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"The moment you doubt whether you can fly, you cease forever to be able to do it" - J.M Barrie

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Let's make a person glide.

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We have a man wearing a wingsuit on a platform.

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Let's increase the area of the wingsuit to be proportionate to a flying membrane of a flying squirrel.

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Then, make the man run as fast as he can to the end of the platform, and jump off.

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At this point, the airflow speeds up on top of the suit as the result of the suit catching air from below.

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It creates lift.

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If you run as fast as Usain Bolt with this suit, it will support 2.8kg.

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So, naturally this happens.

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For a normal person to glide in a wingsuit like this, the gravity will have to be small and the atmosphere dense.

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Titan, a satellite of Saturn, is one such example that is suitable for gliding with our wingsuit.

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Titan is a harsh environment with a temperature of -179°C and methane rain.

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But its gravity is 1/7th that of Earth, and its atmosphere is four times as dense as our atmosphere.

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We can manage to glide horizontally.

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If you do it on Earth, you'd have be running at 200 km/h in order to glide.

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This person can also enjoy horizontal gliding.

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If you can't run at 200 km/h, you'll need this much suit area.

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Now, let's think about making humans fly by flapping wings.

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A small hummingbird hovers by moving its wings in a "figure 8" motion 80 times per second.

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Let's put some light wings on a 60kg person and make him do the same motion.

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And increase the rate of flapping.

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Try flying at 80 times per second, the same rate as a hummingbird.

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When you are as large as a human, such flapping will only support 3.1kg.

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Ten times that of a hummingbird, 800 times per second, still looks like this.

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At 1540 times per second...

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Our human can now hover.

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Estimates from the data of other birds, a man-sized wing should be 7 meters long.

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You could glide with this wing.

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It can hover at 70 times per second, which is less than that of a hummingbird.

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So, as long as you don't doubt our ability to fly, we can fly.