Patent US 3,945,593

A flight control apparatus for the control of the trajectory and the airspeed of an airplane comprises a measuring equipment for measuring the deviation of the aircraft position from a commanded trajectory, and a measuring equipment for measuring the deviation of the angle of attack from a commanded value. Both deviation signals are applied with appropriate transfer functions to both the throttle actuator and to the control surface actuator. The transfer functions, which in the simplest case are constants, may be selected such that a deviation of the trajectory and its correction is substantially without any influence on the angle of attack and a deviation of the airspeed and its correction is substantially without any influence on the trajectory. According to another aspect of the invention, the apparatus measures altitude, angle of attack, pitch rate and vertical and longitudinal acceleration of the aircraft. There is a pseudo-observer including a number of appropriately dimensioned filters to form a number of additional state variables derived from the variables directly measured, the additional state variables comprising the time integrals of both the trajectory deviation signal and the angle of attack deviation signal, and a signal indicative of vertical speed. All measured and derived signals are applied in linear combinations to a throttle actuator, a spoiler actuator and an elevator actuator. The output of the elevator actuator is applied to a model system simulating the actual elevator movements and applying a feedback signal to the elevator actuator.