Wright Flyer 1903 engine

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Orville and Wilbur Wright returned to Dayton at the end of October 1902, to begin preparing for the next flying season and for what they hoped would be their first powered flight. They needed two essential components - a propeller and an engine. In their systematic way, they went about determining exactly what was required. First they needed to find an engine. In December 1902, Wilbur wrote to ten engine manufacturers with his specifications. He needed a gasoline motor weighing no more than 180 pounds (82 kilograms). It needed to provide at least 8 horsepower (6 kilowatts).

While they waited to hear from the engine companies, they begin working on the propeller. They searched the literature for research on propeller design, but came up empty-handed. Realizing that a propeller was simply an airplane wing that turned on a spiral course rather than moving ahead, they turned to the wind tunnel to provide the information they needed. They built a larger wind tunnel—two feet (0.6 meter) on each of four sides and eight feet (2.4 meters) long—to test their propeller theory. They first used the tunnel to develop their equations; then they tested small-scale models of propellers. In February 1903, they hand-built and tested their first full-size propeller. They ended up with two 8.5-foot (2.6-meter) spruce propellers with tips covered in muslin to keep the wood from splitting.

To eliminate the effect of torque, the two propellers would turn in opposite directions by means of crossing one of the drive chains. When coupled with the motor that the Wright brothers built through the effective chain drive transmission, the propellers provided a combined thrust of 90 pounds (400 newtons), just enough to let their plane rise under its own power, fly, and land. The propellers had a high efficiency of 66 percent. This compared to propellers designed in nineteenth century Europe that had an efficiency of only 40 to 50 percent and propellers designed by Samuel Langley with an efficiency of 52 percent. (Propeller efficiency is defined as the power output of the propeller divided by the shaft power input from the engine, expressed as a percentage.) In practical terms, the propellers converted two-thirds of the energy applied to them to thrust.

In the meantime, they had heard from the engine manufacturers. All replies were negative—no one had an engine that met the Wrights’ specifications and no one was willing to develop one. They decided to build their own engine with the help of their talented mechanic, Charlie Taylor.

Their first engine had four horizontal cylinders, displaced 201 cubic inches (3,294 cubic centimetres), weighed about 200 pounds (91 kilograms) fully equipped, and produced 16 horsepower (12 kilowatts) at startup and dropped off to 12.5 horsepower (9.3 kilowatts) when underway. It had no throttle, and the engine could run only at full speed. The crankcase of the engine was built of aluminium to save weight. Taylor had a local foundry cast the crankcase and the four cylinders as a single unit. It was water-cooled, and fuel was gravity-fed from a can mounted several feet above the engine on an inboard wing strut.

Taylor machined the engine in six weeks. They ran it for the first time on February 12, 1903. It ran well, but soon glowed red hot around the exhaust valve area. The Wrights enriched the air-fuel mixture, but it was too much. Gasoline dripped, and the engine seized, freezing the bearings and shattering the crankcase. They had to completely rebuild the engine, but it was running smoothly by May. This engine formed the prototype for the approximately 200 engines the Wrights built during their aviation careers.

The airplane on which they planned to mount the engine and propellers was their largest so far—40 feet (12.3 meters) from wingtip to wingtip. Orville referred to it as the “whopper flying machine.” It was too large to assemble in Dayton, and the brothers packed up the parts to assemble when they arrived at Kitty Hawk, North Carolina. On September 23, 1903, Wilbur, Orville, the parts of their machine, and a launch system they had constructed, left Dayton for Kitty Hawk.

In March 1903, nine months before they would launch their flying machine, the brothers filed an application for a patent for a “Flying Machine.” They received a disappointing response from the U.S. Patent Office. Their application was rejected because the Patent Office said it was not the first such claim, their drawings and written description were inadequate, and obviously, the device could not perform its intended function. The Patent Office had received so many similar applications over the past 50 years that it had decided to automatically reject all applications for machines that had not already flown. The Wrights tried again, but their second application was also rejected. Not until 1906, long after their first flight and only after they had engaged the services of a patent attorney, were they successful in obtaining a patent that protected their invention.

Source: U.S. Centennial of Flight - Wright Brothers