Sikorsky X2 coaxial heli developments.

[av8rbpm]

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

http://www.prnewswire.com/cgi-bin/stories.pl?ACCT=109&STORY=/www/story/06-01-2005/0003769537&EDATE=

[ShyTorque]

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

[imabell]

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

:ok:

[Ascend Charlie]

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?

[SASless]

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

[407 too]

whats wrong with knots per hour ??

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

[zhishengji751]

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

[overpitched]

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

[Dave_Jackson]

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 (http://www.unicopter.com/0891.html) 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.

[Graviman]

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

[Dave_Jackson]

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

[Graviman]

"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

[Dave_Jackson]

Graviman,... you have to plug the retreating blade "hole" from upwashYou use the retreating blades and reverse velocity to add to the overall lift. See 'Cruise' on Interleaving - Morphing (http://www.unicopter.com/1372.html)

Dave

[Graviman]

"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

[hotzenplotz]

http://www.sikorsky.com/Images/SAC_Sikorsky_Aircraft_Corporation/US-en/X2_Demonstrator_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/0,3036,CLI1_DIV69_ETI2088,00.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

[TheFlyingSquirrel]

Is that Nick on the right seat?

[Graviman]

"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

[Graviman]

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

http://aeronode.com/aero/18/sikorsky-twin-rotor-x2-ground-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.
: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/0,3036,CLI1_DIV69_ETI2088,00.html
http://www.flug-revue.rotor.com/FRtypen/FRSikX2.htm
http://www.aerospace-technology.com/projects/model333/

Mart

[Dave_Jackson]

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 (http://www.airscooter.com/).

___________________________________
Edit

Perhaps posts #28 and #32 on A challenge ~ for those who are not technically challenged. (http://www.pprune.org/forums/showthread.php?t=244146&page=2) belong on this thread. :)

Dave

[IFMU]

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

[Dave_Jackson]

IFMUWhat's the sine of 45 degrees?
I 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

[NickLappos]

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.

[Dave_Jackson]

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



http://josmom.typepad.com/photos/uncategorized/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 (http://www.unicopter.com/1465.html)and the XH-59A ABC (http://www.unicopter.com/0891.html). 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

[Graviman]

Virtually all of nature's creatures have lateral symmetry in respect to interaction with their environment.

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

[IFMU]

Virtually all of nature's creatures have lateral symmetry in respect to interaction with their environment.
I suppose that is true. But why isn't my heart in the middle of my chest?
-- IFMU

[Dave_Jackson]

Aw Mart,

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

Dave, ...... most folk are not ambidextrous... Discussing mobility within one's enviroment. ~ Do you mean that most folk swim with one arm? http://www.unicopter.com/Drowning.gif


IFMU,

But why isn't my heart in the middle of my chest? Didn't you say that you gave it to your spouse a number of years ago. :O


Dave

[Graviman]

Discussing mobility within one's enviroment. ~ Do you mean that most folk swim with one arm?

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

[Dave_Jackson]

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.

you should argue the case for your concepts on weight and aerodynamics benefit.I do. I also seek and appreciate technical critique.
On the web pages, the potential faults are noted, as well as the potential attributes.

Nick said;
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.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

[NickLappos]

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.

[Dave_Jackson]

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

[NickLappos]

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....

[Dave_Jackson]

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

[NickLappos]

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

[toolguy]

Fight's On! :}

[IFMU]

Already X2 design indicates a need to index the blades, so perhaps intermeshing will hold some advantage :ok:
Mart
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

[Dave_Jackson]

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

[Graviman]

Fight's On!

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

[NickLappos]

Those lips are too much to resist, Dave!!

Nick

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

[Graviman]

Some other web refs:

http://www.aiaa.org/pdf/inside/05_TC_Highlights/aiaa-vstol.pdf#search=%22sikorsky%20x2%20first%20flight%22

http://www.commsdesign.com/press_releases/prnewswire/showPressRelease.jhtml?&CompanyId=1&HeadlineId=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

[Dave_Jackson]

Update on the X2 (http://www.vtol.org/issues.html#sik)

[Graviman]

Good for Sikorsky/Schweizer! :ok:

Must admit i was astonished at the original intention to get the thing flying by last year. To me it shows a responsible realisation within the organisation that the engineering for such a project is far less expensive when the time frame is given to trouble shoot problems.

I'd be interested to know more about the Moog active vibration control though. I could have a reasonable guess at how it might work, but will dig up some papers.

Mart

[NickLappos]

Grav,
The Moog system is the same as that in the S-92, and it works like a charm. I understand the EC225 has a similar system.

The Moog vibration absorber is a electronic motor is digitally controlled to have very precise rpm capability. The digitally controlled motor spins counter rotating weights which are driven eccentrically in and out by separate jackscrews to produce higher or lower vibration amplitudes. Because the rpm of the motor is precisely controlled, the phase of the counterrotating weights can be adjusted, where the phase is the precise direction of the maximum amplitude of the weights. As a result the vibration absorber is capable of being adjusted to precise RPMs and to precise vibration absorbtion direction (lateral, vertical, horizontal). It can also be adjusted automatically by a computer as the aircraft flies. A vibration pickup is located near the place where you want to quell a vibration the most. Using that pickup the computer determines the best way to tune the weights to drive the rpm to its lowest. The computer uses precise logic that learns as the flight conditions change and so the computer becomes specific for the aircraft it is installed in. You can use up to six absorbers with the computers so that it's quite possible to quell the vibration across a very large area. Each of the absorbers weighs around 40 pounds and the amplifier maybe 10 pounds.
Try this patent number: 6,869,375

[Graviman]

Thanks Nick, glad i asked.

Patents online (http://www.freepatentsonline.com/6869375.html)
or
US Patent Office (http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=6869375.PN.&OS=PN/6869375&RS=PN/6869375)

Not sure if DOD prevents you giving details, but what sort of vibration control system was used on Comanche to allow the high roll rates? I guessed it might be a system to trim pitch around azimuth to tune out vibration, again requiring predictive software to deal with system lags. This may once again be the engineer seeking out the most complex solution to a simple problem. :}

Mart

[NickLappos]

With the five blades and small diameter (high frequency for n/rev) as well as the narrow, stiff fuselage with two strong keel beams, the Comanche had no vibe absorbers, and needed none!

This illustrates something that is counter to another of those helo pilot myths, that vibration is not normal, and it indicates "something wrong" with the rotor.

N/rev vibration is a part of every helicopter. It is created by the rotor is a natural function of the way each blade chops up the amount of lift that is needed by the aircraft. The amount of natural vibration at the rotor head is almost purely due to rotor head hinge offset, number of blades and their stiffness, and the speed range of the helicopter. How much vibration the pilots and passengers feel is almost purely due to the way the fuselage responds to the vibration the rotor is providing. A wide, long, soft cabin will respond worse to vibration and have hot spots and cold spots where people feel more and less vibration. A narrow, stiff fuselage will prevent the vibration from creating hot and cold spots and generally provides a more comfortable ride. In reality the amount of vibration the pilots feel is driven by many factors it's quite possible to change a helicopter in some way (by cutting a door or moving the seats around) and discover that the perceived vibration is made vastly better or vastly worse.

I should also point out that in fact the vibration felt at the seat is often due to the way the seat itself responds to the vibration. It is quite possible for some pilot seats to multiply the N Per Rev vibration of the rotor by a factor of two or three! Often an aircraft vibration "gets worse" and all you have to do is tighten down the seat mounting bolts.

The inventor of that patent, Bill Welsh, is a great vibration engineer at Sikorsky, I worked with him on two projects.

[Graviman]

Thanks again Nick. Certainly overturns another misunderstanding i had about blade 5P modes (or 5/4 wavelength eigenmodes) being significant. Then again the 15% hinge offset will push blade 5/4WL above rotor 5P, by between 1.1 to 2.7 times (say 1.7 or 8.6P). A combination of this and good internal damping lets 5 bladed system work.

Albeit not aero (:( ) i can definately concur the importance of seat dynamics in perceptions of overall vehicle tranfer function. As part of a small team i am the dynamics and durability engineer (as well as designer, draughtsman, general dogsbody and teaboy ;) ). I like to amaze folks with how well a BIG truck actually can ride&handle (and oversteer if nobody is watching ;) ).

I would imagine that composites make life a little easier, because of the construction techniques allowing good joins between beam members, and the material having inherent damping properties. A larger machine with more panel area, and tough weight requirements, introduces all sorts of new eigenmodes which in the auto industry can be dealt with by swaged stiffeners. Composites allow thicker/stiffer sandwich construction, with some of the panels on EH101 proto being amazing (Heli museum UK).


Edit (24/01/07):

Using flexural waves (frequency dispersive bending wave) for blades in combination with rotating frequency gives:

Rotating_Blade_Freq = SQRT( (N^2 x Static_Nat_Freq )^2 + ( N x Rotor_Freq)^2 ) ; where N = blade N/4 wavelength mode.

For Comanche example this would gives "actual" flexural modes within ranges:
1/4 mode: 1.12P - this mode causes the swashplate lead angle
3/4 mode: 3.36P to 5.44P (1.12 to 1.81 x 3P) - say 4.28P
5/4 mode: 5.60P to 13.56P (1.12 to 2.71 x 5P) - say 8.71P
7/4 mode: 7.84P to 25.69P (1.12 to 3.67 x 7P) - say 14.19P

The range is because the calc does not consider construction, so that lower range is for stressed skin only and upper range is for solid section. This is not confirmed in FE, but would explain why high offset results in such a smooth helicopter. Nick, i imagine Bill Welsh is pretty knowledgeable...

Mart

[IFMU]

Update on the X2 (http://www.vtol.org/issues.html#sik)
Cool picture there:
http://www.vtol.org/news/X2GroundTestStartnightime.jpg
They must have really been burning the midnight oil!! Either that or it is really an NHRA picture. Maybe it is so top secret they only test at night.
-- IFMU

[Dave_Jackson]

http://www.unicopter.com/1465.gif

[Graviman]

Good looking machine, however you view it. :ok:

Mart

[Collective Bias]

I always thought lateral and horizontal vibration was the same. What would be the diffrence, or is lateral another word for roll vibration?



CB

[Dave_Jackson]

From Market Watch article on the delay of the X2 project. (http://www.marketwatch.com/news/story/sikorsky-expects-restart-x2-research/story.aspx?guid=%7B805A1774-B34E-469E-97DC-C800D8AA5D3C%7D)"New helicopter technology is waiting on a market that's not going to happen for decades," said aircraft analyst Richard Aboulafia of the Teal Group, a Washington-area consulting firm, in a Friday telephone interview.

:confused:


What a strange remark.

Is he is saying that technological advancements do not create markets?

If this is the attitude of the industry then it's no wonder that the American Helicopter Society didn't publish my provocative letter. Perhaps they believe that rotorcraft is a 'sunset industry'.


Is this an example of technologically driven capitalism being replaced by monetaristically driven capitalism?

[Graviman]

I always thought lateral and horizontal vibration was the same. What would be the diffrence, or is lateral another word for roll vibration?
CB

CB,

I have come to appreciate on this forum that a helicopter is a collection of vibrations that come together to form a flying machine. The best any engineer can do is to make sure they don't coincide. The local aerodynamics are best off not affecting the various blade flexural modes, the blade flexural modes are best off not affecting the cabin modes, the cabin modes are best off not affecting the seat modes and acoustic modes. The pilot is best off being vibration tolerant.

Lateral generally means side-to-side, but can be taken loosely as horizontal. As a blade flexes it's mass to hub radius alters so you get coriolis vibration, normally solved with lead-lag dampers. Depending on the general layout of the machine all of these can cause either lateral or roll vibrations. I understand the theory, but that is not the same as a lifetimes experience solving helicopter specific problems.

Dave,

I imagine Sikorsky are internally justifying the engineering budget on a conservative market. If helicopters had not been developed there would be no helicopter market. I imagine that once the machine practically proves it's capabilities, market growth will be exponential...

Mart

[slowrotor]

Dave,
Sikorsky builds large helicopters for the government. The risk of lawsuit is low compared to the profit per unit. For Sikorsky or any large company to build a small helicopter would be foolish.
New technology must come from new entreprenuers that have limited assets.

If your interest is the private market, then look at Robinson for ideas about capitalism in the helo market.

[Dave_Jackson]

slowrotor,

I agree with some of your remarks and politely disagree with others.

Even the US military has expressed its frustration about the inability of rotorcraft to meet its requirements. The X2 is a prototype for a suite of coaxial-ABC helicopters; from small to very large.

I understand that Sikorsky acquired Schweizer, in part, so that it would have the ability to do fast prototyping and development. Unfortunately, the cost of today's technology and regulations, combined with the limited assets of a 'start-up', makes it difficult for an individual to bring something 'new' onto the playing field.

_______________________________

From the Barber's Gazette, (where everyone gets a rumor as they get clipped);

The X2 delay has to do with the transmission. A secret document says that Sikorsky has realized the obvious and is going from the 'I' configuration to the 'V' configuration. :O


Dave

[NickLappos]

slowrotor,
The X2 is small because it is a technology demonstrator, a full scale X2 could be the size of a house.

I know Richard Aboulafia well, he is a smart fellow, but he has no crystal ball.

[Jack Carson]

I disagree with Nick. Scale up is always an issue. Just look at the growing pains associated the XV-15 evolution to the V-22. A smarter individual than me once said, “The bicycle was designed and built at turn of the last century, yet today you see very few two wheeled Greyhound buses.”

[IFMU]

I disagree with Nick. Scale up is always an issue. Just look at the growing pains associated the XV-15 evolution to the V-22. A smarter individual than me once said, “The bicycle was designed and built at turn of the last century, yet today you see very few two wheeled Greyhound buses.”
I'd have to disagree with this analogy. At the turn of the 1900's we had powered flight, now we have 747's which fly quite well. In 1939 we had the VS300, and the helicopter grew up quite nicely from this humble start. But, there are some concepts that work very well for small things, like bicycles and model airplanes that hover, and don't scale up well. It seems to me that this latest Sikorsky machine is still a helicopter, and I would expect it would scale up like most helicopters.

-- IFMU

[Jack Carson]

IFMU
I agree in principle. Igor Sikorsky flew the Grand, a 4 engine, 5 ton machine in 1913. Sixty years later that vehicle evolved into the 747. Similarly, he flew the VS-300 in 1939. 35 years later Sikorsky flew the 35 ton CH-53E. However, some subsets of rotorcraft technology may approach physical limits due to power requirements or material limitations. To draw a slightly different analogy, I believe that the VTOL Harrier and F-35 are approaching practical limits for turbo-fan thrust born flight. Co-axial rotor systems may have just such a boundary.
Jack

[Dave_Jackson]

IFMU,

"In 1939 we had the VS300" AND it had 3 tail rotors.

Two of these tail rotors were removed by abortion. Or; - were they abortions, which were removed?

The third tail-rotor only grew up because it was force fed.


Dave

[IFMU]

Two of these tail rotors were removed by abortion. Or; - were they abortions, which were removed?Dave
The two were aborted because they promoted lateral symmetry!

-- IFMU

[Graviman]

IFMU
I agree in principle. Igor Sikorsky flew the Grand, a 4 engine, 5 ton machine in 1913. Sixty years later that vehicle evolved into the 747. Similarly, he flew the VS-300 in 1939. 35 years later Sikorsky flew the 35 ton CH-53E. However, some subsets of rotorcraft technology may approach physical limits due to power requirements or material limitations. To draw a slightly different analogy, I believe that the VTOL Harrier and F-35 are approaching practical limits for turbo-fan thrust born flight. Co-axial rotor systems may have just such a boundary.
Jack

Jack, your comment is spot on. The boundary you are refering to is compressibility. By opting for a counterrotating main rotor system you avoid the retreating blade stall, but the limit you now hit is the advancing blade shock wave formation. Improved modelling and damping of blade modes will allow Nr to reduce at higher speeds without fear of structural divergence. Eventually the machine will operate at speeds approaching turboprops, so Sikorsky are being sensible with a 250kias start - remember it has to work.

One day in the distant future speed might get into the turbofan arena. Much work on blade dynamics will be required - likely with active systems. This is similar to commercial fixed wing struggling to justify projects over M1...

Mart

[Dave_Jackson]

Originally Posted by Jack Carson;
".. some subsets of rotorcraft technology may approach physical limits due to power requirements or material limitations. ... Co-axial rotor systems may have just such a boundary."


A link to this subject of; Empty Weight and Payload;

Why the Coaxial-ABC can never Compete with the Intermeshing-ABC (http://www.unicopter.com/B183.html)


The spread between the Coaxial-ABC and the Interleaving-ABC will be even greater.

Dave

[IFMU]

The spread between the Coaxial-ABC and the Interleaving-ABC will be even greater.
Dave
Dave,
What is the drag penalty for those two masts sticking up, with not only double the profile drag, but also interference between them? That's one thing that seems unequal.
As far as the 15% benefit with respect to disk area, how much of that is undone by the fact that the lift vectors of the synchrocopter waste some of their effort against each other, since they are inclined outwards? You could probably do a ROM estimate of the lost lift of each rotor by multiplying it by the cosine of the shaft angle.
I have read that the original ABC had big vibration problems. It had two 3-bladed rotors. How is anything with 2-blade rotors going to be better? I would bet you would have a hard time getting to respectable single rotor helicopter speeds before you lost your fillings, or busted something.
-- IFMU

[Dave_Jackson]

IFMU,

What is the drag penalty for those two masts sticking up, with not only double the profile drag, but also interference between them? That's one thing that seems unequal. The rotors on both craft are identical. Four blades each (http://www.unicopter.com/1220.html), etc., etc. The induced, profile and parasitic drags should be equal.


As far as the 15% benefit with respect to disk area, how much of that is undone by the fact that the lift vectors of the synchrocopter waste some of their effort against each other, since they are inclined outwards? The upper blades, which are facing outward, are the retreating blades. They produce little thrust compared to the advancing blades during cruise.

I believe that this offers an advantage over the Coaxial. A problem with the Coaxial is that on one side of the craft the low thrust retreating blades are located underneath the high thrust of the advancing blades. In addition, the Coaxial's lower retreating blades span the full length of the upper blades. This is source of strong rotor-to-rotor vibration.

I think that it has something to do with symmetry. ;)


I have read that the original ABC had big vibration problems. It had two 3-bladed rotors. Yes. It's top speed was limited by excessive vibration. These pages are on the subject of rotor induced vibration on ABC, 3 and 4 blade rotors.
OTHER: Aerodynamics - Vibration - Rotor Induced - Analysis of Coaxial (http://www.unicopter.com/0893.html)
DESIGN: UniCopter ~ Rotor - Disk - Lateral Dissymmetry of Lift and Drag? - (3-blades) (http://www.unicopter.com/0871.html)
DESIGN: UniCopter ~ Rotor - Disk - Lateral Dissymmetry of Lift (Drag?) - 4-blade Rotors (http://www.unicopter.com/1218.html)

Dave

[Graviman]

As far as the 15% benefit with respect to disk area, how much of that is undone by the fact that the lift vectors of the synchrocopter waste some of their effort against each other, since they are inclined outwards? You could probably do a ROM estimate of the lost lift of each rotor by multiplying it by the cosine of the shaft angle.


IFMU, in theory the intermesher will not lose efficiency since the downwashes force each other back to vertical. The rotors may actually improve the way the wake contraction is handled, although a ring rotor would offer greater benefits for coaxial only.

The main arguement for interleaving to my mind is maximising rotor area for a given weight. If you see aircraft width as a constraint, this points towards tandem layout. However, rear rotor will suffer from losses due to inflow.

I'm jus gonna sit right here on my fence...:}

Mart

[levo]

Sikorsky X2 Might be flying soon

www.sikorsky.com

[Graviman]

Great news! Any snipets of info come your way, Levo?

Mart

[22clipper]

Neat set of ideas if they can just get 'em together for critical mass? Wonder if the synergy really works to 250 kts? If it does then X2 is to Osprey as nailgun is to sledge hammer?

[hotzenplotz]

The Sikorsky website is not available for me.
Is it down?
If not, could anybody please post the news here, that we have conserved it?

Thanks

[IFMU]

hotzenplotz,

When I looked all I saw was a picture on the homepage. Not a real picture, just a CAD rendering. Unless I missed something.

-- IFMU

[hotzenplotz]

When I click the link than this happens:

http://img525.imageshack.us/img525/6593/unbenanntje6.jpg

:confused:

[Graviman]

Hotzenplotz, link/site seems to be down at the moment. I followed it and couldn't see any new info. Levo may just have been fishing for an update.

Mart

[hotzenplotz]

Thank you for the info.
Now I know thats not a problem of my provider.

[Dave_Jackson]

Hotzenplotz,

Homeland Security has control over the Internet. They check every attempt to access a defense supplier's site.

You have been denied access because your 'Location' is questionable. :)

[hotzenplotz]

:} :ok:

http://img144.imageshack.us/img144/1978/ixnay37homelandip1.jpg

[levo]

Hi try typing it in then enter just tryed it and its ok sikorsky site seams to work for me its a twin rotor with a propeller on the rear instead of a tail rotor tis is what it says inthe mag

Although the project was temporarily shelved in 2006 due to industrial action ,Sikorsky says it plans to resume development of its x2 next genaration helicopter later this year. The x2 has a coaxial design (2 rotors on the sane axis) and a pusher prop to provide additional forward propulsion. Its expected to reach speeds of 250 kts soon to fly as soon as project starts again.

[hotzenplotz]

Yes, the site is up again.

But I can’t find any real news about the X-2 program.

Too bad, I expected to find the date for the first flight or something… :(

[NickLappos]

Sit tight, Guys, the X2 is coming. Sikorsky folks are getting ready to shake it down, but these things take time.
I flew the original ABC upon which the X2 is based, and can assure you, the X2 will be worth the wait!

[Graviman]

Seriously looking forward to this one, Nick!

Let the Sikorsky/Schweizer design team know we are all enthusiastic, but pragmatic with it. I'd much rather wait to see a well sorted prototype, than end up discussing what went wrong with the program. :ok:

Mart

[22clipper]

More detail Nick. How do they test systems for a co-axial with pusher on a bird that isn't?

[NickLappos]

22clipper,
I am not sure what your question is.

[22clipper]

I was just curious what you'd been doing in the ABC? I'd read that they had tested a lot of the X2 concepts using standard helos as a test bed & I wondered how you could test something so radical on a conventional machine?

[IFMU]

I was just curious what you'd been doing in the ABC? I'd read that they had tested a lot of the X2 concepts using standard helos as a test bed & I wondered how you could test something so radical on a conventional machine?
22clipper,
I have followed the X2 in the media. If you go back through the old press releases, they flew X2 FBW on a 333, and lately they show pictures of ground test of a brand new airframe. Don't get confused with that other thread where they talk about that swing tail thing, that was old news.
I saw a clip from aintv, with an interview from Jeffrey Pino. He said that they had all the parts collected & the fuselage built or something like that.
http://www.aintv.com/home.asp?CATEGORY_ID=30&ID=112&FMT=WM
There is a little X2 animation, apparently from their HAI booth, but that was the only X2 picture.
-- IFMU

[NickLappos]

22clipper,

The old ABC demonstrator flew in the 1970's and early 80's and was the predecessor of the X2. Here is Dave's excellent site:
http://www.unicopter.com/0891.html

The X2 plan is to develop the airframe, the FBW controls and then the X2 rotor, so it is being flown that way. The first two steps have been accomplished, the third is approaching (the blades are going thru qualification, I think, and flight test is being planned).

[hotzenplotz]

@ IFMU

... lately they show pictures of ground test of a brand new airframe ... Are these pictures online accessible?

[IFMU]

http://www.vtol.org/news/issues107.html

[hotzenplotz]

Thank you :ok:

[Dave_Jackson]

The following patent was issued today;

US 7,229,251 ~ Rotor hub fairing system for a counter-rotating, coaxial rotor system (http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=7,229,251.PN.&OS=PN/7,229,251&RS=PN/7,229,251)

[Dan Reno]

This may be off base on this thread but the Sikorsky Cypher slowly faded and it was a counter-rotating vehicle, though unmanned. What ever became of it and besides not having a pusher and the noise issue, was it of any help with this new aircraft? Nick? Jack?

[NickLappos]

Dan,

The Cypher fell to company decisions on where the UAV future was, back in 2001. The Cypher was small and inexpensive (so that many units had to be built and sold to make any appreciable profit) but engineering labor intensive, so it was put on the back burner.

[Dan Reno]

Thank you Nick.

[Dave_Jackson]

This posting is placed here in the Sikorsky SX Coaxial thread since the following US Patent Application is including the SX coaxial configuration.

____________________



Nick,

As you probably know, I have an interest in the concept of 'Variable Speed Rotors and Propellers', having posted this publicly displayed thread (http://www.pprune.org/forums/showthread.php?t=181575&highlight=variable+speed) in PPRuNe five months before the filing date of the following Patent Application.

Therefore, it was interesting to read your US patent application 20070125907 ~ Variable speed gearbox with an independently variable speed tail rotor system for a rotary wing aircraft. (http://appft1.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PG01&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.html&r=1&f=G&l=50&s1=%2220070125907%22.PGNR.&OS=DN/20070125907&RS=DN/20070125907)

A question comes up, which I am sure you can answer.

The patent's tittle includes "...with an independently variable speed tail rotor system for a rotary wing aircraft.". In addition, Claim 2 says "... said tail rotor system at an independently variable speed relative said engine speed.", and Claim 14 says " ... and an independently speed-variable tail rotor system ...".

However, there are no details on this variable-speed tail-rotor ("transitional thrust system 18 and 18' "). In addition, the associated drawings only show a blank box.

I understand that the US Patent Office does not review the Claims in a Patent Application, but my question is why is there an 'all-encompassing' claim in the patent application?


Dave

[IFMU]

Dan,
There was another Cypher, it had a pusher:
http://avia.russian.ee/foto/sik_cypher2.jpg
And according to this page:
http://en.wikipedia.org/wiki/Sikorsky_S-69
There is this:
... 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 ...
-- IFMU

[NickLappos]

Dave,

The prior art in that field is vast. The work that was documented to support that and previous patent applications dates back years before your thread (it was while I was at Sikorsky, and I left months before your thread, for example.)
Not being a patent expert, I can't comment on how claims are worded or handled. Like the Michael Keaton character in "NIght Shift" I'm the idea man....

"What if you mix the mayonnaise in the can, WITH the tunafish? Or... hold it! Chuck! I got it! Take LIVE tuna fish, and FEED 'em mayonnaise! Oh this is great. [speaks into tape recorder] Call Starkist!"

[Graviman]

Not sure how many patents do get through - especially the overunity energy claims etc. It is difficult to really invent something new, since most ideas are a new application for an old concept. Must make patenting process more difficult to control.

With the headache that patenting presents to the private inventor, the thing that seperates a good company from a bad company is finantial reward for a patent which is incorperated. This encourages thought outside the box.

[Dave_Jackson]

Nick,

Thanks for the reply. Perhaps your departure from Sikorsky resulted in the legal objectives overriding your technical objectives, when the lawyer was writing the Patent Application.

Incidentally, your Patent Application includes a coaxial configuration drawing. This drawing was used six months earlier in three coaxial-ABC Patent Applications. In your Patent Application, the lawyer, perhaps in a rush to pump out coaxial-ABC patents, didn't even reference the text to this drawing correctly.


Mart,

Times have changed.

Recently, much has been written about the growing abuse of US patent system and its inability to now serve its basic objectives.

Yesterday's article in the highly respected Globe & Mail 'Tech Crusaders Are No Match For Mighty U.S. Patent Lobby (http://www.theglobeandmail.com/servlet/story/RTGAM.20070612.wibworld12/BNStory/robColumnsBlogs)' is just one more example. The year-by-year increase in number of US patents is phenomenal. Most of these patents are insignificant drivel. However, one of the things they do is allow large corporations to use their vast wealth as the hammer, and their irrelevant patent as the excuse, to 'squash' the under-funded legitimate invention.

You may find the last line in this quote from the above article of specific interest.

"The U.S. drug industry has no interest in anything remotely approaching an overhaul. It is lobbying furiously behind the scenes to make sure this legislation dies or is seriously diluted. Joining the drug companies are a broad group of blue-chip manufacturers, including United Technologies and 3M Co."


Dave

[Dave_Jackson]

http://www.unicopter.com/Temporary/KamovPoutine.jpg

Stolen from quadrirotor off of another forum with out any permission whatsoever. :uhoh:

[IFMU]

http://www.ainonline.com/news/single-news-page/article/x2-could-make-first-flight-by-months-end/?no_cache=1&cHash=da381315d6

The hardcopy has a picture in it.

-- IFMU

[Graviman]

Interesting article. Good luck X2 development team. :ok:

[Dave_Jackson]

IFMU saidThe hardcopy has a picture in it.


Is this the picture? :O

http://www.unicopter.com/Temporary/Rieseler_R_II.jpg

You've got to admit that those are darn close rotors for a mid-1930's helicopter.

Dave

[Graviman]

Dave, i'm impressed with that Rieseler RII - 250KIAS back in the '30s! ;)

[IFMU]

Is this the picture?
Nope, pic I saw was greener.
-- IFMU

[Dave_Jackson]

Mart,

Walter Rieseler is referred to, in Germany at least, as the 'forgotten pioneer'.

I think that you will find his unique control system very interesting. Here is information on it;

Wilford WRK Gyroplane (http://www.aviastar.org/helicopters_eng/wilford.php)
On the NACA Search page (http://ntrs.nasa.gov/search.jsp) and Enter Search Term 'TN-492'.
US patent 1,975,124 (http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=1,975,124.PN.&OS=PN/1,975,124&RS=PN/1,975,124)____________

IFMU,

The grass is always greener on the other side. ;)


Dave

[IFMU]

In searching for the picture, I found this:

http://www.aviationtoday.com/Assets/Image/Schweiz-X2Up1-Left-Quad.jpg

But this looks like an old picture compared to the december issue of AIN.

[Graviman]

Unable to download NASA pdf of control system analysis, but yes it was ahead of it's time. It certainly demonstrates that a cost effective hingeless gyro is practical. Maybe even manouvreable.

I think part of the difficulty with modern hingeless rotors is that the rotor frequency is so much higher now, due to the higher speeds and lower rotor mass. This means that any rotor eigenmode is comparable to the rotor frequency, so there is inevitably lead angle required in the pitch link. Although the tip radius was quite small, those tip heavy blades would likely have all sorts of interesting modes.

Actually, there are days when i catch myself wondering whether you are right about laterally seperated rotors. It would push roll reaction times way down, since heli does not have to pendulate to new equilibrium. I have even pondered about smaller control only rotors, like Sikorsky's early VS-300! But these days a good SCAS control system can response shape the cyclic input to get a reasonable response. I think keeping the cost and weight of the machine down is more important.

It will be interesting to see how the X2 development engineers overcome the difficulties if the envelope is pushed above 250KIAS. Clearly active tip control will become critical to avoid blade divergence. I would be curious how much higher the blade 1st bending frequency is pushed too. So roll response may approach that of fixed wing...

[Dave_Jackson]

Mart,

In IFMU's article it says; Grant emphasized that the X2 is a demonstrator for a “suite of technologies” that might have applications for future-design civilian and military rotorcraft, but it was unlikely that the twin coaxial main rotor system could be applied to smaller aircraft with smaller rotors due to its rigidity and resultant weight. “You’re probably not going to see these applications in the 3,000-pound weight class,” he said. “This [6,500 pounds] is around the size we would want to be the book end for the low end of the weight class. It is a lot easier to go big.”


You mention;I think keeping the cost and weight of the machine down is more important.


Why does Sikorsky feel that 6,500 pounds is the lower end for ABC helicopters? There does not appear to be any technical reason for this remark. Perhaps, Sikorsky has no interest in them, or in other companies, building ABC helicopters with less than 6 seats.

_____________


Rieseler's means of producing 'Absolutely' Rigid Rotors (http://www.unicopter.com/B329.html#ARR) by using aerodynamically balanced pitch instead of aerodynamically balanced flap is ingenious.

I'm going to look into it further, since it might be a logical step toward the UniCopter's and the Nemesis' Advancing Blade Concept. (http://www.synchrolite.com/B263.html#ABC) It will be posted as a separate topic on a new thread from this X2 thread if it continues to look good.


Dave

[IFMU]

Here's another similar picture I found on some German site:
http://img505.imageshack.us/img505/861/x2wj0.jpg
and this one was from last year:
http://www.vtol.org/news/X2GroundTestStartnightime.jpg
-- IFMU

[quadrirotor]

Rieseler, helico or tail-sitter???

What difference with a tail-sitter?
http://www.rotaryforum.com/forum/attachment.php?attachmentid=38335&d=1189528965

[quadrirotor]

An other tail-sitter:

http://www.dailymotion.com/search/h%C3%A9licopt%C3%A8re/video/x3pj1w_helicoptere-personnel_extreme

[Dave_Jackson]

quadrirotor,

The Austrian (OOPS make that German) pilot of the little coaxial must have gone on a diet. This time he was able to keep the craft off the ground. :)


Are you here to steal back the picture I stole from you?
Or, are you the one who just stole IFMU's X2 picture. :eek:

Dave

[Graviman]

IFMU,

It's nice to see the X2 in the flesh at last (or was this a mockup?). Somehow it looks all innocent there, despite what it is going to achieve. I'm always amazed how a pile of parts can slowly, but magically, become a machine in the hands of talented test fitters.

I bet it's starting to look the business at Schweizer now...

[Graviman]

http://en.wikipedia.org/wiki/Sikorsky_X2
http://upload.wikimedia.org/wikipedia/en/c/cb/X2_attack.JPG
Artist conception of a potential armed high-speed escort/attack variant of an X2 aircraft. X2 technology is envisioned to be applied to a wide range of typical rotorcraft roles.
:ok:

[quadrirotor]

I think this one has a better handling, as she could have a vectorizing tail...


http://www.rotaryforum.com/forum/attachment.php?attachmentid=40120&d=1194272226

[IFMU]

I think this one has a better handling, as she could have a vectorizing tail...

What would that buy, besides a more aft CG? Consider that a rigid rotor helo has lots of control power an zero airspeed already.

-- IFMU

[LupinIII]

At an all-hands meeting, Jeff Pino claimed first flight target date is 1/15.

A bare rotorhead run was performed late last month.

[heli1]

Looking at those pix reminds me of the ill fated Cheyenne......too complex for what you achieve.
P.S. Jeff Pino seems to be slipping the date again...first flight was supposed to be before Christmas.

[Graviman]

At an all-hands meeting, Jeff Pino claimed first flight target date is 1/15.
A bare rotorhead run was performed late last month.


Great news! :D

Take your time guys, and make it the success it deserves to be.
Us X2 fans have waited patiently this long...

[IFMU]

At an all-hands meeting, Jeff Pino claimed first flight target date is 1/15.
A bare rotorhead run was performed late last month.
I often wonder if the people at any big aerospace company that release flight dates are in touch with the project, or are isolated from it by layers of management. Maybe this is not the case here, but I wonder.

I guess we'll find out, in another month!

-- IFMU

[Graviman]

IFMU, i can only speak from the perspective of having been involved in the design, analysis, testing & development of many ground vehicles for various industries (it still ain't helicopters :sad:). Any particular objective date will be more a target for the engineer's to aim towards. A well run project will adjust to the development activities, but will not dictate them.

Let's face it this is a complex helicopter program, not a train timetable!

[Dave_Jackson]

Mart;
The originally promised date was late 2006.
You say;-
"Any particular objective date will be more a target for the engineer's to aim towards." Perhaps the Engineering dept. should set the Engineering dept's target date. Not the Hyperbole dept.

Perhaps you recall;"They’re calling their cocktail of integrated digital, aerolelastic and compound technology the X2 and say that its unique co-axial/pusher prop design will do 250 KTAS knots by the end of 2006. ..............

......... Jeff Pino, now in charge of Sikorsky’s strategic programs put his people in special shirts, had a mock-up ready, and pulsed people’s cell phones to get them to come to a briefing.

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.

Finger paused, then turned away, body language suggesting this was no time - no time at all - to engage in a debate on the esoterics. ................."

David S. Harvey

[turboshaft]

Dave,

The original date communicated to subs when the program started was actually mid 2006.

[Dave_Jackson]

turboshaft,
http://www.unicopter.com/Temporary/Time_Flies.jpg
Dave

[IFMU]

Dave, in his own style, has captured the essence of what I was saying. Flight dates have been published before, and have not happened. It's not just a sikorsky thing, not just an experimental aircraft thing. Look at the headlines for the Boeing dreamliner slips. Look at the eclipse jet. It would seem to me to make more sense to quietly chug along, fly or certify whatever it is you are working on, then announce it to the world. Maybe that works better for experimental stuff, as there is no customer waiting for an airframe.

-- IFMU

[turboshaft]

Nick & co. will have better insight, but I'd hazard a guess that the 'depriorization' of the X2 demo in late 2006 - officially attributed to the demands of SAC's bread & butter (H-60/H-53) programs - was in reality driven by early intel coming out of the JHL CDAs confirming the Army's preference for a tilt solution. Post-JHL, the X2 focus now appears - going on SAC's representation at Quad-A etc - to be on a 6K UCAR (coincidentally sized around the demo ship! :E).

(As for tempus fugit, let's just hope that Mr. tempus regularly checks for TFRs, otherwise he'll soon discover he has company! :E)

[Peter-RB]

About 1945/7 Avro of Manchester started to manufacture and build the Avro Shackleton Long rang Maritime aircraft, so good was this aeroplane that it only left service about 1989, what might you be asking has this got to do with the current disscusion regarding the contra prop Sikorsky X2 hybrid Helicopter, well my twopen'th is this. the Shackleton was powered by 4 Roll Royce Griffon 58 V12 piston engs mated to a very strong almost agricultural gearbox with a huge siamesed propshaft that drove Two Contra rotating props, originally with the early marques of the Griffon both props were equal in diameter, but as the engine was powered up through the years the design guys realise that the propellor tips were comming perilously close to each other at certian power settings and in fact had in some case acutually hit each other, the clever guys at a local factory to me here in Lancashire realised that the tips passing each other were causing supersonic shock waves this had the effect of bending the tip of both front and rear blades inwards towards each other, after much testing they decided that the rear prop would be longer than the front prop and the cord of the rear one would be altered to take out this possiblity of inward bending when under certain power conditions, it worked and from about the early 50's the props fitted to the Griffon 58 had a greater diameter at the rear.

Is/ or could this have any bearing on the two different diameter rotors on the Sikorsky X2 hybrid ?

Peter R-B
Vfrpilotpb

[IFMU]

Is/ or could this have any bearing on the two different diameter rotors on the Sikorsky X2 hybrid ?

Peter R-B
Vfrpilotpb


Peter R-B,

covered earlier in the thread:

http://www.pprune.org/forums/showpost.php?p=2868961&postcount=3

IFMU

[Peter-RB]

IFMU,

Thanks for pointing that out, I missed seeing it , proves my mind/memory still works though!!:ooh:

Peter R-B
Vfrpilotpb

[Graviman]

Peter, this was my error in looking at the profile CAD rendering. The rotors on X2 are, to the best of my knowledge, the same diameter. I believe that same thread cleared that up.

However you have given the nail a glancing blow on the head. Any project of this nature is going to encounter things which set it back. Is that because the engineer's don't know what they're doing? Is that because the timing dates have not been sufficiently agreed. A resounding "NO!!" to both of those questions. This project is pushing the boundaries of what has been done before. Like the NASA space program it has setbacks, of either technical or financial nature, which alter the timing.

Actually, i agree with IFMU that Sikorsky have taken a responsible approach to this project (since there are no waiting customers). Don't forget there are shareholders, and the mightly United Technologies, to satisfy - often these folk do not have an appreciation of the technical difficulties but can understand targets. The compromise is that the project rolls on at a responsible pace, while arbitrary deadlines are set.

We will all be singing the praises of X2 soon enough - let 'em get on with it at a pace which gets it right...

[Dave_Jackson]

.
If Sikorsky is unwilling to rectify it's erroneous statements about the past (http://www.pprune.org/forums/showthread.php?p=3311712&highlight=Bunker+Hill#post3311712) why should anyone believe its present statements about the future?

.

[NickLappos]

Lots of drivel about schedule written here, much of it by folks who never built a flying machine in their lives.

The schedule is what it is, driven by money and luck, especially when new technology is being developed. No helo will fly before it is ready, and maybe not even then!

If you don't like the statements made by well-intentioned people whose crystal balls are not as shiny as yours, too bad. I happen to know the people involved in the various statements, they would probably resent the nefarious reasons drummed up by folks with too little to do. Sikorsky spent less than they wanted last year, because they had to produce enough profit to make their shareholders happy. Remember, money is what buys schedule, and all R&D cash for a real company (one owned by its shareholders and not by its government) comes off the bottom line. For companies owned by their national governments, all that is needed to fund some more R&D is to run the printing presses at the mint for a few hours longer.

[Dave_Jackson]

Nick,

There is much truth in what you say. However, I would politely ask that you consider what you have said and the words that you have used. Considered your comments, not in the context of helicopters, but in a socio-economic context. You have felt it necessary to use the words; "money", "spent", "profit", "shareholders", "money", "buys", "cash", "bottom line", "fund", and "mint".


Remember back when the vast majority of immigrants to the United States came from Europe. Many were of Germanic and Anglo-Saxon origin and they brought with them the technological knowledge that they had learnt in the 'old country'. Many of them became entrepreneurs who took pride in their company, its products and its services. They tended to respect and serve the customers, the employees, the suppliers and of course the owner.

Today the vast majority of the immigrants are coming from the south and unfortunately they are unable to bring much in the way of formal training. Today the so-called prestigious positions are that of lawyers, marketers and stock promoters, plus the 'kings of the hill', the CEOs of large impersonal corporations. The Anglo-Germanic philosophy has been replaced by the Jewish philosophy. The United States has acquired a preoccupation with money.

Regrettably, this Neo-Con 'Need for Greed' has now started to undermine the once almighty dollar and thereby the purchasing power of the vast majority of Americans.

Dave

[Graviman]

OK guys enough Sky bashing for now, please! :)

I started this thread to discuss, and keep pace with, X2 developments as they happened. Lets keep it friendly.

Until X2 flies the market place, and it's criticism, is wide open for any of us..

[NickLappos]

Dave, I think you have it backwards. Edison, Ford, Tesla all worked, thought, dreamed of building "things" because they could sell them. The exchange of money is the way the world works, we must recognize that essential truth. This does not mean we must dump our values, because the ethical balance must also be fully considered, but the profit is the thing. If true accounting of issues were actually done (a rare thing) the ethical/environmental issues would automatically be covered, because they would be valued appropriately.

I admit to tossing in a bit of red herring about national investments, to stir the pot. It is true that the US are facing an extremely difficult challenge: The new communism, where state owned enterprises enable vast not-for-profit investment that sways the balance of competition. European companies that have their state as their largest shareholders and China where the state is everything are awesome competitors, IMHO. There are European "newspeak" counterclaims of US Gove investment, but that is hogwash that placates the reporters. If I could get the free loans that Airbus has gotten, for example, I could run a team that could make London Bridge hover.

svenestron talks about the NH-90 success story, but doesn't know that Finland had selected the S92 as their choice over the NH-90, until EADS (or should I say the French government) bought the largest Finnish aviation house. The day after they were bought, the Sikorsky phone calls were not answered. Period. The Swiss selected the Black Hawk as their mountain rescue helicopter back in the 1980's until Mitterand visited the Swiss president, upon which a completed turnaround occurred! I could go on, but it has all been said before (and countered by folks who think a billion dollars of free subsidy is a Government's right and duty - which it is, as long as we don't call it free market!)

[zalt]

Boo hoo, poor little Americans, they would never make political decsions to feather their own pork barrel (so to speak) and the rest of the world is just gangs up and is plain nasty to them when every American knows their products and (foreign) policies are always the best and that FAA, DOD & NASA don't subsidise their industry, mearly place research contracts and US industry never puts work out to foreign suppliers simply to curry favour.

Good to see you sticking to your ethics that the (foreign) customer is always wrong and probably corrupt. BTW You don't have Francois' presentation there do you Nick?

I guess the old Francophonic or Commenwealth influences are neats way to explain any sales Gulfstream loses to Bombardier eh?

[Dave_Jackson]

SvenestronCant’s say I see any point in what you’re writing.. sorry..Hell, neither can I. It was simply a plagiarization of the great futurist, Mr. Chicken Licken.



Mart (affectionately known to his friends as Graviman) brought Mr. Licken to my attention many years ago. Mart believes very strongly in the predictions of Mr. Licken. In fact, his previous post; OK guys enough Sky bashing for now, please! was the direct result of reading this latest prediction by Mr. C Licken (http://en.wikipedia.org/wiki/The_Sky_is_Falling).



Nick. The prediction must be a lie. In reality, I understand that recent Sikorsky profits have been the highest ever.

In addition, I understand that many of the components in the X2 were loaned/gifted to the project by potential Subs. It is fair to speculate that Sikorsky's development costs of the X2 are less than the renumeration package to the CEO, over the same time frame.

Last punch.;) It is unfair to consider Tesla and Edison in the same breath. Tesla was a humble unassuming inventor where as Edison was ........http://www.unicopter.com/Tape.gif.........


Dave

[160thfan]

Man, I have to watch a steady stream of "I hate America" crap on the news every night and now we have to paste it all over a discussion of my favorite topic of future helicopters, too.

All future helicopter designs will be paid for with money. To decry profit and earnings makes no sense. CEO wages are set by the board, balanced by performance. As a guy at the bottom of the ladder, my goal is to climb closer to that level. My best, fairest chance, to ever do that is in America. When Canada starts great advances in helicopter design maybe I will move there, but I doubt that will happen soon.

If Canada has some great disaster, who is going to be giving millions of charity dollars to help? Those dollars come from "earnings" "profit" etc. every time. Sure there are scumbag Americans but there are many,many more that work hard and give to charity needs.

Can we go back to the topic?

[Graviman]

cross-land, that video has really got my spirits up!

That is one serious looking machine - if it looks that good in a powertrain run-up, i can't wait to see those rotors whirling. This is regardless of any political b*llsh*t.

A good design is a good design, no matter who makes it... ;)

[160thfan]

I hope the video gets put up again. I saw it last night and wanted to watch it again. It was a Youtube post of a test run and it looks good.

[Graviman]

160thfan,

I think that was a sneak preview for us fans who have the vision to see beyond the immediate political horizon.

Good luck on the test flight program X2 team. :ok:

[160thfan]

That was pretty good Dave. I apreciate a good joke too.

[Dave_Jackson]

Mart,

Here is some information on the X2 rotors.

http://www.unicopter.com/Sikorsky_Blade.jpg

The 2 interrelated patent applications are;

20060269418 ~ Rotor blade for a high speed rotary-wing aircraft
20070110582 ~ Rotor blade twist distribution for a high speed rotary-wing aircraftThe blade planform and the twist that they are using to optimize the Figure of Merit in hover and improve forward flight performance are intriguing.

In addition, the upper blades have a different twist from that of the lower blades. Because a coaxial is not bilaterally symmetrical they are attempting to compensate by making the two rotors vertically unsymmetrical. Time will tell if two wrongs make a right. :rolleyes:

__________________

We were talking about disk loading and specifically the unevenness of the loading over the area of the disk, on another thread (http://www.pprune.org/forums/showpost.php?p=3782342&postcount=12).

The coaxial disk(s) on the drawing below is based on information in the above patents. Identical intermeshing and interleaving disks have been add for comparative purposes.

http://www.unicopter.com/1506-B.jpg

Dave

[Graviman]

Dave,

That is quite interesting. It shows where S69 program lessons are being carried forwards. Have a lookout to see whether vertical stabilisers are forward swept for improved autorotation yaw control, and whether there is a flow seperation keel plate to avoid shuffle in hover.

It looks to me like the hover performance has been slightly compromised in order to reduce the high speed reverse air flow circle down thrust. Aerofoils suffer divergence in reverse flow, so this is quite a sensible idea. I wonder whether that interesting planform, which will be slightly more expensive to manufacture, will find it's way into conventional helicopters.

The potential advantage of coaxial is that there is no loss of downwash in the reverse flow region. I realise your arguement is that interleaving avoids downwash over the fuselage, but good aerodynamics should allow the flow to pass without too much transition to turbulance. I wonder whether that blade profile helps here too.

[Dave_Jackson]

Mart,

Your first two paragraphs are valid.

I should have been clearer about the use of the disks. They were presented to show the aerodynamic interaction of two main rotor disks, and specifically the regions of high and low induced velocities.

As you know, high induced velocities are less efficient than low induced velocities. The fixed wing is far more efficient then the rotor blade simply because the fixed wing generates a fairly constant induced velocity over its surface.


As an aside;

Momentum Theory is a reasonable method of performing an initial assessment of rotor performance. This is because all single rotors are basically the same except for the nuances such as; twist, taper, etc., plus blade count.

However, IMHO, Momentum Theory totally breaks down when it come to the consideration of multiple, aerodynamically interactive main rotors.

This is why I express my disappointment that Igor led rotorcraft away from the aerodynamically superior twin rotors. It should be noted that virtually all of the research and development followed along behind the single rotor.

Rotorcraft have always been inefficient. However, when electric drives start permeating the fields of transportation the rotorcraft industry must look back to the past for it to move forward into the future.


Dave

[Graviman]

Well perhaps, Dave. I think Sikorsky have taken the engineering approach most likely to yield a successful project. Moving away from an S69 led design would just be too risky. Like Nick comments, X2 improves Vh by sacrificing some hover performance.

Once X2 does "what it says on the tin", there will be plenty of opportunity for aerodynamic refinements. My own thoughts are that there will be opportunities for a helicopter entrepreneur to introduce active blade twist. ;) Remember successful innovators identify the market gap, and taylor their devlopment to fill it...

[Dave_Jackson]

Mart, you say;
I think Sikorsky have taken the engineering approach most likely to yield a successful project. Me says;
I think Sikorsky has taken the approach most likely to yield http://www.unicopter.com/Temporary/Dollar.jpg



Mart, you say;
Moving away from an S69 led design would just be too risky.
Me says;
Au contraire. My complaint is that they did move away from the S69 design; 30 years ago.
And please, please don't use 'advances in technology' as the reason for the 30 year gap.


Theodore Shadow

[Graviman]

Sikorsky need to pay all those nice technicians, engineers and test pilots a salary so that they can pay their mortgage and put food on the table. All those selfish individuals won't work for peanuts, claiming instead that they want some security in their old age. Amazing really. :rolleyes:

Regarding shareholders, well, that's just the way the economy works. In the UK we regularly see some engineering company or another close because "the city" doesn't like the idea of long term investment for a small return. In fairness, i'm impressed Sikorsky continues to function only 12 miles from New York.

But these are not topics for this thread, please!

Concerning the 30 year gap from S69 to X2, i agree it can be seen as a shame. However it has been 35 years since Gene Cernan set the lunar challenge of today to forge man's destiny of tomorrow in Taurus-Littrow, and only now are Moon return missions being planned. In both cases the required market interest, to justify further development investment, just wasn't there.

Let's face it no one else has even tried to push a pure helicopter to 250kts.
But Sikorsky have now picked up where they left off, and frankly should be congratulated for making the effort.

[Dave_Jackson]

Mart said;
"Let's face it no one else has even tried to push a helicopter to 250kts."


Leishman holds the Minta Martin Chair of Engineering and is a Professor of Aerospace Engineering at the University of Maryland. His new book is showing that he is not an enthusiastic proponent of the tiltwing.

Here is one unflattering statement. ~ "at its maximum gross weight, the V-22 cruises at a true airspeeds closer to 220-250 kts (not 300 kts as superciliously claimed in various sources, including the manufacturer's own publicity materials) at altitudes of above 4,000 feet," ~ Source THTF - page 21 (http://www.unicopter.com/B281.html)

[21st Century]

Tha BA609 has done 310kts. So far... Can't wait for the 'B' model!
:}

[21st Century]

I thought that would end the discussion!!!
;)

[Graviman]

21st, i changed my post to say that no one has pushed a "pure helicopter" to 250kts. And indeed congrats are in order for the BA609.

The V22 is generally cited for tiltrotors, but the discussions are not favourable because of the high disk loading in hover. This means the tiltrotor does not lift as much payload as a comparable helicopter.

The reason X2 has generated such interest is that it has the diskloading of a conventional helicopter, but also overcomes the retreating blade stall limitations. On paper this means X2 derived machines will gave tiltrotors like the BA609 a run for their money.

X2 will open the door for a new generation of helicopters... :ok:

[21st Century]

Mart,
You're quite right, many things in aviation require a trade off. Both aircraft will likely perform very well. The tiltrotor will always have the edge on speed, and the X2 will have better lifting capability relative to power available.

[JohnDixson]

The X-2 will be able to autorotate.

John Dixson

[21st Century]

Apparently the BA609 will be able to autorotate as well. Unlike the V-22 that would have in the area of a 4-6000fpm ROD, the 609 may be in the area of 3000fpm (double an avg helicopter). So the best thing to do would be to land it like an airplane when possible, and if not, autorotate and expect to walk away with a dinged up aircraft (the penalties of combining very high speed with vertical t.o. and landing capability). The X-2 variants won't have the same limitations (or the same top speed capability). Dual turbine engine flameouts can occur (i.e., fuel contamination, etc.), but what is the occurrence rate?

[IFMU]

21,

ROD is only part of the story. You have to arrest that ROD too, even if it is "only" 3000 fpm.

-- IFMU

[21st Century]

"Only" 3000 fpm!!?? :eek:

[Graviman]

What does the H-V curve for BA609 look like?

I'm curious what the criteria for a tiltrotor are...

[21st Century]

Hasn't been released by BAAC yet.

[JohnDixson]

Sorry, should have made my post more specific:

I meant to observe that the X-2 configuration will be able to meet the power off landing requirements.

John Dixson

[Dave_Jackson]

John,

Re: Autorotation;

From; Department of the Army Historical Summary - FY 1976, on the Coaxial - Sikorsky ~ S-69 (XH-59) ABC

"Flight testing of the XH-59, advancing blade aircraft, resumed during the year. The tests confirmed certain advantages and shortcomings of the advancing blade concept, which is a coaxial counterrotating, hinge-less rotor system. The aircraft control system was quite responsive, noise levels were low, retreating blade stall was virtually eliminated, and hover performance was improved by the absence of a tail rotor. Structural loads in the rotor and control system ranged from low to moderate and indicated potential for substantial weight reduction. Weak directional control power in partial power descents and autorotation was observed. In future testing, improvements in autorotation directional control at low collective settings and high flare angles will be emphasized."


In autorotation, it will be interesting to see how the; Driven, Driving and Stall Regions play out, if the blade profile on above posting #102 is used.

Dave

[JohnDixson]

I recall that issue Dave, and as I remember, there were discussions about how best to dress that situation up, but I don't recall if there was a specific future solution ( for example, the Kamov approach ) that was decided upon. Having a fly-by-wire control system certainly improves the ability to implement whatever option is selected.

John

[IFMU]

If you read Prouty's "More Helicopter Aerodynamics" he has a chapter on coax and synchrocopter configurations. He mentions the S69 and how the rudder was swept aft, like a c172. In autorotation, the airflow was up the hinge line. Prouty makes some comment about how that would be a lesson learned for the next time around. If I can find the Prouty book I could post his statement more accurately, maybe somebody else has it.

-- IFMU

[Dave_Jackson]

IFMU,

Yes, he does mention the change that Sikorsky would make to the hinge angle of the rudder on a future ABC.

I would quote it, however, when reading the last sentence in the chapter my eye's watered up and the book had to be put down.

"The synchropter may be an idea whose time has come and gone. On the other hand, it may have been ahead of its time and just the right configuration for some future helicopter requirement." :)

Dave

[Graviman]

Dave, synchropter has a compact gearbox and rotor configuration. The rotor mast shafts are short, so minimise flexure. Access of control links to swashplate is straight forwards. It also offers the performance advantages of coaxial.

The only possible disadvantage is head clearance... :eek:

[Dave_Jackson]

http://www.unicopter.com/FlettnerPrincipalAssy.gif
The Flettner FL282; Transmission plus Flight controls plus Rotor-hubs.

Graviman, The only possible disadvantage is head clearance... I assume that you are talking about the low blade tips at the sides. That ain't head clearance. Hell, Herman Goering kicked one of the blades with his boot. :)

The Flettner FL282 (http://www.unicopter.com/0474.html) had an angle of 24-deg between the two masts. Kellett (http://www.unicopter.com/0896.html) wanted to go to 3-bladed rotors with greater rigidity, however lack of funding and his demise ended that endeavor.

Extremely rigid rotors result in a smaller angle between the two masts, plus no blade droop. The blade at 90-deg azimuth on the proposed wide stagger UniCopter (http://www.unicopter.com/1097_Wide_Stagger.gif) actually has a positive angle of 1-deg.

Dave

[Graviman]

CEFOSKEY, that is still good news to hear. What CAD package is being used?

[IFMU]

http://www.aviationtoday.com/rw/topstories/19065.html

http://www.aviationtoday.com/rw/issue/departments/rotorcraftreport/18916.html

[Graviman]

That said, Sikorsky President Jeff Pino told Rotor & Wing his marching orders to the X2 team have been: "Fly when you’re ready."


That says it all really. This is the sign of a well run project, lead by a guy who understands the technical difficulties.

I'm tempted to head back Houston way just to see this - probably a little short notice for flights etc.

Good luck Sky, and take your time. The X2 fans will patiently wait. :ok:

[Dave_Jackson]

But we may revive the VDTR.Well, I'll be damned.

Dave

[IFMU]

But we may revive the VDTR.

Well, I'll be damned.

Dave
What this industry really needs is a good variable diameter coffee mug.

-- IFMU

[Graviman]

CEFOSKEY,

Those are some pretty neat concepts. It would be great to see some of these take to the skies in the future.

Why would Variable Diameter Tiltrotor be of interest to Sikorsky? :confused:

[NickLappos]

Some pics floating around the net:

http://webpages.charter.net/nlappos/X2%201.jpg

http://webpages.charter.net/nlappos/X2%202.jpg

[22clipper]

With that 6 bladed pusher & 4 times as many rotor MR blades as I'm used to, that machine must be all my fixed & rotary wing fanatasies rolled into one?

Boy when they stiff MRBs, they do mean stiff eh?

[IFMU]

That is a bad ass looking machine.

-- IFMU

[Graviman]

Definate quickening of the pulse on seeing that.

Any word on who the lucky TPs are going to be, or is it bad form to ask such a thing?

[Graviman]

CEFOSKEY, that is one seriously sexy looking ship. Even without all the fairings. ;)

Nick, i'm suprised you're not popping back to Sikorsky for some stick time with that good looking bird!

Good luck on the tether test flying. Although excited, your fans are still patient - this is a challenging project.

[maxtork]

Good looking machine for sure! At first glance it almost seems as if there is not enough vertical fin area. The cabin section ahead of the mast looks like it is a good bit larger than the back half. I'm sure it is fine as there are far smarter people than I putting it together. Maybe it will look different once the last cowlings are on over the oil cooler in the back. Nevertheless I can't wait to see this thing go!

Max

[Graviman]

That's an interesting point, maxtorque. The yaw control is entirely dependant on differential collective pitch of the main rotors. Excessive weathervane stability may have adverse affects yaw control. I have been trying to work out if the central rudder is steerable for autorotation.

I must also admit to wondering whether the fly-by-wire is doing a lot more than just the normal pitch and roll stability and control augmentation. It may also extend to eliminating any tendancy for dutch roll, which is the norm in fixed wing now (non FBW favoured spiral divergence). The guy behind the Comanche control system has some pretty remarkable ideas for extending the fatigue life of all the main systems. I would not be suprised to see that implemented here too.

Also notice the small diameter of the main rotors. This is the necessary compromise of increasing disk loading in hover to push up the min power speed (Vy), which improves cruise efficiency. The added benefit is a higher natural frequency of the rotor blades, which pushes up the effective hinge offset for a snappier response.

That pusher prop also looks capable of sinking a lot of power at lower than cruise speeds (Ct/Sigma). I wonder whether the old Cheyenne trick of using the pusher prop for holding various pitch attitudes in hover is being saught.

If ever there was a machine which looked fast standing still this is it... :ok:

[maxtork]

Graviman,

I agree...doing Mach 2 without moving in my eyes!

I wonder also if there is a gearbox at the end of the boom for the pusher prop or if it is a direct driveshaft from the main box. It looks as if the latter is the case and if so that would put the driveshaft running right OVER the engine. I guess it isn't a big deal but just out of the ordinary.

Speaking of disc loading, how is it figured for a coaxial aircraft? Do you figure the disc area for both rotors or just one since they are acting on the same stream tube?

Max

[Graviman]

maxtorq, that's one for Dave Jackson and his magic spreadsheet. ;)

In a nutshell you assume the same column of air is being induced by the blades in both rotors at the same time (ie on a single plane). There is a pedantic argument that the lower rotor sees a higher induced flow, but Nick would go to lengths to point out that only works in ideal hover conditions. At cruise the flow outwash contraction will be some way behind the machine before you need to overly worry about this. I would imagine the FBW uses a laser gyro to trim differential collective for precise yaw control. I'll give you a better answer though when i've read the Leishman paper on my desk.

The other feature to notice is the blade profile. The tips have a nice elliptical taper to produce large vortices with reduced local velocities. The inboard section uses an inverse taper so that the retreating portion in the reverse flow circle can be feathered. Again a compromise which sacrifices some hover performance for improved cruise efficiency.

I'm not sure about that rear structure being a reducer gearbox though. It looks more to me like a pusher prop collective pitch mechanism. Driveline failure is generally the result of joints failing. It can normally be contained by designing a surrounding structure which limits the radial movement of the broken driveline. In the worst case that the single LHTEC800 engine was damged, the main rotor and flight controls still allow an autorotation. FBW will be triplex or quadruplex.

This is an experimental machine, so Sikorsky are naturally being gradual about performance expansion. With 17 engine failures under his belt i'm sure Nick, or indeed any TP, would heartily agree that this is a wise philosophy.

[IFMU]

This will also benefit autorotation, by providing an additional source of windmill brake power.
Would this be a big benefit? Wouldn't that cause a lot of drag, which would require a higher descent rate in turn? I would think a lower disk loading main rotor would be a lot better at capturing that energy.

Good luck on the tether test flying.
Are they really going to do that? Igor Sikorsky did tether tests on the VS-300, according to my history books, but I thought they gave it up after that.

Any word on who the lucky TPs are going to be, or is it bad form to ask such a thing?
Sounds like a good question for our resident X2 inner circle guy, CEFOSKEY. Maybe he will tell us after heli-expo.

-- IFMU

[Graviman]

IFMU, that pusher prop windmill brake power comment has been removed since i realise it was probably in error. [edit 23Feb08]

However, a potential advantage is that the pusher prop could be used to pull energy out of the airstream. The immediate advantage would be a lack of need to drop collective and flare in autorotation from cruise. This would also means that the main rotor would not have to be at flat pitch during autorotation, with forward cyclic, to allow good yaw authority. Coaxials can suffer reduced yaw control in autorotation, as the differential collective pitch does not transfer torque as when in level flight.

I imagine the pusher prop has an additional twist grip on the collective. Alternately the system may automatically trim the prop for all flight conditions. The system has good potential.

Once the machine has been tether tested, and the flight testing gently expands the envelope, i'm sure the TPs will have all sorts of interesting information. I for one will be very keen to learn and understand the TP feedback.

CEFOSKEY, I imagine all the engineers are mildly frustrated at the moment not having access to the X2. Prototype access is always a balance between the marketing department and development. Still at least the design breif of "take your time" means the X2 design can progress in a sensible manner - it is not always so. ;)

[Dave_Jackson]

Originally Posted by Graviman
IFMU, the advantage here is that the pusher prop can be used to pull energy out of the airstream. The immediate advantage is a lack of need to drop collective and flare in autorotation from cruise. This also means that the main rotor does not have to be at flat pitch during autorotation, with forward cyclic, which allows good yaw authority. Coaxials can suffer from poor yaw control in autorotation, as the differential collective pitch does not transfer torque as when in level flight.

Mart, would you please provide your source(s) for these intriguing statements.

Dave

[Graviman]

Dave, this stuff was cited by Prouty about the AH-64 Cheyenne in Helicopter Aerodynamics. Cheyenne was a compound helicopter which settled on a seperate pusher prop after eliminating various alternatives. Having a pusher prop doesn't eliminate the need to do anything in autorotating, but it does give the pilot more choices. It makes sense to me that X2 would take advantage of these. I think you can also make out a rudder line on the X2 central vertical stabiliser.
http://upload.wikimedia.org/wikipedia/commons/d/d3/Ah56a-lc1_b.jpg
http://en.wikipedia.org/wiki/AH-56_Cheyenne

Also i just noticed the use of NASC delta shaped intakes on the X2. I wonder if there is an advantage to be had here for spinning out debris from turbine ingestion. I've got X2 as my workstation backdrop, and it attracts a lot of interest. I think Sikorsky is onto a real winner with this project.

[JohnDixson]

I think I recall reading that the AH-56 had an automatic prop beta control, which would feather the pusher in the event of failure of the single T-64 engine.

John Dixson

[Dave_Jackson]

Mart,

Thanks for the reply.

IMHO, IMFU's concern about efficiency is valid. Why add the aerodynamic power loss of the propeller, plus the mechanical power loss of the powertrain to drive the main rotors when they can be driven directly from the airflow?

John mentions the feathering of the propeller. In addition, Sikorsky might have found it wise to insert an overrunning clutch in the propeller's powertrain for safety. This will preclude back-driving the rotors.


Prouty state that "One of the problems inherent in the compound helicopter configuration is that when entering autorotation at high speed the wings tend to produce so much lift that the rotor is starved for for the necessary thrust to keep it spinning.".....
.... the pilot could reduce the pitch of the propeller - thus converting it into a windmill that could extract energy out of the passing airstream. This could keep the entire drive system turning until the aircraft had slowed down to about 80 knots, at which speed it was put into conventional autorotation.

It would appear that this problem only exists because of the wings. I speculate, that this may only be applicable to the X2 if Sikorsky has a future intention of locating small wings under the large root cutout area of the new 'reverse taper' blades, to improve the craft's high speed performance.


Since we are limited to speculation;
I speculate that significant technical information on the X2 may be a long time in coming, if at all. Unlike the original coaxial-ABC, this project is not funded by the government and there may be little incentive on the part of Sikorsky to divulge much more than information for marketing purposes.
__________________

PS. You may wish to reassess you last statement regarding coaxials and yaw control.


Dave

[busdriver02]

While I agree that loads of info won't be forthcoming from Sikorsky any time soon, however if they do win a contract based on this tech, we might get some more good info then.

[Graviman]

Dave, John, agreed now that the pusher prop is probably of limited use in autorotation. Most likely it would be feathered to minimise drag, and may well have an overrun clutch. I'll go back and see if i can reword that post to avoid any misinformation.

Dave, i thought that coaxials could suffer reduced yaw control in autorotation for a given pedal movement? The little vector sketch in Prouty shows the rotors in windmill brake state generating some torque, so is probably not that valid. That central rudder will likely overcome any reduced effectiveness though.

CEFOSKEY, that's a shame that the X2 technology is being constrained in the marketplace before it has demonstrated it's potential. Hopefully that armed escort contract will allow this development to market. To my mind it is the right way to go for high speed helicopters.

[Dave_Jackson]

Some calculations from CEFOSKEY's links: (http://www.unicopter.com/1465.html#Calculation)

[IFMU]

http://www.shephard.co.uk/Rotorhub/ShowReportItem.aspx?ID=eb824920-6640-4324-aa22-2077277627c1

http://www.aintv.com/ then look for "x2 revealed"

Dave,

That disk loading seems amazingly low compared to an S76 or other high performance single rotor helicopter.

-- IFMU

[Dave_Jackson]

IFMU.

:uhoh: You are correct. The weight was WAY out.

The page has been corrected and the disk loading is now 7.6 lb/sq-ft.

Thanks

_________________

For comparison these are some of the specifications on the previous Sikorsky S-69 (XH-59A) ABC (http://www.unicopter.com/A064.html#ABC)

Dave

[Graviman]

Hmmm, some interesting technical information there, Dave. Noticeable how the X2 disk loading is higher than S69. That is almost a statement of intent that X2 will be a fast machine.

Chris, if X2 looks good now then those fairings will just be the cream on the coffee!

[Graviman]

Dave, i'm about half way through that Leishman paper. It is interesting to note that a practical coaxial with vertical rotor seperation will only suffer about 22% increase in power over widely seperated rotors, and not the 41% often quoted. To my mind this provide further justification of the X2 design over the lateral seperation of say a V22.

For a given disk loading, hence power required for HOGE with a specific payload, Sikorsky's X2 concept will always be able to land in places too tight for any tilt rotor. Also the lower roll inertia means X2 based designs will be better suited to landing on the heaving deck of a ship. The numbers just add up.


Maxtork, this paper details how you estimate coaxial performance:

http://www.baldwintechnology.com/MTR_AHS06.pdf


Expect to see X2 spawn a new generation of transport concepts... :ok:

[Dave_Jackson]

Mart,

I totally agree that twin main rotors (or perhaps an even number of main rotors :)) is the future.

The question of Rotorcraft vs PropRotor, and the sub-questions related to which configuration in each of the above two categories is optimal will probably depend on the specific applications for the craft, plus what future technological advancements come about.

IMHO, the coaxial-ABC is a step in the right direction but it is inferior to other twin-rotor alternatives. Maybe we will eventually find out why the coaxial-ABC was rejected from the VHL completion.

Dave

[Graviman]

Dave, get your ABC intermesher project off the ground and i might agree. ;)

For big government contracts, politics plays as much a part as engineering.


I congratulate Sikorsky for having the gumption to do X2 on it's own to prove to the world that this design will work.

[chopper2004]

heres a pics I took on Sunday in Houston
http://photo.ringo.com/255/255543268O120395390.jpg


http://photo.ringo.com/255/255640007O824056798.jpg

[IFMU]

Thanks for posting the pics chopper2004. Mart, looks like there is a name on the canopy on the second photo, maybe that answers your question about who is flying it. 007?

Maybe we will eventually find out why the coaxial-ABC was rejected from the VHL completion.
Mebbe it shows so much promise that somebody is concerned to see it compete against a tilt rotor.

-- IFMU

[Graviman]

Good luck with the first flight of X2, Chief Test Pilot K. Bredenbeck. :ok:

Thanks for the pictures Chopper2004, it looked like a great event.

IFMU, i think that was very much the concern for the JHL contract. V-22 represents many 1000s of man-hours investment. To simply pull the plug on tilt-rotor would leave a lot of folks very annoyed. Sikorsky have taken a very sensible approach and developed X2, in the same way that Bell originally developed XV-3 (http://en.wikipedia.org/wiki/Bell_XV-3) and XV-15 (http://en.wikipedia.org/wiki/Bell_XV-15), as a technology demonstator aircraft.

In the long run, i believe that X2 represents the next generation of helicopter development. The fact that the engineering numbers describe a machine with good payload-range performance means that there is great commercial potential. I wish Sikorsky luck because i would like to see the potential realised.

[Dave_Jackson]

Mart,The fact that the engineering numbers describe a machine with good payload-range performance ....Would you please provide the source of this fact.

Thanks
Dave

PS.
Here is another interesting article on coaxials that you might like.
A Survey of Theoretical and Experimental Coaxial Rotor Aerodynamic Research (http://ntrs.nasa.gov/archive/nasa/atrs.arc.nasa.gov/975555_coleman/975555_coleman.pdf)

[Graviman]

Dave, compared to V-22, X2 will have a lower disk loading so will require less power for a similar MAUW. My source:

http://en.wikipedia.org/wiki/V-22_Osprey
Disc loading: 20.9 lb/ft² @ 47,500 lb GW (102.23 kg/m²)

http://en.wikipedia.org/wiki/Sikorsky_X2
Disc loading: ? lb/ft² (kg/m²)

http://www.unicopter.com/1465.html#Calculation
Disk loading at GW: 6.2 lb/sq-ft - S69 spec quoted

Even accounting for errors and design difference in X2, the difference is disk loading is such that coaxial has to have better hover performance.
I'm confused, i thought you had a guestimate disk loading for X2 at some point?

CEFOSKEY, it a bold experiment indeed. Good luck to all involved! :ok:

[Dave_Jackson]

Mart,
"... compared to V-22 ...Thank God. For a moment, I thought that you might have been comparing it to the Interleaving-ABC. :E


I'm confused, i thought you had a guestimate disk loading for X2 at some point? It was removed because of the problem in determining 'Effective' Disk Area.

Dave

[IFMU]

http://www.youtube.com/watch?v=G9ZTfbcao1M

Quick! Before they pull it!

-- IFMU

[HOSS 1]

This pilot is "007"???

C'mon, EVERYBODY knows it should say "Bart" :ok:

[Dan Reno]

Gee, thought it would be much bigger!

[Dave_Jackson]

http://www.npl.washington.edu/cgi-bin/counter.cgi?av_27

[Graviman]

IFMU, that video is excellent! Looks like the CX2 was done by someone within Sikorsky. A lot of knowledge about the fuselage details. I wonder whether it was done while X2 funding was a little tight - i know the frustration that can cause. Any inside info CEFOSKEY?

This is the talk given at Heli Expo on X2:

http://www.youtube.com/watch?v=ILI_vaWCf5g&feature=related

The thing i find amazing is that X2 disc loading is similar to S-76! Hence has a similar autorotation ROD! This for a helicopter which could leave most ground vehicles (including an F1) behind is awesome. Also you can see the rudder hinge lines on the outboard vertical stabilisers for good yaw authority in autorotation. Flight safety has not been compromised for the additional performance.

The horns imply that there is a mechanical connection to the rudder control at least. I have been trying to work out whether the FBW head is hydraulic or brushless DC. I assume the central shafts hold a concentric spider arrangement for the coaxial rotors. This means there would be good access to both swash plates for either actuator. What was Comanche?

I can't wait to see the YouTube video of the real thing. :ok:

[Dave_Jackson]

Graviman,The horns imply that there is a mechanical connection to the rudder control at least. :confused:
Please elaborate.

Thanks.

[IFMU]

I have been trying to work out whether the FBW head is hydraulic or brushless DC.
Graviman,

You lost me here. Are you implying they are using IBC? I haven't seen that in any of the propoganda, surely if they were that far ahead they would drum their chest about it.

-- IFMU

[NickLappos]

ifmu, when you say propaganda, it means that you dont believe what they are saying - a pox on you! Those guys who are working on the X2 are just like you and me (except they know what they are doing, mostly.)

Grav, the FBW control systems are hydraulic, the FBW works a dual valve on the servos.

To my knowledge, the full electric servos that have been propagandized on other aircraft have some real problems, and those programs are a bit behind, due to that. jamming and wear on the jackscrews is reported thru the grapevine.

[212man]

To my knowledge, the full electric servos that have been propagandized on other aircraft have some real problems, and those programs are a bit behind, due to that

Does that include the B787?

[Dave_Jackson]

A month or few ago, Jeffery Pino said that electric servos are to be Sikorsky's next R & D project.

The accuracy of the above recollection is subject to an Alzheimer's and a dementia test.

[Graviman]

Heli Expo unveiling of X2 (FastForward to 29 sec):
http://www.youtube.com/watch?v=FlrqYowMgNI
Although Rotorheads got a sneak preview, including that beautifully engineered bearingless rotor hub. :ok:


Dave, what i mean is the rudder horns visible at the lower tips on the outboard vertical stabilisers. These increase the aerodynamic loading ahead of the hinge line. They are a mechanically simpler method of fitting trim servos to keep the control forces down.

Nick, that's interesting about full electric servos being difficult to implement in helicopters. I imagine the duty cycle must be far more extreme than even a manouvreable fixed wing, since there will be 1P load variation from aerofoil moment changes. With the upper rotor causing various additional pitch link loads on the lower rotor, from spanwise variations in AOA at least, X2 designers sensibly opted for a hydraulic solution proven on Comanche.

212man, check out the 5th story on this link:
http://www.vtol.org/news/issues106.html

Agusta Westland Starts Fly-By-Wire EH101

Agusta Westland has launched the Helicopter Electro Actuation Technology (HEAT) program for the Royal Navy EH101 Merlin HM Mk.1. The HEAT system introduces an all-electric primary flight control system with electro-mechanical actuators. DC brushless motors, high speed motor controls, and quadruplex fly-by-wire primary flight controls will eliminate hydraulics, accessory gearboxes, and most mechanical flight controls. HEAT promises to enhance EH101 reliability and reduce crew workload, aircraft weight, and aircraft maintenance costs. The system will introduce Advanced Control Technology, including active side-stick controllers and is expected to open ship operating limits in adverse weather and improve tactical handling in low-altitude flight. Agusta Westland previously projected first flight in late 2006.

The third-generation fly-by-wire development effort follows the award of the Merlin Capability Sustainment Plus (MCSP) contract announced by the UK Ministry of Defense (MoD). The contract upgrades 30 Royal Navy Merlins with an option for a further eight aircraft to address systems obsolescence and introduce an Open Systems Architecture (OSA). The Royal Navy Merlin bought 44 Merlin HM Mk. 1s. The aircraft became operational in 1999 and is expected in service past 2030. Lockheed Martin UK Ltd was named preferred contractor in 2003 to assess Merlin upgrades and remains responsible for mission system improvements. Work at Yeovil starts in 2010, and the first modernized Merlin is expected in service in 2013.

The HEAT consortium teams Agusta Westland, BAE Systems, and Claverham Ltd with the UK MoD Merlin Integrated Project Team. BAE Systems provides the fly-by-wire system while the Claverham division of Hamilton Sundstrand supplies the actuators. Agusta Westland has had a HEAT integration rig working at Yeovil in the UK since November 2005 and will integrate the technology into the helicopter.

[Dave_Jackson]

Graviman,

The reduction of control forces by locating the pitch axis of an airfoil at approximately 25% of plan-view area (25% of chord) is understood.

You said;The horns imply that there is a mechanical connection to the rudder control at least.
:confused: Why must it be mechanical? Or, do you mean a mechanical connection without any power assist?

______________________


For comparative purposes; here is a picture and a drawing of the of the S-69 (XH-59) rotor hub.

http://www.unicopter.com/0891_Enlarged.jpg


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

[IFMU]

ifmu, when you say propaganda, it means that you dont believe what they are saying - a pox on you! Those guys who are working on the X2 are just like you and me (except they know what they are doing, mostly.)
Nick,

I would guess that the guys working on the X2 are not the same ones that dish out the propoganda, or marketing if you prefer. Personally I'm a fan of the concept, it will be interesting to see how many of the spin-off aircraft from the marketing become real, or not.

-- IFMU

[IFMU]

I thought I read somewhere that if you are down to 1 channel of the HEAT actuator, that you can't react all flight loads. That's a lot different story than hydraulics. Am I remembering that right?

-- IFMU

[NickLappos]

IFMU,
It really depends on the design constraints, you can make it do anything.

Grav, you hit the nail on the head. The typical helo servo is working like a dog in the 5% region around its cruise setting, and it can really take a beating there. A FW application is more routine, IMHO.

That being said, I diid not know that the 787 was going pure electric. Dave got a reference?
Thanks

Nick

[212man]

Yes: good old MOOG supplying the actuators!

[Dave_Jackson]

Nick,

Sorry. I know very little about the Boeing 787.
Perhaps 212man does.

Dave

[IFMU]

I imagine the duty cycle must be far more extreme than even a manouvreable fixed wing, since there will be 1P load variation from aerofoil moment changes.

I would think that each time a blade passes over the spot on the swashplate where a servo is, it would give it a whack. That would make it an NP phenomenon.

-- IFMU

[Graviman]

CEFOSKEY, don't forget to post pics when your project looks the part. :ok:

Dave, that S-69 bearing arrangement is interesting - reminds me of the axle installation i am currently doing. I can see why X2 opted to go the bearingless rotor route of Comanche though - less parts to life.
PS: Regardless of Sky's need for X2 to be a marketing success, the project alone deserves credit for the foresight shown. :rolleyes:

IFMU, agreed duty cycle would be nP, but one of the X2 suite of technologies is active vibration control. There will be an accelerometer somewhere in the hub which alters the input signal to the hydraulic servo dual valves. Although movements will be more, this should actually help reduce the pitch link forces. Rotor figure of merit will benefit too, along with increased frame life.

Nick, i meant to ask whether the dual valves were for failsafe? I'm still reading your Heli Expo presentation for safer heli design.

[IFMU]

IFMU, agreed duty cycle would be nP, but one of the X2 suite of technologies is active vibration control. There will be an accelerometer somewhere in the hub which alters the input signal to the hydraulic servo dual valves.
Mart,
Don't forget back in post 24 you asked:
I'd be interested to know more about the Moog active vibration control though. I could have a reasonable guess at how it might work, but will dig up some papers.
And Nick replied in post 25:
Grav,
The Moog system is the same as that in the S-92, and it works like a charm. I understand the EC225 has a similar system.

The Moog vibration absorber is a electronic motor is digitally controlled to have very precise rpm capability. The digitally controlled motor spins counter rotating weights which are driven eccentrically in and out by separate jackscrews to produce higher or lower vibration amplitudes. Because the rpm of the motor is precisely controlled, the phase of the counterrotating weights can be adjusted, where the phase is the precise direction of the maximum amplitude of the weights. As a result the vibration absorber is capable of being adjusted to precise RPMs and to precise vibration absorbtion direction (lateral, vertical, horizontal). It can also be adjusted automatically by a computer as the aircraft flies. A vibration pickup is located near the place where you want to quell a vibration the most. Using that pickup the computer determines the best way to tune the weights to drive the rpm to its lowest. The computer uses precise logic that learns as the flight conditions change and so the computer becomes specific for the aircraft it is installed in. You can use up to six absorbers with the computers so that it's quite possible to quell the vibration across a very large area. Each of the absorbers weighs around 40 pounds and the amplifier maybe 10 pounds.
Try this patent number: 6,869,375

[Graviman]

IFMU, thanks for reminding me about that discussion...

I'm not sure whether the long term intention of "active vibration control" in X2 is simply the Moog eccentric weight type (as fitted to S-92), or the type that is generally known as Higher Harmonic Control. Higher harmonic control would be suited to a fast reacting FBW system, and offers the advantages mentioned. It may be that the Moog eccentric weight system will be fitted with the soon-to-fly hydraulic FBW, but i would be suprised if development stopped here. Part of the long term objective of fully electric FBW might be to fit direct blade vibration control, such as this system being developed at ONERA:

http://www.onera.fr/zoominthelab/17-helicopters.php
http://www.onera.fr/zoominthelab/images/17-helicoptere-actif-rpa-s3.gifhttp://www.onera.fr/zoominthelab/images/17-helicoptere-actif-rpa1.jpg

To make further progress in developing a silent and comfotable helicopter, "active" solutions need to be found, solutions where the angle of incidence of the blades can be modified. In effect, during rotation, the blades do not experience the same effects when they move in the same direction as the helicopter (advancing blade) as when their movement is in the other direction (retreating blade). Transonic flows may appear at the end of an advancing blade, whereas separated flows appear on a retreating blade and may cause the rotor to stall. In an active governor rotor, it is possible to vary local lift optimally with the help of trailing edge flaps etc. The objective is that the vortices are less intense and pass further away from the following blade. The increase in lift plays a critical role: when the lift is stronger as the vortices get closer then they are pushed further down and make less noise. This effect has been confirmed by calculations and in the wind-tunnel. Other parts of the helicopter may be made active, like the horizontal tail wing (ensuring the stability of the machine and controlling its attitude) or the vertical fin. But work on these aspects is less well advanced.

Development status given here:
http://www.dlr.de/fa/Portaldata/17/Resources/dokumente/institut/2004/2004_05_atb_riemenschneider.pdf

[IFMU]

There is a new X2 video on aero news network. Views of the cockpit, closeups of the head ect. They posted it Thursday 3/20 on aero-news tv, article title is "Aero-TV Gets A Close Look At Sikorsky's Exotic X2!"

http://www.aero-news.net/

-- IFMU

[Bravo73]

Great vid, IMFU! :D:D:D

This should be a direct link to the X2 feature (http://www.aero-news.net/index.cfm?ContentBlockID=fd8b3cc7-f5ed-4857-b1f2-ae36edd881b6&).

I can't wait until it starts flying. :ok:

[Dave_Jackson]

Which one are they going with?

Sikorsky's patent 7,229,251 ~ Rotor hub fairing system for a counter-rotating, coaxial rotor system (http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=7,229,251.PN.&OS=PN/7,229,251&RS=PN/7,229,251), ->[Images], ->[Drawings] show a number of interesting and radical aerodynamic considerations.

[bat1]

The patent can be seen on google with full images
here is a link to the images
http://www.google.com/patents?id=AjeAAAAAEBAJ&pg=PA2&source=gbs_selected_pages&cad=1_1

The fun starts after fig. 3a

[Graviman]

Congratulations X2 team for being the star of HeliExpo 2008! Thanks also to Peter Grant for giving a clear overview of the project development status. I wish Sikorsky every success with this clever development of the advancing blade concept.

CEFOSKEY, i'm actually glad the fairing wasn't there for all the publicity. Those rotorheads are extremely clever and it would be a shame to hide them. That said, the weathervane fairing is also a very clever development, and i can't wait to see it installed. What was the thinking behind the opposed twin cambered horizontal aerofoils on the patent? Are you trying to ensure flow stability behind the mast, like the doghouse platform on a single rotor mast design? I am also trying to work out what is the function of what looks like cooling fins in the position to be occupied by the fairing? They look a little too complex to just be bearing mounting flanges. Is the weathervane motorised, so that what is seen is a mounting spline?

I also notice the patent helo looks interestingly like an X2 development of S76 - now that would really be something! :ok:

[Bravo73]

The patent can be seen on google with full images
here is a link to the images
http://www.google.com/patents?id=AjeAAAAAEBAJ&pg=PA2&source=gbs_selected_pages&cad=1_1

The fun starts after fig. 3a

I like the line drawings of the larger, 18(?) seat version. It looks like it's got a stretched 76 nose. :ok:


Edited to add: Doh. Should have read the whole of the proceeding post before posting. :O

[Dave_Jackson]

CEOFOSKEY,

Thanks for the additional information.


On a related subject;

A rotorhub provides no lift and much drag. For a number of years now an idea has been bouncing around my few remaining neurons. It consists of giving the "doughnut fairings" a larger diameter and thereby a shallower elliptical X-section.

If this "doughnut" was allowed to teeter as it rotated and it was held up at the front-end of the mast, it might act as a lifting body.


Dave

[Graviman]

So how about it S-76 drivers: Would you swap your ride for an otherwise similar machine, but that could get the boss there at >4 times UK motorway speeds? ;)
http://hometown.aol.co.uk/martingarrish/images/s76_x2.gif

CEFOSKEY, thanks for the explanation. Even the plain vanilla fairing looks good, but those vortex generating turning vanes are a nice touch. I'm still confused by what looks like corrugation on the rotor shaft between the hubs. This is inside the machined casting structure for attaching the fairing bearings.

Dave, the hub fairing works best by blocking the blade root vortices which would otherwise form. Simply avoiding the fountain effect will improve rotor efficiency. It is a mechanically very simple way to achieve a useful gain.

[Dave_Jackson]

Mart,

The rotorhub represented 50% of the drag (parasitic only - I think) on the earlier ABC. This was a serious concern.

IMHO, a secondary concern may the rotorhub generated turbulence, plus the root vorticies, due to their interactaction with the propeller (which did not exist on the earlier ABC).

Why do you believe that the 'fountain effect' is detrimental? It is probably detrimental to a tiltrotor during hover, but it could be beneficial to a helicopter in ground effect.

Dave

[bat1]

New downloads available on Sikorsky's website
http://www.sikorsky.com/sik/Attachments/MISSION%20DOWNLOADS/1559_X2-007_Trifold.pdf

looks like a glamour shot with the hub fairing on.


Also some coment on the attack varient mock up. Why not have an integrated flir to reduce drag instead of the nose ball? Why have the cockpit as a complete bubble? It would seem that integrating the rear of the cockpit into the fuse would make better sense. Why have the exhaust coming out of two flaring cones? I would think that an internal vent like the Comanche had would be better. Also the tail boom could be styled to flow tapering from the rotor hub down to the tail prop. Overall the concept drawing looks cool but feels more like a franken drawing of stealth fighter jet mated to a bell cobra with x2 mechanics.

[Graviman]

Dave, the fountain effect is the result of the slightly higher static pressure under the rotor forcing air past the rotor hub (now that Rotorheads have established that there is a measurable pressure increase). Since leakage causes lost lift for a given power requirement, it represents a loss in Figure of Merit. The best FM is always obtained for a uniform induced velocity. Above the fuselage this induced velocity clearly needs to be zero, but not negative.

The hub doughnut fairings, designed by CEFOSKEY, will reduce drag by reducing hub turbulence with the turning vanes forcing the flow to remain attached until the seperation point. It is like all things a compromise, but FM will go up.

I can understand how your mechanism would reduce drag, by aligning the "flying saucer" to the induced airflow. But this rotor system already has two swash plates, and i can't think of an aerodynamic way to make the fairings sit where they would need to be. The turning vanes are a simpler solution.


Bat1, great poster there. :ok:

[Dave_Jackson]

Mart,

Thank you for defining 'fountain effect'.

Perhaps you may wish to look a little further into the subject. You may wish to consider its effect on an 'aerodynamically dirty' underbody, such as open landing gear doors.


i can't think of an aerodynamic way to make the fairings sit where they would need to be.

Perhaps a Gimbel joint at the center of the lifting-body. This will put it's 'theoretical' pitch axis at 50% of chord. Then give it a slight 'dish' shape between the four blade roots.


Dave

[bat1]

Thanks Cefoskey,
I guess I am a little suprised that the 3d rendering of the attack version was also patented. Seems like a waste of time for just a concept drawing for publicity purposes. Though in the end whatever brings in the money is worth doing.

[Dave_Jackson]

CEFOSKEY,

You are probably correct, in that the complexity etc. may not justify any possible advantage.

The idea is from the Department of Demented Designs. :8
It is one of many considerations for directing sufficient air at the upper quadrant of the propeller disk on the UniCopter (http://www.unicopter.com/UniCopter.html) concept. This problem may not be so serious on the X2.


The X-wing is a good looking craft. A stated objective in one of the patents was "to provide a stopped rotor X-wing aircraft with low drag and high speed forward flight, including aerodynamically efficient supersonic operation;". It appears that the craft was flown on its wings, but never flown with the rotorhead attached.

Dave

[Graviman]

How they convinced themselves this was going to work before the days of computerized CFD is beyond me.


CEFOSKEY, i was once offered a position at Dunlop aerospace. At the time they were considering the rotorbrake for the X-wing. During some informal talks with the engineer doing the FEA for the system, i asked: how are you going to stop all that inertia in one revolution? His reply: I don't know. ;)

[bat1]

A drawing looking just like the rendering was patented
http://www.google.com/patents?vid=USPATD526269

Five other concept patents are listed on the unicopter website
http://www.unicopter.com/1465.html

[Dave_Jackson]

The following article is not directly related to the ABC coaxial, however it is an interesting evaluation of the coaxial configuration.

Operational considerations for a co-axial, contra-rotating rotor.
(http://www.helosim.com/coaxialarticle.htm)

[IFMU]

Some of the statements there seem hokey to me. Like:

As air blows through the tail rotor in the direction it is blowing air, efficiency is lost and the rotor pitch needs to be increased (possibly leading to a tail rotor stall).
If this was true, airplanes everywhere would be stalling their propellers at high speed, as 'air blows in the direction it is blowing air.'


High level of yaw authority, extending well into the flight envelope. As yaw authority is not totally limited to that of the aerodynamic capabilities of a tail rotor, being dependant on that of the differential rotational inertia applied to each disc, being used to generate a yawing motion, operability extends beyond that of the tail rotor system.
What about autorotation? We have batted this back and forth before, I think in this thread. Coaxes and synchrocopters are bad here. Generally they need long tails & rudders to cope. Look at the KA50, the K-max, ect. Plus I thought it was differential torque, what is this differential rotational inertia thingy he refers to?

-- IFMU

[Dave_Jackson]

IFMU,

This is only speculation, however it would appear that the text on the web page is a slightly crude translation of writings from another language, perhaps Russian.

The first quote may relate to a Kamov affectionado believing that a helicopter with tail rotor is unable to stay on target under gusty conditions.

In the second quote he may have used 'inertia' when he meant 'torque'. I understand that the coaxial has a very powerful yaw authority, due to the differential torque. In autorotation the pedals must be reversed. It appears that Kaman and Kellett initially thought they could get away with shorter tail booms because they did not have a tail rotor. Look at the size of Flettner's vertical stabilizer.

http://www.unicopter.com/0474.jpg


Just speculation.

Dave

[relyon]

The Gyrodyne QH-50 series of antisubmarine drones solved the coaxial autorotation yaw control reversal problem using rotor tip mounted drag brakes. Many QH-50 models have no directional control surfaces at all and those that do have small fixed vertical fin(s) indicating they are for forward flight stability not fundamental yaw control.

There's lots of information at http://www.gyrodynehelicopters.com/.

Bob

[Graviman]

CEFOSKEY, the rotor retard idea would work since the machine would turn to keep the same airspeed for each rotor system. Transient performance would also be good as the rotor inertia was transferred to the fuselage during braking, until forces reached equilibrium. However, you would lose some power and generate heat - particularly in HOGE where you might not want to (pusher prop tail might force lots of peddal work in strong winds). Still in principle rotor retard works better than the tip brakes, since the rotor retard system would directly control yaw rate while the tip brakes only controlled yaw torque.

That does raise an interesting point about the differential collective in X2 though: Does the system only produce a good yaw rate control, in all flight regimes, because of the yaw laser gyro in the control system? Nick, has commented that S69 was not as positive in yaw as a tail rotor.

[Dave_Jackson]

Tip brakes (and tail rotors) consume additional power. Differential collective has very little effect on power consumption.

The blades on the two rotors of a coaxial are set so that they always cross at a specific azimuth, to minimize vibration. This rules out the use of a rotor brake, since the brake would slow both rotors.



From the Department of Demented Designs
Where the lights are never turned off ~ because the light never really came on.


This is a concept for yaw control on a coaxial rotorcraft. It does not brake or consume additional power and it does not require differential collective. Unfortunately, it does not maintain a fixed blade crossing at a specific azimuth.
OTHER: Miscellaneous - Thoughtless Idea - Coaxial Transmission w/ Yaw Control (http://www.unicopter.com/0954.html)


Dave

[relyon]

This is a concept for yaw control on a coaxial rotorcraft. It does not brake or consume additional power ...
While admittedly an interesting concept it does use power, no matter how little that may be. It takes energy to move mass which to my knowledge can't be avoided.

Bob

[maxtork]

I had a similar idea to Daves without the gears. When I worked for Erickson we had a test cell that would run one engine and one main gearbox at the same time. Power that was being absorbed by the cell was redirected to the input of the gearbox that was not occupied by the engine. Why not use this for yaw control on a coaxial? I was thinking more along the lines of a motor/generator on each mast. When you apply a field current to one as a generator it will create a drag on that rotor mast. The energy absorbed by that generator would be sent to the motor on the opposite mast to recoup the lost power. In an of itself it me not be perfect as the motor/generators would obviously add weight and complexity it could also be useful as a hybrid drive of sorts. During cruise flight equal current could be drawn from both systems to charge a battery pack which could be used as additional boost of power in the case of engine failure. You could even use it for normal operations and scale down the engine such that a max power take off may require both engine and battery power and then the smaller engine package is left to carry the load during cruise. Of course that wouldnt be such a great thing for an aircraft destined for long hover times as sooner or later you are going to run out of battery power!!

Like I said,...just a thought

Max

[Dave_Jackson]

This might be of some interest for those who want to look deeper into the subject.

The July 26, 2001 posting by H-43 mentions the only problem that I have heard of; that of the systems linkages not knowing whether to apply CW or CCW yaw at low collective settings. I understand that this is applicable to Intermeshing and Coaxial.

http://www.unicopter.com/0742.html#Yaw


Relyon,While admittedly an interesting concept it does use power, no matter how little that may be. It takes energy to move mass which to my knowledge can't be avoided. True but the power is going into thrust.


Dave

[IFMU]

The idea of rotor momentum is what allows yaw control on fixed-collective coaxial RC helicopters. However, this is controlled via variable differential Nr through the throttle of two seperate motors.
I highly doubt that rotor momentum plays a big part in yaw control. Unless you are considering they have so little momentum that it is easy to accelerate/decelerate them quickly. The torque generated is predominantly a function of rotor speed, and not the acceleration of the rotors. But maybe this is what you were saying.

-- IFMU

[bat1]

any news on test flights?

[Graviman]

Bat1, i was just wondering about "ping"ing this thread again... ;)

I suspect that having generated much good publicity on the potential for high speed helicopters X2 has been handed back to the engineering development team for the various ground/tethered test activities which precede a test flight. Machines are now just too complicated for the jump in and see what happens approach of the past. It will probably undergo some strain guage durability proofing to demonstrate that everything is behaving the way that FEA said it should.

With Nick finally giving in to Dave, and moving over to the dark side of lateral symmetry, i'm not sure how us X2 fans will get our fix. :)

[Brilliant Stuff]

I was made to understand the X2 was ready to fly and would have had it's maiden flight if the Expo had not been scheduled for the same week.

[Graviman]

Give it time guys. Did your final exams benefit from letting the examiner stand over your shoulder? ;)