Loss of Tail Rotor Effectiveness (LTE) in Helicopters


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LTE can occur in certain conditions when hovering. Image by Helen Krasner

When is LTE Likely to Occur?

Typically, this problem occurs when a great deal of power is being applied to the main rotor.  Thus it is most common at stages of flight with high power requirements, such as flying at low airspeed and out of ground effect, perhaps on a photo sortie where the helicopter is being operated in a high hover.  The situation will be exacerbated by high altitude or hot weather, since again, more power will be required.  Since so much power is being generated by the main rotor, a similar amount of thrust will be required from the tail rotor, and sometimes there is simply not enough there.  LTE can also happen when making turns in the hover in strong wind conditions, and this must always be done very carefully.

How to Correct LTE

As with many things, prevention is better than cure, so you should avoid LTE if at all possible. In relatively strong winds, it is best not to operate at low airspeed with a tailwind.  You should avoid out-of-ground-effect hovering and situations demanding high power, such as low speed downwind turns.  Finally, always be aware of the wind direction and strength, and stay alert to changing conditions generally.

If you should be unlucky enough to encounter LTE, I recommend the following recovery technique.  Firstly, apply full left pedal.  Simultaneously, move the cyclic forward to increase the airspeed. This will move air past the vertical stabiliser, which will help to stop the rotation.  If you have enough altitude, lower the collective and reduce the power, since this will reduce the tail rotor thrust requirement.  Then, as you start to recover, adjust the controls for normal flight, and start to breathe normally again!

Loss of Tail Rotor Effectiveness

However, while pilots need to know about LTE, it is not something which they should endlessly worry about. If you know about the forces involved in it, you are halfway to preventing it.  Staying out of low-airspeed high-power situations when possible, and concentrating 110% if you really need to fly in these conditions, should mean that you never encounter this problem.  And if you recognise it, correcting action is quite possible and not all that difficult, at least in the very early stages.   So don’t panic, but don’t take unnecessary risks.

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