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F-15SA deliveries drawing nearer

Posted 26 August 2015 · Add Comment

Deliveries of the first Boeing F-15SA Eagles to the Royal Saudi Air Force (RSAF) are now imminent following the solution of an unspecified problem with the aircraft's all-new digital fly-by-wire (FBW) flight control system. Jon Lake reports.

The F-15SA flight-test programme was originally planned to last for 18 months, ending in July 2014, using three instrumented aircraft as ‘prototypes’.
The delivery of the first few full-series production aircraft to a US base was expected to begin in September 2014. These aircraft were to have been used for training an initial cadre of US Air Force and RSAF instructors in the USA.
Aircraft deliveries to King Khalid Air Base (KKAB) in Khamis Mushayt were then expected to follow in January 2015.
None of these deliveries have taken place and, at the time of writing, the flight-test programme was still under way, although about six ‘full standard’ production F-15SAs are believed to have been completed, painted and test flown, before being stored, in addition to the three instrumented aircraft currently being used to support the flight-test programme.
The first three instrumented production F-15SAs are being used as ‘prototypes’ in the flight-test and development programme. The first of these made its maiden flight at St Louis on February 20 2013, beginning the planned 18-month flight-test effort.
This was an unusually lengthy test programme for a variant of an existing aircraft type, though it was explained that this was necessary because the F-15SA’s new FBW system had to be cleared and recertified across the entire F-15 flight envelope.
The three ‘prototype’ aircraft were each allocated individual responsibilities within the programme. SA-1 (12-1001) was to be used for weapons testing, SA-2 (12-1002) for flutter and aerodynamics, and SA-3 (12-1003) for electronic attack and awareness testing.
The first two F-15SAs were subsequently given conspicuous DayGlo orange markings on their intakes, wingtips, tailerons and tailfins, using a very similar design to that of the very first F-15As in the early 1970s.
The third aircraft retained its standard Saudi air force camouflage, though all three carried USAF serials and US ‘star and bar’ national markings, the latter applied in black ‘outline’ form.
The stored production aircraft are now awaiting the conclusion of flight-testing, when they will receive the definitive FCS Software Solutions load. This will allow deliveries (and aircrew training) to begin.
In April 2015, photos emerged on social media of unidentified guests being shown around the first full production aircraft (12-1020) at St Louis, though this aircraft is understood to have been completed and flown some time before that. In January 2015 images had emerged showing later Saudi F-15SAs (including 12-1023 and 12-1025) being test-flown from St Louis, fully painted, and wearing toned-down US national markings in light grey.
Beyond brief announcements of the roll-out and first flight, Boeing has never commented on the F-15SA programme and has resolutely refused to help journalists requesting further information. But it is understood that flight-testing was put on hold due to engineering issues with the digital FBW system in the first week of April 2013, resuming in October.
A ‘stand-down’ from flight testing had always been planned to allow further control law development, system ground tests, and simulations, but it apparently occurred earlier, and went on for rather longer than expected, and envelope expansion with the new FCS was also slower than anticipated.
Many of the features of the new Saudi F-15SAs have already been seen on the Republic of Korea Air Force’s F-15K Slam Eagle, or on the Republic of Singapore Air Force’s F-15SGs, including the AN/APG-63(V)3 AESA radar (the most advanced radar available for export F-15s), the BAE Systems digital electronic warfare suite (DEWS), and the AN/AAQ-33 Sniper targeting pods and LANTIRN Tiger Eyes navigation pods, with the integrated Lockheed Martin AN/AAS-42 infrared search and track system in the Sniper pylon.
The F-15SA is also believed to incorporate a new ‘wide field of view’ head-up display (HUD) for the pilot, and may feature a new ‘wide area display’ in both front and rear cockpits.
Several of these systems have, therefore, already been integrated and fully tested on the F-15. But the new FBW control system, wide area display and wide field of view HUD, have not.
Compared to all other production F-15 variants, the F-15SA has two extra outboard under-wing weapons stations to allow increased weapons carriage. These new pylons (known as stations 1 and 9) are technically not new at all, however.
Every F-15 built has had provision for pylons in the same positions. These outboard hardpoints were originally designed to accommodate tactical electronic warfare suite (TEWS) pods on the original F-15A, before this equipment was abandoned. This was just as well, as wind tunnel testing had shown that the use of these stations would have destabilised the aircraft longitudinally to the extent that the original control system would not have coped.
In order to allow the use of these outboard under-wing stations, Boeing designed a new digital FBW flight control system for the F-15SA. It was also hoped that this would provide improved handling qualities and a significant reduction in maintenance compared to the original electro-mechanical control system. The new system was developed using experience from the F/A-18 and F-15 S/MTD control systems, and from Boeing’s unsuccessful X-32 JSF contender.
It had always been planned to transfer flight-test activities to Air Force Plant 42 at Palmdale (part of the Palmdale/Edwards complex in California), reflecting the F-15SA’s status as a US Air Force foreign military sales (FMS) programme, where Boeing was a sub-contractor and the US Air Force Life Cycle Management Center at Wright-Patterson Air Force Base was the US Air Force’s decision authority. The move was undertaken on November 1 2013.
The move to Palmdale also reflected the need to conduct higher risk activities in the less restricted airspace of the vast Edwards and Nevada ranges. These included flutter testing, stores separations, and flight at high angles of attack and with different stores configurations.
There were clues that progress was being made in early 2015, when the second F-15SA prototype was photographed carrying twin AMRAAM launchers on stations 1 and 9, while small, low-resolution photos on social media indicate that Boeing has been ‘fit-checking’ a variety of weapons load outs on F-15SAs and on a number of Boeing test assets, including an F-15E that seems to be in use as a test-bed for ‘advanced F-15’ derivatives.
The Saudi F-15SAs may use some of these weapons and load configurations.
One loading seen included an AGM-88E advanced anti-radiation guided missile (AARGM) outboard, a KEPD-350 Taurus cruise missile inboard, and a JDAM on the conformal fuel tanks (CFTs) ‘shoulder’, with small diameter bombs on the pylons under-slung below the CFTs.
An alternative air-to-air fit included no fewer than eight AIM-120 AMRAAM BVR missiles and eight close-range AIM-9X Sidewinders.
There remains the possibility that the Saudi F-15SA could be supplied with the conformal weapons bays (CWBs) that can be fitted in place of the standard CFT, and which still appear to be under development. The CWBs were originally developed for the F-15SE Silent Eagle, which also featured a number of F-15SA features.
The F-15SA has been used for testing of the new, digital JHMCS II version of the joint helmet-mounted cueing system (JHMCS), which began flight trials in SA-2 during June 2015.
The new version of the helmet features a newly developed high-definition, colour, smart-visor system that operates in both day and night modes, and which is more reliable and more affordable than the original JHMCS, as well as being less fatiguing for pilots to wear.
Vision Systems International, a joint venture partnership between Elbit Systems of America and Kaiser Electronics, produces JHMCS. It is not known whether an F-15SA was used for the helmet trial simply for convenience, or whether the new version of the helmet is being supplied to the Royal Saudi Air Force.
Spotters have yet to photograph the F-15SA prototypes flying with heavy air-to-ground load-outs, or in asymmetric configurations. This might suggest that a significant amount of testing remains to be completed.
A Boeing spokesman, however, gave a rather different picture. “The F-15SA flight-test programme is now proceeding at break-neck speed and deliveries are awaiting the imminent conclusion of the programme,” he said.
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