Gasser range check/plug resistance

[FCM]

Hi everybody,

Thought it was time to add to the gasser section here (been a bit quite) so I have cut and pasted my original posting from another forum.

Just tried running up my G230RC Benzine with a new NGK CMR7H plug installed and noticed that the Rx was going in and out of fail-safe as soon as it started.

Stopped engine and installed a used Champion RZ7C and the Rx interference has stopped.

I then checked the resistance of both the Champion and NGK plugs and these were the reading obtained:

NGK CMR7H 14 Ohms

Champion RZ7C 24 Ohms

I am running with the standard unsupressed Zenoah plug cap. I have a NGK supressed cap that has a 7 Ohm reading on its own. When you attach the NGK plug to it you get 24 Ohms.

All the measurements were taken using my very cheap and simple multi meter so the figures are not 100% accurate.

Does this mean that you should not run the NGK CMR7H without a surpressed cap? It certainly would appear to be the case.

I had intended to change to NGK plugs due to the dreadful quality of the Champion plugs that I have been getting i.e. centre electrode off-centre with the outer body hole machined off-centre as well!

I would be interested to hear from anyone who has the knowledge and experience with running these plugs in their engines.

Thanks,

Paul.



Managed to do some engine-on range checks today.

Champion plug, unsupressed cap fitted.

Set up throttle fail-safe to 'cut' and was able to listen to the engine dropping down from its set fast idle speed (clutch engaged without main or tail blades fitted) as I went in and out of range.
Tx set with antenna fully collapsed (JR X-8310 PCM-S) and facing directly at the heli.

Worst range was with heli nose/side on me at a 3/4 position which made sense to me as the engine and camera mount (machined alum.)are effectively blocking the Tx antenna. I got approx. 33-36 paces/yards range at this position.

All the other 3 positions I tried gave me approx. 49 paces/yards.

Engine off gave me at least 60 paces/yards before I could no longer see the moving tail rotor blades at all 4 positions so this may be a conservative figure.

I consider that the 49 paces is a 'good' range with the engine running but am unsure about the worst case of 33-36. Sounds a bit 'short' to me.

Comments/opinions gratefully received!

Thanks, Paul.

[WillJames]

Your worst case test of 90 to 100 feet with the antenna collapsed sound like an excellent distance with the antenna collapsed to me. I don't think I can get nearly that far with my 9Z antenna collapsed.

180 Feet with the antenna collapsed is really good in my opinion. I KNOW I cannot get that far with my 9Z and the antenna collapsed. WOW you got a HOT radio!!

[FCM]

Thanks for your response William.

I must admit I was wondering if I was expecting too much from my radio. I cannot remember what to expect with a range check as I have never had a suspected range radio problem before. I do range check (engine off) before every flying session but I normally get 'out of sight range'.

The incident with the NGK plug got me worried hence the range testing today. The truth is, I have been flying with the Champion plugs for over a year and have not had a noticable range issue so as nothing else has been changed, I guess I shouldn't be using the NGK plugs without a suppressed plug cap.

Your right about my radio being hot - weather was sunny and approx. +34C before the rain came!

Cheers,

Paul.

[WillJames]

I would get advice of more experienced gasser people. With my gasser planks, I alwasy checked the range with and without the engine running. It can make a huge diference. Hopefully some more people will see this today and add some expertise.

[bigrcr]

Your range check does seem to be reasonable. The key is that when you check the range, remember what it was and compare a known "base" range to subsequent range checks. That way, if you do suspect a problem you can actually catch it.
I do not do engine OFF/ON range checks for the simple reason that I am scared to do it :shock: with that much power sitting there on the ground running and knowing that I am purposely looking for the time that it either goes out of control :shock: , or locks out!(or fails to)!!

Any r/c type resister plug as it ages (or is bad) CAN start to break down and cause RF interference. You cannot usually tell this condition from looking at the plug. Whenever in doubt with small glitches or tail "hits" always try a new plug to see if it stops. I do not run a suppressor cap on my ignition lead and have had no problems.
When in doubt change the plug to a new freshly gapped one and see.

The Champion plugs IMHO are generally not very good for r/c usage. They break down quickly and actually give less power in the gas motors than a NGK plug. However, I have had good success with the RZ7C plug that is supplied by Zenoah. I have moved to the NGK plugs and have had very good luck with these also. The NGK equivalents to the RZ7C are much less expensive.

The plug gap also plays a factor with the running and possible RF energy "bleed" around the plug cap and coil wire area. The best plug gap I have found is at twenty thousandths and I set all the plugs there. If the gap gets real wide, the energy at the plug goes way up as the gap for the spark gets "larger" trying to bridge the gap. This will also cause the end of the plug at the boot to "bleed" energy as there is also a small friction fitted gap here also.

The main thing is to do a range check initially and try to optimize it. This can be done by relocating your whip antenna (please don't use a full wire one that comes with the radio on a gas machine), relocating parts under the canopy and making sure all is right with the radio system.
Then the initial range check can be used to check the system anytime you suspect a problem or do a general range check at the field. If it is different at the same conditions, FIND OUT WHY! You will be glad you did.

Make sure during range checks that your transmitter antenna is collapsed to where it should be for your system. Some TX RF decks are to be checked at fully collapsed state and some need to be fished out to a point. Find out and do that. Also the signal is the very worst off the tip of the TX antenna as the signal radiates out from the sides of the length of it. There is very little to no signal immediately off of the tip. That's why I use worst case and point the collapsed antenna at the model during testing, this is as bad as it gets. Normally you can do nothing more than turn the transmitter pointing straight up and the range will increase, try it.

Hope this helps!

[FCM]

Thanks for all the info John.

I will certainly check my plug gap and make it 0.020" if it isn't already.

I am running with a standard Rx antenna and after reading your comments about whip antennas, I was wondering what the benefits are from using one of these instead of the standard.

I may have an installation issue with a whip antenna as my Rx is located behind the rotor shaft just about the tail boom with the antenna curled down and forward. Not sure where I could install a whip - maybe I could post a pic and you could suggest a position?

Thanks for your help.

Paul.

[FCM]

Here are a couple of still images taken from video of my current Rx antenna installation. The cream coloured box just below the tail boom is a 2.4 GHz downlink Tx but has never been an interference issue for me.

Hope these pics make sense to you!

(Free uploads here - I love it!)

Paul.

[bigrcr]

One place may be on your gyro tray above the receiver, it can point backward as good as it can toward the front. Just make sure that the antenna whip is away from all engine electrics and at a place where it is not shielded by a carbon or metal frame. Test different locations by range checking. The whip antenna has only about 5 inches of stock antenna that it solders to, so the location will need to be in the proximity of the receiver.

The standard long antenna has a much higher tendency to pick up Rf from the motor ignition component than the whip does. I know of too many folks that have had terrible issues with the standard antenna on a gas model.

Hope this helps!

[FCM]

Sounds like a good idea to fit the whip antenna. I have always wondered about the proximity to the spark plug to the end of my present antenna.

Thanks for the ideas re: mounting of the whip. I have ordered a whip from our local dealer here - I think he stocks Deans antennas so the quality should be good.

Thanks again,

Paul.

[bigrcr]

Hope it all works well for you!

Later,