I recently purchase a H9 PNP 1/4 Scale J3 Cub and have about thirty (30) flights on the airframe with no problems until today. The plane came equipped with a Zenoah 26 cc gas engine CDI Ignition. I added an Rcexl gas engine kill switch v1.3 upon receiving the airframe. Today the plane flew erratically and it displayed the typical radio interference problems to be associated while using a FM PCM receiver. I throttled back and regained full control and landed. I proceeded to do a range check with the engine off and transmitter antenna removed and got 120 paces before loss of signal. Next I performed the same range test with the engine running and got only 15 feet of range. I have a problem so where should I start? IMO it is ignition related and I'm new to gas engines.

Take the kill switch off.

I don't recommend flying without a kill switch but for troubleshooting I'd take it off and see what happens. Also look at your system and ignition switchs. Check for loose connections....If you're running a seperate battery for ignition look all those connections over well. Perhaps a change of spark plug would be in order...get the good ones from your auto parts store and don't forget the gap. If you can't find anything it might be your ignition module or lead

Your the secnd individual today who told me the same thing. Can you please explain why the kill switch would stop working. I plan to take the switch out of the loop and perform another engine on range check.

Make sure the spark plug cap is fully seated.

Anything can fail....besides if you remove the kill switch which is easy to do....You don't have to physically remove it just use a servo extension to bypass it. then you start to eliminate things that are good. if you eliminate all the good things you'll find the bad part enentually.

"Can you please explain why the kill switch would stop working"

The way toggle switches are constructed, they can allow vibration to "make and break" contact. A slide switch would eliminate this problem.

Les

Your problem is much more apt to be a poor connection at the spark plug or a break in the spark plug shielding than to be the kill switch. Of course removing the kill switch for trouble shooting will cost you nothing but time so it will not hurt to check that out. You might also check to see if there is some metal to metal connection that has become loose and is vibrating or some insulation or touching wires have become frayed and now intermittently touching when the engine is running and vibrating. Most probable cause is spark plug wire or shield followed by some metal to metal contact that is now occuring. What ever you find, please pass on to us what the solution was for our education.

It may not be a case of the kill switch failing. Sometimes, in some installations, the kill switch will allow the ignition Rf noise to be transmitted back to the receiver, causing interference like problems. I'm not familira with your particular switch. Just check it to make sure it is installed properly. Also, I know early Hitec 2.4 receivers had issues with kill switches, they correcetd with a software update.

If elimatimng or disconnection the switch corrects the problem, then you know it was either the switch or the installation. since you indicate you didn't have the problem until you installed the kill switch, it only makes sense it is one or the other.

The kill switch was installed prior to the initial flight. As I stated after thirty flights the problem appeared.

You remove your antenna and transmit for a range check? Don't know about 72 MHz at 100 mw, but that will fry a 25WVHF radio. Collapsed is the way to do it - not removed. You're not transmitting at all with it removed.

If the engine is running the kill switch is likely OK. If it is failing intermittantly so would be your engine spark &ignition. Do you have a servo within 10" of the engine magneto or e-ignition module? That will cause inductive electronic problems in the Rx circuit (don't forget that includes the throttle and any choke servo). Metal throttle rods, or any metal to metal contact can bugger 72MHz signals. Even metal geared servos can vibrate at a harmonic &cause glitching.

As has been suggested, the first place I'd check is the plug boot.

I see talk of slide versus toggle switches but if you read the original post, thats not the case here, he's talking about an electronic optical kill.

Try it without, it wont hurt anything.

Subscribed so as to learn what is discovered to be the cause.

If all the above fails you might try changing your Rx crystal (if you're not on 2.4). A bad crystal + vibration from a gasser could cause the symptoms you are seeing.

Terry

This is the exact reason I still suggest to seperate ignition components and RX components. Everything is fine until ONE item starts acting up and then RF gets into the RX. The ignition or the optical switch has an issue and is flooding the RX with RF noise. Removing the kill switch will most likely fix the problem. Do check the plug cap for damage and the braided sheilding on the plug wire.

Sounds like you are using A JR radio as they are the only brand that I am aware of that suggest a range check with the antenna off. Continue to range check as per JR instructions.

I know alot of people will not fly a gasser without an optical kill switch, I never have. I usually set the failsafe to close the carb and then run a choke servo. IMO a link between the ignition and RX is established when using one and for me I just won't go there. If you must run one take a look at some other brands. Smart Fly would be at the top of my list due to the fact that if you do have an issue you can call and speak with the owner/designer directly.