A study of the effect of leading-edge modifications on the flow over a 50-deg sweptback wing at transonic speeds

Abstract

An investigation has been made in the N.P.L. 18 in. x 14 in. Tunnel of the effects of leading-edge modifications on the flow and forces on an untapered wing of 50 deg leading-edge sweep, at stream Mach numbers between 0.60 and 1.20. Seven leading-edge profiles were tested, ranging from a drooped extension of 18 per cent of the chord of the basic sharp-nosed section to a round-nosed section with a leading-edge radius of 1.0 per cent of the basic chord. Leading-edge droop was found to increase the wing drag near zero lift but to reduce appreciably the lift-dependent drag component, except at the highest test Mach numbers. Droop also increased the lift coefficient at which leading-edge separation occurred on the upper surface at moderate subsonic speeds, but in addition reduced the Mach number for transonic flow attachment. The appearance of the forward shock (but not the rear shock) is considerably delayed when the leading edge is drooped. With the undrooped sections an increase in leading-edge radius was accompanied by successively earlier appearances of the forward shock, and hence the outboard shock with its attendant separation. The conditions at which the rear shock first appeared changed only slowly as the section was changed. The variations in wing flow pattern as the leading edge is modified are discussed and related to measured changes in the wing lift and drag. An attempt is also made to estimate the local Mach numbers on some parts of the wing from the oil-flow patterns; this material is used to assess the flow conditions appropriate to shock-induced separation. The main section of the Report concludes with a tentative discussion of the significance of the present results to the design of swept wings. In an Appendix results obtained with the wing in a sweptforward configuration are briefly considered.