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In
order to sustain flight, an aircraft must generate a
lifting force that is equal to its own weight. If the
lift is substantially less than the vehicle weight,
then the vehicle cannot maintain level flight. Lift
is generated by the inclination of the wing surface
to the direction of movement, and its speed of movement.
The back of the wing, called the trailing edge, is inclined
downwards, so that as the air leaves the wing some of
it is traveling in a downwards direction. The air approaching
the wing is also affected by this motion at the back,
and surprisingly, is deflected upwards before it gets
to the wing. Both the upper and lower surface of the
wing contributes to the lift, the lower by experiencing
higher pressure than atmospheric (pushes it up), and
the upper surface by having a lower pressure (sucks
it up).
The
lift is caused by the reaction of the wing, as it redirects
the air from going upwards in the front, called the
leading edge of the wing, to downwards at the back.
This is exactly the same as though one were to roll
a ball along the floor towards a hard wall. The ball
hits the wall and bounces back. This collision generates
a force by pushing the wall away from you. In fact,
if the ball were heavy or fast enough, it would create
enough force to knock the wall down! Lift in fluids,
air and water, is caused by an identical effect.
A
century of clever development has gone into the design
of the cross-sectional shape of wings (called the airfoil)
to produce airfoils that create lot of lift for a given
speed. The airfoil has a characteristic streamline shape
- rounded in front and sharp at the back. In the early
days, the airfoil was actually modeled on the shape
of a trout viewed from above. The main place where the
airfoil shaping is important for lift is the upper surface.
A
paper glider is a fun model to demonstrate some of the
features of lift. The airfoils of these are not streamline
shapes, meaning they do not have a teardrop shape, as
do the wings of birds and airplanes. The paper wing
is much cruder, and consequently does not fly as well
as a more refined wing might. A bird with a wing like
the one we are going to make wouldn't survive long!
We will make two gliders that will demonstrate some
of the characteristics of lift.
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OBJECTIVE
This
activity page will offer an introduction to wings and lift
and a hands-on experience in constructing two paper gliders,
as well as an opportunity to explore how position of the center
of weight and wing size affect flying characteristics.
MATERIALS
- Standard 81/2X11" paper
- Pencil
- Ruler
- Scotch tape
- Scissors
PROCEDURE
PART 1 - MONOPLANE GLIDER
- Select either of the shorter edges of a sheet of paper.
Position your pencil about 1/2 inch from this edge. Use
your ruler to draw a parallel line.
- Make five more parallel lines all about 1/2 inch apart.
- Fold and crease the paper's edge along the first line
your drew. Fold back this creased edge and flatten the "lip"
against the sheet.
- Fold and crease the paper along the second line. Keep
the fold direction the same. FYI: Elementary school teachers
like to call this a "roll fold" as opposed to the fan-like
"accordion fold".
- Keep folding up the paper until you've folded along the
last line. Firmly crease the stack of rolled folds so that
it maintains its shape. You may need to secure it with a
piece of tape.
- Imagine a midline that runs from the middle of the folded
"leading" edge back to the middle of the trailing edge.
Gently fold and crease your paper along this axis. Try not
to disturb or warp the leading edge fold.
- To produce the "fuselage" of the glider, you'll need to
fold down each wing from either side of the central crease,
as shown.
- Add stability to the glider by adding a 1" fin that is
created by folding up on the tip of both wings as shown
here.
 
- Hold the glider by the fuselage and throw it gently in
a horizontal direction.
- Experiment with increasing and reducing the number of
folds. .
QUESTIONS
- Why was the folded edge called the leading edge?
- How did removing a wing fold affect the glider behavior?
- How did adding an extra fold affect the glider's behavior?
PART
2-Ring Wing Glider
- Proceed as in steps 1 through 5 of the Monoplane instructions.
This time however, mark ten folding lines instead of six.
- Keep folding up the paper until you've folded along the
last line.
- Gently roll this folded paper into a cylinder that resembles
a large bracelet. Both ends of the folded (and leading)
edge should align. Slip one of the folded edges into the
other so that the pressure of the folds binds them together.
You may need to secure this shape with tape.
 
- Hold the glider as though it were a football and throw
it gently in a horizontal direction.
- Test fly it again putting some spin in about the axis,
as though it were a football. See if there is any difference
in flight.
QUESTIONS
- What part of the glider acted as the wing?
- How can you increase the lift of this design at a given
speed?
THINK
ABOUT IT
Have
you ever placed your hand in a stream of rushing water?
If so, what happened as you angled your finger tips in the
stream flow.
Why?
Suppose you angled your hand down?
What would happen if you keep your hand level?
WEB
CONNECTION
Building
Paper Airplanes
Links to several paper airplane sites
Aviation
Museums
A comprehensive list of aviation museums worldwide
The
activities in this guide were contributed by Michael DiSpezio,
a Massachusetts-based science writer and author of "Critical
Thinking Puzzles" and "Awesome Experiments in Light & Sound"
(Sterling Publishing Co., NY).
Special
Advisor to this Guide:
Peter Lissaman, Ph.D., Aerospace Engineering, University of
Southern California
Academic
Advisors for this Guide:
Corrine Lowen, Science Department, Wayland Public Schools,
Wayland, MA
Suzanne Panico, Science Department, Fenway High School, Boston,
MA
Anne E. Jones, Science Department, Wayland Middle School,
Wayland, MA
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