O.Thetford, P.Gray German Aircraft of the First World War (Putnam)
Friedrichshafen FF 31
Only two FF 31 seaplanes were built (Nos. 274 and 275), and they were delivered to the German Navy in May 1915. No. 275 is illustrated. Span, 16.85 m. (55 ft. 3 3/8 in.). Length, 10.15 m. (33 ft. 3 5/8 in.). Height, 3.9 m. (12 ft. 9 5/8 in.). Area, 60 sq.m. (648 sq.ft.). Weights: Empty, 1,040 kg. (2,288 1b.). Loaded, 1,530 kg. (3,366 lb.). Speed, 98 km.hr. (61.25 m.p.h.). Armament, one manually operated Parabellum machine-gun.
J.Herris Friedrichshafen Aircraft of WWI (A Centennial Perspective on Great War Airplanes 21)
The outbreak of war made arming aircraft imperative, and in the absence of a reliable synchronizing gear at the time, an obvious solution was the pusher configuration. This provided a gunner with a flexible machine gun in the front cockpit an unexcelled field of fire forward without the problem of safely firing the gun through the propeller arc. Moreover, at this time, before any experience with air-to-air combat, the precedent for aerial combat was naval combat between ships with rotating gun mounts, so lack of a synchronizer was not considered a serious drawback if it was considered at all.
Friedrichshafen's approach to this problem for seaplanes was the FF31, two prototypes of which were ordered in August 1914. Their naval class designation was CB, indicating a two-seat reconnaissance airplane with machine gun armament; later this would be simplified to class C. These two aircraft, Marine Numbers 274 and 275, were delivered in May and August 1915.
The FF31 built on the experience of the earlier FF27 design. To expedite these aircraft, the wings and floats of the FF29 were used. Pushers had more drag than equivalent tractor designs with conventional fuselages, and the FF31 was fitted with a 160 hp Maybach, which had notably more power then the 120 hp engines used by the FF29 then in production.
The two FF31 prototypes were thoroughly evaluated. Performance was thought satisfactory for a reconnaissance type, but the speed and climb were certainly not adequate for an interceptor. In addition, the pusher configuration was not favored due to its vulnerability to attack from the rear, and no further FF31 aircraft were ordered.
Friedrichshafen FF31 Specifications
Engine: 160 hp Maybach Mb.III
Wing: Span Upper 16.85 m
Span Lower 15.80 m
Area 60.0 m2
General: Length 10.15 m
Height 3.70 m
Empty Weight 1,063 kg
Loaded Weight 1,535 kg
Maximum Speed: 98 km/h
Climb: 500 m 9.5 min
800 m 16 min
Range: 500 km
Flight, October 16, 1919.
SOME FRIEDRICHSHAFEN "MILESTONES"
"The F.F. 31
is shown in Fig. 2. It was a reconnaissance machine designed also to carry bombs. As the machine was required to have a free field of fire in a forward direction, the tail was carried on open tail booms and the Maybach (160 h.p.) engine was placed in the rear of the nacelle and drove a pusher airscrew. The observer was placed in front with his moveable machine gun, and the pilot occupied the rear seat. Behind the pilot was the radiator. As the main floats were also fairly short in this machine a tail float was fitted.