On October 24, 1998, about 1530 central daylight time, a Peters Strojnik S2A amateur built motor glider aircraft, N70136, registered to an individual, landed hard at Coastal Airport, Pensacola, Florida, while on a Title 14 CFR Part 91 personal flight. Visual meteorological conditions prevailed at the time and no flight plan was filed. The aircraft received substantial damage and the private pilot was not injured. The flight originated from Pensacola, Florida, the same day, about 1400. The pilot stated that he took off using the engine of the motor glider and climbed with engine power to 4,000 feet. After about 1 hour of gliding he returned to the departure airport. He approached to land without engine power. As he flared for landing the aircraft suddenly lifted back up to about 40 feet. He stated he does not know if he encountered a wind gust or a thermal. He nosed the aircraft over to regain airspeed and noticed that he was running out of runway. He forced the aircraft onto the runway touching down hard.