eli5: Why is it not possible to build bird-like attachable wings that account for body proportions to allow humans to fly or glide around?
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Wings are only half of the story, birds also have hollowed bones and massive chest muscles.
Probably other people can give better more detailed answers, but for birds everything in their bodies is built to fly. Their bones are lightweight and they have feathers, their muscles are designed to power wing movement. Humans are simply too heavy and our shoulder muscles too weak to ever fly like that.
Because people are heavy. An adult peregrine falcon weighs between 330 and 1500 grams (about .75-3.3 lbs) and has a 1 meter (3.3 ft) wingspan. If we figure the wings are about 1 ft / 0.33 meters wide as a “rectangle” thats 3300 square centimeters of lift surface area. For lets say 3 lbs. Take a light adult human, say 63.5 kg / 140 lbs. That is 46 times heavier than a falcon. If lift surface requirement was proportional that would require 15.18 square meters (151,800 cm^2) of wing. In other words, a hang glider sized wing. Theres no way we have the upper body strength to flap a hang glider. Birds are all chest muscle to flap those giant wings and are very light with porous, hollow bones.
Edit: corrected my sucky math. i carried too many and too few zeros on my arithmetic.
Edit 2: In response to a lot of the replies about mechanical advantages like pullies and/or engines / motors sure. That “thing” is called an ornithopter. Ornitho meaning bird. And pet/ptere meaning to fly. A machine that flies like a bird. If you saw the new Dune movie, that is where the dragonfly-like planes came from with flapping wings rather than something like a helicopter or jet. Frank Herbert specifically described them as “ornithopters” in the novel.
However, If pursuing powered flight, fixed wing planes or helicopters are, today, far more efficient and compact than anything we could build that flaps while being far less complex. Its just not technically practical (currently) at the scale of a human being to build a flappy bird machine as cool as it would be.
Edit 3: Some folks pointed out that bird bones are actually as heavy or heavier than terrestrial animal bones and that seems to be true…thanks for the TIL. However, it does not invalidate my statement that birds are light and birds have hollow bones. (Hollow like air bubbles not hollow like a tube). Not only does it make them more flexible (think about how much further you can cast with a flexible fishing rod than a stick, or how a flexible club shaft on a golf driver increases distance…the flexibility creates power at the wing tips) but more importantly, they use their bones to to help them breathe more efficiently. Birds can drown in their own blood from broken bones like a human with a punctured lung. Their bones are directly connected to their respiratory system and they use them to store additional oxygen which comes in handy for all that heavy lifting…The average wattage per kilogram of muscle for a bird in flight is 100w/kg. Some hummingbirds are > 130.
Comparatively, Top pro cyclists generate 6 or maybe 7 watts per kg body weight over the course of a race and humans cap out around 20 watts per kg of muscle for peak power. But Its not just a raw power/weight issue. A human trying to flap fly around would be doing a cardio workout from hell. The in flight glide position of a bird is basically the “iron cross” from gymnastics. The world record hold for that is 39.23 seconds. Now alternate body weight chest flyes and back flyes multiple times per second in between holds. We’re just not physiologically built for it from a strength or stamina standpoint and i took OPs question as an “Icarus”-like set of wearable, human-powered wings, otherwise were just talking about a stark enterprises engineering project.
Thanks for all the interesting replies, questions, TILs and upvotes. Was not expecting my response to gather so much attention.
Imagine you had artificial wings that could get a solid “grab” on the air and then you could use that to lift yourself up. You’d essentially be doing a pull up. How many pull ups can most people do?
Gliding is entirely possible, wingsuits are a thing. Flying requires thrust that is, at a minimum, equal to your bodyweight, and humans just aren’t built to do that.
Grab onto something and try to hold your full weight off the ground long enough to fly somewhere. Now imagine you have to do that, plus flap hard enough to lift your whole weight against gravity. Humans are built to do a lot of things but they don’t have the upper body strength to overcome their weight regardless of how fancy the wings are.
Birds do not scale up well. Making its body proportions twice as big makes it have 8 times the weight and so requires eight times as much ‘wing’ which would be about 2.8 times as long.
Humans are significantly bigger than birds, and to worsen this, we’re much denser. Then, we don’t have the muscles that birds do to keep us moving.
Humans are much too heavy for bird-like attachable wings powered by muscles alone. Our bones are too dense, among other problems.
Were we to construct a large, air-filled habitat on the Moon, it might be possible for a human to fly in such a manner there. [This has appeared in science fiction at least once.](https://en.wikipedia.org/wiki/The_Menace_from_Earth)
When you see a picture or statue of an angel or other person with wings, it’s like the wings are just stuck on their back. Wings on birds don’t work that way.
Birds have massive chest muscles that move the wings. When you eat chicken, that’s most of what you’re eating (other than the drumsticks). The breast meat (muscles) is attached on one end to that white rubbery cartilage keel in the bird’s breast. The other end is attached to the wings.
Think of eating chicken wings. They are tiny, bony things in comparison to chicken breasts, but that’s supposed to be enough for an angel to fly. It isn’t.
some people have had slight success with it, but the problem is that our arms arent stong enough, and our fingers arent elongated, like a birds are (yes, birds have finger bones in their wings.)
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