TOPIC: Circular airfoils
DESCRIPTION: A spinning paper tube generates lift as it travels forward.
CONTRIBUTED BY: Dale Bremmer, NASA HO
EDITED BY: Roger Storm, NASA Glenn Research Center
Center tube from paper towel roll 5 feet of surgical rubber tubing 3 ft of
cloth ribbon (do not use slippery ribbon)
2 ft of bell or iron wire
1. Fold over about 1 inch of the rubber tubing and wrap it tight with a piece
of wire. Twist the wire tight with the pliers and as doing so, form a loop
about 1 inch in diameter in the wire.
2. Attach one end of the ribbon to the other end of the rubber tub with a
piece of wire. Twist the wire tight.
3. Slip the wire loop over the screw shaft of the C-clamp. Tighten the clamp
to the end of a table.
4. Lay the tube and ribbon across the table. Place the paper tube on top of
the ribbon at its free end and roll it up snugly in the ribbon.
5. While keeping the ribbon from slipping, pull the paper tube back to stretch
the rubber tubing. Release the tube. The tube will be spun as the ribbon is
pulled off the tube while at the same time it is pulled forward by the contracting
rubber tube. With enough speed and spin, the paper tube will lift off the
table and may fly a loop through the air.
When the paper tube is released, two motions are imparted to it. The tube
is pulled rapidly through the air and at the same time it is spun. The combinations
of motions generate aerodynamic lift. When seen from the side, air is made
to flow over and under the tube as the tube moves forward. The tube's surface
experiences a small amount of friction with the air. As it spins, the friction
drags air in contact with the tube's surface around with it (see the figure).
On the top of the tube, the air being dragged around with the tube and the
air flowing over the tube are traveling in the same direction. Below the tube,
the air being dragged around the tube and the air flowing under it are traveling
in opposite directions. There, the air piles up and creates a small zone of
relatively high pressure. On top of the tube the pressure is lower. If the
tube is moving fast enough through the air and spinning rapidly enough, the
over versus under pressure difference will be greater than the weight of the
tube. The tube will begin flying and it will do so as long as its air speed
and rotation are maintained. This is aerodynamic lift.
airfoils have been added to the wings of some high-performance airplane wings
to increase lift under certain flying conditions. At least one early airplane
designer unsuccessfully tried to build a plane with rotating cylinders instead
of wings (see the film "Aeronautical Oddities").
What do you
think would happen if the paper tube were rotated in the opposite direction
as it moved forward? Place the ribbon on top of the paper tube and wind it
up turning the top of the tube away from the rubber tubing. this should wind
the ribbon in the opposite direction as the first trial. What happened when
you stretched and then released the rubber tubing? Did the tube have any lift?
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Objects that Lift
Lift of Rotating Cylinder
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