How much more efficient is an aircraft with no windows (in terms of operation)? Consider the hypothetical situation where you have two aircraft identical in every way, except one of them has no passenger windows. Or is the difference so small that its negligible?

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    $\begingroup$ Technically, not a duplicate because the premise of the question is different. This question asks if the aircraft are identical in every way except for windows. One could presume that the identical comparison aircraft has window-shaped cutouts with window-sized opaque material installed. However, given that premise, the question does not make any sense. If the comparison aircraft has exactly the same cutouts for windows, empty weight, and drag associated with these structures then the fact that some "windows" are not transparent makes absolutely no difference in performance. $\endgroup$
    – RudyB
    Oct 20, 2017 at 2:06
  • $\begingroup$ @RudyB Why are you philosophizing this, isn't it self-evident that "has no windows" means a fuselage without holes!? $\endgroup$
    – ares
    Oct 20, 2017 at 6:21
  • $\begingroup$ @RudyB a window is a window regardless of the material (or lack of) used to fill the void. I think the question means if there were no window related cutouts or reinforcements, otherwise all you’re changing is the material the window is made from, which is purely a weight change question. I think this question is a combination of the two now flagged as dupe. $\endgroup$
    – Notts90
    Oct 20, 2017 at 8:36
  • $\begingroup$ No surprise this question was closed as duplicate instantaneously... however there is more to say about windowless aircraft than drag. Airbus is currently thinking of this with "Transpose" for the future. This is a serious concept, contrary to the CPI nth "revolutionary concept". $\endgroup$
    – mins
    Oct 20, 2017 at 14:46
  • $\begingroup$ Many aircraft have "windows" that are not functional (for example in the area where on the interior there is a lavatory). A fuselage without holes is a very different issue, and cannot possibly be "identical in every way" as the original question asked, to a fuselage with windows. There are issues of rigidity of the structure, strength, drag, etc. There are manufacturing issues regarding cost and efficiency. Plenty of cargo vans have sheet metal "windows" because the window frames are stamped into the parts whether or not those frames will have glass placed inside them in the end. $\endgroup$
    – RudyB
    Oct 21, 2017 at 8:44