[dave in australia]

The big downfall of this engine is that it runs on avgas. Avgas is on the way out, at least here in Australia, and it becomes more and more expensive to fill up. One of the local aero engine shops here is developing a 4cyl diesel. It is a flat 4, and 2 pistons go toward each other so there is no head, and the combustion chamber is the space between the pistons at TDC. It is a 2 stroke, so there are few moving parts.