German Empire (1917)
Fighter Plane – 320 Built

The Fokker Dr.I was a triplane built by Fokker-Flugzeugwerke during the First World War. The design, based off of Britain’s Sopwith Triplane, is well known thanks to the Red Baron, Manfred von Richthofen, for being the plane in which he scored his final kills.

A Borrowed Idea

In the early part of 1917 the Sopwith Triplane of the Allies began appearing on the battlefield, quickly trouncing German Albatros D.III fighters with its superior maneuverability and climbing ability. The Idfleig, the German bureau overseeing aircraft design immediately ordered development of a triplane, known as dreidecker (3 winged) in German.

Nearly all of the German aircraft manufacturers followed suit. Fokker set about to develop its own triplane by modifying an unfinished prototype biplane. This initial prototype, like Sopwith’s design, utilized a rotary engine and steel tube fuselage. However the initial prototype, the V.4 did not have external interwing bracing. The next prototype, the V.5 introduced bracing between the wings to minimize flexing on the upper wing. The prototypes were met with much excitement for their exceptional maneuverability and climb rate over anything else the Germans had previously produced. The Red Baron himself, Manfred von Richthofen was believed the Dr.I held much promise for the fortunes of German air power and demanded his superiors to commence production immediately, as well as promising his men that they would soon be able to “move like devils and climb like monkeys.”

Construction

The appearance of the Dr.1 is characterized by its three-wing design – therefore dubbed a ‘triplane.’ The design also featured small sustentation surface of an aerofoil shape mounted between the wheels of the landing gear. The tail was also completely mobile with unbalanced ailerons possessing more surface area than the ailerons of the upper wing. The wings had deep section hollow box-spars that provided lightweight strength to the wings. The lack of interplane struts on the initial prototype resulted in excessive wing vibration during flight, so interplane struts were added. The ribs were of plywood, as well as the leading-edges covers at the spar, with the leading-edges made of wire. The middle wings had some cut-outs to improve downward visibility of the pilot. The fuselage was constructed using welded steel-tubing bracing with diagonal wires to create the rigid box-shaped structure, being a fabric-covered with triangular plywood fillets, except the undercarriage and center-section, which were made of steel streamlined tubing.

The tail-plane had a triangular shape, being framed in steel tubing the same way as the balanced rudder and elevators. The wheels featured an elastic shock cord, while a steel-tipped tailskid was installed at the rear.

Evaluation

The first prototype Dr.1 flew in July of 1917. Production of the Dr.I commenced on August 11th of 1917. In preproduction the triplane carried the designation F.I. Two were made and issued to Richthofen and Leutenant Werner Voss. These two aces promptly used these planes on the battlefield, scoring kills within the first few days of flying in early September. Voss took to the skies on August 28th and by September 11th had scored 8 kills.

The result of this evaluation period led Voss and Richthofen to recommend the Dr.I for production as soon as possible, declaring it superior to the Sopwith Triplane. Orders were placed for 300 Dr.I’s.

On September 14th the commander of Jasta 11, OberLeutnant Kurt Wolff was shot down whilst flying Richthofen’s F.I by a new Sopwith Camel of Britain’s Naval 10 squadron. Voss, whilst flying on September 23rd, scored his 48th victory just before being shot down in an epic dogfight wherein he managed to damage all 7 of his opponent’s SE-5a’s in the skirmish.

The Fokker Dr.I in Use

The Dr.I, upon its arrival to the battlefield in October was well regarded for its climbing ability and light controls. The ailerons were not very effective, however the tailplane elevator and rudder controls were very yielding. Rapid turns to the right were very quick thanks to the directional instability afforded by the rotation of the rotary engine, a characteristic that was taken advantage of by pilots.

Although not a particularly fast plane, it balanced this shortcoming with great maneuverability thanks to its light weight, while also having good upward visibility. It also had a decent climb rate, characteristics that all seemingly made the Dr.I a formidable adversary to its Allied opponent, the Sopwith Camel. This made of the Dr.1 a good aircraft for dogfights, yet structural and construction problems in the wings would hamper the aircraft’s promising initial assessment.

The Dr.I was armed with twin 7.92 Spandau machine guns, which could fire simultaneously or independently in synchronization with the propeller.

The Dr.I, for all its improvements over previous German aircraft, had numerous  shortcomings. Among them was its tendency to ground looping upon landing. This occurs when the aircraft tilts on landing such that one wing makes contact with the ground. For this reason skids were attached to the wingtips of the lower wing on the production version. Also while the Dr.I had excellent climbing ability, its dive and level flight speed were less than desirable, leaving it vulnerable to faster Allied planes in many situations.

Wing Problems

Following the proper introduction of the production model Dr.I in October, by the end of the month two consecutive top wing failure accidents promptly caused all triplanes to be grounded. The wing structure of the Dr.I was thoroughly investigated and numerous problems were discovered, the first of which was weak attachment of wingtips, ailerons, and ribs. Further, the doping of the fabric and wood varnishing was found to be of poor and inconsistent quality, leading to water absorption and premature rot in crucial wing spars.

Fokker’s corrective action was to improve quality control on the production line, as well as modifying and repairing existing models. The problem was believed to have been solved, and the Dr.I continued to see use well into 1918, but later the wing failures returned.

Much later in 1929, research at NACA revealed that a triplane configuration like the Dr.I’s exerted as much as 2.5 times more lift coefficient on the upper wing. The extreme difference in this force no doubt contributed to many of the wing failures seen in the Dr.I over its operational lifespan. Examples such as this show the importance of research and competence in advanced aerodynamics during the design phase of an aircraft.

Legacy

As had been seen in September 1917, the Dr.I was inferior to the capabilities of the British Sopwith Camel by the time production had commenced. Despite this, German production went on for the initial 300 ordered.

Fokker D.VII would eventually replace the Dr.1 on the battlefield, with surviving dreideckers relegated to training and home defence units, re-powered with a Goebel Goe II 100 hp engine. By the time of the armistice was signed, the Dr.1 was tested by Allied pilots at fighter flying schools in Nivelles (Belgium) and Valenciennes (France), being deemed as an aircraft with impressive performance.

Variants

• V.4 – The initial prototype
• V.5 – First production prototype
• V.6 – Enlarged prototype powered with a Mercedes D.II engine
• V.7 – Prototype with Siemens-Halske Sh.III engine

Dr.1 Specifications
Top Wingspan	7.12 m / 23 ft 4 in
Mid Wingspan	6.23 m / 20 ft 5 in
Lower Wingspan	5.7 m / 18 ft 8 in
Length	5.77 m / 18 ft 11 in
Height	2.95 m / 9 ft 8 in
Wing Area	18.66 m² / 200.85 ft²
Engine	1  9-cylinder rotary Oberursel UR II engine (110 HP), or a LeRhône Type 9Ja (110 HP)
Maximum Take-Off Weight	586 Kg / 1,291 lb
Empty Weight	406 kg / 895 lb
Loaded Weight	586 kg / 1,291 lb
Climb Rate	5.7 m/s (1,122 ft/min) or 1000 meters in 2’45’’
Maximum Speed	185 km/h / 115 mph at sea level; 165 km/h / 102,5 mph at 4000 m
Range	300 Km / 186 miles
Maximum Service Ceiling	6100 m /20,000 ft
Crew	1 (pilot)
Armament	2 X 7.92 mm Spandau 08/15 with 500 rounds each

Gallery

Sources

Guttman, R. (2011). The Triplane Fighter Craze of 1917. HistoryNet., Berger, R (Ed.). Aviones [Flugzeuge, Vicenç Prat, trans.]. Colonia, Alemania: Naumann & Göbel Verlagsgessellschaft mbH., Donald. D. (2009). Aviones Militares, Guia Visual [Military Aircraft. Visual Guide, Seconsat, trans.]. Madrid, Spain: Editorial Libsa., Dwyer, L. (2013). Fokker Dr.I Triplane. The Aviation History Online Museum., Leivchentritt, L. (2013). Fokker Dr.I Specifications. Fokker Dr.I.com., Old Rhinebeck Aerodrome (2016). Fokker Dr.1 Triplane. Cole Palen’s Old Rhinebeck Aerodrome., The Aerodrome (2016). Fokker Dr.I. The Aerodrome., Fokker Dr.I. (2016, June 19). In Wikipedia, The Free Encyclopedia. [Images] Dr1 Black-White Livery by Neal Wellons / CC BY-NC-ND 2.0, Dr1 Dark Red by Geoff Collins / CC BY-NC-ND 2.0, Dr1 Cockpit by Phil Norton / CC BY-NC-ND 2.0, Dr1 Flight by Ian / CC BY 2.0, Dr1 Engine by Erik Wessel-Berg / CC BY-NC-ND 2.0, Plane Profile Views by Ed Jackson