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Like
all flight vehicles, micro-air vehicles, or MAVs, must
maneuver in three dimensions, forwards, sideways and
upwards. Changes in lift are needed to change the flight
path. Most aircraft depend on control surfaces, such
as elevators, rudders and ailerons to vary the lift
of the surface to which they are attached.
These
control surfaces are often flaps on the trailing edges
of the wings and stabilizing surfaces of the vehicle.
The normal effect of inclining a surface downwards is
to cause more air to flow downwards, thus increasing
the lift of the surface to which the flap is attached.
Sometimes the flaps extend backwards too, so that the
area of the wing is slightly increased, but this effect
is small relative to the effect of the downward tilt.
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OBJECTIVE
Here we will construct a model of an open jet wind tunnel that
uses a household desk fan to produce a flow of air. Using this
airflow generator we can test small wing and see the effect
of control surfaces. We will also see that the lift of the wing
depends on the tilt or angle of attack of the wing surface.
MATERIALS
- Desk fan
- Metal coat hanger
- Book about 10X6X2"
- Pliers with wire cutters
- Soda straw
- Scotch tape
- Corrugated packing cardboard
- Scissors
PROCEDURE
PART
1 - Constructing the Model Test Strut
- Unbend the hanger. Bend a triangular base to locate it
on a table with a vertical strut about 12" high. Place a
heavy book on the base, so that the strut sticks up.
PART
2 - Constructing the Test Wing
- Cut a 3" square of cardboard.
- Make a hole about the diameter of the straw on the center
and ¾" from the leading edge
- Draw and score a line parallel to the trailing edge and
¾" from it
- Insert a 2" section of the straw into the hole perpendicular
to the wing surface. Secure it firmly with Scotch tape.
PART
3 - Testing the Control Surface Effect
- Mount the wing on the test strut.
- Place the fan several feet from the test strut. Have instructor
check set-up before plugging the fan in.
- With instructor approval, turn on fan. Hold wing about
half way up strut and release. See what the wing does.
- Bend scored flap downwards at about 15 degrees. Repeat
the experiment
- Bend scored flap upward. Repeat experiment.
QUESTIONS
- What did the strut do?
- How
does bending the trailing edge upwards affect the lift characteristics?
Explain.
- How
does bending the trailing edge downwards affect the lift
characteristics? Explain.
EXTENSIONS
WING TEST
Construct
a set of two new test wings, without flaps. Secure a straw
in each wing, at about 10 degrees from normal to the surface
on one and at 20 degrees on the other. Test the wings at the
different angles of attack. Note which wing seems to have
the most lift.
ON
YOUR OWN
The tail section of many aircraft has an upright fin called
the vertical stabilizer, or fin, as in fishies! This fin keeps
the aircraft, or fish pointing directly into the flow. The
vertical stabilizer, or fin, has a control surface at the
trailing edge called the rudder. Make a model of aircraft
including a vertical stabilizer and rudder. Observe the effects
of rudder position.
WEB
CONNECTION
An
Introduction to Micro-Air Vehicles (MAVs)
More
on MAVs
Contains many helpful links
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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