Design and development
In February 1917, the Sopwith Triplane began to appear over the Western Front. Despite its single Vickers machine gun armament, the Sopwith swiftly proved itself superior to the more heavily armed Albatros fighters then in use by the Luftstreitkräfte. Fokker-Flugzeugwerke responded by converting an unfinished biplane prototype into the V.4, a small, rotary-powered triplane with a steel tube fuselage and thick cantilever wings, first developed during Fokker’s government-mandated collaboration with Hugo Junkers. Initial tests revealed that the V.4 had unacceptably high control forces resulting from the use of unbalanced ailerons and elevators.
Instead of submitting the V.4 for a type test, Fokker produced a revised prototype designated V.5. The most notable changes were the introduction of horn-balanced ailerons and elevators, as well as longer-span wings. The V.5 also featured interplane struts, which were not necessary from a structural standpoint, but which minimized wing flexing. On 14 July 1917, Idflieg issued an order for 20 pre-production aircraft. The V.5 prototype, serial 101/17, was tested to destruction at Adlershof on 11 August 1917.
Richthofen first flew 102/17 on 1 September 1917 and shot down two enemy aircraft in the next two days. He reported to the Kogenluft (Kommandierender General der Luftstreitkräfte) that the F.I was superior to the Sopwith Triplane. Richthofen recommended that fighter squadrons be reequipped with the new aircraft as soon as possible. The combat evaluation came to an abrupt conclusion when Oberleutnant Kurt Wolff, Staffelführer of Jasta 11, was shot down in 102/17 on 15 September, and Leutnant Werner Voss, Staffelführer of Jasta 10, was killed in 103/17 on 23 September.
The remaining pre-production aircraft, designated Dr.I, were delivered to Jasta 11. Idflieg issued a production order for 100 triplanes in September, followed by an order for 200 in November. Apart from the straight leading edge of the tailplane, these aircraft were almost identical to the F.I. The primary distinguishing feature was the addition of wingtip skids, which proved necessary because the aircraft was tricky to land and prone to ground looping. In October, Fokker began delivering the Dr.I to squadrons within Richthofen’s Jagdgeschwader I.
Compared to the Albatros and Pfalz fighters, the Dr.I offered exceptional maneuverability. Though the ailerons were not very effective, the rudder and elevator controls were light and powerful. Rapid turns, especially to the right, were facilitated by the triplane’s marked directional instability. Vizefeldwebel Franz Hemer of Jasta 6 said, “The triplane was my favorite fighting machine because it had such wonderful flying qualities. I could let myself stunt — looping and rolling — and could avoid an enemy by diving with perfect safety. The triplane had to be given up because although it was very maneuverable, it was no longer fast enough.”
As Hemer noted, the Dr.I was considerably slower than contemporary Allied fighters in level flight and in a dive. While initial rate of climb was excellent, performance fell off dramatically at higher altitudes because of the low compression of the Oberursel Ur.II, a clone of the Le Rhône 9J rotary engine. As the war continued, chronic shortages of castor oil made rotary operation increasingly difficult. The poor quality of German ersatz lubricant resulted in many engine failures, particularly during the summer of 1918.
The Dr.I suffered other deficiencies. The pilot’s view was poor during takeoff and landing. The cockpit was cramped and furnished with materials of inferior quality. Furthermore, the proximity of the gun butts to the cockpit, combined with inadequate crash padding, left the pilot vulnerable to serious head injury in the event of a crash landing.