Helicopters

[ShakeyBurt]

If a helicopter with a tail rotor has engine failure it can still land using 'auto-rotation'. But how does a helicopter without tail rotor drive shaf system but an exhaust system, combat torque reaction?

[Hippy]

When the unfortunate helicopter looses power the main rotors are driven by the motion through the air and form a sort of "wing" to keep the aircraft aloft. The hydraulic controls over pitch and tilt can still be applied to the rotor blades so that they can mimic flaps and aelerons to tilt the aircraft and control a descent.

During powered flight the tail rotor counteracts the reaction between the motor and the rotors making the rotors turn and not the aircraft. However, during atogyration this is uneccessary, but the tail normally has a rudimentary fin which, aided by the vertically mounted tail rotor, helps the autogyro go where it is pointing.

Twin rotor aircraft, like the Chinouk, employ counter rotating rotors to stabalise the motor reaction forces. The rotors are cleverly connected so that they never touch. This gearing still works during autogyration, although I understand that the ineffiecencies in the system and the weight to potential autogyro lift makes this sort of aircraft a rather unreliable platform in the event of engine failure.

[boognish76]

My cat's breath smells like cat food.

[straz]

Hippy, There are plenty of film clips of helicopters loosing complete control & crashing when they suffer tail fan failure, so does that mean all a pilot has to do is switch his engine/ engines off if he suffers from a tail fan failure?

[Jimbo1234]

When a helicopter loses its drive to the tail rotor, there is no longer anything to oppose the torque reaction produced by the engines pushing the rotors round. This means that the body under the rotors will spin at the same rate (but in the opposite direction) as the rotors. If you stop the engines then the reaction is not there and there will be no requirement for the tail rotor. However you have to stop the engines fairly quickly (within a couple of seconds) or the rate of rotation will build up too quickly and the helicopter will be uncontrollable from inside.

Helicopters with no tail rotor (such as the NOTAR) use a combination of exhaust thrust and downwash from the main rotors over the tail boom to create sideways 'lift', preventing the tail from spinning.