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Investigation of rotorcraft-pilot couplings under flight-path constraint below the minimum-power speed

Published online by Cambridge University Press:  03 February 2016

L. Lu ,
G.D. Padfield  and
M. Jump
L. Lu
Affiliation:
[email protected]
G.D. Padfield
Affiliation:
Flight Science and Technology Research Group, Department of Engineering, University of Liverpool, the Quadrangle, Liverpool, UK
M. Jump
Affiliation:
Flight Science and Technology Research Group, Department of Engineering, University of Liverpool, the Quadrangle, Liverpool, UK
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Abstract

In some situations, closed loop control by the pilot can result in the combined pilot-aircraft system becoming marginally stable or even unstable. This can happen whether the pilot is controlling attitude or flight path. In this paper, an investigation into helicopter stability under flight-path constraint below the minimum-power speed is reported. The work provides a theoretical basis for flight path handling qualities criteria particularly for flight on the, so-called, back-side of the power curve. The research uses the theory of weakly coupled systems by partitioning the helicopter longitudinal dynamics to investigate three interacting subsystems – classically the surge mode, the phugoid mode and the heave mode. Under certain conditions, strong control of flight path or vertical speed is shown to drive the aircraft-pilot system unstable and a conflict is shown to exist between feedback gain values to guarantee stability of both the surge and the flight path motions. This conflict constitutes a potential source of adverse rotorcraft-pilot couplings. The problems are exacerbated in cases when the use of collective control is restricted. The phenomenon is explored in both ground based simulation and flight test to provide a verification of the theory.

Type
Research Article
Information
The Aeronautical Journal , Volume 114 , Issue 1157 , July 2010 , pp. 405 - 416
Copyright
Copyright © Royal Aeronautical Society 2010 

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