KenV,
I would like to point out a couple of things:
The development of the F-18 E/F did come from the earlier F-18 airframes. But, there were changes. The length increased 4 feet, the height by a 1 foot and the wing span by 4 feet (a new wing). The maximum gross take off weight increased by 14,100 pounds and the range increased by 200 miles.
Indeed. Which was exactly my point. When making changes to an existing mature product that effort is an ideal candidate for concurrent engineering. Yet even when doing a (seemingly) simple thing like scaling up an existing design, not everything scales well and brand new, completely unforeseen problems arise. Like the slots in the upscaled LEX causing transonic drag, and the wing fold mechanism causing stall issues. When the product is all new, there are far too many unforeseens and unknowns to enable concurrent engineering.
The F135 engine is a derivative engine from the F119 engine used on the F-22. The F135 engine is not a completely new from scratch engine.
Indeed. But no one anywhere had ever modified ANY turbo fan engine to extract 15,000+ HP, and mechanically couple it to a lift fan. Nor had anyone anywhere ever built an airplane with a clutch that could reliably engage/disengage that level of power. Nor had anyone anywhere ever built an engine nozzle that could reliably swivel 90+ degrees. Nor had anyone anywhere ever integrated an engine with all the above plus roll control jets into a stealth platform. Nor had anyone anywhere ever built control software that controlled all the above, especially during the extremely critical transition from engine borne to wing borne flight. Not only are these all massive unknowns that do not lend themselves to concurrent engineering, no one anywhere had ever attempted to concurrently engineer all the above into an entirely new airplane with entirely new avionics that were themselves being concurrently engineered. Huge problems were essentially guaranteed.