Design > Stunt design
A Rudder isn't necessary for a Control Line plane.
Steve Thompson:
While maybe not the greatest lie ever told...
Real planes have rudders, but they don't fly in constant yaw.
My evidence:
Saw friend flying a non-flapped kick-about CL plane. I don't remember the exact plane, something like a Flying Clown. A flip over on landing knocked the rudder off. "That's OK, control line planes don't need a rudder anyway", was the sentence uttered. The flight sans rudder was quite chaotic and lasted only a couple of laps. It was flying fine before that. The crash left it needing more than a rudder reattached. So, I kind of concluded they were a good idea.
I had a Super Ringmaster that eventually lost the outboard wing. Performance was diminished, but it still flew and did loops. The inboard wing flew "a bit high", and it didn't like hard control inputs. So, I do understand that flying without appendages can be done. But it looked dumb and flew better with a wing.
So, with consideration of concepts like Center of Pressure, Weathervane, lead-out rake, Hinging, and such...
- Do control line planes need a rudder?
- How much rudder offset is right? (Just use what the instructions says?)
- How do you know if you have too much or too little rudder/offset?
Brett Buck:
--- Quote from: Steve Thompson on December 14, 2023, 02:50:32 PM ---While maybe not the greatest lie ever told...
Real planes have rudders, but they don't fly in constant yaw.
My evidence:
Saw friend flying a non-flapped kick-about CL plane. I don't remember the exact plane, something like a Flying Clown. A flip over on landing knocked the rudder off. "That's OK, control line planes don't need a rudder anyway", was the sentence uttered. The flight sans rudder was quite chaotic and lasted only a couple of laps. It was flying fine before that. The crash left it needing more than a rudder reattached. So, I kind of concluded they were a good idea.
I had a Super Ringmaster that eventually lost the outboard wing. Performance was diminished, but it still flew and did loops. The inboard wing flew "a bit high", and it didn't like hard control inputs. So, I do understand that flying without appendages can be done. But it looked dumb and flew better with a wing.
So, with consideration of concepts like Center of Pressure, Weathervane, lead-out rake, Hinging, and such...
- Do control line planes need a rudder?
- How much rudder offset is right? (Just use what the instructions says?)
- How do you know if you have too much or too little rudder/offset?
--- End quote ---
In my opinion, In general, what it needs it to be at least neutrally stable in yaw without counting on the lines. Whether you need a fin/rudder to achieve that depends mostly on how much lateral surface area you have in front of and behind the CG - say a big deep forward fuselage and a stick to hold the stab/elevator, then it will probably be unstable and require a fin/rudder. Short skinny nose and a big turtledeck fuselage is probably stable without a fin/rudder.
More subtle effects matter too, like how much yaw the prop induces, more stable and the more power/prop diameter you can handle without excessive yaw motion.
In general, you don't need rudder offset, and airfoiled fin, or anything like that. You do not want the airplane to want to crab sideways, limited only by the lines pulling it back straight. I think what you want is to fly tangent to the circle, and have as little yaw motion induced in the corners as possible.
How much offset is the right amount is best determined by test flying, start out with it at zero offset, or at least just enough to make sure it is not nosing you inboard. Set the leadouts where they would naturally fall either by using the LINEII or LINEIII computer program, or using various rules of thumb. Then fly it and adjust the offset until you get the minimal yaw motion in the corners. That will line up the leadout position and rudder offset to be consistent with each other, and if the leadouts are in the right place, you will be flying nominally tangent to the circle.
Too much/too little rudder offset (for your leadout position) will cause the airplane to yaw as you enter corners, and generally, yaw the same way on both insides and outsides. Too much inboard might cause it to come loose and chase you, or get abnormally light on the lines.
Most kit plans show large amounts of rudder offset. This seems to be to compensate for too-far-forward fixed leadouts and/or cover the possibility that the airplane is not straight, or just to add additional line tension, at the cost of cornering smoothly.
Brett
Ken Culbertson:
--- Quote from: Brett Buck on December 14, 2023, 03:44:05 PM --- Too much/too little rudder offset (for your leadout position) will cause the airplane to yaw as you enter corners, and generally, yaw the same way on both insides and outsides. Too much inboard might cause it to come loose and chase you, or get abnormally light on the lines.
--- End quote ---
This is the main reason I use the "cam" rudder. Whether it is up or down I get an extra 1/8" outboard movement at the TE of the rudder in all corners. I fly with a slightly forward leadout position and just as the line whip starts to yaw the plane in, the cam kicks in and yaws it out so what happens is it stays straight. I get no rudder at all for the first 5 degrees of elevator, so it doesn't mess with the rounds and eights like the Rabe does. It is most noticeable in the 2nd corners of the triangles and hourglass where you have a natural loss of tension. A well fed active timer can do the same thing. I like having both.
Ken
Paul Smith:
A rudder might not be needed, but a tail fin helps.
I always include a tail fin in my designs to equalize the side area of the front of the fuselage, even it the rules do not require it.
john e. holliday:
Years and years ago the late Bob Palmer wrote an article about control line planes for stunt and combat. He stated it depended on the design if a rudder was needed or not. Can't remember the plane but he stated the plane was doing an acceptable pattern. But on a flight he got too low inverted and knocked the rudder off. Any way the plane still flew the pattern with little effort. He also stated that one plane he plew would make you work your tail off to do the pattern with out the rudder. Main thing was that no rudder wit left turn would never work. This was way before Al Rabe came up with the movable rudder. I my self have set rudders straight or a degree or two off set to out side of circle. I do know too much rudder is worse than no rudder. D>K
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