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This sort of came up on a discussion of steep spirals without being resolved. Maybe you know enough about aerodynamics to answer it.
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I'm really pretty weak at aerodynamics. I try to stick with *practical* stuff that I can use day-to-day.
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The increased AOA in a level turn is because of increased load factor resulting from the two lift vectors needed for the wings to support both maintaining altitude and the turn itself.
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The way that I think of it is that the AOA has increased because I'm pulling back on the stick/yoke to maintain altitude. I like to oversimplify and think of the elevator as my AOA controller.
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So "it sounds" like AOA would be less in a descending turn since altitude isn't being maintained. But is that accurate? Aren't the lift/weight/thrust/drag vectors in equilibrium in any steady state flight, whether straight, climbing or descending? Isn't the AOA pretty much the same for a stable descent as it is for level flight at that same airspeed (the relative wind is still coming straight at the airplane - the airplane's direction is downward; the relative wind is upward).
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I don't like to think in terms of all those vectors, just relative wind. Yes, I believe that the AOA *can* be the same in a descending turn as it is during level flight. It all depends on what you are doing with the elevator to control the rate of descent. Pull back to slow the rate of descent, AOA goes up. Push forward and you will reduce the AOA.
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Isn't an airplane in a straight ahead descent with a stabilized airspeed and descent rate pulling 1G? If that's the case, bank angle should still affect G-loading realtive to straight flight, which means increased load factor and increased stall speed.
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Only if, when you enter the turn you increase the force on the elevator to maintain the same descent rate. If you allow the descent rate to increase as you increase the angle of bank you can maintain the same AOA, with no resultant change in indicated stall speed.
You can put a plane in a 90 degree bank without stalling. You can do it without increasing stall speed by even 0.0001 knot. You will have to accept a high descent rate (i.e. falling like a rock), but the stall speed is
not affected by bank angle (at least not directly) but by Angle Of Attack. Stalls have everything to do with the direction that the air is hitting the wings (AOA), and nothing to do with the plane's attitude (other than how the attitude is related to the movement of the plane).
Don't ask me to explain the aerodynamics, though.