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New Aspects of Higher Harmonic Control on a Four‐Bladed Hingeless Model Rotor

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To investigate the effect of Higher Harmonic Control (HHC) on a hingeless rotor, a wind‐tunnel demonstration was performed with open‐ as well as closed‐loop tests. Whereas the open‐loop tests aimed at a systematic examination of the rotor dynamics in the case of HHC inputs, the main aspect of the closed‐loop tests was the behavior of an implemented adaptive controller. A first data evaluation showed that the controller reduced the vibrations considerably at steady‐state as well as at time‐varying flight conditions. Surprisingly, however, all dynamic rotor forces and moments could be influenced simultaneously by single HHC input signal. Furthermore, a nearly constant phase shift of the rotar transfer function was ascertained within the whole flight envelope. These rotor characteristics are demonstrated by wind tunnel data and theoretical explanations are provided. Theoretical explanations are supported by simulation results obtained with different aeroelastic rotor and rotor downwash models, showing the influence of various aerodynamic and aeroelastic parameters on the measured rotor characteristics. Finally, a controller that works with a constant feedback phase shift of the rate transfer function is presented and compared with a fully adaptive one.

Document Type: Research Article


Affiliations: DLR Institute for Flight Mechanics, Braunschweig, Germany

Publication date: July 1, 1992

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  • The Journal of the American Helicopter Society is the world's only scientific journal dedicated to vertical flight technology. It is a peer-reviewed technical journal published quarterly by AHS International and presents innovative papers covering the state-of-the-art in all disciplines of rotorcraft design, research and development. (Please note that AHS members receive significant discounts on articles and subscriptions.)

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