Tail rotor drive shaft coupling failure
Tail rotor drive shaft coupling failure
(OP)
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
RE: Tail rotor drive shaft coupling failure
www.sparweb.ca
RE: Tail rotor drive shaft coupling failure
It conceals all other traces of damage.
If this shaft failed recently, then the obvious cause is corrosion. Period.
If it failed a very long time ago, and allowed to corrode since, then traces of the real cause may be lost now.
www.sparweb.ca
RE: Tail rotor drive shaft coupling failure
It'd be odd not to see the characteristic 45 degree shear if its a torsion failure.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Tail rotor drive shaft coupling failure
RE: Tail rotor drive shaft coupling failure
Got a side view of the failed male coupling half, its hard to work out what exactly we are seeing with a photo with no discernible depth.
What is the time in service(hours & calendar) plus is it the same for both halves.
The female coupling half, clockwise or counter clockwise rotation and is the power transmitted on to or out of it (trying to work out which side is the wear face of the teeth).
Plus piston or turbine engine?
RE: Tail rotor drive shaft coupling failure
RE: Tail rotor drive shaft coupling failure
RE: Tail rotor drive shaft coupling failure
I know I sound like I jumped to conclusions in my first reply, but I would like to know more. Can you describe the sequence of events in the helicopter accident?
Not just starting from the failure, but instead starting from the phase of flight, kind of operations the helicopter was used for, and step by step series of events, as far as they are known to you?
For example, it would be an important difference if the helicopter were engaged in a cruising flight at the time of the accident, versus being engaged in a vertical cargo lifting operation. If you cannot tell us these details, then please just let us know that it is not known or cannot be told.
www.sparweb.ca
RE: Tail rotor drive shaft coupling failure
RE: Tail rotor drive shaft coupling failure
For example, let us say that a crack may be in a driveshaft for a year before causing an accident. In this example, the crack will grow when the helicopter is operating, and it will corrode when it is not. The area of that crack would have deep corrosion pitting that had developed over that year, which would not be possible for a part recently broken. An investigator could look at that corroded part, and compare it to a recent fracture, and know that the more corroded part was the start. Once that "old" corrosion can be found, then the depth and cause of the corrosion can be examined more closely which will help identify the initial cause.
www.sparweb.ca
RE: Tail rotor drive shaft coupling failure
RE: Tail rotor drive shaft coupling failure
RE: Tail rotor drive shaft coupling failure
RE: Tail rotor drive shaft coupling failure
Asking the maker to determine if the helicopter was badly maintained might save the failure of another helicopter, but if maintaining it is a problem, then not having a helicopter at all is the safer option.
Let the maker of the helicopter determine the cause of the failure and involve the country civil aviation regulatory agency.
RE: Tail rotor drive shaft coupling failure
FYI it appears there is debris in the coupling, teeth show abnormal wear and damage. this coupling could have seized. thus causing damage to the shaft.
metal in between the teeth is very bad. if this coupling is inspected and repacked with grease once a years. it will need more frequent inspection and greasing.
corrosion was a good possibility initial cause of damage. all conjecture with the limited info.
a formal failure analysis will be required. all parts will require sent to metlab. an electron microscope analysis will be required.
far as 3DDave advice it sounds very sound. take very careful pictures of each details of the assembly. and cataloged. as not to accidently
remove evidence. good luck.
RE: Tail rotor drive shaft coupling failure
I presume that... in addition to Your NTSB-equivalent accident investigator... the helo manufacturer [???] sent a representative to the accident investigation!? IF NOT... WHY??? The NTSB/OEM will-be [should-be] remarkably well equipped to look at/adjudicate EVERY FACET of the damage to the helo in excruciating detail... and help/guide you likewise.
For my one-and-only Class A MIL helo mishap investigation, we had an outstanding Sikorsky investigator on-site within 1-week of the mishap... astonishing level of expertise/experience [lots of this type have crashed over the years].
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]
RE: Tail rotor drive shaft coupling failure
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]
RE: Tail rotor drive shaft coupling failure
RE: Tail rotor drive shaft coupling failure
Most of us who use this forum are aware of the safety standards involved, including the ICAO obligations to conduct investigations of such accidents. Therefore your questions do pique our interest.
Within the bounds of professional discretion, what can you tell us about the tools and methods available to you as you investigate?
www.sparweb.ca
RE: Tail rotor drive shaft coupling failure
RE: Tail rotor drive shaft coupling failure
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?
www.sparweb.ca
RE: Tail rotor drive shaft coupling failure
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]
RE: Tail rotor drive shaft coupling failure
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/...
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]
RE: Tail rotor drive shaft coupling failure
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]
RE: Tail rotor drive shaft coupling failure
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]
RE: Tail rotor drive shaft coupling failure
RE: Tail rotor drive shaft coupling failure
RE: Tail rotor drive shaft coupling failure
thanks for the feed back and clouser