[gurps] Dragon Aerodynamics

[Anthony Jackson]

Susan Koziel wrote:
> For winged flight look into the aerodynamics of bats (no feathers to
> mess with your calcs)... if you want a really fantasy like critter. 
> Or really large birds (geese) if you want something much more
> realistically lizard like... since birds are much more closely
> realated to lizards in body form then they are to mammals.

Well, in body form neither one is particularly much like a dragon. 
However, we can certainly use birds to get a figure of merit estimate, 
because the scaling laws I derived are valid.

A typical bald eagle is something like 10 lb with a 7' wingspan. 
Multiply its scale by 5.7 and we get 1850 lb with a 40' wingspan, which 
is actually pretty close to our (light-weight) dragon.

A scale of x5.7 requires strength per unit area 5.7x greater, and a 
power to weight ratio of 2.4-2.5x greater; for 2,000 lb that's 6.2x 
greater (significantly below the 35x I derived); however, dragon wing 
structures, while substantial, don't seem to be anywhere near as 
dominant a structural component as bird wings are in a bird, so the 35x 
is probably still fair (and, in any case, was not derived from the laws 
of aerodynamics). In addition, we have to multiply speed by 2.4-2.5, 
with the same effect on power to weight ratios (much lower than before, 
but birds have way higher power to weight than humans). I'm not sure of 
an eagle's minimum speed, and it probably doesn't stall as such, it just 
flaps harder, but a minimum move of 4 is probably justifiable, and its 
soaring speed is about 12, migratory speed is about 16. Scaling up, that 
gives a minimum move of 10 (vs 18), soaring of 30, migratory of 40, 
which is surprisingly close to the eyeballed figures I used.

> And frankly "a dragon that's 10 hexes long, half of which is tail,
> and is probably no more than 8' at the shoulder" would be enough to
> scare me spit-less.

Sure, but classic images of dragons are utterly enormous.