Understanding the Effect of Rotor-to-Rotor Interference on CH-47D Helicopter Dynamics

During the development of the Boeing CH-47D helicopter flight simulation model, test pilots reported mismatch between the flight simulator results and flight test data of the hover and low speed lateral axis handling qualities, especially for the case without the automatic flight control system. In addressing the observed mismatch, the gains of the longitudinal and lateral components of the inflow model were selected to be significantly higher than their theoretical values. In this study, a detailed understanding of the rotor-to-rotor inflow interference is pursued using a recently developed multi-rotor Pressure Potential Superposition Inflow Model (PPSIM). It is shown that couplings between the inflow gradients of individual rotors exist in a tandem rotor, which can be approximated by using higher values for the longitudinal and lateral inflow gains of individual rotors. Further, it is shown that the need for empirical tuning of aerodynamic hub moment influence factors can be eliminated by properly accounting for the rotor-to-rotor interference in the inflow model.