Formation Flying of Commercial Aircraft, Variations in Relative Size/Spacing - Induced Effects & Control Induced Effects & Control

Abstract

The idea of flying commercial aircraft in formation to reduce fuel usage, has been around for some time. There are many results available using idealized approaches e.g. vortex lattice formulations. In view of the greater importance being attached to environmental aspects, the need has arisen to evaluate the possible advantages and disadvantages. A previous paper was concerned with a limited number of flight formation configurations comprising identical wings. Even then the predicted induced drag reductions of near 30%, affording overall drag reductions of the order of 15-20%. This paper steps up the analysis level exploiting a recently developed design method that allows span loading and camber control on wings without and with winglets. The method has been adapted to assess the aerodynamics of wings in formation and then to re-design them to eliminate induced roll effects. We have extended the analysis by enlarging the formation size, varying the spacing parameters (x, y and z) and varying the relative sizes of the aircraft within the formation The technique has proved to be easy and robust in use. It is enlightening as it gives, at every stage, a feel for what is happening in terms of camber development, pressure distributions and Centre of Pressure location. We have been able to define areas of specific interest that are worthy of further analysis in terms of formation geometry. Conversely, formation geometries that are not beneficial (drag penalties or the need for prohibitive control surface deflections) can be avoided. Lift induced drag reductions of up to 60% may be achieved on a Trail aircraft following a larger Lead wing. A limited number of results using an Euler solver reflect benefits of the same order for equiand varying sized aircraft in formation. Several avenues of further work and development have arisen.