Engines are sized for failure at take-off. At that time they are at maximum power, the aircraft is heavy with fuel, and the ground is mighty close. I see no ev

Engines are sized for failure at take-off. At that time they are at maximum power, the aircraft is heavy with fuel, and the ground is mighty close. I see no evidence that larger engines are more efficient than smaller ones. Larger total frontal area (counting all engines together) is more efficient, as is a higher bypass ratio. Both of those tend to lead toward larger engines, but you could leave those unchanged while modifying the number of engines. For example, switching from 2 engines to 8 engines, you could maintain the same frontal area by changing the diameter from 10 feet to 5 feet. The bypass ratio, which is the portion of air that bypasses the combustion, could be 12-to-1 or 10-to-1 or whatever, and need not change with engine diameter.