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What are possible solutions, if aircraft manufacturers can't fit ever larger turbofans onto the standard low-wing passenger jet configuration?

Below, we see a 737 with large turbofans. If a new engine generation were to emerge with significantly larger fan diameter, would aircraft manufacturers

  • change to a high-wing design, as with the C-17
  • change to a low, gull wing design to make additional room
  • or apply other solutions

A 737 with large turbofans

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    $\begingroup$ All of these are possible. The question is how much is the effort required to implement those. You might have to develop a new airframe. This in turn will have different flight characteristics, which means extensive test schedule. That will then cause the need for pilots to qualify for that airplane. All of which add to the costs of buying and operating the plane. Thus the reason for Boeing trying to avoid it - which kinda came around and put them on the ground the hard way now. $\endgroup$ – Adwaenyth Mar 22 '19 at 8:44
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    $\begingroup$ Nothing is wrong with your question's premise, but it's phrased as a multiple choice (or open ended discussion), my recommendation is to narrow it down to a practicable problem. Also related: Is there less vertical space for an engine under the wing of a 737 Max than for an A320neo? $\endgroup$ – ymb1 Mar 22 '19 at 8:50
  • $\begingroup$ @ymb1 I am aware, that there can't be one answer to this. However, there could be arguments that make one approach preferable over others. A high wing configuration has been done before. On the other hand, Boing introduced folding wing tips with the 777X, which is something rather new in the world of passenger jets. I am interested in the merits of the approaches I stated, and in possible alternatives. $\endgroup$ – Dohn Joe Mar 22 '19 at 9:26
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    $\begingroup$ Engines are not designed in a vacuum. The engine manufacturers don't go off and design an engine and then show up to Boeing and say, "here's our new engine, it's 98" in diameter, now try to fit it on your plane". The engine and the airframe are designed together, in parallel, as a partnership. Fan diameter will be agreed upon by the two companies as they both try to design the optimal system. If the airframer decides the benefit of a bigger fan outweighs the cost of a wing redesign, then they will do it. Otherwise the fan will stay the same size as previous generation. $\endgroup$ – Daniel K Mar 22 '19 at 10:48
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The easiest way to accommodate a larger engine under the wing is to increase the landing gear size. This has some other implications like more space needed in the landing gear bay (although there are clever solutions like this one for the 737 MAX 10) and higher weight, but if the larger engines with better efficiency outweigh the costs for these changes, it will certainly be done.

Changing the design to high-wing or tail mounted engines comes with other drawbacks, as already discussed here:

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I think tail mounted engines, where there is more ground clearance would best solve the problem. See Picture A and B

Picture A enter image description here

Picture B enter image description here

Over the years one of the main problems with tail mounted engines has been difficult maintanance, however with larger engines mounted at the tail, leaving as much clearance as the smaller wing mounted engines of today, that ceases to be a problem. Secondly adjustable scarfolding hydraulic powered will elevate the mechanic, technician or engineer and his tools closer to the engine.

Source picture A

Source Picture B

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    $\begingroup$ While empennage mounted, hi-bypass turbo fans may come in the future, there are quite a few drawbacks to mounting them there, which is why there are so few transport category aircraft being built with them today. This question explains a lot. $\endgroup$ – FreeMan Mar 22 '19 at 13:08

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