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Old Oct 24, 2012, 01:56 PM
Complete RC Idiot Savant
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One more silly question regarding glow to ignition conversion

Hi all,

Finally happily flying with the spark-conversion. Not sure if the claimed advantages in power and fuel efficiency are really paying off, but at least the engine is running smooth and constant, and the easy starting and reliable idle allready are a great improvement, and worth the price.

Now my (silly) question: I am currently using the spark plug supplied with the RCExl set.
It seems to me, there would be more brands of spark plug in the glowplug-size.
But I would not know any brand, or where to buy them.
I wonder if there is difference between the different brands (like heat grade, life span, etc etc), and does anybody have any experience with the several different spark plugs?

Especially the differences between the various brands, and users experiences I am interested in.

Thanks in advance,

Brgds, Bert
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Old Oct 24, 2012, 02:12 PM
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Rimfire

NGK This plug is available from a variety of sources.

Dale Detrich

Some of the old stuff is still around on Ebay. Stitt, Champion, etc, but they often sell at collector prices.

Rimfire seem to be the most robust and I prefer them. I've heard the latest production of the RCEXL is improved. The old ones where much inferior to RImfire, but still lasted plenty long for the typical modeler.

These small engines don't generally run hot enough for heat range to matter and there is no selection. They will foul over time because there is so much oil in the fuel.

Greg
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Old Oct 24, 2012, 02:56 PM
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Yes those are the different brands that are out there as noted by Greg.
There are a number of "no brand" Chinese plugs available too. The Chinese plugs are getting better over time. But the regular brands tend to last longer and perform a little better too.
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Old Oct 24, 2012, 02:58 PM
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Well.... I have never been able to determine cylinder temperature, but the exhaust gasses are hot enough to soften up Aluminium exhaust mufflers, and I would not be surprised if the cylinder head temp locally exceeds 150 degrees, as the engine itself stays fairly clean, but the head is pretty discoloured in the area below rocker cover and around the exhaust boss and plug. And I do not use castor, so that is not the source of discolouration.

Running 10% oil, but compression and valve seal are still OK, and valve clearance does not really change much over time: I adjusted them for the 3rd time since I bough the engine 12 years ago, and it has always laboured hard and hot (running full RPM and at least 80~90% of its max output throughout the flight)

There is for example NO liquid oil present in the exhaust gasses, and the engine leaves no smoketrail (only at idle it smokes blue like any other glow engine).

The slightly unusual running conditions made me wonder if there were different heat grades and if so, what would be the difference (Spark ignition is more or less where my biggest lack of knowledge is).

Brgds, Bert
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Old Oct 24, 2012, 03:10 PM
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In a FS-91 the plug will probably run clean. In my smaller engines they didn't run very clean, but never dirty enough to be a problem. These ignitions are pretty strong. It also depends on the fuel and oil types.

Greg
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Old Oct 24, 2012, 03:17 PM
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You check the plug often?

Is there anything that can be concluded from how the plug looks, similar like on 2 stroke gassers?

Just wondering....

Brgds, Bert
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Old Oct 25, 2012, 08:46 AM
I HATE GLOW PLUGS!
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Quote:
Originally Posted by earlwb View Post
Yes those are the different brands that are out there as noted by Greg.
There are a number of "no brand" Chinese plugs available too. The Chinese plugs are getting better over time. But the regular brands tend to last longer and perform a little better too.
Not sure about loingeveity, but the $12 made in China plugs idled a better than the rimfires & seemed a bit more stable & WOT RPM in my 300T.
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Old Oct 25, 2012, 08:54 AM
I HATE GLOW PLUGS!
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Quote:
Originally Posted by Brutus1967 View Post
Hi all,

Finally happily flying with the spark-conversion. Not sure if the claimed advantages in power and fuel efficiency are really paying off, but at least the engine is running smooth and constant, and the easy starting and reliable idle allready are a great improvement, and worth the price.

Now my (silly) question: I am currently using the spark plug supplied with the RCExl set.
It seems to me, there would be more brands of spark plug in the glowplug-size.
But I would not know any brand, or where to buy them.
I wonder if there is difference between the different brands (like heat grade, life span, etc etc), and does anybody have any experience with the several different spark plugs?

Especially the differences between the various brands, and users experiences I am interested in.

Thanks in advance,

Brgds, Bert
Every Saito engine I have tested for both CDI & GI ran 22% to 23% longer on a given size tank of fuel when converted to spark ignition. You have to just let the engine run @ WOT until you detect the 1st bit of surge iunder both ignition systems to determine the fuek usage.

WOT RPM increaesed by 150 to 200 RPM, but that sometimes requires more soark advance than the standard 28* initial setting. 34* to 36* seems to make the best power when runni g CDI/methanol.

(surface) CHT measured between the rocker covers runs a bit higher when running CDI/Methanol, but nort nearly as high as CDI/gasoline.

10% oil might be a bit low IMO as you are running a lower volume of fuel through the engine for a given power output.
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Old Oct 25, 2012, 08:56 AM
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Since nobody is sure about longevity....

Does anybody have any rough figures on that? lifetime, either in running hours or in years combined with an average flying regime?

Does a spark plug in methanol application announce its oncoming faillure?

If so, how?

I am fairly new to this particular area of model engines, and the trouble is: I knew that engine like the back of my pocket.... but now it is a complete stranger to me... Hardly gives any indication on rich or lean, no indication on running hot or not....
And it's a helicopter, so gently gliding down to mother earth and taking your time figuring out where to set her down, is out of the question....

Brgds, Bert
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Old Oct 25, 2012, 08:58 AM
I HATE GLOW PLUGS!
SrTelemaster's Avatar
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Quote:
Originally Posted by Brutus1967 View Post
You check the plug often?

Is there anything that can be concluded from how the plug looks, similar like on 2 stroke gassers?

Just wondering....

Brgds, Bert
Given the higher oil content of the fuel, it's kind of hard to "read": the plugs.

If you are getting discoloration around the exhaust port, put some teflon tape around the male threads on the exhaust pipe. You are probably leaking some oil around the exhaust pipe.

Retarded ignition timing will also result in higher EGT.

Set you timing @ about 34* BTDC for CDI/methanol.
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Old Oct 25, 2012, 09:04 AM
I HATE GLOW PLUGS!
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Quote:
Originally Posted by Brutus1967 View Post
Since nobody is sure about longevity....

Does anybody have any rough figures on that? lifetime, either in running hours or in years combined with an average flying regime?

Does a spark plug in methanol application announce its oncoming faillure?

If so, how?

I am fairly new to this particular area of model engines, and the trouble is: I knew that engine like the back of my pocket.... but now it is a complete stranger to me... Hardly gives any indication on rich or lean, no indication on running hot or not....
And it's a helicopter, so gently gliding down to mother earth and taking your time figuring out where to set her down, is out of the question....

Brgds, Bert
Any problems I ever had W/spark plugs occured @ starting, never in the air.

I keep some spares soaking in acetone @ home & blow them out W/compressed air after a long soak, then store theme in a glow plug wrench.

When a plug gets fouled (usually during starting) I switch it out for a fresh one.

You can observe the electrodes & take a plug out of service when they start to show visable (W/magnification) errosion. That takes many gallons of fuel. I burned a gallon of fuel a week for 1 1/2 seasons before I saw any visable errosion.

The Rimfire plugs seem to be suceptable to cracked insulators.
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Old Oct 25, 2012, 09:09 AM
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These small engine are essentially run as lean as they can be. They do not detonate. The needles and detents are fairly course so one click can be enough to be too lean or rich, not so much with glow fuel. I'll have to look through my parts numbers, I think there is a finer needle to fit the carb on the OS FS-91S II.

I've read about 300 hours on the Rimfires and they were not dead. It was said that the Chinese plugs failed long before this.

Quote:
Originally Posted by Brutus1967 View Post
I am fairly new to this particular area of model engines, and the trouble is: I knew that engine like the back of my pocket.... but now it is a complete stranger to me... Hardly gives any indication on rich or lean, no indication on running hot or not....
That's the best thing about about SI. The variables are relatively fixed. A spark ignition engine when set up with proper air cooling will not run hot due to needle setting, like a glow engine. The lean break is sudden, though, when the lean mixture can't support ignition, there just isn't any and it quits. Rich is certainly obvious with a prop. I don't know how to tell if it's rich in a heli. Rich mixture doesn't delay ignition like it does in glow so the effect is not as severe.

Greg
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Old Oct 25, 2012, 09:36 AM
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Originally Posted by SrTelemaster View Post
Retarded ignition timing will also result in higher EGT.

Set you timing @ about 34* BTDC for CDI/methanol.
I have the impression, that EGT was the same or slightly lower compared to glowplug operation.

Not to be a nuisance, but are you sure about that 34 degrees? Currently I am running 26 to 28 degrees before TDC. The guy who sold me the system, Pe Reivers, was absolutely convinced it should be 26~28 degrees, no difference between gas and methanol according to him.

I have always been running 10% Nitro, 10% Oil, but today I just wanted to try 2 (two) %Nitro, 15% Oil, as that is the fuel I use in my 2-strokes.
Never really measured on the 10/10 fuel, but today I tried measuring with an IR gun, using the 2% Nitro, 15% Oil
I ran regime of 2 minutes hovering with some climbs, than set down and measure, etc etc.

I can only measure from the top, that is, the entry side of the cooling air, so the cylinder temp might have been a bit higher actually.
I did 4 measurements
Backplate: 1) 40 deg, 2) 55~60 deg, 3) 55~60 deg, 4) 55~60 deg
Cyl head: 1) 85 deg, 2) 95 deg, 3) 105~110 deg, 4) 100~105 deg
Exhaust muffler: 1) 295 deg, 2) 280 deg, 3) 265~270 deg, 4) 255 deg

At the end, I measured a piece of material that was free suspended in the cooling air outlet, that showed 28 degrees (ambient was 8 degrees)

The measurements on the head were a bit difficult to get a good reading.
I tried to measure the finned area of the cylinder casting as well, but that was not really consistent. I got the impression, it never exceeded 90~95 degrees on the cylinder body.

I used the needle settings for the 10/10 fuel unchanged, and the engine did seem exactly as powerful with the 2%, and even a bit more consistent....

The things I noted:
Obviously it takes around 3 minutes at load to reach more or less constant operating temperature
Backplate (thus running gear) temperature seems OK.
I noticed that the exhaust temperature gradually reduced, and that is something I have no explanation for.
After these 8 minutes of flying (plus the idle time needed for the measurements) 11 cc of oil was expelled from the crankcase breather which is fairly consistent with the 17 cc that is usually expelled on a 12 minute flight.
Exhaust gas smelled a lot less pungent (it used to smell like the engine was "really hot"), and the smoke at idle was a lot less dense.
All in all I do not think, this fuel will harm the engine.

Brgds, Bert
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Old Oct 25, 2012, 09:53 AM
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Originally Posted by gkamysz View Post
These small engine are essentially run as lean as they can be. They do not detonate. The needles and detents are fairly course so one click can be enough to be too lean or rich, not so much with glow fuel. I'll have to look through my parts numbers, I think there is a finer needle to fit the carb on the OS FS-91S II.

I've read about 300 hours on the Rimfires and they were not dead. It was said that the Chinese plugs failed long before this.



That's the best thing about about SI. The variables are relatively fixed. A spark ignition engine when set up with proper air cooling will not run hot due to needle setting, like a glow engine. The lean break is sudden, though, when the lean mixture can't support ignition, there just isn't any and it quits. Rich is certainly obvious with a prop. I don't know how to tell if it's rich in a heli. Rich mixture doesn't delay ignition like it does in glow so the effect is not as severe.

Greg
I don't use the stock carb, but the "7H" carb with the 3 "needles".

300 Hours is plenty. this engine has run a lot, but not over 100 Hours I think...

So if I am understanding correct, the mixture has less influence on running temperature compared to glow, and lean running does not cause overheating?

I have not yet much experience obviously, but as far as I can tell, when running rich, the engine starts to run rough and seems to loose a bit power.
Lean I tried to avoid, and in this particular helicopter it is very hard to tell (severely underpowered), but I got the impression, when leaning it out carefully, the power just didn't increase anymore. At that point I backed off the needle 2 clicks.

For now, since I did not have readings from the 10/10 fuel, if just judging by smell after the helicopter is shut down, it seems to run less hot on the 2/15 fuel, and I do not notice any power difference.
Since Nitro is way more expensive compared to oil, I think it is safe, to use this 2/15 fuel as soon as the 10/10 remaining is finished....

Brgds, Bert
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Old Oct 25, 2012, 10:01 AM
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With glow the mixture also influences ignition timing. A glow engine runs hot when lean because the timing advances beyond ideal.

Backing off the needle is to avoid a lean running condition as the tank drains and it's harder for the engine to draw fuel. Your needle setting will depend on what you're comfortable with here.

Greg
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