The pilot had limited solo experience in powered aircraft and had never flown the accident aircraft type before. He said he had been conducting taxi tests with no intention of flying. However, about three quarters of the way down the runway the aircraft unexpectedly became airborne, on somewhat less than full power. Assuming there was insufficient runway remaining for a landing, the pilot climbed to what he assessed to be a safe altitude and turned left without changing the power setting. He was concerned at the low indicated airspeed and when the right wing dropped he thought the aircraft had stalled. He immediately applied full power and lowered the nose. No other control inputs were made and the aircraft flew into the ground under high power in a shallow descent. The pilot's instructor said he noticed the pitot head was misaligned before the aircraft was assembled on the morning of the accident. He realigned the head but noticed that it rotated reasonably easily in its mounting. He noticed the head was again misaligned after the accident. If the head had been misaligned during the flight the indicated airspeed would underread. This could explain why the aircraft unexpectedly became airborne, then cause the pilot to think he had stalled when the right wing dropped at low indicated airspeed.