Pilots were also experiencing chronic problems with the Dr.I’s 110-hp rotary engine, which had been designed to be lubricated with castor oil. A product of the tropical castor bean plant (Ricinus communus), genuine castor oil was unavailable to the Germans due to the Allied blockade. The Germans had to make due with a synthetic substitute that severely shortened engine life.

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Rotary engines were in such short supply that many Fokkers, including those flown by Voss and Richthofen, were powered by engines salvaged from captured Allied aircraft. Fokker built experimental triplanes with other engines, but none of them amounted to much. The most bizarre variant was the V.8, a modification of Fokker’s Mercedes-powered V.6 triplane prototype. The V.8 actually had five wings-three forward and two more aft of the cockpit-with ailerons on both sets of upper wings. Reliable sources allege that Anthony Fokker personally flew the V.8 on at least two occasions. It is certainly difficult to imagine him persuading anybody else to fly it. By the spring of 1918, however, Fokker’s fighter designs were taking a more conventional form. When Manfred von Richthofen was killed on April 21, 1918, after achieving his 80th aerial victory, he was eagerly awaiting the replacement of his unit’s triplanes with a new biplane fighter, the Fokker D.VII.

Of the plethora of triplane fighters developed in Germany during 1917, the only one that came close to matching the success of the Fokker was the Pfalz Dr.I. Produced in October 1917, the Pfalz Dr.I was a three-winged version of the experimental D.VII biplane. Careful attention was paid to visibility by designing the Pfalz with wings of three different chords, the narrowest being in the center and the widest on top. The streamlined wooden monocoque fuselage blended with the cowling of the plane’s rotary engine. The Pfalz Dr.I could outclimb its Fokker counterpart by at least as great a margin as the Fokker could outclimb the earlier Albatros D.V.

Manfred von Richthofen, who flew the Pfalz Dr.I in December 1917, was very impressed with it. Although only 10 Pfalz triplanes were produced, nine of them were sent to the front. One reason why more of them were not built may have been that the Pfalz was a more complex and labor-intensive aircraft to produce than the Fokker. The Germans were also becoming disillusioned with the triplane formula by the time it appeared on the scene.

In addition, the Pfalz was powered by the 160-hp Siemens und Halske Sh-III, a unique rotary-radial engine in which the crankcase rotated in one direction while the crankshaft rotated in the opposite direction. By the time the new engine was perfected, Siemens had developed an airplane of its own for it, the SSW D.III biplane, which would eventually be developed into the D.IV, arguably the best German interceptor of the war.

With one notable exception, the triplane fighter craze was over by mid-1918. That exception was the Curtiss- Kirkham 18T, a two-seater built for the U.S. Navy in July 1918. Powered by a 400-hp engine designed by Charles B. Kirkham, only two 18Ts were built. With a speed of 160 mph, they were among the fastest aircraft in the world-and certainly the fastest triplanes ever flown. The plane’s Kirkham K-12 engine was later developed into the well-known Curtiss Conqueror, which was used in many aircraft during the 1920s and early 1930s.

By the early 1920s, the triplane fighter concept was dead, although the use of the triplane configuration to increase the lifting capabilities of bombers or commercial aircraft would be explored for several years more. The last military triplane to be produced in any quantity was the Mitsubishi Type 10, a singleseat torpedo plane; 20 were built for the Imperial Japanese Navy in 1922. The Type 10 had been created by a new chief designer whom Mitsubishi had recently recruited from an economically depressed postwar Britain: Herbert Smith, creator of the Sopwith Triplane.

This article was written by Robert Guttman and was originally published in the March 2001 issue of Aviation History magazine.

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