The first comprehensive analysis code (C81) is developed
Saturday, March 31, 1973
"The complexity and multidisciplinary nature of rotorcraft aeromechanics problems demands a software tool called a comprehensive analysis: applicable to a wide range of problems (performance, loads, vibration, response, stability) and operating conditions (hover, cruise, maneuver), and a wide class of configurations (blades, hubs, rotors, aircraft), in all stages (research, conceptual design, detailed design, development) and all aspects (design, testing, evaluation) of the engineering process."
The first such code was C81, developed by Bell Helicopter (supported by the US Army). This milestone is represented by the publishing of the a paper in the AHS Journal by the developers of C81. The reference is provided below,
Blankenship, B. L., and Harvey, K. W.: A Digital Analysis for Helicopter Performance and Rotor Blade Bending Moments. Journal of the American Helicopter Society, vol. 7, no. 4, Oct. 1962, pp. 55–69
Note: Only the month and year of this milestone are known - March 31 has been chosen as an approximate but conservate date