Improved jet engines are key to longer range sixth gen fighter and improved F35
brian wang | August 25, 2017 
The US Air Force is finalizing technology requirements for a new fighter jet to enter service sometime in the 2030s. Known as “Penetrating Counter Air,” the new fighter will replace the F-22 Raptor and maintain American air superiority in future conflicts.
* US Air force developing concepts for replacing the Lockheed F-22 after 2030, which includes updating existing designs with new technology.
* Re-engining the F-35 with an adaptive cycle, 45,000lb-thrust engine.
The U.S. hasn’t designed a clean-sheet fighter in twenty years, and Penetrating Counter Air (PCA) will differ from the F-22 and F-35 in some ways to deal with new strategic realities. PCA will emphasize range to fly escort missions for B-2 and B-21 bombers over Russia and against China in the Asia-Pacific.
The Air Force hopes for the best of both worlds with so-called “three-stream propulsion,” which uses a third air stream to make the engine more efficient or provide more thrust.
PCA will also be stealthy, and likely lose vertical tail fins that are standard on all aircraft, from the P-51 Mustang to the F-22 Raptor.
Funds are being requested to create a new super missile – Air Dominance Air-to-Air Weapon to replace the 30 year old AIM-120 AMRAAM.
Future engines are the key
The Air Force Research Laboratory has been working with GE and Pratt and Whitney on adaptive, “three-stream” engine technology for several years, under a science and technology program called Adaptive Engine Technology Development (AETD).
Fixed-cycle engines powering today’s military aircraft are limited to one capability: either maximum power or fuel efficiency. The adaptive engine concept enables new engines to switch between the two. Where most fighter jet engines have two “spools” of air, the adaptive engine design adds a third stream around the outside of the engine. By changing that air stream, engineers can adapt the engine to get optimal performance throughout the flight envelope.
“It’s like shifting a gear in your car, shifting a gear on your bicycle,” Kenyon explained. “You change the way the machinery works together so you match the conditions you are running out.”
The AETP funds building and test full-up engines. AETP program should boost fighter and bomber engines by 20% thrust and 25% fuel efficiency and range by 30% in mid-2020s.
In 2016, GE Aviation was awarded a $1billion contract to continue maturing its three-stream adaptive cycle engine via the Adaptive Engine Transition Program (AETP). AETP is scheduled to run through 2021 with extensive component, rig and engine testing.
In June 2017, Pratt and Whitney has unveiled a development pathway for thrust growth, fuel-burn reduction and other improvements in the F135 engine powering the F-35 Lightning II Joint Strike Fighter (JSF). It could result in the U.S. armed forces fielding improved versions of the basic F135 for land-based, STOVL and carrier-based F-35s as early as 2020.
Pratt and Whitney sees its F135 development pathway as essentially a two-step program, which would result by the mid- to late-2020s in an entirely new engine employing a third airstream, which would allow both an adaptive-cycle compressor and an adaptive-cycle turbine and also would allow weapons-system cooling technologies.
Steven Burd, P&W’s chief engineer for advanced programs and technology, said an additional intermediate step could allow further improvements to be made—beyond the first upgrade step—to the substantially modified F135 engine-and-lift-system combination that powers the STOVL (short take-off, vertical landing) F-35B flown by the U.S. Marines and the British Royal Air Force.
These new technologies offer a 5 to 6 percent fuel-burn improvement and a thrust bump of 6 to 10 percent over the F135’s 40,000-pound validated maximum-thrust, throughout the F-35’s flight envelope.
P&W may already have run its three-airstream AETP adaptive-cycle fan and core in a demonstrator engine. When asked if P&W had already done so, Bromberg declined to say ‘yes’ or ‘no,’ but, he added, “We will be announcing the results of tests in the near future. We feel very good about where we are.”
