The pilot of the light sport airplane reported that he was flying to an uncontrolled airport to attend an airshow later during the day. The destination airport traffic pattern was busy with several airplanes in the traffic pattern and a flight of three north of the airport. The pilot entered the traffic pattern by overflying the airport and crossing midfield onto a left downwind leg. At that point, a life flight helicopter reported 2.5 miles southwest. The pilot subsequently heard a report from the helicopter again and asked him where he was. The helicopter stated that he was on the right base leg for runway 11 and number two to land. The pilot of the airplane announced turning to final for runway 11. He was over the threshold at 20 ft above ground level when he saw the helicopter cross the runway several hundred feet ahead of him. The airplane then encountered the rotor wash, rolled right inverted and struck the runway, coming to rest on the runway. The pilot of the helicopter reported that he departed his home base about 2.5 miles from the airport to attend an airshow public relations event at the airport. He entered a right base leg for runway 11 and stated intentions to land No. 2 as there were four airplanes in the traffic pattern and airplane No. 3 (the accident airplane) was turning from left downwind to left base. The helicopter approached the runway numbers, sidestepped north to taxiway A1, and landed at a predesignated position on the taxiway for the airshow. After shutting down, the pilot was told by ground personnel that the airplane following him was involved in an accident.