Airplanes are such a wonder. When I grew up, I wanted to become a pilot. I actually took a Diploma so that I would have more than the minimum requirement to apply for one. That interest is still within me and goes hand in hand with the hobby right now.
Here is an analysis of frame work from fore to aft of the fuselage of the Japanese World War 2 fighter plane. If we study the drawings, there is an extensive use of lightening holes. Of interest is the location and shape of the holes. Some holes were ‘drawn’. Drawn holes are those that have ridges along its perimeter. Drawing is pulling material away from its original shape. Sheet metal can either be Cold Drawn or Hot Drawn. They were not just mere gaps in the structure to reduce weight. Drawn holes are formed to increase strength of the structure.
Imagine if you have a table with four legs. If the table was wide enough, the middle of the table would sag if you put heavy weights on it. Now if you had a table with eight legs, it can stand a lot more weight. This is an analogy. In truth, the load of the frame (or former in the fuselage) comes from the skin of the airplane, on the outside of the frame. The former needs to be thick enough to stand the load. In some cases, the former has flat lands on each side. It would look like the letter “I”. In structures and civil engineering, we call this the I-beam. So the former can withstand no just pressure from the outside, but is rigid.
Many automobiles monocoque structures heavily relied on designs from airplanes. In fact, Colin Chapman was an Aeronautical Engineer before delving into the world of automotive engineering.