Aircraft with Internal combustion Engine
For larger and heavier models, the most popular powerplant is the glow-engine, a form of internal combustion engine . Glow-engines appear similar to small gasoline motorcycle-engines, but glow-engines are considerably simpler in operation. The simplest (and cheapest) glow-engines use a two-stroke cycle engine, glow plug to burn fuel, and an external ignition system (a dry cell or other low voltage source.) The fuel is a mixture of slow burning methanol, nitromethane, and oil lubricant (castor oil or synthetic oil.) The reciprocating action of the cylinders applies torque to a crankshaft, which is the power-output of the engine. Vendors of model engines rate size in terms of engine displacement. Common sizes range from as small as 0.01 cubic inch (in3) to over 1.0 in3 (0.16 cc - 16 cc). As Richard Feynman mentioned in his famous There's Plenty of Room at the Bottom lecture, the speed an engine can rotate without breaking tends to go as the inverse of the linear dimension (inverse cube root of the displacement). However, the intake air flow improves less quickly than that with small scale, due to decreasing Reynolds number and, eventually, to viscous flow.
Not all simple internal combustion model aircraft engines use glow plugs. There are also "diesels", that are popular in Europe and the world over. These also are carbureted, not fuel injected. They have an adjustable compression ratio and burn a more easily ignited mixture of ether and kerosene (with lubricating oil). These are preferred for endurance competition, because of the higher energy content of the fuel.
Internal combustion (IC) engines are also made in upscale (and up-price) configurations. Variations include four-strokes, multi-cylinder engines, and even spark ignition gasoline powered units. All IC engines generate substantial noise (and engine exhaust) and require routine maintenance. In the 'scale-R/C' community, glow-engines have long been the mainstay until recently.
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