Go Back  PPRuNe Forums > Aircrew Forums > Rotorheads
Reload this Page >

Sikorsky X2 coaxial heli developments.

Rotorheads A haven for helicopter professionals to discuss the things that affect them

Sikorsky X2 coaxial heli developments.

Old 15th Oct 2009, 01:12
  #501 (permalink)  
 
Join Date: Dec 2000
Location: Arlington, Tx. US
Posts: 696
Likes: 0
Received 11 Likes on 7 Posts
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
The Sultan is offline  
Old 15th Oct 2009, 02:48
  #502 (permalink)  
 
Join Date: Oct 1999
Location: Den Haag
Age: 57
Posts: 6,242
Received 329 Likes on 183 Posts
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.
212man is offline  
Old 16th Oct 2009, 00:52
  #503 (permalink)  
 
Join Date: Dec 2000
Location: Arlington, Tx. US
Posts: 696
Likes: 0
Received 11 Likes on 7 Posts
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
The Sultan is offline  
Old 16th Oct 2009, 01:28
  #504 (permalink)  
 
Join Date: Mar 2005
Location: Poplar Grove, IL, USA
Posts: 1,088
Received 72 Likes on 53 Posts
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
IFMU is offline  
Old 16th Oct 2009, 02:45
  #505 (permalink)  
 
Join Date: Apr 2003
Location: Vancouver, BC, Canada
Posts: 1,635
Likes: 0
Received 0 Likes on 0 Posts
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 and addressing Sikorsky's problem.

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.



Dave

Last edited by Dave_Jackson; 16th Oct 2009 at 13:48. Reason: changed link
Dave_Jackson is offline  
Old 16th Oct 2009, 11:22
  #506 (permalink)  
 
Join Date: Jul 2005
Location: UK
Posts: 915
Likes: 0
Received 1 Like on 1 Post
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.
heli1 is offline  
Old 16th Oct 2009, 11:59
  #507 (permalink)  
 
Join Date: Feb 2003
Location: Somerset
Posts: 282
Likes: 0
Received 0 Likes on 0 Posts
nice idea

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


DM
dangermouse is offline  
Old 17th Oct 2009, 07:19
  #508 (permalink)  
 
Join Date: Sep 2007
Location: USA
Posts: 601
Likes: 0
Received 0 Likes on 0 Posts
Mast moments

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
riff_raff is offline  
Old 17th Oct 2009, 22:48
  #509 (permalink)  
 
Join Date: Mar 2005
Location: Poplar Grove, IL, USA
Posts: 1,088
Received 72 Likes on 53 Posts
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
IFMU is offline  
Old 18th Oct 2009, 10:03
  #510 (permalink)  
 
Join Date: Jul 2005
Location: UK
Posts: 915
Likes: 0
Received 1 Like on 1 Post
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.

Last edited by heli1; 18th Oct 2009 at 10:04. Reason: Couldnt spell
heli1 is offline  
Old 19th Oct 2009, 02:12
  #511 (permalink)  
 
Join Date: Mar 2005
Location: Poplar Grove, IL, USA
Posts: 1,088
Received 72 Likes on 53 Posts
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.

Originally Posted by heli1
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.

Originally Posted by The Sultan
(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
IFMU is offline  
Old 19th Oct 2009, 03:07
  #512 (permalink)  
 
Join Date: Oct 1999
Location: Den Haag
Age: 57
Posts: 6,242
Received 329 Likes on 183 Posts
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!
212man is offline  
Old 19th Oct 2009, 07:55
  #513 (permalink)  
 
Join Date: Jul 2005
Location: UK
Posts: 915
Likes: 0
Received 1 Like on 1 Post
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 .
heli1 is offline  
Old 19th Oct 2009, 15:51
  #514 (permalink)  
 
Join Date: Oct 2002
Location: 1 Dunghill Mansions, Putney
Posts: 1,797
Likes: 0
Received 1 Like on 1 Post
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 is offline  
Old 19th Oct 2009, 17:50
  #515 (permalink)  
 
Join Date: Oct 2002
Location: 1 Dunghill Mansions, Putney
Posts: 1,797
Likes: 0
Received 1 Like on 1 Post
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
Ian Corrigible is offline  
Old 19th Oct 2009, 18:14
  #516 (permalink)  
 
Join Date: Nov 2004
Location: Cambridgeshire, UK
Posts: 1,334
Likes: 0
Received 0 Likes on 0 Posts
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

Last edited by Graviman; 19th Oct 2009 at 18:30.
Graviman is offline  
Old 19th Oct 2009, 19:15
  #517 (permalink)  
 
Join Date: Apr 2003
Location: Vancouver, BC, Canada
Posts: 1,635
Likes: 0
Received 0 Likes on 0 Posts
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. 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 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 is offline  
Old 19th Oct 2009, 20:00
  #518 (permalink)  
 
Join Date: Apr 2003
Location: Vancouver, BC, Canada
Posts: 1,635
Likes: 0
Received 0 Likes on 0 Posts
CEFOSKEY,

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

Dave
Dave_Jackson is offline  
Old 20th Oct 2009, 00:52
  #519 (permalink)  
 
Join Date: Mar 2005
Location: Poplar Grove, IL, USA
Posts: 1,088
Received 72 Likes on 53 Posts
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

Last edited by IFMU; 20th Oct 2009 at 00:53. Reason: Clarification
IFMU is offline  
Old 20th Oct 2009, 11:52
  #520 (permalink)  
 
Join Date: Nov 2004
Location: Cambridgeshire, UK
Posts: 1,334
Likes: 0
Received 0 Likes on 0 Posts
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.
Graviman is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.