RE: Why the Speedboy Patriot went 170 mph
Good information on the APC airfoils and zero thrust angles on the APC props Mike. However, I’m afraid that just a change in prop to 9x10 will not achieve 200 mph even if the airplane dove straight down from altitude. Just not enough power available from the engine and conversion of the aircraft’s potential energy. However if another 2.5 lbs. of weight is added to the aircraft (estimated now at 6 lbs.), you might be able to reach 200 mph briefly. The pullout from a vertical dive had better start before you reach 150 feet AGL if you want to keep the g loading below 20 g’s.
You need to do a little more research on the concept of prop efficiency. I’ve seen it referred to on RCU quite often, and almost all have it wrong.