Method and apparatus for reducing unwanted sideways motion in the aft

Abstract

A method and apparatus for reducing the unwanted sideways motion of an airplane by reducing the lateral side loads and upsets caused by atmospheric turbulence and gusts is disclosed. A rudder modification command that causes the rudder command of the airplane to be changed in a manner that relieves the net force across the vertical stabilizer of the airplane caused by atmospheric turbulence and gusts is produced. More specifically, the pressure differential across opposite sides of the vertical stabilizer is measured and used to produce a rudder deflection value that is roll rate and yaw rate compensated. The compensated deflection value is high-pass filtered with a corner frequency that is twenty-five percent (25%) of the Dutch roll frequency of the airplane. The result is a first rudder deflection value that is subtractively combined with a second rudder deflection value. The second rudder deflection value is derived by gain adjusting and low-pass filtering the inertial sideslip angle rate value produced by the airplane's yaw damper. The low-pass filter has a corner frequency that is also twenty-five percent (25%) of the Dutch roll frequency of the airplane. The combined rudder deflection value is modified by a steady sideslip gain value and filtered by a gain shaping filter. The gain shaping filter increases the gain above the Dutch roll frequency of the airplane. The resultant rudder modification command is subtractively combined with the yaw damper rudder command to produce a rudder command. Preferably, a flow separation monitor is included to prevent the rudder modification command from producing a rudder command that exceeds allowable structural limits. Also, preferably, the rudder modification command is used to produce a lateral control command that is used to suppress rigid body roll response and improve handling qualities by gain adjusting and low-pass filtering the rudder modification command.