Military Aviation

Former Lockheed Martin Flightline Quality Assurance Manager explains why the first F-35s required chilled fuel if temperatures on the day of flight were above 80°F

‘The F-35 is the most advanced fighter jet to date in terms of technology and that requires a tremendous amount of computing. As you know heat is the biggest threat to computers,’ Earl Belz, Former Lockheed Martin Flightline Quality Assurance Manager.

The F-35 is designed to replace aging fighter inventories including US Air Force F-16s and A-10s, US Navy F/A-18s and US Marine Corps AV-8B Harriers and F/A-18s. With stealth and a host of next-generation technologies, the F-35 is far and away the world’s most advanced multi-role fighter. There exists an aging fleet of tactical aircraft worldwide. The F-35 is intended to solve that problem.

With nine countries involved in its development (United States, United Kingdom, Italy, Netherlands, Turkey, Canada, Denmark, Norway and Australia), the F-35 represents a new model of international cooperation, ensuring US and Coalition partner security well into the 21st Century. The F-35 also brings together strategic international partnerships, providing affordability by reducing redundant research and development and providing access to technology around the world. Along these lines, the F-35 will employ a variety of US and allied weapons.

‘Something interesting about the first F-35s we flew is that they required chilled fuel if the temperatures on the day of flight were above 80° F,’ Earl Belz, former Flightline Quality Assurance Manager at Lockheed Martin, told The Aviation Geek Club.

‘There are several articles about it. Jalopnik explained that “The F-35 channels its strong thermal loads created by the avionics and sub-systems on-board, as well as the engine, into its fuel. The fuel works as a giant heat sink. If the fuel is already warm upon start-up, there is less capacity to exchange the heat from their aircraft’s simmering systems. Therefore the jet must shut down or risk overheating.”

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‘Chilled fuel was a requirement only for the first test articles because of the temperature on the ramp in Texas and the first flights required longer start-up and systems checking while on the ground. As explained in a post appeared on F-16.net, the fuel temperature problem of the F-35 had to do with hot fuel while the aircraft is just getting started. If you start an aircraft with the fuel already hot, the fuel acts like a heater instead of a coolant. The Environment Control System, which runs off engine power, has to deal with the surplus of heat stored in the fuel first before it can deal with the heat generated by the avionics. The problem is not just the surplus heat itself but the aircraft not flying. The ECS works off air being forced through it via the aircraft’s forward movement. With the aircraft on the ground, the ECS is operating at minimum effectiveness.

‘The F-35 haters were really playing dog pile on the doggy when they heard that the fuel had to be chilled. As your post pointed out, the SR-71 isn’t the only jet that uses fuel as a cooling agent [CLICK HERE to read our article on how the Blackbird used the fuel as a heat sink]. The F-35 is the most advanced fighter jet to date in terms of technology and that requires a tremendous amount of computing. As you know heat is the biggest threat to computers. So, as I pointed out, during the early flight tests when there was a lot time spent on the ground testing and checking, they wanted to make sure the fuel would cool the processor’s while sitting on the ramp for so long so they chilled it.’

Belz concludes;

‘They were even painting white some of the fuel trucks out in the field at hot locations in an attempt to keep the fuel cool longer.’

Photo credit: U.S. Air Force

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Dario Leone

Dario Leone is an aviation, defense and military writer. He is the Founder and Editor of “The Aviation Geek Club” one of the world’s most read military aviation blogs. His writing has appeared in The National Interest and other news media. He has reported from Europe and flown Super Puma and Cougar helicopters with the Swiss Air Force.

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