Hi Richard.
The engine is tiny and light! It is designed to tolerate the fine-carbon soot of a diesel, which makes its brand new oil as black as coal. There are a number of things about it that suggest it has room to evolve toward a slick, high-volume design some day. Right now it's still an aircraft engine(!)
The wake impeller design is still under wraps. The prop we stuck on 'for the heck of it' is a prop I designed for the RV-7.
I'm not sure what you mean by "using air pressure as a duct," but everything looks good to the eye so far in the cooling department. Sometimes things change when you get them out of the computer and into full scale, but I haven't found too much to worry about yet.
As I've been saying for a long time now, there aren't many new discoveries in aerodynamics, just old ones we didn't quite recognize. I remain excited by our prospects, as all of our refinements to details and mass flow seem to be in very good harmony with our preliminary calculations.
Quite a bit of IP is involved in this effort and we are doing fine there. The only surprise is the same one we've marveled at all along, which is how many people would have the gall to insist on things happening 'all by themselves' for their viewing pleasure. Fortunately the core EAA member seems to be a lot more realistic, and many have gone to extreme lengths to help assure this continues at a reasonable pace.
We've been idled for several months now and that makes life a challenge, but the overall prognosis is spectacular in the long term. Too many people are starting to follow along with the premise and the plan now, and when the dominoes we've set start to fall we'll have a truly unique opportunity.