Biplanes became the first airplanes to enter service due to their structurally efficient design being more suitable for the weak materials then. This efficiency comes from the two wings acting as the chords of a very deep truss.

Another structurally favorable factor was the reduced wingspan and thus moment allowed by distributing lift across stacked wings.

Yet another weight saver was the reduction of wing loading, which enabled thus use of less powerful engines for slower flight.

However, the extra wing only produces 20% more lift with 100% parasitic drag increase. Ironically, this interference drag is even more severe at the lower speeds which biplanes are optimised for.

A braced monoplane has most of the structural advantages of a biplane, with less of the aerodynamic disadvantages. So it would seem to be a more logical design than a biplane, given the same materials and engine.

Yet biplanes were built in large numbers. Why?

  • $\begingroup$ Related: Can biplane or triplane designs be revived with modern materials? $\endgroup$
    – user14897
    Mar 4, 2021 at 10:48
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    $\begingroup$ BTW I honestly question the lower wing gives only 20% more lift. It may be more, if set up properly, the lower wing puts the upper wing in perpetual ground effect. It would be a great study, but, as Peter says, the upper wing does most of the lifting. $\endgroup$ Mar 4, 2021 at 17:33
  • $\begingroup$ Guy Inchbald's answer was pretty accurate. $\endgroup$
    – Koyovis
    Mar 5 at 7:39
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    $\begingroup$ @AbdullahisnotanAmalekite just to understand why the bounty: what is missing in the answers that you got so far? $\endgroup$
    – sophit
    Mar 7 at 12:09

2 Answers 2


Back in the pioneer days both types competed fiercely. The braced monoplane has similar structural depth to the braced biplane but less than twice the total wing area, so many argued in its favour. On the other hand, the shallower angle of its bracing wires introduced greater compressive forces in the wing spars, so they had to be strengthened and that added weight.

The monoplane suffered its first drawback around 1911 when, first in France and soon after in Britain, examples started falling out of the sky and for a time they were banned from military service. The French problem turned out to be a mistaken design assumption leading to over-thin bracing wires, the British to be the Ministry-specified cowling fasteners coming adrift. They were soon flying again, but the damage to their reputation was done.

Nevertheless, a few types were still in service when war broke out, especially with Germany. The Etrich Taube and Fokker Eindecker helped to restore their reputation, especially when Fokker developed interrupter gear for the machine guns, unleashing the Fokker scourge. But this would prove the high point of the braced monoplane's career.

The advantages of the biplane you mention - high strength and short span - proved to give greater manoeuvrability, stiffness and damage tolerance when it mattered, and the monoplane quickly became obsolete.

The biplane remained dominant until engine powers rose sufficiently to take planes beyond 200 mph or so, where the greater weight of the unbraced or cantilever monoplane was a price worth paying for cleaner aerodynamics.

  • $\begingroup$ The biplane lost its dominance already during WW I, at least in Germany. Most new types were monoplanes: Fokker DVIII, all new Junkers, Dornier or Rohrbach (Zeppelin Staaken) designs, you name it. New biplanes were mostly designed for aerobatics and pilot training. $\endgroup$ Mar 7, 2021 at 8:49
  • $\begingroup$ @PeterKämpf That is a false picture full of mistakes. The parasol monoplane mounted only a modest challenge, and that mainly in France. The most significant Dornier was the D.1, a cantilever biplane, Junkers had built cantilever monoplanes throughout but only in penny numbers, Rohrbach were a postwar company; biplane houses such as Fokker and Albatros dominated German skies to the end. French fighters would serve your case better, but companies such as Lioré et Olivier long continued the biplane tradition in other sectors. $\endgroup$ Mar 7, 2021 at 10:44
  • $\begingroup$ Rohrbach worked at Zeppelin in Staaken. That's why it included the subtle hint that you close to overlook. The Dornier D.1 was partially responsible for the demise of biplanes. None of the many Albatros biplane types after the D.V were ordered in numbers. Fokker changed to monoplanes in 1918. Dornier and Rohrbach designed the planes you call postwar in 1918. Should I continue or do you see where the misconceptions are? $\endgroup$ Mar 7, 2021 at 11:58
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    $\begingroup$ Zeppelin Staaken did not build Rohrbach's monoplane until the war was over, and one obscure prototype doth not a revolution make. The Fokker D.VIII monoplane was smaller and lighter than the D.VII biplane but no faster, and the company went back to biplanes for what little was left of the war. Yes, I think we can all see where the misconceptions lie. The simple fact of history is that monoplanes remained a curiosity until engine powers rose to justify the structural inefficiency of the cantilever. $\endgroup$ Mar 7, 2021 at 14:39

Four elements of the aviation matrix compete, as always: structures, aerodynamics, engine power, and stability/control. The very first powered flight of the Wright brothers took place in a biplane with a 12 hp engine, and was hard to control. It took almost a year after the (brilliant) first flight before they could execute a full 360 degree turn, and six of their aircraft delivered to the US Army crashed. From the wiki:

Army accidents

In 1912–1913 a series of fatal crashes of Wright airplanes bought by the U.S. Army called into question their safety and design. The death toll reached 11 by 1913, half of them in the Wright model C. All six model C Army airplanes crashed.

How to make aeroplanes stable and easy to control? One solution was implemented by the young Anthony Fokker: simply eliminate controllability in the roll axis. `In the pic below from the Wiki article about the Fokker Spin, Anthony sits behind the engine structure, and the two wing halves can be distinguished supported by a spider web of bracing wires (Spin translates as Spider). Large wings => low wing loading!

enter image description here

The two wing halves can be seen to tip upwards, providing passive roll stability. No ailerons, the flight direction was commanded by the rudder only. Flying slowly in a straight line, turning gently with rudder only. And then WW1 started. At first aeroplanes were just observers, then came to be pursued by enemy aeroplanes to eliminate the flying artillery scouts. Airborne manoeuvring was now applying large loads on the structure, and the monoplane consisting of two wing halves held in place by wires could not compete anymore. For one, more wires were required, creating way more drag.

So the solution was the inherent strength and stiffness of the biplane structure. First the rectangle was crossed out by wires, later by more aerodynamic wooden bracing. At the end of WW1 the most feared plane was the Fokker DVII, which was particularly mentioned in the peace treaty.

Does the lower wing of a biplane account for only 20% of the lift? For sure if its area is 20% of total wing area. Aerodynamically an unbraced monoplane is superior, structurally a biplane is simpler. If the function of the plane is transport for low costs, a single wing with a large aspect ratio is the design goal. A small aerobatic plane might still be a biplane though (Pitts Special, from the wiki).

enter image description here

  • $\begingroup$ I fail to see how a Mono wing requires more wires. $\endgroup$ Mar 5 at 8:34
  • $\begingroup$ A modern mono win does not, because of the uninterrupted construction through the hull. In 1911 it did: the two wing halves can flap like a bird if not wired. $\endgroup$
    – Koyovis
    Mar 7 at 4:38
  • $\begingroup$ So they made the mistake of having the wing split by the cockpit? $\endgroup$ Mar 7 at 5:03
  • $\begingroup$ Well that was the technology at the time. The structurally uninterrupted monoplane came later - I had actually posted a question about this, the Junkers F13 of 1919 seems to be the first unbraced monoplane $\endgroup$
    – Koyovis
    Mar 9 at 7:45

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