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If the plane is in a flat spin, what would happen if you put the flaps down to cause the backward turning wing to be pushed down, and the forward turning wing up, to tip it out of the spin.

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No.
The chordwise airspeed at the flaps (mounted about twice as close to the CG than the ailerons, rudder, etc.) would be about half the airspeed felt by those already mushy-nearly-ineffective primary control surfaces. So the roll moment imparted by the flaps would be so slight that it might take hundreds of rotations, and tens of thousands of feet of falling, before significant bank developed. And then the primary controls are still as mushy as before, so you're no closer to recovering. See Is it possible to recover from a flat spin?

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  • $\begingroup$ At 2 rotations per second, the flaps are moving at 20 mph if they are mounted 2.3 feet from the center of rotation. I'm pretty confident most airplanes don't have flaps mounted that far inboard. I also wonder if the extra drag from the flaps could help dampen the yaw rate? I'm not sure but it sounds plausible. $\endgroup$
    – Chris
    Oct 5, 2023 at 16:33
  • $\begingroup$ Thanks for doing the math, Chris! That showed me how to streamline the logic. As far as yaw drag goes, flaps are small and have little leverage compared to the aft fuselage plus fin. It would slow yaw rate (so, hey, might as well deploy them) but not by much more. $\endgroup$ Oct 5, 2023 at 18:56
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    $\begingroup$ Thanks! I suspected it wouldn't have much effect, with the flaps so close to the fuselage. I heard that they turn the rudder hard the other way, which, I assume, increases the sideways drag of the tail to flip the nose out of the spin. I have used flat spin to drop a piece of tissue paper, like toilet paper straight down onto a spot of water on the floor. I usually goes straight down. I would hate to be in a plane doing that. The gyroscopic effect would be your worst enemy. $\endgroup$ Oct 8, 2023 at 6:51
  • $\begingroup$ @Camille Goudeseune Is my assumption about how the rudder flips the nose out correct? And, the other method, pulling back on the yoke or stick, which would push the tail down when facing to the back, and upward when facing forward: I assume, if the plane as a whole acts like a spinning top, would get pushed up on the side facing the oncoming air and down on the side facing back. That, with the gyroscopic effect would tip the plane sideways (to the right out of a LH spin) is that correct? $\endgroup$ Oct 10, 2023 at 4:15
  • $\begingroup$ @PeterR.McMahon those two or three new questions would be better asked as fresh questions on this Q&A site, than as conversation. They would be made clearer by using the terms yaw, pitch, and roll. And (as often happens to me) while still typing in that question, stackexchange might offer you a suitable answer :-) $\endgroup$ Oct 10, 2023 at 16:04

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