On August 4, 2000, at 1330 central daylight time, a Kollier Pitts S1C, N87V, operated by an airline transport rated pilot, collided with the terrain while performing aerobatic maneuvers in Salem, Indiana. The pilot received minor injuries and the airplane was substantially damaged. The 14 CFR Part 91 personal flight was operating in visual meteorological conditions without a flight plan. The flight originated from the Salem Municipal Airport, at 1320 cdt. The pilot reported that after takeoff, he climbed to 2,800 feet above ground level (agl). He reported that he performed an inside snap roll, rolled inverted to check and make sure his harness was secure, then he performed 2 outside snap rolls, followed by 1 rolling 360 degree turn at 2,500 feet agl. The pilot reported that he then climbed back up to 2,800 feet agl to practice an inverted flat spin. He reported he climbed inverted and as the airspeed reached 80 miles per hour, he reduced the power to idle. He reported he then added full forward stick and right rudder to enter the spin. He stated that the spin entry was normal. He reported he added stick pressure in the direction of the spin and added power to make the spin flatten out. After 1 1/2 turns, he neutralized the stick pressure and brought the power to idle. He then attempted to recover from the spin by adding left rudder followed by aft stick pressure. The pilot reported that although he did not recognize it at the time, he believes in hindsight, that the airplane then transitioned to a very nose low, accelerated upright spin in the same direction as the inverted spin. He reported that after approximately 15 turns, when he was unable to recover from the spin, he decided to let go of the flight controls. He reported that the spin remained steady and he still believed that he was inverted. He reported that just prior to impacting the terrain, he added right rudder and forward stick pressure. According to the pilot, the spin stopped with the airplane in a nose low attitude. The pilot reported that he added back stick pressure to raise the nose. The airplane impacted the ground in an upright attitude at high velocity after which it nosed over.