TECHNICAL HMORANDUM
FOR AERONAUTICS .
N(). 448.
l!EC:HANlCAL PROPERTIES OF SOME MATERIALS USED
lH AIPJ?LANE COiWTRUCT ION.*
By 3. E).Wolff and L. J. G. Van Ewijk.
Since IiShtliess is desirable in airplane construction,
greater stresses must be tolerated tilan in other kinds of con-
struction. It is therefore necessary to lmve a more accurate
knowledge of the greatest stresses that i?lay occur and of the
actual properties of the materials used. The “Rijk& StUdied-
ienst voor de Luchtvaart” (.4eronautic Research Laboratories)
took the limit of elasticity as the basis of the strength cal–
culat ions. Many tests were made of different steels, woods,
aluminum alloys, and fabrics.
The limit of elasticity of many metals cannot be accurately
deter-mined. In the case of soft metals, the practical limit is
termed the yield point, and the permanent eloilgation is fixed
at 0.5$ of the
dLurat ion.
Obviously
measured Iengt-n for a load test of 15 seconds
this applies only to calculations of static load
>. tests or to those in which, by the introduction of an overload
“ factor, the calculation can be made as a static one. In some
*“Iv!echanischeeigenscha.ppen van eenige mater ialen, die voor den
vliegtuigbouw ‘nierte lande ge”bruiktworden. ” Report M 219 of
the “Rij”ks-Studiedienst voor de Luchtvaart, ” Arflsterdam. Trans-
lation of a reprint from “De Ingenieur” of August 7, 1926.
IT.A. C.A. Technical.M eiTIOrandWIl
shock or variable–load tests,
No. 448 2
the limiting values lilUStbe in-
-.
treduced. This method, however, does not cover all possibil-
ities. There are cases for which the tolerances are not fully ,:
established. In such cases the engineer i~ust be governed by
practical considcra.tions.
In order to determine theinechanical properties of locally
availa,’olcinaterials for aiiplsme coiwtruction, as the ‘oasis for
calculations, the R.S.L. (“Rijks-Studiedieilst voor de Lucht-
vaart” ) has made a lar~;cnumber of tests cluriilgthe last few
years. The results will be contained i-nseveral reports, of
which this is the fir~t onc to be published.
Iilorder to compare tficfitness of various materials for
any ~iveilstructure, a n-um’~erwas determined which expressed
the ratio between the allowable stress (te-nsileor compressive)
and the
lighter
s-pecificSravity. The ,greaterthis ratio is, the
the structure can be for a specified overload and safe–
ty factor.
There are also other factors, aside
whit’h affect the fitness of a material.
from the strength,
In the first place,
there is the question of durability i.e., as to the effect of
temperature and moisture variat ions on wood, corrosion on met-
als, weatilering on fabric, etc. It ,should be here noted that
the life of an airplane, which a few years ago was expressed in
hundreds of hours and less, has been greatly lengthened. We do ..
not yet know the length of life of some types, since airplanes
3ij.A.C.A. Technical Me.mora-ndumNo. 448
of these types have already flown several thousand hours without
,..
showing any signs of deterioration.
, It must also be taken into account that some materials are ‘
subjected to centinuous vibrations j concerning the effect of
which we do not yet have sufficient data. Table I contains a
few clataon the principal airplane materials, in order to give
an idea of the relation between t’heallowatile stress and the
specific gavi%yb
TABLE 1.
Steel tubii~g
It II
P iano wire
Duralumin
II
Spruce wood
Pine wood
Allowable stress T I Wecific
Tensile
30
160
30
in kg/mm2
—.
IOifl-pressive
35
30
3.50
3.75
‘gravity
S.G.
7.8
7.8
7.8
2.8
2.8
0.42
0.48
Ratio
.—
S:(2.
3.9
4.5
20.5
10.7
10.7
8.3
7.8
It is seen that some icindsof steel have the highest val-
ues; that light alloys, Sue-has duralumin come next; that some
kinds of wood do not come far behind; and that soft steel and
.
iron come after wood.
It is obviously important to make a
properties of wood and the light alloys.
special study of the
This has been done by
.N,A* C.A.”Technical llemorandum No. 448 4
the R.S*L., although on a Iiini.ted scale. (For previous tests;
a. . .
see Report M 17 a, “Ve“rslagen cn,Verhandcli’ngen van den Rijks–
Studied ienst voor de Luchtvaart, flPart I, 1921.) The data are
tabulated under the heads of light alloys, woods, steels, and
fhbrics. They were determined in part by ‘~heR.S.L. and were
collected in part from other sources, including the prospectuses
of the :Ianufacturers.
Li@t ELll OYS. - Duralumin is the only light alloy which has
been used to any considerable extent in airplane construction.
It may bc noted, in the first place, that the ratio, T :
is greater for duralumin in the normal, cold–worked state
for oral.iilarykinds of steel and, secondly, that very good
S.G.,
than
results
were obtained
regards these
“alud-ur” fall
from compressioil tests with duralumin tubes. As
ratios, the newer alloys, IIle.uta,l,”‘taeroil,flai~d
in the same class with cluraluminand compare very
favorably with unalloyed aluminum.
tyO od.- The most tests were made with wood, because its prop-
erties as a building material were less generally known. Only
selected specimens of woods suitable for airplane construction
~~ere used, the most important being the conifers, spruce and
pine, and selected plywood.
The extensive data of the Forest Product Laboratory, some
of which are given in these tables, also include other conifers,
such as red spruce (picea rubens) and white spruce (picea cana–
IT.A.C.A. Technical Memorandum No. 448 5
densis) for which the same values were obtained.
As regards the data given in the tables for spruce and pins,
it must be further noted that the principal distinction is ‘oc–
tween pla ii~wood and plywood. Data on the former are much nore
abundant thailon the latter. Although in the R.S.L. tests, the
maximum values for plain wood.and plywood differed but little,
it can be said, in :;eneral, that test samples from the s,ame
p iecc of wood gave lower values as plywood than
form. A special report on pl~ywoodwill contain
and 3 more thorough discuss io-nof this quest ion.
in the plain
further data
Tilei]loistur~content could not always be ~iven in these ta–
bles because it was not always included in the a,vaila’~ledata,.
Although it may be assuined that, in the various sources from
which the data were taken, the figures were based on a normal
moisture conte-ntof 12—17%, the variat ions in some of the data
must be ascribed to variations in the inoisture content (Sec
Boultoil, ~ ~.t10% of Moisture!’).“Properties of WOOC.
Ii addition to the ‘fi:~res for spruce, pine, and three--ply
VJOOd, Table III contains data on a few 1ess-known woods (“merawan[’
and Carolina pine), which were tested by the R.S.L. and which seem
to have very good properties for airplane construction, as like-
wise ,ona few heavier woods (such as walnut and mahogany) , which
,.
are suitable for propellers.
.
One very peculiar wood, balsa, has an exceptionally low
specific gravity ai~da rather favorable D/S. G. ratio. In
America it is used as filling material in seaplane hulls and in
t’he le’adin~edge of wings. For structural work, the large di-
me-nsions required to transmit a ~iven force generally constitute
a disadvantage.
For the different woods, excepting plywood, the compressive
strength is taken as the basis, since it is so much smaller than
the tensile strength that it is generally taken as the basis of
the calculations. When known, the ratio of the tensile strength
(T) to the specific gravity (S.G.) is also given, so as to
enable comparison with the metals.
exist
Steels .- As shown by Table IV, so great discrepancies/in
the strength ratios of the various steels that no direct conlpar–
ison with other inaterials is feasible. If we take 5.7 and 27
as the extreme limits, it then appears that, as compared wit’n
the weakest metal, the D/S. G. ratio of wood is very favorable,
while the D/S.GO of the special-steels and hard-drawn wire,
on the ot’nerhaild, is inuchmore favorable than t%t of wood.
The low ratios 5.7-8 embrace the more comiionsteels, and it
is remarkable that wood compares so favorably with them.
Fabric .- Although the strength of the fabric is not taken
into account in the design of airplane parts which.are covered
with it, and the various mechailical tests of fabrics serve only
for comparing their quality, comparative figures for a few fab-
rics are given in the tables. As regards the ratio of the ten-
N.A.C.A. Technical Memorandum No. 448 7
sile strength to the specific gravity, which is taken as the
standard, this is determined in the usual manner, i.e., by di-
viding the tensile strength in kg/m@ by the specific gravity.
.
Although quite large variations can occur in fabrics, for
example, in the two directions of the warp and filling, and al-
though the deterioration
materials, these figures
mate those for the other
from wear is greater than for other
show that the strength ratios approx”i–
groups . “The lowering of the ratio by
doping is due to the fact that the increase in weight is not
offset by a corresponding increase in strength.
It is intended, in several future reports, to go more into
the details of the R.S.L, methods and tl+eresults obtained with
various materials. Special attention will be given to glued
wood joints and to structural parts composed of small pieces of
wood assembled with the aid of glue.
.
1
N.A. C.A. Technical Memorandum No. 448
TABLE II.
Strength Ratios of Various Air_olaneNaterials,
Aluminum and Its All&s.
Source of
data
R. S. L.
H. G. Knerr
H.o.M. Ae.(1~
Holland i~ate-
rial speci-
fications
Duren Engine
Works
Lautawerk
prospectus
R. S. L.
II
Manufacturer
II
II
II
R. S. L.
Material
Sheet Al.
Ditto
Ditto
Sheet dural
of varying
hardness
Sheet lauta:
of varying
hardness
Ditto
Aludur
Silumin
Scleron
Aeron
K.S, sea-
water
F VII annex
Dural. tubef
4 kinds
S.G.
2.66
2.73
2m75
2.75
2.75
2.83
2.75
2.75
2.7
2.57
2.97
2.75
2.8
8
.
Tens
F3reaking
strength
T kg/mrfl~
8-22
8.4-15.4
8.5
12.0
15,5
40-60
30-60
32-38
25-40
16-30
40-50
36-42
23-32
ile T
Tensile
stren th
5T kJ mm2
5-20
28- +60
21-59
20-25
30
20
Sts
.:
Elonga-
tion $
20-7
15
10
5
20-2
20
28-18
20–5
30-5
20-10
25–18
14-1
Compress ive Te sts
,
2.85 33-44 23-38 11. 6-15.6
(1)Handbook of Modern Aeronaut its, by W. Judge.
s
S.C+.
8.2-13
.
. ,,,. -— ———. . - - ! ------- ..— ..,—— . . . . . . . . . . . . . . . . . . ..-.. —. —-. .. ——-. —.——
—N.A~ C~Ac Technical Memorandum No. 448 9
TABLE II (Cont.)
Strength Ratios of Various Airpldne Materials.
--------
Aluiiinum and” Its Alloys.
Source
of
data
R, S. L.
H. G, Knerr
H.o, M, Ae. (1)
Holland mate-
rial spc5ci–
ficatiolls
Du~en Engine
works
Lautawerk
prospectus
R, S. L.
II
Manufacturer
II
II
tl
Mat erial
Sheet Al.
.Dit to
II
Do.
II
II
Sheet dural.
of varying
hardness
Sheet lautal
of varying
hardness
Ditto
Aludur
Silumin
Scleron
Aeron
K. SO sea-
water
SJG.
2.66
2,73
.
2,75
2,75
2*75
2,83
2.75
2,75
2.7
2.57
2.97
2.75
2.8
T
-Kiz-
3-8,25
3*1-5.65
9
3,10
4,36
5.5
14,2 -21.2
10.9-22
11,6-13.8
9.3-14.8
6.25-11.7
13. 5-16.9
13.1–15.3
8.2–11.4
I
ST
S.Gi
1.9-7.5
—
10- +21
5.8–21. :
7.3-9.1
10.1
7*3
,.,
Remarks
Limit ing
values in
tests
Determined
by R.S.L.
tests
In normal
condition
(1)Handbook of Modern Aeronautics, by W. Judge.
N.A. C.A. Technical Memorandum No. 448 10
TABLE III.
Strength Ratios of Various Airplane ,Materials.
Wood,
Sourae
of
data
R. ,S. L.
!1
II
II
II
A.B..C. of
Aviation(2)
H. C. Knerr(3)
Holland rflater–
ial specifi–
cations(4)
Jenkin(5)
Eaumann(6)
Forest Products
Laboratory(7)
II
R. S. L.
II
II
II
A.13.C. of
Aviation(2)
H. G. Knerr(3)
Baumann(6)
Tarest Products
La’ooratory(7)
Holland mater-
ial specifi-
cations(4)
Kind
Spruce
II
II
II
II
!1
II
II
II
II
II
II
II
!1
II
II
!1
fl
S.G.
0.46--0.45
o.3’a-o.47
0.41
0.42–0,45
0.47-0.45
0.49
0.43
0.35-0.4
0.43
0.53
0.41
0.43
0.62
0.53
0.66
0.57
0.465
0 l 545
0.46
0:43
0.42-0.5]
0.45-0.5
D
Compressive
stre-nth
7in kg rflm2
3.80-5.12
3.61-4.32
3.17-3.39
3.49-4.33
3.65-4.22
3.15-4.20
3.00
3.50
4.90
5.75
3.05
4.20
6.22-6.52
5.07
5.13
3.8 -4.8
2.1 -4.2
4.55-7
3.15 ,
4.35
3.15-4.27
4
D
S.G.
8:3-11.3
9.5- 9.3
7,3- 8.3
8.4- 9.7
7.8– 9.5
6.& 8.6
7
10 -8.75
11.4
10.8
7.45
9.8
lo–lo. 5
10.5
7.7
6.>7.5
4.5-9
8.3-12.8
6.8 “’
10.5
7.5-8.35
See fOotnOtes”next page.
N..4.C.A. Technical Memorandum No. 448 11
TABLE zII (Cont.)
>-.
‘StrentithRatios of Various Aimlane Mate~<als,
WOO (3A-
source
of
data
R. St ~i
II
II
II
Forest Products
Laboratory(7)
II
H. G. Knerr(3)
R. S. L.
II
Kind
Ca201ina
Pine
“Merawa-n”
Uahogany
Walnut
Mahogany
Walnut
Balsa
Balsa
j3irch
!3-31-y
D
~AG, Compressivestren-t’n
7in kg mrna
0.52-0.57” 4.02-5.34
0.56 5.43–5.93
0.72 4.50-4.22
0.62 4.10–4.35
0.50-0.54 3.57–3.85
O.56 4.27
0.12 1.54
0.128 0.68
10.85 5.63
-.
D.
S*G.
“7.7-9.3
9.7-10.3
5.8- 5.9
6.6- 7.0
7.1- 7.12
7.6
12.8
5.3
6.6
(2 A.B.C. of Aviation, PaSe.
[1
3 H. G. Knerr, Autoi~otive Industries, p.869.
4 Holland material specifications for Aviation, Nos. 21–22.
(5) Jenkin, Lt. Col. Co F., Report 011 Materials of construction
Used in Aircraft and Aircraft Engines.
(6) Baumailn, R., Results of Wood Tests in Laboratory of Technical
High School, Stuttgart.
(7) Forest Products Laboratory of the U. S., Properties of Woodsat
10z Moisture, by B. C* Boulton, H.ankinson, and MuCook Field.
L
+
.
-.2
w
. b
C-D
II
&
&
Plain
IN.A. C.A. Technical Memoraniium No. 448 13
TABLE 111(Cont.)
Strength Ratios of Various Ai
Source
of
data
1%.S. L.
!1
II
II
Forest i“rod.La’o.(7)
II II II
H. G. Knerr(3)
R. S. L.
II
Woc
Kind
Carolina,
Pine
“U~faWan”
MahO@fl y
Walnut
Mahogany
‘,:~alnut
Balsa
Balsa
~5irch
(3–ply
See footnotes on Page 11.
.
rplane Materials.
d.
S.G.
0.52-0.57
0.56 I
ok7.2 !
OJ62
0.50-0.54
0.56
0.12
0.128
10.85
Mois-
ture
content
iil$
14.3
9.9
20.4
15.6
10
10
R~i,larks
Plain
11
{
Cube com-
posed of
~~any layers
,,,, ,- .,,.,..,-, , .,,,,,. ,, , . ,, ,,, ,., ,,, , , ,,, ,,, , ,, ,, ,,, , , ,, ,,, , ,,.,. ,,,, ,,, --.-..-.,.- ——
N.A. C.A. Teclmical Manorandum No. 448 14
TABLE IV.
,, .,.., ,, Strength Ratios of Various Airplane Materials.
Source
of
data
R. S. L.
II
II
II
!1
1!
Boulton(8)
Holland Spec.(4~
Kint.
—. —
Birch
3–p ?.y
1!
II
II
II
II
Birch
3-ply
Birch
3-p17
S.G.
Wood;
0.88
0*E18
0.73
0.73
0.87
C*37
0.73
0.73
0.85
0.85
T
Tensile
strength
@/mmz
14.4
8.2
10.8
7.-
16.5-
8 .-
9.2
5.4
7.5
5
T
S.G.
16.3
9.3
14*7
9.6
19.-
9.2
12.6
7.4
8.8’
5.9
Moisture
centent
in $
.4.2-15.4
14-16
(4) Holland Material Specifications for Aviation, No. 23.
Direction
with
respect
to Srain
Length-’
wise
Crosswise
Lengthwise
Crosswise
Lcn.:thwise
Crosswise”-
Lengthwise
Crosswise
Lengthwise
Crosswise
(8 ) The Manufacture and Use of Plymood and, Glue, by B. CO Boulton.
IJ;A, C.A. Teclmical X e;fiorandum No. 448 15
“.
Source
of
data
R. S, L.
Eng. syIeo-
ifica--
tions
Ditto
Holland
specifi–
cat ions
TABLE V l
Strer@h Ratios of Various Aizmlane Materials
Kind
—
Soft car:oon–’
steel tubes:
etc.
Ditto, hard–
ened
Sip,ec ial Cr,
~Ji,refined
D itto, hard.-
f~~led
soft car’i30n-
S“tccl tubes
Soft car120n-
SteelA
Tens
.-——
S.G. Breaking
s‘tirengtl
IT k~mm =
7.”8 40
7.8 I 60
7.61 130
\
7b6 160
7.85 210
7.6 I 43.4
7.6 I 1.32
I
I1
\
ile!
Te-nsile
stren@h
7ST kg l!ll:
28
50
120
3.40
—
27.8
—
25
12
10
8
3
25
ressive Tests
steel, 17.8 \ 36-4-6
~h~.ets,
tubes, etc. i
for lattice I . ..__
~7Jorlk
J-’cor’p fCompres- Teixsile ‘
sive strength D s
strength ~b.ch S.G.
I D ‘kg/i~z s ‘kg/rllm2
—-.-.___.—._,._
T
.—— ——-—
?L..s. L. E–N.A.B.1. 7.8 41-47.”5 39-”41” 5.3-6.1 5-5.3
steel tubes
4-kinds
~
I
1’
N.A.C.A. Technical NiemorandurnITo.448 16
TABLE V (Cent. )
Stren~th Ratios of Various Airplane Materials.
Source
of
data
Krupp
R. So L.
Eng. spec–
ifica-
tion
Ditto
Iio1la-rid
spccifi–
cations
St eela
Kind
soft carborl-
steel tubes,
etc.
Ditto, hard-
eiled
Special Cr,
Ni, refined
Ditto, hard-
ened
?iano wire
Soft carbon-
ated tubes
soft car:30n–
steel,
s“neets,
tubes, etc.
for lattice
work
S.G.
7.8
7~8
7.6
7.6
7.85
7.6
7.6
7.8
1
SiG.
—
5bl
7,7
17
21
27’
5.7
18.4
4.75-6.05
!
Remarks
3*6
6.4
15.8
1844
—
3.7
Mean values
Ii !1
N.A. C.A. Teclxnical 17
. Source
of
data
R. S. L.
II
II
It
Source
of
data
R. S. L.
II
II
II
Source
of
mat erj-al
De Kooy
11
L. A.
II
II
K.~.M.**
II
Source
of
material
De Kooy
II
L. A.
II
II
K.L.M.**
1!
,,
TABLE VI.
Fabrics.
.. ...
—,
G/M2in
gr.
160
330
139
245
235.
132.5
243
.—
Tensile
strength
T kg/nqn2
18.5
20.5
16.6-20,
17.5-22.3
17-22
9–14.9
5-6
TABLE VI (cont.)
Fabrics.
G/M2 in
gr.
—.—..—.
160
330
139
245
235
132.5
S:G.
11.6
6.2
12-14.4”
7.1!5-9.3
7.25-9.4
6.7–11.2
243 5.92-8.35
Elon ation
g’
1+-10*
7.!+5
16.5-7.5
12-5.5
1>5.5
18-7
Remarks
Undoped.
Doped.
Undop ed.
1)oped
II
Freed from dope.
I and wax.
Doped and waxed.
i2T ,.,
*The first n~ber applies to direction of warp; second number to
direction of filling.
**Fabric froii-the rudder”of a commercial airplane, tested after
long use.
Translat ion by Dwight M. Miner,
National Advisory Committee for Aeronautics.


Mechanical properties of some materials used in airplane construction

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