A mechanical device designed to impart forward motion to
an airplane or ship, operating on the screw
principle. It generally consists of two or more inclined blades (airfoils)
radiating from a hub, and the amount of thrust
it produces is proportional to the mass of the fluid it acts on and the
rate at which it accelerates the fluid. The inclination, or pitch, of the
propeller blades determines the theoretical distance moved forward with
each revolution. A variable-pitch propeller can be adjusted
while in motion, to maximize its efficiency under different operating conditions;
it may also be possible to reverse the propeller's pitch, or to "feather"
it – i.e., minimize its resistance when not rotating. John Fitch,
in 1796, developed the first marine screw propeller; John Ericsson
perfected the first bladed propeller (1836).
|Historical image of an advanced propeller model in
NASA Lewis Research Center's 8 × 6 foot supersonic wind tunnel