On 11 December, the Boeing F-15E Strike Eagle marked the 26th anniversary of its first flight, but the venerable strike fighter will continue serving with the US Air Force well into the 2030s.
"There are no plans to replace the F-15E for the foreseeable future," the USAF says. "It is true that the F-15E, like all of our legacy aircraft, are accumulating more flight time than used to be typical, but given current fiscal realities, the AF [air force] fleet will continue to age well past the point at which they would have been replaced in pre-Desert Storm days."
As a result, the service is taking steps to keep the Strike Eagle "a viable, sustainable, and fully capable platform". The USAF will conduct a full-scale fatigue test to determine an updated service life for the jet, and to discover if the aircraft needs any structural modifications or repairs.
The service is also replacing the F-15E's Raytheon APG-70 radar with the new Raytheon APG-82(V)1 active electronically scanned array (AESA), "which will greatly enhance the F-15E's ability to detect and very accurately locate ground targets", the USAF says. Additionally, it is upgrading the jet's electronic countermeasures suite with the Eagle passive/active warning and survivability system (EPAWSS). "These actions all demonstrate the [air force's] intent to keep the F-15E a vital part of the inventory for quite some time to come," it says.
But with an average fleet age of about 21 years, and around 6,000hrs on each airframe, the USAF will eventually have to either replace the jet or forego its capability.
It is not surprising that the USAF does not have a plan in place to replace the F-15E, says Mark Gunzinger, an analyst at the Center for Strategic and Budgetary Assessments. "They have a lot of things to address right now, for example, funding in this pretty ugly budget environment for their three top priorities, which remain the [Lockheed Martin] F-35, [Boeing KC-46] tanker, and the [Long Range Strike] bomber."
The most obvious candidate to replace the F-15E is a variant of the F-35, Gunzinger says. There is no money to develop a clean sheet design. "I do think they'll do some kind of an F-35E or whatever kind of F-35 variant," he says.
Indeed, industry sources say detailed studies have been undertaken for a two-seat F-35 along with extended-range models. Both are "do-able," and are not mere theoretical constructs. And, if the Air Force Research Laboratory's (AFRL) adaptive engine technology development (AETD) programme yields an operational powerplant, it could help extend the F-35's range, particularly if the AETD delivers its promised 35% fuel efficiency increase over the existing Pratt & Whitney F135. Pratt & Whitney and General Electric are working on competing designs for the AETD programme.
Gunzinger does not doubt that building a two-seat F-35 is feasible, but questions if there is a need to do so. What would be more important, he says, is extended range and increased payload. Adding a second seat would require a more extensive redesign, which on a stealth aircraft is even more challenging than on a conventional jet, Gunzinger says. In any case, building a larger version of any stealth aircraft is practically as challenging as designing an all new aircraft. "Could you do it? Yeah, but it's probably more expensive than sticking with a single seat."
Dan Goure, an analyst at the Lexington Institute, disagrees. "What would you replace [the F-15] with? It's not an F-22, and it's not an F-35. Here we go starting to talk about sixth-gen or something," he says. It would have to be a clean-sheet design, but there is probably not going to be enough money to pay for an F-15E replacement given that the USAF will need to pay for a large number of aircraft procurements in the 2030 timeframe."
Goure says that significantly modifying the F-35's design to add greater range and payloads, let alone two seats, would result in practically a new aircraft. Goure says that if the F-35 is modified to take on the F-15E's role, it would be closer in scope to Lockheed's abortive F-22-derived FB-22 concept than the Joint Strike Fighter. And, if the aircraft were to be designed for service entry in the 2030s, there would also need to be major avionics and stealth technology upgrades. "You can call it an F-35, like we used to talk about an FB-22, but it's hard to see it not being at that point of a new aircraft," Goure says. There may also have to be compromises between range, payload, stealth and cost. "If it's stealth, and it's bigger, and it's a two-seater, it costs," he says.
The USAF ultimately may choose not to directly replace the F-15E with a new aircraft. "You might even want to question the need for an F-15E replacement," Gunzinger says. There is always the option of foregoing the mission space between the fifth-generation fighters and the next generation strategic bombers, Goure says.
Instead of an F-15E replacement, the USAF could increase the number of long-range strike bombers (LRS-B) it buys, Gunzinger says. But it could also develop some kind of stealthy unmanned aircraft, basically a "bomb truck". That unmanned aircraft could be "tethered" to a manned strike aircraft-like the LRS-B-to perform missions similar to the F-15E, he says.