Sikorsky S-92: [Archive Copy]
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Tokunbo,
No way am I slagging RB, just a little inter-company ribbing, I was questioning the 100hrs as they just took delivery of the Machine [ Okay they were obviously training on it long before delivery ]
No apoligies for the 332l teething problems though.
Cheers,
TC
No way am I slagging RB, just a little inter-company ribbing, I was questioning the 100hrs as they just took delivery of the Machine [ Okay they were obviously training on it long before delivery ]
No apoligies for the 332l teething problems though.
Cheers,
TC
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Oil System Design - 101
First...Lu, it's great to see you back here posting. 
HC said:
The design of a pressurized oiling system is performed basically along these lines. First, the engine or transmission will have various bearing surfaces and perhaps oil pressure activated devices that need to be supplied. Channels and passages (for the pressurized part of the system) will be incorporated into the design to accommodate these needs.
From these basic requirements, a flow rate of pressurized oil will be derived from either calculations or actual testing on prototype assemblies. The basic flow rate will be derived from the number of bearings, bearing surface sizes and clearances, and will also be affected by expected operating temperatures and oil viscosity. Channels and passages will be sized to accommodate the expected flow rates.
Then a pumping system will be designed to accommodate the expected flow rates. The pumping system has to exceed the expected flow rates by a certain amount for a variety of reasons. Oil, like water, is uncompressible and therefore the pumping system has to have a pressure relief system of some kind (usually a pressure relief valve), to dump the excess capacity back to the sump.
Various criteria are used to determine a design working pressure for the system. One of the reasons that a pressurized system is considered, is because the designer may prefer that the oil not linger at the bearing too long, because it can overheat and break down prematurely. It's better to provide a continuous flow of cooled oil that will stay in good condition longer and provide better lubrication. Working pressure also determines how fast the oil will move through the bearing's various clearances, and in this way working pressure also contributes to the system's overall flow rate.
In an oiling system, volume flow substantially determines pressure. At a given temperature, oil condition, and bearing wear condition, there's a point where once the pump's capacity exceeds the volume required, pressure goes up dramatically until the pressure relief point is reached (due to incompressibility).
Now in aviation, flight safety is a factor in the design, so having two pumps is an excellent solution. However with two pumps, the volume and pressure question gets a little more complicated. Each pump could be designed to exceed the capacity needs of the system, but with two identical pumps running, there's a great deal of excess capacity causing lots of extra oil to be dumped back into the sump through the pressure relief system. This isn't very efficient, and causes both pumps to run at high pressures and stresses.
A case can be made, even with aviation safety requirements in mind, that each pump could be designed to provide most, but not all of the system's volume needs. This would be acceptable, if it's known that the system can run safely for a known period of time without damage at the reduced volume. This safety case can be made, based on the fact that a system running on a surviving pump, will be running at substantially reduced pressures because the surviving pump CANNOT supply the full volume requirement (and pressure goes up dramatically once volume is exceeded) and thus the surviving pump is PROTECTED from failure because its running at substantially reduced pressures and stress. Again, the case can be made that this enhances flight safety in a single pump failure mode.
Nick can elaborate, but since this particular S-92's transmission was almost new, and it's nearly certain that the failed drive shaft reduced the output of the failed pump to virtually nil, the reason the pressure dropped as far as it did, is perhaps because the remaining pump was purposely designed to provide somewhat less than the full flow requirements for the transmission.
HC said:
If one pump was still working, how come the pressure was nearly at the bottom of the scale?
From these basic requirements, a flow rate of pressurized oil will be derived from either calculations or actual testing on prototype assemblies. The basic flow rate will be derived from the number of bearings, bearing surface sizes and clearances, and will also be affected by expected operating temperatures and oil viscosity. Channels and passages will be sized to accommodate the expected flow rates.
Then a pumping system will be designed to accommodate the expected flow rates. The pumping system has to exceed the expected flow rates by a certain amount for a variety of reasons. Oil, like water, is uncompressible and therefore the pumping system has to have a pressure relief system of some kind (usually a pressure relief valve), to dump the excess capacity back to the sump.
Various criteria are used to determine a design working pressure for the system. One of the reasons that a pressurized system is considered, is because the designer may prefer that the oil not linger at the bearing too long, because it can overheat and break down prematurely. It's better to provide a continuous flow of cooled oil that will stay in good condition longer and provide better lubrication. Working pressure also determines how fast the oil will move through the bearing's various clearances, and in this way working pressure also contributes to the system's overall flow rate.
In an oiling system, volume flow substantially determines pressure. At a given temperature, oil condition, and bearing wear condition, there's a point where once the pump's capacity exceeds the volume required, pressure goes up dramatically until the pressure relief point is reached (due to incompressibility).
Now in aviation, flight safety is a factor in the design, so having two pumps is an excellent solution. However with two pumps, the volume and pressure question gets a little more complicated. Each pump could be designed to exceed the capacity needs of the system, but with two identical pumps running, there's a great deal of excess capacity causing lots of extra oil to be dumped back into the sump through the pressure relief system. This isn't very efficient, and causes both pumps to run at high pressures and stresses.
A case can be made, even with aviation safety requirements in mind, that each pump could be designed to provide most, but not all of the system's volume needs. This would be acceptable, if it's known that the system can run safely for a known period of time without damage at the reduced volume. This safety case can be made, based on the fact that a system running on a surviving pump, will be running at substantially reduced pressures because the surviving pump CANNOT supply the full volume requirement (and pressure goes up dramatically once volume is exceeded) and thus the surviving pump is PROTECTED from failure because its running at substantially reduced pressures and stress. Again, the case can be made that this enhances flight safety in a single pump failure mode.
Nick can elaborate, but since this particular S-92's transmission was almost new, and it's nearly certain that the failed drive shaft reduced the output of the failed pump to virtually nil, the reason the pressure dropped as far as it did, is perhaps because the remaining pump was purposely designed to provide somewhat less than the full flow requirements for the transmission.
Iconoclast
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Transmission lubrication 101
Many years ago the US Army wanted to consolidate the lubricants used on their helicopter transmissions. The result was the change from mineral based oils with a relative high viscosity and higher film strength to the oil used in the gas turbines powering the helicopter and these oils have a lower viscosity and lower film strength as compared to the mineral based oils previously used.
With the advent of this change there were a lot of transmission failures due to inadequate lubrication. The use of gas turbine oil in transmissions was later adopted by all of the military and carried over to the civilian sector.
The gas turbine oil was designed to operate in a gear train and on bearings that had minimal point contact loading. In the transmission application the point contact loading in the gear mesh was considerably higher and the oil was operating at a point where lubrication film strength was at a minimum.
Unlike mineral based oils, which have a higher viscosity at operating temperature, and multi grade oils, which increase both viscosity and film strength at operating temperatures the gas turbine oil drops in viscosity and film strength at transmission operating temperatures. This required the development of two types of oil. One for warm theater operations and one for winter. This is good for the gas turbines but does not provide the same results when used in a helicopter transmission. Newer helicopter designs cater to this oil application using closer tolerances but the point contact loading of the gears is still the same if not higher with increased torque on larger helicopters.
This use by the military resulted in a higher maintenance rate with the decreased frequency between oil changes, which effected operating costs for the helicopter. Civilian operators were also effected in the same way.
With the advent of this change there were a lot of transmission failures due to inadequate lubrication. The use of gas turbine oil in transmissions was later adopted by all of the military and carried over to the civilian sector.
The gas turbine oil was designed to operate in a gear train and on bearings that had minimal point contact loading. In the transmission application the point contact loading in the gear mesh was considerably higher and the oil was operating at a point where lubrication film strength was at a minimum.
Unlike mineral based oils, which have a higher viscosity at operating temperature, and multi grade oils, which increase both viscosity and film strength at operating temperatures the gas turbine oil drops in viscosity and film strength at transmission operating temperatures. This required the development of two types of oil. One for warm theater operations and one for winter. This is good for the gas turbines but does not provide the same results when used in a helicopter transmission. Newer helicopter designs cater to this oil application using closer tolerances but the point contact loading of the gears is still the same if not higher with increased torque on larger helicopters.
This use by the military resulted in a higher maintenance rate with the decreased frequency between oil changes, which effected operating costs for the helicopter. Civilian operators were also effected in the same way.
Sikorsky S-92 Wins Korean Competition
Word on the street is that Sikorsky has won the Korean Presidential competition. I should imagine its Budweiser’s all round in Connecticut then.
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S-92 CHOSEN AS KOREAN PRESIDENTIAL
US S-92 Chosen as Presidential Helicopter
US Sikorsky S-92 Selected as Presidential Helicopter
By Jung Sung-ki
Staff Reporter
The U.S. Sikorsky S-92 model has been selected to replace the VH-60 transport helicopter for the president, the Air Force said Friday.
An S-92 helicopter, made by U.S. Sikorsky Aircraft, is pictured in this file photo. Korea Times
Sikorsky, a U.S. aircraft firm, won the helicopter procurement contract over Agusta Westland, a consortium of the United Kingdom and Italy, which offered its EH-101 model, Shin Bo-hyun, deputy chief of staff of planning and management at the Air Force, said in a media briefing.
``The Air Force has conducted test trials since last November, and Sikorsky's S-92 had more points of comparison in terms of operational requirements and cost-efficiency,'' Shin said. Eight experts from the Air Force, the Joint Chiefs of Staff and the Agency for Defense Development conducted the test trial.
Chong Wa Dae approved the plan earlier in the day, he said.
The presidential helicopter project was launched last year as the VH-60 has been used for 14 years, exceeding the operational period of 10 years, Shin said.
Under the contract, Sikorsky is expected to deliver three S-92s worth some $127 million (127 billion won) by 2007, Air Force officers said.
The 17-meter-long S-92 helicopter has a seating capacity of 18 and flies at the maximum speed of 165 knots (295 kilometers) per hour. It also can stay in the air for three hours, which are 40 minutes longer than the VH-60. The maximum cruising radius is 390 nautical meters (702 kilometers).
Three countries_ the United States, the United Kingdom and Norway _ are currently operating S-92s, and seven other countries have ordered 59 S-92s, according to the Air Force. Sikorsky plans to build some 700 S-92 helicopters by 2019.
US Sikorsky S-92 Selected as Presidential Helicopter
By Jung Sung-ki
Staff Reporter
The U.S. Sikorsky S-92 model has been selected to replace the VH-60 transport helicopter for the president, the Air Force said Friday.
An S-92 helicopter, made by U.S. Sikorsky Aircraft, is pictured in this file photo. Korea Times
Sikorsky, a U.S. aircraft firm, won the helicopter procurement contract over Agusta Westland, a consortium of the United Kingdom and Italy, which offered its EH-101 model, Shin Bo-hyun, deputy chief of staff of planning and management at the Air Force, said in a media briefing.
``The Air Force has conducted test trials since last November, and Sikorsky's S-92 had more points of comparison in terms of operational requirements and cost-efficiency,'' Shin said. Eight experts from the Air Force, the Joint Chiefs of Staff and the Agency for Defense Development conducted the test trial.
Chong Wa Dae approved the plan earlier in the day, he said.
The presidential helicopter project was launched last year as the VH-60 has been used for 14 years, exceeding the operational period of 10 years, Shin said.
Under the contract, Sikorsky is expected to deliver three S-92s worth some $127 million (127 billion won) by 2007, Air Force officers said.
The 17-meter-long S-92 helicopter has a seating capacity of 18 and flies at the maximum speed of 165 knots (295 kilometers) per hour. It also can stay in the air for three hours, which are 40 minutes longer than the VH-60. The maximum cruising radius is 390 nautical meters (702 kilometers).
Three countries_ the United States, the United Kingdom and Norway _ are currently operating S-92s, and seven other countries have ordered 59 S-92s, according to the Air Force. Sikorsky plans to build some 700 S-92 helicopters by 2019.
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Korea was very nearly another runaway bride... The S-92 selection is widely believed to have been made last December, but Seoul got cold feet after the VH-71 Kestrel selection.
Nice to see the ink's finally dry.
I/C
Nice to see the ink's finally dry.
I/C
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Big smiles in Connecticut, I hear. Rumors are that there were direct calls from Tony Blair to the "Blue House" (Presidential Quarters) in Korea to try and stop the sale, similar to those made in the US for the VXX.
http://times.hankooki.com/lpage/nati...7155611970.htm
http://times.hankooki.com/lpage/nati...7155611970.htm
Will the S92 win every presidential helicopter competition except for in its own country? Hmmm.
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If it's any consolation, many of us would far prefer the S-92 to Tony Blair....... 
The Sultan
I think you are being a little harsh on the Koreans in their ability to decide which aircraft offers the best combination of technical and commercial benefits for their requirements.
I read recently that since certification, the S92 has beaten the EH101 in every international competition to date. How true this is I’m not sure, but I am aware of only one civil EH101 and that should make the likes of you and me question why this is?
I think you are being a little harsh on the Koreans in their ability to decide which aircraft offers the best combination of technical and commercial benefits for their requirements.
I read recently that since certification, the S92 has beaten the EH101 in every international competition to date. How true this is I’m not sure, but I am aware of only one civil EH101 and that should make the likes of you and me question why this is?
AD issued for S-92 MGB Lubrication System
Helicopter Monthly had this article about the recently issued AD for the S-92 Main Transmission Lubrication System.
AD Issued On Sikorsky Aircraft Corporation Model S- 92A Helicopters
HM Staff
This amendment adopts a new airworthiness directive (AD) for Sikorsky Aircraft Corporation (Sikorsky) Model S-92A helicopters. This action requires replacing the main gearbox (MGB) lubrication/scavenge pump vespel spline adapters (vespel spline adapters) before further flight, and thereafter, replacing them at certain intervals. This amendment is prompted by a reported incident of an in-flight loss of oil pressure. The actions specified in this AD are intended to prevent loss of lubrication to the MGB, which could cause failure of one or both engine input drives, or planetary gear to sun gear tooth mesh failure, resulting in loss of power to the rotor system and subsequent loss of control of the helicopter.
The full AD can be found at faa.gov .
AD Issued On Sikorsky Aircraft Corporation Model S- 92A Helicopters
HM Staff
This amendment adopts a new airworthiness directive (AD) for Sikorsky Aircraft Corporation (Sikorsky) Model S-92A helicopters. This action requires replacing the main gearbox (MGB) lubrication/scavenge pump vespel spline adapters (vespel spline adapters) before further flight, and thereafter, replacing them at certain intervals. This amendment is prompted by a reported incident of an in-flight loss of oil pressure. The actions specified in this AD are intended to prevent loss of lubrication to the MGB, which could cause failure of one or both engine input drives, or planetary gear to sun gear tooth mesh failure, resulting in loss of power to the rotor system and subsequent loss of control of the helicopter.
The full AD can be found at faa.gov .
Hoist ops S-92?
How is a hoist fitted to the S-92?
Surely it has been designed in SAR config with hoist option and I was wondering how the door problem is solved.
The door is big and wide with a upper half sliding door and airstair type lower half. There must be a different solution for hoisting.
Photo courtesy of "Canadian Rotorhead"!
Surely it has been designed in SAR config with hoist option and I was wondering how the door problem is solved.
The door is big and wide with a upper half sliding door and airstair type lower half. There must be a different solution for hoisting.
Photo courtesy of "Canadian Rotorhead"!
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I think that they have done away with those unreliable, dangerous winch things. The aircraft is so good you can lower the airstair door right onto the deck of the vessel so your casualty can just hop aboard.
Good point Aesir.
Good point Aesir.
92's don't need winches....civvies know naught bout it you know.