How far can upgraded F-15s take us against large threats?
All F-15s were built with air-to-ground capability, and are wired for the carriage of air-to-ground ordnance. They were originally intended as dual-role aircraft, but the ground attack role was abandoned in 1975 and the relevant software was never incorporated. Trials of an air-to-ground F-15 began during 1982, when McDonnell Douglas modified the second TF-15A as the ‘Strike Eagle’, funding the project itself. The aircraft was conceived as an ETF (Enhanced Tactical Fighter) replacement for the General Dynamics F-111 and was chosen in preference to the ‘cranked wing’ F-16XL Fighting Falcon. The ‘Strike Eagle’ demonstrator was joined by an F-15C and an F-15D which conducted trials with a variety of fuel and ordnance loads, usually with CFTs fitted. The resulting F-15E was given go-ahead on 24 February 1984 and the first production aircraft made its maiden flight on 11 Dec. 1986. McDonnell’s ‘Strike Eagle’ name was not adopted, though some unofficial epithets such as ‘Beagle’ (Bomber Eagle) and ‘Mud Hen’ have been used on occasion.
Although the slogan of the F-15’s original design team was “Not a pound for air-to-ground,” the F-15 has long been recognized as having superior potential in the ground attack role. In 1987 this potential was realized in the form of the F-15E Strike Eagle. The mission of the Strike Eagle is as succinct as that of its air-to-air cousin: to put bombs on target. The F-15E is especially configured for the deep strike mission, venturing far behind enemy lines to attack high value targets with a variety of munitions. The Strike Eagle accomplishes this mission by expanding on the capabilities of the air superiority F-15, adding a rear seat WSO (Weapon Systems Operator) crewmember and incorporating an entirely new suite of air-to-ground avionics.
The F-15E is a two seat, two engine dual role fighter capable of speeds up to MACH 2.5. The F-15E performs day and night all weather air-to-air and air-to-ground missions including strategic strike, interdiction, OCA and DCA. Although primarily a deep interdiction platform, the F-15E can also perform CAS and Escort missions. Strike Eagles are equipped with LANTIRN, enhancing night PGM delivery capability. The F-15E outbord and inboard wing stations and the centreline can be load with various armament. The outboard wing hardpoint are unable to carry heavy loads and are assign for ECM pods. The other hardpoints can be employed for various loads but with the use of multiple ejection racks (MERs). Each MER can hold six Mk-82 bombs or “Snakeye” retarded bombs, or six Mk 20 “Rockeye” dispensers, four CBU-52B, CBU- 58B, or CBU-71B dispensers, a single Mk-84 (907 kg) bomb F- 15E can carry also “smart” weapons, CBU-10 laser guided bomb based on the Mk 84 bomb, CBU-12, CBU-15, or another, laser, electro-optical, or infra-red guided bomb (including AGM-G5 “Marerick” air-to-ground) missiles.
Conformal Fuel Tanks were introduced with the F-15C in order to extend the range of the aircraft. The CFTs are carried in pairs and fit closely to the side of the aircraft, with one CFT underneath each wing. By designing the CFT to minimize the effect on aircraft aerodynamics, much lower drag results than if a similar amount of fuel is carried in conventional external fuel tanks. This lower drag translate directly into longer aircraft ranges, a particularly desirable characteristic of a deep strike fighter like the F-15E. As with any system, the use of CFTs on F-15s involves some compromise. The weight and drag of the CFTs (even when empty) degrades aircraft performance when compared to external fuel tanks, which can be jettisoned when needed (CFTs are not jettisonable and can only be downloaded by maintenance crews). As a result, CFTs are typically used in situations where increased range offsets any performance drawbacks. In the case of the F-15E, CFTs allow air-to-ground munitions to be loaded on stations which would otherwise carry external fuel tanks. In general, CFT usage is the norm for F15Es and the exception for F-15C/D’s.
The F-15E Strike Eagle’s tactical electronic warfare system [TEWS] is an integrated countermeasures system. Radar, radar jammer, warning receiver and chaff/flare dispenser all work together to detect, identify and counter threats posed by an enemy. For example, if the warning receiver detects a threat before the radar jammer, the warning receiver will inform the jammer of the threat. A Strike Eagle’s TEWS can jam radar systems operating in high frequencies, such as radar used by short-range surface-to-air missiles, antiaircraft artillery and airborne threats. Current improvements to TEWS will enhance the aircraft’s ability to jam enemy radar systems. The addition of new hardware and software, known as Band 1.5, will round out the TEWS capability by jamming threats in mid-to-low frequencies, such as long-range radar systems. The equipment is expected to go into full production sometime in late 1999.
The Defence Department plans to sustain production of the F-15E for at least two more years, purchasing three aircraft in both FY 1998 and FY 1999. Without FY 1998 procurement, the F-15 production line would begin to close in the absence of new foreign sales. These six additional aircraft, together with the six aircraft approved by Congress in FY 1997, will sustain the present 132-plane combat force structure until about FY 2016. Under current plans by 2030, the last F-15C/D models will have been phased out of the inventory and replaced by the F-22.
Service Life
Designed in the 1960s and built in the 1970s, the F-15A – D aircraft has now been in service for over twenty years. While the Eagle’s aerodynamics and manoeuvrability are still on a par with newer aircraft, quantum leaps in integrated circuit technology have made the original F-15 avionics suite obsolete. The objective of the Multi-Stage Improvement Program (MSIP) was to set the Eagle in step with today’s vastly improved information processing systems. Some F-15C/D aircraft (tail numbers 84-001 and higher) came off the assembly line with MSIP in place. All F-15A/B/C/D aircraft produced before 84-001 will receive the MSIP retrofit at the F-15 depot. Improvements incorporated via MSIP vary between F-15A/B and F-15C/D aircraft; the C/D MSIP has been completed. However, all air-to-air Eagles gain improved radar, central computer, weapons and fire control, and threat warning systems.
The purpose of the F-15 Multi-stage Improvement Program (MSIP) was to provide maximum air superiority in a dense hostile environment in the late 1990s and beyond. All total, 427 Eagles received the new avionics upgrades. Along with later model production aircraft, these retrofitted aircraft would provide the Combat Air Forces (CAF) with a total MSIP fleet of 526 aircraft. The MSIP upgraded the capabilities of the F-15 aircraft to included a MIL-STD-1760 aircraft/weapons standard electrical interface bus to provide the digital technology needed to support new and modern weapon systems like AMRAAM. The upgrade also incorporated a MIL-STD-1553 digital command/response time division data bus that would enable onboard systems to communicate and to work with each other. A new central computer with significantly improved processing speed and memory capacity upgraded the F-15 from 70s to 90s technology, adding capacity needed to support new radar and other systems. The original Eagle had less computer capacity than a 1990s car. Some of the work prefaced the addition of the Joint Tactical Information Distribution System, adding space, power, and cooling that would allow the new avionics to run in the harsh environments in which the Eagle operates. The new programmable armament control set (PACS) with a multi-purpose colour display (MPCD) for expanded weapons control, monitoring, and release capabilities featured a modern touch screen that allowed the pilot to talk to his weapons. A data transfer module (DTM) set provided pre-programmed information that customized the jet to fly the route the pilot had planned using mission planning computers. An upgrade to the APG-63 Radar for multiple target detection, improved electronic counter-countermeasures (ECCM) characteristics, and non-cooperative target recognition capability enabled the pilot to identify and target enemy aircraft before he was detected or before the enemy could employ his weapons. An upgrade of the advanced medium range air-to-air missile (AMRAAM), that carried up to eight missiles, represented an improvement that complimented the combat-proven AIM-7 Sparrow by giving the pilot capability to engage multiple targets to launch and leave, targeting and destroying enemy fighters before they could pose a threat. The upgraded Radar Warning Receiver (RWR) and an enhanced internal countermeasures set (ICS) on F-15C/D models improved threat detection and self-protection radar jamming capability that allowed pilots to react to threat and to manoeuvre to break the lock of enemy missiles.
The F-15 initial operational requirement was for a service life of 4,000 hours. Testing completed in 1973 demonstrated that the F-15 could sustain 16,000 hours of flight. Subsequently operational use was more severely stressful than the original design specification. With an average usage of 270 aircraft flight hours per year, by the early 1990s the F-15C fleet was approaching its service-design-life limit of 4,000 flight hours. Following successful airframe structural testing, the F-15C was extended to an 8,000-hour service life limit. An 8,000-hour service limit provides current levels of F-15Cs through 2010. The F-22 program was initially justified on the basis of an 8,000 flight hour life projection for the F-15. This was consistent with the projected lifespan of the most severely stressed F-15Cs, which have averaged 85% of flight hours in stressful air-to-air missions, versus the 48% in the original design specification.
Full-scale fatigue testing between 1988 and 1994 ended with a demonstration of over 7,600 flight hours for the most severely used aircraft, and in excess of 12,000 hours on the remainder of the fleet. A 10,000-hour service limit would provide F-15Cs to 2020, while a 12,000-hour service life extends the F-15Cs to the year 2030. The APG-63 radar, F100-PW-100 engines, and structure upgrades are mandatory. The USAF cannot expect to fly the F-15C to 2014, or beyond, without replacing these subsystems. The total cost of the three retrofits would be under $3 billion. The upgrades would dramatically reduce the 18 percent breakrate prevalent in the mid-1990s, and extend the F-15C service life well beyond 2014.
The F-15E structure is rated at 16,000 flight hours, double the lifetime of earlier F-15s.
