Radio Control Engines

		Nitro Engines for RC Cars, Airplanes and Boats
		Two stroke The traditional rc engine is based on compression-ignition technology, colloquially referred to as 'two stroke'. This covers both 'glow' and 'diesel' engines. The vast majority of rc engines are glow engines - so called because to ensure ignition each cycle, they are fitted with a glow-plug in the cylinder head. This has the appearance of a spark plug, but has a small coil fitted in it's center instead of an electrode. To start the engine a low voltage power source is applied to the glow plug to make the coil glow red hot, this then ignites the fuel. Once the engine is running the residual heat from each explosion cycle, together with a chemical reaction initiated by the catalytic platinum plug element, ensures that the glow plug element remains hot enough to ignite the fuel on the next cycle and the power supply to the plug can be removed. The fuel is primarily methanol, with up to 25% oil for lubrication, and usually a smaller percentage (around 10% is typical, but it can be much higher for specialist applications) of nitromethane, a chemical additive which improves the combustion efficiency of the methanol. An alternative type of 2-stroke is the diesel engine. This is outwardly similar, but instead of a glow plug, there is an adjuster which moves a 'contra-piston' in the cylinder head, altering the compression ratio of the engine. The fuel used is a mixture of ether, kerosene and oil. The ether component has a low flash point, and when compressed by the engine, the temperature rise caused by the compression is sufficient to cause ignition. The adjuster is used to vary the compression ratio, and the ignition timing until smooth running is achieved. This type of engine, because of the adjustable available, can be set up to turn a bigger prop than a similar capacity glow engine. Four Stroke These engines are more complex to manufacture, hence more expensive, and have always had a lower specific power output. Because they tend to have a quieter exhaust note, and to most ears a more realistic sound, they are very popular in scale models. The disparity in power output is not as pronounced as it used to and they are now a good choice for any type of model. They work in the same way as the familiar car engine, complete with overhead valves, but tend to be pushrod operated not overhead cam. There are also variations with side valves or rotary valves. A recent development is a rotary sleeve valve. The illustration shows a typical engine: the pushrods are at the front, operated by a cam driven by the crankshaft, and the carburetor is behind the cylinder. The flap underneath the carb. is a rod operated choke, often needed because the position of the carb. makes it difficult to choke the engine with the traditional finger! The exhaust exits from the cylinder head on the other side, and is sometimes just a plain header pipe, but more often incorporates a small silencer. The engines illustrated are single cylinder, but there are multi cylinder versions of both types of engine. You may find in-line, horizontally opposed or radial versions available. These can be particularly effective when used in scale model airplanes.
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