The Airplane - Jay Spenser [92]
The difference between rotary and radial aero engines is striking. Having blazed a trail of glory over war-torn Europe, rotaries all but vanished after the 1918 armistice. In contrast, radials would rise to prominence in the 1920s and play a major role right through to the jet age.
In 1905, Laurent Séguin dropped out of college to join his older half brother Louis in a far more interesting venture. Together they formed an automobile engine company, Société des Moteurs Gnome. Two years later, as aviation interest heightened in France, they set out to develop an aero engine that would be a complete departure from existing European practice.
What these young technologists came up with was a seven-cylinder rotary engine called the Gnome, and it was an odd beast. For starters, what looked like its propeller shaft actually faced backward and bolted to the airplane’s firewall. As for the propeller, it bolted to a fixed shaft on the engine’s other side. Consequently, when the Gnome ran, its cylinders and propeller spun as a single unit.
Strange as it may seem, there were good reasons for spinning the engine too. One was adequate air cooling, a constant challenge in those early days. Other aero engines required liquid-cooling systems with bulky radiators, but not the Gnome. Another benefit was smooth operation in an era when most engines ran roughly if at all. But the best thing about the Gnome was its high power-to-weight ratio.
First run in the spring of 1909, the Gnome reliably produced 50 hp for a total weight of just 165 pounds (75 kilograms). It was the first successful aviation rotary.5 Following Gnome’s lead, rival company Le Rhône came out with an excellent rotary engine in 1912. Gnome and Le Rhône competed head to head and licensed other firms to build their respective products, among them Bentley, Clerget, Oberursel, and Thulin. Consequently, Italy, Germany, Great Britain, Russia, Sweden, and the United States also produced rotary aero engines.
A Gnome rotary engine spins together with its propeller in this Nieuport 28 as it prepares for takeoff in World War I.
Museum of Flight, Seattle
A 1915 merger ended the initial rivalry by creating Société des Moteurs Gnome et Rhône. By then, Europe was embroiled in World War I. Rotary engines played a starring role in this conflict, but for all their benefits, it was their downside that made World War I aviation so colorful. Fuel and oil had to be fed to them through the hollow shaft that was their single point of contact with the airplane. This meant those liquids had to be mixed together, which in turn dictated the use of castor oil, the only high-temperature metal lubricant for which gasoline is not a solvent.
Most engines have an oil sump through which engine oil is recaptured and recirculated. Rotary engines could have no sump, of course, so the castor oil was drawn into the cylinders and burned along with the gasoline. This produced copious quantities of a gummy exhaust that the fast-spinning cylinders sprayed in every direction.
To deal with the mess, rotary-powered World War I fighter planes often had aluminum engine cowlings cut away at the bottom like a horse’s collar to direct this exhaust away under the airplane. Even so, pilots invariably inhaled large amounts of castor oil. It being a laxative, diarrhea was a frequent occupational hazard. Fortunately for wartime pilots, blackberry brandy quickly emerged as the preferred antidote.
That filmy exhaust also gummed up windshields and goggles. One reason aviators wore silk scarves was to have something to wipe their goggles with. The other, or so it is said, was to tickle the back of one’s neck as a constant reminder to look around for enemy fighters.
Another odd characteristic of rotary engines was that these fast-spinning masses of metal proved to be extremely