The pilot lost control and collided with the runway while maneuvering for landing. The pilot and passenger were testing atmospheric conditions with meteorological equipment in conjunction with noise testing of a Boeing 707 'hush' kit. The Cessna took off heading SE. It climbed to 800 ft AGL and began doing descending right-hand turns over an unidentified object on the ground. After descending to about 50 ft AGL, the Cessna climbed to about 100 ft AGL. At this point the pilot attempted to align the aircraft with the runway. Heading SE crossing over the runway at an angle, the aircraft was turned left to be aligned with the runway. During the left-hand turn the aircraft stalled and entered a left-hand spin. The aircraft made 1/2 to 3/4 revolution prior to making contact with the ground. Examination of the aircraft did not disclose any evidence of mechanical failures or malfunctions. The aircraft was being operated in an overweight condition.