I am getting some bad interference with a 27% extra and da50 engine, brand new. Weird part is that with the engine off I get no glitches at all. I have over a foot between all the engine components and receiver. I even used all plastic rods to go into the engine box. At first I had the antenna inside, then moved it outside the airplane with a little bit better but I still get glitches. It gets worse as engine power is increased.

Checked all the linkages and all are tight. I am using pull-pull and the wires are not crossed and not chafing anywhere. Without the engine running I have a perfect range check. Engine running I have half the range check before the glitches begin, rudder and throttle glitches. All the radio gear and servos are brand new, with a new engine. I am trying everything with this thing and not getting any great results. I have been running gas for awhile and never had any problems like this before.

More ideas would be great, thanks.

Try a new crystal and or receiver, also try it with all the servos unpluged except the throtle servo then start plugging one servo at a time until it happens.

Albert

How old is the DA? Try replacing the spark plug with a new one.

You say you have 1 foot seperation. Does that include all wires??? Interference can travel down servo extensions.

PCM or PPM?

Not uncommon to have interference only with engine running. Just figuring it out can take a tad bit.

Can you provide pictures of your radio compartment? So we can try to help.

What about your batteries? Are the RX batteries seperated from the ignition by a foot? Ignition battery up front--not by the RX? Switches? 12" from ignition? Ignition switch 12" from RX?

brand new DA, and I do have over a foot between engine and receiver for the wires. All that is going to the engine box is fuel tubing and two nylon pushrods. I have battery mounted to one side of engine box, and ignition to the other. I'll try a new spark plug and see what happens. I know all the servos are all good and receiver, only get it with engine running. Going to try to mount everything in even more foam and keep trying.

Just starting to get a little frustrated with this problem.

picture

I'd put my money on the receiver or the crystal. Yes, I know you said you get good range without the engine running, but it could very well be vibration causing the problem. The thing that points me in that direction is your saying that the glitches increase with more power. The only real change with more power is more vibration. Yes, the spark plug will fire more often, but I don't think the rx would notice much of a difference between 1500 times per minute and 6500 times per minute. Both are going to be multiple times per second, so vibration is most likely the culprit. Find a way to vibrate the receiver and see if the glitches come back. Sometimes even tapping it will cause the servos to jump. It could also be a loose connection that is aggravated by the vibration, but I do feel that the vibration is the source of the problem.

HTH
Jim

check that the plug cap is tight on the base of the spark plug.this has been alot of the trouble on several gassers

I too feel vibration influences on the receiver are the cause of all evil in this case, plus the untwisted wiring, which passes all glitches unrestrained ovet the entire radio system. Twisted wires function like a choke, and prevent a lot of RF system noise.

I disagree. Twisted wires do not function as a choke. Twisted wires cancell transient cross coupling in wires. They are no help in RF interference problems.
The most likely cause of trouble in gas models is leakage of the interference from the spark plug wire. Make sure the connections are good with no breaks in the shielding and the ignition system is grounded to the engine.
Vibration can cause trouble in any component even if it is new. As suggested above remove components one at a time and check. Pay particular attention to the switches. Just bypass them one at a time and check.

thanks for all the e-mails. Are there additional ways I can ground the ignition unit to the engine? running an additional cable from ignition unit to one of the mounting bolts.

What is your exhaust setup? (stock muffler, tuned pipe...)?

That's all thats needed.
Normally ignition units are grounded thru the shield on the spark plug lead. If that does not make good contact you will have problems. Running an additional wire from the case of the ignition unit to the mounting lug will help in that case

I am running the stock pitts muffler from da. I am going to try new crystal tomorrow, grounding even more the ignition unit, new spark plug, and then another receiver.

One at a time and then see where the problem is, I'll let you know what I find, hoping that it will be an easy fix.

I would think this is vibration related (metal-metal noise induced). You have a good range check with the engine off which would indicate your electronics are working as expected. Does the reciever ever go into fail safe as the engine rpms are increased?

Make sure your pitts muffler is snug.

Dirtybird,
They do act like a choke. The twisted wire is a small diameter long stretched coil. Over here ALL longer leads are twisted so they do not pick up and/or transmit RF signals to and fro, and it seems to work very well. I twist all leads quite tightly, and heat seal the twist using a heat gun to make it permanent. As an additional advantage, the leads become more flexible and less prone to fatigue failure. Too many goodies to just pass up.

How do you have your spark plug cable set up. If the cable that goes from ignition module to spark plug is close to your muffler and as you increase power it tends to hit the muffler on and off that's where its comming from. That spark plug cable should not touch any part of your engine or muffler. Strap it to the cowl with a ziptie and test again. Interferance problems can be really frustrating but do one thing at a time and test before you go to the next change. Doing bunch of mods and test won't show you the exact problem.
Good Luck

Was out today and made a big difference. I did as some of you suggested, changed the spark plug, more foam for the receiver, and routed the cable for spark plug through the cowl with a zip tie.

Range check is good now, though I still have some interference when the antenna is inside, but I am going to keep it on the outside. This is going to be an airplane that will teach me a lot and take a good beating. After this one I'll probably goto the areoworks yak.

thanks all for the help, big relief that it's all good.

Just a question for some of you, I am wondering how much fuel some of you burn through a new gas engine before hitting the air.

If this is a DA50, break it in in the air. Running it on the ground will over heat the engine and it's not good. Run 2-3 gallons of lawnboy ashless and then switch to amsoil 100:1.
As long as settings are not extremely rich or extremely lean, you will not get a deadstick so don't worry about that. Do you have a pull-pull system? I'm thinking maybe your pull-pull cable near your anettena causing some interferance. It's not a bad idea, that you run a nyrod over one of the pull-pull cable if they cross each other.

Good Luck

Run it on the ground enough to get the needles set and as noted keeping it on the rich side is way better than being too lean. Be careful about how much time you spend setting the high speed needle as the engine will get hot pretty quick doing full power runs on the ground.

A choke is many turns of wire usually over an iron core. Just a few twists over no core cannot begin to create the inductance to call it a choke.
I have observed quite a few hot airplanes at contests over the years. Some have had twisted leads but most have not. They all seem to work equally well.
To get the benefit of twisted leads you need balanced input to the circuit. None of our equipment has balanced inputs.
Twisted leads fall into the grey area created by some partially electronic literates who think it might help. Note that very few of the manufacturers provide twisted leads on their pigtails or on their extensions. Its a waste of time and money.