Adaptive Engi nes irpower is nothing with- air vehicles and applications,” Steven H. strike aircraft, bomber aircraft, tactical out propulsion, and this Walker, then deputy assistant secretary of aircraft.” A summer, USAF made a the Air Force for science, technology, and The potential for an adaptive, variable $213.6 million down payment on its fu- engineering, testified in February. cycle engine is enormous. As Walker said, ture by launching a new Adaptive Engine fuel efficiency buys range in combat. As Technology Development (AETD) re- Exciting Advances a result, a new engine family “will also search program. With the adaptive engine “This effort really does leverage off increase the unrefueled range for several program, USAF is laying the foundation of some fairly exciting technological platforms engaged in [anti-access, area- for a new class of engines that go beyond advances” and opens the door to “all of denial missions],” he said. the limits of today’s fixed cycle engines. industry that may want to participate,” Take the case of a future long-range The goal is clear: Demonstrate a variable testified Gen. Janet C. Wolfenbarger bomber powered by a new adaptive en- cycle propulsion system enabling a 25 in May. gine. Adaptive technology opens up the percent or greater specific fuel consump- “This engine could be used in a whole possibility for fuel savings that could be tion reduction. host of platforms should it ever reach the utilized in many ways: lighter vehicle Senior officials say that success in point of being a development program,” weight, supercruise dash while preserving adaptive engine technologies can deliver said Wolfenbarger, who was then USAF’s fuel efficiency, and of course, a longer better range, persistence, performance, three-star military deputy for acquisition. combat radius. and energy savings for multiple types of “Right now, it’s just a question of ensuring Flying a segment at higher speed— combat aircraft. that we are ready to go, should we as an without a big fuel penalty—could help “AETD technologies are expected to Air Force decide that we want to embrace bomber aircrews get from a theater base improve fuel efficiency, durability, and this opportunity to really reduce the fuel to the target area for faster response thrust performance for a wide range of consumption in future generations of ... time. Then they could use the variable The Air Force hopes an adaptive engine can give fighters new gains in performance and efficiency. 62 AIR FORCE Magazine / September 2012 Adaptive Engi nes By Rebecca Grant cycle engine to add bursts of speed for a tactical dash through enemy SAMs and fighters to get to the target and out safely. In short, the investment in adaptive engine technology has the makings of a game changer. The funding commitment comes as overall spending on RDT&E accounts is heading for a 10 percent decline from Fiscal 2012 through 2016, according to the DOD comptroller’s budget tables. In recent years, rapid acquisition for USAF photo by TSgt. Justin D. Pyle immediate war needs took top priority. An F-22 in afterburner. Today’s high-performance combat engines date to the 1990s, During this time, USAF kept alive a when the F119 engine was selected for the Raptor. five-year engine research program run by the Air Force Research Laboratory. Two decades have passed since the was selected for the F-22 fighter. The from long production runs, and carry Air Force introduced the current family production F119 later became the basis over to commercial applications. of high-performance combat engines, for the F135 engine for the F-35 strike A good example was the GE F101. This which dates back to the early 1990s, fighter. 30,000-pound-thrust engine was designed when the Pratt & Whitney F119 engine However, the technologies leading in 1970 for the original B-1 bomber to the F119 took root in research that program. When the Air Force restarted began in the late 1960s and 1970s. The the B-1 program in 1981, GE tweaked backstory sheds light on why investing the engine to become the F101-GE-102 in long-term research on propulsion is and the Air Force ultimately bought 469 so important. of them for the bomber. Decades ago, aircraft programs drove engine development. Radical designs From B-1 to U-2 such as the SR-71’s Pratt & Whitney A nonafterburning version of the engine Artist’s conception by Erik Simonsen J58 engine and the General Electric J93 became the F118 for the B-2 bomber, designed for the supersonic XB-70 Val- which first flew in 1989. Then it morphed kyrie bomber—both capable of Mach 3 into another derivative to power the flight—highlighted this period. upgraded U-2R as the F118-GE-101 in With a steady flow of aircraft pro- a 1990s program. grams under way, engine development The F101 fed a big commercial suc- was robust. “The 1960s were glory days cess, too. In 1974, after much political of aircraft engine development,” found wrangling, GE set up a 50-50 joint venture authors William S. Hong and Paul D. company with the French firm Snecma to Collopy in a case study of jet engine produce the CFM56 family of engines. development published in the fall 2005 The CFM56 was based directly on the issue of the Journal of Propulsion and F101 core. Part of the deal was a royalty Power. An average of one new engine payment to the US to compensate for the per year was introduced in the 1960s. F101 technology flow. By 2011, the joint Engines were developed as complete venture had delivered more than 22,208 products with research advances taking CFM56 family engines to worldwide place inside the scope of the engine work. customers. “Every program provided opportunities Even in the midst of plenty, USAF pro- to develop new components, explore pulsion managers noticed the innovation new material temperature capabilities, curve was leveling. Already it was taking and work in new aerodynamic regimes,” longer to develop new engine technology they wrote. When a new engine debuted, than to design airplanes. An adaptive, variable cycle engine it was usually produced in quantity and The Air Force stepped in with a series could be used on a host of airplanes. often modified over time. This allowed of long-term research and development Shown here: an artist’s illustration of a engine innovation to piggyback on programs to maintain continuous effort hypersonic aircraft. aircraft development programs, benefit on breakthrough propulsion technologies. AIR FORCE Magazine / September 2012 63 the F117 engine for the C-17, the buy is largely complete. Even the buy of the F135 for the single-engine F-35 variants is unlikely Pratt &Whitney photo to top more than 3,000 engines over two decades. The military engine market has collapsed into a prestigious but tiny niche. Since market forces alone won’t drive the kind of research needed for combat applications, what are the incentives to continue advanced propulsion develop- ment? The Air Force answer has two parts. One is continuing to take the lead for the basic work toward the revolutionary performance enhancements that are now within reach. The second is finding common areas of interest between commercial and combat designs, such as fuel efficiency. The F135 engine—shown here in a test—powers the F-35. It is a derivative of the F119 that powers the F-22, so it, too, has its origins in the 1990s. The Air Force has maintained its leadership role in engine research and development through the 2000s. Final The first of these began in the 1960s. It Next came the Integrated High Per- research under IHPTET showed that was called the Advanced Turbine Engine formance Turbine Engine Technology engineers were on the cusp of advances Gas Generator (ATEGG) project, which initiative. Like other programs before in efficiency and refinements pointing took a different path by focusing not it, IHPTET deliberately reached for new toward adaptive engine technology. The on a specific engine but on component technology breakthroughs. Program man- Air Force Research Laboratory planted technologies: materials, fan, compressor, agers set an ambitious goal of doubling more seeds of innovation with a batch of modeling of the engine environment, engine thrust-to-weight ratio. The initia- no-fuss engine research projects under yet and so on. tive was active from 1987 through 2005. another acronym: VAATE, or Versatile Seeding funds to industry advanced The Joint Advanced Strike Technology Affordable Advanced Turbine Engines. propulsion teams was essential to the (JAST) program, which begat the F-35, “After the success of IHPTET, we strategy. The USAF propulsion direc- carried out engine work within IHPTET. faced an uphill battle bringing VAATE torate in Air Force Systems Command Money came from both industry and on board,” the first VAATE program funded research study and work at all government. manager, Larry Burns, told Flight Global the major engine makers of the day. in 2007. According to Burns, “People A sample of the kind of work done On Their Own believed turbine technology had peaked under ATEGG was a 1969 report on The ... commitment to IHPTET was a and asked why we needed another mul- diffusion titanium bonding and other major step for both the government and tiyear program. It was a fierce battle to material topics by Frederick G. Groh the engine companies with respect to convince military planners to put research of Pratt & Whitney. The work was programs and funding stability,” observed and development money into technology funded by USAF’s Aero Propulsion Hong and Collopy. for next generation turbine engines.” Lab’s longtime chief of the Turbine The Air Force was fortunate to have AFRL won the battle.