Pratt Forges Ahead With F-35 Engine Upgrade Plans, Eyes Next Gen
Jun 5, 2017 Lara Seligman and Guy Norris | Aviation Week & Space Technology
Pratt & Whitney reached a new milestone in its road map for upgrading the F135 turbofan that powers the Joint Strike Fighter, and is looking to leverage that success to help secure the next generation of fighter propulsion.
The engine maker recently completed key tests of a proposed core upgrade package for the F135, confirming the potential for substantial fuel savings and higher thrust as soon as 2020. Crucially, the improved performance would come at a reasonable price to the U.S. government; the upgraded powerplant is “cost-neutral” from a procurement perspective, says Matthew Bromberg, president of Pratt & Whitney Military Engines.
But the F-35 is planned to fly far beyond 2020—until 2070, if recent Pentagon estimates prove correct. The fighter will need an engine that can keep pace with technological advancements for the next five decades. For now, as prime contractor on the F-35 powerplant, Pratt has a foothold in current and near-term U.S. fighter propulsion. But as threats and technologies evolve, that may change.
PATH AHEAD FOR F-35 ENGINE
Pratt and Whitney’s GO 1.0 upgrade promises 6-10% more thrust and 4-6% fuel-burn reduction
Upgrade package would be “cost neutral”
GO 2.0 would incorporate additional adaptive engine technology in development through AETD/AETP
Adaptive architecture seen as “umbrella” for future fighter propulsion
Both Pratt and General Electric are working under the U.S. Air Force-led Adaptive Engine Technology Demonstration (AETD), as well as the follow-on Adaptive Engine Transition Program (AETP), to test technology for a new generation of fighter engines. Under AETP, Pratt and GE are developing demonstrators—Pratt’s XA101 and GE’s competing XA100—to pave the way for an adaptive, 45,000-lb.-thrust-class combat powerplant, as well as the possible reengining of the JSF.
Hoping to stave off competition from GE and other engine makers, Pratt has framed its F135 upgrade effort as the first step in a long-term plan for fighter propulsion based on adaptive engine technology. That not only refers to the three-stream adaptive cycle that industry is developing, but also adaptive controls, an adaptive sustainment system and eventually perhaps an adaptive core that can handle unique operating pressure ratios, Bromberg says.
Pratt’s F135 modernization plan is envisioned as a seamless bridge to a next-generation fighter engine—the initial core upgrade package, or Growth Option (GO) 1.0, is just the first step.
“As each upgrade becomes available, we will look at taking the elements of that architecture suite and inserting that into the motors as available,” says Bromberg. “Adaptive architecture is the umbrella for the future of fighter engine propulsion, and Growth Option 1.0 will be the first incarnation of upgrading the JSF.”
GO 1.0 represents the first phase in a two-stage improvement road map scenario for the F-35 engine first unveiled in 2015 and promising 6-10% more thrust and a 4-6% fuel-burn reduction (AW&ST April 13-26, 2015, p. 26). It builds on a suite of core technologies evaluated since 2013 under the U.S. Navy-sponsored Fuel Burn Reduction (FBR) program. It also incorporates design improvements developed by Pratt under earlier technology programs including the Air Force-supported component and engine structural assessment research, known as Caesar, which focused on the F135’s predecessor, the F-22’s F119 engine.
Evaluation of the package, which is focused on the high-pressure compressor, turbine and combustor stages, was done using testbed engine FX701-01 at Test Site A3 at Pratt’s West Palm Beach, Florida, facility. Although not a program of record for the F-35, Pratt says risk-reduction work performed on the test rig has proved GO 1.0 can be executed as a low-cost means of improving the aircraft’s range and acceleration.
“We feel very confident that we could launch a program, complete the testing and EMD [engineering, manufacturing and design], and have a production change or retrofit available by 2020,” explains Bromberg. If given “the green light” to begin work on a formal improvement package this year, Bromberg says the development would align with the JSF’s planned Block 4.2 upgrade.
Pratt believes GO 1.0 is attractive to the F-35 community, primarily due to affordability. After the “relatively short” EMD program, the U.S. government would have to swap out the old engine for the new, upgraded system across the fleet, but that could be accomplished on an attrition basis during scheduled depot maintenance.
“We could cut it into production and we could cut it into depot retrofits . . . if you did it on an attrition basis when you are replacing hardware anyway, the cost of the hardware is roughly the same,” Bromberg points out. If the government decides to force a retrofit, it must pay for the core module, but that would be “the incremental cost.”
A key advantage of GO 1.0 is that it fits into the existing sustainment structure for the F-35, including the troubled Autonomic Logistics Information System (ALIS) that provides the maintenance backbone of the fleet. Lockheed Martin has encountered challenges integrating the Pratt engine into the latest ALIS iteration, 2.0.2, and just started delivering the new system to the fleet in April.
“It’s just a drop in part number change and suite of health management tools that will go right into ALIS, so [there are] no changes to ALIS” aside from updating part changes and the new health-monitoring algorithms, says Bromberg. “If you go to a new core it’s an entirely new engine. It requires an entirely new instance of ALIS or a complete upgrade.”
In addition, GO 1.0 is “variant common,” so it can be dropped into any of the three U.S. JSF variants or partner aircraft, Bromberg says.
The second phase of Pratt’s F135 road map, GO 2.0, would incorporate additional adaptive engine technology features in development through Air Force and Navy-supported initiatives, primarily including AETD and AETP. Both Pratt’s XA101 and GE’s XA100 are initially sized for potential application on the F-35.
GO 2.0, which also could include elements of the Navy’s variable cycle advanced technology program, would introduce more radical changes including adaptive features in the low-pressure compressor and turbine. Pratt has said the second upgrade phase has the potential to generate a thrust improvement of up to 15% and as much as a 20% reduction in fuel burn. It could be developed in the next “4-8 years” depending on the timing of the first upgrade and the continuing development of the AETP, Bromberg says.
Similarly Pratt also sees potential for elements of GO 1.0 to pave the way for elements of XA101.
“The primary purpose of the FBR is to test the core, the geometry and the coatings. We feel good about it and it reduces the risk of Growth Option 1.0. But definitely some of the technologies in that core are directly applicable in terms of growth materials and aerodynamic geometry, and that will go into XA101,” Bromberg explains.
Meanwhile, Pratt has started tests of a three-stream fan mounted on an F135 under AETD and is poised to begin evaluation of an all-new core to prove the technology at the heart of its future adaptive engine. The core run is “in front of us, and is further risk reduction for the XA101 program,” says Bromberg. The three-stream fan test engine also is configured with a specially modified augmenter and exhaust system to handle the adaptive-cycle flow demands.
At its core, Pratt’s overall strategy is to provide options for whatever path the Air Force chooses.
“We have this umbrella strategy of adaptive architecture and we will start proving out the technologies one by one,” Bromberg says. “We are trying to provide options to spiral them in at relatively low-risk, low-cost programs.”
PHOTO
ratt & Whitney is proposing an initial upgrade package for the F-35 engine that promises fuel reductions of up to 6% and as much as 10% higher thrust as soon as 2020. Evaluation of the package, which is focused on the high-pressure compressor, turbine and combustor stages, has been undertaken using testbed engine FX701-01 at Test Site A3 at Pratt’s West Palm Beach, Florida, facility. Credit: Pratt & Whitney
