Supersonic Aircraft Formation Flying to Increase Flight Efficiency

摘要

Flying aircraft in Close Formation Flight (CFF) to reduce fuel usage, is well appreciated. Results are available for conventional aircraft using idealized approaches e.g. vortex lattice formulations in subsonic regime with reductions in lift induced Drag (Cdi) of 30-50% predicted. With greater importance of Oblique Flying Wing aircraft (OFW) and the research programme (e.g. the supersonic DARPA & USAF “SwitchBlade”), a need has arisen to evaluate the possible advantages and disadvantages of OFW in CFF. Compared with conventional symmetric aircraft flying in formation, asymmetric OFW present different and “handed” geometric relationships. Earlier work, in the transonic regime, showed reductions of more than 35% Cdi for trailing OFW in CFF, after redesign to eliminate lift and roll increments. However, there is little background on the Supersonic regime, hence prompting this paper. Typical spacing parameters have been considered for OFW at 60o sweep. Formations with single Trail aircraft to the right (Core 1) and also to the left (Core 2) of the Lead aircraft are assessed. Multi-Formations are also considered. Lift increments on trail OFW in favourable CFF geometries are trimmed out by reducing AoA. Benefits of up to 35% or more in Cdi reduction occur for the trimmed (1-DoF) trail aircraft. An accurate modelling the Lead aircraft trailing wakeis needed. Brief assessment of Trailing edge flap deflections required to trim trail OFW in CFF, eliminating induced pitch roll and lift is shown. The use of camber design methods to re-design the trail wings to eliminate CFF induced forces and moments has been outlined. The geometry changes for control are of course immediately applicable to morphing wing technology. Several avenues of further work and development have arisen.