But you don’t have to be a superhero to experience this kind of flight. If you have a set of carbon-fiber wings and four engines, you can fly like Yves Rossy, also known as “Jetman.”
Flying Like a Rocket
Iron Man doesn’t have wings. He doesn’t need them. Instead, his armored suit (which is most likely not made of iron) gives him augmented strength, some type of blaster fire from his hands, and most importantly—flight. Iron Man appears to fly using something like rockets located on his feet and hands.
I’m not exactly sure how his suit produces thrust, but it seems to work like most rockets do, in that mass—the exhaust—shoots out of the thrusters. Since this expelled exhaust has mass and velocity, it also has momentum. But to change the momentum of an object (like the ejected exhaust mass), you need to apply a force. If the suit pushes on the ejected mass, then the mass pushes back on the suit, creating a basic thrust force. This is the same way a rocket flies through Earth’s atmosphere on its way to space. (Here’s way more detail about the “rocket equation” than you probably ever wanted.)
But there’s an important difference between a rocket and a jet engine. Both of these push mass out the back to produce thrust. An airplane’s jet engine scoops up air from outside the plane and uses fuel combined with the air as the ejected mass. However, a rocket engine only uses fuel. It doesn’t need air. That’s why rockets work in outer space, but airplane engines don’t.
In my opinion, the Iron Man suit is more like a rocket than a jet engine—but I should point out that Gravity Industries made a flying suit that’s a lot like Iron Man’s but uses jet engines.
Vision, from Avengers: Age of Ultron, is a synthetic life-form. He has many of the classic superpowers (like strength, speed, durability), but he can also change his density. For that reason, when Vision flies, I assume it’s because he’s actually just floating in the air.
Is it physically possible to get a superhero to float? The answer is yes. Anything will float as long as it has a density equal to air, at about 1.2 kilograms per cubic meter. For example, if you need to build a floating metal sphere that can serve as your supervillain lair, you can—as long as it’s big enough that the density of the air inside is equal to the density of the air outside.
In the real world, this is the principle behind flying machines like blimps. Basically, air has mass. If you take a cube 1 meter on each side and fill it with air, that air will have a mass of 1.2 kilograms (2.6 pounds). Since air floats in air, that 1 cubic meter of space must have an upward-pushing force equal to the weight of that air. If you replace the cube of air with anything else, the outside air still pushes up on it with a force equal to the weight of the displaced air. And if you replace it with something lighter than air, like helium, the air pushes the cube upwards and it floats—just like a blimp.