For the proper lift distribution, afaik either of the twist are used? Is there any significant difference having one over another and both? Thank you. The above question has one line answer and both questions can be merged into one.

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    $\begingroup$ Can you say how you think geometric and aerodynamic twists differ? I never heard of one without also doing the other. $\endgroup$ – Guy Inchbald Sep 10 '20 at 17:02

A wing has geometric twist when, from root to tip, its chord line changes angle, typically without changing the airfoil shape. This is colloquially known as washout when the root stalls before the tip (or, much more rarely, its opposite, wash-in).

A wing has aerodynamic twist when, from root to tip, its airfoil changes in camber and thus in shape, typically without changing its chord line's angle.

Both twists have a similar effect, in that the zero lift axis changes angle from root to tip, commonly to inhibit tip stalling.

Of these two, geometric twist is easier to design, construct, and analyze, because there's only one airfoil instead of a (possibly continuous) blend of multiple airfoils.

Adding geometric twist to aerodynamic twist might, for example, let you avoid a nonconvex airfoil shape where the camber is large. Convex shapes are easier to build strongly and stiffly, so that would lighten the wing.


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