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S97 Raider

Old 20th Oct 2015, 00:00
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I'm wondering if there are any implications for LoL situations with a split torque design
SA- That's actually quite an interesting question.

The answer to your question would depend on the specific configuration of split torque transmission. And since the number of potential split torque configurations is quite large, let's just compare the split torque and improved planetary designs considered for the 53K in terms of LoL operation.

First, compare two well known cases where LoL caused overheating and structural failure of a gearbox component, which resulted in loss of MRGB function, and finally loss of the aircraft with everyone aboard. There is the 1982 CH-47 accident in Mannheim and the 2009 S-92 accident in St. John's. What both accidents have in common are the components that failed first after LoL - a spiral bevel pinion and the tapered roller bearings supporting it. With the CH-47 MRGB, the spiral bevel pinion was part of the interconnect drive between the F/R rotors. With the S-92 MRGB, the spiral bevel pinion was part of the tail rotor drive. However, where these two cases differ is the extent of the LoL condition. With the CH-47, there was only LoL at one point in the circuit. The oil jet for the failed spiral bevel pinion bearings became clogged with debris. With the S-92, there was a filter housing leak that resulted in loss of all lube oil.

When comparing the two 53K MRGB configurations, it's important to note that they both use spiral bevel gear meshes for the engine inputs and tail rotor drive. So one design characteristic that has proven to be an issue with LoL conditions is still present in both gearboxes.

The two gearbox components most affected by LoL are bearings and gears. During LoL conditions the greatest concern is scuffing/scoring producing excess heat buildup at the contact surfaces, locally weakening the material, and causing local yielding or structural failure. Lots of design/analysis effort goes towards addressing this issue. The overheating problem can be especially difficult with the bearing inner race surfaces and rolling elements since they have very limited conductive heat transfer ability to surrounding structures. The outer bearing races are usually not an issue since they are in contact with large/cooler housing structures.

The one advantage I can see with the split torque design vs the improved planetary in terms of LoL performance is elimination of the highly loaded planet gear bearings. These planet bearings are mounted in a rotating carrier structure and are fairly well thermally isolated. On the other hand, all the gearshaft bearings (outer races) in the split torque design are mounted in fixed structures with good conductive heat transfer paths.

Designing a helo MRGB to provide the necessary operational capability under LoL conditions is no simple task. It involves expertise in heat transfer, metallurgy, tribology and kinematics. Things would also be much easier if weight wasn't such a big concern.
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Old 20th Oct 2015, 14:26
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RR, good summary.

Sikorsky designs in particular tend to utilize numerous tapered roller bearings, which seem to be rather intolerant of insufficient lubrication relative to non-tapered versions.
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Old 20th Oct 2015, 17:06
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John, I know "Sultan" well, in spite of his on line bluster, he is really a fine person, and quite knowledgeable within his particular field,, which has nothing to do with the care and feeding of propulsed, rigid coaxial rotors. Like some folks, anonymity helps increase his expertise, confidence and self-aggrandizement.

He is not qualified to make about half the pronouncements he makes.
Regarding the Sikorsky rigid coaxial designs that are revolutionizing helicopters, he has no practical knowledge at all. Like Percival Lowell's intricate maps of Martian canals, Sultan's intricate pronouncements on details of Raider or Defiant will prove to be pure bull.
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Old 20th Oct 2015, 18:33
  #124 (permalink)  
 
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Sultan, Taxpayers and Structure

Actually, Nick, I was interested in what " structure " ( that you single handedly got Bell to build ) could possibly lead to dissatisfaction by both Sultan and the taxpayers. The post by IFMU and link make it sound like a very overdue project to provide more modern and industry competitive facilities for the Bell employees. Good for Bell, one would think. So, I remain interested in the explanation.

John
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Old 20th Oct 2015, 19:22
  #125 (permalink)  
 
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I would assume he was referencing the high whirl tower at the XworX facility that has seen less use than anticipated.
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Old 20th Oct 2015, 21:05
  #126 (permalink)  
 
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Xworx

Some background:
Xworx
Could it be that Sultan is implying the whole Xworx business unit is not performing?

SLB
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Old 20th Oct 2015, 21:58
  #127 (permalink)  
 
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Perhaps we might get a HUMs expert to investigate the vibrations emanating from a set of Lips down in Texas.....as there must be a pair fluttering at an awful rate.
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Old 22nd Oct 2015, 00:09
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Sikorsky designs in particular tend to utilize numerous tapered roller bearings, which seem to be rather intolerant of insufficient lubrication relative to non-tapered versions.
What you note about tapered roller bearings is essentially correct. The sliding contact between the inner race shoulder and roller end faces generates quite a bit of heat, especially on high speed shafts. The main reason a pair of tapered roller bearings might be used to support a spiral bevel pinion is because it is attractive from a weight and packaging standpoint.

In the AHS paper I linked there is a table (table 7) showing scoring results from the trade study Sikorsky conducted comparing split torque and improved planetary designs. For the "technical risk - oil out" attribute, the split torque design scored 7.5/0.75 (raw score/weighted score) and the improved planetary design scored 5.0/0.50. A raw score of 10.0 is best and 0.0 is worst. So based on the results of this trade study Sikorsky seems to conclude the split torque design is superior overall to the improved planetary design in LoL performance.

One other interesting thing I noted about both designs described in the Sikorsky trade study was that they appear to use a duplex angular contact ball bearing/cylindrical roller bearing arrangement to support all of the spiral bevel pinons, rather than a pair of tapered roller bearings. The 3 bearing arrangement is larger, heavier and more expensive than a 2 bearing (tapered roller) arrangement, but it should perform better in LoL conditions.
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Old 22nd Oct 2015, 13:50
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In that case, it would certainly appear they have heeded some lessons learned, which is a good thing.

One wonders if this sort of change was working it's way into the S92 IDMGB before it essentially vanished.
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Old 25th Feb 2016, 21:25
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From Avweek:

There are two industry-funded Raider prototypes. The first took to the air in May 2015 and is being used for envelope expansion.
What envelope expansion?

The Sultan
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Old 26th Feb 2016, 14:07
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Does anyone know if the 2nd ship has even flown yet? I cant imagine SALMC (did I get that right?) would not be shouting it from the mountaintop like the 1st flight from nearly a year ago.
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Old 28th Feb 2016, 06:48
  #132 (permalink)  
 
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Hilife

Sikorksy's PR dept would put out a glowing release if they hovered again with increased tire pressure. No press release at HAI would tell the tale. Maybe they will actually have one. Whatever they do the 97 is too late to fix any issues with the Defiant.

The Sutlan
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Old 29th Feb 2016, 02:33
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Sikorsky is going through a change in ownership, and the S97 project is internally funded. So it would not seem unusual for the project to be idled until the business situation at Sikorsky is all ironed out.

Sikorsky also has its hands full getting the SB-1 flight demonstrator ready for testing by mid-2017. They are under contract to fly this JMR aircraft, so it would have priority over the S97 project.
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Old 29th Feb 2016, 13:33
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However, Sikorsky claims S-97 is risk reduction for SB-1.

Only thing that is certain about the Defiant is that it appears to be a full year behind the Valor from a schedule standpoint.

Thus one would imagine they would be flying the pants off the S-97 as risk reduction since it has been "complete" (or so we were led to believe) for over a year.
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Old 1st Mar 2016, 21:33
  #135 (permalink)  
 
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From Sikorsky reports progress with demonstrators:
Since its first flight in May last year, the S-97 has performed a number of flights, including one on February 4 ... Sikorsky is planning up to 60 hours of flight tests on the aircraft for 2016.
I/C
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Old 1st Mar 2016, 23:08
  #136 (permalink)  
 
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IC

So did announce at least another flight that's good. The wording suggests they are still getting a handle on hovering and air taxing.

Interesting in less time the Bell 525 privately funded with FBW has surpassed 200 it's, and it can actually carry a meaningful load.

The Sultan
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Old 2nd Mar 2016, 00:57
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In the past two weeks the Army has issued RFI's for the FVL small variant (CS1) and medium variant (CS3). Definitely worth a read. Some of the desired capabilities are interesting. For example, the small variant RFI (CS1) lists "5.1.9. Aerial refuel capable."

Sikorsky definitely has put themselves in a good position for FVL so far. They now have the massive resources of L-M available, and they have two related flight demonstration aircraft efforts with S97 and SB-1 (JMR TD). Most likely SB-1 & Bell's V-280 will be parked after the test phase of JMR wraps up at the end of FY19. But probably the most important benefits to Sikorsky from the S97/SB-1 programs are a greatly increased technical knowledge base of their concept and an established team of suppliers for all critical subsystems, which will be invaluable for their FVL effort.
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Old 3rd Mar 2016, 19:04
  #138 (permalink)  
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FVL Crystal Ball

Riff-Raff,

The LM Sikorsky & Boeing team are very well positioned both politically and with legacy products. But technically?there is not enough accumulated flight hours to really claim anything. Especially reduced development risk.

After FVL, the Defiant may very well be parked. But the Valor is already being marketed by Bell as a low cost alternative to the V-22. And based on the commercial 525 FBW technology and manufacturing experience, Bell is well positioned to control costs.

My crystal ball sees the Valor flying in 2017 and the Defiant being 6 months to a year late. This will not matter to the US Army because they will move the first flight requirement date to keep the Defiant in play.

As the Army conducts a decade long evaluation, Bell will obtain Valor buys from the USMC, USAF and foreign military buyers. Because the aircraft is heavily based on commercially developed technology, export restrictions are not an issue.

Meanwhile using their enormous political clout, the Army will continue to fly Blackhawks and Apaches for another 40 years.

As far as the Scout mission? Armed UAVs and legacy platforms will be the choice for cost.
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Old 5th Mar 2016, 05:54
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CTR- I agree that Bell was smart to place a big emphasis on cost reduction with their V-280 design. Things like a non-tilting engine and a straight, single piece wing structure reduce both manufacturing and maintenance costs. I also think tiltrotors are likely the best approach for most of the FVL requirements.

However, there are still a couple other potential contenders for FVL besides Bell and Sikorsky. Airbus Helicopter with their compound concept is one example.
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Old 6th Mar 2016, 20:28
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What is the S-97 mission?

I ask this question seriously, without any bias. Can any experienced Army pilots explain what old, new or future role the S-97 would fill?

The OH-58 was old and under powered. But it was cheap and reliable.

The Army also is dumping all their TH-67 trainers. Stating all future platforms will be 2+ engines. The S-97 is single engine in a platform that will cost an order of magnitude more than an OH-58.

Will appreciate an explanation that makes sense.
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