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According to this graph,plain flaps have their highest Cl at about 2 and stalls at about 15°,my question is how then do airplane flaps reach 25°+ of delflection when this gragh clearly states that stall is at 15°? enter image description here

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  • $\begingroup$ The flaps being deployed 25 degrees doesn't mean your AOA is now 25 degrees... My Cessna can deploy flaps up to 40 degrees. $\endgroup$ – Ron Beyer Jun 20 '18 at 19:13
  • $\begingroup$ @Sanchises: I agree, but the answer in the other question is rather terse and deserves a more complete explanation. This is probably the reason for the new question. $\endgroup$ – Peter Kämpf Jun 20 '18 at 22:40
  • $\begingroup$ @Peter I've agree (I was just trying out how short answers rather than answer-as-a-comment would be received). Regardless, they're duplicates. Perhaps close the other as a dupe of this one? $\endgroup$ – Sanchises Jun 21 '18 at 6:05
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    $\begingroup$ @Sanchises: Well, I voted to close this one and wrote a more complete answer for the other question. $\endgroup$ – Peter Kämpf Jun 21 '18 at 8:58
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The X-axis this is the angle of attack of the wing and not the angle of deflection of the flap. When the angle of deflection of the flap is 25%, the angle of attack of the wing will be much less.

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The flaps increase the camber of the wing, not the angle of attack.

I agree the graph can be misread to mean it's the flap airfoil's angle of attack. However, from its content, it's quite clear it refers to the wing's angle - cL=2 is inconsistent with any short airfoil at a=0.

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