After Launoy and Bienvenu, the next important figure in rotating-wing history is an Englishman, Sir George Cayley. A baronet, whose estates were at Brampton in Yorkshire, Cayley was born in 1773 and lived until 1857. A remarkable "amateur" scientist, engineer and experimenter, his interests were so broad and far-ranging that it is difficult, if not impossible, to categorize him. He played an active role in the growth of British engineering during the crucial first half of the eighteenth century, but he was also a member of Parliament, a writer, and a reformer active in the struggle to abolish Negro slavery. His interests included such diverse and unlikely fields as the design of theaters, theoretical aeronautics, the rights of labor, the construction of steam engines, and the design of artillery shells. Cayley's work in heavy engineering, especially the design of railway equipment, was well recognized in his own day.

In recent times, considerable evidence has been uncovered revealing the remarkable extent of Cayley's work, which began as far back as the 1790's. Bringing together all the existing knowledge (in 1661 another brilliant Englishman, Robert Hooke, had written an important treatise, Resistance of Air to Bodyes Moved Through It), Cayley formulated his basic approach to the problem of flight: "to make a surface support a given weight by the application of power to the resistance of air. . . ." He then proceeded to work out many of the practical problems connected with the creation of a flyable aircraft. Rightly convinced of the correctness of his approach to airplane design, Cayley predicted over a hundred and fifty years ago the movement of "passengers and goods more securely by air than by water, and with a velocity of from twenty to one hundred miles per hour. . . ."

Interestingly, illustrations of the principle of flight had existed long before Cayley's work or even that of Da Vinci. The lifting of a kite in the wind, the force generated by the sails of windships-both were ancient examples of what could be accomplished by the movement of air against a resisting surface. The ordinary kite is a prime example; it is in fact a kind of tethered glider, an unpowered airplane held stationary in a flow of air. The principle is simple: the lifting force is created by the push of the air against the underside of an inclined surface-a surface set so that its edge is raised at a slight angle to the airflow. (This angle is termed the "angle of attack.") Obviously, the lifting effect will be the same if the flow is created by the movement of the surface through the air-this, in fact, is the essence of the flight of an airplane.

Cayley realized that this was the answer to the riddle of flight, and, being a practical engineer as well as a theoretician, he then proceeded to the design of aircraft that could actually fly. Of necessity, two questions in particular had to be answered: how to propel the lifting surface (wing) through the air, and then how to stabilize the wing so that it would maintain the correct angle of attack to the air. Eventually the solutions came, but with one important exception-he could not overcome the lack of a suitable engine.

In 1809, Cayley described an experimental internal combustion engine built by a friend, William Chapman, that used benzene as a fuel. The device was impractical-the cost of running it was eight times that of a steam engine of the day. But, in commenting on this failure, Cayley plainly foresaw the modern internal combustion engine. "Probably a much cheaper engine might be produced," he wrote, "by a gas-tight apparatus and by firing the inflammable air generated with a due proportion of common air under a piston."

Although he was stymied by the lack of a suitable engine, this British pioneer's work was nevertheless so remarkable that in his own day he was recognized as the "Father of Aerial Navigation." Of his little-known achievements, perhaps the most remarkable was a monoplane glider with most of the important features of a modern aircraft. There is strong evidence, recently uncovered, that this glider actually flew at Brampton in the 1850's, if not earlier. The details of the incident are based upon the accounts of a long-forgotten eyewitness, Cayley's granddaughter, and his paper, written in 1852, misleadingly titled "Governable Parachutes." Published in the Mechanics Magazine of London that year, the paper went unrecognized for over a century; it described, with drawings, an aerodynamically sound glider with a movable tail surface. From other records, and the granddaughter's account, it would seem that this glider, or another very much like it, with Cayley's coachman as pilot, flew some 500 yards from the top of a hill at his Brampton estate, probably in the year 1852. (Cayley was then almost eighty years old.)

Remembered largely for his fixed-wing experiments, Sir George Cayley pioneered in rotating-wing aircraft design as well, and the drawings for at least one machine of the helicopter type have survived. His earliest aeronautical work, a twin-rotor helicopter model built in 1792 when he was nineteen, resembled the device constructed by Launoy and Bienvenu in 1784. Half a century later, in 1842, he credited this first effort with the inspiration for his later work. With rotating-wing aircraft, Cayley appears to have accomplished less-at least in terms of models that could fly-than with his fixed-wing designs.

Nevertheless, with vertical-rising helicopter types as well as with fixed-wing, Cayley was uncannily prophetic in describing what would he needed. In a letter sent to the Mechanics Magazine in 1843, he emphasized that the ability to take off straight up, hover, and land in tight areas was important.

He added: "Very great power, in proportion to the weight of the engine, is necessary."

In the light of what we now know, Cayley's design for a helicopter seems ponderous, but it faced up to the major problems. The two sets of lifting rotors turned in opposite directions to cancel out torque. Two pusher propellers in the rear were intended to drive the craft through the air, and twin rudders were furnished for steering. An intriguing feature was the ability of the large fanlike rotors (eight blades for each rotor) to close down flat to form a lifting surface for forward flight.

Encouraged by Cayley's work, another Englishman, W. H. Phillips, designed a small steam-powered model helicopter that flew in 1842; it seems to have been the very first model aircraft in history to fly powered by an engine rather than with springs, clockwork, elastic whalebone or other such wind-up contrivances. The little single-rotor model incorporated a form of rotor drive not unlike the tipjet systems used on a few modern helicopters. Steam from a miniature boiler passed up through the hollow rotor shaft and out to rearward-facing holes at the tips of the blades; in effect, a form of jet propulsion. Although a steam system was impractical fpr a man-carrying aircraft because it was far too heavy, the Phillips model-exhibited at the Crystal Palace in London in 1868-had considerable effect on the scientific thought of the day and encouraged others to strive for more efficient engines.

After Cayley, the deluge. He died in 1857, and during the last half of the nineteenth century, there were helicopter inventors everywhere-but no flyable helicopters. The most critical problem of course was still the lack of a suitable engine.

• Laterally located counter-rotating main rotors
• Very rigid rotors
• Advancing Blade Concept
• Pusher propellers