Achenbach, a German, designed an aircraft with a single rotor to ensure lift and also featuring a transverse airscrew to counteract torque.

P.Lambermont "Helicopters and Autogyros of the World", 1958

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This model by the German Achenbach was the first to use a tail rotor to counteract the torque from the main rotor.

G.Apostolo "The Illustrated Encyclopedia of Helicopters", 1984

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