PAK-FA Secrets

[ORAC]

From AWST (Ares): PAK-FA Secrets Via YouTube (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%3ac3f1c693-d1d6-4f37-b3fd-e7f16e087b2e&plckScript=blogScript&plckElementId=blogDest)

Just popped up on YouTube, a couple of interesting T-50 videos. The first is an overview of some of the technologies involved in the aircraft.

Noteworthy points: the video highlights a new honyecomb core material designed for high temperatures. It also states that the T-50 will have no fewer than five radar arrays: the 1500-module forward active electronically scanned array (AESA), two side-facing X-band sub-arrays and two "decimetric" (L-band) arrays in the leading-edge root extensions. It also states that the goal is to fight the F-22 by closing within visual range.

Another new video shows a novel inlet radar blocker.......

[glad rag]

Hmm we need to do two things, put cats on the carriers and buy these!!

[barnstormer1968]

So, as a serious question, and as a bit of a sub thread, so as not to have two on this subject, Which aircraft would we be better off buying.

I have no idea myself, as I have no real knowledge of the modern systems involved. So, what do techies or pilots want?

This is assuming we could only buy one of the types (forgetting politics), and that the Typhoon could become the A to G future platform only. If those conditions don't suit you, just add your own:ok:

[Shaft109]

There are some comments on this video about forward swept wings manufactured from composites, basically that the Russians are the first to do this. But I thought it had been done back in the 1980's with the Grumman x-29?

[bobward]

Forward swept wings have been around for a long time. The Germans seem to have lead on this, with the Hansa Jet in the 1960's. Before that, they tested the idea on (I think) an Arado jet bomber during WW2.

I remember seeing an old B&W picture of a machine with a jet pod either side of the nose, and FSW.

Anyone else out there remember this?

[Groundgripper]

Junkers 287?

Junkers Ju 287 - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Junkers_Ju_287)

[ORAC]

Utilised in the civil market post wAR, not just in WWII prototypes.

HFB-320 Hansa Jet. (http://en.wikipedia.org/wiki/HFB-320_Hansa_Jet). Flew in service (http://www.hansajet.de/indexeng.htm) as a VIP transport for over 20 years.

http://www.hansajet.de/bilder/1025/1025manching-aussen-2.jpg

[LowObservable]

I'm fairly sure that the X-29 wings had metal internal structure, and this may be what the Russians are talking about.

[Machdiamond]

Unrelated to PAK-FA but, LO you are correct about the X-29:

"The [X-29] wing structure primarily is composites with special aeroelastic tailoring to help compensate for a forward swept wing's tendency to wash-in under load and, in so doing, to increase the wing's divergence speed. [...] The wing sub-structure is aluminum and titanium."

From: Jay Miller - The X-Planes.

[Double Zero]

By aerolastic tailoring, I presume what is meant rather than aerodynamic aids ( though I'm sure they're involved ) is the technology I read about a long time ago, where carbon fibre is 'trained' at the manufacture stage to 'grow' inwards under load, helping avoid tip divergence.

What strikes me as must be the especially tricky bit is getting the stuff to respond at a suitable rate to correspond with airspeed...

Oh and more importantly, don't forget Thunderbird 2...

[ORAC]

From Air Power Australia. (I know a lot of people on here have a thing against Kopp, but the paper isn't by him, so can we keep any ad hominem attacks out of it?)

Why the F-22 and the PAK-FA have the “Right Stuff” and why the F/A-18 and the F-35 do not (http://www.ausairpower.net/APA-NOTAM-300310-1.html)

[Double Zero]

I'd like to be the next Tom Clancy too, but I've actually worked with AMRAAM, and anyone who has will have first raised eyebrows then have laughing fits...

Similar response to the Russian PAK 50 job P.R. Which claims it's aim is ' to get in close to the F-22 and engage in close combat ' ?!

From personal experience, I would make a fair bet that the Russian engineers and Test Pilots are beating the P.R. people with planks...

[barnstormer1968]

Double Zero




Russian engineers and Test Pilots are beating the P.R. people with planks...

The Russians are moving on in leaps and bounds in their technology.....In cold war days it would have just been plain old sticks:}

[racedo]

The Russians are moving on in leaps and bounds in their technology.....In cold war days it would have just been plain old stickshttp://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/badteeth.gif

Ah the benefit of moving from a Communist country controlled by a small group within the party to a free Country controlled by a small group who have lots of partys.....NO ?

[Naked_recommiting]

4983 posts ORAC and you offer a paper from APA?

[John Farley]

DZ

Your post 10

Not quite. It is simpler than that. The 'grain' or direction of the plies in the carbon fibre structure is optimised so that if you picked the aircraft up by its wing tips the wing would not twist. Or if you prefer the structure's torsional axis is aligned with the direction of the spars.

JF

[petit plateau]

JF,

Are you sure that it is a simple as you say ? (or am I not understanding you which is more probable).

I recall discussing forward sweep issues as part of a conceptual design group and my colleagues (who were NASA) explained to me that it is not just the static forces but the dynamic forces. Setting aside the very stiff wing approach one needs to use composites. To prevent them becoming unmanageable one needs to lay up the composite so that it benefits from bend/twist coupling to counter the aerodynamic loads. We discarded this architecture but I put it in my mental file of difficult things. I now find myself in an industry (wind turbines) where people are actively playing with the same structural approach of building in coupling to address a similar aerodynamic issue hence my keeping an eye on this.

I think it is best explained here, certainly better than I can:

Grumman X-29 - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Grumman_X-29)

In a forward swept wing configuration, the aerodynamic lift produces a twisting force which rotates the wing leading edge upward. This results in a higher angle of attack, which increases lift, twisting the wing further. This aeroelastic divergence (http://www.pprune.org/wiki/Aeroelasticity#Divergence) can quickly lead to structural failure. With conventional metallic construction, a torsionally very stiff wing would be required to resist twisting; stiffening the wing adds weight, which may make the design unfeasible.[5] (http://www.pprune.org/#cite_note-Pamadi-4)
The X-29 design made use of the anisotropic (http://www.pprune.org/wiki/Isotropic) elastic coupling between bending and twisting of the carbon fiber composite material to address this aeroelastic effect. Rather than using a very stiff wing, which would carry a weight penalty even with the relatively light-weight composite, the X-29 used a laminate which produced coupling between bending and torsion. As lift increases, bending loads force the wing tips to bend upward. Torsion loads attempt to twist the wing to higher angles of attack, but the coupling resists the loads, twisting the leading edge downward reducing wing angle of attack and lift. With lift reduced, the loads are reduced and divergence is avoided.[5] (http://www.pprune.org/#cite_note-Pamadi-4)

Also see:

Aeroelasticity - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Aeroelasticity#Divergence)

Regards,

pp

[LowObservable]

The aeroelastic tailoring was explained to me by a fabric analogy: the skins are "cut on the bias" - the plies don't go direct from root to tip, so that if you bend them up they want to shear fore or aft.

Next, put opposite bias in the upper and lower skins so that one shears forward and one back.

Bolt skins to substructure so that shears oppose each other. The wing then bends without twisting.

[petit plateau]

My understanding is that you are correct about the bias (although it can be achieved through orientation of the internal structure as well as of the composite - there's more than one scale available to work with).

However the aim is to make it twist, but to twist the opposite way to that which one would expect.

"As lift increases, bending loads force the wing tips to bend upward. Torsion loads attempt to twist the wing to higher angles of attack, but the coupling resists the loads, twisting the leading edge downward reducing wing angle of attack and lift. With lift reduced, the loads are reduced and divergence is avoided"

[Double Zero]

JF,

Thanks, I do fear it's not as simple as all that, but Petit Plateau mentioning ' twist ' is getting us into a whole different bag of snakes I think you'd agree.

As I read it, the carbon fibre for forward swept wings was pretty special, and the wingtips did indeed lean forward under aerodynamic load.

Of course that was just an article and whether this theory was ever put to the test is another matter, unless the Russians are doing it now.

You're in a position, in so many ways, to know !

The important thing for me, ( as you know I'm not going to be dogfighting or BVR'ing in the things anyway ) was that after many, many years of my Dad taking the p' out of Thunderbird 2 " they've put the wings on the wrong way round ", I was finally able to put the article and pic's of the X-29 under his nose !

DZ