I just can't imagine how much this unit will weight! Plus it need to be balanced to turbine tolerance...WHAT IF ... duct and fan are 1 part. So, you let rotate the duct too. I guess it is not such a problem to do that. A central bearing at front and rear and a driving belt. No more blade tip clearance problems. But ... would it improve the performance?
Why we need to "invent bicycle if it's already was invented"? - Basic DF design is working just fine, if it's build right