"The engine's overheating and so am I. Either we take off or we blow up - which is it going to be?" Michael Caine's rant from The Battle of Britain might ring all too familiar for engineers on the Joint Strike Fighter program.

"Heat dissipation is a huge problem" for JSF, according to Jean Lydon-Rogers, president of the General Electric/Rolls-Royce F136 engine team. The JSF team, she says, is still "brainstorming approaches to thermal management" even as assembly continues on the first batch of "optimized" test aircraft - that is, the first JSFs built to the lighter post-2004 design.

As a stealth aircraft, the JSF is designed without air-cooling vents that can create thermal hot-spots, which can in turn give the airplane's presence away to infra-red sensors. Instead, heat from the engine, electronics and power systems is dumped into the fuel and lost when the fuel is burned. At some times, says Lydon-Rogers, "even the engine is a heat sink", providing a mass of metal that can survive high temperatures. The process is managed via a complex power and thermal management system which also starts the engine, provides electrical power and makes the tea.

Like Caine's Spitfire, the critical point is when the aircraft is at idle, says Lydon-Rogers, and is not using fuel fast enough to get rid of excess heat.

Meanwhile, the F136 team is talking more directly than in the past about the engine's potential for developing more thrust and how it could help resolve performance challenges. The major difference between the primary engine, the Pratt & Whitney F135, and the F136 is that the GE/RR engine was designed later, after the weight growth problems that the JSF encountered in 2004-2005.

Part of the solution to that problem, Lydon-Rogers says, was a larger inlet (which increases the engine's thrust potential) and the F136 design takes advantage of this with a bigger mass flow. While both engines are being delivered to the same specified thrust, she says that the F136 offers thrust growth with less risk.

Tests have "confirmed indications of growth capability, if and when that's called for", Lydon-Rogers says. "We have a plan for growth that does not require a major redesign." Single-digit increases - which could easily restore the bring-back margin of the STOVL version - could be accomplished with a software change "and double-digit increases are feasible without a major redesign."