Disk loading is an indication on the efficiency of a rotor system, and so a helicopter's performance.
Disk loading is the comparison of the helicopter's mass to the area of the main rotor disk. In general, the lower the loading, the more efficient the rotor, and so the better performing the helicopter.
Disk loading is a very "rough and ready" measure of performance for three reasons:
- It is common to consider the entire disk as a lifting area, even though the rotor head itself takes up some of this area and provides no direct lift.
- The blades are moving at vastly different speeds at different points of the disk and therefore have vastly different performance.
- The blades used affect performance significantly.
- A typical 450-sized electric helicopter may weigh 800 grams (0.8Kg) and have a rotor diameter of 70cm (0.7m), giving a disk loading of:
- 0.8/(pi*(0.7/2)^2) = 2.1Kg per square meter
- A Trex 600e weighing in at 3kg has a main rotor diameter of 1.35m, giving a disk loading of:
- 3/(pi*(1.35/2)^2) = 2.1Kg/m^2
- A Compass Knight 3D weighs 4kg all up, and has a main rotor diameter of 1.34m, giving a disk loading of:
- 4/(pi*(1.34/2)^2) = 2.83Kg/m^2
- For comparison, the AH64A Apache weighs in at 8000kg and has a rotor diameter of 14.63m, giving a disk loading of:
- 8000/(pi*(14.64/2)^2) = 47.5Kg/m^2
- It is doubtful that a model helicopter would be able to fly with such a high disk loading: for 3kg helicopter this would be a rotor diameter of about 30cm!
- Another comparison, the Robinson R22 weighs in at 417kg loaded and has a rotor diameter of 7.7m; a disk loading of:
- 417 / (pi*(7.7/2)^2) = 9.0kg/m^2
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