Originally Posted by
Capt Fathom
If the aircraft didn’t need 4 engines, it would have been designed with only three!
AFAIR (but those who were there will correct me) the 747, and other four-engined aircraft, were designed with four engines so that they could get off the ground at max weight in a reasonable distance. But they were also designed, as all multi-engined airliners must be, so that having reached takeoff speed, if one engine fails the aircraft can continue takeoff and climb. Thus, the 747 does need four engines, but only to get off the ground! After that it’s perfectly safe on three.
I’m simplifying a bit, naturally.