So Dave how do you like your Toro?

So camcclellan did you ever get to fly your showtime with the sthil 26 on gas/glow? if you did how did it fly? is it a good combo?
please let us know I'm curious maybe I'll try that plane.

No I didn't. Aero nut I could not get the engine to run right. I have not giving up. I just haven't had the time to play with it.

sorry to hear that, what seems to be the problem?

I think it is a carb issue. I believe it needs a new carb. I rebuilt the carb and played with the needle vaules. It still won't run right.[:@]

did you ever adjusted the regulator needle below the diaphragm? it has to be slightly higher than the surface of the case.

Ralph,
I really like them. I have half a dozen of them in different configurations.

Dave

POCO242 should get the parts on Monday.
I'm planning on setting it up for Gas/Glow.

What do you think about running 2 glow plugs so I can play with the timing?
What is your favorite setup and why?

What size prop and what RPM should I expect?


Thanks

Ralphbf: I think the heigth of ports and deck heigth may have more to do with timing than glow plugs. I think 2 glow plugs will only double cost for plugs. Just my opinion. Capt,n

There was talk on a thread that basicly said with 2 glow plugs you could advance your ignition timing.

You would run 2 different heat ranges and a higher rpm the 2nd glow plug would heat and change/advance the timing.

Someone said years ago it was a common practice. It made sence to me but have not found enough evidence to try it.

Ralph,

I've been in the hobby some 40 years and way back, two glow plugs was done occasionally, my recall was that of an English made Irvine. Far too long ago, don't remember how well that worked or if there was a differing heat range strategy.

It's worth a try but how would you install two glow plugs into a conversion?

But your having mentioned it now has got me thinking of making yet another head for my Tanaka conversion. If that comes to pass and it works as you describe, I'll be sure to post the results. Neat.

You can drill and tap another hole for the second glow plug...I once put 4 more plugs in each cylinder of a racing 289cc twin...Worked well, the 4 others were still working when the center one got too hot and flame was coming out the hole...Melted the hex just like a cutting torch
Turns out they weren't needed, we ran one of the engines for two seasons with changing plugs..Worked so well we were afraid to change...They were McCoy #9s...
Glow plugs come in different heat ranges, the timing will change with the heat range...
Cold plug, retarded compared to a hot plug...

RCIGN1,

I haven't used an insert that replaces the spark plug yet but I've seen them. The glow plug threads are dead center, doesn't look like enough room for a second plug.

Or, do you mean drill and tap directly into the cylinder head?

I'll be making a clamp on head so I can custom make anything I want to try. Easy when you can see the underside.

Thanks for the tip on cold versus hot plug. I assume then that you energize the cold plug to start and then depend on the hot plug to kick in and advance the timing at full bore?

Sounds very workable. Thanks for the ideas guys.

But geez, five plugs,,, flame out the center hole, geez,,, woulda loved to have seen that.

Forgive me but I've been involved in the really itty bitty engines for a while. I assume you're referring to Reno type racing?

Reno style 100" racers...
Never though about two different heat ranges, could maybe work...
The heads on larger engines have room, no problem that way...

Ralph,
The hottest plug is going to fire first. Once ignited, the charge has no use for a second colder plug. I would run some test with different heat range plugs and take tacometer reading to see which is best. Remember that the hotter 4 cycle plugs have been used in gas/glow to keep it running without a battery. Maybe a glow driver with variable current would be a good experiment. All of the dual plug heads that I have seen were used reliability, because years ago plugs weren't as durable as in recent years. I also could see using two plugs to start the flame front at two points in a large bore engine. They use two spark plugs in many large aircraft engines for this reason. Then again, it does sound like a fun project.

Dave

Here's a thought. The head I'm making is round and has a seperate clamp affair to secure it to the cylinder. This will allow installing the glow plug off center. This allows you to orient the plug at different locations. As in closer to the incoming charge as opposed to closer to the exhaust side. Any value in trying this?

Pictured is the head in its dieselized form.

Putting the plug closer to the incoming intake charge might cause problems with the plug getting cooled off and "doused", especially at idle when the plug is having a harder time keeping hot, or at "idle up", (transition), when sometimes a blast of rich fuel is shot through the transfers if the idle is a touch rich.

I don't see how two (or more) plugs could be used to vary timing. The hotter plug is always going to set off the mixture first....

I think the most productive experiments (with glow plugs) would just be to test various heat range plugs, and see which one a given engine, load, fuel, & atmospheric condition combination likes.... It's going to be different every time one of those variables changes.

AV8TOR

AV8TOR,

Good point. But I wonder if location AND manipulation of heat range might not yield useful data. Say you're right that the incoming charge tends to cool off the plug at the intake position. So, you use the hotest plug you can find.

Or, alternately, positioned at the exhaust side, use the coldest plug you can get.

Mix and match differing positions and plug heat ranges. What might that reveal,, if anything?

In any case, a couple of hours work and nothing ventured till you try etc. Neat.

Things are always a compromise in engines, as I'm sure you know. I believe the fine line in plug selection, just as it is with spark plugs, is that getting one heat range to work ideally for all conditions is nearly impossible. The best compromise is all one can do. Experimenting is always good.

Good luck with your experiments.

AV8TOR

I have restarted an engine while diving from high up.

That said you would, heat one glow plug.
At higher RPM the 2nd plug would start to glow.
So the 2nd plug would need to be a colder plug, I'm guessing.

That would give you advance with a curve.
Both plugs the same would also give you advance with out a curve

Ralph,

I'm inclined to agree. As combustion temps go up, the colder plug may start to glow and enhance ignition. That's the theory, now on to prove it.

I've had the experience where a small glow engine would stop. Two seconds later, the starter was applied without glow heat and the engine fired right off. Three seconds later though, would give a no go. Clearly the element wasn't glowing. However, residual heat along with compression heat along with the catalytic effect of the platinum filament allowed a start. Never thought of it at the time but it would have been useful, maybe, to play with heat ranges when doing this stunt. What might we learn? That's been added to the to do list for this season.


AV8TOR,

Agree that one plug is not good for all conditions. Maybe that's where multiple plugs might have some benefit? I'd guess though that with all the R & D the engine companies have done over the years, they would have discovered the validity of this scheme. But what if they just never bothered? Here we have a gas/meth/nitro mix working very well in many cases. Something the engine companies never thought of it seems. And doing this in big engines might translate very well to small engines like a .15, for instance. Consumption of expensive glow fuel in a .15 isn't that much an issue but what if, with the smaller cubes, for whatever reason yet to be discovered, we can go with less nitro? Less methanol? That seems counterintuitive but who knows.

I've been making Biodiesel and with a little luck, I seem to have made some good product. One of the tests to determine this is to mix 10% fuel with 90% methanol and see how much is absorbed. If some fuel drops out, you have that percentage not converted to Biofuel. However, my product will mix with methanol in any ratio. This leads me to the speculation that we may have a new, hybrid fuel/engine. A diesel that uses a glow plug but is far more tolerant of compression ratio.

What for? Well, a pure glow engine delivers its best power at high rpm on smaller props. Small props are less efficient so running a diesel with more torque allows a larger prop with its attendant higher efficiency. Many have tried to make fixed compression diesels and the issue is always that even ambient temps will affect the optimum compression ratio. With a glow/diesel hybrid, this handicap might be reduced or eliminated.

So we have a hybrid fuel large gasser. We may also stumble on a hybrid diesel. Fun to try anyway. Will keep all posted on our progress.

And about plugs. On the 1/2A forum, I posted a method for making heads to take turbo plugs as used on RC cars. This can be done with a drill press and some simple hand tools. Might there be some benefit to using a turbo plug on a gasser/glow hybrid? Don't know but that's another addition to the to do list.

What makes a Turbo Plug different?

Somewhere I recently read about a guy making diesel conversions with nothing more than a slug of copper as the "glow plug". There was also a pic of something he made with the same deal, a piece of copper, but above the copper was a glow plug to heat up the copper. Different...

AV8TOR

Ralph,

In the 1/2A world, as in a Cox engine, the entire head is the glow plug. Why did they do this? If you take one of these heads and bore it out and tap for a standard glow plug, and you maintain the correct compression ratio, you lose up to 1.5K RPM, (out of 18K).

Turbo plugs have a tapered seat at the bottom of the plug, isolating the threads from the combustion chamber. If you install a turbo into a Cox head, you get back your 1500 RPM and in some cases get a little more. This allows you to play with the multiple heat ranges available. Larger engines don't use turbos because this effect is less pronounced. In this case, with a gasser, that'll likely be true as well but for a couple of hours work, no more than making a head with stock plugs, it's worth a try. Just to see.

AV8TOR,

Yes, I'm familiar with the concept. However, to work it depends on using a very expensive, all ether fuel along with the oil. The heated copper slug was to allow more leeway with compression ratio. A neat idea that's workable but that ether,,,,

A stock, diesel fuel contains typically, 50% kerosene, 30% ether and 20% oil. There are many variations on this, notably lots more oil, up to 30% for traditional, cast iron diesels. Imagine running such a fuel in a 23cc diesel. Which isn't necessary, all that oil is typically because of the bushed rods in stock model engines. We have bearings all around and this allows us to get away with down to 1% oil in some cases.

My diesel dabblings led me to try running these engines with no ether at all. Considered impossible, I managed to do just that as long as you use a high ether prime mix along with using an electric starter. This last is considered a WMD by the general diesel community for good reason but with care, it can be done. Illustrated here.

http://www.youtube.com/watch?v=OOS9eVC0fjo

From there, the idea is to run a diesel gasser conversion with just kerosene and very little oil, down to a minimum of perhaps 5%. That would depend on the oil and that's where the experimental fun really begins. The really crazy notion is to run a pure kerosene fuel. Kerosene in another form is called home heating OIL. That means the fuel itself has SOME lubricating properties. How much? Will it be adequate? I hope to find out. [:@]

Any news on the diesel/glow? what about regular diesel and methanol with glow plug? do you think it will work.