Sikorsky X2 coaxial heli developments. [Archive] - Page 2

LupinIII

21st May 2008, 14:59

First Ground run w/ blades installed:

First ‘Blades-On’ Ground Runs Conducted Successfully
For Sikorsky’s X2 TECHNOLOGY™ Demonstrator

HORSEHEADS, N.Y. May 21, 2008 – Sikorsky Aircraft Corp. achieved a major milestone on its X2 TECHNOLOGY™ Demonstrator program by successfully ground testing the aircraft with rotor blades installed and spinning for the first time. Sikorsky is a subsidiary of United Technologies Corp. (NYSE:UTX).
The initial “blades-on” ground test was conducted May 13 and went according to plan. The ground tests are continuing at Sikorsky’s Schweizer Aircraft Corp. rapid-prototyping facility in Horseheads, N.Y., in preparation for the X2 TECHNOLOGY Demonstrator’s first flight.
"The entire X2 TECHNOLOGY Demonstrator Program Team is extremely pleased that we continue to move our experimental program closer and closer to first flight,” said James Kagdis, Program Manager, Advanced Programs. ”We anticipate that reaching this particular milestone, as with those yet to come, will continue to pique the interest of our military, commercial and international customers regarding the potential that X2 TECHNOLOGY could have on their diverse missions around the globe."
The X2 TECHNOLOGY Demonstrator combines an integrated suite of technologies intended to advance the state-of-the-art, counter-rotating coaxial
rotor helicopter. It is designed to demonstrate a helicopter can cruise comfortably
at 250 knots, while retaining such desirable helicopter attributes as excellent low speed handling, efficient hovering and autorotation safety, and a seamless and simple transition to high speed.
Among the innovative technologies the X2 TECHNOLOGY Demonstrator employs are:
·Fly-by-wire flight controls
·Counter-rotating rigid rotor blades
·Hub drag reduction
·Active vibration control
·Integrated auxiliary propulsion system

Sikorsky Aircraft first announced the initiative to develop an integrated suite of technologies called X2 TECHNOLOGY in June 2005. The project is funded solely by Sikorsky.
Sikorsky Aircraft Corp., based in Stratford, Conn., is a world leader in helicopter design, manufacture, and service. The company’s long commitment to safety and innovation is reflected in its mission statement: “We pioneer flight solutions that bring people home everywhere … every time™.“ United Technologies Corp., based in Hartford, Conn., provides a broad range of high-technology products and support services to the aerospace and building systems industries.

See also this article:

http://www.theregister.co.uk/2008/05/21/sikorsky_x2_ground_spin/

Graviman

21st May 2008, 16:33

Hey, this is fantastic news Lupin!

Are there any videos or photos of the event?
My screensaver needs updating. ;)

Bravo73

21st May 2008, 17:01

This comes from that Register article:

One also notes that variable-rotor-revs tech like that of the X2 is quite rare, most whirlycraft spinning their blades at a fixed rate. Boeing's unmanned A160T uses variable-spin, and is said (http://www.theregister.co.uk/2008/04/01/a160t_back_in_black/) to be "four times quieter" in the hover than a regular copter - not to mention having advantages in fuel economy.

Apologies if this has already been covered in this thread but this is the first time that I've seen a mention of this variable rrpm. Is this really going to happen or have the Register managed to get their technologies confused?

LupinIII

21st May 2008, 17:19

Unfortunately, I can't share any of the photos I've seen.

Dave_Jackson

21st May 2008, 19:43

Where the rubber meets the road.

Many years ago Nick mentioned that Sikorsky does 90% of its helicopter development after the prototype has been built and is in testing. Some might suggest that most of the development should take place after the craft meets the notepad, not after it meets the helipad.

But then, who would dare question The Big Sikorsky? :E

The full technical information on the performance of the X2 may involve a long wait. Or it may never be made public, since this is a privately funded project. For the fun of technical speculation, and perhaps discussion, the following is put forth.

The blades on the X2 have a reverse taper. Presumably, this is done so that the airfoil portions of the blades are subjected to minimal reverse airflow during fast forward flight. However, this will result in disadvantages. The reverse taper will increase the induced velocity in the outer regions of the two overlaid rotor disks but reduce the induced velocity in their inner regions; as compared to today's conventional rotors. Actuator Disk Theory and Bernoulli's principle assumes that the aerodynamic loading is distributed uniformly over the disk.

During hover; ~ One disadvantage may be the reduction in the Figure of Merit; particularly when considering that Dr. Gordon Leishman (http://www.agrc.umd.edu/facstaff/j_gordon_leishman.html) has said;- "... it had taken the industry sixty years to realize a helicopter with an average increase in rotor hovering efficiency (figure of merit or FM) of only 13%".

During cruise; ~ Another disadvantage may be the reduced Lift/Drag Ratio. In addition, the aft-located propeller (pusher configuration) will probably strip away some of the lift that is generated by the coaxial rotors. Consider the remark by Carson (http://www.carsonhelicopters.com/composite_blades.htm) "...on average, the maximum L/D of the helicopter has only increased by less than 10% in the last 30 or more years."

If the above concerns are valid, can the X2 be a viable contender in the field of VTOL craft?

Dave
_________________________________

Bravo73,

The earlier XH-59A ABC had a two-speed transmission. To my recollection, a variable speed transmission for the X2 has been inferred but never stated outright.

Bravo73

21st May 2008, 22:01

Thanks, Dave.

CEFOSKEY - as our 'inside man', have you got any more gen on the variable rrpm?

Bravo73

21st May 2008, 22:17

Thanks. :D

IFMU

22nd May 2008, 01:21

The earlier XH-59A ABC had a two-speed transmission.
I'm having visions of that Airplane! movie where they were rolling down the runway for takeoff, and the pilot was shifting gears. Wonder if that was how they did it on the XH-59A, or if it was more like a 2-speed powerglide automatic?

Some might suggest that most of the development should take place after the craft meets the notepad, not after it meets the helipad.
Ahhh, the beauty of a paper airplane. It has no faults, nothing to fix, as long as you never build it.

I thought it was a neat picture in that article that Lupin III linked to:
http://regmedia.co.uk/2008/05/21/sikorsky_x2.jpg

"...on average, the maximum L/D of the helicopter has only increased by less than 10% in the last 30 or more years."
In the .pdf file that bat1 had posted the link to (post 256), they show a chart with the L/D way higher than an S92. Looks more than 10%, unless they are doing some funny chart thing to make a small gain look big. They also show a rotor RPM schedule, where it drops 20% from 210 to 280 kts.

-- IFMU

Dave_Jackson

22nd May 2008, 02:09

IFMU,

How dare you suggest that Sikorsky is "doing some funny ..... thing"s.

Is this another funny thing? (http://www.youtube.com/watch?v=mo8_C5J3F3o)

Dave :)

Graviman

22nd May 2008, 11:54

Dave, that's an interesting movie.

http://en.wikipedia.org/wiki/Flettner_Fl_185

Re inverse taper that is just the price paid for increasing the cruise speed. Future technologies could include independant root and tip control, but best to get the concept flying reliably first. I think Nick's comments were more to with the fact that on any project 90% of the development happens as the prototype reveals the machines characteristics - you get what you can right before hand, but simulation doesn't always capture everything.

Graviman

23rd May 2008, 11:47

With Catia V5R? being the main cad package, i'm guessing Abaqus CAE for the FEA?

Best of luck that strain guages don't reveal any unexpected loads - it is not often the case. :ok:

heli1

23rd May 2008, 14:16

Still some way to go for an X2 first flight from what I've seen.The initial ground runs with blade on also had the rear end and propellor missing !

Dave_Jackson

23rd May 2008, 17:15

Mart & CEFOSKEY,Many years ago Nick mentioned that Sikorsky does 90% of its helicopter development after the prototype has been built and is in testing.

Perhaps we have differing perspectives as to the meaning of '90% of helicopter development'.

IMHO, development is all inclusive; from the initial product conceptualization on through to the start of production.

What is done once the prototype is built and outside the barn door (flight testing, etc.) consists of refinements to the engineering that was previously done inside the barn.

Dave

PS. :)

The X2 ain't bilaterally symmetrical. :=
The engine is on the port side and the propeller's drive-shaft is on the starboard side.

But, since it's on the inside and doesn't affect aerodynamics ...... ;)

Dave_Jackson

24th May 2008, 16:05

CEFOSKEY:

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

_______________________

TRIVIA:

The XH-59A ABC was the forerunner of the X2.

Perhaps this was the forerunner of the XH-59A ABC. (http://www.aviastar.org/helicopters_eng/hiller_x-2-235.php)
"As a result of the NACA tests, Hiller initiated redesign of the X-2-235 to incorporate three-bladed coaxial rotors augmented by an aft-thrusting rear propeller. The reworked craft was obviously geared to flight at speeds substantially higher than those attained by existing helicopters."

Dave

NickLappos

24th May 2008, 17:19

Yep! High hinge offset coax, Hiller never flew it, it appears:

http://www.aviastar.org/foto/hiller_x-2-235.jpg

Graviman

28th May 2008, 11:53

Any feedback on the ground testing?

Is the X2 behaving the way it's meant to?

Graviman

28th May 2008, 18:00

That's great news! :ok:

My fingers are crossed that everything behaves itself.

BTW, looked at Ansys 10/11 recently: very capable analysis package. For my own part i'd prefer to use Hypermesh as preprocessor - still it's nice to crawl out from under Ideas 12NX. Transition going smoothly...

Obi Offiah

10th Jul 2008, 18:11

Does anyone know what the top speed of the S-69 ABC helicopter was, in level flight without the two jets strapped to its side and what speed did (with and without the jets) would retreating blade stall and/or blade collision become a problem?

Also what is meant by rotor hinge offset?

Thanks
Obi

Graviman

12th Jul 2008, 12:50

Obi,

Effective hinge offset is a measure of how stiff the blade is, and can be related to blade natural frequency over rotor rpm. As a flapping hinge moves outboard the centrifugal effect pushes up flapping frequency, hence the term "effective" hinge offset.

Actually i've been doing nothing but effective hinge and cyclic Lead angle calculations all week for my FEA invetsigations. I've even developed a nifty spreadsheet to calculate rotor lift and induced velocity. Alas not for rotors, but for high horse power cooling fans. I'm working closely with some ex-Rolls guys to really get to grips with turbine compressor design too - interesting field. ;)

---

Delta3, are you still out there? When time permits i'm going to have a go at the Leishman algoritm myself.

---

CEFOSKEY, how is the X2 doing? I've lost touch... :sad:

My busy work schedule leaves me less time now to check this forum, but the interest is still there...

Hilico

12th Jul 2008, 18:23

If this post is crap, one of the experts please tell me and I'll delete it.

Obi - the way I think of hinge offset is this. Imagine you're doing gymnastics and you're hanging from a bar by one hand. Difficult to move sideways isn't it? You need a very strong wrist. Now change that to hanging from the same bar but with two hands, shoulder-width apart or wider. Total different experience. The difference between an R22 (or a 206) and a 105.

As I say, experts please pile in if required.

Aser

12th Jul 2008, 18:27

From rotor&wing:

13 May first run with rotors on.
The test program calls for about 65hr of run time with the main rotors on the X2. followed by 10 hr with no changes to its flight control before the aircraft could be cleared for first flight

Dan Reno

12th Jul 2008, 21:57

I'm certainly no expert but:

Effective Hinge Offset: [(e/R)eff]
The ratio of the hinge offset divided by the radius of the rotor.

Shawn Coyle

13th Jul 2008, 11:34

Dan:
Your formula is right for an articulated rotor - the problem comes with rigid rotors and bearingless rotors where there is no physical hinge.
For those rotors, the 'effective' hinge offset is a calculation of where it would be if there were a real flapping hinge.
For those rotors, you can say that the flapping hinge was replaced by a flapping hinge plus a spring.

IFMU

17th Jul 2008, 02:57

aero-news net x2 article (http://www.aero-news.net/news/commbus.cfm?ContentBlockID=fb7fe9f4-2597-4a86-bb57-e05bd7a55148&Dynamic=1)

heli1

17th Jul 2008, 11:22

The company deflected the real questions on the X2 status at Farnborough but I was told that they have had transmision development problems ,especially integrating the prop drive system ....anyone else heard that ?

Dan Reno

17th Jul 2008, 11:41

Uh-oh, they better scrap this program while they're ahead.

Dave_Jackson

17th Jul 2008, 21:31

The earlier Sikorsky XH-59A ABC had two-speed rotors. (http://www.unicopter.com/A064.html#ABC) The tip-speed was 650 ft/sec in helicopter mode (hover to medium forward speed) and 450 ft/sec in compound mode (high-speed cruise).

The Sikorsky-X2 ABC uses a rotor-propeller relationship that is yet to be made public; to my knowledge. One of the patents appears to imply that the rotors are to have variable speed. The tip-speed is 700 ft/sec in hover and 560 ft/sec during high-speed cruise. (http://www.unicopter.com/1465.html#Calculation)

The Stepniewski ABC (http://www.unicopter.com/1093.html) has slow constant-speed rotors, with a proposed tip-speed of 513 ft/sec. This slow speed works in conjunction with wide chord blades.

_______________________________

There are a number of other interesting differences between Stepniewski's ABC and Sikorsky's ABC. Perhaps in the near future these differences will be placed on a separate thread, so those with a technical interest can evaluate and discuss them.

Dave

IFMU

18th Jul 2008, 01:09

Another X2 article. Seems like the media reports one thing, then another.

http://sikorsky-x2-first-flight-could-slip-to-2009.html (http://www.flightglobal.com/articles/2008/07/17/225807/sikorsky-x2-first-flight-could-slip-to-2009.html)

-- IFMU

Graviman

18th Jul 2008, 11:55

If the program slips by a year, this is a reflection of how difficult the concept is to achieve. Nothing more.

While it is frustrating for us fans, i am far happier with the "slippage" of an internally funded project than the idea that all development has stopped.

The point is that the concept of a low disk loading VTOL with a narrow ground profile is a worthy pursuit. When all the technical issues, associated with any new engineering project, have been resolved we will all be singing X2's praises...

CEFOSKEY, that LUH is a good looking ship - definately a vision of things to come.

Dave_Jackson

25th Jul 2008, 07:29

CEFOSKEY, Thanks for the clarification on the variable rotor-speed.

GRAVIMAN, Stepniewski is not going to be building a rotorcraft and Sikorsky is, therefore this subject may be better on this thread,
_______________________________

Aerodynamic comparison: Sikorsky-ABC v.s. Stepniewski-ABC

The Sikorsky-ABC pictures appear to show that the thrust-line of the rotor is perpendicular to the thrust-line of the propeller and fuselage. If the rotor is to operate in autorotative mode during cruise then the rotor, fuselage and propeller will have a nose-up attitude.

The Stepniewski-ABC evaluation work takes into account that the forward propulsion from a rotor is more efficient that that of a propeller, up to an angle of incidence (http://www.unicopter.com/B263.html#Incidence) of about 9-degrees. It therefore would appear that having the angle between the thrust line of the rotor and that of the propeller less than 90-degrees will offer a meaningful increase in the efficiency during cruise with no detriment during hover.

If there is any interest in debating the subject, http://www.unicopter.com/Group.gif
Stepniewski's calculations and an elaboration on the above are available here; Angle of Incidence - Rotor & Propeller (http://www.unicopter.com/1656.html)

Dave :8

Graviman

25th Jul 2008, 11:40

Dave,

Why do you conclude that X2 will operate in autorotation during cruise? I would have though the objective was in trim cruise. It just has full autorotational capability from this flight condition. It will be a compromise, but i would have thought the design optimised to suit 250ktas.

Any details on how variable Nr is achieved?

BTW, i've been thinking about puller vs pusher while generating a vortex panel model of a fan aerofoil. You could think of the puller as an additional vortex line generator (like the HIGE rotor image) so that the main rotor is operating in more favourable inflow over a pusher application. In a nutshell the puller wins out because a larger total area is ingesting air. Then again if the rotor is sized sufficiently this is less of an issue.

Dave_Jackson

26th Jul 2008, 00:15

Graviman, Why do you conclude that X2 will operate in autorotation during cruise? No conclusion. The reason for the preceding post was to invoke technical consideration and speculation. The subject of integrating the rotors, propeller, transmission, motor, and flight controls, in an optimal aerodynamic package, and mechanical package, is challenging.

Stepniewski and Sikorsky present a number of different potential solutions for consideration. On the subject of the rotors being in autorotation during cruise, this additional information has be added to the notes on the previously referenced web page (http://www.unicopter.com/1656.html). It is discussing Sikorsky's earlier XH 59A - Coaxial-ABC.

"In the auxiliary propulsion mode, the ABC rotor power requirements are reduced with increasing airspeed with maximum rotor L/D being achieved at or near autorotation."

"However, with the rotor flying at close to autorotation at high speed, differential collective pitch has little impact on yawing moment ....."

ABC aircraft could be considered as a unification of gyrocopter and helicopter. A similar subject has recently been discussed on a gyrocopter forum, where they were considering the pros and cons of a partially powered rotor.

Any details on how variable Nr is achieved?CEFOSKEY may be the first PPRuNers to look under the hood (bonnet).

Re Pusher v.s. Tractor propeller aerodynamic:
I think that the Intermeshing-ABC will work better than the Coaxial-ABC when considering the subject of the propeller. This is because the stream-tubes of the Intermeshing rotors are a little more out the sides and away from the streamtube of the propeller.

I've got to be a little carefully using the word 'Intermeshing' since the boss may get mad. :)

Dave

Graviman

29th Jul 2008, 11:25

Nick, my confusion comes from the fact that XH-59 had two rotor speeds while X-2 has apparently a variable rotor speed. Being honest i'm not sure how this is accomplished with such a high natural frequency blade - i just imagine Campbell plots with lots of red accel contours where each Nr order crosses the spin stiffened frequency...

IFMU

30th Jul 2008, 00:26

Some of the statements on this thread seem to assume different things. For example:

Nick, my confusion comes from the fact that XH-59 had two rotor speeds while X-2 has apparently a variable rotor speed.
I think it has been stated previously in this thread that the XH-59 had two rotor speeds, and I interpret the discussion as though there were a physical gear change, like a motorcycle or car. This seems odd. Then we get:

Dave is right, the ABC cruised in autorotation at about 250 knots. The collective was raised so that the rotor rpm settled at about 88% Nr.
Now, does this imply that the gearshift was connected to the collective? Or they used collective pitch to control RPM just like any helicopter in autorotation? Or is there something more sinister going on, like the CVT (continuously variable transmission) in my 1971 Harley golf cart?

-- IFMU

Dave_Jackson

30th Jul 2008, 03:55

The attached page is from a document on the XH-59A ABC after a 128 hour flight test program.

The center paragraph in the right hand column is directly related to the subject of your post.

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

It has been said that the rotor hub constituted 50% of the craft's total drag. This combined with other information on this page could be related to the current subject.

Maybe the lower RRPM for high-speed flight was not actually 'geared' into to the craft. Maybe it was an aerodynamically generated rotor speed. http://www.unicopter.com/NoIdea.gif

Dave

Jack Carson

30th Jul 2008, 18:32

As I recall, the transition to thrust augmented flight was relatively benign. For takeoff we set the collective at approximately 25-30% then performed a traditional airplane takeoff and transition using the thrust from the J60s. As the airspeed increased the Q from the PT-6s decreased to 0% and the rotor speed settled in at 88% with the freewheeling units disengaged. The transition from for forward flight was just as benign. We reduced the thrust from J60s. As the airspeed decreased the PT6 torques increased to bring the rotor speed back to 100%. We then adjusted the collect and proceeded to fly a traditional helicopter. All and all, an easy aircraft to fly. Back then I would have rated it an E ticket ride.:ok:

Dave_Jackson

17th Aug 2008, 20:22

X2TD Power Train:
- "The engine output shaft drives the input of a splitter gearbox mated to the rear of the coaxial gearbox through an overrunning clutch. The splitter gearbox drives the coaxial gearbox and a shaft that drives the auxiliary propulsion gearbox located in the tail. The variable-pitch auxiliary prop is therefore geared to the main rotors at all times."

Rotor lift/drag comparison between XH-59A and X2TD (http://www.unicopter.com/1465.html#LiftDrag)
- Additional technical information has been added to this page.
- More stuff can be added if requested.

Graviman

18th Aug 2008, 16:00

Dave, that web page is getting interesting! Have you got the rest of that XH-59 document?

Jack, thanks for clearing up the confusion. With an overrun clutch allowing autorotation i can now understand an Nr of 88%. I imagine that the J60s did not produce much thrust at low speeds, so that the PT6s actually generated most of the "airplane" thrust (through the rotor). So you were using the collective to trim for level flight (or climb/descent) as the speed increased/decreased? Was there a particular speed where you found you were retrimming the collective more regularly?

CEFOSKEY, do tell! Has the bird made a hop yet, or did it just go light on the gear?

Dave_Jackson

18th Aug 2008, 20:44

Mart, Dave, that web page is getting interesting! Have you got the rest of that XH-59 document? Yes. The page on Posting #303 is from 'An ABC Status Report'

These are the Technical Documents that I have;
Technical Documents on S-69 (XH-59) ABC: (http://www.unicopter.com/0891.html#Technical_Documents)
Technical Documents on X2 TD ABC: (http://www.unicopter.com/1465.html#Technical_Documents)

On this subject of Rotor Shaft Angle, this section has been added to the X2TD web page. (http://www.unicopter.com/1465.html#Rotor_Shaft_Angle)

Dave

Dave_Jackson

19th Aug 2008, 01:20

CEFOSKEY

Thanks. The change has been made. That's; one error down, hundreds to go.

Apparently the craft went under a number of designations, such as; XH59, XH59A, S69, proposed XH59B,
but never S76 :O

________________________

IFMU is probably going to ask Graviman;how do you connect a turbojet to a turboshaft engine?

Use the turbojet as the compressor stage? http://www.Unicopter.com/High.gif

Dave

IFMU

19th Aug 2008, 02:32

I imagine that the J60s did not produce much thrust at low speeds, so that the PT6s actually generated most of the "airplane" thrust (through the rotor).

I would think the rotors and PT6's were decoupled from the J60's, so as the rotor RPM wound down the J60's would be singing their hearts out. After all, how do you connect a turbojet to a turboshaft engine?

-- IFMU

Graviman

20th Aug 2008, 11:35

Wow, and it's contained in its own con-di nozzle too! I gotta get me one of those...

IFMU, what i mean is that the J60 thrust would be very low at slow speeds, increasing with airspeed - this is a turbojet not the later turboshaft version. This is because the intake area is relatively small, so needs airspeed to get enough mass flow. So to get up to that speed the rotor would have done most of the work, even though the J60s were spooling themselves silly. That's why the collective at low speed is 25-30%, since the PT6s are doing most of the work. With airspeed the PT6 Q, and collective, goes down to zero as the J60 takes over providing the thrust.

PT6s and J60s are connected together by means of sitting in the same airflow. ;)

Graviman

21st Aug 2008, 11:24

CEFOSKEY, this does my head in too. Jack Carson's comments are not dissimilar to the test pilot comments on the Lockheed XH-51 (similar to S69 with PT6 driving rotor and J60 Turbojets) and BELL 533 (T53 driving rotor and J69-T-9, later J69-T-29, turbojets), in that the rotor was providing most of the thrust at low speed. I read this in Prouty somewhere (i think).

Turbojet Thrust (http://www.grc.nasa.gov/WWW/K-12/airplane/turbth.html)

http://www.grc.nasa.gov/WWW/K-12/airplane/Images/turbth.gif

Bell 533 - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Bell_533)
Lockheed XH-51 - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Lockheed_XH-51)

tonyosborne

27th Aug 2008, 20:07

X2 flew for the first time today...

HORSEHEADS, N.Y., Aug. 27, 2008 – Sikorsky Aircraft Corporation today successfully completed the first flight of its X2 TECHNOLOGY™ Demonstrator, maneuvering the prototype aircraft through hover, forward flight, and a hover turn, in a test flight that lasted approximately 30 minutes. Sikorsky is a subsidiary of United Technologies Corp. (NYSE:UTX).

Sikorsky Chief Test Pilot Kevin Bredenbeck conducted the test flight at Sikorsky’s Schweizer Aircraft Corp. rapid-prototyping facility in Horseheads, N.Y. The milestone culminated more than four years of design, development and testing of the Demonstrator aircraft’s suite of technologies that are intended to advance the state-of-the-art, counter-rotating coaxial rotor helicopter.

“Today’s achievement is the result of dedicated effort by the entire X2 TECHNOLOGY Demonstrator Program Team,” said James Kagdis, Program Manager, Advanced Programs. ”It is proof of the complete commitment by Sikorsky Aircraft to this program and to the exploration of innovation in aviation. We look forward to expanding the flight envelope for this Demonstrator and will continue to conduct market analysis to determine the next steps for this important program.”

The X2 TECHNOLOGY Demonstrator is designed to establish that a helicopter can cruise comfortably at 250 knots, while retaining such desirable helicopter attributes as excellent low speed handling, efficient hovering, and safe autorotation, combined with a seamless and simple transition to high speed.

Sikorsky President Jeffrey P. Pino said the successful first flight attests to the company’s commitment to excellence and to industry-leading innovation.

”X2 TECHNOLOGY has crossed a major threshold,” Pino said. “The team’s achievement sets the stage for the next series of tests eventually leading to maximum speed. It also sparks the imagination for what ultimately the technology can mean to the future of the rotorcraft industry. We are far from having a product, but closer than ever to realizing the potential.”

Graviman

28th Aug 2008, 11:36

Seriously well done X2 development team!! :ok:

http://www.aerofiles.com/collier-trophy.jpg

Your fans will patiently wait, while the flight envelope is explored, to see what this new type of flying machine brings...

Mart

Collier Trophy (http://www.aerofiles.com/collier-trophy.html)

quadrirotor

28th Aug 2008, 12:42

Video please!...

quadrirotor

28th Aug 2008, 15:30

A photo:

http://www.sikorsky.com/sik/images/x2_2.jpg

Bravo73

28th Aug 2008, 16:44

And the other one:

http://www.sikorsky.com/sik/images/x2_1.jpg

Glory

28th Aug 2008, 21:35

You must all be seeing something I can't.

No retractable u/c, back end sits on a trolley when on the ground, counterote is old technology and looks like only a two person capacity?

The only use I can see is for business users and there are others already established on the market. However as a concept vehicle, it's another step forward.

Glory

28th Aug 2008, 21:51

Understand that but other than improving technology? So, it can go faster - yes, why?

Bravo73

28th Aug 2008, 22:57

So, it can go faster - yes, why?

Er, to get there sooner. :rolleyes: Why else would you want any vehicle to travel faster...?

Dave_Jackson

28th Aug 2008, 23:13

Understand that but other than improving technology? So, it can go faster - yes, why?

The answers may be in this technical document from the AHS May 2008 Conference;

X2 Technology™ and Emerging Applications ~ by Eadie, Alber & Tinker

Dave

Brian Abraham

29th Aug 2008, 00:22

From Aviation International News today.

Compound Sikorsky X2 Makes First Flight
Thirty-eight months after Sikorsky’s formal announcement of the X2 “technology demonstrator,” the compound helicopter made its first flight yesterday at the Sikorsky-Schweizer rapid prototyping facility in Horseheads, N.Y. During the 30-minute flight, Sikorsky chief test pilot Kevin Bredenbeck conducted slow forward flight, hover and hover turn maneuvers. The rear propulsor was not engaged during the inaugural flight, and the X2 reached a maximum forward speed of 20 knots, 10 to 15 knots sideways and 40 feet agl. More slow flight testing will be conducted at Horseheads before the X2 is transferred to Sikorsky’s larger West Palm Beach, Fla. flight-test facility. Sikorsky is self-financing the fly-by-wire X2 with an eye to deploying its key components in future manned and unmanned military helicopters. The X2 is designed to have a maximum forward speed of 250 to 265 knots. Power for the X2 comes from a single LHTEC–Light Helicopter Turbine Engine Company, a Rolls-Royce and Honeywell partnership–T800 turboshaft engine rated at up to 1,680 shp. The T800 drives the twin four-blade Eagle Aviation contra-rotating main rotors and the Aero Composites six-blade pusher propeller mounted at the end of the tailboom.

IFMU

29th Aug 2008, 01:33

No retractable u/c,
In the marketing artwork it shows retractable u/c. However, how many aircraft with retractable u/c have actually retracted them on the first flight, fixed wing or rotary wing? Not many I would bet.

Cool!

-- IFMU

IFMU

29th Aug 2008, 02:28

Sikorsky's X2 spends 30 minutes in the air - The Connecticut Post Online (http://www.connpost.com/businessnews/ci_10324143)

Graviman

29th Aug 2008, 11:42

Glory, what you are not understanding is that this prototype helicopter has the potential to significantly improve top speed without severly affecting it's primary role as a VTOL machine compared to other helicopters. This technology is also scalable to medium size and larger helicopters. Such machines would be more expensive to operate, but would have a great impact on the flexibility of the helicopter concept. There is also no compromise to the helicopter's ability to autorotate.

----

I made a recent decision to get back into engine design (as well as returning to Cambridgeshire), and am enjoying the challenges associated with the role. That said, i wish the guys at Sikorsky-Schweizer rapid prototyping facility in Horseheads (N.Y.), and Sikorsky's flight-test facility at West Palm Beach (Fla.) every success in expanding the envelope of what promises to be an amazing actual flying machine! :ok:

Andy Healey

29th Aug 2008, 12:10

Does anyone have data on X2 fuel consumption?

heli1

29th Aug 2008, 14:13

Ahhh...perfecting and engaging the rear propulsor will be the tricky bit.

Dave_Jackson

29th Aug 2008, 18:29

Mart,I made a recent decision to get back into engine design ... and am enjoying the challenges associated with the role.At this years Annual AHS Forum,
'Nikolsky lecturer and former Sikorsky engineer Dr. Ken Rosen told the audience, "We have a wonderfully creative workforce... What is missing is leadership." He contrasted yesterday's drive for tiltrotors and X-Wings with today's "sparkling mediocrity" and he noted, "When a company is in the hands of active exciting leaders, thats when a concept can take hold."'

Dr. Ken Rosen also said "We are not in a sunset industry..."

It would be interesting to know who he meant by "We", particularly when considering that there are 60,000 American engineering students in universities as compared to 900,000 Chinese engineering students in universities.

Mart, this is no time to leave Aerodynamics. :ok:

The Sultan

30th Aug 2008, 01:00

IFMU

30th Aug 2008, 02:00

Viewing the photos of the flight (which were accompanied by all of the "best ever" required comments to get the bonus) I would suggest move the pilot station to the back cockpit and use vertically challenged pilots to avoid a decap during maneuvers.

I thought they were rigid rotors? If they are not worried about the two rotors hitting each other then surely the guy in the front is ok.

-- IFMU

The Sultan

31st Aug 2008, 00:06

IFMU

There are stiff rotors, but no actual rigid rotors. Simple dynamics. Helicopter history has shown everyone underestimates the flexing of the blades. Proto 60, 61 63 and 64 are clear evidence of this.

The Sultan

widgeon

31st Aug 2008, 16:44

I wonder is the State Farm INsurance sign has any significance :O

The Sultan

31st Aug 2008, 21:47

CEFOSKEY

There you go thinking statics, not dynamics.

Relative to your picture notice they were smart enough to put the pilot next to the mast(s).

The Sultan

Dave_Jackson

31st Aug 2008, 23:48

WidgeonI wonder is the State Farm Insurance sign has any significanceYes. State Farm was the first company to ever provide tip-weight insurance for helicopters.

It can be seen in the picture that the craft has exceptionally heavy tip-weights, for dynamic stiffness. The insurance was to protect the company, should the tip weights come off during flight.

_____________

Trivia.
The following was only a rumor.

A few years ago the blade manufacture for the X2 produced a prototype UAV. It had extruded aluminum blades. Then steel shafts were epoxied into them as leading edge weights. Rumor has it that during a display in front of armed services personnel the epoxy in one of the blades cracked and launched its shaft.

I wonder if the insurance company would have paid if some of the generals had been 'shish kabobed' with the flying shaft.

Graviman

1st Sep 2008, 11:56

The Sultan, as a fan of the ill fated AH-56 Cheyenne i feel your advice is well worth heeding. The big difficulty is that the longer the rotor mast, the more flexibility you design into the rotor system. I imagine that the current design came after a lot of careful consideration, and simulation, of the dynamics. From the pace to date, i don't imagine Sikorsky will be rushing the flight test program until the dynamics are proven out. Maybe CEFOSKEY can give us more insight into the passage of the program from CAD to test?

CEFOSKEY, i'm looking forward to that video! Just knowing that X2 is a real flying machine is exciting enough, but one of my favourite MPEGs is a highspeed flyover of Commanche at West Palm Beach - the noise alone is amazing!

Dave, despite Nick's kind help, i was recently passed over by Westlands. Being honest, from BAE experience, i suspect that a paycut would have been required. My current role allows me to gain the experience in analysis and test that i crave, while being able afford the cost of UK living. Actually my first job has tempted me to write my own Vortex Panel Method software:

Vortex Panel Method (http://www.engapplets.vt.edu/fluids/vpm/index.html)

slowrotor

1st Sep 2008, 15:14

The two guys standing on the blade tips of the Hiller (previous post) are putting their weight on all four blades.

Graviman

1st Sep 2008, 17:55

Slowrotor, i have no wish to start that debate again, but the Hiller photo can be seen as a demonstration in the difference between statics and dynamics. What it really comes down to is how much the blades weigh in comparison with the two guys straddling them. The deflection can be proportioned to frequency, which from the photo implies a relatively high frequency 1st order flapping mode.

My earlier debate with Dave was that this still does not significantly reduce the pitch link lead angle. Basically one 1/4 cycle of the spin and bending stiffened blade is not much less azimuth than the 1/4 cycle of a spin only stiffened blade, for such a long blade. So dynamically even a high effective hinge offset blade can be seen as relatively soft.

Don't forget that for a blade strike to occur you really need two things: reduced g on the fuselage and large cyclic inputs causing blade flexure. For the first point i'm sure we can rely on Chief TP Kevin Bredenbeck not to rush into anything without thinking about it. For the second point i'm sure that a relatively stiff rotor will reduce the cyclic input required for a given pitch/roll rate. There is the uncertainty of a new FBW system, but this will have had most of it's shakedown on the Schweizer 333 development prototype.

All in all guys, lets not hex this thing before Sikorsky have had a chance to prove it. :ok:

Dave_Jackson

1st Sep 2008, 22:35

Mart,

The Vortex Panel Method software looks interesting.
Have you seen the the freeware program NVFoil (http://www.geocities.com/CapeCanaveral/Hangar/2524/nvfoilen.html), and had a chance to compare the two?

You may be underestimating the rigidity of Sikorsky's ABC blades.

[Source ~ Rotor-Wing Aerodynamics ~ W.Z. Stepniewski / C.N. Keys ~ Book I]
Sikorsky S-69 (XH-59A) ABC ~ Flapping hinge offset: Flapping frequency ratio (v/n) ≈ 1.4 [p.39]. From the graph [ p.18] it appears that the equivalent (virtual) flapping hinge offset will be approximately at 50% of rotor radius.

The information that is available on the new X2-ABC indicates that Sikorsky is increasing the rigidity even further.

This page on phase lag may be informative (http://www.unicopter.com/0998.html)

Dave

212man

1st Sep 2008, 23:53

Don't forget that for a teetering blade strike to occur you really need two things: reduced g on the fuselage and large cyclic inputs. For the first point i'm sure we can rely on Chief TP Kevin Bredenbeck not to rush into anything without thinking about it

Sorry - have I missed something here? :confused:

Graviman

2nd Sep 2008, 11:31

212man, i've reworded that post to avoid further confusion... :uhoh:

Dave, from memory the graph on p.18 of Stepniewski is a linear approximation, which is only valid at low hinge offsets. Using

(e/R)effective = 2[ (wn / W)^2 - 1 ] / [1 + 2 (wn / W)^2 ]

gives for wn/W=1.4 a value e/R=0.39 or 39% , but i came unstuck using the standard Prouty lead angle calcs for very high wn/W fan blades. :rolleyes:

An easier simplification to work out lead angle is that wn/W of 1.4 means that 90 degrees of blade bending cycle will occur in (90 deg)/1.4 = 64 degrees of the azimuth, so requiring a delta3 angle of 90 - 64 = 26 degrees. The aerodynamic damping (Lock number) will also have a small effect by altering the simple harmonic motion phase angle, as per formula on wikipedia:
Harmonic oscillator - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Harmonic_oscillator#Damped.2C_driven_harmonic_oscillator)
I'll have to figure how to convert Lock number to damping factor r at some point.

For whatever reason i've struggled to get NVfoil to run, and have found the vortex panel JAVA a nice straight forward utility for any arbitrary aerofoil shape.

Dave_Jackson

3rd Sep 2008, 18:01

Jim Kagdis, advanced program manager said;

"The T800-powered X2 will fly initially with the tail-mounted propeller installed, but not connected, Kagdis says. The demonstrator will be used as a 'flying wind tunnel' to determine the aerodynamic interaction between the rotor and propulsor. Other areas on interest will include optimization of the rotor shaft angle for performance and blade tip clearance for maneuvers, the company says."

________________

The AHS Montréal – Ottawa Chapter invites you to a presentation by
Jim Kagdis – Sikorsky Aircraft Corporation, “X2 Technology Demonstrator”
Thursday October 2nd , 2008 at 5:30 pm

Graviman

4th Sep 2008, 11:40

CEFOSKEY, you missed a trick here - just slow down the frame rate until the flight looks nice and controlled. ;)

It may just be that this machine has a much snappier response rate than most helis, since most machines just ignore cyclic stirring. Possibly the gain factor on the control just needs to be reduced. Is this a force control sidestick or is there a reasonable amount of movement?

At this stage just some decent resolution photos would do me!
Showing engineers a low resolution blow up of what might be a helicopter doesn't do the X2 first flight justice...

Dave_Jackson

4th Sep 2008, 19:15

CEFOSKEY,

Good pictures. :ok:

Here is a test flight that I was at a few years ago. It is also a coaxial, and it got a "bit twitchy" at the end of the flight.
First Test Flight Video (16.5MB) (http://www.mech.ubc.ca/~hph/aug10vids/aug10_first_try.avi)

Dave

Graviman

5th Sep 2008, 11:17

CEFOSKEY, some great photos! :ok:

The best metric of success for X2 flight envelope testing will be Kevin Bredenbeck's grin at the end of each flight. ;)

BTW, when are we going to see your rotor fairing? :8

Dave, looks more like intermeshing to me... :ouch:

busdriver02

6th Sep 2008, 01:54

If the AF is interested as you implied, hopefully they through some money Sikorsky's way and this develops a bit faster. I can only hope the bureaucratic involvement doesn't push things faster than is reasonable.

IFMU

12th Sep 2008, 01:43

Star-gazette X2 article (http://www.stargazette.com/apps/pbcs.dll/article?AID=/20080911/NEWS01/809110316&referrer=FRONTPAGECAROUSEL)

Dave_Jackson

12th Sep 2008, 05:18

Mart,

You asked;CEFOSKEY,
when are we going to see your bits? Your request is a little unusual. But if you must, this should satisfied your desires. (http://www.dailyhaggis.com/2007/03/05/new-x-ray-device-can-see-your-bits/)

IFMU,

Your article says;
"In the new design, the vertical tail rotor is moved to a position similar to a submarine's propellers."

Let's see now. http://www.unicopter.com/Think.gif

The gross weight of the X2 is 5,300 pounds.
The engine delivers 1,452 horsepower.
Propellers can deliver a thrust of 5 pounds per horsepower.

No! No! Igor. Don't change the X2 to a Nose Sitter (http://www.unicopter.com/Temporary/Nose_Sitter.gif).

_____________

OK. No more jokes. A serious question.

How come Russian-American Igors like tail-fans?
Igor Sikorsky is the father of helicopters that have tail-rotors, and
Igor Bensen is the father of gyrocopters that have pusher-props.
:confused::confused::confused:

Dave

Graviman

12th Sep 2008, 17:55

That's probably about right CEFOSKEY. At 100% collective this works out at roughly 2.1g, meaning that a turn tighter than about 60 degrees would require height loss.

IFMU

13th Sep 2008, 02:07

That's probably about right CEFOSKEY. At 100% collective this works out at roughly 2.1g, meaning that a turn tighter than about 60 degrees would require height loss.
Graviman,

I think that means it could pull 2.1g's vertically from hover, for a moment, if you yanked the collective to 100%. With translational lift I would expect you could do better. A 60 degree bank turn in hover doesn't make sense.

-- IFMU

Graviman

14th Sep 2008, 18:45

CEFOSKEY, I thought about that point after i had logged off for the day...

Don't forget that for a given thrust there will be a velocity for minimum power due to translational effect. Above this velocity the power requirement goes back up again until at dash speed it is probably about the same as it was at hover. So by designing a rotor which can handle 2.1g in the hover it also means it can do this at all airspeeds. Even so this probably means that X2 could pull ~4g without loosing height at minimum power speed, which is no mean feat.

Conventional helicopters are limited by the retreating blade stall, mostly in terms of ability to pull collective. I suspect that the X2 aerodynamics guys wanted to make sure that the manouvre margin was equally good at all airspeeds, with the FBW limiting g loading if required.

That said, being able to pull 2+g at low speed is still an impressive performance. :ok:

Dave_Jackson

26th Sep 2008, 05:01

Competition?

http://pvo.guns.ru/images/expo/helirussia2008/P1040759_DCE.JPG

More. (http://www.network54.com/Forum/211833/thread/1211736244/1211890413/HeliRussia+2008)

Dave

darrenphughes

26th Sep 2008, 06:41

Ok, if they can make that KA-92 a reality it will easily replace the Super Puma at the top of my list of stuff I wanna fly during my career!! Pity it's just an idea and not yet, if ever a reality.:(

Graviman

26th Sep 2008, 11:58

KA-92 demonstrates the risk in letting something out of the bag. It's a two edge sword - it attracts the money men, but also inspires competitors...

I'm hoping the X2 flight test team are being cautious about expanding the envelope, but not overly cautious. My big worry is that the current financial pinch sees X2 development slow.

The ABC helicopter is a good concept. Expect to see more.

bat1

26th Sep 2008, 17:09

Wow!
it really is a new Russia! Since when did the Russians start caring about the asthetic value of thier designs? We all know Russia makes the ugliest helis :) Mother Russia would never let a heli that beautiful leave her soil.
Though it is most likely just propoganda that model is beautiful. Maybe Sikorsky can rip off thier concept style.

Dave_Jackson

26th Sep 2008, 17:56

The propulsor is coaxial, also. :ooh:

IFMU

26th Sep 2008, 23:47

Flightglobal:X2 Second Flight (http://www.flightglobal.com/articles/2008/09/25/316429/sikorsky-iterates-x2-control-feel-on-second-flight.html)

Graviman

29th Sep 2008, 08:55

Pleased to see that development is gently stepping up a gear. :ok:

Interesting that the FBW gains have been trimmed for flight 2. This definately shows the benefits of a carefully considered flight test program. Fingers crossed that all of the development stays just fine tuning a good design.

http://www.flightglobal.com/assets/getAsset.aspx?ItemID=24902

Sikorsky plans to build 3h of flight time before grounding the coaxial rotor high-speed helicopter to integrate the pusher propeller into the power train and control system for faster flights planned in phases two, three and four in West Palm Beach, Florida. Kagdis says the pusher system should be integrated by year's end, after which the remainder of the 15h in phase one will be completed in Elmira.

Phase two will see the aircraft flying as fast as 80kt without the aid of the pusher prop. In phase three, test pilots will engage the rear propeller to attain speeds of 120kt, In stage four, Sikorsky will attempt to reach 250kt or more.

bat1

29th Sep 2008, 10:21

I fly rc helis and adjusting gains on the first couple of flights is always the primary focus especially when all the other mechanical aspects check out. So I would think that mechanically it is working like a singer sewing machine :) Hopefully 3 hours will go by fast, and then they can get that prop working.
if we can't get video can we get a sound byte? I love listening to the unique sound mae by each type of heli

IFMU

8th Oct 2008, 02:15

The new issue has the X2 as the cover story. You can read it online here:

Rotorcraft Professional (http://www.rotorcraftpro.com/)

They have a nifty 'virtual paper' link that lets you flip through the current edition.

-- IFMU

IFMU

15th Oct 2008, 01:17

From UTC Photo Contest (http://www.utc.com/photo_contest)

(week 4, page 23, you can get a higher resolution pic here too)

http://mbx.itworx.com/photocontest/web/photocontestimages/big_thumb_770.jpg

Also, link to the online version of Rotor & Wing, X2 cover and article inside:

Rotor & Wing - October 2008 (http://www.rotorandwing-digital.com/rotorandwing/200810/?u1=texterity&cache=3871d50f5340db22729d8f3ab82692f4)

-- IFMU

Graviman

27th Oct 2008, 12:23

Cefoskey, I'm actually slightly suprised Kamov haven't thought about ABC technology before. It's a logical next step from coaxial. I guess this just means that the time is right for helicopter cruise/dash speeds to go up. Post credit crunch that is. :uhoh:

Has Kamov done any development into the high effective hinge offset blades? I can imagine this being a greater challenge for such a large machine. The alternative would be to accept advancing blade compressibility limitations or an increase in coning angle. Either way KA-92 will not be competing with S-92 instantly...

Graviman

9th Jan 2009, 11:44

Anyone heard any news on X2?

I've not pinged this thread for a while, since i assume Sikorsky are as hard hit as the rest of us by the credit crunch induced recession... :sad:

Dave_Jackson

10th Jan 2009, 05:16

Its in hibernation down in WPB from what I hear. Something smells. (http://www.youtube.com/watch?v=6PeXjGfictg) :)

Could this be the reason for the X2 hibernation? (http://www.aviationweek.com/aw/blogs/defense/index.jsp?plckController=Blog&plckScript=blogScript&plckElementId=blogDest&plckBlogPage=BlogViewPost&plckPostId=Blog%3A27ec4a53-dcc8-42d0-bd3a-01329aef79a7Post%3A36f8aeda-b332-433e-9d4a-25f9404ee5f2)

Dave

Graviman

12th Jan 2009, 11:26

CEFOSKEY, as long as it is only in hibernation. It would be a great shame if this machine did not reach its full potential.

Dave, that article was written back in July 08, before the greedy bankers successfully broke the economy. :ugh:

VDTR just looks like more stuff to go wrong to me. Something about keeping the design simple. :uhoh:

Dave_Jackson

12th Jan 2009, 21:15

Mart (Graviman),VDTR just looks like more stuff to go wrong to me. Something about keeping the design simple. Earlier, you were understandably concerned about the complexity of the AeroVantage's transition mechanism.

At the risk of appearing promotional, what about this newer mechanism?

DESIGN: AeroVantage - Transition Mechanism - Proposed Method - 1x2 - Extendable Tubes (http://www.unicopter.com/1694.html)It extends and retracts the forward PropRotor, in a manner similar to Sikorsky's VDTR, except w/o the problem of centrifugal force.It rotates both PropRotors in a manner similar to, but simpler than, Bell's V22.
___________________

Is it time to start a thread on Sikorsky's Variable Diameter Tilt Rotor? ;)

Dave

zorab64

12th Jan 2009, 22:37

I remember doing project about ABC in early '80s - it struck me as a fantastic concept with plenty of scope for development. It seemed rather a pity that it appeared to have been dropped in favour of the tilt-rotor, which is surely a more unweildy machine?

Times move on & things develop but great to see the X2 flying - how about something of this ilk for Police work? Must be the coolest way to improve response times!!:ok: Pretty good for corporate work too!

The Sultan

13th Jan 2009, 00:40

Zorba

The tilt rotor you diss (the 609) reached 383mph. Not too bad. The X-2 has done what? 10, 20?

The Sultan

heli1

14th Jan 2009, 09:53

Have they actually connected the airscrew drive yet ? This was going to be the next stage as I recall ?

zorab64

14th Jan 2009, 20:54

Sultan, I don't diss the tilt-rotor, just remark that it appears "unwieldy in comparison". When one landed on a UK aircraft carrier last year, it was impressive, but there's no way you could strike one down into the hangar as easily as an ABC type machine.

That said, horses for courses, the two design types ought to be able to fulfil completely different roles. T/R for vertical or STO lift of troops/pax with rapid transport & delivery; ABC for rapid response (but probably shorter range) delivery of sensors/weaponary to an area and/or efficient loiter on task - hence my comment about Police role. I would have thought that hovering over a built-up area at midnight in a T/R machine would be a complete waste of its talents! :=

True, the ABC has not yet fulfilled its design/speed potential but "with plenty of scope for development", had it had the same billions poured into it since the 80s that have funded T/R development, I would expect that speeds wouldn't be dramatically different - despite the two designs being quintessentially for different roles. ;)

ChopperFAN

15th Jan 2009, 07:05

I say good on ya to Sikorsky for finally spending time and effort into helicopter design and concept prototyping

In the current world almost anything is possible, movement in the helicopter industy compared with other trends is pittyfull...

If helicopter manufacturers and designers thought as the guys at IBM did im sure the helicopter would be so differtent and refined by now, a computer can calculate optimum blade desigh without even flying the thing... beoing 777 designed completely from CAD plans all wing design testing too

Y is it so hard for things to change... The way helicopters are made to day is the same as it was 50 years ago... im sure a safer, stronger and lighter airframe can be developed using modern techology

So much weight could be reduced by using modern materials, Run the whole helicopter and all its status and hours straight to a small as computer downloadable by the engineers

make a difference and push boundries, we are human

Good on ya guys its a start in the right direction

:D

Dave_Jackson

15th Jan 2009, 17:03

ChopperFAN said;
"Y is it so hard for things to change..." Things are changing.

While the West is preoccupied with fiscal capitalism, one more company in the XMiddleX Far East is advancing productive capitalism; $1.2-bn helicopter production facility c/w research & development (http://www.sindhtoday.net/world/50317.htm)

Dave
______________

Trivia;

The Islamic religion does not believe in charging interest for the loaning of money (usury). The Christian religion did not believe in charging interest for the loaning of money until the 16th century. The Jewish religion has allowed the charging interest for over two thousand years, but not to charge interest to other Jews.

The interest on debt (personal, corporate & governmental) is the reason for today's problems.

heli1

16th Jan 2009, 16:21

Hate to correct you Dave Jackson but I think you'll find China is in the far east !
Please don't be like the lady in an education shop in California who asked me to show her and her children on a globe where " Eyerak" was after pointing at Brazil !!!

Dave_Jackson

16th Jan 2009, 19:55

heli1;
Thanks for the correction.

Dave

Graviman

20th Jan 2009, 11:38

Dave, as long as your AeroVantage uses only pivots, with no sliding mechanisms. Bushes are light and reliable, sliding mechanisms under load (at say 2g to allow some manouvreability) are heavy and prone to sticking as they become worn/notched. The high disc loading will still limit hover capability (failsafe), and i'm still not sure why try to keep both prop/rotors in the same streamtube (but only in one ideal flight condition).

---

Good to see support for X2 is still out there. CEFOSKEY, thanks (again) for keeping us informed about this fascinating project.

I started this thread because i recognise that X2 (ABC) is a relatively simple solution for the high speed helicopter. There are (many) other solutions out there, and i wish all good luck. To me X2 remains the best compromise engineering solution....

OFBSLF

20th Jan 2009, 16:08

If helicopter manufacturers and designers thought as the guys at IBM did im sure the helicopter would be so differtent and refined by now, a computer can calculate optimum blade desigh without even flying the thing... beoing 777 designed completely from CAD plans all wing design testing too

Y is it so hard for things to change... The way helicopters are made to day is the same as it was 50 years ago... im sure a safer, stronger and lighter airframe can be developed using modern techology
I'm not particularly following what you are trying to say here. I can tell you that during the 1990s Sikorsky was using the very same 3d CAD software (CATIA from Dassault Systemes) to design the Comanche that Boeing used to design the 777.

Graviman

21st Jan 2009, 11:28

CEFOSKEY, i recently considered moving across into the testing side of helicopters. It strikes me as a fascinating area to develope in. I chose to move into diesel piston reciprocating engines because most of the development FEA/CAD software and techniques are similar. Ultimately it came down to me beating a path homewards - not that i didn't enjoy five years in Scotland...

----

ChopperFan, one must be careful comparing electronic hardware to mechanical hardware. A silicon chip can advance without any fundamental increase in the material performance - you improve the manufacturing technique to make each transistor smaller. A helicopter must test the fundamental stresses of the materials for any reasonable performance.

Actually there have been many significant advances in helicopter design, but only apparent to specialists. The materials allow for increased time between overhauls, the exhaust emissions have gone down, and the same payload can be carried further for less fuel. Of course these have been brought about by the silicon revolution, but ultimately this just shows how up against the limits the mechanical systems are.

Dave_Jackson

21st Jan 2009, 21:04

Graviman,
Thanks for the comments, particularly your concern about the wear on the extendable mechanism. The twin-rotor hover ~to~ coaxial-rotor cruise I would argue, but this is the X2 thread. :ok:

Dave

ChopperFAN

22nd Jan 2009, 09:19

Graviman, I agree with you on me comparing it... its not the best way to compare them. I was poorly trying to say how its good that Sikorsky was getting out there and spending money on new drivetrain concetps... its breaking new ground... Thats awesome

Sorry Svenestron, I ment more airframes developed and concets tested and used in the comercial market. Im sure almost all havent changed much from their base designs... cant we find a better, safer airframe? Most are sheet and rivets and we all know how soft aluminium is, any time it doesnt come down straight chances are so slim... Im sure a way to get the human cargo and yourself to the ground can be found? saftey chute, pod or airbag stlye systems

Wouldnt there be a better way to design most parts too, even avionics should be tiny in helicopters by now, cant mechanical gauges be made lighter and way more acurate... when did they change last?

People thinking and someone listening is the only way things change

I like thinking of new ways to do things, im always drawing and making things like a backyard mcgyver, but what change can i have...?

Sorry if i offend... Im obviously not very smart, but i have a peal passion for helicopters, and i wanna break new ground before i die and make an impact

Simon :sad:

Dave_Jackson

22nd Jan 2009, 17:03

The subject of improvements to rotorcraft invariably brings up phrases such as;

Composite construction
More efficient engine
Light weight avionics
Piezoelectric actuators

The above sounds like Igor when he said that he had to wait for OTHERS to develop a better power/weight engine.
Meanwhile Focke and Flettner were building and flying their helicopters.
____________________________

This thread is discussing the regurgitation of the previous XH-59A ABC. IMHO, any serious desire to improve the ABC concept will require research and development that is rotorcraft specific, such as;

Active blade twist.
Reverse velocity blades.
Higher cyclic rate flight controls

The essence of rotorcraft is the 'Rotor' http://www.unicopter.com/Chairshot.gif
________________________

China has ten times more engineering students than the US. If the 'West' wants to decrease the rising unemployment it might consider spending its tax dollars on sending hundreds of thousands back to school.

Or, do we just wait until Rotorland moves to the far east?

Dave

Graviman

27th Jan 2009, 11:21

Dave, my "threadjacking" light just came on. Agreed that the technologies you mention are important lines of development though. New thread? :ok:

CEFOSKEY, is Catia V5 also used for all of the powertrain design (ie rotating components)?

Dave_Jackson

27th Jan 2009, 22:03

Mart,

Dave, my "threadjacking" light just came on.:ooh: http://www.unicopter.com/lightbulb%20idea.gif :).
The three unfulfilled requirements mentioned in post #400 are directly related to the 'Sikorsky X2 coaxial heli development' and its ability to achieve high speed flight.

Interestingly, all three of these unfulfilled requirements are also directly related to; a rotating airfoil, where the axis of rotation is normal to the free stream velocity.
Is Darwin trying to tell us something? http://www.unicopter.com/Think.gif

Dave

Graviman

28th Jan 2009, 11:25

This thread is discussing the regurgitation of the previous XH-59A ABC. IMHO, any serious desire to improve the ABC concept will require research and development that is rotorcraft specific, such as;

Active blade twist.
Reverse velocity blades.
Higher cyclic rate flight controls

Dave, agreed but these are still to emerge technologies for production helicopters. Active tip servo flaps for vibration suppresion is also another important future development - this could be argued as superceding higher harmonic control. Active blade twist (when developed) will be the next significant performance improvement technology.

The X2 design team has neatly considered available "off the shelf" technologies and adapted them to a practical flying machine.

IFMU

3rd Feb 2009, 01:27

Have they actually connected the airscrew drive yet ? This was going to be the next stage as I recall ?

From aero-news network:

Sikorsky Conducts First X2 Pusher Prop Ground Runs (http://www.aero-news.net/news/commbus.cfm?ContentBlockID=cfc83907-473f-4ccf-a001-f193e9619a11&Dynamic=1)

-- IFMU

Graviman

3rd Feb 2009, 11:34

Hey, that's great news! So X2 still active. :ok:

Any flight testing intended for later on this year?

Graviman

4th Feb 2009, 11:23

Everything whirling away! Exciting times.... :D

Thanks, CEFOSKEY. Fingers crossed there are no setbacks.

Rigid Rotor

8th Mar 2009, 13:11

Viewing the photos of the flight (which were accompanied by all of the "best ever" required comments to get the bonus) I would suggest move the pilot station to the back cockpit and use vertically challenged pilots to avoid a decap during maneuvers.

The Sultan

@The Sultan (post 333) - what sort of flapping hinge equivalent offset are we looking at ? Would it be in the region of about 50% of rotor radius given the fact that the designers appear to be sufficiently confident of seating the Chief Test Pilot so far upfront !!;)

Notwithstanding all that, the X-2 is definitely promising - will hopefully prove to be the long overdue bootstrap for chopper designs from its present stagnant state.

ramen noodles

8th Mar 2009, 17:31

Rigid,
You are right on, the Sultan yet again shows how little he knows about rotorcraft when he applies zero-offset thinking to a high offset rotor.

He is, however, quite correct when he reminds us of the differences between demonstrated high speed capability (609) versus promised (X2).

SASless

8th Mar 2009, 18:06

How many 609's in the commercial fleet?

It one thing to talk of demonstrated speed and all that but the Sikorsky ABC already proved that long before the 609 test flights occurred.

What is the difference between the ABC and the X-2....similar concept are they not and one builds on the earlier technology?

Dave_Jackson

8th Mar 2009, 19:08

What is the difference between the ABC and the X-2....similar concept are they not and one builds on the earlier technology?

There is extremely little difference between the X2 and what was recommended at conclusion of the XH-59A ABC thirty years ago.

IMHO, the main concern for the X2 (and for the Unicopter (http://www.unicopter.com/UniCopter.html) for that matter) is the essential requirement for a blade that can obtain lift from the reverse velocity airflow region, which is greater than any resulting loss of lift from the forward velocity airflow.

The 5.300 GW X2 may achieve 250 knots with its 1,450 SHP, but 3.6 lbs / HP is far from efficient.

The V-22 is 4.3 lbs / HP.

The Sultan

8th Mar 2009, 22:51

Sasless,

You forgot the XV-15 tilt rotor demonstrator kicked the ABC to the curb 20+ years ago. What concept is in production, what concept is doing operational deployments. It sure is not the ABC.

The Sultan

Graviman

9th Mar 2009, 12:52

Guys, lets keep a nice peace-ible debate! :ok:

Both tilt-rotor and advancing-blade have their reasons for being, and fascinating history of concept development. To my mind the advantage of ABC is a very compact configuration, and the ability to autorotate from any flight regime without relying on stored hydraulic energy - i'm not sure what the system is in V-22 during transition.

Dave, are you sure about those figures? If you mean HP/lb then it makes sense. Advancing-blade should have a lower disc loading over tilt-rotor.

Both concepts will lose out to a conventional because they must carry extra mass to accomplish cruise speed. Also the blade radius, planform & twist will be suited to a higher cruise speed.

I've no problem with argueing the merits, but let X2 step up to the mark first. Another perfectly good flying machine, Space Shuttle, is being grounded because the Columbia accident review board thought it would be a good idea to force re-certification on a 30 year old design. I'd hate to see a good concept like X2 quashed because the engineers weren't given the opportunity to get everything just so... :ouch:

JohnDixson

9th Mar 2009, 19:12

Anyone know if this testing has been completed and if the data is available?

Thanks,
John Dixson

Dave_Jackson

11th Mar 2009, 20:34

Hi CEFOSKEY,

Think control systems.
Research & Development, IMHO, is that of advancing technology. Was not the flight control system already developed for the Comanche?

The CEO of Sikorsky said that their next project is to be Individual Blade Control. Developing IBC on a test stand, then in a wind tunnel, and finally on a craft (perhaps the X2) would be R&D.

One unknown is the technique and specifics on the rotor-propulsor integration, particularly during transitioning. This may be new and interesting.

Dave

Dave_Jackson

12th Mar 2009, 19:42

Risk mitigation is still a part of things I would think.Agreed.

However, a couple of years ago the Coaxial-ABC was Sikorsky's proposal for the Joint Heavy Lift requirement. Apparently it was rejected. Then Sikorsky changed horses and started to promote the Variable Diameter Rotor system.

With cynicism, I suspect that the X2 craft, its Design Patents (http://www.unicopter.com/1465.html#Design_Patent), and its promotion, collectively suggest that the craft may have originated in the Marketing department and not the Engineering department.

My question and that of others has been; Assuming that the aerodynamic and aeromechanical features of the Coaxial-ABC configuration are potentially viable, why wasn't there a low-budget and low-profile continuation of research and development on the Advancing Blade Concepts during the past 30 years, since the XH-59A ABC.

Dave

Rigid Rotor

13th Mar 2009, 13:31

Any reason why the ducted pusher-prop variant XH-59B (which was a natural follow-up to the 59A) was abandoned ?:confused:
We have lost about 35 years as a result of that decision !

- And now we have even the Russians hopping onto the 'ABC boat' with their Ka-92 project -I believe that the Kamov Design Bureau has sufficient expertise in production of coaxials - they had some serious fleet reliability problems in their coaxial swashplates and linkage controls which they have largely overcome. They have progressively increased the flapping hinge offset in the Ka-50 (although as of yet nowhere near the 'true ABC' requirements). Its quite possible that they will be able to evolve their coaxial designs into the Russki ABC. In fact they have declared their intent to productionalise the ABC Ka-92 (or its derivative) by 2020.

Ian Corrigible

13th Mar 2009, 13:56

Actually the army reversed course on JHL again last time I heard.
AATD's focus is squarely on the High-Efficiency Tilt-Rotor (HETR), but the $15+ billion development cost (and $40+ billion acquisition price tag) probably represents a bigger hurdle than the technical and operational challenges. A Variable Diameter Tilt Rotor (VDTR) study was one of the 13 risk reduction studies performed using FY-08/09 drip feed funding, hence SAC's revisiting of the TRAC VDR study.

Any reason why the ducted pusher-prop variant XH-59B was abandoned?
From Ray Robb's article in AHS Vertiflite (http://www.vtol.org/vertiflite), Summer 2006: "A proposal for the development and flight test of the XH-59B was submitted to the Army, but Sikorsky’s refusal to share costs (in part due to the resource strains on the company that resulted from the simultaneous development of the UH-60 Black Hawk, SH-60 Seahawk, CH-53E Super Stallion, and civil S-76) resulted in the Army not awarding a contract. As a result, the XH-59B was never built."

I/C

Dave_Jackson

13th Mar 2009, 16:46

Rigid Rotor,Any reason why the ducted pusher-prop variant XH-59B (which was a natural follow-up to the 59A) was abandoned ?
Here is more information related to your question. (http://www.unicopter.com/0891.html#Why)

Perhaps the larger question might be; What developmental work has Sikorsky done that was not funded by the government?

Perhaps a related question might be; Would the helicopters have been Intermeshing-ABCs if Charles Kaman had not been told "Charlie, we have our inventor at United Aircraft. His name is Igor Sikorsky. We don't need another one."

Dave

JohnDixson

14th Mar 2009, 02:09

Hello David Jackson.

I believe you wrote the following:

"Perhaps the larger question might be; What developmental work has Sikorsky done that was not funded by the government? "

My memory is far from perfect, but here are a few items that were funded with Sikorsky/UTC money:

S-61F. High speed reaearch aircraft with twin J-60 tourbojets. Took a basic SH-3 airframe, added a wing, ailerons, an entire new tail ( vertical and horizontal, with a rudder experiment ).
SH-3 Pusher tail rotor. Tail rotor/tail rotor gear box was gimbaled to rotate 90 degrees in flight so as to obtain forward propulsive thrust from the tail rotor. Incorporated a rudder.
S-67 Blackhawk. Took various S-61 drive components, built a totally new airframe, added a wing and horizontal stabilizer ( was a stabilator for awhile ), Incorporated wing-mounted speed brakes. Had an aerobatic envelope.
S-67 Fan-in-fin. Incorporated a Hamilton-Standard fenestron-fan in a new tail structure. Had a rudder but this was never fully developed.
S-61R. This was a company funded S-61 derivative that won the competition with the Vertol 107 for the USAF contract that turned it into the original HH-3C. But, the S-61R was a company funded design and flight tested aircraft.
The ABC. This one you seem to have been aware of.
S-60 Skycrane. A crane designed using S-56 components, but in a totally new conceptual heavy lifter.
S-64 Skycrane. The original S-64 was designed and flown on Sikorsky /UTC funds. By the way, that included a UTC investment in having Pratt & Whitney design and test the original JFTD-12 engines ( taking a J-60 turbojet and adding a power turbine assembly to make it a turboshaft engine ). The US Army contract came later.
Canted tail rotors. Company funded and originally developed and flown on a company owned S-61R.
S-76. All models were company funded and developed.
S-92. Ditto as for the S-76.
S-76 Fantail. Risk reduction for the Comanche ProgramThere is another category of development, wherein the company could bail an aircraft from the government, and then do development programs using its own money for that engineering work. I am thinking of the CH-53 IRB ( improved main rotor blade ) work and the S-70 composite blade development.

Lastly, there was some discussion about the X2 being just a version of the XH-59. Possibly so, in the same sense that the Wright Flyer and the B-777 are both airplanes. The similarity ends there, however.

Thanks,
John Dixson

IFMU

14th Mar 2009, 02:15

To add to what John said, is not the X2 Sikorsky funded? Thought I saw that in the press somewhere. The original Cypher UAV was company funded too, I believe.

-- IFMU

Dave_Jackson

14th Mar 2009, 05:51

Thanks John. Your knowledge and recollection of Sikorsky is impressive. That is quite a list. :ok:

Out of curiosity I did a little research and found this on the first item #1. "Officially listed as an HSS-2, the U.S. Navy's BuNo. 148033 was actually a Sikorsky S-61F compound research helicopter sponsored by the Army and Navy." (http://www.aviastar.org/helicopters_eng/sik_s-61f.php)

As to the last item, the original Cypher mentioned by IFMU was Sikorsky funded, where as with the later Cypher II Sikorsky is currently [was]under a $5.46 million contract to deliver 2 prototypes and 4 ground stations (http://www.aviastar.org/helicopters_eng/sik_cypher2.php)

________________________

Lastly, there was some discussion about the X2 being just a version of the XH-59. Possibly so, in the same sense that the Wright Flyer and the B-777 are both airplanes. The similarity ends there, however.

Interesting, but it misses the essence of the discussion. The discussion related to why the ABC concept was not pursued back then; and why it is [or was] being pursued now.

IMHO the esential question has always been; ~ Is the fundamental ABC concept viable, or is it not viable?

They stated very clearly back then what the aerodynamic and dynamic improvements should be (http://www.unicopter.com/1465.html#Calculation) and they have now incorporated them, 30 years later. Today's new abilities, to fly-by-wire, fly-by-light, or fly by mental-telepathy represent an improvement for all aircraft. They are not unique to the ABC helicopter.

Dave

JohnDixson

14th Mar 2009, 13:36

As to the S-61F, I was told upon arrival at SA in 1966 that the 61F was an internally funded design. Of course there were US Gov't. funds involved later. Anyway, I have two inquiries going to former SA people who may ( or may not ) confirm my belief on that subject.

US Gov't. funding sometimes is obtained after a concept is designed and flown with internal company funding. An example not in my previous list is in that category: Two engineers, Sean O'Connor and Don Fowler, with SA money, designed an automatic sling load stabilization system in the late 60's/early 70's that we flew on a bailed CH-54A. Low density/high volume loads like mil-van type containers were always among the worst actors, stability-wise, and this system enabled the Crane to fly quite well at 70 kts with these containers, vice about 40 without the system. Thus it enabled IFR capability and a terrific safety improvement. The Army was ambivalent, but then gave some support and we did a simulation study with them to prove the systems value. End of story was that they still didn't incorporate the system in the Crane, but now the technology was in the public domain, and a few years later the system showed up down in Philadelphia on a CH-47 variant. As I recall it didn't make it to production there either.

On the subject of why the ABC was not supported thru the 80's, I confess to only knowing part of the story. I do know that there was a substantial number of the tech community at SA who favored this concept for the LHX, but I do not know the background as to why the SA/Boeing team decided on the concept that became Comanche. Obviously their assessment ( and the Army's ) was that speed wasn't of prime importance. So there wasn't a good idea of where an ABC product would fit in. At that time, the S-76 was absorbing all of our efforts in the small civil market, and while there were some who appreciated what an ABC could do in that market, the decision to build the S-76 essentially closed that opportunity. These are just my personal guesses.

I am curious, Dave: have you ever seen the ABC up close, in person?

Thanks,
John Dixson

JohnDixson

14th Mar 2009, 18:21

Received the following note from a former collegue at SA who was in a position to know at the time:

"Not dead certain, but I do not believe so. S-61F was one of four contracts for compound and aux propulsion research issued in the mid 1960s by Ft Eustis - whatever they were calling themselves at the time. The other three were Kaman -modified UH-2A -, Lockheed - modified XH-51, and Bell 533 which was a modified YH-40 (original Huey bought under Air Force contract). I remember us being faster than Kaman but not near Lockheed and Bell. It was a real lesson in interference between wings and stub wings for the J-60s. One thing that rarely gets remembered is that the Bell machine could easily have come apart (mainly tail rotor} when they hit 300 mph. A point they never dared repeat."

I was therefore wrong in stating that the 61F was a company funded design.

Thanks,
John Dixson

Dave_Jackson

14th Mar 2009, 19:54

Hi John,I am curious, Dave: have you ever seen the ABC up close, in person? No, neither of them. Nick got to fly the XH-59B and said that he was really impressed.

I was therefore wrong in stating that the 61F was a company funded design. WOW! Thanks for the response.
My method is to drop the subject and very quickly move on to a different one. ;)

Dave

The Sultan

14th Mar 2009, 22:37

Dave,

I saw the ABC from inside and out. The first thing I noted was that the majority of the cabin was taken up with transmission. Maybe Sikorsky could dispell this by showing what is behind the pilot on the X-2. The tilt rotors put less complex transmissions on the wings and free up the entire fuselage for useful load.

The Sultan

Dave_Jackson

15th Mar 2009, 03:53

TS,

Directly behind the rear pilot's area in the X2 are the force generators.

http://www.unicopter.com/1465-2.gif

__________________________

The tilt rotors put less complex transmissions on the wings and free up the entire fuselage for useful load.
The AeroVantage (http://www.unicopter.com/AeroVantage.html) puts the PropRotors fore & aft and frees up the entire area for downwash.

http://www.unicopter.com/1681_1x2_Micro_Hover.gif
-
http://www.unicopter.com/1681_1x2_Micro_Cruise.gif

http://www.unicopter.com/Devil.gif The devil made me do it, 'cause I don't have a large marketing budget. :)

Dave

Graviman

16th Mar 2009, 12:49

Some interesting technical discussion going on here! :ok:

Good point about ABC fuselage being taken up by transmission. In principle, since each rotor only handles half the torque in hover over conventional, i am not sure why ABC would require a significantly larger transmission. The only reason i can think of is that each rotor would need to handle more torque during high speed manouvre, because advancing and roll upwards side doing more lift. The shaft and hub mechanisms would clearly need to be much stiffer/stronger, but this is true of any high effective hinge offset rotor.

Although inherently good lateral Cm comes naturally with tilt-rotor, i suspect that this would be offset by the need for more power/torque for the higher disc loading. I have no figures to compare on this point.

Dave, that's a handy resource you have there. Any chance of the two technical papers you mention?
1. Aerodynamic Design of the X2 TD Main Rotor Blade - Ashish Bagai (May 2008)
2. Dynamic Design Characteristics of the Sikorsky X2 TD Aircraft - R. Blackwell
(May 2008)

PS: Hardly even get time to check this site out now...

Mart

SASless

16th Mar 2009, 13:22

Dave,

Have you seen this article about the SpeedHawk concept being applied to the Chinook?

Very similar concept to what you offered....but with less colorful drawings.

Patent alert: Chinook augmented by vectored thrusters - The DEW Line (http://www.flightglobal.com/blogs/the-dewline/2009/01/patent-alert-chinook-augmented.html)

Dave_Jackson

16th Mar 2009, 16:59

Mart,

You've got mail.

SASless,

Had not seen. Thanks.
It would be interesting to see a performance comparison between it and this. Boeing 347, Tandem w/ wing (www.combatreform2.com/boeing347banking.jpg)

Dave

Ian Corrigible

16th Mar 2009, 17:35

A Chinook with only one wing is so passé... :E

ULOR (http://www.aviationweek.com/aw/blogs/defense/index.jsp?plckController=Blog&plckScript=blogScript&plckElementId=blogDest&plckBlogPage=BlogViewPost&plckPostId=Blog%3a27ec4a53-dcc8-42d0-bd3a-01329aef79a7Post%3afbf422c7-8568-41f8-87e2-2b3e5c5f806a)

I/C

Graviman

18th Mar 2009, 12:38

Interesting articles SASless & Ian. :ok:

There may also be a good case for developing ABC tandems, since the powertrain layout is already there. There would be a weight penalty because the high hinge offset rotors would load up the transmission, and the fuselage would also be loaded in torsion. I imagine the loss of payload would still allow a good payload mass-speed product.

Anyone know how much Chinook powertrain weighs? An initial guestimate would be to double powertrain mass (since engine power also goes up), and see how much payload/fuel capability is eaten up...

Dan Reno

19th Mar 2009, 15:44

http://www.aero-tv.net/index.cfm?videoid=f60d7e95-5329-4ce4-8c75-6b909930dc48

bat1

22nd Mar 2009, 05:36

finally some inflight footage:ok:

Graviman

23rd Mar 2009, 12:38

Thanks, Dan.

Always interesting to hear the TPs comments.
Some interesting commercial aviation potential there too.

Notice how there is a reducer g/box for the tail prop, with d/shaft coming in along starboard side. I assume/guess the clutch is near the main g/box, while the pitch mech is in the tail g/box. It's always good to get a peak at the powertrain installation...

Dan Reno

23rd Mar 2009, 21:16

So the rumour was true about replacing all carbon-based stick actuators!

Ian Corrigible

27th Mar 2009, 15:12

After watching Alexander Korda's 1936 big screen interpretation of H.G. Wells' "Things to Come" (http://www.imdb.com/title/tt0028358) on TCM last night, I discover that Sikorsky has been working on the X2 concept for over 70 years now...

http://i.imgur.com/8YPTnK2.jpg

Wells/Korda apparently had little faith in the coaxial rotor, preferring a more conventional layout instead. Still, the good news is that the program seems to be ahead of schedule - Wells predicted that the concept wouldn't appear until 2036...

:E

I/C

Dan Reno

13th Apr 2009, 10:57

(Westland sour grapes?)

Historic helicopter venture zooming to town

By STACEY SINGER ([email protected])
Palm Beach Post Staff Writer
Monday, April 13, 2009
In a place where eagles and ospreys soar, a helicopter tarmac awaits an exceptionally rare bird.
Sikorsky Aircraft Corp. is about to truck its one-of-a-kind X2 helicopter prototype to an airfield 12 miles west of West Palm Beach, where the aircraft will try to break the helicopter speed record.

Sikorsky Aircraft's schedule calls for the X2 to pass the 250-knot mark — 287 miles per hour — by year's end. It would make the X2 the fastest helicopter and shatter the belief that helicopters cannot exceed 250 mph without spinning out of control.
The Sikorsky Aircraft Development Flight Center is tucked between the J.W. Corbett Wildlife Management Area and the Beeline Highway, off the radar of most. Despite its low profile, the West Palm Beach-area flight center has become a winner in a difficult economy.
In its 20-year history in South Florida, Sikorsky Aircraft has never employed as many people as it does now. In 2008, the firm added 365 workers, bringing its head count to 878, said General Manager Pete Ladyko.
Part of United Technologies, Sikorsky Aircraft's home is in Stratford, Conn. The addition of the X2 to its local operation will require several Connecticut-based employees to relocate here, at least temporarily, Ladyko said, but it won't add substantially to the number of local workers.
Most local Sikorsky employees are building next-generation Black Hawks and the aircraft that Canada is using to replace its aging maritime helicopter fleet, the CH-148 Cyclone.
Others are test pilots and engineers dedicated to refining and customizing models such as the 19-passenger luxury bus called the S-92, often used to carry workers to oil platforms. Five aircraft development programs are in testing here.
Last week's budget briefing from Defense Secretary Robert Gates suggested the company would continue to grow under the Obama administration. Gates said helicopters are "in urgent demand in Afghanistan."
Thirty to 35 UH60-M Black Hawk helicopters are made each year near West Palm Beach, Ladyko said.
The next-generation Black Hawks, like the X2 and Canada's CH-148, feature a computer technology called "fly-by-wire" that replaces mechanical controls with digital ones. The fly-by-wire software must be refined in test flights.
Test pilot Rick Becker handled the controls for the first flight of the CH-148 near West Palm Beach in November. The systems had been analyzed for more than 100 hours on the ground before going airborne, Becker said.
"It does have an exhilarating quality to it the first time you lift off, but it's the logical culmination of what we've been doing," he said. "You build up to it."
A similar process is under way for the X2.
The X2's first flight was Aug. 27 at the Sikorsky-Schweizer Hawk Works near Elmira, N.Y. The pilot initially ran the aircraft at slow speeds, assessing stability and basic systems.
The helicopter speed barrier could be breached this summer after the X2's unusual boat-like pusher-propeller is tested.
Most helicopter designs include a tail rotor that counters a helicopter's tendency to rotate opposite the blades' direction. Having twin rotors gives the same balance and means the tail can be freed to push the aircraft forward at high speeds. It also gives maneuverability and enables the aircraft to carry up to 40 tons, according to the journal Aerospace Testing International.
Sikorsky Aircraft says the X2 is designed to "cruise comfortably" at 287 mph. That would be exceptional.
"The speed record for any helicopter is held by the Westland Lynx at 249 mph, or about 220 knots, but this was a one-time record," said helicopter pilot R. Randall Padfield, the editor of Aviation International News.
That Westland Lynx sits in a museum today.
Breaking the helicopter speed barrier would be exciting. Will the market embrace it?
Padfield is skeptical because the X2 needs a runway for landings rather than a heliport.
"I think the market is not as great as helicopter promoters like to say it is," Padfield said.
The X2 is intended to lead to development of a commercial or military aircraft. Its ultimate price is unknown. Sikorsky Aircraft is paying for the X2's development, a company representative said.
http://www.palmbeachpost.com/localnews/content/local_news/epaper/2009/04/12/a1a_sikorsky_0413.html (http://www.palmbeachpost.com/localnews/content/local_news/epaper/2009/04/12/a1a_sikorsky_0413.html)

gittijan

13th Apr 2009, 13:21

Having twin rotors gives the same balance and means the tail can be freed to push the aircraft forward at high speeds. It also gives maneuverability and enables the aircraft to carry up to 40 tons, according to the journal Aerospace Testing International.

Now that is a good payload as well as speedy.:rolleyes:

IFMU

14th Apr 2009, 02:04

Maybe the X2 needs a runway when it is loaded up to 40 tons, like it says in the article. That would seem to be a pretty good tradeoff to me. I don't know where they would fit 40 tons though. Time to call in Dr. Who.

Aero-news had a little interpretation of the article too:
Sikorky's X2 Expected To Conduct Speed Trials In West Palm Beach (http://www.aero-news.net/news/featurestories.cfm?ContentBlockID=23ee3419-5676-4385-b79e-3484500aad5f&Dynamic=1)

Funny how they call it a helicopter/airplane hybrid. Where are the wings?

-- IFMU

Dave_Jackson

14th Apr 2009, 02:33

The Aerospace Testing International article (http://viewer.zmags.com/publication/22a2bbe8#/22a2bbe8/26), which was mentioned in the Palm Beach Post article.

Graviman

14th Apr 2009, 11:35

X2 has already demonstrated the ability to hover in flight test.

Much better to stop then land, than land then stop... :ok:

When X2 does what it was designed to do i have no doubt that the world will beat a path to Sikorsky/Schweizers door. Take a good design concept, identify the limitations, and evolve the concept. Sounds like a recipe for success to me - i'll certainly be excited when that magic 250kts is reached!

Graviman

15th Apr 2009, 11:31

CEFOSKEY,

I've done some traditional back of envelope calcs to convince myself that scaling up X2 technology is feasible (i did waver earlier in the thread). As the rotor diam goes up 1st flap and torsion frequencies linearly reduce, but so does NR (for constant tip speed). So any offset hinge achievable with X2 would also apply to the scaled up machine. The technology is scalable.

Interesting to see whether faster point-to-point passenger service becomes a driver for the technology...

bat1

15th Apr 2009, 17:44

That looks pretty sweet!
truth is I would love to see a medical version of one of these go screaming by on its way to the Hospital :) Medical helicopters give me my daily fix

IFMU

16th Apr 2009, 01:32

The palm beach post published a correction:

Correction: A previous version of this story about Sikorsky Aircraft's X2 high-speed helicopter suggested the aircraft requires a runway to land. Sikorsky says the X2 is capable of vertical takeoffs and landings.

Can be seen at the original link: Palm Beach Post X2 article (http://www.palmbeachpost.com/localnews/content/local_news/epaper/2009/04/12/a1a_sikorsky_0413.html)

-- IFMU

Graviman

16th Apr 2009, 11:38

CEFOSKEY, seeing these machines flying around in service will make for exciting times!

IFMU, that's feedback in action. :ok:

riff_raff

26th Apr 2009, 02:26

It's too bad they're going to cover the X2 rotor hub with a fairing. That rigid rotor hub structure is a real pretty piece of design work. I wonder if most people really appreciate how difficult it is to design a lightweight hub structure and pitch bearing mechanism capable of handling the huge moment forces produced by a rigid rotor. It was likely a difficult design problem at the small scale X2 demonstrator. One can only imagine how hard the problem will be to solve with the exponentially larger moments imposed by a larger diameter rigid rotor.

Don't know what's in store for the X2's future though. It was dropped from consideration in the JHL/JFTL program. Apparently it didn't fare too well against conventional tiltrotors in the JHL trade studies. To make up for it though, it looks like the program management threw Sikorsky a bone by suggesting they dust off their VDTR concept.

ramen noodles

26th Apr 2009, 05:35

riff raff,
Dont worry about JHL, its as dead as a doornail, because FCS is dead. Imagine using 250,000 lb rotorcraft to carry tanks, the enemy would surely be defeated - they'd laugh themselves to death!

Dave_Jackson

26th Apr 2009, 18:42

riff_raff, I wonder if most people really appreciate how difficult it is to design a lightweight hub structure and pitch bearing mechanism capable of handling the huge moment forces produced by a rigid rotor. It was likely a difficult design problem at the small scale X2 demonstrator. One can only imagine how hard the problem will be to solve with the exponentially larger moments imposed by a larger diameter rigid rotor.
http://www.unicopter.com/1506-A.jpg

This is one of a number of advantages that the Interleaving-ABC (http://www.unicopter.com/Nemesis.html)configuration offers.

For the same disk-loading as the Coaxial-ABC (http://www.unicopter.com/1465.html)the Interleaving-ABC, and the Intermeshing-ABC (http://www.unicopter.com/UniCopter.html), will have physically smaller disks and therefor blades with shorter spans.

Dave

Graviman

30th Apr 2009, 11:34

Dave,

Does the circle density in your plots relate to induced velocity? I'm a bit bothered that your calc does not account for interaction between one rotor and another. There should be some azimuthal variation with each rotor.

Interesting point about interleaving reducing the blade loads for a given rolling moment (ie snapiness). The problem is this does not help you in level flight. The retreating side needs to be off loaded regardless of config.

CEFOSKEY, riff_raff don't like your fairings. Is you jus' gonna take that? ;)

Riff_raff, agreed hub is a nice piece of design. Not sure about loads going up exponentially with radius, though. All components are scaled up equally, and stress reduces with depth^2. Since a machine twice the mass would require twice the rotor diam then hub bending moment also goes up 2x2=4, which keeps stresses in a hub twice the size in trim. Problem is generally MGB which now handles twice the power at half the output speed...

Commercial sector wouldn't mind a fast helicopter. :D

Dave_Jackson

30th Apr 2009, 16:28

It is with some trepidation that I comment on perceived improvements to rotorcraft, since Senior Pilot has made it apparent that it is not a subject for this forum.

Mart (Graviman)

Going off-topic related to the X2, but staying on-topic related to the ABC.

Does the circle density in your plots relate to induced velocity?Yes. The above drawing shows the the rotor disks as having the same diameter. In reality, the disks of the Interleaving would be smaller for a comparable craft with the same gross weight. In the drawing, the density of the circular lines represents the induced velocity during hover.

I'm a bit bothered that your calc does not account for interaction between one rotor and another. There should be some azimuthal variation with each rotor. ........ The retreating side needs to be off loaded regardless of config. http://unicopter.com/Nemesis_Drg_Smaller.gif

The above drawing shows the craft with its rotors. There should not be any significant interaction between the two rotors.

Regarding aerodynamic interaction between the rotors and the fuselage;During cruise, the retreating sides of the rotors are over the fuselage. The retreating blades will be producing minimal thrust due to the ABC. During hover, the downwash on the fuselage would be reduced due to the inclusion of Active Blade Twist (http://www.unicopter.com/B372.html). In both the above cases, the passage of 8 blades over the fuselage will increase the frequency of any downwash, and this is a benefit.

Dave
Just trying to find and disseminate improvements in VTOL craft.

IFMU

5th May 2009, 01:06

From cnet news:

Sikorsky 'progressing' with X2 helicopter effort (http://news.cnet.com/8301-11386_3-10232687-76.html)

http://i.i.com.com/cnwk.1d/i/bto/20090504/Sikorsky_270x405.jpg

-- IFMU

Graviman

6th May 2009, 11:51

CEFOSKEY/IFMU, I gotta get me one of those! :ok:

Judging by trees/fence: Is that a full size mockup?

----

Dave, i've been quietly developing my own calc for rotor performance (based on Blade Element Momemtum Theory & Vortex Panel Method - but only capable of hover currently). I'm not convinced about the rotors not interfering in the intermeshing zone. For a given segment of air you are potentially doubling the lifting force, so that in practice induced velocity in this region will go up to reestablish stream function pressure equilibrium. Induced velocity will be far from uniform during hover, which will reduce benefit of greater rotor area.

Besides, my point still stands: During cruise the retreating side will still become unloaded - this is a limitation of stall BVI from vortex shedding. So intermeshing still needs a high hinge offset to work.

As long as ideas are kept practical, i have no problem with technical challenges. A good idea should be able to survive on its merits - X2 is a good idea... :)

maxtork

6th May 2009, 13:44

Yeah it's full size alright. I got to look around it a bit yesterday. Pretty slick looking machine thats for sure!

http://i7.photobucket.com/albums/y275/maxtork/x2mockup2.jpg

Max

Dave_Jackson

6th May 2009, 20:44

Mart,

My previous posting obviously needs some clarification, or elaboration, regarding hover.

The Advancing Blade Concept (ABC) (http://www.synchrolite.com/0890.html) allows for dissimilar thrust between the 'advancing' and the 'retreating' sides of the rotors. During hover, each of the intermeshing rotors will be asked to produce 2/3 of their lift on their outside (advancing side during cruise) and 1/3 on their inside (retreating side during cruise). This will result in a relatively uniform induced velocity over the total effective disk area.
As previously mentioned; during hover, the induced velocity directly over the fuselage, will be further reduced due to the inclusion of Active Blade Twist (http://www.unicopter.com/B372.html).
These are two very significant advantages that the Coaxial-ABC cannot exploit. In addition, the intermeshing configuration is proposed for transportation requirements (http://www.metacafe.com/watch/892026/worlds_largest_helicopter/). In this capacity a significantly greater portion of the craft's time will be spent in transit v.s. hover. In cruise the advantages of an Intermeshing-ABC configuration will again be greater then those of the Coaxial-ABC, AND those of the Intermeshing-ABC.

_________________

As long as ideas are kept practical, i have no problem with technical challenges. A good idea should be able to survive on its merits - X2 is a good idea... :)
In addition. I have three practical concerns about the merits of a small or medium Coaxial-ABC, which are also of some concern to the Intermeshing-ABC.

One concern:- Consider the high disk-loading of the coaxial rotors, as shown in the above pictures. Then consider that the pusher prop is at the rear of the combined disks. It will be 'pulling the rug out from under this disk'. In other words, the propeller will be stripping a significant portion of the 'lift' out from under the two rotors.

Dave

Graviman

7th May 2009, 11:44

CEFOSKEY,

One or two questions (you might know the answers):
How does that collective work? Rearwards for increased thrust?
Does sidestick include yaw control?
Is the terrain display something Sikorsky is actively working on or is it just on the wish list?

----

Dave,

That prop position is just a compromise required by the drivetrain. Don't forget that tail rotor drivelines will be designed to all sorts of inhouse analysis procedures. Besides prop is only really active in cruise where mass flow is high enough to reduce required thrust. The other way to see it is that any streamline passing through rotor disk and prop disk is effectively just being revectored by prop so that rotor does all the hard work of increasing total pressure (treating aerofoils as a planar pumping machine). I've read up a bit since that stimulating discussion about ground effect pressure under the rotor. ;)

So your intermesher is a sub 200kts machine then? In that case it is not ABC and cannot be compared to X2 (threadjack caution light :eek:). If it was ABC then my point about retreating blade unloading stands, by definition of ABC. In hover, if you fatigue the rotors hard enough, you could achieve any downwash pattern you wanted. Best to keep mechanism simple = durable...

Dave_Jackson

7th May 2009, 20:18

Mart,...... in cruise where mass flow is high enough to reduce required thrust.Are you saying that the thrust [lift] from the rotors is less in forward flight than it is in hover????

So your intermesher is a sub 200kts machine then?Who said that????
Please, look at the [Line of zero airflow. Mu = 1.0], in the drawing on post #465.

P.S. You have a couple of PPRuNe private messages and emails, dated mid-March and a week ago.

Dave

Graviman

8th May 2009, 11:55

CEFOSKEY,

Me thinks heli training just got a whole lot less expensive! :}
It does look like a seriously capable system though.

----

Dave,

X2 papers are much appreciated! :ok:
I've been doing a lot of hours recently so didn't check my email computer - apologies... :uhoh:

If your intermesher can fly above 200kts then it must unload the retreating blade, unless you have some super new way of pushing up stall rel-AOA. But let me back peddle a little: a low hinge offset rotor could rely on rotor coning to generate the advancing side lift. As long as rotorheads are not teetering advancing side does not need to balance out lift with retreating side. So with lateral symmetry there will be no net rolling moment in flight.

OK, i agree with you: You can use laterally seperated low hinge offset rotors with retreating side unloaded. The lateral seperation then allows a fast roll response time.

For you question about prop position, what i mean is that for any streamline:
thrust = (mass_per_sec x velocity_induced) + (press_local - press_farfield)
At cruise mass_per_sec is higher so you need less induced velocity.
Also pusher prop is effectively just revectoring streamtubes, but main rotor is generating most of the total pressure increase required for lift and thrust. Pusher prop effectively has it's power reduced since it is drawing air from a region of higher total pressure under the main rotor system.

Dave_Jackson

8th May 2009, 16:08

Mart,But let me back peddle >-------> less induced velocity.Sorry, but I do not understand.

Also pusher prop is effectively just revectoring streamtubes, ....... .I respectfully disagree. This subject is considered here; DESIGN: UniCopter ~ Pusher Prop - General - Tractor vs. Pusher (http://www.unicopter.com/1538.html)
__________________

As an aside; Re your mentioning of retreating blade (reverse velocity airflow).

There is an ongoing PPRuNe thread on the V-22 Osprey. The discussion basically relates to the effectiveness of the Tiltrotor configuration, and its Achilles’ heel, which is the difficulty of its blades to serve the requirements of both a propeller and a rotor.

The ABC configuration has it's own Achilles's heel, that being the extremely high drag/lift ratio from its retreating blades.

Eventually, there may be an interesting 'showdown' between the Tiltrotor and the ABC for 'Best in Breed', where the breed is 'VTOL+speed'.

Dave

IFMU

9th May 2009, 02:04

It will be 'pulling the rug out from under this disk'. In other words, the propeller will be stripping a significant portion of the 'lift' out from under the two rotors.
Why then does a long-ez or other canard fixed wing work? Or is it because the propeller is aligned with the wing, and therefore strips an equal amount of sink above the wing as the amount of lift it is stripping out below the wing?

As a conventional helicopter moves forward, does the relative wind push the lift out from under the blades?

-- IFMU

Dave_Jackson

9th May 2009, 05:39

Hi IFMU,Why then does a long-ez or other canard fixed wing work? Or is it because the propeller is aligned with the wing, and therefore strips an equal amount of sink above the wing as the amount of lift it is stripping out below the wing?

Both the canard and the HS provide an aerodynamic upward pitch on the craft, which offsets the moment from the CG that is located ahead of the main wing's center of lift.

A canard creates a lift at the front of an airplane, whereas a horizontal stabilizer creates a downward force at the rear of an airplane. In other words, the canard is a contributor to the overall lift on the craft.

It appears that the centerline of the Long-ez's propeller is above the chord of the wing. I would speculate that this 'elevated' propeller would tend to increase the velocity of the air that is passing over the top of the wing in relationship to the air that is passing under the wing. This should also enhance the lift.

As a conventional helicopter moves forward, does the relative wind push the lift out from under the blades?
Using 'ground cushion' as an example, I would say yes.

During the transition from hover to forward flight, the helicopter will at some velocity "run off of the ground cushion". Logic suggests that if a tractor propeller was operational at this time it would contribute to the stripping of this 'ground cushion' from under the rotors.

Dave

rjsquirrel

9th May 2009, 13:45

"push the lift" is not physically correct in any way, IFMU. I truly hope you didn't find such logic in any aero discussion!

As Dave says, a canard is the same thing as a horizontal tail - it balances and controls the main wing. The big difference and advantage of a canard is that it can do this balancing act with an upforce - lift - instead of the downforce that a tail must use. Thus, a canard shares the lift, while a tail pushes down, making the main wing lift more - and use more power. The Wright Brothers used a canard for that reason.

No the prop cannot blow the lift anywhere, lift can't be blown away.

The collective on the X2 is a fly by wire stick that raises two swashplates, one below the transmission that pushes control rods inside the beefy mast to control the upper rotor, and one above the transmission that is rather conventional and controls the lower rotor.

Graviman

9th May 2009, 14:01

Dave,

I would be more convinced if the maths was there to back up your pictogram logic.

In the code i mention, actually designed for cooling fans, i have assumed that each streamline passes through the fan then through a cooling pack before accelerating away as thrust. Along each streamline total pressure (static+dynamic) must sum to zero, although will increase through the fan and decrease through the cooler. What is really happening is that a different streamline leaves the same position in a different direction as the aerofoil passes, but that would require a full 3D vortex panel model (ie much bigger matrix). It is early days but the results tie up well with testing. After i finish my OU physics degree i intend to adapt it for high speed helicopter design studies like yours.

The typical assumption in textbooks of total pressure being uniform under the rotor disk is just that: an assumption. It allows momentum methods to calculate a figure of merit, but beyond that does not tell you what the aerodynamics look like. The 1g lift must remain constant by definition. What changes is the power required to achieve that lift. A pusher prop will require less power than a puller prop, but will increase power required by the rotor. Total power requirement all balance out so that Lift=Weight and Thrust=Drag...

With equal respect, i would say that a refresher on first principles of aerodynamic theory would allow discussions of performance quantities rather than qualities for your project. The discussion about pressure increase below rotor in ground effect made me go away and do some reading to understand which of my assumptions were wrong. :ok:

----

RJS, interesting technical detail about X2 swashplate layout.

Dave_Jackson

9th May 2009, 15:25

With equal respect, i would say that you need to read some textbooks on basic aerodynamic theory. This will allow you to discuss performance numbers rather than make qualitative statements. Your project will then be taken more seriously by other engineers.

Mart,
Your above paragraph shows absolutely no respect.
In fact, it says little about me and perhaps much about you. :=

IFMU

10th May 2009, 00:07

"push the lift" is not physically correct in any way, IFMU. I truly hope you didn't find such logic in any aero discussion!
Sorry, I was being obtuse. I find the idea of a prop stripping the lift out from under the rotors as ridiculous. The canard example was to point out that in a long-ez the wing is right by the propeller, so shouldn't the lift be stripped out from the wing too? I was talking about the type, not the little surface waaay out front away from the prop.

Using 'ground cushion' as an example, I would say yes.
I think the ground cushion works at any speed. It is a function of height.

-- IFMU

IFMU

10th May 2009, 00:24

Found this pic on airliners.net
Photos: Sikorsky X2 Aircraft Pictures | Airliners.net (http://www.airliners.net/photo/Sikorsky-Aircraft/Sikorsky-X2/1495885/L/)

IFMU

IFMU

10th May 2009, 02:21

hwusQWZBXjg

Dave_Jackson

10th May 2009, 03:37

IFMU,

Please view the first picture in your link on post #483 and envision that the slow turning rotors represent wings. The X2 pusher prop is totally below these 'wings'.
IMHO, the propeller is removing some of the lift from under a portion of these 'wings'. This removal is by; physical removal, and/or by causing the the velocity on the wing's lower surface to now exceed the velocity on it's upper surface.

Here is an example of a pusher propeller working with only a wing. (http://en.wikipedia.org/wiki/File:Northrop_N-1M_Udvar-Hazy.jpg) These propellers are drawing most of their free-stream air from the upper surface of the wings.

Dave
__________________________________________

The following was to be the response to your post, until the above simple explanation came about.

For the very bored here it is.
_________

The use of 'ground cushion' may not have been the most appropriate example but since it was used, the following is an elaboration on it.

"Note that for operation IGE the power increases rapidly as the helicopter transitions from the hover state. This is because of the formation and the influence of flow recirculation at the leading edge of the rotor disk, which causes the rotor to experience a higher induced inflow than hover in OGE, and so power requirements will increase slightly." [Source ~ PHA Page 188] (http://unicopter.com/B281.html)

http://www.unicopter.com/Temporary/Prouty_Fig_3.gif[Source ~ RWP1 Fig. 3.11] (http://unicopter.com/B281.html)

IMHO, the implication is that the flow recirculation causes a reduction in the pressure (1) differential between the higher pressure below the rotor and the lower pressure above the rotor. Therefor additional power is required to maintain lift.

Perhaps the better example of the same thing is Argument #2 in the link on above post #476.
No one can argue against the fact that two closely spaced coaxial rotors require significantly more power than two distantly spaced rotors, for the same amount of thrust. In other words, the upper coaxial rotor would be more efficient if the lower rotor was not 'consuming' the stream-tube from the upper rotor.
My position is that 'consuming' a PORTION of the X2 rotor's stream-tube is also of some detriment to the lift.

Graviman, should wish to present a position, please do. However, attack the subject and not the person.
Use the language of 'English' or the language of 'Math', your choice.
Use Momentum Theory or use String Theory; but provide the supporting algorithms and define the symbols if you wish to put forth an argument.

(1) The use of the word pressure could be argued until hell freeze over. Therefore please accept this easy to understand concept.

IFMU

11th May 2009, 01:02

Dave,

I learned something that I didn't know- the slight increase in power when accellerating in ground effect. I never would have thought it true, either academically or from flight experience in little helos. So, thanks for the chart.

Regarding the stripping of lift, I still have a hard time with that one. When will the propeller be pulling lots of air? At high speed. Will the rotor downwash even be hitting the propeller? At Sikorsky's claimed 250 kts, that is a lot of air zipping under the rotor. If the prop did anything bad to the lift, I wonder if it would be measurable.

-- IFMU

Graviman

11th May 2009, 18:05

Graviman, should wish to present a position, please do. However, attack the subject and not the person.

Dave, you are reading way too much into my last post. :ouch:

After the PPRuNe discusion on pressure from ground effect, i went away and relearned stuff that at uni i thought i had understood. The fact that you are mentioning "pressure", but not qualifying it as "total pressure", "static pressure" or "dynamic pressure" means the discussion gets completely stuck on fundamentals. Total P = Static P + Dynamic P , and must be constant along one streamline, but can be different between two streamlines .That is why pitot-static ports are best placed on a probe in the same streamline for experimental work. When considering a streamline through a disk the assumption is that the same streamline passes through the disk with an increase in total pressure (which can be induced dynamically or statically). What actually happens is that the assumption that the same streamline flows normally through the disk plane is just a mathematical convenience. From the moving aerofoil reference frame, the actual streamlines are helixing into the disk then helixing out at a steeper angle. Downstream the flow contracts or expands which determines whether the assumed total pressure increase is actually static or dynamic.

This was all stated concisely in my last post. How you came to feel that this was a personal attack is quite beyond me! :confused:

This is getting away from X2.

----

Interesting walkaround the LTH mockup, IFMU.,

Dave_Jackson

11th May 2009, 22:20

IFMU,

When will the propeller be pulling lots of air? The propeller must be pulling air at a higher velocity (plus from a larger area) then the 'remote velocity'' if it is to provide thrust.

If the prop did anything bad to the lift, I wonder if it would be measurable. There must be some way. Perhaps, in a wind-tunnel.

CEFOSKEY,

I am still curious with regards to the mixing between pilot inputs and the resulting FBW controlled servo movements.

Prouty's column 'Fly-By-Wire' in the Spring 2009 issue of Vertiflite gives an overview of this subject.

Graviman,

Thanks for the elaboration. As you know, there are probably dozens of 'theories' on aerodynamics, with each one attempting to get closer to the ever-elusive reality.

Your position, which proposes a consideration of the individual rotor-blade and the individual propeller-blade helix interactions has probably never been computed; at least not in a non-coaxial arraignment. The basic question relates to the interaction of a lower tractor propeller and a rotor, and this should not necessitate the consideration of helix-helix interactions.

Dave

Graviman

12th May 2009, 11:45

Dave,

This is all textbook stuff. What i have described is the basic principle behind combined blade element and momentum theory. My vantage point is that i have also created a vortex panel method, which can be as accurate as CFD but without the computational overhead (mine should eventually cope with drag, trailing edge stall, and transonic flow). Integrating VPM and BEMT in one rotor/fan model has left me with the understanding about the helices described above. I think it is this lack of perspective which leads to a lot of misunderstanding (including my own a while back) about how flow alters the power required for a given thrust/lift.

Regarding X2, it does not matter where the prop is located relative to the rotor. If you think of the helicopter as being in a black box, it will require thrust power to cruise and to lift power to hover - This will not change significantly with configuration as long as rotor and prop area are constant. In some flight conditions puller prop will allow a slightly greater total area of induced flow, ie prop & rotor streamlines are kept apart, reducing power requirement. In power hungry conditions of hover and cruise-dash i doubt power requirements are any different with puller or pusher prop. Transition is one example of a single flight condition, but it a transient event requiring perhaps a brief blip in power increase for a given envelope.

Dave_Jackson

12th May 2009, 23:45

Regarding X2, it does not matter where the prop is located relative to the rotor.

From the NACA report;

WIND-TUNNEL TESTS 0F SINGLE- AND DUAL-ROTATING PUSHER PROPELLERS HAVING FROM THREE TO EIGHT BLADES (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930093333_1993093333.pdf)"The single-rotating pusher propellers were from 0 to 7 percent less efficient than the corresponding tractor propellers and from 0 to 10 percent less efficient than the tractor propeller tested with the wing. The dual propellers provide about the same efficiency, within a few percent, irrespective of whether they were tested as tractors or as pushers and whether or not the wing was present."The first sentence suggests that a pusher propeller is less efficient than a tractor propeller.

The second sentence suggests that Kamov knows what they are doing when they put contra-rotating propellers on their proposed Coaxial-ABC ~ [post #362] (http://www.pprune.org/4421744-post362.html)

Dave

Graviman

13th May 2009, 11:42

Dave,

Are we discussing rotor-propeller interaction, fuselage-propeller interaction, or wing-propeller interaction here? The objective of the discussion, hence the reason for my explanations, seems to be constantly moving. :confused:

The results in the cited NACA report do not even begin to suprise me. This is the difference between drawing in laminar air and turbulent air. Turbulent air is caused by the fuselage boundary layer. The counterrotating prop gains efficiency by not producing downstream swirl, but the penalty is the rear prop is already running in turbulent air off the front prop. Hence fuselage turbulence becomes insignificant, so pusher or puller makes no difference.

Non of this says anything about how rotor effects the prop inflow. You will notice that in both designs the prop is pushed as rearwards as possible so as to minimise the cyclic variation as main rotor blade passes overhead. Cyclic loading from uneven inflow distribution is the main cause of fatigue failure in propellers. A simplistic evaluation of streamlines just can't capture this, but it must too be considered.

Like i stated earlier pusher prop is a compromise, mostly chosen from deciding just how far into the unknown a new design should venture. Since X2 is gently accumulating flight time i would say they got it right...

Dave_Jackson

13th May 2009, 20:39

Are we discussing rotor-propeller interaction, fuselage-propeller interaction, or wing-propeller interaction here? The objective of the discussion, hence the reason for my explanations, seems to be constantly moving. From the beginning, the subject has been directed at the aerodynamic related location of the propulsion (propeller) in respect to the location of the lift (by; gyro-rotor, heli-rotor or airplane wing, which all do the same thing). Don't move your explanations.

The report in post #491 make mention of a 3% advantage for the tractor. Two previous aerodynamic arguments for the tractor are mentioned by other people in the middle of this page (http://www.unicopter.com/1538.html).

There is no argument with your basic algorithms related to thrust. However, it appears that the interaction of these two streamtubes does more than just re-vector the thrust.

Coincidentally, that report also discusses contra-rotating propellers. The 0-7% advantage due to the fuselage is of related interest, since the smaller ABC helicopters will have their propulsors located on the centerline of the craft. It is also of related interest since Kamov appears to be moving in that direction.

Mart, you have previously criticized me for hopping from concept to concept. I'm not building a helicopter, therefore there shouldn't be a bias. Personally, I would prefer the pusher for a number of reasons unrelated to aerodynamics.

Since X2 is gently accumulating flight time i would say they got it right... The principle objective of the X2 is the, yet unachieved, high-speed flight. IMHO, salesmen should be optimists. Engineers must be skeptics.

Dave

Edited, in red, to correct error, 'tractor' was typed by mistake.

Graviman

14th May 2009, 11:53

Well - OK, Dave. I'm just a little concerned since the discussion is moving away from the thread title Sikorsky X2 coaxial heli development (which is now actually accumulating flight time) towards various unspecified concepts (which are not). As i've commented before, i find it very difficult to provide constructive feedback, since i am never sure which concept i am meant to be considering. This is part of the engineer mentality: figure out the best solution using available data, then make it work - it is a well proven method of getting things done. That does not disallow future improvements, but often does mean that the solution is a compromise of keeping all of the designers the least unhappy. That's just the way of things...

One of my favourite quotes comes from Aaron Cohen, the program manager who kept Space Shuttle development within budget:
"Better is the enemy of good."

Let us agree that in principle the tractor does offer some aerodynamic advantages in certain parts of the flight envelope. However, a tractor would not suit a machine which is after all still a helicopter. Powertrain packaging would be my main reason. But, putting engineering issues asside, visibility of touchdown point will also never be as good with a tractor.

Let X2 prove that 250kts is possible in a helicopter - that is already a challenge. Once this is done the we can discuss improvements until the cows come home... :ok:

Dave_Jackson

14th May 2009, 15:31

Graviman & CEFOSKEY

Sorry, a BIG mistake was made in my previous post when the word 'tractor' was typed instead of the word 'pusher'. It has now been corrected.

Dave

Graviman

14th May 2009, 18:37

Dave, CEFOSKEY,

It sounds like we are all in agreement then about X2 being the best compromise configuration for this application. :ok:

Dave, you have a tendancy to take my comments personally - please don't. They are always intended to provide constructive feedback, and never intended as a putdown. As a design analyst, i am generally under pressure so am very used to providing a response that i feel accurately sums up the situation. If i comment that you would benefit from reading up on aerodynamics that is exactly what i mean, and i am in no way having a poke at your considerable general knowledge about helicopters. You have put together a great web-resource for helicopter design, and i enjoy the fact that you challenge current thinking. By accurate use of aerodynamic and materials terminology your arguements would carry considerable weight, which would make the "experts" have to think much harder to dismiss them.

Mart

Dave_Jackson

14th May 2009, 23:48

Mart, your remarks are well taken.

That said, some people strive to be experts by focusing their field of vision. Others strive for a holistic perspective, albeit with a reduced depth of understanding. Different strokes for different folks.

I 'assume' (due to limited knowledge) you will agree that it would be ineffective to present an oral dissertation on quantum mechanics to a Buddhist convention.

___________ Back to the Future __________

This thread appears to be the last of the technical ones on PPRuNe-Rotorheads. Fortunately, it is kept alive because of its relationship with an active helicopter development program.

Mart, you are correct when you insist that the postings must be tightly coupled to the Sikorsky-X2. However, if all technical discussion had been excluded, the posts would have been little more than links to infrequent promotional releases, and subsequent platitudes.

Perhaps this long running thread also serves to debate technical subjects that are directly associated with the X2 and its ABC feature.

One, or more, directly related subjects might be;
The current tractor vs. pusher arguments,
Single vs. contra rotating propellers,
Airfoils and flight controls for operating in reverse velocity,
Variable speed rotor vs. Stepniewski's fixed slow speed / large chord ABC rotor.
Variable speed propeller vs. constant speed / variable pitch propeller.

None of the above can be considered as a critique of the X2 since they are little more then hypothetical considerations until proven, as is the developing X2.

Then again, perhaps those who participated in and enjoyed the earlier rotorcraft technical discussions have moved on.

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

Dave

relyon

15th May 2009, 02:13

Exactly. Think P-39 with a rotor system. I wouldnt want to be on that transmission design team.

Another complex arrangement: BUGATTI Model 100 Racer (http://www.airventuremuseum.org/collection/aircraft/Bugatti%20Model%20100%20Racer.asp)

Then again, perhaps those who participated in and enjoyed the earlier rotorcraft technical discussions have moved on.

FWIW, I enjoy reading these discussions, though I'm somewhat reluctant to join in. That's an interesting list of topics Dave, as is your website.

Bob

Dave_Jackson

15th May 2009, 15:39

Bob,

Thanks. Just trying to push the envelope.

Dave

riff_raff

16th May 2009, 01:22

So what's a better overall compromise- Sikorsky's X2 coaxial or Bell's Hybrid Tandem Rotor configuration?

http://www.flightglobal.com/blogs/the-dewline/hybrid%20tandem%20rotor.jpg

Graviman

16th May 2009, 15:33

Relyon,

That Bugatti looks well thought out. Very low frontal area and as simple a profile change as possible to minimise velocity hot spots. I'm slightly suprised that supine position didn't catch on more in powered fixed wings. The risk with a drive shaft is torsional resonance, particularly with direct drive. With a gearbox the inertia of the propellor is reduced on the shaft (proprtional to ratio^2), shifting the frequencies up (proportional to ratio). That said i imagine this would only be a concern when the prop was at low thrust pitch, since there would be damping at high thrust pitch.

riff_raff,

That is the million dollar question - actually the market will likely be billions.

I'm not wanting to upset our tilt-rotor friends here, but for me it all comes down to lowest disk loading and smallest landing area planform. I notice that this new concept reduces from full tilt to just enough tilt to achieve cruise. That goes a long way towards answering the concerns about autorotation from transition, particularly if the tilt mechanism is passive using rotor to vector tilt (would need a damper rather than an actuator). I would imagine that the wings make up for the retreating blade loss of lift, so basically a laterally seperated ABC. Looks like the influence of one particular highly regarded engineer and TP. ;)

My own view is that the market will be big enough for both concepts to have a share. That said X2 ABC is a purist concept. The engineers started from a machine designed to hover and scratched their collective heads to figure how to make it go faster. A wing is always going make life awkward for the hover: they want to take up room and will always stall as speed reduces. To my way of thinking a rotor capable of reacting low rpm lift at high speed will be lighter.

Time will tell...

bat1

16th May 2009, 20:03

Just in terms of size the htr concept will always have the disadvantage of taking up more space, which is a concern when planning to ship these by air to bases around the world. That is one aspect of the coaxial design that the russians have capitalized on.

heli1

3rd Jul 2009, 14:10

I see Sikorsky have got the propellor to go round but could someone please point out to them that the world speed record to beat for a Compound Helicopter is 311mph ,not 250mph .Still way to go !

IFMU

5th Jul 2009, 01:00

Is the X2 truly a compound helicopter? It has no wing.

Edit: found this on aero-news.net.

http://www.aero-news.net/images/content/general/2009/Sikorsky-X2-0709a.jpg

X2 flies with prop (http://www.aero-news.net/index.cfm?ContentBlockID=80f58e73-5ee8-4883-8186-360996baf9b9&CFID=66855087&CFTOKEN=54889771)
-- IFMU

Ian Corrigible

5th Jul 2009, 01:38

Somebody from the IOC should check those vertical stabs for growth hormones... :E

I/C

NickLappos

5th Jul 2009, 16:58

IFMU,

Here are the definitions:

A compound helo has auxiliary propulsion - a jet or prop. It is said that the world record Lynx used about 7% aux thrust from its engines (a small enough percentage to allow it to be classed as a true helicopter).

A winged helicopter has a wing that develops lift.

A winged compound has both.

Graviman

5th Jul 2009, 17:14

That 52 kts presumably marks the bottom end of where the prop starts to have advantages over the rotor for forward thrust. I'm keeping my fingers crossed that the envelope expands nicely all the way up to 265kts. :ok:

The three vertical fins had me confused for a while - just a matter of perspective...

IFMU

6th Jul 2009, 00:37

Thanks Nick, that clears up a fundamental misunderstanding I've been carrying along. Glad to see you back with us.

Heli1,
The boys at Sikorsky may have gotten their speed records mixed up, but they haven't gotten knots confused with MPH yet. They are talking 250 kts, which is 288 MPH or so. What is interesting is they talk of a record of 250 kts and a comfortable cruise at 250 kts. I would think the record and the comfortable cruise would be separated a bit.

-- IFMU

FH1100 Pilot

6th Jul 2009, 02:47

Now, I'm no aeronautical engineer, but with regard to those fins/endplates...

When-oh-when will manufacturers figure out beforehand that any helicopter that has more surface area ahead of the rotor than behind is going to have stability problems in flight?? You'd think this was rocket science or something!

I looked at that photo of the X-2 on airliners.net and noted the vestigal fins back there. The very nice profile view shows a classic "teardrop" shape of the fuselage, which should be nice and aerodynamic, but...the mast is waaaaay aft of where it "should" be, and it doesn't take an engineer to see that. I'd bet real money that it wasn't tons of fun as they went faster and faster in forward flight - not to mention horrible weathercock stability. Ergo, they ended up with those barn doors back there.

Has anyone ever seen fins/endplates that shrank over time? Not! Dear Lord, look what happened in the transformation from 105 to 117. So methinks the X-2 is stuck with those endplates.

Graviman

6th Jul 2009, 11:38

FH1100 Pilot,

Agreed that X2 will not likely loose those vertical stabilisers, unless flight testing reveals a reason to. I was suprised by the area when seeing X2 from front (took a while to understand what i was seeing).

The problem (as you point out) is fuselage centre of pressure relative to centre of mass. I'm not really sure what could have been done different, since engines behind rotor reduces likelyhood of control damage in the unlikely event of catastrophic engine failure. The rotor is already as far forwards as possible, considering package for MGB, swash plate & actuators, vibration control system etc.

Fuselage has been kept as short as practical, so the penalty is the additional vertical stabilisation. I don't see it causing practical difficulties though.

Shawn Coyle

6th Jul 2009, 13:28

I'm no stability and control expert, but I'll bet the prop in the back contributes mightly to directional stability...
And the X-2 has a pretty awesome fly-by-wire system. Perhaps we're witnessing the dawn of the RW equivalent of the F-16 (which can't be controlled without the computers...)

IFMU

7th Jul 2009, 01:53

When-oh-when will manufacturers figure out beforehand that any helicopter that has more surface area ahead of the rotor than behind is going to have stability problems in flight?? You'd think this was rocket science or something!

Methinks it is harder than rocket science. Rockets have nice clean airflow running down their length, put some silly little fins on the bottom and you are good to go. But, like you imply, a lot of the manufacturers seem to end up redesigning the tail. The F28A I learned to fly in didn't have enough vertical area, or maybe it was enough but the air back there was not flowing backwards nice and orderly like it does on a rocket. I used to fly the enstrom with the ball a little out to keep it from wagging itself to death.

When I look at the airliners.net photo, it seems the distance from the mast to the tip of the nose is about the same as from the mast to the tip of the tail, just forward of the prop. However the tip of the nose is a skinny little thing, the tail offers a lot more surface area at the same displacement even in its original version. Also in the airliners photo it looks like he is talking on a hand mike. They should really have given him a boom mike.

In the FW world the older glasairs and lancairs had small tails optimized for low drag. They were of course unfettered by regulations for certified aircraft. The later versions seemed to grow bigger tails for better longitudinal and yaw stability. It's a classic fight between performance and handling qualities.

At the speeds they have been to would the tail have even been much of a player yet?

-- IFMU

JohnDixson

7th Jul 2009, 16:07

FH1100,

Your quote: "You'd think this was rocket science or something!", struck a respondent chord.

I'd bet that the advanced design groups at Eurocopter, Bell, Boeing and Sikorsky, and MIL and everyone else for that matter, might argue that arrangement of all the pieces and parts of a new helo design so that the CG comes out in at least a controllable position and so designing the tail surfaces so that they provide the required static and dynamic stability, while not creating some of the known tail surface forced probem areas, is in fact a lot tougher than "rocket science"!

Thanks ,
John Dixson

slgrossman

7th Jul 2009, 16:23

Shawn Coyle said:

I'm no stability and control expert, but I'll bet the prop in the back contributes mightly to directional stability...
And the X-2 has a pretty awesome fly-by-wire system. Perhaps we're witnessing the dawn of the RW equivalent of the F-16 (which can't be controlled without the computers...)

Shawn,

It seems to me, at least intuitively, that having the propeller thrust behind the CG would actually be a destabilizing factor in yaw (and perhaps pitch as well). During deceleration I imagine the reverse is true. However, as you go on to say, the FBW/AFCS probably makes it transparent to the pilot.

-Stan-

Graviman

14th Jul 2009, 11:40

John, agreed - rockets don't have to do anything to the air other than move it out of the way. :ok:

Shawn,

That's an interesting thought. I think it is just a question of the advantages of FBW becoming more significant as the envelope increases, especially for a coaxial machine. Pilot will not be able to trim cyclic laterally to compensate for any pitch-roll coupling (opposing rotor control), although differential cyclic is required to offload retreating rotor. Also the lead angle can be tuned to compensate for any altitude and coning angle (load factor). There is also some wisom for a performance machine if pilot reflexes can become tuned to exactly the same pitch & roll rates, for a given stick input, in any flight condition.

I wonder if the FBW goes as far as the system on Euro-fighter Typhoon where pitch and roll are referenced from flight velocity vector rather than pitch attitude vector (control advantages at high AOA)? Maybe there is also some collective control to avoid VRS and deal with engine failure? I need to read up some of the articles/papers i have accumulated...

JohnDixson

14th Jul 2009, 20:46

Graviman, you are on target w/re to your comments to Shawn. And the areas where FBW are of advantage only begin with the subjects that you noted. All of the controls in the XH-59 were mechanical, thus there was this very sturdy looking crank in front of the copilots shins that was a swashplate phase angle adjuster! Actually, it is a tribute to a very smart team that they accomplished what they did.

And then there is the very basic subject of control sensitivity vs needed control range. That always present compromise was as you might imagine exacerbated by the very high control power/sensitivity of the rigid rotored ABC. In fact, a control system change in the direction of lower sensitivity ( thus lower range ) was at the heart of the accident in the first prototype and one could easily argue that with a FBW control system, the "problem" would have been a non-issue.

So as the X2 proceeds, they have the tools within the FBW system to develop the solutions to the complex tasks and implement them behind the scenes, so to speak, such that after development is complete, a relatively simple, straightforward flying task should present itself to the operational pilots.

Thanks,
John Dixson

IFMU

15th Jul 2009, 00:39

It seems to me, at least intuitively, that having the propeller thrust behind the CG would actually be a destabilizing factor in yaw (and perhaps pitch as well).
-Stan-

I thought in the fixed wing world that tractor propellers were considered destabilizing and pushers stabilizing. If I remember correctly there were issues with pitch stability on the old Northrup flying wings when they transitioned from pusher propellers to jets.

If you consider the thrust vector to be normal to the pusher propeller disk, I think it would be stabilizing. Consider a disturbance which pushes the nose up so the airplane is at a positive angle of attack. Then break the vector into a thrust which is orientated in the direction of travel, the left over vector (for a pusher) will try to push the tail up, reducing the angle of attack.

-- IFMU

slgrossman

15th Jul 2009, 22:23

IFMU said:

If you consider the thrust vector to be normal to the pusher propeller disk, I think it would be stabilizing. Consider a disturbance which pushes the nose up so the airplane is at a positive angle of attack. Then break the vector into a thrust which is orientated in the direction of travel, the left over vector (for a pusher) will try to push the tail up, reducing the angle of attack.

Now that I see your explanation I realize you're right. What I was thinking of was the aircraft's response to power changes, but that's not really a matter of stability.

Thanks very much,

-Stan-

ramen noodles

16th Jul 2009, 11:32

You guys are a bit off base. The rigid pusher does not simply deliver a thrust, it responds to flow changes with surprising changes in its thrust and moment. If the nose goes up, the prop will see a strong "P factor" that causes a yaw (remember the right rudder on climbout in an airplane?) This means the prop is always destabilizing, and often cross coupling as well (where yaw makes it cause a pitch probelm and vice versa).

Graviman

27th Jul 2009, 11:40

John,

Interesting feedback about FBW. Of course the other realisation is that castings and machined parts (like the shin height phase adjuster :eek:) would require time consuming redesign to adjust flight characteristics. Software potentially requires recertification, but i imagine as many variables as can be thought are programmed in from the start. So much of the risk of envelope expansion by flight test is reduced to being control optimisation.

Was much of XH-59 flight testing taken up by stability optimisation?
I imagine that a with a snappy response the there can be a tendancy for the aircraft to have poor gust rejection, although faster response will produce less tendancy for PIO.

Ramen,

I imagine that a prop acts as a very high effective hinge offset rotor. So there will be a degree of flapback for any sideslip/yaw/pitch. I've heard Spitfire pilots talk about cross coupling controls (rudder for pitch, and stick for yaw). Of couse as an engineer i can't help but think about designing a teetering mech with delta3 for self-alignment, but i still admire the level of control required.

JohnDixson

27th Jul 2009, 20:49

Graviman, an anecdote to answer your question:

Nick Lappos and I were invited to help fly the ship back from a static demo at FT Rucker Alabama, where there was a US Army Aviation Commanders Conference. I got to fly from OZR to JAX and Nick flew down to West Palm.

Going cross country was a kick,, well, sort of. Get out on the runway via the rotor and the PT-6 twin pack, then start the J-60's and firewall those things, climb like a fighter to 10K level off and cruise for a few minutes, then shut down the J-60's because the fuel guage is going down as fast as the sweep second hand on your watch. Do a cruise/decerating descent to 1000 ft and flutter along at 80-100 kts. NO SAS.

Tail surfaces were sized for the high speed flight part of the envelope and stability up there was generally ok, but at 80-100 in the typical south Alabama summer afternoon, one kind of herded it. If you've flown an A Model CH-47 or CH-53A with SAS /AFCS turned completely off, you get the picture.

The flight test program had prioritized the flight envelope and performance assessment, and the basic controllability of the vehicle. Short and long term stability, required augmentation, vibration control and attenuation and the like, were yet to be addressed.

Thanks,
John

Graviman

9th Aug 2009, 18:41

John,

Genuine thanks for reply - i've had internet provider problems for the past week or so and couldn't thank you earlier.

I'd really have relished the opportunity to fly machines like the Chinook and Stallion. An ear infection as a kid meant i didn't get into flying until too old for any of the services. Now i have to get whatever experience i can between UK housing boom/bust gobbling up my hard earned cash. :mad:

Interesting about yaw stability of the coaxial XH-59 though. There must be some yaw stability from torque generated by rotor whirling in same sense as fuselage, but i can see that most would come from tail surface. I imagine the X2 will benefit from various rate gyros to give the machine a much crisper pedal response. Actually i wonder if this means rotors end up reducing response rate at 250+ kias.

By "short term stability" i imagine you mean response time to a given input (ie dynamic stability), and by "long term stability" you mean the need to retrim conrols (ie static stability)? I'm starting to realise that vibration attenuation at rotor blade source is very much in its infancy, with the Moog vibration absorber inherited from S-92 an interim step.

Something i have often wondered is how was the "fixed-wing" J60 control integrated with the PT-6 control? Was there just a seperate throttle? This is something i am curious about for X2, as i imagine the collective has sprouted some additional features. Would a mech to allow fore-aft movement of the twistgrip allow adequate control of longitudinal thrust (be it prop pitch or J60 thrust)?

Mart

Dave_Jackson

9th Aug 2009, 20:36

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

http://www.unicopter.com/Temporary/Onera.gif

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

Dave

Shillin3

9th Aug 2009, 22:32

Future fast helicopter to push 250 knots advances | Pilotbug (http://www.pilotbug.com/?p=211)

Sikorsky helicopter is testing its X2 demonstrator in hopes of combining the flexibility and hover of helicopters with the speed and range of airplanes. Flight tests continued with the first engagement of the rear pusher propeller which, in theory, should enable the hybrid to speeds of 250 knots. The helicopter generates lift with two counter rotating main rotor blades, in addition to the rear pusher. This arrangement makes torque more manageable and needs only to be addressed for the pusher rotor.
Sikorsky’s challenge in attempting a 250 knot helicopter was to counter the loss of lift of the retreating main rotor blades as the airframe travels forward. This is being addressed by using a rigid rotor which uses the Advancing Blade Concept (ABC) with which the retreating blade produces little or no lift. First pioneered with the Sikorsky XH-59A, a turbojet powered experimental helicopter, the ABC allowed it to reach 240 knots in 1973. Then current technologies made it impractical, though. More advanced “fly by wire” flight control systems have allowed greatly improved handling characteristics in the X2 demonstrator.
http://www.pilotbug.com/wp-content/uploads/2009/07/Sikorsky-XH-59A.jpegSikorsky XH-59A

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

JohnDixson

9th Aug 2009, 22:46

Graviman,

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

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

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

Thanks,
John Dixson

Dave_Jackson

10th Aug 2009, 15:52

CEFOSKEY, :ok:

The essence of rotorcraft is The Rotor.

In my limited opinion, Active Blade Twist (http://www.unicopter.com/B263.html#Active_Blade_Twist) and Reverse Velocity Utilization (http://www.unicopter.com/B263.html#Reverse_Velocity_Utilization) are also necessary for an actuator disk to fly edgewise, in an efficient manner, in it's environment.

Dave

Graviman

11th Aug 2009, 11:46

John,

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

Chris,

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

Dave,

I am also convinced that active blade twist would improve helicopter performance. Especially when you allow the same rotor to hover/cruise/climb/autorotate with as efficient a downwash pattern as practical. The problem is the same reason that fixed wing ailerons haven't adopted full span twisting (like the original wing warping), although the ideal system would be root control for lift and tip control for roll. This is that the design has to be aimed at a practical fatigue life of 10'000 hours. If blade is twisting at once per rev this may be hard to achieve. (Study Goodman lines on Haigh diagrams to get a feel for what i mean)

Ian Corrigible

11th Aug 2009, 14:48

CEFOSKEY -- The SAC/HamStan effort was covered in a paper given at this year's AHS65 forum (Active Rotor Development for Primary and Secondary Flight Control, Wake, Chaudhry, Lorber, Bagai & Collins).

I/C

IFMU

13th Aug 2009, 00:30

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

-- IFMU

Graviman

14th Aug 2009, 11:54

IFMU,

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

IFMU

15th Aug 2009, 01:31

Probably damn cool!

IFMU

9th Oct 2009, 00:42

Anybody see the new popular mechanics?

Coaxial Rotor X2 Sikorsky Helicopter - Breakthrough Awards Innovators 2009 - Popular Mechanics (http://www.popularmechanics.com/science/air_space/4332910.html)

http://media.popularmechanics.com/images/x2-chopper-470-1109.jpg

http://media.popularmechanics.com/images/btawards09_2_630_1009.jpg

-- IFMU

Graviman

9th Oct 2009, 11:48

IFMU,

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

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

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

So, well deserved congratulations are in order. :D

riff_raff

10th Oct 2009, 01:29

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

So, while I can see a bright future for smaller sized X2 rotorcraft, I personally don't think that it will turn out to be practical for larger helos.

Hilife

10th Oct 2009, 06:33

Future prospects for the X2

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

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

Time will tell.

IFMU

11th Oct 2009, 00:37

Either I missed it the first time, or they added a little video of some forward flight:

Popular Mechanics (http://video.popularmechanics.com/services/player/bcpid16382224001?bctid=44280215001)

-- IFMU

The Sultan

11th Oct 2009, 21:17

Have they needed anything faster than a Bell 47 to chase it? Last I heard they have only gone 52 knots, which gives the 47 plenty of time to get ahead of it to take pictures.

The Sultan

Ian Corrigible

11th Oct 2009, 23:40

106 kts was the last I heard.

I/C

Graviman

12th Oct 2009, 11:44

Woah guys! Give it time to get there! ;)

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

riff_raff,

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

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

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