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Helicopter down outside Leicester City Football Club

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Helicopter down outside Leicester City Football Club

Old 6th Dec 2018, 19:30
  #941 (permalink)  
 
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Originally Posted by nodrama

What the report is saying is that the duplex bearing failed, for whatever reason, and stopped doing its job of allowing the spider to rotate freely around a stationary rod. The rod then started rotating with the spider. Because the rod would rotate anti-clock wise, it tightened the big nut up as far as it’s cotter pin would allow, and then the big nut would continue to rotate with the rod. At the smaller nut end, the effect would be the opposite. The locking wire and cotter pin would prevent the nut from undoing, and the smaller nut would turn with the rod. This caused friction against the carrier, eventually welding the smaller nut to it. The nut is now part of the fixed servo link. The rod would be turning against a cotter pin and locking wire, which it seems, from the report, that it sheared, and wound itself out of the nut.

The pitch change rod would now be no longer attached to the servo link to provide feedback of its position, and the servo would continue to move in the direction of its last input.
Agree, been here since my #944, the words used in the report just make it tricky. As far as the direction of movement of the servo input, it will depend upon the forces acting after the disconnection of the input nut and it's contribution (now removed).

OAP
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Old 6th Dec 2018, 19:52
  #942 (permalink)  

 
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nodrama
Maybe I can help clear some of the confusion.....the duplex bearing failed, for whatever reason, and stopped doing its job of allowing the spider to rotate freely around a stationary rod. The rod then started rotating with the spider. Because the rod would rotate anti-clock wise, it tightened the big nut up as far as itís cotter pin would allow, and then the big nut would continue to rotate with the rod. At the smaller nut end, the effect would be the opposite. The locking wire and cotter pin would prevent the nut from undoing, and the smaller nut would turn with the rod. This caused friction against the carrier, eventually welding the smaller nut to it. The nut is now part of the fixed servo link. The rod would be turning against a cotter pin and locking wire, which it seems, from the report, that it sheared, and wound itself out of the nut.
You did. (clear up confusion). Thank you!

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Old 6th Dec 2018, 20:15
  #943 (permalink)  
 
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Well, EASA EAD 2018-0250-E, back on 21 November required the duplex bearing on all 169s and 189s to be inspected before they flew again.

Finding out exactly what the inspection is looking for requires access to Leonardo AMPs. I'd dearly like to know what they were looking for.
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Old 6th Dec 2018, 20:28
  #944 (permalink)  
 
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I don't care how many times you practice in the sim, that one is pretty unrecoverable from that height and speed.
I'm curious how this could possibly be recovered given any amount of height/speed. As I understand, even entering autorotation wouldn't help - the TR is in full right pitch and you'll just rotate all the way down. I suppose with an infinite amount of good luck it MIGHT be possible to flare and touch the ground with this going on and survive, if the cabin integrity remained. But who could realistically fly an auto while rotating at what, once every couple of seconds?
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Old 6th Dec 2018, 20:34
  #945 (permalink)  
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I can't see clearly from the diagrams in the SB, but I think that if you have the actuator rod able to rotate on the duplex bearing then setting the correct torque on the castellated nuts is going to be difficult during assembly or maintenance.

Is there a method to do this or is it a matter of getting the nut to a position where the split pin can be fitted. That does not guarantee the final position of the nut, so any torque value would be at best vague.
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Old 6th Dec 2018, 20:41
  #946 (permalink)  
 
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I am not an engineer or a pilot, but involved in healthcare risk management.
In summary, there is no pilot error, he was faced with an impossible situation.
Now, is the remaining situation a design error, a maintenance error, a build error or a combination of all three?
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Old 6th Dec 2018, 20:53
  #947 (permalink)  
 
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Originally Posted by mercurydancer
I am not an engineer or a pilot, but involved in healthcare risk management.
In summary, there is no pilot error, he was faced with an impossible situation.
Now, is the remaining situation a design error, a maintenance error, a build error or a combination of all three?
You could add manufacturing and materials quality.
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Old 6th Dec 2018, 21:22
  #948 (permalink)  
 
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Originally Posted by Feathers McGraw
I can't see clearly from the diagrams in the SB, but I think that if you have the actuator rod able to rotate on the duplex bearing then setting the correct torque on the castellated nuts is going to be difficult during assembly or maintenance.
Figure 5 in the SB seems to show a square-section end to the actuator rod which could be used to prevent the rod from rotating while the nut is torqued.
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Old 6th Dec 2018, 21:28
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....and a surprise conclusion after the conjecture in this thread. This must have quite a relevance to many other Rotaries in operation not just the same model.
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Old 6th Dec 2018, 21:33
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Originally Posted by Speed of Sound
Figure 5 in the SB seems to show a square-section end to the actuator rod which could be used to prevent the rod from rotating while the nut is torqued.
I had just prepared the screenshot -

https://assets.publishing.service.go...018_G-VSKP.pdf
Fig 5.
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Old 6th Dec 2018, 21:44
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Originally Posted by jimjim1
I had just prepared the screenshot -

https://assets.publishing.service.go...018_G-VSKP.pdf
Fig 5.
Well spotted. And now you've mentioned it, Figure 2 also appears to show flats at the other end, slightly obscured behind the lock wire.
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Old 6th Dec 2018, 22:24
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The torque on the castellated nut retaining the shaft in the duplex bearing has no effect on the function of the bearing. It's an opposed angular contact set-up, with solid inner races. The torque applied to the nut will have no effect whatsoever on the internal bearing clearances. Any over-torque of the nut would serve only to stress the shaft, most likely in the waisted section immediately below the thread, and that doesn't seem to have occurred give the photos above.
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Old 6th Dec 2018, 22:31
  #953 (permalink)  

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Originally Posted by n5296s
I'm curious how this could possibly be recovered given any amount of height/speed. As I understand, even entering autorotation wouldn't help - the TR is in full right pitch and you'll just rotate all the way down. I suppose with an infinite amount of good luck it MIGHT be possible to flare and touch the ground with this going on and survive, if the cabin integrity remained. But who could realistically fly an auto while rotating at what, once every couple of seconds?
As I wrote earlier, once the aircraft fuselage begins spinning in yaw, the original trimmed position datum for the cyclic no longer exists because it (the fixed swashplate) is also rotating.
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Old 7th Dec 2018, 04:48
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" Year by year, the AAIB reports get to the point with diligence and logic whether the object of the investigation is a dinged gyrocopter or something very much more significant. How long shall we be provided with such a service ? "


In an age of replacing technical excellence and genuine quality with mitigation and perception management (for both financial and political "Gain") across much of business and life, I understand and share your concern.
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Old 7th Dec 2018, 05:07
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This made me think that with the right software and servo's you can fly down a helicopter without a working tail rotor . Biggest problem will be for the soft to select the place to land or allow some form of human input , but from a technical point of view what i seen above means automation can fly a TR-less heli indefinitely
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Old 7th Dec 2018, 06:30
  #956 (permalink)  
 
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n5296s - it could be survivable from a low hover or a situation where you are so close to the ground that an immediate landing could be made (probably still roll over though).

In the high speed cruise it might not be so dramatic until you slow down so perhaps a very high speed running landing might be possible, drooping the Nr to reduce the TR power (again you are probably going to roll over)

Other than those two extremes I don't believe there is any solution - they were extremely unlucky.
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Old 7th Dec 2018, 07:47
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Originally Posted by Ahernar
https://www.youtube.com/watch?v=9XMfhKxwo2c

This made me think that with the right software and servo's you can fly down a helicopter without a working tail rotor . Biggest problem will be for the soft to select the place to land or allow some form of human input , but from a technical point of view what i seen above means automation can fly a TR-less heli indefinitely
Ah, Iím a mechanical man, not a software guy, so youíll have to excuse my ignorance that software can now overcome the established laws of physics.

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Old 7th Dec 2018, 08:24
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Software cannot overcome the laws of physics but it can
  • diagnose the problem in millisecond,
  • analyze 100s of possibilities in a few millisecond more,
  • apply the scenario that would maximize the chance of survival.
The key to that is more sensor distributed throughout the aircraft and a huge onboard database

Did you hear about the self recovery button on the cyclic of the H160 I think this a sign of things to come
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Old 7th Dec 2018, 08:48
  #959 (permalink)  
 
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Originally Posted by Ahernar
.....This made me think that with the right software and servo's you can fly down a helicopter without a working tail rotor . Biggest problem will be for the soft to select the place to land or allow some form of human input , but from a technical point of view what i seen above means automation can fly a TR-less heli indefinitely
You seem to be missing a fundamental point: A helicopter turns its main rotor by having an engine, (or engines), pushing round - via a small gear wheel - a large horizontal ring gear which is connected to the main vertical shaft that drives the main rotor.

Newton’s third law states that ‘every action has an equal and opposite reaction’, so the turning force that the engine(s) are applying to turn the ring gear against the forces from the main rotor also pushes back on the engine(s). On the ground, this reaction force is not enough to move the helicopter when it is sitting on its skids/wheels, but in free air the reaction force pushes the engine(s), and therefore the helicopter to which they are bolted, in the opposite direction to the turning of the main rotor. The engines are effectively trying to ‘climb round the main ring gear - similar to a motorbike doing a wheelie.

To compensate for this, a tail rotor is fixed at the end of a long boom to apply a side force to oppose this reaction torque. The tail rotor has to produce a variable force to allow adjustment for varying main rotor torque, so it is made variable pitch, controlled via foot pedals. This also allows the pilot to yaw the aircraft when required, similar to the rudder of a conventional aircraft.

Having a tail rotor pushing sideways, will push the whole helicopter bodily sideways, (in the air), so the main rotor is usually offset sideways from the vertical by a small amount so a component of the lift force pushes in the opposite direction to the tail rotor, and stops the sideways drift.

When a helicopter loses its tail rotor drive, it will start turning in yaw due to the reaction to the engine torque on the main ring gear. If it has sufficient forward airflow past its tail fin, the heli will be able to fly straightish, but on slowing and landing, will yaw round and round. I am not a heli pilot but I understand the recovery is to idle the engine(s), which removes the turning torque, and gives the pilot a chance of an auto-rotation landing. This video of a ?Wessex lifting an air-con unit from a building roof and losing tail rotor drive illustrates all of this very clearly.

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Old 7th Dec 2018, 08:53
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Originally Posted by Agile
The key to that is more sensor distributed throughout the aircraft and a huge onboard database
Sensors can also provide bad data, to systems which will make the wrong decision as a result.
You can push a problem upstream, but it does not get rid of it.
If a servo doesn't know when it should stop, it doesn't matter whether it was someone's foot or a digital system that gave it the instruction to initially move.
You can't engineer out failures, the more underlying complexity, the more failure points are introduced.
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