When deciding what radio control airplane you want, you need to know what engine to get. Numbers like 25, 40, or 60 after the name of an airplane refer to the size range of engine the airplane needs. Although the true size is in hundredths of a cubic inch, such as .40 cu. in., the size is informally expressed as a "forty" or a "sixty". Trainer-style airplanes usually fly best with smaller displacement engines (i.e. a .40-size engine will work fine with "40" size trainer). Sport planes usually need a displacement size from the middle of the recommended range. Many aerobatic planes use the biggest engine possible which necessitates more throttle control from the pilot, but can result in better aerobatics.

Glow Plugs
Most model engines have a simple, two-stroke, diesel-like ignition system which uses a glow plug rather than a spark plug. A glow plug will cause combustion by itself once the engine is running. Glow plugs do not require an on-board battery or ignition system and make model engine operation easier.

Carburetor
The carburetor in model engines is very simple compared to full-size cars or airplanes.
All R/C model engines have:
A venturi to allow air into the engine.
A needle valve to control the fuel flow (and therefore, the fuel to air mixture).
A rotating throttle "barrel" or valve to open and close the venturi.
Correct air-fuel mixture adjustment is important not only for performance, but also for engine life because glow fuel for a model engines contains lubricants. Model airplane fuel is made up of mostly methanol (a type of alcohol) with about 16-20% oil and 5-15% nitro methane (for more power and better acceleration). Consistently flying the engine with a lean setting (very little fuel) will prematurely damage an engine. Most engines come with detailed directions, and they should be read before operating the engine.

2-Stroke vs. 4-Stroke
Two-stroke engines fire on every revolution. They are easier to adjust, less prone to failure from high stress or misuse, and offer more power for their size and weight. Four-stroke engines fire every two revolutions. This equates to more torque, less propeller RPM, and a quieter running engine. However, four-stroke engines need more maintenance and are harder to adjust. They offer better fuel economy but produce less power for their size. For example, a Magnum XL46A two-stroke and an FS52A four-cycle weigh about the same and produce similar power. However, the .46 uses more fuel. The .46 also swings a slightly smaller propeller at a higher speed, thus giving higher top speed but less climbing ability.

Most trainers work great with a two-stroke engine. Also, because they are easier to operate and less expensive, buying a two-stroke for a first engine is a good place to start.


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