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I recently watched the following video:

In the video there is a mention that there are 'dimples' visible on the fuselage of a Boeing 747, when it is on the ground. It then goes on to explain that once the fuselage is pressurised - the expansion helps to "smooth" out the dimples and it will be flat.

I am curious as to what the structural significance is for 'dimples' on the aircraft?

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That's just oil canning of the unsupported areas of skin between stringers and formers, and when pressurized the skin stretches enough to remove them (18:00 in the vid). The fuselage diameter will swell a little bit, maybe 1/8 or 1/4 inch, when pressurized.

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    $\begingroup$ Would I be right to assume that these "dimples" are, therefore, found on every semi-monocoque aircraft? $\endgroup$
    – Nauman Shahid
    May 13, 2018 at 4:35
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    $\begingroup$ Only the pressurized airplanes. No such dimples on unpressurized Cessnas for example. $\endgroup$
    – CrossRoads
    May 13, 2018 at 13:52
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    $\begingroup$ No not necessarily. Sometimes you see oil canning, sometimes you don't. It's more prevalent on really big airplanes where the skin, in relation to the overall size of the structure, is thin you might say. $\endgroup$
    – John K
    May 13, 2018 at 18:23

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