Can Dragons Really Fly?

Could a dragon really fly? If evolution had taken a different path on earth, would it be possible to have something like large dragons soaring through the air?

The most straight forward approach to analyzing this is by analogue. What is the largest flying creature in earth history? That proves to be, as far as is known, the impressive Quetzalcoatlus from the Late Cretaceous, estimated at anywhere from 150 pounds to as much as 550 pounds. It was quite the hefty creature with a wingspan of nearly 40 feet. That’s a large creature but it is far short of dragon proportions.

Dragons such as the ones in the picture above would weigh several tons and a dragon like Tolkien’s Smaug might weigh tens of tons. There seems no way to get such a creature airborne on Earth.

What about the Pandora solution? A lower gravity world, perhaps with a denser atmosphere? Turns out that that helps but a little lower gravity and a little thicker atmosphere only makes so much difference. To really loft even a griffin of maybe 1000 pounds, you would need something more like the Moon’s gravity and maybe 10x denser atmostphere. You could call it good at that but did you notice the humans in the movie Pandora hopping around like the astronauts on the moon? And 10x denser air may not seem like much of a difference but it is no small matter. I live where it is a short trip to the Columbia River gorge where you can experience 50mph winds frequently. It’s hard to move in such winds. Imagine a 50 mph wind with 10x denser air: it would be the same as a 500 mph wind on Earth. Of course, the winds wouldn’t be that fast, it would take too much energy. Instead, the thicker air would mean both wind and aerial creatures would move slower. And while the thicker air increases lift for a given speed, it also increases drag. On net, it doesn’t really help all that much because your flying creature would stall and fall from the skies.

One thing often overlooked, however, is scale. What if your humans were smaller? Remember how much larger the world seemed when you were a child? Your perception of the world around you matches your size. So if everyone in the world was 50% smaller, then to those people a Quetzacoatlus would seem much bigger and just as importantly a world peopled by fellow small folk would look to them much like our world looks to us, except they would have (to them) taller trees, bigger animals, etc. Our half height humans would weigh one eighth of a normal human’s weight since weight is a function of volume which scales cubically. So instead of a 200 pound rider (maybe 160 pounds for the person and 40 for the riding gear), you would have a 25 pound person and harness. That’s certainly carryable by a Quetzacoatlus, especially if you tweaked gravity and density a little bit. And the wingspan would appear to be 80 feet to the mini-human. That is getting to be dragon sized. You would have to posit human intelligence in a brain of one eighth the mass but that seems feasible (more efficient neurons?) At least it pushes the problem farther down the road.

So can dragons fly? Not for us, but maybe on other worlds in our universe with smaller sentient creatures. And in the realm of fantasy, there can certainly be dragons: it is all part of the suspension of disbelief.

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7 thoughts on “Can Dragons Really Fly?

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  2. I remember reading some story somewhere where dragons had a hydrogen-filled gas bladder that made them lighter (and also provided the fuel for their breathing fire). I’m assuming flaming arrows could be an effective weapon against such creatures.

    But another issues with dragons (even relatively small ones), as they are usually portrayed, would be their proportions. Flying creatures need relatively rigid torsos and short (or at least stiffened) tails if they depend on flapping flight. The three groups of flying vertebrates, Pterosaurs, birds and bats (and insects, the invertebrate group that mastered flight) all have rigid spinal columns and relatively short, stiff tails. A long, un-fused spine (of the sort often depicted) and long, flexible tail would produce a “flopping” motion that would make flapping flight extremely inefficient.

    And of course the standard four legs plus two wings body plan is a departure from the evolutionary vertebrate model of four limbs. It is tough to imagine where the wings and their associated musculature attach/articulate in a standard vertebrate body plan. Perhaps dragons are from an alternative version of evolution where land vertebrates derived from six finned fish? The game World of Warcraft had fun with this notion by portraying most of their large, dinosaur-like/reptilian creatures (even Dimetrodons, which are actually related to mammals and not dinosaurs/reptiles/birds) as six legged. This didn’t explain where the normal four-limbed birds came from in Azeroth, though 😉

    But flying dragons are portrayed as magical creatures in most fantasies, and so perhaps a certain amount of telekinetic magic is involved. I still love them.

    1. Interesting observations on the vertebrae- I hadn’t considered that. The six-limb bit though certainly stands out. I use griffins (which are also six-limbed) in my current world but they were created so who’s to say?

      The hydrogen gas bag you mention was from a TV show (Dragon hunters(?)), at least that is one place it appeared. A hydrogen gas bag could explain a breath weapon but NOT bouyancy. A void in the dragon filled with hyrdogen gas would not make the dragon’s net-density less than air 🙂 It would take a huge gas bag to do that. Compressed hyrdogen gas might provide a great flame source but compressing hyrdogen just increases its density. In the end, hydrogen gas for list doesn’t come close to working unless your dragons look like the Goodyear blimp 🙂

      I think scale is the easiest way to have flying amounts. If you imagined a world where everyone thought they were our size by were actually 1/4 or 1/8 our size, you could have dragons of roughly the size as depicted. But for human sizes, it will take something else. In my current project, I have the dragon wings able float on magic Ley lines.

  3. The gas bag wouldn’t make it more dense than air, but I think the idea was it lightened the creature enough that flapping flight was possible. But once you get into that sort of thing, then you might as well invoke magic, I think.

    1. I think magic is the way to go 🙂

      The following is just for fun (please don’t take it wrong) but it would take a very large amount of hydrogen gas at low pressure to float a dragon:

      As a rough estimate, a cubic meter of hydrogen gas, at atmospheric pressure (i.e., not compressed inside a creature, which would increase its density and lower its lift capacity), can lift about 1.2 kilograms. A cubic meter of dragon is going to be about 1000 kilograms (assuming rougly the density of water). This means that for neutral buoyancy, the dragon requires a gas bag about 800 times the volume of the non-hydrogen part of the dragon. Any gas bag you could stick inside a dragon that doesn’t materially change its shape is only going to lift a tiny part of the dragon’s weight. Another way to look at it is that the net dragon density of hydrogen gas + dragon flesh/bone must be less than the density of air to be buoyant. Hydrogen gas is not very dense but dragons are very dense: it takes a lot of hydrogen to float a dragon.

      Even allowing for some lift from the wings, I think your dragon would have to look like he swallowed a dirigible for hydrogen gas sacs to make a different 🙂

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