It's Back To The Future For U.S. F-15C Eagles And Conformal Fuel Tanks 

Paired with a new missile launcher, the conformal fuel tanks won't only improve the Air National Guard F-15C fleet's range, but also its combat punch.

Boeing

Boeing posted an image today of a Louisiana Air National Guard F-15C wearing a pair of conformal fuel tanks (CFTs). The tanks are part of a new initiative to give the F-15C fleet more gas and weapons carrying capability in order to execute what the Air National Guard calls future "persistent air dominance missions." The 159th Fighter Wing "Bayou Militia" is the first unit to receive the tanks for testing and evaluation.

Boeing's Randy Jackson stated the following in an email to the The War Zone:

"The first flight with the tanks was achieved in just 10 months after the start of the program and marks a major milestone in establishing the operational utility of the conformal fuel tanks. Boeing received a multimillion dollar contract from the NATO Support and Procurement Agency in early 2017 for initial integration, testing and support, and delivered the tanks ahead of schedule. The first test flight on January 31st lasted two hours and took place over the Gulf of Mexico."

The little-known of program is officially called the F-15 Persistent Air Dominance Enabler. Here's an excerpt from the Air National Guard's 2017 priorities document that explains the program and its costs:

USAF

This major upgrade is part of a series of upgrades—which include a new digital countermeasures suite, infrared search and track system, new cockpit, among other enhancements—that are slated to allow the F-15C/D fleet to soldier on till 2040 and possibly beyond. The aircraft that receive these upgrades are called "Golden Eagles."  

It is worth noting that last year the USAF repeatedly questioned the F-15C/D Eagle's long term future, with the bringing up its structural longevity as a major concern and floating the idea of replacing the type entirely with upgraded F-16s. Currently the USAF has only eight operational F-15C/D squadrons, with five of those belonging to the Air National Guard.

As the excerpt alludes to, the CFTs will not only extend the F-15C's range, but they will also allow the jet's two wing hardpoints to be freed up for more weapons. Currently two air-to-air missiles and a 600 gallon drop tank are commonly carried on each wing station. 

The new multi-rail launcher mentioned in the official document has been displayed on Boeing's advanced F-15 Strike Eagle derivatives before, and can hold up to four AIM-120 AMRAAMs. It remains unclear exactly how many weapons, and exactly type of weapons, the F-15C's new CFTs can carry beyond AIM-120s. 

Boeing

The ability to carry at least an extra four AIM-120s without severely limiting the F-15C's fuel load will go a long way in giving the jet more combat punch, and will help with the implementation of cooperative tactics where the F-15s can act as arsenal ships for stealthy fighters operating forward of the Eagle's position, deeper into contested airspace. We have described these tactics multiple times and you can read about them here. It also opens up new tactical opportunities should the F-15C receive a very-long range air-to-air missile, and/or more numerous and smaller hit-to-kill air-to-air weapons that are currently in development. 

The CFTs could also help free up space and minimize drag for Eagles carrying large networking systems, like the Talon Hate pod, or other future outsized modular systems. 

The Eagle's conformal fuel tanks, also known as "FAST packs," have been around almost as long as the F-15 itself, first being test flown in 1974. I wrote all about the Eagle's CFTs and their origin in a past feature about how the Israeli Air Force has modified the F-15 since early on for its unique needs, stating:

"One of the features that the F-15E would be built with was conformal fuel tanks, otherwise known as “FAST Packs,” as in Fuel And Sensor Tactical Packs. These flank hugging 849 gallon tanks were not new to the F-15 with the advent of the Strike Eagle, in fact they were envisioned as an option for the F-15C/D and even retrofittable to the A and B models early on, with the first test flight being flown with them attached to an Eagle in the mid 1970s. They were envisioned to carry everything from fuel to cargo, although the majority of these concepts never made it to fruition."

Public Domain

Early FAST pack configurations drawing from the 1970s.

"USAF Eagles only took limited advantage of FAST packs, with some jets deployed to Iceland or stationed in Alaska using them sporadically for the long-range air sovereignty role. The IAF on the other hand saw the great utility in these conformal fuel tanks, not just to enhance range, but to make their air superiority focused Bazs true multi-role heavy fighters.

Like those found on the F-15E, F-15 Baz’s conformal tanks could be fitted with hardpoints for air-to-air missiles or for bombs. This allows for the Baz [Israel's name for the air superiority F-15A/B/C/D Eagle] to fly missions with a pair of underwing tanks and even a centerline tank while still being able execute air-to-ground missions. Today, many Bazs can be seen fitted with indigenously developed FAST Packs built by IAI, but the fact is these were flying on the IAF's F-15s many decades ago."

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USAF F-15s flying air patrols and intercepts out of Iceland during the Cold War wore FAST packs. 

Conformal fuel tanks on the F-15C add nearly 12,000lbs of gas to the jets 13,850lbs of internal fuel with only slight performance penalties and are much more aerodynamically efficient than the 600 gallon drop tanks normally carried under the F-15C's wings and fuselage. This begs the question: why did the USAF stop using CFTs in the first place? 

That is a complicated question, but by some accounts the time it took to pull the CFTs of for maintenance was one issue. The fact that the USAF had a surplus of virtually everything, including tankers and F-15s, following the end of the Cold War meant that squeezing every bit of performance out of every tactical aircraft simply wasn't a high priority. The fighter-pilot dominated culture of the USAF may have also played a part in the decision. 600 gallons tanks can be dropped in an instant to give back the F-15's maximum maneuverability and kinematic potential during combat. CFTs on the other hand can't be jettisoned, and the small performance penalty they dock from the jet is there as long as they are attached. 

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FAST packs sit alongside an F-15C back in the 1980s.

Although these factors may help explain why the USAF never fully adopted the CFT concept for their own F-15C/D fleet during and shortly after the Cold War, it doesn't explain why it took so long for them to show up again on USAF Eagles. Considering the drawdown in force size to roughly just 200 F-15C/D Eagles over the last two and a half decades, the fact that the type guards America's maritime borders, and the harsh realities of future anti-access/area denial combat environments where tankers will be increasingly vulnerable to attack, the need for CFTs on America's F-15C/D fleet has never been greater. And once again, Israel has shown just how useful the capability can be over decades of service, and the USAF's own multi-role F-15Es only operate with their own CFTs attached.

But the old adage "better late than never" is very relevant here, and the fact that the Air National Guard is betting big on CFTs is downright exciting. This, along with the other upgrades slated for the oldest of America's Eagles, will make the jet more potent and independently capable than it has ever have been. The addition of CFTs to the Guard's Eagle fleet will also make arguments for replacing the 40 year old jets with updated F-16s less potent as an F-16 equipped with its own conformal tanks cannot compete with a CFT equipped Eagle in terms of range, and it's not even close when it comes to missile carriage capabilities. 

USAF

A Bayou Militia Eagle fires off an AIM-120 AMRAAM.

Although new sensors and podded system are in the Air Guard's F-15C/D's future, the addition of CFTs with extra hardpoints could also point to the possibility that the F-15C/D could finally get a secondary air-to-ground role like their IAF counterparts. I know this sounds like blasphemy to the "not a pound for air-to-ground" F-15C/D pilot cadre, but even a limited strike capability could help preserve the type's existence into the future. 

We'll keep you informed as to how the Air Guard CFT integration progresses, but one thing seems glaringly clear—like a fine wine, the F-15 just gets better with age and the Air National Guard has the vision and the guts to make the world's most proven and deadly jet fighter the best it can possibly be.

Contact the author: Tyler@thedrive.com