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Dynamic inflow modelling for autorotatingrotors

Published online by Cambridge University Press:  03 February 2016

Y. Murakami and
S.S. Houston
Y. Murakami
Affiliation:
University of Glasgow, Glasgow, UK
S.S. Houston
Affiliation:
University of Glasgow, Glasgow, UK
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Abstract

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The dynamic inflow model is a powerful tool forpredicting the induced velocity distribution over arotor disc. On account of its closed form andsimplicity, the model is especially practical forstudying flight mechanics or for designing controlsystems for helicopters. Scant attention has,however, been paid so far in utilising the dynamicinflow model to analyse an autorotating rotor, whichis different from a powered rotor in the geometricrelation between the direction of the inflow and therotor disc. Autorotation is an abnormal conditionfor helicopters, but for gyroplanes it is the normalmode of operation. Therefore the theoreticaldiscussion on an autorotating rotor is of importancenot only to improve the understanding of presentgyroplanes, but also in the development of newgyroplanes and to analyse the windmill-brake stateof helicopters. Dynamic inflow modelling is reviewedfrom first principles, and this identifies amodification to the mass flow parameter. Aqualitative assessment of this change indicates thatit is likely to have a negligible impact on the trimstate of rotorcraft in autorotation, but asignificant effect on the dynamic inflow modes incertain flight conditions. This is confirmed bynumerical simulation, although considerabledifferences only become apparent for steep descentswith low forward speed. It is concluded that whilemodification of the mass flow parameter is perhapsmathematically accurate, for practical purposes itis required only in a limited area of the flightenvelope of autorotating rotorcraft.

Information

Type
Research Article
Information
The Aeronautical Journal , Volume 112 , Issue 1127 , January 2008, pp. 47 - 53
Copyright
Copyright © Royal Aeronautical Society 2008 

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