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A ducted propeller, also known as a Kort nozzle, is a marine propeller fitted with a non-rotating nozzle. It is used to improve the efficiency of the propeller and is especially used on heavily loaded propellers or propellers with limited diameter. It was developed first by Luigi Stipa (1931) and later by Ludwig Kort (1934). The Kort nozzle is ...
In aeronautics, a ducted fan is a thrust-generating mechanical fan or propeller mounted within a cylindrical duct or shroud. Other terms include ducted propeller or shrouded propeller . [ 1 ] When used in vertical takeoff and landing ( VTOL ) applications it is also known as a shrouded rotor .
A pump-jet, hydrojet, water jet, or jet drive uses a ducted propeller (axial-flow pump), centrifugal pump, or mixed flow pump to create a jet of water for propulsion. These incorporate an intake for source water and a nozzle to direct its flow out, generating momentum, and in most cases, employing thrust vectoring to steer the craft. [30]
A rim-driven thruster integrates an electric motor into a ducted propeller. The cylindrical duct acts as the stator, while the tips of the blades act as the rotor. They typically provide high torque and operate at low RPMs, producing less noise. The system does not require a shaft, reducing weight.
Unlike ducted engines, rockets give thrust even when the two speeds are equal. In 1903, Konstantin Tsiolkovsky discussed the average propulsive efficiency of a rocket, which he called the utilization ( utilizatsiya ), the "portion of the total work of the explosive material transferred to the rocket" as opposed to the exhaust gas.
A ducted fan or propeller also has certain benefits at lower speeds but the duct needs to be shaped in a different manner than one for higher speed flight. More air is taken in and the fan therefore operates at an efficiency equivalent to a larger un-ducted propeller.
An airbreathing jet engine (or ducted jet engine) is a jet engine in which the exhaust gas which supplies jet propulsion is atmospheric air, [1] which is taken in, compressed, heated, and expanded back to atmospheric pressure through a propelling nozzle. [2]
The tilting ducted fans or shrouded propellers, such as the Doak VZ-4, the Bell X-22, were built in 1950s and 1960s. However, ducts designed for static conditions degraded in performance at high advance ratio, whereas a duct designed for axial cruise could regain good high-speed performance at the expense of static figure of merit.