7.14  Which statement concerning vortices caused by helicopters is correct?

1. Helicopter vortices are generally weak and dissipate rapidly when formed near the ground.
2. The size and weight of the helicopter has a direct influence on the intensity of the vortices.
3. Helicopter vortices are less intense than the vortices of an aeroplane of the same weight.
4. Wind does not influence the movement of vortices generated by a helicopter in hovering flight.

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