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We know that birds can fly in a weightless environment from experiments with pigeons on the Vomit Comet. But on a very large O'Neill cylinder space station, could they fly the same way they do on Earth?

Most birds fly by flapping their wings to climb and using gravity to dive, descend, and land. But inside a giant centrifuge, the "gravity" is supplied by the spinning of the cylinder itself. A bird in flight is not in contact with the cylinder anymore. While it seems plausible that a bird should be able to complete relatively short flights, because it will leave the ground with enough tangential velocity to complete a basic ballistic trajectory, I'm somewhat skeptical about a bird's ability to stay in the air for a very long time, and travel a long distance, without eventually losing its "downward" (outward) acceleration, and thereby its ability for "normal" flight.

I've been told I'm wrong on this, because reference frames, but the only explanations and examples I can find are rather generic and unsatisfying. Am I wrong on this? What am I missing? And for that matter, what about airplanes? I'm sure a plane could get airborne, but how far could it fly before flipping over?

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You're forgetting about the air. Thanks to drag, the air inside the cylinder will have essentially the same reference frame as the cylinder itself. So a bird (or plane) flying parallel to the axis will experience something close to normal gravity (modulo the usual gyroscopic distortions that all rotational artificial gravity has) as it rotates around the axis with the air and the cylinder, and the walls come up to meet it like gravity.

Flying with or against the rotation of the cylinder is more interesting, though. Because a straight inertial path would lead to the ground coming up like gravity, flying faster than rotation is largely the same as powered diving, while flying slower can turn into a sideways hover if the airspeed is the same as the tangential speed at that radius. But any bird or plane that can manage this would be able to do it in an equivalent gravity field, since it requires continuous power to maintain acceleration against drag.

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    $\begingroup$ I'm not sure about that. I would not expect the air to carry the birds along a matching circular path with the ground at the same rate friction with the ground would. For example, astronauts inside the space station actually do not keep up with the space station when it accelerates (blogs.discovermagazine.com/badastronomy/2011/11/10/…). The air does not carry them. The only significant force acting on the bird in flight should be the tangential velocity it started with, and that is a straight line vector, not a circle. $\endgroup$ – Janet Jun 7 '18 at 8:30
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    $\begingroup$ @Janet: The straight-line inertia is the gravity simulation (that's what makes the cylinder walls come up to meet them). As far as air carrying the birds along, it would have to: what else is going to slow them down? Only drag, which is air friction. $\endgroup$ – Nathan Tuggy Jun 7 '18 at 8:45
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    $\begingroup$ This is correct. To lose its pseudo-downwards acceleration, the bird would have to zero its spinward velocity. $\endgroup$ – Erin Anne Jun 8 '18 at 1:15

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