Angle of Attack: True or False

zaitcev said:
With some qualifiers, yes (well behaved airplanes, not flying upside down, etc.). Stick position controls the AoA - and vice versa. And the best part is, people wrote about it in books in 1944! 75 years later we still have pilots who fail to understand how it works.

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Love that book.
 
Four+ pages of acrimonious debate on angle of attack. It's an indication, I believe, of the lack of relevant instruction in ground school, or the ignoring thereof. When I was an instructor I often encountered PPLs or higher that didn't have a good grasp of AoA theory and how it relates to stall, load factor, airspeed, lift, Va and so on. On POA and other sites we regularly see the very misleading term "full-stall landing," an indication that too many think the flight's over when the wheels are on the ground, a dangerous assumpton that breaks a lot of airplanes. The buzz-job with zoom climb is stark evidence of failure to understand AoA. One of the largest factors in crashes is loss of control while maneuvering, and that involves AoA pretty much every time.
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Bobanna said:
Pure crap-monkey nonsense: incidence is built-in, not under a pilot's control. The elevator may be used to adjust (control) the angle-of-attack.
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I believe he's trying to get at the concept of "decalage;" the difference between the angles of incidence of the wing and stabilizer.

There's one regime that the elevator does not control AoA. An upward gust increases AoA without any elevator movement at all, and an aggressive enough gust will stall the wing. At the point of stall (and subsequent unloading) the airframe stresses are high and things can break. Hence the Va, maneuvering speed, in your POH. Theoretically, if you are at or below that speed, the wing will stall before the load limit is reached (i.e. FAR 23, 3.8G). Above that speed you might bust something important. It also means that a sudden, full-throw control deflection shouldn't break anything at or below Va. Shouldn't. As the fleet ages......

Va decreases as weight decreases, too, just like stall speed. The airplane will move upward easier when light, and upward movement translates into a lower AoA, perhaps preventing the stall and increasing the stresses.
 
Dan Thomas said:
Va decreases as weight decreases, too, just like stall speed. The airplane will move upward easier when light, and upward movement translates into a lower AoA, perhaps preventing the stall and increasing the stresses.
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The first statement is correct but the explanation "upward movement translates into a lower AoA" makes no sense. Lower AoA would reduce the lift, which would reduce the load factor, and stress, on the airplane. Va decreases with weight because stall speed decreases with weight.
 
From Aviation Stack Exchange:
What are the advantages of a Trimmable Horizontal Stabilizer?

The main advantage is smaller elevator deflection angles. This comes handy in two cases:
  • When high-lift devices are deployed, the center of pressure on the wing shifts backwards by up to a third of wing chord. Fowler flaps add wing area aft of the trailing edge, and slotted flaps are able to generate high suction peaks. The result is a massive change in trim, and the empennage now has to generate generous downforce. Changing the lift on the empennage by elevator deflection alone will exceed the maximum practicable deflection angle and leave no margin for control. By adjusting the stabilizer incidence, the elevator can be held near its neutral position and has reserves for control.
  • In transsonic flight the elevator might not always have a linear characteristic... (deleted to stay on topic).

Thus, the term "incidence." Not of the wing, of the horizontal stabilizer.
 
dmspilot said:
The first statement is correct but the explanation "upward movement translates into a lower AoA" makes no sense.
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He was referring to the reduction of the angle of the relative wind during upward movement of the aircraft.
 
IK04 said:
He was referring to the reduction of the angle of the relative wind during upward movement of the aircraft.
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Yeah, reducing the angle of the relative wind reduces the angle of attack. Thank you once again for gracing me with your stunning insight. Now explain how reducing the angle of attack increases load factor...wait, it doesn't.
 
dmspilot said:
Yeah, reducing the angle of the relative wind reduces the angle of attack. Thank you once again for gracing me with your stunning insight. Now explain how reducing the angle of attack increases load factor...wait, it doesn't.
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Reducing the AoA prevents the stall that unloads the wing.
 
Silvaire said:
Okay, I'm struggling to figure out how three and a quarter fatal stall/spin accidents happen during cruise flight.
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We've just been discussing Va, which can apply to turbulence, which can cause loss of control and a stall/spin.

Some underpowered homebuilts had cruise and stall speeds that weren't very far apart.
 
dmspilot said:
Reducing AoA unloads the wing.
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But in certain turbulence situations, not enough. The loads keep building until something breaks. Speeds over Va, for instance. You could be right at Va and get a gust coming at you from both below and ahead, say at 45°, and the airspeed is suddenly above Va.
 
Dan Thomas said:
But in certain turbulence situations, not enough. The loads keep building until something breaks. Speeds over Va, for instance. You could be right at Va and get a gust coming at you from both below and ahead, say at 45°, and the airspeed is suddenly above Va.
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A gust from below and ahead would increase AoA, and increase speed, I agree that is a bad thing.
 
Dan Thomas said:
We've just been discussing Va, which can apply to turbulence, which can cause loss of control and a stall/spin.

Some underpowered homebuilts had cruise and stall speeds that weren't very far apart.
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If it's underpowered enough, it only counts as a quarter of an accident? ;)
 
Cooter said:
POA has once again complicated something otherwise easily understandable.
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To wit, there is not a consistent relationship between yoke position and a stall (or the angle of attack of the wing). Elevator power varies with the square of the airspeed - you need more yoke travel at lower speed to get to the same angle of attack or to stall at a lower wing loading vs. a higher wing loading (accelerated stall for example). Also, gear, flaps, and power can shift the elevator (and thus yoke, or stick) position relative to stall even at the same speed.
 
Capt. Geoffrey Thorpe said:
To wit, there is not a consistent relationship between yoke position and a stall (or the angle of attack of the wing). Elevator power varies with the square of the airspeed - you need more yoke travel at lower speed to get to the same angle of attack or to stall at a lower wing loading vs. a higher wing loading (accelerated stall for example). Also, gear, flaps, and power can shift the elevator (and thus yoke, or stick) position relative to stall even at the same speed.
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Exactly. The "yoke position" thing comes, I think, from learning by rote instead of gaining an understanding of the theory behind it all.
 
Dan Thomas said:
Exactly. The "yoke position" thing comes, I think, from learning by rote instead of gaining an understanding of the theory behind it all.
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I just think everybody knows not to take it literally, it's a relative expression.
 
Dan Thomas said:
Exactly. The "yoke position" thing comes, I think, from learning by rote instead of gaining an understanding of the theory behind it all.
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YES! THANKS!

dtuuri said:
I just think everybody knows not to take it literally, it's a relative expression.
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But there's a reason we're taught that ailerons control roll and elevator controls pitch (not AoA), and that the stick moves these flight surfaces. AoA for some reason tends to be a nuanced concept for many, and this is why the idea that "stick position controls AoA" bothers me as it runs a very real risk of teaching an important concept to someone without the understanding of what AoA is and how a wing works
 
All wrong. Horizontal stabilator angle of incidence is controlled by movement of the collective. ;)
 
Tantalum said:
this is why the idea that "stick position controls AoA" bothers me as it runs a very real risk of teaching an important concept to someone without the understanding of what AoA is and how a wing works
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'cept for the last hundred or so years, the system has been churning out thousands and thousands of successful pilots who don't have a clue on how a wing works or the actual relation between AoA, speed and lift. For example, I was watching one of Kermit Weeks videos - a pretty darn successful and talented pilot - and he started talking about curves and distances to explain how a wing generates lift.

Found it. 8:45... Air hold hands
 
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Capt. Geoffrey Thorpe said:
pilots who don't have a clue on how a wing works or the actual relation between AoA, speed and lift
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it is pretty incredible, isn't it. But that helps explains why the leading causes of general aviation accidents or as banal as fuel exhaustion, controlled flight into terrain, loss of control when inadvertent IMC, etc. people assume they're going to die in a big heroic fiery played crash, when really chances are it's going to be something completely dumb, like miss judging the turn to final and trying to cheat it in with the rudder just a little too hard!


Capt. Geoffrey Thorpe said:
Air hold hands
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Oh God.. not my first facepalm moment with this guy.. I love his videos but all of them has something a little cringe worthy
 
Dan Thomas said:
We've just been discussing Va, which can apply to turbulence, which can cause loss of control and a stall/spin.

Some underpowered homebuilts had cruise and stall speeds that weren't very far apart.
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More likely aircraft that have encountered icing conditions in cruise.
 
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