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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, 14:31
  #1001 (permalink)  
 
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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, 14:48
  #1002 (permalink)  
 
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Originally Posted by Sky Sports View Post
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, 16:01
  #1003 (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, 17:32
  #1004 (permalink)  
 
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Originally Posted by SASless View Post
Uplinker,

In your video....that was a Sikorsky S-58T that had the tail rotor drive failure.
. Thanks, I wasnít 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, 18:27
  #1005 (permalink)  
 
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Originally Posted by ShyTorque View Post
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, 18:45
  #1006 (permalink)  
 
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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, 19:16
  #1007 (permalink)  
 
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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, 19:26
  #1008 (permalink)  
 
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Originally Posted by [email protected] View Post
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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Old 7th Dec 2018, 21:14
  #1009 (permalink)  

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Originally Posted by Pozidrive View Post
Interesting, but your hub nut still has a split pin?
No, it doesn't have a split pin. The outer edge or lip of the nut is turned to a thinner profile and once the nut is torqued up the lip is knocked with a hammer and punch into a longitudinal groove on the end of the stub axle. From personal experience, this isn't quite as secure a method as a castellated nut and split pin. However, a car can also be driven in reverse so it is important to secure it in both directions. Unlike a tail rotor, which only runs in one direction.
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Old 7th Dec 2018, 21:52
  #1010 (permalink)  
 
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Originally Posted by sycamore View Post
Would the HUMS `indicators` to show an increase in t/r vibration due to the duplex bearing`s ongoing failure...?
The HUMS sensors will be looking at the TGB internal gearing, the TGB input (Driveshafts and input pinion) and the TGB output (Tail rotor vibration) - Iím not so sure if that particular duplex bearing would be monitored or not.

Everyone familiar with U.K. offshore O&G ops will know HUMS is downloaded and reviewed numerous times a day, VIP though? Once a week? Once every 10/25hrs? They certainly wonít have the same requirements. Havent heard of the operators being asked to check anything specific in the HUMS data which probably suggests there was nothing?
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Old 7th Dec 2018, 22:25
  #1011 (permalink)  

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Originally Posted by Ahernar View Post
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 ) .
If the cabin rotates at 130 rpm, this will result in a net loss of 130 rotor rpm. This would almost certainly result in the same outcome - it is a loss of almost half the rotor rpm needed to sustain lift and the integrity of the disc would probably be lost, especially as the aircraft would be descending at a high rate.
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Old 7th Dec 2018, 23:01
  #1012 (permalink)  
 
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Originally Posted by ShyTorque View Post
If the cabin rotates at 130 rpm, this will result in a net loss of 130 rotor rpm. This would almost certainly result in the same outcome - it is a loss of almost half the rotor rpm needed to sustain lift and the integrity of the disc would probably be lost, especially as the aircraft would be descending at a high rate.
Out of interest where does the 130rpm come from?
The only other time I've seen data from an event like this it was about 120 deg/sec.
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Old 8th Dec 2018, 05:41
  #1013 (permalink)  
 
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Originally Posted by dClbydalpha View Post
Out of interest where does the 130rpm come from?
The only other time I've seen data from an event like this it was about 120 deg/sec.
An exageration from my belly ( sort of worst case scenario for the control system ) . I would have to calculate real rpm values . The airframe coud be further designed to lower this value , with an enlarged fin aft , maybe even a little pirotechnically launched drogue chute (that's my new ideea , lol ).
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Old 8th Dec 2018, 08:05
  #1014 (permalink)  

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(that's my new ideea , lol ).
Actually, neither of those are new ideas. The late Ray Prouty discussed both in his books, years ago.
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Old 8th Dec 2018, 08:32
  #1015 (permalink)  
 
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There will be a reason for the bearing failure that probably is the main cause of the subsequent accident. Questions about the overall design of the input assembly might come into it. However, there will be great effort made to identify why the bearing failed and, the mitigation of that process. It might be anything from: a major redesign, an improved bearing, improved QC of the bearing, revised servicing or an improved inspection.

OAP
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Old 8th Dec 2018, 08:43
  #1016 (permalink)  

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Let's hope so!

I'm sure that all the RW pilots reading this are very concerned that the failure of a relatively small but highly critical item such as this bearing could bring down an aircraft and that the design wasn't in any way "fail safe". I certainly am.
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Old 8th Dec 2018, 09:34
  #1017 (permalink)  
 
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Originally Posted by ShyTorque View Post
Let's hope so!

I'm sure that all the RW pilots reading this are very concerned that the failure of a relatively small but highly critical item such as this bearing could bring down an aircraft and that the design wasn't in any way "fail safe". I certainly am.
'Twas always thus. Years ago, I was fortunate to notice the clutch light flicker a couple of times during run-up on an R22 and shut down. It turned out to be the upper sheave bearing breaking up. Not a good failure to have.
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Old 8th Dec 2018, 09:59
  #1018 (permalink)  
m25
 
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Can anyone explain why the "big nutĒ holding the damaged bearings onto the shaft tightens up in this scenario? Looks from the photo to be a right handed thread and I would have thought it would tend to be undone a little if the bearings failed, assuming the appropriate direction to undo the small nut at the other end....?
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Old 8th Dec 2018, 10:52
  #1019 (permalink)  

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As someone who has been flying helicopters for a living for almost four decades, the prospect of this type of tail rotor control failure has always greatly concerned me.

I've been writing about it on this forum and elsewhere (initially when I flew RAF helicopters) since the mid 1980s. Some would say I "bang on" about it, but imho with good reason. This situation is a helicopter pilot's worst nightmare. Tail rotor control is completely lost and the tail rotor pitch then goes to either full power at "push" or "pull". I don't know of any present helicopter where this situation is recoverable by the pilot, whatever his level of skill and experience.

The answer is to mandate that by design that all helicopter tail rotor control systems are equipped with a centreing device for the servo valve mechanism, to prevent a servo runaway in the event of the pilot's flight yaw controls becoming disconnected, such as now appears to have occurred here. With such a device fitted, the servo is automatically biased to move to a fixed, central position enabling controlled flight to still be available and a safe landing of some sort to be carried out.

Some aircraft manufacturers, such as Sikorsky, having been fitting such devices to their aircraft for many years. Other manufacturers, as appears to be the case here, obviously still do not.

These devices are not difficult to design. Most consist of a simple spring mechanism. The simplest one I've seen (Super Puma) consists of something that looks very much like a bicycle tyre pump, with a spring either side of a piston, sitting inside a cylindrical body. The body of the device is attached to the aircraft structure and the "piston rod" is attached to the servo control valve arm. The piston rod moves in and out of the body under the influence of the normal movement of the servo valve mechanism, such as when the pilot moves the yaw pedals. As it moves it compresses one spring and relaxes the other and is "invisible". However, in the event of a pilot's control input disconnection (e.g. a cable break), the springs equalise to bring the piston to a central / neutral position, so that the servo valve cannot not run away. The Sikorsky devices I'm familiar with are slightly more sophisticated and consist of quadrant arms controlled by springs, but the devices all work in a similar way.

Had such a device been fitted to this 169, the outcome might have been very different.
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Old 8th Dec 2018, 11:36
  #1020 (permalink)  
 
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As ShyTorque says, it is probably one of two things we, as helicopter pilots, would worry about failing the most, save for a rotor blade departing in flight. Ok so three. But a main gearbox failure (we don't carry a spare) or a tail rotor failure (for which we can only practice in the sim, and then its what the computer modellers/engineers and designers 'think' will actually happen).

My personal worry is a tail rotor failure, everything else we are pretty much well trained for, but in this day and age of modern technology, the 169 design does appear very simple. Too simple?
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