There are a few people who have converted the CM F16N to a ducted fan and CM even boasts on the packaging that this is a viable option to the prop set-up. However, the general consensus is that it is not worth the trouble. You could build a Yellow A4 in half the time it would take to convert a CM F16N to a ducted fan. If you're interested in DF, then bite the bullet ($) and get a model that was really designed for one. Also, ...a turbine in an all-foam model, ...that's a scary thought.

-Steve