True, engine efficiency is kind of flat-lined. Turbines aren't efficient for most GA operations, but there are new diesel aviation engines coming online. Aerod

True, engine efficiency is kind of flat-lined. Turbines aren't efficient for most GA operations, but there are new diesel aviation engines coming online. Aerodynamically, I don't know about big gains. Something like a Lancair Legacy is pretty low drag. You can make lower-drag planes, but that typically comes with much higher stall/takeoff/landing speeds that make the plane harder to fly and much less safe in the event of a forced landing.