On June 30, 2004, about 1500 eastern daylight time, a homebuilt Tango 2, N56KC, registered to a private individual, experienced a loss of control during a high speed taxi test, became airborne, and descended on airport property near the runway at the Williston Municipal Airport, Williston, Florida. Visual meteorological conditions prevailed at the time and no flight plan was filed for the high speed taxi test. The airplane was substantially damaged and the airline-transport rated pilot, the sole occupant, sustained minor injuries. The high speed taxi tests started approximately 15 minutes earlier. The pilot stated that he had just performed two high speed taxi runs; the first was to 40 knots and the second was up to 60 knots indicated airspeed (KIAS). He planned on performing one more taxi run and when the airspeed was at 60 knots, he checked the engine rpm, then noted the airspeed was between 60-70 knots. The airplane then began drifting to the left and he reduced throttle and applied right rudder input. The airplane continued off the left side of the runway and he added power and rotated the airplane to a nose-high attitude. The airplane became airborne but was, "...wallowing in the air." The airplane descended, and contacted the ground in what he thought was a wing low attitude. He reduced power, and the airplane then nosed over. He exited the airplane with assistance from bystanders. He reported there was no preimpact mechanical failure or malfunction.