Heilcopter Wake Turbulance  

I can tell you, real world.

I was over the New Iberia sugar cane mill a year ago.  I observed a AW-139 pass about 500ft higher than my current alt of about 600ft.  He was coming in from offshore and had a straight tailwind blowing him.  Wake turb should not have been an issue as he was about a half mile from me.  5 min after he passed, his turb was still coming in from offshore behind him....with about a 15mph south wind.  I flew right through that wash in a clear blue day with no clouds and very little thermal activity.  Then it hit me.  I got spit sideways, wing stayed open, didnt collapse but I saw the center of my wing even with the horizon.....I got yanked sideways so hard.  Just as soon as it spit me sideways it let me go.  I was like what the heck was that???

Then I realized after reviewing my go pro footage, it was from the heli that crossed my path, rather I crossed his path after he had long since passed. 

Today we had an EC-135 cross us.  I climbed above as he was at about 600ft and I can quickly get to 1000.  He was flying east to west across a south wind, so the breeze about, 10mph had a chance to dissapate his wash.  I didn't feel anything at all.  My friend was down low about 200ft.  He didn't take any action.  He didn't feel any wake either. 

It all depends on distance from wake, and mostly mass of airframe, and secondly Direction of wake travel , against or with the wind.  Wake 90 degrees from prevailing wind is not near as bad as a wind that is carrying all the wake in one big straight column with a direct tail wind on the heli.