Gravity
Gravity
is the only reason paper airplanes don’t fly forever.
If gravity’s downward force wasn’t acting on the
plane, it would have no reason to descend. However,
gravity is counteracted by the plane's lift.
Lift
For
“real” airplanes, lift is typically explained with a
diagram of the wing, displaying how the curve on top
the wing forces air to travel quickly over it, while
the air below it travels more slowly. This cause a
difference in pressure, and this pressure is what
lifts the plane up. (2)
http://ambitiontofly.files.wordpress.com/2011/10/wings_flow_air2.gif
However,
paper airplanes clearly don’t have this same feature,
so where do they get their lift?
Well,
the principle is still the same, but the method is
different. Paper airplane wings are angled so as the
body travels forward, the air has to spend more time
rushing over it. In fact, try building a plane so the
wings angle downward sharply toward the nose and up
toward the back. When you throw this plane (at any
somewhat horizontal angle), it should have so much
lift that it will immediately shoot straight up and
fall to the ground. A paper plane does not have very
much weight to it, so the wing/body ratio and the
amount of lift generated are very important to
moderate. Too much lift can easily throw the plane out
of stability. (4)