OK on the original question here is the real answer from an old retired aerodynamicist. On the original question (airplane and engine combination) if you chose to use other than a 14/6, 15/6, or 15/4 you will suffer a condition known as "chronic unhappiness". When this occurs take a deap breath, sit down, open a cold beer (other than the USA) a cool beer, relax. Go back to using the 3 props mentioned and the " chronic unhappiness" condition will subside.


Denis