Silent Eagle

Ostensibly developed for export only, the new F-15SE will see the standard conformal fuel tanks (CFTs) mounted on the engine intakes and lower wing root of later generation F-15s replaced with similar shaped conformal bays capable of carrying internally a variety of air-to-air or air-to-surface weapons, thus eliminating radar signature enhancing externally carried stores, as well as a small amount of fuel.

Boeing says weapons such as the AIM-120 AMRAAM and AIM-9 Sidewinder AAMs, 500kg GBU-32 and 250kg GBU-38 JDAMs and their derivatives, and the 120kg GBU-39 SDB can all be carried in the conformal bay. On the mockup at the reveal, the two CFTs were each replaced with a conformal weapons bay, each of which had a common bay with two doors and two weapons racks, although the mockup showed no sign of the increasingly familiar signature-reducing cerated forward and rear facing edges common on the weapons bay doors of fifth generation fighters and bombers.

Perhaps most importantly for an air force looking to maximise the flexibility of such an aircraft, the new conformal bays can be removed and replaced with the more familiar F-15E style CFTs within two hours to provide additional fuel and the ability to carry weapons externally when low observability is less critical. Such a capability may be deemed attractive to operators such as Israel and Korea, both of whom operate late model F-15s and who have requirements for a ‘first day of the war’ capability. But both of these countries along with fellow F-15 operators Japan and Singapore have also expressed a wish to acquire fifth generation F-35s or F-22s to fulfil this requirement, and may instead leverage the F-15SE as a bargaining chip when it comes time to sign for their next capability. Japan in particular may be a realistic target, considering its desire for the F-22 is unlikely to be met by a recalcitrant US administration.

Boeing is no doubt happy for the F-15SE to be seen as an F-35 or even F-22 alternative, and indeed has promoted the Silent Eagle’s reduced frontal radar cross section which it says it comparable with the VLO-rated F-35, even though most experts say VLO has to be designed in to an aircraft and cannot be added as an after thought. But the more likely customers will be those considering bolstering their current F-15 fleets or as bridging capabilities, or new customers who are also considering other ‘4.5 generation’ aircraft such as the Eurofighter, Rafale, Gripen NG, Su-30MK, MiG-35, and, perhaps ironically for Boeing, the F/A-18E/F Super Hornet.

Boeing says the range penalty that comes with substituting the CFTs for the new weapons bays is in the order of about 180nm (330km), but this is somewhat offset by the aircraft being much cleaner without the external weapons and hardpoints, and the company says it is also looking for ways to put more internal fuel into the F-15 airframe including, according to one report, the substitution of the aircraft’s huge dorsal airbrake and its associated mechanisms with additional fuel. Boeing is also studying the possibility of incorporating a fly-by-wire flight control system onto the F-15SE, but has reportedly said a customer would need to underwrite the reported US$70m (A$102m) cost of developing such a system. Other elements to be included on the F-15SE ‘options list’ include GE F110-220 engines and the APG-63(v)3 Advanced Electronic Scanning Array radar as ordered by Singapore, a pylon-mounted Infra-Red Search & Track (IRST), and a range of weapons options which have been added in recent years through the Korean and Singaporean programs such as the Harpoon Block II anti-ship missile.

And while Boeing wouldn’t specify what radar absorbing external treatments and shaping would be applied to the F-15SE, as that would require US government releasability approval, there is little doubt this would include a frangible cover over the gun muzzle, and the incorporation of a radar ‘blocker’ in the engine intake, known colloquially within Boeing as ‘The Device’ on the similar equipped Super Hornet. But it did say the aircraft would be equipped with a new BAE Systems Digital Electronic Warfare System (DEWS) which is designed to be integrated with the AESA radar and has been derived from architecture which also forms the basis for similar systems on the F-22 and F-35. The new composite vertical tails, which are canted outwards 15 degrees from the vertical, not only provide improved lift and reduced weight, but they also reduce the side-on radar cross section of the aircraft.

Boeing says whilst the USAF has been briefed on the F-15SE, that service remains focussed on acquiring only fifth generation aircraft such as additional F-22s and the F-35. More likely is that elements of the F-15SE will find their way into any mid-life upgrade of the more than 200 F-15E Strike Eagles which is due early next decade and which would see that aircraft serve through to the mid to late 2020s.

Boeing expects to commence flight and weapons release trials of the Silent Eagle configuration on its company ‘E-1’ development aircraft from early 2010.