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In theory: if I wanted to build an model aircraft with (zero zero) wing/tail incidence, how would washout affect the root incidence required?

E.g. if a wing has 2 degrees washout at the tip, would the root have 1 degree + incidence so that the 'average' angle of the wing is zero ?

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That depends on the taper ratio.

In the end, the wing with washout should produce the same lift as the one without. For a rectangular wing and 2° washout, your reasoning is right and the root should have 1° incidence so the whole wing produces the same lift as the one without washout and 0° at the root. If the wing has a triangular planform, however, the tip contribution to overall lift is much lower and the root incidence should only be 0.667°.

For a general rule, pick the position along the span at which half of the wing area is inboard of this position and pick the root incidence such that the local incidence at this position is 0°.

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  • $\begingroup$ Excellent - many thanks for clear explanation. $\endgroup$ – Lee Aug 23 '18 at 9:26

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