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National Advisory Committee for Aeronautics, Technical Notes - A Theoretical Analysis of the Effect of Several Auxiliary Damping Devices on the Lateral Stability and Controllability of a High Speed Aircraft

A theoretical analysis has been made of the effect of several
auxiliary damping devices on the lateral stability and controllability
of a high-speed aircraft. The systems investigated included stabiliza-
tion devices which deflect the rudder or an auxiliary Surface propor-
tional to the yawing velocity, rolling velocity, or rolling acceleration
and one which deflects both aileron and rudder proportional to the
rolling velocity. An idealized control system without phase lag was
assumed for the analysis.

The present investigation indicated that each of the assumed
stabilization systems is capable of improving the damping of the lateral
oscillations of the assumed aircraft. The system which deflected the
rudder proportional to yawing velocity made necessary increased pedal
forces in steady turns, and the systems which deflected the rudder or
rudder and ailerons proportional to rolling velocity required unnatural .
rudder deflections to maintain zero sideslip subsequent to an applied
rolling moment. The system which deflected the rudder proportional to
rolling acceleration introduced adverse yaw subsequent to applied yawing
or rolling moments.

Recently much interest has been shown in automatic stabilization
devices as a means of improving the damping of the lateral oscillation
of some aircraft designed for transonic and supersonic flight. The
investigations reported in references 1 to 3 were concerned primarily
with the effect of these devices on the damping of the aircraft lateral
oscillation, with little or no emphasis on the problem of lateral
controllability. Investigation, therefore, of the effect of a number
of stabilization systems on the lateral controllability, as well as
oscillatory damping, of present-day high-speed aircraft seemed desirable
since both factors are significant in a pilot's evaluation of the flying
qualities of an aircraft equipped with a particular stabilization system.

The type of stabilization devices which are analyzed are those
which deflect a control surface proportional to the angular velocity in
either yaw or roll, or to one of their time derivatives. The assumption
is made that there is zero phase shift in the stabilization system, and,
that the stabilization system gain is independent of frequency.

The results of this investigation are presented in the form of
aircraft motions subsequent to rudder or aileron deflections, comparisons
of the time to damp to half amplitude and the period of the lateral
modes of motions, and plots of the rudder motion required to perform a
perfectly coordinated turn for a given aileron deflection, for each
stabilization system discussed. In addition, the effect of each assumed
stabilization system on the ratio of aileron deflection to rudder deflec-
tion required for a steady turning maneuver is discussed.