# Why does elevator input move the turn coordinator ball in steep turns?

When practicing steep turns, I'm running into an unusual phenomenon. If the airplane is losing altitude in coordinated flight and I apply aft stick pressure to pitch up and correct, I notice that the ball swings to the outside of the turn indicating a skidding condition. Conversely if the airplane is gaining altitude and I release back pressure to the stick to descent, the ball always swings to the inside of the turn, indicating a slip. This seems counter intuitive as one would think that an increase in AoA to gain altitude would result in increased adverse yaw, requiring more rudder pressure in the direction of the turn and less rudder pressure when the nose is lowered resulting in a lower AoA and adverse yaw.

I suspect the reason here has to do with the direction the nose is being forced in by the elevator input during the turn. At a steep bank angle the nose is inadvertently being pulled inside the turning flightpath which results in a skidding condition, which should, therefore, be countered by less rudder pressure in the direction of the turn. Conversely when elevator pressure is reduced, the nose would tend to stray outside of the tangential flightpath, resulting in a slipping condition. The end byproduct of this would be reduced or even cross control inputs needed to maintain coordinated flight. Can anyone else confirm this?

• What kind of airplane is it? – GdD Jan 14 '19 at 16:30
• C172, PA28, you name it. – Carlo Felicione Jan 16 '19 at 22:23
• Comments are not for extended discussion; this conversation has been moved to chat. – Farhan Apr 8 '19 at 18:08

In a steep turn you are making power changes, pitch changes and also making constant corrections with aileron to hold the bank angle, without even realizing it. Once established in the turn some airplanes require a bit of in-turn aileron to hold the bank angle, some hold the bank with neutral aileron, and some require top aileron to keep from overbanking. The top and down aileron inputs are inducing constantly changing adverse yaw forces which come and go, changing torque effects from the engine with power adjustments are producing changing yaw forces, and gyro precession from the prop from pitch motions are inducing yaw forces which come and go, and there are bumps, and you start running into your own wake.

In other words, you are in a machine pulled along by a big torque producing gyro that is slithering and sliding around in a gas with half a dozen forces and moments interacting on it simultaneously. With all the subtle forces and inputs happening during a turn, I don't think you can identify and act on a single phenomenon like that. What you have to do is, well, just do whatever it takes to hold the bank angle, altitude and center the ball and don't overthink it.

If you fly gliders, which use a yaw string that is more sensitive than a ball, even without the torque and gyro effects of an engine, the yaw string drifts this way and that while in a turn, seemingly independent of the aileron position some of the time. You generally make stabs of rudder in concert with aileron, but sometimes the yaw string seems to have a mind of its own and you just do what you have to do with your feet.

It is important to realize the "ball" is simply rolling back and forth in a curved glass tube to indicate the direction of net G forces. It is also known as an inclinometer. What is happening in your steep turn is the elevator/wing orientation is now at an angle to gravity, so pulling "up" also tightens your turn radius, forcing the "ball" to the outside. In a steep turn the elevator becomes more "rudder-like". If you roll to 90 degrees, the elevator IS your rudder, and the rudder will pitch your nose up or down.

Your thought to "step on the ball" is correct, as rudder input will raise nose and help hold altitude. Try adding a bit more power too. Pulling alot more elevator to hold altitude in a steep turn is not good technique as it can lead to a stall or spiral dive. Sometimes just rolling to a slightly lower bank angle will do the trick.

I would review this with an instructor, but a little "rudder to the sky" may help here.

• Sorry Robert I'm not sure this is good advice. It sounds like you are introducing the concept of adding top rudder to hold the nose up in a turn, which is a slipping turn, and which has resulted in countless stall spin accidents. Rudder to center the ball. Period. If the airplane isn't going where you want it, pitch, power, roll, whatever, but the ball should always be centered and you do whatever you have to do with your feet to keep it centered. – John K Jan 14 '19 at 16:47
• @John K. I really like your practical experience. This is why this should be reviewed with a qualified instructor. Please note though, in a steep turn, especially if CG is forward, the nose will tend to drop. A little opposite rudder (which would center the ball) would be the least of my worries. Excessive elevator the biggest. Adding power helps, and I (cheated a little) by rolling to a slightly lower bank too. – Robert DiGiovanni Jan 14 '19 at 16:57

If the airplane is losing altitude in coordinated flight and I apply aft stick pressure to pitch up and correct...Conversely if the airplane is gaining altitude and I release back pressure to the stick to descent

What you really want to do is to change your technique.

Your goal (assuming for example a steady 60 degree AOB) is to roll into the turn, set your G (2G = what you need for 60 degree AOB) and then lock in the back pressure while varying your AOB to set your nose position relative to the horizon. Climbing? Over bank a little to let your nose slice down, and then reset the bank so it holds fixed to the horizon. See what that gives you. Descending? Do the opposite. But don't pump the nose to go up or down. Particularly if you are near a stall AOA, it can cross you over and you can lose control.

This will smooth out your flying and result in constant radius turns.

• Absolutely, no rule says it has to be exactly 60 degrees. Much safer. – Robert DiGiovanni Apr 5 '19 at 19:31
• Also, power can be added or taken out to control altitude. – Robert DiGiovanni Apr 5 '19 at 19:35
• I had a long answer on why the ball went one way or another and posted it, and then realized I was completely wrong. :) Still puzzling on it. – MikeY Apr 5 '19 at 20:16

Imagine a banked plane in four scenarios. In each scenario the plane maintains the same vertical speed (it does not accelerate up or down).

1. The plane is banked but not turning. The aircraft creates 1G of lift by angling through the sky in an uncoordinated manner and does not turn at all. The direction of lift is pointed straight up, and the ball moves to a position opposite it, pointed strait to the ground.

2. The plane is banked, but in a slip. The aircraft does turn but not as much as it should given the angel of bank. The aircraft is generating 1G of lift in the vertical direction, but not enough lift in the horizontal to put the combined vector perpendicular to the wings. The ball falls partway towards the ground.

3. The plane is in a coordinated turn. The aircraft is generating 1G of lift in the vertical direction and just enough lift in the horizontal direction to put the combined vector perpendicular to the wings. The ball is centred in the gauge.

4. The plane is in a skidding turn, it is turning faster than it should given the angle of bank. The aircraft is still generating 1G of lift in the vertical direction, but now it is generating more than the required amount in the horizontal direction, and the combined vector is past perpendicular. The ball moves to the outside of the turn.

The essential part here is that unless the aircraft is entering a climb or coming out of a dive, it is producing 1G of lift in the vertical direction. If the plane increases or decreases the amount of total lift produced, the direction of the vector will change accordingly. If the direction of the vector does not match the angle of bank you will be uncoordinated. Too much bank, or not enough lift gives a slip, too little bank or too much lift gives a skid.