I'm converting my old Line Controlled planes to R/C, and I was planning on simply building a larger rudder with a hinged control surface, in addition to the elevators that are already there. However, someone mentioned on the Control Line board that all the planes he converted had aileron and elevator control with a fixed rudder. He didn't elaborate as to why, though.

So basically, I'm curious if I can get away with just building a new rudder. I have no doubt the plane will fly, but how it will fly is another story entirely.

Also, it seems that these line controlled planes are a little nose-heavy. Should I alter the COG at all? How far back from the leading edge of the wing should the balance point be?

Thanks.

Charles.

You can do both, but you need to know a few things first..
Planes with rudder and elevator typically have a lot of dehidral at teh wing joint. Not to mention are typically a 'high wing' airplane. With lots of dehidral, the plane tends to right itself. It's a typical thing of trainers, to have big dehydral, as it offers a self righting airframe. The rudder tends to 'kick' the tail in the desired direction, initiating the turn, and teh plane will then level out to a level (neutral) attitude once the rudder input is neutral.

If you don't have dehydral, or at least very little (typical of most low wing airplanes)*, you'll need something to help bank the airframe for a turn, typically done with ailerons. Once the plane has banked, the elevator can be used to pull into the bank, causing a turn. But the more you bank, the more you'll slip sideways (side slip) and will most likely need a bit of 'up' once the turn is made. The nose will tend to start to dip down durignthe turn.

As for eh CG, it's typcially 30 - 35% of teh MAC - mean average chord of teh wing.. that is, if it's a constant chord wing (straight, no taper or sweep) it'll be about 30 - 35% of eh total wing width. For tapered or swept wings, you have to do some math.. I can't remeber most, but you need to find teh average middle of the wing by adding the root chord to the tip chord, and then adding diagonal lines from the LE tip the E tip, and visa versa, where they cross will give yo the MAC...

I'm sure some else can sound in with the theory and practice. You might want to look in teh 'Aerodynamics' forum as well for this particular subject. And a plane is always more stable being nose heavy - slightly nose heavy.

*Most airplanes have some degree of dehidral. Most 'stunt planes' (Caps, Extra, Sukoi...) semingly have none. But do have a slight agle on the underside of the wing. That's why these plane 'defy normal physics' when flying.. and are considered 'harder to fly'

Sorry, I beleive the CG location shoudl be about 25% - 30% MAC, not the 30 - 35% I previously mentioned..

dr wogz has it generally right. However unless you have a good bit of experience flying R/C, I believe you would be better off cutting the wing and building in a little dihedral. If converted with a flat wing, even though they might fly, I believe they would be a significant challenge to a beginner. As to the cg, if I remember correctly, the cg on C/L aircraft was quite a bit further forward than a free flying airplane requires. 25%MAC is the most forward it should be.

Remember that without throttle control, every flight will be flat out and every landing will be dead stick. A better choice would probably be to build in some dihedral, use the rudder for primary flight control, and put the throttle on the second channel. The throttle can be used to make the airplane climb and descend, and will give you control over landing. A variety of aerobatics can be done with rudder only control including snap rolls, loops, spins wingovers, etc. They will certainly get a more vigorious workout than tethered with a wire.

All of these posts have some great merit. Take a look at the design of the airplane, rather than taking the whole thing apart and re building dihedral and rudders and etc... you might be able to throw a couple of mounts inside the wing, run some wires through it and run individual servos to the ailerons. with the advent of micro/mini servos so much is possible. I might even consider cutting servo mounts in the aft part of the fuse and running individual servos for Rudder/elevator. Just oppose them with arms on opposite side of the fuse. Typically models especially fast models are easily flown with aileron and elevator. Rudder may be used for aerobatics, slips, coordinating into cross wind etc.... but you can get away without it. Rudder in full size airplanes predominately is used to coordinate turns to prevent a sliping, or skidding turn. in the first post the gentleman mentions side slip, what he is actually describing is a skid, when the nose of the aircraft falls in the turn. This is a great reason to learn how to use your left stick and apply it other than using it as a throttle hand. So if it were my airplane, Throw some ailerons on it cut some opposing holes in the aft of the fuse (strengthen the area of course) hook up rudder, aileron and elevator. Then throw a throttle servo up there using the same method. Then go out and have fun. Micro/minis should be more than adequate for torque and will save weight also. AS far as cg goes for me I HATE MATH so if you balance off the main spar youll be in flying CG range 99 % of the time. or you could be figuring out stations, weights, arms and moments which is a pain in the arse

enough blabber LETS GO FLY

JB