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Comment by rdtsc | Hacker News Reader

> Planes actually fly by stretching air over their wings (creating low pressure) and the higher pressure air below pushes the plane up (to fill in the void)

So why can planes fly upside down then?

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Whenever I've played a flying simulator, if I've put the plane upside down, to maintain altitude I need to push the joystick forward. In an upright plane it would cause a nose dive, on an upside down plane, it creates lift. Due to it's not optimal aerodynamics, it also requires more thrust to maintain. Basically you are changing the shape of the wing to compensate for the non-conventional position.

Doesn't extended upside-down flight require pointing the nose up (as in away from the ground) in order to compensate for the decrease in lift? I've yet to try this (I suppose I could; I've got an X-Plane-running flight sim rig about 10 feet away from me), but my intuition and understanding suggests that if the only difference between two planes flying in the same exact atmospheric conditions is that one of them is upside-down, the upside-down one will start losing altitude.

Yeah give it a try if you have a minute out of curiosity. X-Plane, if I remember correctly, prized itself on a pretty good airfoil model.

So I tried it in some simulated Cessna, and as I predicted, upon rotating so that my head pointed at the ground, the plane started to descend. I'm a pretty terrible pilot, though :)

I think this has a lot to do with the wing's angle of attack (most planes' wings have a slight upward tilt; when upside-down, that tilt goes downward instead). It would be more interesting to see the effect on something without an AoA bias.

I just posted a brief answer above that may explain it better: https://news.ycombinator.com/item?id=10218403

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