Power to weight ratio

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The power to weight ratio is an indication of the performance potential of a helicopter.

As helicopters get bigger their power systems can generate more power, but unless the power to weight ratio improves the helicopter's performance (ability to maneuver and climb) will remain the same.

A helicopter typically requires about 200W per kg to hover out of ground effect at sea level.

While it's commonly called a ratio, it's not really as the value has units and is not just a pure number.


  • A typical 450-sized electric helicopter may weigh 800 grams (0.8Kg) and have 400 Watts of power available, giving a power to weight ratio of:
400 / 0.8 = 500W per kg
  • A T-Rex 600e weighing in at 3kg may have a motor capable of generating in excess of 2000W, giving a power to weight ratio of:
2000 / 3 = 667W/kg
and thus far better performance, assuming that power can be well used by the rotor system.
  • A Compass Knight 3D powered by an OS 50 SXH produces 1.8hp (1.3kW) and weighs in at 4kg all-up, giving a power to weight ratio of:
1300 / 4 = 325W/kg
  • For comparison, the AH64A Apache weighs in at 8000kg and has 2 turboshaft engines rated at up to 1490kW each, giving a power to weight ratio of:
(2 * 1490000) / 8000 = 372.5W/kg
In practice, the transmission is probably not rated to cope with even this amount of power, at least not for any length of time.
  • Another comparison, the Robinson R22 weighs in at 417kg loaded. powered by a Lycoming piston engine derated to 93kW (more in more recent models), giving a power to weight ratio of:
93000 / 417 = 223W/kg

See also

External links

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