Disk loading

[1] The V-22 Osprey tiltrotor aircraft has a high disk loading relative to a helicopter in the hover mode, but a relatively low disk loading in fixed-wing mode compared to a turboprop aircraft.

For a given weight, a helicopter with shorter rotors will have higher disk loading, and will require more engine power to hover.

[5][6] Typically, an autogyro (or gyroplane) has a lower rotor disk loading than a helicopter, which provides a slower rate of descent in autorotation.

Maximum efficiency is reduced as disk loading is increased due to the rotating slipstream; using contra-rotating propellers can alleviate this problem allowing high maximum efficiency even at relatively high disc loading.

This energy transfer from the rotor to the air is the induced power loss of the rotary wing, which is analogous to the lift-induced drag of a fixed-wing aircraft.

Conservation of linear momentum relates the induced velocity downstream in the far wake field to the rotor thrust per unit of mass flow.

Conservation of energy considers these parameters as well as the induced velocity at the rotor disk.

The momentum theory applied to a helicopter gives the relationship between induced power loss and rotor thrust, which can be used to analyze the performance of the aircraft.

Viscosity and compressibility of the air, frictional losses, and rotation of the slipstream in the wake are not considered.

Since the flow far upstream of a helicopter in a level hover is at rest, the starting velocity, momentum, and energy are zero.

developed over the disk is equal to the rate of change of momentum, which assuming zero starting velocity is: By conservation of energy, the work done by the rotor must equal the energy change in the slipstream: Substituting for

[10] This article incorporates public domain material from Rotorcraft Flying Handbook (PDF).