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Once again, I'm Jacob and in this video we're talking about Loss of Tail Rotor Effectiveness (LTE). Beginner pilots might have heard stories of other pilots "getting into LTE", having an uncontrolled spin, and almost losing control of the helicopter. Or they were forced to fly out of it / do a go-around. It can be quite a pucker factor and so it is important to understand what LTE is and where it comes from so you can prevent getting into these situations in the first place.

LTE is the uncommanded, rapid yaw rate that does not subside of its own accord and which, if not corrected for, can result in loss of helicopter control. This yaw rate is generally to the right in counterclockwise rotor systems and to the left or clockwise rotating systems. This is not related to a break in drive system and is not a stall in the tail rotor. Some commonly say it is because the tail rotor stalls but this is a misconception. The tail rotor trust is merely insufficient, but not stalling. LTE is a wind issue which occurs when operating at airspeeds less than effective translational lift.

Flight and wind tunnel testing has identified a few relative wind regions that can cause LTE. The first is generally from the 4 o'clock to 8 o'clock position and is known as weathercock stability. When winds impact the fuselage from this region the helicopter tends to pivot around the mast towards the wind or "weathervane" into the wind. Unless existing pedal and put is made, and on command it turned to the right or left will develop. Attempting to have her in this region can result in excess of pilot workload. The next region occurs when winds impact the tail rotor between the 8 o'clock and 11 o'clock positions. This creates a tail rotor vortex rings state. This is just like main rotor vortex ring state that I discussed in a previous video (Vortex Ring State / Settling with Power Part 1    • Vortex Ring State / Settling with Pow...  ) only hear it happens to the tail rotor. Your tail rotor is essentially settling with power. The tail rotor is meant to counter the torque effect of the main rotor by pushing the tail clockwise or to the right. But when enough of a left crosswind occurs, this creates the vortex ring state laterally in the tail rotor which reduces the effectiveness of the tail rotor's ability to counteract the torque affect.

Wind velocity is from the 9 o'clock to 11 o'clock regions can cause LTE due to the results of main rotor disk vortex/interference. This occurs when the winds literally push the wingtip vortices of the main rotor into the tail rotor which causes the tail rotor to operate in turbulent air. This causes angle of attack fluctuations and an eventual, sudden and rapid yaw. Helicopters are extremely susceptible to this type of LTE when operating at an Out of Ground Effect (OGE) hover with a left, quartering headwind. The last region generally doesn't get much coverage but is still very much a part of LTE. This occurs between the two and 4 o'clock positions when the right crosswind impacts the tail rotor and causes an Angle of Attack (AOA) reduction. The crosswind increases induced flow of the tail rotor which results in a decrease in thrust. Aside from just hovering in this region, this one typically sneaks up on pilots who are hover taxiing in a tailwind and start a right pedal turn to "hook it into parking." What happens is the aircraft begins turning to the right, it's this LTE region, and the nose does not stop turning to the right.

Attention must be paid to these regions because they can build on each other. Main rotor disk interference can start the right turn that puts you in tail rotor vortex ring state to then a weathercock stability state. If Loss of Tail Rotor Effectiveness is experienced, the best recovery technique is to apply forward cyclic while applying as much pedal inputs as possible to maintain heading control. If altitude permits, collective reduction can aid in reducing the yaw rate.

That wraps up LTE. It's the uncommanded yaw that does not subside on its own accord and is a result of operating at airspeeds less than ETL with certain wind conditions. It is not a mechanical break in drive system components or a stall condition in the tail rotor. It results in high pilot workload and potential loss of aircraft control.

Thanks for watching! Don't forget to hit like and subscribe. As always, safe flying!

If you want to further your professional helicopter education with advanced helicopter concepts, I'd recommend reading Cyclic and Collective, by Shawn Coyle - http://amzn.to/2ifQGLx