Horizontal Stabilator Utilization for Post Swashplate Failure Operation on a UH-60 Black Hawk Helicopter

A flight simulation model for the UH-60 Black Hawk, based on Sikorsky's GenHel model, is modified to simulate a locked failure of a main rotor swashplate servo actuator, which is compensated by using the stabilator as a redundant control effector. Steady-state trim analysis is performed to demonstrate feasibility of trimmed flight in various conditions with different locked servo actuator positions for the forward, aft, and lateral actuators. A model-following, linear dynamic inversion controller is implemented and modified to account for locked actuator position. Postfailure, the controls are reconfigured to partially reallocate the control authority in the longitudinal axis from the main rotor longitudinal cyclic to the stabilator. This is done by manipulation of only the control allocation relating pilot stick inputs to servo actuator positions, whereas the feedback control gains and mechanical rigging between servo actuators and rotor pitch controls remain identical to the baseline. Flight simulation results demonstrate the ability of this reallocation to compensate for locked failure of the forward main rotor swashplate servo actuator, as well as the ability of the aircraft to decelerate from cruise at 120 kt to 50 kt, slower than the published safe rolling landing speed of 60 kt. A similar range of locked positions of the forward and aft actuators is demonstrated to be feasible for aircraft recovery using control of the stabilator. Feasibility of aircraft recovery for locked positions of the lateral servo actuator is also considered, as well as the effect of variation in gross weight, speed of actuator locking, and delays in fault detection and identification.