Redundant Control Allocation Strategies for the RACER Compound Rotorcraft Configuration

This article presents the development, implementation, and evaluation of dynamic inversion (DI) flight control laws for compound rotorcraft with auxiliary propulsion systems, with application to a configuration representative of the Airbus Rapid And Cost-Efficient Rotorcraft (RACER). The RACER features a single main rotor, a boxed wing, and two lateral pusher propellers that provide both torque balancing and thrust compounding. The DI control laws are structured using a multiloop architecture and incorporate redundant control allocation to the pusher propellers via a pseudo-inverse (PI) strategy. A primary objective is to investigate control allocation approaches that minimize pitch attitude excursions during acceleration and deceleration maneuvers. A generic multirotor/wing simulation model is adapted to model the flight dynamics of the RACER configuration. The model is trimmed and linearized at discrete speeds from hover to cruise, and control reallocation is used to enable trimming at arbitrary pitch attitudes. Model-order reduction techniques are applied to obtain reduced-order models suitable for control synthesis. Both a baseline DI controller and a PI variant are implemented and tested in closed-loop simulations using the full-order nonlinear model. Three representative maneuvers are considered: (i) a hover-to-cruise transition, (ii) a combined transition, climb, and coordinated turn, and (iii) a cruise-to-hover reverse transition. The PI-based control law reduces pitch attitude variation by reallocating control effort to the auxiliary propulsion system, while achieving comparable tracking accuracy, as well as similar performance and handling-quality metrics relative to the baseline controller.