Hi!
I have a GEE BEE R-2 (Great Planes ) model powered by a MVVS 15cc (.91) engine, that has a much bigger cowl then a Top Flite Corsair and using a 15x4 APC which flies the model real well at 5kg (around 10-10,5 Pounds). I tried several other prop sizes (14x6, 14x5N and 15x6) but the APC 15x4 woks best and gives that model rather good aerobatic performance.
It's very important the choose the right prop brand and not just use the prop that looks "good on the ground"!
I fly from sea level and mostly use 5% nitro in my fuel and I can say from experience that never ever should you use a white tipped MA prop on any cale (or sport plane ) if you want good performance. The props to use is always APC, RAM or Graupner G-Sonic. And of course only two blade props should be used . If you know how to carve and modify a wooden prop, of course it could be used with good performance too.
My 40 year experience tells me that a .60 size warbird like the Top Flite Mustang or Corsair powered by a .91-95 two stroke at sea level could well be flying with a 15x4 prop. Any 12 or 13" prop has to little diameter! And don't shot at a particular rpm .in this case 11000rpm. A much better way of obtaining good flying performance is trying some props and see which works best.
For instance my GEE BEE R-2, I tried several props and choose the one that worked best giving no though to how much rpm the engine delivered
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