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National Advisory Committee for Aeronautics, Report - Investigation at Low Speeds of the Effect of Aspect Ratio and Sweep on Rolling Stability Derivatives of Untapered Wings

A low-scale wind-tunnel investigation was conducted in
rolling flow to determine the ejects of aspect ratio and sweep
(when varied independently) on the rolling stability deriva—
tives for a series of untapered wings. The rolling-flow equip-
ment of the Langley stability tunnel was used for the tests.

The results of the tests indicate that, when the aspect ratio is
held constant, an increase in the sweepbach angle causes a
significant reduction in the damping in roll at low lift coejlcients
for only the higher aspect ratios tested. This result is in
agreement with available swept-wing theory which indicates
no eject of sweep for aspect ratios near zero. The result of
the linear theory that the damping in roll is independent of
lift coejlcie—nt and that the yawing moment and lateral force
due to rolling are directly proportional to the lift coejicient was
found to be valid for only a very limited lift-coejicient range
when the wings were highly swept. For such wings, the damp—
ing was found to increase in magnitude and the yawing moment
due to rolling, to change from negative to positive at moderate
lift coejicients.

The eject of wing-tip suction, not accounted for by present
theory, was found to be very important with regard to the
yawing moment due to rolling, particularly for low-aspect-
rat—io swept wings. An empirical means of correcting present
theory for the eject of tip suction is suggested.

The data of the present investigation have been used to
develop a method of accountingfor the ejects of the drag on the
yawing moment due to rolling throughout the lift range.

In order to estimate the dynamic flight characteristics of
an airplane, a knowledge of the stability derivatives is neces-
sary. The static-stability derivatives are easily determined
from conventional wind-tunnel tests. The rotary derivatives,
however, have usually been estimated in the past from avail-
able theory because of the lack of a convenient experimental
technique. Such a technique has been developed, and the
rotary derivatives can now be easily determined by the
utilization of the curved—flow and rolling—flow equipment in
the Langley stability tunnel. This equipment is being
utilized for the purpose of determining the efiects of various
geometric variables on the rotary and static stability char-
acteristics of wings and complete airplane configurations.