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