• Version
• 95 Downloads
• 1.54 MB File Size
• 1 File Count
• January 20, 2017 Create Date
• January 20, 2017 Last Updated

National Advisory Committee for Aeronautics, Technical Notes - Some Effects of Aspect Ratio and Tail Length on the Contribution of a Vertical Tail to Unsteady Lateral Damping and Directional Stability of a Model Oscillating Continuously in Yaw

A fuselage-vertical-tail combination with tails of two aspect
ratios, each of which was tested at four tail lengths, was oscillated
in yaw through a range of reduced-frequency parameter corresponding to
the lateral motions of airplanes. The tail force caused by yawing, and,
hence, the approximate contribution of the tail to the damping in yaw,
was measured for each condition as a phase angle between.the lateral
force on the vertical tail and the displacement in yaw of the model.
These phase angles were measured with the tail in the presence of the
fuselage.

A reduction in the contribution of the vertical tail to the lateral
damping took place as the frequency was reduced to low values and became
more pronounced as the aspect ratio and.tail length were increased.

A complementary theoretical analysis based on the finite-span theory
of Biot and Boehnlein indicates certain conditions of tail length, aspect
ratio, and reduced-frequency parameter for which the lateral damping of
an isolated vertical tail goes to zero and then becomes destabilizing.
Although testing within these regions of indicated negative damping was
not possible, a condition of negative damping was obtained experimentally
in a region of theoretically predicted positive damping.

The analysis indicates that, for each vertical-tail aspect ratio,
there is a tail length for Which the lateral damping is minimum. This
tail position is forward of the center of gravity for small aspect ratios
and the higher frequencies and moves rearward with increasing aspect
ratios and lower frequencies.

Two of the more important geometric variables which affect the lateral
damping of an airplane are the_aspect ratio of the vertical tail and the _
distance between the vertical tail and the airplane center of gravity (or
tail length). Although both of these variables have been investigated
extensively for steady flight conditions, almost no information is availa-
ble to indicate any effects of variations in these geometric parameters
on the unsteady damping of the vertical tail, that is, the damping during
a lateral oscillation.