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Sunday, July 31, 2016

Building the F-22C "Super Raptor": Improvements Part - II

While the F-22 is unambiguously the most lethal air-to-air platform in existence, the F-22 was designed during the 1980s and 1990s under a different threat and technological environment. Namely the F-22’s antiquated internal computing capabilities, software, limited combat radius, and high maintenance requirements degrade the utility of the F-22 within the context of operating in the Asia-Pacific against increasingly capable great power threats. Part II will examine these deficiencies further in preparation for an analysis of what features an F-22C could include which would both correct these shortcomings and add new capabilities to the F-22 airframe in Part III.

1980s Hardware & Software

Image 1: F-15C cockpit vs. F-22A. F-15C image courtesy of Eagle.RU forums. 

            The avionics suite of the F-22 is among the most capable of any fighter in service in terms of raw performance, the AN/APG-77 active electronically scanned array (AESA) and ALR-94 radar warning receiver (RWR) provide unmatched active and passive detection capabilities. Data collected from the F-22’s avionics suite are fused and presented on six liquid crystal displays in the cockpit providing unmatched situational awareness when compared to primarily analogue switches and cathode ray tube based displays within 4th generation cockpits. However, the original internal computing hardware and software that manages the F-22’s avionics are obsolete.

Image 2: F-22 internal computing systems. Image Credit: F-22 avionics handbook, Ronald Brower, 2001. 

            Two Hughes Electronics designed common integrated processors (CIP) provide the computing backbone of the F-22 avionics and flight systems which enable dissemination of radar, communication, electronic warfare, and systems data.[1] The CIP is a modular design composed of 66 Standard Electronic Module Size – E (SEM-E) units each which are in turn connected to Dual Data Processing Elements (DDPE) on each side of the SEM-E units; the DDPEs feature two 32-bit, 25-MHz, Intel 80960 (i960) processors which collectively provide the bulk of the F-22’s processing capability to support its integrated avionics suite.[2] Polyalphaolefin liquid coolant provides thermal management for both the CIP racks and AN/APG-77 radar. Each CIP is capable of computing 10.5 billion calculations per second and have a maximum memory capacity of just 300 megabytes each. The software which runs the F-22’s hardware is equally dated.

Image 3: F-22 CIP. Image Credit: Hughes Aircraft Co, 1996.  

Of the 1.7 million lines of code responsible for running the F-22s various systems, 90% is written in Ada - a prehistoric programming language developed in 1980. In a Wall Street Journal editorial against the F-22 program, former Secretary of the Navy John Lehman sarcastically remarked, “At least they [the F-22] are safe from cyberattack since no one in China knows how to program the '83 vintage IBM software that runs them”.[3] Despite the limitations of the F-22’s current hardware and software, Lockheed Martin engineers ensured the aircraft had significant growth margins to accommodate future computing advances.
            A total of 19 SEM-E slots in CIP 1 and 22 SEM-E slots in CIP 2 are vacant to facilitate future growth.[4] Furthermore, provisions were made within the F-22 airframe to facilitate future incorporation of a third CIP.[5] Production of the i960MX ceased in 1997 and it’s likely that the CIP’s original hardware was upgraded, but these upgrades are not well documented. Under the common configuration program (CCP), Defense Industry Daily reports, “F-22A Block 10s were retrofitted to Block 20/ Increment 2 status, but retain the original core processor [implying a new processor has been fielded]”.[6] In 2001, Military and Aerospace Electronics, reported that PowerPC processors would be integrated into lot 5 production aircraft:

…an upgrade to a new PowerPC processor already is on the drawing board, beginning with Lot 5 production of the aircraft around 2004…When the time comes, designers say they expect to replace the signal processor with a PowerPC using AltiVec technology, Motorola's high-performance vector parallel processing expansion to the PowerPC RISC processor architecture. AltiVec adds a 128-bit vector execution unit operating in concert with the PowerPC's existing integer and floating point units to provide highly parallel operations, as many as 16 simultaneously in one clock cycle.
The full extent of the CIP’s upgrades are not apparent from public sources, but it’s likely the original obsolescent parts were at least partially replaced for sustainment purposes since Lot 5. Given the additional sensors and networking capabilities envisioned in an F-22C, which will be detailed in Part III, it’s likely the current baseline computing hardware will require additional upgrades. Furthermore, the USAF ought to examine the feasibility and relative utility of upgrading to a C++ or non-Ada based operating system while also keeping cybersecurity in mind. The Integrated Maintenance Information System (IMIS), the rough equivalent of AILIS for the F-22, is currently being upgraded to the C++ standard.[7] The Air Force’s budget materials for FY 2017 under “F-22 Small Projects” lists “Windows XP migration” as a planned upgrade.[8]

[UPDATE 9/25/16]: Forecast International reports a third CIP was added on lot 5 production aircraft and beyond. 


Image 4: F-22A range comparison, the chart is somewhat biased against the F-15E given the HLLH configuration. Image Credit: Lockheed Martin. 

Arguably the most substantial limitation of the F-22 is its limited range. On internal stores only, the F-22 has a subsonic combat radius of 590 nautical miles (nm). With the addition of a pair of 500 gallon drop tanks, which are mounted from detachable pylons on the wing to enable reestablishment of the F-22’s stealth outline, is 850 nm. However, even a range of 850 nm is fairly limited when compared to the vast geographic expanse of the Asia-Pacific. The original advanced tactical fighter requirements were tailored to the strategic situation of the Cold War in which the U.S. air campaign would be fought from a network of bases in the U.K. and Western Europe which were comparatively close proximity to Warsaw Pact forces.
            In order to both improve the relevance of the Raptor to the Asia-Pacific and reduce the strain on aerial refueling assets during a high-end conflict, the F-22C would add both variable cycle engines and conformal fuel tanks. Variable cycle engines are likely to be among the defining traits of six generation aircraft, provided such a platform centric approach is pursued, and provide numerous performance benefits when compared to current turbofan engines:

To alter bypass ratio, variable-cycle engines add a third airflow stream outside of both the standard bypass duct and core. The third stream provides an extra source of airflow that, depending on the phase of the mission, can be adapted to provide either additional mass flow for increased propulsive efficiency and lower fuel burn, or to provide additional core flow for higher thrust and cooling air for the hot section of the engine, as well as to cool fuel, which provides a heat sink for aircraft systems. During cruise, the third stream can also swallow excess air damming up around the inlet, improving flow holding and reducing spillage drag.[9]
Variable cycle engines have the potential to provide between 25% and 35% greater range and 10% greater thrust when compared to traditional turbofan engines.[10] Furthermore, the third stream of air provides additional heat sink capacity which would facilitate both the incorporation of additional avionics – which often generate excessive heat, and directed energy weapons.[11]

Image 5: F-22A drop tank test. Image Credit: Lockheed Martin. 

            The addition of conformal fuel tanks would greatly expand the Raptor’s range at minimal cost to maneuverability, for example, the F-15’s Fuel And Sensor Tactical (FAST) CFTs provide an additional 1,698 gallons of fuel while the F-16C Block 52’s CFTs provide 900 additional gallons, and the Advanced Super Hornet’s CTFs provide 3,000 pounds of additional fuel combined. The addition of variable cycle engines and CTFs could expand the F-22B’s combat radius to approximately 825 nm or greater than 1,180 nm with two drop tanks.[i] However, the addition of CTFs would degrade the F-22’s stealth performance by virtue of disrupting the careful balance of planform alignment, the process in which multiple flight surfaces of an airframe share the same angle such that they reflect radar waves way from the source; shaping techniques provide between 80-90% of radar cross section (RCS) reductions while radar absorbent material (RAM) coatings provide the remainder.
            The relative utility of mounting CFTs for the F-22 would depend upon the extent of RCS degradation and the expected threat environment. For example, even if the CTFs would entirely negate the F-22’s stealth characteristics, CTS would still be useful for ferry flights between distant Pacific bases such as Joint Base Pearl-Hickam in Hawaii and Kadena Air Base in Japan. However, it is unlikely the addition of CTFs would entirely negate the F-22’s stealth when shaped appropriately and treated with RAM. Israeli Aerospace Industries has explored adding CTFs to the F-35.[12] Similarly, both Boeing’s Advanced Super Hornet and Silent Eagle proposals incorporate CFTs and are able to maintain a relatively low RCS. If the addition of CTFs does not degrade the frontal RCS of the F-22C significantly beyond that of the F-35, it might be appropriate to use in moderately contested threat environments; it would not be used in highly contested SEAD/DEAD missions against near-peer competitors.

Availability Rates & Sustainment

            Banal details related to maintenance, repair, and overhaul (MRO) programs and their impact fleet readiness is a dimension of defense analysis that is often lost upon most armchair generals. Despite the unmatched air-to-air capabilities of each individual F-22 and the extensive training of each Raptor pilot, the small fleet of primary aircraft inventory airframes (PMAI) translates into an even smaller number of planes which are ready for combat at any one time. For example, the USAF has two broad terms to describe an aircraft fleet’s readiness: mission capable rates and availability rates. Mission capable rates (MCR) are equal to the mission capable hours divided by the unit possessed hours while the mission availability rate is equal to the mission capable hours divided by the total aircraft inventory (TAI) hours; MCR is generally a satisfactory level of determining readiness at the unit level while availability rates are indicative of broader fleet level readiness.[13] For example, of the 183 F-22s in the USAF inventory, on average roughly 115 are airworthy and able to execute assigned missions at any one time with an availability rate of 62.8%, the corresponding mission capable rate for the PMAI F-22 component fleet is 72.7% or roughly 89 of 123 PMAI aircraft would be ready to execute missions at any one time.[14][15]

Image 6: Image Credit GAO, 2014. 

            The U.S. can effectively increase its fleet of deployed F-22s by improving readiness rates such that the existing limit fleet size translates into the most combat capability possible. For example, a 10% improvement in MCR among PMAI aircraft would effectively boost the available PMAI fleet size by 13 aircraft – more than half a squadron worth, to a total of 102 up from 89. With such a small fleet size and the prospect of restarting production low, ensuring maximum fleet readiness is vital given the F-22’s unique role as the only high-end survivable air superiority asset in the USAF inventory for the foreseeable future. The USAF has a goal of achieving a fleet availability rate of 70% by 2018 up from the current 62.8% through the reliability and maintainability maturation program (RAMMP). RAAMP modifications include:
Mighty Tough Boot Development [toughens the seams between aircraft panels to facilitate easier maintenance and mitigate damage to RAM coatings], Aircraft Mounted Nozzle Shield (AMNS) Liner Redesign, Integrated Forebody (IFB) Rain Erosion Nose Cap, Canopy Topcoat Redesign, Stored Energy System (SES) Air Filter, Auxiliary Power Unit (APU) Plenum Sealing, Gland Redesign, Automated Backup Oxygen System, Secondary Multi-Function Display (SMFD) Backlight to Lower Power LED, Gland Redesign, and Driver B RF Circuit Redesign[16][17]

Image 7: RAMMP. Image Credit: Flight Global. 

According to Lockheed Martin, 50% of all maintenance activities for the F-22 relate to maintaining its RAM coatings. The limited resilience of the F-22’s RAM coatings contributes towards its astronomically high cost per flight hour to operate at $59,166 compared to $20,318 for the F-16 and $32,000 (projected) for the F-35 as of 2015 data.[18] A total of $1.7 billion will be spent on RAAMP associated upgrades through 2020, but additional modifications – particularly to the F-22’s RAM, are likely required and ought to be incorporated to any F-22C.

Part III will detail capability improvements such as enclosed weapon pods, HMD, IRST, etc. 

[10] Ibid.
[11] Ibid.

[i] Assumes 3,000 pounds additional fuel from CTFs and 25% greater fuel efficiency from variable cycle engines. Does not factor drag or other important factors i.e. this is a “napkin math” type calculation that provides a rough estimate of expected performance.