Boundary layer control – high lift devices

For efficient flight, the wing must produce a good ratio of lift to drag at the designed cruising speed. This requires the use of a wing section with only a modest amount of camber. The wing should also be as small as possible, so as to minimise the weight and the surface area, since both of these factors affect the drag.

Remembering that for level flight,

Lift = Weight = – pV2 (Area) CL,

it can be seen, that as the aircraft slows down, the lift coefficient required increases, so for landing, it is necessary to generate very large values of CL. Simply increasing the angle of attack may be insufficient if the aircraft is designed for a cruising speed that is much higher than its landing speed, and it may be necessary to use other methods of increasing CL for landing.