Question: Why Can't Humans Fly?

This question and answer came from a discussion in Oak Class. Read through to help your understanding. What new questions do you have? What makes sense to you? What do you need more information about? How could this explanation be improved? Are there any inaccuracies?

If birds can fly by flapping their wings, why can't we by flapping our arms?

All birds flap their wings at some point in order to fly. Some birds, including eagles, condors and several species of sea bird, can fly for hours - or even days - with very few flaps. They do this by utilising the behaviour of the wind and 'soaring' like gliders. Most birds, however, flap their wings regularly to fly.

This has caused humans over the centuries to experiment, dreaming of emulating birds and flying under their own power. You may notice that, no matter how hard you flap your arms, they simply won't propel you into the sky like birds' wings. Throughout history, people have tried to improve upon their human arms by attaching large, bird-inspired, lightweight wings, and yet none to these attempts have succeeded in powered flight.

Wearing a wingsuit - a whole body covering that looks something like a flying squirrel - allows humans to control their rather rapid glide when jumping from a height, but wingsuits do not result in flight, just slightly slower, more controlled falling.

So how can birds fly by flapping their wings when humans can't? It all comes down to the forces acting on each species. For a bird’s wings to produce enough lift to overcome the pull of gravity, they have to generate a huge downward force in comparison to their weight. The mass of a bird, compared to its strength, is incredibly low next to a human. They are relatively light. Humans are relatively heavy. Birds have lightweight, hollow bones that are both strong enough to cope with the forces of flight, while being light enough to keep the lift required low.

Humans are not built this way. Our ratio of power to weight is a lot lower. Although we are much stronger than most birds, we are also much, much heavier. No matter how strong or how light a human is, they cannot generate enough power to overcome their own weight by flapping their arms, even with ingenious wing-shaped devices attached to them. The strongest human would be far too heavy. The lightest human would be nowhere near strong enough.

However, humans make up for their lack of power-to-weight ratio by applying their brains through science and engineering. Not only can they fly by attaching engines to aeroplanes, they have even been able to harness human power alone - not by flapping wings, but by pedalling - all the way over the English Channel in a flying bicycle called the Gossamer Albatross.

Mr. Oliver-Dean