A few final remarks on planform

In Chapter 5 we discussed the sudden drag rise which takes place in the transonic speed range. Different aircraft are designed to operate efficiently over different speed ranges. All are required at least to be able to take off and land subsonically and to accelerate or decelerate safely through the transonic range. Some, however, such as the Tornado we discussed above, may need to operate for prolonged periods at a variety of transonic and supersonic Mach numbers. The selection of a suitable planform must thus be a compromise.

Figure 8.17 shows how the drag of different planforms varies with Mach number and from it is possible to see why the various planforms shown in Figs. 8.1—8.4, 8.8, 8.16 and 8.18 were selected to satisfy particular perform­ance requirements.