Moderators: richierich, ua900, PanAm_DC10, hOMSaR

 
User avatar
N328KF
Topic Author
Posts: 6024
Joined: Tue May 25, 2004 3:50 am

Swing-wing aircraft - why the swing away?

Thu Nov 05, 2020 6:40 pm

We no longer see swing-wing aircraft being developed as a solution to mixed performance requirements. The Tu-160, decades old, is the newest significant offering in this space.

What was the specific advance that allowed for a mixture of good low-speed and high-speed performance that meant that the complication of swing wings were no longer required?
“In the age of information, ignorance is a choice.”
-Donny Miller
 
VMCA787
Posts: 225
Joined: Fri Sep 04, 2020 9:31 pm

Re: Swing-wing aircraft - why the swing away?

Thu Nov 05, 2020 7:38 pm

I would say there wasn't a specific advance but more a realization that the increased weight to allow the swing-wing isn't worth the hit in payload. That coupled with the emphasis on low observables, has led to more emphasis on designing the aircraft to minimize reflectivity. The high speed "dash" coupled with the increase in SAM effectiveness has resulted in the push for low observables too.

I would look at your question in that framework.
Fly fast, live slow!
 
User avatar
Dutchy
Posts: 12368
Joined: Sat Nov 03, 2007 1:25 am

Re: Swing-wing aircraft - why the swing away?

Thu Nov 05, 2020 9:14 pm

Delta is better in the high-speed environment and the more straight wing will be better at low speed. So swing wing is the best of both. worlds. Tradebacks: heavy, complex, expensive and indeed not good for stealth profile.
Many happy landings, greetings from The Netherlands!
 
ThePointblank
Posts: 3716
Joined: Sat Jan 17, 2009 11:39 pm

Re: Swing-wing aircraft - why the swing away?

Fri Nov 06, 2020 12:40 am

Variable swept wings also take up valuable room inside the airframe, which means you have less room internally, for stuff such as fuel, weapons, avionics, etc.

With advances in engine technology, aerodynamics and avionics, the need for a variable swept wing is much less now. Engines are much more powerful and efficient, and advances in design in high lift devices such as flaps and slats mean that you can design a wing that's optimized for high speed flight, but with the right combination of flaps and slats, you get pretty decent low speed performance. Also, Fly By Wire systems also expedited the killing off of variable swept wings; the reason variable wing is utilized in an aircraft design is to make it perform well on different flight envelopes, mainly slow and high speed handling. Swept wing is good for high speed work but perform poorly at low speeds and vice versa.

Digital FBW systems however fixes that. You can tell the computer to manage how the aircraft handles in all flight regimes, and it will do that for you regardless of the wing shape. For example, the Mirage 2000 with it's FBW systems can very comfortably fly low speed, high AoA, when delta wing aircraft were not well known for that sort of capability.

Variable swept wings are also an absolute bear to maintain... lots of complicated hydraulics inside the wing box to handle the sweep mechanism, and the structure holding the wings to the airframe are also under a ton of stress using high strength, but fairly brittle materials which requires frequent and time consuming inspections. Look up the Cold Proof testing procedure for the F-111 for starters, and the F-14's issues with the hydraulic wing sweep mechanism.
 
User avatar
smithbs
Posts: 572
Joined: Wed May 17, 2017 6:09 pm

Re: Swing-wing aircraft - why the swing away?

Fri Nov 06, 2020 2:38 am

They weren't easy to make either. The wing box design for a swing wing aircraft is a challenge, and production required exotic methods, such as those required to weld titanium.

However, recall that the most prolific swing wing producer was the Soviet Union. They had quite a few designs of that type, although sometimes you could tell they were cutting a corner by setting the pivot further out on the wing.
 
cpd
Posts: 6748
Joined: Sat Jun 28, 2008 4:46 am

Re: Swing-wing aircraft - why the swing away?

Fri Nov 06, 2020 9:02 am

ThePointblank wrote:
Variable swept wings also take up valuable room inside the airframe, which means you have less room internally, for stuff such as fuel, weapons, avionics, etc.

With advances in engine technology, aerodynamics and avionics, the need for a variable swept wing is much less now. Engines are much more powerful and efficient, and advances in design in high lift devices such as flaps and slats mean that you can design a wing that's optimized for high speed flight, but with the right combination of flaps and slats, you get pretty decent low speed performance. Also, Fly By Wire systems also expedited the killing off of variable swept wings; the reason variable wing is utilized in an aircraft design is to make it perform well on different flight envelopes, mainly slow and high speed handling. Swept wing is good for high speed work but perform poorly at low speeds and vice versa.

Digital FBW systems however fixes that. You can tell the computer to manage how the aircraft handles in all flight regimes, and it will do that for you regardless of the wing shape. For example, the Mirage 2000 with it's FBW systems can very comfortably fly low speed, high AoA, when delta wing aircraft were not well known for that sort of capability.

Variable swept wings are also an absolute bear to maintain... lots of complicated hydraulics inside the wing box to handle the sweep mechanism, and the structure holding the wings to the airframe are also under a ton of stress using high strength, but fairly brittle materials which requires frequent and time consuming inspections. Look up the Cold Proof testing procedure for the F-111 for starters, and the F-14's issues with the hydraulic wing sweep mechanism.


The F111 had it's material problems with that carry through box supporting the wings. I have a great book on the F111 (done by one of our airforce people who had experience in the F111) that details the problems clearly. But it also showed that it ended up being a great plane. Fortunately it was never used for the intended purpose.

https://www.raafamberleyheritage.gov.au ... ting-edge/

Extremely well written and produced book from Air Commodore Mark Lax OAM, CSM.

One thing putting these planes out now is that we don't have the focus on speed, it's on stealth. Mach 0.8 to 0.9 stealthy flying wings, like the Northrop (??) drone we saw photos of the other day are what we see more commonly now. If the forces need speed, they won't be mucking around at M2.0 or M2.5, they'll be going 120,000ft+ and much, much faster, if they are...
 
ELBOB
Posts: 374
Joined: Sun Jun 21, 2015 6:56 am

Re: Swing-wing aircraft - why the swing away?

Fri Nov 06, 2020 9:24 am

ThePointblank wrote:
Digital FBW systems however fixes that. You can tell the computer to manage how the aircraft handles in all flight regimes, and it will do that for you regardless of the wing shape. For example, the Mirage 2000 with it's FBW systems can very comfortably fly low speed, high AoA, when delta wing aircraft were not well known for that sort of capability.


FBW is not a pancea. With a deliberately unstable airframe it can provide remarkable handling but always within the aerodynamic capabilities of that airframe. You can't make a wing do something it can't do.

Approach speed for a Mirage 2000 is around 150 to 170 kts, similar to a Mirage III, compared to 125 to 140 kts for a substantially bigger F-14 with the wings forward. Even the Earth Pig, the F-111, can come over the threshold at 115 kts! And similarly the Tornado had a VG wing to provide good airfield performance because the initial Warpac strikes were expected to be against NATO runways.
 
mxaxai
Posts: 2591
Joined: Sat Jun 18, 2016 7:29 am

Re: Swing-wing aircraft - why the swing away?

Fri Nov 06, 2020 10:22 am

I'm just gonna point you here for one previous discussion, but feel free to ask further unanswered questions: viewtopic.php?f=10&t=1386691
 
User avatar
N328KF
Topic Author
Posts: 6024
Joined: Tue May 25, 2004 3:50 am

Re: Swing-wing aircraft - why the swing away?

Fri Nov 06, 2020 5:59 pm

mxaxai wrote:
I'm just gonna point you here for one previous discussion, but feel free to ask further unanswered questions: viewtopic.php?f=10&t=1386691


Thanks, I tried to find a previous thread but could not.
“In the age of information, ignorance is a choice.”
-Donny Miller
 
744SPX
Posts: 473
Joined: Mon Jan 27, 2020 6:20 pm

Re: Swing-wing aircraft - why the swing away?

Sat Nov 07, 2020 1:33 am

I'd say its mostly because of stealth. The swing-wing is a victim of the "put all your eggs in one basket" philosophy.

That being said, Lockheed did propose a swing wing version of the F-22 for the Navy.
 
User avatar
smithbs
Posts: 572
Joined: Wed May 17, 2017 6:09 pm

Re: Swing-wing aircraft - why the swing away?

Sat Nov 07, 2020 5:29 am

Stealth did have a role to play in putting variable geometry wings away, but other factors were in play as well.

VG was basically a fad of the 1960s. For fighters, there was really only the F-14 and MiG-23. The models that followed in the 1970s - the F-15, F-16, F/A-18, MiG-29 and Su-27 - showed that VG was no longer necessary to requirements. The stealth fighters would take another generation to appear, and even then at a slow rate: F-22 and 35.

VG was more for strikers: F-111, Tornado, Su-17/22, Su-24, Tu-22, etc. Even then, it was dying out in the 1970s as a new design feature, and it would end with the B-1 and Tu-160.

Some could claim stealth did this, but not entirely. The F-117 was very niche and no competitor to the F-111 or B-1 mission. The B-2 was and remains very niche as well. Making everything multi-role, combined with new precision and stand-off weapons of the 1980s, meant the F-15E, F-16C and F-18E could take most of the pedestrian missions. Not until the arrival of the F-35 has stealth been applied en masse, decades after VG was left on the shelf.

I don't think drones have contributed in any way to the disappearance of VG. The current mission and capabilities for drones has no overlap for what VG strikers do.
 
User avatar
spudh
Posts: 363
Joined: Fri Jul 17, 2009 11:00 pm

Re: Swing-wing aircraft - why the swing away?

Sat Nov 07, 2020 1:25 pm

I think a significant cause was the acceptance that Mach 2 plus speeds were no longer a primary design requirement for fighters. This freed up designers to optimise wing geometry (and engine inlet arrangements) for more meaningful areas of the flight regime.
The incorporation of 'free' high lift devices like LERX etc added further to the low speed regime.

So in effect the removal of the dash speed requirement moved wing swept angle away from high sweep angles, FBW allowed relaxed stability high AoA approaches and canards for the deltas increasing low speed lift.

Each of the above weighed less and were simpler than VG.

What has been lost however is sheer low level speed and the ability to sustain that speed. The F-111, Tornado, Mig 23 and F-14 could sustain low level speeds that I don't believe can be touched by any subsequent or previous design.

If defense technology ever forces penetrators back down into the weeds it will be interesting to see which airframes can manage best.
 
User avatar
smithbs
Posts: 572
Joined: Wed May 17, 2017 6:09 pm

Re: Swing-wing aircraft - why the swing away?

Sat Nov 07, 2020 3:58 pm

spudh wrote:
I think a significant cause was the acceptance that Mach 2 plus speeds were no longer a primary design requirement for fighters. This freed up designers to optimise wing geometry (and engine inlet arrangements) for more meaningful areas of the flight regime.
The incorporation of 'free' high lift devices like LERX etc added further to the low speed regime.

So in effect the removal of the dash speed requirement moved wing swept angle away from high sweep angles, FBW allowed relaxed stability high AoA approaches and canards for the deltas increasing low speed lift.

Each of the above weighed less and were simpler than VG.

What has been lost however is sheer low level speed and the ability to sustain that speed. The F-111, Tornado, Mig 23 and F-14 could sustain low level speeds that I don't believe can be touched by any subsequent or previous design.

If defense technology ever forces penetrators back down into the weeds it will be interesting to see which airframes can manage best.


Agree 100%.

While the USA and USSR had more involvement with VG, Europe did not and was largely limited to the Tornado. I think the conclusion from that program was that it was a headache. Also, they were behind in fighters and needed to concentrate on that field as 1980 passed, and the "Euro canard" fad took hold.

The F-15 and Su-27 showed that raw power and other aerodynamic treatments would get you far, while the F-16 and 18 showed that compromising away the super high speeds was actually a good thing for the overall package.
 
744SPX
Posts: 473
Joined: Mon Jan 27, 2020 6:20 pm

Re: Swing-wing aircraft - why the swing away?

Sat Nov 07, 2020 11:34 pm

spudh wrote:
I think a significant cause was the acceptance that Mach 2 plus speeds were no longer a primary design requirement for fighters. This freed up designers to optimise wing geometry (and engine inlet arrangements) for more meaningful areas of the flight regime.
The incorporation of 'free' high lift devices like LERX etc added further to the low speed regime.

So in effect the removal of the dash speed requirement moved wing swept angle away from high sweep angles, FBW allowed relaxed stability high AoA approaches and canards for the deltas increasing low speed lift.

Each of the above weighed less and were simpler than VG.

What has been lost however is sheer low level speed and the ability to sustain that speed. The F-111, Tornado, Mig 23 and F-14 could sustain low level speeds that I don't believe can be touched by any subsequent or previous design.

If defense technology ever forces penetrators back down into the weeds it will be interesting to see which airframes can manage best.


Also agree about the dropping of mach 2 speed requirements (and low-level sustained supersonic requirements) - didn't think about that but it makes a lot of sense as to the move away from the swing-wing

Worth noting as well that the decision to remove the wing glove vanes on the F-14A+ and D was also a result of a new strategy that didn't involve flying at mach 2 speeds. The glove vanes enabled the F-14A to pull 7g at mach 2. Probably the only aircraft that can do that now is the F-22 when its using thrust vectoring. Possibly the Eurofighter as well...
 
RJMAZ
Posts: 2322
Joined: Sat Jul 09, 2016 2:54 am

Re: Swing-wing aircraft - why the swing away?

Sun Nov 08, 2020 5:37 am

I would love to see data comparing the F-14D versus F-15C with 75% internal fuel capacity and four missiles. With the following four metrics:
1) roll rate.
2) instantaneous turn rate.
3) sustained turn rate.
4) acceleration per second.

Having the data at three altitudes 1,000ft and 10,000ft and 40,000ft each done at three speeds say 500km/h, 1,000km/h and 1,500km/h would be excellent.

This would show the strengths and weaknesses of each design. I would like to see where the high lift and low drag F-14 wing could make up for having a much lower thrust to weight ratio.

The same information on the Super Hornet would no doubt show it being stronger at low speeds and altitudes but weaker at high speeds and high altitudes.
 
zanl188
Posts: 3837
Joined: Sat Oct 21, 2006 9:05 pm

Re: Swing-wing aircraft - why the swing away?

Sun Nov 08, 2020 12:52 pm

As far as the US Navy is concerned I believe the move to light weight fighters (F-18) had something to do with it. Both the F-8 and F-14 needed variable geometry to get aboard a carrier.
Legal considerations provided by: Dewey, Cheatum, and Howe
 
User avatar
smithbs
Posts: 572
Joined: Wed May 17, 2017 6:09 pm

Re: Swing-wing aircraft - why the swing away?

Sun Nov 08, 2020 3:10 pm

zanl188 wrote:
As far as the US Navy is concerned I believe the move to light weight fighters (F-18) had something to do with it. Both the F-8 and F-14 needed variable geometry to get aboard a carrier.


I didn't think to included the F-8 as a VG. :checkmark:
 
User avatar
smithbs
Posts: 572
Joined: Wed May 17, 2017 6:09 pm

Re: Swing-wing aircraft - why the swing away?

Sun Nov 08, 2020 3:11 pm

smithbs wrote:
zanl188 wrote:
As far as the US Navy is concerned I believe the move to light weight fighters (F-18) had something to do with it. Both the F-8 and F-14 needed variable geometry to get aboard a carrier.


I didn't think to included the F-8 as a VG. :checkmark:


F-18 is about as much as they can handle on that regard. The A/C models were highly limited in their carrier trap weight.
 
HaveBlue
Posts: 2177
Joined: Fri Jan 30, 2004 3:01 pm

Re: Swing-wing aircraft - why the swing away?

Sun Nov 08, 2020 5:02 pm

smithbs wrote:
zanl188 wrote:
As far as the US Navy is concerned I believe the move to light weight fighters (F-18) had something to do with it. Both the F-8 and F-14 needed variable geometry to get aboard a carrier.


I didn't think to included the F-8 as a VG. :checkmark:


At the risk of being pedantic the F-8 was variable incidence, not variable geometry. The F-8 has never been called VG.
 
LightningZ71
Posts: 596
Joined: Sat Aug 27, 2016 10:59 pm

Re: Swing-wing aircraft - why the swing away?

Mon Nov 09, 2020 3:41 pm

Lots of great information here. I watched a documentary on fighter design many years ago, the name and producer of which I have long forgotten, that covered some of why variable geometry has disappeared from fighter design. The two biggest ones were weight, as the mass of the structure and equipment needed to reliably allow the changes in wing sweep and for that same equipment to survive the rigors of air combat, was considerable, and of course, stealth. Having a wing change it's sweep angle plays poorly with carefully aligned body panels and edges. However, there were other developments that also influenced the move:

Lifting body research advanced a lot around the end of the swing wing era. This allowed air frames to be able to provide a degree of lift in addition to the wings. The advancements at the end were that they were still able to provide this lift without causing excessive drag and limiting top speeds too greatly. The resulting product was aircraft that were capable of high speed flight while still possessing manageable low speed flight characteristics.

The Cranked Delta wing, which was further refined into more modern hybrid wings that have LERXs. These allowed aircraft to have wings that were able to have different regions optimized for different flight envelopes. While some of this is now hidden in the lifting body, in that the wing's have shrunk a bit as compared to body volume, and the effective sweep of the "body" section much greater than the wing itself. Effectively, the end result is that the "lifting" section of each airframe can now be optimized for different flight envelopes in different areas, allowing for usable efficiency in both low speed and high speed regions of operation. It's not quite as effective as a swing wing, but it also doesn't have the huge mass and complexity penalty, making the trade off worth it.

Canards. While Delta wings are great designs for high speed flight, and have considerable wing area allowing for low wing loading, they aren't the most effective at being nimble. Canards can make up for this by both providing disturbed airflow over the Delta wings, which aids desired instability while maneuvering, and also providing additional pitch and roll authority to brute force things when needed. The problem is that canard designs are tricky and complicated to maintain proper control in different phases of flight, thus not being ideal until full digital fly by wire was perfected. Oh, it worked before, but, it wasn't as effective as modern designs. The Euro-Canards have shown that you can have highly maneuverable and effective fighter designs with delta wings.

Essentially, we have discovered that, while it was preferable to have the wing sweep vary with speed and maneuver need, the mass and complexity wasn't worth what you gained, and we found that other design characteristics could gain you a lot of what you were hoping for from swing wings without the same costs. Stealth changes almost everything, except for the fundamentals of aerodynamics. With stealth, you simply can not have major surfaces on the aircraft changing alignment and hope to retain the low observable qualities that you desire. It has gone so far that thrust vectoring systems have been developed to allow limited maneuvering without deflecting any control surfaces to maintain optimal edge alignment.
 
texl1649
Posts: 1762
Joined: Thu Aug 02, 2007 5:38 am

Re: Swing-wing aircraft - why the swing away?

Mon Nov 09, 2020 4:23 pm

Engines are also vastly more powerful today than in the 60's/70's. This negates some of the need for maximum lift at different speeds. Internal space for weapons/fuel is the real premium designers have to engineer through all the trade offs now. For manned platforms, the thrust capacity/surfaces negate any need for even thrust vectoring (can't realistically go above 9G for more than a second).

The greatest combat aircraft never built/in service, the F-23, illustrated well the tremendous agility modern stealth can achieve without resorting to variable geometry wings. Many programs today are trying to achieve what it offered, potentially, 25 plus years ago (including in Europe/Japan/Russia). None of them are remotely considering VG planforms.

The Tomcat to me remains the ultimate swing wing fighter, but that also contributed to its demise; maintenance cost was the real handicap vs. the 'super hornet.'
 
tomcat
Posts: 735
Joined: Thu Sep 28, 2000 4:14 am

Re: Swing-wing aircraft - why the swing away?

Thu Nov 12, 2020 1:17 am

Here is a great video about the F-14 design presented by Mike Ciminera, one of the fathers of the Tomcat. The presentation is quite technical, it's really interesting, especially about the layout and structural optimisations and the lessons learned from the F-111B. Also at 43:54, a glimpse of the very high angle of attack (70° AoA) flight tests.

https://www.youtube.com/watch?v=SsUCixAeZ0A

I believe that most of the arguments have already been provided upthread about the reasons why the VG wings aren't used anymore. All in all, each combination of technology and aerodynamic states of the art combined with a given set of performance and mission requirements will lead to an optimum design for a given budget.

I also want to point out that among the 4 4th generation US fighters, the F-14 had the greatest internal fuel capability and in spite of its relatively heavy empty weight, it boasted a very comfortable combat radius as well as a great loiter capability. The Super Hornet hasn't matched this capability in spite of of being lighter than the F-14 and having an overgrown wing. In the same token, it probably requires as much gas if not more to the F-15E to achieve a similar combat radius than the F-14D with any significant bomb load.

This being said, comparing the performances and maneuverability of the F-14 vs the F-15 is not really relevant when considering the significant differences in their design requirements. The F-15 was not meant to land on an aircraft-carrier with 4 Phoenix missiles while having a wingspan of just over 10m in parking condition. That made the F-15 much lighter than the F-14.
 
744SPX
Posts: 473
Joined: Mon Jan 27, 2020 6:20 pm

Re: Swing-wing aircraft - why the swing away?

Thu Nov 12, 2020 3:21 am

The F-14 was handicapped from the minute they cancelled the F401 engine. The F110 had a smaller fan than the F401 and was designed to fit in the F-15 and F-16 as well. The F401 was purpose built for the Tomcat and was more powerful and far lighter in the early 70's than the F-110-GE-400 (the lowest thrust version of the F110) was in the late 80's. Had it been developed along with its F100 brother as intended, it would have been producing over 34,000 lbs of thrust for the Tomcat by the late 80's/early 90's, and over 38,000 lbs thrust if you extrapolate from the never-produced F-100-PW-232. Also consider, the A model Tomcat with the F401 had an empty weight of 38,000 lbs compared to a porky 43,500 for the F-14D with the F110's and extra sensors.
The Tomcat was always intended to have 10k lbs more thrust than the F-15. It was designed for a 28-30k lbs engine from the outset which the F401 delivered in 1973. The best it got was 26.9k in 1988 after 3k lbs in weight gain from other areas. Too little too late. The Tomcat never got a chance to show its true performance, but even so it was still an honest mach 2.5 aircraft even with the TF-30's (as multiple 70's pilots attest to).
 
LMP737
Posts: 6227
Joined: Wed May 08, 2002 4:06 pm

Re: Swing-wing aircraft - why the swing away?

Sat Nov 21, 2020 2:17 am

ThePointblank wrote:

Variable swept wings are also an absolute bear to maintain... lots of complicated hydraulics inside the wing box to handle the sweep mechanism, and the structure holding the wings to the airframe are also under a ton of stress using high strength, but fairly brittle materials which requires frequent and time consuming inspections. Look up the Cold Proof testing procedure for the F-111 for starters, and the F-14's issues with the hydraulic wing sweep mechanism.


None of the wing sweep hydraulics were in the wing box on the F-14, or the box beam. The sweep actuators were aft of the box beam and were attached to the aft end of the wing box. The sweep mechanism was pretty reliable overall. The overall swing sweep, flap/slat system was very complex as you said. I saw more issues with flap/slat lockouts than issues with the sweep system. You had a bunch of interlocks/safeties in the whole system to keep you from damaging the aircraft, pilot/sailor proofing.

The box beams and wing box were both titanium, made for a strong airframe. In a lot of crashes the box beam would be recovered intact.
Never take financial advice from co-workers.

Who is online

Users browsing this forum: No registered users and 16 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos