On September 20, 1994, at 1305 eastern standard time, an amateur built Dooley Velocity, N107JD, experienced a hard landing on the approach to runway 27 (6,000' X 100' dry/asphalt), at Valparaiso, Indiana, following an inadvertent flight while the pilot was making high speed taxi tests. The airplane sustained substantial damage. The pilot reported no injuries. The flight occurred in visual meteorological conditions. No flight plan was on file. The local flight departed at approximately 1300. The pilot stated that while making a high speed taxi test, the airplane became airborne inadvertently. At that point he was unable to reduce the nose up attitude of the airplane and maintained flight by using the throttle. He said that he was able to return for a landing by use of the throttle, but was unable to accurately land the airplane on the runway. The airplane struck a light stanchion short of runway 27. A Federal Aviation Administration inspector examined the airplane subsequent to the accident and found that the pitch trim on the airplane was activated by an electric trim control on the yoke. He found that the trim switch was activated by an on/off switch, likewise located on the yoke. The switch was in the off position. When the inspector asked the pilot what the purpose of the switch was, the pilot was unable to describe accurately the use of the switch.