Hi,

Another one of my stupid questions. I have a Avistar and have been just messing around on FMS with the keyboard, since it is the winter here. When you turn how do you know whether to use the ailerons or the rudder, I can't understand?


Thanks,

Rider

Hi Rider,

Making a turn in an aircraft is actually more complicated than it looks.

You have to roll towards the desired turn direction (using the ailerons) then 'climb' into the turn, using the elevator, so that height is maintained.

Just the initial roll isn't going to change your direction (it will just roll and stay on the same path!) it's only when you give up elevator that you make the turn.

The rudder can be used to make a better, or more 'coordinated' turn. By that I mean just using aileron and elevator tends to make the plane yaw away from the turn (that is the top wing 'holds back' making the plane yaw out of the turn) and giving a small amount of rudder in the same direction as the turn helps to make it smoother by getting rid of this yaw.

Hope that helped!!

Good luck!

David C.

David is basically right, except trainers with dihedral and flat bottom wings will often turn with only aileron input. It will turn at a faster rate by adding elevator and aileron. While you are in the early stages of learnig to fly only use the rudder while the plane is on the ground. Once you are airborn at a safe level then you can turn using ailerons and elevator if neccesary. It takes some practice to do coordianted turns.

Have fun!!!

Dave's answer is correct, but I have a more graphic way that I like to explain it.

Look at the image below. Now, for this example, let's say that the wing is symmetrical, so there's little or no lift involved in the process.

When the wing is banked, the plane still wants to fly straight. However, as gravity pulls the plane down, it will want to slide in the direction of Arrow "A".

When backpressure is applied to the elevator stick, the elevator will cause the nose to go in the direction of arrow "B".

The combination of "A" + "B" will bring the plane in direction "C".

So it's really a balancing act, too much elevator will cause the plane to climb through the turn, while too little will cause the plane to dive.

Now, with a flat bottom wing, we add lift to the equation. As the plane turns, the outer wing is moving through the air faster than the inside wing, therefore, it is generating more lift. The dihedral gives the wing a lot of self-righting characteristics, but you CAN get into a situation where the turn becomes so tight that the plane will want to flip over due to the excessive speed/lift of the outside wing. This is something to be careful of when hot-rodding with a trainer type plane.

Now let's look at a Rudder turn.

Typically, a 3 channel plane will have a flat bottom wing, so as the rudder is applied, the outside wing moves faster causing the plane to bank, but as the plane banks, the rudder is now turning the nose toward the ground. Up elevator helps, but only to a point, and can likely cause the plane to go into a spin. Ok, so you manage to avoid a spin, but now the plane is banked, and you want to correct the turn, so you apply opposite rudder. Since the plane is banked, the rudder also now acts to RAISE the nose, causing a Ballooning effect when you pull out of a turn.

There is some controversy as to whether or not the Wright Bros were the first to fly. It really doesn't matter, what the Wright Bros WERE the first to do, was to fly a plane that could BANK through a turn! We still use a version of their idea today.

Hey Mike,
Do you happen to teach Geometry in the real worl? Just because you and I understand what you just wrote, doesn't mean very many newbies will. []

rider,
Minnflyer's is a very nice, detailed answer to the question. I hope you will take the time to read it, and try to really understand it. Use your hand to act out the explanation, and try to visualize the air moving under the surfaces.
Dennis-

Thanks a lot guys, that is good. I was confused as to what people used when they were turning.


Rider

Rider,

There are some good answers here, and I don't want to take from them. Some of the technicalities are muddled, though.

There are a lot of factors determining how an airplane will turn including the airfoil, dihedral, etc.. blah blah. Be clear on this, though, the rudder is not for turning. Yes, it can be made to turn an airplane if there is enough dihedral, but in a 4-channel airplane that's not the intent. The rudder is for controlling yaw. To visualize yaw, imagine you're standing above the plane. Drive a stake (in your mind!) straight down through the top of it at the center of gravity. Now if you rotate around the stake that's your yaw.

The ailerons are for roll. Look at the plane from the front. Drive your imaginary stake through from nose to tail. Rotation about that stake is you roll.

The elevator is pitch. Looking at the plane from the side, dust off your stake and send it through again (at the CG). Rotation about this one (nose up/down) is pitch.

To turn you use the ailerons to roll in the desired direction. Then you apply some up elevator to pull the plane around. With smaller aircraft, that's all you need to do. You can bank and yank. It's not the "purist" approach but 9 times out of 10 it works fine.

Now, each side of the wing acts differently in the turn. One side has to produce more lift and hence more drag (called induced drag). This causes the airplane to yaw. To conteract that yaw you use the rudder. This is more pronounced in larger airplanes and some scale types (a Piper Cub is a good example). To make a coordinated turn you would apply some aileron followed by a little rudder (in the same direction) and up elevator.

Not all planes are created equal. Some don't require much rudder at all. I have an RV-4 that I can bank and yank with no noticable yaw. Some require a lot. I have a 1/4 scale Fly Baby that almost won't roll into a turn without ailerons and rudder applied simultaineously.

No explaination will tell you how to fly YOUR airplane, but knowledge of the theory will give you a good place to start fine tuning your technique. So take all this arm chair advice to the flying field and play with the controls.

One final "insight" into rudder use in turns .....

The "easiest" turn to make is (and I like that expression) to bank and yank. Roll the plane to the desired degree of bank, and pull back on the elevator (gently) to make the turn. Then, the "purists", and "full-scale" pilots tell you you have to co-ordinate the turn with Rudder.

What they are telling you is two things...

When you bank and yank, the fuselage is not actually pointing in the direction of the turn, it is typically pointing slightly above the arc of the turn. By way of description, if you bank to 45degrees, and then apply just enough elevator to keep the turn "level", the nose of the plane will be pointing up. Ths creates a (slight) inefficiency and you loose a small amount of speed because the wind is hitting the side of the fuselage, rather than running around it. The solution is to use a very little rudder in the same direction of the turn, to "yaw" the plane so that the fuselage is pointed in the direction of travel. This means that you save (a small amount) energy in the turn, which purists will notice, and appreciate, but beginners really don't need to worry about.

The Full-scale pilots need to co-ordinate turns for the above efficiency reasons, but the *real* reason is that if they do not co-ordinate their turns, their passengers will all get air-sick. Co-ordinating the turn properly means that the people on the plane feel the "G" force of the turn perpendicular to the floor of the cabin ... i.e. The passengers are not thrown from side to side when the plane turns.

So, co-ordinated turns are a big thing, but for a beginner, there is no real reason to try to add rudder to a turn.

On the other hand, the rudder is a useful control surface in the air, but IMHO, other than taxiing, landing, and take-off, you can pretty much forget that the (propperly trimmed) rudder even exists (that is, unless you are doing aerobatics).

Back to your original question... When to use rudder or aileron to turn with your avistar...

You CAN turn using just the rudder on the avistar (because of it;s dihedral), but you will not be able to do the same with your next plane. So, learn to turn with the aileron/elevator combination. Bank the plane using ailerons to about 30 degrees (a little aileron until the plane is at the right angle... then return the ailrons to neutral). Then, pull back gently on the elevator, and the plane will execute a nice gentle turn.

gus

Thanks gus, this is the best explanation of rudder use I've ever read!

Dave