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onemorepilot

Let's talk LTE

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Hmmm...

Lots of views, but no replies. Let's throw in another teaser...

What happened today, is the same thing I've done thousands of times in 12,000 plus hours and over 25 years as a utility pilot. The truth... We push the helicopter to it's limit to make a living. That limit is not always the (maximum certificated takeoff weight).

The other part of the truth... What we are taught about LTE is not the whole story. Here is what we are taught... LTE is a risk when we take off heavy at high DA with a left crosswind (Bell). If we are honest, we will admit, that we do this ALL THE TIME.

My question is, why did this happen today?

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It's an aerodynamic process.  We don't control the winds, it only takes a small puff to go from maximum efficiency to none.  As we know from basic theory, the most lift will be created right before the stall.

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I did and more than once when I was working at High Altitude in the Chilean Andes (B205). Also experienced many times the "retreating blade stall condition" as well. The reason being is I was exceeding the limits of the aircraft. Experienced the same with a B204 in the Rockies especially with a -13 in it. Never had that problem with the -11.

Video of one instance of LTE, the beginning anyway. The operator sitting in the back was filming at the time but stopped when we entered LTE. Too bad it would have been a good instruction video on how to recover from the condition without loosing the bird hanging 75ft below the aircraft. I have no videos of retreating blade stalls.

 

CT

 

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Loss of Tail Rotor Effectiveness (LTE) 7.6.1    Aim: For the candidate to identify and react to a loss of yaw control of the aircraft.     Loss of tail rotor effectiveness can be described as the tail rotor not having enough authority to stop the aircraft from yawing. This can be caused by the tail rotor physically not having enough control (Such is the case with the 204 and 206.  The 204 has a long tail boom and a large vertical fin with small tail rotor blades.  When the wind hits the fin at a 90-degree angle there is not enough control to stop the yaw rate.) The other type of Loss of tail rotor effectiveness is an aerodynamic phenomenon.  The aircraft basically has two different directions of airflow, causing a vortex ring to be set up through the blades.     On a North American aircraft when viewed from overhead the main rotor blades rotate counterclockwise.  This causes the fuselage to want to rotate clockwise. In order to counter this, the tail rotor puts out thrust, which stops the clockwise rotation. The air comes out the left side of the tail rotor. Any time we have a direction of wind trying to go the opposite way it can cause the tail rotor to get into vortex.     There are numerous ways to impart an airflow that goes the opposite direction through the tail rotor disc. 1.    Downwash from the main rotor blades with a slight wind from the 11:00 position can drift through the tail rotor disc. 2.    Wind, hitting the large vertical fin from the right side, can cause the aircraft to start to rotate to the right.  This will result in a flow of air through the tail rotor disc in an opposite direction than the air already coming out of the disc.  If the aircraft rotation continues to accelerate, the pilot tries to counteract by putting in more left pedal and causes more air to come out of the left side tail rotor.  This condition now has two directions of airflow and will cause a vortex ring. 3.    If not corrected soon enough the aircraft rotates faster and the pilot puts in more pedal thereby making the condition worse. 4.    Downwind flights at a low airspeed with moderate winds can also set up the components for a loss of tail rotor effectiveness. While flying downwind we usually have a higher power setting and hence more left pedal applied. Should the relative wind cause the aircraft to start to rotate right there is insufficient tail rotor control left to stop the rotation. The rotation develops very quickly and there is an induced airflow through the tail rotor that is opposite to the direction of the thrust and vortex ring develops.     Should you get into a loss of tail rotor control, the corrective actions are to reduce power and increase forward speed (into wind) if possible; if the conditions or your altitude do not allow this, enter autorotation. The best way to avoid LTE is to recognize and avoid the conditions that are conducive to LTE.

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On 9/30/2019 at 10:32 PM, simpleton said:

You want us to all to just whip out our crystal balls to interpret your rather vague post?

what? the self described rotary god doesn't have the crystal ball answer??

you let us all down. #fail

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