O.Thetford, P.Gray German Aircraft of the First World War (Putnam)
Friedrichshafen FF 40
Carrying a crew of three, the FF 40 was a patrol seaplane powered with a single 240 h.p. Maybach engine mounted in the fuselage and driving twin tractor airscrews between the wings. Only a single aircraft (No. 669) was built and supplied to the German Navy during March 1916. Span, 21.0 m. (68 ft. 10 7/8 in.). Length, 12.43 m. (40 ft. 9 1/2 in.). Height, 4.4 m. (14 ft. 5 1/4 in.). Area, 88.9 sq.m. (960 sq.ft.). Weights: Empty, 1,829 kg. (4,024 lb.). Loaded, 2,539 kg. (5,586 lb.). Armament, one manually operated Parabellum machine-gun in nose.
Flight, October 16, 1919.
SOME FRIEDRICHSHAFEN "MILESTONES"
"The F.F. 40.
"This was a very interesting experimental machine, fitted with a 240 h.p. Maybach engine driving two tractor screws placed between the planes (Fig. 20). The performance and general handling of this machine were good, but the transmission was too heavy in proportion to the engine power.