Philipp Witte Extended Essay

4-8-03 Frau Haardoerfer

Planning A and Planning B

Introduction/ purpose: Ever since I was a little boy experiencing the world on a rather naïve level, I pondered about the possibility of flight. I was not yet aware of the difficulties and complexities of flight. I had not heard of Bernoulli or Newton, of lift or drag, even of wings or rotors. I only knew that I was not capable of flying, but I was aware of the ability of other animals to do so. I always wondered why we couldn’t just simply run until our feet left their grasp on the ground and we lifted off towards the sky. What kept me on the ground were the same two factors that kept our early flying machines and all current aircraft from simply lifting up and gliding in the air effortlessly: drag and gravity. To overcome gravity, lift is produced by air flowing over an airfoil. To overcome drag, thrust is produced by a power plant. Because of lift’s importance and drag’s adverseness, a high lift to drag ratio is a very desirable characteristic of an aircraft. The pioneers of flight, Orville and Wilbur Wright, were well aware of these two characteristics and their significance in flight. In order to achieve a desirable lift to drag ratio, also known as the glide ratio, Wilbur and Orville constructed a simple wind tunnel, not much different from the complex wind tunnels now being used by NASA. It was out of the same curiosity of flight that decided to construct a simple wind tunnel similar to that of the two early pioneers of flight. Yet, at the time at which I constructed the wind tunnel, I merely wanted to observe the affects of simple changes made to a wing or model, and not to gather data to relate them by a mathematical relationship. Now, with additional knowledge of physics and the uncertainties that must be taken into account during data gathering, I wish to improve the accuracy of my wind tunnel and test various airfoils and wing shapes in it in order to determine their lift to drag ratio. So, my research question is, how do different wing shapes and profiles affect the performance (lift to drag ratio, also the glide ratio) of a model aircraft using a baals wind tunnel?

Hypothesis: The airfoil that will result in the least drag is Eppler 205 because of its narrow appearance. Yet, I believe because of its small upper curvature, it will result in comparatively little lift. Eppler 210 however has a much larger upper curvature, which should result in the most lift of all of the airfoils. It is hard to tell which airfoil will result in the highest lift to drag ratio. The wing shape that will result in the most lift is the rectangular wing, because I assume it has the greatest average chord for surface area of all of the wing shapes. Yet, I believe that the rectangular wing will have a lot of drag because of vortexes formed on the leading edges of the wing. The wing that should have the least drag is the elliptical wing because its shape should minimize vortexes on the leading edges of the wing. Again, it is hard to tell which wing will produce the best lift to drag ratio, but I assume it is the rectangular one. I base this assumption on the fact that gliders, which rely on their lift to drag ratio to achieve flight distance, use a rectangular wing.

Variables:

Independent

Airfoil

E205

E210

E214

E228

E374

E387

Wing shape

Rectangular

Tapered

Swept back

Elliptical

Swept forward

Delta

Dependent

1. Drag

2. Lift

Uncontrollable

· Effect of wall of wind tunnel on the flow of the air in the wind tunnel

· Friction between the pulley and cord

· Friction between the pivot rod and pivot

· Irregular air currents

Constants

· The constants for this experiment are the components in the equations for lift and drag (lift= ½ C_L x R x V² x A, and drag = C_D x (1/2 RV²) x A) other than the lift and drag coefficients(which are used to describe the lift and drag of a body based on its shape, surface and other factors):

-Area (average wing chord x wing span)

-R (density of the air)

-V (velocity of the air traveling over and under the wing)

Materials:

Materials for the original wind tunnel:

A cardboard box with the dimensions of about .26m x .26m x 1.22m (a box with these specifications can be purchased at Mailboxes Etc.)

Glossy white latex paint

A .2, x .2 m sized piece of Plexiglas

Silicon cement

A sheet of wax paper

A 2 x 1 x 72 inch wooden beam

Duct tape

A coat hanger

Pliers

A household fan (preferably with variable speed settings)

Materials for the improvements to the wind tunnel

A 12-volt hobby people starter motor for RC glow engines

A 12-volt power supply

A 3-blade propeller (12 x 8)

A profiled model airplane metal tube

Materials for the test models

A plentiful supply of wooden blocks

Coarse and smooth sheets of sandpaper

Acrylic paint

A handsaw

Miscellaneous materials

An anemometer

A digital scale with a .01 resolution

Method:

Method for constructing the wind tunnel

1.In order to make the model more visible inside the wind tunnel and make the interior surface smoother to avoid interference of the wind tunnel wall with the airflow, paint it with latex based enamel paint.

2. Cut a .25 by .20 m rectangle into one side of the wind tunnel so that the longer side of the rectangle is parallel to the length of the box.

3.Cut a .25 by .20 m rectangle out of Plexiglas and glue it into the rectangular hole made in box so that the glass is flush with the interior surface of the box. This will reduce interference of the glass in the airflow in the wind tunnel.

4.To support the box, build two rectangular frames out of the wooden beams to fit onto the box. Hold the frames together by attaching two wooden beams to the rectangular frames so that they are parallel to the length of the box.

5. The flaps of the box will serve as the restrictions in the airflow to result in higher air flow speeds. Place the backside of the household fan into one end of the box so that the four flaps touch the circular protective frame of the fan. To make the connection airtight, add a sleeve around the flaps from a piece of plastic bag.

6.To form the restriction at the front of the wind tunnel, bend a coat hanger into a .38 by .38 m square. Tape each of the four sides of this square to one of the flaps of the box opposite of the side on which the fan has been attached, using duct tape.

7. To reduce unwanted irregular air currents from coming into the wind tunnel, especially those caused by the powerful exhaust from the fan, fashion a honeycomb grid of cardboard that will fit snuggly into the box.

Method for making the necessary improvements to the wind tunnel

1. To begin the improvements to the wind tunnel, remove the silicon rubber spinner insert and aluminum drive cone, unscrew the bolts from the front end of the starter motor, and take off the front end of the motor.

2. Carefully remove the casing and rear end from the core of the motor, making sure to collect all the springs and disks that fall from it.

3. De-solder the wires from the switch by holding a hot soldering iron to it for a few seconds. After the solder on the wires is hot, remove the wires from the plates of the switch.

4. Solder on the two wires directly onto the contacts of the brushes on the bottom end of the motor.

5. Insert the springs into their slots, and the brushes over them. Then place all of the necessary disks back onto the core of the motor, and insert the motor into the bottom plate. Slide over the metal protective casing over the core. Then, replace the top part of the motor and attach it with the screws and bolts; however, do not replace the case for the switch.

Method for making the test models

Method for collecting the data

Appendix

Caught in a Wind Tunnel

by Shawn Carlson

WIND TUNNEL, fashioned from a cardboard box, allows amateur experimenters to make a variety of aerodynamic measurements.

Controlled fiight might be the most vexing experimental problem ever to be solved. Some of the greatest thinkers through the ages have attacked it, including Leonardo da Vinci, who penned more than 500 drawings and 35,000 words on the subject. Of the many intractable difficulties human fiight posed, aerodynamic stability ultimately proved to be the hardest to master. An airplane can pitch up and down, roll left and right, and yaw side to side. Straight and level fiight requires all three of these motions to be managed simultaneously.

That challenge was finally answered by two of the most talented amateur researchers the U.S. has ever seen. Although most people think of them more as working-class do-it-yourselfers, Orville and Wilbur Wright would be better remembered as gifted scientists. One of their greatest contributions began in 1901, when they developed the wind tunnel into a precise research instrument. The Wright brothers used it to perform thousands of systematic measurements, the first truly reliable determinations of this kind in the emerging field of aeronautics. That effort made possible their success two years later at Kitty Hawk, N.C.

Wind tunnels still afford amateurs countless research opportunities in aerodynamics and beyond. Of course, a wind tunnel will allow you to tailor the design of kites, model airplanes, sailboats and racing cars for improved performance. In fact, a wind tunnel will let you study almost anything that is affected by moving air. For example, you can observe the interplay between waves and wind on a liquid surface. Environmentalists may want to examine evaporation through different types of soils or measure the wind's velocity profile above a tray of grass, soils or asphalt. With a wind tunnel, you can also investigate how insects cope with strong breezes or mount the chamber vertically to find the terminal speed of waterdrops suspended on a column of air. With a little imagination, the possibilities for exploration are probably endless.

For my own experiments, I recently put together an inexpensive wind tunnel that uses a household fan to draw air through the test region. A long cardboard box, available from Mail Boxes Etc. or other similar shipping outlets, forms the central tube. Mine measures 30 by 30 by 122 centimeters (12 by 12 by 48 inches), but the precise dimensions are not important. Just make sure that the length of the box is at least four times its width. Painting the interior of the box a glossy white will make your experiments easier to see. To keep slight air currents from passing directly through the cardboard itself, you should double-coat the exterior with latex-based enamel paint.

A sheet of Lucite forms the window. Have your local hardware store cut a rectangular pane 20 by 30 centimeters (eight by 12 inches) in size. Trace the windowsill around the pane [see illustration for placement] and cut out the opening using a box cutter. Temporarily place waxed paper behind the hole and support it with a wide scrap of wood. Then run a bead of silicone cement around the Lucite and press it into the sill so it is fiush with the wood. Make the seal airtight by caulking the joint with silicone cement.

To bolster the tube, fashion three tight-fitting rectangular frames from wood slats and glue them to the outside of the tunnel. Horizontal slats help to make the structure more rigid and support the measuring equipment.

PING-PONG BALL suspended from a string serves to measure wind speed.

DRAG APPARATUS uses a pivot and weights to gauge the aerodynamic force.

Some household fans can drive wind as quickly as five meters per second. Adding a restriction, like the one shown in the illustration on the next page, increases the speed of the airfiow (just as putting your thumb over the end of a garden hose shoots the water more rapidly). Decreasing the cross-sectional area in the test region by two thirds will, for example, nearly triple the airspeed you can attain. If you need still stiffer winds, check your local industrial liquidators for more powerful fans. Most commercial fans use a four-position switch to control their speed. For finer adjustment, replace this unit with a household light dimmer. Use duct tape to attach the fiaps of the box to the fan. Plastic trash bags, slit at the bottom, make excellent airtight sleeves. Slip one over the fan and the box and tape it into place.

Flair the entrance to the wind tunnel by bending the fiaps on the opposite side outward and attaching them to a square fashioned from two wire coat hangers. Epoxy and then tape the wire square to the outside of the fiaps as shown. Afterward, place another garbage-bag sleeve around this end of the tunnel to make it airtight as well.

The exhaust from the fan creates air currents in the room, and some of these swirling eddies will invariably drift back into the tunnel. A single layer of window screen at the mouth of the tunnel helps to smooth out these unwanted irregularities. Staple the screen to a wood frame that fits snugly inside the opening. Line the outer edge with felt to prevent air from leaking in around the sides. You will need access to the interior, so do not affix the frame permanently. Glue four ice-cream sticks onto the inner walls just deep enough inside from the mouth to keep the screen in place during tests. A "honeycomb" assembly (really, a square grid of cardboard baffies) just downstream of the test region helps to maintain a smooth fiow of air for your experiments.

You can measure the airspeed inside the tunnel using a number of devices, including a hot-ball anemometer [see The Amateur Scientist, November 1995, for construction details], a cup anemometer from an old weather station, a manometer or an ultrasonic anemometer. Or you can combine a Ping-Pong ball, a protractor and a length of white thread into a simple instrument. The angle the string attains will depend on the relative strengths of the forces of gravity and aerodynamic drag on the ball. Use the equation given in the illustration. The value you obtain should be good to about 10 percent, but because of certain subtleties of fiuid dynamics, it is valid only between 0.5 and 40 meters per second.

People with a passion for aeronautics will probably want to measure aerodynamic forces. Determining all possible forces and torques requires six simultaneous measurements. But experimenters are often interested in just one quantity--the lift on a wing or the drag on a surface, for example. The two setups shown will let you measure either lift or drag (but not both simultaneously). Mounting your models sideways takes gravity out of the equation.

To measure lift, increase the counterweight until the model remains in place when released. The weight then equals the aerodynamic force on the model. For drag, the counterweight applies a torque that balances the torque applied by the drag force. The drag force then equals the ratio of the moment arms (a/b) times the counterweight. If you don't have a set of calibrated weights, loose change will do. If you have more sophisticated needs, the references listed on the World Wide Web site of the Society for Amateur Scientists describe more elaborate balance systems. As a final challenge, you may want to figure out how to record the forces electronically.

For information about this project or other activities for amateur scientists, write the Society for Amateur Scientists,4735 Clairemont Square, Suite 179, San Diego, CA 92117. You can also visit the society's World Wide Web site at, call (619) 239-8807 or leave a message at (800) 873-8767.

Images: Micheal Goodman

Sources Used

Mohr, Steven. Unlisted Plans. 26 Jun 2001. <http://members.fortunecity.co.uk/

slmohr/unlisted_plans.htm>. 14 Apr. 2003.