From my PERSONAL experience...ages ago (in the USN) at an airshow in Boulder City, NV (just outside Vegas) there was an airshow. We were a static display (Seahawk) parked between a CH-53 and a Chinook. After the show, we had to split so we opted to lift and depart from between the two other aircraft.
Now, the Seahawk puts out a lot of downwash, but not enough to be a problem for our neighbouring aircraft. However, about 50 metres along our departure path, a whole row of porta-loo's went ass over teakettle as we passed overhead...OOOPS! Fortunately nobody 'aboard' those babies when they went ass up...just a few embarassed moments for us to ponder.
Come to think of it, on another occasion inbound to McCarran Airport in Vegas we were directed to air transit from the threshold of the duty runway to the parallel taxiway to land. As we did so (at about 60-80 feet) we blew up a TREMENDOUS cloud of dust which caused tower to have to 'waveoff' the inbound RPT aircraft (which, I believe, was the reason for the direction to air taxi to land on the taxiway)...as soon as we switched to Ground we were told "call me as soon as you shutdown" by the controllers (uh, oh). Fortunately, after explaining that we were moving on the aerodrome as directed by them, they cooled down a bit...no harm done.
There have been instances (not me, thank Christ) where Seahawks have blown corrugated panels off the roofs of buildings and, on at least one occasion, blown light civil aircraft over on the flightline (YOINK!). I guess when you're flying 10 tonnes of aircraft it takes a bit of energy to do it and that energy, in the form of the downwash, can do nasty things.
HP