Modern tests and theory agree about the devil, but not about the monkey. If the Dr.I could, in fact, outclimb the Sopwith Camel biplane that it often fought, it was not because it had an extra wing but, Bennett suggests, because its propellers were pitched to deliver maximum power at climbing rather than cruising speed. Fokker Triplanes did in fact lack in top speed what they possessed in climb.
The Fokker Triplane actually did exhibit one extremely important design innovation, but it wasn’t the three-wing arrangement. It was the thick cantilever wings. Unlike most airplanes of its era, the Dr.I needed no struts or bracing wires to hold it together, as Fokker was fond of demonstrating by having a couple dozen of his shop workers pose on
The idea of the thick cantilever wing seems to have originated not with Fokker, however, but with German Hugo Junkers, who came into his own as a manufacturer only after the war. Junkers’ all-metal monoplanes, a decade ahead of their time, had no external bracing at all.
It isn’t clear how Junkers came to the realization, around 1915, that a thick wing would not produce any more drag than a thin one. It was a counterintuitive notion; throughout the war, the British persisted in believing that thick-wing airplanes must be naturally inefficient.
Thick airfoils had a great advantage besides the structural one. Compared with thin wings, thick wings could produce more lift, by about 25 percent, because the gentle roundness of the leading edges helped air follow the curvature of the airfoil and not break away. The added lift did not affect climb rate, but it improved maneuverability, because the space within which an airplane can turn is determined by its maximum lift.
Triplanes could also fly in a very nose-high attitude, because the thick wing kept producing lift at angles at which the sharp-edged wings of Allied fighters had already given up. A U.S. pilot, James Hall, wrote of the Fokkers’ “trick of standing on their tails beneath one” with guns firing upward.
After von Richthofen’s death in 1918, another fighter, now considered the best of the war, quickly supplanted the Triplane: the Fokker D.VII. The D.VII had many assets, not least its Mercedes engine and uncluttered design. It was a sesquiplane, with a lower wing smaller than the upper.
Both sides conducted wind tunnel work during the war, but much of it was misdirected. A lot of effort was dedicated to determining the amount of camber, or curvature, a thin airfoil needed to produce the most lift. The correct answer was that camber did not matter as much as a thick, well-rounded leading edge; a highly cambered thin airfoil might produce more lift than a less cambered one, but it also produced more drag. Only the thick airfoil offered the best of both worlds.
Biplane fighters were still being built well into the 1930s, but the all-metal, low-wing monoplane, the type pioneered by Hugo Junkers, would dominate World War II. As a computer would show, a simple, uncluttered shape provides a total drag much less than that of a D.VII half the size. A suitable computer would have colored Fokker, who died in 1939, green with envy.