eli5: Why do small jet aircraft, like regional jets and private jets, have engines on the rear, but larger jet planes have engines on the wings?
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well, another reason is flight. Smaller planes don’t need two or more engines, so it is impractical to have two. And you can’t go putting an engine on one wing and not on the other, so the only practical way to do this is to put the thrust (propellers in front, jet engines in the middle or built into the tailfin) along the centre of gravity (CoG) so that deviations in thrust least affect the movement of the plane.
Something else to look at is that if you were to look at the forces applied to larger planes’ engine thrust output, you can see that they will combine only above or below the CoG, never either side from it. It is also difficult to control the thrust output on the wings so that it doesn’t yaw uncontrollably to one side if the thrust is not exactly the same as the other side.
Also, bigger planes need increasing space, so putting the space-consuming engines on the outside saves a lot of space for cargo/passengers. It is also impractical to have 4 or 5 engines inside the fuselage as there would be little room (if the exhaust goes into another engine, the efficiency becomes so low, you may as well not have that engine.) So at best you can only really fit two engines in the fuselage, and the effort required to get the engines on the wings becomes worth it.
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