I disagree that they don't have one FFF.
Most do have one its just you can't change it in the air. Same with the wings.
I agree you don't teach the use of it apart from "see that bit of metal it's meant to be bent, please leave it alone"
From memory they are ment to be adjusted so that at cruise power at 2.5A the plane should be able to be flown with hands off and feet off the pedals. The ball should be in the middle and wings should remain level.
To adjust them if you grip them between your hands with the muscle bit at the base of your thumb and then ease them over in the opersite direction to what you require in the way of trim. It works just like a servo tab its just fixed. And it is worth doing and spending a few trial lessons getting them set up right. Makes it alot easier for the students doing nav to have a stable and in trim aircraft in all directions. Set the rudder first then the roll.
It has been known for students who have not been told about not fiddling with them to think that they have been bashed and really the plane would look much nicer with them striaght. Next trial lesson this cause's the instructor to exit the aircraft slightly grumpy and with a sore leg from having to sit with half a foot of rudder in for the last hour.
How to use it though if its fitted, its exactly the same as the pitch trim. You apply the control force required to do what you want and then adjust the trim until you require zero force. Thats in theory but most people after a while on SEP's fly it on the trim and without puting the force in with their feet they just screw the rudder trim until the ball is in the center. Its pretty much redundant on training aircraft and if say you were to see one on a school C172 I would ask first before using it. The tank selector and the rudder trim tend to be unused and have been known to break with there first use in 5 years. Not so bad with the rudder trim its just a sore leg but the tank selector could give you problems.
MJ
Last edited by mad_jock; 29th June 2006 at 20:39.