An aircraft performs during the aviation festival "SKY: theory and practice" in Moscow, Russia, May 22, 2021. The festival is held annually in Moscow featuring performances by aerobatics teams, vintage airplanes, helicopters and a competition of homemade aircraft. (Photo by Alexander Zemlianichenko Jr/Xinhua)

Airplanes perform during the aviation festival "SKY: theory and practice" in Moscow, Russia, May 22, 2021. The festival is held annually in Moscow featuring performances by aerobatics teams, vintage airplanes, helicopters and a competition of homemade aircraft. (Photo by Alexander Zemlianichenko Jr/Xinhua)

An airplane prepares to take off during the aviation festival "SKY: theory and practice" in Moscow, Russia, May 22, 2021. The festival is held annually in Moscow featuring performances by aerobatics teams, vintage airplanes, helicopters and a competition of homemade aircraft. (Photo by Alexander Zemlianichenko Jr/Xinhua)

An aircraft performs during the aviation festival "SKY: theory and practice" in Moscow, Russia, May 22, 2021. The festival is held annually in Moscow featuring performances by aerobatics teams, vintage airplanes, helicopters and a competition of homemade aircraft. (Photo by Alexander Zemlianichenko Jr/Xinhua)