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Tail Rotor failure in flight

If the tail rotor fails in flight, engine torque can no longer be countered by the tail rotor, and uncontrolled spinning of the aircraft is a possibility. Most manufacturers call for an immediate autorotation. Some call for a running landing, instead. At higher speeds, most aircraft have enough weathercock stability so that limited amounts of power can be used to stretch the glide or even to maintain altitude until a suitable landing area is reached.

Autorotating

An autorotation is a natural way to deal with an inflight tail rotor failure since it reduces torque to zero. One problem with an autorotation is that it will be difficult or impossible for the pilot to align the landing gear with ground track during touchdown. If the helicopter touches down with forward speed, this could cause a rollover. In calm wind, it is often very difficult to not have some slide.

One possible solution is for the pilot to use the throttle to help align the landing gear. Normally transmission drag will yaw the nose slightly to the left, and engine torque can be used to yaw the nose to the right until it is lined up with ground track. The major problem is that throttle manipulation is tricky, and very slow in a turbine aircraft. Meanwhile, the touchdown phase happens very quickly, giving the pilot little time to use the throttle.

Running Landing

A running landing can be used to land the helicopter at very low power settings. If the approach can be set up with a left crosswind, that will allow even more power to be used without inducing a right yaw. The throttle can be used to align the skids, and because everything is happening very slowly, the pilot has more time to react with the throttle.

One negative to this sort of a landing is that pilots tend to practice autorotations more often than running landings. Touchdown speed in a running landing with no tail rotor is on the order of 10-20 knots. If the pilot makes an error and the helicopter is rolled over, people can easilly get hurt at such high speeds. Autorotations on the other hand tend to terminate at just a few knots, even on a calm wind day. Mistakes which cause a rollover are less likely to cause injury because the speeds are probably lower.

Another way to do the running landing

If a shallow approach is possible, another way to land the helicopter is to make an approach similar to a running landing, but with slightly higher airspeed. When the skids are quite close to the ground, the pilot flares to kill ground speed. As airspeed drops off and the helicopter starts to settle, the pilot uses power to hold the aircraft off the ground, meanwhile he continues to use cyclic to stop all ground speed. The power will instantly start torquing the aircraft to the right, but if the pilot continues to use cyclic to stop ground speed, throttle may be chopped just as ground speed comes to zero. A normal hovering autorotation is then used to land the helicopter. As soon as the throttle is chopped, most rotation will stop, and since the ground speed is zero what little rotation is left is unlikely to roll the aircraft over. This is my preferred method, and normally I get about 90 degrees of rotation before I am able to roll off throttle. The rotation is normally stopped well before touchdown, and I usually induce a little motion in the direction the skids are pointed with the cyclic, in order to get a really soft touchdown. Don't use this technique unless you can get someone to show you how, but if you can find an experienced pilot to show it to you, I think you'll agree with me this is the best way to land sans tail rotor. (that doesn't mean ignore the manufacturer, though).

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

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