Soar! Wind Tunnel

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The Soar! Wind Tunnel is a project I used for a science fair a few years ago (which happened to win :) ), and improved upon thereafter. It consists of building a small working wind tunnel and then testing different shapes of 3D-printed wing sections in it, to determine which design performs better by measuring the lift that they generate. Included in this Thing are the instructions for building the wind tunnel, as well as the wing designs (.stl format) that I used. I also made .stls for the wing support structure: they slide together. The Soar! Wind Tunnel can be used for more projects later on, such as to test lift in model airplanes, or downforce and drag on models of cars. All it takes is changing the position of the scale. Video Project: Soar! Wind Tunnel Project Name: Soar! Wind Tunnel Overview & Background: Inspired by a wind tunnel used by the Wright brothers on display at their museum at Kitty Hawk (NC), The Soar! Wind Tunnel is a project that will teach those who complete it about the physics of lift and drag. It aims to help students understand why airplanes fly, and how engineers work to optimize their designs for wings in planes. In addition, after the suggested project is completed, whoever completes the project will still have a functional scaled wind tunnel, which can be used for many other interesting projects. Audiences: This project is designed for middle and high school students, but can be extended to lower grades or higher, by adjusting the scope and complexity of the experiments. (Ex. Calculating a drag coefficient). Subjects: This project encapsulates math, physics, engineering, and design. Skills Learned: Completing the Soar! Wind Tunnel project teaches about lift, as well as a little bit of fluid dynamics (Bernoulli Principle, Venturi Effect). Newton's Third Law of Motion comes into play as well. Depending on the level of the students, the amount of physics involved in the project can vary. Additionally, if the students make the wind tunnel, it can teach woodworking and building skills. Of course, the design of additional objects to test in the wind tunnel using 3D software is highly encouraged, and can therefore also be a learned skill. Lesson/Activity: Building the Wind Tunnel These instructions refers to the model I have built, but they are very flexible. in particular they were adapted to be manageable in an New City apartment, and to fit the extractor fan I used, which was 30 cm in diameter. Different measures can be used as needed, and in fact larger mouths to the funnel will generate faster air-speed (as more air is forced in the test area). Funnels: To build the funnels, first you must measure out the foam poster board to the shapes needed. The intake funnel is made of asymmetrical trapezoids that are cut to have one 45cm base and one 15cm base. For exact measurements, refer to the Intake Funnel Schematics. Then, duct tape the pieces together (in general, care should be taken to minimize leaks, to optimize air flow). The extractor funnel is also 45cm long, but has a smaller opening, at 30cm (to match the fan I used, which had a diameter of 30cm), while still closing in to the 15cm testing chamber. Refer to the Extractor Funnel Schematics. The air straightener is used to create laminar airflow, and is made of foam board and straws. You must take the straws, and cut them into thirds (about 5cm long). This allows you to have both enough straws, as well as keeping them at a reasonable length. Refer to the Air Straightener Schematics for the foam board pieces, then fill with straws until very tight (see picture), then fit the straightener into the intake funnel. As a note, it is much better to have the fan extract the air from the back rather than push it in from the front, as the air coming through the chamber is much less turbulent. Testing Chamber: The testing chamber is made of 1/4" plywood and 1/8" clear acrylic. The plywood needs to be cut to the different sizes shown in the Testing Chamber Schematics. Some pieces are indicated as "2x", and two need to be cut. They can either be glued together or attached with screws. In one of the orange pieces, a 1.5cm x 0.5cm slot must be made in the center. This will allow for the wing arm to pass through to the scale. A second, longer (4cm) slot is cut a few centimeters behind it to allow the slanted arm needed to measure drag. Assembly is shown in the Testing Chamber Assembly images. For added strength, a brace can be put across from the front pillar to the back wall, on both sides. The acrylic also needs to be cut to the specified dimensions (transparent pieces). The top is glued in place, as are the door rails. The door is left to slide up and down freely. Use the self-adhesive foam to pad the door and make it a tight seal. It is important to minimize air leakage in the chamber, to ensure laminar flow and to get better airspeed You can also use the foam under the base as soft feet. The Fan: Cut a hole in the fan's own box on both sides, to let air through. Set the fan to the highest setting, and have the cord exit the box. Seal the box with tape, leaving the front and back holes. Making the wing sections The wings were designed in SketchUp and printed in PLA using a PrintrBot Simple. Wings are 80mm wide and printed resting on one side. they include 4mm channel holes to house the screws that secure them to the holding pieces. it shouldn't matter which of the holes you use (when more than one are available), Two were provided to allow for proper control for the the low camber center airfoil, but in my measurements they didn't make any difference. Design for seven wing airfoils were tested (scroll down for images): A. flat squared. This is our control 'wing'. it has no aerodynamic or camber. it should provide the worst lift and drag/turbulence performance and lower stall angle. At an angle, the entire lift is provided by the air pushing on the bottom (Newtonian). B. flat rounded. This is similar to A, but with smooth edges. the airflow should be a little improved, with less drag and turbulence. C. flat tapered. This starts to look like a typical wing section. The airflow should be greatly improved, but since it is a symmetrical design, the air on the top and bottom go at the same speed and thus again there should be no lift contribution by the Bernoulli effect (which contributes at low speeds and/or in horizontal flight) D. low camber front. The camber should provide lift. the tapering towards the back should decrease drag and turbulence. This can also be mounted 'backwards' to test this aspect E. low camber center. The camber lift should be similar to above, but this shape should have worse drag/turbulence performance. F. high camber. Similar shape as D, but higher curve. More camber should have more lift, possibly at the expense of drag. it should also affect the stall angle. G. double camber. The upper curve is the same as F, but the bottom is also curved, like a bird's wing. Naturally, students can and should design and test different airfoils. Keep in mind that if you make a design, you should also make a similar 'control' airfoil which is mostly the same with one characteristic that is different. Finally, air speed is a very important component. The air speed in my wind tunnel is fixed and it is relatively low. It mimics low-speed flight (a cool side project would be to design an anemometer and measure wind speed). At higher speed (like in jets or fighter planes), turbulence (and drag) become much more important and the shape of the wing is much more 'flat' as the camber becomes much less important for lift. A more powerful, multi-speed fan would help to test different airspeed conditions. Setting Up The Experiment Join all of the pieces of the wind tunnel and tape together as airtight as possible. As mentioned, the fan goes on so that it pulls air through, rather than pushing it. This significantly decreases turbulence. Place the precision scale under the testing chamber, secure with double-sided tape if necessary. Build wing support from erector set pieces (see picture) to rest on the scale in the lower chamber, or print the provided wing support pieces. The Experiment Attach the wing you want to test to the support structure with screws and secure it to the scale at the desired angle of attack (0°, 15°, 30°). Use a piece of foam cut at the right angle to ensure consistency. Tare the scale with the wing on it. Turn on the fan (you will need to use an external power strip as a switch). Record the negative weight recorded on the scale. This is your lift. (Repeat steps 3 and 4 as many times as you want for a good dataset. I used the average of 5 recordings.) The two main variables i tested where wing shape and angle of attack. To make sure the angles of attack were consistent, I cut foam poster board wedges at pre-determined angles (0°, 15°, 30°) and used them to set the wing sections. To measure drag, an additional slot was included in the base plate (orange) so that an additional, longer erector piece slanting down pushes against a scale put at an angle in the lower chamber (see slide for example). This is a bit more complex and will need tinkering to make it work properly. The experiment was designed to test the lift created by different wing shapes at different angles of attack. It can be expanded to include testing of the drag and stall angle of the wings, in order to get a more complete picture of the wing shape's performance. If these aspects were to be tested at different airspeeds, it can show what wing shape is best equipped for different airplanes. Some questions that can be asked are: What wing shape provides the most lift? What wing shape gives the least drag? What angle of attack works best? At what angle of attack do the different wings stall? What combination of wing shape and angle of attack is best for lift? Drag? How does airspeed affect these results? Duration: The length of this project is very variable. If all of the participating students work together to build one or two wind tunnels, the construction should take less than one hour. If each student makes their own, which is best done with few participants at a time, it will take longer, from one to three hours. The printing time of the wings depends on print settings and printer. With a Printrbot Simple, at 0.3mm layer height, it took two and a half hours per wing. The testing of the wings itself is fairly quick, with each wing taking a couple of minutes to set up and test. Preparation: In order to complete this project, you need to have certain materials other than the 3D printer. Wind Tunnel: Foam poster board A fan with a diameter of 30cm. I used the Honeywell HT-900. If the fan you use is of a different size, the foam board shape of the extractor funnel changes ~500 straws Duct tape Measuring Chamber: Plywood sheet High Precision digital scales Erector toy set (or equivalent printed parts provided) Small screws, screwdriver, or wood glue Wood saw Clear acrylic panels Hot glue for acrylic panels (wood glue can also work, but I recommend this) Knife to score acrylic for cutting Screws to hold wing in place Self-Adhesive foam sheet (soft) 3D Printing 3D printer with at least 10cm x 10cm x 10cm build volume 3D modeling software of your choice (I recommend SketchUp or SolidWorks) References: These sources are nice to learn about wind tunnels and what they are used for, as well as the basics of how wings generate lift. "History of Wind Tunnels." History of Wind Tunnels. NASA, n.d. Web. 02 Mar. 2014. https://www.grc.nasa.gov/www/k-12/WindTunnel/history.html. Brain, Marshall, Robert Lamb, and Brian Adkins. "How Airplanes Work." HowStuffWorks. HowStuffWorks.com, 26 May 2011. Web. 03 Mar. 2014.http://science.howstuffworks.com/transport/flight/modern/airplanes.htm. Hitt, David. "What Are Wind Tunnels?" NASA. Ed. Sandra May. NASA, 25 June 2014. Web. 11 Aug. 2016.http://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-are-wind-tunnels-58.html Rubric & Assessment: By the end of the project, students should know how wind tunnels work, what causes lift, as well as what makes a wing design good. They should be able to use their new knowledge to design a wing with better lift properties, or, if your version was more complex, a good combination of lift and drag. Possibly, another way to assess learning would be to have students design other objects to test in the tunnel. Handouts & Assets: The included .pdf is the original powerpoint from my project. It goes into detail about the science behind lift and the experiment that I performed.