Glow Plug Tutorial Please...
 

Howdy,
As a new flier I was curious about glow plugs and which do what. I am flying an Alpha Trainer with an evolution engine. I am suppose to use the evolution glow plug, but instead I am using what the store had an "A3". The glows look different AND the new one is not as long as the old one. Does anyone have a good tutorial or fill me in on the finer knowledge of glow plugs?

Thanks

Lefty [sm=thumbup.gif]

RE: Glow Plug Tutorial Please...
 

This is a really good thread:
http://www.rcuniverse.com/forum/fb.a...078&tostyle=tm

gus

RE: Glow Plug Tutorial Please...
 

For some reason OS has a different definition of "long" for glow plugs than everyone else. The good news is that it usually doesn't affect the performance much. The Evo engine is powerful, but actually fairly conservitive, so it will work with a wide variety of plugs. the A3 should be just fine.

RE: Glow Plug Tutorial Please...
 

OK Gus,
I read the thread, yet still would like to know what the difference is between the different values...like how does an A3 differ from a Fox #8. Length only? What is the hottest plug I can or should use and why? Why would I use a hotter plug or a cooler one for that matter, engine life? What are all the different plug sizes I Could use if I choose to?

Still trying to lean "everything" at once. Can't fly, to darn windy and th snow keeps piling up, no matter how tall I make the skis :eek:.

Lefty [sm=thumbup.gif]

RE: Glow Plug Tutorial Please...
 

The numbers you're seeing, ie A3 vs Fox #8 are meaningless in themselves, they are just names. There is no "standard" labeling of plugs, and as you noticed with the OS plugs, the size can change a bit too.

As I said above, for the most part, the length of the plug isn't critical for you. If you run some of the smaller engines, you need a shorter plug to keep it from getting too close to the piston (or maybe hitting it), and 4-strokes often require a longer reach plug to get all the way down to the combustion chamber. But for the vast majority of 2-strokes in the "common" sizes, the differnece in length with the OS plugs doesn't matter. However, it's worth noting that the longer plugs do increase the compression of the engine slightly, and some ABC engines when new can wind up "over compressed" with a longer plug and higher nitro. I've seen this twice on OS .46FX engines on 15+% fuel. A longer plug lead to the engine not running right at full power, but a shorter OS plug ran it fine. (I suspect that if we had a colder plug around in those cases, it would have also fixed the problem).

The "important" thing about plugs is the "heat range" of the plug. You'll see plugs referred to as "hot" "cold" or "medium". Most sport engines run just fine on a medium plug, and most of the plugs you pick up will be pretty much in the medium range.

A "hot" plug causes the fuel/aix mixture to ignite sooner, a colder plug causes it to ignite later. It's a lot like adjusting the timing on a spark ignition engine (like an auto engine).

An engine with too cold of a plug will not idle or transition well, the plug isn't staying hot enough at the lower speeds to keep the engine running.

And engine with too hot of a plug will run in to pre-igintion problems. In the extreme, this is rough, ragged running at the high end that you can't fix with the mixture no matter what you try. Usually it's more noticed with a sizzling or "frying egg" sound when the engine is running.

As I said, most sport engines using "normal" fuel will prefer medium plugs. If you raise the compression, use a tuned pipe, run really high RPMS and high nitro, you'd want a colder plug. (and a stronger, heavy duty plug element to keep it from being sucked though the engine).

On the other hand, 4-strokes and engines set up to swing a big prop at a lower RPM will often benifit from a hotter plug. Most "4-stroke" plugs are just hot to very hot plugs with a slightly longer reach to them. You can run a 4-stroke plug in a 2-stroke, and vice versa, but you'll often get the kind of problems mentioned above.

The best way to pick a plug is to try it and see how it runs in your engine setup, on your fuel. If the engine works like you want it to, you're good to go. In theory, you can use an accurate tach to check the engine RPMS, and the plug with the best rpm is the best plug for the engine, as it's causing igntion at the right time. But you're talking about small enough changes that most cheap tachs won't show it anyway. Beyond that, you can buy plugs by price and local availability. A more expensive plug may last longer in your engine or perform better, or it may not. Guys tend to stick with a plug they like just because familiar is good, and once your engine is set up and working right, the less you mess with it, the better.

RE: Glow Plug Tutorial Please...
 

I have an EVO engine. I don't have my booklet in front of me. But if you look in the book it came with it it had some kinda reason. It said something about the shape of it effected the fuel or something. I think its just a stunt to try and get people to buy their plugs personally. I could be wrong. I do know that the plugs I have now are not the same kind that came with it and it runs the same.

RE: Glow Plug Tutorial Please...
 

I'm confused on the plug types also. I heard on here that os#8 had the greatest longevity. I went to a hobby shop and they said the no. 8 was the hottest. It seems to me that the hotter the plug is, the shorter the life would be.

RE: Glow Plug Tutorial Please...
 

Wouldn't the max temp depend on how much current you put to it?

RE: Glow Plug Tutorial Please...
 

Or the the amount of resistance to flow of current

RE: Glow Plug Tutorial Please...
 

Ya, but you can crank up the amps, you can't really change the resistance.

I guess what I mean is, you can pretty much make any as hot as you want by turning up the current on your panel, right?

RE: Glow Plug Tutorial Please...
 

I have one of those wireless ignitors. I don't have any control. The current flow is a constant for me. The only variable would be resistance for me (brand of plug) Have you had your 4 star up yet wings?

RE: Glow Plug Tutorial Please...
 

The plug isn't on the glow driver the vast majority of the time. :)

RE: Glow Plug Tutorial Please...
 

Ha! Yeah that might be important. So what is the hottest plug?

RE: Glow Plug Tutorial Please...
 

Not yet,

I plan to tomorrow if it is not raining!

Wings

RE: Glow Plug Tutorial Please...
 

You have to come to an agreement between your 'plug' and the amount of nitro in your fuel! If you remove your glow starter and the engine sags a lot, you might bump up the % nitro OR install a 'hotter' plug.

Jerry

RE: Glow Plug Tutorial Please...
 

Remember, a glow plug is a catalyst and does not depend on external sources for energy when normally running. The characteric (hot, cold, etc.) is determined by the area of the surface exposed to the alchohol in the fuel. A fine wire, multiple turn coil of tungsten will provide more surface area than a coarse wound large diameter wire will and therefor be classified as a hotter plug.

RE: Glow Plug Tutorial Please...
 

I'm just checking here.
You guys do understand that once you pull your glo driver off, electricity has nothing to do with plug temp.
It will almost immediately achieve it's working temp based on design and fuel type once the glo driver is removed.
The chemical reaction between element and fuel is what keeps the plug hot.

RE: Glow Plug Tutorial Please...
 

I was talking about the temp while the driver is plugged in. I do realize that without a voltage drop resistance doesn't mean jack squat.

The glow plug pretty much does nothing after the driver is removed right? So if it were possible (which I realize it is not), you could just plug the top of the engine after it gets going.

Isn't it some what similiar to a dieasle engine? Except they can ignite at room temperature. You have to have the right combo of pressure, temperuature, and the characteristics of the fuel.

RE: Glow Plug Tutorial Please...
 

http://www.holdfastmac.com.au/howglowplug.html
According to this, the glow plug does work after removing the ignitor.

RE: Glow Plug Tutorial Please...
 

That was an interesting article Zetor. I learned something.


By the way, I went to the field today to try my new plane. The engine would not run. I think I need a new one. Its bandaided together. It ran fine while at home taxying, but we could not get it to run today.

What ever the problem may be, if it requires buying more parts, it is better if I just order a new engine.


Wings

RE: Glow Plug Tutorial Please...
 

There are a lot of myths and misinformation about glowplugs.

First off, they DO keep working after the ignitor's been removed. The platinum element gets hot when exposed to methanol. It also catalyzes the combustion process. Yes, a certain amount of compression is needed to allow the fuel/air mixture to fire, but you also need the catalysis of the platinum element of the glow plug. This catalysis happens when the temperature of the plug and the compression in the engine reach a certain point. You use the battery to heat the plug to get it started. Further combustion then keeps the plug hot. If the engine needed no plug to keep going, then it wouldn't quit when the plug's element gets beat up. There are cases where the plug will glow when you apply the battery, but the engine won't run. That's because the element's become contaminated, and it can't catalyze the engine's firing.

The heat range of the plug is used to contol detonation. "Hot" fuels (high nitro) need "Cold" plugs, and vice-versa. If you're engine's detonating, and you can't control it with compression or mixture, then you need to go to a colder plug.

Plugs such as the O.S. Max #8 and #A3 are general-purpose plugs that work in most two-stroke engines running on fuels with nitro content up to 15%-20%. Above that, then go to the colder plug.

RE: Glow Plug Tutorial Please...
 

Guys, will I notice a dfference if I'm running a magnum .46XLS with an A8 10 nitro when i switch to 15% nitro?

RE: Glow Plug Tutorial Please...
 

I want to throw this in here. Everyone wants to know about "Hot and Cold". To put it simply hot and cold refer to the plugs ability to transfer and retain heat. A "Cold" plug transfers heat away easily. Thus in a high rpm or high nitro/compression situation this is a desirable feature.

A "Hot" plug however would transfer heat slowly. Thus it would retain heat easily. This would help in a low rpm or low nitro/compression situation. This is why 4 stroker plugs are the hottest out there.

One last point to throw out there. Any internal combustion engine is basicly a heat pump. You convert chemical energy (fuel) into kinetic energy (in our case prm's and heat). The heat generated in copmbustion must be eliminated or at least lowered. Thus the cooling fins on our engines. The heat left in the engine can affect the operation of a glow plug. A coweled engine may benefit from a cooler plug. Whereas one in the front of an ugly stick may benefit from a hotter plug even if both planes use the same engine.

Picking a plug can cause your hair to fall out. I would reccomend picking a favorite manufactuer (Fox in my case) and just buy a couple of each of thier plugs. Try them all in your application. You will find that one will work the best in your unique set-up. Then use it religeously. Don't forget that changing fuels or radical changes in temprature may cause you to have to change plugs. Flying at low temps in the winter will probably need a hotter plug.

I hope this helps clear up a totally muddy subject.

Mark Shuman

RE: Glow Plug Tutorial Please...
 

What is detonation - firing before the piston reaches the top?

RE: Glow Plug Tutorial Please...
 

Detonation is when the fuel/air mixture doesn't burn smoothly. Yes, it just doesn't explode in the cylinder, but combustion progresses like a wave from the glowplug to all points inside the engine until all of the fuel/air mixture can be consumed. In some cases, it's continuing after the exhaust port opens and keeps burning in the exhaust manifold. You see this on dragster engines when flames are coming out of the exhaust pipes. The fuel's still burning.

When an engine gets too hot or too lean, the fuel/air mixture doesn't burn smoothly, but goes all at once. This is explosive and doesn't provide as smooth a push on the piston. In fact, it's like hitting the piston with a hammer. It's also hotter than a normal burn.

If an engine is run too long while detonating, a hot spot under the glowplug can actually start to vaporize the aluminum of the piston. Eventually a hole will be burned into the piston, and the engine will quit because of the loss of compression. The hot exhaust gasses will also tend to erode the piston as it escapes, burning a trough into the piston there.

Sorry the pic is a tad blurry, but it does show the hole eroded in the piston crown, and the erosion at the exhaust port side. This is a badly-abused ducted-fan piston that got too lean and experienced severe detonation.

Detonation adds a "frying egg" sound to the exhaust note.