Aircraft spiral dive attractors due to actuator saturation

Under extreme adverse flight conditions, such as extreme turbulence, the aircraft controller may send a large control command attempting to counter the resulting forces and moments on the vehicle. In doing so, it may cause the actuator to saturate and operate at its extreme limit. The sustained actuator saturation may cause a loss of control authority and force the aircraft to move towards an undesired dangerous attractor instead of the desired flight trim. In the case study of F/A-18, two of these types of undesired spiral dive attractors have been identified. Once an aircraft is seized by the attractor, it would lose altitude and crash if no proper action is taken in time. A two-mode switching scheme has been incorporated into the LOC (loss-of-control) recovery controller to successfully prevent sustained actuator saturation, eliminate the threat of the spiral dive attractors, and enhance the LOC recovery control.