Fenestron

A fenestron is an enclosed tail rotor of a helicopter with tail rotor configuration. It is used to compensate the torque of the main rotor and as the sheath is retracted in the propeller tail boom installed.

The term is trademarked by the fenestron - protected French company Sud Aviation - now leavened in Eurocopter.

While conventional tail rotors have a maximum of six blades, Fenestron have 8-18 leaves. These are sometimes arranged in a varying distance, so that the operation noise is distributed over multiple frequencies and thus the whole appears quieter. With a smaller diameter of the fenestron is operated at a higher speed than a normal tail rotor.

Advantages:

• Increased safety for people on the ground, since rotating tail rotors of the largest sources of risk include the helicopter.
• Larger ground clearance of the tail boom and a low susceptibility to foreign bodies in military helicopters also against fire.
• Noise greatly reduced because the blade tips do not rotate freely; this and the higher number of sheets also lead to lower vibrations.
• Smaller radius at the same and pushing the same services on the basis of the beam spread due to the geometry of the jacket.

Cons:

• Greater weight by encapsulating
• Higher construction costs
• Increased energy demand by the smaller size
• Shielding the tail rotor during rapid forward flight. Leads to reduction of effectiveness.
• Higher swirl loss by eddy in the effluent. Use of Drallausgleichsstatoren.

Fenestron the tail rotor was first used in the late 1960s on the second experimental model of SA 340, the later model Aérospatiale SA 341 Gazelle. Besides Eurocopter and its predecessors was the fenestron (only B variant ) and also the U.S. military helicopter project, Boeing - Sikorsky RAH -66 Comanche used in a novel prototype of the Sikorsky S-76, which was set in 2004.