Sikorsky + Boeing pitch ‘X-2’-based design for US Army JMR TD effort

[SansAnhedral]

I should qualify that thick roots are not necessarily penalizing due to reverse flow, but with a typical helicopter the thick root would likely see closer to zero flow on the retreating side (and subsequent lower drag). They basically add to the overall rotorhead effective area.

Also, ever wonder why Sikorsky never got the rotor fairings to work? Those were one of the trumpeted key differentiators to making X2 an improvement over XH59A.

Symmetrical airfoils help with profile drag to a degree, but the drag is primarily driven by overall thickness and chord length.

And yes, TPP is driven by flapping at high speeds. Im sure Sikorsky would gloss over the fact that their speed is a "dash" straight line capability, as even with the X2 I would be very wary of trying a 1G pullup or bank at speed. Let's hope they dont want to try NOE flying or SAM evasion!

On any rigid rotor the flapping and coning values are going to be relatively low (hence the higher loads). That said, can you build a blade that can accommodate these loads at a large rotor radius that:

Doesnt weigh an astronimical amount
Is stiff enough to keep flapping under control with rotor spacing that keeps hub drag low enough to hit high speeds
Does not overload the hub attachment/components with beam/chord loads and mast with hub moment
Is dynamically tuneable

The answer to this is yes for small-ish GWs. Current composite materials allow for a solution to this equation, but not for the elevated loads of a 24,000 lb FVL-M demonstrator.

[IFMU]

At the AHS talk IIRC they said they didn't fly the fairings because they had already met the goals and the company objectives moved the focus to raider. I believe they also said they would expect a speed increase of15 kts, same increase as documented here:
Sikorsky X2 Hits 250-knot Target, Setting New Record | Aviation International News

It would be odd if they designed for 1G at 250 S&L. That would be dangerous. Would a big company like Sikorsky really take a risk like that?

Can you publish the math that says 12K lbs is the limit? Or will you get in trouble with work? In case you work at Sikorsky, I don't know.

Bryan

[SansAnhedral]

Still have yet to hear an explanation as to why the fairings never made it on the aircraft from the onset.

1G was a swag number, I was attempting to illustrate any given substantial maneuver on a coax (i.e. not specifically X2 either).

The point remains; what is the effect of maneuver loads and flapping at speed? Sikorsky has been remarkably silent on this point.

I am not sure what you mean by "the math" regarding a GW limit. We are dealing in pure hypotheticals here, unless you want to dive into the strains on specific blade designs, chord loads, tuning profiles for given stiffnesses, t/c etc. Suffice it to say, the idea of rigid rotors has long been abandoned for large rotorcraft for these very reasons.

To demonstrate "the math" would be an exercise in full-on rotor design, hardly what I was trying to do here. Merely an observation that I dont think a large GW ABC coaxial ship is remotely feasible, and its awfully telling that suddenly the S-97 is going to be leveraged by Sikorsky as a demonstrator for an aircraft that seems technically impossible to actually build at the current time.

The term bait-and-switch comes to mind. I am sure that Sikorsky is doing this for one of 3 reasons:

• Kill FVL entirely
• Drive the FVL requirements to a much smaller aircraft
• Drive the FVL requirement to a much lower speed

[Set1SQ]

Sans - Your 3 reasons are interesting. Occam's Razor says there may be a simpler explanation. Given that 3 fairly reputable, experienced, high integrity organizations are willing to invest more than $100M each in the JMR TD, maybe they genuinely believe it scales up. Why would Boeing abandon the tilt rotor otherwise? It will be interesting to see how things play out. I am hoping that the FVL is a desperately needed opportunity to take an important step forward. I applaud all of those who are engaged in advancing rotorcraft technology.

[riff_raff]

Patent for Karem's tilt-rotor blade root:

https://docs.google.com/viewer?url=p.../US7972114.pdf

[IFMU]

So rather than doing "the math" we have an off the cuff generalization that says it won't scale up. Sikorsky therefore has either done an off the cuff generalization that says it is good, and they are wrongly proceeding, or they have done a rotor design that says it is good, and they are proceeding, or they have done a rotor design that says it is bad, and are proceeding anyway as a way to perpetuate the Blackhawk indefinitely.
Bryan

[SansAnhedral]

Originally Posted by Set1SQ

Given that 3 fairly reputable, experienced, high integrity organizations are willing to invest more than $100M each in the JMR TD

The JMR TD paper proposal did not cost $100M. Sikorsky basically confirmed they were going to fly the essentially-existing S-97 as the demonstrator, despite it clearly being far undersized for FVL-M. The S-97 was built to answer a call the government never made for AAS (a high speed scout), and its usage for FVL means that they and their partners dodge the bullet of having to spend the money ($100M) on a dedicated JMR-TD aircraft...and also dodge the bullet of having to actually build a working large scale ABC rotor.

If I was AATD, I would tell them to put their money where their mouth is and not provide the government offset money unless they build the proper tech demonstrator for the contract at hand.

Originally Posted by Set1SQ

Why would Boeing abandon the tilt rotor otherwise?

Because they are in the same boat as Sikorsky. They have a current revenue stream with the Apache, like Sikorsky, and not much incentive to supplant that with a new aircraft with potential profit-sharing with another OEM.

Originally Posted by IFMU

So rather than doing "the math" we have an off the cuff generalization that says it won't scale up.

Um, yes. This is PPRuNe, not Wolfram Alpha.

Nevertheless, what you discount from me as "off-the-cuff" is precisely the same amount of information that Sikorsky/Boeing have historically presented to indicate that a large scale ABC rotor is feasable. Your argument seems to be "Well they are big companies with smart people, so I am sure there is a way". (Note: I remember back at AHS circa 2005 or so watching as the design chief of Kamov bureau stood up while Steve Finger was presenting on the X2, and basically chastised them for pursuing the idea of a scalable ABC.)

Well, you have chosen to ignore that same sentiment when it comes to the true occams razor....Sikorsky and Boeing are very smart...and they know exactly what they are doing.

They are acting on the calculated risk that the Army will conclude (with their input, of course) that the JMR aircraft with its requirements is too expensive. When that happens, they will have sunk the least amount of investment by having flown the S97 as their demonstrator, while simultaneously having avoided or at least delayed having to tip their hand that the tech does not exist to build a high speed large scale ABC yet.

We will all see in time, obviously.

[IFMU]

I believe Mr. Tischenko didn't challenge the scalability, just the viability of the whole project:

There were some interesting sidelights: the legendary Marat Tischenko, head of Mil under the communist USSR rose to his feet to challenge Finger on making ‘a mistake’ by selecting the co-axial design.

Good comment about pprune vs Wolfram Alpha, I liked that. Also I agree, we will see in time.
Bryan

[SansAnhedral]

Ah good catch, my initial recollection was that he was from Mil, but for some reason I thought Kamov due to their historical experience with coax.

[IFMU]

Perhaps Mil and Kamov argue like Bell and Sikorsky! Would be hard to imagine a Kamov guy saying bad things about a coax.

[Ian Corrigible]

The big question remains how large X2 technology can be scaled up to. Sikorsky itself admitted that the concept has sizing limits, but will FVL fall within its sweet spot? As previously covered, the FVL mission set may drive a platform closer in size to the CH-47 than the UH-60, so where does the "medium class" end?

I/C

[Dave_Jackson]

IFMU said;

So rather than doing "the math" ........

No math ~ honestly;

Sikorsky's electric Firefly was a much publicized project.
You may recall the two page Vertiflite article, by the new head of Sikorsky R&D, where he extoled the department and its accomplishments.
Buried in the article was a single sentence mentioning the Firefly's demise.

OK a little math;

$5,000,000,000.00.
It had to do with an earlier project called the .. ..Tonto???

Dave

[Ian Corrigible]

Now officially the Sikorsky Boeing SB>1 Defiant.

Which, given that Bell has already taken "Valor" for the V-280, leaves the AVX and Karem PR teams to choose between "Get Some," "Hooah" and "Balls of Steel" as the names for their JMR TD offerings.

I/C

[SansAnhedral]

SB>1?

Assuming SB is Sikorsky-Boeing

What is with the ">" ???

[Ian Corrigible]

The Stinson family must have a good attorney.



I/C

[SansAnhedral]

Perhaps Gene Roddenberry's estate made out well





Not exactly militarily unique

[horlick97]

The largest helicopter in production by the western world is the Sea Stallion. It employes the typical configuration of having a single main rotor with a tail rotor for counter torque.

The next biggest is the Chinook. It uses the tandem configuration. Due to this, it does not need a tail rotor for counter torque. A key advantage of this configuration is that all of its power can be used to generate lift and forward thrust.

My question, why was the larger helicopter like the Sea Stallion not based on the tandem configuration? Would it not be a relatively simple up scaling of Chinook to achieve the dimensions and lifeting capacity (or in fact more, due to the savings from not requiring the tail rotor) provided by the Sea Stallion?

Thanking you in advance for all your expert input.

[The Sultan]

Horlick

For boat based vertical lift rotor turnings deck length must be kept to a minimum. Tandems have largest lb per deck length. Also one round through the interconnect shaft on an intermeshing rotor is normally catastrophic as the rotors destroy themselves.

The Sultan

[riff_raff]

Sikorsky looks to be making good progress with their S-97 demonstrators.

While the X2 technology may present some performance limitations for the heavier JMR configurations, Sikorsky will definitely benefit in several ways from this S-97 flight demonstration program. They are demonstrating the capability to design and build a high-quality TD aircraft in a reasonable amount of time and budget. The S-97 TD effort also serves nicely as "practice" to work out any issues with partners they will team with on JMR. Flying the S-97 TDs also reduces the perceived level of technical risk for the X2-based JMR candidates. And we all know how risk-averse the US DoD can be when it comes to large production aircraft programs. Lastly, successful flight testing of these S-97 TDs will likely attract substantial interest from foreign customers. So the S-97 may turn into a production program even if the X2-based concept is not selected for the final JMR design.

[SansAnhedral]

Flying the S-97 TDs also reduces the perceived level of technical risk for the X2-based JMR candidates.

Sikorsky will do their best to use the S97 as a flying billboard for the FVL X2 based technology, despite the fact that scaling issues are unavoidable, and I maintain that the demonstration of yet another light gross weight ABC vehicle does nothing to mitigate the risks associated with the technical barriers to building a significantly larger version of the ABC rotor.

I would hope that the Army is astute enough not to drink the kool aid.