Induced Flow Near a Helicopter Rotor: A Review of Present Knowledge

The basis and the extent of theoretical induced velocity calculations are reviewed. The theory is then applied to interference problems involving additional rotors, wings, and tails in the flow. For such cases, the interference effects can be calculated with acceptable accuracy. For hovering, superposition is used to introduce ground effect into the calculations. The resulting flow field offers a qualitative explanation of several previously observed phenomena. It is shown that, because of assumptions inherent in the analysis, the present induced‐flow theory cannot be used to predict the detailed aerodynamic loading on the rotor blades.