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This question already has an answer here:

It is widely understood that the curved shape of a typical airfoil (such as a Clark Y) causes a pressure difference that creates lift. How do symmetrical airfoils do this when the top and lower surfaces are the same shape and length?

enter image description here

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marked as duplicate by Jan Hudec, Federico, mins, J Walters, fooot Jun 21 '17 at 20:54

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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By using a non-zero angle of attack. When the trailing edge is pointed downwards, and assuming the airstream leaves the trailing edge smoothly, the exiting airstream is deflected downwards. This causes lift via conservation of momentum. Increasing the angle of attack will increase your lift until such time as the airstream over the trailing edge becomes non-smooth. (When this happens, you're close to stalling.)

enter image description here

(Image from this page, which unfortunately appears to be down)

As you can see from the above graph, a symmetric airfoil at zero angle of attack generates no lift; see this site from NASA as well as the above Wikipedia page.

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