Why is using opposite rudder and aileron necessary in left turn for coordination?

Question

This question goes against everything I've read or heard with the exception of a suggestion from my CFI in my last flight lesson, so I was hoping to get some clarification:

During a left turn into our crosswind leg my instructor informed me that I shouldn't be using so much left rudder, and in fact, might even need to use some right rudder to stay coordinated due to the left turning tendencies of the plane. I could somewhat understand given that I definitely noticed a tendency for the plane to roll more when turning left than right, but still I would think the antidote for that would just be less left rudder, not opposite rudder.

This does not make sense to me. In what situations would I need to do this? I was still able to perform my turns just fine with slight right rudder on my left turns, but I would like to understand this more.

FYI - I'm flying a Piper Cherokee 140 (PA-28-140)

Answer 1

First and foremost you should always be looking at the turn coordinator to see what is going on and applying rudder as necessary.

In your specific case (if we want to discuss the physics), basically what your instructor is saying is that you are using the ailerons to bank (turn) the plane and the rudder to counteract the propeller's yawing moment. The rudder is simply counteracting the Adverse Yaw: the inputs will change depending on how steeply you are banking. If opposite rudder is called for on your ball, then step on it.

Perhaps more importantly, what your instructor is actually stressing is during your crosswind, base and final turns you should really be paying attention to staying coordinated. A great deal of Stall -> Spin -> Crashes happen in the pattern as planes slow down and dirty up, thus it's extremely important in the pattern to watch your speed and your turn coordination.

Answer 2

You should just look at the ball and that will remove all doubt. If the ball is to the left, you use left rudder. It's that simple.

After a while, like a couple hundred hours, you will start to feel when the aircraft is coordinated naturally, but until then just look at the ball. Don't fixate on it, though. Just glance down at some point when you are making your turn.

Answer 3

There are already good answers, so I won't dwell on the standard advice to look at the slip indicator and do the necessary, but I'll answer to clear up a possible misunderstanding.

You do not use rudder to correct for adverse yaw when turning. You use rudder to correct for adverse yaw when rolling into the turn. When you turn left, you put the stick left to roll to the correct bank angle, and then you put the stick in the centre to maintain that bank angle throughout the turn. While the stick is on the left, you should be applying left rudder, but as the stick goes back towards the centre, so you should be reducing the left rudder. You don't keep that left rudder in for the whole turn. Later, when you roll out of the turn, you use right rudder then while your stick is on the right, and then return the rudder to the centre when you return the stick to the centre.

When you're turning across the wind direction, you'll definitely need to adjust the rudder position because the direction of the airflow against the aircraft changes. Exactly what is different in different situations (of wind direction and turn direction). Once you've completed the roll, you need to use the correct rudder for the situation. The fact you're in a left turn doesn't mean you can only use left rudder.

Answer 4

The other answers have good general discussions of engine- and propeller-induced left turning tendencies, but I don't think anyone's addressed the exact situation your instructor gave you that piece advice in, namely the crosswind turn in the traffic pattern.

At that particular point of the pattern, unless you've extended your upwind leg until you've reached pattern altitude and leveled off, you will still be flying at a relatively slow speed (so flight controls are less effective, including the little rudder trim tab on your vertical stabilizer), with a high engine power setting (so lots of torque and a nice, fast spiraling slipstream), and in a nose-high attitude (so p-factor comes into play in a big way).

All of these things combine to impart more left-yawing and -rolling tendencies on the aircraft than at just about any other point in the traffic pattern. Quite a few aircraft, in fact, require minimal, if any, inputs to initiate a left turn from this attitude. As you've seen yourself, you might have to add opposite rudder just to keep the aircraft coordinated while it's doing its thing.

If you're looking for more practical demonstrations of this (as well as how this differs from making turns to the right from this attitude), I recommend asking your instructor to give you a brief introduction to chandelles. They're great for demonstrating and understanding the turning tendencies imparted by the engine at different airspeeds and pitch attitudes (and a lot of fun to boot).

Answer 5

I'm assuming that you are climbing at full power as you're turning left. In this position everything thrust related is essentially creating both left roll and left yaw. Left Yaw in a left bank creates a nose down tendency and may indeed un-coordinate your turn to a point whereas right rudder may be needed which is admittedly cross sticking, BUT IS IT??? Essentially the torque and particularly the P factor may be providing "too much Yaw input" all by itself and the only way to lessen it is to apply right rudder. AKA the p factor and many other "full power" attributes is already adding what is "effectively" "too much" left "rudder input" (even though it's P factor input) and in extreme cases (as is full power and turning left), especially if airspeed begins reducing too, there will be a point whereas the pilot would need right rudder in a left turn. The Ball doesn't lie, step on it!!!

Answer 6

That's all going to be dependent on aircraft type, configuration and flight characteristics, but your instructor is right.

Rudder is necessary to correct for adverse yaw due to the drag created by the upraised aileron in a turn. In steep turns, the outside wing is traveling faster through the air than the inside wing, generating more lift than the outside wing and causing a tendency for the airplane to continue to increase its angle of bank. This would be counteracted by opposing aileron input, which in turn creates adverse yaw toward the outside of the turn. Opposite rudder will be required to correct for this. This would be particularly pronounced during flight at slower speeds where it is much more noticeable.

The total required control inputs may be composed of a number of factors, most of which are related to the propellor, such as p-factor, prop wash on the fuselage, gyroscopic precession, etc. but yes, your instructor is right and you may see a skidding turn as a result.

Answer 7

I agree that this sounds counterintuitive, and my gut tells me that there is some misunderstanding here.

Torque and p-factor will have a greater effect at the lower speed in the traffic pattern. If, in level flight, you are holding right rudder, then maybe when you're rolling left all you need is a reduction of right and not necessarily input of left in order to maintain coordination.

I have very strong doubts that what your instructor is telling you is that you should add right rudder, in the sense of increase it, as you roll left. If anything it is a decrease of right rudder.

However, a reduction of right rudder during the roll is still right rudder in the same way that turning a car's wheels toward center, but still being in a right turn is not considered turning your car left.

Answer 8

just thought I would note that I believe torque causes rotation around the longitudinal axis (left wing down)and is corrected with aileron input. P-Factor causes rotation to the left around the vertical axis (yaw) and is corrected with opposite rudder as needed.