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I'm not a professional at world building or character building, still starting out, but I do want to make an attempt at having my fantasy character be somewhat realistic.

He's 11 years old, 4.8 ft (1.64 m) and roughly 80 pounds (36.2 kg). He's a little tall and skinny for his age, and has digitigrade legs with a tail that reaches the ground. (Have not yet factored this into his weight.)

Can someone please help (or educate) me on how long and/or heavy his wings would have to be to lift him off the ground and sustain flight (beyond gliding or soaring) under Earth's gravity?

I would be so, so grateful.

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The type of body you're looking for and the sort of flying your character will be doing have a significant bearing on what sort of wings they'll need. The "ideal" bodytype would perhaps be harpy-like, without unaerodynamic things like clothes or extra limbs (which would also be dead-weight when flying). Deep chest with massive muscles. Much more lightweight bones. Probably a pointier head. Much less weight and muscle in the legs and buttocks (again, deadweight, no good for flying). Actually, lets just cut to the chase... the ideal shape is "a bird". Every deviation from the basic bird bodyplan will probably lead to a heavier and less aerodynamic body which will need bigger wings to stay aloft and stronger muscles to take off.

The type of flying you intend to do also has a big impact on wing shape, and one which I'm not going to go into detail on here


So, in the absence of more information, lets consider one of the largest known flying birds, Pelagornis sandersi. Upper weight limit was about 40kg, conveniently about the weight of your guy. Wingspan was over 6m.

Remember this is a bird, so was optimised for life on the wing, not tottering around on the ground, holding tools, chatting with other beings, wearing clothes, etc etc. I believe this species was assumed to be a seabird, and those very long slender wings certainly look quite albatross-like, optimised for long efficient glides over great distances and extended times.

Pelagornis sandersi

A much heavier bird (up to 70kg or so), Argentavis magnificens, had a similar wingspan, but much deeper wings (there's probably a better term in the aviation or ornithology worlds, but I'm not aware of it) to support that extra weight. Again, bird, optimised for flying (or at least soaring), none of the other people things you might be interested in.

The condor also in this picture weighs up to about 15kg and has a wingspan of over 3m. This should probably tell you that you can't just give your dude big fat condor-style wings and have him fit in a confined space... there's not too much chance you'll get away with wings under 4m, though it is tough to provide a more realistic minimum for you.

Argentavis size comparison with condor and human

These should give you some idea of the sheer size needed, even if they don't give you a good idea of how radically different the body plan of a flyer is compared to a human (apparently a tree-dwelling ape who took up endurance running and burning things). Trying to combine the two bodyplans will be tricky, to say the least, but there are pages and threads and questions out there ad nauseam about anatomically plausible flying humans.

For a more unusual bodyplan, consider a pterosaur:

Comparison of quetzalcoatlus size with human

Frustratingly, no-one seems quite sure about how much those things actually weighed. Early estimates were ludicrously low. That Quetzalcoatlus sp. probably weighed at least as much as an adult human, with a 6m wingspan. Smaller pterosaurs obviously existed, but no-one knows how much they weighed either, but the possibility exists that with pterosaur style wings you might be able to give your guy a wingspan as low as 4m. Positively petite!


As a closing note, consider the attempts to make mere humans fly under their own power. Paragliders, outstretched wingspan of 8.4m. Hang-gliders 9m. Both are for adults, and both add 20-40kg, but they only scale down so far and only allow unpowered takeoff. Ornithopter... 32m, still needed an assisted takeoff. Pedal-powered propeller... 34m. Both of those needed olympic-class athletes to operate, which should give you some idea as to the athleticism and stamina your character needs to have in order to fly.

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  • $\begingroup$ The wing words you are looking for are "chord" and "aspect ratio". See also "wing loading". $\endgroup$ – Harper Aug 13 at 8:08
  • $\begingroup$ @Harper thanks for that! $\endgroup$ – Starfish Prime Aug 13 at 10:35
  • $\begingroup$ For pterosaur weight, this link gives some information on that. You're looking at a weight range of around 180-250kg for the Quetzalcoatlus northropi, which is certainly greater than the OP's 40kg character (you could even plausibly get away with dropping the wingspan from 10m to around 6-7m at that point), but these huge fliers needed an actual reason to spend the energy of taking off. As for how a character with a 6m+ wingspan could be portrayed, that's a problem for the author. $\endgroup$ – Palarran Sep 1 at 22:17
  • $\begingroup$ @Palarran no, that's just a recent estimate (and one with very long error bars). No-one really has a clue. It is more likely to be closer to 180 than the 80 that some other researcher suggested at least. I didn't talk about Northropi because it was clearly too big to be relevant here. $\endgroup$ – Starfish Prime Sep 2 at 6:38
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You could model your flyer on Argentavis. It weighed about 80 kg. It had wings 9 meters wide.

argentavid

https://en.wikipedia.org/wiki/Argentavis

Prior published weights gave Argentavis a body mass of 80 kg (180 lb) but more refined techniques show a more typical mass would've likely been 70 to 72 kg (154 to 159 lb), although weights could've varied depending on conditions.[8][4][9] Argentavis retains the title of the heaviest flying bird known still by a considerable margin, for example Pelagornis weighed no more than 22 to 40 kg (49 to 88 lb).[6] For comparison, the living bird with the largest wingspan is the wandering albatross, averaging 3 m (9 ft 10 in) and spanning up to 3.7 m (12 ft 2 in). Since A. magnificens is known to have been a land bird, another good point of comparison is the Andean condor, the largest extant land bird going on average wing spread and weight, with a wingspan of up to 3.3 m (10 ft 10 in). This condor can weigh up to 15 kg (33 lb).

9 meter wide wings will make it tough to dance. Might I suggest you give your flyer a preternaturally slim, elfin build. Taking his weight down from 80 to 30 pounds will let him have 9 foot condor wings.

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    $\begingroup$ Blargh, that'll teach me to crawl google image search for 20 minutes before posting. Just ended up with more or less the same stuff you already wrote ;-) Have a +1 for efficiency ;-) $\endgroup$ – Starfish Prime Aug 12 at 21:47
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It's not just a question of wingspan. Most birds have (sort of) hollow bones, which helps to keep weight down. And that's really important.

Additionally, actually getting into the air requires speed, and powerful muscles to flap the wings to achieve lift.

Another consideration is the weight of the wings themselves, and the strain placed upon the spine by them. Bigger means more weight, and more weight means more strain. If big enough, the kid could be a cripple by 20.

In order for your character to be able to get into the air and fly, it would need:

  1. Powerful legs to build speed for lift.
  2. To rely on wind,or high drop offs to build enough speed for lift.
  3. Powerful chest and shoulders to flap for extended periods to brute force it into the air.
  4. Any combination of the above.

Muscles are dense, no matter where on the body they are, and that adds weight. In order to protect the spine, said child would need to have well developed chest, shoulder and back muscles, and be extremely lean. Bones would have to be, as previously mentioned, hollow-ish(think of a honey-comb structure), which makes them less resistant to breakages, and has a lower hard limit on how much weight they can sustain before breaking.

Nature imposes these limits on us all the time. We are the size we are, because anything bigger tends not to survive (giants have heart attacks, and skeletal problems due to weight).

So let's assume a wingspan of 10 feet on the child. By the time that child is 20, that wingspan will need to increase, and as such will also increase in weight.

Eventually, the muscle mass required to even move the wings would put enormous strain on the heart and skeleton(because humanoids have a leverage based skeletal/muscle structure), so flapping to generate lift would necessarily give way to soaring and taking advantage of thermal updrafts later in life. There is a reason that large birds tend to live in aeries: So they can jump out and build up enough speed to glide and soar. It's actually very difficult(and energy intensive) for them to get off the ground without strong wind. This means your flying child would have to have incredibly powerful legs, so that he could either jump VERY high in the air, or run REALLY fast to generate enough speed for the wings to generate lift efficiently.

The reality of your character is that even at 11 years old, he would look like a miniature body builder, and would be an athlete rivaling Olympic medal winners. And even whilst folded, those wings would reach well above his head, and would drag along the ground when he walked.

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    $\begingroup$ I'm not sure the size argument entirely holds water... giants are abnormally tall compared to other humans, and so demonstrate that you can't just trivially scale up small designs to big designs. We are the size we are due to a whole bunch of things, including environmental demands and nutrition and mate selection and the fact that things can't generally be changed significantly in a short period of time. $\endgroup$ – Starfish Prime Aug 13 at 14:44
  • $\begingroup$ I refer to the square cube law: If an organism doubles in length isometrically then the surface area available to it will increase fourfold (square), while its volume and mass will increase by a factor of eight (cube). Therefore the strength (and thereby calorific and oxygen consumption) required also increases eight-fold. Eventually, you reach a size that cannot be sustained by the oxygen concentration of our atmosphere. This is also an engineering problem: As you increase mass, you need more lift, but to increase lift, you need bigger wings, which means more mass. Repeat ad nausium $\endgroup$ – Ian Young Aug 14 at 12:17
  • $\begingroup$ Uh, I'm gonna have to point out here that organisms exist that are larger than humans. Sometimes substantially larger. Clearly it is possible to be bigger than human and not just break. That's why I was clear to distinguish abnormal size differences in my comment. $\endgroup$ – Starfish Prime Aug 14 at 13:08
  • $\begingroup$ Indeed, but a grand total of zero of those creatures walk upright and fly. The spine simply cannot handle the weight without reinforcement, which adds yet more weight. $\endgroup$ – Ian Young Aug 14 at 13:12
  • $\begingroup$ You are conflating multiple issues. I commented solely on your assertion that human size is limited given that people who are abnormally large have health problems. $\endgroup$ – Starfish Prime Aug 14 at 13:27
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It greatly depends on flight conditions.

Paragliders has wingspan about 8-12 meters (4-6 half-wing). It is able to takoff from ground and land more or less safely. Jet wing have only 2.5 meters wingspan, but needs a "drop down" takeoff.

Both support much more weight than 30 kg (about 90-120). But wingspan depends on weight more like sqrt(x). It means you can divide this values by 2 at max. It means 2-3 meters for takeoff and hardish landing from/to ground for very thin bat-like unnaturaly strong wings

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    $\begingroup$ "Wingspan", not "wingspawn"... $\endgroup$ – Graham Aug 13 at 15:14
  • $\begingroup$ Jetwings manage to fly with a small wing because they fly fast, which takes a lot of power - far more than muscles can produce. They also use a parachute to land, as their minimum flying speed is still much faster than a human can run. $\endgroup$ – Robin Bennett Aug 14 at 8:36
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I would suggest looking at bats instead of birds. They are more apt to be tool users since their wings are effectively webbed hands / fingers. Plus bats are more efficient than birds according to this article I found.

https://www.livescience.com/1245-bats-efficient-flyers-birds.html

If you think of how much lighter some stretchy skin could be compared to a mass of feathers you've got a much simpler body configuration and possible webbing between other body parts.

If you add retractable spines with skin between like maybe Dimetrodon mixed with toothless from the Dragon Rider movies you could have a huge amount of flexible, flapable, retractable surface area.

This lets you have bat like powered flight, super maneuverability or maybe flying squirrel like gliding.

I'll leave the wingspan to the others since they seem to have already figured that out, but I think you can reasonably get away with less with this alternate configuration.

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