A Fenestron is a shrouded tail rotor of a helicopter that is essentially a ducted fan. The housing is integral with the tail skin, and, like the conventional tail rotor it replaces, is intended to counteract the torque of the main rotor. It was originally conceived by Sud Aviation in the 1960s. Sud Aviation became part of Aerospatiale which merged with Daimler-Benz Aerospace AG to form Eurocopter in 1992. Eurocopter has since become part of the European Aeronautic Defence and Space Company (EADS).[1]
While conventional tail rotors typically have two or four blades, fenestrons have between eight and 18 blades. These may have variable angular spacing, so that the noise is distributed over different frequencies and thus sounds quieter. The housing allows a higher rotational speed than a conventional rotor allowing it to have smaller blades.
The term Fenestron is a trademark of Eurocopter. It comes from the modern French for a small window, and is ultimately from the Latin fenestra ("window")[2][3]
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Advantages
- Increased safety for people on the ground. The smaller size allows it to be higher above people or objects on the ground, and the enclosure provides peripheral protection.
- Less susceptible to foreign object damage. The higher ground clearance and the enclosure also makes it less likely to strike foreign objects or to suck in loose objects such as small rocks.
- Greatly reduced noise. Since the blade tips are enclosed; this and the greater number of blades leads to reduced vibration.
Disadvantages
The Fenestron's disadvantages are those common to all ducted fans when compared to propellers. They include:
- Higher weight and air resistance of the enclosure
- Higher construction cost
- Higher power requirement for a given thrust
History
The Fenestron had been developed, conceived and produced to replace classic tail rotor to improve security and performance for rotor-craft, and was used for the first time at the end of the 1960s on the second experimental model of the SA 340 by Sud Aviation, and on the later model Aérospatiale SA 341 Gazelle SA341/342.
After the integration of Sud Aviation to Aérospatiale, and more recently to Eurocopter, many rotor craft in the world uses the Fenestron as tail rotor, for light, intermediate and medium weight helicopters.
The Fenestron can be found on many Eurocopter helicopters, like the EC120 Colibri, EC130 ECO Star, EC135 (and EC635 the military version of the EC135), the AS365 N/N3 Dolphin (also known as the HH-65C widely used in the USCG), the EC155 Super Dolphin (a wider, heavier and more advanced version of the AS365 N/N3 series of the Dolphin Helicopter), and more recently on Hélicoptère Guimbal with the small single piston engine, the Cabri G2.
Other than Eurocopter and its predecessors, a ducted fan tail rotor was also used on the US military helicopter project Boeing-Sikorsky RAH-66 Comanche, which was canceled in 2004. It has also been used in the Russian Ka-60 (but only 8 helicopters have been produced), and also on the military Japanese helicopter, the Kawasaki OH-1 Ninja.
See also
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Wikimedia Commons has media related to: Fenestron |
References
- ^ Helis.com
- ^ Prouty, Ray, Helicopter Aerodynamics, Helobooks, 1985, 2004, pg 266
- ^ 30 Years of Innovation
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