The Airplane - Jay Spenser [93]
The short noses of rotary-engine fighters also helped maneuverability by concentrating the airplane’s mass near its center of gravity. Together these factors made rotary-powered World War I fighters perhaps the most maneuverable fixed-wing airplanes in history. Their prowess in swirling dogfights was fearsome, although enemy pilots always knew in which direction their adversaries would turn.
Another foible of rotaries is that they lacked throttles and generally ran at full power all the time. To slow sufficiently to land, pilots employed a coupe button or “blip switch” on the stick that momentarily interrupted the ignition. When the button was pressed, the engine fell silent; when released, it erupted into life again because inertia kept it spinning. Care had to be taken not to blip for too long or the spark plugs would foul and the engine would not restart.6
A Sopwith Camel returning from a mission would trace a sawtoothed profile as it approached its home aerodrome. It would dip and bob with each successive brrrpp-brrrpp-brrrpp as the pilot blipped its engine. Only when sufficiently slowed down would the pilot plunk down the airplane, cut its master switch, and let the tail skid’s drag on the grass bring him to a stop.
Wartime urgency accelerated all aspects of flight technology, aero engines included. One way to get more power out of an airplane’s engine was to make it turn faster so that there were more explosions in its cylinders per given unit of time.
From 1914 through 1918—the span of World War I—the rotational speed of inline aero engines rose from 1,200 rpm to upward of 2,000 rpm. Unfortunately, rotary engines couldn’t pull off this same trick because running the engine faster exposed the spinning cylinders to a self-defeating rise in aerodynamic braking. As the war went on, therefore, inline engines outstripped the capabilities of rotaries. Mercedes manufactured a large number of six-cylinder vee engines for many different German fighter types of World War I. Fine as those engines were, however, the Allies had an even better one, thanks to an inventive Swiss engineer working in Spain.
Born in Geneva in 1878, Marc Birkigt designed mining equipment before relocating to Barcelona at the start of the 20th century. A gifted designer of engines and luxury automobiles, he soon distinguished himself as the engineering genius behind the appropriately named Hispano-Suiza company.
Birkigt opened a factory in Paris in 1911. When World War I broke out a few years later, he turned it over to Gnome for mass production of their rotary engines and returned to Barcelona. It was there that he conceived of an aero engine built a radically different way. The result was the Hispano-Suiza V-8.
Initially developing 150 hp, this engine introduced monoblock construction, whereby thin steel liners were screwed into the cylinders of the cast aluminum block, resulting in a strong, lightweight engine that was easy to manufacture. The casting included cored passages for cooling water to circulate. Corrosion was avoided because this water never touched steel. The overhead cams actuating the valves were completely enclosed.
This engine caused a veritable sensation when the French saw it in the summer of 1915. Adopted for military use, Hispano-Suiza engines powered the famous SPAD series, France’s most widely produced fighter. The 150-hp “Hisso” powered the SPAD VII and an improved 220-hp version, incorporating reduction gearing, powered the SPAD XIII. A 300-hp version was also developed before the war ended but suffered from teething troubles.
The Hispano-Suiza—the world’s first cast-block engine—was the most technologically advanced power plant to emerge from World War I. Built by fourteen