On May 2, 2009, about 0740 central daylight time, an amateur-built Hawkins Aventura II airplane,N20GH, was substantially damaged during an in-flight collision with terrain after takeoff from runway 26 (4,900 feet by 75 feet, asphalt) at Griffith-Merrillville Airport (05C), Griffith, Indiana. The flight was being conducted under 14 Code of Federal Regulations Part 91 without a flight plan. Visual meteorological conditions prevailed. The pilot sustained serious injuries. The local flight departed immediately prior to the accident. The pilot stated that the airspeed indicator failed during takeoff. He elected to continue the takeoff because there was insufficient distance to stop on the remaining runway. The pilot intended to remain in the traffic pattern and return for landing. However, as he turned to left crosswind the airplane became difficult to control, pitched down and impacted the ground. The pilot noted that he was briefly knocked unconscious. When he regained consciousness, the engine was still running and he shut it off. The airplane came to rest in a swampy area about 600 feet south of the runway. The amateur-built aircraft sustained damage to the left wing and left side of the nose. A post accident examination revealed a discontinuity in the pitot-static system. Specifically, tubing from the pitot tube was disconnected from a mating length of tubing located at the left wing root. The left wing remained attached to the fuselage at the wing root and the wing root structure was intact. Flight control continuity was confirmed. No other anomalies associated with a pre-impact failure were observed.