Abstract: Adapted for high-speed, stealth and maneuvering flight, the low-aspect-ratio flying-wing aircraft adopts the large sweep delta wing profile to meet the uncommanded lateral motion caused by the asymmetric leading vortex breaking similar to delta wing. In order to research the motions and related control methods, aerodynamic/flow integration measurement test, free-to-roll test and numerical simulation are carried on a low-aspect-ratio flying-wing model with leading edge sweep 65° and aspect ratio 1.54, which successfully captured the commanded lateral motions including wing drop and wing rock at Mach number 0.8 and 0.9, angle of attack 15°-20° conditions in wind tunnel. The Figure of Merit in free-to-roll test show that the lateral flight quality has declined obviously. The frequency spectrum and phase plane portrait of free-to-roll trajectories confirm that the departure motion characteristics are chaos or multi-periodic broadband oscillation. The combined control surfaces including leading edge flap 10° and all aileron 10° are used to free-to-roll wind tunnel test. The results verify that the combined control surfaces can restrain the uncommanded lateral motion at Mach number 0.8, angle of attack 20° condition. The flow principle is also given by numerical simulation. The shock-wave/vortex interactions above the wings at transonic cause the flow breaking asymmetric. There are high and low frequencies in the roll moment, which finally bring out the self-excited oscillations of the low-aspect-ratio flying-wing mode.

Key words: low-aspect-ratio flying-wing, transonic, lateral departure motion, wing drop, wing rock, flow principle