The main competition is the Rotax 912 some of which
 is liquid cooled so why pursue air cooling?


How about: simplicity, access and ease of maintenance?

The one photo you posted, Two-Sach-quest-mark, sure looks like a neat installation to me.

I drive a Dodge 2500 with a Cummins diesel.  Reason?  Look under the hood and it reminds a guy of how engine compartments looked 50 years ago.
Look under the hood of GM or Ford diesel pickup truck, and you cannot even find the engine.

I sure would like have an aircraft engine in the 100 to 150 HP range for my current project that would come in under 200# and be as simple as that two-rotor Sachs

Robin Berglund

Their out there. You might find some on Ebay.
Note the power robbing fan between the two sections.

Paul Lamar