Experiments on a delta wing with jet-assisted lift

Abstract

Summary. This report describes an investigation into the effect of blowing a jet stream, simulating conventional jet engines, downwards from the lower surface of a slender delta wing (aspect ratio unity), for the purpose of obtaining additional lift at take-off and landing. Initial experiments investigated a spanwise jet sheet blown respectively from 70, 80 and 90 per cent of the mid-chord from the apex, and a trailing-edge jet flap. It was found that a spanwise jet blown forward of the trailing edge was inefficient in providing lift; a flow investigation showed that this was associated with a region of low pressure behind the jet and a strong vortex at the outer edge of the jet. Further experiments were then carried out using a narrow chordwise jet sheet and a concentrated group of jets on the wing centre-line, to avoid the adverse effects of the spanwise jet. The concentrated jets proved far more efficient than the other two arrangements, and a total recovery of the thrust component and up to 75 per cent recovery of the lift component of the jet reaction (for the jet directed at 60 deg to the wing plane) was achieved. Tests with the concentrated jets were also made with ground effect and elevator control. The experiments indicated that it does not seem possible to realise more than 90 per cent of the lift component of the jet reaction from any suitably located jet.