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From my superficial understanding of physics, it seems that large flying creatures like your typical Western dragon wouldn't be possible on Earth, specifically because they would always be too heavy.

Because of the square-cube law and how muscles work (again, superficial knowledge), adding more muscle and bone to a creature increases its weight more than it increases its strength. Smaller creatures have plenty of strength compared to their weight, but as you get bigger, that ratio starts to shrink. A creature can optimize its weight, but eventually there would seem to be a threshold where the amount of strength required matches the amount supplied by muscle and bone, and anything bigger would be unable to move or would collapse under its own weight.

My thought is that reducing the gravity of the planet being considered would reduce the weight per unit of muscle/bone, but it wouldn't reduce the strength per unit. Thus it should push the threshold higher.

First off: does the above make sense? If so, starting from an Earth-like planet as a model, would changing the gravity alone be a viable solution to creating a world with dragon-like flying creatures? Or would the amount of change required be so great as to create other problems or significant differences from Earth?

Keep in mind that the creatures, in addition to carrying their own weight, would also have to carry the weight of their food, as well as some amount of cargo or passenger weight (maybe on the order of 1 to 3 humans, who themselves would weigh less due to this scenario).

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    $\begingroup$ This at present would be a generic yes/no Question, but you've tried to slip another couple of questions under the radar. Instead of that, could you highlight the actual question you want answered, with whatever constraints you wish. $\endgroup$ – A Rogue Ant. Apr 21 at 1:37
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    $\begingroup$ @ARogueAnt. I've tried to make my question and constraints clearer. As this is my first time asking here, please feel free to give me (or point me toward) guidance on any aspect of my question that isn't correct. $\endgroup$ – Keith Stein Apr 21 at 1:49
  • $\begingroup$ For a lower bound on practical flight-sizes, human muscles with a wingsuit would be sufficient on Titan. xkcd.com/620 what-if.xkcd.com/30 Of course, there are some slight problems for humans there, as noted in the second link. Your dragons can be well-suited to the environment, though. $\endgroup$ – Anon Apr 21 at 2:51
  • $\begingroup$ Hi Keith, welcome to Worldbuilding. Please note that Stack Exchange's basic model is one-specific-question/one-best-answer. One of the reasons to vote to close a question (needs focus) is that you've asked more than one question. You have, indeed, asked more than one question. The simple answer to your question is yes, lower gravity would allow larger flying creatures. In the future, please restrict your questions to, literally, a single question. Thanks. $\endgroup$ – JBH Apr 21 at 4:32
  • $\begingroup$ Yes, absolutely. But no, less than you think. Air density is much more important.half the gravity will allow a creature to be 25% bigger. Double the air density will allow a creature ~ 50% bigger. $\endgroup$ – PcMan Apr 21 at 15:07
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Yes, under the assumption that atmospheric density is kept the same, or increased. Planets with thicker atmospheres and weaker gravity than Earth will harbour more living things capable of flight, as these conditions make it so it takes less force for an flying creature to stay airborne. The largest animal capable of flight known to science was the Quetzalcoatlus, with a wingspan of 10 m and a mass of 200 kg, at lowermost estimates. It could carry about 50 extra kg. Let’s set the goal of the mass to be carried at 250 kg. It will require 5 times less gravity or 5 times more atmospheric density, or half gravity and 2.5 times denser atmosphere. And, the building materials of the body won’t be affected in terms of strength by gravity, so that could exist.

Of course, I’m using a real animal to model your fictional scenario, but that should help.

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Even humans can fly in zero gravity.

flying people in zero g

https://www.space.com/zero-gravity-resumes-weightless-flights-coronavirus-pandemic.html

Is flying so different from swimming? The body of the flyer must be suspended against gravity in the liquid medium either via buoyancy or through the efforts of the flyer. The flyer propels itself via bodily efforts against the liquid medium.

In water, many humans are largely suspended via buoyancy and with a life vest are completely suspended, with the only issue then being propulsion.

In air at earth surface gravity, considerable effort is needed to suspend our bodies. As gravity decreases the energy needed to oppose it (either via buoyancy or effort) decrease until at zero gravity there is no energy needed to oppose it. Then the only issue is propulsion which humans can achieve in air with motions similar to what we use in water.

In a low gravity situation suspension of the body in the medium becomes easier and so larger (denser) fliers become possible.


The issue is how a low gravity world retain an atmosphere dense enough to fly around in and does not have the gas molecules fly off into space. A separate issue! Maybe L.Dutch will post that gas escape / temperature / gravity graph. It has been a while.

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