How did the B707 and DC-8 fight stress at the windows? As it is evident from this  question, 4 (or 3) de Havilland Comets crashed because of stress building around the rectangular windows. 
How did DC-8 and B707 fight this problem, especially as it is quite clear that both of them had rectangular windows as well?
No, the Boeing 707 and the DC-8 used radiused corners on all their windows to avoid the problems of stress concentration factors, plus additional pad ups around the openings in the skins for the Windows themselves.



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