On December 16, 2017, about 1230 eastern standard time, a Cessna 182Q, N199RN, and a Piper J3C-65, N25786, collided in midair near Burlington-Alamance Regional Airport (BUY), Burlington, North Carolina. The private pilot of the Cessna and the commercial pilot of the Piper were not injured. The Cessna and the Piper both sustained substantial damage. Both flights were conducted under the provisions of Title 14 Code of Federal Regulations part 91 as personal flights. Day, visual meteorological conditions prevailed, and no flight plans were filed for either flight. The flights originated at BUY about 1220.The Piper pilot reported that he had recently performed maintenance on the smoke generator system and installed a new fuel pump. Prior to the flight, he asked the Cessna pilot to fly adjacent to him to verify the smoke system operation. After departure, the Piper pilot flew on the right side of the Cessna and both pilots acknowledged each other visually. The Piper pilot turned on the smoke system and the Cessna pilot verified that it operated normally with a "thumbs up" signal. The Piper pilot then broke off to the right to leave the formation. The Piper pilot subsequently elected to fly inverted to check the oil system and mixture control. After clearing for traffic and tightening his harness, he rolled inverted. The systems operated normally, so he rolled again to level the airplane upright. During the return to level flight, he heard a loud noise and the airplane rolled to the right. He believed that he had experienced aileron flutter. He was able to control the airplane and returned to BUY and landed without further incident. It was after landing that he realized that he had collided with the Cessna. The Cessna pilot reported that, after checking the smoke system on the Piper and giving a thumbs up signal, the Cessna pilot climbed and disappeared from view due to the high wing on the Cessna. Subsequently, while still in straight and level flight, he observed a flash of yellow at his 9 o'clock position, which was the Piper in a descent. He reported that the Piper struck his left wing. He was able to maintain airplane control and returned to BUY for landing. An inspector with the Federal Aviation Administration examined both airplanes. The right wing and aileron of the Piper were structurally damaged, as was the outboard portion of the Cessna's left wing. Numerous paint transfer marks were noted on both airplanes. No other damage was noted.