Helicopter down outside Leicester City Football Club
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.
OAP
nodrama
You did. (clear up confusion). Thank you!
airsound
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 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.
airsound
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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.
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.
I don't care how many times you practice in the sim, that one is pretty unrecoverable from that height and speed.
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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.
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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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?
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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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?
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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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.
Avoid imitations
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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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" 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.
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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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
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.
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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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
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
Software cannot overcome the laws of physics but it can
Did you hear about the self recovery button on the cyclic of the H160 I think this a sign of things to come
- diagnose the problem in millisecond,
- analyze 100s of possibilities in a few millisecond more,
- apply the scenario that would maximize the chance of survival.
Did you hear about the self recovery button on the cyclic of the H160 I think this a sign of things to come
.....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
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.
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.