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In my fantasy setting exists a creature called Wurm. After a long infancy phase where they feed on a magical, floating ore and an omnivore diet, they pass through a metamorphosis, exchanging their cumbersome rocky body for a serpent like one, with bones and chambers made/filled of the ore.

My question is, how would such a creature move through the air? Would similar limbs and structures used by sea creatures, like flippers, fins and tails, work, even considering the difference of air density (between air and water), or there is another, better way? Would a whale-like body work better in this case? How would turbulence affect its movement?

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    $\begingroup$ Your animal sounds like a combination between a bird and a blimp. It will probably move using some hybridization of those propulsive methods. $\endgroup$
    – Matthew
    Commented Jun 4, 2021 at 2:46
  • $\begingroup$ I'm concerned how it defies gravity, being made of rock. It strikes me you'd need a very lightweight rock, like pumice or expanded mica, pearlite like substance, mostly gas bubbles - and a very dense atmosphere perhaps. The denser the atmosphere gets, the more like syrup it behaves, that would affect what sort of "swimming" would be necessary to move. $\endgroup$ Commented Jun 4, 2021 at 2:57
  • $\begingroup$ @ A Rogue Ant it doesn't float while it is rocky. The adult phase is light weight. About defying gravity, it's an innate property of the material when in contact with mana, the magical source of the world, although is more like mass reduction than outright flying, so there as limit of how high it can go. The ore gains more or less buoyancy depending on how much mana is shoved on it, up to a hard limit. $\endgroup$ Commented Jun 4, 2021 at 3:04
  • $\begingroup$ It sounds like your Wurm is related to the Aztec myth of Quetzalcoatl. Many depictions of that flying serpent include wide spread wings which would serve as they do our real world avians but with less effort because they don't have to simultaneously provide momentum and fight gravity. $\endgroup$ Commented Jun 4, 2021 at 3:04

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while air is similar to water, as in it behaves like a fluid, it is a lot less dense, this has benefits and costs. a benefit of the low density mean that the drag is far lower than in water, and the drag is dependant on density, this means that most body shapes would be able to "swim" well, assuming that they can push on the air well.

Which leads to the problem of low density, things move through water by pushing the water behind them, then from newtons third law pushing the water back pushes you forward. but the lower density means that for the same amount of fluid (either air or water)air gives less of a push forward, which is why astronauts cant "swim" in zero G, they can't push enough air behind them to start moving, at a good speed.

But if your creatures have over sized fins (approximately ~$25-30$ times longer and wider) then it should be able to work, keeping in mind that once it starts moving it won't slow down from drag, as much as it would in water.

why ~$25-30$ times bigger: As the density of water is $1000Kg/m^3$ and the density of air is ~$1Kg/m^3$, and for the thing to push approximately the same mass of air back, it need have a $1000$ times bigger area, which means that each side needs to be ~$\sqrt{1000}=31.6$

So the fins need to be approximately $31$ times longer, you would be able to go slightly lower if you want you creatures to accelerate slower, as the drag is minimal they will just keep going.

hopefully that helps

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    $\begingroup$ It helps. The fins bigger than its body and the fact it can sail with is momentum through the air also goes with the ambiance I'm aiming for the beast, a relaxed part of the world. $\endgroup$ Commented Jun 4, 2021 at 3:14
  • $\begingroup$ Glad to hear, i was concerned that you needed it to be highly manoeuvrable, which would be a bit harder. $\endgroup$
    – Nyra
    Commented Jun 4, 2021 at 3:20
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Wings

You ask if there is a different, better way. For that we can look at creatures that are already moving through the air. Birds, bats and others use wings. These are excellent at pushing against the air, creating lift and movement. Your creatures have the advantage of not needing lift, so they can focus on speed. The wings can probably be less large.

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Exactly the way fish move in water, or somewhat similar to birds.

They are neutral buoyancy, and could move in the various forms of locomotion that sea creatures use.

Possible mode of motion: From worst to best:

  • drifting along like a balloon.
  • tentacles or other appendages, grasping and pulling along solid objects.
  • flapping fins and tails (fins will need to be proportionally larger, to account for less dense medium, but also less friction with the medium impeding motion. Not much bigger than for water)
  • variant of fins worth mentioning separately: Undulation of the whole body, like an eel. This is a partially Aerodynamic wing, not just a bigger tail.
  • jet propulsion. The creature could ingest air at the front, then expel it to the rear. Much like a squid. Note that due to the low density of air, this is much less effective in air than the equivalent in water. Still, it could work for either very slow, almost effortless motion, and for a single burst of escape-or-attack speed that required replenishing afterwards.
  • Actual wings. Note that wings are not mere fins, that shove the surrounding matter away. They are aerodynamic surfaces that use the pressure differential possible in a gas for propulsion, not mere shoving of the mass of the medium. Having neutral buoyancy, the wings will not be the normal gravity-aligned wings of a bird. Ideally, the wings would be articulated for active stroke in both flappable directions, regardless of orientation.
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  • $\begingroup$ The tentacle one could really work for some beholder-like creature. Thanks! $\endgroup$ Commented Jun 5, 2021 at 23:22
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This creature can move the same way like certain spiders do:

When a spider wants to travel long distances, it simply casts out a strand of silk, captures the breeze and "flies" away. They are known to travel hundreds of miles, even ending up on islands in the middle of the ocean.

Now scientists have figured out how this mode of transportation works. They also discovered that spiders have very little influence where they're flown when caught in a stiff wind.

Researchers at Rothamsted Research redesigned the model to allow for elasticity and flexibility in the spider's dragline, its most sturdy line of silk used for moving about and snagging prey. When the dragline is caught in a turbulent breeze, it becomes highly contorted, catching air like an open parachute and sending the spider on an unknown journey.

The spider has virtually no control of where or how far it travels by this means, said Andy Reynolds, a Rothamsted Research scientist. This is how a "ballooning" spider can end up in the ocean hundreds of miles from shore.

In more calm breezes, though, spiders can drift just a few yards to invade new territory or surprise prey.

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  • $\begingroup$ Interesting! Although I don't think it would quite mesh with this particular beast, it gave me a lot of ideas for new flying critters. Thanks! $\endgroup$ Commented Jun 5, 2021 at 23:19
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Is it gauche to recycle answers? Well, it would not be my first time. And I like sidewinders!

Recycled from Diversity of speculative evolution flight mechanics? Attempting to design a megafaunal, aerial diving predator

Sidewinding up through the air.

Sidewinding is a form of locomotion used by certain desert snakes. A loop of body is stationary on the sand and used as a base to throw another loop of body forward through the air.

In the resultant movement, the snake's body is always in static (as opposed to sliding) contact when touching the ground. The head seems to be "thrown" forward, and the body follows, being lifted from the prior position and moved forward to lie on the ground ahead of where it was originally. Meanwhile, the head is being thrown forward again. In this way, the snake slowly progresses at an angle, leaving a series of mostly straight, J-shaped tracks. Because the snake's body is in static contact with the ground, without slip, imprints of the belly scales can be seen in the tracks, and each track is almost exactly as long as the snake.

https://en.wikipedia.org/wiki/Sidewinding sidewinder gif

Your creatures use a similar mode of locomotion, but use control over their serpentine body shape to affect air resistance. The "stationary" loop is flattened into a ribbon to provide maximum air resistance. The snake pushes against the resistant flap loop to throw wedge-shaped aerodynamic body parts upwards through the air. Then those body parts flatten and the previous flattened loop becomes aerodynamic and is thrown forwards.

These snakes climb through the air rather than gliding. Once high enough they glide downwards in the manner of flying snakes. Real flying snakes of course must gain altitude by climbing trees. The proposed animal uses the same undulatory mechanism to "climb" the air.

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    $\begingroup$ Thanks. From the perspective of some one into the ground, it would look like chinese dragons. It could spawn quite some legends for the world. $\endgroup$ Commented Jun 5, 2021 at 23:20
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Use More Magic

This wurm, in addition to the floating ore, also eats another type of ore, which contains special crystals that can push against nearby air when provided with mana. When they mature, these crystals are formed into special scales that can push the air in a specific direction, allowing it to fly through the air

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As @matthew states in a comment, the Wurm sounds like a blimp.

As you state, the Wurm eats magical ore. Within the gut of the Wurm the digestion process produces hydrogen in large quantities which goes into a bladder and keeps the Wurm afloat.

To move through the air, the Wurm expels hydrogen from the bladder.

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