Redistributed Allocation for Flight Control Failure on a Coaxial Helicopter

Abstract

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.