RE: K&B .48 vs OS 46 VXDF
I think the first 'dedicated' K&B ducted fan engine was the 7.5 with rear exhaust and rear, drum rotor induction. Just before K&B closed business they redesigned it into the 48 version and only made a few. Larry Wolfe was flying a couple and liked it very much. A lot better than the earlier 7.5. At about the same time, OS redesigned "their" 46VR engine (which had the rear, disc induction and smallish carb) into the currently available 46VX-purple head with a huge carb and drum induction. According to Larry the OS purple head is THE 45 size DF engine to use. It's available, proven and performs. If you already have a different engine and want to use it, fine. But if you are looking to purchase a new one, this is it. The only fan I have experience with is the Turbax. I think most people in the US use this and most people in europe/UK use the Thorjet.
For what its worth, I have a Jethangar A4Skyhawk that weighs 10 1/2 pounds empty and it's powered with a Turbax and OS46VR, the earlier engine. With 10% nitro fuel and at our Utah field (4200 feet elevation) it flies fairly well. We'll call it 'scale-like'...not a missle, but OK.
Hope this helps.