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Sikorsky S-92: From Design to Operations

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Sikorsky S-92: From Design to Operations

Old 6th Nov 2010, 23:05
  #1921 (permalink)  
 
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the MGB in question, did not fail within 10 mins. it has been proved that the rotors were still turning on impact with the water, and the gearbox was removed from the aircraft wreckage and examined. yes the tail rotor drive pinion was damaged but thats hardly surprising given the loads going through it. but the main rotor was still turning. the evidence in the report shows that they appeared to be in an attitude cosistent with a flare, their words not mine. suggesting they still had some control.

also, the filter bowl and attachment is no longer the same desing. the line changable parts are now secured to the box with a ring of 6 bolts. allowing for one or more to break without the ability to unseat the filter bowl.

time you did a bit of research of your own instead of repeating the words of the uneducated as your own.
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Old 6th Nov 2010, 23:08
  #1922 (permalink)  
 
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the MGB in question, did not fail within 10 mins. it has been proved that the rotors were still turning on impact with the water,
Bobby, so you are saying that there was no failure of the MGB. Perhaps the bit that drives the tail rotor (that failed big time), does not count as MGB in your book? I hope you will not be maintaining the transmission on my helicopter!...

And yes, after 2 major failures the filter housing has been modified. Pity it was not done expeditiously after the first failure, or better still, adequately designed in the first place in "the world's safest helicopter".

Last edited by HeliComparator; 6th Nov 2010 at 23:51. Reason: Found out who ironchefflay is!
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Old 6th Nov 2010, 23:18
  #1923 (permalink)  
 
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Is it still a flush mount with an O ring , I think they might be referring to other ones where the seal is on the outside diameter of the filter and there is a circular recess in the gearbox housing that the filter will slide in to. ( I could not find an illustration of this )
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Old 7th Nov 2010, 01:28
  #1924 (permalink)  
 
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Thanks HC.

I did fly the 332 for a couple of years and while I remember the MGB Cool light (I had a few as well as chips in the early days of the 332) I cannot remember what the filter assembly looked like.

it has always been a mystery to me why anyone would install a manual bypass system on a new helicopter. I believe it's about to be automated on the S-92!
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Old 7th Nov 2010, 09:49
  #1925 (permalink)  
 
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II

It was probably manual because it was introduced very late in 2002 and their was a massive rush (even though 2 years before entering service) to certify to meet the presidential helicopter deadline.

The S-92 filter is still bolted to the casing with 3 bolts (a crazy arrangement as with 4 bolts they would have been able to survive failures). The oddity is by splitting the housing, Sikorsky have introduced another flange that can leak!

Sikorsky should have been more aware of leaking filters, as the S61 had problems there in the early years.

The 332 family has a more robust screw fitted filter with a simple locking mechanism that is far less prone to human error. I understand that even the original 332L lasted longer on test after a lost of oil than the S-92, the L2 over 3 times as long and the EC255 over 5 times (with the glycol cooling active). Hardly progress from Sikorsky? EC didn't claim credit for the margin on the L2 but did use the 52 minutes test on the EC225 to claim a 30 minute period in the certified Flight Manual as per the EH/AW101.

SM - some interesting terminology about the type being "non-preferred" for a time. I wonder who that was communicated with. I'm not sure the seniors at Shell would want those sorts of statements in the public domain now if they covered up their concerns at the time. Or was that just Shell Aircraft bluster to look proactice when actually they were pretty powerless after finding they had really screwed the pooch by advocating that newer was always better?

ironchefflay
Is this what you think an un-failed gear box looks like? (TSB photos)


Tail rotor take off gear on right as compared to a new pinion on the left
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Old 7th Nov 2010, 17:12
  #1926 (permalink)  
 
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Iron - the selective disgruntledness may be because all aircraft have had and will have accidents but only the S-92 has been continually trumpeted as the safest helo on the market.

Adding the word 'probably' doesn't make it so, since Carlsberg is marketed as probably the best lager in the world whereas most people realise it is gassy, flavourless p*ss.
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Old 7th Nov 2010, 21:08
  #1927 (permalink)  
 
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Steady on Crab - if it was flavourless at least it would be drinkable.
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Old 7th Nov 2010, 21:18
  #1928 (permalink)  
 
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HB Any answer to squib's questions?

Crab, does that make NL a "gassy, flavourless p*ss" artist?
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Old 8th Nov 2010, 03:04
  #1929 (permalink)  
 
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"it has always been a mystery to me why anyone would install a manual bypass system on a new helicopter. I believe it's about to be automated on the S-92!"

insider,

Most high power MRGB lube systems have lots of bypass valves, all of which are passive (for lack of a better term) devices. There are high and low pressure relief valves, filter element bypass valves, and cooler thermostatic bypass valves.

I don't know specifics of the S-92 lube system. Where does the manual bypass route oil from and to?

Thanks.
riff_raff
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Old 8th Nov 2010, 10:32
  #1930 (permalink)  
 
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It just cuts off the oil from going to the cooler. The 332 was automatic in 1982!
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Old 9th Nov 2010, 12:12
  #1931 (permalink)  
 
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A quick question for any gearbox design gurus out there......

Is the normal operating reliability reduced by the 30 minute run dry regulation? For instance does the 30 min run dry requirement result in more fancy materials and are those materials just as reliable as those used in a similar gearbox without a 30 minute run dry capability?
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Old 9th Nov 2010, 12:30
  #1932 (permalink)  
 
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Have you seen the latest S-92 filter mount? Have you seen the 6 bolt mount on the new casting?
I have, and I would say that if one were ignorant of the history behind it, one could almost consider it "over engineered!"

The earlier comment about still having 3 mounting bolts is disingenuous and is only a very temporary measure relating to the Phase 1 MGB casing. There are very few of those in service and, in any case, the point is that those studs are no longer interfered with during filter changes.

It just cuts off the oil from going to the cooler. The 332 was automatic in 1982!
Many other types were automatic long before that!

Bobby (why Flay - surely 'Marimoto' would have been a better choice!) I think your downplaying of the severity of the failure mode is misplaced. To be presented by a tail rotor drive failure at 500 ft, while concentrating on an attempted ditching in moderate seas, is a nightmare scenario. The likely successful outcome is remote - as was proved, despite obvious valiant efforts (throttles back by 300 ft etc.)
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Old 9th Nov 2010, 12:59
  #1933 (permalink)  
 
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When is the Canadian TSB report due to be published?

That should bring this thread to lightspeed as people freak out about the findings.
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Old 10th Nov 2010, 16:21
  #1934 (permalink)  
 
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The contract for procurement of 12 AW-101 helicopters for the Indian Air Force was signed between Ministry of Defence and M/s Agusta Westland Ltd., United Kingdom at a total cost of Rs. 3546.17 crores on 8th February 2010.

The Ministry of Finance had raised certain issues relating to costs that were clarified while placing the proposal for consideration of the Government.

AW-101 is a three engine helicopter, whereas, Sikorsky S-92 is a twin engine helicopter. The S-92 did not comply with certain mandatory Services Qualitative Requirements (SQRs) of the Request for Proposal and hence its commercial proposal was not opened.

This information was given by Defence Minister Shri AK Antony in a written reply to Shri MV Mysura Reddy in Rajya Sabha today.
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Old 10th Nov 2010, 17:51
  #1935 (permalink)  
 
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i could be in the minority here, but the s-92 and the AW101 are not exactly comparable? are they? certainly not in cost !
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Old 10th Nov 2010, 22:12
  #1936 (permalink)  
 
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albatross - the TSB are conulting the parties about the report. As two parties are in a court case you can bet that the lawyers put a lot of comments in and it will suit them if it takes a long time for TSB to resolve those comments. While the TSB evidence is not admissable in a court case, if the report comes out first there would be a media frenzy in court.

ic - yes their are many differences, with pros and cons of each aircraft.

The Crown has said publically they won't accept the S-92 MHP in Canada without a run-dry gearbox (subtext: as in their EH101 Cormorants)
Ottawa won't accept helicopters without run-dry capability - The Globe and Mail
I'm sure many people would like to know when that certification test is complete.

Perhaps that test result is one of the hundreds / thousands of technical requirements that was in the Indian RFPs.

I also hear a rumour that the 101 has been ordered to replace the presidential S-92 in Turkmenistan and the Canadian Military have surveyed the cancelled VH-71s.
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Old 11th Nov 2010, 02:07
  #1937 (permalink)  
 
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"Is the normal operating reliability reduced by the 30 minute run dry regulation? For instance does the 30 min run dry requirement result in more fancy materials and are those materials just as reliable as those used in a similar gearbox without a 30 minute run dry capability?"

Droopystop,

There are two different issues you may be confusing- reliability and fault tolerance. Reliability is the statistical failure rate of a particular component or system. Fault tolerance is the ability of a system or subsystem to tolerate faults/failures and maintain function.

To answer your question, achieving a 30 minute loss-of-lube capability in an MRGB usually involves (among other things) adding redundant components/systems. All other things being equal, adding more components to a system will naturally decrease the overall system statistical reliability rate. However, at the same time, adding that redundant hardware may also increase the system's level of fault tolerance.

The biggest problem with loss-of-lube in an MRGB is overheating of the highly loaded gear teeth and bearings. Impinging lube oil flow is how these parts are normally cooled, since they have very limited conductive heat paths to structure. If there is no cooling oil flow, the gear teeth and bearings will build up heat. Standard gear (9310 steel) and bearing materials (E52100) are capable of operating at temperatures around 350degF max before their heat treatment begins to be affected (de-tempering), weakening their structure and eventually causing failure. There are high temp gear (X-53) and bearing (M50NiL) steels, and these can operate up to temperatures of about 600degF. But these materials are currently somewhat more costly than standard materials.

Taking into consideration only the material itself (and not heat treatment, processing, manufacturing precision, etc.) with regards to reliability effects, there should not be a big difference between standard and high temp alloys. Reliability factors of gear and bearing steels is based mostly on their metallurgical cleanliness quality (low presence of inclusions), and double vacuum melt quality is always used regardless of the alloy.

Hope that answers your question.
riff_raff
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Old 11th Nov 2010, 15:53
  #1938 (permalink)  
 
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Perfect,

thanks Riff_Raff
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Old 11th Nov 2010, 20:30
  #1939 (permalink)  
 
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More than a runour Zalt....HeliData News ran the Turkmenistan story two weeks ago...and says the S92s are up for sale.
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Old 12th Nov 2010, 06:42
  #1940 (permalink)  
 
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Turkmenistan Purchases Two VIP S-92 Helicopters
<H3>July 18, 2004

FARNBOROUGH, United Kingdom - Sikorsky Aircraft Corp. today announced that it has sold two S-92 helicopters to Turkmenistan for presidential transport.

Upon inking the $53M deal in Ashgabat on June 28, Turkmenistan President Saparmurat Niyazov noted the reliability and quality of Sikorsky helicopters...

"The S-92 is a natural fit for VIP presidential transport.

It was designed from the outset to meet the most rigorous safety standards in the world," said Jeff Pino, Sikorsky Vice President of Marketing and Commercial Programs.
</H3>Obviously not then.
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