Hélicoptères Guimbal
SERVICE LETTER
CABRI G2
SL 12-001 A
2 / 10
Original issue
4. Specific characteristics of the Fenestron
Compared to conventional tail rotors as fitted to most small helicopters, the
Cabri G2 Fenestron features a higher disk loading and a shroud that allow a
high thrust capability, but with different shape of the curve Pedals position / Tail
rotor thrust :
The helicopter also features a large, airfoil-shaped vertical fin.
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The primary purpose of this fin is to provide adequate stability in yaw in
forward flight.
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It is also set at an angle of attack to the left, thus producing most of the
thrust required in forward flight to counter the main rotor torque, and
increasing overall efficiency. This also permits safe powered flight in case of
a tail rotor or transmission failure.
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This implies that this lift is unwanted in autorotation, requiring the pilot to
apply significant left pedal for symmetrical flight. However, unsymmetrical
flight is not dangerous; it should be corrected for best gliding ratio, and
before touchdown.
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The tail rotor thrust is null when the left pedal is about 3 cm forward
(6 cm between the two pedals).
LH
s
top
RH
s
to
p
Tail rotor
thrust
Pedal position
Comparison of thrust curves for
identical performance tail rotors
Conventional / Fenestron
Conventional
Fenestron
Zero
thrust
Hover
Cruise
Fenestron
Cruise
conventional
Pedal travel to hover
