A propeller engine is commonly a piston-driven, internal combustion engine which powers a propeller aircraft. With the exception of turbo prop aircraft, most propeller engine combinations are piston-driven engines turning propellers via a gear box or directly off of the engine's crank hub. Unlike an automotive engine, which creates power through high revolutions, a propeller engine typically operates at lower revolutions and uses a variable pitch propeller to create more power and higher speed. The typical propeller engine uses a very high octane gasoline for power; however, most aircraft engines can burn less expensive automobile gasoline provided they are tuned for it.
The common small engine aircraft uses a propeller engine that is very similar to an automobile engine. Commonly carbureted or fuel-injected, these piston-driven engines use most of the same parts that are common to engines found under the hood of most automobiles. Spark plugs, distributors and spark plug wires adorn the outside of a propeller engine. Valves, cam shafts and pistons fill the internals of the engines. Electrical charging systems maintain battery levels, and an electric starter is used to turn the engine over and bring it to life.
An aircraft's fuel delivery can sometimes be impacted due to extreme temperature changes from ground level to flight levels. To prevent the fuel from freezing while at flight altitudes, the fuel is treated with special anti-freeze conditioner additives as well as special features added to the carburetor in the form of carb-heat controls. By adding the heat controls to the fuel system, the pilot can prevent the fuel from freezing and stalling the propeller engine. A knob on the instrument panel is pulled to apply carb-heat as the aircraft rises into the colder air. This acts much like a manual choke in an automobile application.
Unlike their automotive cousins, the propeller engine must undergo annual inspection including an annual tear-down to examine the condition of the internal components and evaluate the engine's ability to fly. Examining the engine in advance is done as a preventative measure to help avoid crashes and problems. Once a propeller engine has been examined and any questionable parts are changed, it can be reassembled by a certified aircraft mechanic and the plane returned to service. If any major issue is detected within the engine, such as a worn piston cylinder, the entire assembly must be exchanged for a new piece before it is allowed to return to flight.
