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

[keesje]

Sikorsky and Boeing plan to submit a joint proposal to a develop and build a new prototype helicopter based on Sikorsky's X-2 high speed rotorcraft design for the US Army's Joint Multi-Role (JMR) technology demonstrator (TD) phase 1 programme.

http://www.flightglobal.com/Assets/GetAsset.aspx?ItemID=49748

Link to FG article: Sikorsky and Boeing to pitch (http://www.flightglobal.com/news/articles/sikorsky-and-boeing-to-pitch-x-2-based-design-for-us-army-jmr-td-effort-382897/)

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

[chopper2004]

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

[JohnDixson]

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.

[SansAnhedral]

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.

[keesje]

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 (http://defense-update.com/20130228_sikorsky-boeing-team-to-offer-next-generation-medium-helicopter-to-the-us-army.html)

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/images/article/188135_heavy_lift_concept__valley.jpg

[Lonewolf_50]

4 bladed Chinook.

Fantasy or the next step forward for that design?

[Ian Corrigible]

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

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

I/C

[keesje]

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 (http://www.shephardmedia.com/news/rotorhub/ila-2012-eurocopter-carrying-out-risk-reduction-re/)

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

[JohnDixson]

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!".

[Heli-News]

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

August 2, 2013, 6:00 PM

Contract negotiations between the U.S. Army Aviation Applied Technology Directorate and AVX Helicopter, Bell Helicopter and the Sikorsky/Boeing team–the potential Phase I vendors for the joint multi-role technology demonstrator (JMR-TD)–are nearing completion. Announcement of the awards for a new U.S. Army medium helicopter are planned for September, according to an Army spokesman. However, “like many other efforts, this schedule is challenged by furlough effects,” he said.

JMR is the precursor of the future vertical lift program, which has the goal of developing a series of helicopters with “leap-ahead technology” in four sizes: light scout to replace the Bell OH-58 Kiowa; medium utility and attack to replace the Sikorsky UH-60 Black Hawk and Boeing AH-64 Apache; heavy cargo to replace the Boeing CH-47 Chinook; and ultra (large) with performance similar to that of the C-130J Super Hercules. The initial focus is on the medium configuration, which represents the Army’s greatest need–some 4,000 aircraft.

U.S. Army Set To Announce Demo Contracts For Radical New Rotorcraft | Aviation International News (http://www.ainonline.com/aviation-news/ain-defense-perspective/2013-08-02/us-army-set-announce-demo-contracts-radical-new-rotorcraft)

[riff_raff]

All 4 JMR study participants announced (http://www.aviationweek.com/Article.aspx?id=/article-xml/awx_10_02_2013_p0-623233.xml).

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/pbcsi.dll/bilde?Site=M5&Date=20130923&Category=DEFREG02&ArtNo=309230013&Ref=AR&MaxW=640&Border=0&Sikorsky-S-97-Raider-Begins-Final-Assembly

[SansAnhedral]

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.

[HeliTester]

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.

How do you know this?

[SansAnhedral]

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.

[IFMU]

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

[SansAnhedral]

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.

[riff_raff]

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.

[SansAnhedral]

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.

[IFMU]

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?downloadfile=EB393010-E91A-11E0-8A940050568D0042&typename=dmFile&fieldname=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 (http://www.unicopter.com/1465.html)

Bryan

[IFMU]

Rotor spacing is a function of tip path plane deflection (flapping & coning modes)

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

[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 (http://www.ainonline.com/aviation-news/2010-09-16/sikorsky-x2-hits-250-knot-target-setting-new-record)

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=patentimages.storage.googleapis.com/pdfs/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]

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.

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.

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. http://i360.photobucket.com/albums/oo45/kelly73_photos/thpop1.gif

[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 (http://www.defensenews.com/article/20110914/DEFSECT01/109140306/X-2-Maxes-Out-Medium-Sized-Role-Sikorsky-Executive), but will FVL fall within its sweet spot? As previously covered (http://www.pprune.org/rotorheads/512284-new-bell-product-bell-v280.html#post7787468), 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 (http://www.sikorsky.com/Innovation/Technologies/Firefly+Technology+Demonstrator)was a much publicized project.
You may recall the two page Vertiflite (http://vtol.org/publications/vertiflite-magazine) 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 .. http://www.unicopter.com/Thinking.gif ..Tonto???

Dave

[Ian Corrigible]

Now officially the Sikorsky Boeing SB>1 Defiant (http://www.flickr.com/photos/theboeingcompany/10404910465).

Which, given that Bell has already taken "Valor" for the V-280 (http://www.pprune.org/rotorheads/512284-new-bell-product-bell-v280.html), 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

[SansAnhedral]

SB>1?

Assuming SB is Sikorsky-Boeing

What is with the ">" ???

[Ian Corrigible]

The Stinson (http://en.wikipedia.org/wiki/Stinson_Aircraft_Company#Stinson_SB-1_Detroiter) family must have a good attorney.

http://cmsimg.defensenews.com/apps/pbcsi.dll/bilde?Site=M5&Date=20131021&Category=SHOWSCOUT&ArtNo=310210030&Ref=AR&MaxW=300&Border=0&Sikorsky-Boeing-Unveil-Defiant-JMR (http://www.defensenews.com/article/20131021/SHOWSCOUT/310210030)

I/C

[SansAnhedral]

Perhaps Gene Roddenberry's estate made out well

http://images2.wikia.nocookie.net/__cb20090215194746/memoryalpha/en/images/f/f9/USS_Defiant,_NCC-1764.jpg

http://upload.wikimedia.org/wikipedia/en/9/97/DefiantDS9.jpg

Not exactly militarily unique

http://upload.wikimedia.org/wikipedia/en/thumb/6/6b/USS_Defiant_%28YT-804%29_returning_to_Bremerton_2012_June_25.jpg/800px-USS_Defiant_%28YT-804%29_returning_to_Bremerton_2012_June_25.jpg

http://upload.wikimedia.org/wikipedia/commons/thumb/0/08/USS_Defiance_%28PG-95%29_during_trials_c1969.jpg/745px-USS_Defiance_%28PG-95%29_during_trials_c1969.jpg

[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 (http://www.upi.com/Business_News/Security-Industry/2014/06/17/Sikorsky-powers-on-S-97-avionics/1321403016117/).

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.

[IFMU]

Perhaps the army will plot the data for the 6000 or so LB Schweizer X2 against the twice as heavy Sikorsky raider and make up their own minds.
Bryan

[Ian Corrigible]

Sikorsky-Boeing select T55 to power SB-1 Defiant demonstrator (http://www.flightglobal.com/news/articles/sikorsky-boeing-select-t55-to-power-sb-1-defiant-demonstrator-400556/)

Interesting development, given that the parallel AATE/ITEP engine development program is currently focused on the 3,000 shp class GE3000 & HPW3000. It also reinforces the point made previously (http://www.pprune.org/rotorheads/512284-new-bell-product-bell-v280.html#post7787468) with regards to the FVL's sizing.

Sikorsky looks to be making good progress with their S-97 demonstrators
...Though it's interesting that this (http://www.popularmechanics.com/technology/aviation/news/the-rise-of-radical-new-rotorcraft-16850989) article -- clearly written with the blessing of Sikorsky -- suggests that FF has slipped to 2015.

I/C

[IFMU]

I/C,
I had missed the date in the PM article, thanks. I had heard nothing but first flight this year. Usually the programs folks spin only in one direction. There was a classic AIN article that predicted an early X2 flight:
X2 could make first flight by month?s end | Aviation International News (http://www.ainonline.com/aviation-news/aviation-international-news/2007-11-26/x2-could-make-first-flight-months-end)

The actual first flight took about another 9 months if memory serves. I followed X2 avidly back then.
Bryan

[SansAnhedral]

Perhaps the army will plot the data for the 6000 or so LB Schweizer X2 against the twice as heavy Sikorsky raider and make up their own minds.


That would be prudent, provided they understand the idea of diminishing returns and non-linear relationships.

2 data points does not make a curve.

[The Sultan]

With the need to use the T55 the $ per seat mile looks to be about double an equivalent tilt rotor. I guess the defiant is as draggy as it looks and one rotor always in the dirty air of the other brings into question hovering efficiency.

The Sultan

[riff_raff]

I would hope that the Army is astute enough not to drink the kool aid.According to Defense News (http://www.defensenews.com/article/20140505/DEFREG02/305050028/Step-by-Step-US-Army-Slowly-Nears-Apache-Black-Hawk-Replacements) we should hear who the Army selects to build the JMR TDs by the end of next month.

The technical requirements for FVL would seem to favor a tilt rotor, but Sikorsky decided to go with a compound. Sikorsky is not stupid and they have spent quite a bit of time over the past 2 or 3 decades studying tilt rotors (anyone recall their VDTR concept (http://halfdome.arc.nasa.gov/publications/files/NASA-CR-2010-216384_Germanowski_final.pdf)?). If they felt a tilt rotor was a better technical approach they definitely have the expertise to design and build one. Maybe Sikorsky thinks the Army operating a large tilt rotor will create too much friction with the (fixed-wing) Air Force, so the only politically acceptable option for an Army FVL heavy configuration would be a rotary-wing aircraft.

It will fun to see what happens in a couple weeks when the TD selection is announced!

[horlick97]

Please pardon my ignorance. May I seek some help on the following:

What's the difference between X2's coaxial and AVX's coaxial?

I read that X2's rotors are rigid. Does that mean AVX's are not?

What is the implication of this difference? Is it solely limited to the separation between the two rotors?

I understand the larger the separation, the larger will be drag. But, it can't be worse off than Chinook (i.e. adjusted for similar size of the aircraft) which tendem rotors also need to be similarly separately vertically, can it?

In fact, due to the tandem configuration, the rotors in the Chinook have to be vertically separated more than if they were to be coxial (i.e. for similar lifeting capacity). This is due to the lateral geometry on how the rotors will flex. You know what I mean? Sorry I can't sketch it here.

Bottom line is, if the rigid rotors meant for the Defiant cause too much problem for upward scaling, can they be replaced by conventional coaxial rotors, or something in between, i.e. less rigidity and more vertical separation? Again, my premise is that the vertical separation can't be worse off than that in the Chinook.

Likewise, if the vertical separation of the AVX is causing to big a drag penalty, could it not add some rigidity in the rotors and reduce the vertical separation so as to reduce drag.

Isn't Defiant's and AVX's offering using the same technology along the same continuum?

Apologies if my trend of thought is confusing. Appreciate anyone's help.

[horlick97]

Another question I have is what's the difference between Defiant's forward thrust propellers and AVX's ducted fans?

Wouldn't AVX's split to two ducted fans require and additional differential/transmission which will impose weight penalty?

[riff_raff]

AVX's website (http://www.avxaircraft.com/cruise-performance) gives their side of the story on why their coaxial compound is better. Your comment about the added complexity and weight penalty of two pusher props (or fans) versus one is correct, but the weight penalty is probably not significant. The benefit of using two smaller pusher fans is that they can be located well off center and up, which allows a rear fuselage ramp door.

One thing that I suspect all of the JMR competitors have considered, both for the tilt rotors and compounds, are variable speed drivetrains. In the case of AVX their design has small forward wings. So at high cruise speeds it appears they might be planning to slow the main rotors and use the wings for added lift, while diverting a greater percentage of power to the pusher fans. Sikorsky just stated that their SB-1 JMR design will use a T55 turboshaft engine that will be modified to allow a wider range of operating speeds (probably something like 85% to 105%). So it appears Sikorsky also plans to slow their main rotors in cruise.

[SansAnhedral]

If they felt a tilt rotor was a better technical approach they definitely have the expertise to design and build one.

That is a bit of a stretch. Concept development is one thing, but expertise in helicopter design does translate especially well to the world of tiltrotors, especially in the arena of rotor dynamics.

But I think your suggestion of the political implications of a single mast un-winged craft is more to the point.

And regarding scaling:

"There is a question on the scalability on the X-2 technology at the medium class," said Scott Starrett, Sikorsky's vice president for government business development. "When you get to the utility-medium or attack-medium class, it scales nicely." However, with size and weight increases "you starting getting up to that kind of payload and physical size and it gets to be a different challenge for the technology."

For the so-called "ultra-class," which would be a vertical lift machine the size of a C-130 tactical fixed-wing transport, Starrett said that tilt-rotor technology would be the technology of choice. (http://www.defensenews.com/article/20110914/DEFSECT01/109140306/X-2-Maxes-Out-Medium-Sized-Role-Sikorsky-Executive)

So back to the entire premise of Joint Multirole - a single design paradigm spread out among different size classes. If FVL-H is out of the box for an ABC coax, how is it the technology relevant to the fundamental pursuit of the program?

[SansAnhedral]

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.

Well this certainly is interesting

Boeing proposes high-speed Apache, heavier Chinook - 6/26/2014 - Flight Global (http://www.flightglobal.com/news/articles/boeing-proposes-high-speed-apache-heavier-chinook-400777/)

[henra]

I understand the larger the separation, the larger will be drag. But, it can't be worse off than Chinook (i.e. adjusted for similar size of the aircraft) which tendem rotors also need to be similarly separately vertically, can it?


Tandems don't have to be vertically separated. In certain (most) flight regimes the Chinook blades will be intermeshing. Due to axis Offset the tips will be moving in the same direction where they intermesh. In a Co-ax they will only intermesh once and that only very briefly...
Plus the Chinook wasn't designed primarily for all out speed.
So no comparison here.

[riff_raff]

Sans- Thanks for the article link. As the article stated the Army would like to see some of the technologies being studied under JHL/JFTL/JMR make their way onto existing platforms since these aircraft will remain in service for many more years.

During the JHL program Boeing was given a $3.4M study contract for their Advanced Tandem Rotor Helicopter (http://www.gizmag.com/go/4646/) concept, which was basically an improved CH-47. There were also spin-off efforts from JHL such as FARDS and ARCD. Sikorsky got one of the ARCD contracts for a vibration reduction system and just announced some results of testing on a Black Hawk (http://www.army-technology.com/news/newssikorsky-lord-test-hmvs-technology-on-us-army-black-hawk-helicopter-4273263). Bell signed a $30M contract for a FARDS program (http://investor.textron.com/newsroom/news-releases/press-release-details/2010/Bell-Helicopter-and-US-Army-Sign-Cooperative-Agreement-to-Develop-Drive-System-Technologies/default.aspx) that will test multiple new technologies on a 407 transmission. The Sikorsky HMVS definitely seems promising, and some of the drivetrain technologies being tested at Bell look very worthwhile. These types of technologies can be incorporated into existing rotorcraft without too much trouble, so we may see them put into service in the near future.

[horlick97]

Thanks Henra.

It is interesting to learn that the tandem's rotors need not be vertically separated due to the axis offset. Though I note this configuration would only be applicable within a very narrow range of situations, eg, limited to 2 or at most 3 bladed rotors, requiring a relatively larger longitudinal separation in order to minimise the intermesh, etc.

Having said that, I am still excited about this. Without the need for vertical separation of the two rotors in tandem, would this not make the tandem configuration viable for optimisation for speed? So, instead of the AVX's Defiant's coax with 2 fans for forward thrust, would a tandem (with both rotors intermeshing in the same plane) fitted with 2 forward thrust fans perform better for speed?

[riff_raff]

horlick97-

The CH-47 is actually a fairly fast helo for its size, and a bit faster than a UH-60. The CH-47's rotors are interleaving in planform (http://upload.wikimedia.org/wikipedia/commons/thumb/4/4a/CH-47_Chinook_Line_Drawing.svg/400px-CH-47_Chinook_Line_Drawing.svg.png), but they have a fair amount of vertical offset with the rear rotor plane being higher. Boeing recently proposed a rather strange compound version of the CH-47 with mast mounted wings above each rotor called ULOR (http://www.aofs.org/wp-content/uploads/2012/11/121122.18-Rotorcraft-Back-to-Future-Davis.pdf). Boeing seemd to think they could achieve a >250kt cruise speed with this concept. And then there was the BV-347 (http://www.aviastar.org/foto/bvertol_347_1.jpg) from around 1970, which Boeing actually built and flew. Lastly, fore/aft interleaving rotors is not the only configuration possible. You can also locate the interleaving rotors side by side as shown here (http://www.unicopter.com/Nemesis.html).
(http://www.unicopter.com/Nemesis.html)

[horlick97]

Thanks riff_raff. I learnt something new.

The ULOR is interesting, though I must acknowledge I do not understand fully by the 'offset'. Anyway, I wonder why boeing did not offer this or the JMR. Could it be because the concept is still too new and there were not enough validation yet?

It is also enlightening for me to learn that the CH-47's vertical separation is strictly not needed but for noise minimisation. The interleaving would have ensured the rotors do not clash.

Back to the ULOR. Can the present CH-47 be fitted with forward thrust fans and allow the rotors to be unloaded during cruise? Isn't the X2 using this approach?

[SansAnhedral]

The CH-47's rotors are interleaving in planform, but they have a fair amount of vertical offset with the rear rotor plane being higher.

The rotor center of rotation is at a higher waterline, but the disc declination puts them at interference. In the -47 the rotors intermesh at any Nr > 0 where CF stiffening and flapping/coning is in effect. So basically, all the time.

http://i.imgur.com/e10GOXe.png

A functioning synchronization shaft between the 2 rotors is absolutely essential, or the aircraft will instantly self destruct, (see: Mannheim 1982 (http://www.leagle.com/decision/19841297586FSupp711_11158.xml/IN%20RE%20AIR%20CRASH%20DISASTER%20AT%20MANNHEIM,%20GERMANY) )

[riff_raff]

Sans- Thanks for clarifying my crappy description of the CH-47 rotor arrangement. I'm not an aero guy, but I believe the reason for locating the rear rotor on a pylon at a higher WL was to reduce the impact of downwash from the forward rotor on the rear rotor during forward flight or autorotation.

And an interconnection between the CH-47's two rotor drives to maintain phasing is indeed critical. The 1982 Mannheim crash you referenced is well known to rotorcraft drivetrain engineers. The root cause of the accident was loss of oil flow to the rear mast bearings, causing them to overheat and seize. After losing phasing the front/rear rotor blades impacted each other, and soon after the rear pylon/rotor separated from the airframe. The loss of oil flow to the rear rotor mast bearings was determined to be caused by debris clogging the bearing oil jet orifices. The debris was blast media (walnut shell) used to clean the gearbox housings during overhaul that was not completely removed from the oil galleries. As a result of this particular accident all rotorcraft transmission lube oil jets now typically incorporate a "last chance" debris filter.

[Hilife]

riff-raff

The root cause of the accident was loss of oil flow to the rear mast bearings, causing them to overheat and seize.

Blocked oil jets yes, but not the rear mast bearings, but the forward transmission pinion assembly.

This was followed by failure of the forward synch shaft, the result of which was that the forward blades took out the aft rotor.

A terribly sad day.

[Lonewolf_50]

Walnut shells.

[horlick97]

Does anyone know the status of the Groen Brothers Gyrolifter concept? Would this not be a promising concept also? In fact, would the Fairley Rotordyne not have proven the concept?

[riff_raff]

We should be hearing from the Army in the next 2 weeks who they have selected for JMR TD contracts. Too bad the forum moderator does not permit gambling, or we could start a betting pool on who the contract winner(s) will be. :ok:

[riff_raff]

Looks like the Army made a decision on JMR, but apparently we'll have to wait until all the contract details are hammered out before they announce who got the funding.

Army Narrows Playing Field for Joint-Multi Role Helicopter, But Few Public Details Announced - Blog (http://www.nationaldefensemagazine.org/blog/Lists/Posts/Post.aspx?ID=1572)

[horlick97]

It will one of each system.

Coaxial: Either Boeing-Sikorsky or AVX.

Tiltrotor: Either Bell or Karem.

It will be good if award would allow the combination of the features to be employed, eg, Bell non-tilting engine with Karem's variable speed, or AVX's configuration with Boeing-Sikorsky's rigid rotors. But, from the article, it seems this approach is not on the cards.

[riff_raff]

It will be good if award would allow the combination of the features to be employed, eg, Bell non-tilting engine with Karem's variable speed, or AVX's configuration with Boeing-Sikorsky's rigid rotors.Based on what the Army has stated publicly I'd guess that all four competitors will get some amount of funding. But I'm pretty sure only Sikorsky and Bell will get contracts for flight demonstrators. This is a very high-profile development program for the Army, and I can't imagine them being willing to risk one of the flight demonstrator contracts on small companies like Karem and AVX that have limited resources and no track record managing projects of this scale.

I agree with you that the rotor systems proposed by AVX and Karem appear to provide some worthwhile performance benefits. But these rotor systems will also likely add cost. One thing I liked about the Bell concept was that they made an effort to reduce cost (ie. the single piece straight wing, non-tilting engines, etc). The Army does not want a repeat of the massive budget overruns and schedule delays that become common with all aircraft programs.The US defense budget is rapidly shrinking and funding for development programs is one of the first things to get cut.

[KenV]

A few corrections are in order.

1. The S-97 Raider will NOT be the demonstrator for JMR-TD. The SB-1 Defiant demonstrator will be a full-scale 30,000 lb class machine. Sikorsky/Boeing is very confident the configuration will scale up to this size. But that is near the size limit for this configuration. Significantly larger rotorcraft will require a different configuration, either single rotor, tandem rotor or tilt rotor.

2. Sikorsky/Boeing and their partners have ALREADY spent $250M of their own funds, and plan to spend roughly 4x what the government will provide to develop and build the SB-1 demonstrator.

3. CG envelope for just about any aircraft is quite limited at max payload. However, CG envelope for lighter payloads is much larger on an inline tandem rotor than either a single rotor or side by side tandem like a tilt rotor. Since 90% or more of missions are performed at well below max payload, that is a significant advantage operationally.

4. Sikorsky/Boeing perceives they have an advantage over Bell/Lockheed's tilt rotor based simply on the fact that this is an Army program. The US Army is not keen on tilt rotors and has bought not a single V-22. Bell has some serious selling to do to overcome this Army bias. However, similar conventional wisdom in the 90s was that USAF would never buy a turboprop to fill their JPATS requirement. Beechcraft proved them wrong. We'll have to wait and see if the alleged Army bias against tilt rotors is true.

[horlick97]

Thanks KenV for the insightful discussion.

May I enquire:
What is the factor that limits the X2 configuration to only upto FVL-M? Is it due to the difficulty in having rigid rotors beyond this size?

Now that SB Defiant has been shortlisted for the JMR-TD, but it will have no way to go beyond FVL-M, this will mean the services will have to rely on another configuration for the bigger machines. That being the case, we'll see:

Upto the size of blackhawk - rigid conaxial rotors, ABC, X2 configuration.

Beyond that: a combination of tiltrotors if speed is needed, or tandem if speed is non critical.

Is the going to be the case? Will this approach lead to sub-optimality?

[Hilife]

There are bound to be compromises, but I don’t think so.

JMR is the precursor to FVL and it has always been my understanding that the end solution is likely to be 3 airframes of varying sizes in order to cover the Apache/Black Hawk/Chinook weight range, so you never know, we might even see a high speed 60,000lb tandem coaxial, contra-rotating rotor Chinook replacement.

[JohnDixson]

You posted:

"3. CG envelope for just about any aircraft is quite limited at max payload. However, CG envelope for lighter payloads is much larger on an inline tandem rotor than either a single rotor or side by side tandem like a tilt rotor. Since 90% or more of missions are performed at well below max payload, that is a significant advantage operationally."

This argument always seemed to show up in CH-47 vs CH-53 foreign sales competitions. The points we always responded with from the SA viewpoint is that one does not spend the millions to fly a big aircraft light, and when the 53 and 47 were loaded up, guess what, the CG ranges were about the same. In fact there were some comparisons where we had a slight ( very ) edge.

Just sayin'

[SansAnhedral]

May I enquire:
What is the factor that limits the X2 configuration to only upto FVL-M? Is it due to the difficulty in having rigid rotors beyond this size?

Rigid rotor tip path plane divergence at larger rotor diameters.

The rotor scales essentially infinitely aerodynamically on paper. Building sufficiently light and rigid blades is the issue.

You can increase spacing to allow for blade flapping (particularly in maneuvers), but then drag increases exponentially as ~40% of helicopter drag is from the hub.

Note the published tip clearance from the 6000lb, 26 foot rotor diameter X2 was only ever measured in level flight, and was reduced by nearly 50% between 120 and 240 kt

http://i.imgur.com/F0vzuNO.jpg

[KenV]

It MAY be true that a user would want to fly a big expensive aircraft at or near its payload capacity, but the reality is that that is seldom the case in the real world for either fixed wing or rotary wing aircraft, especially military cargo aircraft. From the C-5, to the C-17, to the C-141, to the C-130, all carried average payloads far below their max payload, and that is equally true of the CH-53, CH-47, CH-46, CH-3, V-22 and others. Military missions are far too diverse to enable the users to fill the aircraft to anything near their capacity. Further, many (most) military missions "cube out" before they "gross out", meaning the cargo hold volume is filled before it reaches its payload weight capacity.

As for wide CG envelope, when you're under fire or about to be under fire, it's very nice to be able to load up quickly and take off before taking the time to calculate the CG. This is done routinely all over every theater of operations in which the US and its allies are engaged. A wide CG envelope is also very helpful when doing sling loads. The CH-47's three sling load hooks and wide CG envelope provide a very flexible external load capability.

[KenV]

Coaxial rotor systems are limited by the rigidity of their rotor systems. The bigger the aircraft, the bigger the rotors, and the bigger the rotors, the more the rotor blades bend up and down at the tips. With contra rotating rotors tip divergence will cause the rotor disks to strike each other, especially under maneuver loads. That would certainly be a very bad day for the crew. The only solution is to make the rotors more rigid, which dramatically adds weight and causes other problems, or space the rotors farther apart, which dramatically increases drag. So the advantages of the coaxial configuration are cancelled out by the increasing size.

To give some perspective of how much the blade tips bend under maneuver loads, consider both the MH-47 and MH-53 which are inflight refuelable. The pilots are warned and trained to NEVER "chase the basket". Chasing the refuel basket can result in maneuver loads that cause the rotor tips to impact the helo's refuel probe, which when extended extends beyond the rotor disk. A very bad situation for the crew.

Here's a video of an H-53 crew that survived a rotor/probe impact during aerial refueling:

tO0sRWCf9k4

BTW, this was a VERY experienced HAC at the controls. It can happen to the best.

[JohnDixson]

They are also taught that, once engaged in the drogue, pick it up vertically, such that an inadvertent release will result in the drogue going down, not up into the rotor.

[horlick97]

Thanks for all the input regarding the limitations of the coaxial configuration when you scale it up.

The being the case, the only way to still employ the counter rotating rotors (so as to negate the need of a counter torque tail rotor) is to use the tandem configuration with the rotors interleave as in the Chinook.

I therefore thought an upsized Chinook will be a good idea for the heavylift solution. A further improvement could be to add a pair of wings and even hang a pair of forward thrust props for speed enhancements. With the wings, the main rotors may be slowed in forward flight, and part of the engine power shifted to power the forward thrust props.

Why the above was not considered?

[busdriver02]

KenV, not chasing the drogue has nothing to do with rotor blade flex. It's an issue of PIO, you're trying to chase the end of a whip instead of watching the hand that controls the whip.

[tottigol]

http://www.diseno-art.com/news_content/wp-content/uploads/2013/01/boeing-347.jpg

you mean this?

[riff_raff]

horlick97- There has been a substantial amount of effort put into performance simulations over the past 7-8 years in support of what is now the JMR program. Simulations were performed of every rotorcraft configuration you can imagine. Some of the simulation work was performed by companies participating in the program on their own proprietary designs, while other simulation work was performed by independent groups like NASA based on generic designs they created.

Here is a 2007 performance simulation study (http://www.dtic.mil/dtic/tr/fulltext/u2/a519252.pdf) conducted by a group from NASA & AMRDEC, which includes a 250kt, 150klb GTOW coaxial rotor concept and a 300kt, 139klb GTOW compound tandem rotor concept. The individuals responsible for the work (like Wayne Johnson) are well respected in the industry, so the results of this study do have some credibility.

[Shawn Coyle]

What about what Piasecki has been up to recently??
Winged, augmented thrust showed pretty good promised, from what I saw.

[SansAnhedral]

The X-49 fell well short of its speed goals, and the tech was not chosen to be pursued in JMR mainly due to those concerns.

[Ian Corrigible]

The X-49A suffered from serious rearward CG, which resulted in a high AOA in the hover (and approach). This was also a concern with the AVX proposal.

I/C

[KenV]

horlick said: the only way to still employ the counter rotating rotors (so as to negate the need of a counter torque tail rotor) is to use the tandem configuration with the rotors interleave as in the Chinook.

Actually, no. Sikorsky's coaxial rotor is an ABC (Advancing Blade Concept) rotor system. That means only the advancing blade makes lift. The retreating blade makes no lift. The problem with high speed in any conventional rotor system is that the retreating blade will stall at high airframe airspeed. By unloading the retreating blade it cannot stall. But that means you have to have two advancing blades on a common center, hence a coaxial configuration. If the two advancing blades are not coaxial (as in a tandem configuration) the lift will not be symmetrical about one axis making control impossible.

Picture a Chinook with the forward rotor generating lift only on its left side and the aft rotor generating lift only on its right side. To bank right the forward rotor would generate more lift (more lift on left side) and the aft rotor less lift (less lift on right side). But this would not only generate a roll moment to the right, but also a nose up pitch moment. Rolling left would generate a nose down pitch moment. And changing pitch would result in a roll. And because the rotor centers are nowhere near the CG, rolling would also generate a yaw moment. So all three control axes would be coupled to each other. It would be uncontrollable.

[KenV]

KenV, not chasing the drogue has nothing to do with rotor blade flex. It's an issue of PIO, you're trying to chase the end of a whip instead of watching the hand that controls the whip.Chasing the drogue results in large control inputs. Large pitch control inputs load and unload the main rotor. Watch the video. The HAC (helicopter aircraft commander) initially overshoots the drogue. This resulted in rotor downwash pushing the drogue down. As the drogue moves down, the HAC chases the drogue downward. This unloaded the rotors and they flexed upward. You can actually see the rotors flex up in the video.

By itself, this is no big deal, but in aviation, nothing happens by itself. Unloading the rotor does two things: it reduces drag (which increases airspeed) and reduces the rotor downwash. The increased airspeed results in the overshooting getting worse, which means the drogue is well inside the rotor disk, but below it. Reduced downwash means the drogue starts moving back up. Since the drogue is inside and below the rotor disk, the HAC must chase the drogue up or risk having the drogue move up into the rotor disk. That would be very bad. When the HAC commands nose up, the rotor loads up again and you can actually see the rotor flex down in the video. In this case the blades flexed downward enough to impact the probe tip.

Note that the helo in the video never went into PIO. The HAC immediately leveled the helo and stopped its climb right at rotor/probe impact and then moved the helo aft and outward, away from the KC-130 tanker.

[SansAnhedral]

Defiant?s delay due to blade manufacturing challenges (http://www.defensenews.com/digital-show-dailies/dsei/2017/09/11/defiants-delay-due-to-blade-manufacturing-challenges/)

Well, clearly they already knew this was an issue when they announced that everything was on schedule earlier this year.

[Ian Corrigible]

Especially interesting given the previous discussion (http://www.pprune.org/rotorheads/524130-s97-raider-9.html#post9714060) on the S-97's rumored blade supplier issues (through, ironically, the supplier in question (http://www.compositesworld.com/news/eagle-technologies-to-participate-in-v-280-valor-program) is now on the competing V-280 program (http://www.pprune.org/rotorheads/512284-new-bell-product-bell-v280.html)).

I/C

[The Sultan]

Ian

The only thing on blades is to ask which team has an aircraft with blades ready to run and fly to the schedule? It's Bell.

[CTR]

Defiant?s delay due to blade manufacturing challenges (http://www.defensenews.com/digital-show-dailies/dsei/2017/09/11/defiants-delay-due-to-blade-manufacturing-challenges/) .

Excuse me? The reason the Sikorsky-Boeing Defiant is 6 to 10 months late is solely due to problems manufacturing the rotor blades?

This must mean the Defiant PDR, CDR, and Fuselage delivery milestones were also caused by manufacturing difficulties with the rotor blades.

If just having acceptable for flight blades was the cause for the program delay there would be Defiant program press release photos of the aircraft rolled out of the hanger with not for flight blades installed.

Even system checks and limited ground runs with not for flight blades should be possible.

Maybe a dog ate the Defiant program master schedule is a more believable excuse.