On July 10, 2004 at 1138 eastern daylight time, an unregistered experimental Adventura II, owned and operated by Quality Contracting Services Inc., collided with the ground shortly after takeoff from runway 23 at Naples Municipal Airport, Naples, Florida. The personal flight operated under provisions of Title 14 CFR Part 91. Visual meteorological conditions prevailed at the time of the accident and no flight plan was filed. The airplane was substantially damaged. The pilot was not injured, the passenger suffered minor injuries. The flight originated from Naples Municipal Airport, Naples, Florida, on July 10, 2004 at 1137. The pilot completed one high speed taxi on runway 23, and then started a second high speed taxi at which time he attempted to take off. The pilot applied full power and climbed to approximately 100 feet above. As he continued the climb, he noticed the airplane was not performing properly. The passenger stated she heard the airplane engine surging. The pilot reported the engine problem to the control tower and his last transmission stated "I need to make a 180 and come back". The 180-degree turn was never completed and the airplane landed hard at the end of runway 23. The flight was never cleared for a takeoff. Examination of the airplane revealed the main landing gear collapsed, the aluminum support tubes fractured, and the float attachment tube fractured.