Materials and Methods of Construction in Light Structures Page: 28 of 38
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N.A.C.A. Technical ienrioandum nTo. 515
regard it as unreliable. The strength of the weld cannot
be calculated and cannot be tested on the finished piece.
A riveted junction can be calculated by long-established
formulas, though the inside of the rivets cannot be in-
spected and a feeling of confidence is instilled only by
their great number. These doubts apply also to shipbuild-
ing, which occupies a position similar to airplane build-
ing, as regards reliability and safety. In the former,
however, the process of welding is being increasingly em-
The great reliability of welded junctions has long
beeoon demonstrated by innumerable laboratory and practical
tests and many years of experience with suitably welded
airplane parts, especially fuselages. Of course, certain
conditions are requisite, such as experienced welders,
suitable materials for holding and allowance, oven in the
designing, for the special peculiarities of the welding
process. There is urgent need of those conditions, and it
is accordingly to be expected that the work already begun
in many places will be successful.
Another disadvantage is the relatively low strength
of the welded junctions, which is about 35-40 kg/mm2
(49,780 tt 56,890 1b./sq.in.) for the metals now commonly
used. This does not matter so much in fusolagos whore
there are always slender compression struts whid buckle
under oven slight stresses, It is loss satisfactory for
wing structures or other parts which are subjected to ton-
silo, compressive and bonding stresses, lMany endoavors
are being made to discover by systematic experimentation
stool ealloys with a high tensile strength and yield point
in the annealed state and with good welding properties.
There is a good prospect of obtaining wolds with a tensile
strength of 60-70 kg/mm2 (85,340 to 99,555 lb./sq.in.).
The advantages of welding will then be still greater, es-
pecially for large structures. I may add that the D.VY.L,
is giving muc; attention to this matter,
Engineer Fock e.- Referring to Dr. Rohrbach's address,
I shall endeavor to make, from the standpoint of wooden-
airplane construction, a compari son of the properties
which result from the peculiarities of both materials in
1. In England, after a period of transition, only
metal airplanes are to be ordered by the military authiori-
ties, It is said, hovrcver, that this decision is not at
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Rohrbach, Adolf. Materials and Methods of Construction in Light Structures, report, May 1929; (https://digital.library.unt.edu/ark:/67531/metadc65364/m1/28/: accessed May 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.