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Range Check Problem

Old 05-22-2006, 10:00 PM
  #1  
kevod
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Default Range Check Problem

Hey Guys,

I am having some problems with my Lanier Laser/ZDZ 80.

I am running a ZDZ 80RV on a Lanier Laser guided by a Futaba 9C/R149DP PCM receiver. The radio is set to run in PCM mode.

I started having problems at a IMAC competition in California with my plane.
The throttle would randomly drop to an idle and then almost immediately return to where it was.
It was quick enough that I am not sure of this, but I originally did not think that it was going into failsafe. It did not seem to have any effect on the other control surfaces.

I took the airplane apart and found out that the spark plug wire had a small wear spot in it, which I taped up with electrical tape.
I flew it 1 more time that day, and 2 more times the next day and did not have any sort of problems.

The next week after getting home I flew it again and did not have problems for the 1st flight, but it started showing up again on the 2nd flight of the day.
Once again I took it apart and re-taped the wire, and did not experience any problems for 3 or 4 more flights when it started again, but worse.
The plane would go into lockout for anywhere from 1 - 4 seconds (this was not fun, I was in the air with 3 other planes at the time).
After I landed I did a range check and could not get more than about 30-40 feet before it would start to act up.

I let the airplane sit for about 30 minutes and did another range check (no changes to the airplane were done), and I was able to go about 150 feet with no problems at all.
I again let it sit again for about 20 minutes and did another range check, and I could not get more than about 30-40 feet again.
I originally thought that it was the ignition wire causing problems, but would that not be more consistent?

Another pilot thought that it might be the receiver, since it is so random.
I have already received and installed a new receiver in the plane and did a range check and it did awesome, but I am not totally sure of it yet.
I think that I will also be ordering a new ignition module to replace the current one. I have another ignition lined up to borrow, but have not received or installed it yet.

This plane has about 80 flights on it or so with not even a glitch, but parts do wear out over time.

I also have tried eliminating any metal to metal connections. I took off the flying wires, I disconnected the choke servo and unplugged it from the receiver. I also undid my tail wheel steering. None of these had any effect on the problem.

I thought that mayby the radio was having problems, but I have been flying a 40 size Extra since this starting happening and have had no problems at all with that airplane.

Is it possible for an ignition module to cause random interference?
Has anybody had this sort of random problem before?
Anybody have any other ideas of what to look for or do?

Thanks,
--Kevod
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Old 05-23-2006, 12:28 AM
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Gremlin Castle
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Default RE: Range Check Problem

If your R149DP receiver was 3 to 4 years old there is some chance that it could have developed a problem.

I had two in that age range fail completely. One exhibited similar behavior that you are describing. Futaba service center could not duplicate the mode of failure and returned them un repaired. I trashed them and went on.

The new one should be as reliable as anything out there but I do understand about being uneasy after experiencing that kind of failure. I reverted back to the older and no longer available R129DP and have yet to decide what to do when these start to fail. Maybe the 2.4 gig will be working for the big stuff by then.
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Old 05-23-2006, 08:14 AM
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b-mccor8
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Default RE: Range Check Problem

Kevod,
When you did your range test and got the plane to act up I assume the engine was running? Is this correct? how long have you been flying with this setup? I would start with that ign module. Also put in a new plug!!!!!! Heat can affect the porcelin around the plug and arch causing random problems. Also possible when you move the wire it pulls on the spark plug? Look for any linkages that could be worn and causing chatter esp. metal to metal... Brenden
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Old 05-23-2006, 10:17 AM
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Default RE: Range Check Problem

I'd fix whatever is rubbing on your spark plug lead.

I think it's the spark plug lead. If it's rubbed through the outer sleeve--then it could be bleeding out electrical energy. I wouldn't trust electrical tape to provide a shield against that RF leaking out.

Something as simple as a Zip tie can be used to pull the plug lead up and away from the cowl, or muffler--whatever is causing the rubbing. If your worried about the Zip tie rubbing through the plug lead--just slap a piece of 1/8" heat shrink tubing around the Zip tie before you snug it up. The heat shrink will act as a cushion between the plastic Zip tie and your soft plug lead.

You can put a very small EYE bolt in the firewall if you need an anchor point for the Zip tie. I'm always a bit shy about Zipping my plug lead to a bolt or bracket on the engine. Too hot near that cylinder head. Just screw a little EYE bolt right into the firewall and run your Zip Tie through that.

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Old 05-24-2006, 10:44 AM
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kevod
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Default RE: Range Check Problem

Thanks for the replies everybody!

Gremlin:
That is about the timeline that I would have thought that a receiver would go out, but I have only had that one in the plane for 9 months.

mccor8:
Yes the motor was running when doing the range checks. I already did the metal to metal checks and eliminated them as the problem.

I just ordered a new ignition and spark plug today (I had not even thought about a new spark plug).
It is the original spark plug. This motor has about 16 gallons of fuel through it so far.

rcpilet:
Thanks for the ideas, I will figure something out and do it next.

-- Kevod
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Old 05-24-2006, 09:45 PM
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Default RE: Range Check Problem

Interesting hearing you talk about "When these RXs start to fail". What would you consider to be a mean time (or number of flights) to failure for a properly constructed RX? You really don't hear about many going bad.
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