Lynn, I've looked into trying to calculate such several times
and after getting a headache each time I gave up. Prop calculations
makes duct calculations appear simple {:>). Having said that here is
one equation (below) that relates Thrust "T" and propeller diameter
"D". There are only three other significant factor in the equation.
There is the speed of the air stream into the prop disc "v" and the acceleration
imparted to the air stream by the prop "Dv" - air
density is what it will be and you can't affect that (except by where you
fly).
so if you look at the factors one could conclude that Prop
diameter appears to be the most signficant factor (at least in this momentum
equation). The Thrust is directly proportional to the square of the
diameter. So if all else is equal then a 74" dia prop would produce 74^2 =
5476, whereas 76 " dia prop would produce 76^2 = 5776
or approx 5467/5776 = 0.9467 giving approx 5% more thrust
for the slightly longer prop.
I went from a 68" prop to a 76" prop when I switched from my
2.17 to the 2.85 gear box. I was very impressed with the change in take
off performance. So comparing the two (Yes, RPM went down a bit on the
prop with the 2.85 so in real life the comparison is skewed), but in any case at
the same PROP rpm. The 66^2 = 4356
going to the 76 gave me 5776, comparing thrust for the two
4356/5776 = 0.75 or a gain of 25% in thrust for the same prop rpm - now that
will get your attention.
However, this equation clearly does not take prop chord into
effect and based on the simple chart of three data points - it would appear to
play a major role in static rpm and thrust.