A Second Approximation To The Induced Drag Of A Rotor In Forward Flight

The method of determining the induced drag of a wing from the distribution of circulation in its wake has been adapted for an infinitebladed helicopter rotor. Using this method, a "rotor induced efficiency factor" can be determined which will result in computing more realistic induced drag values than the conventional momentum method. The factor is shown to be a function of rotor geometry and flight conditions and is plotted for several combinations of these parameters.