It's hot out there

Unlike conventional aircraft that have plenty of drain holes, vents, scoops and so on, stealth aircraft have to limit the number of apertures in order to be low-observable. This makes it harder to get rid of heat generated by the aircraft systems.

Workable if you have a simple aircraft like the F-117 which doesn't have the complex systems of an F-22 or F-35.

Getting rid of all of the heat generated by the various aircraft systems (power, flight controls, and mission avionics) is difficult for the F-35. Excess heat that cannot be shed means systems may shut down. Assumptions on parts life can be thrown off, causing more maintenance issues. And, maybe even mission failure.

As an example, try using a push-mower on your lawn; in the middle of a hot summer; wearing a snowmobile-suit, gloves and boots. That is the challenge faced by the F-35 now stuffed with a large number of heat-generating systems. Interesting as at the beginning of the JSF concept, the jet was to get much of its' situational awareness from off-board nodes. As an aside, someone must have also been thinking that this gave the JSF program a shot at being simple and affordable. Later in the JSF concept, it was decided to load up the aircraft with lots of heat-generating systems and make it more of a network content producer and less of a network content consumer.

Fortunately the U.S. never fights where it is hot.

Look at the following slides on "legacy" vs. F-35 assumptions. I will put a comment at the bottom of each. Click each image to make it larger.


The good old days (note the logo in the upper-left-hand corner). Things were so much more simple then, when all you had to do was tell Congress you knew what you were doing and "trust us" had a better chance of working.

"Improved Efficiency and Lower Equipment Count Enables Smaller, Lighter and Lower Cost Aircraft".

Alrighty frighty.


The link says 2011 but I wonder. The legacy flight control system (upper-left-hand-corner) is mentioned as a heat generator, but the fact that it was known even at this time that a "JSF first", the 270-volt flight control system, generates a lot of heat.


I give them points for the last words at the bottom which admit to adding complexity.

This article two and a half years ago mentions heat build up. With, Block 1 software...

In particular, three aircraft flying with Block 1 software will strain the F-35's thermal management system as never before, Beesley says. The aircraft's electrical and power system radiates heat that must be cooled or dumped into "heat sinks", such as fuel. The challenge is most acute when the F-35 taxis on hot days.

"So far the (F-35's thermal management) concept seems to have worked well," Beesley says, but adds: "When it gets to be 105°F (40.6°C), that's when you want to look at it. It's a great question to ask by the end of next summer and see how did it go."

Thermal issues have been mentioned in various GAO and DOD test reports. Shedding the excess heat produced by numerous aircraft systems is a large challenge for the program.

Large enough, to have a serious impact on operating cost and sortie-generation assumptions, made so many years ago.

While it may alter the left side, every overly optimistic item on the right side of this chart will be affected by adverse thermal issues.


(click image to make larger)