Originally Posted by The African Dude
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Reduction in weight is important for aero engines. The heavier the aircraft, the greater lift required, requiring greater airspeed, thus greater thrust and therefore more fuel is consumed. The heavier the engines, the more fuel used to get from A to B. Therefore you'll find engine manufacturers will only increase the weight of their shiny new engine design in comparison to an old one of similar thrust if there's a much more compensatory increase in efficiency as a result. Bluntly speaking that's never going to happen...
Well --- not quite.
It's total propulsion SYSTEM weight that's important. Don't forget to count the weight of the mission fuel.
So on a short-range aircraft, specific fuel consumption (ie engine efficiency) might be less important than paring engine weight to the bone, because the fuel carried is a smaller weight compared to the payload.
On a long-range bird it's the other way around. The fuel load at TO is a LOT heavier than the payload, so the emphasis is all-out on efficiency - sipping fuel like tea. To do this might require a slightly heavier engine carcass and more system optimizing - a reasonable tradeoff IF it saves fuel.
So in the real world - the answer is "It all depends..."
