The Austrian Bruno Nagler began work in the rotory-wing field in 1929 when, with Raoul Hafner, he built his RI Revoplane at Aspern Airport, near Vienna. This was a single seat machine with a rotor driven by a 45 hp engine and had a vertical torque-balancing surface acting in the rotor downwash. This machine, and also similar RII machine of 1932, was successfully tested in Great Britain.