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Sikorsky X2 coaxial heli developments.

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Sikorsky X2 coaxial heli developments.

Old 9th Aug 2009, 20:36
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Mart said:
I'm starting to realise that vibration attenuation at rotor blade source is very much in its infancy, with the Moog vibration absorber inherited from S-92 an interim step.
Vibration attenuation at rotor blade source may be a little more advanced then we think.



"Active control blades: a technology breakthrough in the pipeline. This could well be the disruptive technology in helicopters for the coming decades. Onera [French Aerospace Lab] is working on the development of rotors with active control blades, in which the shape of the blade changes according to its position in each revolution, thus ensuring maximum efficiency.Two main concepts are being studied: active flaps, and active twist blades. Wind tunnel tests to date have generated very positive results."

Dave
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Old 9th Aug 2009, 22:32
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Future fast helicopter to push 250 knots advances

Future fast helicopter to push 250 knots advances | Pilotbug

Sikorsky helicopter is testing its X2 demonstrator in hopes of combining the flexibility and hover of helicopters with the speed and range of airplanes. Flight tests continued with the first engagement of the rear pusher propeller which, in theory, should enable the hybrid to speeds of 250 knots. The helicopter generates lift with two counter rotating main rotor blades, in addition to the rear pusher. This arrangement makes torque more manageable and needs only to be addressed for the pusher rotor.
Sikorsky’s challenge in attempting a 250 knot helicopter was to counter the loss of lift of the retreating main rotor blades as the airframe travels forward. This is being addressed by using a rigid rotor which uses the Advancing Blade Concept (ABC) with which the retreating blade produces little or no lift. First pioneered with the Sikorsky XH-59A, a turbojet powered experimental helicopter, the ABC allowed it to reach 240 knots in 1973. Then current technologies made it impractical, though. More advanced “fly by wire” flight control systems have allowed greatly improved handling characteristics in the X2 demonstrator.
Sikorsky XH-59A

Recently, Sikorsky announced the X2 TECHNOLOGYTM Light Tactical Helicopter (LTH) in anticipation of flight tests confirming the capabilities of its demonstrator. It is envisioned to compete with other smaller combat helicopters like the Eurocopter AS 550 Fennec and HAL Light Combat Helicopter (LCH).
“These technologies can potentially bring new rotorcraft capabilities that, to date, have been unachievable by the industry,” said Sikorsky President Jeffrey P. Pino. “In addition to doubling the speed of helicopters, this technology can improve hot/high performance, maneuverability and low acoustic signature. Sikorsky’s Light Tactical Helicopter concept demonstrates a way to package these capabilities into an airframe that is tailored to meet a range of military missions.”
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Old 9th Aug 2009, 22:46
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Coax Controls etc

Graviman,

The XH-59 had collective twist grips for J-60 power modulation.

I haven't seen the X-2 Fly By Wire control schematics, but assume that even in its basic mode, it has what I would refer to as some augmentation, i.e., some electronic control input shaping and some basic feedback aimed at a modicum of short period ( or dynamic ) stability*. (Unlike the basic electronic control mode of the CH-54 backseat cyclic, which was a straight 28vdc input to the AFCS servo).

* I may see some of the X2 troops next week, and if its not proprietary information, I'll let you know what the basic control mode offers.

Thanks,
John Dixson
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Old 10th Aug 2009, 15:52
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CEFOSKEY,

The essence of rotorcraft is The Rotor.

In my limited opinion, Active Blade Twist and Reverse Velocity Utilization are also necessary for an actuator disk to fly edgewise, in an efficient manner, in it's environment.


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Old 11th Aug 2009, 11:46
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John,

It would be great to have pilot's perspective on X2 in this thread. Since X2TD will eventually filter out to commercially available machines then this would interest anyone likely to be gain ABC helicopter ratings. I don't know how much of the Comanche style FBW will filter down into these commercially available machines. My interest in particular is how you combine controls for cruise and hover in one control system to make the machine instinctive to fly.


Chris,

I'd be interested in learning more about the AATD active rotor. Are there any papers i should be reading? Clearly there will be some commercial sensitivity for a new development.


Dave,

I am also convinced that active blade twist would improve helicopter performance. Especially when you allow the same rotor to hover/cruise/climb/autorotate with as efficient a downwash pattern as practical. The problem is the same reason that fixed wing ailerons haven't adopted full span twisting (like the original wing warping), although the ideal system would be root control for lift and tip control for roll. This is that the design has to be aimed at a practical fatigue life of 10'000 hours. If blade is twisting at once per rev this may be hard to achieve. (Study Goodman lines on Haigh diagrams to get a feel for what i mean)
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Old 11th Aug 2009, 14:48
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CEFOSKEY -- The SAC/HamStan effort was covered in a paper given at this year's AHS65 forum (Active Rotor Development for Primary and Secondary Flight Control, Wake, Chaudhry, Lorber, Bagai & Collins).

I/C
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Old 13th Aug 2009, 00:30
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Originally Posted by Graviman
Since X2TD will eventually filter out to commercially available machines then this would interest anyone likely to be gain ABC helicopter ratings.
I am pretty sure there will be no ABC rating. Just need a helicopter rating. They would even let me fly it if I had the bucks. Ultimately, isn't the X2 just a helicopter that goes fast, rather than its own device requiring its own rating? This is one thing that would distinguish it from powered lift.

-- IFMU
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Old 14th Aug 2009, 11:54
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IFMU,

My comment was more a gentle nudge that it would be nice to get an "inside the cockpit" feel of X2. John and Nick's anecdotes about XH-59A are well received, and it would be nice to get a similar idea about what it is like to fly X2TD...

Last edited by Graviman; 16th Aug 2009 at 16:53. Reason: Typo
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Old 15th Aug 2009, 01:31
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Probably damn cool!
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Old 9th Oct 2009, 00:42
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Popular Mechanics

Anybody see the new popular mechanics?

Coaxial Rotor X2 Sikorsky Helicopter - Breakthrough Awards Innovators 2009 - Popular Mechanics





-- IFMU

Last edited by IFMU; 9th Oct 2009 at 00:45. Reason: Second image
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Old 9th Oct 2009, 11:48
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IFMU,

I'm glad X2 is beginning to gain it's place in the history of technical developments. I have no doubt it will deliver on its speed promise.

Does it deserve to be regarded as a new innovation? The answer is a resounding "YES". Each individual aspect of X2 is not new and has been around in other forms for many years. The brilliance of the Schweizer/Sikorsky design team was to recognise the potential of each aspect by selecting just the right ones to solve the problem of high speed helicopter flight. So the innovation is in getting all of these individual solutions to work together in a practicable helicopter.

Will it benefit civil or military? I hope it benefits both. Like all machines it will have its limitations, but it will earn its keep in the suite of machines available for flight between inconvenient landing sites. My hope is that it very nicely ushers in an era where folks think nothing of being whisked away from point to point with reasonable speed and efficiency. One day some will owe their livelyhoods to such a capability, and some will owe much more.

So, well deserved congratulations are in order.
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Old 10th Oct 2009, 01:29
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Future prospects for the X2

I'm not intimately familiar with the X2 (and my aero knowledge is very limited), but I do believe the X2 rotor uses rigid blades rotating in a set of hub-mounted rolling element bearings. This rigid rotor feather bearing and hub design is not too difficult with the flap and lead/lag moments produced by an X2 scale rotor. But I believe the rotor mast moments increase exponentially as the rotor grows larger. And it would seem to me that the hub structure and feather bearing system size and weight necessary to handle the exponentially larger mast moments would quickly get out of hand.

So, while I can see a bright future for smaller sized X2 rotorcraft, I personally don't think that it will turn out to be practical for larger helos.
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Old 10th Oct 2009, 06:33
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Future prospects for the X2

If the X2 demonstrator establishes ABC technology as a viable platform solution, then as a result of its intended high speed capabilities any X2 follow-on market would likely be targeted at the military as an armed escort or battlefield reconnaissance/attack platform.

However, all that technology comes at a price and I should imagine the rotor system will be subject to very high cyclic loading which in turn may result in very high LCF costs, so usage as a civil platform might not make financial sense in the early years.

Time will tell.
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Old 11th Oct 2009, 00:37
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Either I missed it the first time, or they added a little video of some forward flight:

Popular Mechanics

-- IFMU
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Old 11th Oct 2009, 21:17
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Have they needed anything faster than a Bell 47 to chase it? Last I heard they have only gone 52 knots, which gives the 47 plenty of time to get ahead of it to take pictures.

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Old 11th Oct 2009, 23:40
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106 kts was the last I heard.

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Old 12th Oct 2009, 11:44
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Woah guys! Give it time to get there!

Remember there is only one X2 in the whole world so if it gets dinged the concept will suffer a major setback. My own preference would be for this to be the first high speed helicopter program that doesn't suffer any serious setbacks.


riff_raff,

"Mast moments increase exponentially" means that for each similar increase in size the moments would double. I can assure you that basic engineering theorem says that doesn't happen - the root moment will be proportional to mass^1.5 (allowing longer blades for similar disk loading) but parts are also sized appropriately. Besides the S69 ABC, which has already flown at speed, was a medium size helicopter.

The effective hinge offset required to make ABC work requires that the blade has its own stationary natural frequency which is a given proportion of rotor rpm. A bigger helicopter runs a lower rpm, so while the blade is less stiff the frequency ratios stays the same. The tradeoff comes in the form that a larger helicopter normally wants as much payload as possible, which the rotor system mass will nibble into.

There are some applications which will benefit from ABC, there are some applications which will not, but better to have ABC available for those that do...

Last edited by Graviman; 19th Oct 2009 at 18:24. Reason: Correction: Original estimate of moment proportional to mass^1.33 was wrong. Thanks Riff raff!
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Old 14th Oct 2009, 19:13
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RRPM

Any ideas what RRPM the X2 runs at? In the video above, showing slow forward flight, it sounds like one of those mad indoor r/c micro helicopters that do a full "3D" aerobatic routine, HIGH!

Presumably this helps increase the speed at which the retreating blades stall?

For those in the UK that get "The Engineer" magazine, do have a look at the interview with Sikorsky's Marc Poland in the 12th October edition. I like the pull quote on helicopters that: "in terms of aircraft vibration, if you wanted to design a way to torture metal, this is it"...

Also on line, but without pictures, here:

Blade runner - The Engineer

Best regards

nrh
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Old 14th Oct 2009, 19:38
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446 rpm in hover, 360 rpm at high speed.

I/C
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Old 14th Oct 2009, 20:05
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Question

I/C.

Is there any information on the transmission; particularly in respect to the rotors and propeller being, two-speed or variable speed between the two operating values?


Dave
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