Science
Paper Airplanes

Materials: Paper (copier or computer printer paper works best), some 1/2" or 3/4" cellophane tape, and a paper clip. (make a copy of the "Bernoulli Plane" template so you can make several and experiment with different ways of making it fly)


  Procedure

Build a special paper airplane to demonstrate how airplane wings work and how most birds can fly (when they're not flapping their wings).

Click Plane Template to see and print the airplane.

Cut out the airplane's shape along the dark solid line. Next, fold the top half at the dotted line so that it meets the bottom half. Don't, however, fully crease the paper at the fold (we want to make a nice 'tear drop' air foil shape). After folding the paper back, put a small piece of tape at the wing tips and at the center at the points marked A, B, and C. Now fold the plane along the center crease so that it creates a flattened out 'V'. The angle of the 'V' should be no more than about 15 degrees.

Test fly the plane and adjust its stability. Keep the nose of the plane from rising (stalling) by adding a small weight to the nose (point D), a paper clip or two does nicely. You can also adjust how much the plane dives or climbs by cutting small slots in the tail of the plane and bending the paper at the cuts up or down. Experiment with putting them up or down and seeing what effect that has on the way the plane flies. People who know about airplanes call these little 'tabs' an elevator if it makes the plane go up or down and a rudder if it makes the plane turn right or left.
   
  What's going on?

Well, for many years as an avid modeler, I believed, incorrectly, that the majority of lift created by a wing passing thru air was due to a principle known as Bernoulli's Principle. The summary of Bernoulli's Principle is: "...as air travels faster [than surrounding air] across a surface, the air pressure against it is reduced...". What that means is that the air pressure where air travels faster drops, literally "sucking" that surface at that point.

This notion also includes the statement that says that the air passing above the wing surface must meet the air passing below at the same time. And this implies that if you curve the top of an airplane wing so that the distance along the top surface is longer than the bottom, that the air must move faster (to meet a the trailing edge of the wing), thereby satifying Bernoulli's Principle.

Unfortunately, only a few percent of the total lift of a wing is created from this "speeding up" of the air passing over the wing. The Bernoulli Principle is valid, but is NOT the reason why most planes fly. And using this description of creation of lift doesn't explain how planes can fly upside-down or how a plane's lift changes as the "angle of attack" of the wing changes. (It's Newton's Effect that is really at work - the same effect as when you are traveling in a fast moving car and you put your hand out into the passing air and direct your hand up and down, tilting it like a wing.)

Even with all of this information, I still believe that the "Bernoulli Plane" is a good project to demonstrate how some planes fly and to help explain airfoils are used in airplanes.
   
  Mess Factor

Scraps of paper all over the floor as we cut out the plane(s).
 


Things to Remember

Bernoulli's Principle is a relation discovered by the 18th-century Swiss scientist and mathematician Daniel Bernoulli. He discovered that the faster a fluid (such as air) moves, the lower is the pressure that it exerts.

This material can be found in more detail in "Understanding Flight", by David Anderson and Scott Eberhardt, McGraw-Hill, 2001, ISBN: 0-07-136377-7.






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Last Modified: October 9, 2009