| Popis: |
The idea of flying aircraft in Close Formation Flight (CFF) to reduce fuel usage, has been appreciated for some time. There are many results available for conventional winged aircraft using idealized approaches e.g. vortex lattice formulations focussing on the subsonic regime with reductions in lift induced Drag (CDi) of 30-50% predicted. In view of the greater importance being attached to Oblique Flying Wing aircraft (OFW) and the existence of a research programme (e.g. the DARPA “SwitchBlade” program) being conducted in USA, 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 appreciably different and “handed” geometric relationships. Earlier work, in the transonic regime, has shown reductions of more than 35% CDi for trailing OFW in CFF, after redesign to eliminate lift and roll increments. There is little background on the Supersonic regime. In this paper we look at the potential of CFF in the context of supersonic flight. Typical spacing parameters have been considered for OFW at 60 sweep. Formations with single trail aircraft to the right (Core 1) and also to the left (Core 2) of the Lead aircraft are assessed. Formations with more than two aircraft are also considered. Lift increments on trail OFW in favourable CFF geometries are trimmed out by reducing AoA. We show benefits of up to 35% or more in CDi reduction for the trimmed (1-DoF) trail aircraft. The implications of accurately modelling the Lead aircraft trailing wake have been highlighted. A brief assessment of Trailing edge flap deflections required to trim trail OFW in CFF, eliminating induced pitch roll and lift has been carried out. The use of camber design methods to redesign 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. |
