What happened to FSW

[JohnR]

What happened to the various Forward swept wing concepts and projects.

In the late eighties early nineties there seemed to be loads of projects involving FSW the Grumman X29 and the Sukhoi S37 were the flying examples, but now nothing.

Were the concepts proven wrong? Did something better come along? Or what?

Look forward to your answers.

Regards

 

[quellish]

What happened to the various Forward swept wing concepts and projects.

In the late eighties early nineties there seemed to be loads of projects involving FSW the Grumman X29 and the Sukhoi S37 were the flying examples, but now nothing.

Were the concepts proven wrong? Did something better come along? Or what?

Look forward to your answers.

Regards

It's pretty difficult to make them stealthy head on. That's a primary reason the concept fell out of favor.

 

[Just call me Ray]

There were also some twisting and rigidity concerns too, though the advances in materials since that time have made that issue no longer an issue, at least by what I have been told.

If we can figure out how to make it stealthy, if stealth just becomes no longer worthwhile due to anti-stealth radars - or if those "plasma fields" actually work - we may see some FSW designs after all. We might see some FSW civilian designs too, though it doesn't seem there's a lot of enthusiasm for them.

 

[Merv_P]

http://forum.keypublishing.co.uk/showthread.php?t=51199&highlight=fsw

Great minds think alike... ;D I asked the same question in the Key Publishing forums a couple of years ago. The replies were pretty comprehensive - you might find some help there.

(edit) and this thread in whatifmodelers:

http://www.whatifmodelers.com/index.php/topic,19361.0.html

 

[flateric]

It's pretty difficult to make them stealthy head on. That's a primary reason the concept fell out of favor.

This is bullshit, sorry. At least one operational FSW vehicle exist, and one of the reasons forward-swept was choosen for it, is, in fact, reducing RCS.

The problems that have arised, eveng using top-notch composite materials, are still wing divergence, causing damage to wing strucrure and unsolved aerodynamics problems at high subsonic and supersonic speeds. Later was only discovered in real life and didn't show up during WT tests and scale model drop tests.

At least that what did happen to S-37. While aircraft continues intensive test flight program, being involved in PAK FA development program (weapon bay tests, etc), its flight envelope was significally downgraded due to microcracks they have discovered in wing carry-through box. Test pilot Igor Votintzev's remarks of what happening to Berkut at M=0,95 are not unlike of those stories of 'sled drivers' when they talk of Habu engine unstart.

 

[Spring]

Saying that everything was designed in the AGM-129 to be stealthy..is what i call bullshit.

Same overhipping bullshit as in the Tacit Blue, it have conventional wings, these have nothing to do with the so-called "stealthy" features, but mostly, because aerodynamic balance.

 

[quellish]

It's pretty difficult to make them stealthy head on. That's a primary reason the concept fell out of favor.

This is bullshit, sorry. At least one operational FSW vehicle exist, and one of the reasons forward-swept was choosen for it, is, in fact, reducing RCS.

The problems that have arised, eveng using top-notch composite materials, are still wing divergence, causing damage to wing strucrure and unsolved aerodynamics problems at high subsonic and supersonic speeds. Later was only discovered in real life and didn't show up during WT tests and scale model drop tests.

At least that what did happen to S-37. While aircraft continues intensive test flight program, being involved in PAK FA development program (weapon bay tests, etc), its flight envelope was significally downgraded due to microcracks they have discovered in wing carry-through box. Test pilot Igor Votintzev's remarks of what happening to Berkut at M=0,95 are not unlike of those stories of 'sled drivers' when they talk of Habu engine unstart.

I disagree, and we'll leave it at that.

 

[Avimimus]

At least that what did happen to S-37. While aircraft continues intensive test flight program, being involved in PAK FA development program (weapon bay tests, etc), its flight envelope was significally downgraded due to microcracks they have discovered in wing carry-through box. Test pilot Igor Votintzev's remarks of what happening to Berkut at M=0,95 are not unlike of those stories of 'sled drivers' when they talk of Habu engine unstart.

Interesting, indeed. I remember the official reason given for the removal of FSW configurations at an early stage in the PAK FA program was that the production process was slow and couldn't be automated (requiring a lot of skilled labour). Thus, it was felt to be unaffordable for a mass production aircraft. Unfortunately, I don't remember the reference.

 

[flateric]

Wing box (http://www.technologiya.ru/tech/compositee/index.html) was made by my hometown based NPO Tekhnologia (http://www.technologiya.ru/tech/misc/maine.html), known as production plant for Buran shuttle TZMK-10 and 25 insulation tiles and bunch of other hi-tech composite things, like S-300 missiles nosecones. While producing prestressed prepreg for FSW aircraft wing is tryly complicated process, they have enough experiense to make this process automated - well, Topol-M components filament-wounding is no less tricky.

Remarks of S-37 problems go from Sukhoi and TsAGI insiders, and were confirmed by Sukhoi hi-rank engineer in Rusian edition of Popular Mechanics. Heavy buffeting at certain speeds and AoA.

 

[OM]

This is bullshit, sorry. At least one operational FSW vehicle exist, and one of the reasons forward-swept was choosen for it, is, in fact, reducing RCS.

...Care to cite source on that one? Except for the X-29, I can't recall any operational vehicle that was FSW, and it damn sure had no claims on lowered cross section. The damn thing was a modified F-5!

 

[flateric]

...Care to cite source on that one? Except for the X-29, I can't recall any operational vehicle that was FSW, and it damn sure had no claims on lowered cross section. The damn thing was a modified F-5!

Well, once more...

 

[sferrin]

It's pretty difficult to make them stealthy head on. That's a primary reason the concept fell out of favor.

This is bullshit, sorry. At least one operational FSW vehicle exist, and one of the reasons forward-swept was choosen for it, is, in fact, reducing RCS.

Couple things to keep in mind in this case: 1. it's got dihedral so the reflection off the leading edge is going to go off the horizontal plane and UP. 2. The fuselage has a lot of RAM on it as I recall so it absorbs at least some of the bounce.

Biggest reason I've heard for no FSW is they suck in practice One old engineer made the comment regarding the FSW "we have to try it again every forty years or so to remind us of why we didn't choose it in the first place". Also for stealth, keep in mind that part of being stealthy is being able to accurately know WHERE your return is going. A FSW is going to flex more than a conventional wing (unless your wing weighs a ton) so now your leading edge has some curve to it when you turn. Basically the pluses of a FSW are far outweighed by their negative aspects.

 

[flateric]

Some evil tongues insist that both Sukhoi FSW TD and unsuccessfull initial T-10 'gothic' wing shape were just an experiments performed using state funds for someone's Sc.D. thesis...

 

[Sundog]

Some of the limiting factors to FSW are

1) Max. Mach number of 1.7. Sure, you could make one for a higher Mach number, but it's weight penalty would be higher than that of a conventional swept wing, therefore, it's a net loss, not a gain for the design.

2) Aircraft with broad chords at the root and a small chord at the tip are more structurally efficient, such as delta and diamond shaped wings, and tend to offer more internal volume which is great for carrying fuel. That's why they are typically chosen over a FSW.

We know we can "make" FSW's, but just because you can doesn't mean you should. If a FSW was better than a conventional wing for a given mission, it would be used. That's why that stealthy cruise missile has it; for the given performance specs and how they had to put the package together, that was the best solution they could come up with at the time. You don't see it on a combat aircraft because there are better solutions for those design configurations satisfying those missions.

After all, one of the main reasons FSW were investigated was for their performance at high AOA. However, as we have seen through the use of thrust vectoring and advanced FCS's, we don't need FSW for the high AOA regime. As such, one of the reason's for the FSW have been rendered moot. I also think it would be interesting to know if the weight fraction of a FSW is higher than that of a conventional wing for a given performance/mission, as they both will be aero-elastically tailored, only the more conventional wing won't have to contend with divergence like the FSW does. Of course that last part is probably directly proportional to the limiting speed. i.e.- the higher the speed the greater the weight penalty in direct relation when compared to a conventional wing planform.

 

[frank]

Does the Hansa jet count as being operational?

This is bullshit, sorry. At least one operational FSW vehicle exist, and one of the reasons forward-swept was choosen for it, is, in fact, reducing RCS.

...Care to cite source on that one? Except for the X-29, I can't recall any operational vehicle that was FSW, and it damn sure had no claims on lowered cross section. The damn thing was a modified F-5!

 

[Jemiba]

"Does the Hansa jet count as being operational?"

On the Flugzeugforum (http://www.flugzeugforum.de/), you can find a complete
list of the built examples and their fate, just click "Forum", then "Suchen" and type in
"Hansajet". Several aircraft even had a military career, but it should be added, that the
forward swept wing was chosen for similarv reasons as in the Ju 287. The designers
wanted to get a cabin unobstructed by the wingspar.

 

[Airborne2001]

"Does the Hansa jet count as being operational?"

On the Flugzeugforum (http://www.flugzeugforum.de/), you can find a complete
list of the built examples and their fate, just click "Forum", then "Suchen" and type in
"Hansajet". Several aircraft even had a military career, but it should be added, that the
forward swept wing was chosen for similarv reasons as in the Ju 287. The designers
wanted to get a cabin unobstructed by the wingspar.

Nice find with a non-UAV example.

With the issues of FSW at speed, maybe (I'm not an expert so don't judge me lol) a light attack aircraft would work? A maneuverable plane to dodge missiles and ground fire, though I wonder how storing weapons under the wing would work...

Maybe that would help the problem? The addition of the podded engines under the Ju-287 wing helped to fix flexibility problems.

Again, not an expert, but I think this is an interesting thought experiment.

 

[publiusr]

In addition to handling airflow--were variable geometry set-ups developed that would move the wings as a suspected radar was passed?

 

[FlyGuy369]

In addition to handling airflow--were variable geometry set-ups developed that would move the wings as a suspected radar was passed?

I mean Northrop Grumman seemed to think so.

 

[samardza]

I mean Northrop Grumman seemed to think so.

Different speed range but the v-22 is forward swept

 

[FlyGuy369]

Different speed range but the v-22 is forward swept

I feel that if more engineers were willing to go further and get down and dirty with forward swept wings to the point that remedies could arise to make them practical, then we could better appreciate their utility.

 

[overscan (PaulMM)]

Some engineer said something along the lines of 'every twenty years we take FSW off the shelf and confirm again that it doesn't work'.

 

[Archibald]

Some engineer said something along the lines of 'every twenty years we take FSW off the shelf and confirm again that it doesn't work'.

Just like SSTO or nuclear fusion, then... or hydrogen aircraft. So many dead ends.

 

[TomS]

Different speed range but the v-22 is forward swept

But not very much and only to provide adequate clearance for the flapping prop rotors. They would have preferred not to have if swept at all because it introduced a lot of mechanical complexity in the cross shaft. Hence the V280 having a dead straight wing instead.

 

[Airborne2001]

Some engineer said something along the lines of 'every twenty years we take FSW off the shelf and confirm again that it doesn't work'.

"Reality is often dissapointing." ):

That being said, I feel like FSW would work better for most things that aren't fighters. The AGM-129 and Hansa Jet are at least a little proof of this.

 

[Scott Kenny]

But not very much and only to provide adequate clearance for the flapping prop rotors. They would have preferred not to have if swept at all because it introduced a lot of mechanical complexity in the cross shaft. Hence the V280 having a dead straight wing instead.

With even greater flapping in the proprotors, too.

-----------

IIRC, the X-29 demonstrated that the FSW in practice didn't offer enough advantages. Wing ends up heavier, and just using 3-surface aircraft and/or thrust vectoring you get just as much performance at high AOA.

 

[sferrin]

Some engineer said something along the lines of 'every twenty years we take FSW off the shelf and confirm again that it doesn't work'.

See post #12 Was from some Discovery documentary on the X-29 years ago.

 

[riggerrob]

"Reality is often dissapointing." ):

That being said, I feel like FSW would work better for most things that aren't fighters. The AGM-129 and Hansa Jet are at least a little proof of this.

The primary reason for installing a FWS on Hansa Jet was to route the main wing spar aft of the cabin pressure vessel. It was a matter of packaging.
Consider how other business jets have solved the same packaging problem. Piaggio Avanti routes its main wing spar aft of the cabin. For balance, it adds a small canard. Try to think of Avanti as having a two-piece main lifting surface. Avanti still has a conventional elevator mounted on the rear horizontal tail surface.
Most other business jets mount their wing spars under the cabin floor (ala. airliner) or completely under the cylindrical fuselage.