Firstly, i'm new to these forums, and I'm not sure what the prefixe in creating this thread is supposed to be... (i'm assuming it is to judge to question's level)? saw some threads without prefixes but i can't post one without... maybe i missed a stickied thread or a readme? Alright, so, first of all let me give a bit of a backstory as to where this question comes from, it might help answer the question a little bit better. I am in the process of writing a book, i'm doing research in animal flight physics so i can know how big the animals in my world can be before it can physically no longer fly (I'm trying to make things 'real', to make sense in terms of physics, biology and all, as my "world" does not have "magic" or thing that just happen for not apparent reason), i'm not exactly sure this is the place to post this, but it seemed the most appropriate i could find. The first question is, how big can an animal be before it becomes to large to fly? there are some large birds like the vulture, but from my calculations, their wing size is, propotionally speaking, significantly larger then let's say a common pigeon. This seems to agree to some other research i found that says thrust produced by muscles increases more slowly then the drag and resistance increase as the animal becomes bigger. and it seems the easiest and most ecological way of bypassing this is simply to have larger wings producing larger amounts of lift. (this is to say, if you took any animal and simply scaled it up, it will not be able to fly as well) Secondly, according to this post: https://www.physicsforums.com/threads/lift-calculations.630078/ one can calculate the lift of a plane, but this is hardly comparable to the wing of a bird or a bat, i believe the bat's wing is flat (flat aerodynamics or something?), then what of a bird? they both bend and "flaps" which planes do not. so i assume the calculation those not work for bats, birds and etc... So, is the calculation simply the displacement of the air? does the mass of the air moved (displaced by the wing) equal to the lift produced? and if it does, or if it is close enough to be used as a rough method of telling the lift, how can it be calculated? So, summing it up, here's a few question I'd like to find an answer to: how can one person calculate the lift produced by a wing from an animal? (other than physically measuring a bird's lift - i do not have the capability to do this) Is there a size or weight limit on this animal's size? There are different types of wing, those of insect are different then those of bats or birds, which produce the most lift? which are more efficient? i assume each are more specialized or suited to different styles of flight, what are they?