Modern aircraft are equipped with so much technology that they are effectively flying computers. The Lockheed Martin F-35 is no exception. The multi-role combat aircraft is packed with sensors that enable it to detect threats and flight computers that allow it to perform maneuvers that would have older 'legacy' jets dropping from the sky.
Cameras around the aircraft feed images to a display in the pilot's headgear, making it possible to 'see through' the plane. The complexity of these systems involved a lengthy development process, but the F-35 is now beginning to enter service with militaries around the world, including the US, UK, Italy and Japan.
Among the F-35’s groundbreaking features is its battery. It is the first military aircraft with a lithium-ion (Li-ion) backup battery for mission-critical roles, such as providing emergency power for the F-35's flight-control surfaces. The technology will change the way military aircraft are made by providing high-power backup with much lower weight.
The F-35's maneuverability is down to digital technology that intelligently adapts the flight controls – the flaps, rudder and horizontal tail. Test pilot Colonel Arthur Tomassetti told Air & Space Magazine: "You are telling the airplane to go up or down, speed up or slow down, go left or right. And the computers figure out what’s the best way to do that, and they’re going to move the flight controls to do it. And the interesting thing is, they may not do it the same way twice."
If part of the plane is damaged, for example, then the control systems are intelligent enough to know that the plane needs to compensate. And if something goes wrong with those systems? That's where the battery comes in – or one of them. The F-35 actually has two Li-ion batteries made by Saft, one of 270V and one of 28V. The 270V battery can power the flight-control systems if the aircraft loses power. It's also used to start the engine on the ground, or restart it after an in-flight emergency.
The other battery provides backup power to the plane's electrical systems – vital in an aircraft as technologically advanced as the F-35.
Of course, a backup battery is standard for any aircraft. It's the use of Li-ion batteries that makes the F-35 different. When Saft became involved in the project in 2003, it was clear that the aircraft needed a cell that was small and light, but with good energy density.
Saft was already working on Li-ion batteries with the space industry. Launching a spacecraft is expensive, so the lowest possible weight is a priority. The defense sector was more cautious and particularly concerned about safety. If the battery is hit by a bullet, for example, will it catch fire?
However, the advantages were clear. Li-ion provides not just a smaller battery, but one that is lower maintenance and capable of delivering high power in low temperature conditions. The batteries went through a rigorous qualification process to ensure that safety, reliability and performance would meet military standards. The US Navy, in particular, had a stringent testing system because the planes will operate onboard aircraft carriers.
Saft delivered the first F-35 battery in 2006 and production began in 2009. Around 700 have now been made, most of which are already in use. The battery technology has continued to improve – the development process for the F-35 was so long that Saft was able to update the batteries to a newer version.
The improvements made along the way also fed into Saft's work in Formula One racing. There, in contrast to the long lead times of the defense sector, the emphasis is on pushing the limits of performance every year. However, some of the most demanding applications that Saft is currently working on use the experience gained from developing batteries for the F-35.
The F-35 has been a pioneer in battery technology, and with size and weight being key constraints on military aircraft, it is safe to assume that Li-ion batteries will soon be standard in the sector. They are becoming more common in other parts of the military, too; the US Navy’s DDG-1000 stealth ship and the Joint Light Tactical Vehicle, due to enter service with the US military in 2019, both include Li-ion batteries.