The supersonic swept wing and the boundary layer

We have made very little reference to the role of the boundary layer in the development of the flow over the swept wing. The spanwise component of velocity, which we have so far assumed to have no effect on the flow will, in fact, modify the way in which the boundary layer forms. In Chapter 3 we saw that, because the flow due to this velocity component is directed towards the tips on a swept back wing, the boundary layer will tend to be thicker at the tips than it is at the centre section.

In designing a swept wing we must therefore bear in mind the various difficulties outlined in Chapter 3. The tip region will be most prone to bound­ary layer separation leading to local stalling of the wing, which will be of par­ticular concern in highly loaded manoeuvres and in the approach to landing at low speed. The tip is a particularly bad location for this to happen first because a change here will produce the maximum change both in pitching moment and also in rolling moment if one tip stalls before the other. Worse still a flow separation in this region is likely to severely affect the aileron effectiveness so roll control will be lost.