Flight Control Energy Saving via Helicopter Rotor Active Morphing

Abstract

Helicopter main rotor active morphing is investigated to save helicopter flight control energy in the presence of constraints on outputs. For this purpose, the nonlinear equations of motion of the helicopter are linearized around straight level flight. Then, several main rotor active morphing scenarios such as blade radius, blade chord length, blade twist angle, and rotor angular speed variation are analyzed individually (i.e., each active morphing scenario is implemented one at a time). Output-variance-constrained control is used for helicopter flight control system design, and the control energy savings due to active morphing with respect to a conventional helicopter are evaluated. An extensive circumstance in which all active morphing concepts are implemented simultaneously is examined to obtain larger control energy savings. The possibility of using morphing controls for trimming is also considered, and stochastic optimization is used to solve the resulting simultaneous trimming and control design problem. Extensive analysis, including closed-loop system responses, is carried out for the most energy-efficient active morphing procedure. Comparisons with a helicopter designed using passive instead of active morphing are also performed. Finally, some robustness properties of the closed-loop system corresponding to the active morphing scenario are examined.