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=

Looks great but I think they put the tail on upside down. I presume it will have a tailwheel? :ok:

200 knots per hour????? is that 200 nautical miles per hour per hour.... very quick.

:ok:

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?

They are of Russian origin....maybe that has to do with deciphering Cyrillic.

whats wrong with knots per hour ??

a knot is a measure of distance, nothing to do with time - or am i missing something here ??

a knot is a measurement of speed (nautical miles per hour).. so knots per hour is more akin to acceleration.

Someones playing semantics.
A nautical mile is a measure of distance. A knot is 1 nautical mile per hour

The Good, the Bad and the Ugly
 

The Good: :ok:
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: :uhoh:
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: http://www.unicopter.com/NoNo.gif
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.

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

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

"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... :yuk:

Mart

Off topic ~ For a moment.
 

Graviman,You use the retreating blades and reverse velocity to add to the overall lift. See 'Cruise' on Interleaving - Morphing

Dave

"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

Sikorsky X2
 

http://www.sikorsky.com/Images/SAC_S...r_Aircraft.jpg
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:
http://avia.russian.ee/vertigo/foto/sik_s-69.jpg
http://avia.russian.ee/vertigo/foto/sik_s-69_1.jpg

Is that Nick on the right seat?

"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

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

:D

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

Mart;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

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

IFMUI don't know. Will this do? http://www.unicopter.com/Peace2.gif


Mart you naughty boy.

Yes, Sikorsky is going 'Back to the Future' by regurgitating the 30 year old coaxial ABC. However, suggesting that they went way back to the time when some produced coaxials with unequal rotor diameters is going toooo far. :ok:


Dave

some comments:

1) Dave's idea of perfect symmetry is like a mantra to him, and of absolutely no validity from any standpint but his own. No physically symmetrical system has any degree of symmetry from the standpoint of forces and moments produced, due to all the other aspects that influence the aerodynamics.
2) He is all wet with his calculations about different rotor diameters and the ensuing loss of "symmetry" since the X2 has two identical rotor diameters, and blade sets. The illusion that ppruners have spun into a physical fact is just that, an illusion. The rotors are indexed so that they do not cross at the cardinal 90 degree points, so you see them as if they were different diameters. A gold star to IFMU for explaining this to Dave!
3) There is little similarity between the ABC/X2 and any other coax or syncropter, because the ABC type rotors are extremely stiff, with hinge offsets above 15%. This allows near stall maneuvering, a fact that is lost to those "expert" web sites that compare the X2 to a typical Kamov design.
4) The KA-50 has a hinge offset of 7.5% on the lower rotor and 2.5% on the upper, making the flapping motions quite large, and forcing the rotors to be very widely separated, with a great deal of drag (about 15% more than necessary). This low offset also makes the flapping near stall much greater, so that there can be little maneuvering at high speed, and therefore no high speed. In fact at least one and probably two KA-50's were lost to self-midair.

All in good fun. http://www.unicopter.com/StickPoke.gif



http://josmom.typepad.com/photos/unc...snakeoil_1.jpg
Nick you're doing it again. You've got to put that bottle down.


Your strong support of the tail-rotor configuration would have made Igor proud. I hope you didn't hurt your neck a year ago when you did the quick about-face and started to champion the coaxial configuration.

Rebuttal comments;

!) We have had this discussion before. Virtually all of nature's creatures have lateral symmetry in respect to interaction with their environment. Virtually all of mankind's vehicles have lateral symmetry in respect to interaction with their environment. Are you saying that Darwin's evolutionary survival of the fittest is wrong? When you mention aerodynamics, are you saying that birds and airplanes have no reason for lateral symmetry?

2) What thread have you been reading? Mart said, "Interesting that top rotor diam is NOW smaller than lower rotor." Are you suggesting that I should not believe it when Mart says that Sikorsky has changed the rotor diameter?

3) You said; "There is little similarity between the ABC/X2 and any other coax or syncropter," Not so fast Quick Draw. There is much similarity between the ABC/X2 and the XH-59A ABC. Just think where the helicopter industry would be today if Sikorsky had taken that 1965 study, the subsequent XH-59A craft, plus the concluding recommendations; and then continued to improve and produce the coaxial configuration.


Dave

Dave, don't mean to put the dampener on what is turning into another interesting thread, but most folk are not ambidextrous... :ouch:

IFMU, thanks for pointing that out - my goof. I imagine indexing rotors to cross at +/- 22.5 deg to the 90 deg azimuth points reduces vibration from both blade slap above structure, and having downwash from two blades impinge structure simultaneously.

Mart

I suppose that is true. But why isn't my heart in the middle of my chest?
-- IFMU

Aw Mart,

First you give Nick the opportunity to beat me up :ouch: and now you try to promote Round 2.

Discussing mobility within one's enviroment. ~ Do you mean that most folk swim with one arm? http://www.unicopter.com/Drowning.gif


IFMU,

Didn't you say that you gave it to your spouse a number of years ago. :O


Dave

No, but if you watch horses gallop they lead with one foot, and most sprinters will start with one foot. Not beating you up old boy, but X2 does allegedly have a hub drag similar to single rotor aircraft. Intermeshers main benefit is reduced drag by having a low hub profile. Interleavers can't be as aerodynamically competetive due to outriggers etc.

Nature produces the solutions it does, by optimising it's "designs" over time to suit their environment. We have the advantage of understanding ours (Navier-Stokes and compressible flow in this case - or using CFD). While perhaps the response provoked was a little strong for what was just an honest mistake on my part, you should argue the case for your concepts on weight and aerodynamics benefit. Already X2 design indicates a need to index the blades, so perhaps intermeshing will hold some advantage :ok:

Mart

At the risk of belaboring a point.
 

Mart,

Being ambilevous is a mental decision, which is made by the 'operator'. His physical body is latterly symmetrical and it can operate equally either way.

Rolling an airplane is a mental decision, which is made by the 'operator'. The physical fuselage is latterly symmetrical and it can operate equally either way.

I do. I also seek and appreciate technical critique.
On the web pages, the potential faults are noted, as well as the potential attributes.

I would suggest that lateral symmetry is very important in two respects;

1/ When Nick's unequal forces and moments are imparted to a craft, either by the pilot or by perturbations, lateral symmetry makes it much easier for the craft to return to its neutral position.

2/ Lateral symmetry allows a craft to spend less of its power and resources fighting dissymmetry.

Dave

Mart,

About 20 pprune-years ago, I tried to get Dave off his symmetry mantra, and it did no good then, either! Good luck! No argument can work because he believes it in his heart, where logic can't unseat it.

Mart,

About 20 pprune-years ago, I tried to get Nick off his tail-rotor mantra, and it did no good then, either! Technical logic didn't work. It took a move by Sikorsky to convince him. :D



Nick,

Please tell why lateral symmetry is not an advantage, or why it is a disadvantage :confused: :confused:


Dave

Dave,
I am constantly amazed at those who show faces on Mars, apricot-pit cures for cancer or lateral symmetrical reasons to screw up a helicopter's general arrangement, and then say to others "Prove me wrong!"

Give it a rest, Dave, or at least give it some data. People who have been studying, designing and building helicopters for 70 years have relied on data to make decisions, not quasi-religious theories....

Nick,

Your post mentions; 'faces on Mars", "apricot-pit cures for cancer", and "quasi-religious theories".

I have more than 1,000 web page, all technical and all related to rotorcraft. Yes, many, many have errors and many are theoretical concepts.

You don't have to "Prove me wrong", but if you wish to attack, please load your gun with technical ammunition.

http://www.unicopter.com/Peace.gif

Dave

Lots of web pages, all symmetrical. Any real helicopters, Dave???

Fight's On! :}

I think all intermeshing rotors need to index the blades, less they become intersmashing rotors. One advantage to a coaxial is you can index them wherever it makes sense for aerodynamic or whatever reason, and it won't cause intersmashing.
Conversely, any coax needs some indexing, assuming they use gears with teeth. Now, if the X2 technology uses a transmission like the one in my 1971 Harley golf cart, then indexing would be yesterday's news.
-- IFMU

Nick,

http://www.unicopter.com/Kiss.gifPretend that the're attached to Nicol Kidman.


Let's disappoint toolguy.
Let's kiss and make up. http://www.unicopter.com/KissingFaces.gif

Dave

Returning to the subject of the X2..
 

The thought of Nick bearing down in a Snake is enough to make me quake in my boots! That and the poor engineer who tried to defect to Eurocopter, being disuaded by a minigun... :eek:

Seriously, I have a great respect for Nick's authority on Helos. I genuinely consider myself priviledged that a pilot of his standing not only considers my postings, but will willingly share his design and piloting experience with us heli industry wannabes.

Hip Hip...Hoorah!


On with the thread: I can see how 15% effective hinge offset would allow near stall maneuvering without producing unwanted blade oscillations. The 4 blade rotors of the X2 should also reduce vibrations over S69 3 blade rotors. I guess a lot was learnt on Comanche which will benefit X2.

How much of the Comanche FBW has been reincarnated for X2? I imagine the Schweizer 333 test flights were more systems integration development than a major hardware redesign.

Mart

Those lips are too much to resist, Dave!!

Nick

BTW, they appear lusious and, dare I say it, they look to be Sy _ _ _ _ _ _ CAL!

Done some more homework...
 

Some other web refs:

http://www.aiaa.org/pdf/inside/05_TC...st%20flight%22

http://www.commsdesign.com/press_rel...lineId=X391647

The last site gives some info on FBW system:

Engine: LHTEC
Data Concentrator Units: Hamilton Sundstrand:
Central Processing Units: Honeywell.
Rotor Blades: Eagle Aviation
Cockpit Display: Chelton Flight Systems.

Perhaps early considerations:

http://avia.russian.ee/helicopters_eng/sik_s-2-r.html

Mart