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Can someone elaborate on why the right rudder is needed during stall recovery for a small single engined training plane like cessna C152 or C172?

Some possible answers are: A. When recovering from a stall, you need to add power. The increased power induces a torque in the opposite direction.

My problem with this answer is that torque will result in roll and usually ailerons are used to control the roll. Why rudder in this case?

B. This could be to counteract the P-Factor

Since the airplane is pitched down, the ascending blade on the left side will have a higher angle of attack and will produce more thrust, resulting in a yaw to the right. This should need left rudder and not right?

C. This is a variation of A. Since torque induces roll and yaw is a byproduct of roll, you need to apply right rudder. However, in this case we are not using ailerons, so there is no additional drag which will result in a yaw.

Since this question is causing confusion I am adding steps to reproduce the stall and stall recovery and the point at which rudder control is required. See answer from abelenky below which I think is the correct answer.

Step 1: Get to 3000ft, perform clearing turns etc
Step 2: Add Carb heat, Reduce power to 1700RPM, Add flaps and slowly start descending at 55-60KIAS as if you are really planning to land.
Step 3: Idle the power and increase AOA until the plane stalls
Step 4: As the plane stalls, the nose falls, remove back pressure from the yoke and allow the nose to fall

At this point of time you have successfully stalled the plane

Step 5: Remove Carb Heat, Add full power, set flaps to 20 Deg, apply right rudder
Step 6: As the plane recovers and regains airspeed, remove flaps above 60KIAS
Step 7: Gradually return to 3000ft and resume or retry if you want to.

The question is related to Step 5.
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    $\begingroup$ Right rudder is not required for stall recovery, its required to keep co-ordinated flight after recovery. $\endgroup$ – Jamiec Jul 14 '17 at 12:01
  • $\begingroup$ @Jamiec Yes, I agree. But the question was not a flying question, it was a physics question. I was trying to understand how exactly the rudder helps in keeping the flight co-ordinated. $\endgroup$ – Prashant Saraswat Jul 14 '17 at 17:31
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You wrote:

When recovering from a stall, you need to add power. The increased power induces a torque in the opposite direction.

My problem with this answer is that torque will result in roll and usually ailerons are used to control the roll. Why rudder in this case?

I think you already know that a stall happens when you no longer have smooth airflow over the wings. Because you don't have effective airflow over the wings, your ailerons are not working. (they may be partially effective, or have no effect at all)

You are right that ailerons are used to control roll during nominal flight; but a stall is not nominal, and the ailerons are no longer effective.

The rudder, as a vertical surface, is not stalled the same way that the wings are. So while it may not be the ideal way to counter a roll moment, its more reliable than the ailerons.

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  • $\begingroup$ Yes, this is what I have been suspecting. You really don't want to use aileron's in this situation because you want to provide as much lifting surface as possible to recover from the stall quickly. And as you said, even if you were to use the ailerons, they may not be very effective at the low speed the plane is. That leaves the rudder as the only option to provide a counter-acting force. $\endgroup$ – Prashant Saraswat Jul 14 '17 at 17:15
  • $\begingroup$ Someone posted this link in a comment to this question yesterday. It said basically the same thing you are saying in your answer. Oddly, the comment seems to have disappeared. $\endgroup$ – bclarkreston Jul 14 '17 at 20:53
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I'm not aware that rudder input is necessary for a stall recovery. It may be used in the slow flight and pre stall segments prior to the stall to counter P-Factor, particularly during a power-on stall, in order to track a straight heading. The only other use I could think of for rudder use in a stall is to induce a spin, or to prevent inducing one, but that would not be a standard for a typical stall recovery.

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  • $\begingroup$ No, this is what is actually happening. I went thru this less than a week ago multiple times. The plane does have a tendency to go left and to maintain heading I had to use right rudder. $\endgroup$ – Prashant Saraswat Jul 13 '17 at 23:52
  • $\begingroup$ Well, that's what I described. During slow flight and pre-stall with high AOA, you're also going to have a lot of P-Factor causing the nose to drift to the left I'd uncorrected with rudder. As the stall onsets and you begin to recover, adding power and reducing your AOA, the P-Factor should be alleviated, requiring less or no left rudder input. As you establish your climb at Vy, right rudder will be required again to track a heading, but will be the same as the amount required for best rate of climb. $\endgroup$ – Carlo Felicione Jul 14 '17 at 0:29
  • $\begingroup$ The rudder is required 'after' the stall and as soon as the power is added in an effort to recover, not before. $\endgroup$ – Prashant Saraswat Jul 14 '17 at 1:20
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    $\begingroup$ @PrashantSaraswat An aircraft can stall with a nose-up attitude, I know a few aircraft that can hold a nose-up in a full stall all the way to the ground if you wanted to. The aircraft also does have a high AoA, you may want to revisit the "definition" of a stall. $\endgroup$ – Ron Beyer Jul 14 '17 at 3:59
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    $\begingroup$ No. An airplane stalls when you exceed the critical angle of attack defined as the angle between the chord line and the relative wind. This can occur at any airspeed, flight attitude, or power setting. The airplane can also maintain a high AOA while stalled unless control pressure is relieved, reducing the AOA. I'd suggest you re-read the Airplane Flying Handbook pp 4-5 thru 4-13 and the Pilot's Handbook of Aeronautical Knowledge pp 5-25 thru 5-26. $\endgroup$ – Carlo Felicione Jul 14 '17 at 10:07

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