Size of Dragon Hydrogen Bladders

[McC]

I think this goes here, as it's a question of science and biology more than anything else.

Recently, Animal Planet aired their "Dragons: A Fantasy Made Real" special. In it, they propose that dragons had 'hydrogen bladders' that they tapped for both fire-breathing and for creating a buoyancy that allowed their large forms to take flight. Is this realistic? How big would a hydrogen bladder such as this need to be to enable something as big as an adult dragon to fly?

[Crossroads Inc.]

How big would it need to be to providse usable lift? Um... gee, about 10x the size the Dragon itself?

Next question!

[GrandMasterTerwynn]

I think this goes here, as it's a question of science and biology more than anything else.

Recently, Animal Planet aired their "Dragons: A Fantasy Made Real" special. In it, they propose that dragons had 'hydrogen bladders' that they tapped for both fire-breathing and for creating a buoyancy that allowed their large forms to take flight. Is this realistic? How big would a hydrogen bladder such as this need to be to enable something as big as an adult dragon to fly?

Imagine a blimp. Failing that, imagine a largish balloon.

Now, imagine calling your cable/sattelite provider and complaining about how Animal Planet is putting horseshit like that on the television.

[McC]

C'mon, guys. Not even an attempt at calcs?

[Crossroads Inc.]

Ok, how about just rough estimates?

A normal sized blimp can carry around 250lbs,
How much did one of those Dragons weigh?

Adjust the the size of the blimp to match.

[Darth Raptor]

The "flight bladders" only helped in flying and swimming. The fins/wings did the majority of the work, and the skeletons of the aerial species were really lightly built. In the flightless species, it served only as ammo for the flamethrower.

I'm no physicist, as should be obvious, but the wings did the flying. Does that change much? Anything?

It was entertaining, but I like large reptiles that eat people.

[SirNitram]

The fact the wings did the flying and the bladder just lightened the load somewhat helps a bit; it mostly reduces the wingspan requirements into the realm of possibility.

But really, any discussion of calculations requires the dimensions of the critter.

[McC]

Echoing what Raptor said, the hydrogen wasn't doing the flying, it was simply helping 'lighten the load'.

[Alan Bolte]

But really, any discussion of calculations requires the dimensions of the critter.

Then turn it around. What's the largest size reasonable? You just need to figure out an upper limit on the size of the bladder relative to the dragon, come up with numbers for the bone density, as well as that of all the organs and other fleshy bits, take into account changes in musculature and bone size needs as you scale up, and then scale up until the buoyancy no longer offsets things enough, and you end up the with all the usual problems of a creature that big being anything like the creatures of fantasy. Not being a student of biology, I have no idea how to go about that.

[Mayabird]

Well...in Guards, Guards the noble dragon's fire burning the ground creates thermals that give it extra lift to fly. The dragon weighed several tons, though.

But this is from Terry Pratchett's Discworld series, and let's not go into those poor swamp dragons.

[SirNitram]

Well...in Guards, Guards the noble dragon's fire burning the ground creates thermals that give it extra lift to fly. The dragon weighed several tons, though.

But this is from Terry Pratchett's Discworld series, and let's not go into those poor swamp dragons.

Noble Dragons also require excessive amounts of magic to exist, because they can't live in a world that's too 'real'. And when Discworld is too real for you, you're pretty unreal.

[Gunhead]

Not that dragons need to be that big to be dangerous.
In a RPG I played in once, we had dragons that were about the size of a small horse+wings. Yes those would weight over 250lbs, but man they were nasty.

-Gunhead

[Petrosjko]

Well, one would have to go for the infrastructural design that would make flight possible in the first place, hollow bones and so on, and then...

Well...

Maybe if they glided, a la pterodactyls.

[Broomstick]

Quetzlcoatlus, one of the pterosaurs, had a wingspan (depending on who you quote) between 36 and 50 feet. So, apparently, soaring/flying creatures are capable of evolving at least that wingspan.

Hydrogen has a lifting capability of approximately 2 ounces per cubic foot. Meaning using it to lift 250 lbs would require 4,000 cubic feet of hydrogen. I'll leave it to one of our mathmaticians to convert that to metric.

Back in the golden age of zepplins some of the ships had a lifting capacity measured in tons. Whether or not an animal could replicate that... I don't know. How many cubic feet in the body of a blue whale? A hypothetical flying dragon would wind up roughly whale-sized, and probably whale-shaped, or at least streamlined. How much of that volume could be occupied by hydrogen and still leave a functional animal?

Happy speculating.

[Civil War Man]

A depiction of a possible real-life dragon I read included characteristics like this:
- Adult: about the size of an SUV or a VW minibus
- Hollow bones to aid in flight
- Catlike eyes for better night vision
- Claws, teeth, scales, wings, etc.
- Breath weapon largely the result of the digestive system

Fire breathers, for example, would have a bladder which stores methane and one that stores phosphorous (not sure how they'd obtain that), and uses the latter to ignite the former.

Cold breathers would have a bladder which highly compresses gas (probably nitrogen), and then spits it out as an attack.

Acid breathers just vomit up stomach acid.

A consequence of this breath weapon hypothesis is that a starving dragon would not be able to use it.

[Stark]

Hang on - are we seriously talking about dragon viability?

We all know the answer: to be large and flight-capable, an animal wouldn't be much like a fantasy dragon at all. So I guess the answer is 'no'... but surely you knew that already. 2 ounces per cubic foot...

Someone even mentioned the breath weapon... hahahahahahahaha... oh, mercy.

[Cykeisme]

What's the density of Earth's atmosphere at sea level, and what's the density of hydrogen at the same pressure (sea level)?
Probably easily Googled, but pointing out that these two numbers will easily reveal how much buoyancy a hydrogen ladder of arbitrary size would provide.

I do believe that for a dragon of fixed size (volume), the presence or absence of hydrogen bladders would effectively only cause a difference in the mass of the dragon. I doubt the difference between a hydrogen bladder and an air bladder would be significant.

[Darth Raptor]

These creatures are barely on the cusp of being able to fly anyway. They can't take off if they have an undigested meal in their stomachs, and they're forced to land if they breathe too much fire.

They aren't gliders either. Unlike pterosaurs, the wings of these dragons are supported by an entire arm and very muscular. Flap, flap flappy. Like no other flying creature of that size. Come to think of it, did it ever say just where the third pair of limbs in modern dragons came from? They're supposed to be adapted from the fins of Cretaceous marine forms, but where did THOSE come from? Four-armed vertebrates just don't happen on Earth.

[Pick]

Any dragon that is viable in this world is not the kind of dragon I want to imagine.

[Alyrium Denryle]

I think this goes here, as it's a question of science and biology more than anything else.

Recently, Animal Planet aired their "Dragons: A Fantasy Made Real" special. In it, they propose that dragons had 'hydrogen bladders' that they tapped for both fire-breathing and for creating a buoyancy that allowed their large forms to take flight. Is this realistic? How big would a hydrogen bladder such as this need to be to enable something as big as an adult dragon to fly?

This idea they probably drived from the FLight of Dragons by Peter Dickenson... I need to find a copy somewhere...

The wings would of course do the flight, but by expanding their bodies with hydrogen it would be possible if they were small enough to take some of the load off of their wings.. I have no idea how to run the calcs though, and sadly missed the special...

[wolveraptor]

These creatures are barely on the cusp of being able to fly anyway. They can't take off if they have an undigested meal in their stomachs, and they're forced to land if they breathe too much fire.

They aren't gliders either. Unlike pterosaurs, the wings of these dragons are supported by an entire arm and very muscular. Flap, flap flappy. Like no other flying creature of that size. Come to think of it, did it ever say just where the third pair of limbs in modern dragons came from? They're supposed to be adapted from the fins of Cretaceous marine forms, but where did THOSE come from? Four-armed vertebrates just don't happen on Earth.

apparently, a freak mutation occurring in Sea dragons provided the animals with 6 limbs. The Cretaceous dragons were bipedal, using their forearms to fly.

some stats from the animal planet site

prehistoric dragon:

in excess of 1 ton

probably meaning a little over a ton, but its open to interpretation i suppose and

a wingspan upwards of 35 feet

kind've small if you ask me.
also, the bones were honeycombed and filled with hydrogen (in addition to the bladders). It was the largest species of dragon.
http://animal.discovery.com/convergence ... plore.html

mountain dragon: the only other flying dragon. it had all of the bone features and hydrogen bladders of the former dragon, but was smaller. unfortunately, no dimensions are provided.
http://animal.discovery.com/convergence ... ntain.html

[General Brock]

Wonder how long it will be before somebody gets the bright idea to genetically engineer a fire-spitting dragon. They played with fruit flies, why not small lizards, as the tech for handling DNA from a more complex organism matures. Then you could test out that hydrogen bladder thing for real. Hydrogen gas is so explosive, I don't think any natural organism has evolved a mechanism to separate and contain it for any purpose.

Fish might be a round-about start. They separate the O from H2O with their gills. You just need a way to collect the hydrogen. They come with air bladders for buoyancy already.

I never saw the special. I'll have to catch the DVD. It may not be anywhere near realisitc or practical to do, but fun to speculate on.

[AMX]

Fish might be a round-about start. They separate the O from H2O with their gills. You just need a way to collect the hydrogen.

Wrong.
They only collect the O2 that's in solution in the water; they don't break up the water itself.

[Broomstick]

I'd like to point out that my earlier calculation of 4,000 cubic feet of hydrogen being required to lift 250 lbs was a little off - I inadvertantly left the lift number for helium in when I did it. You need "only" 2,000 cubic feet of hydrogen to lift 250 lbs.

That's still whale-sized - or at least orca-sized. Just for the lifting bladder. You'd somehow have to wrap the 250lbs of living animal around it.

What's the density of Earth's atmosphere at sea level, and what's the density of hydrogen at the same pressure (sea level)? Probably easily Googled, but pointing out that these two numbers will easily reveal how much buoyancy a hydrogen ladder of arbitrary size would provide.

Already stated - hydrogen lifts 2 ounces per cubic foot at sea level pressures.

Which brings up a good point - the bouancy will drop off rapidly as you rise, unless the hydrogen bladders expand rapidly. This might be possible if it was thin-walled, but one problem with H2 is that the molecules are so small they leak out of almost anything. And if you poke even a small hole in the side of such a dragon it won't be able to fly due to loss of bouancy.

I do believe that for a dragon of fixed size (volume), the presence or absence of hydrogen bladders would effectively only cause a difference in the mass of the dragon. I doubt the difference between a hydrogen bladder and an air bladder would be significant

Depends on the volume vs. the mass - something like the Hindenburg could transport tons of material and circumnavigated the globe at least once. It also displaced a greater volume than the Titanic. The question is whether an animal able to replicate the feat could evolve.

I don't think obtaining the hydrogen would be impossible - there are a number of chemical reactions that will yield hydrogen, one or two might be suitable for the purpose. The problem is the volume to mass ratio. You might be able to come up with a small dragon, about the size of a chihuahua. I don't know if you could wind up with a dragon the size of the average SUV - in aviation size does matter. Of course, small, flying lizards with a tendency to explode are probably bad enough. But it's hard to imagine a life form with expolosive tendencies being viable in the long run. Well, maybe that's why we don't see them anymore, ay?

[Lord Zentei]

Flight of Dragons used limestone + stomach acid to produce the H2.

Seriously, are you expecting to find a bio-chemical means of producing enough hydrogen to not only lift a large animal but the H2 production units as well? Forget it. You would be better off with boi-fusion or something.