Well said Dick.

There is no better test than real-world, real-time, real air.

I've gone to the field with 6 absolutely identical racing props. CNC machined, purpose designed. All identical. One ALWAYS ends up faster than the others.

Why? It could have been those 10 minutes of change in time, or the +0.80667543 deg in air temperature. Often its hard to tell. There are so many variables to deal with once you get into a dynamic situation. Combine those with know variables, and its almost a guess. Sometimes thats the best you can do. Make your best educated guess, try it. Then try to repeat it.

A wise man, and a very estute engineer, once quoted to me "Everything happens once in a row. When it happens 15 or 20 times in a row, come see me."

Bob