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Knocked Off The Perch? USAF F-15C/D Eagles Under Threat

Justin Bronk
RUSI Defence Systems, 30 March 2017
Aerospace, Air Power and Technology, Military Sciences
It is a tired cliché in airpower circles that the F-15 is the most successful fighter in history with more than 100 kills to no losses in air-to-air combat. While no longer supreme, the replacement of the veteran air superiority fighter – currently being discussed in Washington – would leave serious capability gaps

The US House Armed Services Committee has heard that the US Air Force is at the ‘pre-decisional’ phase of evaluating whether or not to replace the service’s remaining 180 or so F-15C/D Eagle air superiority fighters with upgraded F-16 Vipers.

From a budget control standpoint, the F-15C/D fleet is a tempting target. Designed from the outset to defeat hostile aircraft through superior energy management, radar performance and missile arsenal, the F-15C/D is large, fuel-thirsty and complex. The aircraft was designed and manufactured to a target airframe fatigue life of 8,000 flight hours, and many jets in the F-15C/D fleet are now well past 10,000. Older airframes means higher maintenance burdens, more frequent fatigue testing and higher operating costs.

However, until the recent announcement, the plan had been for the USAF’s entire F-15C/D fleet to receive new wing-spars and various other structural mid-life upgrades to push the jets out to at least 18,000 equivalent flight hours, as well as potentially allowing them to carry up to double their current payload of eight air-to-air missiles.

A portion of the F-15C fleet has also recently received an expensive upgrade to the new and extremely potent APG-63(V)3 active electronically scanned array (AESA) radar as the platform’s primary sensor, with the assumed intention of upgrading all front line F-15C/D units with the new radar in the coming years.

This is important because an F-15 with the APG-63(V)3 can generate almost fifth-generation levels of situational awareness at the long ranges which it is intended to engage enemy air threats (including cruise missiles). In addition to the new enhanced range AIM-120D model of the venerable AMRAAM, which has long provided the Eagle’s core armament, the APG-63(V)3 represents an almost generational leap in the F-15C’s already formidable beyond visual range (BVR) air superiority potential.

It also means that the type remains leagues ahead of the latest F-16 Block 70 concepts in terms of BVR capabilities – able to carry more missiles, launched from higher and faster for longer reach, and guided by a larger and more capable AESA radar. This is critically important for the future high-end warfighting capabilities of the USAF (and by extension NATO as a whole) because of the tiny 123-strong fleet of combat coded F-22 Raptors the USAF procured notionally to replace the F-15C.

The stealthy, supercruising, sensor and missile package that is the F-22 remains the uncontested king of air superiority fighters in the world today, but there are simply too few of them to allow the USAF to take on a high-end air force such as China’s or Russia’s in a full scale engagement. To overcome the scarcity of F-22 assets for the various theatres in which the USAF must be able to operate, the F-15C fleet is a crucial asset, supporting the stealthy jets closely with large numbers of missiles, a decent fuel fraction and powerful radar of their own.

In hugely oversimplified terms, the F-22s fly above and sometimes even behind oncoming enemy aircraft and designate targets unseen for the non-stealthy F-15s. This allows the F-15s to expend their fuel and missiles while the F-22s conserve their own for any particularly urgent threats or until the final stages of an engagement.

To fulfil this role without forcing the F-22s to significantly rein in their own kinematic performance, the F-15C has to fly very high and very fast – typically above 50,000ft. This is exactly where the airframe was designed to excel and is one of the reasons why the F-15C/F-22 pairing has proven so devastatingly effective at successive exercises such as the annual Red Flag series.

The F-16V might be cheaper and more efficient to run, and is an extremely capable multirole fighter with an AESA radar and conformal fuel tanks, but with its single engine and significantly smaller wing area, its performance drops off significantly at altitudes over 40,000ft. It cannot, therefore, integrate with the F-22s in the way that the current F-15C/Ds do.

Furthermore, the F-22 has limited waveforms available to pass data to other fighters without compromising its own survivability. The F-15C community has been trialling a purpose-built pod called Talon Hate which allows it to exchange data covertly and at relatively high bandwidths with the F-22 without needing an aerial gateway relay such as an EQ-4 NetHawk. It will also give the fighter an infra-red scan and track sensor to help with passive detection and tracking of targets including low-observable threats. F-16 has not been trialled with Talon Hate and would require a new and expensive integration, flight trials and certification process, assuming the pod is even compatible with the F-16V mission system architecture.

If the USAF chooses to replace the F-15C/D Eagle fleet with modernised F-16s, they will significantly reduce the overall capabilities of NATO’s premier air superiority fleet – the F-22 Raptors. The F-16 is inherently less capable at high-altitude, cannot sustain supersonic speeds for as long during combat manoeuvres with air-superiority loadouts, and carries a smaller radar array which limits its own potential as a sensor platform.

The F-15C also has significant capability growth potential despite its venerable design due to its large airframe and impressive thrust to weight ratio. It can already mount low-drag conformal tanks, and upgrades are under consideration to give it more powerful electronic warfare suites such as the Eagle Passive/Active Warning and Survivability System (EPAWSS), and carry double the current maximum loadout of AMRAAMs in the ‘missile-truck’ support role for the F-22s.

If cost-cutting efforts force this to go ahead, it will most likely increase the value to the USAF of the F-22 community’s close relationship with the RAF, which operates the only aircraft even more suited to the F-22 support role than the Eagle, the Eurofighter Typhoon. The RAF (and other Eurofighter nations to a lesser extent) is a regular partner for the F-22 community at Red Flag and in various other exercises.

The other Eurofighter nations such as Germany and Italy (and Saudi Arabia) might also find more of an appetite from the USAF for close collaboration with the F-22 community, although at present their cooperation and mutual exercises are less doctrinally integrated than the RAF–USAF air superiority relationship.

In the ongoing and no doubt necessary effort to find efficiency savings in the USAF fleets, the expensive and ageing F-15C/Ds are a tempting target from a fiscal standpoint. However, if the USAF cannot win air superiority over a high-end opponent, then all the multi-role assets and close air support capability in the huge F-16, F-18 and A-10 stables, supported by the F-35 as it comes into service, may not be able to be brought to bear.

Justin Bronk
Research Fellow for Combat Airpower and Technology, RUSI

Author

Justin Bronk
Research Fellow, Airpower and Technology

Justin Bronk is a Research Fellow specialising in combat airpower and technology in the Military Sciences team at RUSI. He is also... read more

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