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Glow Engines

There are a lot of different manufacturers of engines and they come in all shapes and sizes. With glow engines you will come across names like O.S., Enya, SuperTiger, GMS, Thunder Tiger, Y.S. to mention only a few.  If it’s two stroke petrol you will hear names like DA, 3W, DLE, OS, RCG.

Each manufacturer makes a variety of sizes and models. Some might have roller bearings, others plain bearings, some are suited to helicopters, others to pylon racing etc.

Most model engines are measured in cubic inches,or parts thereof. The most common sizes glow plug engines would be the .25cu .40cu .46cu. .61cu and 1.20cu.There are smaller and larger models too. A 1.20cu  is a equivalent to 20cc engine so work it out from there if you like to work in cc. All glow plug engines run on a mixture of methanol and oil plus a few other additives. (See section on fuels) A 1.5v current is applied to the glow plug to get it to glow initially, once the engine is running the plug will keep itself glowing.

Glow engines come in two stroke and four strokes versions but they both use the same fuel. The four stroke operates on the genuine 4 stroke cycle and has valves, rockers, cam etc. A two stroke works on the typical two stroke cycle, same as most lawn mowers etc. A two stroke motor develops more power than the equivalent four stroke.

You can also get diesel engines but they are rarely seen nowadays. They operate very similar to the full size diesels, firing on compression. You have to be a bit of a wiz to tune them as not only do you have to tune the mixture you also have to get the compression right. Most older modellers have a few diesels tucked away just for old time sake, I certainly do.  Don't be tempted to buy one as your main engine as the fuel is almost impossible to get these days. (See the section on fuels)

Years ago there was a huge difference between engines from the various manufacturers and you had to be careful what you bought. Nowadays with computerised milling etc most engines will do the job.  I'm not saying all engines are the same but most run okay and do the job.

I think if you ask any modeller they will tell you that O.S. is one of the best all round glow engines. They have been in R.C. Modelling almost from day one. They are definitely not the cheapest around but you get what you pay for.

Most glow engine trainers and general sports models are made to suit a .40 to .46 size motor. If you get one of these you will be able to change this size engine from model to model as you move along in the hobby. If you can afford it buy yourself a .46 they have quite a bit more grunt. Talk to your supplier about the various models of .46cu, like everything in the hobby, buy as good as you can afford.  You don't have to have the 'wiz bang' ball race motor to get started, the standard .40cu and .46 is more than enough for your average trainer and sport plane. I have an O.S.40fp (your real basic job) which is so old and done so many hours I am sure it should be in a museum, but I have never had the head off and it still has plenty of grunt. Treat them right and they will treat you right.

Almost everyone loves a four stroke, they look and sound great.... unfortunately they are also more expensive. If you can afford a four stroke for your trainer, great, but they are heavier and don't put out as much power so you might need a bigger one, probably at least a .60-.80cu to get the same power as your .46 two stroke.

The carburettor on a glow plug engine generally has two mixture controls, the low-mid range mixture and the high end mixture. The large needle that sticks out of the side of the carbie is the high end mixture. Opposite that needle on the other side of the carbie there is usually a small screw which changes the low-mid end mixture. When you buy your engine feel free to fiddle with the high end mixture (the big needle) before you start it but definitely leave the low end alone, this is usually factory set and does not need to be touched. Check the literature that comes with the motor for initial mixture settings.

It is imperative that you do not run your engines too lean. This causes them to not get enough oil and to run hot. This is particularly true when the engine is new. New engines need to be 'broken in'. The more careful you are at breaking in an engine the better it will behave later and the longer it will last. For the first few runs they should not be run flat out and with a great load on them for any long period of time.  Read the instructions that come with your motor about breaking it in.

Engines come with multi cylinders, pumps, super chargers, tuned pipes, whatever you can think of there is probably one out there, there's even radials and rotaries’. When you're starting out use the old KISS principle, keep it simple. It's hard enough when you're learning to tune them let alone worrying about pumps and back pressures etc. Save that little challenge for down the track.

Engines do not come with a propeller and usually not with a glow plug either. There is a large variety of plugs and props available.  Props are measured by their length and amount of pitch, so a 10x6 is a 10 inches long with a 6 inch pitch. It's tricky matching the right length and pitch to your engine, it depends on what type of flying you will be doing. Some props are more efficient than others and will give more pull. For a .46cu use a 11x6 and for a .40cu use a 10x6. As for the glow plug, just buy a standard mid heat range plug.  Four strokes have their own type of plug which are longer and need to glow a bit hotter. Most or your smaller engines (40 & 46) come with mufflers. As larger engines usually require custom mufflers you seldom get one with the engine.


Okay, if you decide to use a glow plug engine what should you buy as a beginner?

Obviously buy a new engine if you can. The engine needs to match the place you are installing it in, the documentation in the kit should tell you the recommended size. Any of the brands mentioned above will do the job, go O.S. if you can afford it. As for which model of motor, well buy as good as you can afford, for example with the OS motor an LA is fine but an FX is better. Don't be pressured into the wiz-bang job if you can't afford it.

You can usually save yourself a few dollars if you buy your engine at the same time as the radio and aircraft (Package deal). At the very least your dealer should throw in a few goodies like a prop and glow plug or some fuel.

If you can't afford a new engine and are going to buy second hand, get an experienced third party to look over the motor before you part with your dollars. A simple jiggle here and there will soon tell an experienced ear what sort of condition the motor is in. Check for compression, for broken fins, damaged mufflers, carby and mountings.  Feel for slop at the top and bottom end.  Look in the exhaust port for marks on the piston. What does the general appearance look like, does it look like it's been looked after. It is VERY EASY to get caught with a dud motor, having said that there are some real bargains out there. 

                                                                                           Contributed by Brian Carson  - SMF Senior Instructor (Note from Bob Cottle - Webmaster)

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