Can Humans Fly With Wings?

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Humans have wing envy. For thousands of years, we’ve been dreaming
up hare-brained schemes to fly like birds. The ancient Greeks conjured up Icarus and
Daedalus, who made wings from bird feathers, strings and wax. Leonardo da Vinci put a little more thought
into it, drafting plans for a mechanical winged contraption known as the ornithopter. While 20th-century humans are perfectly capable
of taking to the skies, there’s something intrinsically unsatisfying about doing so
in an aluminum behemoth. We still want to fly like birds, taking off
under our own power and gliding effortlessly once we’re airborne. After at least two millennia of thoughtful
engineering, why are humans still trying to figure out individual flight? Why can’t we strap on a set of wings and take
off? To understand why, consider the physics of
liftoff. In order to leave the ground, the forces driving
a body upward must overcome the downward force of the body’s weight. You can see this in action during a jump. When you push your feet down into the ground,
Earth provides an equal and opposite reaction, forcing the body upward. You can’t rely on the ground when trying to
achieve sustained flight, since the whole point is to uncouple yourself from Earth. So flying creatures and machines have to push
air down into the ground, instead of pushing on the ground itself. There are two ways to manage the problem of
pushing down enough air to achieve liftoff. You can accelerate a small amount of air downward
very quickly, as a hummingbird does. That takes incredible power, and none of the
muscles in the human body muscles can even come close to accelerating air that quickly. Alternatively, you can accelerate a large
amount of air more slowly, which is the more efficient technique, especially for heavier
fliers. (That’s why a pelican’s wings don’t flap as
fast as that of a sparrow or hummingbird.) You might think, then, that we could just
build really, really large wings and flap them quite slowly. But there’s a problem here, too. Bigger wings, and the muscle required to move
them, add weight to the equation. The amount of power required to take off increases
by the square of the additional weight. So a doubling of weight requires a fourfold
increase in power output. Unfortunately, our arm and back muscles just
aren’t that strong. Our more powerful quadriceps and gluteal muscles,
stretching from our thighs up, however, can almost do the job. For a human to take flight on flapping wings,
your body would have to be made almost entirely of muscle. In other words, humans make terrible hummingbirds. With flapping and spinning apparently non-starters,
a couple of options remain. Some birds, including albatrosses, take to
the air by riding thermal updrafts. They coast between the rising and falling
air currents to manage their trajectory and execute a landing. It’s a phenomenon similar to hang-gliding. But the whole process is totally dependent
on the right wind conditions, and many scientists think albatrosses can’t fly on a still day,
and therefore consider the birds technically flightless. We could attempt fixed, airfoil-shaped wings,
as we use in airplanes. When a plane gets going fast enough, the air
moving over the top of the wing is at a slightly lower pressure than the air underneath, creating
the phenomenon known as lift. The problem is that you have to get going
far faster than your legs can carry you. The frustrating physical reality seems to
be that, unless we can lose a lot of weight without losing any strength, humans simply
aren’t destined to fly any significant distances under their own power. But there is a happy ending, of sorts, to
this story. The jet pack, probably the closest thing a
human will ever get to flying like a hummingbird, is right around the corner. A New Zealand-based company has developed
the Martin Jetpack, essentially a helicopter backpack. Working with the same basic problem that faces
human-powered flight, power requirements increase at the square of added weight, Martin developed
a rotary wing system with the lightest engine capable of turning the rotors. What he ended up with was an automobile-style
piston engine. It’s lightweight, and it forces far more air
through the rotors than it uses to combust the gasoline that powers the engine. While it’s not exactly soaring like a majestic
bird, it’ll save you the hard work of flapping your way up there.

 

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