Critical mach numbers for swept-back wings

Summary

The effect of yawing a wing in high-speed flow is to delay the onset of shock waves and to increase the critical Mach number. This is because shock waves can only develop along the isobars (running parallel to the edges of the wing, which is assumed untapered and infinitely long), and therefore only the velocity component normal to the edges is significant. To some extent the same is true for a finite sheared or swept-back wing, though the problem is made more complicated by the various additional factors, such as finite aspect ratio (tip effect), plan form (e.g. taper effect) and, what is perhaps the most important, the central kink effect. The experimental technique is extremely cumbersome because of the many shape parameters involved (see Figs. 1, 2, 3), and since analytical solutions present fundamental difficulties and pitfalls, designers tend to favour rule of thumb methods. The present paper contains a general review of the theoretical work done at The Royal Aircraft Establishment, which was limited to the case of zero incidence. This limitation is not a severe one, as flight at high speeds often implies low incidence. Incidences which are not negligible involve the solution of another fundamental problem (that of the lift distribution).