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For starters, allow me to define more carefully what I am asking. For now I am not worried about any of the following, as if this question is answered they will be covered in later questions:

  • The aerodynamics or feasibility of its flight, covered Here

  • Metabolic requirements.

  • How such a creature evolved or the plausibility thereof.

What I am asking is: How well will my proposed adaptations work and what other adaptations may the dragon need?

I figured that whether or not my dragon could get off the ground, this question and subsequent answers might supply the basis for others who come to this site who are interested in devising large flying creatures.

Warning - Math Ahead - Warning - Product of Someone with to much Free Time

A Drawing of the dragon in question. enter image description here

Height: 6.5 meters

Length: 19 meters

Volume: 11.9 cubic meters

Head/Neck Volume: 1.3 cubic meters

Average Density: 0.614 g/cm^3*

Weight: 7310 kilograms

Wingspan: 38 meters

Wing area: 304 square meters

Wing loading: 23 kg/m^2

Wings+Legs+Tail muscle cross-section: 43,000 cm^2

Muscle strength*** newtons/cm^2: 35 n/cm^2

Wings+Legs+Tail muscle strength: 1,474,900 watts

Liftoff time: 1 second

Height leaped in Liftoff**: 20.6 meters

Liftoff force on body: 2.1 gravities

Wing muscle cross-section: 21,600 cm^2

Wing muscle strength: 756,000 watts

Flap time: 2 seconds

Flap acceleration**: 21 meters a second

Adaptations Facilitating Large Size + Flight:

Strength giving minerals in bones replaced by Graphene Foam, Giving enormously increased strength and reducing density from 700 kg/m^3 (bird density) to 650 kg/m^3.*

Collagen replaced by material similar to dragline spider silk,Giving enormously increased strength and reducing density from 650 kg/m^3 to 614 kg/m^3.**

Carbon Nano-tubes worked into the nervous system, allowing for increased signal relay speed. And into the Connective tissue where greater stiffness then the dragline adaptation would allow for.

Lungs Like those of a bird, considerably more efficient at gas exchange than most tetrapod lungs.

Because of the increased connective tissue strength, the patagium may remain quite thin, allowing for gas exchange to be preformed across the area of the wing, as occurs in bats.

Are there any issues with these adaptations, or will they work as I would expect? What other adaptations might the dragon need in order to survive and function as such a large flying organism?

*The body is ~15% bone, which is ~50% mineral, the primary constituent of which is calcium, with a density of 1.54 g/cm^3, as opposed to graphene foam with a density of 0.06 g/cm^3.

** The dragons body should be ~16% protein, ~35% of which is collagen. Collagen has a density of 5 g/cm^3, as opposed to the density of dragline silk, at 1.3 g/cm^3.

Question: How well will my proposed adaptations work and what other adaptations may the dragon need?

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    $\begingroup$ I suggest dropping the hard-science tag, because this will render your question effectively unanswerable, and replacing it with the science-based tag. Hard-science requires citations and equations, these aren't necessary for your question. $\endgroup$
    – a4android
    Apr 7, 2017 at 5:42
  • $\begingroup$ @a4android will do. $\endgroup$
    – Myrdden Wyllt
    Apr 7, 2017 at 12:42
  • $\begingroup$ Your diagram actually reminds me of similar diagrams of the Quetzalcoatlus (wingspan is almost 4x though). One additional modification you might make is to simply stretch out the wings a bit more. $\endgroup$
    – Michael Richardson
    Apr 7, 2017 at 14:54
  • $\begingroup$ @MichaelRichardson although increasing wingspan and thus wing area would reduce wing loading and increase lift, if you follow the link at the top of the post, you will find my question about the aerodynamics. As far as I can tell the wings on the dragon are more than sufficient, so I will treat them as such unless someone can provide reasons they would not be in the aforementioned thread. I simply want to avoid making the dragon to unwieldy, and I think where it's at right now is a good balance. $\endgroup$
    – Myrdden Wyllt
    Apr 7, 2017 at 15:20
  • $\begingroup$ You have likely already seen this but.. worldbuilding.stackexchange.com/questions/30184/… $\endgroup$
    – Erin Thursby
    Apr 7, 2017 at 15:31

2 Answers 2

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This is not a dragon. This is an aircraft

This series of questions is fundamentally flawed. What we have here is a 7 tonne entity shaped sort-of like a bird, with structural members made of exotic materials ("graphene foam"), with flight surfaces made of silk, with signal conduits made of carbon nanotubes, capable of producing 2600 horsepower. This is an aircraft, not a biological entity.

Yes, we know that aircraft of this size can fly, there is no question about that. No, there is no way for this to be a living thing. Living things are not made of graphene foam.

2 MW (2600 hp) is 478 kcal/sec. Let's say that in flight the entity uses 50% maximum power; that's about 240 kcal/sec. Muscles have an efficiency of about 20%, that is, to produce 1 W of mechanical power they consume 5 W of chemical energy, of which 4 W are dissipated as heat. Let's say that the dragon has better muscles with 33% efficiency, and let's say that it eats bacon (5000 kcal per kilogram). For five minutes of flight the dragon needs 300 × 240 / 0.33 = 216 000 kcal, or about 43 kg of bacon (or 80 kg of lamb): it needs to eat one pig for 5 minutes of flight. It must dissipate 2 MW; let's say that it has a superb heat transfer system able to dissipate 40 W/m² per degree centigrade, and it has 400 m² of area available: the temperature difference between the blood and the air would need to be 2 000 000 / 40 / 400 = 125° C; it the air is at 20° C then the blood must be at 145° C...

And that's above and beyond its basal metabolism; by necessity it must be warm-blooded in order to be able to regulate its internal temperature; a 7 tonne warm-blooded animal dissipates somewhere around 7 kW (1.67 kcal/sec) at rest. In one day it requires 24 × 3600 × 1.67 = 144 516 kcal, or about 30 kg of bacon (or 60 kg of lamb) per day just to keep on living.

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    $\begingroup$ To be fair, the horsepower numbers are entirely reached through math based on human muscle power. Seeing as Graphene foam is a material composed entirely of carbon, it seemed a plausible material to give the bones strength, of the is a good reason it is not, I would be interested to hear it. As for spider silk it is a fibrous material composed primarily of proteins, much like collagen. And carbon nanotubes, like Graphene, are entirely carbon, of the is a problem with a biological entity being able to produce them, that is far more relavent than any similarity to wiring. $\endgroup$
    – Myrdden Wyllt
    Apr 7, 2017 at 17:00
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    $\begingroup$ Heat dissipation does indeed seem like it would be a problem, and that is within the scope of the question, how or whether or not it could be overcome is something that I'm glad you addressed. However, I specifically stated that I was not concerned with metabolic requirements at this time. $\endgroup$
    – Myrdden Wyllt
    Apr 7, 2017 at 17:01
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    $\begingroup$ The silk would not be woven, but arranged much like the collagen structure it replaces. If there is, as you say, no way to produce carbon nanomaterials through a biological process, that is a much more helpful thing to tell me then that no organism currently does it. If you have some objection to any given aspect of the dragon, that's fine, I put this up here largely to hear people's objections. I just appreciate seeing the reasoning behind the information I'm given. $\endgroup$
    – Myrdden Wyllt
    Apr 7, 2017 at 17:13
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    $\begingroup$ @cobaltduck: Quetzalcoatlus had 70 to 250 kg for a wingspan of 10 to 12 meters. The OP's dragon has 7000 kg for a wingspan of 38 meters: it's 25 to 100 times heavier and 27 to 54 times more voluminous. This kind of size difference matters quite a lot. $\endgroup$
    – AlexP
    Apr 7, 2017 at 21:07
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    $\begingroup$ Although your math is impressive, we really only need active wing-flapping while adjusting speed or height. Otherwise this thing should be able to glide quite efficiently, thus a pig might be enough for up to 30min of flight, which should be enough to hunt more pigs? $\endgroup$
    – dot_Sp0T
    Apr 8, 2017 at 11:16
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Adding graphene will make the bones stronger but it will not make them any lighter.

You can't reduce the animal's weight by switching out the bone material because then it needs to store that calcium and phosphorous in some other fashion, you can't eliminate them only move them. living things with muscle need a very narrow range of calcium concentration in the body to function. Having a solid mass of calcium's distributed around the body is the most efficient way to do that. Dinosaurs, birds, and pterosaurs, make bones hollow to make a larger structure for the same weight, the total ratio of bone surface area to body mass remains the same. In fact you really can't change that ratio very much because the bone surface area (exposed to body tissue) cant change much. http://rspb.royalsocietypublishing.org/content/early/2010/03/13/rspb.2010.0117.short

So your dragon bones will be stronger, but you won't drop any weight.

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