How to correct a roll due to turbulence?

Question

I fly a Piper Cherokee 180 (PA-28-180) in an area that has frequent turbulence. When turbulence causes the aircraft to roll to one side I usually try to correct by using aileron and rudder in the opposite direction of the roll.

However my flight instructor says that I should use rudder only to correct for the roll. I can get the wings level by using only rudder but it seems to me that using aileron and rudder would be the most effective method. Can someone please explain to me why I should use only rudder in this instance?

Answer 1

I'm not sure I would agree with the advise of your instructor, but this is perhaps what he wants you to learn.

The Piper Cherokee has a small amount of dihedral built into it's wings. This dihedral angle is used to "self right" the aircraft in the event of a roll.

The way it works is when an airplane starts to roll it loses altitude parallel to the slip direction:

So with a dihedral angle the wing facing the slip direction now produces more lift:

With enough time dihedral wings will right themselves, or as your instructor is telling you, you can make this faster with the rudder by turning the lower wing into the relative wind speed making it produce even more lift.

Why your instructor is preventing you from using any ailerons I'm not sure, but perhaps he has reasons you should ask him about.

This might not be the best example, but I have something personal that probably relates to what your instructor's getting at.

I ride horses quite a bit, and we have something called "no stirrup Thursday".

It's as the name sounds, when you ride on Thursday the stirrups stay in the barn.

Stirrups help you balance your weight so by spending a day without them we force ourselves to learn to balance better and ultimately stay on the horse given a situation when our feet slip out of the stirrup.

It's not unheard of that control sticks break and all your left with is the rudder pedals.

It's also not uncommon for new pilots to use the ailerons too much to correct roll and this causes the plane to roll the other direction, which they then switch the ailerons back again to try and correct it.

But I'm really just speculating at this point, you should ask your instructor directly why he is preventing you from using the ailerons.

Answer 2

Your instructor needs some... instruction. Inducing roll using rudder alone is something you do when you are right on the edge of a stall because a downgoing aileron can potentially induce a stall when right on the edge. In a normal climb, using rudder alone is totally nuts.

Apply only the rudder required to keep the ball centered with the application of whatever aileron is necessary. If you needed all the roll power you can possibly get, you would apply full aileron and full rudder to use the resulting skidding to increase the roll rate.

Answer 3

I'd urge you to exercise caution using this technique. After all, this is how American Airlines 587 got down.

The pilot used rudder aggressively in an attempt to get the plane out of a jet wash - so aggressively that his rudder input caused structural failure and the entire vertical stabilizer snapped. In post-crash interviews with other pilots who have flown with the accident pilot, others stated he like to use very large rudder inputs even in minor turbulence. When questioned about this technique, he said he was taught to use the rudder this way. Further investigations revealed that many pilots in the airline have a wrong concept of flying an airplane, namely using the rudder way too aggressively to correct the airplane's attitude.

Using the rudder is a very effective way to correct an upset situation. Say I find myself in a left bank 135 degrees (so I'm upside down) and nose down attitude. Full right aileron and full right rudder would be my input. My rudder input has two purpose. First, the roll-yaw coupling (on most planes) means my right rudder with cause induced right roll. Second, once the plane is at the vertical (90 degrees roll), the rudder pushes the nose up instantly. As I transition to upward flight, somewhere between 60 degrees to 45 degrees of bank perhaps, I'd slowly let go of rudder input and at the same time gradually pull the stick/yoke aft, careful not to stall or cause abrupt input, depending on airspeed.

But that's more of an extreme situation.

Another use case, told to me by a Boeing 737 training captain: in case of complete hydraulic failure, a slight pedal input will bank the plane in the desired direction. Again, this is an emergency situation, not normal flying.

Like others here, I do not agree with your instructor, or at least not in your presentation (you may have misunderstood him, which led to the rest of us misunderstanding him as well). For small attitude deviations, use the most direct method to correct. Use rudder to keep the balls centered. For larger deviations, aileron + rudder would be the most effective method. Again, we cannot judge how big those deviations are here. All I can say is - if you're dancing on the rudder pedals, it is definitely a wrong technique.

Answer 4

Perhaps this is of some use. AOPA put out a video recently about using rudder to correct for some turbulence. I can't re-watch it just now, but as I recall it doesn't recommend always using rudder instead of aileron. Rather, it talks about recognizing when bank is induced by crosswind gusts and using the rudder appropriately.

Answer 5

Not necessarily the best technique, but, in practice, say on a long cross country flight, use of rudder-only allows for the use of your hands to manipulate charts, plotters, portable electronics, etc. I have found myself doing this many times over the years. Just a thought.