User manual

DodoSim 206 FSX User Manual

Page 41

3.4.1.6.3 Tail Rotor Transmission Failure

The tail rotor transmission failure models a physical breakdown of the tail rotor gearbox and can

occur after repeated or prolonged aggressive tail rotor pedal inputs.

Indications of a failure are a high speed grinding noise and loss of tail rotor control. The pilot must

land immediately. As the airspeed decreases on approach to landing, the pilot will not have the

pedal control required to counter the torque-induced yaw and the nose may attempt to swing to the

right. To mitigate this, the pilot can attempt to maintain heading using careful engine power

application, (via the collective lever), to control the magnitude of torque-induced yaw created and

attempt a run-on landing. Alternatively; since torque-induced yaw only exists when the engine is

driving the rotor, the engine can be throttled back to idle and the helicopter auto-rotated to a safe

landing, using lateral cyclic and taking advantage of the helicopter’s weather-vaning tendency to

perform turns before the airspeed drops too low.

Tail rotor transmission failure – time to land!

3.4.1.7 Rotor RPM Modulation

Whilst the force exerted by the engine attempts to drive the rotor to its optimum operating speed,

aerodynamic forces apply influences that can force the rotor to either slow down or speed up.

The direction and strength of airflow through the rotor in flight can have an effect on rotor speed.

For instance, descending with a bottomed collective lever reduces the pitch on the rotor blades and

can cause the up-flow of air through the rotor to drive the RPM higher, much like a windmill. The

pilot must use both the collective lever and cyclic pitch to ensure that the rotor RPM does not over-

speed the green, (inner), arc on the gauge. Raising the collective pitch or lowering the nose, (in

forward flight), will cause the RPM to decrease and vice-versa.

During a “quick-stop” flare, the pilot raises the nose and lowers the collective to prevent a

“ballooning” in altitude. In this condition the rotor RPM may rise sharply. Careful use of the

collective lever is required to keep the rotor RPM within limits.

As the rotor RPM rises toward and above the top of the green arc, the Gas Producer, (Compressor

Turbine N1), needle can be observed to decrease as the governor reduces fuel in an attempt to

lower rotor RPM. Once any effects of airflow driving the rotor RPM up are gone, the rotor RPM will

Tail rotor has stopped