@Tinman:
As you are/used to be an air force guy...I read once that it might be a good idea to put more effort in putting turboprop planes back into the air.
Energy-wise this technology could be made a lot less wasteful than current jet engine tech. As it currently stands the two technologies match each other.
Besides this, commercial airliners fly as slow as they can get away with already for years now, to keep fuel costs down. Almost negating the advantage a jet has over a turboprop (speed).
From that article I understood that using similar maintenance procedures/intervals for turboprops as is done for jets, current turboprop tech is as reliable and almost as fast current jets fly, but a lot cheaper with fuel.
I keep saying article, but it could also have been a paper or case-study... -Shades
While turbo-props do have much better gas mileage, they'll never be nearly as fast as a jet engine. I've read over the years how they were testing diesel aircraft engines (piston) that use bio-fuel, but I haven't kept up with the technology and don't know if it's in the plans or not. Perhaps now that they're trying to save so much fuel, the piston diesel engines will become a reality. Another thing they've been testing is rotary engines. They claim more power with better economy over the turbo-props. But if they're anything like the old Mazda rotary engines, the upkeep will be a major factor.
I really do need to catch up on which direction the industry is taking, but they change their minds about as much as my ex-wife.... soooooo :o