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.

J.Herris Friedrichshafen Aircraft of WWI (A Centennial Perspective on Great War Airplanes 21)

Friedrichshafen FF40

   Friedrichshafen's FF40 was another prototype to explore to potential of a non-standard configuration, in this case a fuselage-mounted single engine driving two propellers via gears and drive shafts. Like the FF34 and FF44, it was powered by a 240 hp Maybach and was a fairly large floatplane. It was a two-seater, class CFT, with the observer/gunner in the front cockpit, where he had an unobstructed view and field of fire. Unfortunately, the pilot was well aft, making communication and cooperation between the two crewmembers difficult during flight. Marine Number 669 remained the only prototype.

Friedrichshafen FF40 Specifications
Engine: 240 hp Maybach Mb.IV
Wing: Span Upper 21.00 m
Span Lower 19.00 m
Area 88.9 m2
General: Length 12.43 m
Height 4.45 m
Empty Weight 1,829 kg
Loaded Weight 2,539 kg
Maximum Speed: 125 km/h
Range: 650 km
Climb: 800 m 8 min
1,000 m 10.5 min

Журнал Flight

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.