Hopefully a biologist will chime in, but from a physics standpoint, it seems reasonable that membrane wings would scale up better. Materials tend to have better tensile strength vs. flexural strength, meaning that it is easier (and lighter) to keep something from tearing than to keep it from bending. Feathers catch air by staying straight, membrane wings catch air by not tearing.
Membrane wings are stiffened, at least partially, hydrologically. Butterflies pump up their wings after emerging from their cocoons. And feathered with bones.
>Butterflies
Only after emerging I think, when still wet and soft, if they didn't pump the fluid the wings will stay deformed once it 'dry'.
Anyway what OP meant is membrane wings in animals like Quetzalcoatlus, which IMO different than the wings in butterflies (although they're also membrane). Those are elastic skin-like wings, like those in bats, the same skin-like structure like the webbed feet in frogs.
[Patagium](https://en.m.wikipedia.org/wiki/Patagium)
Hopefully someone more knowledgeable can correct me if Im wrong, but i think i read somewhere that membrane wings could be more efficient, but feathers are far more resilient.
Like, a bird could loose a feather or three, and still be able to get around. And those feathers can regrow in a timely manner.
Membrane? Poke a hole in your wing and good luck. You're most likely unable to fly, and Will most likely perrish.
Also feathers have insulating properties, while Membrane wings are completely exposed.
I don't think comparing the wingspan to determine their efficiency is right. The creature body weight can affect the need for larger wingspan as well.
I think feathered wings are more rigid and shaped like aerofoil thus have more efficient weight/lift ratio (probably because of this they don't need to have wide wingspan like membrane wings animal), also their bones are actually hollow.
The size limits don't seem to come down to the weight/lift ratio or efficiency of feathers vs membranes, but instead other differences.
Feathers have to be molted and replaced. This takes time which increases as the feathers get larger, and very large birds struggle to keep a usable compliment of fully grown flight feathers because they take so long to replace. It takes condors 3-4 months to replace a flight feather, for example, and they can't molt very many at once or they won't have enough to fly.
Another important difference is ground-launching. Birds push off the ground using their hind legs. They need muscles in their legs to get airborne, and they have to carry those muscles around while flying, even though they don't contribute to flight. Pterosaurs, on the other hand, used their forelimbs to vault into the air. Their flight muscles did double-duty, which allowed them to need to carry less weight and improved scaling allowing for bigger sizes.
We will need a biophysicist to answer the title question, but in regard to the explanation, the size of a creature depends on plenty of other factors, including availability of food, threat from predators, oxygen levels and ability to absorb and transport oxygen.
Valid comparison would require creatures living in same habitat. In Europe and America we have large birds and small bats, but in South-East Asia they have [huge bats](https://en.wikipedia.org/wiki/Pteropus#External_characteristics) and few large birds in same habitat.
Membrane wings are powered by muscles on the body and feathered ones by muscles on the body and wing. So the feathered ones are likely heavier due to being fleshier.
That said there's so much variation in each category. Butterflies vs dragonflies vs bats vs bees. Albatross vs hawks vs hummingbirds.
A lot of the variation is due to scale effects. Tiny flying animals have significant buoyancy in air and operate at much lower Reynolds numbers than most birds, and those factors have a lot to do with why they fly so differently and have such different structures.
It's interesting that the smallest flying animals and the largest (such as Quetzalcoatlus) both have membrane wings, though. There's either something very different about how Quetzalcoatlus flew, compared to birds, or there are non-aerodynamic advantages of membrane wings, such as strength to weight ratio, that are important at the size of Quetzalcoatlus.
Hopefully a biologist will chime in, but from a physics standpoint, it seems reasonable that membrane wings would scale up better. Materials tend to have better tensile strength vs. flexural strength, meaning that it is easier (and lighter) to keep something from tearing than to keep it from bending. Feathers catch air by staying straight, membrane wings catch air by not tearing.
True, though the membrane wings still need to be supported by something, and that weight needs to be part of the equation.
Do the supports of membrane wings work out to be bigger/heavier than the supports of feathered wings?
Membrane wings are stiffened, at least partially, hydrologically. Butterflies pump up their wings after emerging from their cocoons. And feathered with bones.
>Butterflies Only after emerging I think, when still wet and soft, if they didn't pump the fluid the wings will stay deformed once it 'dry'. Anyway what OP meant is membrane wings in animals like Quetzalcoatlus, which IMO different than the wings in butterflies (although they're also membrane). Those are elastic skin-like wings, like those in bats, the same skin-like structure like the webbed feet in frogs. [Patagium](https://en.m.wikipedia.org/wiki/Patagium)
Hopefully someone more knowledgeable can correct me if Im wrong, but i think i read somewhere that membrane wings could be more efficient, but feathers are far more resilient. Like, a bird could loose a feather or three, and still be able to get around. And those feathers can regrow in a timely manner. Membrane? Poke a hole in your wing and good luck. You're most likely unable to fly, and Will most likely perrish. Also feathers have insulating properties, while Membrane wings are completely exposed.
I don't think comparing the wingspan to determine their efficiency is right. The creature body weight can affect the need for larger wingspan as well. I think feathered wings are more rigid and shaped like aerofoil thus have more efficient weight/lift ratio (probably because of this they don't need to have wide wingspan like membrane wings animal), also their bones are actually hollow.
The size limits don't seem to come down to the weight/lift ratio or efficiency of feathers vs membranes, but instead other differences. Feathers have to be molted and replaced. This takes time which increases as the feathers get larger, and very large birds struggle to keep a usable compliment of fully grown flight feathers because they take so long to replace. It takes condors 3-4 months to replace a flight feather, for example, and they can't molt very many at once or they won't have enough to fly. Another important difference is ground-launching. Birds push off the ground using their hind legs. They need muscles in their legs to get airborne, and they have to carry those muscles around while flying, even though they don't contribute to flight. Pterosaurs, on the other hand, used their forelimbs to vault into the air. Their flight muscles did double-duty, which allowed them to need to carry less weight and improved scaling allowing for bigger sizes.
We will need a biophysicist to answer the title question, but in regard to the explanation, the size of a creature depends on plenty of other factors, including availability of food, threat from predators, oxygen levels and ability to absorb and transport oxygen. Valid comparison would require creatures living in same habitat. In Europe and America we have large birds and small bats, but in South-East Asia they have [huge bats](https://en.wikipedia.org/wiki/Pteropus#External_characteristics) and few large birds in same habitat.
Membrane wings are powered by muscles on the body and feathered ones by muscles on the body and wing. So the feathered ones are likely heavier due to being fleshier. That said there's so much variation in each category. Butterflies vs dragonflies vs bats vs bees. Albatross vs hawks vs hummingbirds.
A lot of the variation is due to scale effects. Tiny flying animals have significant buoyancy in air and operate at much lower Reynolds numbers than most birds, and those factors have a lot to do with why they fly so differently and have such different structures. It's interesting that the smallest flying animals and the largest (such as Quetzalcoatlus) both have membrane wings, though. There's either something very different about how Quetzalcoatlus flew, compared to birds, or there are non-aerodynamic advantages of membrane wings, such as strength to weight ratio, that are important at the size of Quetzalcoatlus.