Ground state-fly state transition control for unique-trim aircraft flight control system

A system for controlling an aircraft, having landing gear and defining a pitch axis, a roll axis, a yaw axis and a lift axis, during a transition between a fly state, when no landing gear contact ground, and a ground state, when landing gear contact ground, comprising:

• controller means for producing a control input representing a desired value of an aircraft variable, wherein said aircraft variable comprises at least one of attitude with respect to the pitch axis, attitude with respect to the roll axis, heading with respect to the yaw axis, and altitude with respect to the lift axis;
• sensing means responsive to the landing gear for providing sensor signals corresponding to the condition of each landing gear and representing whether each landing gear contacts ground;
• landing gear ground contact means responsive to said sensor signals for producing signals indicating aircraft operation in the fly state and ground state;
• means responsive to said sensor signals for developing a transition variable, whose magnitude changes over a predetermined interval from a first value corresponding to initial ground contact of the landing gear to a second value at the end of said predetermined interval;
• and
• feedforward shaping filter means responsive to said transition variable, signals from said landing gear ground contact means and said control input, for developing a feedforward command whose frequency response changes during said transition as a function of said transition variable magnitude, the feedforward command having the frequency response of a lead/lag filter in the fly state, having a response that is independent of frequency in the ground state, and having a frequency response that changes with said transition variable magnitude during the transition between these states;
• a first summing junction for combining the feedforward command and a trim command, and for producing therefrom a control surface command;
• and
• automatic trim means responsive to signals from said landing gear ground contact means and said control surface command for producing a trim command, for removing by integrating over time the effect of steady-state control input from the control surface command when operating in the fly state, and for producing a control surface neutral position command during operation in the ground state with all landing gear in ground contact.