Thread: AOA indicator
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Old April 14th 16, 12:05 PM posted to rec.aviation.soaring
Bruce Hoult
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Default AOA indicator

On Wednesday, April 13, 2016 at 9:54:17 PM UTC+3, kirk.stant wrote:
On Tuesday, April 12, 2016 at 10:43:26 AM UTC-5, son_of_flubber wrote:
In a skidding turn is the low wing AOA higher than high wing AOA?


No, it I lower. This is basic aero, but can be easily understood with a simple visual aid - or a good scale model of a glider.

First, made a simple paper or cardboard wing, about the size of a standard foot-long ruler. Has to be stiff enough to support its own weight.

Hold it at eye level as if it was a glider flying directly at you. Tilt a bit to simulate a flying angle of attack. Now rotate in yaw, and notice that the apparent angle of attack of both wings is the same, despite the yaw.

Now Bend the wing a little in the middle, simulating a reasonable amount of dihedral. Rotate again, and note the difference in apparent angle of attack between the forward and aft wing. That's why you can roll (slowly) using only rudder.

Now, bank your wing as if in a turn, and repeat the yawing exercise. Remember, a skid will have the upper wing forward (too much rudder into the turn) while a slip will have the lower wing forward (not enough rudder).

It should be pretty obvious what is happening to the AOA of each wing and why.

See also the threads about using a bit of a slip to counter the overbanking effect of long wings (the "yaw string to the outside" discussion).

Now the 64 K question - which way and why will you spin out of a skidding turn?


Well, you're right that it's basic aero, but you've somehow managed to get it backwards.

Both wings are descending through the air at the same speed (or you'd be rolling). The inner wing is travelling less distance therefore the angle of attack is greater.

Looking at it another way, the inner wing is travelling slower but has to generate the same amount of lift, therefore its angle of attack must be greater.

Stable slips or skids and dihedral don't make any difference to this. Of course if you kick in some yaw then at the moment the speeds and distances traveled will be different. Putting in some slip/top rudder will accelerate the bottom wing and (briefly) take it to a lower AoA -- and possibly even out of stall if it was a little bit stalled.