I saw the four engine jet come in for a landing Thursday. "What is that?" I says to myself, "It's not a 747".
It's not a jet! It's a nine cylinder radial engine (cylinders mounted radially around the drive, not in line or in a V like on your car). If you think of an old 40s or 50s car, that's basically the level of technology they had in the 1940s -- no electronics to speak of, and nowhere near the metallurgy we have today. The four engines on the B-17 were Wright R1820s, and (I had to look this part up) each one had 1823 total cubic inches of displacement and a six inch stroke. In other words, they were HUGE and they were HEAVY. But the plane was still famous for being flown home with only two, or even one, engine and very extensive damage to the body after a bombing run. The whole thing was a pretty amazing feat of engineering.
(damn plane just flew over the house again while I was typing, too)
For people who love mechanical stuff and old guys as much as I do, here's one of numerous YouTube videos showing and describing the engine: