I need to know how big the wings would be for a dragon of a particular size. The dragon is 20 foot long and weighs 6 tonnes. How wide and long would the wings need to be for it to fly?

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    $\begingroup$ Welcome to the site Harvey, please take the tour and read up in our help centre about how we work: How to Ask We'd need some more details: What's the local gravity like and how does atmospheric density - say - compare to that of Earth in the world that you're building? You can edit your question with the details. $\endgroup$ – BLT-Bub Mar 13 '19 at 16:52
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    $\begingroup$ Depends on how fast it can fly in a straight line $\endgroup$ – nzaman Mar 13 '19 at 16:55
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    $\begingroup$ What is the shape of the dragon? If he is a 18-feet diameter sphere with extra 1 foot for head and tail each, it can fly without wings if it is full of any gas that is lighter than the surrounding air. $\endgroup$ – Renan Mar 13 '19 at 17:03
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    $\begingroup$ Well, in Romania we have quite a few Russian-born MiG-21 dragons, 48 feet long, weighing 6 tonnes empty and 9 tonnes full, and they fly really fast with a wingspan of 23 feet. The bad part is that they eat jet fuel. So the question is, what is the mechanism of propulsion of your dragon? Is this 6 tonne object supposed to fly by flapping its wings? $\endgroup$ – AlexP Mar 13 '19 at 17:23
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    $\begingroup$ Does your dragon needs to take off or does he just glide from cliffs or high places? $\endgroup$ – kikirex Mar 13 '19 at 18:20

It depends on some other factors, but the answer is: REALLY BIG

The equation we need is: $$ A = \frac{L}{0.5 v^2 \rho C_L} $$

Where $A$ is the area of the wing, $L$ is the mass of the dragon, $v$ is the velocity that the dragon needs to achieve flight, $\rho$ is the density of air, and $C_L$ is the lift coefficient (usually close to 1 for most flying creatures).

So if we make some assumptions

$L=6,000\,$kg, $v=7.0\,$m/s (about the same as T-rex), $\rho=1.225\,$kg/m^3, and $C_L=1$.

Then the wing area is about $200\,$m^2, or $100\,$m^2 per wing. Wings are usually at least twice as long as they are wide, so something like $6.9\,$m$\times14.5\,$m would be about right.

Note that this answer changes drastically with the velocity value, as the area is inversely proportional to the square of the velocity. So a dragon would need much larger wings if it needs to be able to take off without a running start or jumping from a high place.

  • $\begingroup$ Is this assuming a lot of flapping or a negligent amount of flapping of the wings? $\endgroup$ – Mast Mar 13 '19 at 17:36
  • $\begingroup$ Flapping just increases the factor "V" by the speed you move the wing. $\endgroup$ – Mathaddict Mar 13 '19 at 21:19

My initial thought is that a a real life adult European style dragon would be much to heavy to fly no matter how large a wing span it might have. Most flying creatures have hollow bones, but dragons as they are usually depicted just look super heavy.

However let's look at at wingspan to weight ratios of some of the largest know flying creatures.

Teratornis a vulture like bird had a wingspan of about 12 feet and weighed about 33 pounds. That is works out to 2.75 pounds per foot of wingspan.

Quetzalcoatlus a pterodactyl like creature had a wingspan of about 36 feet and weighed about 500 pounds. That is works out to 13.9 pounds per foot of wingspan.

On of the heaviest extant flying birds is the Mute swan. The largest specimens come in at 32 pounds with a wing and of 7.8 feet. That is works out to 4.1 pounds per foot of wingspan.

The Kori bustard can weight up to 44 pounds and have a wingspan of 9 feet. That is works out to 4.8 pounds per foot of wingspan.

The Magnificent Argentine bird had a wingspan of 19 feet and a weight of 156 pounds. That is works out to 8.4 pounds per foot of wingspan.

This gives us a range from about 3 pounds per foot of wing span to 14 pounds per foot of wingspan.

Your dragon weights 12,000 pounds.

That works out to a wingspan of 4000 feet to 857 feet. Such a large wingspan does not seem feasible. A semi realistic wingspan of 300 feet the size of a football field would require a figure of 40 pounds per foot. Several times any real life example.


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