Wind Tunnel Tests Confirm It: Bats Can Fly

[gopher65]

Where's the traced Batman logo to go with it??

I left it with the Professional Clear Plastic Binder unfortunately.

[awdz]

So much for that guaranteed "A", if you left that binder behind.

[Pharcellus]

I still like Discovery's conclusion on dragon flight.

One of the most efficient ways of providing lift AND fueling fire breath at the same time: internal bags of hydrogen and methane. With a little platinum chewing, you have fire.

Unfortunately, that is about the most unscientific proposal for flight to date. Unless Dragons are going to be HUGE blimps, it is unlikely that there would be enough lift to even glide, let alone get off the ground to fly.

Hydrogen works off of the same principle that allows battleships to float: density displacement. The problem is that the density of hydrogen is only slightly less than that of air at the same pressure, so it takes a LOT of it to life anything significant. Hence why dirigibles were monstrous to carry not much more than a couple railcars.

That doesn't even begin to touch on the other problems, such as loss of gas from injuries in storage bladders from fights, etc.

That was about the only real qualm I had with the show, well, besides the breathing fire/cold on the eggs in an egg rotisserie to make them incubate.

[C`gan]

The lift provided didn't have to be 100% of body weight. Only a margin to assist in powered flight.

[Pharcellus]

Well, the problem is that it wouldn't be even 0.01% of body weight for most depictions of Dragons, unless they were literally blimps.

Remember, it is about DISPLACEMENT, not just the "weight" (and hence, the density difference) of the gas itself.

Air by itself doesn't weigh very much. Hydrogen gas doesn't weigh all that much less than air, and not much at all as a comparative ratio of air to body mass.

Compression defeats the whole purpose of a "lifting gas", because making it more dense is the exact opposite of what you want for "lift".

[gopher65]

Compression defeats the whole purpose of a "lifting gas", because making it more dense is the exact opposite of what you want for "lift".

Exactly. People need to think how subs work (some, not all). If you have a tank filled with water (or blood, or bone, or anything that is the same or greater density than your surroundings), then you sink. If you fill it with air, you float.

Airships (and blimps, and balloons, and such) are just like subs, except they are buoyant in air instead of water. In order for a dragon to have any significant buoyancy in air at standard pressure it would need gas bags that could be filled and deflated at will. Their wings would mean they won't be the size of blimps, but they would need to be bloated up like a blowfish. That'd be a funny looking dragon, that's for sure.

[Spirit]

hmm dragons flying for real...

The thing is with gas bladders, you need an awful lot of that gas to make any real difference. Your dragon would literally look terribly fat with gas. I think you're better off looking at pteranodons and adapting them towards a more dragon-like appearance. Looking at it... a dragon would need every weight saving measure you could think of such as hollow bones and structures designed for strength in limited ways like birds do. I understand a birds' skull is strong for impacts going forwards, but not as good for other directions. As a bird is most likely to have a prang flying forwards, this makes sense. The woodpecker is the best example of this going a bit further. Birds also save weight by having a limited gut length, and as such they waste quite a bit of energy that could be gained from food. This is why they can make such a mess on your car... just imagine if they were more solid!

Perhaps gas bladders, if any benefit could be gained that outweighed the structures required.

I'd also say that a dragon would lay eggs, and any dragon laden with any real number of them would be grounded. Birds manage it though so perhaps there's a way to scale this up...

It's the whole powered flying thing that makes this hard. Even with all the weight saving measures, considering the size of a pteranodon and that they were half the average human weight. A dragons wingspan would be Huge, and to flap the muscles required would be equally immense. I have no doubt that a dragon could glide/soar with big wings, but flap those big wings at a rate enough to take off or cruise for a longer flight? Perhaps they'd be more like an albatross and need a running start or a cliff ledge. You could make the wings a smaller area, meaning higher wing loading and a higher flight speed ... so flapping would be easier but you'd have to flap harder to fly faster, and getting airbourne could be harder as a result. Perhaps there's a magic wing span and muscle layout that could achieve it... nature is like that.

Of course gas bladders could produce the fire (that Discovery docudrama)... but if the dragon did that inflight? Probably crash afterwards if too much gas was used...

I'm sure nature would have a way to help something like a dragon fly and be a dragon, but I wonder if the result would look anything like the dragons we know.

Rakku

[gopher65]

It's the whole powered flying thing that makes this hard. Even with all the weight saving measures, considering the size of a pteranodon and that they were half the average human weight. A dragons wingspan would be Huge, and to flap the muscles required would be equally immense. I have no doubt that a dragon could glide/soar with big wings, but flap those big wings at a rate enough to take off or cruise for a longer flight?

And here you just hit on another crucial problem. Things doesn't scale up well. This is why we don't have 2 metre across spiders (on land), or dragonflies the size of buses. They couldn't even breath, never mind fly. I can almost *almost* believe that a dragon could glide short distances, with sufficient design changes. But fly? Nope. Here's why:

Lets say you have a.... beetle. Beetles are good. Nice and crunchy. Now you say to yourself "hmmm, I want a beetle with more meat on it", so you increase the size of your beetles by ten times. But your beetles can't even move now! What's wrong?

Mass (and weight) increase by a cube. This is intrinsically obvious. As you increase the length of your beetle (say, 10 times), you increase its volume. Volume is a cubic function of length (or radius or whatever. Same thing). But the tensile strength of an object (and therefore muscle strength) is determined by the cross-sectional area of an object. This is kinda obvious too if you thing about it. "The weakest link in a chain breaks." You don't have to completely obliterate an object to break it, you only have to snap one part of it. But cross-sectional area is a square function, not a cubic one. So for your poor beetle you get this:

Size = 10^1 = 10 times original
Strength = 10^2 = 100 times original (!)
Mass (weight) = 10^3 = 1000 times original

So our creature now has 100 times the strength of its smaller sister, but it is now 1000 times more massive. So its strength to mass ratio is only 1/10th that if its smaller brethren. Ouch. 10% the strength.

Now you can change the design of animals to account for this. Elephants aren't built the same way beetles are. But elephants have intrinsic design problems due to their size. I can't imagine an elephant flying under powered flight, and they are as big most dragons.

So really, you can't just scale up a moth, or a bird, or a pteranodon, or a bat, or a bumble bee. None of those flight models work on a large scale. You could however have a jet powered fixed wing dragon like in Guards! Guards!.

[Spirit]

Yeah I should have put more emphasis on the Huge bit... I meant ***freakin'*** huge, but then you consider the muscles to move them and it all goes a bit fubard.

Rakku

[Wirevix]

(Onoes, replying to an old discussion!)

Amusingly, the Discovery channel special's "method of dragonflight" was either inspired by or overly-coincidentally similar to the method described in the Flight of Dragons book.

While "Flight of Dragons" the movie was a fantasy story with magic and fairies and whatnot, "Flight of Dragons" the book (which is referenced in the movie in a marvelous warping of the fourth wall) was posed as mostly nonfiction speculating on the nature of dragons in general.

In Flight of Dragons the dragons were blimps, their entire bodies expanding hugely while in flight, their insides resembling a honeycomb so they could fill numerous compartments. They did have a huge danger of expelling too much fire while flying, and in fact that was mentioned as a competition between male dragons in territory flights--who could breathe the most fire and not go crashing down to their death?

The dragons also had to have very careful methods of maintaining a very specific weight so they didn't get grounded, part of which avoided building up very much muscle, which was posed as an explanation of why dragons seemed to spend so much time sleeping in caves.

They weren't terribly impressive dragons. Hehe. But then, the real creature is rarely as impressive as the fantasy version, even for actual animals like lions and turtles.