The original requirement called for the 7 G with safety factor of 1.8
That is precisely written by Jiro Horikoshi in his book. I can quote this even :
By 1932, a new standard called "Summary of Airplane Planning" had been established which had to be adhered to in airplane design. It contained a rule that called for a safety factor prescribing the strength of structural members. This safety factor was defined as the ratio of an airplane's destructive load to the maximum load it was expected to be subjected to during operations. According to the legal regulation, this factor must be 1.8 regardless of the type of airplane, the application of the force or the material characteristics. In other words, the rule required the airplane not to be destroyed by loads less than 1.8 times the maximum load experienced in flight. For fighters, the maximum load had been established as seven times the force of gravity, or 7 Gs. Thus, when the 1.8 factor was applied to this, all airplane parts must be able to withstand a load of 12.6 Gs. Even when the airplane went through a maneuver of 7 Gs, which was the maximum load to which it would be subjected, the strength of all parts must have additional capability equal to 5.6 Gs
Source : Page 37 of "Eagles of Mitsubishi. The Story of the Zero Fighter" by Jiro Horikoshi, translated by Shojiro Shindo and Harold N. Wantiez. University of Washington Press.
It also has a fancy drawing showing precisely the stages of the material under the G loads, when up to 7 G's material returns to original shape and is fully reusable, above that it may not return to original shape and eventually is not reusable, and the breakage at 12.6 Gs.
Going through the book "The Zero fighter" which contains a full reprints of factory documentation and maintenance manuals for Zeros model 11 to model 63:
- for A6M2 there is table same as presented in the first post in this thread which contains the 7.0 G value with safety factor of 1.8 - this is point 3.2.1 or page 220 in my book.
- for A6M3 models such table is also available, with exactly the same value of 7.0 G and safety factor of 1.8 - page 315 of my book.
- etc.
What is more I also checked the Ki-61-I (Tony I) flight manual - it has written :
" Section VI. Flight Limitations
a. Pull Out ..... 7 G "
Same thing is also in Ki-84 (Frank I) flight manual, where its in table 7 G normal and 12.6 maximum. And same values I found in Ki-44 manual.
Basing on what Jiro wrote and what all the manuals and documents I have indicate it seems that all Japanese fighters built throughout the WWII had same safety values for maximum G overloads, which seems to be logical considering there was a legal obligation to design the aircraft with such measurements.
Regards,
Hiro