I am posting a question about propeller choice. At first look, it seems that the best way to choose a prop is to first decide how fast you want the plane to fly, and choose the pitch that gives you that speed for the rpm you want to run your engine. Then increase the diameter until the engine runs at the rpm you selected. That way you get the right speed and the most thrust.

Say I want my Conquet to fly at 90 mph top speed and I think the engine will turn 10,000 rpm. I would choose a 9.5 inch pitch. Then I would have to go up to 13 or 14 inch diameter prop to slow the engine down to 10,000 rpm.

In reality, most pilots use an APC 12 x 12 for the Hanno. I also found some words from Dave Patrick, who designed the Conquest, saying he used a 12.5 x 11 APC prop. (and probably a YS 61 AR, which is similar to a Hanno)

Why is my logic wrong? I know there is some slip, but I ahve read that the slip is minimal with APC props and a clean airframe like a pattern plane. Do we incease the pitch to keep a load on the engine and avoid significant rpm changes with speed?