Graham Warwick Washington

What began as a program to tackle heat issues on stealth fighters is evolving into the centerpiece of a U.S. initiative to address aircraft energy demands, and leading the drive toward engineering methods based on dynamic models.

At the heart of the Energy Optimized Aircraft (EOA) national plan will be the U.S. Air Force Research Laboratory's (AFRL) Integrated Vehicle Energy Technology (Invent) program, which is developing adaptive, smart aircraft power systems using model-based design.

Invent will be one of four core technical products of the EOA plan. The program's goal is to integrate hybrid-electric systems to maximize energy efficiency, minimize thermal challenges, and provide power and cooling on demand, based on the duty cycles of individual aircraft systems.

The Pentagon's EOA plan will set the goals for a broader technology initiative to enable energy-efficient aircraft with enhanced operational capabilities, minimized thermal constraints and increased power growth capacity.

Invent and the EOA plan to address two interrelated challenges: increasing aircraft fuel efficiency to reduce Pentagon energy demands and managing thermal issues on stealth aircraft that have nowhere to dump waste heat but into the fuel. “More efficient engines shift the balance—25 percent less fuel burned is 25 percent less heat that can be dumped,” says Steve Iden, AFRL Invent program manager.

“And it will only get worse,” he says. The Lockheed Martin F-22 and F-35 have up to five times the heat load of the company's F-16, and the next generation of fighter will be the first with directed-energy weapons, which will require megawatt-class power and cooling. “All that power does not leave the aircraft. It turns into low-quality heat in the aircraft, which becomes a flying thermos bottle,” says Iden.