Winging It Make a Wind Tunnel On the Wings of Insects Quiz

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.

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
• Pliers with wire cutters
• Soda straw
• Scotch tape
• Corrugated packing cardboard
• Scissors

PROCEDURE

PART 1 - Constructing the Model Test Strut

1. 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

1. Cut a 3" square of cardboard.
2. Make a hole about the diameter of the straw on the center and ¾" from the leading edge
3. Draw and score a line parallel to the trailing edge and ¾" from it
4. 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

1. Mount the wing on the test strut.
2. Place the fan several feet from the test strut. Have instructor check set-up before plugging the fan in.
3. With instructor approval, turn on fan. Hold wing about half way up strut and release. See what the wing does.
4. Bend scored flap downwards at about 15 degrees. Repeat the experiment
5. Bend scored flap upward. Repeat experiment.

QUESTIONS

1. What did the strut do?
2. How does bending the trailing edge upwards affect the lift characteristics? Explain.
3. 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.

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

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).

Peter Lissaman, Ph.D., Aerospace Engineering, University of Southern California

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