Sikorsky X2 coaxial heli developments.

[The Sultan]

Gravi

I thought this was ready for production based upon the praises heaped on it.

I will admit that 106 knots is progress so they will probably need an R-44 or 206 to chase it.

The Sultan

[212man]

I thought this was ready for production based upon the praises heaped on it.


As what - a one man run-around? It's not going to go into production - it's a proof-of-concept development test bed.

[The Sultan]

212

It looks in the picture that 7 people "starring in their own movie" (translation: boorish spares) are walking away from this 70's tech vehicle after a wonderful flight.

The Sultan

[IFMU]

What makes it 70's tech? The FBW? The rotor system? The fact that it isn't everything that Dave Jackson hoped it would be?

I'm not quite sure what a boorish spare is. Does that imply they are models hired for the job? You would have thought they would have hired better looking ones than the 7 than they had there, were that the case!

-- IFMU

[Dave_Jackson]

The fact that it isn't everything that Dave Jackson hoped it would be?
It's more than that. The current X2 can never be what I would hope it to be.


In the middle of the last century a lot of work was being done to develop a viable VTOL craft. Over time, creative new concepts have become fewer and fewer. It eventually became apparent that a rotorcraft with high reliable & low acquisition cost, was becoming an oxymoron.

Improvements such as composite construction, fly-by-wire, and piezoelectric are coming from outside the industry and they can improve any aircraft.

The two current rotorcraft originated ideas, that of the tilt-rotor and the coaxial-ABC, are simply regurgitations of 40 year old ideas.
Bell is trying to use the wing for forward flight and then have rotors that act as propellers.
Sikorsky is trying to use the propeller for forward flight and then have rotors act as a wings.

IMHO, simply taking that which 'outsiders' provide does not advance the unique needs of rotorcraft.
Bell has got to find someway to vary the disk size and vary the induced velocity, for the tiltrotor to be effective in both realms of flight.
Sikorsky has to find someway to have the rotor-blades work efficiently in reverse air-flow, for the coaxial-ABC to be effective in both realms of flight.

These are my attempts at addressing Bell's problem (http://www.unicopter.com/1612.html) and addressing Sikorsky's problem (http://www.unicopter.com/B473.html).

Is the 'Western world' to sit back and assume that rotating blades were never intended to travel radially within their environment? Or to assume that nature's evolution cannot be challenged.

Some may think otherwise. http://www.unicopter.com/ChineseSmiley.gif



Dave

[heli1]

Hey Sultan....after it gets too fast for a JetRanger they can use the Lynx speed record holder to keep pace out to 400KMH...which is about the proposed X2 max speed anyway.

[dangermouse]

and G-LYNX didnt need a pusher prop to get there (23 years ago!)


DM

[riff_raff]

Graviman,

To be perfectly honest, I don't know squat about rotor dynamics. But for a brief period, I was involved in the mechanical design of a large diameter, high power, rigid rotor system. It was much larger than the X2's rotor. Designing a lightweight hub structure and blade feather bearing system was incredibly difficult, due to the flap and lead/lag moments the rigid rotor produced at the hub. We did design studies for several different rotor diameters, and if my memory serves me correctly, the mast moments increased at something much greater than the 1.33 power of the rotor diameter.

Regardless, from the photos of the X2's rotor that I've seen, it's a very elegant piece of design work!

riff_raff

[IFMU]

I wonder if Sikorsky would have launched into the X2 technology demonstrator if they thought there was no hope of scaling it up? Not like they are known for building small helicopters. I think the original ABC was a much larger machine, something like twice the MGW.

-- IFMU

[heli1]

CEFOSKEY....Isn't that what I said or can't you convert km into mph......Anyway after the Lynx they can use the Bell UH-1 with a jet pack that went to well over 250kts or a Model 609 tiltrotor that will go faster still...Both are variants of true helicopters with pusher thrust...as is the X2
Don't get me wrong...I admire the technology but not the PR dishonesty.

[IFMU]

Whether the X2 manages to best G-LYNX's speed by a little or a lot matters little regarding the accomplishment of the team that pushed their aircraft past 400kph over 23 years ago. I bet the people who are really behind creating the technology on X2 have nothing but respect for G-LYNX and the team behind it. It was, and still is, an outstanding achievement.

If I am not mistaken, there are no more 400kph Lynx's running around. Load them up with payload and fuel and the speeds drop back to something more normal. The record that was set was not setting an operational precedent. It was a showcase of the technological prowess of the company. This is where I think the X2 is different. The promise is a family of helicopters that not only can go fast, but can haul payload and fuel while doing so. And, on top of that, still retain some of the important characteristics of helicopters that come with a low disc loading - hover performance, efficiency, and ability to autorotate. The X2 demonstrator is only a two seater, it's not going to haul the mail as 212man observed. However it is a lot like the VS300 - its purpose is to show what is possible, then onto building the machine that is up to the mission. The VS300 was the step that allowed the R4 to succeed and the whole line of Sikorsky helicopters that followed. We have seen some of the prospective "X2 R4's" in this thread and on the web - the LTH for one.

Don't get me wrong...I admire the technology but not the PR dishonesty.
Could you spell out what the PR dishonesty is for me? I'm not too observant, and I missed it.

(translation: boorish spares)
I'm still looking for this definition. I googled it but came up empty. Maybe it is a cultural thing I have no hope of understanding. If you could enlighten me on this one I won't press you on the 70's tech thing.

One other thing I wonder about is how fast other conventional helicopters can go when they are not carrying a load. We are Nick-less, it seems, but I wonder if John Dixson could tell us how fast a stock 60 or 53 could go with minimal payload and fuel. Would be interesting trivia.

-- IFMU

[212man]

One other thing I wonder about is how fast other conventional helicopters can go when they are not carrying a load

Even with a load, I know for a fact that the MIL-35 (export Hind) does about 180 kts. Having been overtaken by a formation of them, whilst doing 160 kts myself, I was quite impressed!

[heli1]

212 man...I am being pedantic but Sikorsky keeps claiming the X2 will be the world's fastest helicopter and I am just pointing out that is not true.The FAI gudelines clearly state that it cannot have add-ons like pusher props to qualify for the World Helicopter Speed Record.
If they said it would be the world's fastest compound helicopter, that would be correct,although they'll have to go some to beat the Bell .

[Ian Corrigible]

CEFOSKY,

Where does your 518kph figure for the XH-59A come from? The highest speed in level flight that I've seen attributed to the type is 238 kt (and 263 kt in a dive), with the Bell 533 generally considered to be the fastest compound (274 kt).

I/C

[Ian Corrigible]

CEFOSKEY - Thanks for the source. With all due respect to Steve Harding, I think that's a typo. All of my SAC sources (paper and flesh) say 240 kts.

Dave - Sorry, missed your earlier question wrt rotor speed. SAC is being coy with regards to what they publish on the X2's xmsn, but you could - I suppose - read something into the fact that the rotor speed is referred to as "446 to 360 rpm" rather than "446 and 360 rpm." Perhaps.

I/C

[Graviman]

Gents, just before the squabble involves throwing lumps of Westland at each other! :\

I have seen G-LYNX and it is a beautifully engineered machine. It is fair to comment that it's only objective was to achieve the pure helicopter speed record (although some jet thrust was overlooked). Production machines were never intended to get to that speed.

X2 is innovative because it has taken all of the best ideas. This includes the concept of well engineered rotor dynamics and aerofoil concepts that worked so well for Westland. The design of course has benefited from 20 years of CAE technique development. BUT, the intention this time is to put these high speeds into production for real world situations.

This comment from Marc Poland (from link above) interested me - particularly the power requirement:



We have a demonstrator craft, called the X2, flying now. It hovers off the main rotors, transitions into forward movement by tilting the rotor, but over the range of speed it trims back out as the pusher prop starts to deliver thrust. The view from the development engineers is that we’ll get well north of 200 knots, maybe as far as 240–250 knots, with a power level roughly the same as a conventional helicopter.



----

Riff_raff,

I'd be genuinely interested to learn more about the project you were involved in. Can you say which machine the work was for?

My original guestimate took about five minutes with engineer's beam theorem. However, I made a mistake in that moment should be proportional to mass^1.5 (now corrected). But of course you are considering rotor radius, and if you allow the same disk loading then this means moment is proportional to radius^3. Then again that means root depth only ends up radius^1.5 for the same mean surface stress. There may be some additional moments from lead-lag dynamics, since bending flexure could go up.

Perhaps a little pedantic on my part (i didn't realise you were another mech eng), but exponential generally implies that the problem gets out of hand. I just wanted to show with some numbers that the difficulties are not insurmountable with a larger helicopter. :)

Mart

[Dave_Jackson]

Ian, thanks for the reply.

_______________

IMHO, the eventual top speed limitation of the X2 will be determined by its blades. This Sikorsky report discusses the retreating blade drag problem of the XH-59A (http://www.unicopter.com/ABC_Status_Report.jpg). Power should not be a limitation since its 1,450 SHP can, theoretically, drive the craft vertically on its propeller.

The X2 is only a modification of a previous attempt at improving rotorcraft. Only the future, not the hyperbole, can say whether the revised blades will increase its viability and practicality over its forefather.

Then, the next question becomes that of, can today's US military or civilian companies afford to buy and operate such a craft?


Dave

Edit

Mart,

1465 (http://www.unicopter.com/1465.html) Note that this shows the moment arm to the center of lift on the X2 blades is greater than that on the XH-59A

[Dave_Jackson]

CEFOSKEY,

The 263 knot maximum speed was apparently achieved in a dive. Reference; the first paragraph in the link in my previous post.

Dave

[IFMU]

What I have seen regarding the XH59 agrees with what Ian Corrigible posted:
238 kt (and 263 kt in a dive),
Not that I am the authority or anything.

-- IFMU

[Graviman]

The limiting speed for X2 is likely to be from compressibility of the advancing tips. So some simple calcs are in order:

RRPM: cruise: 446rpm ; speed:360 rpm.

Blade radius 13.2' or 4.02m

So hover tip speed is 4.02m x ( 2pi x 446rpm / 60 ) = 188m/s (56% sound)

while rotational component of tip speed at cruise is
4.02m x ( 2pi x 360rpm / 60 ) = 152m/s (45% sound)

So if we let tip get up to 85% sound then machine can travel at
85% - 45% = 40% sound

334m/s x 0.40 = 134m/s or 260kts (301mph)

I think this then shows what sets the upper speed limit. :ok:

[dangermouse]

The post above quotes the FAI as follows;

HELICOPTER: A rotorcraft with a power driven rotor system whose axis (axes) is (are) fixed and substantially perpendicular to the longitudinal axis of the rotorcraft (my underlining)

by defintion this means the X2 isnt a helicopter but more correctly a

ROTORCRAFT - An aerodyne that derives the whole or a substantial part of its lift from a rotary wing system

or am I reading it wrong?

I don't doubt the X2 may prove to be a fast machine, whether this technology can be upscaled to a useful rotorcraft remains to be seen rather than a one man whizz about. Ultimately I believe that the G-LYNX record will never be beaten by a conventional (non augmented) helicopter.

DM

[Dave_Jackson]

Mart [graviman]

"while rotational component of tip speed at cruise is
4.02m x ( 2pi x 360rpm / 60 ) = 152m/s (45% sound)

So if we let tip get up to 85% sound then machine can travel at
85% - 45% = 40% sound"

Check your algorithms. Do you not mean 2 x 4.02m x (pi x 360rpm / 60 )
_______________

"The limiting speed for X2 is likely to be from compressibility of the advancing tips."

Lets hope you are correct.

It appears that the limiting speed on the XH-59A was caused by the drag of the retreating blades. This high drag wanted to drive the rotors at a rotation speed faster then the engine was providing.

This appears to be the reason for the change in the X2's blade profile. They must now put up with the drag of the long 'spar' at the root of the blades, but they have eliminated the negative lift (and its drag) that was created by the reverse velocity causing a negative lift at the root of the XH-59A's retreating blades.


Dave

[Graviman]

Dave,

Don't forget that X2 uses autorotation for cruise, so there will be a longitudinal cyclic trim position for minimum total drag (obviously with collective lowered). Actually, i'm not sure whether the FBW would need to keep an eye on longitudinal trim as well as collective. The idea of having to watch NR limits while cruising is an interesting thought - one for the TPs...

Ultimately, i have no doubt that X2 has been subject to the very latest CAE analytical techniques. So the question really remains how accurate are the predictions. If the project engineers believe the machine has the capability to achieve 240-250kias then i have no real reason to doubt them.

Chris, was all of the aero-mechanical-dynamics done in Ansys? Were there any other test beds to validate the CAE model?

----

Dangermouse,

G-LYNX will always remain the worlds fastest single rotor helicopter. Credit where credit is due.

If i read the FAI definition properly then X2td still falls into the category of pure helicopter. X2 is a rotorcraft with a power driven coaxial rotor system whose axes are fixed and substantially perpendicular to the longitudinal axis of the rotorcraft. I is confused? :confused:

[Dave_Jackson]

Mart

"Don't forget that X2 uses autorotation for cruise" :=


PS. I was wrong to correct your algorithm. Haste makes waste. Sorry

Dave

[IFMU]

HELICOPTER: A rotorcraft with a power driven rotor system whose axis (axes) is (are) fixed and substantially perpendicular to the longitudinal axis of the rotorcraft
I think this describes x2 exactly. However, a bit back in this thread we came up with:

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.

So if we believe Nick, it is a compound helicopter. It seems clear to me that the X2 can never take away G-LYNX's record, as it is a different class of machine. None of that is necessarily bad.

-- IFMU

[IFMU]

Found this link on the previous PM page I referenced before:
X2 Sikorsky Helicopter Aviation Inspiration - Engineering Inspiration for the X2 Sikorsky Helicopter - Popular Mechanics (http://www.popularmechanics.com/science/air_space/4284157.html)

http://media.popularmechanics.com/images/x2_inspiration_470_1009.jpg

It has some interviews of some of the boorish spares. Funny they hid the young guy in the back. Must be one of those "old age and treachery overcoming youth and skill" sort of things.

-- IFMU

[Graviman]

IFMU,

Agreed. G-LYNX was the climax of the single rotor helicopter, while X2 opens a thrilling new chapter on compound helicopters.

Having read the article i must admit to finding this project inspiring. I started this thread what feels like years ago to capture as much technical detail as practical about what i recognised to be a revolution in helicopter design. It is the closest i can currently get to being involved without actually being there.

[dangermouse]

my view (for what it's worth, not much probably) is that the X2 shouldnt be referred to as a helicopter by just the use of that one word.

IFMU, the X2 rear rotor AXIS is not perpendicular to the longitudinal one, it's along it thereby eliminating it from the pure helicopter definition.

so, it is a compound helicopter/rotorcraft.

I know its just pedantic but coming from that part of the world G-LYNX originated from it's a matter of some pride here!!

effectively for rotorcraft we have 5 types of vehicle that could hold seperate speed records.

Helicopter; rotor lift, no augmentation - Lynx, UH60 etc
Winged Helo; Rotor and wing lift no augmentation - Mil24, Mil6
Compound helo; rotor lift+ thrust augmentation - X2
Compound winged helo; rotor and wings lift + thrust augmentation - AH56
Tilt rotor - V22, BA609

until of couse someone invents something new.

hypothetical question; how fast would the cuurent fastest coaxial helo go with a pusher prop (say a KA50 with a prop on the back) :\

DM

[IFMU]

IFMU, the X2 rear rotor AXIS is not perpendicular to the longitudinal one, it's along it thereby eliminating it from the pure helicopter definition.
dangermouse,

I'm good with that, for what it is worth. I would argue the thing on the back is a propeller and not a rotor, but I agree X2 is not a pure helicopter. I do think it has some pure helicopter attributes that come along with low disc loading, such as hover efficiency and autorotation capability, but it would seem to me that it can't steal G-LYNX's record based upon the definitions that we all seem to agree on. If X2 accomplishes what they say it will, then its accomplishments will stand on their own merit without having to compete against G-LYNX.

Furthermore, you should be pround of G-LYNX. Heck, I'm proud of G-LYNX and I have no ties to Westland. No real ties to England either, as we are two countries divided by a common language and that little spat back in 1776 or so. But, the helicopter tribe is small enough, that when somebody in it does something exceptional, how can you not sit back and say "hey, that was cool." I think that people who cannot appreciate other's achievements have perhaps never achieved anything themselves, and are therefore ignorant of what it really takes.

-- IFMU

[Graviman]

I'd like to make sure this thread captures the technical excellence that is G-LYNX

http://www.hmfriends.org.uk/images/glynxriat60.jpg
http://www.hmfriends.org.uk/images/glynx3q6.jpg

Lynx – The World’s Fastest Helicopter 20 Years On (http://www.sbac.co.uk/community/cms/content/preview/news_item_view.asp?i=12405&t=0)


The 11th August marks the 20th anniversary of the Westland Lynx helicopter setting a new world helicopter speed record of 249.1 mph (400.87 kph). Although other attempts have been made, 20 years on Lynx retains the title as the world’s fastest helicopter.

The Lynx helicopter, registered G-LYNX, flew a 15km course across the Somerset Levels at 500 ft on a calm hazy evening back in 1986 with Westland Chief Test Pilot Trevor Eggington at the controls and Derek Clews, Flight Test Engineer alongside. The average speed achieved over two runs was 249.1 mph (400.87 kph), beating the record held by a modified Mil “Hind” helicopter by over 20 mph (32 kph).

The world record flight was made possible by the introduction of the advanced technology composite blades developed as part of the British Experimental Rotor Programme (BERP) project. The BERP programme was carried out in co-operation with the UK Ministry of Defence to produce an advanced technology rotor blade, which would exploit the advantages to be gained by aerodynamic tailoring through the use of modern composite materials and construction methods. The first BERP blades were flown on 9th August 1985 and such was the progress achieved G-LYNX was able to claim the World Speed Record just one year later. The BERP blades are now fitted to all Lynx helicopters in service and the same technology was used for the EH101 main rotor blades.

The three month programme to modify a standard Lynx to world speed record configuration was launched on 22nd May 1986 and included installing more powerful Rolls-Royce Gem 60 engines. These engines were cleared to operate at their maximum contingency rating, thereby boosting power by 45%. Engine power was further boosted by utilising a water-methanol injection system. To improve yaw control a new low set tail plane with vertical fins was fitted which also offload the tail rotor.

A drag reduction exercise was undertaken involving the fairing of the main rotor head, removal of external items such as steps, aerials and windscreen wipers, while joints were sealed and cooling ducts blanked where possible.


Dangermouse, nobody is trying to take away the Westland record for world's fastest pure helicopter.

Along with Concorde this has inspired a generation. But, technology inevitably marches on and the coaxial compound helicopter looks to be the way forwards. I would see X2 compound helicopter a spiritual successor, using the latest available techniques. One day X2 must also gracefully look on as it's spiritual successor goes from VTOL to even higher speeds. This is is just the way of things.

A conventional coaxial would have no chance at high speeds. The secret to X2TD is the advancing blade technology developed for XH59/S-69 helicopter (not sure if this was defined as compound).

Mart

[dangermouse]

didnt mean that to happen!

let's get back to the X2 and how its going...

so how's it going?

DM

[IFMU]

A little more popular media coverage:

http://www.popsci.com/bown/2009/product/sikorsky-x2-helicopter

But not much meat there. Who knows what they are up to. No sign of the boorish spares.

-- IFMU

[Graviman]

This is the briefing given by Carey Bond at Heli Expo 2009:

1QYLYCMQMQo

And by Kevin Bredenbeck at HeliExpo 2009:

rWVPh5Q1qi8

RFCAHibb8UU

Also a general video of the potential of ABC in LTH applications:

oLNyiqB7jgE


The point i found most interesting was the explanation of the twitchy control of the first flight. At that time the FBW was direct stick to head control with no feedforward/feedback stability augmentation. The pitch and roll control was actually slightly higher than had been anticipated by the predictive processes used to develop X2 control systems. The flight has since been analysed to understand the actual pitch & roll moments for a given swashplate movement which will then be incorporated into the control algoritms.

An interesting insight into the world of flight test there. Even more so as the rotor dynamics head into ABC regime. This is likely the main reason the flight test is being done in three distinct speed phases.

What i will be interested in understanding is how the control for the pusher prop developes to make it intuitive to use. Especially once the main rotor has gone into autorotation. I would imagine that collective would be automatically trimmed to keep Nr constant while TP varies thrust. I would imagine that prop pitch will also be automatically trimmed so that TP is only controlling engine power with twist grip.

Hopefully future briefs on this amazing machine will be just as informative...

[Hunt3r]

Well, just to toss in a (probably rehashed somewhere) idea, why not have some wings? Short wings like the X-49A, but I imagine it'd make it more stable, make high speed maneuvering better, and it gives a CAS/attack helo version using this tech a nice place to mount weapons on. If it improves range, makes it easier to land with dead engines, makes it more maneuverable or stable, and all that jazz, then why not? It seems like they have added stub wings to it at some point, but I'm interested in knowing why.

Feel free to flame me and pick it apart. Also, yes, I do not know the math involved. :}

[darrenphughes]

Anything sticking out from the fuselage like a pair of stub wings would probably increase the power needed to hover. It may affect the ability to autorotate also. I'm no expert but that would be my slightly educated guess. They're probably looking for all the efficiency they can get right now.

If a military model were to be produced I'd imagine you'd see guns or pods hanging out the side, like the last video 2 posts up.

[Hunt3r]

Well, if they find that hover performance is decreased significantly and it does more bad then good, yes it's a bad idea and it's fine not to use it.

I guess I'm just thinking about the helo as the modern AH-56 :}

[Dave_Jackson]

Article ~ 'High-Resolution Computational Investigation of Trimmed Coaxial Rotor Aerodynamics in Hover'.

Excerpts from ~ 'Conclusion':

"4) The overall performance is well predicted for the coaxial system. The bottom rotor showed a degradation of performance due to the influence of the top rotor wake (~40% increase in power at same thrust at higher thrust levels). Interestingly, even the top rotor showed slight degradation in performance....."

"6) The interactions [of the blades on the two rotors] resulted in a fluctuation of 5%-10% in the integrated Quantities. Such a fluctuation could be significant for vibration and acoustic characteristics. ...."

______________________________

Forks in the road.

If United Technologies had kept Charles Kaman, logical evolution (such as today's movement toward highly rigid rotors) suggests that the advantages of the Intermeshing configuration would have established it as the predominant one.


Dave

[JohnDixson]

Dave, I had always heard that Mr. Kaman left Sikorsky over his pushing the servo-flap design approach, not intermeshing or coaxial main rotors. That not the case?

Thanks,
John Dixson

[Dave_Jackson]

John,
Dave, I had always heard that Mr. Kaman left Sikorsky over his pushing the servo-flap design approach, not intermeshing or coaxial main rotors. That not the case? You are correct in that Charles Kaman's proposal to the Engineering Manager at United Aircraft was the servo flap. But the servo-flap may have been only part of his reason for leaving.

Perhaps the following two excerpts from his book 'KAMAN ~ Our Early Years' clarifies his reasons for leaving.

At first I was mainly concerned with stability and control forces, and I applied my aerodynamics training to a new concept for rotor control.

I felt that somehow we had to find a means of aerodynamically stabilizing the rotor, while at the same time making it easier to fly. Since that was not part of my daily job at Hamilton, I continuously worked on the problem on my own time.

Primary among those potential improvements was my idea for aerodynamic servo flaps on rotor blades. My initial thought was that such a flap would be mounted on the trailing edge of the main rotor blade and would be connected by mechanical linkages working through a swash plate to the pilot's controls. It would be a good while before I would understand that this system would not achieve the desired result, and that it would have to take the form of a true servo system to see success. But this is getting ahead of the story.

The use of intermeshing rotors-a feature I would later envision for the Kaman K-125 helicopter-promised a significant power saving and greater efficiency over tail rotor designs. A tail rotor, used to counter the torque of the main rotor, used precious power without providing lift. But proposing an alternative to the tail rotor would have been premature - and out of the question for United Aircraft - as Sikorsky was completely committed to the tail rotor configuration.

___________________________


"Erle, I'd like to develop this system for United . I'll continue to function with my own basic job, and I'll do this work on overtime or extra time, or however. All I ask is that you pick up the costs and provide me with the place and a technician to the basic spade work."

His answer was swift, decisive and clear. "Charlie, we have our inventor at United Aircraft. His name is Igor Sikorsky. We don't need another one."


I think that his first patent was US 2,455,866, and it shows the servo flap on an Intermeshing helicopter.

Dave

[Graviman]

Hunt3r,

The advantage of ABC is that you get the benefit across the full speed range. Sikorsky/Schweizer spent a lot of time optimising the blade section/twist/span for the performance saught. Stick on wings just were not required to get the cruise/dash performance.



Dave,

I know that the original X2 design studies used the then available non-coaxial codes, and that wake contraction will affect the results for the lower rotor. However, in forward flight i don't imagine there to be much difference between coaxial or intermeshing. In hover there probably are some advantages to the lateral symmetry of intermeshing. The down side of intermeshing is tip clearance, which might have affected operational considerations.

When i (finally) get my physics degree out of the way next october, i'll pick up my rotor simulation tool again. I'd like to adapt it to handle ABC type of configs. It would be interesting to do a design study comparison of optimised coaxial vs intermeshing vs interleaving. Finally take some of that speculation out of our discussions. ;)

[Dave_Jackson]

Mart,

The primary advantage of the Intermeshing over that of Coaxial is the reduced disk-loading for physical identically rotor-disks. In hover, the Intermeshing's larger 'effective disk area' provides a greater efficiency (Figure of Merit). In forward flight, the Intermeshing provides a more equitable disk loading because the rotor-rotor overlap of both rotors is in the 'reverse velocity' region.

I have no ties to any specific configuration, and change concepts of interest faster than changing the bed sheets. Your proposed research into the ABC concept would be challenging and hopefully productive. I would constructively suggest that your focus should be directed toward the segments of the blade that are required to work in the reverse velocity region during fast forward flight. The profile drag and negatively induced lift are the biggest hurdle for the ABC concept; be it Coaxial or Intermeshing.

IMO,the current blades on the X2 are an attempt to 'sweep the problem under the rug' and not an attempt to confront the problem head-on. In all fairness, perhaps the X2 is intended as a working platform upon which ideas to improve the blade can be tested ~ with your help. :ok:


Dave

[Hunt3r]

Well, it wouldn't make much sense in a normal config (transport etc) but in the attack role it'd make sense to have some stub wings, since you can mount weapons on it.

Six pylons, titanium bathtub, ABC tech, good hot/high perf, and good avionics/sensors would be a godsend for attack helicopters I think.

[IFMU]

In the fall 2009 edition of vertiflite, they have a 5 page X2 article written by Frank Colucci. One quote from page 28 of the article:

For all the challenges, the ABC demonstrator was exceptionally responsive. The XH-59A flew snap turns, high-rate sideslips, and level transitions from hover to forward flight. It pulled 2g turns at 240 kt, limited by design considerations. One Sikorsky pilot estimated the ABC was 50% more maneuverable than a single-rotor helicopter of the same size, and the Army concluded that the XH-59A, with no anti-torque rotor to waste power, was more efficient in a hover than conventional helicopters. Plans for a fixed auxilliary wing on the XH-59A proved unnecessary. According to Art Linden, "the one thing we proved beyond a shadow of a doubt is we did not need the wing... [the rotor system] developed all the lift you could ever use."

So I would think you would not need a wing. The ability to generate lots of lift also can translate in the ability to pull G's, or to manuver. The LTH mockup shown in the same article shows some rocket-pod looking things. No sense putting wings on, that is only more drag. If adding more wings always made things better, we would all be flying around in triplanes.

I wonder how well the servo flap idea would work on the x2.

-- IFMU

[JohnDixson]

Thanks for the expanded answer, Dave.

I doubt if the aerodynamic impact of higher speed helicopter flight was on anyone's mind at the time Mr. Kaman pulled out of Sikorsky to start his own company, but the blade pitching moments created at free stream mach numbers above 0.92 have proven to create some problems, and one wonders whether the tie bar design present in the SH-2 design, for instance, is strong enough to prevent destructive behavior. I'm told that when Kaman did a higher-harmonic control system design that went into the wind tunnel, it had a pushrod as well as a servo flap, but that might have been for other reasons.

Thanks,
John

[Dave_Jackson]

John, this may, or may not, answer your last sentence.

Rick Andrew thinks that Kaman has a patent on a rotor blades control where a swashplate sets the root pitch and his servo-flap sets the 75% of span pitch. He is going to look up his copy of this and send it to me. I could not find anything relevant by doing a patent search on 'Kaman Aerospace' and by reviewing the Kaman folder. September 13, 2002He came across the article. It was 'CTR Control System', on the Seasprite, in Aviation Week & Space Technology ~ Aug 5, 1968 ~ March 31, 2004

The only relevant meaning for the acronym CTR that I can find is Civil Tilt Rotor.
Very mysterious. http://www.unicopter.com/Spy.gif


Dave

[Graviman]

Hunt3r, have you heard something about a DoD contract then? :ok:



The primary advantage of the Intermeshing over that of Coaxial is the reduced disk-loading for physical identically rotor-disks. In hover, the Intermeshing's larger 'effective disk area' provides a greater efficiency (Figure of Merit). In forward flight, the Intermeshing provides a more equitable disk loading because the rotor-rotor overlap of both rotors is in the 'reverse velocity' region.

Dave, i think the fairest comparison (when i get around to it) would be to compare machines capable of landing in the same ground box area. This would allow the benefits of better FM through such things as reverse velocity utilisation to be evaluated in a holistic way.

[Graviman]

Chris, those pylon mounted rocket pods don't look very "low observability". I'll bet that if the project goes that way then Comanche style features begin to reappear...

[Hunt3r]

Well, it'd be nice if this X2 attack version were really meant for CAS. A-10 tough. Big bullets, lots of rockets, etc.

The Apache/A-10 combo leaves a pretty big gap in terms of CAS. Not enough rockets/missiles.

I guess I'm thinking of the X2 as a fast, survivable, and heavily armed attack helo. Something that can really lay down the lead.

[The Sultan]

Like the Beech Starship pushers do not do well with FOD and such. Looks like a Hellfire will blow the pusher off.

Another thing, how fast has the X2 gone, seems really quiet so there most be little to report.

The Sultan

[Ian Corrigible]

Still stuck at 106 kts according to today's (http://www.shephard.co.uk/news/4803//) rehash (http://www.verticalmag.com/control/news/templates/?a=12500&z=6) of last (http://www.shephard.co.uk/news/4567/) month's (http://www.verticalmag.com/control/news/templates/?a=12365) Popular Science award.

Still, there's still another 3 weeks to hit that 250 kt goal (http://www.sikorsky.com/vgn-ext-templating-SIK/v/index.jsp?vgnextoid=00de6eb78fa78110VgnVCM1000001382000aRCRD&vgnextchannel=65f9e39d40a78110VgnVCM1000001382000aRCRD&vgnextfmt=default&pressvcmid=d9f44c668373f110VgnVCM1000004f62529fRCRD)... :E

I/C

[Hunt3r]

Cmon... 250 knots... 106 knots is pitiful for a design that could reach above that with some turbojets.

[Graviman]

Don't forget this is very much an experimental flight test program.

This means that for every little stretch of the envelope:
The stress engineers will be carefully pouring over the strain gauge data to see that the stress / fatigue calcs are correct.
The dynamics engineers will be carefully pouring over accelerometer data to see that the rotors flex in the way that was predicted.
The control engineers will be pouring over the FBW logs to see that the actuators are responding as anticipated.

Frankly, i would be astonished if this was the only program to achieve its stated aims without one group finding something that they need to understand better. Look at how many redesigns occured between first flight of VS-300 and R4. That's just engineering.

The most important aim for every flight is to walk back into the office... ;)

[riff_raff]

Sikorsky is probably taking it slow with the X2 flight test program due to still being a little gun-shy with control of a rigid rotor aircraft. Recall that they had a crash very early in the flight testing of the XH-59 (ABC) program, that set them back about 2 years.

One thing I find interesting about the X2 is the unique sound that its rigid rotors produce. It sounds more like a turboprop than a traditional helo's rotor or even the V-22's prop-rotors.

As for the max speed with the X2, I've seen lots of recent patent applications from Sikorsky covering two-speed drivetrain arrangements. Does anyone know if the rotor system on the X2 is intended to run at variable speeds?

[Graviman]

Riff_raff,

The main rotor reduces RPM with speed. I seem to recall that the design is two speed with autorotation for cruise. Not sure what the scheduling is, but the idea is to hand over power for forward thrust to pusher prop with speed. This keeps the fuselage (and hubs) level to minimise drag. The pusher prop also becomes more efficient as speed increases air mass going through it.

The tip noise on X2 should be far less pronounced than other helos. Normally a square tip produces very concentrated tip vortices, but the profile used on X2 will allow a much larger tip vortex with reduced vorticity. If you look at the just flown A400M you can see a similar idea in its turboprops - the other benefit being improved flow at high tip mach numbers. In a helo much of the noise (particularly during manouvres) comes from Blade Vortex Interaction (BVI) so less localised vorticity helps to reduce "blade slap".

[gwelo shamwari]

I find it pretty interesting that there has been so much hype about the X2, especially as the Russians have been operating the KA-50 for a number of years. It is a contra-rotating co-axial rotor system thought it does lack a pusher prop. Is the hype because of the design or because of the technology being applied to the design or because a western corporation is developing the product?

[gwelo shamwari]

:ok: Thank you for pointing me in the right direction...

TGZ

[Hunt3r]

TBH, I don't think that the X2 would really quite fit in the recon role like the Commanche. It should be able to do recon, but should also be able to fulfill CAS and anti-armor roles effectively.

[IFMU]

Hunt3r,

Is the X2 technology really only applicable to attack? I bet it would be just as applicable to other missions, like utility, offshore oil, executive transport, SAR, etc. It is still just a helicopter. If they succeed it will be a fast helicopter, with longer legs to boot.

-- IFMU

[turboshaft]

...or this one circa 1973...

http://www.turboshaft.com/images/xh-59a_concepts.jpg

http://www.jonrb.com/emoticons/getmecoat.gif

[Hunt3r]

Well a faster helicopter would be better for everything. As transport in general, attack, recon, etc.

Also, the AH-59 would be a nice thing to think about...

[riff_raff]

While the BA609 might have some autorotation capability under certain AEI conditions, I don't believe it has enough power from one of its PT6's in an OEI condition to maintain a hover. Does anyone know different?

Also, you should take into consideration the fact that most tilt rotor aircraft are capable of increased GTOW's using a STOL technique on a conventional runway.

And finally, I still would be concerned about how well the X2's rigid(?) rotor system will scale up. I don't honestly believe they will ever get a satisfactory solution for an X2 rotor configuration with a 30 or 40 ton payload aircraft like they proposed for JHL. A rigid rotor system at that scale would have horrifying forces and moments to deal with.

Regardless, I think the X2 has a bright future for smaller VTOL applications in the near term. Mostly because it is already flying......

riff raff

[Hunt3r]

Well, if they can find a way to keep vibration down, then it's all good.

Servo flaps, anyone?

[NonSAC]

Dave,

Check out US 5,409,183; seems to have cover a bit of what you're looking for in connection with Kaman's work in this technology.

This particular patent, issued in 1995, has lapsed for non-payment of maintenance fees. Perhaps they were too far ahead of the art with this particular innovation.

Kaman's patent and patent publications are fairly easy to locate by searching the USPTO's assignment database. Just go to USPTO Assignments on the Web (http://assignments.uspto.gov/assignments/?db=pat) and pop in 'Kaman Aerospace' as the 'assignee;' this will show you what is assigned to Kaman Aerospace - currently some 64 patents and patent application publications.

- Cheers

[The Sultan]

Merry Christmas all.

Question: Did the X-2 reach 250 knots yet? I noticed the A400 cleared its envelope in two flight in less than two weeks.

The Sultan

[Dave_Jackson]

NonSAC, Thanks.


I'm told that when Kaman did a higher-harmonic control system design that went into the wind tunnel, it had a pushrod as well as a servo flap, but that might have been for other reasons.

John It looks like NonSAC may have found what you are referring to. The mentioned patent, US 5,409,183, has leading and trailing flaps, non-swashplate hydraulic pushrod control and a higher harmonic control of the leading edge flap.

The patent even mentions electrically energized flap actuators, which are now starting to look promising. A couple of types are piezoelectric actuators (http://en.wikipedia.org/wiki/Piezoelectricity) and linear electric motors (http://www.festo.com/rep/en-gb_gb/assets/pdf/Eureka_Nov_09_Electric_drives.pdf).

Dave

[The Sultan]

CEFO

Gee those simple fixed wings do not have any problems which require anything such as wing and tail flutter testing, testing of the radical prop configuration for coupled whirl modes etc...(ever heard of the Electra?)

Is the X-2 delay hardware or software related?

The Sultan

[Hilife]

I have it on good authority, that re-booting of the velocity nowhere curve using the Buckminster fullerene method should enable expansion of the linear trajectory in the New Year. ;)

[Dave_Jackson]

CEFOSKEY

While I certainly know the answer and details to this question, I'm curious as to what you've heard.

We're curious as to what you've heard. :)



Dave

[Graviman]

Aw, come on guys! :rolleyes:

Helicopters are four times more expensive to develope than fixed wings. So this means that either 4 times the number of engineers are involved or it just takes four times as long. Lots of moving parts...

The fact that the unrealised potential of XH-59 has raised its head in this discussion tells me that X2 is now of its time. So what if the machine takes a while longer to do its thing? I can wait. :cool:

Nobody ever said that redefining the potential of the helicopter was going to be a walkover. In fact it's a very difficult project, which is why it didn't go forwards in the 70s. The design, development, and flight test teams should be commended for having the gumption to take it on.

[Ian Corrigible]

Is the X-2 delay hardware or software related?

According to this week's Av Week, the X2 TD experienced a transmission failure during a ground test. The aircraft will shortly enter rebuild, with ground testing tentatively resuming in March.

I/C

[Hunt3r]

Hopefully they keep pushing at it, and sometime within this year they finally hit the 250 knot barrier...

[Graviman]

According to this week's Av Week, the X2 TD experienced a transmission failure during a ground test. The aircraft will shortly enter rebuild, with ground testing tentatively resuming in March.


Not read the Av Week article, but that's just any new product development i'm afraid... ;)

If the story is true then don't forget this is the first time this gearbox has ever seen this helicopter!


In general, fatigue is a very complex subject indeed! Predicting component failure rates is right at the edge of feasible (eg Brown-Miller). If you are lucky and have data for many many test samples then you can put reasonable statistics into the fatigue code. Even if you have this, it is unlikely to have been tested beyond 10'000'000 cycles. A helicopter will gobble up this number of cycles in less than 700 hours. As a compromise process, the stress engineers will do their utmost by comparing the mean and alternating stress to the material UTS and endurance stress (eg FRF of a Goodman line on a Haigh diagram). But this will only get you so far because many assumptions have to be made about material degradation with time and service. This is even more difficult if the stress cycle is not exactly as the simulations predicted, which is seldom the case.

Basically, it is difficult enough to get it right for the car you drive. In a helicopter this is even more difficult because you are constantly chasing every last kg of mass to shave off. This is why Nick Lappos often explained about loading components as like taking beans from a jar. The engineers do their absolute level best to work out how many beans were there to start with, so you can nibble away at a steady rate. But when the beans run out the jar breaks....


Frankly, if the story is true, then the fact that it was identified and dealt with in a safe manner is testament to the Schweizer/Sikorsky test program put together for X2.

All in all: no big deal. I look forward to March, or later if required. :ok:

[Ian Corrigible]

Good to see Alastair Campbell has found a new job. The X2TD's problem has gone from being a "transmission failure" (http://www.google.com/url?q=http://www.aviationweek.com/aw/generic/channel_.jsp%3Fchannel%3Dawst&ei=xn-AS4rLPJG0tgfrj_3oBg&sa=X&oi=smap&resnum=1&ct=result&cd=3&ved=0CA8QqwMoAjAA&usg=AFQjCNE8SKA_eB9TVrc94cVChuy2lUKVHA) to the "detection of a gearbox manufacturing problem" (http://www.flightglobal.com/articles/2010/02/17/338307/sikorsky-x2-down-but-not-out.html) to being "currently out of service for transmission upgrades." (http://www.ainonline.com/news/single-news-page/article/industry-perspective-sikorsky-1) :E

I/C

[Dave_Jackson]

Should have built the ABC in an Intermeshing configuration.
.
.
.
.
Here is the transmission proposed by Flettner for his Fl 339; 70 years ago.
http://www.unicopter.com/1509-C.gif

[Lt.Fubar]

Dave, no wonder they didn't do it.. I see worm drive in there :}

Good in differentials, not good for efficiency, and in this case - flight safety. Without torque from the engine, it's a brake.

[Dave_Jackson]

Dave, no wonder they didn't do it.. I see worm drive in there http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/badteeth.gif

Good in differentials, not good for efficiency, and in this case - flight safety. Without torque from the engine, it's a brake.

Basically you are correct. http://www.unicopter.com/ThumbsUp.gif

However; :)

Low-ratio worm drives have a much lower friction than the normally used high-ratio worm drives.
On ratios of 10:1 and below the wheel cannot brake the worm.
The newer 'Double Enveloping Worm Gearing' offers additional advantages.
Ball Worm drives are under development and limited use.
Additional related information (http://www.unicopter.com/1509.html)


In fact, Sikorsky's earlier S-69 ABC didn't even need a gearbox for the rotors during cruise. Unintentionally, the rotors were driven aerodynamically like a gyrocopter.

I suspect that the X2, even with its modified blade, will experience similar problems.
IMHO, specific improvements such as; reverse velocity utilization (http://www.unicopter.com/B473.html), active blade twist (http://www.unicopter.com/B372.html), and variable speed rotors and prop (http://www.unicopter.com/Variable_Speed.html) need to be done by an Engineering department before the Hyperbole department is unleashed.

_______________

If thread becomes quiet this year, to stop it from being closed perhaps a posting should eventually be placed.

Perhaps the preliminary submission and subsequent rejection of my offer to deliver a paper on 'An Intermeshing ABC Helicopter' to the American Helicopter Society, three years before Sikorsky reopened the ABC with their X2 might be of interest.

[IFMU]

Building a flying machine, getting to 106 kts, projecting expected performance = Hyperbole.

Building a website, slagging the big helicopter company that is actually trying to do something, and promoting some creative old German designs = ?

I am a simple person. None of this adds up for me.

-- IFMU

[JohnDixson]

In fact, Sikorsky's earlier S-69 ABC didn't even need a gearbox for the rotors during cruise. Unintentionally, the rotors were driven aerodynamically like a gyrocopter.

Dave, perhaps I misunderstood, but if the "unintentionally" wasn't there, we could have agreed. The S-61F work led the way on that particular rotor behavior question, along with one or two others, the most attention getting being the tip mach related rotor stability issue.

Thanks,
John Dixson

[Lt.Fubar]

It would be a shaft brake, but not necessarily a rotor brake, as I am sure there is a sprag-clutch-type device buried somewhere in there.There could be one, but the worm gear is also what coordinates both rotors there. If at some point they would rotate freely from the worm gear - the helicopter would beat itself to death with it's own rotor blades... the ground tests would be fun to watch :ok:

Dave, it's been a while since I was into worm gears, but one allowing the worm gear to be driven by the wheel gear, with the same efficiency as the other way around would be, well... revolutionary. Worm gears are great when the power have to be transfered in one direction, they allow very high ratios with compact and cheap design, but it all comes at a price.

The transmission design like on the Flettner drawing, look unsafe, and probably less efficient than a hydraulic drive would be, and you can do a lot with those... although with the price of efficiency too. I wouldn't be too attached to the design details from the pioneers times... after all , we all know how this one ended:

http://www.ctie.monash.edu.au/hargrave/images/phillips_1904_500.jpg

;)

Ok, back to X2.

[Dave_Jackson]

John;

My web server is currently down. Therefore any linking to it will not bring up the supporting data.

I think that the intended speed for the S-69 ABC was 250 knots. The craft had plenty of power, however the unexpected high profile and negatively-induced drag at the root end of the retreating blades was aerodynamically driving the advancing tips to a speed of nearly Mach 1. To achieve the 250 knots the blades would have entered and exit supersonic flight at a rate equal to the rpm of the rotors.

I believe that gyrocopters operate at a tip speed ratio of around 0.35. It has been said that applying 10 - 15% of the engines power directly (mechanically) to the rotor will increase the forward speed and the efficiency of the gyrocopter.

It can be assumed that X2 airfoil is intended to reduce the high profile and negatively-induced drag at the root end of the retreating blades.


Lt.Fubar;

allowing the worm gear to be driven by the wheel gear, with the same efficiency as the other way around would be, well... revolutionary. No disagreement. However their is no need to drive from wheel to worm.

An advantage of the worm and wheel is the simplicity of fewer gears and lower weight. A reciprocating engine would direct drive the propeller, and require only 1 worm and 2 wheels to drive the rotors plus assure synchronization.

Probably the most important consideration must be the time that the craft is intended to spend in hover v.s. in cruise. During cruise only a small amount of power need be mechanically directed to the rotors, since the rotors will then be acting like wings.


Dave

[Graviman]

Good to see Alastair Campbell has found a new job. The X2TD's problem has gone from being a "transmission failure" to the "detection of a gearbox manufacturing problem" to being "currently out of service for transmission upgrades."

Ian, this failure will have resulted in a huge investigation into root cause within Sikorsky (sometimes called a six sigma investigation). The engineers involved would have systematically checked out each possible reason in turn until establishing exactly what the trouble was. This is the only way to be sure that it does not reoccur. While doing this exercise nobody would have understood exactly what the failure meant.

I mentioned earlier about the fatigue analysis depending upon many coupon tests representing the part. These all assume that the part was manufactured to a fixed process. With prototypes the process is often still in development so can be subject to more variation than anticipated. On a highly stressed part this variation is tested even more so. This does not mean anybody made a mistake, just that the manufacture of the design is still settling down.

Clearly it is not an ideal situation, but that is why flight testing is so conservative. It was picked up in a ground test specifically designed to pick up this nature of problem. Nobody was put at risk and the problem has been resolved.


Dave, that intermeshing config would not be immune from this type of problem. Don't forget that these are very high hinge offset rotors designed for a machine with a snappy response. This application would make even the most hardened stress engineer squirm in his boots. ;)


That is just the devlopment of any engineered product. You can take my word for it that the car you drive will have seen many many problems at prototype, which were all resolved for production. X2 is a high profile project so you are getting to see the development process up close and personal.

[JohnDixson]

Dave, in my previous note I was referring only to the S-61F's prior experience with cruise main rotor autorotation, as applied to the background with which the ABC proceeded. Byron Graham was a pilot in each.

Your sentence with re to the X2 airfoil is to the point: the airfoil is the most complex I have seen on a flying prototype, and to date I believe that the X2 team is happy with it. The next testing phase is where we shall find out.

Thanks,
John Dixson

[riff_raff]

CEFOSKEY,

I find the explanation of "metal flaking" in the X2 MRGB quite reasonable. This "metal flaking" is most likely due to case spalls on the bearing races or gears. It is typically a fairly benign failure mode that is easily picked up by the lube system chip detectors. And if you're going to have a drivetrain failure, this is the type to have.

In the particular case of the X2 MRGB, I would speculate that the metal flaking is probably from the final stage gears. The reason I say this is that the X2 appears to have a fairly rigid rotor system with high mast moments. It is very difficult to isolate the MRGB output gear meshes (usually a planetary gearset) from these high mast moments, which tend to cause misalignment at the gear mesh points. The misaligned planet gear meshes tend to edge load and/or not load share properly, which in turn leads to excessive tooth contact stress levels and premature failures like case spalls or pitting.

Designing a lightweight transmission for use with a rigid rotor system is a very difficult engineering task. Sikorsky's drivetrain group definitely has their work cut out for them. I'm sure more drivetrain problems will continue to pop up as they push the performance of this aircraft. It's just the nature of the business.

riff_raff

[Dave_Jackson]

Perhaps Nick has the answer.

He was involved with the patent application 20070125907 ~ Variable speed gearbox with an independently variable speed tail rotor system for a rotary wing aircraft (http://appft1.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PG01&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.html&r=1&f=G&l=50&s1=%2220070125907%22.PGNR.&OS=DN/20070125907&RS=DN/20070125907).
Item 18' is shown as a blank box. It transmits power for primary forward thrust during a high speed flight. However, the patent does not show what is inside this box. Could it be a box of corn flakes?

:yuk:
OK, so much for corny jokes.

_________________________

Speculation;

The center of lift, and perhaps the centers of drag, percussion and mass etc. etc., have been moved further out the blades then they were on the earlier ABC. This will have increased the length of the moment arms and thereby increased the loads on the transmission.
If the rotor speed IS variable then here is better speculation. "In conventional helicopter flight operations, the rotor speed is designed to operate at a fixed value. A constant rotor speed is chosen to avoid a host of dynamic conditions that would increase rotor vibration and blade loads. Rotors that operate over a wider range of angular velocities will surely encounter more diverse dynamic conditions as changes in centrifugal stiffening modify blade structural mode frequencies and increase (hingeless) bending moments. While the design of the rotor must account for the dynamic conditions, there may still exist in the flight envelope dynamic conditions that result in unacceptable loads. " From ~ OPTIMAL AEROELASTIC TRIM FOR ROTORCRAFT WITH CONSTRAINED, NON-UNIQUE TRIM SOLUTIONS (http://smartech.gatech.edu/dspace/bitstream/1853/22654/1/schank_troy_c_200805_phd.pdf)CEFOSKEY you don't have to say what the problem is. Just node to the left for 1. or node to the right for 2. :)


Dave

[IFMU]

Dave,

What if it is neither 1 or 2? Seems like you gotta give CEFOSKEY a choice 3. It is entirely possible, actually probable that they designed the thing based upon real analysis and historical data.

It would not suprise me in the least if some of the media has gotten some of the details wrong. Often screwed up media makes for good threads here on pprune.

-- IFMU

[Dave_Jackson]

IFMU,

You are correct. The post is speculation. The 'delay' could be due to other reasons.



CEFOSKEY, Please fill in the blank, :O3. ________________________________________


Dave

[NonSAC]

Dave,
You’ve asked an interesting question. Reviewing the relevant publication helps to an extent, but doesn’t definitively answer the question.

2007-0125907 is the publication number of US Patent Application No. 11/292,556, since issued and now US Patent No. 7,434,764 (the ‘764 patent).

To understand the ‘black box’ 18’ referred therein you can look to the patent application incorporated by reference. More specifically, the specification of US 7,434,764 describes 18’ as a translational thrust system and incorporates by reference US Patent Application No. 11/140,762. This application, published as US 2006-0266883 and now US Patent No. 7,413,142 (the ‘142 patent), describes a translational thrust system where a transmission shaft 46 drives a spur gear 84, preferably a sun gear, located between a multitude of planet idler gears 86, and spur gear 88 with inwardly [toward axis of rotation of tail rotor drive shaft] facing gears, thereby driving the translational thrust system 30. See the ‘764 patent at paragraph [0035], Fig. 2, and Fig. 3.

The transmission described in the ‘142 patent is fixed ratio; Fig. 3 describes an embodiment with engine, main rotor, and tail rotor rpm’s of 2100, 320, and 2140 respectively. The innovation here seems to be the counter- rotating main rotor blades and tail rotor system.

The ‘764 patent, in contrast, describes a rotary wing aircraft where the innovation includes counter-rotating main rotor blades having variable velocities with respect to the tail rotor speed, albeit through a very different transmission.

Comparing claim 1 of the '764 patent as filed to the allowed claim 1, and reading paragraph [0026] while looking at Fig.2, it appears that the variable speed functionality is effected in the main gear box rather than the black box out on the tail boom. Regrettably, there is very little additional disclosure about the specific means - the variable speed systems 30A and 30B – beyond their placement on the main rotor drive and being downstream from the tail drive.

I wonder whether the X2 transmission more closely resembles an embodiment disclosed in the ‘142 patent rather than one of the embodiments disclosed in ‘764 patent. As the ‘142 patent includes counter rotating main rotor blades and a pusher system, whereas the ‘764 includes counter rotating main rotor blades, a pusher, and a means to decouple their respective speeds, I would guess the X2 in its present form to more closely resemble one of the less ambitious embodiments of the ‘142 patent.

On an unrelated note, review of the prosecution of the ‘764 patent illustrates how claims can get narrowed during prosecution - a subject discussed previously in the context of the electric motor driven transmission Sikorsky patent application now before the PTO. Notable and applicable here is that the ultimately allowed claim 1 is much narrower, and I believe much clearer, than the originally filed claim.

Cheers!

As-filed claim 1:
A main gearbox of a rotary-wing aircraft comprising:
a gear box;
a tail rotor system driven by said gearbox; and
a variable speed system driven by said gearbox downstream of said tail rotor system.

Allowed claim 1:
A main gearbox system for a rotary-wing aircraft which drives a main rotor assembly and a tail rotor system comprising:
a main gear coaxial with a main rotor shaft of the main rotor assembly;
an input shaft driven at engine speed;
a tail-take-off shaft driven by said input shaft, said tail-take-off shaft driven about a tail-take-off shaft axis of rotation;
a reduction stage shaft driven through said tail-take-off shaft to drive said main gear, said reduction stage shaft driven about a reduction stage shaft axis of rotation which extends across at least a portion of said main gear;
a variable speed system upstream of said reduction stage shaft and downstream of said tail-take-off shaft, said variable speed system operable to drive said main gear speed at a variable speed relative to the engine speed; and
a tail rotor system driven through said tail take-off shaft, said tail rotor system driven at a constant speed relative to the engine speed.

[Dave_Jackson]

NonSAC

Unfortunately, my posting #642 was not very clear. In addition to mentioning the blank box [item 18'] to the propulsor it should have also mentioned the blank cylinder [item 110] to the rotors.

Both of these blank enclosures represent the undefined variable-speed units.

IMHO, this requirement to drive a pair of main rotors and a propulsor, while simultaneously providing variable speed to the rotors and propulsor, present an extremely difficult challenge for the power-transmission section of any engineering department.


However having said that; the title of application 20070125907 and subsequent patent 7,434,764 says;
"Variable speed gearbox with an independently variable speed tail rotor system for a rotary wing aircraft."

Please correct me if I am wrong, but it appears to me that Sikorsky can patent their 'gear-trains', as shown, but in no way can they consider this as patenting anything related to the design of variable speed mechanisms. This being the case, why does the phrase "variable speed" have such prominence in the title of their patent? Why does the phrase "variable speed" appear 25 times within the patent. :confused:

________________________

Thank you for the side note related to the narrowing of claims during prosecution.
Interestingly, the above patent 7,434,764 has a divisional application patent 7,651,050, dated January 26, 2010.


Thanks for your much-appreciated explanations.

Dave


Edit: 1/ Bold - by me. 2/ Clarified.

[Rigid Rotor]

What are the vibration levels on the X2? With all that hinge-offset, how have they managed it? I remember the early flights on a prototype hinge-less rotor with 14% offset (without vibration dampers then) - the vibrations did threaten to shake loose our teeth fillings! :ooh:

[The Sultan]

CEFO

Unless he is phote'ed with missing teeth or blood coming out of one or more orifices a test pilot will say it is smooth, ready for production, what are we waiting for, etc...

I remember on the Commache first flight that this was their response, forgetting to mention all of the cockpit screens went blank.

The Sultan

[Ian Corrigible]

Not wanting to put words into his mouth, but I seem to recall Nick once saying that his main concern on the vibration front was the interaction between blade wake and the pusher prop at high speeds.

Interesting quote from Mark Miller in the article posted by CEFOSKEY ("open to teaming or investors"). Reminiscent of the lukewarm commitment to the project's future given by some of SAC's execs over the past year. Without wanting to provoke Mart (again :E), I'm beginning to wonder whether we will ever see an application for the technology, or whether the beancounters are now questioning its cost/benefit ratio in the marketplace.

Regardless, Jeff Pino himself seems more optimistic about the project's progress once flights resume, saying last week that he expects to see the 250 kt milestone achieved by July.

I/C

[IFMU]

The TD incorporates a lot of AVD parts from the 92 In this old video, they mention the vibration control is there to smooth it out as they push up to the high speeds. I wonder if they have turned it on yet.

RFCAHibb8UU

Unless he is phote'ed with missing teeth or blood coming out of one or more orifices a test pilot will say it is smooth, ready for production, what are we waiting for, etc...
Standard work up in your parts? If they really have a problem I sure hope them boorish spares are up to the task.

I remember on the Commache first flight that this was their response, forgetting to mention all of the cockpit screens went blank.Too bad Nick isn't here anymore. Maybe John Dixson can confirm that Comanche shook like you say.

-- IFMU

[JohnDixson]

IFMU:

One of the things re the RAH-66 was the vibration story. I refer to 1/rev and n/rev. Just to be sure I sent a note to the project pilot Rus Stiles and he confirmed that from start to finish, they never made a 1/rev adjustment on the original blades and never had to do anything about the 5/rev. I only flew that machine once with Rus and from hover to Vh ( ~165 KIAS or so ) it was remarkably smooth. It was also amazingly easy to fly. It was.....but I'd better not get started down that road.

I had to send another note back re the screen issue. I recall that they did lose some screens, but I think the instrumentation screens were working fine so they continued. I'll let you know further when Rus gets back.

Rev 1: From Rus Stiles:

All the screens went blank – but, yes we had critical parameters on both the instrumentation and a display driven directly by the flight control computers.

This back up display shared media with the far right screen – when it detected loss of communication from the avionics, it automatically switched over to the flight control computer. It had critical warning/caution messages, air data and performance information.


Rus refers to the two large MFD's in each cockpit. That glitch was fixed and did not recur.



Thanks,
John Dixson

[IFMU]

John,

Thanks for the update. When I re-read The Sultan's post, he does not state that vibrations made the displays fail. I must have jumped to a conclusion, I am sure he was going somewhere else with that thought.

In surfing around today, I found the UTC annual report has an X2 video clip. One quote from the video: "Vibration levels, I tell you what, very nice." Maybe that is code for screens going blank, they don't say though. In the video clip I could only see the left screen and it seemed to be working.

Video at:
UTC Annual Report (http://www.utc.com/About+UTC/Company+Reports/2009+Annual+Report+English)
You can skip the intro, though it has one X2 picture on it. When you get past that, click on the technology picture with the turbofan engine on it. Then there is a link to the video on the left.

-- IFMU

[JohnDixson]

The X2 team is happy with the vibration levels at the modest speeds achieved to date, but of course the next testing phase will be challenging in that respect as well as several others. As opposed to the XH-59 design, however, they have S-92 style active vibration absorbers installed and available for use if need be. I'm just a rabid fan on the outside now, but I have high hopes for that team.

Thanks,
John Dixson

[Dave_Jackson]

The XH-59 was was built to accept vibration dampers. Apparently they were never installed because Sikorsky stop work on the craft after it lost the competition.

In retrospect, it is unfortunate that they did not slowly continue with R & D, since testing the craft with dampers, etc. might have been beneficial to the development of the X2.

[NickLappos]

Dave said, ".......Sikorsky stop work on the craft after it lost the competition."
There was no competition, Dave. The XH-59 fulfilled its contract, a follow-on was discussed but not funded, and later (much later!) the X2 was built. A sister contract at the same time was the XV-15, both were administered by the same Army engineering group.

Ian, I believe what I once posted was concerns that the small prop on the X2 was in some pretty poor air behind the fuselage, so that it wouldn't be as efficient as one would hope.

The RAH-66 Comanche was pretty smooth, vibration was never an issue in any maneuver or speed I had flown, and there was no vibration absorber or suppression system ever installed. This is typical of stiff, thin gunships, where the structure is very rigid. Big open cabins with door cutouts and flat spans breed vibration problems.
Pilot lore that "bad" rotor heads produce vibration is just that, mythical. All rotors produce vibrations, what we feel is how the fuselage reacts to that vibration.

[IFMU]

Too bad Nick isn't here anymore. -- IFMU
I stand corrected! Welcome back Nick.

-- IFMU

[Dave_Jackson]

Hi Nick,


Me said; Apparently ...... Sikorsky stop work on the craft after it lost the competition. Nick said; There was no competition,David Lednicer said;"I worked on the ABC late in its life .... The US Army decided they didn't want it. The tilt rotor helped bring about its demise."
Me say; I stand corrected; also.


CEFOSKEY get ready to apologize to Nick; also.
Years ago he corrected me to the fact that the XH-59 didn't crash. It had "a hard landing".
_____________

It's good that your back and fighting. Perhaps stimulating technical discussions can return to PPRuNe.


Dave

Editrd to add remark by David Lednicer.

[Dave_Jackson]

CEFOSKEY

This is all I know. (http://www.unicopter.com/0891.html#Doman) http://www.unicopter.com/NoIdea.gif

Dave

[Dave_Jackson]

CEFOSKEY,

The Web page has been revised.

Thanks.
Dave

[IFMU]

XH-59B was a proposed variant similar to the X2TD + Piasecki speedhawk, a ducted fan pusher prop configuation, however transmission tech at the time was the limiting factor back in 1983 (or so Ive been told by a few "old timers").
Sikorsky has not been claiming new transmission technology as part of the X2 suite. Reference this quote from the Sikorsky website:

The Sikorsky X2 TECHNOLOGY™ demonstrator aircraft will incorporate several new technologies and demonstrate them in a flight environment. These technologies include an integrated Fly-by-Wire system that allows the engine/rotor/propulsor system to operate efficiently, with full control of rotor rpm throughout the flight envelope, high lift-to-drag rigid blades, low drag hub fairings, and Active Vibration Control.

Found here:Sikorsky X2 info (http://www.sikorsky.com/vgn-ext-templating-SIK/v/index.jsp?vgnextoid=40c96eb78fa78110VgnVCM1000001382000aRCRD )

-- IFMU

[Graviman]

Nice to see that the X2 discussion is still along the lines of technical merit of X2. :ok:

Nick, your occasional considered comments are very welcome. Hopefully the thread will stay non-political so that any technical feedback you care to offer will not tread on the toes of other well considered high speed helicopter development.

----

An explanation of just how complicated helicopter vibration can become!:uhoh:


The best analogy of how a blade behaves in flight is to look at a skipping rope dangling in the effect of gravity (ie one end free the other held). If you wiggle the end at various speeds you can induce any number of tension wave modes along the fixed length. In a rotor this tension is clearly generated by the centrifugal force. The tension waves are also being sped up by bending waves which are themselves a combination of shear waves (wavespeed independent of frequency) and flexural waves (wavespeed proportional to frequency^0.5), but this only really alters the resonance frequency at which each tension wave occurs.

The fuselage will potentially respond to any of the the blade modes transmitted through the hub. Ideally the number of blades and Nr is chosen to avoid any excitation of the structural modes of the fuselage. The combination of blades resonating around the azimuth at relative phases can produce symmetric modes and antisymmetric modes in the axis symmetry of the rotorshaft. The fuselage sees the symmetric modes acting vertically on the rotor head, but for antisymmetric modes there is the complication that the rotor is in a rotating frame while the fuselage is in a static frame. This means that the antisymmetric mode frequency will apply a bending moment to the rotorhead with two simultaneous frequencies, shifted higher and lower by Nr/60 Hz than the original resonant frequency in the blades. To explain this would require use of DeMoivres elegant theorem, multiplying two Euler number representations of sinusoids for rotating and static frame. Anyone up for imaginary numbers?


Of course all of this is then actually excited by the cyclically varying aerodynamic loads, which will increase as the helicopter speeds up and the swash plate moves to keep the blades flapping to equality...:bored:

----

Suffice to say the X2 rotor dynamicists will have been extremely busy to get all of this right!;)

On X2 the vibration is absorbed at (or close to) the hub by phased eccentric balancers. This means that even if there was a potential to excite the fuselage then the Moog system should take care of it. The best measure of blade dynamics is really how the tips move, for which there are sensors in X2. Even the tail prop behaviour in the pulsing rotor downwash is likely to have been studied in some detail in either testing of coupled CFD-FEA analyses. So the flight test program is ideally just looking for unexpected interactions.

Hopefully, all will go smoothly when new gearbox is fitted up. But don't expect anything to happen quickly. The reason for flight test is to explore the unknown, so the best way to proceed is very carefully. That way by the time this technology becomes commercially available the major risks will have been found and corrected. This is true of any well managed project... :)

[JohnDixson]

Dave Jackson,

The following note from Andy Ruddell, who ran the aero and rotors side of that program, provides the story:

You brought back a flood of memories John. Yes there was one designed (and built). It happened during the great rotor index debate - 0 deg vs 60 deg. At 60 deg the predominant vibration is lateral and longitudinal at 0 deg. The aircraft was phased at 0 deg when you flew it. A lateral absorber was designed, built and shipped to West Palm. It was big enough to almost fill the entire cabin. It was never installed. Shortly thereafter we went to 0 deg phase. That is a whole other story.


Thanks,
John Dixson

[Dave_Jackson]

John, thanks for the information.


Mr Ruddell wrote a number of extremely interesting technical documents on the craft back then. In fact, his documents significantly motivated my interest in the ABC concept.


Dave

[riff_raff]

The US Army AATD is also getting serious about sources of NVH other than the rotor system. They just issued a $20 million RFP (https://www.fbo.gov/index?s=opportunity&mode=form&tab=core&id=143e9f132387ec3a2580012126cb7b46) for build and test of drivetrain hardware that (among other things) can demonstrate an 18dB reduction in drivetrain generated noise versus a baseline year 2000 Army rotorcraft. That's pretty significant. Especially since most MRGB's are hard mounted to the airframe directly above the crew area, and thus efficiently transmit annoying, high-frequency drivetrain disturbances through the structure.

Should be good for Army aircrews and would definitely have commercial spin-offs.

[JohnDixson]

The proposal asks for a 55% increase in the drivetrain hosepower to weight ratio compared to US Army year 2000 levels. Any of the drivetrain engineers out there think this is a practical goal?

Thanks,
John Dixson

[turboshaft]

Sounds like an objective reqt. RDS-21 asked for a 35% delta in power/weight, but the split torque face gear xmsn which eventually emerged from the effort for AB3 has an improvement closer to 20%.

[Dave_Jackson]

CEFOSKEY

Speculation #4;
Another attempt at uncovering the source of the elusive shavings. http://www.unicopter.com/Think.gif

Sikorsky's patent US 7,296,767 is for a "Variable speed transmission for a rotary wing aircraft'. As in the previously mentioned patent US 7,651,050, this patent also states 'variable speed' 25 times.

The following sketch is from this patent.
http://www.unicopter.com/Temporary/Patent 7296767.gif

This patent actually describes a two-speed transmission. The rotors turn at a high speed when the clutch is engaged and at a low speed when the clutch is disengaged.
The only way that these rotors can operate at speeds in-between the high and the low is by having the clutches slip.

Does 'riding the clutch' produce the so-called 'Variable Speed'?
Did 'riding the clutch' produce the shavings?

If speculation #4 is correct then just transfer this emoticon to your reply. ~ :D


Dave

[IFMU]

Why would you need to continuously vary the speed for a rotorcraft? That sounds more like golf cart technology to me. Perhaps two speed on that patent means two speed.

-- IFMU

[asianj0e]

To build on what Graviman said and to speculate based on my knowledge of Dynamics, variable rotor speed is probably the best way to go for a high speed coaxial helicopter, but it is not without its difficulties.

If you want to run at one rotor speed for hover up to 250+ kts, the rotor speed will either be so slow that hover performance is lousy (max thrust roughly proportional to the square of RPM) or there will be extremely high drag on the advancing blades at high speed due to compressibility. Neither of these cases is satisfactory and using a high rotor speed in hover and lower in high speed flight solves both problems.

A rotor blade has natural frequencies in both bending directions (beamwise and chordwise), and torsion too. ALL of them change with rotor speed. The issue with vibration is that the blade are excited by airloads at harmonics of the rotor speed. If a rotor turns at 10 Hz (600 RPM) then the blades will be forced at 10 Hz, 20 Hz, 30Hz, 40Hz, etc. A rotor blade had better not have any natural frequencies at those multiples at its intended operating speed, especially if one wants to cut down on cabin vibration and increase blade service life. The big problem with variable rotor speed is that the blade natural frequencies have to be kept away from those multiples for ALL intended rotor speeds. Keeping them located correctly is hard enough at one rotor speed, let alone a range.

[Dave_Jackson]

IFMU,
Why would you need to continuously vary the speed for a rotorcraft?
The accepted definition for a variable speed drive is "a mechanism that is used to transmit motion from one shaft to another which allows the velocity ratio of the shafts to be varied continuously".

The X2 is probably intended to cruise at any speed between hover and maximum forward velocity. Therefore, an optimal situation will be to have the propeller start turning slowly near transitional forward velocity. Then, as the craft accelerates toward maximum forward velocity, the rotational speed and the pitch of the main rotors will proportionately decrease, while the rotational speed and the pitch of the propeller proportionately increases.

This is significantly better than 'shifting gears' on a two-speed gearbox. However, a problem with variable speed power transmission devices is that they consume an unacceptable amount of the power for helicopters, IMHO.

Perhaps two speed on that patent means two speed.
This being the case, why does Sikorsky incorporate the phrase 'variable speed' so widely throughout the above patents? Could it be an attempt to fight off others who seek to develop true 'variable speed transmissions, ( including mine (http://www.unicopter.com/1466.html))?


Dave

[Graviman]

asianj0e,

:D

Talking about torsional and bending frequencies excited by aerodynamic loads might set folks hearts a flutter ;) . Most folks eyes seem to glaze over when the subject of order shifting for antisymmetric modes comes up...


Dave,

AsianJoe has it spot on when he talks about avoid rpms. If there was a need to have more than two rpms then the lightest way is a multispeed epicyclic transmission. In helicopters the engine speed is sometimes varied as a function of indicated airspeed.

Does X2 not have autorotatation for cruise-dash speed ranges?
This would allow any rotor rpm...

[riff_raff]

Thar Sikorsky patent describes a two speed transmission. It gets variable speed the same way the V22 does, by changing engine speed. Turboshaft engines tend to have a narrow range of usable operating speeds. Usually something like 70 to 100 percent under ideal conditions. A two speed transmission would essentially double that range.

However, that transmission schematic shows two types of clutches, a friction clutch and a sprag clutch. And each of those clutches will likely have some reliability issues the way they are being employed.

The friction clutch is being used to synchronize two shafts when the high speed gear ratio is to be engaged. The friction clutch must provide slip until the two shaft speeds are equal, which requires the clutch pack to absorb a great deal of heat energy without failure. That requires a large mass of friction material like CRC. Also, being a device that transmits power solely through friction and not having a reliable way to monitor its condition, good design practice would probably dictate that the friction clutch should be mechanically shunted (with a dog clutch or some similar positive engagement device) once it has fully synchronized.

As others have noted, driveline shaft dynamics can be a real nightmare. The varying and aggressive friction characteristics of carbon materials makes it near impossible to smoothly modulate the slip of a carbon clutch pack. This issue was a real problem for Rolls/Allison on the F-35 lift fan clutch.

As for the sprag clutch, they do not like to operate under overrun for extended periods, such as this Sikorsky design concept would require.

Since they have two engines with an interconnect, they would be better off doing a fully synchronized shift using dog clutches with the speeds controlled by the FADEC's.

[HOSS 1]

Was driving around South Florida today and saw a strange looking coaxial flying machine being chased around the sky by a S-76.

Looked to be going pretty fast,too.

[IFMU]

What model S76?

-- IFMU

[IFMU]

Doesn't say much, but this popped up today:

Aero news x2 article (http://www.aero-news.net/news/aerospace.cfm?ContentBlockID=0d4b17a0-22cf-4e71-ad46-c020e667f9da&Dynamic=1)

[Graviman]

If sightings are X2 then has the new gearbox been installed and ground tested yet? :confused:

----



AATD Drivetrain RFP

The proposal asks for a 55% increase in the drivetrain hosepower to weight ratio compared to US Army year 2000 levels. Any of the drivetrain engineers out there think this is a practical goal?


John, i've given this a little thought, although am still to attend the Cranfield (UK) gear design course (which could make me think again).

The only way the set target is remotely possible is if an epicyclic final reduction was put in just below the rotorhead. Have a look at the differential bevel reduction geartrains driving some propeller installations. With the sort of reduction required for typical helicopter Nr it would likely end up being at least one stage of in plane epicyclic gearsets (with each stage input to sun and output from panet carriers). The potential weight saving would come from having lower torque at the geartrain from each engine (and first reduction stage if two stage reduction was selected).

In terms of materials i would have thought that helicopters have already carefully selected steels with the best tooth contact fatigue life. I'm not very familiar with helicopter gearbox designs - do they already use heat fitted toothed rings over aluminium/titanium hubs?

[JohnDixson]

Graviman, I should have realized that with an RFP out there, the gearbox/drivetrain designers are hardly likely to respond to questions now.

My skepticism re the 55% number is based on watching what the SA engineers, and those at Eurocopter, Boeing and Bell have been doing with each new model. The improvements have been incremental, both in materials and processes. Durability, reliability and ballistic survivability usually countervail the weight reduction process, and it seems like a 55% number is unachievable with the technology available to the designers. Maybe that is a challenging enough statement to draw some rejoinder!

For certain: someone comes up with a 55% lighter drivetrain on a larger helicopter, one that can take ballistic hits, mis-procedures by the maintenance folks, tolerant to production machining realities, and boast high MTBO's, and you'll be looking at the next Engineering VP at that company!

Thanks,
John Dixson

[riff_raff]

John,

A 55% improvement in the average year 2000 gearbox power to weight metric is definitely achievable with currently available aerospace design tools, materials and manufacturing processes. As far as gear and bearing materials, the best option is X-53 for gears and M50NiL for bearings if you need to meet a 30 minute loss of lube requirement. The serious weight reduction will come from novel and clever arrangements of gears, and not from new materials.

The most effective approach to reducing gearbox weight is by minimizing the amount of gear and bearing steel used. Using a gear configuration that keeps the shaft speeds as high as possible going into the final gear stage is beneficial. Higher shaft speeds means less transmitted torque, and less transmitted torque means smaller gears and bearings. However, this concept requires that your final gear stage has a very high reduction ratio, which is difficult with a conventional planetary.

Another current approach is to employ torque splitting. Dividing the torque among many small driving pinions symmetrically arranged about a large bull gear to give balanced mesh forces, usually ends up being lighter than a single larger mesh with fewer parts. Once again, the difficulty here is getting proper load sharing among the many gears.

The other goals in that AATD program will be harder to meet. Improvements in noise, reliability and support costs can be achieved. But I can't foresee a 35% reduction in manufacturing costs. In fact, I would predict just the opposite occurring. Higher performance and reliability will cost more money, not less.

The X2's MRGB is a good example of where rotorcraft gearboxes are headed. It only has a single engine input, but it has coaxial, counter rotating outputs and multiple speed ranges. MRGB's are becoming more complex, which naturally means they will become more expensive.

Regards,
riff_raff

[Graviman]

Riff_raff,

(if that is your real name ;) )

I imagine helicopter gearboxes use straight cut gears for improved power to weight. Helical gears were invented to reduce geartrain NVH, and might help with the noise concerns (it was mentioned somewhere). To avoid the side thrust the norm would be to use two mirror image helical teeth (herringbone). If hobbing machines required an excessive central gap then two seperate gears could be bolted or friction welded together.

Load sharing between multiple planets is an interesting problem. The first solution which springs to mind is the idea of a compliant mount for each bearing housing, restrained by a guide plate to limit radial movement - the problem would likely be how to avoid transmission resonances excited by the rotors. If a hydraulic system is allowed on the planet carrier then each planet could be postioned by a small oil hydraulic ram, so that all planets see equal load. The next problem is then how to stop the rams all bottoming out over time if the oil in the hydraulic circuit is not replenished. This implies the need for a complex mechanical load sharing arrangement. Either way the clever stuff needs to happen in the planet carrier(s).

Of course all this assumes that tail rotor drive requires the one-way clutch to act on the high rpm side of the transmission (otherwise worm gears would get a mention). Are electric motor driven tail rotors outside the scope of the project?

Mart

[IFMU]

I have often wondered why helicopter gearboxes use straight cut gears, when helical gears were invented to reduce geartrain NVH.
Is this really true? I thought that a bunch of the helo gears I've seen were helical cut.

-- IFMU

[Dave_Jackson]

Face gears were being considered for rotorcraft about 10 to 15 years ago. Are they still being considered?

Dave

[riff_raff]

IFMU,

I don't mean to drag the thread off-topic, but to answer your question about the type of gears used in recent helo drivetrains, non-parallel shaft gearsets are predominantly spiral bevel, parallel shaft gearsets are preferably double helical, and planetary gearsets tend to be spur. Each type is used for practical reasons.

While a spur gear might be best for efficiency, spiral bevels or double helicals give better performance with regards to the dynamic tooth loads produced in the typical rotorcraft geartrain with high pitch line velocities. This is due to their better face contact ratios.

MRGB planetaries tend to use spurs gears simply due to the fact that it is very difficult to assemble a planetary with double helicals. Single helicals are not used much since they always have an unbalanced thrust load which makes the bearing arrangement more difficult.

As for Dave Jackson's comment about face gears, NASA spent a huge amount of time and money trying to develop the analysis and manufacturing technology for high performance face gears. Initially they had a lot of promise, but in the end what became apparent is that they had many practical issues that limit their theoretical performance advantages. The main one being sensitivity to mesh displacements under load. Regardless, I believe the Apache block III upgrade includes a face gear in its MRGB.

Regards,
riff_raff

[Graviman]

Riff_raff,

Your comments about gearbox design are most welcome.
Anything which gives technical background will add to the discussion about X2.

[riff_raff]

Graviman,

I'm glad that you found my gearbox comments helpful.

While I know a bit about helo gearbox design, something I'd really like to learn more about are details of the X2's rotor hub and feather bearing design. To me, that seems like a very challenging piece of design work!

riff_raff

[Graviman]

Yes, more info on X2 gearbox and rotorhead would be interesting.


As for Dave Jackson's comment about face gears, NASA spent a huge amount of time and money trying to develop the analysis and manufacturing technology for high performance face gears. Initially they had a lot of promise, but in the end what became apparent is that they had many practical issues that limit their theoretical performance advantages. The main one being sensitivity to mesh displacements under load. Regardless, I believe the Apache block III upgrade includes a face gear in its MRGB.


riff,

Regarding sensitivity to bearing/housing movement: The norm for ground vehicle axle differentials is to use spiral bevel gears for crownwheel and pinions. The spiral allows the line of contact (generally over 3 teeth) to rotate about a point above or below the axle line. This means the differential housing can flex without causing the teeth to spall at the edges. Another side benefit of this is that some worm gear action can be designed in to reduce the ratios a little more, albeit at the cost of efficiency.

Mart

[Dave_Jackson]

riff-raff,

Thanks for the information.


Mart,

The face gears were intended for ratios higher then the Crown & Pinion's maximums of; Spiral Bevel @ 4:1, and the Straight Tooth @ 6:1


Dave

[Graviman]

Apologies, Dave. I could have been a little clearer in my post. :)

What i was driving at is that by putting a spiral in the gears (as opposed to a simple helix or even no helix) then the the gear contact position can rotate about a point offset from the face gear axis. This means that the bearings can flex a little without causing fatigue hot spots near the tooth edges.

For this application i would imagine that it would work if the spiral centre was in plane with the driving gear axis (at contact centre) and the bearings were allowed to float axially. Any flexure in the casing would be taken up by the driving gear moving about the spiral centre to keep an even pressure.

Gear hobbing of crownwheels is done by a tool rotating at the spiral centre. Since i am not sure how face gear profile changes with radius are generated then i cannot be certain whether what i suggest is practical.

[riff_raff]

Graviman,

I believe face gear teeth can be made with a helix angle if desired, or possibly with a shaft offset like a hypoid. Here's a neat website (http://zakgear.com/) on weird bevel gear geometries.

With shaft angles at/near 90deg, face gears begin to have serious limits on face width, due to thinning of the outboard tooth tips on the gear. Of course spiral bevel gears also have face width limits. I believe Gleason recommends no more than about 30% of the outer cone distance as a rule of thumb.

What was a big development issue with the Apache face gear design was the tendency for the mesh contact to move from heel to toe under load. Some of this can be compensated for using lead correction or face profile mods, but these changes may also reduce ultimate load capacity. The Apache xmsn engineers also tried things like cutting the pinion teeth using a slightly tapered blank to improve their face gear performance.

riff_raff

[Graviman]

Riff, that website (and the consultancy) looks pretty good:

http://www.zakgear.com/images/CrWild.gif

So the geometry of face gears is similar to bevel gears, but with the addendum/deddendum radii changing across the contact zone to keep the gear flat. It makes more sense to me now.

I had wondered about contact shifting from heel to toe due to tooth separation loads: One thought that occured was to fit the pinion (if that is the correct terminology for a face gear set) to a spline cut with some spherical curvature. As long as the spline at the pinion centre has more tooth contact area than the gear contact then the stresses would be sensible. The idea is for a simple face gear to mesh with a pinion free to misalign its axis, with the spline acting as a CV joint. The balance of contact forces would make the pinion align itself to the face gear teeth, compensating for any bearing and xmsn distorsion. This could save a bit of weight in the casing etc.

I'll have to get myself onto the next Cranfield (UK) course with some of these ideas in mind. It would be nice to have a better understanding of X2 xmsn first... :8

[riff_raff]

Graviman,

For the most basic form of face gearing, the pinion is simply a conventional spur gear. And that is why face gears seem appealing at first glance, the spur pinion does not require an accurate axial location like the pinion of a spiral bevel gear set would.

Where face gears become tricky is due to the change in pressure angle of the face gear tooth as you move radially along the face width. It is a lower pressure angle at the toe (inner edge) and a higher pressure angle towards the heel (outer edge). This makes them very difficult to grind accurately.

There's lots of good face gear tech data on NASA's server. If you want a good text book, get Faydor Litvin's (http://www.amazon.com/Geometry-Applied-Theory-Faydor-Litvin/dp/0521815177).

Good luck.
Terry

[heli1]

Let me preface this question with the fact that I am not an engineer but I am confused regarding the X2 drive system.
OK...so theMGB has to drive the coax/contrarotating main rotor ....but also presumably the auxiliary propulsion airscrew too or is that driven separately from the engine in some way? Thre's obviously a cluch in there somewhere too to help transfer the power.
I've tried looking at patent diagrams but still can't figure it out so obviously need a primary grade explanation !

[Dave_Jackson]

Mart (graviman)

Simple envisionment: Consider the face gear as having an infinite diameter. In this scenario, its teeth would be cut to gear rack specifications and a perfect mesh would exist. This implies that very high ratios will allow for better fitting teeth.


Heli1'..... I am confused regarding the X2 drive system." You are not alone. Everyone, outside of the X2 project, must be confused.
Perhaps those inside the project are also confused; which is not totally unusual for R&D.



I sometimes wonder if the X2 project is nothing more than a unique marketing campaign that keeps the brand name 'Sikorsky' in public view while little else is going on.


Dave

[riff_raff]

heli1,

As far as I can tell, the aft propeller runs at a fixed speed relative to the main rotor speed, and is shaft driven from the MRGB (without a clutch) similar to a conventional tail rotor. Based solely on the recent patent applications I've seen from Sikorsky, I believe the main rotors/aft propeller of a production X2 are designed to be run at two discreet speed ranges. The MRGB can be shifted between the two speed ranges during forward flight, but probably not during hover. The main rotors/aft propeller torque (or load) split is accomplished via blade pitch control of the main rotors/aft propeller.

All of the multi-speed MRGB concepts I've seen really need at least two engines to achieve a safe, fault tolerant drivetrain architecture. The X2 TD only has a single engine. So if the X2 TD does have a gear shift function, it is likely using a friction clutch somewhere in the MRGB, as that is the only practical way to synchronize shaft speeds with one engine. While this might be acceptable for a TD vehicle, in my opinion it would not have adequate fault tolerance capability for any commercial or military application, due to the temporary interruption of drive power from the single engine to the rotor during a shift sequence.

Regards,
riff_raff

[Dave_Jackson]

riff_raff.

Perhaps there's a future for face gears.

Boeing obtained the following patent last Tuesday.
Method of making a pinion meshing with a given face gear in accordance with altered design parameters (http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=7,698,816.PN.&OS=PN/7,698,816&RS=PN/7,698,816)


Dave

[NickLappos]

No clutches, guys. The whole drive system is tied together, rotors and prop shaft. My guess is that the "permanently" geared prop is a variable pitch assembly that can run at flat pitch, as well as positive (forward push) and negative (aft pull) pitch. If no prop thrust is desired, the pitch is flattened. Prop thrust could be done with a separate thrust lever in the cockpit, near the collective.
The engine governors automatically increase power as prop pitch is increased.
The ABC concept went to ultra speed by slowing down the rotor systems down to about 82% rpm, because the tip mach is the bad actor at ultra high speeds. A guess is that the advancing blade will be at Mach .96 or so at Vmax, so that the tip will be going at .96 Mach - about 1000 fps - as the rotor is turning at 82%Nr at 250 knots. Also, the cyclic pitch is set so that the aft sweeping blade is essentially feathered as the speed increases, since no lift is needed on that portion of either disk (since the other disk has an advancing blade on the same side to provide the lift).
The old ABC pulled about 2.0 G at 25,000 feet, which sent the retreating sides into deep stall, but retained high cyclic control power (the advancing sides retained lots of control.)

[Dave_Jackson]

The following is an addition to Nick's comments about the excessive tip-speed on the advancing blades during high-speed cruise.

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

To reduce this tip-speed, Sikorsky is attempting to minimize the drag at the roots of the retreating blades during high-speed flight. An earlier patent outlined the removal of the airfoil from the root end of the blades, plus some unique blade twisting.

To further minimize this drag Sikorsky was granted US patent 7,695,249, Bearingless rotor blade assembly for a high speed rotary-wing aircraft (http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=7,695,249.PN.&OS=PN/7,695,249&RS=PN/7,695,249) on April 13, 2010. The new patent is for transmitting the blade pitch directives via a torque-tube directly out to the airfoil portion of the blade.

This results in a fixed pitch at the blade root, which is effectively a spar with no induced drag nor negative lift. Perhaps at a later date they may place an independent controlled airfoil over the root spar, with the objective of increasing lift in all flight realms and reducing the moment arm lengths.


Dave

[Graviman]

Dave,

Do you have any section drawings available for X2 blades? Just email me direct if you do. My heli performance program can now flap a single rotor to equality, so I'd like to see how X2 lift/downwash looks with cyclic trimmed for forward flight. It's early days so i am still developing the algorithms to handle inflow roll and counterotating configs. :8

---

Nick,

When you comment about S-69 retreating blades going into deep stall at 2.0g at 25'000ft how was this noticed? Was there increased vibration from tip vortex shedding (multiples times per pass) or did the drive torque go up (or autorotating collective down). If rolling to a bank was there a need to monitor the pedals to stop any uncommanded yaw?

[Dave_Jackson]

Mart,
Do you have any section drawings available for X2 blades?Nope.

You may wish to use the information on patent application US 20070110582 (http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PG01&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.html&r=1&f=G&l=50&s1=%2220070110582%22.PGNR.&OS=DN/20070110582&RS=DN/20070110582) to get an approximation of cross sectional data.


Dave

[riff_raff]

"No clutches, guys. The whole drive system is tied together, rotors and prop shaft."

NickLappos,

So if I understand you correctly, you're saying the X2 TD drivetrain is a single, fixed gear ratio. With rotor speed changes effected only through engine throttling (ie. like V-22), and torque split controlled through rotor and prop blade pitch settings?

It's not that a multi-speed geared rotorcraft transmission can't be made to work with a conventional friction clutch for shifting. Boeing's (unmanned) A160 uses such a system, as did the Bell XV-3 (I believe). Although neither has been/was shifted during flight on a regular basis due to safety concerns.

You also say that the ABC TD could slow the rotor to 82% via engine speed throttling, which sounds like the engine guys (Pratt?) were being very conservative, even with mid-70's turbine engine technology. I'd guess that a modern turboshaft engine with variable compressor geometry, digital FADEC and a well sorted combustor could probably run satisfactorily at 70% engine speed or less.

Would something like a 100% to 70% speed range be satisfactory for what the X2 wants to do?

Thanks for the input.
riff_raff

[Dave_Jackson]

Mart,Do you have any section drawings available for X2 blades? ... My heli performance program can now flap a single rotor to equality, so I'd like to see how X2 lift/downwash looks with cyclic trimmed for forward flight. You have previously commented on the coaxial-ABC operating in an autorotative state. You may therefore find this report of value, due to the large stall region at the root end of the retreating blades. Observations in flight of the region of stalled flow over the blades of an autogiro rotor (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930081508_1993081508.pdf)


Dave

[Graviman]

Dave,

I didn't realise blade element method went back as far as 1939. That paper ranks right up there with the paper by Doris Cohen explaining the origins of vortex panel method as applied to P45 Mustang! :ok:

The biggest difference between theory and practice is the distortion of inflow that results from ingested air passing over other blade elements first, and the distortion of outflow from fuselage/empennage. I'm going to try to account for both in my code once it starts to take shape. I briefly had the cyclic trimming to requested flight speed and climb last week - but it is early days and results are not always stable. Unfortunately my weekends are being gobbled up currently, since i am doing one last surge to get my phys degree finished. :rolleyes:

[Dave_Jackson]

Sikorsky's X2 needs some competition. :eek:


http://www.unicopter.com/Interleaving_Bolkow.jpg
Derschmidt High-speed Rotor Idea (http://www.unicopter.com/1742.html)

[Ascend Charlie]

Wow, that looks like a 25-30% hinge offset!

[fleigle]

DATE:20/05/10
SOURCE:Flight International
Sikorsky X2 breaks helicopter speed barrier
By John Croft

Sikorsky reports that its X2 advancing blade concept technology demonstrator has achieved 168kt (311km/h) forward speed, putting the dual counter-rotating pusher-prop compound beyond the typical maximum speed for traditional helicopters and outside the reach of the company's S-76 chase vehicle's 155kt capability.

A follow-on flight, expected the week of 24 May, is to see X2 test pilot Kevin Bredenbeck accelerate the LHTEC T800-powered fly-by-wire pusher to 180kt, completing the third of four planned envelope expansion test phases. Phase four, which could begin as soon as mid-June, includes the first attempts to slow the X2's main rotors while opening the speed envelope to 250kt or more.

The prototype is designed with no clutch between the main rotors and propulsor, which requires the pilot to increase forward speed through the variable pitch control on the six-bladed rear propeller. Once in the 180kt realm, the X2's computer will automatically slow the main rotors and increase collective pitch to prevent tip speeds from entering high-drag transonic region, with Bredenbeck correspondingly increasing propulsor pitch to increase the X2's speed as the propulsor also slows.

Ahsish Bagai/Sikorsky

[IFMU]

Article here, some more info than was in the clip in the post above:
sikorsky-x2-breaks-helicopter-speed-barrier.html (http://www.flightglobal.com/articles/2010/05/20/342211/sikorsky-x2-breaks-helicopter-speed-barrier.html)

Interesting they used the photo from Airliners.net, and seem to have misspelled the photographer's name. I wonder if they goofed anything else up in their edit.

http://cdn-www.airliners.net/aviation-photos/middle/5/8/8/1495885.jpg

Looks like they can no longer consider using a Bell 47 (http://www.pprune.org/rotorheads/245168-sikorsky-x2-coaxial-heli-developments-27.html#post5246766), R44, or Bell 206 (http://www.pprune.org/rotorheads/245168-sikorsky-x2-coaxial-heli-developments-28.html#post5253679) to chase it. If this frustrates anybody they could always pick on the boorish spares in the PM article.

-- IFMU

[Ian Corrigible]

I wonder if they goofed anything else up in their edit.
Funny you should say that: the aircraft is now flying in 'high-speed' configuration, with pylon fairing, full-length vert stab fairing and retractable gear, and this is the configuration with which the 168 kt figure was achieved ~3 weeks ago. The airliners.net photo shows the low-speed configuration.

http://i.imgur.com/guS0S6M.jpg

I/C

[Graviman]

Fantastic news! :ok:

Just when some folk were disparaging Sikorsky for technical issues that really are not that unusual for any new development. ;)

So now begins the patient wait to see how the speed envelope unfolds.
Fingers crossed that all goes smoothly. But, remember this is a totally new type of helicopter so nothing can be rushed.

Good luck X2 development team.

[The Sultan]

Only 22 more knots and they reach the speed I have flown routinely in Cobras. 150+ more knots and they can see a tilt rotor pass them by if they look quickly.

The Sultan

[IFMU]

I/C,

Where did that picture come from? I think that is the first pic I've seen on the web of the gear up. Looks great.

Great post Sultan. I had no idea that the cobras were so fast. Why do we even have Apaches?

-- IFMU

[jim63]

Is Sikorsky getting some competition?
370 mph Helicopter? (http://vtolblog.com/?p=2853)

Vertolety Rossii (Russian Helicopter) made an interesting announcement recently in Moscow. They plan to spend $1 billion on researching what they are calling a fifth-generation helicopter. What are the requirements? It must be radar invisible, have extended range (no specifics on what that means,) be equipped with an intellectual arms system, be able to combat fighter jets and reach speeds of 370 mph. They believe that with additional government funding they could have it built in as soon as five years.

The figure of 370 mph is of particular interest to me. Currently, the speed record for a production helicopter was set back in 1986 using a modified Westland Lynx ZB500.

http://vtolblog.com/wp-content/uploads/2010/05/westland_lynx_record-325x243.jpg
Westland G-Lynx Record Holder

That aircraft managed to reach 249.1 mph. What has been preventing us from going faster? Several items, including retreating blade stall which is a problem introduced due to the advancing blade generating more lift than the retreating blade. Another thing to consider is wave drag and the problems of supersonic blade tips. Apparently, they have a plan for how to get around these problems. Maybe they will be using a tilt-rotor setup such as the Osprey V-22? If so, can you really call it a helicopter still? But wait, was the Lynx really the fastest?

http://vtolblog.com/wp-content/uploads/2010/05/sikorskys69-325x115.jpg
Sikorsky S-69

Back in the early 1970s, Sikorsky came up with a way to eliminate the retreating blade stall problem. They developed the S-69 as part of the Advancing Blade Concept program which used a co-axial design and a “feathering” of the blades. This eliminated retreating blade stall and allowed the advancing blades to carry the load. Maximum speed is listed as 322 mph. If Kamov is involved perhaps we’ll see (or not see) an evolution of the KA-50? Alternatively, if they don’t go with a co-axial setup, I’ll be really interested to know how they overcome RBS at such a high speed. What are your thoughts?

[widgeon]

Hmm Intellectual arms system. Does that debate the agressor helicopter into submission ??.

[Ian Corrigible]

IMFU - From an old SAC buddy during AHS last week, but it looks like Wired (http://www.wired.com/images_blogs/autopia/2010/05/x2-flight-9_03-2010.jpg) has a second photo from that same shoot.

jim63 - Sounds like they're describing the Ka-90 (http://sites.google.com/site/stingrayslistofrotorcraft/kamov-ka-90), but that's one of those "we'll believe it when we see it" programs. On the subject of hokum, Kamov is also playing with a jet-assisted Ka-50 (http://sphotos.ak.fbcdn.net/hphotos-ak-ash1/hs525.ash1/30852_391067316265_237472611265_4564525_5613695_n.jpg).

I/C

[riff_raff]

"The prototype is designed with no clutch between the main rotors and propulsor, which requires the pilot to increase forward speed through the variable pitch control on the six-bladed rear propeller. Once in the 180kt realm, the X2's computer will automatically slow the main rotors and increase collective pitch to prevent tip speeds from entering high-drag transonic region, with Bredenbeck correspondingly increasing propulsor pitch to increase the X2's speed as the propulsor also slows."

I'd be interested to see a schematic of the X2 driveline. If there is no clutching (ie. gear shifting) then the only way to reduce the speed of both the main rotors and pusher prop at the same time is by reducing engine speed, which would be rather inefficient for the turbine engine. If both main rotors and pusher prop are mechanically coupled through the drivetrain at a fixed ratio, then changing pitch of one/both will only change load, and not relative speeds.

A change in relative speeds between the main rotors and pusher prop (one speeds up while the other slows down) could possibly be achieved without gear shifting through the use of a single input/dual output differential gearset. Where each of the two output drive speeds are a function of the relative rotor and prop loads. Such a drivetrain configuration could change the relative output speeds with blade pitch (load) changes.

Or maybe Sikorsky convinced Honeywell to add a second power turbine spool to their engine so that the main rotors and pusher prop can be driven independently. Hey, just because it's never been tried before doesn't mean it won't work!

Maybe someone can shed some light on how the X2 drivetrain changes rotor speeds. :confused:

riff_raff

[IFMU]

This was back at post 700.
No clutches, guys. The whole drive system is tied together, rotors and prop shaft. My guess is that the "permanently" geared prop is a variable pitch assembly that can run at flat pitch, as well as positive (forward push) and negative (aft pull) pitch. If no prop thrust is desired, the pitch is flattened. Prop thrust could be done with a separate thrust lever in the cockpit, near the collective.
The engine governors automatically increase power as prop pitch is increased.

[Graviman]

Cattletruck, don't forget that autorotation just means that the main rotor does not require positive torque to rotate. So a clutch is not a requirement for an autogyro flight mode. I would not be surprised if during the proposed 265kias dash speed the main rotor actually supplied torque to the pusher prop.

Sultan, nobody says that 168kts is fast. But, it does prove that the technical issues have been overcome and that the ship is back on the path of a 250kts cruise. Imagine how routinely cruisiing 68+kts faster than your Cobra would feel. ;)

Once X2 has proven itself, i would not be surprised if a 3rd generation ABC (counting S69 as 1st) began to consider what would be required to develope a rotor system which could approach turboprop speeds. Early days...

Chris, that the aerodynamics near the root are more complicated than the CFD predictions does not surprise me. I was actually impressed that the flow was sufficiently non turbulent to allow a vane type of device. Can you give any specifics of the difficulties encountered?

[Rigid Rotor]

@CEFOSKY-That would be assuming 100% serviceability for conventional helicopters, which definitely is not the case!
-typical serviceability would be in the region of 75-80%.

[Rigid Rotor]

you're right on that one CEFOSKEY - I wonder whether the Osprey or any other tilt rotor with all that additional complexity and possible failure modes will ever reach the serviceability & reliability levels of a conventional helicopter....

And on that note, the X2 is definitely the correct way ahead:ok:

O/T - did The Sultan routinely fly at 190 kts in a Cobra? That's its listed VNE, isnt it?

[Dave_Jackson]

#1
The X2 may set a new speed record; due to its very large engine.

#2
The X2 may have an overall efficiency comparable to, or below, that of the V-22.

#3
Outside funding for development will not materialize.
The added hype from #1 will be unable to cover up the aerodynamic and mechanical limitations in #2.

[Rigid Rotor]

Could you elaborate on #2 & #3?:confused:

[Dave_Jackson]

Rigid Rotor,Could you elaborate on #2 & #3? #2
The concerns about the efficiency of the X2 relate to;
The aerodynamics in respect to the effects of reverse velocity, the high profile and parasitic drag and the rotor/propeller interaction.
~ and ~
The power train in respect to independently controlling the speed and torque distribution to the rotors and the propeller. You have commented on the use of a load splitter such as spider gears or 3-way planetary gear, to which I agree. However IMHO, there also must be a means of controlling the specific power distribution to the rotors v.s. propellers in addition to changing their collective pitch setting.
All of the above has been elaborate on in the previous 700 posting and the many linked web pages.

To my knowledge, Sikorsky has not addressed or solved these specific problems.

The primary shortcoming of the V-22 is that of limited capacity (hover). The primary shortcoming of the X2 will be forward speed (cruise). Both craft will/would spend more of their time in forward flight then in hover, which works to the disadvantage of the X2.

#3
I suspect that the Armed Services have become very despondent over the V-22 and the Comanche. When this is combined with the current and future economy, it is doubtfully that any external money will be forthcoming for the X2.

Perhaps Sikorsky should spend more time under the hood (Engineering) and less time polishing the paint job (Marketing). http://www.unicopter.com/Duh.gif


Dave

[Dave_Jackson]

Mart,

Here is an engineering challenge for you.

The earlier S-69 used a pair of jet engines to provide forward thrust. On the X2 the single propeller must produce the large thrust during high speed and high drag flight.

This thrust will be accompanied by a large torque, which must be counteracted by the fuselage. Airplanes have a large wing area to handle this torque, however the X2 has a very small blade area. What effect will this laterally unsymmetrical loading have on the craft?

From pictures it appears that Kamov's solution is coaxial propellers.


Dave

[IFMU]

The Osprey has about the same installed power as a CH53E. It has payload slightly in excess of a Blackhawk. That would be about 12,300 hp and a 14,360lb useful load. This was from Nick's old presentation. On another 174 hp, the CH53E ekes out 36,515 lbs of useful load. The Blackhawk is listed as 10,484 lbs useful for its 3780 hp. Clearly, the Osprey is in the Very Large Engine camp.

Maybe at speed, tilt rotor technology can be more efficient than X2 technology. We will have to see what the numbers are when the X2 boys are done. Partly you have to look at the mission to determine efficiency. If you are just going to use the VTOL capability to takeoff, then go boring a long distance with little payload, then land VTOL, it is a lot of effort to build/pay for/maintain a tilt rotor compared to going a few extra miles to a runway with a real turboprop. If you are flying somewhere for a rescue, with a bunch of hovering, I bet the X2 technology comes ahead in efficiency pretty quickly.

If they achieve 250 kt cruise can you really say that cruise is a shortcoming?

Regarding the propeller torque effect in high speed cruise, I recon it would be about the same as any large turboprop - nothing. There is ample control power in both airplanes and helicopters to deal with things like that. You are getting blade area confused with control power.

Perhaps Sikorsky should spend more time under the hood (Engineering) and less time polishing the paint job (Marketing).
You crack me up! Spend a little less time polishing that website and build something! Or keep polishing the website but why slag off the folks who are actually doing something?

-- IFMU

[Dave_Jackson]

IFMU

Interesting rebuttal.

....... who are actually doing something?
Should technical discussion stop?
Perhaps people will stop reverse engineering Sikorsky's 'something'', if Sikorsky stop marketing their 'something'.

My original post said 'speculation'. That remark still stands.
And, when asked to support a position, I will.


Dave

[Graviman]

Gents,

There are some interesting technical discussions going on here, which is a good thing. :ok:

There is some mud slinging going on, which is a bad thing. :rolleyes:


Can i just ask that we keep the debate about technical merits nice and peacible? :{


I ask this because i know that there are many technical contributors out there who have to make a judgement about whether or not to contribute to this thread. By discussing pros/cons at a technical level without flames it attracts these folks. If the thread descends into acrimony and flames any technical contributors will clam up and we all suffer.

This in not aimed at anyone in particular - i can just see some squabbles brewing.

Thanks. ;)

[Rigid Rotor]

Re- controlling the prop torque-
- The closest example we have for inference is perhaps the AH-56 Cheyenne – I understand it did pretty well and had achieved a dash speed of around 210 Kts during flight testing. Of course, it did have wings with asymmetric incidence angles – perhaps to offset the prop torque?
- So then, given the fact that the Cheyenne (a single rotor configuration) managed the prop torque (with a bit of help from its wings), there’s perhaps little reason why the X-2 with two rigid rotors (and far superior control power) can’t manage it.
- The Cheyenne had a collective mounted twist grip to control its prop pitch – the pilot could dial in the required prop pitch angle and haul up on the collective – that’s quite the dream solution for a pilot to accelerate an attack helicopter!!:}
- However, I understand it also incorporated an automatic system to reduce prop pitch, so as to prevent main rotor RPM decay, in the event of engine failure – I’m sure the X-2 will be having something similar...
- So then - just a question from a simple dim-bulb test pilot -
-what's the fuss all about?

[Dave_Jackson]

Post #728 is simply one person's speculation.

Speculation on this forum, be it about new rotorcraft or rotorcraft accidents, is open to reasoned rebuttal.


A short historical perspective:

Some of the more obvious improvements to the Advancing Blade Concept were presented in reports at the conclusion of the S-69 project. These consisted of; replacing the four engines with one, utilizing a pusher propeller, and significantly reducing the twist on the blades, etc.

At the time, some people were disappointed that the development was not continued. They believed that the ABC presented a unique and potentially viable way of providing rotorcraft with a meaningfully higher cruise speed. Later so did I, and therefore spent a few thousand hours researching, conceptualizing and developing potential methods of creating functional and practical solutions.

It eventually became apparent that my limited neuronal count was unable to find satisfactory answers to the concept's remaining limitations. However, I was willing to freely provide these ideas to others, on the Net and at an AHS convention, with the hope that they might 'spark' a better idea in others. I then moved on in search of other potential areas for VTOL improvement. Shortly thereafter, Sikorsky, with great fanfare, revived the thirty-year-old project.

Over time it became apparent that X2 was little more than a regurgitation of the old and that Sikorsky was not, in my opinion, addressing these meaningful limitations. At this point I began to question the motivation behind this 'project'.


If Sikorsky is has secretly developed one or more advancements, which overcome the ABC's limitations, AND the X2 was designed 'bolt-ready' to accept these advancements, I will sincerely apologize and eat crow.


Dave

[IFMU]

Meanwhile, a flurry of news on X2 announced on the anniversary of Igor Sikorsky's birthday:

Sikorsky-s-X2-chases-world-speed-record (http://www.ctpost.com/news/article/Sikorsky-s-X2-chases-world-speed-record-499655.php)

http://www.ctpost.com/mediaManager/?controllerName=image&action=get&id=190048&width=628&height=471

Chasing a world speed record, Sikorsky Aircraft's chief test pilot finally got the opportunity Tuesday to open up the Stratford company's latest helicopter, flying the X2 at 181 knots.

Kevin Bredenbeck took the aircraft out for a high-speed spin, putting the 216.5-knot speed record clearly on the horizon.

In 2005, Sikorsky unveiled its unique design that includes stacked, overhead counter rotating blades and a propeller at the rear of the aircraft instead of the traditional tail rotor. The company announced plans to go after the 250-knot goal in 2009, when it moved the project to its West Palm Beach, Fla., facility for high-speed testing.

The world's fastest helicopter flight was clocked at approximately 216.5 knots, or 249 mph, in August 1986 by John Eggington and Derek Clews aboard a Westland Lynx in England, according to the Federation Aeronautique Internationale of France.

Sikorsky said it could hit 250 knots, or 287 mph, within months, but much will depend on performance review and weather conditions. But the helicopter is meeting expectations, according to the program manager.

"The X2 technology demonstrator today exceeded average helicopter speeds of a conventional helicopter, generally 160-170 knots," said Jim Kagdis, program manager of Sikorsky Advanced Programs. "The demonstrator is proving out the technologies very well, from the active vibration control system to the fly-by-wire controls. There are no show-stoppers here so far, and now the program turns a corner, as this completes phase three of four. We are flying forward to the 250-knot cruise speed."

Analysts have said the X2 is one of the bright spots in a helicopter industry in need of more creativity and excitement.

If all goes as expected, the X2 could challenge for a number of potentially large military contracts, especially for reconnaissance.

Sikorsky announcement (http://www.sikorsky.com/vgn-ext-templating-SIK/v/index.jsp?vgnextoid=00de6eb78fa78110VgnVCM1000001382000aRCRD&vgnextchannel=162f45d57ef68110VgnVCM1000001382000aRCRD&vgnextfmt=default&pressvcmid=cafeb0da24fc8210VgnVCM1000004f62529fRCRD)

-- IFMU

[Helierez]

Hi, I'm an engineer working on X2. I find the discussions going on here interesting. Though I can't really comment on what hasn't been publicly disclosed, I will say this, the people working on it are some of the best in our company, if not the industry.

The ABC struck me as a good idea and I wanted the company to revive it as well, and soon after the X2 program was started in 2005. Seeing it from the ground up has been a once in a lifetime experience, and being there for first flight was one of my most cherished memories.

Dave, I've gone through your site, and appreciate your collection of information there. However, I feel you've been knocking our small team unfairly. Not quite sure what limitations you are referring to but let's go through them shall we?

1) Vibration - ABC vibration was wicked at high speed. I mean the instrument panel was a blur! We are using AVC (in a novel way for Sikorsky), as has been stated in the press releases. Besides that we have a 4 bladed rotor, which helps. Test pilot comment is that its like sitting on a couch watching TV.
2) Loads - ABC vibratory loads were quite bad, due to hingeless rigid rotor at high speed. It also had high maneuvering loads. Obviously we have better materials to handle the high loads now as well as fly-by-wire.
3) Performance - L/D ratio was just as poor as every helicopter, 3-4. Though we don't have the 250 knot data yet, I expect we will double that. I know you've gone through Mr. Bagai's blade patent. I work with him and can tell you that figuring out the final solution was not easy. The shaft fairing, which can be seen in the popular sci article is another important invention for reducing drag.
4) Workload - the ABC required 2 pilots to fly. X2 has 1.
5) Acoustics - The ABC J-60's were loud. A prop can be clutched.

So...I'm sorry its not a Synchro (honestly, I doubt there would be much difference with a synchro ABC vs. coax...we can discuss if you wish), or that it doesn't go 400 knots like the Russians claim their magic VTOL does. Ideas are a dime a dozen in this industry. What matters is putting your thought into action, design, build, test, and fly!

[Senior Pilot]

Helierez,

Welcome to Rotorheads, and thank you for taking the time to give us a factual post :ok:

[Graviman]

Helierez, many thanks for your thoughts - i'd be interested to learn more about the concept work for X2.


Chasing a world speed record, Sikorsky Aircraft's chief test pilot finally got the opportunity Tuesday to open up the Stratford company's latest helicopter, flying the X2 at 181 knots.


I am just starting to hold my breath a little now. This is getting exciting!


----

Dave, nobody would fault your enthusiasm and efforts to stimulate development in the helicopter industry. As designers & engineers we both know that to take an idea forward requires many stages of investigation: evaluation, optimisation, validation, development, costing, & fabrication. This requires everyone involved to buy in to the numbers, which means that ideas tend to get driven towards the conservative. In helicopters, which among other things save lives, this is a good thing. I am quite sure your questions will have been considered at great depth during the early stages of X2.

One of the reasons i am developing my own helicopter performance calculation methodology is to allow me to ask exactly these sorts of questions and then produce the numbers. Good engineering relies on accurate numbers, without which any answer given cannot be complete.

[riff_raff]

The Army spent a good deal of money performing trade studies and simulations comparing an X2 configuration against both twin and quad tilt rotor configurations for their 20ton Joint Heavy Lift program. I believe the results of those studies suggested the twin tilt rotor configuration was best. However, the study requirements also may have been focused more towards speed, altitude and range, which would naturally favor a fixed wing airframe.

Full tilt ahead: What will follow the V-22?-07/11/2006-Washington DC-Flight International (http://www.flightglobal.com/articles/2006/11/07/210369/full-tilt-ahead-what-will-follow-the-v-22.html)

Of course, the X2 was a more mature technology than either of the JHL tilt rotor candidates. And the X2 is currently in flight test (with private funding), while the QTR and OSTR concepts have not progressed much beyond powerpoint slides (paid for with $30 million of DoD money). So you've got to give Sikorsky's X2 group credit for that.

[Dave_Jackson]

riff-raff,

I think that two of the five entrants were dropped from the competition, then Sikorsky was given some funding to prepare a presentation on their Variable-Diameter Tilt Rotor concept.

Variable-Diameter Tilt Rotor Dusted Off for JHL Study (http://www.aviationweek.com/aw/blogs/defense/index.jsp?plckController=Blog&plckBlogPage=BlogViewPost&newspaperUserId=27ec4a53-dcc8-42d0-bd3a-01329aef79a7&plckPostId=Blog%3a27ec4a53-dcc8-42d0-bd3a-01329aef79a7Post%3a36f8aeda-b332-433e-9d4a-25f9404ee5f2&plckScript=blogScript&plckElementId=blogDest)


Dave

[riff_raff]

Dave,

Actually, three of the original five were dropped. Two concepts from Sikorsky and one from Boeing.

The three concepts that were dropped probably had the lowest technical risk. But apparently, they also did not give the performance leap that the program was looking for.

As for the VDTR, Sikorsky spent a great deal of time and money looking at that. And in the end they apparently came to the conclusion that the rotor's mechanical system would be too complex and unreliable. So I don't know why the JHL program would go back down that path. A variable speed drivetrain is much easier to do than a variable diameter rotor.

Regards,
riff_raff

[Dave_Jackson]

riff-raff,
A variable speed drivetrain is much easier to do than a variable diameter rotor. Totally agree.


IMO, the engine should be operating near its optimal RPM at all times. During hover the rotors should be receiving 100% of the allocated power, and, this power allocation should smoothly transition, so that the Xrotors areX propeller is receiving 80-90% of the allocated power during cruise.

A major limitation is that existing variable power transmission devices, which would control this allocation, can consume a meaningful percentage of the engine's power.

This web page (http://www.unicopter.com/1511.html) is the conceptualization a potential variable controller for an ABC helicopter. Theoretically, it will not consume power during hover and during cruise. However, it will consume approximately 3% of the power at the mid-range between hover and cruise. It also has some detail concerns. It was openly presented 5-years ago so that anyone can freely copy it, or improve on it.

One might hope that Sikorsky would openly or secretly develop a variable controller. One might also assume that this 'unexciting device' would be developed and tested before completing the envelope to wrap around it.


Dave

[riff_raff]

Dave,

A major limitation is that existing variable power transmission devices, which would control this allocation, can consume a meaningful percentage of the engine's power. Depending upon what your definition of "meaningful percentage" is, I might agree or disagree. Here's a traction CVT (http://www.aerodrive-inc.com/content/cvt) that I've been working on. I did a design study for a split path MRGB variator sized for roughly 400 ft-lb at the variator input and a drive ratio of 2.0. The variator components would have added about 105 lbs to the MRGB. The variator input-to-output efficiency would have ranged between 93% and 95% during variable speed operation. With a traction drive, these losses are primarily due to EHL contact spin loss.

Being a split path configuration, only half the power passes through the variator. So worst case, the variable speed device itself would produce less than a 4% loss. Not as good as a gear system, but not too bad either.

The biggest issue with using a traction device like a CVT (ie. a power transfer device lacking positive engagement) in an aircraft drivetrain is how do you demonstrate that it has adequate fault tolerance/reliability?

Regards,
riff_raff

[Dave_Jackson]

riff_raff,

Your patent for a variable speed transmission c/w elastohydrodynamic lubrication is intriguing and thought provoking.


This is just rudimentary musing but, ~ Without a differential in the power-train, the propeller on the X2 may work reasonably well with only a disengagement clutch and a feathering system.

The range of horsepower to be transmitted by the rotors will be large but their rotational speed change will be relatively small. Might a reduced version of your transmission serve the rotors? Any small slippage can be compensated for by the central processing unit.

In addition, could the backside of your cone (30) provide positive transmission when it is fully 'pressed against the backing crown gear (48). If this is possible, there shouldn't be any loss during hover, a medium loss during transition, and a very small loss during cruise, because in cruse the rotors will be receiving a significantly small percentage of the total power.

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

[Graviman]

Hmmm...

N41AX
N525SA

Same machine with different registry? :confused:


Riff,

Thanx for answer on hydraulics thread - wasn't sure what "EMAD" or "AMAD" mounting stood for in mechanical drive pumps?

I imagine you can't go into many details in public space, but is your CVT a lighter / higher power version of the torotrak transmission? Torotrak | Home (http://www.torotrak.com/IVT/works/variator.htm)
http://www.torotrak.com/OneStopCMS/Core/ImageServer.aspx?guid={702e63ea-1e89-464c-86df-514206426b83}&width=263&height=273

How close to production is it or are you just doing the concept work?

Keep an eye out for the Milner drive - large contact area: Milner CVT for High Torque Applications (http://cvt.com.sapo.pt/MCVT/MCVT.htm)


Mart

[Graviman]

There was me wondering if another X2 had come out to play! ;)


BTW roughly what size of team was involved in developing X2?
I'm guessing there was a core concept team that then subcontracted systems to specialist groups like yourself.
Was the team based at Elmira or Stratford?

Mart

[Senior Pilot]

From Flight Global: (http://www.flightglobal.com/articles/2010/06/01/342527/comment-revenge-of-the-nerds.html)

Sikorsky earlier this year took a series of "glamour" shots of the engineering team for its X2 advancing blade concept pusher helicopter. With the help of dark shades, techy helicopter backdrop and slick threads, the engineers did in fact look like cool dudes.
Looks can be deceiving however, and in the case of the X2, that's a good thing.
In a world where immediacy and appearance have become paramount, there are still those who go to work in a cubicle every day and perform a seemingly astonishing feat called thinking. Call the engineers nerds if you like, but you have to like what they do.
In the case of the X2, the engineers were given extra years to think. X2 was "supposed" to fly in 2006 but didn't until 2008. But Sikorsky was in no rush, convinced the future of rotorcraft is to blend the a helicopter's vertical lift with the speed of a fixed-wing aircraft.

http://www.flightglobal.com/assets/getAsset.aspx?ItemID=34420

Like a fine wine, such a vehicle could not be served before its time. Sikorsky had tried in the 1970s with its XH-59A, an advancing blade concept design that was fast but impractical before advances like active vibration control systems.
The Bell Boeing tiltrotor approach can dash at 270kt (500km/h), but Sikorsky believes configuration changes like swivelling the engines to change the lift vector are not the way to go. But while the advancing blade concept's counter-rotating coaxial main rotors overcome the retreating blade stall barrier to rotorcraft speed, the problem remains that in acceleration past 180kt to the X2's planned 250kt cruise speed, the blade tips would go supersonic and thus need to be slowed - no mean feat.
These quandaries took thinking time to solve. Air shows came and went with Sikorsky chief Jeff Pino telling an impatient press that the X2 "will fly when we're ready for it to fly".
The engineers were ready in 2008 for a maiden flight, part of a methodically thought-out four-phase flight test plan - with no hard dates attached.
Last week test pilot Kevin Bredenbeck finished phase three of the flight-test programme, hitting a speed of 181kt in cruise, beyond what's possible for most traditional helicopters. The engineers' automated algorithms successfully slowed the main rotors for the first time, making phase four and its ultimate end goal of 250kt a very realisable goal.
When will it happen? When the thinkers at Sikorsky - the engineers - are ready for it to happen. It will be worth the wait...

[riff_raff]

Senior Pilot,

I was amazed by that photograph you posted. If you know any engineers, you'd appreciate that it must have taken quite a bit of work by the photographer to round up seven Sikorsky engineers that owned suits and dress shoes. ;)

Who knows, maybe the suits were rented?

riff_raff

[Shawn Coyle]

The new MIB!!

[Dave_Jackson]

Hellerez;

Your respected posting appears to address two related but distinct subjects.

The first is the challenges that the Advancing Blade Concept faces in its attempt to become a new generation of rotorcraft.

The second is the assessment of which configuration; the Coaxial, the Intermeshing or the Interleaving is best suited to optimize the ABC, should the above challenges be overcome.


I, and no doubt others, would be pleased to discuses and provoke thought regarding the above, should Senior Pilot not object.

Dave

[Ian Corrigible]

Meanwhile, a flurry of news on X2 announced on the anniversary of Igor Sikorsky's birthday

Which explains the question asked by Graviman in post 748 (http://www.pprune.org/rotorheads/245168-sikorsky-x2-coaxial-heli-developments-38.html#post5729803), 5/25 being Igor's brithday. Hence the new N reg (N525SA) seen on the SHM-41A on flight 12.

I/C

[riff_raff]

Dave,

Besides rotor configurations, another comparison worth some discussion might be how does X2 stack up vs. Boeing's A160 OSR. The OSR is specifically designed for variable rotor speed, so one would imagine that it should be capable of high forward speeds. Right?

riff_raff

[Dave_Jackson]

riff_raff,

True they both have highly rigid rotors but their applications are very different. Here is an earlier discussion about the craft; A160 Hummingbird rigid rotor design (http://www.pprune.org/rotorheads/257363-a160-hummingbird-rigid-rotor-design.html)

The A160 has no need to consider the reverse velocity airflow on the retreating side of its rotor. However, for the ABC, the ability to deal with this reverse velocity is at the heart of whether the concept can be viable.

Earlier in this thread Hellerez mentioned the Russian ABC proposal with its coaxial propellers and its targeted speed of 400 kts. Their knowledge of coaxial propellers (http://en.wikipedia.org/wiki/Tupolev_Tu-95) exceeds that of all others. It will therefore be very, very interesting to see what they propose to overcome this 'reverse velocity' barrier, particularly at their higher speed.

Dave

[IFMU]

Their knowledge of coaxial propellers exceeds that of all others.
Coaxial propellers are not unknown in the western world. Perhaps the knowledgeable western world scientists have decided there is no real benefit to coaxial propellers that is not worth their additonal cost and weight? Surely if they were that good, would not the C130 have them, and every other western military turboprop?

-- IFMU

[Dave_Jackson]

AN-70: Wide-Body Transport Aircraft with Short Take-Off and Landing (http://www.ukraine-eu.mfa.gov.ua/eu/en/publication/content/12651.htm)


Airbus : Extensive Testing A30X Configurations (http://www.pprune.org/tech-log/361585-airbus-extensive-testing-a30x-configurations.html)

[Graviman]

The second is the assessment of which configuration; the Coaxial, the Intermeshing or the Interleaving is best suited to optimize the ABC, should the above challenges be overcome.


I, and no doubt others, would be pleased to discuses and provoke thought regarding the above, should Senior Pilot not object.


Dave, it's a little late for X2 to change configuration now ;) . We could have this discussion on another thread if you wish. X2 configuration would have been chosen using the least risk approach - always a good idea when doing something this new. Optimisation of similar future concepts is another discussion.

[riff_raff]

One approach to aero development that seems to be gaining wider acceptance these days is sub-scale model flight test. This is being done with Boeing's BWB (X-48) (http://en.wikipedia.org/wiki/Boeing_X-48) and with Saab's stealth fighter concept (http://www.flightglobal.com/blogs/the-dewline/2010/04/video-stealth-fighter-demonstr.html) .

Maybe a sub-scale test of the various ABC rotor configurations Dave mentions would be a worthwhile endeavor for someone. It wouldn't be a garage/hobbyist level project. But I'm sure something like a 1/16th scale powered model with interchangeable drivetrain, rotors and some basic data acquisition/instrumentation would be well within the budget of most any university's aero engineering dept. It could even be validated with some CFD work by a few grad students. Seems like a better academic research project than most of the ones I've seen.

riff_raff

[Senior Pilot]

Whats the deal with "hellerez" apparently posting and then immediately deleting the posts in this thread? I have yet to actually catch one, only mentions of them in the subsequent responses.

His post is here: (http://www.pprune.org/5715284-post739.html) No 739. Not at all sure why you don't seem to be able to read it :hmm:

[Dave_Jackson]

Originally Posted by Senior Pilot
His post is here: (http://www.pprune.org/5715284-post739.html) No 739. Not at all sure why you don't seem to be able to read itThe posting by 'hellerez' disappeared at some point in time after your reply to him.
In fact, at the time of his missing post 'hellerez' was not even listed as a member of PPRuNe.:confused:


Dave


Probably because there is no 'hellerez' registered with PPRuNe. The Rotorhead that we are discussing is 'helierez', and his post was there throughout the period being discussed.

Senior Pilot

[Graviman]

I had the same experience, Chris. At first I couldn't see it then when i checked back after reading Dave's post there it was. I figured Hellierez had deleted after posting.

[Dave_Jackson]

X2 Technology™ Demonstrator Achieves 225 Knots, Sets New Top Speed for Helicopter (http://sikorsky.com/About+Sikorsky/News/Press+Details?pressvcmid=a4a2962fa4f0a210VgnVCM1000004f62529 fRCRD)

[The Sultan]

CEFO

Yes it is faster than I have been in a rotorcraft.

Still 8 knots short of what James May has done on a road with a streetworthy car, and 150 knots short of what a tiltrotor can do.

The Sultan

[heli1]

Well done Sikorsky....for continuing the spin. The X2 will have to reach 274 kt to beat the Bell Model 533 and even then neither are true helicopters so arguably it has to also beat the V-22 tilt rotor at 302kt.

[dangermouse]

As discussed many times here

the X2 aint a helicopter, it's a compounded rotorcraft so the Lynx record still stands


(if I fitted a J79 to a Bell47 it would probably go faster than 250 kts but you wouldnt call it a helicopter)

DM

[Graviman]

Congratulations Sikorsky/Schweitzer X2 design team & flight test team: for designing, building & developing the worlds fastest practical VTOL machine! :ok:

Congratulations to Kevin Bredenbeck: for having the gumption to fly it! :ok:

Practical because disk loading is no higher than an S76, so this remarkable machine can safely access the same sites that any conventional helicopter can get into. The concept may have its detractors, who will point out that the machine has not achieved any specific target first. However, the overall capability of this machine from hover to dash speed will revolutionise the helicopter concept. In the near future folks will argue the merits of other configurations against the conventional coaxial configuration...

[NickLappos]

Sounds like some sour grapes from some ppruners regarding what is a helicopter. First thing I did this am was run to the FAI site to find the same words posted below. While common usage differentiates between helos, compounds (aux thrust) and winged compounds, the FAI does not.

Regarding aux thrust, I also recall that the Lynx (whose picture, signed by Trevor Egginton hangs 5 feet from me on my office wall as I write this) had a shaped exhaust to extract all the thermodynamic power the engines had that the transmission couldn't handle. It had 7% aux thrust, as I recall, a big push, indeed.

Having flown the old ABC to these speeds, I guess I too could claim a "record" but wouldn't until the FAI was around, and the aircraft was sealed by their representative. Having helped set a bunch of records back in the day, the official system is fair and the ONLY way a record is set. I also know that the WPB X2 bunch will have them drop by shortly, and blow away the existing helo records.

Having known the previous record holders, all great pilots and great gentlemen, I know they will not grouse like those ppruners below. The daring that is shown when an S67 Blackhawk, or a Russian A10, or a vastly modified Lynx is flown to impossible speeds is also coupled with a sense of dignity and respect. When the X2 sets that record, those pilots, wherever they are, will salute and smile, because they know that we are all fighting something far greater than each other, we are fighting the forces of nature, a much more challenging adversary.

Congratulations, Kevin.

PS, I told Kevin once that he could come to Xworx and do his flying, and be assured of great speed, regardless. If all else failed, he could load the X2 into an Osprey and get to at least 275 knots! ;)

[HeliTester]

Well said NickLappos,

Refreshing to see a post that celebrates the achievement and the achievers!

[Svenestron]

All due respect to NL and a big WORD! to what he wrote.. (this to the passages about test pilots, NL's considerable life achievement as one and so forth..)
I would still contend that:
HELICOPTER: A rotorcraft with A power driven rotor system whose axis (axes) is (are) fixed and substantially perpendicular to the longitudinal axis of the rotorcraft.Substantially perpendicular to the longitudinal axis of the rotor craft..? Now remind me.. What is the position and direction of this “pusher prop”?

Talking of 7% aux. power on the Lynx..
At 225/250 knots, what percentage of the forward thrust do the two main rotors achieve on an X2 in flight..? is it more like 7% than 93% ???
I’m just asking.. cause I do not know.. this is a fact..

[heli1]

Not sour grapes Nick and Cfosky but fact.
The FAI will not judge the X2 as a pure helicopter and so it cannot claim the world helicopter speed record.
There are FAI records for compound helicopters...in fact the Rotodyne was one of the first back in 1959,and if we are talking auxiliary thrust then the Bell 533 compound speed record in 1969 would stand too.

Yes the X2 is a fine achievement but don't let's cheat !

[Graviman]

Helicopter


Cambridge advanced learners dictionary

a type of aircraft without wings, that has one or two sets of large blades which go round very fast on top. It can land and take off vertically and can stay in one place in the air.


Oxford advanced learners dictionary

an aircraft without wings that has large blades on top that go round. It can fly straight up from the ground and can also stay in one position in the air


Dictionary.com

any of a class of heavier-than-air craft that are lifted and sustained in the air horizontally by rotating wings or blades turning on vertical axes through power supplied by an engine.


thefreedictionary.com

... Helicopter was borrowed from the French word hélicoptère, a word constructed from Greek heliko- and pteron, "wing." Heliko-, the combining form of helix, "spiral," has given us helico-, which can be joined with other words and word forms to create new words. The consonant cluster pt in pteron begins many Greek words but relatively few English words. English speakers unfamiliar with Greek are thus not likely to recognize the word's elements as helico-pter; many analyze the word into the elements heli-copter, as is shown by the clipped form copter.



Why not just acknowledge the recent X2 flight as a brilliant piece of engineering, and a brilliant piece of flying, in the tradition of a long line of brilliant pioneering endeavours...

[JohnDixson]

The Talmudic discussion about whether or not the recent flight can claim a record is interesting, but as I listened to Kevin debrief the flight, I was struck by a comment he made in reference to some SAS gain changes that had been made.

Almost as an aside, he said something like: " you know you guys have the in-cockpit cameras on me, and as you probably noticed, my hand was on the cyclic only every 5-8 seconds or so".

That said quite a lot, to me anyway.

Thanks,
John Dixson

[Shell Management]

Would the X2 have a lot of Titanium in it for weight saving reasons?


Footnote for those who lack a classical education:

Talmudic
–adjective 1. of or pertaining to the Talmud.
2. characterized by or making extremely fine distinctions; overly detailed or subtle; hairsplitting.
Talmud
–noun
the collection of Jewish law and tradition consisting of the Mishnah and the Gemara and being either the edition produced in Palestine a.d. c400 or the larger, more important one produced in Babylonia a.d. c500.

[Dave_Jackson]

" you know you guys have the in-cockpit cameras on me, and as you probably noticed, my hand was on the cyclic only every 5-8 seconds or so".It may be of interest to note that in this video of the Flettner 282 the pilot has his hand off the controls for at least 7 seconds.

MdYPQLvuJh8

It may also be of interest to know that this video resulted in Sikorsky removing their claim to being the first to land a helicopter on the deck of a ship.

[IFMU]

Still 8 knots short of what James May has done on a road with a streetworthy car, and 150 knots short of what a tiltrotor can do.

If all else failed, he could load the X2 into an Osprey and get to at least 275 knots!

225 + 150 = 375 if my math is correct. However Nick only offers up 275 kts. Nick, are you holding out on your good buddy Kevin?

All record talk and griping aside, anybody who cannot appreciate or understand the achievement should get off the internet and do something useful! Beyond the 250 kts, assuming they achieve it, is the promise that this 250 kts is not just a flash in the pan. It is a useable technology to really make a rotorcraft faster and retain the good things that make it a helicopter. Low disc loading, and helicopter-like complexity rather than what we ended up with on the Osprey some would see as a plus. There is no marketing or spinning that can achieve 225 kts. That is all engineering.

There is no 't' in Schweizer!

(if I fitted a J79 to a Bell47 it would probably go faster than 250 kts but you wouldnt call it a helicopter)
Do you really think so? That is something I would like to see.

I think this is pretty cool. Way faster than anything I fly. Half the speed of the long tubes I sometimes pay to fly in where I get to sit in the back and drink overpriced beer.


-- IFMU

[IFMU]

Sikorsky's X2 speeds to 259mph - Connecticut Post (http://www.ctpost.com/news/article/Sikorsky-s-X2-speeds-to-259mph-593970.php)

I like the last bit in the article:

Company officials said that the X2's shot at the 250-knot goal will be made in a few months. This raises the question: How fast will it go?

"I'd say that at about 300 knots, you'd start running into other issues," Cizewski said.

http://www.aero-news.net/images/content/general/2010/Sikorsky-X2-Demonstrator-0710a.jpg

[Jack Carson]

One has to ask, what will the limiting factor be? One of the limiting factors in the X-59 was the close proximity of the advancing and retreating blade tips as the speed increased. It appears as if the blades, at the 3 o clock position, are getting very close.

[IFMU]

I wonder if the right bank with respect to the photo frame gives the illusion of closeness.

-- IFMU

[Graviman]

This is just an optical illusion - blades would have to be parallel in the image. There is instrumentation on board X2 to monitor blade tip proximity.

Dave, Flettner definately deserves recognition as a very capable helicopter pioneer. His designs were clever to the point of being ahead of their time.

Dangermouse, none of this detracts from the achievement of the G-LYNX team. It is still the fastest single main rotor helicopter.


Personally i feel that all Rotorheads should be unanimous is wishing the X2 team, and Keven Bredenbeck, the very best of luck & talent in getting this remarkable machine to show its true potential. Another significant step in the history of pioneering aircraft development. :D

[Dave_Jackson]

Graviman

If the technical side of the Advancing Blade Concept is still of interest, you may find the document 'Influence of Lift Offset on Rotorcraft Performance' (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080047716_2008046462.pdf) informative.

The author, Wayne Johnson, wrote the 1088 page book 'Helicopter Theory'.


Dave

[delta3]

Dave

What is the precise definition of lift offset ?

The article you refer to uses the "optimal range" for coaxial at 0.25 which seems low to me. This may rather structurally limited and not aerodynamically optimal.

For instance at 120 knots a theetering rotor produces variations of 35% minimum - 65% maximum on the blades (50%-50% would be equal load in my definitions). How much lift offset is this ?

d3

[Dave_Jackson]

Hi d3,

IMHO, the precise definition of 'lift offset' is; the distance between the center of a rotor's mast and the center of the rotor's thrust vector.

Assuming I understand your your 120 knots example properly, if the teetering rotor was replaced by an 'Absolutely' Rigid Rotor the offset will be; (35% + 15%) = (65% - 15%). I.e it will be 15%

Entering the phrase 'lift offset' into your Internet's [Find box]. after bringing up the following 2 web pages, will get Sikorsky information on the phrase.

0891 (http://www.unicopter.com/0891.html)
1465 (http://www.unicopter.com/1465.html)

Perhaps the lift of the small wing is reducing the offset in Johnson's example craft.

__________________________

It is interesting to see that Johnson is looking favorably at the Side-by-Side-ABC. Stepniewski's last publication before his death recommended the Intermeshing-ABC. Two highly respected rotorcraft aerodynamics have now shown support for the Bilateral-ABC configurations

Sikorsky has apparently hung its hat on the coaxial configuration. If some other company, or perhaps some other country, decides to embrace the Bilateral-ABCs, things could get really interesting.


Dave

[Dan Reno]

CEFOSKEY

Did the latest speed run use the high-speed, low-drag rotor fairing? If so, any pics?

[Graviman]

Dave,

Paper looks interesting, particularly the use of free wake geometry in Camrad II. Interesting that tandems require similar power to coaxials - that may be one to watch.

The side-by-side configs will always apparently fair better because they increase the span of the lifting system. To compare apples with apples i think a constraint of the config should be to define the span then size the rotor accordingly - this defines the landing areas the machine can access. I suspect that coaxial starts to look better with this constraint.

At some point (after proj deadline in Sep) i would like to do a more basic comparison. I've now got a reasonable model for reverse flow, and am just starting to think about inflow effects (critical for counterrotating machines). Don't hold your breath just yet though!

[Dan Reno]

I recall you saying it would provide for some great performance/speed increases. Any guess~timate how much AS it would have added to the last flight using the same power/Q pulled if installed?

[Graviman]

Have any details of rotorhub system ever been released for XH-59/S-69? I recall mention of internal pitch links for top rotor and conventional swash plate for lower rotor.

I imagine that in cruise the air between the rotors is sourced from rotors in starboard azimuth (upper lift and lower reverse flow) and sunk from rotors in port azimuth (upper reverse flow and lower lift). This would set up a crossflow which would tend to pull any hub fairing to port slightly (tapered roots will help reduce this). Also the fountain effect in hover could be lots of fun'n'games.

Early days of a new type - teething troubles are to be expected.

[Dave_Jackson]

Graviman

This voluminous report should provide a wealth of data on the XH-59A for the program that you are developing.
Performance and Loads Data from a Wind Tunnel Test of a Full-Scale, Coaxial, Hingeless Rotor Helicopter. (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19820004167_1982004167.pdf)

Also, a US patent on the faring between the X2's rotors is available on the net.


Dave

[IFMU]

Courant article about reaching 235 kts, and debating if the X2 is a helicopter or not:
courant x2 story (http://www.courant.com/business/hc-sikorsky-helicopter-reaches-250-kn20100817,0,799021.story)

Maybe they got the idea from us here!

-- IFMU

Sikorsky Aircraft's quest to produce the world's fastest helicopter raises one question above all: How fast?

As of Tuesday, the date of the X2 prototype's most recent flight, the answer was 235 knots, the latest increase in a steady advance toward the avowed goal of 250 knots, or 287 mph. That's nearly 100 knots faster than conventional modern helicopters' top speed.

Another, more philosophical question has also been popping up lately: Is the X2 really a helicopter?

Stratford (http://www.courant.com/topic/us/connecticut/fairfield-county/stratford-PLGEO100100201200000.topic)-based Sikorsky, one of the world's biggest, most famous helicopter makers, says yes. But in the wonky world of aviation enthusiasts, there's debate. And Sikorsky's steady stream of public announcements about the X2's boundary-pushing progress has prompted some observers to raise the question — and answer it with a resounding no.

"The X2 is a compound aircraft, not a true helicopter," said Elfan Ap Rees, the editor of Helicopter International magazine in Great Britain, who objected after Sikorsky's July 26 statement that the X2 had reached 225 knots, setting an unofficial speed record. "…The X2 is a fine technological achievement with great promise and Sikorsky should be proud of that and not belittle its success with inaccurate claims."

The 5,000-pound, single-pilot X2 has one engine, two counter-rotating main rotors on top — and a rear "pusher" propeller to give it extra thrust.

Geoff Russell, a spokesman for AgustaWestland, a Sikorsky competitor in Europe, also said the X2 does not qualify as a "pure helicopter" because it generates power from a device other than the main rotor atop the aircraft.

"The X2 therefore will not be able to claim the speed record set by the Lynx helicopter in 1986," he said, referring to the souped-up version of a Westland helicopter still on record as the fastest.

(According to the Washington (http://www.courant.com/topic/us/washington-PLGEO100104900000000.topic)-based National Aeronautic Association, a non-profit U.S. organization that certifies aviation records, a Westland Lynx remains the record-holder for speed, at 216 knots, or 249 mph. Sikorsky plans to invite an NAA representative to attend a test flight of the X2 once it reaches 250 knots, expected later this year.)

But Sikorsky is making no apologies for its innovations, and confidently insists the X2 is no mere rotorcraft, a broad term that includes helicopters, but a bona fide helicopter.

"We stand by our claims," company spokeswoman Marianne Heffernan wrote in an e-mail.

The Fédération Aéronautique Internationale — an international organization based in Switzerland that certifies world aviation records (and which X2 critic Elfan Ap Rees serves as honorary president of the rotorcraft committee) — defines helicopter in a way that would appear to include the X2.

Section 9 of the group's Sporting Code for rotorcraft, available on the NAA website, says a helicopter is a "rotorcraft which, in flight, derives substantially the whole of its lift from a power-driven rotor system whose axis (axes) is (are) fixed and substantially perpendicular to the longitudinal axis of the rotorcraft."

By the FAI's own definition, Sikorsky's X2 seems to fit. It generates lift from its main rotors — the ones on top — which spin on an axis perpendicular to the lengthwise axis of the aircraft's body.

While the axis of the pusher prop is horizontal, like the aircraft's lengthwise axis, the pusher prop does not generate lift — only thrust, Sikorsky said. The X2 does not rely on wings for lift, or anything else; it has none.

"The X2 demonstrator is considered a pure helicopter because all of its lift is derived from its rotor system rather than being augmented by wings," Steve Weiner, Sikorsky's director of engineering sciences and head engineer for the X2, said in a statement. "No other helicopter meeting these criteria has cruised at 250 knots to date."

Other helicopter-like aircraft have traveled at 250 knots and faster, such as the V-22 Osprey, a high-speed aircraft made by a partnership of Bell Helicopter and The Boeing Co. (http://www.courant.com/topic/economy-business-finance/manufacturing-engineering/aerospace-manufacturing/boeing-co.-ORCRP017215.topic) But it has large wings and two dramatically adjustable rotors. The experimental Bell 533, which traveled at more than 270 knots, had stub wings and jet engines.

Whatever the squabbles among helicopter purists, advances in aircraft technology are blurring the lines between long-recognized types of flying machines — even for people who have been flying them for decades.

"It's actually a good question," said Jay Brown, a former Army helicopter pilot in Vietnam who is the executive director of the Combat Helicopter Pilots Association. "It's come up before when we talk about people who are eligible for membership in our organization."

Brown said his group has concluded that the V-22, for example, a so-called tilt-rotor helicopter, should not count as a helicopter, because its rotors swivel from a horizontal to a vertical orientation for forward travel.

"The V22 is not a helicopter," he said in an interview. "When it shifts from hovering flight to forward flight, it becomes an airplane." (Boeing, one of the V-22's producers, agrees, describing it as a tiltrotor aircraft that takes off and lands like a helicopter, but converts into a turboprop airplane.)

Brown says the X2, despite the pusher propeller at its rear, meets his concept of a helicopter, because its top-mounted rotor system "stays where you expect a helicopter rotor system to be."

"If you were in theory to remove the rotor system, it would stop flying," Brown said of the X2. "It has to have the rotor system spinning in order to maintain flight. I think it's still a helicopter."

The American Helicopter Museum and Education Center, near Philadelphia (http://www.courant.com/topic/us/pennsylvania/philadelphia-county/philadelphia-%28philadelphia-pennsylvania%29-PLGEO100101023010000.topic), keeps things simple by opting for a flexible definition.

Said president Sean Saunders, "It changes with every new invention."

[Dave_Jackson]

The X2 is a union of the helicopter's powered rotor and the gyrocopter's powered propeller.
Perhaps it should be called a UniCopter. http://www.unicopter.com/RollLaugh_1.gif http://www.unicopter.com/RollLaugh_2.gif

[Hilife]

Geoff Russell, a spokesman for AgustaWestland, a Sikorsky competitor in Europe, also said the X2 does not qualify as a "pure helicopter" because it generates power from a device other than the main rotor atop the aircraft.

That device being the Gas Generator, eh Geoff. ;)

On the subject of [other] power (lift/thrust), many conventional helicopters with in-line gas turbine engines (including Lynx) derive some of their forward thrust from the ejection of the engine exhaust gas stream in a rearwards direction, so that’s Lynx discounted is it not Geoff?

And what about lift/thrust derived from a canted tail rotor assembly (BlackHawk/CH-53 etc). With application of forward cyclic, does not the resultant lift/thrust moment generated by the tail rotor assembly - now angled slightly forward – contribute to overall forward thrust, thereby producing some additional force from a device [other] than the main rotor atop the aircraft?

Does this mean that any helicopter with an canted tail rotor does not qualify as a “pure helicopter?”

And so the debate goes on..........

[heli1]

Hilife is absolutely right.The canted tail rotor produces lift and thrust ,as does the main rotor.This qualifies it as a helicopter.The X2 prop only produces thrust and becomes the driving force in forward flight,not the rotor system which is actually slowed to produce less power in forward flight.

The Lynx got away with it because the power was all through the rotor system and the aft facing engine exhausts produced only the residual thrust as is common on many helicopters, such as Bell 212,Hughes OH-6 .Some others redirected to one side ,to counterct torque and others up into the rotor system.

[Graviman]

235 knots! Congratulations test pilot, test team and design team.

X2 hovers like a helicopter, transitions like a helicopter, cruises like a helicopter, and has the ability to autorotate like a helicopter.

When the ABC technology is handed down to commercially available machines i have no doubt what the machines will be called.

[heli1]

Because it looks like a duck, waddles like a duck, and swims like a duck doesn't meant it is a duck Graviman !
Could X2 stay aloft at high speed on slowed down main rotor lift alone......that is the question.

[IFMU]

Could X2 stay aloft at high speed on slowed down main rotor lift alone......that is the question.
I would expect it would stay aloft on main rotor lift alone, after all what else is keeping it aloft in the first place? If the thrust went away, surely it would decellerate though.

I guess I am in the camp that thinks the X2 fits this definition exactly:
Section 9 of the group's Sporting Code for rotorcraft, available on the NAA website, says a helicopter is a "rotorcraft which, in flight, derives substantially the whole of its lift from a power-driven rotor system whose axis (axes) is (are) fixed and substantially perpendicular to the longitudinal axis of the rotorcraft."

-- IFMU

[Graviman]

This all reminds me of the recent astronomical debate to decide upon the fate of Pluto. Planet or planetoid, i'm sure Pluto really wasn't overly concerned. ;)

Whatever definition is selected to accurately describe X2, it is a significant step in pioneering aviation. This makes Kevin Bredenbeck a pioneering aviator. These flights have demonstrated that a machine with low disk loading can achieve high speed flight without significant compromise to its low speed performance. Ultimately this means that ABC technology can filter out to EMS and other arenas where the ability to get to destination is as important as the ability to hover over or land at destination. I doubt the beneficiaries of such a service will concern themselves with how the machine is defined...

[heli1]

Graviman...Absolutely agree with you so why do Sikorsky muddy the waters by claiming X2 is something it plainly isn't?

The FAI clearly agrees if the statemnent attributed to their president is true,to whit the only way it can be a true helicopter is for all the dynamic lift and power to go through the rotor sytem (apart from engine exhaust Cfoskey).Otherwise it is clearly a compound...or even a gyrodyne as some of the autogyros also used a powered rotor sytem to jump/take off before switching to prop power for forward flight and the rotor to provide just lift.

Reminds me of Sikorsky's long ago argument about being the first to fly the (practical)helicopter when Igor actually had to rely on Cierva patents to make the VS300 work and even then was beaten by the French,Belgians ,Brits and Germans!!

[IFMU]

The FAI clearly agrees if the statemnent attributed to their president is true,to whit the only way it can be a true helicopter is for all the dynamic lift and power to go through the rotor sytem (apart from engine exhaust Cfoskey).
I think they said power-driven rotor system , nowhere do I see that all the power has to go through the rotor system. If this is true, then a conventional helicopter is not a helicopter because it has power going to the tail.

[Shawn Coyle]

Heli1:
The record-setting Lynx had the engine exhausts very specifically modified to generate quite a lot of thrust. Westland never released any photos of the modified exhaust, but it contributed significantly to the forward thrust.

[heli1]

I can see our colonial cousins are never going to be satisfied

IFMU seems to think that a pusher prop is the same as a tail rotor (which has pitch links et al and actually takes power out of the dynamic system).I would argue there is a big difference between this and an airscrew that takes power away from the rotor.

Shawn is correct in part although there are pictures of the aft facing exhausts on G-Lynx,in particular in the book " Putting the Record Straight "by Dave Gibbings ,senior Westland flight engineer at the time.He explains how the engines were boosted in power using water injection to feed the uprated transmission and how the exhausts were turned to face aft to get rid of the 600lbs of residual thrust. The importance here is that it was residual and not the prime means of forward speed.The aircraft was also fitted with additional tail fins because the tailrotor could not counteract the increased torque suppiled to the main rotor.Again evidence that the drive was predomimantly through the rotor system.

[riff_raff]

The X2 has less power (essentially zero) going to the tail rotor/pusher prop in hover than the G-Lynx does.

[Graviman]

This thread is actually turning into an interesting discussion on where the boundaries lie for what folks consider to be a helicopter. Part of me can't help but hear the nostalgic cry for the way things were... ;)


heli1, what i understand you to be saying is that Sikorsky/Schweizer engineers should have compromised the design, maybe by tilting the rotor system to do away with the pusher prop, in order to keep the coveted title of "helicopter"?

Let me turn the problem around by asking what anyone has to gain by denying X2 the title "worlds fastest helicopter"?

Also, regarding tail-rotor/pusher-prop then i wonder how long it will be before the prop becomes teetering to remove any sideslip/climb pitch/yaw cross coupling. Once this happens then how long before a cyclic mechanism is introduced to improve yaw response characteristics (say FBW to vector powered flight and autorotation correctly).


Personally, my interest in X2 is that it promises to bring high speed helicopter flight to the wider fleet which is constrained on landing/hanger space and operational cost. What it is called does not affect my interest in the ship.

[heli1]

Graviman.....Of course Sikorsky/Schewizer are pursuing a very useful and potentially valuable course and no way would I suggest they should have compromised the design.
What they have is a fine Compound Helicopter ,in the traditions of the Piasecki 16H,Lockheed Cheyenne and similar high speed designs with pusher airscrews ,some of which went faster than contemporary helicopters of the same period but still could not qualify for the absolute title as " The World's Fastest Helicopter" .
Compound is what it means..a mix of powered rotary wing and aeroplane ,unlike the autogyro which is a mix of unpowered rotary wing and powered aeroplane .Further the FAI has a category for Compounds although I admit it isn't published on their website but ....I recall the Rotodyne set up a closed circuit record for compound helicopters in the late fifties so it must exist.
Finally what we are talking about here is not about anyone gaining anything but accuracy and getting things right instead of dumming down technological and historical progress. .

[Landroger]

I'm not a chopper pilot, though I wish I was, indeed no kind of a pilot at all - an engineer, who has found this thread to be very interesting indeed. The current question of whether the X2 is a 'proper' helicopter and relative speeds etc., reminded me of the machine I saw at Farnborough all those years ago. It seemed like a good idea at the time, but it obviously wasn't. :sad:

From what I remember, the Rotodyne was an autogyro? I know it used engine bleed gas for the tip 'jets' (?) and I vaguely remember reading something about 'afterburning' the bleed gas in the tip pods to provide something. But that would defeat the autogyro principle would it not?

In any event, does anyone remember how fast the Rotodyne was, what with those big old Dart's pulling it along. I know it was damn noisy! :eek:

Roger.

[Jack Carson]

My minimal experience in the X-59 (ABC) lends me to believe that both arguments may be correct. At lift off to a hover the X-2 is a pure coaxial rotor helicopter just like the X-59. Once the X-59 accelerated to more than 200 KIAS under power from the J-60s, the engine torque from the 2 PT6 rotor drive motors dropped to 0%. At that point the helicopter was an auto-gyro. The question is, at 235 KIAS is any of the S-2's engine torque going to the main rotor system.

[Dave_Jackson]

At lift off to a hover the X-2 is a pure coaxial rotor helicopter just like the X-59. Once the X-59 accelerated to more than 200 KIAS under power from the J-60s, the engine torque from the 2 PT6 rotor drive motors dropped to 0%. At that point the helicopter was an auto-gyro.
http://www.unicopter.com/ThumbUp.gif


The question is, at 235 KIAS is any of the S-2's engine torque going to the main rotor system. IMO the answer is; A portion of the power should be delivered mechanically to the rotors during all cruise speeds. These slow turning rotors are then partially contributing to the forward thrust and not representing such a large drag.
It is claimed that even the simple gyro-copter will benefit from some mechanically powered rotor-assist.

However, this calls for Reverse Velocity Utilization (http://www.unicopter.com/B473.html) and Variable Speed Transmission (http://www.unicopter.com/Variable_Speed.html); two features that Sikorsky appears to be unwilling or unable to provide.


Dave J.

[slowrotor]

Heli1 has almost got it right... the X2 is almost a compound helicopter because the X2 lacks a wing surface.

"COMPOUND HELICOPTER- rotorcraft with driven rotors, additional means of propulsion, and using aerodynamic lift." (from VTOL by Mike Rogers 1989).

The words aerodynamic lift in this definition refers to a fixed wing.


The X2 is not a "pure helicopter" but it is also not exactly a compound because it lacks a wing.
slowrotor

[heli1]

Slowrotor.....So that big tail surface doesn't contribute lift at the aft end ??

[XV666]

So that big tail surface doesn't contribute lift at the aft end ??

Since it appears to be an inverted aerofoil giving a downthrust (a normal helicopter design requirement) what do you think?

If it was producing lift, there would be quite an issue with aft cyclic authority to keep the fuselage level!

[slowrotor]

The surfaces at the tail are for stability or trim.
A lifting wing must be attached at or near the aircrafts center of gravity.
slowrotor

[Graviman]

Interesting that non of these definitions state a requirement for level flight... :E

X2 would be able to sustain high speed flight in descending flight without the pusher prop. Not sure what ROD would be required for 235kias.

[heli1]

I suspect the definitions are in the small print as it would be obvious that any aircraft can go faster in a dive.... however that assumes it can complete the set distance ! The aircraft also has to complete two runs in opposite directions to get an average.

[riff_raff]

If you simply move the tail rotor to the starboard side of the fuselage and face it forward, is it still a helicopter? (ie. the Fairey FB-1)

http://www.airwar.ru/image/idop/heli/gyrodyne/gyrodyne-2.gif

ps. This should make Dave Jackson smile. (http://www.theregister.co.uk/2010/08/25/kaman_unmanned_cargo_win/)

[Dave_Jackson]

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

[heli1]

The fairey FB1 was a gyrodyne...as was its big brother the Rotodyne.
The main rotor became unpowered in forward flight.

[TXSIK]

Sikorsky X2 Technology Demonstrator Achieves 250-Knot Speed Milestone (http://www.sikorsky.com/About+Sikorsky/News/Press+Details?pressvcmid=9f0cd4ef0661b210VgnVCM1000004f62529 fRCRD)



September 15, 2010

http://www.sikorsky.com/vgn-ext-templating-SIK/v/images/flags/U.S.A..gif WEST PALM BEACH, Florida - Sikorsky Aircraft Corp.’s X2 TechnologyTM demonstrator today successfully achieved a speed of 250 knots true air speed in level flight at the Sikorsky Development Flight Center, accomplishing the program’s ultimate speed milestone. Sikorsky is a subsidiary of United Technologies Corp. (NYSE:UTX).

The speed, reached during a 1.1-hour flight, is an unofficial speed record for a helicopter. The demonstrator also reached 260 knots in a very shallow dive during the flight.
“The aerospace industry today has a new horizon,” said Sikorsky President Jeffrey P. Pino. “The X2 Technology demonstrator continues to prove its potential as a game-changer, and Sikorsky Aircraft is proud to be advancing this innovative technology and to continue our company’s pioneering legacy.”
“Our primary key performance parameter has been met,” said Jim Kagdis, Program Manager for Sikorsky Advanced Programs. “The 250-knot milestone was established as the goal of the demonstrator from its inception. It’s exciting to imagine how our customers will use this capability.”

Kevin Bredenbeck, Sikorsky’s Director of Flight Operations and Chief Pilot for the company and for its X2 Technology program, manned the milestone flight. Bredenbeck said the demonstrator has been performing well, meeting expectations of performance predictions and progressing with every test flight.
“I’m proud of what the X2 Technology team has accomplished,” Bredenbeck said. “This was truly a collaborative effort that demanded a tremendous sacrifice from the full team. This dedication enabled the demonstrator to hit this historically high mark.”
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 that a helicopter can cruise comfortably at 250 knots while retaining such desirable attributes as excellent low-speed handling, efficient hovering, and a seamless and simple transition to high speed.
The X2 Technology program began in 2005 when Sikorsky first committed resources and full funding for the program’s development.
Mark Miller, Sikorsky Vice President of Research & Engineering, said: “The X2 Technology program is an initiative of our Sikorsky Innovations team, and today it offers a clear and exciting validation of our ability to take on the toughest challenges in vertical flight.”

[IFMU]

Outstanding!

-- IFMU

[Dan Reno]

FANTASTIC JOB SIKORSKY !!

It'll be interesting to see what the competition can do in the future.