Robert Dorsett - 1994
Everyone's saying something a bit different, but the bottom line is that
the 757's wing-flap geometry can produce *relatively* heavy wake vortices,
but not *spectacularly* heavy for airplanes of its weight. The *risk* of
the vortices comes from the 757's performance: it can out-climb just about
every other transport out there by a factor of 1.5 to 2. This means that
classic restrictions on vortex separation may not work: you can't stay "at
or above" another airplane's wake if you can't stay at or above the other
airplane.
NOAA Testing - 1990
Nearly 250 flybys were flown passed the INEEL Test Range 200-ft tower. The vortices were measured by an array of 100 high-speed hot-film anemometers and visualized with an array of colored smoke-emitting grenades. The highest velocities of any previously measured aircraft were generated by the B-757. However, when normalized relative vortex circulation is compared, the vortex strengths of the B-757 were comparable to other aircraft in its weight category. Anecdotal evidence indicated a relationship of atmospheric stability to vortex longevity. However, statistical relationships could not be conclusively drawn.
Linky to NASA report - 1998
http://techreports.larc.nasa.gov/ltr...8-cr206933.pdf