A cheap and accurate way is to measure off 1/16 of a mile, station 2 helpers at either end of the course [it helps if both helpers have a fixed object to reference, like a pylon pole]. All they need is a pair of cell phones and a stop watch. All you will need to do is fly through the timing zone level, turn around and repeat as many runs as you can while your helpers record the results. The rest is pretty simple math.