Aerodynamics Modeling and Analysis of Close Formation Flight

Abstract

A novel computationally efficient close formation aerodynamic model is presented using the lifting-line theory based on an elliptical lift distribution assumption. Formation aerodynamic effects induced by trailing vortices of a leader aircraft are formulated as functions of both the relative position and orientation between the leader and follower aircraft. The proposed aerodynamics model is validated by comparing the model predictions with published experimental results. The proposed model is considered to be more accurate than the widely used single horseshoe vortex model, and it is at least as accurate as a fundamental vortex lattice model, but the exact knowledge of the lift distribution is not required. Comprehensive analysis is thereafter conducted to investigate the drag reductions in terms of different relative positions, angles of attack, sideslip angles, and leader-to-follower wingspan ratios. Up to 30% loss of the formation benefit is observed, if the optimal region cannot be tracked within 10% wingspan accuracy. In addition, the impact of the relative orientation between leader and follower aircraft is also investigated.