Automatic control system for directional control of an aircraft during landing rollout

Ground roll control apparatus for lateral control of an aircraft during execution of the landing rollout sequence on a runway, said aircraft being of the type that includes a rudder system for aerodynamically establishing lateral control, at least one steerable wheel for exerting lateral control and a braking system with left and right differentially operable left and right brakes for providing additional lateral control, said aircraft being equipped with means for supplying signals representative of the current yaw position of said aircraft, the time rate of change of said current yaw position of said aircraft, the current ground velocity slip angle of said aircraft and the velocity of said aircraft relative to the longitudinal and lateral body axis thereof, said ground roll control apparatus comprising:

• course error computation means for supplying a ground roll course error signal representative of the difference between the current trajectory of said aircraft and a desired trajectory that will maintain said aircraft within the lateral boundaries of said runway;
• steering controller means for supplying a steering control signal for operating the steerable wheels of said aircraft, said steering controller means including integral control means for supplying a first component of said steering control signal, said integral control means being responsive to said ground roll course error signal, said signal representative of the current ground velocity slip angle of said aircraft and said signal representative of said current yaw position of said aircraft, said steering controller further including proportional control means for supplying a second component of said steering control signal, said proportional control means being responsive to said ground roll course error signal and said signal representative of the time rate of change in said current yaw position of said aircraft, said steering controller means further including means for combining said first and second components of said steering control signal to produce said steering control signal;
• rudder controller means for supplying a rudder control signal for operating said rudder system of said aircraft, said rudder controller means including integral control means for supplying a first component of said rudder control signal, said integral control means being responsive to said ground roll course error signal, said signal representative of the current ground velocity slip angle of said aircraft and said signal representative of the current yaw position of said aircraft, said rudder controller means further including proportional control means for supplying a second component of said rudder control signal, said proportional control means being responsive to said ground roll course error signal and said signal representative of the time rate of change in said current yaw position of said aircraft, said rudder control means further including means for combining said first and second components of said rudder control signal, said rudder controller means additionally including rudder authority means for receiving said combined first and second components of said rudder control signal and for supplying said rudder control signal, said rudder authority means exhibiting a gain factor that is a function of the ground roll velocity of said aircraft to supply said rudder control signal at a level that causes said rudder system to provide lateral control that dominates the lateral control provided by said steerable wheels and said braking system during a predetermined high speed portion of said landing rollout sequence;
• and
• differential brake controller means for supplying a brake control signal for operating said differentially operable left and right brakes of said aircraft, said differential brake controller means being responsive to said ground roll course error signal and said signal representative of the time rate of change in said current yaw position of said aircraft to selectively reduce one of the pilot-initiated left and right brake signals by an amount proportional to a weighted sum of said signal representative of said ground roll course error signal and said signal representative of said time rate of change in said current yaw position of said aircraft.