I am trying to come up with a way of measuring air speed in m/s for use in a home built wind tunnel for RC airplanes. What I have come up with sounds a bit involved (structurally) and I am wondering if there is a better way or if someone has done this before.

My idea....

use a 3 blade prop in reverse (9 inch diameter) coupled to a shaft with a disk of known circumference (fraction of a meter) with a single window notch in the solid disk. For example, one rev would represent circumference travel of 8 inches. So I would count pulses over 1 sec time period and multiply by a constant of proportionality to scale it up to meters/sec.

Am I over simplifying it or over complicating it? LOL....all I want to do is wing lift / drag tests on custom wing designs in a wind tunnel. BTW, the fan is an industrial movie fan with variable speed.

Best Regards,
Nick