Dynamic Stability and Control Characteristics of a Ducted Fan Model in Hovering Flight 1954 NACA Langley Research Center (Patreon)

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'In the 1950s, there was an interest in the Armed Forces in vertically rising aircraft.  Tests were necessary to gain information of the stability and control in hovering flight.  This video shows some of the preliminary work in a model that could be assembled quickly from existing components.  The 18-inch dual-rotating propeller is in a 4-foot long shroud.  The building is Langley Research Center's Free Spinning Tunnel.  NASA Langley Film #L-24.'

Silent, with title cards.

Originally a public domain film from NASA, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.

The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).

https://ntrs.nasa.gov/search.jsp?R=19930088196

https://en.wikipedia.org/wiki/Ducted_fan

Wikipedia license: http://creativecommons.org/licenses/by-sa/3.0/

A ducted fan is an air moving arrangement whereby a mechanical fan, which is a type of propeller, is mounted within a cylindrical shroud or duct. The duct reduces losses in thrust from the tips of the propeller blades, and varying the cross-section of the duct allows the designer to advantageously affect the velocity and pressure of the airflow according to Bernoulli's principle. Ducted fan propulsion is used in aircraft, airships, hovercraft, and fan packs.

A jet fan is a stationary ducted fan used to move air through buildings or tunnels.

Ducted fans normally have more and shorter blades than conventional propellers and thus can operate at higher rotational speeds...

In aircraft applications, the operating speed of an unshrouded propeller is limited since tip speeds approach the sound barrier at lower speeds than an equivalent ducted fan. The most common ducted fan arrangement used in full-sized aircraft is a turbofan engine, where the power to turn the fan is provided by a gas turbine. High bypass ratio turbofan engines are used on nearly all civilian airliners, while military fighters usually make use of the better high-speed performance of a low bypass ratio turbofan with a smaller fan diameter. However, a ducted fan may be powered by any source of shaft power such as a reciprocating engine, Wankel engine, or electric motor. A kind of ducted fan, known as a fantail or by the trademark name Fenestron, is also used to replace tail rotors on helicopters.

Ducted fans are favored in VTOL aircraft such as the Lockheed Martin F-35 Lightning II, and other low-speed designs such as hovercraft for their higher thrust-to-weight ratio.

In some cases, a shrouded rotor can be 94% more efficient than an open rotor. The improved performance is mainly because the outward flow is less contracted and thus carries more kinetic energy.

Among model aircraft hobbyists, the ducted fan is popular with builders of high-performance radio controlled model aircraft. Internal-combustion glow engines combined with ducted-fan units were the first achievable means of modeling a scaled-size jet aircraft. Despite the introduction of model-scale turbojet engines, electric-powered ducted fans remain popular on smaller, lower-cost model aircraft. Some electric-powered ducted fan airplanes can reach speeds of more than 320km/h (200mph).

Most types of fans used in computers contain a duct integrated into the fan assembly; the duct is also used for mechanically mounting the fan to other components.