Planetary requirements for Dragons to fly?

[SCAR]

Originally Posted by Brett

Yes, but it diffuses like a bastard, and it's unstable in the presence of oxygen, which would mean that you'd have to constantly replenish it if it were in contact with oxygenated (living) tissue.

If Xenomorph Aliens can have strong acid for blood without dissolving themselves, I think we can handwave a suitable tissue to mitigate the diffusion of the hydrogen?
The reaction with oxygen is a little harder to balance. Possibly the leak could be controlled and the reaction accounts for a fiery breath and/or propulsion / 'maneuvering jets'?

Originally Posted by Anthony

Unlikely the gas bag would be living tissue, though; too heavy that way. Methane might be easier, though; it's only got half the lift of hydrogen, but it's a lot easier to work with and can be readily generated by biological procedures.

The lift gas doesn't need to provide all the lift on its own, it just needs to reduce the weight issue enough for the creatures wings to provide the rest of the lift and propulsion.

Powers suggests Flight could use some kind of surfing on a planetary magnetic field. Not sure thats a particularly plausible biological mechanism, although I have considered the possibility of alien creatures with electromagnetic abilities - biological generation of electric currents works ok, not sure about the required field strengths!

[SCAR]

Biotech gives a simple formula for maximum gravity for a winged human, which seems like a reasonable starting point for other creatures - it does not support flight of a dragon sized creature in a reasonable gravity without serious weight reduction or other factors.
Thicker atmospheres could increase the window, but at the cost of a breathable atmosphere maybe.
Space provides some useful figures for wing span and creature size based on gravity, as well as gravity and atmosphere data.

Using the figures from Dragons (size, weight, strength) and the above data, they aren't going to fly (which is no surprise).
However, some of the figures aren't out by orders of magnitude. Slightly lower gravity, dense atmosphere, controlled gliding flight, low end weights and some extra Lifting ST can pull some dragons into cinematically semi-plausible flight ranges.

[Flyndaran]

I always hated the hydrogen hand-wave for fire breathing.
I prefer an enzymatically active napalm like "vomit".

The real problem with huge honkin' dragons is more of a breaking point of bones and strength of muscle.
Why not have them incorporate small amounts of metal? While horribly expensive calorically in most situations, there are a few special iron sulphide shelled critters in the ocean.

[Agemegos]

Originally Posted by SCAR

If Xenomorph Aliens can have strong acid for blood without dissolving themselves, I think we can handwave a suitable tissue to mitigate the diffusion of the hydrogen?

Yeah, and if pigs could fly Cessna would sell bacon-slicers. If you're happy to concede the existence of the aliens from Alien a large flying reptile shouldn't bother you.

[Agemegos]

Originally Posted by Flyndaran

I always hated the hydrogen hand-wave for fire breathing.

Indeed. Hydrogen burns with a low-luminosity flame. Almost invisible, in fact.

[Agemegos]

Originally Posted by SCAR

Using the figures from Dragons (size, weight, strength) and the above data, they aren't going to fly (which is no surprise).
However, some of the figures aren't out by orders of magnitude. Slightly lower gravity, dense atmosphere, controlled gliding flight, low end weights and some extra Lifting ST can pull some dragons into cinematically semi-plausible flight ranges.

Yep. I think the secret here is not to crunch the numbers, in case they don't work out. Don't say how much less gravity is, how much denser the air is, how big exactly the dragons are. Just remind people that Quetzalcoatlus flew on Earth and say there's denser air and less gravity.

[SCAR]

Originally Posted by Brett

Yeah, and if pigs could fly Cessna would sell bacon-slicers. If you're happy to concede the existence of the aliens from Alien a large flying reptile shouldn't bother you.

It's more that gamers would accept the existence of Aliens in a Sci-Fi game, so they should be willing to extend the same level of suspended disbelief for sufficiently plausible large flying reptiles in a similar context.

[SCAR]

Originally Posted by Brett

Yep. I think the secret here is not to crunch the numbers, in case they don't work out. Don't say how much less gravity is, how much denser the air is, how big exactly the dragons are. Just remind people that Quetzalcoatlus flew on Earth and say there's denser air and less gravity.

The numbers allow me some degree of comfort that the creature is vaguely plausible.
If the PCs were to encounter these creatures, then they would most likely be able to determine the local gravity and atmospheric parameters so they can't just be ignored.
Quetzalcoatlus definitely works as a starting argument for plausibility.

[Anthony]

Originally Posted by SCAR

The lift gas doesn't need to provide all the lift on its own, it just needs to reduce the weight issue enough for the creatures wings to provide the rest of the lift and propulsion.

As a practical issue, there's very little point to going half way with gas lift -- either make it all gas lift or none.

[Fred Brackin]

Originally Posted by Anthony

As a practical issue, there's very little point to going half way with gas lift -- either make it all gas lift or none.

I know that my attempts to mix lift gas and powered lift in Ve2 have proven disappointing.

I tried to design a clever sort of ultra-tech super-zeppelin with vectored thrust and a lifting body shape. The idea was that either lift gas plus vectored thrust _or_ lift gas plus the lift generated by the lifting body hull would be enough to stay in the air.

So you hovered on the vectored lift and used the lifting body in forward flight with the lift gas doing the bulk of the work in either case.

What I discovered was that the lift of the lifting body _grossly_ exceeded the amount provided by filling the hull of the lifting body with hydrogen. At the TL I was working at the powered lift out-competed the lift gas too. The whole vehicle worked better and made more sense if you took the lift gas out of it.

LTA flight is really a niche technology and I don't think it hybridizes at all. You use LTA when nothing else will work.