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Which graph is the correct representation of the trailing edge flaps' effect on the critical angle of attack? Does their extension increase (as depicted on the first graph) or decrease (as depicted on the second graph) the critical AoA?

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    $\begingroup$ @mins Increasing camber using TE flaps also increases the whole wings AoA. Which means critical AoA is reached earlier. Reverse example is extending only LE slats. Result is a reduced wings AoA, which means critical AoA increases. The fact that tips stall last when flaps are down comes from their small AoA, relative to increased AoA, flaps extended wing roots. $\endgroup$ – qq jkztd Sep 29 '17 at 21:59
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    $\begingroup$ @min Then, what about the effect of the leading edge flaps on the critical AoA? You said the increased camber decreases the critical AoA, but the second graph shows extension of the leading edge flap, which also increases the camber of the wing, increases the critical AoA. $\endgroup$ – lemonincider Sep 30 '17 at 14:58
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    $\begingroup$ @qqjkztd is right, the virtual chord line obtained with the extension of the devices changes the measured angle of attack $\endgroup$ – mins Sep 30 '17 at 17:54
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Both right and both wrong, both over simplifications based on unknown airfoils, and so on. Real aerodynamics is complicated and 3 dimensional.

Flaps usually increase the critical angle of attack a few degrees, but they also increase the effective angle of attack for a given pitch. So the net result is that the pitch of the aircraft will be similar at stall with or without trailing edge flaps, but the true AoA will increase.

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