Control of a helicopter during autorotation

Şansal, Kaan
Autorotation is a maneuver that requires no power and it is used in rotorcrafts when last operating engine is lost. It is an extremely complex state of flight and landing successfully after total power loss requires considerable skill. Main idea behind autorotation is that, by descending with a controlled rate, available potential energy is used as a source that turns main rotor at desired speed for providing thrust and flight control. Just before touchdown, ground speed and descent rate must be reduced for safe landing which can only be possible by managing available energy effectively. In this study, an autonomous autorotation controller is developed and implemented to a real-time high fidelity mathematical model of a full-scale light utility helicopter. For developing autorotation controller that consists of a standard inner-outer loop architecture, full linear and reduced order linear models are used which are obtained by linearizing and reducing the order of non-linear helicopter model around different trim points. While designing the outermost loop, autorotation maneuver is divided into five different phases (steady state descent, preflare, flare, landing and touchdown) and different controllers are developed for each of these phases. Collective commands generated from these controllers are blended using fuzzy transitions. These outer-loop controllers also generate references for velocity tracking controllers which provides attitude references to the inner loop attitude hold controllers. While designing attitude and heading hold controllers, Aeronautical Design Standard 33E-PRF (ADS-33EPRF) specifications are used as a guideline for evaluation of helicopter handling qualities. Details of linearization and model order reduction techniques that are used during the study are expressed. Comparison results of non-linear and linearized models are presented together with details of control law formation. For assessing performance of the autorotation controller, real-time simulation results of integrated high-fidelity model are provided from different initial flight conditions. Results demonstrate the capability of the proposed controller for achieving safe power-off landings.


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Citation Formats
K. Şansal, “Control of a helicopter during autorotation,” M.S. - Master of Science, Middle East Technical University, 2018.