Washout (aeronautics)

Washout may be accomplished by other means e.g. modified aerofoil section, vortex generators, leading edge wing fences, notches, or stall strips.

Its purpose is to tailor the spanwise lift distribution or reduce the probability of wing tip stall.

Installation of winglets may necessitate greater aerodynamic washout in order to provide the required resistance to spinning, or to optimise the spanwise lift distribution.

[citation needed] Washout near the tips can also be used to decrease lift-induced drag, since at a lower angle of incidence, the lift produced will be lower, and thus the component of that lift which acts against thrust is reduced, however, it has been theorised by Albion H. Bowers that certain washout characteristics in the tips, that lead to a bell-shaped span loading may in fact produce lift-induced thrust, and upwash.

He thus suggests that birds do not utilise vertical stabilisers, since they do not need to counteract adverse yaw caused by lift-induced drag.

Washout reduces the angle of incidence from root to tip, thereby causing a lower angle of attack at the tips
Washout is clearly visible in this image of a CF-18 Hornet. Note the angle of the Sidewinder missile on the wingtip rail as compared to the angle of attack of the fuselage. The Hornet has approximately 4 degrees of washout.