On July 6, 2019, at 1045 central daylight time, an experimental amateur-built Freeman Super Koala, N220FF, experienced a hard landing during a return to Mercer County Regional Airport (HZE), Hazen, North Dakota, following a loss of aileron control. The commercial pilot was uninjured and the airplane was substantially damaged. The airplane was registered to and operated by the airplane owner under Title 14 Code of Federal Regulations Part 91 as a maintenance test flight that was not operating on a flight plan. Day visual meteorological conditions prevailed at the time of the accident. The local flight originated from HZE. The pilot reported that the airplane had undergone reassembly of its wings and flight control rigging prior to the flight. On the day of the accident, he performed the fourth test flight of the airplane. He reported the airplane was having issues with the ailerons being fully functional once in flight. The pilot and the airplane owner were attempting to diagnose and fix the issue. The pilot preflighted the airplane, taxied out, performed a run-up, and confirmed the controls were free and correct. During the takeoff form runway 14, the airplane "quickly" became airborne and about 15 ft above the ground began to roll to the left. After applying full right aileron, the airplane continued to roll left and descend, which led to a left wing-low impact with the ground roughly 10-20 ft from the runway. The airplane's left wing spar, bottom fuselage, cowling, engine, landing gear, and firewall were substantially damaged. The Federal Aviation Administration (FAA) inspector from the Fargo, North Dakota, Flight Standards District Office reported the airplane was purchased by the current owner from an estate. The airplane was disassembled and transported via trailer to Hazen, North Dakota. The airplane owner along with a FAA certificated mechanic assembled the airplane and they told the inspector they had issues with the aileron cable tensions. The airplane owner reported that he called the kit manufacturer but was unable to get the information he needed. After several attempts to properly adjust the aileron cable tensions, they determined that test flights would be needed. Post-accident inspection of the airplane revealed improper rigging of the ailerons and improper cable tensions. Inspection of the airplane maintenance logbook revealed the airplane was not properly signed off for return to service after maintenance.