• Version
• 148 Downloads
• 902.52 KB File Size
• 1 File Count
• December 14, 2016 Create Date
• December 14, 2016 Last Updated

National Advisory Committee for Aeronautics, Technical Notes - Stress and Distortion Measurements in a 45° Swept Box Beam Subjected to Antisymmetrical Bending and Torsion

An untapered aluminum-alloy box beam, representing the main
structural component of a full-span, two—spar, M50 swept wing with a
carry-through section, was subjected to antisymmetrical tip bending and
twisting loads such that the stresses were kept below the proportional
limit.

The investigation revealed that the antisymmetrical loading magni-
fied the effects of sweep which were previously Observed for symmetrical
loads on the same box beam. The effects are a build-up of normal stress
and vertical shear stress in the rear spar near the fuselage when the
box beam is considered sweptback. _An additional result of antisymmet-
rical loading was the appearance of large shear—lag stresses in the
carry—through section, particularly in the bending case.

The investigation further revealed that the spar deflections of
the swept box beam could be estimated by an approximate method of
analysis; however, this method is less accurate for antisymmetrical
than for symmetrical bending loads because of the shear- -lag effects in
the carry-through.section.

The stresses and distortions of a #50 swept box beam loaded by
symmetrical tip bending and tip twisting loads are presented in refer-
ence l and an approximate method of evaluating the deflections is given.
The test specimen used to obtain the data of reference 1 (see fig. 1)
was again tested with antisymmetrical tip bending and tip twisting loads
applied and the results are presented in this paper. The stresses for
the antisymmetrical loadings are compared with standard beam formulas
and the distortions with those obtained from the approximate method of
reference 1.

The pertinent details of the swept box beam are shown in figure 2.
(Hereinafter the box beam is referred to as sweptback rather than swept;
thus the spars (or sidewalls) may'be conveniently referred to as "front"-
and "rear" without ambiguity.) The sweptback parts consisted of two
boxes with their longitudinal axes at right angles, joined by and
continuous with a short rectangular carry-through section representing
that part of a wing to be found inside an airplane fuselage. The
material of the specimen was 2hS-T3 aluminum alloy except for the bulk—
heads. The bulkheads consisted of rectangular steel sheets with a 90°
bend at each edge, forming flanges for attachment to the spars and
covers. Bulkheads 2, 3, h, and 5 were §%-inch thick, whereas all other
bulkheads were é-inch thick.