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High-speed biplanes

neutrino_cannon

Master Poster
neutrino_cannon
Joined
Dec 13, 2002
Messages
2,574
OK, I'm officially stumped. Why aren't there high-speed biplanes? The answer I'd always heard was the extra drag from the additional wings and the bracing, which forever relegated biplanes to lower speeds.

Looking at these drag curves though:

http://www.mountainflying.com/Pages/articles/images/drag_curve.jpg


I'm stumped. If you delete the rigging from a biplane and have two unconnected wings, or if you have a tandem wing setup you're getting more induced drag from the additional wingtip vortices. According to the above drag curve, induced drag is exactly what one is not worried about at high speed.

Could any of the people who actually know what they're talking about when it comes to the black magic of fluid mechanics enlighten?
 
Aside from the induced drag, which is not so important at high speed, a biplane will usually have a greater frontal area and a greater coefficient of drag. Even without the rigging wires, you still need something to hold the second wing in place.

The power required to push a plane through the air, at higher speeds, goes up as roughly the cube of the airspeed. So if you double the power of the engine you only go about 26% faster. To go twice as fast you have to increase the engine power to eight times its original value - not easy!
 
For speed you generally need as small wings as possible. Biplane is just doubling area of the wings, if you ignore all riggings. That was needed when there were no better engines.
Better engines allowed higher speed, and so smaller wings were enough, which again helped the speed. High landing speed was solved by better undercarriage, better runways, and flaps.
 
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Right. The biplane was the solution to providing sufficient lift with the early underpowered engines. High-performance biplanes exist, so called "aerobatic" aircraft are often biplanes.
But the extra wing just provides more low-speed maneuverability.
With more efficient and powerful engines, no need for the extra wing.
 
neutrino_cannon said:
OK, I'm officially stumped. Why aren't there high-speed biplanes? The answer I'd always heard was the extra drag from the additional wings and the bracing, which forever relegated biplanes to lower speeds.

Looking at these drag curves though:

http://www.mountainflying.com/Pages/articles/images/drag_curve.jpg


I'm stumped. If you delete the rigging from a biplane and have two unconnected wings, or if you have a tandem wing setup you're getting more induced drag from the additional wingtip vortices. According to the above drag curve, induced drag is exactly what one is not worried about at high speed.

Could any of the people who actually know what they're talking about when it comes to the black magic of fluid mechanics enlighten?
Click to expand...

First, let me agree with the others. Second, if I'm reading your post right, I'm not sure you've really grokked induced and parasite drag.

Biplanes are notorious for having high parasite drag, which is exactly the wrong thing for high speed. By having (usually) more wing area, they operate at a lower lift coefficient (CL), so they have lower induced drag but, as you say, induced drag isn't so important at high speed.

Also, biplanes don't necessarily have higher induced drag simply because they have more wingtips. Induced drag is primarily due to wing shape (planform) and CL. If you made monoplane and biplane versions of an airplane, and both planes had the same total wing area and the same wing shapes (the individual wings would have to be smaller on the biplane), they'd have the same induced drag, to first order.

Of course, there are other effects (in aerodynamics, there are always more effects). The wings interfere with each other, the smaller biplane wings would be operating at lower Reynolds numbers, you'd likely have more interference drag, etc.

Finally, if you can build a cantilevered wing with a particular planform, it's simply cheaper to build one big wing than two small ones.

P.S. Don't get me wrong, I love biplanes.

P.P.S. Hot Canary
 
When a space shuttle orbiter is carried on top of a 747, orbiter's wings generate more lift than the orbiter weighs. So that's the world's biggest and fastest biplane!

But it's not supersonic.
 
patchbunny said:
Can someone explain to me why a PhD dissertation on the construction of a supersonic biplane was submitted for a Doctorate in Philosophy? :confused:
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Wiki: "The term "philosophy" does not refer solely to the modern field of philosophy, but is used in a more broad sense in accordance with its original Greek meaning, which is "love of wisdom"."

In English speaking countries, PhD is the doctorate degree awarded to physicists and engineers.

Not in Germany, though. I got a "Dr. rer.nat." ("rerum naturalium", "of the things of nature") as a physicist. But I work in the US now, and no one here understands that. So I typically refer to having a "PhD", unless my real title is necessary for legal reasons.
 
Best photo ever of the Shuttle and the 747...
 

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Mark6 said:
When a space shuttle orbiter is carried on top of a 747, orbiter's wings generate more lift than the orbiter weighs. So that's the world's biggest and fastest biplane!
Click to expand...

Only if you put it on in the right way!
index.php
 
bowlofred said:
Only if you put it on in the right way!
[qimg]http://forum.nasaspaceflight.com/index.php?action=dlattach;topic=5958.0;attach=90592;image[/qimg]
Click to expand...

Some of the guys where I work would still manage to put it on upside down.
 
neutrino_cannon said:
OK, I'm officially stumped. Why aren't there high-speed biplanes? The answer I'd always heard was the extra drag from the additional wings and the bracing, which forever relegated biplanes to lower speeds.
Click to expand...


Higher speed has less to do with the number of wings and more to do with the engine power. If you look at actual high-speed aircraft they tend to have quite small wing area. Compare that with, say, a sailplane, which operates at very slow speed and has enormous wing area. A biplane necessarily has much larger wing area than a monoplane. The reason they existed at all is because more wings means more lift. With early low-powered engines, the aircraft wasn't able to go very fast, which means less lift is generated (wings generate greater lift at higher speed). You add additional wings to increase the lift so the plane stays airborne.

Once engines got more powerful they could pull the aircraft through the air at greater speed, thus increasing the amount of lift generated by a single wing. As a result the additional wings (which introduce a host of practical problems) became redundant. So they got rid of them.

People didn't stop making biplanes because they couldn't go fast enough. People stopped making biplanes because engines got powerful enough that you didn't need biplanes anymore.
 
Roadtoad said:
It's not the fastest plane, but have you Googled the Pitts Model 12? Or for that matter, the Aviat Eagle II?
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The fastest biplane ever was apparently 323MPH in 1941 by a Fiat CR42B with a 753 kW 1010 hp Daimler-Benz DB601A engine. This was a one-off prototype.

By comparison the Bf-109E used the same engine, and had a slightly higher maximum speed of 343MPH, but did this with substantially greater armament and ammunition load.
 
patchbunny said:
Can someone explain to me why a PhD dissertation on the construction of a supersonic biplane was submitted for a Doctorate in Philosophy? :confused:
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Because the guy wanted a PhD in Aeronautics, see the department. There are many kinds of doctorate degrees each being different. PhD's are doctorates in philosophy, hence the Ph.

There are also DSW(doctor of social work), ED(educational doctorate), MD(medical doctor), JD(Jurist doctorate), and so on. That that means is he was writing PhD out in formal words instead of acronyms.

So when you look at the department he was in, it makes rather a lot of sense that this would be a reasonable dissertation for a PhD in aeronautics.
 
As far as I'm aware of no plane has ever broke the sound barrier, it requires a jet engine. And exactly where is the line drawn on what is a biplane apparatus? There have been many supersonic jets with several wings on different planes on the body.
 
Illustronic said:
As far as I'm aware of no plane has ever broke the sound barrier, it requires a jet engine.
Click to expand...

True, if you use a broad definition of ''jet engine," so it depends on how pedantic you want to be. AFAIK, there's never been prop-driven aircraft that could go supersonic in level flight, and the ones that could go supersonic in a dive routinely lost their wings somewhere along the line.

In the case of the F-84 supersonic propeller experiments, the prop blades were supersonic but the aircraft wasn't.

Usually, "jet engine" refers to turbine propulsion, referring to either pure turbines or turbofans. Although the first generation of aircraft turbines were pure turbines, by now they've been almost entirely replaced by turbofans.

So, for non-turbine supersonic flight, there are always rockets. Some of the X-series aircraft did exactly that.

The SR-71/YF-12 used a 'turbo-ram' for supersonic cruise. It operated as a ramjet at high supersonic speed and as a turbine at lower speeds. I know that 'ramjet' has 'jet' right there in the name, so arguably they're 'jets.'

The space shuttle is a supersonic glider, though of course it can't maintain a supersonic speed (or a subsonic speed, for that matter) in level flight.

And exactly where is the line drawn on what is a biplane apparatus? There have been many supersonic jets with several wings on different planes on the body.
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Any definition such as "biplane" is inherently artificial and that makes it subject to endless (and generally pointless) argument. Having said that, I'd say it's a biplane if
1) no single horizontal surface has more than 70% of the total of the total area of all the wing-like surfaces, and
2) the two largest wing-like surfaces are siginificantly vertically superimposed.

As far as I know, neither of those conditions are true for any supersonic aircraft that I can think of.
 
ponderingturtle said:
Because the guy wanted a PhD in Aeronautics, see the department. There are many kinds of doctorate degrees each being different. PhD's are doctorates in philosophy, hence the Ph.

There are also DSW(doctor of social work), ED(educational doctorate), MD(medical doctor), JD(Jurist doctorate), and so on. That that means is he was writing PhD out in formal words instead of acronyms.

So when you look at the department he was in, it makes rather a lot of sense that this would be a reasonable dissertation for a PhD in aeronautics.
Click to expand...
Yep, most doctorates, especially in the sciences, from British style institutions, are awarded as a Ph.D. (philosophiae doctor) these days; few universities offer Sc.D. other than as an honorary degree, my alma mater being an exception.
 
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