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National Advisory Committee for Aeronautics, Technical Notes - Stability and Control Characteristics at Low Speed of an Airplane Model Having a 38.7° Sweptback Wing with Aspect Ratio 4.51, Taper Ratio 0.54, & Conventional Tail Surfaces

A low—speed wind—tunnel investigation was made of a fig—scale model
of an airplane having a 38.70 sweptback wing with an aspect ratio of 1551,
a taper ratio of 0.51;, and conventional tail surfaces. The investigation
was conducted with several leading—edge and tail configurations to
determine the low—speed stability and control characteristics. Good
agreement was obtained between values of the lift—curve slope and the
angle of attack for maximum lift obtained experimentally and the calculated
values obtained by using a cosine relationship with lift—curve slopes and
angle of stall of the unswept wing. A leading—edge modification simulating
a circular—arc wing gave a value of 0.51 for the slope of the tail—off
lift curve and a maximum lift coefficient of 0.88 as compared with corre-
sponding values of 0.59 and 1.01; for the plain wing.

In general, the model showed a large margin of static longitudinal
stability about a center of gravity located at 18 percent of the mean
aerodynamic chord. At lift coefficients near the stall, particularly
with the flaps down, there was a. decrease of stability and sometimes
instability existed through a small lift—coefficith range, which was
followed thereafter by increased stability at stall. The elevator, how—
ever, was capable of trimming the model at maximum lift. The simulated
CUCIflWC wing gave a large variation of longitudinal stability with
lift coefficient. The static margin was large at low lift coeffi’cients,
negative at higher lift coefficients and, at maximum lift, was large again.

The effective dihedral of the model increased with lift coefficient
in a manner similar to that obtained with other swept wings and the
variation of effective. dihedral with lift coefficient for the wing alone
was in good agreement with the calculated value. A good correlation of
wing—fuselage interference effect on effective dihedral was obtained
between data for the test model and other American and German data. This
model gave low aileron effectiveness for all leading—edge configurations
tested.