I am totally new to flying and aerodynamics. My dumb question is, what is the purpose of a rudder when you have ailerons that turn the plane?

The movable rudder is used to coordinate turns and other maneuvers, and do things like cause a sideslip. As you can tell, these are things most appreciated by full scale pilots and planes.

I should add it coordinates level flight as well.

The rudder helps a great deal when taking off and landing. When you become an experienced flyer you will learn to make the airplane fly better in the air. It is somewhat like the throttle for a newby. Most new flyers set the throttle at one position and fly the entire flight. As you learn to fly better you will learn how to modulate the throttle to make the flight look more realistic and help you fly the plane better.
Lee

I think a better explanation would be the rudder controls the yaw axis, which is something the ailerons cannot do. Climbs, descents, level flight, turns, etc, all require varying amounts of rudder to be flown correctly.

Do you really think that someone who doesn't know what a rudder is for will understand what the "yaw axis" is ?

Steve

Aerodynamically an aircraft had three main controls, elevator, ailerons and rudder which in turn control pitch, roll and yaw. The point or rotation is around the point of balance of the aircraft.

Pitch is up and down movement, roll is obvious and yaw is best imagined as an aircraft 'skidding' sideways ie pointing in a different direction to the line of flight, but with the wings level.

Full size pilots use rudder a lot to balance maneuvers, unbalanced maneuvers are uncomfortable for the passengers.

Rudder can be used in model flying for the same thing to make the aircraft behave more realistically (as well as for some aerobatics), however for training purposes you don't need to use it other than to steer the aircraft on the ground. Get used to flying the plane accurately and safely and start experimenting with rudder when you get into your 'solo' phase.

Simon.

Hello, You will find the rudder is needed for take off too. On mother earth, the ailerons have no effect. If you have a nose wheel it will be connected to the rudder servo. Lets say you need to correct right while the wheels are on the ground, the nose wheel will be doing the turning. As you pick up speed on take off, the rudder is also in the right correction mode and it will take over as you leave the ground. NOTE: As speed comes up, even on the ground, the rudder will become increasingly operational. As you leave the ground you "MAY" not need the "right" correction anymore. You can then go back to neutral on the rudder stick and by then the ailerons will start taking over. I mentioned "right" a lot. Most planes will want to wander left from the torque of the engine on take off. I had a BIG, BIG, problem while learning. I usually OVER corrected creating a lot of laughs from the pits as I criss-cross the runway!!!! .. lownslo

Three words: yaw, pitch and roll. Rudder, elevator, ailerons.

The reason most beginners do not use rudder in flight is because the aircraft are designed (excessive dihedral) to couple roll induced by the ailerons to the yaw axis automatically. If you build a trainer without dihedral, you will soon see the need for rudder (yaw) control in flight.

cant lomchevak without a rudder http://www.waterstruck.com/AS/mvc-302v.mpg

again you need rudder for ground control. when landing in a cross wind rudder can help keep the plane straight, co-ordinating turns to keep the nose from dipping or climbing in a turn, and alot of aerobatics require rudder input to pull off (snap rolls, hammer heads, lomchevaks, knife edge, point rolls, rolling circle, torque rolls, etc etc etc)

when you get the hang of flying around expierement with the rudder (at a high altitude) one of the easies to try is a stall turn. bring the nose of the plane to almost striaght up (about 70 degrees) and let the plane slow down to were it just about stops. give it full left rudder and full power. the plane should fall over sideways till its pointed straight down. release the rudder and pull out to level.

for a true hammer head turn you want to be full 90 climb until the plane stops. then when the plane stops and starts to fall backwards full rudder and the wash from the prop will kick it over to the side to a straight down. really cool to see both full sized and RC exp with smoke system going some planes can take it to a next step and do a DOUBLE hammerhead.. thats one and a half times around.. thats alot of rudder.

here is a clip of a FULL SCALE aircraft doing this

http://www.bulldogairshows.com/video...ublehammer.avi

if you look close you can see the rudder in full deflection.

(note with a trainer or other plane with dihydral in the wing you may need to feed in ailerons to keep the wings "level" through the manuver.)

Actually it's the other way round, excessive dihedral is more likely found on trainers with rudder only (i.e. no ailerons) to induce roll from the yawing motion.

When you apply yaw the aircraft rotates sideways and for a split second one wing is flying faster than the other, because of the dihedral it has a greater angle of attack, hence more lift and rolls the aircraft.

The same dihedral makes a plane naturally more stable, the aerodynamics of this are a little more complicated but its all to do with angle of attack and lift generated in different attitudes.

I have flown a number of aircraft over the last 20 years with completely flat wings, no dihedral at all, they could all be flown perfectly well without using the rudder (apart from control on the ground and aerobatics).

Most beginners don't use rudder because they have their work cut out without needing the complication of worrying about a non essential control.

Simon.

Roll, Pitch, Yaw:

Wow, Pictures worth a 1000 words. Great diagram.

One thing everybody forgot to mention:

The main and basic purpose of the vertical fin/rudder is to keep the tail behind the nose!

Isn't that because thats the job of the vertical fin. and the rudder can be used to put the tail infront of the nose