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So, one of the most common theories about how dragons could maybe still fly, the living gasbag theory.

Basically, most of the dragon is a cavity filled with lifting gas or air, in order to reduce its weight and density. Of course, this wouldn't make it even neutrally buoyant.

But, just how much of the dragon can be a glorified balloon without negatively affecting their other life functions and locomotion?

We're still going with the "195 cm tall at the withers, 2,95 meters at the top of the head in a relaxed posture, built like a horse, but the neck is elongated" type. There's also a sleek tail, no longer than the body, with a sharp bony structure (I think they call it a spade) at its end. And finally, a separate pair of wings, so 6 limbs in total.

I know that horses have tendons in their legs, and the actual muscle, sitting above, is connected to those, but I don't know how much I can abuse that.

There's also resilin (thank you, GURPS 4e Bio-Tech), spider-silk and limpet teeth, the efficiency of cold-blooded creatures at digesting food, but again, I don't know how much I can abuse those.

Update:

Let's think about it this way:

We have Mini Smaug with the voulme (determined using water dispacement) n. You can't increase the volume, only decrease the amount of organic material there. How much could you remove before (see bold paragraph).

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closed as unclear what you're asking by Renan, Mołot, Ash, elemtilas, Frostfyre Oct 15 '18 at 12:54

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  • $\begingroup$ Lets put this another way, your dragon is circled in red and weighs about 200 pounds, the rest of it is a helium sack (hydrogen is about 5-7% more buoyant). $\endgroup$ – Draco18s Oct 15 '18 at 1:50
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The lifting power of a gas is not proportional to its density. It is actually proportional to the inverse of its density.

As we all know, the more helium you put into a balloon, the lighter it gets. However, that is not the real cause and effect behind buoyancy. You can test this by wasting a bunch of helium. If you go get a big helium canister, it will be heavy. After you let all the helium out, though, it will be lighter. That is because helium has mass, like all elements. That mass actually doesn't help lift up the canister, it weighs it down.

So how does buoyancy work? Buoyancy is actually about density. If you have an object with low density immersed in a more dense fluid or gas, it will float. The reason a balloon floats, then, is because the helium stretches the balloon, giving it more volume, while not increasing its weight as much as air would. The most buoyant object you can make doesn't use helium or hydrogen at all. A super buoyant object has a large volume compared to its mass. The best you can get is with a vacuum. If you suck all of the air out of a cardboard box, and reinforce the box so it doesn't collapse in on itself, the box can float.

So here is how this relates to your dragon: Your dragon doesn't need high pressures, it needs to be made of mater that has very little density. One way is to decrease weight. Birds have hollow bones to help with this. Another way is to increase the dragon's volume. Puff it up like a balloon by filling it with helium. If you create cavities in the dragon's body and replace them with air, it will make them lighter. But if you fill the spaces with helium, which will have less mass, you can make your dragon even lighter. What you want to achieve is lowering density, so replace any spaces you create with helium. You can give the dragon a swim bladder filled with helium. If you can create a reinforced swim bladder containing a vacuum, that is even better. You can fill the dragon's stomach with helium when it's empty. The stomach doesn't need to have any extra pressure in it, just swap all that air for an equal volume of helium. Using low density materials and adding helium or a vacuum wherever possible will significantly decrease the weight of the dragon without compromising volume.

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  • $\begingroup$ I'm not trying to attack you, but did you actually read the question (the paragraph in bold)? $\endgroup$ – Mephistopheles Oct 14 '18 at 19:52
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    $\begingroup$ @Mephistopheles The answer is that you don't need a glorified balloon. Decreasing density wherever possible will make the dragon lighter. You can fill existing organs and empty space with helium too. $\endgroup$ – John Locke Oct 14 '18 at 19:54
  • $\begingroup$ @Mephistopheles he's challenging your premise. $\endgroup$ – RonJohn Oct 14 '18 at 20:03
  • $\begingroup$ @JohnLocke Isn't he basically asking which of those organs he can fill without affecting its functions? $\endgroup$ – Shadowzee Oct 14 '18 at 23:51
  • $\begingroup$ @Shadowzee I think the question is in what ways can you can store air in a dragon's body, and what organs you can fill is part of that. I answered that in the last paragraph. $\endgroup$ – John Locke Oct 14 '18 at 23:54

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