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Looking at the recent questions on dragons and aviation bureaucracy has got me thinking about some animals I could include in my story.

I want these animals to be jet powered. One of the answers on the first dragons question explains why dragons can't be. However, cows aren't the only animals that produce methane and surely the characteristics of animals must make them more or less suitable for jet modification.

Presumably there's some limit at which an animal can't be jet powered. They'd also need some heat protection, but would thick skin be enough? You tell me. Assuming the hand waving necessary to give these animals wings, which Earth animal is easiest to modify for jets?

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  • $\begingroup$ Any size requirement of the animal (are you trying for it to be large enough to carry passengers?). Insects might be the easiest to explain, but I doubt they'd be the size you want. And are you looking for natural evolved, or can they be tinkered with? $\endgroup$ – Twelfth Jan 22 '15 at 20:29
  • $\begingroup$ @Twelfth Tinker away. No particular size requirements, I just want jets :) $\endgroup$ – ArtOfCode Jan 22 '15 at 21:01
  • $\begingroup$ Writing an answer brought another question up...long distance travel and I assume high altitudes? The extreme cold (and potentially extreme heating from reflected sunlight) is an interesting issue to get around...that and low air pressure. $\endgroup$ – Twelfth Jan 22 '15 at 21:48
  • $\begingroup$ Tried this from a few angles, from pulse to ramjet to turbo jet. Pulse jet engines get far too hot for a creature to survive, more classical jet engines require a compression factor that I just can't get into a reasonable limit for a creature to either create or survive..heat and fuel becomes an issue quickly as well. Modifying animals to test my ideas would result in a lot of burnt flesh and explosively decompressed animals. Best hope was in pulsejet as they contain all stationary components, but they just get far too hot and melt most metals let alone bio-matter. $\endgroup$ – Twelfth Jan 22 '15 at 23:01
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Jet Propelled Animals

There are some animals which use jet propulsion already. No, they mostly don't fly in the air, and no, they don't really use combustion to produce a stream of matter with which to jet. These creatures also tend to not use continuous propulsion, which is much unlike our current jet engines. They do, however, condense and force liquid out of a nozzle, which they then direct to move. I'm talking about Japanese flying squids and those mysterious Salps!

It should be noted that jet propulsion does not mean that the propellant is some flammable material. If you're looking specifically for an animal which uses combustion in their jets, I'm afraid I don't know of any such creature. I also doubt its existence.

The best creatures to modify for jet propulsion are those which have close relatives who already use it! It would be just a matter of figuring out which evolutionary pressures made the organisms develop jet propulsion, introduce those pressures, and let the process of evolution go! Alternatively, you can just mess with their genetics until you get what you need.

Modifications for Flight

Squid would need to be capable of breathing air (without drying out) and using that air to propel themselves. The Salps need a more rigid body in addition to the adaptations that squid need. These creatures may need additional modifications depending on how fast, how far, and how quickly you need them to travel.

If you are still looking for a jet of combusted matter, they would need some major tweaking. Their bodies would need to have a safe combustion chamber. They would need to produce enough combustable material to propel themselves. They would need to regulate how much fuel they have in themselves. Their jet-nozzles would need to become more heat resistant. Their bodies would have to cool their combustion chambers so they don't cook themselves, or be modified so that their combustion chambers are cooled by some other means.

Depending on how high they go, they may need more modifications, such as those found in avian lungs. Avian lungs allow them to maintain their blood oxygen level so they can fly higher. They're also nifty because of their unidirectional air flow!

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  • $\begingroup$ Wayne Barlowe created some plausible bio-jet propelled flyers in his book "Exploration". They don't seem to have combustion involved, just compression or impellers $\endgroup$ – SteveED Jan 25 '15 at 0:25
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The simple answer is no.

I'll first refer back to my answer on the dragon question: https://worldbuilding.stackexchange.com/a/8969/2974

The first problem you face is your definition of "jet power". If you mean something like the dragon question (sustained, at least short term, with a decent travel envelope), it won't work.

Dragons are about as hand wavy as it gets. Since we don't have any "real" dragons, we can pretty much give them any properties we want. Even in that scenario, there is no realistic way to make a dragon jet powered.

The limit of a jet-powered animal is probably an insect because of material requirements, but you're still going to run into problems with fuel capacity and travel distance. The best example is the bombardier beetle, but it has no sustained jet capability; just impulse capability.

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Insects come to mind!
bombardier beetles are already close: they don't propel themsleves, they propel chemicals away from them. I vaguely remember having heard about insects that actually propel themselves... but I cannot find any references, so I may just misremember.

To make insects larger, you need to do something about their breathing-mechanisms: about insect breathing

Personal PS: I want to read that story...

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  • $\begingroup$ Not quite what I was thinking but I like it $\endgroup$ – ArtOfCode Jan 22 '15 at 14:02
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So first, I'd start with something that can already fly, or at least glide. Then, to emulate actual "jet" mechanics, you need to intake air, and then expel it directionally. Since animals are already doing that when they breathe, if we make some structural modifications so that they breathe in through the front and out through the back, or maybe side-gills, they'll get some thrust. Birds already have uni-directional airflow in their lungs, and air sacs that act as bellows to move air around inside them. Configure them with multiple, independent, synchronized air sacs, like cylinders in an engine (or even better, like a multi-chambered set of bagpipes!) and said creature should be able to generate a continuous stream. It's then just a question of whether said creature can generate sufficient pressure to get a useful thrust to weight ratio...

(The associated math is left as an exercise to the reader.)

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