O.Thetford, P.Gray German Aircraft of the First World War (Putnam)

Friedrichshafen FF 41 (compound tail)
   Nine examples of FF 41 were built; in both single and compound tail versions, and supplied from February 1916 onwards. Intended for torpedo-carrying duties; a crew of three was carried. The twin 150 h.p. Benz Bz III engines were encased in neat metal housings and drove tractor airscrews. Span, 21.96 m. (72 ft. 0 3/4 in.). Length, 13.27 m. (43 ft. 6 1/2 in.). Height, 4.7 m. (15 ft. 5 1/8 in.). Area, 112.5 sq.m. (1,215 sq.ft.). Weights: Empty, 2,300 kg. (5,060 lb.). Loaded, 3,670 kg. (8,074 lb.). Speed, 125 km.hr. (78.125 m.p.h.). Range, 575 km. (360 miles). Armament, torpedo and manually operated machine-gun in front cockpit.

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

Friedrichshafen FF41A & FF41AT

   The FF41A was an improved development of the earlier FF35. The aircraft was ordered in February 1916 and was delivered on 30 August 1916. The FF41A was powered by a pair of 150 hp Benz Bz.III engines mounted in tractor configuration and had a central fin and three rudders. The Benz engines were more readily available because the Mercedes was in great demand by other high priority aircraft types, especially the Roland C.II at the time of the order, and later Albatros fighters. The engines were mounted in streamlined, sheet-metal nacelles with the radiators mounted above the engines. Compared to the FF35 the wing span was slightly reduced but wing area was increased to support the slightly higher gross weight on slightly less power. Like the earlier FF35, there were three crew positions, but only one machine gun was provided. A single aircraft, Marine Number 678, was built.
   Another Friedrichshafen torpedo plane of unspecified type, Marine Number 735 powered by two 220 hp Benz Bz.IV engines, may have been an intermediate step between the FF41A and FF41AT, but with different powerplants. One prototype was ordered in May 1916 but the order was cancelled on 18 November 1917.
   The FF41AT was a slightly modified version of the FF41A with a modified fuselage and a single fin and rudder. The engines, dimensions, and armament were the same as the FF41A, but the crew was reduced to two, a pilot and torpedo aimer/front gunner. The first batch of five FF41AT aircraft, Marine Numbers 996-1000, was ordered in October 1916, and the first three aircraft were accepted in May 1917, with the fourth in June and the fifth in July. A second production batch of three aircraft, Marine Numbers 1208-1210, were ordered in January 1917; two from this batch were delivered in July and the third in August.
   On the afternoon of August 21, 1917, Ltn.z.See Wolfram Eisenlohr was aircraft commander of FF41AT Marine Number 1000 flown by Flugobermaat Gruber when they sighted two Russian destroyers at anchor about a nautical mile from the south-eastern coast of Oesel Island in the Gulf of Riga. Eisenlohr directed Gruber to immediately return to their base at Windau to avoid alerting the Russians they had been discovered. Later that day three FF41AT bombers from Windau, each loaded with eight 50 kg bombs in the ventral tunnel designed to hold a torpedo, took off at twilight to attack the destroyers.
   The aircraft found the two Russian destroyers at the location where Eisenlohr had seen them earlier, and initiated a bombing attack from an altitude of 600 meters. The destroyers and land batteries immediately commenced heavy anti-aircraft fire. Eisenlohr, the observer and aircraft commander of the second of three aircraft in the flight, observed the first bomber, which dropped four bombs on each destroyer, miss its targets, all the bombs falling short, with the final bomb in the string falling about 10 m short.
   Eisenlohr determined to hit his target by dropping all eight of his bombs on one destroyer. He attacked the first destroyer, the Stroini, and the fifth bomb in his string of eight scored a direct hit amidships. A plume of fire shot up from the Stroini, which sank in shallow water. The third FF41AT missed its target with all bombs. For his victory, Eisenlohr was awarded the Naval Victory Trophy on March 22, 1918. It turned out the Stroini had run aground, which is why it was in the same location for the bombing attack.
   Eisenlohr also commanded mine-laying missions in the FF41AT. These missions were normally flown at night and the 750 kg (1,654 pound) mines were dropped from an altitude of only 6-8 meters, with a trailing antenna to gauge the altitude. When the tip of the Schlepp antenna touched the water, a small light went on in the pilot's cockpit to indicate he was at the proper altitude.

Friedrichshafen Torpedo Bomber Specifications
Specification FF35 FF41a FF41at FF53
Engines 2x160 hp Mercedes D.III 2x150 hp Benz Bz.III 2x150 hp Benz Bz.III 2x260 hp Mercedes D.IVa
Span (Upper), m 23.74 22.00 22.00 -
Span (Lower), m 21.02 20.97 20.97 -
Length, m 13.50 13.70 13.70 -
Height, m 4.50 4.65 4.65 -
Wing Area, m2 100.00 112.50 112.50 -
Empty Wt., kg 2,292 2,300 2,288 -
Loaded Wt., kg 3,543 3,670 3,701 -
Max. Speed, km/h 114 125 121 -
Cruise Speed, km/h - 115 - -
Climb to 500 m - - 9 minutes -
Climb to 800 m - - 16-18 minutes -
Climb to 1,000 m - - 20-25 minutes -
Range, km 770 575 605 -
Crew 3 3 2 3
Armament 726 kg torpedo & 1-2 Parabellum guns 726 kg torpedo & 1 Parabellum gun 726 kg torpedo & 1 Parabellum gun -

Friedrichshafen Torpedo Bomber Production
Type FF35 FF41a Unknown* FF41at FF53
Quantity 1 1 1 8 3
Marine Numbers 300 678 735 996-1000 & 1208-1210 1663-1665
*This aircraft was powered by two 220 hp Benz Bz.IV engines. It was ordered in May 1916 and the order was cancelled on 18 November 1917.

Журнал Flight

Flight, October 16, 1919.

SOME FRIEDRICHSHAFEN "MILESTONES"

"The F.F. 41A.
   "As a consequence of the good results obtained with the Friedrichshafen land machines of the G type, and with the first F.F. twin-engined type seaplane, the 35, the F.F. works received from the Naval authorities instructions to proceed with the design and construction of twin-engined seaplanes specially designed for dropping torpedoes. Of these the F.F. 41A has done particularly well. This machine, which is shown in Figs. 21, 22 and 23, was fitted with two 150 h.p. Benz engines. As a result of the experience with the large F.F. land machines, the engines were mounted between interplane Vee struts, which arrangement was found to combine great reliability with small weight and low air resistance. The chief characteristics of the F.F. 41A are as follows: Weight, empty and without water, 5,050 lbs.; load, 3,000 lbs.; total weight, 8,050 lbs.; length overall, 45 ft.; span, 72 ft. 6 ins.; float capacity, 135 cu. ft.; horizontal speed, 71 to 77 m.p.h.; speed on taking off, 52.5 m.p.h.; climb to 3,300 ft. in 25 mins.; duration, about 5 hours. The machine is easy to fly, and also possesses good seaworthiness. On account of its large span it is not, of course, so handy as a single-engined machine.