RC Model Airplane Fuel

RC MODEL AIRPLANE FUEL IS AVAILABLE IN A WIDE RANGE OF MIXES, DEPENDING ON ENGINE TYPE AND END USE.

Glow Model Airplane Fuel

As it's name implies, glow fuel requires a glow plug for ignition.

Glow fuel has three main ingredients-

1. Methanol (Alcohol)
2. Lubricating oil.
3. Nitromethane (Nitro)

Methanol is the primary combustible used in rc airplane fuel. Nitro is added to increasepower. It doe this by increasing the oxygen content in the fuel mix. More nitro results in more power, up to a point. The higher the nitro content the more sensitive, to adjustment the glow engine's carburetor becomes. 

For typical sport flying, glow fuels containing from 5 percent to 30 percent nitro produces a good compromise between power and ease of carburetor adjustment. The higher nitro content fuels are more expensive and tend to lower glow plug life. 

Please follow the engine manufacturer's recommendations regarding the fuel mix that should be used in your engine. I rarely exceed 15 percent nitro content and find this to be a good balance.

It should also be mentioned that glow engines run just fine with no nitro. A fuel is available called "FAI fuel" that has zero nitro content. For some international contests this is the only fuel allowed. I use this fuel in my MOKI 1.8 cu.in. glow engine. This motor loves the stuff! (I believe the higher compression ratio may be responsible.)

To lubricate all the internal moving parts of the engine a high quality lubricant must be used. Without this the engine would very quickly overheat and seize up. Typical sport engines should use a fuel with from 15 to 20 percent oil.

There are two types of oil used in today's model airplane fuel for glow engines. The original oil used was (and still is) castor oil. This is produced from the castor bean and makes an excellent lubricant. It maintains its lubricating qualities at high temperatures and  gives good engine protection during lean runs. The disadvantage of castor is that it causes carbon build up inside the engine. This means that the carbon deposits have to be periodically cleaned from the engine, particularly from the combustion chamber and the top of the piston.

The other type is the synthetic oil. The modern synthetic oil has all the qualities of castor oil and it does not cause carbon build up. There is much discussion regarding the type of oil to use in RC airplanes and maybe as a result of this controversy, fuel manufacturers offer a blend of synthetic and castor oils.

The 4-stroke glow engine generally requires a little less oil than its 2-stroke cousin. 15-17 percent oil is the norm, whereas up to 20 percent maybe recommended for the higher speed 2-strokes. Having said that, you may have noticed that we are now being offered a 2-sroke/4 stroke model fuel from some manufacturers!

As mentioned earlier, please follow the engine manufacturers instructions when it comes to selecting your model airplane fuel.

The other ingredients that may be found in today's fuels are anti-foaming and anti-corrosion agents. The anti-foaming agent helps to prevent the fuel from foaming in the fuel tank. The tank should be mounted in foam rubber, to isolate it from vibration, but in some designs of rc airplanes this is not possible.

Regarding the anti-corrosion agents, I am sure they help. At the end of the flying session I always run the tank dry of fuel. It is then recommended to insert after-run oil into your engine. The nitromethane is very corrosive and should be neutralized.

The methanol in model airplane fuel for glow engines is hydroscopic. This means it absorbs moisture from the surrounding air. When you store your fuel at home ensure the fuel container cap is tightly secured and keep the fuel in a cool dry area out of direct sunlight.

Gasoline

The much more familiar gasoline fuel requires a spark plug for ignition and is generally used with the larger displacement 2-stroke engines. Because they are 2-strokes, oil must be mixed with the gasoline.

As always, follow the engine manufacturers directions when it comes to the model airplane fuel mix. The grade of gasoline (high octane or regular) is generally stated as well as is the type and quantity of oil.

There are several types of oil available and synthetics are popular. Pay particular attention to the amount of oil required. Usually a higher percentage is used for break-in. If you use too much oil,  you may find the spark plug is fouling, whilst too little may result in the engine over heating.

Gasoline is the least expensive model airplane fuel, but it is a fire hazard. Use only gasoline specific containers and store it in a well ventilated area. Keep a fire extinguisher at hand in your workshop and at the flying field.

As with all fuels, make sure it is clean by using a good filter in your fuel delivery system as well as in the feed line from the tank to the engine. This will minimize the chances of clogged lines and fittings.