This is coolbert:
With regard to the previous blog entry consider also this Russian Internet Sputnik article:
"F-35A Lockheed Tries to Catch Up With Announced European 'Sixth-Gen' Fighters by Vowing F-35 Upgrades"
"European countries have recently revealed their progress in creating sixth-generation fighter jets showcasing the Future Air Combat System [FCAS] suite of weapons at the Paris Air Show this week."
"Lockheed Martin’s Vice President Greg Ulmer has revealed the company's plans for the future of its key F-35 programme during a briefing, which suggests evolving it to a degree, when the line between the now fifth generation jet and the next generation blurs".
Variants of the F-35 with blocs to continue as long as the plane is in service. [F-35 expected to be in the main American air superiority fighter plane at least until the year 2050!]
Currently the F-35 existing in A variant [air force model], B variant [Marine model] and C variant [navy model].
"Models (A, B, C, D, E, etc.): major changes that affect the entire role of the plane, such as Air Force missions and runways, Marine aviation (sometimes with no runways), or carrier duty."
"Blocs: changes within the models made for 5, 10, 20, or 50 planes coming off the line, caused by the changes found necessary years after the model was designed."
That number of blocs basically unlimited, improvements primarily evolving as modern technology evolves.