An Investigation of Helicopter Dynamic Coupling Using an Analytical Model

Many attempts have been made in recent years to predict the off‐axis response of a helicopter to contrnl inputs, and most have had little success. Since physical insight is limited by the complexity of numerical simulation models, this paper examines the off‐axis response problem using an analytical model, with the goal of understanding the mechanics of the coupling. A new induced velocity model is extended to include the effects of wake distortion from pitch and roll rate. It is shown that the inclusion of these effects results in a significant change in the flap response to a steady angular rate. The proposed inflow model is coupled with the full rotorhody dynamics, and comparisons are made between the model and flight test data for a UH‐60 in hover. Results show that inclusion of induced velocity variations due to shaft angular rate improves correlation in the off‐axis response to cyclic inputs.