Fokker Triplane

The Fokker Dr.I (''Dreidecker'', "triplane" in German), often known simply as the Fokker Triplane, was a World War I fighter aircraft built by Fokker-Flugzeugwerke. The Dr.I saw widespread service in the spring of 1918. It became famous as the aircraft in which Manfred von Richthofen gained his last 17 victories (plus two earlier ones in the Fokker F.I prototype in September 1917), and in which he was killed on 21 April 1918.

Design and development

In February 1917, the Sopwith Triplane began to appear over the Western Front.Franks 2004, p. 9. 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''.Franks 2004, p. 21.Leaman 2003, pp. 30, 32. In April 1917, Anthony Fokker viewed a captured Sopwith Triplane while visiting ''Jasta'' 11. Upon his return to the Schwerin factory, Fokker instructed Reinhold Platz to build a triplane, but gave him no further information about the Sopwith design.Weyl 1965, p.223. Platz responded with the V.4, a small, rotary-powered triplane with a steel tube fuselage and thick cantilever wings,Leaman 2003, p. 34. 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.Weyl 1965, p. 226.

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.Weyl 1965, p. 228. 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.Weyl 1965, p. 229.

Operational history

The first two pre-production triplanes were designated F.I, in accord with ''Idflieg's'' early class prefix for triplanes. These aircraft, serials 102/17 and 103/17, were the only machines to receive the F.I designationWeyl 1965, p. 231. and could be distinguished from subsequent aircraft b
a slight convex curve
of the tailplane's leading edge. The two aircraft were sent to ''Jastas'' 10 and 11 for combat evaluation, arriving at Markebeeke, Belgium on 28 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.Weyl 1965, p. 232. Richthofen recommended that fighter squadrons be reequipped with the new aircraft as soon as possible.Weyl 1965, p. 232. 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.Leaman 2003, p. 53. ''Idflieg'' issued a production order for 100 triplanes in September, followed by an order for 200 in November.Franks and VanWyngarden 2001, p. 22. 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.Leaman 2003, p. 96. In October, Fokker began delivering the Dr.I to squadrons within Richthofen's ''Jagdgeschwader'' I.

Compared with 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.Leaman 2003, p. 95. Rapid turns, especially to the right, were facilitated by the triplane's marked directional instability.Leaman 2003, p. 95. ''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."VanWyngarden 2004, p. 75.

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.Nowarra 1990, p. 12. 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.Franks and VanWyngarden 2001, p. 83.

The Dr.I suffered other deficiencies. The pilot's view was poor during takeoff and landing.Weyl 1965, p. 245. The cockpit was cramped and furnished with materials of inferior quality.Weyl 1965, pp. 244–245. 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.Weyl 1965, p. 410.

Wing failures

On 29 October 1917, ''Leutnant der Reserve'' Heinrich Gontermann, ''Staffelführer'' of ''Jasta'' 15, was performing aerobatics when his triplane broke up.Weyl 1965, p. 233. Gontermann was killed in the ensuing crash landing. ''Leutnant der Reserve'' Günther Pastor of ''Jasta'' 11 was killed two days later when his triplane broke up in level flight.Weyl 1965, p. 233. Inspection of the wrecked aircraft showed that the wings had been poorly constructed. Examination of other high-time triplanes confirmed these findings. On 2 November, ''Idflieg'' grounded all remaining triplanes pending an inquiry. ''Idflieg'' convened a ''Sturzkommission'' (crash commission) which concluded that poor construction and lack of waterproofing had allowed moisture to damage the wing structure.Weyl 1965, pp. 233–234. This caused the wing ribs to disintegrate and the ailerons to break away in flight.Weyl 1965, pp. 233–234.

In response to the crash investigation, Fokker was forced to improve quality control on the production line, particularly varnishing of the wing spars and ribs, to combat moisture. Fokker also strengthened the rib structures and the attachment of the auxiliary spars to the ribs.Weyl 1965, pp. 236, 239. Existing triplanes were repaired and modified at Fokker's expense.Weyl 1965, p. 235. After testing a modified wing at Adlershof, ''Idflieg'' authorized the triplane's return to service on 28 November 1917.Weyl 1965, pp. 238–239. Production resumed in early December. By January 1918, ''Jastas'' 6 and 11 were fully equipped with the triplane. Only 14 squadrons used the Dr.I as their primary equipment. Most of these units were part of ''Jagdgeschwadern'' I, II, or III.Franks and VanWyngarden 2001, p. 55. Frontline inventory peaked in late April 1918, with 171 aircraft in service on the Western Front.

Despite corrective measures, the Dr.I continued to suffer from wing failures. On 3 February 1918, ''Leutnant'' Hans Joachim Wolff of ''Jasta'' 11 successfully landed after suffering a failure of the upper wing leading edge and ribs.Franks and VanWyngarden 2001, p. 25. On 18 March 1918, Lothar von Richthofen, ''Staffelführer'' of ''Jasta'' 11, suffered a failure of the upper wing leading edge during combat with Sopwith Camels of No. 73 Squadron and Bristol F.2Bs of No. 62 Squadron.Franks and VanWyngarden 2001, pp. 26–27. Richthofen was seriously injured in the ensuing crash landing.

Postwar research revealed that poor workmanship was not the only cause of the triplane's structural failures. In 1929, National Advisory Committee for Aeronautics (NACA) investigations found that the upper wing carried a higher lift coefficient than the lower wing – at high speeds it could be 2.55 times as much.

The triplane's chronic structural problems destroyed any prospect of large-scale orders.Weyl 1965, p. 236. Production eventually ended in May 1918, by which time only 320 had been manufactured.Gray and Thetford 1962, p. 100. The Dr.I was withdrawn from frontline service as the Fokker D.VII entered widespread service in June and July. ''Jasta'' 19 was the last squadron to be fully equipped with the Dr.I.Leaman 2003, p. 69.

Surviving triplanes were distributed to training and home defense units. Several training aircraft were reengined with the 75 kW (100 hp) Goebel Goe.II.Leaman 2003, p. 222. At the time of the Armistice, many remaining triplanes were assigned to fighter training schools at Nivelles, Belgium, and Valenciennes, France.Weyl 1965, p. 246. Allied pilots tested several of these triplanes and found their handling qualities to be impressive.Weyl 1965, p. 246.

Experimental engines

Several Dr.Is were used as testbeds for experimental engines. One aircraft, designated V.7, was fitted with the Siemens-Halske Sh.III bi-rotary engine.Weyl 1965, p. 248. The V.7 exhibited exceptional rate of climb and ceiling, but it proved difficult to handle.Weyl 1965, p. 248. Serial 108/17 was used to test the 118 kW (160 hp) Goebel Goe. III, while serial 469/17 was used to test the 108 kW (145 hp) Oberursel Ur. III.Weyl 1965, pp. 249–250. None of these engines were used on production aircraft. One triplane was used as a testbed for an experimental Schwade gear-driven supercharger.

Postwar

Three triplanes are known to have survived the Armistice. Serial 528/17 was retained as a testbed by the ''Deutschen Versuchsanstalt für Luftfahrt'' (German Aviation Research Institute) at Adlershof. After being used in the filming of two movies, 528/17 is believed to have crashed sometime in the late 1930s.Leaman 2003, p. 181. Serial 152/17, in which Manfred von Richthofen obtained three victories, was displayed at the ''Zeughaus'' museum in Berlin.Leaman 2003, p. 181. This aircraft was destroyed in an Allied bombing raid during World War II.

In 1932, Fokker assembled a Dr.I from existing components. It was displayed in the ''Deutsche Luftfahrt-Sammlung'' in Berlin. In 1943, the aircraft was destroyed in an Allied bombing raid. Today, only a few original Dr.I artifacts survive in museums.

Replica and reproduction aircraft

Large numbers of replica and reproduction aircraft have been built for both individuals and museums. Bitz Flugzeugbau GmbH built two Dr.I replicas, serial numbers 001 and 002, for use in Twentieth Century Fox’s 1966 film ''The Blue Max''. Replica 001 EI-APW is the oldest surviving example of the Dr.1. Because of the expense and scarcity of authentic rotary engines, most airworthy replicas are powered by a Warner Scarab or Continental R-670 radial engine.Nowarra 1990, p. 47. A few, however, feature vintage Le Rhône 9J or reproduction Oberursel Ur.II rotary engines."Oberursel UR.II"
''The Vintage Aviator.'' Retrieved: 6 November 2016.

Variants

*V.4 – Initial prototype
*V.5 – First production prototype
*V.6 – Enlarged prototype with Mercedes D.II engine
*V.7 – Prototype with Siemens-Halske Sh.III engine
*Vagel Grip SP.5 Greif - German post-war two seat copy of the Dr.I

Operators

;
*''Luftstreitkräfte''

Specifications (Dr.I)

See also

References

Sources

* Franks, Norman. ''Sopwith Triplane Aces of World War I (Aircraft of the Aces No. 62)''. Oxford: Osprey Publishing, 2004. .
* Franks, Norman and Greg VanWyngarden. ''Fokker Dr.I Aces of World War I (Aircraft of The Aces No. 40).'' Oxford: Osprey Publishing, 2001. .
* Gray, Peter and Owen Thetford. ''German Aircraft of the First World War''. London: Putnam, 1962.
*
*
*
* Imrie, Alex. ''The Fokker Triplane''. Arms and Armour Press, 1992. .
* Leaman, Paul. ''Fokker Dr.I Triplane: A World War One Legend''. Hersham, Surrey, UK: Classic Publications, 2003. .
* Loftin Jr., Laurence K
''Quest for Performance: The Evolution of Modern Aircraft.''
NASA Scientific and Technical Information Branch, 2004. Retrieved on 22 April 2006.
* Nowarra, Heinz J. ''Fokker Dr.I In Action (Aircraft No. 98)''. Carrollton, TX: Squadron/Signal Publications, Inc., 1990. .
*
* VanWyngarden, Greg. ''Richthofen's Flying Circus: Jagdgeschwader Nr I (Aviation Elite Units No. 16).'' Oxford: Osprey Publishing, 2004. .
* Weyl, A.R. ''Fokker: The Creative Years''. London: Putnam, 1965. .

Notes

External links

Fokker DR1.com – Research on the Fokker Dr.I



Fokker Dr. I
– National Museum of the United States Air Force

Cole Palen's rotary powered Dr.I reproduction (US registration ''N3221'') at Old Rhinebeck Aerodrome

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Dr.I
1910s German fighter aircraft
Military aircraft of World War I
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Manfred von Richthofen
Aircraft first flown in 1917
Rotary-engined aircraft