Flugzeugbau Hopfner, at Vienna Aspern, formed 1920 and produced S.1 3-seat monoplane, HV.3 4-passenger transport based on Fokker F.III, improved HV.6 (1928), HS.528 2-seat parasol and HA.1133 4-seat twin-engined amphibian before being taken over by Hirtenberger.