The critical angle of attack seems to be at all (most?) airfoils around 15-20°. Why is that? Why is it in this range and not lower or higher? Is it just the result of optimizing airfoils? Or is it some inherent property of the air an airfoil is moving through that determines it? (Let's limit the question to subsonic flight.)

PS: I read the answer to "Does airspeed affect the critical angle of attack on an airfoil?" and don't think that this is a duplicate since the other one was more generally about "what are the factors that determine the critical AoA" while I'm asking why the critical AoA seems to be always in this range for most airfoils on planes flying nowadays.

  • $\begingroup$ Not an expert, But I imagine that the designer chooses a line somewhere between perfomance v drag, ability to flare and land too little, inability to fly slow, possibly not be able to climb well, too much, and it flys like a brick $\endgroup$ – jeff the tall Mar 15 at 23:02
  • $\begingroup$ Adding my two cents... You can optimize airfoils for higher angles of attack but this does mean the airfoil becomes garbage for normal flight. As Jeff said, it's a compromise. The reason that we see 15 to 20 degrees probably comes from the regulations, especially max allowed stall speed for your aircraft weight category. If stall speed is dictated and your weight is maxed out for your weight category then - with your chosen flap design and optimal wing area - you will probably need those 15 to 20 degrees of AOA to reach the demanded low stall speed. $\endgroup$ – Jan Mar 17 at 20:10

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