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In marine propulsion, a variable-pitch propeller is a type of propeller with blades that can be rotated around their long axis to change the blade pitch. Reversible propellers—those where the pitch can be set to negative values—can also create reverse thrust for braking or going backwards without the need to change the direction of shaft revolution.
Lightly loaded propellers for light aircraft and human-powered boats mostly have two blades, motor boats mostly have three blades. The blades are attached to a boss (hub), and while it can be a big boss, it should be as small as the needs of strength allow – with fixed-pitch propellers the blades and boss are usually a single casting.
The device which controls the propeller pitch and thus speed is called a propeller governor or constant speed unit. Reversible propellers are those where the pitch can be set to negative values. This creates reverse thrust for braking or going backwards without the need to change the direction of shaft revolution.
English inventor Francis Ronalds described what he called a propelling rudder in 1859 that combined the propulsion and steering mechanisms of a boat in a single apparatus. . The propeller was placed in a frame having an outer profile similar to a rudder and attached to a vertical shaft that allowed the device to rotate in plane while spin was transmitted to the propell
A Mark 46 Mod 5A torpedo is inspected aboard a destroyer in April 2005. Contra-rotating propellers have benefits when providing thrust in marine applications. Contra-rotating propellers are used on torpedoes due to the natural torque compensation and are also used in some motor boats.
The Voith Schneider propeller was originally a design for a hydro-electric turbine. [2] Its Austrian inventor, Ernst Schneider, had a chance meeting on a train with a manager at Voith's subsidiary St. Pölten works; this led to the turbine being investigated by Voith's engineers, who discovered that although it was no more efficient than other water turbines, Schneider's design worked well as ...
A propeller (often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon a working fluid such as water or air. [1]
It helps in understanding the efficiency of the propeller at different speeds and is particularly useful in the design and analysis of propeller-driven vehicles.It is the ratio of the freestream fluid speed to the propeller, rotor, or cyclorotor tip speed. When a propeller-driven vehicle is moving at high speed relative to the fluid, or the ...