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In a steep turn, the aircraft is basically sideways. However, when executing a steep turn, one still raises and lowers the nose of the aircraft by using the elevator.

Intuitively, it seems to be that in an extreme bank, the elevator and rudder have essentially changed roles, since they have been rotated with respect to their normal orientation. It seems to me that in a steep turn, pulling back on the yoke should tighten the turn. But this seems to not be the case in practice, since getting the nose up in a steep turn still involved just pulling back on the yoke and/or trim.

Why is this the case?

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  • $\begingroup$ It seems to me like you're switching reference points, saying it does this from the pilot's reference, but looks like that from a ground observer's reference. $\endgroup$ – BillDOe Mar 5 at 20:37
  • $\begingroup$ @BillDOe Quite possibly my confusion is an issue of reference frames, but I do not see how. Could you elaborate? $\endgroup$ – KBriggs Mar 5 at 20:38
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    $\begingroup$ Basically Sideways... The FAA considers steep turns as bank angles between 45 and 60 degrees the aircraft is not quite sideways. Both rudder and elevator input is needed to execute properly. $\endgroup$ – Dave Mar 5 at 20:41
  • $\begingroup$ @BillDOe on further reflection, you are correct. I was basing my question on my observation of the attitude indicator - but an upward motion of the nose on the attitude indicator while banked does not mean a purely nose-up response. $\endgroup$ – KBriggs Mar 5 at 20:42
  • $\begingroup$ @Dave an exaggeration, certainly. The point was that the force exerted by the elevator is not up and down anymore, but has a significant sideways component. But I think I understand better. $\endgroup$ – KBriggs Mar 5 at 20:44
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At 45 degrees Angle of Bank pulling back will both tighten the turn, and cause the nose to rise equally because you are halfway to 90 degrees. You are correct though, at much steeper angles of bank the control inputs function the other way: In a very steep high G turn the angle of bank is used to control altitude, and back pressure is used to control the rate of turn. You definitely don't want to use rudder in this case though, bad things can happen in an accelerated stall with yaw.

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  • $\begingroup$ This is what I was looking for. Can you maybe elaborate on what you mean by AOB being used to control altitude, though? $\endgroup$ – KBriggs Mar 6 at 18:28
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    $\begingroup$ Sure. Let's say you are striving for a max performance, 4G turn at a target cornering speed, and you are at approximately 75 degrees angle of bank. If you are holding airspeed and backpressure, (Gs) constant to achieve the best turn performance but notice you are descending, it is because you have over banked a little. To correct you would lessen your AOB to stop the descent and climb back up. Conversely if you are climbing in the turn you would overbank a little to descend. $\endgroup$ – Michael Hall Mar 6 at 18:37
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    $\begingroup$ ... to take it further, if you held a constant 4Gs and let the airplane roll inverted you'd do a split S. If you held 4Gs and rolled upright you'd do a loop. The minor corrections described above just help keep the nose tracking along the horizon for a hard level turn. $\endgroup$ – Michael Hall Mar 6 at 18:41
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First thing to note is the fact that "tightness" (be it radius or rate of turn) of the coordinated, steady, horizontal turn is determined by airspeed and bank angle. Namely radius for banking angle $\alpha$ and airspeed $v$ is $$ r={v^2\over g \tan\alpha} $$ and rate of turn (degrees per second) $$ \hbox{rate}=360° {v\over 2\pi\cdot r} = {360°\over 2\pi}\cdot{g \tan\alpha\over v} $$

Slowing down takes long, so only straightforward way to increase turn tightness is increasing bank. If you use either elevator or rudder, but try to keep angle the same, you will end with uncoordinated turn at the best case.

Well, uncoordinated turn is not forbidden, so let's analyze this closer.

But first have a look what is needed to feel the turn as tighter. Either you except feeling more G's pushing you into the seat or horizon speeding around before the nose faster. In any case it means that you need more force pointing inside the turn (airspeed unchanged).

Only source of big enough force are wings (any control surfaces are really weak when it comes to generating forces comparable to the airplane weight, the role of control surfaces is slightly turn the airplane in order to make wings to generate lift in right direction). But wing's lift has a direction mostly constant with respect to the airplane and you have limited your maneuvering space by wanting constant bank. Still, increasing lift is your only chance, so let's pull on the yoke.

If we forget about gravity for a moment, pulling on the yoke when 45° banked would result in nice slanted loop (45° inclined w.r.t. horizon and note that angle between wings and horizon would stay 45° all the time). But gravity is here and vertical component of the lift in turn is just compensating it instead of making you fly a loop.

If you pull bit more (say add half of the current lift amount), you will actually ask for flight which is composition of horizontal turn and that slanted loop. Resulting in a "flat" loop inclined 18° above horizon (horizontal component of the force will be 1.5 times original value, new vertical component 0.5 of original horizontal, $\tan^{-1} 1/3 = 18°$).

18° does not seems as a much, but it still means that with 10°/s turn rate the nose will go 3° up in less than second. And this is something, you will notice directly in contrast with less pronounced "more turning".

You can try to compensate with rudder and keep the nose down, but now you are comparing authority of rudder with pitch-wise stability generated by tailplane and wings. Having the same leverage (45° bank) and normal (non-aerobatic) aircraft, it is more or less sure that rudder does not have enough authority and pitch stability wins lifting the nose.

If you would like to continue this "flat loop", you would need to let bank angle to increase slightly. If you compensate instead, you are exchanging even more turning for nose up. And because there is gravity which keeps its orientation in space, your loop won't stay circular anyway. It will end up with some uncoordinated turn soon and if you compensate this, you are back at coordinated turn with original bank angle and therefore the same "tightness".

Your only chance for "tightening" the turn with elevator is having enough rudder authority, so you can hold nose low and fly the skidding turn. But for this you need enough leverage for rudder to overcome pitch-wise stability. Lot of bank in other words. Depending on the particular airplane even 60° does not need to be enough.

Edit: Note that in coordinated turn with constant bank angle the position of nose above or below horizon is not fixed. It will affect power budget of the flight by climbing, sinking and/or changing airspeed, but it has no big and direct effect on turn coordination. So if you struggle to keep you bank angle constant and turn coordinated only thing which can change is just this – angle of nose over horizon. And therefore it is the only change you see when pulling on yoke because you are compensating away the rest of direct effects.

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It's because the airplane doesn't actually know it's banked. To the airplane (and to your body for that matter), gravity is still perpendicular to the wings. It's just that the wings have to lift harder to compensate for having to generate a lateral force to change direction plus still support the airplane's weight in the vertical plane.

And it's elevator that controls how hard the wings have to lift. If you added several hundred pounds of ballast in straight flight, it's the same thing to the elevator.

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Pulling back on the yoke or stick when the aircraft is turning, and therefore banked, will both tighten the turn, and lift the nose relative to the horizon. The amount of each depends on the bank angle. In a shallow turn, increasing up elevator will mostly raise the nose and have little effect on turn radius. In a steep turn, say those over 45 degrees bank, up elevator will act more to tighten the turn, but will still raise the nose, just to a lesser extent.

Only at a bank angle of 90 degrees would the elevator not lift the nose relative to the horizon. So during steep turns,, the elevator will still control pitch attitude, though to a lesser extent than during shallow turns or level flight.

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