Originally Posted by
Ahernar
.....This made me think that with the right software and servo's you can fly down a helicopter without a working tail rotor . Biggest problem will be for the soft to select the place to land or allow some form of human input , but from a technical point of view what i seen above means automation can fly a TR-less heli indefinitely
You seem to be missing a fundamental point: A helicopter turns its main rotor by having an engine, (or engines), pushing round - via a small gear wheel - a large horizontal ring gear which is connected to the main vertical shaft that drives the main rotor.
Newton’s third law states that ‘every action has an equal and opposite reaction’, so the turning force that the engine(s) are applying to turn the ring gear against the forces from the main rotor also pushes back on the engine(s). On the ground, this reaction force is not enough to move the helicopter when it is sitting on its skids/wheels, but in free air the reaction force pushes the engine(s), and therefore the helicopter to which they are bolted, in the opposite direction to the turning of the main rotor. The engines are effectively trying to ‘climb round the main ring gear - similar to a motorbike doing a wheelie.
To compensate for this, a tail rotor is fixed at the end of a long boom to apply a side force to oppose this reaction torque. The tail rotor has to produce a variable force to allow adjustment for varying main rotor torque, so it is made variable pitch, controlled via foot pedals. This also allows the pilot to yaw the aircraft when required, similar to the rudder of a conventional aircraft.
Having a tail rotor pushing sideways, will push the whole helicopter bodily sideways, (in the air), so the main rotor is usually offset sideways from the vertical by a small amount so a component of the lift force pushes in the opposite direction to the tail rotor, and stops the sideways drift.
When a helicopter loses its tail rotor drive, it will start turning in yaw due to the reaction to the engine torque on the main ring gear. If it has sufficient forward airflow past its tail fin, the heli will be able to fly straightish, but on slowing and landing, will yaw round and round. I am not a heli pilot but I understand the recovery is to idle the engine(s), which removes the turning torque, and gives the pilot a chance of an auto-rotation landing. This video of a ?Wessex lifting an air-con unit from a building roof and losing tail rotor drive illustrates all of this very clearly.