Tail rotor drive shaft coupling failure 6

[Rotory helos]

Hello, iam analysing failure of coupling shaft. Iam exactly not able to make out whether it is a failure due to overheating, loss of lubricant or when my tail rotor hit the ground resultantly its impact load caused it. However, i didnot think it is due to sudden impact load. One more thing if OEM is recommending G355 grease in that coupling and iam using G353, Does it affects or not. Picture of failed coupling is attached

 

[Rotory helos]

Thanks for the guidance. Questions which i asked in the start was very basic one as we were at the start of finding root cause. Visual inspection tool was adopted to find cause of failure. Aparently, we reached to a conclusion that gasket between coupling torn out which lead ro dryness of grease and subsequent failure. We have forwarded all damaged parta for SEM and fracture analysis as well. Details i will share once received

 

[Sparweb]

Thank you for the update. I look forward to it.
Are you able to say anything about the gasket failure, for its cause? Can you describe the location of the gasket in the coupling (internal or external)? Are there other ways for the grease to escape? Or for the opposite: ingress of moisture which may have been trapped?
Or were some of these possibilities ruled out somehow?

http://www.sparweb.ca

 

[WKTaylor]

Since YOU are investigating this failure... and details are sparse... it seems reasonable to presume You are the on-site investigator for both the Authorities and Manufacturer...? My curiosity is elevated...

Rotary helos… For clarity.. please advise...

NYCO G353 Grease has an MoS2 filler... typically used in extreme pressure/wear applications... and most greases like this are silvery-gray/black... the photos show distinctly hardened tan-to Brown... more similar to NYCO G355... a conventional lithium-based grease.

Environmental seal failures often introduce atmospheric moisture to grease... which tends to 'thin conventional greases'. The photos show an oddly stiffened-dry appearance... which seems inconsistent with environmental seal failures... except in extreme hot/dry desert climates... which can also expose critical unsealed joints to micro-fine dust...

Is this a one-of-a-kind [prototype] in flight testing?
Ultralight, light or heavy weight category?
Manned? Unmanned?
Amateur-built experimental?
Corporate experimental?
Military experimental?
What kind of 'iron-bird' TRDS drive-train testing was accomplished prior to certification for flight?





Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[WKTaylor]

BTW... FYI, ONLY...

Aeroshell publishes a great reference book on [their] lubricants [greases, oils, SFLs, etc] and fuels... but it is worth downloading as a general-knowledge reference...

Aeroshell E-Book...

https://www.shell.com/business-customers/aviation/aeroshell/knowledge-centre/the-aeroshell-book.html

Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[WKTaylor]

Rotary Helos… are You there?????????????

Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[WKTaylor]

Hmmm... Rotary helos has not logged-on after reading my last couple of posts...

Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[Rotory helos]

Hello, iam back. Actually i was away from internet and trying to spend internet free month. We have got the analysis report of coupling. It failed due to loss of grease from packing which gradually resulted into overheating and material deterioration. So, the point is we have introduced periodicity of greasing after 6months to prevent such failure

 

[Rotory helos]

@Wk taylor, your analysis were spot on, loved to stay in contact with you on technical analysis. Hope you share your email ID with me. Then i can share further details of aerial vehicle

 

[mfgenggear]

Hello, iam back. Actually i was away from internet and trying to spend internet free month. We have got the analysis report of coupling. It failed due to loss of grease from packing which gradually resulted into overheating and material deterioration. So, the point is we have introduced periodicity of greasing after 6months to prevent such failure

thanks for the feed back and clouser