I would imagine static thrust is like horsepower - a calculated value. With variances due to atmospheric pressure (e.g. pressure altitude) thrust varies. Unless you do your measurements at "standard day" you will not ever really know. Even the changes in fuel will effect the out come.

So were I you, put a 14 X 8 on your engine, and tie a fish scale on the tail, run her up to WOT and see what you get. But remember you can change the prop to 14 X 7 or 14 X 6 and get a different number. And you can change the fuel from say 10% nitro to 20% nitro and get a different number.

Good luck,'

Chip