Ah, there’s nothing like the smell of glow fuel in the morning! My apologies to all you movie buffs, but if you fly glow-powered models, you know exactly what I mean! My oldest and fondest memories of the hobby are triggered by the smell of model engine exhaust and castor oil. For modelers new to engine-powered airplanes, the science of starting and tuning a glow engine can seem like magic—but those techniques can be the subject of another article. For now, let’s take a closer look at the magic go-juice we use to power our engine-powered airplanes.
Glow engines run on methanol-based fuel. Typically, giant-scale models use gasoline engines while most trainers, sport, aerobatic and scale models use glow engines. Whether they’re 2-stroke or 4-stroke, glow engines use glow fuel, with the main difference being the fuel’s blend of ingredients. The reason it’s called glow fuel is because the engines use glow plugs to ignite the fuel charge. Without getting too detailed, glow fuel consists of methanol (alcohol), lubricating oil and nitromethane (nitro).
There is also glow fuel that contains no nitro at all called “FAI fuel,” and glow engines do run fine without nitro. Methanol is the primary combustible in glow fuel. Nitro is added to increase power as it increases the oxygen content in the fuel mix. More O2 means more power, up to a point anyway. As the nitro content is increased, the engine’s carburetor tends to become more sensitive to adjustment. Fewer clicks of the needle make bigger changes to the power output.
For typical sport flying, glow fuels containing between 5 and 30 percent nitro provide a good compromise between power increase and ease of carburetor adjustment. You should always follow your engine manufacturer’s recommendation for your fuel’s nitro content.
To keep all the internal moving parts of the engine happy, glow fuel also has a certain amount of oil added. Without this oil, our engines would quickly overheat and seize up from the metal-to-metal friction. Model airplane fuel can contain castor oil, synthetic oil or a mixture of both. Typical sport engines should use fuel with a 15 to 20 percent oil content. There remains an ongoing discussion as to which oil type is best—castor oil or synthetic. Castor oil, which is produced from the castor bean, is an extremely good lubricant and holds up extremely well, even in the hottest running engines. It provides excellent engine protection even when your engine runs lean.
Synthetic oils also do a great job in protecting our engines; the downside is that they don’t hold up as well as castor oil does at higher temperatures. Many glow engine manufacturers recommend fuels containing a blend of both castor and synthetic oil for maximum protection. For more in-depth information on glow engines and glow fuel, check out Volumes 1 and 2 of Dave Gierke’s book, 2-stroke Glow Engines for R/C Aircraft available from airagestore.com.
Use a quality fuel pump and an in-line filter to keep your fuel supply clean.
The methanol in glow fuel is hydroscopic, meaning that it readily attracts moisture from the surrounding air. Water in your fuel does two things: it makes your engine run poorly and it increases the chances of corrosion inside the engine, especially in its bearings. Because of this, you should always run your engine completely dry of fuel at the field and then drain your fuel system before heading home. Treating your engine with an after-run oil is also a good idea. When you store your fuel at home, keep the fuel container cap tightly sealed and store it in a cool, dry area out of direct sunlight. Half-full containers in particular are susceptible to water contamination. For this reason, store smaller amounts of fuel in smaller containers to help keep the air out. Regardless of the type of fuel you use, always include an in-line fuel filter in your model’s fuel system. You should also include one or more in your fuel delivery system to prevent any debris from transferring from your big container into your model’s fuel tank, which will minimize the chances of clogged fuel lines, fittings and ports.
Byron Aero Gen2 Blend
For years we have been using Byron Aero Gen2 glow fuel to power the various glow engine powered airplanes reviewed in Model Airplane News. These fuels feature a wide range of nitromethane and oil percentages and are available in synthetic/castor blends or straight synthetic lubrication. Generally we’ve found that Aero Gen2’s 16% total oil content is more than adequate for optimum performance and reduced engine parts wear. If you are looking for a higher oil percentages Byron also manufactures Aero Traditional Blend with 20% total oil content and their Aero Premium 18 Blend with a total oil content of 18%.