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.