There are many types of tachometers but, for a wind motor, a cheap
little optical tach should work. You hold the tacho from moving and
point it to a target you have marked on some part of the motor that
will occur once per revolution.

You can also measure the distance in feet on a paper roll and see
how long it takes to play a known distance.

I am having difficulty typing so this email needs to be finished.
I can answer questions.

Spencer Chase