My children are watching Dragons: A Fantasy Made Real, a docudrama on DVD from the Discovery Channel. It's hard not to laugh.
Well, no, it isn't.
We'll just hit the major fantasies contained in this docudrama; the ones that leaped out at me. We'll look at ...
It is extremely unlikely that a 900-pound reptile could fly. It's unlikely enough to call it impossible.
The BBC did report on an extinct bird that weighed 70 lbs, which could glide. There's also a Scientific American article suggesting that some flying pterosaurs could have weighed up to 550 lbs., though the lower—and more common—estimate is 250 lbs.
Pterosaurs could fly. David Unwin of the University of Bristol and Natasha Bakhurina of the Russian Academy of Sciences report in a letter to the scientific journal, Nature:
Kevin Padian is a paleontologist at U.C. Berkely, and he is the most cited scientist on the subject of pterosaurs. He says:
Dragons: A Fantasy Made Real suggests these dragons would be 900 pounds. Animals over 500 lbs., and probably over 300 lbs., don't fly.
If dragons—at least dragons like the ones in Dragons: A Fantasy Made Real—existed, we'd have found their fossils.
Think about it. The docudrama brings up pterosaurs and crocodiles. We have tons of fossils of both. No one speculates about whether they ever existed.
900-lb. winged, flying creatures that are not pterosaurs would have been found.
This was the biggest joke of all in Dragons: A Fantasy Made Real.
When I saw this, I laughed out loud, stopped the DVD, and explained to my children what I'm about to explain to you.
Hydrogen is buoyant in air because it is lighter than air in the same way that wood is buoyant in water because it's lighter than water. The difference between the weight of the air and the weight of the hydrogen is how much lift the hydrogen will provide.
According to a fact sheet from Spectrum Laboratories, hydrogen has a lifting power of .076 lbs. at 32o fahrenheit and average barometric pressure (760 mm). (That figure matches what I found at a Los Alamos National Lab page, but the Los Alamos page is down now.)
So let's assume this hypothetical dragon could make room inside itself for a 10'x8'x8' space, the size of a small bedroom. This is exaggerated by a lot, but let's give it the benefit of the doubt.
That's 640 cubic feet. Hydrogen can lift .076 pounds per cubic foot. That totals 48.6 pounds ...
... if it could open up a bedroom-sized space inside itself.
Houston, we have a problem.
Worse, as the dragon got higher, the density of the atmosphere would decrease, so the lifting power of the hydrogen would decrease as well. Also, if you heat the temperature above freezing, the lifting power decreases as well because the air, which is lifting the hydrogen, grows less dense as it heats.
Nor does it do any good to compress more hydrogen inside the dragon. As you do so, the weight of the hydrogen simply increases, and thus its lifting power decreases, not increases. You will get the ultimate lifting power from a vacuum, so you'd want less hydrogen, not more.
Finally, think about the last tank of helium you bought ...
Of course, none of these things happen with helium tanks. They don't happen with dragons, either, despite what Dragons: A Fantasy Made Real suggests. Adding hydrogen, even at the highly exaggerated amount of 640 cubic feet, creates an 850-lb. lift problem rather than a 900-lb. one ... at best.
No 6-limbed creature has ever been discovered.
Dragons: A Fantasy Made Real shows dragons like the statue in Ljubljana ...
Everything that has wings has only two feet. Yes, pterosaurs and bats sometimes go around on their two feet and their wings as well, making them somewhat quadrupedal, but none of them have or had 6 limbs.
This point doesn't make a bipedal—rather than quadripedal—flying dragon impossible (though the earlier points do), but I bring it up to point out that Discovery wasn't trying very hard to be scientific.
There's lots of explanations for this, though I'm not for writing off legends.
There's plenty of indication that the Loch Ness monster never existed. Yet there's been many sightings, and several purposeful hoaxes.
So there's a few drawings of dragons and some stories. The medieval drawings could have been the products of the stories. The stories could have been the product of imagination or of exaggeration of real animals. There are plenty of creatures in the sea big enough to be legitimately considered sea monsters. The stories of world travelers who saw things like a komodo dragons would have led to some pretty outrageous stories.
Is there a possible real basis for dragon legends, so that a large, fire-breathing reptile could exist?
It's hard to say anything's impossible, but the reptile from Dragons: A Fantasy Made Real has to be close.