never like a bird on earth
It's simply an engineering problem of material strength/weight and precision of control. Bird wings are not fixed, solid objects tnat simply move and and down.
Look at this
this picture. He's supporting his weight with his arms. If you could simply build sufficiently light wings that could be precisely controlled rather than flapping up and down, that man could fly. The strength is there.
For example, imagine combining a
wingsuit with flexible, full length wings using something considerably lighter and stronger than aluminum to hold their shape. Now, design them such that when the arms are pulled in, the entire wing folds in on itself. Say...with fist to shoulder and elblow to ribs, the wings contract to a quarter of their fully extended length. Build it so that the contraction and extension can be done as quickly as you can move your arms. Precision control of wing orientation could be managed by adjusting rotation and position of the shoulders. And add a locking position so that the wings could be held in a stationary "glide" position without being supported by any muscles to allow flyers to rest while gliding.
Put that gymnast in those wings...he'd be able to fly. The strength to support his body weight is there. It simply needs to be properly applied to the air.
Finally, keep in mind that there are places with enough wind currents that hang gliders can fly
completely unpowered for hours. As in...no motor, no wings flapping...nothing at all. With a proper wing design, anybody would be able to fly in places like that even without the strength of a gymnast.
Nearest semi-planetary body for that is the moon, where it is legitemitly possible to fly, in an enclosed earth atmosphere pressure dome of course, just by flaping your arms with some quality wings strewn across 'em.
The Moon is a Harsh Mistress. Good book.
But if you're willing to build structures of that sort, there's no need to go to the moon. Just build the wings that I described and go to a
vertical wind tunnel.
It's just as engineering problem, guys. Anything is possible.