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I was wondering why do trailing edge flaps increase the lift co-efficient for a given angle of attack. I am guessing it has something to do with delayed flow separation, but this is quite unintuitive, due to the increased camber. It makes sense for leading edge flaps/ slats, as there is a local flow that mitigates the adverse pressure gradient, leading to delayed flow separation (Fundamentals of Aerodynamics, Anderson). Usually, increased Re lead to a higher CL,max, but why does increased camber for trailing edges lead to higher CL?

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  • $\begingroup$ In your title you ask about CL,max, but in your text you ask about CL -- please edit your question to make it clear what you're asking. $\endgroup$
    – TimWescott
    Commented Feb 15 at 3:57
  • $\begingroup$ It is essentially the same thing. For all the angles of attack, the lift coefficient increases. Also, for the stalling angle of attack. $\endgroup$ Commented Feb 15 at 13:37
  • $\begingroup$ Excuse me? CL,max is the maximum coefficient of lift that the airfoil can generate. CL is the coefficient of lift that the airfoil is generating at a given angle of attack. When I'm flying my stunt model with zero angles of attack, the airfoils are generating zero lift, even though they could generate a much higher coefficient of lift at a higher angle of attack. $\endgroup$
    – TimWescott
    Commented Feb 16 at 14:53

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Lift is a force generated by turning a flow Source.

The trailing edge flaps increase the amount of turning in the flow, it can be seen from looking at the geometry only, they tend to point downward.

I hope that helps.

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  • $\begingroup$ When the flaps aren't deployed, the flow is already separated at the trailing edge. So, despite adding flaps, the flow wouldn't be able to turn, as you said. Or am I missing something? $\endgroup$ Commented Feb 15 at 13:39
  • $\begingroup$ If the flow is stalled or separated then there is no turning, and therefore less lift. With the flaps engaged the wings usually can handle larger angles of attack before separating, so to answer your question it depends on the case. I found this nice image online, researchgate.net/figure/… $\endgroup$ Commented Feb 15 at 13:53
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    $\begingroup$ @ArmaanMohammed How is the flow supposed to separate from underneath the wing? And how is it supposed to separate when the flap is literally moving into its way? youtube.com/watch?v=ZpoK0InPciM $\endgroup$
    – DKNguyen
    Commented Feb 15 at 23:57

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