The flight instructor, who was on the controls, reported that he and a student taxied for departure. Upon arrival at the departure end of the runway, there were four airplanes ahead of them in a run-up area. He added that the first airplane moved to the hold-short line and that, after he completed the engine run-up, they moved forward to the hold-short line behind the first airplane. The other three airplanes, which were biplanes, remained in the run-up area. After the departure of the first airplane, the instructor told the control tower they were ready for departure, and the tower controller replied to stand by. The tower controller then cleared the three biplanes, which were waiting in the run-up area for takeoff as a flight of three. The second biplane in the flight struck the instructor's airplane's right aileron as it taxied past. The pilot of the tailwheel-equipped biplane reported that he was the second in the flight of three. He added that the flight had been holding in the run-up area at a 45° angle to complete their run-up checks when the tower controller cleared the flight for takeoff. He began to follow the lead airplane, and his airplane struck the airplane stopped at the hold-short line. He reported that he never saw the stopped airplane until after the impact. The instructor's airplane sustained substantial damage to the right aileron. In an interview with the Federal Aviation Administration inspector, the flight instructor reported that he was not aware that the three biplanes were part of a single flight awaiting takeoff clearance. He also reported that he had never flown tailwheel airplanes and was not aware of their limited forward visibility. The flight instructor and biplane pilot reported that there were no preaccident mechanical failures or malfunctions with their respective airplanes that would have precluded normal operation.