The pilot had completed construction of the amateur built airplane, and was in the process of initial flight testing. The pilot had accumulated 4 hours of total flight time in the accident airplane. Prior to the accident flight, the pilot secured the side-opening canopy by engaging three interconnected 1/4-inch pins, into three 1/4-inch mating sleeves. Except for a significant amount of friction between the pins and mating surfaces, there was no locking mechanism for the canopy. Although the pilot did not experience any difficulties during several prior flights, the canopy opened during the initial climb of the accident flight, about 500 feet agl. When the canopy opened fully, the airplane became uncontrollable. Due to airflow over the canopy, the pilot was unable to refastened the pins, and had to hold the canopy closed with his hands. The pilot was able to partially control the airplane, and perform an emergency landing on a 5,602-foot-long, 100-foot-wide, asphalt runway. During the landing, the airplane departed the left side of the runway and struck a berm.