Let's make an exclusive homemade Wind tunnel (Final)

Step 4 — Complete the base

• The rest is easy. Cut 4 support blocks sized to lift the floorboard so that its top sits flush with the top of the test stand. I used 2×4 scraps, shaped the middle blocks with a ledge for mounting the control panel, and attached them with wood screws.

 

Step 5 — Build the tunnel and control panel

• Cut 2 pieces of 0.220" Lexan 7"×30" for the tunnel sides, and 1 piece 74"×30" for the top. Cut a test section access door in 1 side. If you’re adding LED lighting, the door should clear the floor by about 1".
• Mount the door with the brass hinges along the top, and attach the handle at the bottom. Air should not leak in around the door during use, so you need to seal it; clear tape works for low velocities, but Lexan is sturdier and better looking. One lesson learned: glue a small block of Lexan inside the door opening to prevent the door from swinging inward.
• Finally, assemble the tunnel by screwing the Lexan sides to the floorboard and using plastic epoxy to secure the top piece.
• Below the access door, create a control panel to house the scale display, fan controls, and LED switch. I used Lexan for better visibility. For the LEDs, I hot-glued 7 of the 10 along the floor near the test section and taped the remaining 3 under the test section, to illuminate the tunnel’s workings.

Step 6 — Mount the fan

• Crack open the fan, extend all its control wires about 2', and remove any unneeded supports. Mount the fan as near as possible to the center of the tunnel, blowing out the back. Seal around it to close any holes between it and the tunnel. I used thin scrap plastic from toy packaging, to preserve the view, but cardboard and duct tape would work fine. Regardless, use tape and hot glue to make the seal complete.

Step 7 — Make a flow straightener

• Make a cardboard sleeve with the same cross- section as the tunnel, and pack it with 2" pieces of drinking straws — this part goes faster with a small- fingered helper. The straws reduce turbulence, but they also cut the wind speed by several mph, and the tunnel will work without them. To improve performance, add a cardboard airscoop in front of the straightener. That’s it!

Step 8 — Test the car!

• Make sure the tunnel is level and stable, for repeatable drag numbers. Tape or block your car wheels on the test section floor.
• Now fire up the fan to test your car— the force in the display is very close to the actual drag caused by the car (set it to “grams” for higher resolution). Modify your shape to minimize that drag. Now set track records at the Pinewood Derby!
• For airflow visibility, run a Halloween fog generator at the intake and take flash photos to capture the stream lines.
• You can measure the wind speed with a mini- anemometer — eBay is a good source.