A Generalized Dynamic Wake Model with Wake Distortion Effects

For many years, analysts have been puzzled by the fact that the off-axis coupling of a helicopter exhibits the opposite sign in flight tests as compared to simulations. Recently, researchers have shown that the effect may be attributable to the bending of the wake during a pitching maneuver, which introduces a fore-to- aft gradient in induced flow that can reverse the predicted sign of the roll coupling. Other research has shown that this result can also be obtained with momentum and vortex theory. In the present work, a generalized model for wake distortion in hover is augmented using the exact relation derived from vortex tube theory. This model is then coupled with a simple flap model to investigate the influence on dynamic coupling.