Now that you have built the three components of the wind tunnel, it's time to put it together and test it! First, you need to get eight springs, as shown in the following figure:
Figure 4A. These springs will hold the three assemblies of the wind tunnel together.
Next, place the three components end-to-end so that they look like the wind tunnel in Figure A. One by one, connect the components by their connection screws, using the springs, and making sure that the gaskets are airtight, and that the 1' x 1' square areas all fit properly together to ensure smooth airflow. See Figure 4B, below, for a visual of one side of the connected wind tunnel.
Figure 4B. The eight springs are used to connect the Diffuser Assembly and the Contraction Cone Assembly to the Test Section Assembly.
The tunnel should now be connected and look like that the one in Figure A. Now, all you have to do is set it up in whatever space you have for it, attach your equipment, and you're ready to test! If you have not already done so, move the three assemblies to the place where you will keep and use the wind tunnel, and reattach them so that they form the full wind tunnel.
Recall that in Section 1, Part B, you and your carpenter/physics teacher designed a Base that would hold the force sensors perpendicular so that they would connect to a single rod coming down from inside the Test Section. Now that the wind tunnel has been built, attach those sensors. The following figure is an example of sensors mounted to the base of the Test Section Assembly. Note the rods and the airfoil mounted inside the Test Section, ready to be tested.
Figure 4C. Two force sensors mounted to the wind tunnel. One is for lift, one is for drag, and they are perpendicular. An airfoil is mounted to the sensor rods.
Again, the figure presents only an example. While it is suggested that threaded rods be used to connect the airfoil to the sensors, it is up to you and your physics teacher to decide the best way to connect the particular sensors you have to any models you may mount. You should also take into account the best way to mount models onto your rods; the Science Buddies wind tunnel uses models carved out of balsa wood, into which threaded casings may be drilled so that they can be easily screwed onto the rods. Finally, don't forget that you can also test models with an angle of attack. For the Science Buddies wind tunnel, the threaded rod can be bent at a predetermined angle and then inserted into the Test Section. Depending on your ideas for testing angle of attack, it may be best to have multiple rods so that they can be replaced when bent, instead of trying to bend them back into their original perfectly straight shape.
Now it's time to attach monitoring equipment to the wind speed sensor (recall that this is the small handheld fan that is mounted in the Diffuser). Obtain a voltmeter, and attach the sensor's fans to the voltmeter so that when the sensor's fan spins, it will produce a voltage in the wires that will register on the voltmeter. See Figure 4D for an example of a voltmeter.
Figure 4D. A voltmeter used to determine the wind speed in the tunnel. Note that the two wires from the wind speed sensor have been attached to the sensor.
The sensor measures voltage, which is indirectly a measure of wind speed. It does not give a velocity reading, but the voltage reading for each speed in your wind tunnel will be constant, so it is reliable. For instance, if you turn the fan on full speed and get a particular voltage reading, such as 2.8 V, and then turn the fan to that same speed on another day, the voltmeter will read just about 2.8 V again. Due to this consistency, your wind speed determinations will be based on relative voltages for different settings on your wind tunnel fan. You may also be able to determine the relationship of velocity to voltage, and develop a conversion chart so that you can look up the voltage you read and determine the wind speed inside the wind tunnel. Talk to your physics teacher about this. It is not necessary to develop such a chart, but figuring out how to do it would certainly add to your understanding of aerodynamics!
The last piece of equipment to attach is the variable AC adapter, which allows you to control the amount of energy the fan receives and thus have a variable wind speed tunnel. Obtain an adapter, plug it into a power outlet, and then plug the wind tunnel fan into the adaptor. Figure 4E shows an example of an adapter:
Figure 4E. This device allows you to control how much electricity the fan gets, so you can have more settings than just "on" and "off."
You have now attached all of the necessary equipment to the wind tunnel. Figure 4F below shows the sensors of the wind tunnel: lift force, drag force, and wind speed.
You can find this page online at: http://www.sciencebuddies.org/science-fair-projects/wind-tunnel-section4.shtml
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