U. Saetti, Z. Chen, J.F. Horn, T. Berger

This paper investigates vibrational stabilization effects in rotorcraft flight dynamics. This study is motivated by the fact that eigenvalues of the rotorcraft flight dynamics identified from flight test often differ from those computed with physics-based simulations, and that some commonly observed mismatches may be ascribed to vibrational stability effects due to rotor blade imbalance or other periodic disturbance on the rotorcraft. Starting from a simple example involving an inverted pendulum, the paper demonstrates the use of the harmonic decomposition method for the study of vibrational stabilization effects. The concept is then extended to analyze the effect of blade imbalance on the flight dynamics of a helicopter. Additionally, vibrational stablization of a slung load in forward flight is investigated using small-amplitude and disturbances on an active cargo hook. Results show that while vibrations induced by rotor blade imbalance do not stabilize the hovering dynamics of a helicopter, these vibrations still have a significant effect on the hovering dynamics. Rotor blade imbalance results in a symmetric effect on the roll and pitch axes, in that it tends to decrease the frequency of the subsidence modes of the hovering cubic, while the unstable oscillatory modes tend to increase in frequency and decrease in damping. On the other hand, the yaw/heave dynamics are relatively unaffected compared to the lateral and longitudinal axes. Moreover, small-amplitude oscillations of an active cargo hook were shown to significantly decrease the amplitude of the limit cycle oscillation of a slung load in forward flight and to stabilize its dynamics. This constitutes a practical solution to the semi-active control of a suspended load.

49th European Rotorcraft Forum 2023, Bückeburg, 2023

Conference Paper

englisch

21,0 x 29,7 cm, 14 Seiten

DGLR-Bericht, 2023, 2023-01, 49th European Rotorcraft Forum 2023 - Proceedings; S.1-14; 2023; Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth e.V., Bonn

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2023