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S97 Raider

Old 8th Oct 2015, 01:42
  #101 (permalink)  
 
Join Date: Dec 2000
Location: Arlington, Tx. US
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Actually I think Sultan is suffering from a case of Intellectual Penis Envy
Sasless

You know how those with the biggest gun are compensating for private part issues. Well anyone driving by south Arlington on I-20 can see the structure Nick had built for his ego for an significant cost to Bell and the taxpayers. Some day it will be torn down never being used. Nick does know how to spend money. When at Bell these expenditures had near zero return.

The Sultan
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Old 8th Oct 2015, 02:12
  #102 (permalink)  
 
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from riff-raff

A week article today reported S-97 program manager statement that flight testing is being halted again for another 9 to 12 weeks. Reason is to wait for more hours to be accumulated on the gearbox test stand units.
Riff this is a very wise move especially after the CH-53K transmission embarrassment. Not sure what the issue would be to keep them from doing moderate 60-100 knots flights, after being released for flight, while isolating problems before pushing to the higher load maneuvers.

The Sultan
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Old 8th Oct 2015, 03:08
  #103 (permalink)  
 
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Nick's Building

And what is the building all about, Sultan? Design Spaces? Test Labs/Rotor Test Stands?

John
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Old 8th Oct 2015, 03:27
  #104 (permalink)  
 
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Sultan's Ego perhaps....if it can be squeezed into the building.
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Old 9th Oct 2015, 00:18
  #105 (permalink)  
 
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Riff this is a very wise move especially after the CH-53K transmission embarrassment.
The 53K MRGB is also a fairly complicated design, but in a different way than the S-97 MRGB. The 53K has three engines driving a single main rotor, while the S-97 has a single engine driving two main rotors.

I would not necessarily consider the development problems with the 53K MRGB an embarrassment. It is a (12 way) torque split configuration designed for very high power (>16,000hp) and low specific weight (over 500lbs less than planetary config). Torque split designs are notoriously difficult to get right because the multiple load paths present a very complex analysis case. The 53K MRGB relies on torsionally compliant quill shafts and precision assembly to provide the required balance of torque distribution among 12 pinions driving the bull gear. Anyone that has experience working with this type of gearbox would agree that getting the torque balance correct requires a detailed analysis effort plus several cycles of bench test/design modification.

The only reason Sikorsky might have to be embarrassed is if they failed to fully appreciate the level of development effort this type of gearbox has historically been shown to require. I also would have expected NAVAIR to foresee these kinds of development issues. NAVAIR has some very competent people and have lots of experience in this field.
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Old 13th Oct 2015, 15:49
  #106 (permalink)  
 
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Originally Posted by riff_raff View Post
The 53K MRGB ... It is a (12 way) torque split configuration designed for very high power (>16,000hp) and low specific weight (over 500lbs less than planetary config). Torque split designs are notoriously difficult to get right because the multiple load paths present a very complex analysis case. The 53K MRGB relies on torsionally compliant quill shafts and precision assembly to provide the required balance of torque distribution among 12 pinions driving the bull gear. Anyone that has experience working with this type of gearbox would agree that getting the torque balance correct requires a detailed analysis effort plus several cycles of bench test/design modification.
If you compare it to the 53E main gear box, is it an order of magnitude more difficult or within the same order of magnitude in difficulty ... given the weight target?
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Old 14th Oct 2015, 01:54
  #107 (permalink)  
 
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I would not consider the split torque design to present an "order of magnitude" greater difficulty than that of the CH-53E. However, simply growing the existing CH-53E configuration to accomodate a 30% increase in power presented some serious design challenges, even without weight concerns. The 53E MRGB uses a spiral bevel 1st stage and planetary 2nd/3rd stages. Early in the 53K program NAVAIR asked Sikorsky to perform an MRGB trade study comparing an improved planetary design to a split torque design. NAVAIR wanted to determine if the advantages of the split torque configuration were enough to justify the greater development risk. Among the advantages provided by the split torque configuration were lower weight, more space for increasing the main rotor shaft diameter, and a more efficient main housing structure.

If you are interested in reading more about the 53K MRGB design trade study work done by Sikorsky, there is an excellent AHS technical paper from 2008.
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Old 14th Oct 2015, 14:47
  #108 (permalink)  
 
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Originally Posted by riff_raff View Post
I would not consider the split torque design to present an "order of magnitude" greater difficulty than that of the CH-53E. However, simply growing the existing CH-53E configuration to accomodate a 30% increase in power presented some serious design challenges, even without weight concerns. The 53E MRGB uses a spiral bevel 1st stage and planetary 2nd/3rd stages. Early in the 53K program NAVAIR asked Sikorsky to perform an MRGB trade study comparing an improved planetary design to a split torque design. NAVAIR wanted to determine if the advantages of the split torque configuration were enough to justify the greater development risk. Among the advantages provided by the split torque configuration were lower weight, more space for increasing the main rotor shaft diameter, and a more efficient main housing structure.

If you are interested in reading more about the 53K MRGB design trade study work done by Sikorsky, there is an excellent AHS technical paper from 2008.
Many thanks, riff raff, this is the kind of post one comes to PPRuNe for. Thanks also for the link.
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Old 15th Oct 2015, 23:39
  #109 (permalink)  
 
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Lonewolf_50- Just a couple final comments regarding the challenge of designing a split torque gearbox.

First, back in 2003 under the AATD RDS-21 program, Sikorsky demonstrated they could get load sharing within 1% in a split torque gear drive using their torsionally compliant quill shaft concept (somewhat similar to what is used at a larger scale in the 53K MRGB). I can tell you from experience that getting load sharing within 1% in any split torque gear drive is pretty impressive. Apparently they were not able to achieve anywhere close to the same result with the 53K MRGB in testing, since they are currently going thru a major redesign. In fact, I would speculate the bull pinion load sharing variation they saw in bench testing of the 53K MRGB was much more than "an order of magnitude" greater than 1%. In my opinion, even a 10% variation in load sharing between the 12 bull pinions would be quite acceptable.

Second, in case you don't get your hands on a copy of the AHS paper I linked, here's the most interesting quote:
"Summary and Conclusion A trade study on two different design configurations of the CH-S3K main gearbox, a new split torque MGB vs. an improved planetary MGB, was performed. The three focusing parameters of the trade study include performance, cost and risk. The advantage and disadvantages of both design configurations were thoroughly studied. The geartrain systems, mounting bearings, and supporting housings of the two different MGB‘s were designed and analyzed for detailed weight calculations. Results of the trade study are summarized below.
1.The split torque MGB design has a significant weight saving (more than 500 lbs) over the improved planetary.
2. The Split torque MGB can save millions of dollars per aircraft in total cost which includes development and production cost.
3. The Split torque design bears slightly higher risk than the improved planetary design due to Sikorsky’s lack of production experience in split-torque gearboxes. But the risk-reduction test of the quill shaft lowered the risk level of the split-torque MGB to the same level as that of the improved planetary.
In conclusion, the split torque main gearbox is a better design and was chosen for the new CH-53K."
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Old 16th Oct 2015, 13:24
  #110 (permalink)  
 
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Originally Posted by riff_raff View Post
Second, in case you don't get your hands on a copy of the AHS paper I linked, here's the most interesting quote:
All that link got me to was a cover page. Thanks for the meat and potatoes summary.
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Old 16th Oct 2015, 14:17
  #111 (permalink)  
 
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I'm wondering if there are any implications for LoL situations with a split torque design
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Old 17th Oct 2015, 22:40
  #112 (permalink)  
 
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Lonewolf_50- here's a later AHS paper on the same subject if you want to spend $30.

https://vtol.org/store/product/load-...arbox-2474.cfm
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Old 19th Oct 2015, 01:35
  #113 (permalink)  
 
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John D

I never said building, that would at least be useful for storage.

The Sultan
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Old 19th Oct 2015, 11:00
  #114 (permalink)  
 
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AUSA Interview

AUSA 2015: Sikorsky?s big plans for Raider (video) - News - Shephard

Interview with Sikorsky at AUSA on the S-97. Not very impressive. The one guy did not get the script, he went beyond the vague press release and stated they got to only 20 knots in forward flights instead of putting no number on it so people could dream of higher speeds.

The other amazing thing stated was the SB-1 would benefit from the S-97 testing. Short of the 97 already uncovering a major design flaw (which is plausible based on the stagnation of the test effort) the SB-1 design is fixed by now. One year ago, at the original schedule, the 97 may have had an impact, but not now.

The Sultan
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Old 19th Oct 2015, 13:28
  #115 (permalink)  
 
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Originally Posted by SansAnhedral View Post
I'm wondering if there are any implications for LoL situations with a split torque design
Loss of lubrication in any gear box is going to have implications. I wonder if they are using ISF (a super-finishing process for gears) as an alternative design strategy.
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Old 19th Oct 2015, 20:06
  #116 (permalink)  
 
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Did the VS300 and R4 have any impact? Of course not, they were Sikorsky machines, right? I thought it was a great interview and video, thanks for the link!
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Old 19th Oct 2015, 20:09
  #117 (permalink)  
 
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Building/Structure

You are correct, Sultan, you used the term " structure ".

My question remains as posed. Just imagine I had used " structure " instead of " building ".

John
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Old 19th Oct 2015, 21:04
  #118 (permalink)  
 
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I am also Curious. What is this self-aggrandizing structure? Perhaps someone could post a photo of it.
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Old 19th Oct 2015, 21:58
  #119 (permalink)  
 
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http://www.bizjournals.com/dallas/news/2014/04/07/a-look-inside-bell-helicopters-new-corporate.html

Perhaps this is what sultan speaks of. Looks ok to me.
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Old 20th Oct 2015, 00:00
  #120 (permalink)  
 
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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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