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I’m really unsure about this question:

Can a supersonic aerofoil have maximum thickness near the middle? so by middle of the aerofoil I mean 50% along the chord

Also, how would you actually calculate location of max thickness of aerofoil please?

I haven’t yet come across one aerofoil that can?

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  • $\begingroup$ If I remember correctly, F-104 used biconvex airfoil therefore with max thickness just in the middle of its chord. And the very first iteration of supersonic airfoils had a typical diamond shape, that is also with max thickness at 50% of the chord $\endgroup$
    – sophit
    Sep 12, 2022 at 19:24

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Yes, the lowest wave drag for a given thickness can be achieved by placing the maximum thickness in the middle.

Any body moving through a fluid must push this fluid aside. When this movement happens at supersonic speed, the fluid has to decelerate via a shock which raises density and pressure. Therefore, all forward-facing surfaces will experience a rise in pressure that increases with the square of their angle of inclination. On the opposite, at the rear where the body contracts, the fluid needs to accelerate via an expansion fan and both density and pressure drop so the fluid can fill the space vacated by the moving body. Consequently, all rear-facing surfaces experience lower than ambient pressure, again proportional to the square of the inclination angle.

Placing the maximum thickness in the middle will give the lowest total of both pressure and suction drag. When you move the maximum thickness either fore or aft, in both cases the drag increase on the now steeper surface will be greater than the drag reduction on the surface with the now lower inclination.

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