Materials and Methods of Construction in Light Structures Page: 7 of 38
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.A.C.A. Technical .~emoranuJ io. 15
because a good metal airplane generally differs as a whole
or in its exterior dimensions from the corresponding wood
airplane, so that a skeptic can have doubts as to whether
the bettor performance of the metal airplane is not ascrib-
able to the more favorable dimensions or to the bettor
Duralumin or Stool?
Corresponding to the specific woights of duralumin
and stool, tension members made of the latter are first
equivalent to duralumin members of the same weight at a
tensilo-strength of 110 kg/mm& (156,460 lb./sq.in.).
Different duralumin parts are generally joined by
duralumin rivets of the same strength, so that. such junc-
tions involve only the weakening of the rivets. In this
respect steel construction is less favorable because thero
are no rivets of 110 kg/rm2 tensile strength, but ordina-
rily of only 30-40 kg/mn (42,670 to 56,890 lbo./sq.in.).
Once relatively many rivets must be used to join such
stool ep rts and, in order to provide sufficient rivet area,
more for stool than for duralumin. If the cross section
of the steel membor is to be fully utilized, there rmust
be an enlargement of the rivet field at tho junction place
in order to rovido space for all the rivets, which in
turn denotes a similar loss in weight. In order therefore
to preserve the equal weight of the whole stool structure,
tho steeool would need to have a strength of about 130 kg/
m:A2 (185,000 lb./sq.ino) with respect to this loss.. Sinco
the tools are not sufficiently stronger than such hard
structural steel, much time would be required for the work,
which would. be accompanied by great wearing of the tools.
Moreover the cross sections of such steel members are
very small., and they must therefore be made in the form
of hollow sections or profiles with respect to an adequate
inertia' moment, the result being a very thin wall. Such
profilos -ust generally be strengthened by all possible _
kinds of longitudinal corrugations, in order to prevent
local buckling. Such profiles are very difficult to join
together and could never be used in practical machines.
Since the hollow riuebers mostly consist of several
parts joined by longitudinal rows of rivets, another dif-
ficulty in connection with the joining is occasioned by
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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/m1/7/: accessed May 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.