Subsonic wind-tunnel tests of various forms of air intake installed in a fighter-type aircraft

Abstract

Tests have been made at Mach numbers up to 0.93 in the Royal Aircraft Establishment 10 ft X 7 ft High Speed Wind Tunnel to examine how the longitudinal characteristics of a fighter-type aircraft are affected by the installation of air intakes in the nose, fuselage sides, or wing roots. None of these intakes alters the lift or pitching moment characteristics significantly, but their effects on external drag vary, and only the nose intake avoids an increase. This superiority derives principally from its low area ratio, the value of which largely determines not only the critical Mach number and hence the behaviour at transonic speeds of the intake fairing but also its sensitivity to spillage and aircraft attitude. Both forms of divided intake cause an increase in profile drag of roughly 20 per cent; on the side intake this is due to the siting of the boundary-layer by-passes and on the wing-root intake to the increased wing thickness. Their high area ratios make them sensitive to changes in flow direction and lead to high suction levels over the intake fairings which are expected to cause drag increases early in the transonic range. Separation in the canopy-intake junctions of the side intake reduces the drag divergence Mach number to 0.87, compared with 0.89 for the other models. The shaping of the wing-body junction which was combined with the nose and side intake installations leads to a marked reduction in drag at transonic speed, an advantage not shared by the wing-root lay-out.