Bradley Perrett at Ares notes that GE/Rolls Royce has had this this thrust number floating around since at least 2002, and would compare quite favorably to the 43,000 lbs of thrust available in the F135.

It’s clear that the F136 has a larger core than the F135, but at this point GE/Rolls is arguing that this can allow for greater reliability, and perhaps a few hundred pounds more thrust in STOVL mode for the F-35 JSF

The latter looks significant, as the Royal Navy is looking at a “shipborne rolling vertical landing,” basically a relatively low speed (under 150 km/h) non-arrested (!) landing on a carrier to increase bring-back weapons load and to reduce wear and tear on the engines, for vertical landings.

My guess, as is Mr. Perrett’s, is that the 56,000 lbs is the number that they are designing to for the purpose of creating a margin which would allow for reduced maintenance and capacity for upgrades.

In order to go from 43,000 lbs of thrust to 56,000 pounds of thrust in the JSF, I think that there would have to be some major airframe modifications, because there has to be more air flowing through that engine to get that performance, so I would expect significantly altered air inlets, no small change in a stealth aircraft, to realize that thrust level.

One interesting aside in the article, is the “cost” of the lift fan system that was chosen as the winner in this competition: both the GE/Rolls and P&W engines for the original fly-off for between Lockheed-Martin’s X-35 and Boeing’s X-32 delivered a lot more thrust in wingborne mode using when configured Boeing’s direct lift concept.