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Wow Loss Of Lte


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  • 2 weeks later...
Guest sharky

I remember reading about this on prune a few years ago. After reading Nick's comments about rotor rpm and frame rate, it helps to maybe understand what happened.


Here's the SAFECOM report


And Mr. Lappos' observations;


That is one great video, and it shows how much we can learn from a good movie. Some comments:


The Crane's tail rotor is very healthy, and giving lots of thrust, but the rotor was drooped a bunch, so the thrust was limited by the reduced rpm, and the spin occurred. Note the way the rotor is "frozen" by the frame rate of the video, like the spokes of a wagon wheel in the movies. The frame rate of a video is 30 per second, so the rotor can be frozen if it has exactly some multiple of the 1/30 second. See how the rotor actually "freezes" when the aircraft is directly overhead, showing the lowest rpm point of the sequence. Note how the rotor speeds up again right afterward, and actually becomes a blur. At that point the rotation stops and the climb occurs. It is no coincidence that the "LTE" stops when the water is fully dropped, so the gross weight of the Crane is low enough.


What happened? My guess:


1) the aircraft was too heavily loaded for the altitude/temp, so the engines could not produce the power needed to hover or even slow down to a slow running hover.


2) the pilot increased collective to hold the aircraft in the running hover. He stopped the descent, but he reduced the main/tail rotor rpm (when he hit the engine limiter). As the rpm reduced, he ran out of pedal, and the turn started.


3) he recovered with a bit of good airmanship, by holding his cool, dumping the weight, keeping in good cyclic control, and when the weight was low enough, reducing collective enough to recover rpm. With the full rpm, he regained yaw control.

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