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Can a draconic or pterosaur-like flying creature weighing about 1-1.5 times that of an average human carry a human through the air for a distance of about 10 miles? If not, what atmospheric and/or gravitational parameters could the planet have to allow such a creature to exist? Metabolic requirements and evolutionary plausibility are not an issue. Based on the Quetzalcoatlus Northropi pterosaur, it seems like such a creature could exist on its own, but I'm unsure about whether it could have a rider.

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  • $\begingroup$ Depends on the amount of lift it produces\ $\endgroup$ Commented May 24 at 18:49
  • $\begingroup$ @Coolcats112 I don't know how much lift it would produce, which is why i'm asking the question. Basically, it has proportions similar to a pterosaur, with similar muscular and bone structure. Under those circumstances, would it produce enough lift to fly carrying a rider? $\endgroup$
    – le_chat
    Commented May 24 at 19:09
  • $\begingroup$ The larger pterosaurs are soaring type. Which means that once in flight they probably could carry that mass but like albatrosses have really high, comparative, stall speed. Which means landing and take off is part that will limit mass to much lower percentage maybe 5 to 10%? $\endgroup$ Commented May 24 at 21:47

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Most earthly birds can carry at most 80% of their own weight, and our old friend the Square-Cube Law says that's much easier for small birds than large ones. The heaviest flying bird currently found is the kori bustard, which at 19kg is less than 1/4 the weight of an average American. They can barely carry their own weight aloft, much less carry anything substantial. Your pterosaur is estimated to be about human-weight, but we have no good information for its potential carrying capacity. Given the aforementioned square-cube issues, almost certainly no pterosaur could support a rider or even carry anything heftier than a toddler. Scientists aren't entirely unanimous on it being able to fly itself.

Since you're opening up unlimited metabolism and evolution, we might be better served looking at hang gliders. Those can carry humans aloft while being easily half the weight of their passengers. Of course they are gliding, not flying, and would need to rely on tall places to jump from and/or implausibly convenient wind currents to get aloft in the first place. That's going to be true for any particularly large flying cargo creature. Also worth noting that carrying their "riders" below their own center of mass is going to be substantially easier than letting them ride on top, with unfortunate consequences to awesome cover art.

Thicker atmosphere helps. Higher wind helps (except when it hurts). Lower gravity helps. Lighter riders help (if you want to keep your mounts close to the same weight as their riders, it's easier if they're both smaller). Turn any combination of those dials far enough and sure, you can have dragonriders without offending physics. All else being equal, an earthly flying creature suddenly finding itself in 50% gravity (but the same atmospheric conditions) could carry its own weight. But its muscles would atrophy over time unless specifically designed or induced to maintain earth-level strength, similar to effects astronauts experience in orbit. And even at full power and half gravity, trying to straddle the neck of a bird or pterosaur-shaped creature with equivalent mass to its rider is about as physically feasible as riding a bike by standing on one end of the handlebars; saddle design will be tricky to say the least.

I know the question handwaved away issues of evolution or natural environment, but it is important to point out that low gravity tends to correlate with thinner atmospheres (thought not always). And an environment that has such dramatically weaker gravity would presumably have a whole host of other changes to its inhabitants and environment, so hopefully our dragon and rider are both relatively recent visitors.

If it's important to stick to familiar circumstances, you have animal-assisted flight on Earth with regular humans as long as you mostly want to glide and DEFINITELY bribed evolution to look the other way; the bone and muscle and metabolism involved would be well outside anything we've got the parts for in our fossil record. And the resulting creature would not be proportioned anything like any animal we've ever seen.

The real question is what you're trying to accomplish. Change enough of your environmental variables and you can justify most anything ("my engineered dragonoids breathe fire because they eat phosphine, fly because they're telekinetic, and can teleport because don't worry about it, that's why"), or stick to strict conditions and let that shape your weird background details ("my dragons are basically walking hang-gliders with carbon nanotube bones, worn as backpacks by the riders"). It's your world, what do you want to do with it?

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  • $\begingroup$ Approximately how much would I have to change gravity and/or pressure to get it to work? $\endgroup$
    – le_chat
    Commented May 24 at 19:44
  • $\begingroup$ Very approximately, reducing gravity by 50% but keeping atmosphere and physiology the same (which is a rather bizarre combination of assumptions) means a flying creature can now carry its own weight, but straddling its neck is still going to be a huge stability/mobility issue if it's shaped like a bird or pterosaur. $\endgroup$
    – Jay McEh
    Commented May 24 at 19:54
  • $\begingroup$ Mixing atmosphere changes, gravity changes, and body shape changes can give different results-- but you need to provide some of those values yourself since each changes the others. $\endgroup$
    – Jay McEh
    Commented May 24 at 19:56
  • $\begingroup$ Ok, thank you. This answer was very helpful. $\endgroup$
    – le_chat
    Commented May 24 at 19:58
  • $\begingroup$ Welcome to the site and thank you for the checkmark, but for the future it's advised to wait a day before accepting an answer-- users can help you shape your question in a way to get multiple potential answers with even better specificity, but are less likely to participate if they see it's already closed. Cheers! $\endgroup$
    – Jay McEh
    Commented May 24 at 20:04
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Check out Titan in this blog post: https://what-if.xkcd.com/30/

To summarize, if the atmosphere is thick enough and the gravity weak enough, then you could fly using your own muscle power, let alone something with wings.

So you have several variables to play with:

  1. Atmospheric thickness
  2. Gravity
  3. Wing surface area
  4. Dragon muscle strength

Titan has surface gravity of 1.35m/s, which is even smaller than the moon's, and 50% thicker, about 95% nitrogen and 5% methane, compared to earth's 80% nitrogen and 20% oxygen (rounded).

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