I heard from a teacher in school that in order to fly, he would need a wingspan much wider than the wood shop where he was standing. Thinking back on it, I assume the number of times you can beat your wings should have something to do with it, since it looks like hummingbirds have shorter wings than eagles.
What even goes into the computation to answer the requisite wingspan for flight, let alone how do you do it?
This may be like How to compute the speed necessary for an airplane to fly? but I think it's significantly different since flapping would be involved.
Also like Is it possible to fly like a bird using semi-motorized wings? but I believe also different because I want to know what wing size whereas that has a general flight/aerodynamics equation.
Finally: would people with no legs have an advantage in flying? (I assume this would be true if they weigh half as much and legs contribute no flapping power. Of course it could be different if you found a way to use leg strength.)