How can higher bypass-ratio turbofans be fitted to conventional planforms of low-wing design ?

This question has gained great importance within the air-travel industry in recent years , primarily because of the financial impact greater fuel-efficiency can have upon an airline's profit margin .

Prior to now , the standard answer was to install wider engines , this in spite of the significant modifications necessary to fit such to aircraft originally designed for much narrower ones .

The drawbacks of this approach are numerous , and involve components such as landing-gear , fuselages , wing-structures , engine-mounts , and even avionics and cockpit layouts . The B.737-Max debacle was a perfect example of how such gerrymandering can go astray , with devastating and possibly lethal consequences .

The most practical answer here is not tail-mounted giant turbofans , or blown-wing architectures , but rather compound dual-fan designs . These would basically be extant turbofan designs , with an add-on free-turbine fan mounted on the rear . Such engines would sacrifice some of the gas-turbine core's turbojet thrust in order to produce much more fan thrust . Making the two fan-disks contra-rotating would give such an engine as much as 30% more thrust while engendering overall efficiency increases of ~ 20% .

*The easiest way to visualize this is to search up cutaway images of the General Electric CJ-805-23 engine , this turbofan having been utilized on the Convair 990 airliner for many years .

Edited July 23Jul 23 by Professor-M
Visual clarification .

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