Silent Eagle joins the Stealth Squad
By Stephen Trimble
Boeing decided last September to launch the F-15 “SilentEagle” 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’tknow me, but I know there’s something going on, and I want to be a part ofit’,” says Brad Jones, Boeing’s manager for future F-15 programmes.
The Silent Eagle is Boeing’s most significant refresh of theF-15 programme since the F-15E entered service in 1988, but the prototype – aground-based demonstrator – publicly emerged within only six months of thelaunch decision. A flying demonstrator is scheduled in the first quarter of2010 to start evaluating aerodynamic qualities, to include firing a missilefrom the aircraft’s newly acquired internal weapons bay.
Need for speed
Boeing realised the programme needed to move fast. A monthbefore the launch decision, a presentation by South Korean air force officialson a pending fighter competition spurred the company to consider options forupgrading the F-15E. The new fighter would be aimed at the South Koreancontract, but also at other opportunities in Asia and the
Boeing acknowledges that proposals for add-ons such asthrust vectoring were also considered, but deemed too expensive. Instead, thecompany focused its attention on reducing the F-15E’s radar cross section andupgrading its analogue and bulky electronic warfare system.
Adding radar absorbent materials to leading edges can softenthe F-15SE’s head-on radar signature enough to be competitive against thefrontal aspect radar signature of the export version of Lockheed Martin’s F-35Joint Strike Fighter, Jones claims. “We know we can get to the
Canting both vertical stabilisers by 15° is intended toreduce radar returns to the side, but also reduces drag slightly on the aftsection. Finally, embedding missiles and bombs inside a heavily modifiedconformal fuel tank also reduces radar signature in all directions, and allowsthe F-15SE to perform its warfighting mission even with “clean” wings.
Boeing acknowledges that the F-15SE’s stealth improvementsdo not help against ground-based radar systems, which are critical for wagingoffensive strikes against opponents armed with surface-to-air missile systems.Lowering the F-15SE’s thermal signature – a critical stealthy feature for theLockheed F-22 Raptor – is also not part of Boeing plans.
But Boeing says the Silent Eagle is aimed at internationalcustomers more likely to use the it for defensive, counter-air missions, ratherthan offensive strikes in defended airspace where all-aspect stealth isnecessary for survival.
Despite the stealth improvements, Boeing says the F-15SEwill not trade off sensor or aerodynamic performance. Its Raytheon APG-63(V)3radar would remain canted slightly forward rather than tilted back, preservingcoverage and range at the expense of head-on radar cross section.
Moreover, Boeing has designed the F-15SE to also function asa non-stealthy, multirole aircraft with the F-15E’s full weapons payload of13,200kg (29,000lb). A conformal fuel tank with an internal weapons bay couldbe quickly removed after landing, allowing the aircraft to take off again witha full payload within 2h, it says.
Another key feature of the
F-15SE is its new EW system. Boeing has selected BAESystems’ digital electronic warfare system design, which includes a digitalradar warning receiver (RWR), digital jamming transmitter, integratedcountermeasures dispensers and an interference cancellation system. Theaircraft could jam enemy radars even as its own radar and RWR continues tooperate, Boeing claims.
The first F-15SE could be available for delivery to aforeign 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.