RE: Electric Conversion Question
You'll need to determine how fast you want (or need) the aircraft to fly. I believe it's 2-3 times the stall speed. Once you know the approximate speed then calculate the rpm x prop pitch to get that speed. Go for the biggest prop that your motor/ESC/batteries can handle without going over max amps. RPM = motor Kv x volts, figure 10 volts for a 3 cell lipo pack.
Bigger prop = more amps needed
Higher pitch = more amps needed
higher prop speed = more volts needed
When I was trying to figure out what to use in a four engine conversion I looked at the props I wanted to use versus how much room for batteries I had in the aircraft. I also wanted 8 min of flight so I figured in how many amps I could pull from the batteries I could carry. I determined I could fit 4000mah 3s lipos in each nacelle, I then selected a prop that gave me the speed I needed (60 mph) and the amp draw I wanted. I cheated a bit too, I used the Hobby-lobby prop charts with the AXI motors they sell to determine what motor/prop combo to use. They also list what size aircraft that motor could fly. My aircraft was going to weigh 18-20 lbs so I selected the AXI 2820-12 since it was listed as being a good motor for 5lb aircraft and turned a 10" prop, I used 4 of them. It had a max amps of 35 which was over what I needed and turned a 10/8 prop at around 25 -30 amps. It turned out to be pretty accurate. The motor/prop combo works perfectly for me.
One more thing - watts per pound- My airplane flies great at around 50-60 watts/pound.
Good luck!