Bob,
I am confused too. BUT having had a mishap at the field the other day the Furias has sustained a fair amount of damage due to winds at landing. TO winds were 3 mph, sun came out from the clouds and it went to 20+ as a storm rolled in all in less than 3 laps. I held of for dear life and at landing it picked it up and slammed it down crushing the cowl and bending one of the main gear and tail wheel and knocking out the Rabe rudder.
I have work to do to get it back in action and building a new cowl is not going to be fun on a plane that is totally finished.
I think the diameter over 13 is causing mucho load. I am just starting at 14 5 as I was using 14 4.5 with tips at 4.25 on your old 56. It was darn near all it could handle and not damamge it. The run was rich but it was up on torque to keep it spinning. It used alot of fuel as well.
You go down in diameter and the load is less, compared to my setup.
Then you choke in some on the throttle to get rpm in right range. Fuel consumption goes up. Here is why I think that happens.
With the larger opening you get two options. Super rich and wont fly the plane and generally not usable, using alot of fuel for nothing.
Or leaner run but too lean and it is fast and not burning much fuel because the load is light. You are actually getting speed off a lean setting not a power setting so to speak.
You choke off the area, or in other words close the throttle, and take down rpm to get a usable speed. BUT you are now on the top of the torque curve and you are not lean. You are in a good mix range to make real power, not high rpm from a lean setting, and you burn more fuel... Make sense?? I know what I am trying to say but I just dont know if I am saying it very well.