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Sikorsky X2 coaxial heli developments.

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Sikorsky X2 coaxial heli developments.

Old 1st Jun 2005, 19:41
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Sikorsky to Build X2

Here's the link to the press release from the AHS show in Texas:

http://www.prnewswire.com/cgi-bin/st...3769537&EDATE=
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Old 1st Jun 2005, 22:10
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fish

Looks great but I think they put the tail on upside down. I presume it will have a tailwheel?
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Old 1st Jun 2005, 23:42
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200 knots per hour????? is that 200 nautical miles per hour per hour.... very quick.

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Old 1st Jun 2005, 23:42
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Makes you wonder how accurate the rest of the info is, when you see that they claim it can fly at "250 knots per hour."

So, after a 2-hour flight we are doing 500 knots?
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Old 1st Jun 2005, 23:57
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They are of Russian origin....maybe that has to do with deciphering Cyrillic.
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Old 2nd Jun 2005, 00:23
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whats wrong with knots per hour ??

a knot is a measure of distance, nothing to do with time - or am i missing something here ??
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Old 2nd Jun 2005, 00:35
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a knot is a measurement of speed (nautical miles per hour).. so knots per hour is more akin to acceleration.
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Old 2nd Jun 2005, 00:38
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Someones playing semantics.
A nautical mile is a measure of distance. A knot is 1 nautical mile per hour
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Old 2nd Jun 2005, 04:49
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The Good, the Bad and the Ugly

The Good:
IMO, the tail-rotor has been the greatest obstacle to the successful utilization and propagation of rotorcraft. The V-22 tiltrotor and now the X2 coaxial should help relegate the tail rotor to its rightful place alongside the gyrocopter.

The Bad:
Lateral symmetry is the predominant characteristic of all living creatures and man-made vehicles, for obvious Darwinian reasons. The coaxial X2 is a significant move toward lateral symmetry. However, if fails to utilize the additional advantages that will be derived from laterally disposed main-rotors.

The Ugly:
If sixty years ago the German helicopter configurations had prevailed, or if thirty years ago Sikorsky had incorporated the recommended improvements to the XH-59A ABC I strongly believe that today there would be far, far more than one civilian helicopter for every half million people.



Edited to remove offensive smilies. Offensive language will stay.

Last edited by Dave_Jackson; 3rd Jun 2005 at 06:35.
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Old 3rd Jun 2005, 16:28
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Brief technical analysis...

It looks as if Sikorsky have gone a long way towards minimising the hub drag normally associated with coaxial helicopters. The "flying saucer" hub shrouds will minimise drag across a small range of attitude trims, while reducing upwash losses. The pusher prop will provide forward thrust without the nose-down attitude normally required by conventionals, thereby minimising the range of attitude trims. Horizontal tail surface will likely help with speed stability. The ABC principle will also reduce power losses associated with retreating blades.

The pusher prop is assumed to be constantly connected. This configuration will offer advantages in height-speed energy conversion, or entry into autorotation. The extreme rearward position of the pusher prop may cause pitch/yaw coupling in fast manouvres. The square tip prop will allow high speed, but is likely to be noisy. Although a rear gearbox is not required, the long driveshaft will need to be of substantial design for the propulsion power.

Yaw control still appears to be by differential collective across the rotors. This will result in reduced yaw effectiveness in reduced g manouvres (hard pushovers) and autorotation. If the vertical tail fin is "ruddered" with the pedals, this will allow good control to maintained with forward speed. The inverted position is likely to be in order to maintain positive yaw control in autorotation.


They say a picture speaks a thousand words...

Mart
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Old 3rd Jun 2005, 20:53
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IMHO

Sikorsky's move back to the coaxial configuration is a belated one, but it is well timed. The largest portion of their business in the near future appears to be the upgrading existing military craft. Their new craft sales will probably be low and therefor this announcement of a radically different helicopter will not be too detrimental.

Bell right now is probably doing some nail biting. It appears that an advanced coaxial ABC will outperform the tiltrotor in all significant respects, with the exception of top speed.

Sikorsky's nail biting is a few years off. Its commitment to, and implementation of, the coaxial will clearly show the advantages of twin main-rotor craft. Some other company in America, Europe, or perhaps the Far East will take advantage of this and bring out helicopters with lateral displaced twin main-rotors.

I predict that the functional superiority of the intermeshing/interleaving configurations will do to Sikorsky's coaxials what Sikorsky's coaxials will do to Bell's tiltrotors.


Dave
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Old 3rd Jun 2005, 22:08
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"It appears that an advanced coaxial ABC will outperform the tiltrotor in all significant respects, with the exception of top speed."

How do the figures look on this? Must admit that variable ABC RRPM will help, as long as the blades have high eigenmodes that are well damped (easilly with analysed in FEA).

"...functional superiority of the intermeshing/interleaving configurations will do to Sikorsky's coaxials what Sikorsky's coaxials will do to Bell's tiltrotors."

Hub drag will be lower for sure. I actually suspect that this will become the next big heli debate. You have to take into account ease of gearbox design/maintenance, reliability, servicability. Pilot preference will also play a large part, so application is important.

From an engineers standpoint intermeshing offers a better overall package. Interleaving doesn't really give any high speed advantages, since you have to plug the retreating blade "hole" from upwash (and need more complex drivetrain). Coaxial needs, well, coaxial hub shafts and control systems reducing parts commonality. I only consider outboard advancing in each case, since this is best aerodynamically, and mech gyro control systems are cheap: Lockheed of couse - non of this Bell/Hiller control mixing stuff...

Mart
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Old 3rd Jun 2005, 22:26
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Off topic ~ For a moment.

Graviman,
... you have to plug the retreating blade "hole" from upwash
You use the retreating blades and reverse velocity to add to the overall lift. See 'Cruise' on Interleaving - Morphing

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Old 3rd Jun 2005, 23:27
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"You use the retreating blades and reverse velocity to add to the overall lift."

OK, but you still have to operate blade away from optimum AOA. My point really is that you get no performance benefit (likely a performance detriment) over the intermesher, for the added complexity of two additional outboard gearboxes and drive shafts. The failure of any one of these makes the arguement "academic" - there are a lot of posts on this forum about tail rotor loss of drive...

Mart
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Old 8th Jun 2005, 17:11
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Arrow Sikorsky X2


Sikorsky Aircraft today announced plans to build and test a demonstrator for a new class of coaxial X2 Technology helicopters that maintain or improve on all the vertical flight capabilities of rotorcraft and whose high speed configuration will cruise at 250 knots.

Sikorsky plans to build and fly its X2 Technology demonstrator helicopter at its Schweizer Aircraft subsidiary by the end of 2006. Preliminary design work for the demonstrator is finished and parts fabrication for the aircraft has commenced.

X2 Technology refers to a suite of technologies Sikorsky will apply to achieve new levels of speed and performance in coaxial helicopters. Coaxial helicopters feature two counter-rotating rotors on the same vertical axis.

The announcement came at the American Helicopter Society International's annual technical forum in Grapevine, Texas, where Sikorsky unveiled new scale models of X2 Technology helicopter concepts in various weight classes and configurations.

"We initiated X2 Technology convinced that the most productive and flexible helicopter is a helicopter which is capable of a significant increase in speed," said Sikorsky President Stephen Finger. "Customers are demanding greater speed but without sacrificing any of the unique capabilities that make helicopters the ideal platform for countless civil and military missions."

X2 Technology aircraft will hover, land vertically, maneuver at low speeds, and transition seamlessly from hover to forward flight like a helicopter. In a high speed configuration, one or more 'pusher props' are part of an integrated auxiliary propulsion system to enable high speed with no need to physically reconfigure the aircraft in flight.

The top cruise speed of helicopters in service today, roughly 150 to 170 knots, are only incrementally better than what they were decades ago due to the fundamental limits of conventional rotor systems.

Previous attempts to develop faster helicopters have resulted in degraded hover performance. Likewise, attempts at fixed wing or hybrid vertical lift aircraft have resulted in aircraft with less hover capability than helicopters.

Sikorsky selected the term X2 Technology in order to: describe a class of helicopters with a coaxial design and to describe the multiplying effects (2X, or times 2) of applying a suite of modern technologies to coaxial helicopters. These technologies include new rotor blade designs, advanced flight control laws, transmissions with greater horsepower to weight performance and the ability to seamlessly transfer power from the main rotor to the aft propulser, and active vibration control.

Sikorsky will also incorporate decades of company research and development into X2 Technology helicopters, including: the XH-59A Advancing Blade Concept Demonstrator which showed high speed was possible with a coaxial helicopter and auxiliary propulsion, the Cypher UAV which expanded company knowledge of the unique aspects of flight control laws in a fly by wire aircraft that employed coaxial rotors and the RAH-66 COMANCHE, which developed expertise in composite rotors and advanced transmission design.

http://www.sikorsky.com/details/0,30...TI2088,00.html







What do you think about this interesting concept?
Is it only for the military interesting, as an VH-22 Osprey escort?
Or maybe a competitor to the Bell 609?

This is the Sikorsky XH-59A from 1971:

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Old 8th Jun 2005, 17:19
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Is that Nick on the right seat?
 
Old 8th Jun 2005, 20:07
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"What do you think about this interesting concept?"

Well, same as ABC only with more efficient pusher prop.
Search "Coaxial" or "Intermeshing", and prepare yourself for a long night in...

Mart
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Old 23rd Sep 2006, 21:29
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Sikorsky X2 coaxial heli developments.

Checking to see any news on X2, came across this article:

http://aeronode.com/aero/18/sikorsky...run-in-october

Aviation Today reports that Sikorsky plans a ground run in October of its X2 concept demonstrator, only 16 months after the program’s inception. The ground run should test basic mechanical and avionics functionality without flight. The X2 uses contra-rotating rotors along with an aft pusher-prop to expand the speed envelope of rotorcraft, with 250 knots a possibilty.


Although quarter 2, this had a good article on page 3:
http://www.sikorsky.com/file/popup/0,3038,1875,00.pdf

Although the picture initially had me fooled, top rotor is same diam as lower rotor. One point about coaxials is that downwash contraction from the upper rotor will alter flow through centre region, but not the tips, of the lower rotor. I'm sure the engineers at Big Sky have done lots of corellated CFD simulations to get it right...

Other resources, since i couldn't find the original thread:
http://www.sikorsky.com/details/0,30...TI2088,00.html
http://www.flug-revue.rotor.com/FRtypen/FRSikX2.htm
http://www.aerospace-technology.com/projects/model333/

Mart

Last edited by Graviman; 24th Sep 2006 at 20:37. Reason: Thanks for pointing that out IFMU.
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Old 24th Sep 2006, 00:30
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Mart;
Interesting that top rotor diam is now smaller than lower rotor.
Unfortunately, the Coaxial configuration does not have true laterally symmetry. This difference in rotor diameters will move the craft even further from symmetry.

Eagle Aviation Technologies is providing the rotor blades for the X2. As I recall, the CEO of Eagle Aviation, Emitt Wallace, was involved with the coaxial Air Scooter.

___________________________________
Edit

Perhaps posts #28 and #32 on A challenge ~ for those who are not technically challenged. belong on this thread.

Dave

Last edited by Dave_Jackson; 24th Sep 2006 at 00:56. Reason: Addition
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Old 24th Sep 2006, 02:32
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Originally Posted by Graviman View Post
Interesting that top rotor diam is now smaller than lower rotor.
Mart, if you look closely, I think you will find the projection of the top rotor span to be approximately 0.707 of the bottom rotor span. And, the bottom rotor seems to picture a blade forward, aft, and one pointing out of the page. The top rotor only seems to have a blade forward and aft. Why do you think this is?
Here's a hint for you (and Dave): What's the sine of 45 degrees?
-- IFMU
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