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National Advisory Committee for Aeronautics, Report - The Effect on Dynamic Lateral Stability and Control of Large Artificial Variations in the Rotary Stability Derivatives

An investigation has been conducted in the Langley free-flight
tunnel to determine the efiects of large artificial variations of
several rotary lateral-stability derivatives on the dynamic lateral
stability and control characteristics of a 45° sweptbaclc-wing
airplane model. The derivatives investigated were the damping-
iwyaw derivative 0", (the yawing moment due to yawing),
the damping-in-roll derivative 0,9 (the rolling moment due to
rolling), and the two cross derivatives 0;, (the rolling moment
due to yawing) and 0,, (the yawing moment due to rolling).

Flight tests of a free-flying model were made in which the
derivatives were varied over a wide range by means of an
artificial-stabilization device incorporating a gyroscope sensitive
to rolling or yawing velocity. Calculations of the period and
damping of the lateral motions and of the response to roll and
yaw disturbances were made for correlation with the experi-
mental results. In order to simplify the analysis, most of the
calculations were based on the assumption of idealized artificial-
stabilization systems, but a few check calculations were made
in which the small constant time lag of the stabilization device
used in the tests was takeninto account. Extensive calculations
were not made by this method, however, because of the eatremely
laborious process involved and because asystematic determina—
tion of the effect of time lag on stability throughout the variation
of the four den'vatives was considered beyond the scope of the
present investigation.

The calculated results were in qualitative agreement with the
experimental results in predicting the general trends in flight
characteristics produced by large changes in the stability deriva-
tives, but in some cases the theory with the assumption of zero lag
was not in good quantitative agreement with the evperimental
results. In these cases the check calculations with time lag taken
into account indicated that the discrepancies could be attributed
to the efiect of the small constant time lag in the stabilization
device used.