Basic Skils: Turns using rudder
 

Another thread got me interested in the turn skill, and I looked up "how to turn" on youtube, came across a video by alishanmao. Wow, I now think I never knew anything about how to turn a plane!!! Practiced the technique/s in RealFlight and made large improvements in control in just two days.

The combination of rudder + aileron was different between planes. On the Albatros, you almost have to use both aileron & rudder in same direction. Switch, Electristar, you need opposite rudder & aileron to successfully turn. I would expect this to be true for physical models as well.

A common problem I've been having is keeping the plane close in. With a tighter turn, it is easier to do that! Looking forward to practicing this in real life

Regards

I doubt that there is any plane that needs opposite rudder and aileron to turn. Perhaps one of your servos is reversed. Most planes turn by banking, which you do with the ailerons. The rudder is used in turns to keep the plane from yawing in the direction away from the turn.

I will start the turn with ailerons but as I add rudder I usually have to reduce ailerons. Now to make a flat turn its rudder with opposite ailerons

Yes, you can make flat turns that way, and it's kind of fun. But it's not the way beginners should be learning to turn. And there are no planes I know of that "need" opposite rudder to turn, which is what the OP was claiming.

It sounded to me like he meant that the trainers required some opposite aileron when he uses the rudder to turn. That's true if you initiate the turn with the ailerons and then feed in rudder, since those planes have such a strong roll coupling with the rudder. A rudder only turn will work fine with those planes, but if you roll into them and then input rudder it will make them roll too much.

I practiced this with 7-8 planes. The effect using this method was
- turns are much flatter. You could even make them completely flat; but that doesn't seem to work as well as "sort of flat but with some bank"
- turns are slower;
- tighter turn

Enough opposite aileron to make a completely flat turn did not seem to work as well as allowing some amount of banking.

My initial exploration into this topic was to learn how to use rudder, as I have mostly (100%) been using aileron only for turns, and only using rudder for take-off. I think rudder is better for landing; banking at low altitude sometimes doesn't work very well (for example, scrape round with one wing!). As I am practicing this maneuver, I am finding that my fingers are becoming better at coordinating between rudder and aileron, which was the original desire.

For some of the planes, starting the turn with aileron only doesn't work as well as starting with rudder, and then introduce aileron. Each plane seems to have its own unique combination of how much rudder vs aileron, and when to apply it, that results in a flat, tight turn. The Albatros didn't like reverse rudder/aileron at all, and just about wouldn't turn with rudder only

But maybe my RealFlight works differently than others!!

When I said "need opposite rudder/aileron to turn successfully", I meant "need opposite rudder/aileron to flatten the turn and turn tighter than by using aileron only".

Regards

Good experimentation! Flat turns are fun to do because they look different, but they are not aerodynamically efficient. In a flat turn the plane is skidding and air flow over the wing is somewhat span wise. There is a myth that had currency for awhile about making flat turns with gliders in order to lose less altitude in a turn, but in fact, it doesn't work.

Jim

Exactly right. Fun aside, there's no reason to try to make your turns flat. On some trainers, the ailerons aren't very effective at low speeds, so using rudder to turn when landing is a useful habit to develop. But of course that's rudder in the direction of the turn. I find it hard to believe that you get "tighter" turns by using opposite aileron and rudder. For a really tight turn you can lay it on its side and give it a lot of up elevator. If using rudder in a turn causes you to bank too much because of roll coupling, the best technique is to add less rudder, not to use opposite aileron.

Some day, when the OP is beyond trainers, using opposite rudder in a turn is going to cause his plane to spin. A stall won't make you spin if you're coordinated when the stall occurs, even in a turn, but if you're not coordinated, it can get exciting.

yup, I was going to chime in for exactly this reason, one of the main reasons for having a turn and bank indicator in a full scale airplane... cross control stalling.

a cub, Sopwith, really any model big enough to NEED rudder in a turn is a thing of beauty in a forward slip, but ooooo boy it gets ugly quickly if you forget the first commandment:
"maintainest thou airspeed lest the ground smite thee"

anytime you're feeding in opposite ailerons and rudder, KEEP THE AIRSPEED UP :)

Jim, as someone who has competed in a US soaring team selection finals, this was a technique I used frequently to expose as much wing to a thermal as possible. It's very useful when the thermal is quite small and would otherwise require more then 40 degree bank angle to stay in the thermal. During a dead air/sink situation you would be correct that it would lessen the sailplanes efficiency.

This works, since the heading change (yaw) occurs quicker. Just use a small amount tho: all things in moderation! Top Gunn is correct in all he's written.

I too don't understand why the OP is using opposite rudder. In modern trainers, just a touch of rudder in the direction of turn is needed for coordinated turns due to the generous amount of dihedral. In earlier aircraft with little/no dihedral (WW1, Cubs with 'barn-door' ailerons), a fair amount of rudder is needed in the direction of turn for coordinated flight. In fact, I find it best in a Cub to lead the turn a bit with rudder, then add aileron. Each aircraft type responds differently of course.

I agree with this.

When you apply aileron the down going aileron produces more lift and the penalty is more drag.

The opposite wing has an aileron that moves up, resulting in less lift and less drag.

If one wing has more drag than the other it causes yaw. In this case it is called 'adverse yaw'

The rudder can be used to compensate for this adverse yaw. By applying rudder in the same direction as the aileron application.

Note that adverse yaw is a function of aileron deflection, not angle of bank. IE you only need to apply rudder while your ailerons are deflected.

This will produce a 'coordinated turn'. If you were in a real aircraft. You would see the balance ball is centred if you apply the correct amount of rudder to compensate adverse yaw.

There are many factors affecting the amount of adverse yaw in a given aircraft design, wing span, wing profile, use of differential or Frise ailerons.

I agree there are many situations where you may want to fly out of balance to achieve a specific objective, eg, thermalling, turning with minimal bank, or side slipping in a crosswind, or aerobatics.

For normal flight, use of rudder will improve your turns by eliminating adverse yaw.

Plenty of good reading if you google 'secondary effect of flight controls'

http://youtu.be/NXMwvEx56Gs

That is right . My flight instructor used to tell me to " Step on the ball " It co-ordinated the turns . Same thing when we fly RC . we need to co-ordinate our turns with the rudder . I agree with Eddie C I like to use both rudder and ailerons to turn my cubs . I find if I don't they will drag their tails especially if your speed is down . If your speed is up its not so bad . I like to fly fairly slow though . Not to point of stalling but slow enough that you are flying on the wing .

Actually, I'm not using opposite rudder. I'm starting the turn with the rudder; the plane banks; I reduce the bank with opposite aileron.
For a left turn, push the rudder to the left. After it starts banking, reduce the bank by pushing the aileron stick to the right.

If the plane is only banking a little bit, this isn't necessary.
If it's banking a bit more than I care for, and one indication of this is that it's losing altitude, then flatten the turn using opposite aileron
If it's losing altitude, dial in a bit of elevator as well.

So this has got lots of fingers going and coordination!!!! Mind you, I'm doing all this experimentation in RealFlight; I don't think I'll just jump into this with the physical model. At least, start with just little corrections and if they don't work-discontinue.

That's not really any different than what I am finding by trying out the different planes. Some of them like opposite aileron; some of them want aileron in the same direction. So, I try a little, if it works fine. If not, think about what it's doing and adjust accordingly.

Regards

Good to experiment in a sim before trying in the real aircraft.

Just letting you know, if you are holding opposite aileron in a turn, it means you have more rudder than necessary to coordinate the turn, and by cross controlling, your aircraft is now in a "skidding turn"

This configuration is setting your aircraft up for a sharp spin entry if you stall.

There is a saying in the full size aerobatic world.

Watch him spin, watch him burn
He held off bank in a skidding turn.

http://www.youtube.com/watch?v=PMhoPJYCvXA http://www.youtube.com/watch?v=swk25weGyYo Here is another good video of an aircraft stalling in a skidding turn (and in slipping turns) you can see a big difference in what happens at the stall.

In a skidding turn the aircraft will drop "into" turn, in a slipping turn it will stall "out of" the turn.

http://www.youtube.com/watch?v=wioGN2SPGps

You do need to correct your bank and bring it back to horizontal flight with the ailerons . This is not so pronounced with a trainer because of the dihedral but when you have little or no dihedral you need to correct your bank with opposite aileron .

I always set up my ailerons W/the servo arm @ 5 O'clock (forward) @ neutral. That achieves mechanical aileron differential, less down than up aileron deflection. That reduced drag on the high wing & also reduces the need for a lot of rudder imput for a coordinated turn.

The skidded turn video is amazing!!! Thanks for sharing!

looks like simulator may be more forgiving than a real plane; maybe more than a model plane. Although I actually find a real model to be easier than RealFlight for some reason.

Some contributors seem to have a fundamental mis-understanding of what the rudder is for.
If you want to steer with rudder, get a boat!
An aircraft is NOT turned with its rudder, if anything the rudder is there to assist the fin to keep it straight on into the airflow, not turn it out of the airflow. Aerobatics such as flat turns, knife edge etc are a different thing - normal balanced flight and proper turns which is what beginners should be doing, use the rudder to keep straight on into the airflow and not to turn or to hold the nose up etc.

An aircraft turns by using the enormous power of the wing lift to move it sideways when the wing is banked. The fin keeps it straight on into the flow thus also making the plane rotate as it changes direction. If the fin does not do the job properly then rudder is used to help it keep the plane going straight on into the airflow. In power planes the slip ball tells the pilot what to do to keep the ball centred, in gliders a yaw string is commonly used. Turns should always be made with the ball/string in the centre, using the rudder if required to keep it there. Turns are never made by pushing the rudder to make the ball/string go off centre. Bank is controlled by ailerons, not by rudder. If you have enough dihedral then a secondary, not a primary, effect of using rudder is to get bank but only after yawing out of balance. Rudder controls yaw, if you want to bank you use the ailerons. If you get adverse yaw while rolling then use rudder to stop it, but that is rudder being used to keep the plane straight to the flow, not to turn it.

You use ailerons to control bank, rudder only if required to keep the plane straight on into the airflow, and as much elevator as required to keep the nose up, even at extreme angles of bank it is the elevator not the rudder that is used to keep the nose up. Please note that a "normal" turn at 90 degrees angle of bank is impossible, by then it has become an aerobatic knife edge manoeuvre, not a normal turn. In general beginners should not be messing about with the rudder during turns as that is the way to get into a spin when turning low and slow coming in to land. Any decent trainer model will not need rudder for turns.

If the nose is dropping and the plane is losing height then it is simply a matter of pulling back further on the elevator. The amount you have to pull back goes up exponentially with the angle of bank, so as the bank gets steeper the extra that you have to pull back goes up more rapidly than the same change at small angles of bank.

Losing altitude in a turn is something you prevent by using up elevator, not by trying to make the turn flatter.

With a model there's no precise way to tell whether your turn is coordinated, because you have no turn-and-bank indicator and you can't feel the seat pushing on one side of your rear end. But you can be sure that if you are cross-controlled your turn isn't coordinated. I get the sense that most of your difficulties come from your apparent belief that flatter turns are desirable. They aren't, except as a way of having fun by making the plane do something that planes don't normally do. Banking is the essence of turning: it makes the lift vector point to the side, and that is what makes the plane turn. The rudder is there mostly to prevent adverse yaw, as Rob2160 explained earlier. It isn't the primary turn control. Even a plane with no ailerons normally turns by banking, because the rudder induces yaw, which, because of the dihedral, makes the plane bank.

http://www.youtube.com/watch?v=uUWZ1M9BxbA
If that's the one you mean, it's a magnificent example of why the average public should not be allowed to publish anything on the internet. It is dangerously and completely wrong. PLEASE ignore what he tells you in that video.

That's funny, being that we are flying models and don't need to worry about passenger comfort or max efficiency I thought we were free to use rudder as we deem fit.

The rudder is used to keep the nose from pointing high or in other words to keep the tail from sinking. Most non-trainer type airfcraft will need the rudder to keep the axis of the fuselage poniting straight in relationship to the path of flight. As mentioned, it is not to prevent loosing altitude, that is the elevator's function. In a scale aircraft, it take ailerons, rudder & elevator for a coordinated turn.

For those that say the rudder is not for turning. Have you ever flown a 3-channel ship? A rudder that is roll coupled will also bank the aircraft when used. My Sr Tel;emaster had so much roll couple in the rudder, I used full cross control rudder/aileron for knife edge & just released the aileron & keep the (up) rudder in to roll out level.

I don't think anyone will disagree that you can use rudder to turn, as it will change the direction of aircraft flight.

You can also use the secondary effect of rudder very effectively to bank an aircraft. (3 channel aircraft without ailerons work this way)

As a training exercise, in real aircraft I would get the student to fly back to the airport and line up on final using nothing except rudder, elevator trim wheel and throttle. IE hands totally off the joystick (This was simulating a total loss of elevator and aileron control ). It was entirely possible to fly the aircraft that way and is easier than one might expect.

I also agree there are many applications where you deliberately would fly out of balance. But if we are talking about performing a smooth balanced 'efficient' turn in an aircraft the rudder is primarily there to balance adverse yaw and the turn is achieved by tilting the lift vector into the direction you wish to turn. IE Banking.

Yes you need more elevator to stop the nose from dropping as the lift vector is no longer vertical. The greater the bank the more elevator you need for a level turn. At 60 degrees bank you need to sustain 2 G for a level turn. That means twice the angle of attack you have in 1 G level flight assuming a constant airspeed, IE that's a lot of elevator,

I know we are talking here about trainers and flat turns, but in many Imac turns, flying in the box, many aileron turns are hard banked and approach knife edge. Opposite rudder is often needed to keep the nose from dropping to prevent down grading in the maneuver

Not really, during an IMAC sequence there are no turns at all per say. All direction changes are done via turn around maneuver. Point rolls and rolling circles however require lots of rudder work both same direction as roll and opposite.

My full-size instructor said to lead with the rudder.

No disrespect to your instructor but that is a habit you will have to unlearn if you ever fly for an airline.

Otherwise each time you make a turn leading with rudder everyone in the back of the plane will spill their drinks or become violently ill.

Airliners and corporate jets use a yaw damper and usually have roll spoilers which allow you to bank without inducing adverse yaw so the rudder pedals are basically foot rests in flight unless an engine fails.

yup, that may be true, for say a 172..
but (in most cases) you don't want to do that in a gulfstream, a C-5 galaxy or a citation even.


different types of airplanes need to be flown differently, full scale or model.

an F3A airplane is flown with a different technique than an ugly stick (or a cub, or an F-4, sopwith, etc)
different airplanes need different technique and different amounts of finesse.
(with some airplanes you can bang the sticks around without worrying, while other airplanes may head south in a hurry if a pilot 'ham fists' the controls)

:D my point exactly! (well, YOUR point, actually Rob. ;) )

Not a problem - the Cessna 172 banks w/o rudder inputs anyway.

That's true....the end box turn around maneuvers are usually combinations of split Ss,, sharks teeth, or 1/2 cubans, but I still maintain that yank and bank turns even for my jets need opposite rudder to keep the nose up.
Also...I'm assuming that Red Bull pylon racers are using opposite rudder as they are almost at knife edge as they turn around the pylons

Kinda depends on the airplane's attitude, I spend some flights in knife edge flight more then wings level while utilizing rudder to maintain altitude, climb, or dive and elevator to keep the axis of the fuse pointed straight to the path of flight. When I am flying knife edge loops, rudder is all about gaining or losing altitude.

Bob

Sure. But this is the beginners forum, and the OP was talking about how to make ordinary turns with a trainer, having gotten the impression from a ridiculous YouTube video that he was supposed to turn without banking much so as not to lose altitude. How we got from that to aerobatics, I don't know. When you're knife edged, the rudder functions much as the elevator normally does, and vice versa. But that information isn't really of much use to the OP, I suspect.

If your nose drops in turns it's a good indication you are nose heavy or have a roll couple when elevator is applied.

Great stuff here!!! I've been looking for information on this in other sites and I have not seen this range of input/information elsewhere!.

After seeing the video about slide turns and looking up coordinated turns, I think that coordinated turns is probably the better thing to do. But, as other(s) have pointed out, knowing that you are a coordinated in a model or simulator's not easy or possible, not like on a real plane.

Which brings up another related topic, the fact that a real plane behaves and has different characteristics than a model, a model has different characteristics than a simulator. For example, I have made continuous 90 degree turns in simulator with a trainer.
- I suspect that a real trainer plane does not have enough power to do this, and would suffer a catastrophic structural failure if it came close to a 90 degree turn.
- I suspect that a model HAS enough power; but some, maybe many, of the trainers/ARFS would suffer structural failure in a 90 degree turn.

Yet it can be done in a simulator.

AND; not only is plane different from model different from simulator, but BIG differences between one model an another!!!

I'll add something else to the thread; some of the points/advice carry with them some context. For example, the statements
"If you want to steer with rudder, get a boat!
An aircraft is NOT turned with its rudder "

Well, I think this completely overlooks 3 channel planes with rudder only, doesn't it!!! The unspoken context here is "for 4 channel aircraft"; with an additional implication of "the design of the aircraft is such that the aileron is the preferred means of turning".

I came to this topic because I was wanting to improve my eye/hand coordination, specifically in the use of the rudder, for 2 issues

1) When coming in for a landing, especially at low elevation, I may want to make some adjustments to direction with little to no bank, so that the wing tip does not hit the ground. I believe that this skill will also help in cross wind landing as well, wouldn't it?
2) What if you lose ailerons? Hasn't happened to me; but I HAVE missed something on pre-flight and gone up with ailerons reversed-twice! In both cases, I quickly understood what the problem was. The first time I didn't have enough skill with rudder to keep the plane from augering in. The second time I WAS able to save the plane!!! So I find that skill useful.

After learning "rudder if aileron fails", I'm thinking of "power if elevator fails". That one seems a bit easier, as we practice that on final approach anyway.

Regards

Full size A/C have a lot of variation in how much rudder is used and when. It's interesting to compare an Erocoupe with no rudder pedals and coupled rudders to same vintage A/C that require rudder input to maintain a co-ordinated turn. Many of the later light A/C really use the rudder very little. I've flown A/C that really only use the rudder to correct torque steer on takeoff. Once in flight,
only very minimal rudder might be needed to keep the ball "in the box".

There is no fundamental difference between the characteristics of a model and a full size. There is only one set of laws of physics! The laws of physics do not recognise "model" or "full-size". There are differences due to size but the difference between a large model and a full size Cessna 150 is a lot smaller than the difference between a full size C150 and a full size Boeing 747, so the phrase that models are different to full-size which is often trotted out, is just plain wrong.

I did not overlook 3 channel planes, if you like to read my whole post i talked about the secondary effect of rudder being roll on a plane with dihedral but that it is untidy since the first thing you get is yaw out of balanced flight. 3 channel models are a hangover from long ago when channels and servos were very expensive, model radios started with just one channel bolted onto a stable free flight models with lots of dihedral. But if you have ailerons, the correct way to control bank is with aileron. Ailerons cause adverse yaw yet you don't hear anyone saying to control yaw with aileron do you? Equally wrong is trying to control bank with rudder! Yes I know you can and in certain circumstances when you have ailerons it is ok or even necessary to use rudder, I have plenty full size experience using rudder in the right circumstances, but usually those are in special and experienced circumstances, beginners should stick to - aileron for roll, rudder for yaw.

You also mention not using aileron at very low level when landing so that the wing tip does not hit the ground. If you use rudder when slow the wing tip will hit the ground very hard as the model starts to flick/spin! The control inputs to generate a flick/spin are up elevator and rudder. If you are slow, then you have a lot of up elevator, so adding rudder is asking for trouble. It's why its so dangerous for untrained people to say use rudder to steer when on landing approach, it's always aileron.

Some say "lead with rudder" which is misunderstanding what some instructors phrase very poorly. You never use rudder before aileron, what they mean but express very badly is be using rudder as you use the aileron to counter a plane that has strong adverse yaw, don't wait for the yaw and then use rudder. Also what they mean is use the rudder to stop the adverse yaw, use the rudder to keep the plane straight, they don't mean use the rudder to turn the plane.

The sims are really games at heart and don't want to make it as difficult as it really is. The model flight sims do have good uses but they also have their limits, I recall one chap in my club telling me he could do rolling circles, turned out he meant on his sim, and he could, I saw him do it, yet in the real world he couldn't fly a level turn never mind a rolling circle!

No plane can do a "proper" turn at 90 degrees of bank, it is physically impossible. By "proper" turn I mean a balanced level turn, not an aerobatic knife edge manouevre. Any plane can do a balanced turn at 90 degrees of bank but it won't be a level turn - a level turn means maintaining height. It must lose height. The wing is what holds a plane up. When banked the lift force is angled away from vertical, that's what makes the plane turn, but there is not enough vertical component so the total lift must be increased. That's why you pull back on elevator, to increase the angle of attack and get more lift, it's also why the stall speed rises when you turn. But at 90 degrees of bank, all the lift force is pointing sideways, there is no vertical component, so no wing lift to hold the plane up. It must either lose height, or the pilot goes knife edge to get lift from the fuz, but for those of you who have no experience of full-size aerobatics, believe me it is most uncomfortable for those not used to it, and the drag rise is a heavy penalty. It is potentially dangerous since it is up elevator and lots of rudder, again the controls for a spin/flick, so should only be done by experienced pilots with a suitable model and safe height.

For HarryC and others more technically inclined:
I usually try to avoid getting to technical as there's a very wide range of knowledge in these forums, easy to get lose in it. Yes, there is only one set of laws of physics. But when we compare models of objects, even if they are "exact scale" models, they don' behave the same.
Dynamic similitude requires that kinematic, dynamic, and geometric similarity all exist simultaneously. When you take a model into a wind tunnel, or a tank, you can get one set of dimensionless parameters to match (eg, Reynolds number), but then another one (mach number) is not representative. The smaller the scale, the worse it gets. That is one of the challenges in wind tunnels, getting a model big enough to be close to similitude, without being prohibitively expensive.
My memory is fuzzy on this as it's been a number of year, but I recall reading about the difficulties in doing hypersonic testing (mach 20); eventually they went to full scale testing rather than rely on scale models. Results on that weren't encouraging.