Silent Eagle joins the Stealth Squad
By Stephen Trimble
Boeing decided last September to launch the F-15 "Silent
Eagle" unveiled on 17 March in
But word of the project travelled fast through the company. "I received an email from an engineer saying: 'I don't know you, and you don't know me, but I know there's something going on, and I want to be a part of it'," says Brad Jones, Boeing's manager for future F-15 programmes.
The Silent Eagle is Boeing's most significant refresh of the F-15 programme since the F-15E entered service in 1988, but the prototype - a ground-based demonstrator - publicly emerged within only six months of the launch decision. A flying demonstrator is scheduled in the first quarter of 2010 to start evaluating aerodynamic qualities, to include firing a missile from the aircraft's newly acquired internal weapons bay.
Need for speed
Boeing realised the programme needed to move fast. A month
before the launch decision, a presentation by South Korean air force officials
on a pending fighter competition spurred the company to consider options for
upgrading the F-15E. The new fighter would be aimed at the South Korean
contract, but also at other opportunities in Asia and the
Boeing acknowledges that proposals for add-ons such as thrust vectoring were also considered, but deemed too expensive. Instead, the company focused its attention on reducing the F-15E's radar cross section and upgrading its analogue and bulky electronic warfare system.
Adding radar absorbent materials to leading edges can soften
the F-15SE's head-on radar signature enough to be competitive against the
frontal aspect radar signature of the export version of Lockheed Martin's F-35
Joint Strike Fighter, Jones claims. "We know we can get to the
Canting both vertical stabilisers by 15° is intended to reduce radar returns to the side, but also reduces drag slightly on the aft section. Finally, embedding missiles and bombs inside a heavily modified conformal fuel tank also reduces radar signature in all directions, and allows the F-15SE to perform its warfighting mission even with "clean" wings.
Boeing acknowledges that the F-15SE's stealth improvements do not help against ground-based radar systems, which are critical for waging offensive strikes against opponents armed with surface-to-air missile systems. Lowering the F-15SE's thermal signature - a critical stealthy feature for the Lockheed F-22 Raptor - is also not part of Boeing plans.
But Boeing says the Silent Eagle is aimed at international customers more likely to use the it for defensive, counter-air missions, rather than offensive strikes in defended airspace where all-aspect stealth is necessary for survival.
Despite the stealth improvements, Boeing says the F-15SE will not trade off sensor or aerodynamic performance. Its Raytheon APG-63(V)3 radar would remain canted slightly forward rather than tilted back, preserving coverage and range at the expense of head-on radar cross section.
Moreover, Boeing has designed the F-15SE to also function as a non-stealthy, multirole aircraft with the F-15E's full weapons payload of 13,200kg (29,000lb). A conformal fuel tank with an internal weapons bay could be quickly removed after landing, allowing the aircraft to take off again with a full payload within 2h, it says.
Another key feature of the
F-15SE is its new EW system. Boeing has selected BAE Systems' digital electronic warfare system design, which includes a digital radar warning receiver (RWR), digital jamming transmitter, integrated countermeasures dispensers and an interference cancellation system. The aircraft could jam enemy radars even as its own radar and RWR continues to operate, Boeing claims.
The first F-15SE could be available for delivery to a foreign customer three years after a deal is signed, says Boeing. Notionally, it estimates the design's unit cost including airframe, spares and training at $100 million.