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Reduction of helicopter vibration through cyclic control of variable orifice dampers

Published online by Cambridge University Press:  04 July 2016

P. Anusonti-Inthra ,
F. Gandhi  and
L. Miller
P. Anusonti-Inthra
Affiliation:
Rotorcraft Center of Excellence, Department of Aerospace Engineering, The Pennsylvania State University, Pennsylvania, USA
F. Gandhi
Affiliation:
Rotorcraft Center of Excellence, Department of Aerospace Engineering, The Pennsylvania State University, Pennsylvania, USA
L. Miller
Affiliation:
Lord Corporation, Thomas Lord Research Center, Cary, USA
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Abstract

The present study demonstrates that cyclically varying the damping coefficient of controllable lag and flap dampers can reduce the 4/rev vibratory hub loads of a four-bladed hingeless rotor helicopter in high speed forward flight. Gradient-based optimization is used to determine the optimal multi-cyclic damping variation inputs that minimise a composite vibration index comprising of all six components of vibratory hub loads. Optimal 2/rev and 3/rev variations in the lag damping coefficient virtually eliminate the vibratory hub drag force and yawing moments, and produce small reductions in the vibratory hub side force. The optimal lag damping variations, interestingly, produce increases in the 3/rev and 5/rev components of the blade root drag shear, that cancel the contributions of the blade root radial shear to the vibratory in-plane hub forces. Despite some increases in higher harmonics of blade response, damper loads, and blade and flexbeam root loads, the lower harmonics and the peak-to-peak values show little change, implying that blade and damper fatigue life would not be adversely affected. When optimal 2/rev and 3/rev variations in flap damping coefficient are introduced in conjunction with the optimal lag damping variations, 30% reductions in the hub vertical vibrations are obtained, in addition to the previous reductions in the vibratory in-plane forces and yawing moment. The cyclic flap damping variations reduce the higher harmonics of the blade root vertical shear. Reductions in hub vibration levels are obtained over a range of forward flight speeds.

Type
Research Article
Information
The Aeronautical Journal , Volume 107 , Issue 1077 , November 2003 , pp. 657 - 672
Copyright
Copyright © Royal Aeronautical Society 2003 

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