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Airlines
Aircraft propellers or airscrews convert rotary motion from
piston engines or turboprops to provide propulsive force. They may
be fixed or variable pitch. Early aircraft propellers were carved
by hand from solid or laminated wood with later propellers being
constructed from metal. The most modern propeller designs use
high-technology composite materials.
The propeller is usually attached to the crankshaft of a piston
engine, either directly or through a reduction unit. Light
aircraft engines often do not require the complexity of gearing
but on larger engines and turboprop aircraft it is essential.
The purpose of varying pitch angle with a variable pitch propeller
is to maintain an optimal angle of attack (maximum lift to drag
ratio) on the propeller blades as aircraft speed varies. Early
pitch control settings were pilot operated, either two-position or
manually variable. Following World War I, automatic propellers
were developed to maintain an optimum angle of attack.
