The key component of any wind tunnel is the fan assembly.  Take a look at the propeller and motor above.  In is mounted on eight springs to reduce vibration.  The whole fan module is then positioned on rubber mounts, which in turn channel vibration through a plywood frame.  The net effect is to pass the vibration through materials with different natural frequencies, so acting as a vibration filter, much like coils and capacitors are used to filter out unwanted frequencies in Hi Fi speaker systems.  Lead weights are also employed to give mass to the base frame unit.

Spring mounted 1hp fan motor

It is necessary to have variable speed control of the main fan unit.  The control panel above shows temperature gauge, amp and volt meters for the main motor and hours run meter.  There are other switches for smoke trails, etc.

Wind tunnel control panel

Strain gauges provided measurement of drag, lift and down-force.  A rotating table was incorporated so vehicle models could be tested in side wind conditions.  Air temperature and wind speed were also monitored and smoke could be trailed over models to visualize airflow, to highlight problem areas.  This tunnel could fit comfortably on an office desk.  It measured just 60" x 40" x 15".  Being a closed circuit design it was not unbearably noisy in operation.  

Five element balance with oil damping units (slightly the worse for wear)

A wind tunnel is a complex piece of engineering.  The Wright Brothers were the first inventors to use such a tool to compile lift and drag tables for various wing shapes.  It is much more difficult to design a balance to measure lift and down-force on each wheel of a vehicle.  When working at such a small scale, accuracy of measurement is essential.  Fortunately, electronics come to the rescue, with compensated amplifiers providing multiplication of movement up to ten thousand.

RS strain gauge amplifier

Five of the above RS strain gauge amplifiers gave separate channels of information to provide a range of measurements to include drag, lift and down-force for each wheel.

Each amplifier is fed information from a bridge of four foil resistors bonded to each element of the balance, two on each side.  There are five elements to the balance, consequently, you will need quite a few (20) strain gauges and some patience during the epoxy bonding and positioning.  The marking out must be exceptionally accurate.

Single laser cut 5mm strain gauge - foil resistor

The components used in the above tunnel, were not exactly cheap if you are on a small budget, but more importantly, with suppliers such a Radio Spares (RS) they at least are widely available to amateur scientists and enthusiasts.

Strain gauges bonded to steel element - 2 on each side

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