According to basic science, and even Stan Lee himself, the X-Men's Angel can't even use his only superpower without crashing down to earth. Though Angel may be a classic character and one of the first five X-Men ever created, even Stan Lee tacitly admitted that he never thought his mutant power completely through, resulting in this glaring error. A retcon in a later issue solved one problem but failed to solve a dozen others, and if real-world physics ever applied to Angel, any attempt to fly would leave him very much grounded.
Warren Worthington III was born into a rich family and was quite conceited, but after discovering wings growing from his back, he discovered that he was a mutant and thought of himself as an outcast and a freak. He ultimately decided to put his ability to soar through the air to good use and became a superhero under the name Avenging Angel, but this was shortened to Angel when he enrolled in Professor Xavier's school for mutants. His tutelage under Professor X humbled him to a certain extent, though he still thought very highly of himself. Unfortunately, no amount of ego could ever save Angel from the fact that his wings are too small to ever lift the poor guy off the ground.
Warren's wondrous wings measure a massive 16 or 4.88 meters feet when fully stretched out for flight. It certainly makes for a striking image on the page, but the average adult male weighs about 180 pounds - and the average adult male requires a wingspan of at least 6.7 meters to lift him off the ground. Add Angel's superhero physique and the weight of the wings themselves, and the result is a mutant who is forced to stay as grounded as Professor X.
Perhaps Stan Lee realized Angel was too heavy to fly (and his wings too short), because a later X-Men issue addressed the issue directly: Angel has hollow bones, just like birds of Earth. Unfortunately, this quick retcon presented another problem: the hollow bones may suit small and lightweight birds just fine, but it would hardly help a six-foot-tall man like Warren. Even if one considers that hollow bones would cut the weight of a 20.5-pound human skeleton in half (and that's being generous), a 170-pound superhero still can't produce enough lift with his 4.88-meter wings.
It's important to note that after losing his wings in a massive explosion, a desperate and despondent Warren struck a deal with the mutant Apocalypse. In exchange for becoming one of the Four Horsemen, Apocalypse granted Angel new organic metal wings that could fire sharp feathers as projectile weapons (the painful process also turned his skin blue); Warren was thus renamed Archangel. These otherworldly wings would be even heavier than his original wings - but it's entirely possible that Apocalypse placed some anti-gravity technology within them. In that respect, metal wings granted by a millennia-year-old mutant could be more believable than Angel's organic wings that marked him as one of Stan Lee's X-Men in the first place.