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National Advisory Committee for Aeronautics, Technical Notes - Experimental Investigation of the Effects of Concentrated Weights on Flutter Characteristics of a Straight Cantilever Wing

Results are presented to show the effects on the flutter character—
istics of mounting concentrated weights at various positions on an
untapered wing model. The model was mounted as a rigid cantilever and
was tested with concentrated weights that were 38, 60, 90, and 100 percent
of the wing weight. The moment of inertia, the chordwise position of the
weight, and the spanwise position of the weight were varied. In several
tests, an end plate was used, which was believed to change the aerodynamic
aspect ratio of the wing. The effects of these variations on the flutter
characteristics are presented in a form which may be conventiently used
for correlation with theoretical results.

Airplane design trends are leading to the placement of heavy
concentrated masses on the outer wing panels and sometimes on the wing
tip. Present—day flutter analysis is based on many simplifying assump—
tions and, with the inclusion of these concentrated masses into the
problem, the analytical solution is at best approximate. Experimental
verification of these simplifying assumptions is needed for more accurate
design criterions. The purpose of this paper is therefore to present a-
consistent series of flutter tests made on a simplified structure in order
that the assumptions made in the various fundamental analyses may be
evaluated.

Dynamically similar models of full—scale airplanes are sometimes used
for flutter testing, but the production of such models is exceedingly
difficult. For this reason simplified models that could be built, tested,
and analyzed more easily are being used to study-the assumptions in the
theoretical analysis. The model wing used for this series of tests was a
straight, untapered, cantilever wing having uniform.properties the entire
length of the wing. Concentrated weights differing in mass and moment of
inertia were moved chordwise and spanwise on the wing. Because of the
simplicity of construction of the model, no attempt has been made to
indicate the most favorable location for a concentrated weight from
considerations of the flutter characteristics of an actual wing. In
order to obtain further information about the character of the air forces,
an unattached end plate was installed at the tip for a few tests.