America's Sixth Generation Fighters: The F-X and F/A-XX - II

Part I 

Program Development Status

Image 6: Lockheed Martin YF-22 technology demonstrator 

Pentagon acquisition chief Frank Kendall reported the FY 2016 budget request will allocate funds towards the development of sixth generation aircraft under the aerospace innovation initiative. The Air Force has set aside $8 million for its next generation air dominance program while the Navy has set aside $5 million for the F/A-XX program (Parsons, 2015). However, neither of these sums represent the total budgeted amount which is under the black budget. Within the Air Force's $7 billion black research development and procurement budget, funds have been allocated towards the Defense Advanced Research Projects Agency (DARPA) which recently completed its Air Dominance Initiative study (Sweetman, Asker, Norris, & Butler, 2015). Frank Kendall estimates that $150 million to $500 million will be allocated towards the development of a sixth generation X plane over the next few years.

The aerospace innovation initiative will be led by DARPA and will produce an X plane type technology demonstrator aircraft. A senior DARPA official speaking to Aviation Week compared the current classified X plane program to the earlier Joint Advanced Strike Technology (JAST) program which produced a technology demonstrator related to the F-35. DARPA will create an aircraft with a similar size to what the services might procure, that would incorporate the desired technologies, and would be capable of flight but it would not be as mature as the YF-22 as to the F-22 in terms of program development (Sweetman, Asker, Norris, & Butler, 2015). 

Higher level defense initiatives such as the Third Technological Offset strategy, the Long-Range Research and Development Program (LRRDPP), Full Spectrum Dominance, and Better Buying Power 3.0 give some indication of how the F-X and F/A-XX programs will proceed and which technologies both planes will incorporate. Deputy Defense Secretary Robert Work, who is (in the view of the author) among the most intelligent and competent individuals within the DoD's leadership, has been tasked with leading the Pentagon's third offset strategy. The first offset strategy focused on developing US nuclear capabilities early in the Cold War and the second offset drove US investments in information technology, stealth, and guided weapons. The third strategy will seek to preserve the US' technological superiority and power projection capabilities in the face of increasingly hostile A2/AD environments posed by near peer military competitors (Work, 2014). A November 2014 press release by then Secretary of Defense Chuck Hagel stated four technologies would take priority but the list is not holistic due to classification concerns: robotics, miniaturization, big data, and advanced manufacturing. In an interview with Defense News, Robert Work outlined the objectives of the Defense innovation initiative and how LRRDPP fits in within the broader Defense Innovation Initiative and the United State's national security strategy:

"within the long range [LRRDPP], we have the advanced capabilities and deterrence panel, which is really focused on state actors. And, as part of the advanced capabilities and deterrence panel, we have similar lines of efforts, strategy, war gaming concepts. But the long-range research and development planning program is designed to tell us how we would want to use technology to gain an advantage over time...We want to remain a resident Pacific power. We want China to accept that, and over time we’re building confidence-building measures, which were just announced by the president. And, we believe that we can do this peacefully. But, we also need to hedge. They are developing certain capabilities that would be very problematic for our allies, and for us in the Western Pacific, and it is important that we create capabilities that deter their use."

LRRDPP has outline five core areas of focus: air, missile and precision guided munition defense, air superiority, space, undersea, and emerging technologies. The following technologies will be developed in the context of the aforementioned broad DoD defense innovation programs with the intent of operating in highly contested A2/AD environments: variable cycle engines, directed energy weapons, GaN avionics & electronic warfare systems, autonomous system integration, and broadband stealth. It is important to note that there are ongoing discussions within the DoD to incorporate some of these technologies into the F-35 as a means to keep it more competitive against developing threats (Sweetman, Asker, Norris, & Butler, 2015).

Sixth Generation Technologies 

Adaptive-Cycle Engines 

Image 7: General Electric ADVENT

Adaptive cycle engines have the potential to revolutionize future fighter aircraft propulsion. Adaptive engines incorporate a third stream of air within the engine which manipulates its bypass ratio enabling supercruise at more fuel efficient rates. Furthermore, the pilot has the option to exit cruise mode and significantly increases thrust as needed. Substantial progress has been made in adaptive cycle or variable cycle engines as a result of the Air Force's Adaptive Versatile Engine Technology (ADVENT) program: 

One of the key technologies behind the adaptive-cycle engine is the adaptive fan, which allows the engine to vary its bypass ratio depending on its altitude and speed due to a third stream of air. Air flows through the third stream as needed to increase or decrease the bypass ratio of the engine—or alternatively use the extra airflow for cooling. 'We can effectively vary the performance of the engine across the flight envelope,' Kenyon said. At high-supersonic speed, the third stream can reduce spill drag by letting the excess air flow through the engine—however performance above about Mach 2.2 is still limited by the physics of air inlet geometry. 'The third stream does help supersonically very much,' McCormick said. The General Electric ADVENT engine has an adaptive-fan, which creates a third stream of air, an extremely high-pressure compressor, a new combustion system, various new materials such as ceramic matrix composites and cooling technologies...the ADVENT demonstrator engine is actually exceeding expectations in many cases including for fuel burn. The fuel efficiency target for ADVENT was to reduce fuel-burn by 25 percent. The AFRL’s follow-on Adaptive Engine Technology Development (AETD) program is intended to bring the technologies developed under ADVENT into a flight-worthy design." - Dave Majumdar, 2014 

Aviation Week's Guy Norris explained sixth generation fighters equipped with adaptive cycle engines could lead to a 25%-30% increase in range and up to a 10%  increase in thrust over conventionally configured turbofan fighter aircraft. Part of the impetus behind funding variable cycle technology is the 500-600 nautical mile unrefueled combat radius of existing aircraft is insufficient in A2/AD environments, particularly in the Pacific theatre (this point will be examined in depth during the roles and missions section). However, the Navy is not as convinced variable cycle engine technology would make a valuable addition to the F/A-XX (Majumdar, 2014).The Navy should adopt variable cycle engine technology given it synergizes with many other potential technologies discussed for sixth generation aircraft. The third stream of air provides additional heat sink capacity that both reduces the aircraft's infrared signature and enables the aircraft to accommodate directed energy weapons (Norris, 2015).

Directed Energy Weapons 

Image 8: Lockheed Martin Falcon 10 test aircraft equipped with Aero-Adaptive/Aero-Optic Beam Control (ABC) laser

Despite the stigma associated with directed energy weapons as a result of the Strategic Defense Initiative (nicknamed STAR WARS), laser technology has steadily progressed since the 1980s to the point at which it is feasible for combat in limited roles. Sydney Freedburg recently explaied, "Not only have lasers gotten better, the military’s expectations have gotten lower — and the urgency of the threat has gotten higher". The Navy, Air Force, and DARPA have concurrently researched high energy aircraft mounted solid and liquid state lasers in the 100kw to 150kw range. In a request for information issued by the Air Force's Research Laboratory, the service seeks:

"The emphasis of this effort is to identify potential laser systems that could be integrated into a platform that will provide air dominance in the 2030+ highly contested Anti-Access/Area Denial (A2/AD) environments,..Laser and beam control systems are being investigated independent of platform in the flight regime from altitudes Sea Level to [65,000ft] and speeds from Mach 0.6 to 2.5,"

Should programs such as DARPA's High Energy Liquid Laser Area Defense System (HELLAD) come to fruition, it is highly likely that both the F/A-XX and F-X aircraft will be equipped with directed energy weapons. As for the tactical usage of lasers on fighter aircraft, lasers would likely be employed as defensive weapons at ranges of 10-15 nautical miles against incoming missiles or small enemy unmanned aerial vehicles. Lasers of the 150kw class can burn through the casings of enemy missiles which will cause them to veer off course or damage the missile's seeker rendering the missile unable to function (Clark, 2014). As lasers continue to improve in power, cooling, and miniaturization, it is conceivable they could be employed against enemy fighter aircraft in the far future.

"[if] a laser weapon can burn a hole through the skin of its target, success is practically assured. Aircraft with wet wings are doomed, similarly fuel cells not protected by substantial amounts of airframe structure. Missiles with solid propellant engines and warheads are also left with little potential to survive. The damage that can be done to guidance or control systems is also vast." - Karlo Kopp, 2005 

An ongoing concern with the F-35 is its limited ammo capacity for its GAU-22 at 180 rounds which fires at a rate of roughly 50 rounds per second. In contrast, lasers are only limited by power and cooling constraints rather than physical ammunition which is both a performance and logistics benefit. Further discussion on how both the F/A-XX and F-X will employ lasers will be discussed in the roles and mission section.

Image 9: Concept of Lockheed Martin ABC fitted to the F-35. Conceivably, a laser system could be fitted to the F-35 in a future upgrade.

Broadband All Aspect Stealth

Image 10: Aviation Week concept of Northrop Grumman's RQ-180. Image Credit: Aviation Week

Amy Butler reported in February of 2015 that, "[DoD] planners are considering broadband stealthiness for sixth-generation fighters—the F/A-XX for the Navy and F-X for the Air Force". Aircraft such as the LRS-B, B-2, and RQ-180 incorporate broadband stealth and do not share the potential vulnerability to VHF systems like smaller aircraft using planform alignment. Bill Sweetman explains how the RQ-180's shape enables it to achieve broadband stealth: [emphasis mine]  

A key feature of the RQ-180’s design is an improvement in all-aspect, broadband radar cross-section reduction over Lockheed Martin’s F-117, F-22 and F-35. This is optimized to provide protection from low- and high-frequency threat emitters from all directions. The design also merges stealth with superior aerodynamic efficiency for increased altitude, range and time on station. The aircraft uses a version of Northrop’s stealthy “cranked-kite” design, as does the X-47B, with a highly swept centerbody and long, slender outer wings. Northrop Grumman engineers publicly claimed (before the launch of the classified program) that the cranked-kite is scalable and adaptable, in contrast to the B-2’s shape, which has an unbroken leading edge. The RQ-180’s centerbody length and volume can be greater relative to the vehicle’s size.

It will be difficult to design a broadband stealth aircraft that is also maneuverable, none of the aforementioned broadband stealth aircraft were optimized for air dominance roles. Rather, all previously mentioned broadband stealth aircraft are intended to cruise at high altitude and perform either bombing or intelligence, surveillance, and reconnaissance (ISR) missions. Northrop Grumman is exploring a tailless concept for the F-X competition and Boeing has similarly shown tailless F/A-XX concepts. The removal of the aircraft's tail could reduce the number of small exposed flight surfaces with respect to the Raleigh scattering region but it remains to be seen if a high degree of broadband stealth is achievable in a maneuverable platform. Furthermore, the Navy and Air Force have diverging opinions on what level of stealth is appropriate for their sixth generation concepts.

CNO Greenert indicated stealth may be less of a priority for the F/A-XX when compared to its ability to suppress enemy air defenses with a high weapons payload and powerful sensors, "You know that stealth maybe overrated...I don’t want to necessarily say that it’s over but let’s face it, if something moves fast through the air and disrupts molecules in the air and puts out heat – I don’t care how cool the engine can be – it’s going to be detectable...It has to have an ability to carry a payload such that it can deploy a spectrum of weapons. It has to be able to acquire access probably by suppressing enemy air defenses". The CNO's statement is consistent with the view of several Navy officials who are skeptical of stealth which is a contributing factor in its prioritization of endurance over stealth the UCLASS' (Unmanned Carrier Launched Surveillance and Strike) requirements and the Navy's decision to slow F-35C buys in its FY 2016 budget submission (Sweetman, 2015). Unlike the Air Force which has operated stealth aircraft since the early 1980s, the Navy has had to rely on its electronic warfare aircraft to carry out suppression of enemy air defense (SEAD) missions. The Navy would have received stealth aircraft prior to 2018 if it were not for the cancellation of the McDonnell Douglas A12 and A/FX programs in the 1990s. Despite the CNO's comments, the F/A-XX will assuredly have some level of stealth but it may not have the same degree of stealth as the F-X. In contrast to the Navy, the Air Force continues to be bullish on the future of stealth and Air Combat Command's General Herbert "Hawk" Carlisle indicated stealth would be incredibly important for the F-X (Butler, 2015).

Gallium Nitride (GaN) Avionics & Electronic Warfare Systems

Image 11: Next generation jammer pod featuring GaNs components. Image Credit: Raytheon

GaN based AESAs and electronic warfare systems will revolutionize fighter avionics over the next two decades with substantial increases in performance and cooling over existing Gallium Arsenide(GaA) based arrays:

"GaN has anywhere from five to 10 times the power density, which is the amount of electrical energy a chip can handle relative to its size. A GaN chip can handle more than double the voltage and amperage of a similarly sized GaAs chip. GaN also has up to seven times the thermal conductivity of the older material, which allows it to run hotter. That means lower cooling requirements and greater amounts of electrical power. In basic terms, Rosker said, a radio transmitter based on GaN technology could put out "an order of magnitude more" power than a similar GaAs-based transmitter, or conversely, produce the same power yet take up a fraction of the volume. It could also operate over far more frequency bands...Colin Whelan, a Raytheon engineer who works on GaN technology, said a GaN-based active electronically scanned array radar could search five times the volume as a similarly sized GaAs-based radar, or at a 50 percent greater range. You could even halve the size of the radar and still deliver greater performance." - Dave Majumdar, 2011 

The addition of a GaN AESA to both the F/A-XX and F-X would greatly increase the detection range of enemy fifth generation aircraft and other low observable targets. The power of a large GaN based fighter AESA would likely result in detection ranges for targets well beyond the range of current weapons like the AIM-120D range. As the roles and missions section will discuss, the power of GaNs will synergize with the Naval Integrated Fire Control-Counter Air—or NIFC-CA concept.

As discussed previously, the emergence of more powerful radars and capable VHF radars will make the employment of electronic warfare in conjunction with stealth a necessity. Defense One's Patrick Tucker reports sixth generation aircraft will likely employ a more advanced version of cognitive electromagnetic weapons:

"Cognitive electromagnetic weapons autonomously find new wave forms to use against planes, tanks, or other threats (or, defensively, find ways to detect new wave forms being used against the system). Full spectrum dominance will mean more of that. It could include intelligence gathering equipment we can’t fathom. 'Today it’s radar but it might be something more in the future,' said Adm. Jonathan Greenert, chief of naval operations, at the expo. Tomorrow’s innovations in radar, jamming and sensing, will emerge from a variety of research outfits but particularly the DARPA Microsystems Technology Office, MTO, designed specifically to tackle those sorts of problems."

Autonomous and semi-autonomous sensors and components, such as cognitive electromagnetic weapons, will be a prominent feature of both the F-X and F/A-XX.

Unmanned & Autonomous System Integration

Image 12: DARPA Collaborative Operations in Denied Environment (CODE) concept

The DoD has hinted at an "optionally manned" F-X or F/A-XX. While there is certainly an institutional desire to leverage the United States' advantage in unmanned systems as part of the third offset strategy, particularly in the Air Force, the possibility of the next sixth generation fighter being fully autonomous is minimal. However, some form of artificial intelligence that integrates sensors and information is plausible and the addition of systems that would facilitate the operation of manned and unmanned systems is a near certainty. Both the Air Force and Navy are looking at integrating  Unmanned Combat Air Vehicls (UCAVs) with fighter aircraft.

USAF Col. Michael W. Pietrucha published, "The Next Lightweight Fighter - Not Your Grandfather’s Combat Aircraft" in which he argued the Air Force should procure a low cost UAV which would act as a force multiplier for manned fighter aircraft. Advances in datalinks would enable UAVs to act as "missile trucks" for the sixth and fifth generation assets which would provide targeting information. The additional supply of air to air missiles provided by UAVs would be advantageous given the limited probability of kill (pk) of most air to air missiles in a digital radio frequency memory (DRFM) jamming environment. Half a dozen Air Force officials interviewed by the Daily Beast stated they expect the pk of the AIM-120D to be reduced by DRFM jammers such that two to three missiles will be required to destroy a single target. Lieutenant General Ellen Pawlikowski is tasked with the Air Force's R&D, procurement, and modernization programs; she is a staunch advocate for usage of UAVs similar to what is described above, "I can see a scenario where you’ve got an F-35 orchestrating an attack with 20 RPAs [remotely-piloted aircraft] that are weapons-equipped and that F-35, with all its sensors and communications, is essentially an orchestrator".

DARPA's CODE program will facilitate the integration of semi-autonomous UAVs with manned assets in contested A2/AD environment's:

"Just as wolves hunt in coordinated packs with minimal communication, multiple CODE-enabled unmanned aircraft would collaborate to find, track, identify and engage targets, all under the command of a single human mission supervisor...CODE aims to decrease the reliance of these systems on high-bandwidth communication and deep crew bench while expanding the potential spectrum of missions through combinations of assets—all at lower overall costs of operation. These capabilities would greatly enhance survivability and effectiveness of existing air platforms in denied environments." -Jean-Charles Ledé, DARPA program manager

As for specific UAV platforms that could serve in this role, a high end requirement UCLASS, configured QF-16 (unmanned target drone variant of the F-16), and optionally manned variant of the F-35 are all possible candidates. DARPA has already discussed the possibility of using an aircraft like the QF-16 in an air to ground role (Bell, 2014). It is plausible that with further modifications Boeing could permit the QF-16 to integrate with manned platforms via datalinks like the advanced tactical data-link (ATDL) or tactical targeting network technology (TTNT) waveform. With respect to an unmanned F-35, Lockheed Martin's Skunk Works has neither confirmed nor denied working on an optionally manned variant of the F-35. Once sufficient economies of scale has been reached with respect to F-35 air frame production, an optionally manned variant could become more feasible in the future. 

Part I - The Need for 6th Gen. and 2030 A2/AD

PART III - Roles and Missions 

PART IV - Works Cited