These are light and can be recharged quickly in about 15 to 30 minutes. Their run time is short, however, usually in the 4 to 10 minute range. In scale boats, weight is not nearly as critical and is quite often required. They don't usually come in small sizes suitable for medium and smaller size models but for the large models they provide good power with a reasonable cost and inexpensive to run. A spark plug provides the fire and no external power is required in starting.
Fuel is usually a gas and oil mixture.
Boat and car versions are usually equipped with a recoil pull starter for easy starting. The major difference in the two types is the way fuel is delivered to and exhaust is removed from the engine during operation. During the upstroke the mixture is compressed and when the piston reaches the top of its stroke, the glow plug ignites the compressed gases, forcing the piston down. On the way down exhaust gases escape through the exhaust port while the fuel mixture enters the chamber. The entire power cycle takes place in 2 strokes of the piston.