How is washout built into a fibreglass foam core wing of a GA Airplane with 40% span flaps, 40% span ailerons.

Does the angle of incidence change gradually over the span of the wing, or is the airfoil rotated downwards to reduce the angle of incidence eg. at the wing airfoil joints and then just flared, eg. over the span of a 1m to a matching trailing edge?

Eg 20% span root wing aifoil incidence no flap, 5deg; 40% span mid wing airfoil incidence with flap, 4 deg; 40% span wing tip airfoil incidence with aileron, 3 deg


1 Answer 1


Washout can be geometric (angle of incidence changes over span) or aerodynamic (airfoil changes over span), or a combination of both. The wing station where that washout starts or ends can be freely chosen, so the airfoil and incidence might stay constant over the inner wing and only start at mid-span. The goal is always to shape the lift distribution over span such that stall starts at the wing root or induced drag or root bending moment is limited.

Washout has to be chosen in combination with chord variations over span: While a rectangular wing rarely needs washout for benign stall characteristics, a taper at the tip to 30% of root chord will definitely require some washout.

A fiberglass wing gives the designer full liberty at choosing both aerodynamic and geometric washout by shaping the foam core accordingly. Some corrections in incidence will still be possible while curing the epoxy matrix, but ideally the core will already have the desired twist already.


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