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The F-35's legs might not be long enough

The Air Force's F-35A Lightning II may debut with a range just under its required minimum, as John writes over at Defense Tech, where he quotes a new report and the indispensable Steve Trimble in explaining why. Basically, they say, the airplanes are running hotter than predicted and with more drag, so they require more engine power and, as such, reduce the distance the jets can fly.

Although it sounds like another strike against an already checkered program, this might not be that big a deal: Combat aircraft seldom test their maximum ranges in the real world, especially when they're loaded with weapons, external fuel tanks or sensor pods. Usually, they gas up in mid-air multiple times during a typical mission, with pilots always keeping an eye on having enough reserve fuel just in case. And by the time the Air Force's fleet of F-35s is flying in numbers, the service hopes to also have a brand new fleet of KC-46As to keep them fueled up.

Still, no pilot will just laugh it off when you tell him his aircraft doesn't have as much range as you first thought it did. Engineers think they can continue to improve the F-35A's legs, as Trimble writes:

One simple change under review is a software tweak that would maximise the amount of fuel taken onboard during in-flight refuelling. Another relatively simple fix is to raise shut-off valves higher inside the fuel tank to create slightly more capacity, a source said, adding: “That gets you back a lot of the fuel that you need to recover” to meet the range mandated by the contract.

A more complex solution also being considered is to install new fuel tanks in a small number of hollow spaces within the aircraft’s structure.

But programme officials are also debating whether to change how the range of the F-35A is calculated, the source said. The equation does not include a buffer margin of 5% of fuel capacity, which is intended to be preserved through the end of the flight test period in 2016. Eliminating the buffer margin adds another 72.4km to the aircraft’s combat radius, the source said.

There's another way to make a distance problem go away -- change the yardstick. Show Full Article

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