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RufusSwink OP t1_izf1mfx wrote

Reply to comment by GenericUsername2056 in What is the theoretical limit to a helicopters speed? by RufusSwink

Why does the efficiency drop so low with a rotor but not with wings on a supersonic airplane?

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GenericUsername2056 t1_izf3xsr wrote

It does, which is why fighter jets for instance have very flat airfoils which are not very efficient for generating lift in subsonic flight. The cross-section of the wings of the famous SR-72 Blackbird reveals a simple ellipse. They require a tremendous amount of thrust to generate enough lift when flying at supersonic speeds, hence why their jet engines have afterburners. When flying at supersonic speeds, airfoil shape is of lesser importance to generating lift.

Aircraft designers are very keen to prevent (local) shockwaves forming on their wings. If you look at a passenger jet, you will notice it has swept wings. These swept wings delay the formation of shockwaves on the wing when flying at transonic speeds, thus increasing efficiency whilst still enabling the aircraft to fly at these speeds.

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RufusSwink OP t1_izgmau4 wrote

That is very interesting, thank you so much for the detailed answer.

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