Studies of a flat wake rotor theory

A computer code was developed at Princeton University to calculate the velocity components in the flow field near a lifting rotor. The induced velocity components in the rotor flow field predicted by this theory are compared with experiment. It appears that on balance, this relatively simple theory gives a reasonable prediction of the average induced velocities in a rotor flow and is quite suitable for such applications as estimating the influence of the rotor wake on the tail surfaces of rotorcraft. The theory predicts that significant induced velocity components are present in all three flow directions in the wake at a lifting rotor. It should be noted , however, that there are a few experimental measurements of the longitudinal and lateral induced velocity components in the rotor wake. This theory, known as the flat wake theory, is essentially the rotary wing analog of Prandtl's lifting line theory. The theory is described in this report. Calculations based on the theory are presented and compared with a modern free wake theory.