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.
An elastic blade flight dynamics model for a coaxial helicopter based on the Sikorsky X2 Technology™ Demonstrator is presented and validated with steady trim and frequency response flight test data. A full authority explicit model following control architecture along with weighted pseudoinverse control allocation is implemented for the model in hover and cruise at 180 knots using CONDUIT® in order to stabilize the vehicle and meet a set of stability, handling qualities, and performance requirements. Different fault scenarios are considered including failure of rotor swashplate actuators and tail surface actuators in hover and forward flight, which are compensated for by recalculating the pseudoinverse control mixing accordingly. The approach is shown to maintain aircraft stability through the fault transient and into a new steady trim state for the vehicle. Though the implemented controller is successful in maintaining the aircraft state, different fault cases lead to violations in rotor tip clearance limits, which will require additional effort to account for in flight.
An elastic blade trim model of a coaxial-pusher helicopter with aerodynamic interference between the rotors is described and validated against existing experimental data for coaxial rotor systems and helicopters. With the trim model in place, parametric sweeps of trim controls are performed to examine different allowable control settings in terms of the swashplate actuator positions on a generalized swashplate geometry at 3 different flight speeds representing a low speed, moderate speed, and high speed flight condition. The effective allowable ranges of locked-in-place positions are established for the 3 actuators on each swashplate, and explanations for the relative ranges are discussed. In low speed, differential moment variation between the rotors allows for actuator settings accounting for approximately 30% of the total range. In moderate and high speed these ranges change due to the moment balance between the rotor and aerosurfaces of the vehicle, with the aft actuator on each rotor trimmable over the entire allowable range, whereas the forward and lateral actuator on the two rotors have allowable ranges accounting for 40-60% and 20-25% of the total range, respectively.
An elastic blade flight dynamics model for a coaxial helicopter platform based on the Sikorsky X2 Technology™ Demonstrator is presented and validated with steady trim and frequency response flight-test data. A full authority explicit model following control architecture along with pseudoinverse control allocation is implemented for the model in hover and cruise at 180 kt using CONDUIT® in order to stabilize the vehicle and meet a set of stability, handling qualities, and performance requirements. Different fault scenarios are considered including failure of rotor swashplate actuators and tail surface actuators in hover and forward flight, which are compensated for by recalculating the pseudoinverse control mixing accordingly. The approach is shown to maintain aircraft stability through the fault transient and into a new steady trim state for the vehicle. Though the implemented controller is successful in maintaining the aircraft state, different fault cases lead to violations in rotor tip clearance limits, which will require additional effort to account for in flight.
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