Modeling the mutual distortions of interacting helicopter and aircraft wakes

Flight procedures that will decrease the following distance between successive aircraft have been considered as a means of alleviating pressures on airport capacity while still conforming to conventional air traffic management rules. A major limitation to the implementation of such procedures is perceived to be an associated increase in the possible severity of encounters with the wakes of nearby aircraft. Modeling efforts have focused on quantifying such interactions in terms of structural loading or degradation in handling and have established that helicopters respond in a fundamentally different way than fixed-wing aircraft to encounters with wake vortices. This paper suggests that, particularly at the low forward speeds typical of terminal phase operations, the mutually induced distortion of the helicopter's own wake and the wake of the interacting aircraft strongly influences the aerodynamics of the helicopter rotor. Results from numerical simulations suggest that neglecting this aspect of the interaction, as has commonly been done in the past, can indeed be valid at high helicopter forward speeds, but can lead to significant misrepresentation of the severity of wake encounters under terminal flight conditions.