WindWise Education LESSON 11: HOW CAN I DESIGN BETTER BLADES?

Transcription

1 WidWise Educatio Wid Eergy Activities for Studets Cotets LESSON 11: HOW CAN I DESIGN BETTER BLADES? Forward...1 Itroductio...7 Uit 1: Eergy...17 Uit 2: Wid Uit 3: Turbies Lesso 8 How Does a Widmill Work? Lesso 9 How Does a Geerator Work? Lesso 10 Which Blades Are Best? Lesso 11 How Ca I Desig Better Blades? Appedix: Advaced Wid Turbie Blade Desig ad Airfoils Appedix to Uit 3 Usig WidWise to prepare for a KidWid Challege Uit 4: Wid & Wildlife Uit 5: Sitig Wid Turbies WidWise Educatio Curriculum Copyright 2011 WidWise Educatio Secod Editio with ew material copyright 2012 WidWise Educatio Third Editio with ew material copyright 2015 WidWise Educatio Reproductio of this curriculum is prohibited except for studet use i the classroom. For iformatio o obtaiig curriculum materials ad to lear more about the WidWise Educatio program, go to ISBN

2 TURBINES LESSON 11 HOW CAN I DESIGN BETTER BLADES? KEY CONCEPT Studets lear how to desig ad costruct differet turbie blades to maximize the power output of a wid turbie. TIME REQUIRED 1 2 class periods GRADES SUBJECTS Physical Sciece Techology/Egieerig Mathematics BACKGROUND Blade desig ad egieerig are two of the more complicated ad importat aspects of curret wid turbie techology. Today egieers strive to desig blades that extract as much eergy from the wid as possible i a variety of wid speeds, while makig sure that they remai durable, quiet, ad affordable. This egieerig process requires a great deal of scietific experimetatio, modelig, ad testig. OBJECTIVES At the ed of the lesso, studets will be able to participate i the egieerig desig process uderstad how blade desig variables affect power output kow how to improve ad optimize wid turbie blades METHOD Studets will use a variety of materials to desig blades that optimize the power output of a model wid turbie. MATERIALS You will eed oe set of the followig materials for each group: 1 model turbie o which blades ca be quickly iterchaged 1 multimeter or voltage/curret data logger or multimeter box 1 box fa A ruler Pictures of wid turbie blades (see the Blade Desig PowerPoit show i Additioal Resources) Studet readig passages ad studet worksheets* Blade buildig materials Balsa wood, corrugated plastic, card stock, paper plates, plastic cups, idex cards, etc. ¼" dowels Duct tape ad/or hot glue Scissors, Exacto kives Protractor for measurig blade pitch *icluded with this activity Additioal Resources for every lesso ca be foud at Resources iclude presetatios, videos, extesio activities, ad other materials. 191

3 HOW CAN I DESIGN BETTER BLADES? CAUTION! Do ot stad i the plae of rotatio of the rotor! You could be hit if your blade flies off durig testig. The spiig rotor blades ad metal rod ca be dagerous. Make sure studets work with cautio. Be careful whe workig with the metal rod. Do ot swig or play with the rod! The eds ca be protected with tape, foam, cork, etc. Wear safety glasses whe testig widmills. Safety glasses must be wor ay time blades are spiig. Stad behid or i frot of the plae of rotatio - ad wear safety glasses! GETTING READY Studets should have completed the Which Blades Are Best? lesso. It is useful to have some blades, turbies, ad hubs ready so you ca demostrate how to safely use the tools ad turbies. Set up turbie testig statios: Place all of the materials i oe cetral locatio where studets ca select items ad you ca moitor their use to make sure that studets are usig them safely. Havig the same fas at each statio would be ideal, but sometimes it is ot possible. Therefore, make sure that studets use the same fa ad at the same speed whe testig the blades. Factor ito plaig that there ca be a wait at the testig statios. While studets oly eed a few miutes to test ad the chage their blades, havig a few statios set up reduces the wait time. Cosider tellig studets to begi the desig process at home i order to save some classroom time, because the costructio ad revisio of the blades ca be time cosumig. ACTIVITY Step 1: Begiig questios for studets Review the results from the Which Blades Are Best? lesso. Discuss which variables had the most impact. Step 2: Blade desig ad costructio Tell all studets to aalyze the data o their ow ad come up with their ow idividual desigs. Ask studets to create a desig pla (this may iclude drawigs ad/or descriptios). Approve it before costructio. Desig costraits Ay materials foud i the classroom resource area ca be used. Metal caot be used Maufactured blades or propellers caot be used Blades caot be more tha 20" log Blades must have o sharp poits or edges Ask studets to use their data sheets to keep track of the materials they use. If studets are costructig their blades i the classroom, set limits o how log they ca work o them. You ca also limit supplies or attach costs to supplies they must purchase with a set budget. This cuts dow o waste ad requires studets to put more thought ito selectig materials. Have studets test their blades at low ad high speeds. To simulate low speed, tur the fa dow or move the wid turbie back 2 meters from the fa. Studets should test their blades at least oce ad optimally twice before presetatio time (oce with the iitial desig ad a secod time after ay desig revisios have bee made). 192 Lesso 11

4 HOW CAN I DESIGN BETTER BLADES? As the desigs progress, ecourage studets to experimet with advaced ideas, such as usig the airfoil shape ad/or makig blades with twisted pitch. Step 3: Competitio Studets blades ca be evaluated i three ways. (You may pick oe or use all three.) Evaluatig projects i all three ways gives studets with differet skills a chace to succeed. Quality of costructio Level of iovatio Power output at low ad high wid speeds AIRFOILS The airfoil shape of wid turbie blades creates lift while miimizig turbulece. Quality of costructio ad iovatio ca be evaluated by the whole class, usig the votig sheets o the worksheet. This allows studets to compare power output to other characteristics that are importat. Studets ca display their blades with a ame label ad sped te miutes walkig aroud ad evaluatig each of the blades. Studets ca also predict which blade desigs will be the best ad why. Tally the votes usig this scale: 1 st = 3 poits, 2 d = 2 poits, 3 rd = 1 poit. The studet with the most poits wis that category. Power output ca be evaluated by testig the blades at low ad high wid speeds. Studets ca act as recorders, timers, ad multimeter experts. Let studets mout ad set their ow blades. Ask studets to describe to the class the mai features of their blades (legth, materials, umber of blades, etc.). Place the turbie at about 1 meter away from the fa ad let the fa ru at high speed for 30 secods. Record the highest voltage umber you see i 30 secods. Tell studets to record these data o their worksheets. Do the same i low speed coditios. To simulate low speed, tur the fa dow or move the wid turbie back 2 meters from the fa. If after a few secods studets wat to adjust the blades, allow them to do so oly oce to limit the amout of time o each blade set. After measurig voltage ad curret, calculate power usig the equatio: P=VI (watts = voltage amperage). Lift Step 4: Wrap up Wrap up the lesso with some of the followig questios Which type of blades worked best at low speeds? High speeds? Why do you thik these blades performed the best? What problems did you ecouter? Which features did you icorporate from moder turbie desigs? EXTENSION Measure the power output ad efficiecy of differet blade cofiguratios. See Lesso 10 Which Blades Are Best? (page 177), for more iformatio about measurig power output ad efficiecy. Read the Advaced Blades Appedix (page 201) to lear about airfoil blades, lift, drag, torque, ad other advaced cocepts i wid turbie blade desig. Lesso

5 HOW CAN I DESIGN BETTER BLADES? VOCABULARY airfoil Teardrop shaped cross-sectio used for wid turbie blades. The airfoil shape is most efficiet because it creates lift while miimizig air turbulece. rotor solidity Measuremet of how solid the rotor is. A rotor with high solidity does ot have a lot of space betwee blades. A rotor with low solidity (like most moder turbies) has fewer blades ad more empty space i the rotor. twisted pitch Blades of commercial wid turbies have higher pitch ear the root ad less pitch at the tip. This is called twisted pitch ad it greatly reduces drag at the blade tips to icrease performace. RELATED ACTIVITIES Lesso 8: How Does a Widmill Work? Lesso 10: Which Blades Are Best? Advaced Blades Appedix Lesso 11

6 How Ca I Desig Better Blades? Studet sheets Name Date Class DESIGN YOUR OWN BLADES Desig 1. Sketch ad describe the desig of your blades (legth, shape, umber, materials, etc). 2. Explai why you desiged your blades this way. Use data from Lesso 10 (if completed) to support your iitial desig. Test Ru 1 Test your blades 1 meter from the fa for 30 secods ad record your data below. Power=Voltage Amps High Wid Speed VOLTAGE AMPERAGE POWER OUTPUT Low Wid Speed Modificatios 3. What modificatios could you make to your blade set to icrease the power output? 4. Why do you thik these blades would work better? Test Ru 2 Test your modified blades 1 meter from the fa for 30 secods ad record your data below. High Wid Speed VOLTAGE AMPERAGE POWER OUTPUT Low Wid Speed Lesso

7 How Ca I Desig Better Blades? Studet sheets AVERAGE POWER IN LOW WIND POWER IN HIGH WIND ADDITIONAL DESIGN FEATURES MATERIALS LENGTH (CM) Competitio NAME NUMBER OF BLADES Lesso 11 HOW CAN I DESIGN BETTER BLADES?

8 How Ca I Desig Better Blades? Studet sheets Name Date Class Questios 1. Describe the blades that seemed to perform the best. What characteristics did they have? 2. Why do you thik they performed so well? Lesso

9 How Ca I Desig Better Blades? Studet sheets Name Date Class Votig form Use these forms to vote o other studets blade desigs. QUALITY OF CONSTRUCTION INNOVATION QUALITY OF CONSTRUCTION INNOVATION QUALITY OF CONSTRUCTION INNOVATION QUALITY OF CONSTRUCTION INNOVATION QUALITY OF CONSTRUCTION INNOVATION QUALITY OF CONSTRUCTION INNOVATION Lesso 11

10 How Ca I Desig Better Blades? Aswer sheets DESIGN YOUR OWN BLADES Desig 1. Sketch ad describe the desig of your blades (legth, shape, umber, materials, etc). Studet observatios. 2. Explai why you desiged your blades this way. Use data from Lesso 10 (if completed) to support your iitial desig. Studet observatio, but it is a good idea for studets to keep their data from Lesso 10 so that they have ideas o which to base their desigs. Test Ru 1 Test your blades 1 meter from the fa for 30 secods ad record your data below. Power=Voltage Amps High Wid Speed VOLTAGE AMPERAGE POWER OUTPUT Low Wid Speed Modificatios 3. What modificatios could you make to your blade set to icrease the power output? Studet observatios. 4. Why do you thik these blades would work better? Studet observatios. Look for chages to their blades based o the aalysis of Test 1 performace ad data from Lesso 8. Test Ru 2 Test your modified blades 1 meter from the fa for 30 secods ad record your data below. High Wid Speed VOLTAGE AMPERAGE POWER OUTPUT Low Wid Speed Lesso

11 How Ca I Desig Better Blades? Aswer sheets Questios 1. Describe the blades that seemed to perform the best. What characteristics did they have? Studet observatios. Some commo themes (these will deped o type of turbie used: direct drive vs. geared vs. weightliftig device): Blades match fa size Blades are smooth Blades go all the way to base of hub 2 4 blades i total Blades are wider at the root tha at the tip Blades might have a twist alog legth of blade (20 degree pitch at base, 0 degree pitch at tip) Blade agle is low, aroud 5 10 degrees Blades have a airfoil shape to icrease rotatioal lift ad icrease blade velocity 2. Why do you thik they performed so well? Studet observatios. Studets ca relate better performace to the observatios above. Great blades capture the eergy of the wid without causig too much drag ad slowig themselves dow Lesso 11

12 APPENDIX TO LESSON 11 ADVANCED WIND TURBINE BLADE DESIGN AND AIRFOILS BACKGROUND Blade desig ad egieerig are two of the more complicated ad importat aspects of curret wid turbie techology. Egieers strive to desig blades that extract as much eergy from the wid as possible i a variety of wid speeds, while makig sure that they remai durable, quiet ad affordable. This egieerig process requires a great deal of scietific experimetatio, modelig, ad testig. With some simple materials ad a bit of creativity, you ca experimet with advaced cocepts i wid turbie blade desig, icludig airfoil shapes ad twisted-pitch blades. You may wat to try buildig three-dimesioal blades that will outperform the stadard flat turbie blades used o most KidWid turbie kits. This guide will help you uderstad the sciece ad aerodyamics behid real wid turbie blades ad how they are desiged. OBJECTIVES OF THIS ACTIVITY Studets will lear: desig techiques to optimize wid turbie blades how wid turbie blades move due to Newto s third law ad Beroulli s priciple how the forces of lift ad drag affect turbie blades why the airfoil shape helps make turbie blades more efficiet SUGGESTED LEVEL TIME REQUIRED 1 2 class periods SUBJECTS Physical Sciece Techology/Egieerig, Mathematics MATERIALS REQUIRED These materials are suggested for desigig/testig advaced blades: Model turbie that allows for iterchaged blades Multimeter or voltage/curret data logger Box fa Ruler Chipboard or card stock Corrugated plastic sheets Balsa wood sheets Cardboard tubes Airfoil-shaped balsa wood Protractor for measurig blade pitch Scissors, Exacto kives Dowels Hot glue WidWiseEducatio.org Additioal Resources for ca be foud at lear.kidwid.org/widwise/. Resources iclude presetatios, videos, extesio activities, ad other materials. 201

13 Advaced Wid Turbie Blade Desig ad Airfoils WHY DO WIND TURBINE BLADES MOVE IN THE WIND? There are two importat reasos why wid turbie blades are able to spi i the wid: Newto s third law ad the Beroulli s priciple. 1. Newto s third law states that for every actio, there is a equal ad opposite reactio. I the case of a wid turbie blade, the actio of the wid pushig air agaist the blade causes the reactio of the blade beig deflected, or pushed. If the blade has o pitch (or agle), the blade will simply be pushed backwards (dowwid). But sice wid turbie blades are set at a agle, the wid is deflected at a opposite agle, pushig the blades away from the deflected wid. This pheomeo ca be viewed o a simple, flat blade set at a agle. If you push the blade with your figer from the directio of the ocomig wid, the blade will deflect away from your figer. Blade deflectio reactio Blade Blade deflectio Wid 2. Beroulli s priciple tells us that faster movig air has lower pressure. Wid turbie blades are shaped so that the air molecules movig aroud the blade travel faster o the dowwid side of the blade tha those movig across the upwid side of the blade. This shape, kow as a airfoil, is like a ueve teardrop. The dowwid side of the blade has a large curve, while the upwid side is relatively flat. Sice the air is movig faster o the curved, dowwid side of the blade, there is less pressure o this side of the blade. This differece i pressure o the opposite sides of the blade causes the blade to be lifted towards the curve of the airfoil. You ca do a small, simple experimet to demostrate Beroulli s priciple. Take two small pieces of paper ad fold them slightly i the middle. Hold the two pieces of paper i your hads so that the outside creases of the folds are facig each other. The blow air i betwee the two pieces of paper. Whe you blow air betwee the papers, would you expect them to push apart or pull together? Were you surprised? Whe you blow air betwee the papers, the speed of the air is higher betwee the two pieces of paper tha outside the papers. Beroulli s priciple tells us that this higher velocity will lead to a lower pressure betwee the papers. That is why the papers are sucked i towards each other! IMPORTANT CONCEPTS IN WIND TURBINE BLADE DESIGN Airfoil shape (blade cross sectio) Wid turbie blades must be optimized to efficietly covert ocomig wids ito mechaical eergy to rotate the mai driveshaft. But i the desig of turbie blades, the real wid is oly oe part of a larger equatio; good blades must also accout for the apparet wid that is experieced as the blade passes through the air

14 Advaced Wid Turbie Blade Desig ad Airfoils Imagie ridig your bike with a fresh breeze at your side. As you begi to ride ad pick up speed, you feel this wid from the side, but also wid pushig back at you from the directio i which you are movig. Whe you stop ridig, there is just the wid from the side agai. This wid that is created as you are movig is kow as headwid. The headwid, combied with the real wid, is kow as apparet wid. A wid turbie blade ecouters apparet wid as it passes through the air. This apparet wid is from a differet directio tha the real wid that has caused the blade to begi movig. Sice the tips of large turbie blades may be movig through the air at speeds up to 322 km/h (200 mph), this apparet wid ca be very sigificat! (A) real wid (R) + head wid (H) = apparet wid (A) (H) The efficiecy of a wid turbie blade depeds o the drag, lift, ad torque produced by the blade. These factors are affected by the size ad shape of the blades, the umber of blades, ad the blade pitch. What is drag? Drag, or air resistace, is a force that is workig agaist the blades, causig them to slow dow. Drag is always importat whe a object moves rapidly through the air or water. Airplaes, race cars, rockets, submaries, ad wid turbie blades are all desiged to have as little drag as possible. Imagie ridig your bike dow a big hill. To go faster, you might tuck your body to expose as little of it to the apparet wid as possible. This is a trick to reduce drag. Now imagie you have a big parachute strapped to your back whe you ride dow the hill. The parachute icreases the drag sigificatly ad this drag force slows you dow. But you would sure be happy to have all that extra drag if you were jumpig out of a plae! Drag icreases with the area facig the wid; a large truck has a lot more drag tha a bicyclist movig at the same speed. Wid turbie blades have to be streamlied so they ca efficietly pass through the air. Chagig the agle of the blades will chage the area facig the apparet wid. This is why blade pitch agles of 10 degrees to 20 degrees ted to have much less drag tha greater blade pitch agles. Drag also icreases with wid speed. The faster a object moves through the air, the more drag force it experieces. This is especially importat for wid turbie blades, because the blade tips are movig through the air much faster tha the base of the blade. The shape ad agle of wid turbie blades chages alog the legth of the blade to reduce drag at the blade tips. More drag Less drag 203

15 Advaced Wid Turbie Blade Desig ad Airfoils What is lift? Lift is the aerodyamic force that allows airplaes ad helicopters to fly. The same force applies to the blades of wid turbies as they rotate through the air. Lift opposes the force of drag, helpig a turbie blade pass efficietly through air molecules. The mai goal of a well-desiged wid turbie blade is to geerate as much lift as possible while miimizig drag. The amout of lift a blade or wig ca geerate is determied by several factors the shape of the blade, the speed of the air passig aroud the blade, ad the agle of the blade relative to the apparet wid. Lift The airfoil shape of the blade helps to geerate lift by takig advatage of Beroulli s priciple described above. Wid turbie blade desigers have experimeted with may differet airfoil shapes over the years i a effort to fid the perfect shape that will perform well i a rage of wid speeds. Eve mior chages i this blade shape ca dramatically affect the power output ad oise produced by a wid turbie. To get some ideas about differet airfoils used i airplae wigs ad wid turbie blades, research the Uited States Natioal Advisory Committee for Aeroautics (NACA). This group was resposible for desigig a wide rage of airfoils i the 1940s. The airfoil profile (shape) of a turbie blade will actually chage alog the legth of the blade, geerally gettig flatter ad arrower toward the tips of the blades. This is to optimize the lift ad miimize drag. The faster the blade is movig, the more drag it ecouters, but the lift force will also icrease as the blades move faster. The tips of wid turbie blades travel much further with each rotatio of the blades, ad therefore move through the air much faster tha the roots of the blades. Sice they are travelig the furthest distace with each rotatio (distace/time = speed), the tips of turbie blades ecouter more resistace or drag. The roots, or bases, of the blades do ot ecouter as much drag because they are passig through the air much more slowly. The faster the air molecules pass over a blade or wig, the more lift ca be geerated. So the tips of real turbie blades geerate much more lift tha the roots. Some large wid turbies have blade tip speeds over 322 km/h (200 mph)! The agle of the blade relative to the plae of rotatio of the blades is kow as the pitch agle. The agle of the blade relative to the wid is called the agle of attack. The agle of attack is very importat, but also complicated because it will chage as the wid speed chages ad the speed of the blade chages. O most airfoil blades shapes, a agle of attack of 10 to 15 degrees creates the most lift with the least drag. Commercial wid turbie blades typically have a twisted pitch meaig the blade agle is steeper at the root of the blade ad flatter further away from the hub. Oce agai, this is because the tips move so much faster through the air. Because of the twisted pitch, the blades are able to take advatage of a more ideal agle of attack alog the legth of each blade. The tips of a real turbie blade may have close to a 0 degree pitch agle, but this sectio of the blade geerates a great deal of lift

16 Advaced Wid Turbie Blade Desig ad Airfoils What is torque? Torques produce rotatio. Whe you use a wrech o a bolt or twist a screw loose with a screwdriver, you are geeratig torque. If you are tryig to tur a wrech, sometimes you eed a lot of torque to loose a tight bolt. Wid turbie blades are like big levers but istead of beig tured by muscles, they are tured by the force of the wid. Torque is equal to the force applied to the wrech multiplied by distace the legth of the wrech. This meas that the loger your blades are, the more torque you ca geerate. For example, imagie you are tryig to loose a tight bolt. Pushig with all your might, you ca exert 100 pouds of force. If your wrech was 1 foot log, you would be exertig 100 poud feet of torque. If you applied the same force to a 2 foot log wrech, you would the be exertig 200 poud feet of torque o the bolt. This additioal torque makes it much easier to loose the bolt! Less torque More torque O a commercial wid turbie, the log blades of the turbie geerate lot of torque to the geerator. Utility-scale wid turbies ofte have large gearboxes that icrease the RPM of the rotor by 80 or 100 times. This big gear reductio demads a lot of torque from the blades. Thik about ridig your bicycle whe you shift ito a higher gear, it may be harder to pedal. A higher gear ratio demads more force which geerates more torque. Various load devices that you try to power with your wid turbie may require more torque as well. A simple illustratio of this is to use your model turbie to power a small LED light bulb ad a small icadescet light bulb. (Icadescet Christmas tree light bulbs work well.) The LED bulb does ot require much torque, so small turbie blades will geerally work. The icadescet bulb, o the other had, requires a lot more amperage to light up, so more torque is eeded from the blades. Very small blades may ot work uder a load like a icadescet bulb or a small water pump. Icreasig the torque geerated by your blades also ofte icreases the drag they ecouter as they rotate. For example, loger blades will geerate more torque ad more drag. Icreasig the blade pitch will geerally icrease the torque ad icrease the drag. Icreasig the umber of blades will geerally give you more torque ad more drag. For this reaso, it is importat to desig your blades to match your load applicatio. If you are usig a widmill to lift a bucket of weights, a slowly spiig rotor that geerates lots of torque will be best. A turbie with a large gear ratio will also eed a lot of torque. But if you are usig a direct drive turbie to light a strig of LED bulbs wired i series, you will eed a rotor that spis very rapidly with very little drag. Real wid turbie blades are optimized to geerate a lot of torque ad lift with very little drag. This is ot a easy task! Wid turbie blade egieers have degrees i aeroautical egieerig ad expesive computer software at their figertips. But by uderstadig the relatioship betwee torque, drag, ad lift, you ca desig some great blades with simple materials

17 Advaced Wid Turbie Blade Desig ad Airfoils DESIGNING ADVANCED WIND TURBINE BLADES Wid turbie blade variables to explore: blade shape blade size umber of blades agle (pitch) of blades Curved or twisted pitch blades May moder wid turbie blades have a twisted pitch. At the root of the blade (ear the hub), the pitch may be close to 20 degrees from the plae of rotatio. The pitch will flatte alog the legth of the blade so the tips are close to 0 degrees. This is a great way to reduce the drag ecoutered by your blades, while also maitaiig the legth eeded to geerate more torque. You ca desig twisted blades by bedig corrugated plastic or cardboard ito a twisted shape. Remember that you wat more pitch ear the hub, ad almost o pitch at the tips. Oe trick is to get chipboard wet, the curve it ito the desired shape ad hold it i place util it dries. It will hold this curved shape whe it dries. blade material airfoil shapes twisted pitch blades rotatio apparet wid real wid drag reactio to deflectio lift force head wid Higher pitch ear root You ca also make some great twisted blades by cuttig blades out of a cardboard poster tube. If you cut a triagle shape ito the cardboard tube, the resultig curved triagle will make a great turbie blade! Lower pitch ear tip Airfoil blades Well-desiged airfoil blades will greatly reduce the drag ecoutered by your blades, while also geeratig more lift! Remember that the airfoil shape is like a asymmetrical teardrop. Oe side is relatively flat, ad the other side has a tapered curve. O a turbie blade, the curved side faces dowwid. The real wid will hit the turbie blade o the flatter side. This way, as the turbie starts to rotate, lift is geerated o the backside of the blade which pulls the blade efficietly through the air. Makig your ow airfoil blades ca be very iterestig ad challegig. Try a few differet desigs ad you will fid that they perform much more efficietly tha a flat blade. Here are a few ideas to get you started i desigig airfoil blades: Shape a wet piece of chipboard. Bed chipboard ito a airfoil shape. Attach a curved surface to flat surface: Start with a flat piece of corrugated plastic, or balsa wood. Tape a piece of card stock or thi flexible plastic to oe side, to act as the airfoil shape. Use airfoil shaped balsa wood or Styrofoam desiged for model airplae wigs 206