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Comment by natoliniak | Hacker News Reader

ok, if the bird's natural speed is that of the ambient air, then how does it stay up? the bird is not lighter than air, so where does the upwards pressure on the bird come from? either the bird must flap its wings to stay up or there must be speed difference between the bird and the ambient air to generate lift.

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There is a speed difference between birds and the ambient air. Birds don't just drift aimlessly with the wind, they flap their wings and gain airspeed. But from their perspective, the "speed" at which they're flying is entirely relative to the mass of air, and not the ground.

This isn't some mystery, it's the same way boats and planes work. Consider a plane flying at 100 knots of airspeed. If the mass of air they're in is moving perpendicular to the plane at 50 knots, the plane will track diagonally across the ground even though it's pointed forward. The plane won't experience side loads because it's tracking 50 units sideways (with respect to the ground) for every 100 units it moves forwards, the exact same as the "wind". If the plane is instead in a 100 knot headwind, it will be stationary with respect to the ground. It won't drop out of the air, but it also won't make headway to its destination either.

From a mechanics perspective, neither the plane nor the bird care about what the ground is doing once they're airborne. The only thing they care about is the mass of air they're aloft in.

If the bird’s natural speed is 7mph, and the tail wind is 7mph, the bird is still flying at 7mph airspeed, its ground speed just increases to 14mph.

No different than a jet flying with or against the jet stream.

https://science.howstuffworks.com/transport/flight/modern/ai...

that is my point - in order to stay up, the bird would need to either flap its wings for 700 miles non-stop (unlikely) in order to maintain velocity difference between it and the ambient air OR glide which basically means he was not traveling at the speed of ambient air, otherwise there would be no lift pressure generated on his wings and he would drop to the ground

Ignore the storm for a moment, and ask whether a bird can fly for 7h+, either from flapping, gliding, or navigating updrafts. The answer is yes, that's trivial for many many bird species, especially those with a propensity for ocean travel. The storm then just changes the baseline ground speed.

There's stuff like dynamic soaring that Albatrosses use to travel thousands of miles over the ocean using little energy.

Some enthusiasts use this to make RC gliders go really fast, and the record is over 500 mph.

https://en.wikipedia.org/wiki/Dynamic_soaring

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