The Airplane - Jay Spenser [31]
The Deperdussin racer’s innovative fuselage was not Béchereau’s idea, however, but rather the invention of a Swiss engineer who had previously been the Antoinette Company’s shop foreman. Eugène Ruchonnet’s breakthrough idea was to make the fuselage skin itself carry the loads of flight, eliminating the need for any internal support.
Ruchonnet achieved this by steaming thin strips of tulipwood, a wood favored by cabinetmakers for its pliability, and laying these softened strips into molds of each half of the plane’s tapering body. Several layers of tulipwood were built up in these molds, one glued atop another with the grain running a different way for added strength. When joined together and covered with varnished fabric, these halves formed a lightweight fuselage so strong that no internal skeleton was required. Ruchonnet called this invention monocoque (single-shell) construction.
Where did Ruchonnet get his inspiration for so different an approach? It may have been from the small boats built in this manner or perhaps from observing the natural world. It could even be that he chanced to see a dragonfly zip past, its rigid body looking for all the world like a miniature airplane fuselage.
If small boats were in fact the inspiration, where did their creators get the idea for a rigid hull needing no internal support framework? The answer may have been the beetle. Unlike birds with their internal skeletons, beetles and many other insects rely on a hard carapace or exoskeleton—a load-bearing skin—to support their bodies and deal with the physical stresses they encounter.
Although most beetles can fly, when not in use their wings are hidden beneath hard covers that blend into the carapace. Thus it’s the dragonfly with its long body and prominent wings that serves as nature’s poster child for monocoque construction.
In 1913, at the height of his success, Armand Deperdussin was charged with fraud, found guilty, and sent to jail. Although he was soon released, it was a shattering blow from which he never recovered. He later committed suicide.
Fortunately for France, Louis Blériot stepped forward that year and bought up the company. He renamed it Société pour l’Aviation et ses Dérivés, thus preserving the famous SPAD acronym, and turned its running over to Béchereau, who went on to create France’s most successful and widely produced fighters of World War I.
Whether in a boat, airplane, or living creature, monocoque construction works better on a small scale than on a large one. The reason is that weight increases exponentially with size. Thus, a small boat can be built as a full monocoque structure, whereas a large one requires an internal framework.
In airplanes, the point is quickly reached where a monocoque fuselage, to be sufficiently strong, must weigh more than a conventional fuselage. With traditional materials in World War I, the Deperdussin racer was about as big as one could go. The solution was to judiciously add a bit of internal bracing—a partial internal skeleton—to reinforce this load-bearing skin in critical places, thus allowing it to be thinner and lighter overall. This internal reinforcement was far lighter than the full skeleton required by conventional manufacture.
This photo of the Deperdussin’s monocoque wooden fuselage marks one of the most important technological emergences in aviation.
National Air and Space Museum, Smithsonian Institution
The Albatros D.Va was one of several German World War I fighter planes with a molded-plywood fuselage.
National Air and Space Museum, Smithsonian Institution
This modification of Ruchonnet’s idea turned out to be the magic formula. Called semi-monocoque construction, it would be one of aviation’s most spectacular successes once people figured out how to apply it to all-metal airplane manufacture. In the meantime, Roland, Pfalz, and Albatros used it to create wooden-fuselage fighter planes for Germany