2fer1: why no jet biplanes? and another German jet Q

Is there something inherently slow about biplane design? Wouldn’t the extra lift of another wing be good for jets? Properly designed of course.
And on this site it seems that the Luftwaffe was about to be equipped with planes and missle types that weren’t in Western Air Forces for another 10 to 15 years. I know that the German aircraft researchers were very advanced, but are these plans for real? And , if they are, was there any chance in hell of an economically stressed and wartorn Germany actually equiping the Luftwaffe with these planes?

I’m not an engineer but I know enough to know that an extra wing would increase lift but it would also increase drag. Since jets are about speed, less drag is more important than more lift.

Yeah, I wondered about the drag question too. But, there are some jets with rather large wing areas. B-2 comes to mind, as do the delta wing interceptors of the late 50s and the B-58 Hustler. Even the F4 Phantom looks to have quite a big wing.

So… why not some biplane designs with swept back (or forward) thin wings?

Looking at bi-plane designs, I see a network of struts and wires connecting the two wings. Even a relatively modern overhead wing small plane (think Pipers or Cessnas) has a rather large strut on each side of the fuselage.

While I am not an aircraft engineer (the first time I’ve used THAT disclaimer) I’ll wager that a bi-plane design must keep the wings from flexing independently of each other, and even an overhead wing design has to have extra reinforcement.

The stresses exerted by a jet engine must be much more severe than a piston engine. Struts and wires not only add to drag, they had an unfortunate tendency to break in the old bi-planes. It’s probably a case where a low-wing design is inherently more stable, unless you have a plane as big as the C5A, where you can add more internal supports.

More wing area equals more lift at a given speed. Thick section and undercambered (concave on the bottom like in WWI era planes) airfoils are made for high lift at low speed. Those properties also give proportionally more drag. Drag increases with the cube of speed. A high drag design may work fine at slow speed but if you try to double the top speed you will need at leat eight times as much power. A J-3 cub can putt around at 80mph with a 65hp engine but to go 160 it would need over 500.

Another reason for biplanes and triplanes is that the design is much more compact for a given wing area. Shorter wings can allow qucker turns as the ailerons are closer to the axis

Jets, as you may have noticed are made for very high speed. Small wing area compared to weight (this ratio is called wing loading, usually in lbs/sqare foot) and thinner wings.

The Luftwaffe had a lot of research going on and in hindsight a lot of wacky ideas. No doubt they could have made a lot of them work but having millions of tons of bombs dropped on them at the time was a bit of a handicap to progress.

The US was much more conservative in experimental research during the war but we did have operational helicopters and a flying jet fighter going by the end. It’s possible the staggering amount of resources put into the Manhattan project had to do with fewer resources wacky ideas in aviation. That came after the war.

NoClueBoy the wings are big on an F-4 but the wing loading is very high. I don’t recall the gross weight off the top if my head but an F-14 which is pretty similar in size might have a takeoff weight of 65,000lbs.

I challenge the notion that biplanes must have wires and struts. That was a product of the construction methods in use when biplanes were in vogue. If someone was so inclined they could use the monocoque construction of a P-51 there’s no reason you couldn’t have a biplane with a 1,600hp Merlin engine. The whole exercise would be pointless though as a biplane design is unsuitable for the flight envelope of a WWII fighter. There are modern designed racing sport biplanes with minimal or no interplane struts.

[THe following response constitutes the opinions of an aviation buff, not an aviation engineer. Expert opinion not included. Any aviation engineers around are welcome to step in and address any errors in this explanation.]

The main advantage of biplane wings is that it allows you to have the same amount of wing area in a smaller, less flexible package than just having a longer wingspan. Imagine slicing that top wing in two and grafting each half onto the wingtips of the lower wing. That’s a long wing. How do you brace it without making it much heavier? In the early days of aviation, the biplane wing was preferred because you could build it like a truss bridge (more-or-less), a structure the engineering world was completely familiar with. The ratio of lifting surface to non-lifting (structural) bracing was slightly better than for monoplane designs of the day (given equal strength – I could be wrong).

Biplane wings do have more inherent drag as speed increases. Each wing tip generates a vortice (tornado-like disturbance of the air it passes through). The biplane has two wings, thus twice the wintip drag. At double the speed, this wingtip-drag is more than twice as much (I’d say four to eight times – but I’d be guessing – it’s been a while since I’ve read up on this).

The sort of planes you are likely to see biplane wings on nowadays are acrobatic planes and slow recreational planes (especially home-built planes). In the case of the acrobatic planes, I believe that the biplane configuration allows a better rate of roll for a given wing area (think of how an ice-skater pulls her arms in when she’s spinning). In the case of recreational aircraft, I think that a biplane configuration allows STOL-like performance with fewer moving parts, as well as (possibly) simplified construction.

Most of these planes were “real” in that, had the Luftwaffe had the time and resources, they would have built them. Not all of them would necessarily performed as well as the Luftwaffe hoped, but many of them would have been on a par with Korean War-era jets. The Mig-15 and the F-86 borrowed heavily from German advances in aviation technology (most notably the swept wings). Both bear a more-than-passing resemblance to the proposed TA-183.

Having said that, there are some proposed german concept aircraft that would have never lived up to expectations. I suspect that the “tail-sitters” (the Fw Triebflugel, for example) would have required extraordinary pilot skill to handle during takeoff and (more critically) landing. Others would very likely required artificial stability enhancement, a technology which simply did not exist at the time.


Couldn’t a plane with a canard wing, such as the Concorde, be technically considered a bi-plane?

I used to work on F-4s in the early days of my AF career. IIRC, the F-4’s ready-to-fly weight (without armaments or external fuel) was in the neighborhood of 37,000 to 43,000 lbs (~8.5-10.5 metric tons). Maximum take-off weight was in the neighborhood of 60,000 lbs (~13.5 metric tons). Of course, these figures vary depending on what authority you consult, but they should be in the ballpark.


Thanks for that, Padeye! I hadn’t even thought about the XF-85 Goblin for a year or two (I just LOVE weird airplanes!)


Jimmy Franklin tours the airshow circuit with his jet-assisted Waco


Feel free to do so; it’s not like the aeronautical thought police are going to fine you for it. IANA airplane engineering guy, but I doubt anyone ever wrote down that the two wings must be within x% size or y% lift of each other in order for a plane to be considered a biplane. And you could just as easily call a conventional olane design a biplane because it has a separate elevator. The two perform the same function, pitch control.

I doubt you would find many people who would agree with your definition, however. I’ve never heard of the Concorde or the Long Easy or any other canard plane being described as a biplane. This is a Saab Viggen, which has as big a canard as I can think of, and I’ve never heard of it referred to as a biplane either.

Biplanes had virtually disappeared from modern fighter designs before jets ever flew. Starting in the middle 1930’s monoplane piston engine designs began to supplant the biplanes, as some flight characteristics, notably maximum speed and rate of climb, were proving to be more valuable assets in combat than maneuverability.

There are a very few biplanes still being manufactured, like the Waco.

As a general rule, biplanes have more drag than comparable monowings, and the faster you go the more the drag is a liability.

Today, even most homebuilt and recreational airplanes have just monowings.

The two wings can also, at least potentially, interfere with each other’s lifting capabilities during flight. I’m not an engineer enough to speculate further, but it seems to me this might also complicate design.

That said, the Germans did come up with some wacky ideas. They even had working, rocket-propelled interceptors that they managed to get into combat a few times. Unfortunately, the rocket planes (and their highly unstable fuel) killed more pilots than the Allies did.

So… multi wings were needed in early designs to provide/improve lift and manueverabilty and speed was basically a result of brute force. Right? As the science of aerodynamics improved, new ways around certain problems were found.

And any multi wing design today would pretty much be only for stunt planes or low horsepowered engine designs.

Are the wing tip vortices THAT powerful? Given the same exact area, would two smaller wings really increase drag that much over one larger wing? Forgive my density, but this doesn’t quite make total sense to me yet.

Well bi-planes did not have the brute force to get the thrust, hence the extra lift of the extra wings.
With more powerful thurst you can have the single wing, which has an added benifit of better visibility for the pilot.

It’s definitely not “standard nomenclature” to call a canard a biplane, despite the fact that there are two “wings”. As I understand it, there are several general configurations:[ol]
[li]Monoplane: Aircraft with one main lifting surface.[/li][li]Multiplane: Aircraft with multiple lifting surfaces, stacked vertically so as to present each wing with air relatively ubdisturbed by any of the other wings. This classification includes the biplane. Up to three wings (triplane) have been used in successful production aircraft designs.[/li]
The above classifications may be subdivided into three general types:[list=a.][li]Conventional aircraft: An aircraft with the wing(s) ahead of the elevators/horizontal stabilizer.[]Canard aircraft: An aircraft with the horizontal stabilizer and elevator surfaces ahead of the wing(s).[]“Tail-less” aircraft: Otherwise conventioinal aircraft that incorporate horizontal stabilization and elevation contol into the control surfaces of the wing(s).[/ol][/li][li]Tandem-winged aircraft: Aircraft with two main lifting surfaces (wings) of similar size, with one set of wings mounted ahead of the other set with little vertical displacement between the two, relative to their horizontal separation. Elevator control is usually incorporated into one or the other set of wings. [/li]
[li]Lifting body[/li]and [li]Flying wing.[/li]Each of these last two can be considered to be an extreme example of the all-wing type of aircraft. A lifting body is no more wide than it is long, and often longer than that. A flying wing, on the other hand, is generally wider than it is long. Both types try to keep all systems not involved with lift or control within the boundaries set by the wing, rather than attaching wings to a payload-carrying structure, (such as a fuselage).[/list]



The Concorde doesn´t have canard planes, it´s a delta wing aircraft; the wing ailerons work in coordination to provide pitch control, that´s why they are called “elevons”.

The similar Tupolev Tu-144 did have retractable canards, for better pitch control at low speeds.

Also materials science. These days, with modern alloys, composites, and other materials we can build a lighter, stronger airplanes than was possible 50 years ago. Less weight means less lifting surface and/or power required for the same performance. Stronger means you can use fewer struts/braces/etc. meaning a further weight reduction.

Well, not necessarially… but they would tend to be niche machines, or acquired by fanciers who just happen to like multi-wings.

They can be.

Let me put it this way - if I flew a four-seat small plane like a Cessna 172 or Piper Cherokee into the wing tip vortice of a much larger airplane like, say, a 737 best case scenario would have my plane tumbling end over end completely out of control. It may even cause structural damage or failure.

Wing tip vortices are a serious matter.

Of course, they’re less powerful on smaller aircraft, but they can be a significant factor when discussing airplanes.

It depends.

There are a number of factors that go into drag - size of the wing, shape of the wing, thickness…

And don’t feel bad about not quite getting it - I’ve been flying nine years now and I can still get confused about this stuff.

Broomstick, nitpick, but the singular of vortices is vortex.

And I am an aerospace engineer, but I’ve arrived in this thread too late to add anything meaningful. It’s been pretty well covered. But I’ll summarize with a little technical reasoning.

LIf is given by the equation L = C[sub]L[/sub]·q·S. And since q (dynamic pressure) is ½·p·V[sup]2[/sup], th equation for lift becomes:

L = ½·C[sub]L[/sub]·ρ·V[sup]2[/sup]·S

C[sub]L[/sub] is the lift coefficient, ρ is air density, V is velocity, and S is surface area of the wing(s).

So, you can make more lift three ways.
[li]Increase C[sub]L[/sub]: More efficient airfoils (there are practical limits to this one)[/li][li]Increase V: Go faster[/li][li]Increase S: Bigger wing(s)[/li][/ul]

The way that biplanes maximize lift is by increasing S. But the penalty for doing this is greatly increased drag, due partly to the increased wetted area, partly to increased drag-due-to-lift (related to the wingtip vortex thing).

Jets, on the other hand, don’t need all that wing are to generate lift, because they make lift with speed. Notice that lift force increases as the square of velocity. So you don’t have to be going all that fast before you don’t need big wings at all.

Thanks for y our excellent glossary SSgtBaloo, but I have a minor quibble with your definition of multiplans not including any successful ones past triplanes. The Department of “WTF were we thinking?” gave us the Wright Qaudaplane and one by V.F.Saveljev. Six ailerons on the Wright, I wonder what the roll rate was.

audiolover, was I correct in saying that drag is a funtion of the cube of speed?