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EC225 crash near Bergen, Norway April 2016

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EC225 crash near Bergen, Norway April 2016

Old 11th Jul 2016, 15:30
  #1501 (permalink)  
 
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Originally Posted by Lonewolf_50 View Post
The "hey, this one's beginning to wear/lose material" trigger gets the box off the aircraft before these critical parts fail.
Excepts when it doesn't.

Humans ofter overestimate their own level of control over things, personally I prefer robust design over overconfidence in monitoring systems as a general principle. That doesn't mean that I think monitoring systems shouldn't exist, it's just not wise to think one has all eventualities covered - because one never has.
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Old 11th Jul 2016, 16:44
  #1502 (permalink)  
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Yes, correct Geoff - 2 x separate load-paths. As Eric says, 'old' technology, but proven, and yes, also, read across from the Hughes 500. Keep it simple (K.I.S.S) ~ VFR
just a shame that the MD 900 gearbox internals were made from the same batch of metal as my old Lancia Beta Coupe!!
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Old 11th Jul 2016, 16:53
  #1503 (permalink)  
 
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Originally Posted by Nadar View Post
Excepts when it doesn't.
No kidding? Head on over to the Robbie 66 crash thread, recent, two fatalities, and the Isle of Mann thread (206), one fatality ... you can die a lot of ways.


The point being I was trying to make is that there is more than one approach to dealing with wear -- a known phenomenon in gear boxes and power trains. If another (better) means of monitoring/warning can be implemented, that's one way to address this. I am not pretending that it is the only way. It was of interest to note that this kind of feature was mentioned in the G-REDL write up, and has been a feature in the current reports coming from the investigators in Norway.


The sub text may be something along the lines of your point: if you can't come up with a better monitoring system, then you have to come up with higher safety factors / wear resistance / shorter inspection intervals.
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Old 11th Jul 2016, 18:18
  #1504 (permalink)  
 
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So what's wrong with the 'dual load path' idea? If you put Kawasaki internals in the box instead of the Lancia versions in the MD product surely this would be a design that the folk who ride in helicopters would prefer? (Kawasaki make gearbox bits for the 139 etc).


G.
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Old 11th Jul 2016, 20:14
  #1505 (permalink)  
 
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While we are at it, let's go back to the rotordyne. No gears needed in the "gearbox" . Dry run shouldn't be a problem just a couple of bearings to lub. Now that shouldn't be beyond the Ken of man.
Then of course there´s the noise and that's an other question.

Last edited by Sevarg; 11th Jul 2016 at 20:15. Reason: Predictive text!!!!!
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Old 11th Jul 2016, 21:36
  #1506 (permalink)  
 
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Originally Posted by Sevarg View Post
While we are at it, let's go back to the rotordyne. No gears needed in the "gearbox" . Dry run shouldn't be a problem just a couple of bearings to lub. Now that shouldn't be beyond the Ken of man.
Then of course there´s the noise and that's an other question.
If you want to get rid of gears in the drive train, we have a thread here on Rotorheads discussing the all electric powered helicopter=> (http://www.pprune.org/rotorheads/426...-electric.html) ... all motor needs no reduction gears!
Not sure if that solves the problem of getting a good sized load of people to and from oil and gas rigs in the foreseeable future ...
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Old 11th Jul 2016, 22:08
  #1507 (permalink)  
 
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In the 50's the rotordyne (Fairy) could take 40 pax not sure of the range but I'm sure google knows. The tech works and it's simple always a plus. I have heardthat the noise problem was solved, mind that would be noise 60 years ago, maybe not good enough for today. Surely a bit of modern tech could sort it.
By the way an electric motor would be high speed and would still need reduction, hence gears.

Last edited by Sevarg; 11th Jul 2016 at 22:12. Reason: Added the electric motor bit.
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Old 11th Jul 2016, 22:16
  #1508 (permalink)  
 
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Originally Posted by Sevarg View Post
By the way an electric motor would be high speed and would still need reduction, hence gears.
You are invited to argue that with Adam Frisch, author of the OP in the link I provided to you. (I included the evil smilie -- -- for a reason. )


On a more serious note, if the rotordyne were the answer, why do you think the industry has not yet provided it?
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Old 11th Jul 2016, 22:33
  #1509 (permalink)  
 
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Noise and from memory a hell of a lot of it. I would also guess it´s not a fuel efficient as current designs. All guesses on my part.
Sorry not able to read the link as yet, cheap phone not doing what it says it will.
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Old 13th Jul 2016, 04:12
  #1510 (permalink)  
 
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Originally Posted by Lonewolf_50 View Post
The cost differential riff mentioned is a non-trivial issue when considering whether to upgrade / replace. Any manufacturer for a civil or military contract has to account for lead times for exotic / specialty alloys, and the cost versus customer requirements (and regulatory requirements) -- a balancing act that goes into any final design or upgrade decision.
Lonewolf_50-

I think the subject of what upgrades/modifications can be made to existing gearbox designs that can provide significant improvement in loss of lube operation versus the cost involved is somewhat relevant to this thread, and is worth discussing a bit further. Your comment about OEMs making decisions that are a balance between manufacturing cost and regulatory requirements is correct. But I don't think the higher raw material cost of C64 is a major factor versus the benefit it provides.

Let's take a look at an example of where C64 gears may have made a huge difference. Consider the 2009 S-92 accident where the main gearbox TTO spiral bevel pinion suffered catastrophic plastic failure of the gear teeth from elevated temperatures during loss of lube operation after just 15 minutes. One could argue that if the TTO spiral bevel gears were made of C64, with its much higher temperature capability, they might have continued to function long enough to prevent the crash.

Below is a table of the cost for replacement spiral bevel pinions/gears used in the UH-60 tail rotor drivetrain. The TTO pinion is $7291 and the gear is $9436. The difference in raw material cost between 9310 and C64 for the 25lb ring gear forging is probably around $250, or less than 3% of the total gear cost. In this example, raw material cost would not seem to be a significant factor. However, the total cost of manufacturing and retrofitting a dozen or more gears would likely run several hundred thousand dollars per gearbox. So the question becomes is that cost worth the added safety/reliability provided?

Here's a good NASA technical paper on the subject of C64 gears if anyone is interested.
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Old 13th Jul 2016, 08:12
  #1511 (permalink)  
 
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Generally, that will go beyond just raw material cost. Stronger materials are often more difficult to machine and often every process has added time and cost. Additional processes may be necessary. New materials can also bring new unforeseen problems.
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Old 13th Jul 2016, 10:51
  #1512 (permalink)  
 
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Is there any time frame for an official update on this investigation, does anyone know?
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Old 13th Jul 2016, 11:35
  #1513 (permalink)  
 
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There have been 4 to date and the last suggested that updates will now be less frequent.

EC225 LN-OJF Accident Investigation Timeline
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Old 13th Jul 2016, 16:26
  #1514 (permalink)  
 
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Originally Posted by riff_raff View Post
Let's take a look at an example of where C64 gears may have made a huge difference. Consider the 2009 S-92 accident where the main gearbox TTO spiral bevel pinion suffered catastrophic plastic failure of the gear teeth from elevated temperatures during loss of lube operation after just 15 minutes. One could argue that if the TTO spiral bevel gears were made of C64, with its much higher temperature capability, they might have continued to function long enough to prevent the crash.
Good example, I've heard a similar point being made about gears with Isotropic superfinishing but am not sure if they could claim the loss of lube protection ... but the point about changes in manufacturing requirements factoring into cost is worth keeping in mind. (Does AH/Eurocopter use ISF to their planet/sun gears in the epicyclic module?)
Here's a good NASA technical paper on the subject of C64 gears if anyone is interested.
Thanks for the link and the table provided.

Last edited by Lonewolf_50; 13th Jul 2016 at 16:39.
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Old 13th Jul 2016, 17:48
  #1515 (permalink)  
 
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Riff

The 92 crash was caused by failure of the xmsn tail rotor output roller bearings which allowed the quill to move and, after it was stripped, loss of tail rotor drive. Main rotor drive was never lost.

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Old 13th Jul 2016, 21:57
  #1516 (permalink)  
 
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Llanelli, had a read up on brushless motors and yes IF batteries can be improved I can see it would be the path to follow. I can see a problem regards the speed of the motor re the wieght. A low speed motor would require large conductors so the weight would be high, high speed motor lower weight but a gear box needed to get to, say, 400 rpm. So your back to the same problem.
All this worked out by an old brain feed on a bit to much red wine, so I wouldn't bet the farm on it.
The more I think about it the jet tip is well worth looking in to, no MRGB, as we know it, and no tail rotor system. I would say a bit more noise well worth the extra safety.
Now I guess I'll have read u on tip jets/bleed air, tomorrow, a clear head needed.
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Old 14th Jul 2016, 09:29
  #1517 (permalink)  
 
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Originally Posted by riff_raff View Post
However, the total cost of manufacturing and retrofitting a dozen or more gears would likely run several hundred thousand dollars per gearbox. So the question becomes is that cost worth the added safety/reliability provided?

Do you really think the benefit of the new material would be spent solely or even at all on improving safety or reliability?
Given that designers and manufacturers would probably apply the same design methods, same approach, codes and practices, same safety factors and design inputs, would they not simply arrive at either a smaller lighter component or increase the design loads on it or increase the TBO on the gearbox?

With limited experience of this new material in service, might they not risk getting caught out by the unexpected at least as much as they have already been with the 16NCD13 gears on the L2 & H225 when performance is pushed to the limit?
Is there not a statement in the conclusions section of the NASA article you linked that there was significant variation in fatigue performance (“However, due to considerable scatter in the UHS test data, the anticipated overall benefits of the UHS grades in bending fatigue have not been fully demonstrated”).

The benefits of new wonder materials will only be realised when consistency can be guaranteed. How consistent I wonder is the 16NCD13 material and the present planet gear's manufacturing processes?

Last edited by Concentric; 17th Jul 2016 at 08:06.
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Old 14th Jul 2016, 13:36
  #1518 (permalink)  
 
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Devil

I fear that it doesn't matter if they make a new gear box out of kryptonite and dilithium crystals, the Super Puma series is DOA on emotions alone.

Nobody will want to touch it with a barge pole. The Super Puma is the new DC-10.

Stick a fork in it - it's done.
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Old 14th Jul 2016, 17:15
  #1519 (permalink)  
 
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Could it be the 225 MGB Design failed to correctly assess Loading on those particular Gears/Bearings? Sometimes it is more an art form than science when trying to determine the true loading of various parts of a helicopter.

I am just suggesting there is more to designing a piece of machinery than meets the eye sometimes and we discover that limitation the hard way far too often.

Some examples....the US Army lost two UH-1's and Two Instructors and Four Student Pilots in one day due to Tail Boom failures at Fort Rucker. That led to needed Mods to the Tail Boom.

PHI in the Gulf of Mexico lost two Jet Rangers due to Transmission Mount failures in one day.

The US Army lost a couple of Chinooks to Incidence Bolt Failures on Rotor Blades.

Sikorsky had Blade problems on the A Model 76.

The Wessex had some gearbox failures.

It is not limited to just one Brand, Type, Model, or any one set of Engineers.
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Old 14th Jul 2016, 22:23
  #1520 (permalink)  
 
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Originally Posted by SASless View Post
Could it be the 225 MGB Design failed to correctly assess Loading on those particular Gears/Bearings?
I have been wondering about this also. The lineage of the AS332L2/EC225 saw it go from 4 blade MR / 5 blade TR in the 332 to a 5 blade MR and 4 blade TR in the 225, this went along with substantial increases in the gross weight and MTOW.

It would be interesting to see what, if any, changes were made to the MGB along the way. Do the 332L2 and 225 have the same part number and mod status MGB, do they have the same part number planetary gears and bearing rollers?

I have heard that at some point along the way going from the SA330 to the 332L to the 332L1/L2 the MGB went from having 9 planetary gears in the primary and secondary reduction stages to having 8 planetary gears. I'm not sure if this is correct or when the change occurred but your comment about assessing the loads especially when increasing max weights is a valid one.
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