Chris
Part of the illusion is the angle of the aircraft as viewed by the
crowd. When the winds are right, the pilot can be flying at an
indicated airspeed that appears to be zero on the ground. Wayne Handley
did it with his Raven but he had so much power that it was easy for him
to just "hang" on the prop, then fly out of it.
It is a combination of pilot skills (and Shawn is a superb pilot and
crop duster as was Wayne) and aircraft capability.
I have the utmost respect for their abilities. I'm also a crop duster
pilot and have known Wayne for 20 years but have only met Shawn in
passing.
Rocky