On September 14, 2018, about 1004 Pacific daylight time, a Aero Vodochody L39C, N139UK, operating as Race 13, and an Aero Vodochody L39, N139PJ, operating as Race 37 collided in midair about 3 miles north of the Reno Stead Airport (RTS), Reno, Nevada. The airline transport pilot of Race 13 and the airline transport pilot of Race 37 were not injured. Race 13 sustained minor damage to the left side of the fuselage and bottom of the left wing; race 37 sustained substantial damage to the right wing and empennage. Race 13 was registered to Black Rock Aero LLC and race 37 was registered to MPE Enterprises Corporation. Both airplanes were operated by the pilots as a Title 14 Code of Federal Regulations Part 91 air race flights. Visual meteorological conditions prevailed, and no flight plan was filed for either airplane, which originated from RTS at 0950.During an in person interview, the pilot of race 13 reported that he was observing the pilot of race 37 flying a tight line on the course and he was observing his line throughout the race, and announced on the race frequency that he was passing race 37 on the right. The pilot said that he had sight of race 37 at all times and that during the 5th lap, in an area of pylon 4, he thought the pilot of race 37 may have rolled right prior to the collision. Following the collision, the pilot of race 13 declared an emergency and landed uneventfully. During an in person interview, the pilot of race 37 reported that during the 4th lap, while passing pylon 7, he recalled hearing the pilot of race 13 state that he was on his right. The pilot said that during the 5th lap, as he was passing pylon 4, it felt like a car crash and that he never saw race 13. Shortly after, he heard the pilot of race 13 declare a mayday and he decided to declare mayday as well, while noting sluggish control responsiveness. The pilot of race 37 was able to land uneventfully. Review of video that was captured by a witness revealed that race 37 appeared to be in a level attitude while nearing pylon 4, and race 13 appeared to be in a slight left bank, behind race 37. Shortly after, race 37 was observed initiating a left bank, while race 13 was rapidly approaching race 37 from behind. Just prior to the collision, race 13 was observed rolling out of the turn to an almost level attitude. Examination of Race 37 revealed that the outboard 24 inches of the right wing and right aileron were separated from the airplane. Additional damage to the bottom portion of the vertical stabilizer and the leading edge of the left horizontal stabilizer was observed. Examination of Race 13 revealed damage to two inspection panels and fairings on the forward left side of the fuselage.