Following an order by the United States Air Force for the first F-15EX heavyweight ‘4+ generation’ fighters, while are slated to replace the aging F-15C Eagles in frontline service and partly compensate for the very limited availability of fifth generation F-22 Raptors designed for a similar role, the Boeing company which developed the aircraft has sought to market them to India under the MMRCA tender. The aircraft will compete with the medium weight F-18E Block III Super Hornet, the lightweight F-21 derived from the F-16E Fighting Falcon and a range of foreign jets including three European designs and the Russian medium weight MiG-35 and heavyweight Su-35 ‘4++ generation’ fighters. While the MMRCA initially stipulated that fighters should be of a light-medium weight, and at first restricted the competition exclusively to single engine aircraft, the Su-35 and F-15X stand out as the only two high end heavyweight aircraft in the competition. The aircraft both represent extensive modernisations of Cold War era designs – the Soviet Su-27 and American F-15C respectively which were both countries’ prime air superiority fighters during the conflict. With the competition bringing both jets head to head, an assessment of how the two designs compare against one another has considerable implications for the future of both fighter programs as well as that of the Indian Air Force.
Both the F-15EX and the Su-35 are twin engine designs capable of operating at high altitudes, and both have the long ranges needed to penetrate enemy airspace and deliver a wide range of standoff munitions for both air to air and air to ground missions. The F-15 does have the advantage of a higher speed however, able to reach Mach 2.5 where the Su-35 is restricted to speeds of around Mach 2.25. Both field radars which are similarly sophisticated – the Irbis-E and AN/APG-82 – although the Su-35’s radar is larger and thought to be more powerful. The Irbis-E can detect most fighter sized targets at ranges of over 400 kilometres, and can track up to 30 airborne targets simultaneously and engage up to eight. Stealth fighters with lower radar cross sections can reportedly be detected at ranges of over 80km. The Su-35 does benefit from a number of advantages in beyond visual range engagements, including its radar cross section reducing profile which leaves its radar cross section at under one third that of the F-15. Whereas the Su-35 is a lot stealthier than the original Su-27 – the F-15 has seen little change to its profit and if anything has become bulkier and easier to detect at range. Plans to similarly reduce the radar cross section of the F-15 under the F-15SE program were cancelled, and have not been incorporated onto the F-15EX design.
Other advantages enjoyed by the Su-35 include its access to R-37M hypersonic air to air missiles – which have a long 400km range, high manoeuvrability, a Mach 6 speed and very powerful sensors. American F-15s today rely on the ageing AIM-120C with a 105km range – although the F-15EX could be marketed with the AIM-120D with a longer 180km range. These missiles have less than half the range of the R-37 and are much slower – with a speed of around Mach 4.5. The Su-35 will in the near future also have access to the K-77, which will make use of a revolutionary new APAA guidance system that will make it extremely difficult to evade. The missile will have a range of approximately 200km. While the F-15EX’s air to air missiles do suffer a quantitative disadvantage, the fighter is able to carry up to 22 of them where the Su-35 can carry just 14. The F-15’s engine thrust is considerably lower than that of the Su-35 however, which if combined with such a heavy weapons payload will seriously compromise manoeuvrability at all ranges and the fighter’s ability to evade missile attacks.
In visual range combat, the Su-35’s advantages are even more considerable. The F-15EX is a much bulkier design with a much lower thrust/weight ratio, allowing the Su-35 to comfortably outmanoeuvre it even without relying on its thrust vectoring engines. Three dimensional thrust vectoring capabilities, however, will make the Su-35’s advantage overwhelming at short ranges.
While the Su-35 is appears to be the more capable aircraft based on an assessment of its capabilities, its main attraction to India over the F-15EX is likely to be its synergy with existing fighters in the Indian Air Force’s fleet. The Su-35 is closely related to the Su-30MKI, of which India plans to field close to 300 with over 250 already in service, and interoperability will provide a significant advantage which the F-15 would lack. Alongside the Su-30, India deploys a number of other Russian jets such as the MiG-29 and MiG-21BiS which use modern Russian munitions such as the R-77 and R-27 air to air missiles – all of which are compatible with the Su-35. The similarities between the Su-35 and the Su-30MKI will also allow pilots to relatively easily transfer between operating the two classes – which with India already having several hundred trained Su-30 pilots is a major advantage. By contrast, integrating the F-15EX into an already very diverse fleet – some would argue too diverse – could provide a logistics nightmare – particularly considering that India deploys no classes of American fighter and no American air to air missiles or maintenance equipment.
Further increasing the attractiveness of the Su-35, the fighter has been offered for licence manufacturing in India alongside transfers of some technologies for its AL-41 engines and Irbis-E radars. A license manufacturing deal is reportedly being tied to a deal to modernise the Su-30MKI to a ‘4++ generation standard’ – allowing the Indian Air Force to upgrade existing fighters with Irbis-E radars and AL-41 engines which would revolutionise their performances. This would also allow the older fighters to make use of new types of munitions such as the R-37M air to air missile. While the F-15EX is a very formidable fighter, it cannot be paired with an upgrade package for existing Indian fighters in any comparable way – which would only be possible if India already operated older classes of American fighter such as the F-15C.
Ultimately it remains uncertain whether India will opt for a heavyweight fighter under the tender – or whether it will stick to its original plan to acquire a lighter and lower maintenance jet such as the MiG-35 or French Rafale. While both the F-15EX and the Su-35 are in many ways comparable, the Su-35’s advantages both at range and in close range engagements are very considerable. The Su-35’s main attractions over the F-15EX, however, is the difficulty of incorporating American aircraft into a service which already operates an overly diverse fleet and does not operate any classes of American fighters or air to air missiles. This advantage is further cemented by the Su-35’s very high level of interoperability with the Su-30MKI, and the possibility of using Su-35 technologies obtained under the contract to upgrade the Su-30 to a comparable ‘4++ generation’ standard. This being said, the United States has applied considerable political pressure against India in the past including threats of economic sanctions on the country – which it has repeatedly been indicated could be lessened if India were to increase purchases of American military hardware. While the advantages of the Su-35 are overwhelming, opting for its American analogue as part of a politically motivated purchase remains a considerable possibility.