Fokker D.VII – the lethal weapon

[3d by Marek Rys]

The first stage took part on January 21 to 28, 1918 and consisted of testing the submitted planes by frontline pilots including Manfred von Richthofen, Adolf Ritter von Tutschek, Bruno Loerzer, Hans Georg von Osten, Erich Löwenhardt and Theodor Osterkamp. Their task was to point out the best plane after test flying each of them.
The second stage was concluded in mid February and consisted of the rate of climb and horizontal velocity trials performed by factory test pilots. To make the tests comparable all planes were equipped with the same type of propeller and flew on the same fuel. Test were conducted in two categories – inline engine powered and rotary engine powered planes.
Still in October 1917 Anthony Fokker wrote a following letter to engineer Seekatz of the MAG Company aviation department: “I would like to inform you that in our experimental workshop we are building a single-seater biplane with a Mercedes engine and externally unbraced wings. I expect great things from this machine. The wing construction is such, that it is all-cantilever and the load factor is eight. It is much lighter than a comparable wire-braced wing cellule. My cantilever wing design is going to be a breakthrough next year.”
The letter was referring to the V.11 (Wn 1883) biplane prepared for the first fighter plane competition at Adlershof. Components of the Fokker Dr.I, like fuselage and tail unit welded of steel tubing, were utilized in its construction. The forward section of the fuselage was modified to accommodate an inline liquid-cooled 160hp Mercedes D.III engine with a rectangular, car-type radiator, the same as in the D.VII. Wing cellule was a completely new design. Both upper and lower, thick profile, two-spar wings were of wooden construction, covered with fabric. The upper wing, moved noticeably forward (there was no need for a cut-out in the trailing edge to provide better cockpit visibility), was attached to the fuselage by a tripod strut pylon made of steel tubes and a single strut. Upper and lower wing were joined by a pair of N-struts.
There were two more prototypes prepared for the competition designated V.9 and V.13. They were of analogous construction, but equipped with 120 and 145hp Oberursel rotary engines respectively.

The middle section of the fuselage with the cockpit and the fuel tank. The fuel hand pump is visible in the foreground.

On December 12, 1917 construction of a second plane designated V.18 (Wn 2116) with longer fuselage and larger vertical stabilizer was commenced. Thus, the centre of gravity was shifted backwards and therefore it was necessary to move the upper wing back, which required a cut-out being made in its trailing edge. The plane was powered by the Mercedes D.III engine. Also, the undercarriage wheel track was increased.
Fokker V.11 (Wn 1883) won the first fighter plane competition in the inline engine powered planes category. The Rumpler 7D4 came second. It had a higher horizontal velocity and rate of climb than the Fokker’s design, but according to pilots its handling qualities were worse.
There is a story connected with the winning aircraft told by Anthony Fokker himself. On the weekend of January 26-27 Manfred von Richthofen flew the Fokker V.11 and after landing he pointed out its essential shortcomings: directional instability in a dive, not the best manoeuvrability and poor upward visibility. Fokker was supposed to bring welders, who lengthened the fuselage by 40cm, relocated the upper wing in which they made a cut-out to improve cockpit visibility. That was how the Fokker V.11/II was created. These modifications substantially improved the plane’s flying qualities. Nowadays, it is hard to explicitly determine if the story is true or if it is yet another legend created by Anthony Fokker around himself and his designs.
The second Fokker V.18 was withdrawn from the competition after an accident that happened during taxing. One of the Oberursel works mechanics, taxing a rotary engine powered Fokker collided with the stationary inline engine powered Fokker V.13 and the Albatros DV. Both damaged aircrafts were put out of the competition.
In the rotary engine powered planes category the leading place was taken by the Fokker V.13. The lack of 115 kW (160 hp) Siemens-Halske engines (they had not been manufactured) forced the use of 90 kW (120 hp) Oberursel engine in the second stage of the competition, which naturally decreased the plane’s performance. It was accepted for mass production as the Fokker D.VI. Sixty planes were built and sent to the combat and home defence units (Jasta 80 and 84), as well as flight schools.
Idflieg ordered 300 Fokker V.11 planes. Serial production aircraft received designation Fokker D.VII. The V.11 and V.18 prototypes were rebuilt to meet production standards and received serial numbers 227/18 and 228/18 respectively.

The Mercedes D.IIIa engine – the left and right side view.

The Fokker D.VII underwent its Typenprüfung (type-testing programme) in February 1918. It included a number of static and endurance tests on completion of which the Idflieg officially authorized the plane’s series production.