General Electric and Pratt & Whitney have been selected over Rolls-Royce for the U.S. Air Force Research Laboratory’s Adaptive Engine Technology Development (AETD) program to mature fuel-efficient, high-thrust powerplants for post-2020 Lockheed Martin F-35 upgrades and sixth-generation combat aircraft.

Selection for negotiations is a coup for Pratt, which in 2007 lost out to GE Aviation and Rolls-Royce North American Technologies for the precursor Adaptive Versatile Engine Technology (Advent) demonstrator program.

“When we were not selected for Advent, we did a lot of our own rig work,” says Jim Reed, Pratt director of advanced engine programs. “But that only mattered if we were selected for AETD. We had to build a strong proposal.” Substantial industry cost-sharing is expected in the AETD demo.

Where Advent is demonstrating high-pressure core and adaptive-fan, “third stream” low-pressure system technology to reduce combat-engine fuel consumption by 25%, AETD will fully mature adaptive engines for possible early entry into engineering and manufacturing development (EMD).

GE’s Advent core will begin testing shortly and Rolls’ core is to follow in December. Both companies plan to run full-engine demonstrators by the middle of next year.

Pratt, meanwhile, will deliver an adaptive-fan test rig — developed largely on company funds — to AFRL in the spring “to jump-start us [on AETD],” Reed says.

Rolls declined to comment on its failure to be selected for AETD, referring all questions to AFRL, which will discuss the engine program Sept. 18 at the Air Force Association convention in Washington.

The 48-month AETD has four goals. The first is to design a new combat-aircraft engine with 25% lower thrust-specific fuel consumption, but 5% more military power and 10% higher maximum thrust than the Pratt F135 now powering the F-35.

“We will take that engine through preliminary design review,” Reed says. The engine must be sized to fit in the F-35 with “only modest modifications,” he says.

The next step is to fabricate and test the high-pressure core for that design, incorporating technologies from the latest commercial-aircraft engines.

The third goal is to test third-stream flow delivery into a stealthy, serpentine exhaust system. Such a nozzle is not part of the Advent demo program, which will use a slave exhaust.

The third stream — an additional flowpath outside the core and bypass duct — will be closed at takeoff for high thrust but opened in cruise to reduce fuel consumption and inlet spillage drag and increase cooling-air supply to the aircraft, engine and nozzle.

The fourth goal of AETD “is to do a host of studies with the airframers on where you can use this core,” Reed says.

Phase 1 of the AETD program, which runs through mid-fiscal 2015, includes completing preliminary design and testing annular-combustor and high-pressure compressor rigs, as well as components using ceramic matrix composites.

Phase 2 of the program, which will conclude in fiscal 2016, consists of fan rig testing and an engine core test, allowing for a notional first full engine test as early as 2017.

In addition to a possible long-term F-35 upgrade, the focus is on powering possible future U.S. Air Force and Navy sixth-generation fighters. The Navy is looking at a notional in-service date of 2028 and the Air Force at 2032.