Loss Of Tail Rotor Effectiveness LTE Live Training Tuesday

Jan 09, 2018

Loss Of Tail Rotor Effectiveness LTE Live Training Tuesday

Loss of tail rotor effectiveness, LTE. What is it? The helicopter flying handbook tells us loss of tail rotor effectiveness, LTE or an unanticipated yaw, is defined as an uncommanded, rapid yaw towards the advancing blade which does not subside of it's own accord.

It can result in a loss of the aircraft if left unchecked. It is very important for pilots to understand the LTE is caused by an aerodynamic interaction between the main rotor and tail rotor and not caused from a mechanical failure. Some helicopter types are more likely to encounter LTE due to the normal certification thrust produced by having a tail rotor that, all though meeting certification standards, is not always able to produce the additional thrust demanded by the pilot.

First, let's cover the three winds that you have to be familiar with so that you don't get yourself in a LTE situation. First, we'll talk about main rotor disk interference. If you have a wind, off the quartering left front, degrees two hundred and eighty-five to three hundred and fifteen degrees, and the wind velocity is from ten to thirty knots from the left front cause the main rotor vortex to be blown into the tail rotor by the relative wind.

Loss Of Tail Rotor Effectiveness LTE Live Training Tuesday

This main rotor disk vortex causes the tail rotor operate in an extremely turbulent environment. Try to visualize a great big huge doughnut of air around the outside of that rotor system. Turbulent air being recirculated and that wind coming on that angle is pushing all that dirty turbulent air into that tail rotor.

The second is weathercock stability. Winds from a hundred and twenty degrees to two hundred and forty, in this region the helicopter tends to weather vane or weathercock it's nose into the relative wind. Unless the resisting pedal input is made, the helicopter starts a slow, uncommanded turn either to the right or left depending upon the wind direction.

If the pilot allows a right yaw to develop and the tail of the helicopter moves into this region, the yaw rate can accelerate rapidly. In order to avoid the onset of LTE it is imperative to maintain positive control of the yaw rate and devote full attention to flying the helicopter. Environmental factors which can lead to LTE include higher operating-density altitudes or temperatures, and high winds.

A high gross weight can also create an LTE-conducive situation. Causative wind-directions may include: Main-rotor vortexes pushed into the tail rotor by wind. This can occur with wind coming from 10 o'clock on North American (counter-clockwise) rotors and from 2 o'clock on clockwise rotors.

Loss Of Tail Rotor Effectiveness LTE Live Training Tuesday

The wind pushes the dirty air and vortexes generated from the main-rotor into the tail-rotor, preventing the tail rotor from having clean air to propel. Wind from the tail (6 o'clock) can cause the helicopter to attempt to weather vane into the wind. The winds passing on both sides of the tail rotor make it teeter between being effective (providing thrust) and ineffective (not providing thrust).

This creates a lot of pedal work for the pilot to eliminate unintended yaw. Wind moving in the same direction as the tail rotor moves air. With pusher tail-rotors, that is wind from the opposite side of the tail-rotor. With puller tail-rotors, that is wind from the same side as the tail rotor. For main rotors with clockwise rotation (European), that is wind from 3 o'clock. For main rotors with counter-clockwise rotation, that is wind from 9 o'clock.

The wind going through the tail rotor causes an actual stall condition as it decreases the effective airspeed of the air through the tail rotor. This condition will cause an unintended yaw that may develop into a spin.

Recovery from this condition may be difficult if no airspeed is available, and will require entry into an autorotation (thus removing the torque of the engine and transmission) LTE Loss Of Tail Rotor Effectiveness Online Ground School. The third one you need to be aware of is tail rotor vortex ring state. These are winds from two hundred and ten to three hundred and thirty degrees. Winds within this region cause a tail rotor vortex ring state to develop. The result is a non-uniform, unsteady flow into the tail rotor.

Loss Of Tail Rotor Effectiveness LTE Live Training Tuesday

Listen to the audio lesson on LTE, and check out the large collection of free helicopter online ground school lesson!

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