RE: Plane choice
Please correct me if I'm off, but I don't think thrust minus drag equals speed. I always thought inches of prop pitch X RPM equal the maximum speed of the aircraft in a perfect world where there is no drag. Since there IS always lots of drag (more the faster you go), you multiply your maximum speed by a percentage of efficiency of the prop, say 80%. This depends on lots of variables and keep in mind drag comes from lots and lots of places. Props, unclean surfaces, airfoil design, control surfaces out of trim or fighting each other, the angle of attack the wing has to maintain if the loading is high, gear, wheels, etc etc etc.....
Try this one Sunday when you are bored. It give you a report card on your building skills. TAC your prop. Compensate for unloading by adding 200 rpm on slow/dirty planes, or 500 or more on fast and clean planes. Best guess here. Multiply rpm x pitch = convert to mph, this is Speed1.
Next, get a buddy to help, stop-watch your plane flying straight and level across a 500' distance both ways. Compute the average mph. It's simply feet per second converted to mph. You can do one leg if the wind is dead calm. No cheating coming out of a dive..... Divide this mph by the computed Speed1 above. The result is your plane's efficiency....
Measure yours against someone elses who plane is faster, but engine, prop, RPM, weight, fuel, and design are equal. Their efficiency will be greater and they'll just smile at you when you ask them what-all they did...... ;o) That's racing boys and girls......
At least that's the way it use to be in the old school...