A search in the archives on the topic of auto engines vs. aircraft engines should reveal a large amount of data relating to their design differences and several educated opinions concerning their use airplanes.
At the risk of over simplification, the biggest difference that I now see between the two is the airplane engine has been engineered to handle the specific loads and working conditions that the airplane and prop combination have been designed for, at the sacrifice of smooth running at all other rpms, etc... Much the way a racing engine is designed to do best in a smaller area of operation, so does the airplane engine. The auto engine however is expected to operate in a much wider range, and behave well. This causes it to be a bigger example of the compromises the designers have to make to achieve this. Hence computers coming on the scene to make adapting to these demands easier. Airplane engines are also now following suit due to public demand for more performance and economy, with better engines. An auto engine properly matched to a PSRU assembly, and prop the way a turbo-jet is matched will live a very long time if maintained with the same attention the airplane engine receives. The same holds true for the direct drive if it is properly modified to do the job it is asked to do, matched with an appropriate prop, and operated and maintained as one would the airplane engine. Colin Rainey
