You do need more power to turn a [/i]substantially[/i] larger multi blade prop. It may be that the 3w 80 is enough motor if a 26x12 2 blade prop @ 7000 rpm = 30x24 4 blade prop at 3500rpm... but my WAG is that your talking about 3x the prop with a 2x advantage... My Zero above flew about the same as another similar size warbird I had with a direct drive G62. IIRC we flew it with a 22X12 2 blade vs. the 24" 3 blade with (of course) more pitch (can't recall exactly, but I think it was around 20" on the 1.75:1 torquemaster. 26" blade set also worked ok, but 28" was too much prop; couldn't get enough rpm's X pitch. Hope I'm wrong, just being a devils advocate here. You can always go down in dia, say to 28, and it will still look cool!

Currently considering a planitary drive to turn 4 blade props on my electric XP-67 project. Love the cool factor of scale flying props.