Power-to-weight ratio

Power-to-weight ratio

Power-to-weight ratio (specific power) is a calculation commonly applied to engines and other mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measurement of actual performance of any engine or power sources. It is also used a measure of performance of a vehicle as a whole, with the engine's power output being divided by the curb weight of the car, to give an idea of the vehicle's acceleration.

Power to weight (specific power)

The power-to-weight ratio (Specific Power) formula for an engine (power plant) is the power generated by the engine divided by weight of the engine as follows:

:egin{matrix}mbox{P-to-W}&= P/W \end{matrix}

A typical turbocharged V-8 diesel engine might have an engine power of convert|250|hp|kW and a weight of convert|450|kg|lb|-2, giving it a power to weight ratio of 0.56 kW/kg (0.25 hp/lb).

Examples of high power to weight ratios can often be found in turbines. This is because of their ability to operate at very high speeds. For example, the Space Shuttle's main engines use turbopumps (machines consisting of a pump driven by a turbine engine) to feed the propellants (liquid oxygen and liquid hydrogen) into the engine's combustion chamber. The liquid hydrogen turbopump is slightly larger than an automobile engine (weighing approximately convert|320|kg|lb|-2) and produces nearly 70,000 hp (52.2 MW) for a power to weight ratio of 160 kW/kg (100 hp/lb).

Examples

Engines

Fuel cells

The inverse of power-to-weight, weight-to-power ratio (power loading) is a calculation commonly applied to aircraft, cars, and vehicles in general, to enable the comparison of one vehicle performance to another. Weight-to-Power ratio is a measurement of the acceleration capability (potential) of any land vehicle or climb performance of any aircraft or space vehicle.

ee also

* Vehicle metrics

References


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