Light aircraft engines have not seen many revolutionary new designs since the years of shortly after WWII.
The Lycoming O-320, as an example, has been continuously in production since 1953. There have been many improvements over the years. Significant ones in metallurgy which lead to drastic increases of TBO. However, basically the design has not changed much. It is an air-cooled 4-cylinder piston engine which comes in carbureted- , fuel injected- , and turbocharged versions, all of them with the propeller bolted directly to the crankshaft.
An air-cooled engine needs to be built with higher tolerances. Higher tolerances lead to a loss of efficiency and higher emissions. That is why we don’t see air-cooled cars on the streets anymore.
The Rotax 915 iS is a radically different design based on the very popular 900 series by Rotax. It is partially liquid-cooled, runs internally at speed of over 5,000 RPM (just like a modern car engine) but drives the propeller at a speed of only around 2,000 RPM. Beyond that, it uses dual electronically controlled fuel injection, dual channel ECU’s (electronic control units). This makes it the most environmentally friendly light piston engine on the market today.
In our application, we will also use a FADEC propeller control system which makes it even more ecologically sustainable.
Dan Johnson has been President and Chairman of the Board of Directors for LAMA, the Light Aircraft Manufacturers Association since 2006. He is very well known and respected in the world Light Sport Aircraft. Here is what he had to say on his blog about the 915 iS last year:
I think the FADEC provides a level of perforce consistency and fuel efficiency constancy that is easily overlooked. Both are important in the business and personal use cases I’m considering. Combined with the dual ECU’s on the 915 iS it seems like you’ll have a uncommonly efficient setup. I’m curious to see the performance specs on such a setup.
Dieter and Grant are knowledgeable, hard working, well focused general aviation enthusiasts. If anyone can bring this project to fruition, they can. Just like with the advent of electric cars, today’s avgas for general aviation will soon be obsolete. While wishing them well, I shall be following this project with enthusiasm.