From Aviation Week

 

Boeing Unveils New Stealthy F-15

Mar 17, 2009

Amy Butler/St. Louis, Mo.

 

Boeing unveiled the prototype of a new variant of the F-15 Strike Eagle aimed at the Asian and Middle East markets that will incorporate stealthy coatings and structure here on Mar. 17.

 

Company officials hope the new aircraft will garner up to 190 orders, extending the F-15 line beyond the current backlog of 38 aircraft for South Korea and Singapore. Since the company lost the Joint Strike Fighter contest to Lockheed Martin, the future of its St. Louis manufacturing facility has been uncertain. Continued F-15 sales, as well as additional orders for F/A-18E/Fs and EA-18Gs, are the only work in the foreseeable future for the plant.

 

Major design changes in the new "Silent Eagle" version include internal bays within the existing conformal fuel tanks that can carry a variety of air-to-air and air-to-ground weapons. Each tank will be configured to hold two air-to-air missiles, including the AIM-9 and AIM-120 or a combination of the two.For the air-to-ground mission, 1,000- and 500-pound Joint Direct Attack Munitions can be carried or four 250-pound Small Diameter Bombs per tank. Weapons loadout can also be split between the AIM-120 and JDAM for a multirole mission.The Silent Eagle configuration includes 15-degree outward-canted V-tails - a shift away from the characteristic vertical fins of the F-15 that reduces the radar cross-section.

 

The Mach 2.5 speed of the Strike Eagle is maintained, but the cost is about 180-200 nautical miles of range capability because of the reduce fuel in the conformal tanks, says Brad Jones, program manger for F-15 future programs.

 

The new design includes a digital electronic warfare system (DEWS), made by BAE Systems, that can operate simultaneously with the aircraft's Raytheon active electronically scanned array radar.

 

Stealth coatings, though not yet applied to Boeing's prototype, could be added at a later time. Boeing says the coatings could contibute to an equivalent amount of front-aspect stealth as that offered by Lockheed's F-35. This includes reducing radar returns from sharp edges on the aircraft, including antennae.

 

Stealthiness for the F-15 was explored about a decade ago for the U.S. Air Force as an alternative to the Lockheed-led F-22, but was never pursued. "The internal carriage is what is new. The stealth is not," Jones says, adding "We are not really after the F-22 market or the F-35 market" with this new design.

 

The level of stealthiness exportable on the F-15 is up to the U.S. government to decide, Jones says. Though USAF officials have been given courtesy briefings on the Silent Eagle, talks on stealth exportability have not yet occurred.

 

A radar blocker for engine inlets, already fitted in F/A-18E/Fs, could be added depending on how much radar cross-section reduction is required by the customer and allowed by the government.

 

Jones estimates the cost of a Silent Eagle will be about $100 million per aircraft, including spares, if built new. A retrofit kit including the conformal fuel tanks, DEWS and coatings could be added to existing Strike Eagles, he says.

 

The target market includes South Korea, Singapore, Japan, Israel and Saudi Arabia, Jones says. The first likely customer is South Korea, which is looking for two new fighters, including its F-X Phase III program, which calls for 60 aircraft in the F-15 class.

 

South Korea's Agency for Defense Development is also pushing for a KFX program, which calls for about 120 domestically developed stealth fighters. Jones says coproduction of stealth materials would be subject to U.S. government review and a tough case to sell.

 

Japan and Saudi Arabia are also looking for new F-15-class fighters. And if the Silent Eagle were sold to the Saudis, Israel likely would want a chance to buy the aircraft too to maintain balance of power in the Middle East.

 

Boeing's willingness to integrate indigenous systems, such as electronic warfare suites, onto the Silent Eagle is an option that could be of interest to these customers - especially Israel. Israeli industry was recently rebuffed by U.S. officials unwilling to add foreign EW systems under the F-35 development program.

 

The weapons-carrying fuel tanks, which are affixed to the aircraft with two bolts, and can be removed within about 2.5 hours. Reinstalling the original fuel tanks restores the F-15 to its nonstealthy configuration, which is capable of hauling more and larger weapons, including anti-ship missiles.

 

The Silent Eagle prototype is based on F-15E1, the program's flight test aircraft. To date, it has been outfitted with the conformal tanks and the canted tails, which are for demonstration only and not structurally integrated. The actual canted tails would be added later if a customer requested them. Stealth coatings and engine intake blockers have not been added.

 

Jones says Boeing hopes to begin flight testing the weapons-carrying conformal tanks on the aircraft in the first quarter of next year. Design work on the Silent Eagle concept began in September last year in response to feedback from F--15 customers, he says.

 

 

 

 

 

 

From Aviation Week's ARES Blog

 

Silent Eagle - The Technoid View

Posted by Bill Sweetman at 3/17/2009 12:14 PM CDT

 

Last September, an eight-engineer group at Boeing set out to see what could be done to make the F-15 Strike Eagle more stealthy. The result, unveiled today in the form of mock-up components attached to the F-15E-1 test airframe, is Silent Eagle. Late this year or early in 2010, the same aircraft should be flight-testing the new configuration, including at least one weapon release.

 

The team has desiged internal weapon bay units that have the same aerodynamic shape and aircraft interfaces as the conformal fuel tanks (CFTs) of the F-15E and its export derivatives. The bays can be swapped for the standard CFTs on the flightline. Each side bay has two doors and two weapon mounts, The upper, side-opening door carries a rail launcher for an AIM-120 AMRAAM or an AIM-9-type missile, or a launcher for a single 500 lb bomb. The lower door accommodates a trapeze-plus-ejector mount for an AIM-120, a single 500-lb or 1,000-lb bomb or two Small Diameter Bombs.

 

The other principal change to the Silent Eagle is the adoption of a small outward cant to the vertical tails, which not only reduces side-on RCS to some degree but also, with the aid of a little toe angle, generates a small amount of lift and improves the fighter's trim, eliminating nose ballast. Lastly, the Eagle gets an extensive radar absorbent material (RAM) treatment, including a frangible cover on the gun muzzle.

 

The overall goal, however, is to minimize both changes and the use of exotic technology. For now, the Silent Eagle is aimed primarily at two markets. One is Japan's F-X requirement. The other is international customers who already fly advanced F-15E derivatives, including Singapore, Israel (both of them notionally JSF customers) Korea and Saudi Arabia. So the idea is to use off-the-shelf, exportable RAM, to carry out the program as an international venture and make the modifications retrofittable.

 

The concept is to give the operator a choice between a reduced-RCS configuration and the standard heavy-payload Strike Eagle load-out. The "slick" version would carry internal weapons and no external tanks. Boeing says that the aircraft loses most of the 1500 US gal of fuel in the CFTs, but that other changes - some fuel in the new CFTs and a more compact EW suite from BAE Systems - restore some 550 US gal. With other offsetting advantages - for example, the "slick" aircraft can take off with partial afterburner - the fuel fraction should be enough to provide a reasonable range. Also, the CFTs are cleared for the full envelope of the aircraft, including speeds above Mach 2 - a capability that's been demonstrated in tests of Singapore's new F-15SG.

 

A bar-napkin performance comparison of the F-35 with the Silent Eagle makes interesting reading. The Eagle is a bigger aircraft, with two seats, two engines and almost one-third more wing, and its operating empty weight is 25 per cent greater than the F-35. Clean, the F-35's fuel fraction of 0.375 is better than the Silent Eagle's 0.32.

 

On the other hand, in clean configuration, the Silent Eagle is faster than the F-35, has a lower wing loading and higher thrust/weight ratio (almost 1:1 at its 58,000-pound estimated clean take-off weight, with the latest engines from P&W and GE). It carries the same number of AAMs (until someone figures out a six-AAM arrangement for the F-35) and has an internal rail-launch option for the AIM-9X, permitting lock-on before launch.

 

However, Boeing says that they're not competing with the JSF - and that it was mere coincidence that the design started just as the Israelis started seeing the real price of the F-35A.

From Aviation Week's ARES Blog

 

Opening Doors - Silent Eagle on Video

Posted by Graham Warwick at 3/18/2009 2:32 PM CDT

 

As a coda to Bill and Amy's on-the-spot coverage of the Silent Eagle unveiling in St Louis on Mar. 17. here is a little Boeing video showing how AIM-120 AMRAAMs would be deployed from the internal bays in the conformal tanks. This is a working mockup - Amy tells me they would deploy much faster on the real aircraft.

 

The weapon in the upper bay is attached to the outward-opening door and can be an AIM-120 or AIM-9-class missile, a 500lb JDAM or two 250lb Small Diameter Bombs. The weapon in the lower bay is attached to a trapeze launcher/ejector and can be an AIM-120, a 500lb or 1,000lb JDAM or two SDBs, according to Boeing.