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The origin of this project resides in the finds that MIT brings from time to time. I was surprised when I found 14 old fans (QFR1212GHE SP-01), from the era when computer fans didn’t have to be quiet. The airflow capacity of these fans is a bit nuts, each one consuming 12 DC Volts and 4A, and providing each one with 210 CFM! (nowadays computer fans give 80 – 100 CFM).

With an easy back-of-the-envelope estimation, I calculated that 14 of these and a smaller cross-section of 300 by 300 mm could get a constant speed in the wind tunnel of about 70 km/h.

The architecture of the wind tunnel is the following. It is a suction wind tunnel with a tight honeycomb nozzle area, 3m in length, and at the end of the diffuser is where the fans are located. In the middle, I built a sensing platform with monolithic L-shaped dual load cells able to track forces in the normal and axial components of the speed vector.

With the help of Zach Fredin teaching me how to use the EDM, I designed and cut two L-shaped monolithic load cells, each with a double Wheatstone bridge. All strain gauges were routed for that and attached to classic HX711 amplifiers communicating with a Teensy 3.2. That board will report to a Raspberry Pi 4, which also has the GUI interface for the user to measure real forces in real time.