Originally Posted by
tuna hp
Yes I understand all of this, that to produce X thrust is more efficient in every way out of 2 engines than 3. But there has to be some fraction of X where its more efficient to get it out of 3 engines than 2. For example, 3x5,000lb engines have to use less fuel than 2x50,000lb engines powering the same plane.
I see what you're saying. I don't know the break-even point off-hand, but it's generally known in engineering circles that two engines is more efficient than three.
There may also be structural weight savings, since you have to support all that weight on the tail and also transmit the thrust to the CG. Wing-mounted engines are closer to the CG.