I'm a newbie and have received a lot of advice at different times from club members as to what glow plugs for what types of engines. Could someone please tell me or display a chart as what glow plug goes with 46 size 2 strokes, 61 2 strokes and the difference in long, short idle bar no idle bar. one member only uses 4 stroke plugs in everything and the next says this is taboo :ie a different plug is required for each type of engine. Thanks for explaining.

Short plugs are used only in smaller engines, usually under .15. Idle bar plugs have a bar across the face of the plug, partially obscuring the element. This supposedly prevents raw fuel from hitting the plug and drowning the element. In my opinion, idle bar plugs are only for people who can't properly tune their engines.

In 2 stroke engines from .15 to 1.20, the same plug can be used. I've used McCoy RC 9 or 59 plugs in everything I run for over 20 years. I'm very happy with them, and I don't think there's a better plug around. It's a tough plug, medium heat range, and works well with anything from 10% to 25% nitro.

For 4 stroke engines, you may need a special plug. I'll leave the answering of that question to the 4 stroke gurus.

Dr.1

Start with the manufacturers recommended plug. If it runs poorly, try altering the heat range up or down. I run OS A3s in both my OS LA 46 and my Thunder Tiger Pro 46, and an OS #8 in my Thunder Tiger GP 61. Asking which plug is best is like asking if you prefer Blondes, Brunettes, or Red Heads. Everybody has a different opinion based on their personal experience. When you find the combination that works for you (reliable idle, good transition, high top end with an engine properly tuned), stick with it unless you find a reason to change.

Brad

You mean RC59, right? The RC9 is a cold plug designed for high nitro applications.
I use OS F for 4 strokes and OS #8 for most of my 2 strokes. I actually use lots of RC9s too, great plugs, but in boats where I run 50% nitro.

Welcome to more information than you probably wanted. For the engines you questioned (46 to 61 2 strokes) the OS #8 is all but foolproof. Don't go to extremes with the fuel. I normally run 15% Heli with 2 OZ of Castor Oil added. The castor oil is added to give some protection if a slightly lean run is encountered. Heli fuel is all synthetic lubricant and breaks down at high operating temperatures. This gives a good range of power and ease of running without being difficult in most weather conditions. Don't run the engine "lean" as it won't produce more power it will just wear it out. I have an Enya 50 with more than 500 flights and no visible signs of wear or discoloration using this system.

Now for the idle bar: This was an answer to early engine designs that dumps most of the fuel charge directly at the glow plug. It is un-necessary with modern engine designs. Probably still available since people get used to a specific product. It took me a while to understand this and make the switch. Read articles in magazines and/or read Dave Gierke's book on 2 strokes.

EXCAP232

That's right, Chuck. I should have been more specific. I run the RC 9 in my OS .32s, Webra .32s, and ST .34s which use 25%-30% nitro, and the RC 59 in everything else. I've run as much as 50% when I was running Webra Speed .28s, but that tended to break con rods.

Dr.1

There's only one thing standard with plugs and that's the thread size (1/4x32 UNEF). Long plugs can vary a little in length, depending on the brand, by maybe a thread or so. But both OS and Enya plugs are somewhere in the middle of long and short so call them a medium length. The ideal length is the one where the plug comes just flush with the combustion chamber but it's not really critical for normal use especially with Schneurle (flat top piston) engines. Small baffled piston engines are a different story.

Idle bar plugs generally aren't necessary although some people find they help with idle in inverted engines. Some plugs have the idle bar welded to the body and these have been known to break off...not good. The better ones have the idle bar machined as part of the body.

Then we come to heat ranges which is where things get a bit tricky. Basically the heat range sets the ignition point much like the distributor in a car. A hot plug fires it earlier than a cold plug but what you need depends mainly on the kind of fuel you use. The more nitro the colder the plug should be. If you've got a tacho then the plug giving the highest revs is close to perfect and this could even be a 4 stroke plug. But without a tacho and for general flying without too much nitro the hotter plugs like an OS 8 or Enya#3 are a good place to start.

To get some idea of the affect different heat range plugs have on how an engine runs go to
http://www.modeltechnics.com/glowplug/firepower.html

Pitcrew 232,
I have a lot of planes with engines from 46 to 90 2 stroke. I find the OS #8 is the King of the Hill for performance using Wildcat fuel with 10% Nitro and 16% Castor. I always try not to lean the high end out too much on the ground, as it may lean out more once in the air and die. I'd rather see a trail of blue smoke from being too rich, than being too lean and over heating the engine. Good luck.

"Keep 'Em Flying!"
Flak

My experience is somewhat different. While I have certainly had a few engines that needed specific plug types, I have generally found that most sport engines running on 10% nitro are not at all fussy as to the type of plug. Most of my engines can't tell the difference between an OS #3, #8, Tower generic plug, or even a Fox idle-bar plug.

That changes somewhat as the nitro content rises -- some plugs don't last as long with more nitro & some engines begin to show a specific preference -- but it ain't earth shattering. Similarly, with sport applications, I havent found much difference in engine output between 5% nitro & 15%. At 25% there was definately a difference -- plugs burned out quickly & the engines ran like crap.

My advice is run 5% - 10% nitro & don't get too excited about the plugs.

I used to feel this way too. However, an experience I had in the '80s with my K&B 3.5 outboard changed my thinking. I used to race it. I had always used K&B 1S plugs. I didn't want to be bothered with high nitro, so even when I raced, it was with 15% fuel. Anyway, I got out of racing, but still had the boat. One day I decided to take it out to the lake for fun. At that time I was using Fox idle bar plugs on my plane engines, so I just stuck one of those in the outboard. When I got it on the water, no matter what I did I could not get the engine to run like I knew it should. I knew the boat trim was right, and I tried leaning the engine out as much as I could, but it was still a dog. I finally tried installing a K&B 1S plug and the engine came to life. I'm not saying that the Fox wasn't a good plug, this is more to point out that different plugs will result in different performance. That experience convinced me that I should be more careful with plug selection.

I love a good glow plug debate! I tend to disagree that an idle bar plug is only for those who can't properly tune an engine. Clarence Lee then would fit in this category of "can't properly tune an engine" as he has upon occasion recommended an idle bar plug. That being said, I ONLY use idle bar plugs. Never had the bar come off and they work on every engine I've owned. Do they rob my engine of power? I don't know as I am only interested in sport flying so I do not try to get all out power. Do non-idle bar plugs work? Yes, but I do have some old engines that only like idle bar plugs. I use Fox idle bar plugs exclusively.

4 stroke engines use f type plugs. these are more expensive but the difference between them and 2 stroke plugs is that they have to maintain temperature through the dead cycle of the engine where as the 2 stroke fires every time the piston rises and the 4 stroke fires every second cycle. If you don't need them then don't spend the extra dollars.

If you want a good bit of info on glow plugs, check out www.blueangels.rchomepage.com/glow_plug_info.htm. This article give a good summary of heat ranges of all common manufacturers plugs along with some good tips.

I am having some problems with this issue myself. Some of the guys at the field told me that running an OSF plug will cure any idling problem there is. So I'm going to be playing with my plane hopfully tonight so I can see if I can get it to idle correctly.

Thanks for all the responses! You cleared up many questions and also corrected some misinformation I've been given. Thanks again.

An OS F plug might cure some idling problems because it's a very hot plug but then it might be too hot for full throttle, at worst it could give detonation. Concentrate more on correct tuning for idle and leave the plug selection for full throttle.

this is what i do:

A3 or 8 for 2 strokes
F for 4 strokes

everything else is tuning

I too asked this same question of my father. as I don't have alot of expereience yet, and he does. I noticed that alot of his old stuff he gave me had the bar on them, and the newer stuff didn't. His explanation of the idle bar was very similar to the one EXCAP gave you. Back in the day, he used alot of plugs with an idle bar racing at your fields, usually bringing home your trophies, [sm=lol.gif]and all that from a guy who didn't even know how to tune his engine! That was pretty lucky huh?


Mark

I guess my response here is to ask another question. I noted in one of the replies that it matters somewhat (idle bar vs. no idle bar) with inverted applications. Here goes my two pointed question. 1. I have an Evolution 100 that I am installing in a new (building process as we talk) Excelleron 90. This is installed inverted. Ok. One of my friends has a Quest 90 with the same engine and he is having a hell of a time getting the engine to run properly, at times even getting it to start.

Is running the engine inverted and his starting problems related? (are there some peculiar issues with running an engine inverted? my first experience is with my Venus 40 with an OS 50 (see below). Am I going to run into a problem with the Evo 100 inverted?

How about running it with an idle bar plug? Will that help with the running issues he ran into? (Keep in mind that I have not completed the Excelleron 90 build although I have run a couple of tanks through the engine, but upright on a test stand).

I also have a Venus 40 with an OS 50 inverted. I have to use a set of pincers to close off the fuel line to keep fuel from running into the engine until I start it. So far, though, the OS 50 has run just fine inverted, but that's not to say that I won't have a simlar problem with th Evolution 100.

Thanks.

DS.

Quick edit here.. I am using S&W Hi-Rev 15% fuel with 20% synthetic oil.

Most inverted problems are related to incorrect tank height (too high). That can't be helped in many airframes, so other "fixes" have to be applied -- such as on-board glo systems, idle-bar plugs, hotter plugs, higher idle speed. However, a properly tuned engine should run just fine inverted, following start-up (that can be the difficult bit).

The low end needs to be a little bit leaner in an inverted set-up with a high tank mount, than it would normally be with a 90 deg or upright config. This creates its own problems, such as part-throttle lean-out in inverted flight.

The real fix is to get the tank height correct.

Hey Brit!

Thanks for the reply. So, what you are saying is that the centerline of the tank must be as if the engine was upright. That makes sense, but may be easier said than done. Why do they design the airframes to have the tank not in line with the fuel flow centerline to the carb? (probably rhetorical question).

I don't recall where I put the tank on the Venus 40 but, as I said, the OS 50 runs just fine. I start the thing inverted, then turn the plane over after it's started. The idle is down around 2300 rpm and continues to run there so I assume that it's alright.

Now comes the challenge with the Excelleron 90 and the EVO 100.

Thanks again.

DS.

Brit:

I just remembered that I have the Venus 40 manual with me here at work. The tank neck fits through a hole in the firewall that is in the center of the engine mount. Sort of fixed location, unmovable I guess. But, the fed line is on the top of the neck when inverted (the way I set it up). The pressure line is on the side. I use two tubes instead of the three that they recommend in the manual. I route the tube from the tank, out of the cowel, to a brass tube about, oh, 3/4 inches long, then back to tubing then back through the cowel, then to the needle valve assembly, which on the OS 50, is on the back of the engine. The brass tube setup facilitates refuel and allows access for the 'pinch' mixture test.

On the Excelleron, there is a hole in the former between the firewall and the radio compartment and a 'shelf' that the tank rests on after passing it through the former. I suppose I could move it up or down a bit, but not sure without having a look at the setup, I only have the book in .PDF format on my PC.

I will have to give it a lot of thought when I reach that stage of the build. I intend to glue in the horiz stab tonite, then the vert stab Friday, then on to the linkages, then finally to the tank. Should be interesting.

DS.

I use an A3. How about that. What's the difference b/t the 3 and the 8 plug. I usually run 8's but the LHS only had the A3. Seems to run fine and everything.

~Michael~

The A3 is a tad hotter than the #8 . OS puts them in LA's and smaller engines. They are cheaper and seem to last just as long as the #8. I like the idea that in some small way I buy american made. My only plug I now use is FOX RCLONG the idle bar plug. Works great in every size and brand I own. Maybe the top end might be down a few hundred RPM. But I'm not racing. If the idle bar has saved me from a few deadsticks (praise the lord) HE HE HE

No sweat.

ARF's are sometimes a problem for tank height -- it can require surgery & that is painfull in an already completed airframe. Sounds like your Venus isn't too bad in that regard.