RE: 1/2A ducted fan???
I agree, it is real easy to overload a .049. To make this idea work, a guy will have to get smarter than Mr. Kress and all the others who have already tried. I don't know anything about EDFs, but think you would need to get some for guinea pigs and start doing some carving.
If there are sentimental reasons for trying this with Cox power, fine...but the chances for success would be [obviously] better if using a Cyclon or lower timed GZ .061.