Use of rudder in turns
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Use of rudder in turns
I have returned to Wolfgang Langewiesche's book "Stick and Rudder" after putting it aside for a while and have been pleasantly surprised to find some great information on turns. I had always thought - and I can't remember my FI correcting me - that one applied rudder throughout a turn in order to stop slipping. According to the author one should only use rudder when rolling in or out of a turn - while banked the aircraft does not need rudder and in fact use of the rudder causes it to descend and has to be compensated by excessive back pressure.
Moreover, the excessive back pressure can lead to the wing stalling and a resulting spin. This is especially noticeable in steep turns. I wondered why mine were always going haywire! If one centres the rudder when banked at the desired angle steep turns are easy.
Any comments?
Moreover, the excessive back pressure can lead to the wing stalling and a resulting spin. This is especially noticeable in steep turns. I wondered why mine were always going haywire! If one centres the rudder when banked at the desired angle steep turns are easy.
Any comments?
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The purpose of the rudder is to keep the aircraft in balance, so if the ball is in the middle with the rudder neutral in a turn then so be it. That's situation normal in my Piper.
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David
There is an RAF technique you can try. It involves using the rudder to initiate a turn and then applying aeleron to centre the ball.
It is very smooth and has the aircraft fully balanced in all axis in the turn.
Also when you have the aircraft trimmed for level flight and want to fly hands free try holding your heading by using the rudder pedals. That works too especially if you need your hand for maps books etc.
Pace
There is an RAF technique you can try. It involves using the rudder to initiate a turn and then applying aeleron to centre the ball.
It is very smooth and has the aircraft fully balanced in all axis in the turn.
Also when you have the aircraft trimmed for level flight and want to fly hands free try holding your heading by using the rudder pedals. That works too especially if you need your hand for maps books etc.
Pace
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rudder is linked to the aileron
According to the book it's sound aerodynamics. The rudder is only needed when banking not when banked (if you know what I mean). It makes sense if you think about steep turns - in fact the author says it might be a good idea to teach steep turns before shallow ones! It also goes on to say that turn coordination is primarily with aerelon and elevator back pressure.
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Ok - see what the ball does next time you do a steep turn. If the principle is sound then one can neutralise rudder every time without looking at the ball.
According to the author one should only use rudder when rolling in or out of a turn - while banked the aircraft does not need rudder and in fact use of the rudder causes it to descend and has to be compensated by excessive back pressure.
The aeroplane will generally slip if held at a constant angle of bank in a turn with rudder central. It's the yawing effect of that slip through directional stability that causes the nose to yaw around the turn as the direction of motion over the ground changes. It's perfectly possible to operate an aeroplane in that way. If you want to fly the aircraft in balance, you need to apply some rudder to provide an alternative source of yawing moment.
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Langewiesche has a habit of oversimplifying
There may need to be some rudder even so but I assume the point he is making is that it wouldn't be the same amount as when rolling into the turn.
Last edited by DavidHoul52; 15th Nov 2008 at 12:36.
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That's situation normal in my Piper
A very interesting discussion, though, and ideas which I'll be keen to try out the next time I "commit an aeronautical act" !
Won't be this weekend, though - - can hardly see out of the office window ! . . . . .
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steep turns.
I realise now that I have been fighting the rudder with back pressure. I would have realised this by watching the ball of course but one needs to be watching the horizon when doing
I realise now that I have been fighting the rudder with back pressure. I would have realised this by watching the ball of course but one needs to be watching the horizon when doing
I think you are oversimplifying all the forces involved in a turn and increasing bank.
In any turn around a radius the tendency for the aircraft will be to skid that will show in the turn and slip.
As you bank the rising wing will create more lift, the descending wing less lift that will mean that you will require more pitch to maintain level flight and with that extra pitch more drag.
Applying rudder in level flight will cause a yaw and the nose to turn around the centre of the axis of that yaw that itself will cause one wing to slow and the other to speed up again causing the aircraft to initially pitch up which followed by an increase in drag will then cause the aircraft to pitch down for a set level of power.
The forces are complicated and will take someone with a better description of the aerodynamics and complexity involved other than to say you need to keep all the forces in balance and the use of all your controls including power to maintain a smooth level steep turn.
Pace
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As you bank the rising wing will create more lift, the descending wing less lift that will mean that you will require more pitch to maintain level flight and with that extra pitch more drag.
Applying rudder in level flight will cause a yaw and the nose to turn around the centre of the axis of that yaw that itself will cause one wing to slow and the other to speed up again causing the aircraft to initially pitch up which followed by an increase in drag will then cause the aircraft to pitch down for a set level of power.
Applying rudder in level flight will cause a yaw and the nose to turn around the centre of the axis of that yaw that itself will cause one wing to slow and the other to speed up again causing the aircraft to initially pitch up which followed by an increase in drag will then cause the aircraft to pitch down for a set level of power.
I'm with you in your first paragraph. L emphasizes the need for back pressure when turning - which we all know. Back pressure also stops slip (according to L.)
I don't quite follow your second para. Do you mean "level flight" as in "straight and level" or level flight in the turn? The nose will indeed turn around the centre of the axis of the yaw - but when the aircraft is banked at say 45 degrees that axis will also be at 45 degrees and the turn will be earthward. Thus the tendency for a steep turn to increase it's angle of bank and also descent.
That is my own summary of what L is saying and it makes sense from my own experience. Probably that is what you are saying but perhaps in a different way. As L would be the first to point out the aerodynamics are not that simple, but it does indicate what one would most often expect.
I think most would agree that a high angle of attack combined with a lot of rudder is not a good idea.
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David
No I was referring in that part the effects of rudder only ie set up a level trimmed flight not a turn. Then with your hands off the control column apply rudder only and see for yourself what the aircraft does. Apply right rudder and then squeeze in left and note what happens to the aircraft in heading bank and pitch.
Then do the same apply aeleron only and again watch what happens.
Pace
No I was referring in that part the effects of rudder only ie set up a level trimmed flight not a turn. Then with your hands off the control column apply rudder only and see for yourself what the aircraft does. Apply right rudder and then squeeze in left and note what happens to the aircraft in heading bank and pitch.
Then do the same apply aeleron only and again watch what happens.
Pace
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Pace
Not flying today so can't give you an experiential answer.
I would say you will have yaw in both cases but in opposite directions. Back pressure will be needed in both cases eventually. L says that at slow speed the yaw in the case of banking only with the aerilon can be so severe as to cause the plane to turn in the opposite direction. Has anyone been able to verify that?
Obviously a coordinated turn is needed with both rudder and aerilon. But once the turn is established it's a different scenario. If one neutralises the aerilons at this point does it not make sense to neutralise the rudder too?
I'm not trying to be argumentative (although I like starting a lively discussion). It came as a sort of eureka moment as it explained a number of things I'd noticed while flying. Like why is the ball not where I expect it to be when turning? Why are my 45 degree steep turns suddenly becoming 60 degrees and more? Why am I loosing height? Why I am finding it so difficult to keep the plane level in a steep turn? Why do I need so much back pressure?
Not flying today so can't give you an experiential answer.
I would say you will have yaw in both cases but in opposite directions. Back pressure will be needed in both cases eventually. L says that at slow speed the yaw in the case of banking only with the aerilon can be so severe as to cause the plane to turn in the opposite direction. Has anyone been able to verify that?
Obviously a coordinated turn is needed with both rudder and aerilon. But once the turn is established it's a different scenario. If one neutralises the aerilons at this point does it not make sense to neutralise the rudder too?
I'm not trying to be argumentative (although I like starting a lively discussion). It came as a sort of eureka moment as it explained a number of things I'd noticed while flying. Like why is the ball not where I expect it to be when turning? Why are my 45 degree steep turns suddenly becoming 60 degrees and more? Why am I loosing height? Why I am finding it so difficult to keep the plane level in a steep turn? Why do I need so much back pressure?
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The thing is, all aeroplanes are different....dihedral for starters.
I agree though, in simple terms when you roll into a turn you need *more* rudder - reason is that one aileron goes up, reducing AoA on one wing, one goes down increasing it on the other. Net result increase in drag on one wing and a yawing tendancy towards the downward ailerom. When you are IN the turn and ailerons are the same then this situation doesn't exist any more. Of course then you have other factors like outboard wing travelling faster, dihedral trying to level the plane, whatever......
One good exercise is to fly along S&L and rock the wings 30 deg either side and watch the nose. It scribes a circle in the sky. Now do it and apply rudder as you do and watch the nose stay still.....
I agree though, in simple terms when you roll into a turn you need *more* rudder - reason is that one aileron goes up, reducing AoA on one wing, one goes down increasing it on the other. Net result increase in drag on one wing and a yawing tendancy towards the downward ailerom. When you are IN the turn and ailerons are the same then this situation doesn't exist any more. Of course then you have other factors like outboard wing travelling faster, dihedral trying to level the plane, whatever......
One good exercise is to fly along S&L and rock the wings 30 deg either side and watch the nose. It scribes a circle in the sky. Now do it and apply rudder as you do and watch the nose stay still.....
Last edited by englishal; 15th Nov 2008 at 17:31.
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As far as I know none of the aircraft I have flown have this feature. (You can turn it on in Flight Sim though!)
According to the book it's sound aerodynamics. The rudder is only needed when banking not when banked (if you know what I mean). It makes sense if you think about steep turns - in fact the author says it might be a good idea to teach steep turns before shallow ones! It also goes on to say that turn coordination is primarily with aerelon and elevator back pressure.
According to the book it's sound aerodynamics. The rudder is only needed when banking not when banked (if you know what I mean). It makes sense if you think about steep turns - in fact the author says it might be a good idea to teach steep turns before shallow ones! It also goes on to say that turn coordination is primarily with aerelon and elevator back pressure.
You may be surprised...rudder influence is brought to bear in various light airplanes through interconnect mechanisms of different types. You can usually see it by sitting on the ground and moving the ailerons...you should see the rudder move a little. Conversly, push the rudder a little without touching the stick or yoke, and on airplanes which have some interconnect, you'll often see the stick or yoke moving a little, too. This doesn't mean the airplane automatically "coordinates" for you...just that it's designed to give you a little help. Not all airplanes incorporate this in their design.
The amount of rudder needed in a turn depends on the nature of the turn, as well as the type of airplane. A steep turn has different rudder needs than a shallow turn. One type of airplane may require considerable rudder into or against the turn, whereas another may require little or none.
I'm flying a type right now that requires nearly no rudder input. Feet remain on the floor most of the time; the airplane does it all.
When I was younger and had just started doing ag work (crop dusting), found myself really fighting the airplane in the turns. We would pull up out of a field to clear power lines and trees, and make a steep turn right to the stall buffet, at 75 to 150' above the ground. I found that even though the airplane would be vibrating or buffeting, others could turn considerably tighter than me. I was white-knuckled on the stick, afraid that if I pulled it in any tighter, I'd stall and roll over into a spin. I was holding considerable bottom rudder because that's what I thought the airplane needed. It didn't feel right without it.
After a quick analysis by my boss, a very experienced ag aviator, he succinctly summed up my problem. "You're being stupid."
A more detailed analysis showed that if I used top rudder, as required, in the turn, it made all the difference. Once I tried it and got better at feeling my way around the turn, I discovered that I'd been slipping and skidding through turns. Suddenly I could go a lot tighter, reduce my turn times, and didn't get the rough stall burbles and snatches like I had. We still rode the airplane around the turn close to the stall, as it's part of that kind of a turn in that kind of work, but suddenly I was much safer, no longer putting myself close to a spin-under situation.
As Chuck noted, for a normal turn, keeping the inclinometer, or skid ball in the center of your instrument, is all you're really interested in doing. Whether it takes no rudder input, top rudder, bottom rudder...is really irrelevant. Do whatever is necessary with the control to make the airplane do what you need it to do. Your drag is reduced, your climb performance enhanced, your turn made more comfortable and smoother, and it's safer if you're slow (avoid getting slow).
A good exercise for developing a feel for coordinating your rudder input against other control inputs such as roll, is to practice making roll entries. Roll left to a bank of about 30 degrees, then roll right back to the right 30 degrees. Keep a constant roll rate going back and forth, and concentrate on keeping your skid ball in the center the whole time. Once you get comfortable with that, increase the bank to 45 degrees each way, keeping a constant roll going back and forth. You'll find that after a little practice you can vary the rate of roll and change the rate and amount by which you use the rudder to keep that ball centered. Once you've got that mastered, you'll understand normal use of the rudder, and can move on.
Remember that's normal use of the rudder. The rudder has many other uses too, aside from "coordinated" flight...but for now, and for the purposes of this discussion, keeping the ball in the center of your instrument means using whatever rudder input is necessary. That could be top rudder, bottom rudder, or no rudder at all. Typically because flights don't take place on perfectly smooth days and typically because none of us are perfect, keeping the ball in the center may mean small, smooth corrections involving top, bottom, and center rudder...much of the time. Use whatever is required to make the airplane do what you want it to do.
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Blimey, this is one way of complicating one of the simplest things.
I couldn't care what a book says. Chuck has it nailed.
Don't overcomplicate things, unless you are designing the aircraft from scratch, just do whatever you need to do to make the a/c respond how you want it to.
Rocket science it ain't.
I couldn't care what a book says. Chuck has it nailed.
Don't overcomplicate things, unless you are designing the aircraft from scratch, just do whatever you need to do to make the a/c respond how you want it to.
Rocket science it ain't.