Propeller (aeronautics)
Propellers are most suitable for use at subsonic airspeeds generally below about 480 mph (770 km/h), although supersonic speeds were achieved in the McDonnell XF-88B experimental propeller-equipped aircraft.
[3] The 4th-century AD Daoist book Baopuzi by Ge Hong (抱朴子 "Master who Embraces Simplicity") reportedly describes some of the ideas inherent to rotary wing aircraft.
[8] It was not until the early 1480s, when Leonardo da Vinci created a design for a machine that could be described as an "aerial screw", that any recorded advancement was made towards vertical flight.
His notes suggested that he built small flying models, but there were no indications for any provision to stop the rotor from making the craft rotate.
[9][10] As scientific knowledge increased and became more accepted, man continued to pursue the idea of vertical flight.
Many of these later models and machines would more closely resemble the ancient bamboo flying top with spinning wings, rather than Leonardo's screw.
In 1783, Christian de Launoy, and his mechanic, Bienvenu, used a coaxial version of the Chinese top in a model consisting of contrarotating turkey flight feathers [11] as rotor blades, and in 1784, demonstrated it to the French Academy of Sciences.
In 1784 Jean-Pierre Blanchard fitted a hand-powered propeller to a balloon, the first recorded means of propulsion carried aloft.
[12] Sir George Cayley, influenced by a childhood fascination with the Chinese flying top, developed a model of feathers, similar to that of Launoy and Bienvenu, but powered by rubber bands.
[9] William Bland sent designs for his "Atmotic Airship" to the Great Exhibition held in London in 1851, where a model was displayed.
[13][14] Alphonse Pénaud developed coaxial rotor model helicopter toys in 1870, also powered by rubber bands.
[15] Hiram Maxim built a craft that weighed 3.5 long tons (3.6 t), with a 110 ft (34 m) wingspan that was powered by two 360 hp (270 kW) steam engines driving two propellers.
Mahogany was the wood preferred for propellers through World War I, but wartime shortages encouraged use of walnut, oak, cherry and ash.
[22] Alberto Santos Dumont was another early pioneer, having designed propellers before the Wright Brothers[23] 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 in 1906.
Originally, a rotating airfoil behind the aircraft, which pushes it, was called a propeller, while one which pulled from the front was a tractor.
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.
Propeller research for National Advisory Committee for Aeronautics (NACA) was directed by William F. Durand from 1916.
This is derived from his "Bootstrap approach" for analyzing the performance of light general aviation aircraft using fixed pitch or constant speed propellers.
The maximum relative velocity is kept as low as possible by careful control of pitch to allow the blades to have large helix angles.
[39] Early pitch control settings were pilot operated, either with a small number of preset positions or continuously variable.
Automatic props had the advantage of being simple, lightweight, and requiring no external control, but a particular propeller's performance was difficult to match with that of the aircraft's power plant.
It automatically adjusts the blade pitch in order to maintain a constant engine speed for any given power control setting.
Most feathering systems for reciprocating engines sense a drop in oil pressure and move the blades toward the feather position, and require the pilot to pull the propeller control back to disengage the high-pitch stop pins before the engine reaches idle RPM.
Turboprop control systems usually use a negative torque sensor in the reduction gearbox, which moves the blades toward feather when the engine is no longer providing power to the propeller.
However the added cost, complexity, weight and noise of the system rarely make it worthwhile and it is only used on high-performance types where ultimate performance is more important than efficiency.
A fan therefore produces a lot of thrust for a given diameter but the closeness of the blades means that each strongly affects the flow around the others.
By placing the fan within a shaped duct, specific flow patterns can be created depending on flight speed and engine performance.
