Use of rudder in turns
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In simple terms - as has been stated - you DON'T need rudder once in the turn. You DO need it when rolling in and out of turns in order to counter adverse aileron yaw which occurs whenever the ailerons are deflected from the neutral position i.e. generating lift and therefore drag. Try it in a glider 
.
Maybe I should read Stick and Rudder again but I lost interest the first time after he called the elevators 'flippers' one too many times.
. Maybe I should read Stick and Rudder again but I lost interest the first time after he called the elevators 'flippers' one too many times.
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?
Turns steepen because the outside (top) wing travels faster than the inside (bottom) wing. So there's a net rolling moment into the turn. If you don't hold out-of-turn aileron against that, your angle of bank will increase.
Once you have that angle of bank properly fixed, the next thing to concentrate on is the balanced flight -- non-slipping flight. That will (near enough) minimise the drag and therefore minimise the back pressure you need. The yaw budget in the turn has many contributions working in both directions. You will usually need into-turn rudder for the reason I described earlier, but there are other effects: if your out-of-turn aileron creates enough adverse yaw, you may actually find yourself skidding into the turn.
Different speeds and different angles of bank mean the various contributions net out differently. The only useful rule for minimising drag is "don't slip", which is almost equivalent to saying "keep the ball in the middle".
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you DON'T need rudder once in the turn.
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Turns steepen because the outside (top) wing travels faster than the inside (bottom) wing.
Even in a 60 degree, 2g steep turn at 100 knots the radius of the turn is still 125 meters. This is still less than 5% speed difference between the wingtips, and maybe 2.5% speed/lift difference across the whole wing.
It would seem that even a little turbulence would have more impact than these low numbers. Any comments?
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"Blimey, this is one way of complicating one of the simplest things"
----It's not simple.
"I couldn't care what a book says. Chuck has it nailed."
---You should ...and he doesn't.
"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."
---They are complicated. How do you know what it is you need to "do" to make the aircraft respond the way you want? Intuition ?...say along the lines of slow speed, ground coming up, pull harder on the stick...type intuition.
"Rocket science it ain't."
---Science yes ...rockets...correct at no stage were rockets mentioned.
TIM
----It's not simple.
"I couldn't care what a book says. Chuck has it nailed."
---You should ...and he doesn't.
"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."
---They are complicated. How do you know what it is you need to "do" to make the aircraft respond the way you want? Intuition ?...say along the lines of slow speed, ground coming up, pull harder on the stick...type intuition.
"Rocket science it ain't."
---Science yes ...rockets...correct at no stage were rockets mentioned.
TIM
I can't believe this is really responsible for the steepening of the turn.
If you look at the very small amounts that the ailerons deflect in order to command relatively high roll rates, you'll see that even small differences in lift have a big effect in roll.
so the speed difference between the wingtips is just a hair over 1.1%.
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?
Backpacker, quite right
Even in a 60 degree, 2g steep turn at 100 knots the radius of the turn is still 125 meters. This is still less than 5% speed difference between the wingtips, and maybe 2.5% speed/lift difference across the whole wing.
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I've heard the same thing in a number of places and accepted it as gospel. But I just did the calculation for a PA-28 with a wingspan of 10.66 meters, doing a standard rate turn at 100 knots. I found that the radius of such a turn is 955 meters, so the speed difference between the wingtips is just a hair over 1.1%. Lift is not generated by the wingtips alone but by the whole wing so measured over the whole wing the speed difference, and therefore the lift difference, is more like 0.5%. I can't believe this is really responsible for the steepening of the turn.
While there may not be a huge airspeed difference between the outer wingtip and inner wingtip in a turn, there's a difference in the angle of attack.
... there's a difference in the angle of attack
I've done the same calculations re airspeed difference between the wings and concluded that flies, dirt, rivets, etc. would mean more than that.
The books normally state angle of attack is diffeent, but don't explain !
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I've done the same calculations re airspeed difference between the wings and concluded that flies, dirt, rivets, etc. would mean more than that.
The books normally state angle of attack is diffeent, but don't explain !
The books normally state angle of attack is diffeent, but don't explain !
Increase the airspeed over a wing or section of wing, increase lift, increase drag, and you also experience a change in AoA. Change the configuration of the wing, such as lowering an aileron, and with the mean aerodynamic chord change and effective camber change, you've got a change in upwash and downwash, as well as AoA.
Additionally, as the aircraft is rolled into our out of a turn, changes in local AoA vary with the rising or descending wing, and in a turn when some degree of spanwise flow occurs, changes in AoA follow, along with changes in the lift component of any given wing cross section at any given time.
A simple example of a change in AoA, and lift and drag can be seen by lowering an aileron. As the aileron lowers to raise the wing, effective camber is increased, drag increases and rudder may be required against the drag created by the aileron. This drag, adverse yaw, is part of the reason that rudder into the turn may be required when rolling into the turn. As lift is increased on the wing, drag is increased, and the wing is experiencing an increased AoA. This is one example of one reason AoA may be locally increased during a turn, or turn entry, or sustained in a turn...depending on the design and requirements of the specific airplane or wing in question.
Remember that the increase or decrease in lift and drag isn't linear, and varies with the wing planform...what one airplane sees as a big change under a given set of conditions (airspeed and bank) another airplane will see as a little change. Add numerous other variables ranging from airfoil to control positioning to dihedral to sweep, wing planform, and even center of gravity, etc...numerous factors come into play which affect the stability and habits of the airframe.
The following article contains a couple of tables and graphs using several different wing planforms which might give a little insight. You can see that the drag coefficients go both up and down, depending on what type of wing is in use, of several demonstrated in the computer modeling.
Drag in Circling Flight
In a climbing or descending turn, the differences in AoA and the lift produced are a little more pronounced, and may be a little more noticable. One may not notice it in level flight, or the specific airplane may not require aileron into or against the bank...or it may only be noticable at certain degrees of bank, and not others. During a climbing turn, the outer wing tends to have a higher AoA, and during a descending turn it's the opposite.
-- with all else equal, descending turns are more stable than climbing turns.
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Don't blame the rudder for that.
Turns steepen because the outside (top) wing travels faster than the inside (bottom) wing.
Turns steepen because the outside (top) wing travels faster than the inside (bottom) wing.
Keeping an eye on the ball is obviously the way to go but knowing what to expect in a manoeuvre that has already a high workload is a great help, in my opinion.
Some interesting contributions here though. Thanks!
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David,
I'd caution you regarding microsoft flight simulator for learning about flying. While it can present some general benefits (push forward to go down, pull back to go up), it's not really a tool for better understanding how your airplane flies. Particularly where aerodynamics are involved. Simulators, even games like microsoft, are best used when experience in the airplane is transferred to the tool, rather than the simulation to the actual airplane.
Chuck was quite correct in his assessment earlier. We can talk about the finer points of why this or why that all we like, but the bottom line, and all you REALLY need to know is that the rudder is there to be used for whatever input is required to keep the ball in the center.
A steep turn is a confidence maneuver...it's something that as an instructor we have a student do to build confidence. It's not a high work load maneuver, and it's not a hard maneuver...which is why it's a confidence maneuver. It's a simple task which can be fairly easily mastered, which gives a student a sense of accomplishment prior to moving on to another task. It's also a useful demonstration of stability. In an airplane such as the Cessna 152, you should be able to set up the airplane in a steep turn, trim it off, and let it fly the steep turn hands-off.
I'd caution you regarding microsoft flight simulator for learning about flying. While it can present some general benefits (push forward to go down, pull back to go up), it's not really a tool for better understanding how your airplane flies. Particularly where aerodynamics are involved. Simulators, even games like microsoft, are best used when experience in the airplane is transferred to the tool, rather than the simulation to the actual airplane.
Chuck was quite correct in his assessment earlier. We can talk about the finer points of why this or why that all we like, but the bottom line, and all you REALLY need to know is that the rudder is there to be used for whatever input is required to keep the ball in the center.
A steep turn is a confidence maneuver...it's something that as an instructor we have a student do to build confidence. It's not a high work load maneuver, and it's not a hard maneuver...which is why it's a confidence maneuver. It's a simple task which can be fairly easily mastered, which gives a student a sense of accomplishment prior to moving on to another task. It's also a useful demonstration of stability. In an airplane such as the Cessna 152, you should be able to set up the airplane in a steep turn, trim it off, and let it fly the steep turn hands-off.
Angle of Attack varies as a vector with speed,
and also with the upwash induced by the wing. Upwash is in turn variable with the wing configuration, airflow velocity over the wing, and angle of attack. Increase angle of attack, increase downwash behind the wing and upwash ahead of the wing, and angle of attack increases beyond the simple angle made by the free airstream and the wing chord line...local angle of attack is greater because of upwash.
During a climbing turn, the outer wing tends to have a higher AoA, and during a descending turn it's the opposite.
That is true but rudder has a much greater effect.
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But what exactly do you mean by that?
I thought someone couldn't resist the chance to pontify on the misuse of Flight Sim! Yes I know all that. My point was that it's easily demonstrated in Flight Sim - I didn't "discover" it in Flight Sim. (doh)
I know those of you who have millions of hours can trim off a steep turn and show off going round in tight circles all day but for the rest of us it's still a challenge to keep absolutely level even though we have done it many times. Too much rudder when little or none is needed makes the exercise much more difficult and your confidence drops (as does the aircraft).
Also too much rudder means too much back pressure to compensate with accompanying high angle of attack. Little bit dangerous maybe?
I still think its a good thing to keep in mind and if you guys think its just foolishness I'll just keep it to myself thank you.
I think most of the posters here have missed the point entirely. But never mind...
Last edited by DavidHoul52; 16th Nov 2008 at 10:54.
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"Blimey, this is one way of complicating one of the simplest things"
----It's not simple.
"I couldn't care what a book says. Chuck has it nailed."
---You should ...and he doesn't.
"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."
---They are complicated. How do you know what it is you need to "do" to make the aircraft respond the way you want? Intuition ?...say along the lines of slow speed, ground coming up, pull harder on the stick...type intuition.
"Rocket science it ain't."
---Science yes ...rockets...correct at no stage were rockets mentioned.
TIM
----It's not simple.
"I couldn't care what a book says. Chuck has it nailed."
---You should ...and he doesn't.
"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."
---They are complicated. How do you know what it is you need to "do" to make the aircraft respond the way you want? Intuition ?...say along the lines of slow speed, ground coming up, pull harder on the stick...type intuition.
"Rocket science it ain't."
---Science yes ...rockets...correct at no stage were rockets mentioned.
TIM
When I'm flying I don't think about what the a/c is doing, I just move my hands and feet and magically the machine responds exactly how I want it to. That doesn't change whether I'm flying a helicopter, medium jet, aerobatic taildragger or simple spamcan.
I'm not always perfect, but going into enormous depth about the interrelation between controls is something I understand, but don't think about when I'm flying. I've been teaching it for years, but when flying things like "how much rudder do I need" should be automatic. I don't spend my life staring at the balance ball, after a while my patented inbuilt bumometer lets me know if the thing is in balance. Admittedly it can get confused when I've had a real hamfisted twonk whilst trying to teach them aeros, but 99.99% of the time it is fine.
Aircraft are simple. Pull back houses get smaller. Push forward they get bigger. If you push forward or backwards for long enough they get bigger and smaller of their own accord.....................
Making things overly complex for no real reason is a disease of many PPL's and inexperienced pilots. Don't make life difficult for yourself. Get up there and have fun, you'll soon find that discussions like this seem trivial.
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I'm not always perfect, but going into enormous depth about the interrelation between controls is something I understand, but don't think about when I'm flying.
But your students might want to know why the ball is on the right when they are in a steep turn to the left, especially when they have been told to give left rudder when in a turn. Understanding that the rudder and aerilons go together is helpful I feel. No airelons then no need for rudder (in a turn that is)
To be honest, my FI didn't make much fuss of rudder either other than to occasionally point out that the aircraft was out of balance. And you are right - one feels it without even looking at the ball.
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Student is asked to make a steep level turn. Rolls into it but doesn't input quite enough backstick. Makes a quick glance at the balance ball sees it has dropped into the turn slightly and immediately inputs rudder to remedy it. Congratulations your in a balanced spiral dive. If all the pilot has been taught is "Stamp on the ball" then he's not going to be aware of other possible influences.
I agree wholeheartedly that things can be made overcomplicated and as a result confused. The control of the aircraft has to be almost automatic; but that automatism has to be grounded in good basic knowledge. However things can be dumbed down too much just leading to dumb pilots. I suppose it is all a matter of balance.
Getting the balance right; feeding ideas at a sensible rate; tailoring the instruction the the individual taking into account their interests and background. Like all the good things in life it's.. part art.. part science.
When I was younger I used to subscribe to the view; "those who can do those who can't teach". Not now.. a good teacher is priceless.
TIM
I agree wholeheartedly that things can be made overcomplicated and as a result confused. The control of the aircraft has to be almost automatic; but that automatism has to be grounded in good basic knowledge. However things can be dumbed down too much just leading to dumb pilots. I suppose it is all a matter of balance.
Getting the balance right; feeding ideas at a sensible rate; tailoring the instruction the the individual taking into account their interests and background. Like all the good things in life it's.. part art.. part science.
When I was younger I used to subscribe to the view; "those who can do those who can't teach". Not now.. a good teacher is priceless.
TIM
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Another useful point made in L's book about steep turns is that if you haven't put in enough back pressure it's quicker and easier to regain pitch by rolling a couple of degrees out of the turn, then back pressure and then back to the desired angle.
Off thread - I see that the forum is now titled "The sheer pleasure of flight" which is a nice change.
Off thread - I see that the forum is now titled "The sheer pleasure of flight" which is a nice change.