1. "Vortex surfing" is a phenomenon that is currently being investigated by the US Air Force to save fuel on long-distan

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1 Vortex Surfing Is A Phenomenon That Is Currently Being Investigated By The Us Air Force To Save Fuel On Long Distan 1 (159.04 KiB) Viewed 49 times

1. "Vortex surfing" is a phenomenon that is currently being investigated by the US Air Force to save fuel on long-distance flights. The idea is to fly aircraft in the upward part of the wingtip vortex of a leading aircraft. In 2003, NASA reported that one of its F/A-18 test aircraft had a 29% fuel saving by flying in the wingtip vortex of a DC-8. The DC-8 / F/A-18 flight was an exploratory investigation of large aircraft vortex-induced performance benefits on a fighter-type aircraft. The aircraft flew at 25,000 feet (p = 0.549 kg/m²) with a separation of about 60 m between their respective fuselage centre-lines (see schematic below). The F/A- 18 slowly moved in laterally to explore the vortex effects. The DC-8 has a wingspan of 43 m, fuselage length of 46 m and a mass of 140,000 kg. The wing-tips are located at the fuselage length aft of the nose. The F/A-18 has a wingspan of 12 m, fuselage length of 17 m and a mass of 23,500 kg. The wing-tips are located at 2 the fuselage length aft of the nose. If both aircraft fly at cruise airspeed of 260 m/s, and ignoring the effect of wing sweep (assume both aircraft can be modelled with straight wings), calculate: a) The net upwash velocity experienced by the F/A-18. [Ans: 0.3578 m/s]. b) The reduction in drag of the F/A-18 compared to when it is flying alone at the same mass, speed and altitude. The lift-to-drag ratio of the F/A-18 is 10. [Ans: 1.38%] 60 m