Why Paper Airplanes Fly…and Why They Crash

Did you ever wonder how a bird or an airplane stays in the air? Studying two sheets of paper can help you understand. A wadded-up piece of paper drops to the ground when thrown, while another piece folded into a paper airplane floats gracefully across the room. The reason for this has to do with the forces of gravity and lift.


Each piece of paper weighs the same, so gravity pulls downward the same amount on each. The difference is the paper airplane has wings that create lift, which keeps the plane in the air as if it had an invisible hand holding it up. The wadded-up paper has nothing to hold it in the air, so it quickly drops to the floor. The wings of all birds and airplanes work the same way. As a wing moves through the air, its front edge is angled up a little bit.


Air passing under the wing is slowed down when it rams into the bottom of the wing, creating pressure, which pushes the wing up. At the same time, the air flowing over the top of the wing speeds up, lessening pressure and creating a suction that pulls up on the wing. Together, the two forces are called lift.  The more the wing is angled up, the more lift it creates, until it reaches the stall angle.  A stall is when the wing is at too high an angle for the air to flow smoothly over the top. When the wing stalls, it can no longer create much lift and the airplane will crash.

DRAG AND THRUST When anything flies through the air, from a paper airplane to a jet airliner, the air rushing across it rubs against it and tries to slow it down.

When an airplane is flying level and thrust is greater than drag, the airplane speeds up.  If there is less thrust than drag, the airplane slows down.  As you know, paper airplanes do not have engines.  Your throw initially produces the necessary thrust to get your plane moving.

Then what keeps it from slowing down? Think of a paper airplane as a coasting bicycle.  If you are on level ground and stop peddling (stop producing thrust), the bicycle will slow down (because of drag) and eventually stop. If you coast your bicycle down a hill, gravity becomes the thrust that keeps your bicycle from slowing down.

Paper airplanes work like this, too. If you throw your plane straight out, it will slow down.  If you throw it very slightly downward, gravity will keep pulling your plane forward as it coasts down an invisible hill.



Most paper airplanes that crash actually are able to create enough lift to fly. So why do not the fly? They are unstable. 

STABILITY keeps planes flying smoothly forward. There are three main types of stability: pitch stability, directional stability, and roll stability.  To have a plane with stable pitch, you need weight toward the front.
This keeps the plane is nose from pointing too far up or down.

Directional stability is what keeps the plane flying straight.

Like pitch stability,directional stability is improved by keeping the weight of the plane forward.
Having a tail or fins at the back of the plane also helps keep it directionally stable.

Roll stability keeps the plane is wings level.

A plane without roll stability will begin to circle, turning tighter and tighter until it spins down in a vertical dive.
To give your plane roll stability, make sure that the wings form a slight “Y” shape with the body.

Originally posted 2012-04-05 22:57:32. Republished by Blog Post Promoter

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