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In normal 30 degree bank level turns, instructors teach students that if you are to correct your altitude you also need to change your rudder input. Why is that?

For example if you are descending in your turn you are to pull the elevator and also lessen your rudder input. And if you are climbing in your turn you are to push the elevator and push more rudder.

Is this because of you are tightening your turn when pulling elevator and therefore you are starting to skid and therefore you need to lessen your rudder to compensate. And if you are pushing the elevator you are doint the opposite starting to slip and therefore you need more rudder.

Or is there some other explaination to why you need to do this?

EDIT:

Hi,

no I think you have misunderstood the question. They do not teach to use the rudder to compensate for pitch/altitude.

They teach properly to use the elevator. But they say that when you make a change with elevator to a higher nose you don't need that much of rudder than before. And when you use the elevator to push nose down there is more need of rudder.

The rudder change is just to compensate the need due to change in configuration. Not to use it to change the altitude.

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  • $\begingroup$ Can you give more detail on where you heard this? From several different instructors? In what aircraft? In what country? I don't think I've ever had an instructor tell me this. Langewiesche says something kind of the reverse of this in "Stick in Rudder"-- he says sometimes you want to use the elevator not the rudder to center the ball, especially in a slip (ball to low side of turn), but I've not found that to be accurate either. We find the same statement in some of the earlier editions of "Modern Airmanship", but it was deleted from later ones. $\endgroup$ – quiet flyer Oct 6 '19 at 20:13
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    $\begingroup$ Are you sure they weren't suggesting to roll out a little bit (decrease the bank angle) to help stop a descent? This input would involve coordinated use of ailerons and rudder. If you were basically carrying a significant into-the-turn rudder input throughout the circle, I can see where rolling out might use a touch of rolling-out aileron and a little relaxing of the into-the-turn rudder but still holding some into-the-turn rudder. And sort of the opposite to help stop a climb. Sorry, that might be a bit hard to follow. $\endgroup$ – quiet flyer Oct 6 '19 at 20:16
  • $\begingroup$ Still, for turns that are only banked 30 degrees, I would think most instructors would not teach to use changes in bank angle to help stop a climb or descent. That is more appropriate for much steeper turns, in my opinion. Anyway, please try to tell us a little more if you can. $\endgroup$ – quiet flyer Oct 6 '19 at 20:18
  • $\begingroup$ Just read your edits to question. So your instructors are apparently telling you that as you raise the nose and slow down to arrest a descent, you'll find you need less inside rudder to keep the ball centered? Again see previous requests for info as to what aircraft, what nation, etc. $\endgroup$ – quiet flyer Oct 7 '19 at 15:20
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Instructors that teach that to students are fools. You should be using rudder only as required to keep the ball centered - period. If you are applying rudder to influence the pitch attitude, to "help hold the nose up", this is very very bad, and leads to stall/spin accidents.

Rudder is mostly being used to counteract adverse yaw from the aileron inputs, and to some degree to correct for yawing motions caused by power changes. But in any case it is strictly used to keep the tail lined up behind the nose in the airstream. Anything else and you are skidding or slipping in the turn.

If you are in a 30 deg banked turn, and are descending, the total lift from the wings is insufficient; you need more elevator input, NOT top rudder, which creates a slipping turn, which will make the airplane flick over the top into a spin if you stall while doing it.

Don't overthink it. Ailerons to keep the bank angle, elevator/power to control the pitch and altitude/speed, rudder to center the ball; just do whatever it takes.

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    $\begingroup$ John, also, add power in a turn to stop descending to avoid excessive AOA with elevator. $\endgroup$ – Robert DiGiovanni Oct 6 '19 at 21:12
  • $\begingroup$ Of course. It's pitch/power together for speed/altitude control. $\endgroup$ – John K Oct 6 '19 at 21:51
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    $\begingroup$ excuse the neophyte question, what does "keep the ball centered" mean? $\endgroup$ – Florian Castellane Oct 7 '19 at 8:38
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    $\begingroup$ @FlorianCastellane see en.wikipedia.org/wiki/Turn_and_slip_indicator#Inclinometer $\endgroup$ – alephzero Oct 7 '19 at 10:11
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    $\begingroup$ If you've been flying long enough you don't even need a slip/skid ball and can just go by where the "apparent gravity" that your torso senses is. Slouching to the left, left rudder, and vice versa. Plus if you don't have an engine/prop in front you can dispense with the inclinometer and just tape a piece of yarn to the windshield. Gliders use yaw strings universally, and sometimes you see them on military jets. More precise than a skid ball and you don't have to look down. $\endgroup$ – John K Oct 8 '19 at 3:24
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With 30 degree bank from the ailerons, your wings create a centripetal force to make a turn. Now pitch and power are increased because the vertical component of lift is reduced, and the rudder makes the turn coordinated.
Adding elevator will not only lift the nose, but also add yaw - the same sine & cosine are at work. You reduce rudder to keep the yawing force constant. Yes, that is the whole explanation.

Just imagine a turn with 60 degree bank, or even knife-edge flight. Or look how a V-tail works on the early Beech Bonanza. It is all about splitting and combining force vectors.

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  • $\begingroup$ How does the elevator induce yaw? $\endgroup$ – Michael Hall Oct 7 '19 at 22:15
  • $\begingroup$ @MichaelHall, that depends on your reference frame. In the reference frame of the airplane, no, the elevator won't induce yaw. But in a gravity-aligned reference frame, the elevator will produce a turning force if the airplane is banked. Extreme example: roll the airplane 90 degrees, then apply up elevator. In the reference frame of the airplane, you'd call the resulting maneuver a "loop", but in a ground reference frame, you'd call it a "turn". $\endgroup$ – Mark Oct 8 '19 at 0:36
  • $\begingroup$ I understand, but that isn't my question. The frame of reference for yaw is always the aircraft. Bobby J said that adding elevator would add yaw. I would like him to explain that. $\endgroup$ – Michael Hall Oct 8 '19 at 2:04
  • $\begingroup$ @BobbyJ -- Sustained knife-edge flight is "uncoordinated". The ball is way off-center. Are you saying the same should be true at 60, or 30, degrees bank? Yes a pitching maneuver can change the bank angle (think wingover or chandelle) but correcting for that should involve ailerons as much as rudder. $\endgroup$ – quiet flyer Oct 9 '19 at 0:46
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@Michael Hall. Elevator use changes the aircraft pitch angle to the relative air flow, and hence the amount of P-factor experienced by the aircraft will change. Since this is manifest as a yaw, an appropriate rudder change is necessary. John K. is correct—-this is not the way to teach turns.

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  • $\begingroup$ Good point. However, the original question did not specify that the effect operated in the reverse direction when turning right versus left, as would be the case with p-factor. It would be good if the original question were clarified to address this. Also I'm not sure how noticeable the change in p-factor would be during a typical correction of an unwanted climb or dive in a light plane. Still, good point. $\endgroup$ – quiet flyer Oct 9 '19 at 0:53
  • $\begingroup$ @ABC (original asker) please note comment above-- $\endgroup$ – quiet flyer Oct 9 '19 at 0:56
  • $\begingroup$ Yes, I understand that, I have just never noticed a perceptible need to use any rudder to compensate for minor adjustments in pitch. $\endgroup$ – Michael Hall Oct 9 '19 at 4:13

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