An aircraft propeller or airscrew〔("Airscrew." ) ''Oxford English Dictionary.'' Retrieved: 23 March 2011.〕 converts rotary motion from a piston engine, a turboprop or an electric motor, to provide propulsive force. Its pitch may be fixed or variable. Early aircraft propellers were carved by hand from solid or laminated wood, while later propellers were constructed of metal. Modern designs use high-technology composite materials.
The propeller attaches to the crankshaft of a piston engine, either directly or through a reduction unit. A light aircraft engine may not require the complexity of gearing, which is essential on a larger engine or on a turboprop aircraft.
Italian scientist Leonardo da Vinci made sketches of an “air screw” human-powered helicopter with no practical application between 1487 and 1490.〔Rumerman, Judy. ("Early Helicopter Technology." ) ''Centennial of Flight Commission,'' 2003. Retrieved September 2015.〕
The twisted airfoil (aerofoil) shape of an aircraft propeller was pioneered by the Wright Brothers. While some earlier engineers had attempted to model air propellers on marine propellers, the Wright Brothers realized that a propeller is essentially the same as a wing, and were able to use data from their earlier wind tunnel experiments on wings, introducing a twist along the length of the blades. This was necessary to maintain a more uniform angle of attack of the blade along its length. Their original propeller blades had an efficiency of about 82%,〔Ash, Robert L., Colin P. Britcher and Kenneth W. Hyde. ("Wrights: How two brothers from Dayton added a new twist to airplane propulsion." ) ''Mechanical Engineering: 100 years of Flight, 3 July 2007.〕 compared to the 90% of modern propellers.〔Rogers, David F. "(Propeller Efficiency )", page 3. ''NAR'', 2010. Accessed: 28 August 2014.〕 Mahogany was the wood preferred for propellers through World War I, but wartime shortages encouraged use of walnut, oak, cherry and ash.
Alberto Santos Dumont was another early pioneer, having designed propellers before the Wright Brothers (albeit not as efficient)〔Henri R. Palmer Jr. ''The birdcage parasol,'' Flying Magazine oct. 1960 p51〕 for his airships. He applied the knowledge he gained from experiences with airships to make a propeller with a steel shaft and aluminium blades for his 14 bis biplane. Some of his designs used a bent aluminium sheet for blades, thus creating an airfoil shape. They were heavily undercambered, and this plus the absence of lengthwise twist made them less efficient than the Wright propellers.〔Physical propeller theory was at the time restricted to the Rankine-Froude theory, also known as the "actuator disc theory" or the axial momentum theory. That theory however adequate, does not give indication on the shape that should be given to the propeller. This would be solved regarding that theory only in the 1920s by complement of the Betz law (Goldstein, Betz, Prandtl and Lanchester): William Graebel, ''Engineering Fluid Mechanics'', p144 , ISBN 1-560-32711-1, John Carlton, ''Marine Propellers and Propulsion'', p169, ISBN 978-0-08-097123-0. The Wright brothers however were equating the propeller blade to an airfoil instead, which for they previously had already determined the aerodynamic behavioural patterns: John David Anderson, ''A History of Aerodynamics: And Its Impact on Flying Machines'', ISBN 0-521-66955-3〕 Even so, this was perhaps the first use of aluminium in the construction of an airscrew.
Originally, a rotating airfoil behind the aircraft, which pushes it, was called a propeller, while one which pulled from the front was a tractor.〔Encyclopedia Britannica, 1910 edition, volume 30 (1922 supplement), in the article "Aeronautics" page 20. "Airscrews have been described as 'tractors' and 'propellers', according as the airscrew shaft is placed in tension or in compression by the thrust, and corresponding aeroplanes are usually called by the same names. The first biplanes, those of the Wrights and the Farmans, were of the propeller type, colloquially 'pushers'; almost all monoplanes were 'tractors.'〕 Later the term 'pusher' became adopted for the rear-mounted device in contrast to the tractor configuration and both became referred to as 'propellers' or 'airscrews'.
The understanding of low speed propeller aerodynamics was fairly complete by the 1920s, but later requirements to handle more power in a smaller diameter have made the problem more complex.
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