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just out of curiosity how long do the human arms and legs would need to be so that a connecting patagium, like that of a colugo or a bat, would allow them to glide like one

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marked as duplicate by elemtilas, Renan, L.Dutch - Reinstate Monica Oct 4 '18 at 4:42

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    $\begingroup$ Greetings new person!! Please take a moment to take the tour and check out the help center. These resources will help you understand Worldbuilding Stack Exchange and the expectations this community has with respect to the kinds of queries that are acceptable and on topic and those that are not. This one does not appear to have any particular worldbuilding context. Also be sure to search for similar questions: this one is very similar to the "anatomically correct" series of questions. $\endgroup$ – elemtilas Oct 4 '18 at 4:22
  • $\begingroup$ @elemtilas, thanks for taking care of welcoming new users. I guess it would be even more welcoming if you used their user name instead of a generic "new person". :) $\endgroup$ – L.Dutch - Reinstate Monica Oct 4 '18 at 4:44
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    $\begingroup$ "New Person" is just schtick du jour. I have in the past used actual names, and may at some point switch back! :) $\endgroup$ – elemtilas Oct 4 '18 at 5:27
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Perhaps the best analogue one can think of might be a hang glider. These carry a fair amount of weight in themselves that has to be factored in to the supporting lift, but then on the other hand the human skeleton isn't designed to support its own weight in this manner and arms (& legs) may well need more reinforcement to support the weight in any event.

So; the basics. The 'average' wingspan of a hang glider is around 10m, a little less for more advanced units. The average human arm span is roughly proportional to height, so say around 1.8m for the average person. That's nowhere near enough, but then it's important to note that arms aren't all that bats use to spread their 'wings'.

A bat's arm pretty much only extends to the front middle edge of their wing. The rest of it is supported by elongated fingers. In practice, that means that if you have fingers grow out to around 2.5m, and you have the arms roughly double in size, you might be able to get enough surface area for gliding flight for a human, although there are a lot of other factors to consider.

Another way of putting that last statement is that a human would need to change shape, develop muscles in different areas (to control the shape of the wing), and reinforce lift-bearing sections of the skeleton for any of this to work.

Put yet another way; depending on the final shape, you may be able to get away with less, or you may need more. These figures also assume that the length of a human, particularly between outstretched hand and foot, makes the surface area of the wing correlate to that of a hang glider. This may well not be the case.

Above all, remember the cube square law; the volume (read as mass) of a creature increases much faster than size, meaning that you can't just take the proportion of wing area of a bat's body and scale it up to humans 1:1 as that won't give you anywhere enough lift. You'll probably find that your gliding human will be much more lift area than body for that reason.

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