[Bill Walker]

My exerience started in the late 1960s as well, I'm going by conversations with the old hands. Maybe I'm over simplifying, but dynamic load cases can be treated as quasi-static, with inertia forces added to the free body diagrams. Statically indeterminate loads were handled by hand iterative calculations way back before airplanes, I think early iron boat hulls were analyzed this way. When I started writing Fortran code in 1970 to do this the process was well understood. Computers just replaced rooms full of clerks with slide rules or mechanical calculators. Look for a book called "Slide Rule" by Neville Chamberlin for an interesting description of hand cranked finite element analysis of dirigible structures in the 1920s. Lots of people, using lots of paper and lots of pencils.

I think the limit here may have been in defining the aero loads to apply, as you suggest. If you look at old airworthiness codes, it seems to have been a fairly emprical process. "We know airplanes THIS strong don't break, so make yours just as strong". When that failed, the required loads were upped a little bit in the next amendment. Even today, the fine print in FAR 25 loads state that rolling pullouts may not be covered with great accuracy - so the manufacturers tell you their published g limit is for symetrical loading only. In other words, don't do rolling pull outs in your airliner.

Having said all that, the designer really has no special insight into what is required in an airplane. They have to rely on the customer (like the RAF for the Whitley) asking for the right things. Wrong assumptions can lead to perfectly designed wrong airplanes. It has happened over and over.