kram-RCU

My favorite aerobatic giant is (was) a 33% Extra-330 ARF from Modellmotoren powered by a 3W85 twin, JR 8103 radio with two 8411's on all the surfaces except rudder (pull-pull, 3 ganged 8411's).

I've got about 50 flights, no crashes on it. I went from perfect performance one day, to terror the next, getting multiple "hits" on rudder, elevator and aileron and even thottle on my last flight. By some freaky mix of skill and luck, I was able to land in one piece, partially because the "hits" seem less frequent and less intense at low throttle.

To make a long story short, I've gone over this plane and engine with a fine-toothed cob looking for a noise source. I STARTED with 24" of Nyrod throttle linkage, way-aft receivers, no metal clevises. I've taken apart every bolt and linkage, tried switching out my receivers, even the crystal module on the 8103. But I'm still getting hits on my ground checks, some even with the engine off, but more as engine is running and even more with increased rpm.

Should I change plugs? The whole ignition? HELP!!

mt

Diablo-RCU

My Feedback: (1)

Try swapping plugs first to see if that makes a difference, it's cheap too. The CM6 plugs are not resistor. There's a resistor in each plug cap, perhaps one has gone bad. You can get a set of new boots from Desert Aircraft...$40. See if you can borrow an ignition from a buddy to swap and test.

Geistware

My Feedback: (16)

Diablo,
I never knew this. Why is it that more ignition MFG don't put a resister in the cap so that regular plugs can be used? Does the resistor break down in use? Wire wound vs composite would remedy this.

G.F. Reid

My Feedback: (1)

If you're getting hits with the engine off, it seems to me that you're looking in the wrong place. Naturally if you're having problems, they're going to get worse with the engine running but any hits at all with the engine off would indicate to me that that's where you need to start your search.
The one clear indicator of radiated engine noise is that it happens only with the engine running.

Antique

My Feedback: (4)

The resistor in the cap is not what stops the radiation..The metal cap and shielded wire alone do this..NGK makes a bakelite resistor cap to use with the CM6 spark plug..A properly set airplane doesn't need a shielded wire..Look at all the thousands of Zenoah and US engines flying around out there with the stock rubber cap and no shield at all..I fly with a 20 year old Proline AM transmitter/Ace receiver and have no problems..It can be done....

Tipover

My Feedback: (44)

Lots of solid state ignition manufactures are using the plug wire shield, and shield cap as the only ground return for the plugs spark voltage. A bad idea IMO. With that setup, the shield to cap, and cap to engine connection becomes a very vital connection. Any looseness in the connections, and you have lots of high voltage static outside of the shielded system. All of the magneto systems have the High voltage ground return connected directly to the engine frame. I'd highly advise running a separate heavy ground wire from the ignition modules ground to the engines frame. That takes the load off the shield wire, and lets it do its intended job. Without the separate ground, the shield can break, and the engine will continue to run. The high voltage just jumps the ground gap, just like it does at the plugs gap. The only problem is, you may not no it until its to late.

Kevin

Diablo-RCU

My Feedback: (1)

RCignition said:
The resistor in the cap is not what stops the radiation..The metal cap and shielded wire alone do this..NGK makes a bakelite resistor cap to use with the CM6 spark plug.

That's true, but the resistor minimizes the strength of the EMI created by the secondary side of the ignition. Having a resistor and a shielded ignition is kind of like wearing a belt and suspenders. The resistor might also be protecting the electronic circuit inside the ignition box.

locoworks

if its doing it engine off, id check the receiver out, maybe the aerial is busted inside the outer plastic? could be a servo gone dodgy, unplug one channel at a time and see if one is causing the grief? try a frequency change, just in case something in the area is radiading on your usual one

dave19

My Feedback: (3)

I just had a problem with interfearance. My spark plug wasn't a resister plug. Iwas lucky I didn't crash my 1/4 scale. I put a NGK resister spark plug in and that solved it. I won't ever use any plug now that isn't a resister spark plug.

kram-RCU

Thanks a lot for the input. Sounds like I've got some workshop homework for the next several days.

I'm a relative newcomer to giant scale gas in an area almost purely dedicated to glow, so when something goes wrong, I really appreciate some experienced feedback. Great website!

mt

kram-RCU

Let me ask a very BASIC question to those of you with a lot of gas engine experience:

What distance is an adequate range check for a gas plane? Engine on or off?.....Antenna up or down?

We have an isolated field on flat ground.


mt

dirtybird

My Feedback: (5)

The Zenoah and US engines use resister spark plugs. Just try one of those engines without a resister plug and you will find that the resister does reduce RF.
Automobiles use high resistance wire for their spark plug leads to help hold down the generated RF.

tkg

My Feedback: (1)

Kram its not how far as how much.
Normal range check is a % of engine off vs engine on. Normally 10-15% is max decrease in range for safe flight.

Antique

My Feedback: (4)

Right..Should have said"But not without a resistor plug" after "it can be done"

kram-RCU

I think I've found the problem.

All the chattering seems to emanate from on of the two JR 549 FM receivers in the plane. Swapping it out for an older one consistently stopped the chattering.

NOW the problem is, I've got about eleven of these receivers, and I found similar behavior in one that I put in my yet-to-fly Yellow P-38. That makes two of eleven malfunctioning receivers, none of them crashed, all of them well-padded, one of the failures not even flown yet!

Anybody hear of problems like that? I'm about ready to switch back to Futaba. That's gonna leave a dent in the wallet!

mt

G.F. Reid

My Feedback: (1)

You can save yourself some grief and get some peace of mind by sending the tranny and rx to Tony Stillman at Radio South. I fooled around with a servo jitter problem nearly all summer trying to isolate the cause before I sent mine in. Tony found a blown transmitter final. It cost me $50 to have it repaired and the entire system checked out.

rcpilotjae-RCU

My Feedback: (21)

kram

Not necessary to switch manufactures. There are many good (if not better) receivers made by third party companies. I myself use JR equipment, but for receivers I use HiTec or FMA. Some of the best receivers I've ever used came from them. Never a problem. I've had problems with JR & Futaba receivers, but since I've used the HiTec or FMA the problems disappeared.


G.F. Reid pointed out a well worth endeavor and that's sending in your Tx and Rx to Radio South to see if there is a problem. I believe that all Radio South does is work on R/C Tx and Rx and they know what their doing. (Guys that fly the TOC get their radios tweaked by Radio South.)

And yes, I've seen receivers develop problems over time, even if not crashed or tortured. Just the weather can effect our Tx and Rx. By taking a nice warm plane out into a cold outside (or visa versa) the circuit board of our Rx and Tx expand and contract. This could eventually lead to a cracked circuit board (or part) and problems. This is just one example. Maybe a bit extreme but, different variables like this exist and can effect our expensive Tx & Rx. Even time can detune the transmit circuit in our Tx. It's a wise idea to get a tune up on our equipment after 5 years. (Just a round about figure there, nothing firm. Could be sooner or later, but hopefully not later.) Just some thoughts and my 2 cents. Good luck in finding the problem! And if it does prove to be the Rx, maybe think about a third party replacement. You might be impressed, like I was.

OUTCAST

I have seen this on more than one occasion. If you send in your receiver you will find it to be one of three problems, 1)the crystal 2)the antenna lead 3)receiver tune. The biggest cause for all of these problems is vibration.

kram-RCU

I REALLY appreciate all the input. Getting a broad spectrum of experiential advice is a lot more helpful than just local anecdotal comments.

Now for the future: assuming I've suffered vibration damage to multiple receivers : how best to protect a receiver in a giant gasser? What I'm doing now is a double wrap of 1/2" foam in a plastic baggie which is firmly fixed (not suspended) in the fuselage. Is that good enough?

Also: How to contact this "Radio South" ?

Thanks,

mt

G.F. Reid

My Feedback: (1)

Radio South is at http://www.radiosouthrc.com/ Tony Stillman is the owner and he's the guy you'll be talking to.
As for vibration protection, I've never had a problem with my receivers and this last time was the first problem I've had with a radio period. I've always wrapped my stuff just like you...but recently I was talking with John Benario, the Helicopter columnist for RCM. He happens to be in my club and was looking over my Cap. He strongly suggested that I pitch that stuff and start using the stuff that they ship VCRs, computers and just about any electonics goods in. I can't recall the name of it but it's very thin almost like paper although in reality, it's a type of foam.
I had a large quantity of it and so started using it based on his recommendation and the fact that I noticed that they use it to ship delicate electronics goods in. Besides, I figure if anybody knows vibration, it's a heli guy.

rcpilotjae-RCU

My Feedback: (21)

G.F. Reid

Funny you should mention that stuff. I don't know the name for it either, but I've been using it for about a year now with no problems. I save the stuff whenever I buy some electronic equipment and re-use it in the planes. It's thin, but is almost like foam. Good stuff in my opinion also.

PS...KF2WM (And I use a lot of electronic equipment, like you!)

kram-RCU

Late last fall I posted a question about bothersome radio interference on a big 330 gasser and got a lot of help off this forum.

My winter radio make-over included the following:

1) Switched my FM receivers out to PCM

2) Took my twin receivers' antennae out of parallel

3) One twist/inch to the longer servo leads

4) Fine-tuned the linkages on my ganged servos

5) Adopted the PCM range-check protocol from winter/2002 Horizon Hobby catalog

Now that I've got the first couple of range checks and flights done, I can report complete success. My range checks are normal beyond 250', engine on and off, and I've had no detectable hits after some "stress" flying.

Thank you for all the advice. I feel like you saved my plane from the junk-heap or, worse yet, permanent hangardom.

mt

Basil Yousif

My Feedback: (3)

Have you tried switching the transmitter out?

kram-RCU

Yep. that was one of the first things I tried: first the module, them then the whole transmitter. Neither seemed to have any effect. I suspect that the biggest positive effect was getting away from the mismatched PPM recevers and digital servos.

mt

Forgues Research

My Feedback: (7)

Here is my solution for twin antena
twin antena