Could someone please explane to me what this function is used for, thanx??

Most smaller R/C planes do not need rudder input to complete a clean looking turn but the bigger the plane is, the more rudder it needs to keep from making that sloppy looking sliding turn that ailerons only will produce.

A little rudder (I usually use about 30%) in the same direction of the turn aids the ailerons in the turn and is actually the full scale method of turning an aircraft. Ailerons alone do not do a good job in providing the needed yaw for a turn. Using aileron and rudder together produces what they call a coordinated turn. In larger models it makes a huge difference and computer radios make it very easy once programed correctly.

I'm sure there are many out there who will want to add to my simplistic post here but I hope this helps.

Have fun!

A very good explanation! He is right but if you really want to feel the whole envelope of flying then learn to use that left stick. When you are turning left add a little right rudder and vice versa. I try and teach my beginners after they have soloed to start using that rudder as that's what it's there for.

thanx for the replies, so when turning with the aileron and the plane is banked, the rudder can be used as an elevator, is that right??

But try to see it in the context of the first reply. It really does take some time and experience to feel the difference between smaller and larger designs. Once you've had your hands on the sticks of both, the differences are apparent. Ailerons are on the roll axis. In a purist sense they would do nothing more than move the wings up or down as viewed from inside the cabin. The rudder commands the yaw axis which would move the nose left or right as viewed from inside the cabin. So in theory, neither one alone is giving the desired result which is a coordinated turn. When you say the rudder is actually an elevator while the plane is on it's side is correct in a way, but not this way. We are talking about a large plane doing a scale like shallow coordinated turn, with say 10~15° of bank. If you a relatively new to the hobby, again refferring to one of the replies, start using your left hand on the 4th axis a little at a time. Do you have a particular need for that function on your radio at this time Take care_Bob

"so when turning with the aileron and the plane is banked, the rudder can be used as an elevator, is that right??"

WRONG WRONG WRONG!!!!

The rudder is always used to produce Yaw, whether to overcome adverse yaw or to produce yaw. The rudder is not an elevator. Perhaps one should search on the net for theory of flight.

Art,

I'm a little confused by your post. If I'm turning left don't I want to coordinate the turn by using some left rudder? It seems to me as though right rudder for a left turn would be crabbing.

Thanks in advance.

Doug

When in a aileron and elevator turn the nose will want to drop, so using the rudder will bring the nose back up so you don't lose any altitude. It is really noticeable with a bi-plane. When you apply opposite rudder you will cause the plane to yaw on its axis's.

I'll have to disagree with you.Slam. It is neither completely wrong, nor completely right. There are times when the 'rudder' IS used as the elevator. When doing the knife edge , the rudder IS used as the elevator and the 'elevator' IS used as the rudder. Correct?


I guess you could call it an association to assist RC pilots..

Slam....I gotta agree with Gastronom...once you have one wingtip pointed at the ground, the rudder is now the elevator, and the elevator is the rudder...assuming of course that you desire to keep the airplane in that attitude.
It might not show up on a net search, but you know it's true.
TM

thankyou all for your replies, ill try using the rudder when turning with ailerons and see how it goes.


thanx again

Hello!

Yes rudder could be used together with ailerons ...but it is only used(if ever)on large 2.5-4m slowflying high-winged airplanes...not for fast sport low winged airplanes.
Why !? Because the ailerons on large slow flying airplaens like th CUB sometimes work in the opposite direction. That is left aileron could induce a right turn. On fullscale high-winged aircraft it is normal proceedure to give both aileron and rudder to make a nice turn.
But it is a different ballgame on small models..so my advise is...Forget about coupled rudder and aileron!!! It will give you more problems then you
want.

Regards!
Jan K
Sweden

Oh heck no! The elevator is used to hold the nose up in a turn, the tighter the turn the more elevator is needed to hold it up. Yes, odd as it may seem especially when in a very steep bank where you might think that rudder holds the nose up, it is still held up by applying more and more elevator. This is necessary in order to make the required increase of lift now that the lift angle is so far off the vertical. If you are gaining or losing height in a turn, no matter how steep, then you are using too much or too little elevator, the rudder does not come into it. The rudder is used purely to fine-tune the balance of the turn if the fin is not keeping the turn in balance. in other words the rudder is still just used to keep the plane straight on into its airflow regardless of how much bank is used.

Do not confuse this with knife-edge. Knife edge and all side-slip manouevres are out of balance flight and the rudder is being used to put the plane out of balance. Its job in a turn is to keep it in balance and not to hold the nose up.

I have flown many full-size types from gliders, through low power biplanes to jet fighters and no matter what plane, the rule is the same. In a turn, elevator to hold the nose up and rudder to keep it in balance, whether a shallow bank in a glider or 80 degrees of bank pulling against the buffet in a jet fighter. Please note that no aircraft can make a true turn at 90 degrees of bank since the lift required is infinite. To maintain height the plane would need to knife edge which by definition is an out of balance turn!

Harry

THAT is the best explanation of the use of rudder that I have ever read.

Jet

I think there is some confusing of 2 different things in many of the preceding posts, which is misleading. During a turn there are 2 different events which would require the use of rudder, but only one of these would benefit from aileron - rudder mixing.

During the act of rolling into a turn and out of a turn, there may be yaw caused by the ailerons, there may not be, it depends on the design of the plane. Gliders are particularly prone to yaw by aileron because the long span gives a big leverage. Often the yaw is opposite to the roll, eg left roll right yaw, this is called adverse yaw. During this time while aileron is applied, rudder is required to counter the yaw and keep the plane straight on into the airflow. For this, aileron - rudder mixing is useful.

As soon as the plane has been rolled to the required bank and aileron is back to neutral, any Tx mixing is negated but there may still be a need for rudder. Banking a plane makes it start to move sideways, the fin's job is to act like the feathers on an arrow or dart and cause the plane to rotate around its yaw axis. Note that the wing changes the direction of travel, the fin/rudder change the direction of pointing. If the fin is doing a perfect job there is no need for rudder during the turn. Life isn't always perfect so depending upon conditions such as spiral airflow from the prop, power setting, airspeed etc, you may need a bit of rudder with the turn or a bit of rudder out of the turn to keep the plane pointing straight into its airflow. In full-size we just look at the slip ball, or the yaw string on the glider canopy. If the ailerons are at neutral because the plane is sitting steady in its bank but needs a touch of rudder to balance the turn, Tx mixing will be of no use. Of course some stable planes need a dab of aileron to hold the bank but here any rudder mixed in is countering the adverse yaw of the aileron and is not necessarily keeping the model in a balanced turn - after all it may need more, or possibly even opposite rudder to stay in balance.

So in summary, aileron - rudder mixing compensates for adverse yaw while the ailerons are being used to roll into and out of the turn, but does nothing to keep a balanced turn. That requires you to use your rudder thumb. Judging if you need rudder, and most models can get by without it, is a matter of judging if the model appears to be crabbing sideways into the turn in which case a small amount of into turn rudder will help.

Harry

HarryC summed things up very well. Just as an added explanation, what causes the adverse yaw is the fact that there us usually (and this can vary tremendously from one design to another) more drag on the down aileron than the up aileron. This is caused by the down aileron being in clean air, while the up aileron is in the lower pressure area on top of the wing. For reasons I'm not sure of, the larger the plane the more noticible the adverse yaw will be in a turn. What is called aileron differential can help. The up aileron will have perhaps twice as much travel as the down aileron. This tends to equalize the drag on each wing allowing straighter tracking through turns. Although on my 117" span sailplane I have at least twice the up travel as down, I still have to use some rudder to keep the turn perfectly smooth. By the way, it's right rudder with a right turn and vice versa. As HarryC said, it's the elevator that keeps the nose up.