OAP, George,
Perhaps I didn't do a good enough job of explaining how the F-35 designers went about handling the thermal management issue. I'll try to do better. (While working on the programme, I had a responsibility to monitor the thermal management solutions being developed by the 'Vehicle Systems' team to ensure that they wouldn't affect ship or land basing).
Thermal management was recognised as a high level risk early on in the programme, probably as a result of F-117 and F-22 experience. The team started with some basic simulations of the expected heat loads, which factored in the changing fuel loads throughout mandated mission profiles, as well as many other system parameters. They also reflected the mandated temperature limits applied by the JPO specification. (These certainly included some vary aggressive 'heat soak' requirements for land bases, at least 50 degrees C). These simulations showed that changes were needed to the baseline design to avoid unacceptable limitations on operation of the aircraft. So, a heat exchanger installation with external air scoop was added to the starboard upper wing root. Later on, two intakes were added under the wing just outboard of the landing gear doors.
Meanwhile, the team were developing a more sophisticated model of the entire thermal management system, which included the design performance of the many and various components. These included the liquid cooling systems, which were required to collect heat from various locations in the aircraft (e.g. certain antenna, flying control actuators, etc.) So, yes, OAP, the F-35 does use other cooling media part from fuel. The model also included the expected performance of various heat exchangers, pumps, valves, and the heat loads dissipated by the fuel tanks. At this stage, ever more complex mission profiles were added in to 'stress' the model and see where any 'pinch points' were.
I should add that any and all assumptions over how the aircraft would be operated were approved not only by the recently retired USN, RN, RAF and USAF operators with the programme, but also by the joint LM/JPO test pilots as well as the JPO itself.
As the programme went forward, any change to the aircraft design that affected the thermal management system was incorporated into the model. As key components went into rig test at their suppliers, test data was fed back into the model to improve its accuracy. A dedicated thermal system test rig was also built to provide ever more accurate data as the aircraft design develoed.
At this stage, I should address F-35B landing weight. This is a KPP for the programme, and one which (quite deliberately and quite correctly) drove almost every aspect of the aircraft's design. I can absolutely assure all readers that there was absolutely no possibility of the F-35B carrying additional fuel at landing to handle heat loads.
To date, the main impact of thermal management is the requirement for a cooling rig to be attached to the aircraft on the ground when using external electrical power supplies. This doesn't apply when the aircraft's internal 'Integrated Power Pack' is being used for ground checks.
I suppose what I'm trying (badly) to put over is that nobody made any stupid assumptions about fuel states. when getting to the final design. Designing LO aircraft is a fiercely hard thing across all disciplines, and the people involved have done extremely well to get to where they are.
Best regards as ever to all those doing the hard yards of design,
Engines