Some of the paper airplanes I’ve tried folding always fly upside down. Why? They fly perfectly both ways
In: Engineering
It’s just paper. The wings are flat. They don’t have the curve/arc to them that you normally see on most real plane wings. That reduces their effectiveness a little bit, but it means they don’t care if they’re upside down. The wings aren’t really any different either way.
An airplane can fly with wings that are flat as well, as long as they can take the weight of the plane. It’s more efficient with a proper “airfoil” shape, but with a good angle against the air (Angle of Attack) and enough speed, you’d be amazed what can fly.
I suspect it’s because you’ve got the wings at the top of the vessel. It other words, it’s top heavy.
Paper airplanes tend to fly too slow for ‘airplane aerodynamics’ to matter.
Instead, think of airplanes as a leaf with a handle. Add some weight on one side of the leaf, and the leaf will fall towards that side, which catches air underneath it, which floats the leaf up.
As long as the airplane type can catch air ‘underneath’ it right side up or upside down, this effect will work.
Some weird answers here already…
It’s a center of gravity thing and also a wing anhedral or dihedral thing. If the CG is above the center of lift, then it wants to be upside down.
Try folding it such that the wings are at an upward angle, so it looks like a Y if seen head on. Maybe not quite as much of an angle as that, but close. If it’s otherwise a good paper airplane design and has a deep enough “keel” to its fuselage, it should be stable right way up.
If you instead fold it so the wings are at a downwards angle, chances are it wants to fly upside down or doesn’t care which way it is oriented.
Of course all bets are off if it isn’t quite straight, if the wingtips aren’t trimmed to ensure it doesn’t have any rolling moment.
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