propfan MD   I read that during a period of unusually high fuel costs MD built one  with propfan engines these look like turbofans but with a propellor attached to the rear they are known for their effeicency After some initial hype no orders came and the model I believe it was a oneoff more of a demonstrator than anything else was scrapped There has been intermitent talk of using propfans on civil aircraft since then but it has not come to anyhting