Thanks to all of you so much for your various ideas and solutions on electric trim! The information has been a Godsend!!!
Looking back through old newsletters, I came across the idea of an RC servo with servo tester. I saw this one as problematic from the outset, and that is why I asked for assistance. RC servos are generally pulse width modulated. That means that they always have power applied, and then you move them by sending various width pulses to them via a 3rd line. A nearby transmitter can raise havoc with such a system, especially if the PWM wire isn't shielded. A typical 5 watt AM transmitter might not be a problem, but the typical 200 watt pulse transponder box would likely wreak havoc! After reading all sorts of horror stories about runaway servos in certificated aircraft, I decided that an RC servo wouldn't be a solution. As an electrical engineer, and a 50 year veteran pilot, it seemed to me that having constant power available to ANY type of flight control servo was a bad idea. The obvious (and probably the safest/cheapest) solution, IMHO, would be something like the Allen servo. The big, bad version is $165. It provides 40 pounds of thrust as opposed to standard RC servos which are typically measured in ounces. I am intrigued by mirror motors, window motors, etc., and I'd love to try that, but we live about 900 miles from nowhere! Getting a bolt around here is a challenge, let alone finding the right motor from a junk yard! I have to take another look at the geometry of what is in my KR2 at the moment. My servo will have to be in the fuselage as I'm not going to turn the airplane upside down and cut into a finished elevator to install a servo. I plan on fuselage mounting the servo, and simply hooking it to the rod that goes to the trim tab. I would like to retain the present trim wheel, but it is butt-ugly, and in a poor location, and, well, it is just ugly!!! So there is a good chance that I will relocate the wheel and keep a portion of the existing manual system such that anything the servo does is apparent on the wheel, and the wheel is there for backup. I'll send information as this new project comes to fruition! Thanks again, everybody! Dave.
