|Fokker D.VIII, photo © Philip Makanna|
(Note Wing Thickness)
A selection from the forthcoming collection of essays by the late Javier Arango, The Nature of World War I Aircraft (Ghosts, 2023)—
"The Fokker D.VIII"
Anthony Fokker was one of the most prolific aircraft designers working during World War I. His aircraft became closely associated with many of Germany’s famous aces, such as Oswald Boelcke, Max Immelmann, Ernst Udet, and Manfred von Richthofen. Fokker was an agile and daring entrepreneur and excelled at quick and dynamic experimentation. By the end of the war, he and his team of designers must have amassed a tremendous amount of knowledge concerning fighter aircraft design.
The Fokker D.VIII was his last operational fighter before the Armistice, and as such should have represented the epitome of his design philosophy. The aircraft, however, is something of a paradox. It is extremely modern in some respects but retains some traits that seem rooted in an earlier time.
One of the most remarkable aspects of the D.VIII is the fact that it is a monoplane. Fokker had achieved early success with a wing-warping monoplane, the Eindecker, which became the terror of the skies over the Western Front. He then evolved the Eindecker into a biplane that had only moderate success. Probably Fokker’s most famous and recognizable design was a triplane. Subsequently he experimented with biplanes, triplanes, sesquiplanes, monoplanes, and even one airplane with five wings. That his last design of the war was a monoplane is revealing. Fokker was an expert pilot himself. He had the privilege of experiencing very many configurations in flight and had developed an uncanny ability to sense relative advantages in performance and subtle differences in handling qualities. The D.VIII’s monoplane configuration was no accident. Fokker was exploiting an aerodynamic reality—monoplanes are more efficient than airplanes with multiple wings, each of which inevitably interferes with the airflow of the other.
This fact must have been known to Fokker and to other designers, but the key difficulty was in the execution. The predominant biplane configuration of the day had many practical advantages that compensated for its aerodynamic inefficiency. The engineering of externally braced biplanes was simple and intuitive. It used rectangular, cross-braced trusses, commonly known and seen in many structures, such as bridges. This building technique was easily scalable. The construction of the wings themselves could be imprecise because small errors could be simply “rigged out” by adjusting the lengths of the members joining the wings to one another and to the fuselage.
Monoplanes, on the other hand, had either to support the wing externally with wires, as in the Eindecker, or to provide sufficient internal structure to support the wing as a cantilever. The obvious aerodynamic preference would have been to eliminate the external wires altogether. But then the wing would need a strong, deep spar, which would have made it heavy and thick, two attributes that were considered inimical to efficiency.
Fortunately, Fokker had previous experience with thick cantilever wings. Thanks to his willingness to try any conceivable idea, and even to pull together existing ideas that in isolation had little success, he had experimented with thick wings years earlier. There is speculation as to where Fokker got his idea for the thick wing and whether he copied it from the engineer and industrialist Hugo Junkers, who was building thick cantilever wings made entirely out of metal early in the war. As with many other Fokker innovations, the source of the initial idea may be in doubt, but the successful embodiment of the idea in a practical, useful product is not. Unlike Junkers’ airplanes, Fokker’s were extremely practical and effective. The Fokker Dr.I already used three cantilever wings with thick airfoils. The D.VI turned the triplane into a biplane, still using thick airfoils. The D.VII, arguably the best aircraft of WWI, also used thick airfoils. It was no accident that Fokker felt comfortable enough with his cantilever wings and thick airfoils to produce an internally braced monoplane.
|Early D.VIII Prototype (period photo not in the book)|
Contrary to the view prevalent at the time, the thick airfoil was actually superior. Fokker knew from experience that thick airfoils actually did not add much drag, if any, at high speed, and that they had much better characteristics than thin airfoils when flown slowly, at larger angles of attack. Fokker had the technology to build a single cantilever wing while keeping it within weight restrictions. He avoided metal or other exotic materials—high-strength aluminum alloys were not yet available (Junkers had used extremely thin sheet steel)—and instead used wood. His factory workers required little training to produce the new wing. Fokker achieved a wing that was easy to build, relatively light, structurally efficient because its thin plywood skin, unlike the more conventional linen, was a load-carrying part of the structure, and aerodynamically highly efficient as well. As always, Fokker innovated by combining existing ideas with proprietary experimentation in order to produce a practical, useful machine. The resulting Fokker D.VIII is an astounding aircraft. Its wing looks completely out of place among other WWI airplanes; it seems to belong to a 1940s-era fighter.
I have been fortunate to fly a Fokker D.VIII powered by a 160-hp Gnôme rotary engine. The D.VIII has an amazing climb rate and is also fast in level flight. When maneuvering, the D.VIII shares a very positive characteristic with the other thick-airfoil Fokkers—it can achieve very high angles of attack while giving the pilot a comfortable feeling that the wing will not suddenly stall and go out of control. Contemporary airplanes with thin airfoils, like the Sopwith Camel and the Nieuports, can turn sharply but, without warning, will suddenly fall out of control. The D.VIII will continue to “mush” through a turn, gradually alerting its pilot that it needs more speed. This quality is extremely useful in dogfights, where controlled, tight turns to the maximum ability of a wing confer an important advantage. Landing the D.VIII is also simpler because it stalls gradually toward the ground, giving the pilot a larger margin of error in the flare.
The D.VIII’s most remarkable characteristic, however, is that, unlike most other WWI airplanes, it has ailerons that actually work very well. Fokker had not only perfected his wing design but had also finally come up with the correct configuration for the ailerons. They were very long and narrow and completely embedded into the wing, so that no turbulence-producing gap opened when they deflected. The D.VIII therefore rolls like a modern airplane, sharply and with little of what is called adverse yaw—the tendency of the nose to swing away from the direction of a banked turn, owing to the greater drag of the downgoing aileron.
Given all these successful design characteristics, would I qualify the D.VIII as Fokker’s best fighter? No. The Fokker D.VII, for example, is more powerful, faster, easier to fly, and has a better engine. For dogfighting, the tiny Fokker D.VI, with its short wingspan and very light weight, may be superior to the D.VIII. The constraints of a practical world where Germany was losing a war of attrition and running out of supplies interfered with the D.VIII’s success. The D.VIII was the best Fokker could do given a relatively weak and practically obsolete Oberursel rotary engine. The Oberursel was no match for the new generation of Allied engines or even for the German in-line Mercedes and BMWs that yielded nearly twice the horsepower, but it was relatively plentiful at a time when the better engines were practically unavailable. So the ever pragmatic Fokker designed the D.VIII to be the best airplane it could be, using an outdated engine and facing enemy aircraft that were becoming more dependent on power and speed than on sheer maneuverability. He knew what he was doing. In order to compete with the more powerful fighters, he made the D.VIII remarkably light. It weighed only two-thirds as much as the Mercedes-powered D.VII. To make it easy to build, the fuselage was simply square, not streamlined, and was based on structural techniques already used in previous Fokker aircraft. The cockpit was miserably equipped. The D.VIII was evidently designed to quickly get an effective aircraft to the front. Unfortunately, haste in production and design also led to wing failures that ended up grounding it.
The Fokker D.VIII is a desperate airplane, made not to be the best air-superiority fighter but to be the best fighter that could exist amid the very challenging realities of a nation about to collapse. Fokker did succeed in delivering an easy airplane to build, with an available, though obsolete, engine. The D.VIII’s light weight gave it excellent climb capability. Its rotary engine, which did not need to be warmed up, allowed it to get into the air quickly in order to defend against invading airplanes. Once airborne, it had the advantage of being fast and rolling quickly into turns. And, very important, it could be flown effectively by inexperienced pilots who surely enjoyed the docile handling characteristics provided by its excellent, futuristic, thick-airfoil wing.
[Originally published as "The Fokker E.V/D.VIII" in Jim Wilberg, et al. Aviators of the Great War: The Aviation Art of Steve Anderson. Aeronaut Books, Indio, CA, 2014. Reprinted with permission]
The Nature of World War I Aircraft—Collected Essays by Javier Arango, with photos by noted aviation photographer Philip Makanna is expected to be available for purchase in December. We will alert our readers as soon as it can be acquired. Here are the cover and table of contents for the book: