Pressure distribution and surface flow on 5 percent and 9 percent thick wings with curved tip and 60 degrees sweepback

Abstract

Extensive tables are given of pressure coefficients measured at Reynolds numbers from 1.3 x 10power6 to 3.9 x 10power6 on two half-models of identical planform with 5% RAE 101 and 9% RAE 101 streamwise sections. The planform of aspect ratio 3.899 has a straight trailing edge with 60° of sweepback, constant chord over most of the span and a parabolic outer portion of the leading edge curving to a pointed tip. The overall wing characteristics are obtained from integrated normal pressures and are compared with lifting-surface theory. The low-speed experimental pressure distributions and surface oil-flow patterns are analysed and discussed in relation to the onset of separation and the distinct vortex flows that develop at high incidence. Series of contrasting upper-surface isobars illustrate some features of the different stalling processes of the two wings. The direct influence of the main vortex on local surface pressures is assessed in general terms. A fuller appraisal of secondary surface flow is obtained from the oil patterns, observations in water and measurements of high suction near the trailing edge. Studies of the extent of leading-edge stall and location of part-span vortices, in particular two simultaneous leading-edge vortices on the thinner wing, follow from further analysis of local surface pressures. After a detailed discussion of the effect of Reynolds number and the distinct types of separated flow, a few results with leading-edge roughness are considered in relation to scale effect on separation and the extensive influence of part-span roughness.