Getting Started with R/C Airplanes
Engine Basics
When deciding what
airplane you want, you need to know what engine to get. Numbers like 25, 40,
or 60 after the name of a plane refer to the size range of engine the
airplane needs. Although the true size is in hundredths of an cubic inch, such as .40 cu.
in., the size is informally expressed as a "forty" or a "sixty".
Trainer-style planes 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 planes. 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% nitromethane (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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