|Triumph on the sands of Kill Devil Hills|
Wright brothers were the quintessential American tinkerers who hit the
big time. But their creations were more original in some areas than in
others. For example, the now-traditional structural concept of the
airplane was fairly well evolved by the early nineteenth century, when
Englishman Sir George Cayley made his manned glider flights. Cayley's
wings had no ailerons, but there was a rudder for yaw control, and crude
elevators could be adjusted to make corrections in the pitch axis.
Cayley's wings even had dihedral. From his gliding sorties — and studies
of bird flight — German Otto Lilienthal, like Cayley, understood that
the wing chord must be cambered just so in order to produce optimum
lift. And American Octave Chanute — a railroad and bridge engineer —
devised the biplane concept and the enduring Pratt-truss method of
rigging wing structures, in addition to sponsoring his own glider
flights along the sands of Lake Michigan.
Many others made equally significant contributions to the Wrights' storehouse of knowledge, but there were some gaping holes. Aerodynamic stalls weren't understood (though they had been experienced firsthand), and no one could figure out a method of controlling a flying machine in the roll axis.
Propulsion systems also remained a vexing problem. French electrical engineer Clément Ader used an 18- to 20-horsepower steam engine to power his Éole monoplane 165 feet on October 9, 1890. It was the first piloted, powered flight of an airplane, but Ader himself admitted the flight was "tentative," and in no way could be considered a controlled or sustained flight. Steam engines — state of the art in those days — were too heavy for use in an airplane.
The Aerodrome designed by Smithsonian Institution Secretary Samuel P. Langley used a five-cylinder, gasoline-powered radial engine of 45 hp, designed by Stephen M. Balzer and modified by Langley's assistant, Charles Manly. But the 730-lb (with pilot) tandem-winged, catapult-launched Aerodrome crashed not once, but twice into the Potomac River (it took off from a houseboat) on October 7 and December 8, 1903. Manly, the hapless pilot, survived both dunkings.
The Wrights, of course, triumphed on the sands of Kill Devil Hills, North Carolina, just nine days after the Aerodrome's last flight. What gave them the edge over their predecessors? Better control systems, sure, but propulsion — particularly the propellers — gave the Wrights advantages that no one before possessed.Wilbur Wright wrote that his interest in flying dated back to Lilienthal's fatal glider accident of 1896. Like Lilienthal, Wilbur was a student of bird flight, and he wrote, "My observations of the flight of buzzards led me to believe that they regain their lateral balance when partly overturned by a gust of wind, by a torsion of the tips of the wings." Thus was born one of the more important seminal achievements of the Wrights: wing-warping as a method of roll control
The Wrights' advances in propulsion were equally significant. They thought about using an automobile engine, but knew that it would be too heavy for their Flyer. So they built an engine of their own. Charles Taylor, a machinist in the Wrights' bicycle shop, did most of the engine work. The finished product was a four-cylinder, aircooled, 12-hp engine that weighed 140 pounds.
Although propellers had been used in previous designs, technical data quantifying their performance was absent. Airscrews, they were called, and people reasoned they'd work pretty much like aerial equivalents of their namesakes — the propeller screws that power boats and ships. Visits to the Dayton Public Library showed that this data was almost useless. The Wrights had to develop their own formulas for optimum propeller performance. They made another seminal discovery: Propellers were simply rotating wings.
The brothers figured they'd need 90 pounds of thrust to make their 605-lb Flyer airborne. To achieve that value, the propellers were given eight-and-a-half-foot diameters, carved by hand (using hatchets in the early steps) out of three layers of spruce, laminated, covered with canvas, and then painted. The blades were twisted so as to make them 66-percent efficient. The proper amounts of camber for each propeller section were derived from the information the Wrights used in designing the Flyer's wings — information gleaned with the help of a homemade wind tunnel.
Why two propellers? To achieve enough thrust. Why counterrotating propellers? The Wrights knew from the start that propellers created torque and turning effects. To cancel them out, one propeller's drive chain was twisted, making the propellers turn in different directions. And turn slowly. The Wrights knew that slower-turning propellers were more efficient than faster ones.
How did the Wrights know about propeller torque effects? One theory has its roots in the Wrights' childhood. In the early 1870s, Alphonse Pénaud, a French marine engineer, developed several rubber-band-powered flying toys that had crude pusher propellers. When wound up and released, the toys always flew in a circle. The Wrights reportedly had Pénaud flying toys as youngsters, and presumably remembered the turning behavior of those single-propeller devices.
Twin counterrotating propellers, efficient thrust levels, reduction-gear drives (the sprocket-and-chain arrangement), empirical data from wind tunnels, stability and control methods — all concocted by two self-taught, highly motivated bicycle manufacturers relieved of the burden of a conventional advanced education.
MORE (Wright Plane Crash)
Thomas A. Horne
The Wright’s counter-rotating propellers were ahead of their time. It wasn’t until the late 1970s that manufacturers "introduced" them as valuable safety devices.
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