# Geometry of the Flaps and Control Surfaces

For the aerodynamics of the wing with control surface (flap), the most important geometric parameters as shown in Fig. 8-1 are as follows:

Control-surface angle (flap angle): r? y Control-surface chord ratio (flap chord ratio): f—Cfjc

These quantities have already been given for the whole wing with control surface (flap wing) in Sec. 2-4-2 and in Fig. 2-24. If the control surface does not extend over the whole span, as in, for example, the aileron in Fig. 8-4*2, the span of the control surface bA = 2sA becomes another important geometric quantity. On the horizontal tail plane and the fm, the control surface usually extends over the whole span of the horizontal tail bH and the height of the vertical tail h v,

Figure 84 Geometry of the control surface, (a) Ailerons. Cb) Elevator, (c) Rudder.

respectively (Fig. 84b and c). In many cases the control-surface chord ratio is varied along the span. In this case it is preferable to use the control-surface area ratio A ft A’ instead of the control-surface chord ratio Cf/c, where Af is the control-surface area and A’ is the wing area within the span range of the control surface.