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Tail Rotor Failure at a Hover

There are a couple ways a tail rotor can fail while at a hover. The tail rotor can be stuck at a particular pitch setting, but still be producing thrust, or the tail rotor can stop producing thrust. A slight variation on the second is that if one blade fails to flat pitch, the tail rotor may be producing half the normal thrust.

Stuck Pedals (fixed pitch failures)

A fixed pitch failure of the tail rotor is one kind of failure, but we tend to charactersize it as stuck left, stuck right, or stuck neutral. This is because depending on what pitch setting it is stuck at will determine what kind of a recovery we will do.

Stuck neutral

This is probably the most likely fixed pitch failure to occur. It would happen either because the pitch change mechanism failed while the tail rotor was at flat pitch, or more likely that the pitch change mechanism failed, and air loads drove the tail rotor to flat pitch. In either case, the recovery is the same as if the tail rotor stopped producing thrust; the pilot performs a hovering autorotation.

Stuck right

In this case, the tail rotor and the engine are both producing thrust to the right. The spin will be quite rapid. The pilot should roll off the throttle to get rid of engine torque. This will slow the spin, but not stop it because the tail rotor thrust alone is capable of spinning the helicopter. The next thing the pilot should do is his best hovering autorotation, preferably over a flat piece of hard surface, although he's going to have to take pretty much whatever was under him at the time.

One thing he can try to do is to hold the helicopter off the ground as long as possible with collective. As RPM decays, the tail rotor thrust will decrease and the spin rate should slow, but not stop. The helicopter will contact the ground spinning (but hopefully slowly) and may roll over if the ground is uneven, or the pilot did not hold the skids level. Chances are fair, however, that the helicopter will remain upright on the landing gear.

One thing I was shown by a friend who chopped his entire tailboom off with a wire is that if a pilot is trained properly, he can maintain a helicopter in a level attitude at a very rapid spin. However, most pilots are not given this training which is a shame. Although you can get dizzy from practicing this, it is not dangerous and any pilot can be quickly taught how to keep the skids level even during a very rapid spin.

Stuck Left

(to be supplied)
Paul Cantrell
paul at copters.com (replace " at " with "@" to email me - this avoids SPAMMERS I hope)

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