Is a jet dragon possible?
Are there any known laws of nature, which don't allow the existence of an animal with following characteristics?
- Can fly to the altitudes of modern airliners (around 10 000 meters or 32808 ft).
- One of the sources of thrust are organic jets or rocket engines (details see below).
- The animal can carry up to three passengers (about 240 kilograms, 529 pounds).
- The animal can fly up to 1000 kilometers (621 miles) using his own thrust source (that is, not just gliding or using the wind).
Regarding organic jet engine: There is at least one animal, which produces organic, flammable material - cows generate flammable methane. So, theoretically, an animal could have a combustion chamber in his body, where the flammable gas could be concentrated.
The next thing it needs is some form of nozzle, from which the gas would escape and it must have varying shape, controllable by the animal. Several animals can control the shape of their bodily openings, so it could be possible.
Finally, it needs a spark so that the flammable gas actually starts to burn, but that's easy - as stated in the requirements there is at least one pilot, who could activate a contraption, which generates a spark close to the nozzle.
I imagine that the animal can gain low altitude using wings (one of potentially many thrust sources), then the animal starts to generate flammable gas at the command of the pilot (we train dogs and horses, why not this fictious animal?) and the moment it opens the nozzle, pilot fires the ignition.
Here we go: A VTOL-capable (vertical take-off and landing), jet-powered dragon with at least two power sources (wings, jets - i. e. it is fail-safe).
Notes:
- I say animal on purpose - because of mental inertia I'm thinking about a dragon, but there may be other animals, which can fly with jets.
- There are some military fighter jets with variable sweep wings that an animal could achieve easily (real birds do that all the time).
- An interesting variation would be an organic liquid-fuel rocket engine. Unfortunately, I know too little about rocketry to imagine how it work in an animal. Ideas in this direction are welcome.
This post was sourced from https://worldbuilding.stackexchange.com/q/8962. It is licensed under CC BY-SA 3.0.
1 answer
1.Can fly to the altitudes of modern airliners (around 10 000 meters or 32808 ft).
Take a look at this graph:
At 10,000 meters, the air pressure is about 25% of its value at sea level. Wikipedia notes that pressures this low and oxygen levels this low can cause some problems:
The lower partial pressure of oxygen at altitude reduces the alveolar oxygen tension in the lungs and subsequently in the brain, leading to sluggish thinking, dimmed vision, loss of consciousness, and ultimately death. In some individuals, particularly those with heart or lung disease, symptoms may begin as low as 5,000 feet (1,500 m), although most passengers can tolerate altitudes of 8,000 feet (2,400 m) without ill effect.
At altitudes above 12,000 meters, an oxygen mask is imperative for survival in a non-pressurized environment. So this fellow has to be able to survive without much oxygen, which could be hard because of his size. His body parts also have to withstand the low pressures. These are going to be problems.
2.One of the sources of thrust are organic jets or rocket engines (details see below).
Here's a diagram of a turbojet engine:
According to Wikipedia, the compressor blades may spin at rates of 2,500-50,000 RPM. The dragon is presumably quite large and so will have large engines, so this rate will be towards the lower end of the spectrum. I have a feeling the vibrations will pose problems for his general structure.
This notes that the temperature of gases in a turbojet engine may reach 2000 degrees Celsius. Any organic material at this temperature will be scorched and turned to ashes. There is absolutely no way any carbon-based life form can survive this temperature - especially not for the two or so hours it will take him to travel those 1,000 kilometers.
These are the two main problems I can find with the scenario: pressure/low oxygen and temperature. Because I'm feeling less pessimistic than usual, here are some solutions:
Pressure/low oxygen: You can't really have the dragon hold his breath because of the long duration of flight. So how about having him carry extra oxygen with him? I wrote about fictional pufferpolyps in another answer set in a different context. The feature we can take form them is an easily expandable chamber that can store gas for a while, on tap. You've basically got an inflatable oxygen tank with you.
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Temperature: Take a look at Monty Wild's excellent answer to How could dragons be explained without magic? Monty suggests
By squirting the fuel out fast enough from a duct venting into the mouth as the dragon exhales, it need not ever come into contact with the burning fuel. (Think spraying the flammable gas from a spray can over a cigarette lighter - it doesn't melt the plastic nozzle.) With a change in biology so that a dragon could precipitate metals such as aluminium or magnesium, a dragon might even be able to spit a liquid mixture akin to thermite that would spontaneously combust due to the presence of other reactants.
And therein seems to be our solution. If you go for a traditional jet engine, your dragon is going to be blackened. The hot air will have to go through some sort of cavity, and there's a high risk of it burning up that cavity. So you'll want to go for the rocket approach: shoot out flames like a fire breather, in reality expelling some flammable substance and igniting it as it goes by.
I'm not sure how good an answer this is. I hope it helps.
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