Beater;
Rotor induced fog is quite well known. I once put Aberdeen into low viz procedures doing a ground run before the first departure of the day. The Puma enveloped itself in a small fog bank which then spread as others started up. Took ten minutes to cover the entire airfield. Landing last week in clear, humid conditions the viz was appalling for five minutes after I landed.
Watch your tip vortices in the right conditions and you will see the phenomina.
VH