I've seen what apears to be conflicting information on placement of the throttle servos on gas engines. My Brison manual says to keep anything connected with the ignition at least 12" from anything connected to the receiver. Sounds logical. But the instructions on my 27% Aeroworks Ultimate shows the throttle servo mounted on the engine box. That means the the servo lead will pass within 6" of the ignition battery, leads, and switch. And I just read an article in the Oct '03 issue of MAN describing how to mount a gasoline engine and it uses the same servo placement. What's the true skinny on this issue?

I've mounted the throttle servo for several planes on the motor box. Several types and sizes of servos are included in that group. I've never had a problem with equipment placement or materials used EXCEPT when I used equipment that was either old or had been in a crash before. Use quality stuff and eliminate metal to metal rattles and there should be no problems.

The ideal condition is to keep the two electronic systems at least 12 inches apart.
I have had battery packs for ignition and receiver on top of each other seperated by a 1/8 inch piece of foam. It all depends on how good your ignition system is. Low noise and good ground will allow you to do this. ANY noise will cause a problem. To be safe the more distance the better.

I mount it in the motor box, just run the wires on the opposite side of the fuse from the ignition stuff. I also use a fiber-optic ignition switch. Stay away from clevises on the throttle, I use only Rocket City type ball links and bolt it all together. I had one plane that used to go to full throttle on landing, tried everything, never did figure it out.
Tom

I have mounted the ignition module both ways. Behind the firewall, and on the engine box. I always try and keep the ignition module, a minimum of 8" (more if possible) from my receiver, and I always mount the ignition switch toward the front of the aircraft, and the receiver switch toward the back of the wing, on the opposite side of the plane. By mounting the switches this way, you will avoid any chance of "RF" leakage from the ignition module and switch to the receiver. Todays radios are not as prone to noise as some of the older radios were. But by all means....... The use of a "PCM" receiver, will be a big key to avoiding radio interference from noise. Another important thing to remember is, always use good vibration (foam) protection for the module.

Thanks a lot for the info. I think I'll use the 12" rule when possible and convenient. Also will use PCM and high quality, never crashed quality electronic parts. I have an Aeroworks 27% Ultimate that I'm going to power with a Brison 3.2, and a BME 30% Edge that I'm going to power with a Brison 4.2. I'm new to gassers and really appreciate the assistance. More questions to come, I'm sure.

Mounting the batteries one on top of the other, has no bearing on the noise generated by the ignition. the ignition battery is isolated from ignition noise at the switch. Batteries make, nor do they transmit ignition noise. That's why it's important to keep the ignition switch as close to the ignition module as possible, and the receiver switch mounted as far from the ignition switch as possible. You can use the batteries anywhere you desire to achieve the proper balance.

Thanks for the input, Bob. A related question: How about the wires from the battery to their respective switches? Don't they transmit ignition noise? And if so, isn't it important to isolate ignition wiring from wires connected to the receiver? Also, what causes the switch to isolate noise transmission? Doesn't a switch merely provide a connection to allow the transmission of electrical energy from one side of the switch to the other? I'm not trying to be contrary, rather just trying to learn and understand the technical aspects of gas engines and their associated challenges.

Thanks for the help.

The switch will not have any input in the reduction of RF. I don't know of any that actually have any RF reduction qualities.

My feelings are that if all the connections are tight, clean, and secured RF will not be an issue at any switch location. Few RF problems are actually directly associated with current solid state ignition systems. It's almost always some other component that's the cause of problems. Unfortunately, it's also usually the owner that caused the problem due to poor assembly methods or old and worn out equipment.

Those that are making the transition from glow to gas usually learn the hard way that the methods they used in the past need to be upraded a bit. Secure electrical connections, tight fitting clevises, Locktite on all nuts and bolts, better receiver padding/isolation, antenna routing (that's a BIG cause of problems!), higher end equipment (another big cause), servo checks, stiffer linkages, etc., have a larger impact on RF in gassers than battery and switch locations.

Just my opinion, so don't load up the weapons just yet

DON'T THINK SO
These ignitions do NOT have a nice smooth 500ma (or whatever) draw. They take a big spike of power the instant after the spark happens. Some of the spikes are in the multi amp
range. This spike impresses a noise on the ignition battery that is equal to RPM. A battery is yards of metal and will act as an antenna and "send" the noise to the RX battery.
We spent hundreds of hours developing the "rules" on the installation needed for a CH ignition. Yes these rules were developed with AM and PPM radios. Yes PCM may or may not be better, but remember that PPM and PCM BOTH use the same FM carrier to send the signal and the first several stages of the RX are the SAME. When you lose frames with PPM the rx will send out random noise to the servos and cause them to move erratic. When you lose frames with PCM the servo is frozen. IN NEATHER CASE DO YOU HAVE CONTROL OF YOUR PLANE.
An installation shouldn't be the minmum needed to make a safe flight but the very best you can do. Give your plane a chance to live through a situtation where something has happened to the RF link

It's not the throttle servo extension that is sensitive to noise, it's the rx antenna. So keep that antenna far away from the ignition, any servo/power leads, or metal and it should be ok (not mentioning the metal to metal vibrations, that's another story). If the ignition switch is on it does not isolate the ignition battery from the ignition noise. The ignitions can send noise back to the ignition battery through the power wiring but todays ignition circuits are probably electronically filtered pretty well. The biggest source of noise on the ignition is the spark plug cable and even that is shielded pretty well. Watch out for bad ignition power connectors. They can vibrate with the engine running and that's bad news (intermittent continuity). I use the Deans Ultra for all rx and ignition power wiring on gassers. I tie a piece of nylon sewing thread around the connectors and put a tiny little drop of CA on the thread to hold the knot.

I'd keep the throttle servo on the opposite side of the engine box of ignition module. That way it won't be near the spark plug cable. And even so the throttle servo will still not pickup as much noise as the rx antenna. So I'd keep the rx back at least 12 inches. That's a good rule IMO.

Outstanding! Glad to get all the opinions and technical info. I hope this thread keeps going for awhile before we get at each other's throats. So far here's what I've gleaned: Use separation if you can. Use good equipment. Trash crashed equipment. Make good sound mechanical conections and secure them somehow. Keep asking questions - there's a wealth of knowledge out there -- no sense in reinventing the wheel.

Thanks again for the help - keep it coming

Kirk Brimmer, I'm glad that some of the more seasoned flyer's jumped in and helped with my answer to the switch placement. I stand corrected about the ignition switch. When I mentioned the switch isolated noise to the battery from the ignition, I was incorrect because just as you pointed out, the switch being in the closed, or "off" position will only stop noise when it's in the off position. What Silversurfer and TKG, says is correct. But, the use of a PCM receiver does make a difference in eliminating noise. Not just from the ignition, but also from any other RF noise that may be emitted by the "linkage," or servos. As Silversurfer said, "The placement of the receiver antenna" is very critical because it is receptive to "radio frequency" types of emissions. We should always route and exit the antenna as far away from any other wires in our aircraft as we possibly can. If you do a search on these threads, you'll find that almost everyone who flys "Giant" Gasser's, use PCM receivers. One last suggestion. Always use the brass bushings in your servo grommets. They protect against over-tightning of the servos, which can cause noise if they are mounted too rigidly. I've only been flying the "Big" ones for about 5 years so I, like you still have a lot to learn. Good luck with your project.

TKG, thanks for chiming in. You confirmed what I have said in the past.
Also, PPM and PCM are the same except for the modulation of the RF signal and the checking data that is transmitted in PCM mode that is not transmitted in PPM mode. PCM is better able to ignore the noise. It will still effect the receiver's ablilty to receive a signal.

Don't think that a PCM receiver will improve your reception in a high RF noise situation.

I agree. A PCM receiver will reject some noise, but it will not ignore noise. If the magnitude of the RFI is high enough, a PCM receiver will become just as "swamped" as a PPM version. Either way, the results will be the same except that one will leave the controls in a locked position all the way to the ground. That's my reasoning behind setting up a gasser with a PPM receiver to locate and eliminate noise before installing a PCM receiver.

Kirk
All of what has been said before is probably good advice. I would echo the sentiment that you need to plan your installation with as much separation of ignition components and on board radio components. I almost lost a plane once because on the maiden I had the charge wire from the ignition switch dangling inside the airplane, and it came close to things like the smoke pump, batteries, etc.. I would recommend you not only plan your installation in advance, but if possible run range - checks engine on and engine off, before you finalize (read that cut holes in your fuselage) your swtich postions. I use a CH ignition on my AW Edge, and I had the spark plug lead replaced with a "Bosch" cap and lead. That made a HUGE difference. Also, anything that rattles metal to metal will cause a glitch, so do use things like loctiite on your clevis nuts and things. The bottom line is that every installation will be slightly different and only the range test (running and not running) will show whether it's safe to fly.
Sam