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Biplanes have lower minimum power and material strength demands. However these slow planes have worse glide ratios and thus distance-based fuel consumption. Today with high performance engines and materials these planes are very niche and monoplanes are the norm.

But these traits seem best for maximizing human-powered flight time. Humans are very weak engines, and the aircraft must have airliner-sized wingspans with an under 100kg weight. This presents an extreme material demand which would be lessened in a biplane design. One could argue that time in the air is more important than speed or distance for the purposes of "having a fun toy to play with". Given these demands, why are human powered biplanes not more common?

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  • $\begingroup$ From your quoted question: But the main reason is that they're inefficient, and don't really do much that a monoplane can't. $\endgroup$
    – Jim
    Oct 3, 2022 at 20:52
  • $\begingroup$ @Jim: It's not doing much. A pedal biplane would fly maybe <10 mph and the pilot could be beaten on foot. It's a toy and a teaching tool, not much more. But the power usage in flight would be lower so more people could fly it and for longer. $\endgroup$
    – Kevin Kostlan
    Oct 3, 2022 at 20:56
  • $\begingroup$ Still need to look at the drag from two wings vs from one. $\endgroup$
    – Jim
    Oct 3, 2022 at 20:57
  • $\begingroup$ @Jim: The L/D ratio is worse. But the speed is so low (as described in the linked question) that the minimum power is lower even though the thrust must be higher (at constant aircraft weight). At least that's the hope! And presumably the aircraft could be (even) lighter due to the structural advantage. $\endgroup$
    – Kevin Kostlan
    Oct 3, 2022 at 21:00
  • $\begingroup$ Question could be improved to better specify exactly what you are seeking to optimize. Perhaps, "maximum possible endurance till pilot is exhausted, for 20-year-old male in average physical condition"? Etc you get the idea. Based on existing HPA history, I doubt the biplane will ever come out the winner, but we can at least get a better idea of exactly what problem we are trying to solve--. But I don't think that changing the goal from range to endurance (duration) will decisively tip the scales toward the biplane's favor. $\endgroup$
    – quiet flyer
    Oct 3, 2022 at 21:03

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