What direction does the rotor wash spin during a hoist rescue?
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What direction does the rotor wash spin during a hoist rescue?
Hi all,
Just wondering if someone can provide me with some insight here as I'm a bit confused. During a hoist rescue, it is my understanding that the rotor was creates a downward wind and also a rotational wind that is in the same direction as the rotor (i.e., if the rotor spins clockwise then the rotor wash also spins clockwise). Is this true?
Also, during the hoist rescue, what happens if the load gets stuck in the TFZ/rotor wash? Will it go into a spherical pendulum motion and follow the rotation of the rotor wash? Or does it spin on the hook?
Thanks!
Just wondering if someone can provide me with some insight here as I'm a bit confused. During a hoist rescue, it is my understanding that the rotor was creates a downward wind and also a rotational wind that is in the same direction as the rotor (i.e., if the rotor spins clockwise then the rotor wash also spins clockwise). Is this true?
Also, during the hoist rescue, what happens if the load gets stuck in the TFZ/rotor wash? Will it go into a spherical pendulum motion and follow the rotation of the rotor wash? Or does it spin on the hook?
Thanks!
rbbd: Yes, the downwash would have a rotational component in the direction you describe for a conventional main rotor. In the case of coaxial rotors, or likely also on a KMax, there would be little of any such rotational flow. It seems reasonable that if a helicopter carried say a spherical load under a central cargo hook while in a hover, the load could start to spin around like a pendulum as you are suggesting.
RMK: I think the direction of spinning of a stretcher or other load on a hoist will depend more on its shape and hence aerodynamics than on main rotor swirl. So for example a left handed propeller lifted on a hoist would spin in the opposite direction than a right handed propeller lifted by the same hoist. In those cases the vertical downwash component and shape of load dominate.
RMK: I think the direction of spinning of a stretcher or other load on a hoist will depend more on its shape and hence aerodynamics than on main rotor swirl. So for example a left handed propeller lifted on a hoist would spin in the opposite direction than a right handed propeller lifted by the same hoist. In those cases the vertical downwash component and shape of load dominate.
There is a Rotorheads thread from 2014 titled "spinning sling loads?" with related discussion, and apparently from that thread the topic had been discussed even earlier on. Happy reading!
Underslung and hoist loads may well be affected differently. Never had any trouble with hoists, persons or stretchers. However, doing 'jungle penetrator' tests at Boscombe, the penetrator, on the end of 300' of rope, started to spin at about 30kts forward speed and developed a curious 'sinusoidal whip' motion and, eventually, parted company !
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This footage of an A109 lifting a stretcher has stretcher rotating clockwise although rotor turns counter clockwise viewed from above. Although when the hoisting starts, you can see stretcher was tending to start spinning CCW. They had to lower stretcher and fly ahead to slow the rate of spinning. Poor patient, day was already bad:
