30 min Dry Run Capabilities
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Some interesting wording excerpts from a fairly recent (Dec.2006) SAC international patent application document filed with WIPO :
" ..............
.......The United States Department of Defence (U.S. DoD) currently imposes a requirement that all rotorcraft transmission systems be able to operate for a predetermined period of time in an oil-out condition. That is, the U.S. DoD requires that all transmissions have the capability to maintain flight operations, albeit at reduced power levels sufficient only to sustain level flight operations, under an oil-out condition for 30 to 60 minutes depending on the mission. For example, a transmission is required to operate, for a period of time, in the event that the flow of lubricating oil to the transmission is interrupted or terminated so that the rotorcraft may safely land. ..................
................................
Present Invention
The emergency lubrication system of the present invention will enable a typical transmission to more than double, maybe ten times, the time period under which a transmission system may operate under oil-out conditions. Moreover, the present oil system is capable of satisfying the U.S. DoD imposed requirements for all areas/components within the transmission system. ...................".
So, as we say around here, where's it at ?
" ..............
.......The United States Department of Defence (U.S. DoD) currently imposes a requirement that all rotorcraft transmission systems be able to operate for a predetermined period of time in an oil-out condition. That is, the U.S. DoD requires that all transmissions have the capability to maintain flight operations, albeit at reduced power levels sufficient only to sustain level flight operations, under an oil-out condition for 30 to 60 minutes depending on the mission. For example, a transmission is required to operate, for a period of time, in the event that the flow of lubricating oil to the transmission is interrupted or terminated so that the rotorcraft may safely land. ..................
................................
Present Invention
The emergency lubrication system of the present invention will enable a typical transmission to more than double, maybe ten times, the time period under which a transmission system may operate under oil-out conditions. Moreover, the present oil system is capable of satisfying the U.S. DoD imposed requirements for all areas/components within the transmission system. ...................".
So, as we say around here, where's it at ?
Join Date: Sep 2007
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30 minute loss-of-lube capability.
The 30 minute loss-of-lube MRGB qual test requirement with the DoD and FAA exists because rotorcraft MRGB lube systems are prone to failure by nature. And there is no practical way to make any MRGB lube system fault tolerant enough to have it's failure considered a "remote possibility". The MRGB lube system is simply too complex, and too critical for flight.
Having said that, I don't honestly believe that Sikorsky's engineers intentionally disregarded the safety of the S-92's MRGB design. Achieving a 30 minute loss-of-lube capability in a high torque MRGB is incredibly difficult to do. But that doesn't mean they didn't make mistakes.
For example, take a look at this photo of an S-92 MRGB lube system filter housing from a fatal crash: http://www.flightglobal.com/assets/g...x?ItemID=29667
Although it's hard to say for sure, but it appears that the o-ring seal on this filter housing is a "face type" seal. Normally, a "radial type" o-ring seal would be used for something like this filter housing. The reason being that a "radial type" o-ring seal would not result in leakage like a "face type" o-ring seal would, in the event of a single fastener failure as shown in the photos.
The design of an o-ring groove is just a simple thing, but obviously such design features can mean the difference between life and death in some instances.
Having said that, I don't honestly believe that Sikorsky's engineers intentionally disregarded the safety of the S-92's MRGB design. Achieving a 30 minute loss-of-lube capability in a high torque MRGB is incredibly difficult to do. But that doesn't mean they didn't make mistakes.
For example, take a look at this photo of an S-92 MRGB lube system filter housing from a fatal crash: http://www.flightglobal.com/assets/g...x?ItemID=29667
Although it's hard to say for sure, but it appears that the o-ring seal on this filter housing is a "face type" seal. Normally, a "radial type" o-ring seal would be used for something like this filter housing. The reason being that a "radial type" o-ring seal would not result in leakage like a "face type" o-ring seal would, in the event of a single fastener failure as shown in the photos.
The design of an o-ring groove is just a simple thing, but obviously such design features can mean the difference between life and death in some instances.
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Determination of cause for S-92 oil filter failures?
FAA: Oil filter maintenance error puts Sikorsky S-92A crews at risk-04/12/2009-Washington DC-Flightglobal.com
Apparently, the service manual specified the wrong o-ring part number for the filter housing.
Apparently, the service manual specified the wrong o-ring part number for the filter housing.
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Filter bowl stud corrosion.
Looking closely again at that photo I posted of the failed titanium studs on the S-92 MRGB oil filter housing, I noticed another issue. It appears that the locknuts on those titanium studs are silver plated (MS21043 types possibly?). It is generally poor design practice to use silver plating in contact with titanium, since it has the potential for galvanic corrosion. The lock nuts should have had a dry film anti-seize coating like moly-disulfide, and definitely not silver plate, if they're being used with titanium.
If those locknuts are per OEM requirements, then Sikorsky's engineers definitely should have known better. I wonder if the FAA will catch this one?
If those locknuts are per OEM requirements, then Sikorsky's engineers definitely should have known better. I wonder if the FAA will catch this one?
