HISTORY OF FLIGHTOn August 4, 2017, about 0900 Pacific daylight time, an experimental, amateur-built Rans S-9 Chaos light sport airplane, N519TB, was substantially damaged in a hard landing during an aborted takeoff from Hackney Skypark (ID05), Athol, Idaho. The commercial pilot was seriously injured. The airplane was registered to and operated by the pilot as a Title 14 Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions prevailed and no flight plan was filed for the local flight that was originating at the time of the accident. According to the pilot's son, who was part of the ground crew for the flight attempt, this was the maiden flight of the kit-built airplane. Because the winds were "very light," the pilot decided to use runway 21, which afforded multiple flat fields beyond the runway end. The airplane was fueled with about 12 gallons, and the canopy was left off (a configuration "approved" by the kit manufacturer) for the initial flight. The pilot conducted a "thorough pre-flight and control checks," and radio communication with the ground crew was confirmed. The elevator trim tab was set to neutral, the engine was started and warmed up, and the pilot taxied out uneventfully. He then conducted a "high speed taxi test," which included application of full power, acceleration to about 55 mph, followed by power reduction and rollout. This too was uneventful, and the pilot taxied back for his planned takeoff from runway 21. The pilot announced his departure on the radio and applied full power. According to the pilot's son, the airplane accelerated well, and liftoff occurred about 300 to 400 ft down the runway. About 2 seconds after liftoff the airplane was observed pitching up to a "fairly nose high attitude" of about 15o to 20o, as it reached an altitude of about 50 ft, prompting the son to radio to the pilot about the excessive pitch attitude. When the airplane was at an altitude of about 150 ft, and less than halfway down the runway, the other ground crew member observed it to be descending rapidly. The airplane landed hard, collapsed the main landing gear, and came to rest upright near the right edge of the turf runway. The forward and lower fuselage sustained substantial crush damage. There was no fuel leakage or fire. The ground crew helped the pilot exit the airplane. He sustained head injuries despite his shoulder harness, and was taken to the hospital for treatment. The pilot initially reported to the ground crew that he had difficulty controlling the pitch attitude of the airplane, and that the engine performed normally. In a later statement, the pilot reported that he attempted a steep climb in order to ensure that he cleared trees at the end of the runway. Due to the mid-wing configuration, he lost sight of the horizon in the initial climb, and then had difficulty judging his pitch attitude due to the lack of a cockpit attitude indicating instrument. PERSONNEL INFORMATIONThe pilot held a commercial certificate with airplane single-engine, multiengine, and instrument ratings. He had about 6,000 hours total flight experience, including about 2 hours in the accident airplane make and model. He had also successfully built and conducted first flights of two other make and model airplanes. His most recent flight review was completed in July 2016. At the time of the accident, he no longer held a current Federal Aviation Administration (FAA) medical certificate, and was operating under the light sport provisions via his driver's license. AIRCRAFT INFORMATIONThe airplane was equipped with a 52 Hp Rotax 503 DCDI series engine, and airplane construction was completed a few weeks before the accident. The pilot spent a few weeks conducting engine, propeller, taxi, and ground handling tests, and making minor adjustments to correct noted issues. A data sheet that documented the measured flight control travel ranges indicated that all travel ranges were in accordance with the kit manufacturer's specifications. Prior to the flight, the pilot accomplished multiple weight and balance calculations, including extreme forward and aft CG (center of gravity), as well as the test flight conditions case. The kit manufacturer's CG range was 53 to 62 inches, and the calculated CG for the accident flight was 59.7 inches. For that flight, the airplane was calculated to weigh 677 lbs. The kit manufacturer specified only two maximum takeoff weights; one for airplanes equipped with a 65hp engine (710 lbs) and one for 80/100 hp engines (810lbs). The kit manufacturer did not respond to an NTSB query regarding installation of the lower hp engine. However, the builder/pilot reported that he was told by the kit manufacturer that kit was offered with the 52 hp engine until that engine (Rotax 503) went out of production. The pilot's weight and balance calculations were verified by investigators, but the actual weights and distances were not verified by investigators. The kit manufacturer recommended that for takeoff, the airplane be flown off the ground in the "three-point attitude" (tail wheel still on the ground) instead of the typical procedure of lifting the tailwheel during the takeoff roll. Post accident, the pilot's son reported that during the final high speed taxi test, the airplane "became light" at about 55 mph; he thought this was unusual because the stall speed was cited as 41 mph, and that the airplane should have begun lifting off at a speed below 55 mph. METEOROLOGICAL INFORMATIONThe 0856 automated weather observation at an airport located about 12 miles south of the accident site included winds from 080o at 5 knots, visibility 10 miles, clear skies, temperature 24oC, dew point 12oC, and an altimeter setting of 29.89 inches of mercury. AIRPORT INFORMATIONThe airplane was equipped with a 52 Hp Rotax 503 DCDI series engine, and airplane construction was completed a few weeks before the accident. The pilot spent a few weeks conducting engine, propeller, taxi, and ground handling tests, and making minor adjustments to correct noted issues. A data sheet that documented the measured flight control travel ranges indicated that all travel ranges were in accordance with the kit manufacturer's specifications. Prior to the flight, the pilot accomplished multiple weight and balance calculations, including extreme forward and aft CG (center of gravity), as well as the test flight conditions case. The kit manufacturer's CG range was 53 to 62 inches, and the calculated CG for the accident flight was 59.7 inches. For that flight, the airplane was calculated to weigh 677 lbs. The kit manufacturer specified only two maximum takeoff weights; one for airplanes equipped with a 65hp engine (710 lbs) and one for 80/100 hp engines (810lbs). The kit manufacturer did not respond to an NTSB query regarding installation of the lower hp engine. However, the builder/pilot reported that he was told by the kit manufacturer that kit was offered with the 52 hp engine until that engine (Rotax 503) went out of production. The pilot's weight and balance calculations were verified by investigators, but the actual weights and distances were not verified by investigators. The kit manufacturer recommended that for takeoff, the airplane be flown off the ground in the "three-point attitude" (tail wheel still on the ground) instead of the typical procedure of lifting the tailwheel during the takeoff roll. Post accident, the pilot's son reported that during the final high speed taxi test, the airplane "became light" at about 55 mph; he thought this was unusual because the stall speed was cited as 41 mph, and that the airplane should have begun lifting off at a speed below 55 mph.