Main lesson. We often consider the downward turbulence when a helicopter is hovering (near stationary), but for helicopters with significant horizontally speed, the path of turbulence is at the same height, drifting with the wind and can last several minutes. We can be at risk when we think the helicopter is far away.
I experienced this at Torrey Pines on 2007/10/13, not fun.
Good information! I too have been rotor waked while hang gliding but did not have a severe issue due to my altitude. Let’s not forget what happened to Kevin Williams when he flew into the tip vortex of a fully-loaded fire bomber.
Pro Tip: If an aircraft flies upwind and you begin to smell kerosene turn away immediately.