A Comparison of model following control systems for helicopter flight control near hover

Okçu, Ilgaz Doğa
Helicopters are complex, coupled dynamic systems with unstable behavior. Countless studies have shown that decoupling the helicopter flight dynamics greatly reduces pilot work load and increases the handling qualities. Design guidelines such as Aeronautical Design Standard 33E-PRF (ADS-33E), which are developed as a means of measuring the handling qualities of a given helicopter, emphasizes that coupling between pitch, roll, yaw and heave degrees of freedom are undesired. ADS-33E also gives flight dynamics engineers guidance about the aircraft response characteristics that are preferred by the pilots. Majority of the helicopters are equipped with stability augmentation systems and full authority flight control systems to mimic these response characteristics. Flight control systems stabilize the unstable modes, damp the oscillatory responses and provide functions such as attitude hold or coordinated turn to help ease the pilot work load. Reducing the pilot work load during flight assures a safe flight and increases the helicopter performance. Model following control is best suited for applications for which an ideal plant model, with the desired closed loop performance objectives, can be constructed. It has been used in helicopter flight control applications extensively in different forms. In this study; optimal model following control methods are used to construct decoupling flight controllers for the Bell 206B helicopter using ADS-33E guidelines. Optimal control is preferred for its simplicity and flexibility. The response type of the controllers is attitude command attitude hold (ACAH) in pitch and yaw plus rate command heading hold (RCHH) in yaw and heave. A reference model representing these requirements is constructed. The mathematical basis for the controllers are given. Linear and nonlinear simulation results for near hovering flight cases are presented. Robustness, tracking, and decoupling performances of the controllers are compared in frequency and time domain.
Citation Formats
I. D. Okçu, “A Comparison of model following control systems for helicopter flight control near hover,” M.S. - Master of Science, Middle East Technical University, 2015.