The Airplane - Jay Spenser [3]
Steam was then beginning to power England’s industrial revolution, but steam engines were too heavy to fly. Consequently, Cayley contended his entire life with the frustrating lack of a suitable power plant. This was the single disappointment in an otherwise astonishingly successful career in the branch of science that he founded.
A century before the Wright brothers, George Cayley etched onto this silver disc history’s first-ever imagining of the airplane.
National Air and Space Museum, Smithsonian Institution
For humans to fly, Cayley correctly observed, “it is only necessary to have a first mover that will generate more power in a given time, in proportion to its weight, than the animal system of muscles.”2 The development and successive refinement of internal-combustion gasoline engines during the nineteenth century would provide the Wright brothers and other pioneers with this last missing bit of technology by the start of the twentieth century.
Why is it so significant that Cayley called for a separate propulsion system? Because before he came along, people drew the wrong lesson from nature. They assumed that airplanes, if and when such things were invented, must achieve flight by flapping their wings like birds. We call this flapping-wing aircraft an ornithopter.
The trouble with ornithopters is that they are mechanical nightmares. Models can fly this way, but not full-size aircraft because of the enormous complexity and high stresses of ornithopter flight. To get a sense of just how unwieldy a concept this is, try to imagine a flapping-wing jetliner.
We have the advantage of hindsight, but at the time ornithopters looked like not just the logical way to fly but the only way. Leonardo da Vinci thought so, and he arguably possessed the greatest mind of the Renaissance. When his notebooks were rediscovered and published decades after Cayley’s death, they mesmerized the world.
Sprinkled among Leonardo’s thirteen hundred pages of handwritten notes are more than a hundred drawings that show his fascination with birds and remarkable concepts for human flight. Among these are beautiful illustrations of flapping-wing machines (ornithoptering hang gliders) suggestive of the anatomy of bats and birds. Da Vinci also sketched an unworkable vertical-flight machine that drew inspiration from Archimedes’ screw and anticipated the helicopter.
Like da Vinci three centuries earlier, George Cayley took his inspiration from nature. Studying birds closely, he gleaned insights from their shapes, their flight, and how their wings were articulated and moved. In particular, he was fascinated to note that seagulls, when riding the winds of England’s rugged north coast, soared for extended periods without flapping.
Mulling this over gave Cayley an “aha” moment that was fledgling aviation’s single most crucial epiphany: flight is possible with wings that are held entirely rigid.
This was excellent news indeed. It meant that heavier-than-air flying machines could be designed that would be vastly simpler to construct, operate, and maintain than ornithopters. Yes, rigid wings would do the trick—so long as air flowed over them.
During a descent with gravity tugging, air would of course flow over a flying machine’s wings. But how do you climb or sustain level flight when gravity must be defied? In these challenging flight phases, an impetus would be required to thrust the machine through the air.
This forward thrust had to come from somewhere, Cayley reasoned, and if the wings aren’t flapping, then something else aboard the airplane must provide the push. That in turn dictated a separate propulsion system.
In one fell swoop, young Cayley sidestepped the ornithopter trap that even da Vinci had fallen into. Cayley’s greatest legacy would be the layout for a powered, heavier-than-air flying machine whose wings do not flap because they are called on to provide only lift, not lift and thrust combined. Conceptually,