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Almost all commercial jets today seem to have the fuselage/cabin mounted above the wing, why is this? why isn't it mounted under the wing like some freight airplanes?

Examples of above and under?

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The related post, What are the pros and cons of high-wing compared to low-wing design?, does not address the passenger airliner related aspects.

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    $\begingroup$ I am nominating this question to be reopened because the supposed duplicate asks about high wing military aircraft, and the answers do not substantively address this question. $\endgroup$ – J Walters Apr 3 '17 at 15:55
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Large commercial aircraft have low wings to stow away their long landing gears. Long gears make it possible to stretch the fuselage and still be able to rotate during take-off. Stretching makes it possible to tailor one basic design to a wide range of sizes, lowering the price of a single aircraft.

Large high-wing aircraft with their low fuselage position are easier to load and unload, at the price that the fuselage taper has to start shortly aft of the landing gear, so no stretching is possible. The military doesn't mind and prefers the high-wing variety. That Lockheed likes to stretch their transports (C-130, C-141) anyway is the exception that proves the rule.

Only turboprop-powered civilian aircraft may have a high wing, so there is more space for the propellers and the landing gear can be made short and light. Still, both versions exist. And the ones where the engineers did not know how to attach a jet close to the wing.

Aerodynamically a mid-wing position would be best. This is used when the payload is compact and needs little space, or is hung externally. In bombers, in other words.

In terms of stability and control both configurations are equivalent.

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  • $\begingroup$ "Only turboprop-powered civilian aircraft may have a high wing" That's not quite true: BAe 146. $\endgroup$ – David Richerby Apr 4 '17 at 9:06
  • $\begingroup$ @DavidRicherby: Yes, the exception that proves the rule. Now I need to add another dreaded weasel word. $\endgroup$ – Peter Kämpf Apr 4 '17 at 9:45
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https://www.aircraftintel.com/article/view/high_wing_vs_low_wing_airplanes

Some Considerations:

  • High wing: easier loading
  • Low wing: structurally simpler
  • High Wing: Engines are farther from potential debris
  • Low Wing: Can have shorter landing gear (contra: B-24)

https://upload.wikimedia.org/wikipedia/commons/thumb/a/a3/Eurowings_bae146-300_d-aqua_arp.jpg/1920px-Eurowings_bae146-300_d-aqua_arp.jpg

https://commons.wikimedia.org/wiki/B-52_Stratofortress#/media/File:Boeing_NB-52A_with_X-15_No.1(SN_56-6670)_061219-F-1234S-001.jpg

I have to disagree with the stretching disadvantage to high wings: https://upload.wikimedia.org/wikipedia/commons/thumb/e/e6/C-141A_C-141B_comparison.JPEG/1920px-C-141A_C-141B_comparison.JPEG

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    $\begingroup$ Could you edit your answer so it's not (primarily) a bunch of naked URLs? $\endgroup$ – David Richerby Apr 4 '17 at 9:06
  • $\begingroup$ If this @#$@# should have let me do so (instead of saying invalid file format—JPEG), I would have to begin with. $\endgroup$ – user3344003 Apr 4 '17 at 18:54

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