Formation Flying of Oblique Wing Aircraft, Assessement of Variations in Formation Configuration - Induced Effects & Control

Abstract

The idea of flying aircraft in formation to reduce fuel usage, has been appreciated 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 Oblique Wing aircraft and the existence of a research programme (e.g. “SwitchBlade”) being conducted in USA, a need has arisen to evaluate the possible advantages and disadvantages of formation flying. Compared with conventional symmetric aircraft flying in formation, asymmetric flying aircraft present appreciably different and “handed” geometric relationships. In previous papers, we have stepped up the analysis level of formation flying aspects, exploiting a recently developed design method that allows span loading and camber control on wings with and without winglets. The method has been adapted to assess the aerodynamics of wings in formation and then to redesign them to eliminate induced roll effects. This paper focuses on Oblique Wing formations. Typical spacing parameters have been considered for Oblique Wings at 30 o sweep. Formations with single Trail aircraft to the right and also the left of the Lead aircraft are assessed. Formations with more than two aircraft are also considered. Predictions show benefits of up to 35% or more in lift-induced drag reduction for the Trail aircraft after re-design. A limited number of results using an Euler solver reflect benefits of the same order. The implications of accurately modelling the Lead aircraft trailing wake have been highlighted. The technique has proved to be easy and robust in use. Using the design method to re-design an existing geometry to eliminate rolling moment induced in formation flight has proved enlightening. It provides, at every stage, a feel for what is happening in terms of camber development, pressure distributions and Centre of Pressure location. The resulting changes in camber give an indication of control surface deflection required. These are of course immediately applicable to morphing geometries. Several avenues of further work and development have arisen.