Rhino,
I've mentioned this before, but it might help understand the weight issue. The F-35B's weight issue comes from two factors.
The first was a failure by LM to control the weight of the basic design. This issue affected all three variants, and led to a major redesign of the aircraft in late 03/04 to get around a ton and a half out of the airframe. The problem affected the B most of all, which is why the first redesigned F-35 was BF-01, the first F-35B. To repeat, so I'm not labelled as a 'fanboy' - LM let the F-35 weight get out of control early in the programme. It took them a lot of work to get the toothpaste back into the tube.
The reason the B was the worst affected was the second factor - it's a powered lift aircraft. It is required to perform a VL at specified weights and conditions, and requires the installation of a lift system. This lift system adds weight and consumes volume, and is the reason why the B has to take a performance penalty compared to the A model.
This was recognised n the JORD, where the targets for the B's payload, range and manoeuvre were all less demanding than those for the A.
Simply put, all powered lift aircraft have a very demanding weight challenge. This applies to rotary wing aircraft as well. Tight weight margins are a fact of life on STOVL aircraft, and should not be seen as a failure.
Rhino, you're quite correct on the frame redesign - it will very probably be eating into the margins that are always tight. Sometimes, airframe redesigns can avoid weight increases if it's a matter of optimising load paths. Sadly, more often the only route available is more material - and that means more weight.
Best regards as ever to all those watching the pounds,
Engines
Last edited by Engines; 23rd Mar 2016 at 14:19.