Whats the purpose of having two wings? Biplanes?

[Bythebookie2]

I have always wanted to know. I deduced that it was for manueverability.:rolleyes:

[BMatthews]

Strictly a matter of fashion. You can do everyting a bipe can with one wing and do most of it better.

Back in the early days of full sized aviation some of the early monoplanes had structural problems. As a result the militarys of the time developed a distaste for monoplanes to the point that it was specified that only biplanes were to be considered for war use and that policy was reflected in the public opinion as biplanes being safer than monoplanes.

It was also a good way to concentrate more wing area into a smaller space what with landing fields being so small and the need for slow approach speeds being important as a result. But once the need for speed took over all that other stuff was forgotten.

Nowadays the appeal of biplanes is strictly historical for scale models or a fashion statement that gives the nod to the old way of doing things.

[Majortomski]

Actually that's not quiet correct. The biplane has two linked significant traits. The upper and lower wing, with the associated trusses and wireing form the equivalent of a warren truss bridge. It is much stronger and lighter than the equivalent size wood monoplane wing. Two it has almost twice the area for the same span thus a higer roll rate. The biplane was the engineering solution for the limited power of the early engines.

[vintage1]

I think that is ALMOST right. One of the key things to remember was that pre 1930 no one really calculated anything. The recieved siadn was that airfoils of very thin section like bird wings were most efficient. Lacking depth, they were structurally very weak.

The Fokker DVII and possibly DVIII were thicker sectioned, and could get away with much less strutting...and were totally ignored by everyone until well into the late 30's after the schnieder trophy air races showed that monoplanes could operate with far less drag. Plus advances in aerodynamics were leading to the development of better wing sections of thicker dimenstion, and speeds were higher, so different sections worked better as well.

The biplane was stronger for a given wing area - - needed less span. Not to say a monoplane could not be built, but the bracing wires were more complex.

But I believe the greatest force driving biplanes fowrad in teh 20's was 'we did it that way last time'..the amount of computation required for even the simplest design, the lack of theoretical knowledge of the sorts of structures we now take for granted - all these served to make the biplane a safe choice.

Its a hugely easier task to calculate the stresses in a few rigging wires, against calculating the integrated forces ina stressed skin wing for example.

And no one has yet go siftwatre that can do what a wind tunnel can do, and no one has yet got wind tiunnel that obviates the need for a test pilot either.

[Bythebookie2]

If biplanes were meant for pre 1930's type planes, how do you explain modern aerobatic aircraft like the "Ultimate Biplane"?

[Ollie]

Drag in an aerobatic plane is an advantage since it limits acceleration on the down line and biplanes have lots of drag. For equal wing areas, the shorter span of the biplane, compared to a monoplane, results in a higher roll rate which is a desirable characteristic of aerobats. It also takes up less hanger space. ;)

[vintage1]

Precisely. That is the one thing a biplane does better than anything. Roll!

All other things are worse by and large. More drag and weird construction.

They were useful because they could be made strong with thin wing sections and bracing wires. Early planes were built like, and called, kites :D

[Bythebookie2]

Does this mean that the more wings you put on a plane, the better for aerobatics or combat the plane will be. Combat Example: Red Baron Triplane

www.rcgroups.com/forums/attachment.php?s=&postid=2030058

[Ollie]

The "best" in aerodynamic design is best understood in the context of how the various conflicts of objectives are resolved for some particular purpose.

In the case of combat as a purpose there are two opposing tactics of engagement. One is the "fur ball" style where maneuverability is the highest priority. The other is the "slash" style of engagement where speed in a straight line is the highest priority. In WWII the Japanese Zero was a good example of the fur ball approach and the P38 Lightning was an example of the slash style of engagment. It is interesting to note that the biggest ace in WWII flew a P38 with something like 50 victories. The P38 probably had one of the slowest roll rates of any fighter in WWII.

[Bythebookie2]

Why couldn't people long ago juist increase or decrease airfoil thickness(shorter wings) for speed or mauverability instead of making multi wing planes?

[BMatthews]

Fokker did just that starting with his first Triplane. And the powers that were in charge at the time insisted that he add outer struts and wires because the pilots would not trust a plane without them. It was not until his DVIII that he got his way and produced a pure cantilever wing.

Conservatism played a large part in the evolution from the biplane to the monoplane.

And I DO stand corrected about some cases where the biplane can be superior. To paraphrase Ollie's explanation, you need to look at the question to find the answer. And for some questions the biplane is still the answer.

World aerobatic competition is as much a slave to shifting perceptions as anything else. At one time the Pitts was seen as the old school who's time had faded. It was too small and hard to see and lacked some of what was considered important in the way it performed and looked in the air.... mostly the looked part I suspect. Now we see a return to bipes like the Ultimate. I think a part of that is the perceptions of the judges and what they want to see in the maneuvers rather than any real overall advantage between the bipes and the monoplanes.

[Ollie]

"Why couldn't people long ago juist increase or decrease airfoil thickness(shorter wings) for speed or mauverability instead of making multi wing planes?"

It isn't that they couldn't but that they didn't for the reasons Vintage1 has already given you. Please, go back and read his post #4 and believe it.

To understand why early designers did things you have to know what they knew and believed and ignore what they didn't know and believe. To do that really well you have to understand what the world was like for them seventy and one hundred years ago. During that time aerodynamic research was confined mostly to universities and not widely dissiminated to airplane builders or even much understood by them. Then, it usually took ten to twenty years to put academic discoveries into common practise.

Before the Wright brothers, many prominant scientists thought heavier than air flight was impossible. For about 30 years after the Wright brothers crashes were frequent, public opinion was not supportive and designers were , as a consequence, very conservative in their approach. Aviators were viewed as daredevils and designers as crackpots. When Lindburg flew across the atlantic in 1927 in a monoplane, a massive shift in public opinion had its start.

[uscra112]

Great thread.

Been getting into detail in this very period in aircraft development lately. It's fascinating. The whole industrial revolution is fascinating.

My $0.15 worth:

You also have to understand what tools and materials they had to work with. This is key to understanding ANY level of technology in ANY historical context.

Materials and fabrication methods had to evolve to make the all-metal cantilever wing that we take for granted today a commercial reality.

At beginning airplanes were wood, because we UNDERSTOOD wood. We'd been making wagons and ships and furniture and even weapons out of it for a couple thousand years. And in the USA we had a heck of a lot of it. And we had sawmills, and a man could work it into spars and ribs with handsaws and planes and chisels. In 1903 even high-quality STEEL was a technology that was younger than the personal computer is today! They didn't have the super-strong, corrosion resistant and fatigue-resistant alloys that we had by the end of WW2.

Wood isn't quite good enough for cantilever wings. Yes, Fokker did it, but a wooden-wing Fokker transport was also the plane that killed Knute Rockne. (The consensus was that the spar failed.)

Airplane builders needed a better material.

So the the process of extracting and refining aluminum well enough and cheaply enough had to evolve. Then the knowledge of how to alloy it so it would roll out uniformly into sheets. And then the tools to cut, bend, and form the sheets had to evolve.

In the '20s you find serious technical articles about how to understand the chemistry and microstructure of aluminum. Cracking during forming is STILL an issue with most metals. As Ollie points out, nobody was willing to use it until they were sure it wouldn't fail in flight.

Prior to the aircraft revolution, aluminum was more of curiousity than a commercial metal. It is weak, compared to iron and steel, and almost nothing built in the 19th century needed its' lightness. You occasionally find cast parts, but nobody bothered much with trying to make wrought aluminum do anything until the airplane came along.

Then they had to figure out the corrosion problems. That took a while.

By the late '20s at least, the science WAS being disseminated. Aero Digest, and Flight and The Aeroplane in England, were widely read magazines, and almost every issue has some article of aerodynamic theory in it, complete with headache-level math. Some are a bit laughable, looking at it from 75 years away, but nonetheless it was being published.

After the crash of '29, there wasn't much money to build airplane factories with, even if aluminum fabrication was known. Even in 1935 most of the commercial airplane builders were 100-man shops at most. They could never have afforded the machinery. Douglas and Boeing were able to make the leap to aluminum cantilever airliner construction in the early '30s with the 247 and the DC-2 (not the DC-3, that comes later), but in 1935 Stinson was still building airliners out of welded steel tubing with fabric covering, (the Stinson trimotor), and Curtiss had a twin engine biplane airliner of called the Condor, which was pushed to airlines as "economical to buy". And airlines were buying them. Low initial cost was important because most airlines were still shoestring operations.

While we know that plenty of wild designs were tried out in the first 40 years of flight, most of those guys weren't stupid. They made a heck of a lot out of what they had to work with. The Warren-truss biplane wing made the most of the available materials, money, tools, and skills, as Vintage1 pointed out. Hence, a great many of the planes of the era were indeed bipes.

[Ollie]

My father went to work for C. R. Smith of Trans Texas Airways in 1929. It later became part of American Airways and later still American Airlines. I have vivid memories as a four year old (1934) of a flight in a Curtis Condor, twin engine, biplane airliner between St. Louis and Dallas. There was no effective acoustical insulation. After riding near an engine for an hour or so with nothing but doped fabric in the way, it took a long time on the ground before you could hear again. The flight was low and slow and very bumpy. Air sickness bags were a real necessity and were frequently used by many passengers. Pressurized cabins were a thing of the future and ear popping was frequent. In 1935 or so, American moved its headquarters to Chicago. I remember flying with my mother and brother in a Stinson trimotor monoplane (8 passengers and a stewerdess) when the family moved. That was a much more pleasant experience but temporary loss of hearing and air sickness were still with us. The big advance in flying comfort came with the DC-3 in the late 30's.

[uscra112]

HA ! Maybe he knew something about the Pilgrims that American was using up to about 1935. I'm researching those in particular.

Some Condors were sold set up as sleepers, (or at least advertised as such). How one could sleep with that racket is beyond me.

The Douglas was THE quantum leap, no doubt about it. What an airplane!

[vintage1]

Ther are two books I have read that reaklly bring home te reality o aviatin between the wars

One isn Neville Shutes autobiography "Slide Rule" generally listed as by Neville Shute Norway, his real name.

Another is Ernest K Ganns 'Fate is the Hunter' concerning hs life and times in early commercial aviation.

They are well worth a read to anyone curious as to what it was like to be there...