At 22:09 16 December 2016, Jonathan St. Cloud wrote:
I do not think I had "thermic help" over the hot
concrete/pavement. I
think the tall grass negated the ground effect.

On Friday, December 16, 2016 at 1:51:22 PM UTC-8, Charlie M.
(UH & 002
owner/pilot) wrote:
I would sorta guess you had "thermic help" when over the
pavement while
you may have had sink over the grass.

I would hazard to say that rotorcraft ground effect is not the same
as fixed wing ground effect. That is a whole other ball of wax...
When they took Bin Laden out, they had practiced in a mocked up
area with chain linked fences surrounding the "compound". The
reality was 8' concrete walls which deflected the blast upwards to
create a vortex. As I recall, the temperature inside the compound
was also ~15°F hotter than forecast (or reported by agents in the
field). That pilot did a great job in a controlled crash, as the
conditions inside the compound (vortex, temps, altitude) would not
let him hover at that weight. Rotorcraft (V-22 included) downwash
and vortices are a whole other animal unto themselves. Comparing
them to glider ground effect is "apples to oranges"...

While I do live in "helicopter central" (Close to the main Sikorsky
plant), I only have a cursory understanding of that arena through
education and friends / family in that business. I would leave the
technical answer to your rotorcraft question to a rotary aircraft
specialist. Sikorsky's "Skunk Works" is in Elmira, and I assume
there are some of those employees who are also glider pilots that
can answer your helicopter related question. I know that one of our
old glider club members transferred there to work at the
"Hawkworks" when it first opened.

RO