Rolls Royce told us this week it is in the final build stages for the largest aero-engine technology demonstrator, a native SAF engine that will be just about ready by which time it will need to be replaced with hydrogen. UltraFan will have ceramic composite components and a novel architectures and a better combustion system, and will squeeze 25% more effort out of SAF that existing engines. But is it worth developing at all? A new fan system, claiming the most powerful gearbox in aerospace will result in a higher bypass ratio (the key measure of how combustion efficient works in a fan engine) and in turn will generate 40% less NOx with 35% less noise all made to work…