RC Gas Engines

People not familiar with this hobby often refer to nitro powered engines as RC gas engines. I know that I used to. There is an entire class of actual gasoline powered engines available for RC airplanes. While nitro powered engines are the best choice for smaller size airplanes, gas engines are the best choice for heavy giant scale RC airplanes.

Gasoline vs. Nitro

Which is better, a gas engine or a nitro engine? This depends on how big your airplane is! For giant scale airplanes, gas engines are definitely better. For smaller airplanes around 10 lbs or less, nitro engines are the best and sometimes the only choice.

It takes a slightly larger gas engine to produce the same power as a nitro powered engine. This is because the methanol/air mixture produces more energy than gasoline/air mixture during combustion. A gasoline engine requires an on-board ignition system which adds to the weight even more. This is why gasoline engines are not practical with small airplanes. In fact, gas engines are only available from around 1.2 size and larger.

Ignition System

Gas engines use spark plugs where as nitro engines use glow plugs to ignite the fuel/air mixture. For this reason RC gas engines require on-board ignition systems which provide electricity to the glow plug at precisely the correct time.

There are two types of electronic ignition systems used with gas engines. The first type is a magneto. A magneto uses magnets attached to the rotating engine to create electrical pulses for the spark plug at precisely the right time. This eliminates the need for an on board battery. Your weed-wacker or push power uses a magneto to fire the spark plug. Magnetos are very reliable but add weight to the engine. Since the magneto doesn’t produce electric for the spark plug unless the engine is turning, an engine with a magneto ignition system must be started with an electric starter just as a nitro engine does.

Most RC gas engines available today use an electronic ignition system. This system uses a separate battery to provide electricity to the spark plug. This allows the engine to be hand started. The timing of the spark is critical for maximizing the power from any engine. As the speed of the engine changes, the precise time that the spark plug should fire for optimal performance (in relation to the piston’s position) changes. An electronic ignition system accounts for this and adjusts the timing depending on the engine’s RPM’s. A magneto engine is set for optimal performance at top speed only. An electronic ignition engine adjusts for optimal performance at all speeds. An engine with an electronic ignition system will generally idle better and start easier than magneto engines.

Fuel Consumption

A gas engine consumes close to half as much fuel as a nitro powered engine. Combine that with the fact that nitro fuel costs roughly three times more per gallon than gasoline you can quickly see why most large scale airplanes are gas powered RC airplanes!

RC Gas engines have built in fuel pumps. It is not necessary to hook a vent line to the exhaust as is required for a nitro engine. With an RC gas engine you have the freedom to move the fuel tank anywhere you want within the fuselage. The same fuel tanks designed for nitro engines can be used. The fuel lines must be designed specifically for gasoline. Nitro tubing will dissolve.

A nitro engine utilizes the methane as a coolant as well as fuel. When the fuel is pulled into the carburetor the methanol vaporizes which requires a significant amount of energy. This energy comes from pulling heat from the engine. Gasoline engines require more air across the cooling fins than nitro-engines because of this. This will require larger openings on the cowling of gas engines.

Radio Interference

Gas engine ignition systems are known for causing radio interference. As a general rule the ignition system should be around 12 inches away from the receiver. Metal pushrods should not be used for the throttle.

A common source of interference from gassers is the use of a non resistor type spark plug. When the electric arcs across the gap of the spark plug an electromagnetic field is produced that can interfere with radio signals. A resistor type plug such as a BOSCH WSR6F(found at your local auto store) will greatly reduce this interference.

If special care is taken, radio interference can usually be avoided. If you have a spread spectrum radio system, interference should not be an issue. However, it is important to know that RC gas engines are very prone to radio interference if you are not careful.

Pros and Cons of Gas Engines

Pros

The biggest advantage of an RC gas engine is that fuel consumption is much cheaper when flying gas powered RC airplanes.

Gas engines do not make an oily mess on the airplane.

Easier to tune, no glow plugs to deal with.

Gas engines are generally more reliable than nitro engines.

Gas engines have built in fuel pumps.

Cons

Gas powered RC airplanes are more prone to radio interference.

Lower power/weight ratio than nitro engines.

Two batteries needed for the airplane (one for electronic ignition, one for receiver).

RC gas engines require more cooling than nitro engines.

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