build a wind tunnel

ON-DEMAND PROJECT / BUILD A WIND TUNNEL 1© 2005 PRAKKEN PUBLICATIONS, INC.

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Build a Wind Tunnel

Mike Fitzgerald is technology education specialist, Office ofCareer and Technical Education, Indiana Department ofEducation, Indianapolis. He taught at Driver Middle School,Winchester, IN, when he wrote this article.

By Mike Fitzgerald [email protected]

Photo 1—Completed wind tunnel

THIS article will give youbasic information on con-structing a wind tunnel thatyou can use for instructionalactivities with your students

for many years to come. I will illustrateand describe the procedure and materi-als that I developed in constructing myown wind tunnel, but readers shouldview this information only as a guide.

I am not an expert at wind tunneldesign nor am I an aerospace engineer.I am simply a teacher who wanted touse a wind tunnel with my students. Ilacked enough funding to purchase a unit though a scienceor technology education supplier, so I built my own frombits and scraps! The wind tunnel that you construct mayvary due to parts availability, your personal resourceful-ness and your final design and construction techniques.

I started building the wind tunnel described here in1998. While looking for a suitable fan unit, I learned thatmy father-in-law had an old unit in the storage shed buriedbeneath a mass of bicycles. Two weeks and about $200 ofsimple improvements later, I built my first wind tunnelbased on the TEA Wind Tunnel plans (Chapin & Cook,1988). I had received the plans as an undergraduate stu-dent from the Center for Implementing Technology Educa-tion at Ball State University. I recommend that you locatethe TEA Wind Tunnel guide or a set of similar plans avail-able via the Internet before beginning construction of yourwind tunnel. I will include some basic illustrations, photo-graphic details, supplier information and the recommenda-tions that I would consider if I decide to construct anotherwind tunnel.

BackgroundRoberts (2001) describes hydrodynamics as the study of

how fluids and gases move around an object. He furtherstates that the study of hydrodynamics is important in thatfluid movements help determine the shape and functionof many vehicles. “A ship needs to slip through the waterto move quickly. An automobile needs to divert air aroundits shell to improve fuel economy. An airplane needs toslow down the air traveling beneath its wings to create lift”(p. 10).

Konstantin Tsiolkovsky also experimented with thestudy of fluid movement, in 1892. He developed proto-types of wind tunnels that he used to study and measure

aerodynamics concepts. His contributions helped lead tothe understanding of aerodynamics employed by racecar drivers, pilots and engineers today.

There are basically two kinds of wind tunnels. Onepushes air around a test object, and the other kind pullsair over an object. Using a wind tunnel allows consistenttesting of models in a test chamber, as well as for makingmeasurements. Aerospace engineers use wind tunnels tostudy mockups and prototypes of aircraft, rockets andspacecraft. They collect data so they can design betteraircraft. They may use a wind tunnel to study the flightcharacteristics of a mockup before spending money on aprototype aircraft. They also investigate such factors as thelift characteristics of the aircraft, how the control surfacesreact at various speeds and the aircraft’s drag characteris-tics. Aerospace designers perform these same activities ona prototype before flight testing to help ensure test pilots’safety.

You can learn more about wind tunnels by using soft-ware available on the NASA Glenn Research Center’s website: www.grc.nasa.gov/WWW/k-12/FoilSim download.html.The FoilSim program includes many lessons and activitiesthat students can use to learn about aerospace topics. Allactivities are based on national standards in math, scienceand technology.

Architects and engineers also use wind tunnels to studythe effect of aerodynamics on models of structures likeskyscrapers and bridges. Aerodynamic forces on structures


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Build a Wind TunnelBy Mike Fitzgerald [email protected]

can cause them to sway, resonate, buckle or shear.In the area of automotive design, wind tunnel research

helps determine the best vehicle shapes in terms of thelowest drag coefficients. Lowering the aerodynamic dragon a vehicle improves its fuel economy. Doing so alsoallows a vehicle to attain higher top speeds without havingto increase horsepower. Wind tunnel research also extendsinto nearly all forms of racing. In Olympic events, windtunnel research is even applied to the design of bicycles,skiing gear and bobsleds.

Main AssembliesFirst, locate a suitable furnace blower unit. I was lucky

in that the unit I obtained was already wired with a two-speed switch and a variety of electrical wire taps that Icould change to control the motor’s speed. Many styles offurnace motors and blower styles exist.

In the tunnel that I feature in this article, the motorwas mounted within the blower unit. For safety reasons, Irecommend that you also use a style that has an internalmotor, which helps keep students from getting caught inmoving parts such as belts or pulleys. Also, that stylemakes it easier to construct protective shielding andscreens to keep fingers away from moving fan blades.Finally, the overall appearance of the finished wind tunnelwill have a more polished andprofessional quality.

Next, purchase a section offurnace duct that you can mounton the blower unit. The duct Iselected did not match up to myunit at first, so I had to makeflanges and a mounting surface toconnect the duct to the blowerunit.

Test ChamberAfter you attach the duct to the

motor/blower unit, you will needto cut away the test chamber. Iused a Dremel tool with the appro-priate cutting wheel to open asection that measured 24" x 7". Ichose this size opening to ensurethat students could test the dragon CO2 cars. At this point, youneed to consider what you willtest in your tunnel and, thus, how

large a test chamber you will need. Finally, remember thatyou must shield students from sharp edges. This is espe-cially important regarding the opening you make for thetest chamber. I cut the opening with interior flanges thatwere then neatly bent inward, which left a nice roundedsurface to prevent students from getting cut.

Test Chamber Viewing WindowMy test chamber viewing window measured 24" x 7". I

sealed it with an oversized sheet of scrap Plexiglas thatmeasured 44" x 8". I used a piano hinge to attach the plas-

tic viewing window. The 30" pianohinge was somewhat expensive,but I decided that the ease ofattaching the plastic and the over-all durability that the hinge wouldprovide made it well worth thecost. The weight of the Plexiglashelped to seal the test chamber tosome degree.

At this point, I tried the windtunnel for the first time. I noticedthat even at a low motor speed theviewing window did not com-pletely seal itself through its ownmass. I realized that I would needto make a latch and perhaps a sealto prevent air loss but decided thatI would address that problem later.

Creating a Scalefor Measurement

Many teacher-built wind tun-nels use a mechanical device, like

Photo 2—Another view of the wind tunnel, with the viewingwindow open

Photo 3—Closeup of the digital scale


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a spring gauge or a needle andpointer, to measure drag. Theteacher typically makes the scale.The chief improvement in mywind tunnel is the use of a digitalscale. Digital scales are availablefrom a variety of science and tech-nology education suppliers. Whilethey can be somewhat costly ($100or more), you may be able to pur-chase one cheaply though an of-fice supply store. One unit I foundafter I completed my wind tun-nel—intended for measuringweight for postage—cost just $25!

The measurement device that Iconstructed was based on a leverthat pivots in a block mounted ontop of the test chamber. (See Photo 3 and Fig. 1.) I fash-ioned a coat hanger wire into a “U” shape and glued it tothe plastic lever using cyanoacrylate glue (Super Glue) totack it to the arm. I then glued it permanently in placewith 15-minute epoxy.

I added a spring using 1/4" nuts, a bolt, a spring froman ink pen and a piece of angle iron. This assembly alsomounts on the top of the test chamber. (Be sure to allowenough room for the measurement of test objects insidethe chamber.)

Measuring Wind Speedin the Chamber

Wind speed in industrial/scientific tunnels comes in atvelocities at the subsonic, sonic, transonic, supersonic oreven hypersonic levels! Thus, your tunnel will only beadequate for rough measurement of student-made models.(Anyone considering pursuing serious aerodynamic re-search may want to rent some time at a NASA test facil-ity!)

You can obtain wind speed meters from a variety ofsources, including scientific and technological supplycatalogs. You may not need the ability to measure thevelocity of the air in your tunnel if you plan to use it forrough measurements only. But, if you plan to also use itfor other applications—such as measuring lift on airfoils ordown force on automobiles—it would be good to be able toboth control the air velocity within the test chamber andmake accurate readings. Extension activities could theninclude charting and graphing aerospace concepts.

Sealing LeaksThe final step in constructing

and testing your wind tunnelinvolves sealing air leaks. You caneasily repair many with caulk.One major problem that I encoun-tered was sealing the test chamberdoor. Whenever I turned on thewind tunnel, the door would blowopen with a significant amount ofair loss. I tried mounting a me-chanical latch that I bought at ahardware store, but the latch stilldid not seal the door well enough.After much consideration, Isettled on using a large supply of1" rolled hobby magnets, placing

the magnets around the plastic viewing window. The mag-nets proved sufficient to both seal the chamber and pre-vent air leaks.

Final ThoughtsBuilding a wind tunnel makes a great research and

design project for either high school students or preservicetechnology education teachers. After using my wind tun-nel for more than four years, I have been happy with itsdurability and operation for rough measurements. Yet, Ihave felt that there is still much room for improvement. Iwould consider the following ideas if I were to constructanother wind tunnel.

In the wind tunnel that I constructed, the wind blowson the model and the model pushes on a lever to transmitthe force of drag onto a digital scale. I might considerchanging the placement of the lever to in front of themodel to be tested. To create better airflow, you couldshape the lever’s acrylic plastic to make it more aerody-namic. The test model could then be placed in the tunneland hooked behind the lever. This would help with align-ing lightweight test objects and preventing bad measure-ment data due to alignment issues.

I would also recommend blowing some kind of smokeor fog over the model so that students could easily see andcompare the turbulent air flow and/or the laminar air flowaround a test object, but I have not yet found an easy wayto do this. Finally, I would consider wiring into the tunnelsome controls to better adjust the velocity of the air insidethe test chamber.

Photo 4—A car in the wind tunnel. Note thelever behind the car, which is attached to themeter.


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ReferencesBoyt, D. (1992). Vehicle performance. Muncie, IN: Center for

Implementing Technology Education.Bunch, B., & Hellemans, A., (1993). The timetables of tech-

nology: A chronology of the most important people andevents in the history of technology. New York: Simon &Schuster.

Challoner, J. (1995). Make it work: Flight. Ocala, FL: ActionPublishing.

Chapin, D., Cook, C. (1988). TEA wind tunnel. Muncie, IN:Center for Implementing Technology Education.

Farrar, P. (1990). Bernoulli’s principle. Muncie, IN: Centerfor Implementing Technology Education.

Fitzgerald, M. (2002). Cardboard wind tunnel. Tech Direc-tions, 61 (10), p. 20.

Hobson, D. (1989). Principles of aerodynamics. Muncie,IN: Center for Implementing Technology Education.

Hynes, M., & O’Connor, V. (1997). Mission mathematics:Linking aerospace and the NCTM standards. Reston, VA:National Council of Teachers of Mathematics.

Roberts, L. (2001). Technology concepts: Power, hydrody-namics. Tech Directions, 60 (7), p. 10.

Seymour, R. (1991). Drag. Muncie, IN: Center for Imple-menting Technology Education.

Seymour, R. (1989). Ground effects in vehicle design. Muncie,IN: Center for Implementing Technology Education.

Wright, T. (1988). Designing an aerodynamic vehicle.Muncie, IN: Center for Implementing Technology Edu-cation.


Internet Resources

www.arc.nasa.gov/audience/foreducators.htmlhttp://wind.tamu.eduhttp://windvane.umd.eduwww.advancedtechnologiesinc.comwww.aircraftdesign.com/books.htmlwww.trimodels.comwww.worthey.net/windtunnels

Internet Sources of Blowers and Motors

www.electricmotorwarehouse.com/Furnace_Motors.htm

www.heatcoolparts.com/motorpage.htmlwww.keithspecialty.com/

motors%20and%20acces.htmwww.nelsonmachinery.com/blowers.htm

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Tools and Materials

Furnace fan with internal motor

4' length of furnace box duct

Digital scale (available through science supply catalogs,Pitsco, etc.)

Wire coat hanger

Wind speed gauge (available through science supply cata-logs, Pitsco, etc.)

1-1/2" PVC pipe

30" piano hinge

Wood door pull

Rolled hobby magnet strips

Sheet of clear acrylic plastic, 44" x 8"

Acrylic plastic push arm, 1" x 14"

Two pieces of screen door mesh

Two plywood rings (make to fit)

Plywood base (make to fit)

Two plastic grates

Can of spray primer

Can of spray paint (your choice of color)

2 1/4" nuts

1 4" x 1/4" bolt

1 Angle

Spring from a pen

build a wind tunnel

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