The Prediction of Helicopter Rotor Hover Performance using a ...

UDC 533.662.6 : 533.6.013.67 : 533.6.048.3 : 533.6.013.16 : 533.6.048.1
THE PREDICTION OF HELICOPTER ROTOR HOVER PERFORMANCE
USING A PRESCRIBED WAKE ANALYSIS
by
C. Young
SUMMARY
*CP No.1341
June, 1974
A method of calculating the performance of a helicopter rotor in the hover
is presented. The method combines the downwash velocity distribution induced by
a contracting spiral vortex wake with strip element-momentum theory. The shape
of the wake takes a prescribed geometry developed from an extensive series of
model tests made in the USA.
The predicted thrust and power is in good agreement with measurements made
on model and full scale rotors provided that the aerofoil data is sufficiently
well defined. The calculated load distribution along the blade is also compared
with measurements made on Wessex helicopters. The load distribution is shown to
be very sensitive to a light wind but theory compares well with experiment
when this effect is eliminated.
The hover performance predicted using only the wake induced velocity
distribution is also discussed. The rotor performance is shown to be too
sensitive to the geometry of the wake for the method to be used as a design tool
with confidence, and the mathematical representation of the wake needs improving.
* Replaces RAE Technical Report 74078 - ARC 35652.