On 4/18/83, the ultralight vehicle was damaged by high winds. This necessitated the replacement of the front and rear spars as well as the battens which provided curvature to the upper wing surface. Prior to a test flight, a weighted tail wheel was also installed. Subsequently, a test pilot took off to evaluate the ultralight. Witnesses observed that the pilot climbed to about 1000 ft, then began a series of maneuvers. While performing a maneuver similar to a lazy 8, with bank angles up to 60 to 90 degrees, the ultralight's left wing folded. The vehicle then entered an uncontrolled descent and crashed. An exam of the wreckage revealed that the aft spar tip had rotated around the aft spar in such a manner that the outboard wing panel had bent down and rearward. Holes had not been drilled and steel pop rivets had not been installed, per installation instructions, to prevent the spar tip from rotating. Also, the pilot's blood alcohol level was found to be 95 mg%. The test pilot also performed maintenance on the ultralight.