Flingwing,
Here is the page I referred to in a post above, from Georgia Tech, where the relationship betweem disk loading and downwash velocity is explained. Basically, the disk keeps the helo up by throwing air downward. The heavier the aircraft, and the smaller the disk the more speed the package of air must have to develop the thrust and keep the helo up. The disk loading is a good approximation of the velocity. Two helos with the same disk loading will have the same downwash velocity, and the same vertical speed for getting into VRS. for your helo with 2.9 lbs/sq ft, the downwash speed is 33 miles per hour, or 49 feet per second.
the "p" type symbol in the formula is air density, "rho" and is .002378, if you want to crunch the numbers.
