The FF.40 was designed to meet a German Imperial Navy requirement for a three-seat patrol seaplane. It was a biplane but had an unusual powerplant design. The Maybach Mb.IV was fitted in the fuselage and drove two tractor propellers mounted just forward of and between the wings on each side. Only one aircraft was built.
^Kober, Theodor von; Borzutzki, Siegfried. Flugzeugbau Friedrichshafen GmbH (in German) (1. Aufl ed.). Burbach. pp. 130–131. ISBN978-3927513600.
Bibliography
Borzutzki, Siegfried (1993). Flugzeugbau Friedrichshafen GmbH: Diplom-Ingenieur Theodor Kober [Friedrichshafen Aircraft Company: Diploma-Engineer Theodore Kober] (in German). Berlin: Burbach. ISBN3-927513-60-1.
Herris, Jack (2016). Friedrichshafen Aircraft of WWI: A Centennial Perspective on Great War Airplanes. Great War Aviation Centennial Series. Vol. 21. n.p.: Aeronaut Books. ISBN978-1-935881-35-3.