On September 24, 2011, at 0852, N211KF, an experimental Tom Bins Kitfox IV equipped with floats, sustained substantial damage during a forced landing shortly after takeoff from Lafayette Regional Airport (LAF), Lafayette, Louisiana. The private pilot/owner sustained serious injuries. Visual meteorological conditions prevailed and no flight plan was filed for the personal flight conducted under 14 Code of Federal Regulations Part 91. The flight was originating at the time of the accident. The pilot reported that he departed Lafayette with 15 gallons of fuel on board with the intentions of making just one circuit in the traffic pattern followed by a full-stop landing. Shortly after takeoff, when the airplane reached an altitude of 400 feet, the pilot heard a "swoosh" and a "loud bang" followed by a 50 percent reduction in power. He elected to return back to the runway and initiated a 270 degree turn. As he was turning back, the engine continued to lose power. The pilot was unable to maintain altitude and made a forced landing to a grass field about 1/8 of a mile from the runway. The pilot said he was in “complete control” of the airplane but it "lost lift" when it was 15-20 feet high. The airplane "dropped" on to the ground, landed hard, and flipped over. Examination of on-site photos revealed that the airplane sustained substantial damage to the firewall and the wing struts. Both floats and one propeller blade were also damaged. The engine was test-run under the supervision of the Federal Aviation Administration (FAA). The engine was started utilizing fuel in the carburetor bowls and then run until the fuel was exhausted. The carburetor bowls were refilled and the engine was re-started. This time engine power was increased and both magnetos were checked. No anomalies were noted with the magnetos or the engine.