"On February 2, 1951, in a large building on Wallops Island, Zimmerman mounted the jet board, a plain plywood rectangle, and slipped his feet under straps. Two flexible air hoses made a T connection with a short nozzle of 1 1/4-inch diameter that poked down through the center. Men stood ready at valves some distance away. An overhead crane hoisted him on suspension lines attached to his parachute body harness until he hung a few feet above the floor.
Zimmerman signaled for the air to be turned on. A piercing scream issued from the nozzle beneath him, but he felt nothing, no lift, no sensation. Then he glanced up at the suspension lines. They were dangling slack!
He had risen and was now actually balancing on a jet thrust — and he hadn't been aware of it! For a full minute he stood there, in motionless wonder, then signaled and was let down.
It worked. It worked beyond the best anticipation of his theory. Balance control through the feet was so instinctive that it operated below the level of conscious thought. He went up and experienced it again. Paul Hill tried it. Testing further, they found that besides hovering perfectly by not thinking about it, you could control consciously, too–but here you tended to teeter your feet unnecessarily in a flurry of overcontrol. But you could travel without effort. Almost the wish alone caused imperceptible leaning and foot tilt, taking you to where you wanted to go, and stopping )'On when you reached there. Paul Hill became adept at sashaying around the 15-foot circle to which the dragging hoses limited him.
Outdoors on a windy day, flights were hardly affected by breeze or gusts. You compensated automatically by leaning a little to stay in one place."(Source)