Hi Traian,

This is a very good question. The short answer is: There is NO rule (nor has there ever been one) preventing the use of a CLPA rudder being controlled by a servo, as long as there is NO signal to that servo from an outside source (ex: no ground based TX). The signal must be on board the plane, or it must travel up to the plane through the control lines.

Background: This has been discussed before, and Kim and others are already working on this type of system. You may want to research some of Kim's and Igor's threads on this issue. Kim has gone beyond this with more servo controls, but it is all done well within the rules. Accurately measuring the centrifugal forces and creating a fast feed back loop will be a challenge, but I'm sure this will successfully be done by someone sooner than later. :-) 

Caution: Before the ECL basher's jump all over this issue, please let us be perfectly clear: THIS IS NOT AN ECL ISSUE. This idea can be done on ANY CLPA plane, no matter what type of power it has, WET, Ignition, 4C, 2C, Diesel, etc. There are very small micro servos with small light batteries available to all that can do this as a self contained (<3 oz) system that is not connected to the power system of the plane.

 

I remember. 

Eric said it was illegal but when I confronted with the rule book nothing came out. I was considering a Rabe rudder but a fly by was more appealing using a Diamond D47 servo 7g.

mom says first work (read money), only then toys (read job which I would like to have) 

Sounds like our spousal units are the same the world over.  VERY effective governing modes!!! 

seems like a lot of work and more weight for the same effect you get off a Rabe rudder - which weighs "bugger all" and does the same job.

why add complexity, and another component that could fail

>>>at lower speeds if the motor reduces RPM and the plane slows down you get slack in the lines and the tendency to get the plane fly inside the circle <<<

why??? seems to me like improperly trimmed/designed model ...

active motor controll does not make good model, it must be good before and only then it can be improved by such a thing ... I heard many times from guys around, that they need active controller, because model does not have tension overhead, or fall down there or there ... but it is not solution, it must be perfectly trimmed first, only then can such device help

prop thrust is variable anyway (up hill - down hill, up wind - down wind) .. model must be unsensitive to such things ... the key is keeping constant yaw angle during whole flight, during level fight, overhead, up or down the nose, in stright segment and also in corners

It should fly at constant speed 

but it is undoable, it typically slows down overhead, but still, it if it yaws in, something is wrong, probably motor offset. I would say you fly pusher prop right? it si typical problem. Pushers need mode inboard motor ofset for the rudder.

Try to watch you model at landing, it should keep the same yaw as is during flight. It needs little play with motor offset, rudder and LO. Many people were surprised with my excessive rudder offset, but model fies at the same offset at all speeds, and also in all positions. So I think there is no need for anything else than gyro compensation (and THAT IS speeed depending).

So I do not not want to disapoint you from doing servo rudder, I just think that you are trying to solve something what should be primary solved while trimming. I see good usage for servo on rudder for proper compensation of gyro moment on base of pitchig rate (true pitching rate, not derived from elevator position), speed and line tension - it is really importat in case that you want continue with active motor regulation, yawing and its oscillation will corrupt values from all your sensors. Actually I have only usual Rabe rudder, and it is reason that my regulation tends to hunt in square figures after corners, so I will need to do something in this area as well.