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I often hear about planes stalling when they lose lift due to low airspeed/too high angle of attack. Why don't birds stall? Does it have to do with the structure of their wings and their flexibility, or their higher power/weight ratios relative to aircraft?

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A bird's wings have muscles, unlike the wings of a plane. It's true that we can control them, but they're metal(\m/). Human mechanisms are not as flexible as those of nature.

Compare driving a car with running in your imagination: If you are walking and someone is going to crash into you and you see him, you could dodge it easily. But if you are driving a car and uou want to move left as dodging when you see some of the obstacles, you cannot do that.

It's exactly the same as birds, they can control their wings 100%. We can control planes only half of the bird wings, so it may make a difference.

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    $\begingroup$ Not reasonable, nor backed w/ data. As comments above note, birds choose to stall. Heck, watch an osprey dive some time, tho' that's not a stall, it's just a transition from lift to controlled vertical flight. $\endgroup$ – Carl Witthoft Apr 12 '14 at 12:42
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    $\begingroup$ Seems to me this answer is just an illustrated way of saying "They are more experienced," the same as a comment above that received 3 up votes. Though not particularly thorough, I don't see why this is a "wrong" answer, or one bad enough to merit the down votes. $\endgroup$ – wgrenard Apr 14 '14 at 16:59
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I have qualified to fly airliners, gliders, and various airplanes. I'm a flight instructor, a flight engineer, and trained as an aircraft mechanic. A bird's wing does not stall because the bird's feathers are literally rubbed the wrong way when air tumbles over the top of the wing as it approaches a stall. The bird responds by lowering the angle of attack (leading edge of wing is twisted down into the relative wind) and trailing edge of wing is twisted down to fall with slow moving air over the wing that can now hug a more steeply falling back aft portion of its wing.

1 - A stall occurs when the relative wind, which is wind RELATIVE to the bird and more specifically, relative to the CHORD line of the wing for a given profile of the wing or camber (curvature) of the upper and lower surfaces of the wing, exceeds its stalling angle. Chord line simply runs from the leading edge of the wing to the trailing edge of the wing.

2 - A stall occurs because a bird can actually feel the force of lift decreasing as angle of attack becomes too great.

  1. See www.NASA.gov and type Foil Sim into the search box
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The wings of a bird are flapping, but the wings of an airplane are fixed and cannot be flapping. So birds are not afraid of stall, and even use stall (differential pressure resistance) to generate more force to reduce speed. Note that the bird will flap its wings in the direction of speed when landing.

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