On May 19, 2012, at 1800 central daylight time, a Quicksilver Sprint II experimental light-sport airplane, N3521A, was substantially damaged during a forced landing following a loss of engine power shortly after a takeoff from a private airstrip near Lebanon, Illinois. The sport pilot and passenger sustained minor injuries. The airplane was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91. Day visual meteorological conditions prevailed for the personal flight, which was operated without a flight plan. The local flight was originating at the time of the accident. The pilot reported that there were no anomalies with the engine operation during a before-takeoff engine check or when he applied power for takeoff. He stated that during initial climb, about 35 feet above the ground, the engine suddenly lost power. The pilot reported that he reduced pitch in order to maintain airspeed, but the airplane impacted the terrain in a nose low attitude. The airplane immediately nosed over at impact, coming to rest inverted. The fuselage, empennage, and wings were substantially damaged during the accident sequence. The closest weather observing station was at the Scott Air Force Base/MidAmerica Airport (KBLV), located about 5 miles south-southeast of the accident site. At 1755, the KBLV automated surface observing system reported the following weather conditions: wind 180 degrees at 9 knots; visibility 10 miles; clear skies; temperature 30 degrees Celsius; dew point 15 degrees Celsius; altimeter setting 29.97 inches of mercury. The non-certificated Hirth model 3202 engine, serial number 900607, was manufactured by Göbler-Hirth Engines Ltd in Benningen, Germany, and imported into the United States by their authorized distributor, Recreational Power Engineering of Tiffin, Ohio. The engine was sold to the owner-of-record on July 16, 2007, as a short-block engine assembly that did not include a gearbox, exhaust, electric starter, or fuel injection system. The owner reportedly transferred the additional components from another engine. The engine was installed on the accident airplane on July 30, 2007. The last conditional inspection of the airplane and engine was completed on May 20, 2011. When the accident occurred, the engine had accumulated 152.9 hours since new. On June 01, 2012, the engine was disassembled by the owner/pilot under the supervision of inspectors with the Federal Aviation Administration. The engine disassembly revealed that the crankshaft had fractured at the flywheel/crankshaft interface. The crankshaft and flywheel assemblies were sent to the National Transportation Safety Board's (NTSB) Materials Laboratory Division for metallurgical examination. The crankshaft fracture surface contained crack arrest marks and tear ridges indicative of fatigue. The direction of the observed crack arrest marks revealed a single initiation point on the outer crankshaft surface. The location of the fracture origin coincided with wear marks, consistent with fretting, in a circumferential manner on the outer surface of the crankshaft. The observed wear marks matched those found on the flywheel female taper, consistent with relative movement between the crankshaft and flywheel. Mechanical smearing and chipping damage precluded further examination of the fracture origin. The fatigue fracture propagated through about 90-percent of the crankshaft cross-section. The remaining 10-percent of the crankshaft cross-section exhibited features consistent with overstress. Circumferential wear patterns were noted on the inner surface of the flywheel cylindrical magnet, which also contained accumulated metallic debris.