Effective Power

the power delivered from an engine to a drive mechanism either directly or through a power transmission.

Output power may be termed net, total, or rated. The net output power of an engine is its effective power minus the power expended in actuating auxiliary units or mechanisms that are necessary for the engine’s operation but have separate drives—that is, that are not driven directly by the engine. Total output power is the output power of the engine without the deduction of such power expenditures. Rated output power, or rated power, is the output power guaranteed by the manufacturer for certain operating conditions.

Standards and technical specifications have been established for effective power according to engine type and function. The maximum power, for example, of a reversible marine engine when the propeller shaft is turning at a given rate of rotation and the ship is moving backwards is called backdraft power. The maximum power that an aircraft engine can develop with minimum specific fuel consumption is called cruising power. Effective power is determined by an engine’s size and by its mechanical efficiency; augmentation of the engine’s normal operating process may also contribute to effective power.