On May 20, 2000, approximately 1600 Pacific daylight time, an experimental Gifford TR-4, N1757, collided with trees during an emergency landing which occurred just after takeoff from Pangborn Field, Wenatchee, Washington. The private pilot, who was the sole occupant received serious injuries, and the aircraft, which was owned and operated by the pilot, sustained substantial damage. The local 14 CFR Part 91 personal pleasure flight was being operated in visual meteorological conditions. No flight plan had been filed, and there was no report of an ELT activation. According to the pilot, the aircraft had been on display at a fly-in at his home airport throughout the day, and he started it up in order to taxi it back to the hangar. As he was taxiing, he decided to take the aircraft around the pattern once before putting it away. Because of his change in plans, he did not perform a complete checklist review, and inadvertently did not fully engage the right canopy aft locking pin. Just after liftoff, the right side clam-shell entry door came partially open. As the airspeed built, the front latch also became disengaged, resulting in the door swinging fully open. Instead of continuing around the pattern and making a precautionary landing, the pilot attempted to reach across the cockpit to pull the door shut. As he struggled to close the door, the unsecured seat pan on his side of the aircraft shifted forward and partially restricted the aft movement of the pilot-side control stick. The pilot reduced power and allowed the aircraft to descend into an "open" field directly ahead of his flight path. Although the touchdown was successful, during the rollout, the aircraft entered an orchard of young fruit trees where it was substantially damaged. In a phone call with a representative of Tri-R Technologies, designers of the kit from which this aircraft was built, it was learned that the aircraft is fully controllable in flight with one door open. The representative stated the aircraft has been flown with one door open at normal approach speeds and flap settings, and showed no unusual flight characteristics. The representative also started that if the seat pan is not secured with some type of screw or pin to the bulkhead that it rests upon, there are certain situations where it may become dislodged.