years ago i tried a u.s.41cc gas engine on one of my planes ,,but the radio/receiver picked up so much interference i never could get it to work properly,, I would like to try gas engines again,, can someone tell me ( how important is it to use a PCM radio system with gas engines ??? ( can you get by with a regular radio system ?? and anyone have any tips on how to stop the radio from getting hit by interference ?? your answers and comments are greatly needed,,thank you,,,j.youngblood
My experience has been with converted weedie engines that use magneto style ignition. I have found that if you use a non-metallic throttle pushrod, and keep the throttle servo a good 6" or more away from the engine, that I have no interference problems with a standard FM receiver. I don't know how an electric ignition would play into this.
I'm have a Flybaby with a Zenoah G23. I mounted the receiver and other electronics 12" away from the engine and use a nylon throttle pushrod. I have no interference problems with a standard Futaba FM receiver.
One of the things PCM will hide is ignition interference.
Using PCM is a reasonable approach once you're sure there's no on-board interference, and the way you find out is to test the model/engine with an FM system first.
OTOH, since AM is the most susceptible to ignition-generated RF noise, test with one of those if you can find one. When the AM system is no longer affected by ignition noise, you've got the stuff well and truly killed. Cheers, Fred McClellan The House Of Balsa Dust
Conventional practice is to keep _everything_ electronic in your radio system, including wiring, 10-12" away from the engine and any associated electronics (electronic ignition, its batteries and wiring). A lot of folks cheat on this, because it's not easy to do, and get away with it. This means using nylon for throttle linkage (or non-metallic push/pull cable).
Use of resistor spark plug, and a RF shielded plug connector (usu. metal jacket) helps.
I've flown PCM for years but now fly all PPM, and in neither case have I ever had any ignition interference problems. The type of modulation, PCM or PPM (they're both FM), contrary to what some might tell you, have very little to do with protecting you from RF interference. The IMPORTANT stuff are things like using a resister spark plug, not using a metal pushrod for the throttle, keeping the receiver, antenna, and servo wiring as far away from the engine as practical, using proper grounded servo wire for long leads (you ground the shield to the ground wire ONLY at the receiver end of the extension and leave the servo end open), avoiding ANY metal on metal contact ANYWHERE on the aircraft unless it's bolted TIGHT together and won't vibrate. Stuff like that. That's all I can think of on the fly but I know there are other things to watch for. I've used the different types of ignitions (magneto, points, and electronic) and I have never had a problem with any of them due to RF interference. I'm now using a synthesized transmitter so NONE of my receivers are PCM. The are all FM/PPM and some are positive shift and some are negative shift... no problems. That tells me that a carefully thought out installation of the engine and radio gear is the most important thing for preventing RF interference from ANY source.
MJC
"j.youngblood" wrote in message news: snipped-for-privacy@posting.google.com...
You are right and I also try to maintain 12 inches between all engine stuff and RX stuff. However IF the ignition module begins to splatter things get nasty in a big hurry. Guess how I know!
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