Wind-tunnel tests on the spoiling effects of engine cooling gills on radial air-cooled installations on a wing

Abstract

Information was required on the spoiling drag associated with opening cooling gills on radial air-cooled engine installations on a wing. Maximum lift, drag up to high CL, and cooling flow were measured on a 1/12 scale model of a flying boat, showing 1. the effect of opening cooling gills to 25 deg. and the variation of these effects with gill position relative to the wing; 2. the results of emitting the cooling air at specified regions of the exit; 3. comparison with a scheme for return-flow cooling. The spoiling drag associated with fuliy open gills at high Cz can be very large (of the same order as the wing induced drag) if the gill exit is nearer to the wing leading edge than about 10 per cent. of the local wing chord; but the effect diminishes rapidly as this distance is increased. To avoid the effect it is recommended that the exit of the gills should be at least 15 per cent. of the chord forward of the wing leading edge. The drag due to spoiling is also reduced if the cooling air is kept away from the nacelle-wing junction by emitting it at specified regions round the exit, preferably at the bottom where the lift is a minimum. Larger gill angles would be needed to satisfy maximum flow requirements in this way. The return-flow cooling system, with nose-exit, shows no evidence of large spoiling drag at high cooling flow. The data obtained may be useful for estimating the effects of other forms of discharge of low-energy air in front of a wing leading edge.