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This research paper shows that for a given aspect ratio and wing area, compared to a monoplane a biplane produced a better L/D. So, wouldn't it make more sense to manufacture biplanes for subsonic flight instead when size and wingspan restrictions are involved?

Robert DiGiovanni
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Dwight Schrute
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    Without reading the 100+ pages, could you point to the section where it's claimed that biplanes produce better L/D than monoplanes? That claim runs contrary to what I've always understood. There's much more interface drag for a biplane, and the wings also interfere with each other. Both lead to more D for the same amount of L. – Kenn Sebesta Jun 10 '23 at 12:16
  • @KennSebesta, most of the paper just consists of appendices and the whole thing is just a wind tunnel test experiment, if you want the cliff notes for the lower L/D, check out the conclusion section. – Dwight Schrute Jun 10 '23 at 13:41
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    Would it be beneficial for the Boeing 777x to have a biplane wing design? and Why are there no longer any biplanes? – mins Jun 10 '23 at 15:58
  • So, is the research paper wrong when it claims that biplanes have a lower L/D for a given wing area and aspect ratio? – Dwight Schrute Jun 10 '23 at 18:56
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    I don't think anyone here is going to read a random paper to refute it. It's entirely possible that the linked masters thesis highlights a very specific point where biplanes could conceivably do better. I think if you want an answer here, you need to rephrase the question with the specific point in question so we can address it. – Kenn Sebesta Jun 11 '23 at 12:09
  • Biplane airplanes do have a better L/D but this is true only when the wingspan must be kept short due to some other limitations.

    If you attach a second wing to a monoplane then each wing must generate only ½ of the total lift; being the induced drag proportional to L² then each wing generates now only ¼ of induced drag; the total induced drag is therefore ¼+¼=½ of the monoplane case. Amazing result. Anyway induced drag is also inversely proportional to wingspan squared: the same reduction of ½ can be obtained simply increasing wingspan of some 40%. What's better depends on other constraints

     – sophit Jun 11 '23 at 14:52
  • @sophit actually a good answer if they reopen. A bi-plane configuration would also enable higher altitudes, as was found out in 1938. Imagine a Concorde fuselage with 2 wings, perhaps looking a bit like this. – Robert DiGiovanni Jun 12 '23 at 23:46

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