In 1986, a team of Lockheed engineers at the Skunk Works gathered around a board to invent what became the F-35 Lightning II.

At the time, of course, these engineers had no idea that the fruit of their brainstorming would lead to a contract award 15 years later for the most expensive weapons system in history.

Back then, their brief from the US Defense Advanced Research Projects Agency looked to be impossible.

For decades, militaries across the globe had ambitions to develop a fighter that could operate without a runway. The only viable contender to emerge was the British Aerospace Harrier, later adapted for the US market in collaboration with McDonnell Douglas.

But DARPA had raised the bar: could the Skunk Works design a vertical/short take-off and landing fighter that was as fast as an F-16 and as stealthy as an F-117?

Despite several attempts, nobody had developed a supersonic contender, much less one that was also invisible to radar.

But DARPA had come to the right place. In keeping with Skunk Works tradition, the team led by Paul Bevilacqua took a lateral approach to solving the problem.

As recounted in a 2009 paper by Bevilacqua in the Journal of Aircraft, the team used a design method known as forced associations.

They made three different lists: all the ways to extract power from hot exhaust gas, transfer that power to other parts of the aircraft, and translate it into thrust. Then, they picked the best option from each list: a gas turbine, a shaft and a lift fan. By combining them together, they discovered the core technology at the heart of the F-35B.

Six years later, the head of the US Air Force’s Air Combat Command came to the Skunk Works with an unfunded requirement to replace the F-16.

By then, the shaft-driven lift fan concept had evolved into a conceptual fighter design. To their surprise, the Skunk Works staff discovered that when they replaced the lift fan behind the cockpit with a fuel tank, the overall weight only changed slightly.

For the first time, Lockheed could propose a supersonic, stealthy STOVL fighter that could be adapted to a conventional take-off variant with no change in mid-mission manoeuvre performance.

With the Skunk Works unit having just marked its 75th anniversary, the legacy of founder Clarence “Kelly” Johnson appears to be in good hands.

Source: Flight International