But the issue has always been weight, diesel engines have to be robust, so the power/weight has always been a challenge..
True but the Delta Hawk was a 200hp V4 Diesel with a dry weight of 327 pounds... I think one would fit my Chipmunk nicely...
http://www.deltahawkengines.com/econom00.shtml
I think the DeltaHawk engine has many advantages. One big advantage is the nature of the 2 stroke firing impulses reducing prop and crankshaft harmonics.
Most modern aircraft diesels require wooden propellers, such as the MT prop. The combustion event is so abrubt, the typical aluminum prop is subject to fatigue stress with diesel engines.
While I like the MT props, I very much prefer conventional props. Wood is thicker and much less durable when impact damage is considered. It's amazingly easy to destroy the thin "trailing edge" of an MT prop by touching it with a tool (by mistake) or by hitting a tow bar on it, or by kicking up a rock during taxi. We've had multiple, unnecessary failures of our exceedingly expensive MT props.