﻿ Power-to-weight ratio

# Power-to-weight ratio

The power to weight ratio (correct the mass - value ratio) is the ratio of the mass and the performance of a vehicle, a motor, a battery or similar tools and machines. It is expressed in kilograms per watt.

A physically more precise term is the power density, which is reciprocally expressed in W / kg. This term is, however - partly imprecise - used based on area or volume.

In some cases, such as in cycling, and the reciprocal value is used: the weight -related benefit, ie the quotient of power and mass ( W / kg). It has the advantage that with it, the acceleration and gradeability is also rising.

For drives generally have a low power to weight is sought, since a smaller mass or a higher power allows for greater acceleration and thus against the action of hindering natural forces such as inertia, gravity or inertia. To allow a lower power to weight ratio of a vehicle, for example a higher speed on inclines.

Even with batteries for traction or for portable devices to low mass for money is sought; here, however, usually the stored energy per mass ( Joules per kilogram ) plays a role that should be maximized. See also energy density.

## Examples and importance of vehicles

### Motor vehicles

The acceleration typically specified in motor vehicles, such as " X seconds from 0 to 100 km / h", of a number of parameters (eg torque curve, circuit, traction, air resistance ) is dependent and therefore can not be derived directly from the power to weight ratio. However, in principle applies here: A lower power to weight ratio allows for greater acceleration.

Typical power weights of motor vehicles:

• Formula 1 cars: 1 kg / kW
• GP bike: 0.8 kg / kW (2012 )
• Sport motorcycle: 1.3 kg / kW
• Sports car: 4.2 kg / kW (Porsche 911 Turbo S, 2009)
• Continuous car: 14.7 kg / kW ( 2012)
• Leopard 2 56 kg / kW

Selection of some vehicles:

For light vehicles, the weight of the transported persons gaining in importance.

### Aircraft

In aircraft, a low mass for money means a better climb and a shorter take-off run. Similarly, aircraft with low power density, especially fighter aircraft, long-lasting tight curves with high g - forces can fly, as the result of the high buoyancy ( the need to overcome the centrifugal force ) caused drag a large thrust faces ( dogfight ). For this reason, aircraft have a particularly low power to weight ratio; Combat aircraft are often also equipped with afterburners, booster engines or rocket boosters to briefly increase thrust can. A thrust -to-weight ratio that is greater than one, thus enabling, the acceleration in the vertical climb.

505845
de