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N1641
Topic Author
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Why Do Forward Swept Wings Make Fast Aircraft

Mon Feb 18, 2002 3:07 am

i was watching this thing the other about Nazi prototype aircraft, in a different show I saw they had talked about how the Nazi scientists came up with the idea of the delta wing to increase speed and the way that works makes perfect sense but in this more recent show they where talking about forward swept wings making the aircraft faster, now how does that work?
 
Klaus
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RE: Why Do Forward Swept Wings Make Fast Aircraft

Mon Feb 18, 2002 9:04 am

Russia seems to be developing a new fighter jet with forward swept wings. As far as I remember, I read about it in an article at Jane´s.

As much as I remember the wing design had more to do with agility than speed. Still seems to be a rare exception, though.
 
BWIrwy4
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RE: Why Do Forward Swept Wings Make Fast Aircraft

Mon Feb 18, 2002 12:25 pm

The US experimented with this about 10 (?) years ago, with the X-29. I think they found that it was very agile, but very unstable also. They needed an advanced FBW system to keep from losing control.
 
747Teach
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RE: Why Do Forward Swept Wings Make Fast Aircraft

Tue Feb 19, 2002 3:33 am

N1641: I believe you are referring to a Discovery Channel "Wings" episode that aired recently. Like many other aeronautical "innovations," forward-swept wings have been around for a while. The German Hansa corporate jet has wings that are somewhat forward-swept, but this was done to move the wing carry-through structure further aft in order to provide more cabin space. I don't think the Hansa is any faster or slower than other similar corporate jets. Regards,
 
aeroguy
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RE: Why Do Forward Swept Wings Make Fast Aircraft

Tue Feb 19, 2002 12:03 pm

Forward Swept Wings offer the same high speed drag reduction as Aft Swept Wings. Sweep, whether forward or aft, reduces the local Mach Number of the flow over the wing. This means that a transonic aircraft can cruise faster before encountering significant wave drag. An FSW has the added benefit in stall compared to an ASW. For an ASW, the spanwise flow is in the outboard direction, and the flow separates at the tips first, leading to tip stall. The FSW has spanwise flow that is in the inboard direction so that the wing stalls at the root first. So the FSW has better airflow at the tips for high angles of attack which improves maximum lift while also retaining aileron control in stall.

So what's the catch? Aeroelastic structural divergence for one thing. When an ASW flexes under lift loads, the tips tend to twist in a direction such that the angle of attack decreases. For an FSW, the tips tend to flex in the direction of increased angle of attack. The increased angle of attack causes even greater lift and hence even greater twisting. At some critical speed, the wing tip twist will overcome the structural strength of the wing and the tips will "diverge". The structure can be designed so that the divergence speed is higher than the aircraft will ever see, but there's quite a substantial weight penalty involved. However, composite materials have made FSWs feasible with minimal weight penalty due their stiffness and light weight The fibers in the composite layup of the tips can be oriented to specifically resist the twisting load and therefore yield a high divergence speed.

On top of that, like was mentioned by BWIrwy4, add the complication of the inherent instablility of FSW designs like the X-29, and the overall design problem is not easy.
 
ATR42
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Su-47

Wed Feb 20, 2002 8:43 pm

You might be talking about the Sukhoi Su-47 which has been flying for some time now.

(It was called the S-37 before it was officially named Su-47)
 
Blackbird
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RE: Why Do Forward Swept Wings Make Fast Aircraft

Thu Mar 01, 2007 3:36 am

The HANSA jet though had it's problems (It was totallly underpowered -- it's T:W ratio was almost as bad as an old 707-320)

Andrea K
 
2H4
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RE: Why Do Forward Swept Wings Make Fast Aircraft

Thu Mar 01, 2007 3:51 am




Quoting Aeroguy (Reply 4):
Forward Swept Wings offer the same high speed drag reduction as Aft Swept Wings. Sweep, whether forward or aft, reduces the local Mach Number of the flow over the wing. This means that a transonic aircraft can cruise faster before encountering significant wave drag.

So what's the logic in making the vertical stab on a Cessna 152 or 172....or the horizontal stab of a piston twin....swept? Wave drag certainly isn't a concern, so what benefit could they possibly offer over non-swept tail surfaces?


2H4


Intentionally Left Blank
 
FredT
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RE: Why Do Forward Swept Wings Make Fast Aircraft

Thu Mar 01, 2007 5:19 am

Quoting 2H4 (Reply 7):
So what's the logic in making the vertical stab on a Cessna 152 or 172....or the horizontal stab of a piston twin....swept? Wave drag certainly isn't a concern, so what benefit could they possibly offer over non-swept tail surfaces?

It looks good and increases sales. And that's about it.

I think the subject came up here a while ago? If this was the forum, there should be some good Torenbeek references in there posted by yours truly.

Rgds,
/Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
David L
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RE: Why Do Forward Swept Wings Make Fast Aircraft

Thu Mar 01, 2007 5:35 am

Quoting BWIrwy4 (Reply 2):
the X-29



Quoting 747Teach (Reply 3):
The German Hansa corporate jet



Quoting ATR42 (Reply 5):
the Sukhoi Su-47

Let's not forget Thunderbird 2. Although it never looked as if it was doing any more than 50 kts, it always arrived on-scene about five minutes after Thunderbird 1.

I'll get me coat...
 
dakota123
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RE: Why Do Forward Swept Wings Make Fast Aircraft

Thu Mar 01, 2007 5:50 am

Quoting 2H4 (Reply 7):
So what's the logic in making the vertical stab on a Cessna 152 or 172....or the horizontal stab of a piston twin....swept? Wave drag certainly isn't a concern, so what benefit could they possibly offer over non-swept tail surfaces?

Doesn't it also increase overall moment arm leading to a more effective control?

Dakota123
“And If I claim to be a wise man, well surely it means that I don’t know”
 
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Kukkudrill
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RE: Why Do Forward Swept Wings Make Fast Aircraft

Thu Mar 01, 2007 6:28 am

Quoting Dakota123 (Reply 10):
Doesn't it also increase overall moment arm leading to a more effective control?

Or, in plainer language for the non-technically minded like me, it sets the control surfaces further away from the aircraft, giving them greater leverage.
Make the most of the available light ... a lesson of photography that applies to life
 
FredT
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Joined: Thu Feb 07, 2002 9:51 pm

RE: Why Do Forward Swept Wings Make Fast Aircraft

Thu Mar 01, 2007 6:43 am

Quoting Kukkudrill (Reply 11):

Or, in plainer language for the non-technically minded like me, it sets the control surfaces further away from the aircraft, giving them greater leverage.

But it would be more effective to just elongate the empennage slighty or make the control surfaces bigger.

Rgds,
/Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
EridanMan
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RE: Why Do Forward Swept Wings Make Fast Aircraft

Thu Mar 01, 2007 6:58 am

Longer Eppenage is heavier than swept tail surface....

that said, I highly doubt the sweep is substantial enough to make the longer moment arm worthwhile... I think 'styling' is the best bet Wink

Actually, there _might_ be some merit to the concept that the sweep gets enough of the rudder surface out from behind the 'shadow' of the elevator to make it more responsive in a spin, but I doubt it.
 
metroliner
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RE: Why Do Forward Swept Wings Make Fast Aircraft

Fri Mar 02, 2007 4:33 am

doesn't the mooney series of GA craft have a forward swept emprennage because al mooney believed that it was more effective in a stall?

toni
Set the controls for the heart of the Sun
 
PLANAR
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Joined: Tue Dec 19, 2006 4:37 pm

RE: Why Do Forward Swept Wings Make Fast Aircraft

Fri Mar 02, 2007 4:35 pm

Quoting Aeroguy (Reply 4):

One of the most technically clear explanation of this topic I have ever seen.

Welcome to my RU list...
Flim-Flam Balderdash...
 
tepidhalibut
Posts: 202
Joined: Fri Dec 10, 2004 8:19 pm

RE: Why Do Forward Swept Wings Make Fast Aircraft

Fri Mar 02, 2007 5:24 pm

Quoting N1641 (Thread starter):
Nazi prototype aircraft

On the subject of WW2-era, German prototype aircraft / unrealised aircraft projects, I assume you're all aware of www.luft46.com. Nominally a site devoted to what *could* have been flying in the 1946 Luftwaffe. A load of intriguing plans...

For example, on the subject of forward swept wings...
http://www.luft46.com/bmw/bmw4.html
http://www.luft46.com/bv/bvp202.html
http://www.luft46.com/bv/bvp188-1.html
 
mrocktor
Posts: 1391
Joined: Mon Jan 24, 2005 12:57 am

RE: Why Do Forward Swept Wings Make Fast Aircraft

Sat Mar 03, 2007 2:52 am

Quoting FredT (Reply 8):
It looks good and increases sales. And that's about it.

 checkmark 

Quoting EridanMan (Reply 13):
Longer Eppenage is heavier than swept tail surface....

Not much, if at all. An unswept airfoil permits a very simple structure to be used, with better load distribution and therefore higher structural efficiency. Sweep, taper and twisting impose penalties to structural efficiency meaning the surface will be heavier for a given area. Unswept, untapered surfaces are also significantly cheaper to produce (all the ribs are the same).

In the case of light GA aircraft, probably the weight issue was found to be insignificant and the esthetic effect very favorable.

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