The pros and cons of high lift devices

The high lift coefficients obtained with both leading and trailing-edge devices incur a penalty in terms of drag, but this may be acceptable or even useful in landing, as described in Chapter 13. Note the extreme amount of curvature used on the flaps of the Andover shown in Fig. 3.16.

For take-off, it is normal to use a configuration giving lower CL and less drag. Smaller flap angles are almost invariably used.

There are many versions of slot, slat and flap, in addition to the examples illustrated in Figure 3.13. Their effectiveness depends on the precise geo­metry of the device, and on the type of aerofoil section used. It is therefore impractical to try to indicate a figure for the order of improvement in CL for competing designs. Generally, and unfortunately, the most effective devices tend to be the most complicated and heaviest.