The Airplane - Jay Spenser [4]
Prescient as he was, Cayley missed the bull’s-eye in two regards with his 1799 design. One was his avoidance of rotating propellers even though the concept of the airscrew, or propeller, had been known to him since 1796. Another was his provision for control around two axes but not the third (the Wright brothers would address both these forgivable failures). In at least one key regard, however, Cayley’s thinking outstripped that of the Wrights a century later: Cayley placed the airplane’s elevator, the movable surface that tilts an airplane up or down, at the rear, not the front.
On the other side of his silver medallion, the twenty-six-year-old inventor identified gravity, lift, drag, and thrust as the forces involved in flight. In so doing, he showed himself to be the first person ever to properly understand flight’s underlying scientific principles. “The whole problem,” he later wrote, “is confined within these limits, viz. to make a surface support a given weight by the application of power to the resistance of air.”3
For Cayley, this 1799 breakthrough was just the beginning. Where other early dreamers envisioned flat panels as wings, Cayley realized that curved or cambered surfaces lift better than do flat ones. He thus invented the concept of the airfoil, as the wing’s aerodynamic profile is called (an airfoil is the shape you would see if you sliced vertically through the wing parallel to the fuselage). Cayley was also the first to realize that dihedral, an upward angle to the wings as they extend outward from the fuselage, increases lateral (side-to-side) stability by making the airplane’s wings self-righting.
On the other side, Cayley properly identified the physical forces governing flight.
National Air and Space Museum, Smithsonian Institution
In 1804, Cayley built himself a whirling arm, a device used by ballistics researchers to study the flight characteristics of cannonballs and other military projectiles. Putting this device to a new use, Cayley investigated aerodynamic lift and drag and evaluated different airfoil configurations, backing up these painstaking experiments with rigorous mathematical calculations. This was the first time in history that scientific tools and methods were applied to the investigation of flight, making Cayley the world’s first aeronautical engineer.
That same year, he built a model to the configuration he had defined five years earlier. About 5 feet (1.5 meters) long, this first airplane glider consisted of a fore-and-aft pole with a kite-like wing mounted near the front. This wing he inclined at an angle of 6 degrees. At the rear, Cayley had a cruciform tail angled downward at 11.5 degrees to offset the upward-angled wing’s tendency to pull the glider into a loop. This served to give the glider longitudinal (fore-and-aft) stability.
Cayley attached this cruciform tail with a universal joint. Between flights, he could loosen it and alter its positioning relative to the fuselage. He would then fly the glider again to observe the results. Just as cleverly, this model included a weight that Cayley could shift forward or aft on the fuselage to study the effects of shifts to the center of gravity.
His handiwork pleased him greatly. “It was very pretty to see [this model] sail down a steep hill,” he wrote with satisfaction, “and it gave the idea that a larger instrument would be a better and safer conveyance down the Alps than even the surefooted mule, let him mediate his track ever so intensely. The least inclination of the tail towards the right or left made it shape its course like a ship by the rudder.”4
To again put things in historical perspective, 1804 was when the world’s first rail-mounted, self-propelled steam engine—the locomotive—was tested in Wales. Railroads didn’t even exist yet, and here was Cayley thinking of air travel.
Five years later, Sir George Cayley shared his findings and beliefs in “On Aerial Navigation,” a landmark three-part treatise published in 1809–10 by Nicholson’s Journal of Natural Philosophy, Chemistry and the Arts.