Analysis of the Controllability and Stability of a Hybrid High-Speed Compound Helicopter with a New Configuration

In this paper, the stability and controllability of a new hybrid high-speed compound helicopter are analyzed. The results will serve as a theoretical foundation for subsequent flight control system designs. First, the nonlinear flight dynamics model is established based on the Newton–Euler method under the underlying assumptions. Then, a control strategy for a hybrid high-speed compound helicopter in three modes, namely, low-speed and hover mode, transition forward-flight mode, and high-speed forward-flight mode, is proposed. Therefore, trim analyses of various flight states are conducted and verified with wind tunnel test trim data. Ultimately, the nonlinear flight dynamics model is linearized by applying small perturbation theory, and the stability and controllability of the hybrid high-speed compound helicopter are analyzed. The results indicate that the trim results of the nonlinear dynamics model are highly compatible with the trim results of the wind tunnel test, which proves that the established nonlinear flight dynamics model has a high level of confidence. In addition, the stability increased with increasing forward-flight velocity in all modes except for the longitudinal long-period mode, which is consistently unstable. In yaw control, there is control coupling between the rotor collective and the propeller differential pitch, and the coupling weakens as the forward-flight velocity increases. Furthermore, the control efficiency of longitudinal cycling and lateral cycling gradually increases with increasing forward-flight velocity. In all three flight modes, the control effectiveness of the rudder is weak.