Advent by DARPA

Graham Warwick Washington

There is no guarantee that the next generation of U.S. tactical aircraft will be fielded, as hoped for, some time around 2030. Instead, the adaptive engine and system technology now being developed will find its home first in upgrades to the Lockheed Martin F-35, the only U.S. fighter in production through the 2020s.

Although aimed at the “next-generation air dominance” platforms being eyed by the U.S. Air Force and Navy, the closely related Advanced Versatile Engine Technology (Advent) and Integrated Vehicle Energy Technology (Invent) programs led by the Air Force Research Laboratory (AFRL) are structured to spin off upgrades for the F-35.

And while the F-35 provides a reason to mature adaptive technologies sooner rather than later, the Pentagon is launching a prototyping initiative for the next fighter that includes using the latest automated design tools, modeling and simulation to reduce the chances of inefficient development.

In an early October memo to the Air Force and Navy, Frank Kendall, undersecretary of defense for acquisition, outlined plans to begin exploring next-generation air dominance concepts, leading to a prototyping program to be completed within five years. The program is to begin with an 18-month concept definition effort funded by the Defense Advanced Research Projects Agency (Darpa), says the memo obtained by Bloomberg News.

“It is not too early to begin consideration of the next generation of capability that will someday complement and eventually replace the F-35,” Kendall says in the memo. “In addition, the F-35 has been the only high-performance vehicle in development in the U.S. for approximately a decade … and I am concerned that our ability to design cutting-edge platforms of this type is already atrophying.”

The effort will be an opportunity for design teams to apply the adaptive technologies and model-based tools being developed under programs like Advent, Invent and Darpa’s Adaptive Vehicle Make. AFRL has already selected General Electric and Pratt & Whitney to demonstrate variable-bypass, adaptive-fan engines under the follow-on to Advent, the Adaptive Engine Technology Development (AETD) program.

GE and Pratt will run fan, core and nozzle rigs in 2016, allowing for a notional full engine test as early as 2017. Although intended for a next-generation stealthy, supersonic-cruising fighter, the AETD engines must be designed to fit in the F-35, providing 5-10% more thrust with a 25% reduction in fuel consumption over the current engine.

The Invent integrated ground demonstration, meanwhile, is also planned to culminate in 2016, around the time the initial system upgrades developed under Invent Spiral 1 could be finding their way into production F-35s. One of those upgrades, the capability to calculate the F-35’s remaining thermal capacity in real time, is at the heart of Invent’s drive to move the industry to using dynamic models and away from static specifications.

Being developed under a Phase 2 small-business innovative research contract with PC Krause and Associates, the real-time thermal capacity algorithm “will allow the pilot to know if he is adding heat to the fuel versus cooling it, to know if he is jeopardizing the mission,” says Sam Septembre, a senior analyst with the Navy’s futures branch. If too much heat is being added, the pilot could climb to a higher altitude to let the fuel cool down. The capability could be in the aircraft within 3-4 years, he says.

Initially the algorithm, derived from detailed models of the F-35 thermal-management system and designed to adapt to changing environmental and mission conditions, would be used in the preflight mission planning system. Later the aircraft fuel tank would be instrumented and a gauge in the cockpit would show if heat is being added or rejected, allowing the pilot to take an active role in thermal management.

Spinning technologies off to the F-35 while continuing toward development of an energy-efficient, sixth-generation fighter with high-power capacity and no thermal constraints will be key to sustaining industry’s capabilities over the next decade. Without a “meaningful opportunity for leading-edge design, build and test,” says Kendall in his memo, the U.S. capability to design high-performance aircraft “will not be preserved, and our technological advantage in [air dominance] will not endure.”

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