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

http://www.flightglobal.com/Assets/G...x?ItemID=49748

Link to FG article: Sikorsky and Boeing to pitch

Who will be the other contenders: Bell, Eurocopter, Agusta-Westland? A combination (AW101 and X3) could give a nice blend.

I'm boarding the plane to Vegas for HAI tommorrow and gotta do some business with Sikorsky so I'll pick up a brochure or so (if they have one for this :) )

Cheers

X2 on Static Display
 

Anyone heading for the Honda Classic at the PGA Resort in Palm Bch Gardens can catch the real X2 flying prototype along with an S-97 mockup parked near the end of the " Beartrap" at the 17th green.

In other news, supplies of unobtanium will be running short as Sikorsky will be buying the remaining quantities to construct high-hinge offset infinitely rigid closely-spaced blades at large spans which will not deflect and experience tip path plane convergence.

Curious to see if this is a serious endeavor, or just an obvious effort to dog-and-pony-show FVL and instead sell more UH60X and AH64X ad infinitum. Boeing and Sikorsky already have a revenue stream with those models.

A more extensive article on the topic.

Sikorsky, Boeing Team to Offer Next Generation Medium Helicopter to the US Army | Defense Update - Military Technology & Defense News

It seems two design will be selected for initial evaluations and prototyping. The big questions seems to be who will become the second contender and with what design.. I has to be a 30.000 lbs machine, so bigger the e.g. the Raider that will fly next yr.

Eurocopter seems the 800lbs Gorilla in the industry at this moment. But maybe they'll skip this one, being busy with X4, X6, X9 and X3 technology development.

There was a THT program with Boeing but I haven't seen any recent news on it since Sept '12..

http://www.shephardmedia.com/static/...pt__valley.jpg

4 bladed Chinook.

Fantasy or the next step forward for that design?

"We need to go back, Marty...back to the future!"

http://gunsagogo.org/347~turn.jpg"

I/C

It seems the european requirement is large cabin, significant larger then e.g. CH53 to move serious vehicles.

http://i49.servimg.com/u/f49/11/29/05/29/pub_ht11.gif

On the top end, the old Chinook configuration still seems pretty unbeatable in terms of combined payload, volume, simplicity, cg tolerance, speed..

ILA 2012: Eurocopter carrying out risk-reduction research on Future Transport Helicopter - News - Shephard

Now that Boeing is joining Sikorsky I wonder what Eurocopter will do..

CG Tolerance
 

Keesje,

A lot of people have fallen for the "obvious truth " that the tandem rotor machine will always have a huge advantage in allowable CG range.

What a surprise ( to some, not all ) when the US Special Ops community initiated the MH-60 and MH-47 aircraft. Comparing both at their max weights, one found that the MH-60 had either equal or a tad more ( I cannot recall which, but it was certainly not less ) CG range. I think if you look at the 53E and 53K, and compare to the latest 47 models at max weight, you"ll find approximate parity.

Awaiting a response from SAS, to the effect that: " We'll, SA, you finally woke up and canted the tail rotor 20 degrees, now if you went the extra 70, you'd really have something! ". I might have mentioned that some years ago, in discussion after his presentation to a AHS Northeast Region assemblage, Dr. Marat Tishenko said, in response to my question as to why MIL had never flown a canted tail machine, that " we never could figure out why in the world Sikorsky actually did that!".

US ARMY expected to announce award of Phase 1 developer of Joint Multi-Role Technology Demonstrator (JMR TD) in September

U.S. Army Set To Announce Demo Contracts For Radical New Rotorcraft | Aviation International News

All 4 JMR study participants announced.

In reality it seems to be a foregone conclusion that Sikorsky/Boeing and Bell will be awarded the flight demo contracts, since neither AVX nor Karem appear to have adequate financial or manpower resources to see the project through. Not to mention the fact that by this time next year Sikorsky's S-97 prototype will almost be ready to fly. Check out their composite airframe:

http://cmsimg.defensenews.com/apps/p...Final-Assembly

The mere idea that an S-97 is an appropriate demonstrator for an FVL contract is flat out preposterous. The ABC coaxial design simply does not scale up to the size mandated by FVL-medium and above and maintain any sort of high speed characteristics. Sikorsky knows this quite well.

The fact that Sikorsky (and now additionally Boeing) truly are moving forward under the guise of leveraging what is a lame-duck S-97 aircraft, provided that AAS funding is indeed cut, for their FVL demonstrator is essentially confirmation that they are merely trying to kill the FVL program entirely and keep making money off Blackhawk and Apache variation ad infiniteum.

How do you know this?

An over-simplified explanation (hinted in post #4 above):

• Cruise speed is driven primarily by profile drag at these velocities
  
• ~40% of rotorcraft drag is driven by hub area
  
• Hub area is directly related to rotor spacing on a coax
  
• Rotor spacing is a function of tip path plane deflection (flapping & coning modes)
  
• Tip path plane deflection is driven by rotor and blade stiffnesses (in steady level flight...recall even on X2, Sikorsky never published TPP clearances under high speed maneuver loads!)
  
• An increase in GW to FVL medium size will require a larger rotor radius to maintain disk loading and hover performance
  
• Rotor radius and GW drives loads exponentially, thereby necessitating a reduction in stiffness with current (even experimental) materials
  
• Reduction of stiffeness yields an necessitated increase in rotor spacing

I believe the upper bound of the ABC concept, barring the discovery of unheard-of-strong unobtanium composites, is in the area of 12,000 lbs (and none of this is to speak of the dynamics concerns of the higher GW rigid rotor).

My suspicion is that Sikorsky has not found the magic bullet to allow the scaling of this concept above this size due to some of the political maneuvers they have made in the past few years (i.e. recall ~2005 they used to heavily market very large X2-based machines for JHL and other studies which has all completely ceased). It was always claimed that ABC scaled up...and it does! Aerodynamically

All that said....I am sure that companies like Lord or Moog are desperately working closely with SAC to find a workaround, perhaps some active mass-shifting mechanisms in the blades to alleviate some of the loads. But I am highly suspect they have come up with anything concrete, or feasable.

As helicopters get bigger, do the blades get thicker? Does this affect stiffness? I don't see that in your figuring.
Bryan

Actually, thats part of the entire equation. Structurally, blade "thickness" is a result of stiffness targets and material capabilities.

Generally low speed helicopters live with blades designed to be relatively "fat" near the root section since the velocities there are low. Overall profile drag losses on the blade (a big deal in high speed craft) are predominantly defined by the thickness/chord ratio. So aerodynamically, blade thickness contributes to rotor efficiency and cruise speed.

If you had to accommodate the large loads involved with a scaled up aircraft, thickening up a blade is especially penalizing on the ABC concept because the root section experiences reverse airflow on the retreating side and high free stream velocity on the advancing side (in addition to overall drag increasing for the rest of the blade).

In addition, if you are driven to thicken your blade so much to withstand these high loads, you will likely find yourself with a rotor that no longer will dynamically tune, as it will constantly be raising these frequencies with stiffer blades. Not to mention huge weight penalties.

What most people fail to realize is that you cannot simply increase stiffness infinitely to solve problems, as you will possibly detune the rotor and create a rotor that will destroy itself with any destabilizing maneuvers or even gusts.

This is a very similar situation seen on Abe Karem's paper airplane Optimum Speed Tiltrotor. Except it's an even worse dynamic situation in a pylon/wing mounted rotor.

With a rigid rotor approach, there are definitely some serious blade root structural issues to deal with. And the only practical way to address these huge flap/lag moments is by increasing the section area of the blade root and the structure of the hub attachment.

Of course, the high speed drag issues created by fatter blade roots and hubs is less of a problem with a tilt rotor aircraft like Karem's.

Thats debatable, in airplane mode on a tiltrotor, a high t/c ratio becomes more frontal area profile drag and essentially equivalent to a much larger spinner....all of which put a cap on Vmax. It would be tough to qualitatively determine which design paradigm takes a greater "hit".

But Karem's main problems are weight and tuning.

In the un-simplified version of your analysis, are differential controls for controlling lift offset factored in? They are mentioned here:
https://vtol.org/download.cfm?downlo...dname=filename

I saw Mr. Walsh present this paper, I think it was 2011.

They also show southwell plots and tip clearance in level flight. What do you think will happen as maneuver loads are added in?

Also you mention that thick roots penalize ABC concept aircraft because of reverse flow. The pictures I have seen, from the USPO and shown on Dave Jackson's unicopter site show a symmetrical root end. Will that care if it is in reverse flow or not?
1465

Bryan

Figure 9 in Mr. Walsh's paper shows rotor power as zero, plus or minus, at speed. Would this not make TTP a function of only flapping at high speed? Also, do you think the rotors will cone together at low speed?

Bryan

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.

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

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

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.

Patent for Karem's tilt-rotor blade root:

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

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

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.

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.

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. http://i360.photobucket.com/albums/o...tos/thpop1.gif

I believe Mr. Tischenko didn't challenge the scalability, just the viability of the whole project:
Good comment about pprune vs Wolfram Alpha, I liked that. Also I agree, we will see in time.
Bryan

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.

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

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

IFMU said;No math ~ honestly;OK a little math;Dave

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. :E

I/C

SB>1?

Assuming SB is Sikorsky-Boeing

What is with the ">" ???

The Stinson family must have a good attorney.

http://cmsimg.defensenews.com/apps/p...il-Defiant-JMR

I/C

Perhaps Gene Roddenberry's estate made out well

http://images2.wikia.nocookie.net/__...,_NCC-1764.jpg

http://upload.wikimedia.org/wikipedi...DefiantDS9.jpg

Not exactly militarily unique

http://upload.wikimedia.org/wikipedi...12_June_25.jpg

http://upload.wikimedia.org/wikipedi...ials_c1969.jpg

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.

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

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.

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.