If your looking for a large F4 with twin 90mm fans look here:

http://www.ductedfans.com/jets_conversions_f4.html

This conversion is based on the Yelow Aircraft F4 and used Schuebeler 90 mm fans.

I can tell that the model flies extremely fast and has phenominal vertical power too!

Yet it lands very slow as it's finished weight is on average 2 1/2 lbs lower than it glow powered sibling

http://www.rcgroups.com/forums/showthread.php?t=332845

Bob