|Fokker Dr. I|
|Single-seat fighter and reconnaissance plane|
|One Oberursel Ur. II rotary piston engine|
|Wing area||18.70 m²|
|Maximum take-off||585 kg|
|Maximum speed||165 km/h|
|Service ceiling||6095 m|
|Machine guns||two, fixed|
The Dr.I was mainly designed by Anthony Fokker and Reinhold Platz (although Chefingeneur Möser has been credited with a role), who had been working on a series of experimental planes, the V-series, since 1916. They shared one feature in common, the use of cantilever wings instead of external wire bracing. This led to significantly lower drag, but it also required stronger internal structures in the wing, reducing the advantage. In order to address this, his V.3 design had used three shorter wings instead of two wider ones, so that the loads on any particular wing were reduced and would require less internal structure. In testing, the wings tended to vibrate, so the design was modified with single struts between the wings at the tips, leading to the V.4.
In testing the V.4 – which had a doped fabric-covered tubular steel fuselage and tail and wooden wings – proved to be something of a disappointment. Although the handling was fairly good due to the low angular momentum of the short wings, several modifications were made to improve it, notably the control feel. The main concern was the speed, however: the added wing made the drag high enough that the puny 110hp Oberursel UR.II engine could not drive it to the speeds of then-current Allied aircraft, and Platz introduced a number of V planes with larger engines in an attempt to address this. Platz later turned back to biplane designs for further developments in the V series.
In April 1917 the RNAS started flying their Sopwith Triplanes on the front-line in force for the first time. Their debut was sensational, for the first time turning the tables completely on the Germans and proving to be almost untouchable in combat. Soon the German pilots were clamouring for a triplane of their own. The majority of the German aircraft manufacturers responded with new triplane designs, but most, like the Albatros Dr.I, were nothing more than biplanes with a new wing added. The V.4 however was a purpose-built triplane, well tested and ready for production. The first pre-production examples (F.Is) were ready by the middle of August 1917 and production machines (Dr.Is) were delivered in October of the same year.
Two of the first three F.Is (103/17 and 102/17) were shipped to Werner Voss and Manfred von Richthofen on August 28th 1917 at Marcke in Belgium. Soon both were flying them in combat and racking up successes, exploiting the aircraft's unique ability to perform flat slip-turns, thanks to the absence of a fixed vertical stabiliser. Triplane 102/17 was shot down whilst being flown by Kurt Wolff on 15th September, and 103/17 flown by Werner Voss on 23rd September. However, many of the other pilots were less impressed with the aircraft, while it had good manoeuvrability and an impressive rate of climb, the plane was still slower than most contemporary Allied fighters.
In late October 1917 Leutnants Heinrich Gontermann and Günther Pastor were killed when their Dr.Is broke up in the air at the end of October, and the planes were withdrawn from service. Modifications were then made to the wings for added strength, but the failures continued in service and the triplane never recovered in the eyes of the pilots, and was not supplied to many Jagdstaffeln.
The cause of the wing failures was said to be from poor quality control rather than deficiencies in design. However, the failures always occurred in the upper wing of the aircraft. In 1929 NACA investigations found that the upper wing carried a higher wing loading than the lower wing, at high speeds it could be 2.55 times as much.
Production eventually ended in May 1918, by which time only 320 had been manufactured.