Gosh, what an amazing airframe and service life. Given the nacelles, are these high-bypass fans of some kind of new type? And why not go to conventional big fans?
If I had to guess it’s because of the droop of the B-52 wings when fully loaded. I have friends that have flown the KC-135 with the big fans and they have to be VERY careful about landing with a slight angle of bank for fear of scraping an engine.
