Glow Plugs

Greg,

To go a little further, once firing the plug sustains combustion because of a catalytic reaction between the alcohol in the fuel and the platinum in the plug element. Sometimes impurities in the glow fuel can coat the plug element to a point of not allowing this catalytic reaction. A first sign is an RPM drop when you disconnect the booster not caused by a rich setting. They can get to a point that the engine stops when the booster is disconnected. To check this, peak out the engine with the booster still connected then observe when you remove the booster.

These contaminated plugs will still run the engine with the booster connected so some folks use them for initial runs of an engine when it is breaking in. Then you switch to a new plug for normal running.

Once contaminated I have found no way to remove the contamination. I would suggest either marking these plugs or tossing them.

George

There was considerable discussion several years ago about filament contamination caused by the use of rubber fuel bulbs. NORVEL published a warning in one of their running tips -- initially, I wasn't sure it was true since they were selling an all nylon fueler. But, I did have some plugs develop whitish frost on the filaments, even though rubber was never used in the fueling process.
I had some luck reducing it by soaking the plugs in acetone, but eventually tossed them. They glowed fine, but evidently the coating impaired the catalytic action of the platinum, as George pointed out.

Here's a nice demo of the catalytic effect in action: https://www.youtube.com/watch?v=FSdBB1vBDKY

Thanks, Andrew. I kept wondering how many glow plug elements could have been made with that piece of Platinum wire.

George

I went through the frost epidemic one summer with both Cox and Norvel plugs, exactly as Andrew described. I blamed it on Sig for a while, then on my syringes, but never really knew the source. And have not had it since that one outbreak. I seriously over-use syringes with black plungers and still have had no problems.
Rusty

There is so much to these tiny engines it's amazing. Great info here guys! Learning every day.

Greg

OK, guys -- here's some questions for those of you significantly smarter than I am (which means most).

1. Because of my OCD tendencies, if I have a plug with the filament misshapen, I'm always futzing around with a pin or toothpick trying to straighten it out. But, since ignition is catalytic, as long as it heats, it's shape should not be too important, just the available surface area exposed to the methanol. Thoughts?

2. Are we killing our plugs with our fuel blends? One of the "advantages" of castor is its ability to lubricate in high heat situations, but it does generate varnish, which can be detrimental. Would varnish deposit on the filament, blocking the catalytic action (a surface to gas reaction) or does it get burned off due to the very high heat of the filament. If it does deposit, would we be better off to use less castor and more synthetic oil to ensure a cleaner burn.

3. Lastly, if a plug's performance is lessening, could it be rejuvenated by soaking in a strong solvent to remove any soluble coating on the filament? Platinum is fairly inert and should not be affected at room temps.

Just some musings for you to consider along with your morning coffee.

I threw a couple of gummed up glowheads into my ultrasonic cleaner, the tank was filled with hot tapwater, the heads were in a small glass jar filled with denaturated ethanol.

Filaments seem clean now, I haven't tested them yet. I did check the conductivity and it was OK.

KariFS wrote:I threw a couple of gummed up glowheads into my ultrasonic cleaner, the tank was filled with hot tapwater, the heads were in a small glass jar filled with denaturated ethanol.

Filaments seem clean now, I haven't tested them yet. I did check the conductivity and it was OK.

Did you measure conductivity, or just check that current flowed. Conductivity of course is the inverse to resistance, and I've never checked. How many ohms have any of you measured across a new plug? Average a few new ones together and that'll be your baseline. I'll try it, but I don't have my Fluke anymore, just a yellow Radio Shack sweep meter. But(a big But) if these are platinum plated tungsten, the resistance or conductivity reading is irrelevant, as the tungsten core carries the current alongside the platinum, so the good stuff could have been totally destroyed and the core tungsten carries current happily, but poor catalytic action after power is removed if the platinum is degraded.

I guess that addresses Andrew's question #3.
Rusty

Cox glo heads (and similar) are good for turning the centres out for the fitment of standard glo plugs.  With careful tuning (shims under the plug) you can get albeit the same compression and performance as with a standard head.  It's my usual modus operandi now, for .049s at least.  I use plugs with idle bars almost exclusively now.

andrew wrote:There was considerable discussion several years ago about filament contamination caused by the use of rubber fuel bulbs. NORVEL published a warning in one of their running tips -- initially, I wasn't sure it was true since they were selling an all nylon fueler.

Thanks, Andrew. I've been having a problem with my Norvel using a standard plug adapter head. Engine fires up, I tweak the needle, it goes into a high speed scream for about 20 seconds, then drops down to Babe Bee type speeds. No tweaking of the needle changes that.

I crashed my Q-Tee, because it couldn't penetrate the winds, barely moved forward into the wind, scooted with the winds.

Before, even with the plug adapter head reducing compression, it still have more power than a Black Widow. I don't know what gives. I've been using a Sullivan Rubber fuel bulb, but until now hasn't seemed to give problems. Perhaps the rubber degrades over time, slightly dissolving in the fuel contaminating it?

RknRusty wrote:

KariFS wrote:I threw a couple of gummed up glowheads into my ultrasonic cleaner, the tank was filled with hot tapwater, the heads were in a small glass jar filled with denaturated ethanol.

Filaments seem clean now, I haven't tested them yet. I did check the conductivity and it was OK.

Did you measure conductivity, or just check that current flowed. Conductivity of course is the inverse to resistance, and I've never checked.

Sorry, I did not measure the actual conductivity, just checked with ohmmeter that the filament is not broken. I don't remember the resistance value, but I suppose the glow filament is like the one in a lightbulb where the resistance increases as it gets hot. So I *think* the R was pretty small on a cold plug.

Anyway, the ultrasonic worked well for cleaning the glowheads, could not see damage on the filament, nor any contamination after a few minutes wash. I am in the middle of a kitchen remodel, so my hobby time is limited (summer vacation also ended) but I'll try to check the resistances of the three plugs tonight.

GallopingGhostler wrote:
Thanks, Andrew. I've been having a problem with my Norvel using a standard plug adapter head. Engine fires up, I tweak the needle, it goes into a high speed scream for about 20 seconds, then drops down to Babe Bee type speeds. No tweaking of the needle changes that.

I crashed my Q-Tee, because it couldn't penetrate the winds, barely moved forward into the wind, scooted with the winds.

George, that sounds possibly like the not-uncommon case of the crankshaft fit being too tight and gathering a coating of aluminum that drags it down after heating up. Polishing the crank should relieve the bogging during a run that begins screaming like a Norvel should, but then bogging and slowing. It gets worse until it shuts off all together.
Rusty

KariFS wrote:Sorry, I did not measure the actual conductivity, just checked with ohmmeter that the filament is not broken. I don't remember the resistance value, but I suppose the glow filament is like the one in a lightbulb where the resistance increases as it gets hot. So I *think* the R was pretty small on a cold plug.... but I'll try to check the resistances of the three plugs tonight.

Well, I was sort of confusing with my reply. Resistance may not even be relevant since the core metal still conducts whether the platinum coating is degraded or not.
Rusty

RknRusty wrote:

GallopingGhostler wrote:Thanks, Andrew. I've been having a problem with my Norvel using a standard plug adapter head. Engine fires up, I tweak the needle, it goes into a high speed scream for about 20 seconds, then drops down to Babe Bee type speeds. No tweaking of the needle changes that. I crashed my Q-Tee, because it couldn't penetrate the winds, barely moved forward into the wind, scooted with the winds.

George, that sounds possibly like the not-uncommon case of the crankshaft fit being too tight and gathering a coating of aluminum that drags it down after heating up. Polishing the crank should relieve the bogging during a run that begins screaming like a Norvel should, but then bogging and slowing. It gets worse until it shuts off all together. Rusty

Thanks, Rusty, I had no clue and was really baffling. I'll disassemble the engine and do that. It was running very disappointing, last flight I had zilch wind penetration, which is unusual for a Norvel. That would explain why it initially ran like a top even with the glow plug head. Of course if I put the original Norvel head or used a Cox, I would get even more performance, but even on a sport model the performance still was sparkling with the slightly lowered compression.

Basically at the end I had an OK Cub Norvel, LOL.

George -
The problems you're having quite possibly may be due to the situation Rusty described. Since you're getting a good initial run, the bogging down may be shaft drag when the engine heats up. As soon as it stops, check the shaft journal for heating. If it's exceptionally hot, then pull and polish the crankshaft. I've started with 800 grit and oil, then finished up with 1000 grit to get a mirror polish.

A 20 second run pretty well eliminates running off prime and with no response to needling, binding or over heating would be my next bet. What prop are you running? If it's a 6x3 or a 6x2, I would try 5x3 or maybe a 5.25x3.

andrew

Hi,

Maybe I wrote something stupid but when your engine after the best 20 seconds is a little too hot, what oil % do you have in your fuel ? Which oil type ? All synth or castor synth blend ?

Rémy

navion34 wrote:Hi, Maybe I wrote something stupid but when your engine after the best 20 seconds is a little too hot, what oil % do you have in your fuel ? Which oil type ? All synth or castor synth blend ? Rémy

Using Wildcat 15% nitro aircraft fuel with 16% oil package (80% synth, 20% Castor) to which I added 12 oz Byron Castor to 1 gal fuel. Final oil package is 11.5% synth, 11.7% Castor.

George,

Based on your numbers your nitro content is roughly 13.8%, not much for a Norvel. Not sure if 23% oil is a good thing either, but I can't speak with any knowledge on that aspect.

That 13.8% could be even less if the fuel has been sitting around for a while. Just a thought.

Edit:

Another possibility is compression. I've noticed on Cox engines that as they warm up the RPM's drop off due to the cylinder expanding resulting in a poor PC fit.

navion34 wrote:Hi,

Maybe I wrote something stupid but when your engine after the best 20 seconds is a little too hot, what oil % do you have in your fuel ? Which oil type ? All synth or castor synth blend ?

Rémy

Not stupid at all, Remy, that's one of the first things to address when an engine is doing the lean sag. We see it all the time on the 35 engines on these 100F days. The crankshaft fit is on my mind because I was completely frustrated when it kept doing it after all the usual suspects were eliminated, and I've seen it since then too. We had a case over on Stunthangar which turned out to be that. Polished the crank and zoom zoom.
Rusty

RknRusty wrote:

navion34 wrote:Hi,

Maybe I wrote something stupid but when your engine after the best 20 seconds is a little too hot, what oil % do you have in your fuel ? Which oil type ? All synth or castor synth blend ?

Rémy

Not stupid at all, Remy, that's one of the first things to address when an engine is doing the lean sag. We see it all the time on the 35 engines on these 100F days. The crankshaft fit is on my mind because I was completely frustrated when it kept doing it after all the usual suspects were eliminated, and I've seen it since then too. We had a case over on Stunthangar which turned out to be that. Polished the crank and zoom zoom.
Rusty

i rember last year here in it went to 120.2f and the baby bird i was looking after (im a wildlife officer well me and mum ) died of heat stroke after 4weeks in my care sad

Ron, AFAIK the Europeans and Russia are used to using no nitro or FAI fuel due to the high cost and hard to obtain nitro. Fuel has worked out for me. Yes, it is perhaps not as optimal for an ABC or ABN Schnerle, but it has worked out for me without having to procure separate fuel.

The extra few percent oil of which at least half is Castor provides a sense of prophylaxis. The half synth content prevents excessive varnishing.

I think Rusty and Andrew have hit the nail on the head. I'll know more when I break the engine apart. Before, the engine ran like a top, but over time it has slowly degraded. So, from a performance standpoint the fuel has worked for me. Besides the CL engines, I've used it in my Thunder Tiger ABC .15GP Magnum RC engine, and it doesn't complain. Besides, if I encounter a lean run, it helps to prevent destroying chrome or nickel finish in the cylinder.

Here's the result when combine with flying on a windy Clovis day.

Before:


After:

Yeouch that hurts, George. I look forward to hopefully seeing good results of your surgery on this engine.

Too bad about your baby birdy, Greg. We've nursed a few of them back to life over the years. Some went well and others, not such happy endings.
Rusty

Damit Man !! That hi wing looks like it would have a lot of lift , with the wing Ya'll Have would you not bee better flying low wing airplanes ?? Or did you just lose power ? Eric