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Aerodynamics
What makes a paper airplane fly? Air — the stuff that's all around you.
Hold your hand in front of your body with your palm facing sideways so that
your thumb is on top and your pinkie is facing the floor. Swing your hand
back and forth. Do you feel the air? Now turn your palm so it is parallel to
the ground and swing it back and forth again, like you're slicing it through
the air. You can still feel the air, but your hand is able to move through
it more smoothly than when your hand was turned up at a right angle.
How
easily an airplane moves through the air, or its aerodynamics, is the first
consideration in making an airplane fly for a long distance.
Drag & Gravity
Planes that push a lot of air, like your hand did when it was facing the
side, are said to have a lot of "drag," or resistance, to moving through the
air. If you want your plane to fly as far as possible, you want a plane with
as little drag as possible. A second force that planes need to overcome is
"gravity." You need to keep your plane's weight to a minimum to help fight
against gravity's pull to the ground.
Thrust & Lift
"Thrust" and "lift" are two other forces that help your plane make a long
flight. Thrust is the forward movement of the plane. The initial thrust
comes from the muscles of the "pilot" as the paper airplane is launched.
After this, paper airplanes are really gliders, converting altitude to
forward motion.
Lift comes when the air below the airplane wing is pushing
up harder than the air above it is pushing down. It is this difference in
pressure that enables the plane to fly. Pressure can be reduced on a wing's
surface by making the air move over it more quickly. The wings of a plane
are curved so that the air moves more quickly over the top of the wing,
resulting in an upward push, or lift, on the wing.
The Four Forces in Balance
Long flights come when these four forces — drag, gravity, thrust, and lift
— are balanced. Some planes (like darts) are meant to be thrown with a lot
of force. Because darts don't have a lot of drag and lift, they depend on
extra thrust to overcome gravity. Long distance fliers are often built with
this same design. Planes that are built to spend a long time in the air
usually have a lot of lift but little thrust. These planes fly a slow and
gentle flight.
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