Could bi-planes ever make a comeback?

[onyx39]

Now stick with me before you laugh..

Boeing have just announced a new 777 with folding wing tips, they are clearly looking to increase wing efficiency by increasing wingspan, but airports will obviously limit wingspan.
I know only the basics of how a wing works, but, could you in theory stack two wings on top of each other to maximise lift?

[Simpo Two]

OK anoraks - have their ever been any biplane jets?

I think the main problem is drag.

[0000]

Simpo Two said:

I think the main problem is drag.

This, and the wings interfering with the aerodynamics of each other, I should imagine.

[Super Slo Mo]

I was just going to suggest drag.

I suspect the additional weight and drag outweigh any lift benefits, and you could easily increase lift by altering the cross-sectional area of the existing wing. The penalty is still additional drag and weight, but probably less than a bi-plane arrangement.

That said, I'd be interested to see any theoretical or empirical calculations, if anyone knows more than the info Google/Wikipedia can throw up.

[0a]

0000 said:

This, and the wings interfering with the aerodynamics of each other, I should imagine.

Surely this is where really, really complicated computer models and processing could make the bi-plane stable and efficient.

[mybrainhurts]

Nah, you have to wear leather helmets, white scarves, goggles and be called Biggles before you can fly in a biplane. Don't you know anything?

[Eric Mc]

Simpo Two said:

OK anoraks - have their ever been any biplane jets?

Yes - but I'm not going to tell you any more because you are being so rude to us aeroplane enthusiasts.

[Dr Jekyll]

Simpo Two said:

OK anoraks - have their ever been any biplane jets?

I think the main problem is drag.

There certainly have.

http://www.aviastar.org/air/poland/pzl_belphegor.p...

Plus a few one off conversions.

The only real point of a biplane is that struts between the wings strengthen the structure, and these struts do, as you say, cause drag.

The other problem is that the wings do interfere with each other, you really want high pressure below each wing and low pressure above, obviously tricky on a biplane.

Compare the wingspan of a biplane with a similar sized monoplane, the monoplane tends to have a slightly wider span, but nowhere near twice as wide.

[0000]

0a said:

0000 said:

This, and the wings interfering with the aerodynamics of each other, I should imagine.

Surely this is where really, really complicated computer models and processing could make the bi-plane stable and efficient.

Maybe, but I should imagine even simple models could find decent local minima accurately enough that they'd already be building them if it was worth it. I can't see that changing unless someone can radically change what I expect a biplane to look like or be constructed from.

[jamieduff1981]

For efficiency you want as few wingtips as possible.

Where there's a wingtip, there's a large vortex to shed and that means lots of drag. The longer the wings, the less span-wise flow you get (all else equal).

The reason biplanes used to be popular was because lots of wing area was needed and there was hardly any power density from engines of the day. Something like the Wright Flier as an externally braced biplane would have offered around half the structural weight of the same wing area as a cantilever monoplane.

I don't believe biplanes will be back any time soon. When configured as a classical biplane with one wing above the other, there is very substantial interference between each wing's pressure "fields" which kills the efficiency further. If you went for a tandem wing biplane you could in theory half the wingspan, but you still get the problem of poor spanwise lift distribution and vortex shedding.

Edited by jamieduff1981 on Monday 18th November 19:59

[Simpo Two]

Eric Mc said:

Simpo Two said:

OK anoraks - have their ever been any biplane jets?

Yes - but I'm not going to tell you any more because you are being so rude to us aeroplane enthusiasts.

I call your bluff sir! Spill...

[bostin01]

\

Dr Jekyll said:

There certainly have.

http://www.aviastar.org/air/poland/pzl_belphegor.p...

Plus a few one off conversions.

The only real point of a biplane is that struts between the wings strengthen the structure, and these struts do, as you say, cause drag.

The other problem is that the wings do interfere with each other, you really want high pressure below each wing and low pressure above, obviously tricky on a biplane.

Compare the wingspan of a biplane with a similar sized monoplane, the monoplane tends to have a slightly wider span, but nowhere near twice as wide.

Well, there was this also in 1910. Granted, it is not a true jet, however still way ahead of it's time.

http://en.wikipedia.org/wiki/Coand%C4%83-1910

[mybrainhurts]

Bet you didn't know there was a jet powered Zeppelin...

[maffski]

The box wing has been suggested, claims to have reduced fuel consumption and noise. It's kind of biplaneish.

http://www.aiaa.org/uploadedFiles/About-AIAA/Press...

[bearman68]

jamieduff1981 said:

For efficiency you want as few wingtips as possible.

Where there's a wingtip, there's a large vortex to shed and that means lots of drag. The longer the wings, the less span-wise flow you get (all else equal).

The reason biplanes used to be popular was because lots of wing area was needed and there was hardly any power density from engines of the day. Something like the Wright Flier as an externally braced biplane would have offered around half the structural weight of the same wing area as a cantilever monoplane.

I don't believe biplanes will be back any time soon. When configured as a classical biplane with one wing above the other, there is very substantial interference between each wing's pressure "fields" which kills the efficiency further. If you went for a tandem wing biplane you could in theory half the wingspan, but you still get the problem of poor spanwise lift distribution and vortex shedding.

Edited by jamieduff1981 on Monday 18th November 19:59

This is an elegant explanation of some pretty complex aerodynamics. Nice one

[V8LM]

Elliptical wings? No tips at all:




ETA: I think I understand the idea of winglets. Why were they dropped for the 747-8?

Edited by V8LM on Monday 18th November 22:14

[Hilts]

Anyone know of any aircraft with three sets of wings?

Not like a triplane though, these wings are along the fuselage and about the same size.

[ninja-lewis]

Hilts said:

Anyone know of any aircraft with three sets of wings?

Not like a triplane though, these wings are along the fuselage and about the same size.

Quite a with three flight surfaces in tandem - http://en.wikipedia.org/wiki/Three-surface_aircraf...

Even a triplane-biplane - http://en.wikipedia.org/wiki/Fokker_V.8

[davepoth]

V8LM said:

Elliptical wings? No tips at all:




ETA: I think I understand the idea of winglets. Why were they dropped for the 747-8?

Edited by V8LM on Monday 18th November 22:14

They're still there - look at the way the tips swing up. It's just a bit more subtle.

[AER]

The problem isn't really one of size and economies of scale yet until they can have twin-engined A380's.

The four engined-jets need to shed two engines to compete commercially with 787's and A350's and at A380 scale it becomes a problem of fan diameter and ground clearance.