Tail Rotor Fixed Pitch
Thrust from a tail rotor
prevents a helicopter from spinning and provides yaw control.
The pilot controls the amount of tail rotor thrust by
feathering the tail rotor, which means
changing the pitch of the blades to create more or less lift.
This effectively pushes the tail left/right which yaws the aircraft.
Feathering is controlled by pedals located under the pilots feet.
Pressing the left pedal turns the nose left, while pressing the right pedal turns the nose right.
Although extremely rare, tail rotor feathering can become stuck.
This means the pilot loses most (but not all) ability to control yaw.
Flight is substantially degraded and a safe landing becomes very difficult.
Fixed tail rotor pitch may be caused by
- Stuck pedals. An obstruction at the pedals or somewhere in the control linkages connecting the pedals to the tail rotor could
prevent movement of the pedals and tail rotor pitch.
- Depending on the helicopter model, there are malfunctions that may fix tail rotor feathering to a neutral angle.
The primary symptom is either (1) an inability to move the pedals or (2) a lack of yaw response to pedal movement.
Manufacturers typically recommend against trying to overpower a stuck pedal, which may cause an even worse malfuntion.
The ultimate goal is to land as soon as practical, but the method depends on where the tail rotor is stuck.
The pilot must rely on airspeed and torque modulation (primarily via collective, but also throttle when necessary) to control yaw.
Yaw rates should be kept small at all times.
For an American helicopter (main rotor spinning CCW viewed from above), if the tail rotor is stuck with high
thrust (left pedal) the pilot aims to maintain high torque and execute a vertical landing.
When collective is lowered on the ground the aircraft will tend to yaw left.
If the tail rotor is stuck at low thrust, hovering may not be practical.
The lack of tail rotor thrust will cause the helicopter to spin out of control in hover.
A run-on landing should be used, but at a safe speed.
The pilot may need to manipulate the throttle to maintain heading in the approach.