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what is the use of Rudder when having Ailerons to turn?

#1
Hey everyone,

I have been wondering about this for a few days now: What do planes use their rudder for when they have ailerons? I understand that 3D planes need rudder for their awesome crazyness, but what do 'normal' planes use it for? A plane can turn using it's ailerons right? Or can only delta-shaped planes do that with elevons?
With ailerons you can also make a full turn, so why would you put a rudder on a plane? I don't get it!?
It's possible that I don't understand this because I have never flown a 4 CH plane before... Is the rudder useful to make 'beautiful' turns where the plane doesn't have to completely bank to turn around? Is the rudder useful for making smooth, nice turns? I don't get it. I will probably find out when I buy a PZ T-28 Trojan. It would be nice to know before hand though.

Silvester
 

joshuabardwell

Senior Member
Mentor
#3
Rudder is used to coordinate turns. Coordinated turns are more of an issue for full-scale aircraft, or gliders since efficiency is paramount. Coordinated turns in RC are a mark of a refined pilot.

Rudder is more effective than ailerons at low air speed. Rudder can be used at low speed without stalling the down-elevator wing. When landing, rudder allows you to point the plane straight down the runway without banking the wings. A turn combining rudder and aileron will typically be faster/tighter than a turn with aileron/elevator only.

EDIT: I would also add that, if you have a glider where you have set up crow mixing to help you land without overshooting your spot, the rudder can be used to turn/point the plane while the ailerons/flaps are being used to crow.
 
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Snarls

Gravity Tester
Mentor
#4
Also in full scale aircraft you will want to turn with rudder and ailerons to avoid crazy bank angles or else your passengers will not be very happy. This is because rudder will turn the plane via yawing, while ailerons turn the aircraft via roll. In RC, rudder is less necessary for basic flight. Like joshuabardwell says, more experienced pilots use rudder for clean, realistic coordinated turns. Rudder is not necessary for most flights, but it is used when you get more technical.
 

rcspaceflight

creator of virtual planes
#5
Basically you need rudder if you fly 3D or scale. You can't expect an RC plane to fly like the real thing if you're missing an axis to rotate around.

However, there are some RC planes that don't need rudder and it's a waste of the extra weight to install the rudder. Mainly small fast warbirds. "Bank and Yank" is usually good enough for most RC planes, but it does remove some things you can do. You don't need a 3D plane to be able to knife edge but you do need rudder.

The the main purpose for rudder in the RC world is when you fly in the wind. Rudder is mandatory if it's windy enough out.

The best way to understand the importance of rudder is to fly a 4 channel and use the rudder. It's why simulators where made. Download RC Desk Pilot and play around with the rudder and see what you can do with it.
 

Ace2317

Senior Member
#6
The biggest benefit of (non-3D) RC planes is lining up a landing. You can basically straighten the plane without tipping the wings too far from level. It's been mentioned before, but I thought I would throw my hat in as well.

Also, as you get into bigger planes, it makes it a lot easier to turn without dropping altitude.
 
#7
If you fly an abomination like a correctly powered (read underpowered by our standards) Cub you will find that when banking for a turn the high wing will swing quite a long way back from the direction of travel. This is induced drag (drag made by the creation of more lift on that side then that on the other). This presents, to differing degrees, your whole fuseage to the direction of airflow creating massive amounts of drag. Now, you can use that when landing to help shorten your approach but what most often happens when you don't have an excess of power is your plane slows dramatically, the high wing (that's making soo much lift) stalls first and your plane does an over the top snap. This kills many full scale glider and flying abomination (Cub) pilots.

Now in many cases a goodly amount of people never fly co-ordinated turns. They use the rudder to line up on the runway and sometimes don't use it much into the takeoff roll. If they are flying a scale-ish taildragger they will no the benefits of right rudder. I had a world Air mustang and plenty of SCCA scale warbirds that looked like I had just let go of a control line plane on launch, they would yaw that far to the left. But with the proper use of a rudder you can have a straight as a string takeoff and climbout realeasing rudder pressure as your speed accumulates.

Do you need a rudder? If you're plane is setup for 2 or 3 channel you pick between rudder/elevator or aileron/elevator. But flying 4 channel it's nice to use the whole options.
And flying any 3D as stated, you will be flying rudder, throttle and elevator more then ailerons, at least during high alpha.

All that said, you don't need rudder. You don't NEED ailerons. You don't NEED elevator or throttle. FF pilots don't trim with a box, they trim on the building board, the rest of us are amateurs.

But, if you got em why not learn to use em. Makes life more fun.
 
#8
I would like to add that the rudder is helpful on take off also on a tail dragger with a big engine and prop you get a left "pull" and adding right rudder helps to keep you straight as you take off aka ROG. Sorry I don't know all the technical terms I think it's called yaw.
 

Nerobro

A Severe Lack of Sense
#11
This is going to be a long explanation, but bear with me here, I promise there's a payoff. :)

Generating lift on an airplane, also generates drag. When you want a plane to turn, you need to tip the plane in the direction of the turn, and let it's lift carry you around the turn. Tipping the plane means using the ailerons. If you want a wingtip to go up, you need to generate more lift.

So you're trying to turn left, you tip the stick to the left, and now the plane is tipping left. But for some reason it's also yawing right? Well, since you needed more lift on the right wing, it now has more drag, and is trying to twist your plane away from your turn. This is presenting the side of your fuselage to the oncoming air, slowing you down, and burning energy on drag instead of generating lift. This is not a good situation.

By using the rudder, you can counteract the tendancy for the plane to yaw away from the turn you're trying to make.

There are also other methods for doing this. "Differential aileron" is something that's often built into real airplanes. In that case, the plane lifts the inside aileron a lot more than it lowers the outside aileron. As mentioned earlier, this also helps avoid tip stalls when low and slow while making a turn. If you have a model with independent aileron channels, it's not a bad idea to program it in...

You can also use spoilers instead of ailerons, which can build in turn coordination.

Some planes are more or less naturally coordinated, and rarely need any real application of rudder. Other planes can turn better with rudder than aileron input.

The PZ UM T-28 is a plane that will fly "pretty good" without rudder input, but you really do see a difference when you start feeding in a little rudder for turns. That's a good plane to learn coordination on.
 
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