Glow Powered RC

2-Stroke RC Engines

2-stroke model airplane engines date back to the origins of RC aeronautics. They produce a lot of power for their size and when properly adjusted are generally easy to start and maintain. They are also cheaper to buy due to their relative simplicity. 

4-Stroke RC Engines

A 4-stroke engine produces torque at lower revs, allowing larger more scale sized propellers. The engines produce a lower pitch sound that is more realistic and preferred in scale RC airplanes, i.e. one that has been modeled as a real airplane replica.

All glow plug RC model airplane engines, whether 2-stroke or 4-stroke, are expressed by the engine's capacity. Sizes are usually expressed as just the number, eg a engine would be referred to as a 40 and a engine would be called a 61.  

Airplane are typically designed to be pared with compatible engine of the same number, i.e. a '40 size plane' would be a plane that has been designed to take a 40 - 46 engine.  The size of the engine is usually stamped on the side of the engine casing, making size-identification very easy.