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Helicopter down outside Leicester City Football Club

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Helicopter down outside Leicester City Football Club

Old 7th Dec 2018, 09:03
  #961 (permalink)  
 
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Originally Posted by Agile
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
I'm a big proponent of the capabilities of avionics. But at this point it has lost a major effector. While the auto-stab may have a mode that can help level, it could also help relieve torque, but what would it use to counter a yaw forcing, possibly even beyond the design limits? I suspect nothing, at least nothing that would change the game significantly for the pilot.
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Old 7th Dec 2018, 09:05
  #962 (permalink)  
 
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Originally Posted by Agile
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
One of the most recent heavy jet crashes had its root in a faulty AOA sensor being acted upon by automated systems. Something which has become very clear in recent years is that the interaction between automated systems decision making and pilot initiative is very complex, not least given the added factors of *multi-mode* automation and the cognitive barriers to a pilot avoiding being dangerously 'behind' an automated system. The decision tree in a comprehensive automated system would be dauntingly complex, subject to human error in its creation and subject to sensor malfunction in use: yet it would have to be significantly more robust and reliable than existing systems or would offer no net gain. Even then, pilots would need to defer instantly to the automation... unless the automation was malfunctioning, in which case the pilot would need to instantly fight or disable the automation. Which brings us full circle.

There is surely a case for more intelligent and intuitive safety systems, but this accident seems to have arisen from an unforeseen failure mode leading to a malfunction which in all likelihood was simply not recoverable. You can’t automate 'thinking of what you haven’t thought of' nor program a computer to fix in real time any catastrophe which sets the laws of physics in fundamental opposition to accident survivability.
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Old 7th Dec 2018, 09:33
  #963 (permalink)  
 
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Not going to argue much around this but there are no laws of physics preventing tailles rotor flight . You have to equalise the rotor drag with drag from the body of the aircraft . If this requires 130 rpm , 130 rpm will be necessary ,if that's not humanly pilotable does not mean some autostab will find it impossible too .Most problems will be around oscilations and vibrations in the rotor disk but for an emergency descent it should work
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Old 7th Dec 2018, 10:09
  #964 (permalink)  
 
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Well, EASA EAD 2018-0250-E back on 19 November required inspection of the duplex bearing on both 169s and 189s before they flew again. So hopefully there are no duff duplex bearings in service anymore.

I’d dearly like to know what the inspection was specifically looking for, as that would shed light on why the bearing failed. Knowing that would probably require access to Leonardo AMPs. Anyone know?
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Old 7th Dec 2018, 11:20
  #965 (permalink)  

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Looking at the photo evidence in post#983 above, a thought that crossed my mind - would a simple left handed thread on the shaft have prevented this tragedy?

Having recently changed a rear wheel bearing, even my old car has a left handed thread on the left hand side stub axle, to prevent the hub nut coming loose in service.
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Old 7th Dec 2018, 12:25
  #966 (permalink)  
 
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For those with a good engineering understanding of this failure, would the tail rotor have been harder to turn by hand than normal, pre-flight, given the breakdown of this bearing? Obviously not easy to reach on a 169, but is on most smaller types.
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Old 7th Dec 2018, 12:39
  #967 (permalink)  

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Originally Posted by Ahernar
Not going to argue much around this but there are no laws of physics preventing tailles rotor flight . You have to equalise the rotor drag with drag from the body of the aircraft . If this requires 130 rpm , 130 rpm will be necessary ,if that's not humanly pilotable does not mean some autostab will find it impossible too .Most problems will be around oscilations and vibrations in the rotor disk but for an emergency descent it should work
130 rpm (Nr) is well below the normal operating range of modern helicopters. Most run around 275 - 350 or even higher for smaller machines, with a minimum in flight of 90% of that figure for aerodynamic reasons. Going lower would cause the blades to stall and loss of control of the rotor disc.
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Old 7th Dec 2018, 12:46
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Originally Posted by rotorspeed
For those with a good engineering understanding of this failure, would the tail rotor have been harder to turn by hand than normal, pre-flight, given the breakdown of this bearing? Obviously not easy to reach on a 169, but is on most smaller types.
With the length of the blade and the weight of the rotor, I think it would be very difficult to detect any tightness or "grittiness".
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Old 7th Dec 2018, 12:58
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Originally Posted by ShyTorque
Looking at the photo evidence in post#983 above, a thought that crossed my mind - would a simple left handed thread on the shaft have prevented this tragedy?

Having recently changed a rear wheel bearing, even my old car has a left handed thread on the left hand side stub axle, to prevent the hub nut coming loose in service.
Interesting, but your hub nut still has a split pin? It was once the practice to use LH threads on the left of vehicles, including wheel nuts. I think it was all a bit theoretical and the fact it isn't done any more suggests it wasn't really necessary.

I don't know which way this tail rotor turns relative to the control shaft, but with similar threads the nut at one end would tend to loosen and the other would tighten. One LH and one RH would both try to tighten, or loosen - depending on the rotation.
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Old 7th Dec 2018, 13:08
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# I will let you work out the rest for what happens if the bearing fails and what could possibly happen to the nut.
Apparently so - it will be interesting to see how the design complies with CS-29.

I am surprised that the attachment of the lever mechanism to the control shaft relies purely on clamp up with the nut. No key or index?

Maybe there should be a weak point in the shaft so that the integrity of the feedback is maintained so the servo does not go to full travel?

I am amazed that things like this can still develop in this day and age. Somehow folk have lost sight of the details.
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Old 7th Dec 2018, 13:24
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Originally Posted by ShyTorque
Looking at the photo evidence in post#983 above, a thought that crossed my mind - would a simple left handed thread on the shaft have prevented this tragedy?

Having recently changed a rear wheel bearing, even my old car has a left handed thread on the left hand side stub axle, to prevent the hub nut coming loose in service.
I'm not sure that it would have done. The smaller nut would have tightened up against its cotter pin and still possibly spun with the pitch rod. It may have still welded itself to the pin carrier. It wouldn't unwind, but could strip the threads or break the pin carrier if the turning force was great enough. If the pin carrier failed and detached from the servo feedback link (as it did on VSKP- according to the report, it was found detached and lying in the TRGB cowling), the resulting loss of TR control would be the same.
Or, the tightening of both nuts on each end may increase the clamping effect on the rod and stop it from spinning, despite the failed bearing. Difficult to say really, and one for the design engineers.
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Old 7th Dec 2018, 13:29
  #972 (permalink)  
 
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Uplinker,

In your video....that was a Sikorsky S-58T that had the tail rotor drive failure.

The Pilot controlled the aircraft and was maneuvering towards a safe landing area.

He maintained power until he thought he could make an authoritative landing and cut the throttles to Flight Idle.

After the accident I had the opportunity to talk with him about the crash....and he was very bothered that he was unable to land the aircraft safely.

He did his best....but the odds were against him...but he flew the machine all the way to the ground and did not give up trying to land it.

The failure we see in the 169 under discussion was a very different kind and far more critical than that shown in your video.

It was a loss of thrust in the video and just the opposite (apparently) in the 169 crash.

The 58T was a drive shaft failure.....where the 169 was far more complicated a failure.
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Old 7th Dec 2018, 13:31
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If the duplex bearing seized for an unknown reason, why hasn't the type been grounded like the Puma's were when the Main rotor heads came off for an unknown reason?
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Old 7th Dec 2018, 13:48
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Originally Posted by Sky Sports
If the duplex bearing seized for an unknown reason, why hasn't the type been grounded like the Puma's were when the Main rotor heads came off for an unknown reason?
Because it may be a lot simpler to inspect, check for correct function of, and replace perhaps, a bearing than it is to dismantle a main transmission when the Company in question was damned sure (based on its public utterances) that someone hadn't attached one of the three transmission mounting pins correctly ... which wasn't even the problem.
Put another way, comparing the two accidents the way you are trying to is a category error.
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Old 7th Dec 2018, 15:01
  #975 (permalink)  
 
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Would the HUMS `indicators` to show an increase in t/r vibration due to the duplex bearing`s ongoing failure...?
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Old 7th Dec 2018, 16:32
  #976 (permalink)  
 
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Originally Posted by SASless
Uplinker,

In your video....that was a Sikorsky S-58T that had the tail rotor drive failure.
. Thanks, I wasn’t sure, hence my question mark.

The failure we see in the 169 under discussion was a very different kind and far more critical than that shown in your video.
It was a loss of thrust in the video and just the opposite (apparently) in the 169 crash.
The 58T was a drive shaft failure.....where the 169 was far more complicated a failure.
Fair enough. As I stated, I am not a heli pilot, but I was trying to explain to Ahernar why single rotor helis need a tail rotor, because they seem to think a (single rotor) heli can fly and land without one.
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Old 7th Dec 2018, 17:27
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Originally Posted by ShyTorque
130 rpm (Nr) is well below the normal operating range of modern helicopters. Most run around 275 - 350 or even higher for smaller machines, with a minimum in flight of 90% of that figure for aerodynamic reasons. Going lower would cause the blades to stall and loss of control of the rotor disc.
Ofc , i was meaning the rpm of the cabin !!!
@ Uplinker
You lose TR , you spin faster and faster until at certain rpm the drag from the spinning body of the heli counterracts the rotor drag . Unfortunately no human can control a helicopter spinning like that , but a computer surely can ,go watch that rocket gently land after spinning from several km height . I'm not expecting the control system to be able to keep it right afterward it lands so the machine will be lost but the landing would be gentle and very survivable ( except some bad cases of fire / bad terrain ) .
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Old 7th Dec 2018, 17:45
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Ahernar - I think you place too much faith in computers - an autopilot in a helicopter only has the same controls as the pilot to control its attitude. Yes it works faster and constantly but the sensors required to make them work have limits too.

And btw the rocket in your video didn't land, it crashed.
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Old 7th Dec 2018, 18:16
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@Ahernar How do you think humans deal with a 130 RPM fuselage? I think you might as well crash to the ground...

Since there is a lot of speculation about all kind of (unrealistic or irrelevant) ways to counter this, I'm surprised that emergency tail rotor recovery systems hasn't come up. From what I understand the idea here is to have some alternative way to create anti-torque trust at least for a limited time to allow landing. There's a patent from 2005 here for example, and I'm sure there are other potential solutions. Whether such a system would be able to overcome the trust from the TR going above "full" pitch is a question of course.

I'm more interested in finding the cause of the failure than to speculate about possible solutions without fully understanding the problem, but since it seems to be a returning topic it might be a better starting point than making automated systems for killing people while still in the air.
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Old 7th Dec 2018, 18:26
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Originally Posted by [email protected]
And btw the rocket in your video didn't land, it crashed.
It did not crash, it ditched very softly ...
The high CG and the low lift of the landing legs prevented it from staying upright.

skadi
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