THE r DERIVATIVES (Cv Cv C„r, C*0r, Chr)

When an airplane has a rate of yaw r superimposed on the forward motion V, its velocity field is altered significantly. This is illustrated for the wing

and vertical tail in Fig. 8.16. The situation on the wing is clearly very complicated when it has much sweepback. The main feature however, is that the velocity of the f chord line normal to itself is increased by the yawing on the left-hand side, and decreased on the right side. The aero­dynamic forces at each section (lift, drag, moment) are therefore increased on the left-hand side, and decreased on the right-hand side. As in the case

of the rolling wing, the uasymmetrical lift distribution leads to an unsym­metrical trailing vortex sheet, and hence a sidewash at the tail. The incre­mental tail angle of attack is then

V dr