Stealthy F-15 Could Enliven St. Louis Facility
By Amy Butler
Boeing hopes to extend the life of its F-15 production line with the unveiling of a new variant to incorporate stealthy coatings and structures.
Company officials say the new F-15SE "Silent Eagle" - designed under a secret project called "Monty" - could garner up to 190 sales abroad, especially to nations already operating F-15s. The target market is South Korea, Singapore, Japan, Israel and Saudi Arabia.
With Silent Eagle, Boeing is "slipping into the silent cloak of stealth," says Dan Korte, vice president and general manager of Global Strike Systems.
South Korea is the likely first customer: Seoul expects to embark on its F-X3 program soon, with a goal of buying about 60 F-15-class aircraft. A request for proposals is expected in the first quarter of 2010, with a downselect to a winner later in the year. A contract would follow in the first quarter of 2011.
The current F-15 backlog is 38 aircraft, with deliveries to both Singapore and South Korea pending. The production rate is about 12 per year, and that can be increased depending on demand.
The fate of Boeing's workforce in St. Louis is uncertain beyond the 2014 time frame. That's because Lockheed Martin won the massive Joint Strike Fighter competition and established the "fifth-generation" fighter market, capturing a host of international customers. Boeing also lost out on government-funded stealthy UAV work since losing the Navy Unmanned Combat Air System contract to Northrop Grumman last year.
Orders remain strong for the F/A-18E/F and EA-18G made here; they are expected to carry through 2014, including deliveries to the U.S. Navy and Australia.
St. Louis is also the site of manufacturing for the T-45 and some C-17 structures; but the C-17's future is murky, and the program has survived only with congressional intervention.
The idea behind the Silent Eagle is to capture orders from existing F-15 countries by adding what Boeing officials say are inexpensive modifications to the aircraft. But they say they're not targeting the market already served by the F-35 and F-22.
Stealthiness for the F-15 was explored about a decade ago for the U.S. Air Force as an alternative to the F-22, but it was dashed once the twin-engine Lockheed Martin Raptor program took root.
The Silent Eagle's main addition is the incorporation of a new conformal fuel tank (CFT) under either wing designed to carry weapons internally. "The internal carriage is what is new. The stealth is not," says Brad Jones, F-15 future programs director, adding: "We are not really after the F-22 or F-35 markets" with this new design.
Mark Bass, F-15 program manager, says the Silent Eagle configuration can be used for first-day strike operations that require stealth. The modified CFTs can be removed, and the original tanks outfitted with weapon pylons can be remated to the aircraft within about 2 hr. to conduct missions in permissive airspace. This configuration would allow use of the standard F-15 weapons suite, including larger antiship missiles.
Each CFT was designed to carry 1,500 gal. of fuel. The redesign of each tank incorporates two separate weapon bays. The top bay includes a rail launcher suitable for an AIM-9, AIM-120, a single 500-lb. Joint Direct Attack Munition (JDAM) or two Small-Diameter Bombs. The bottom bay could dispatch these or a 1,000-lb. JDAM. Though this loadout is significantly less than the F-15E's traditional configuration, the internal carriage required for reduced radar cross section (RCS) is a limiting factor; the Silent Eagle loadout is similar to that of the F-22.
CFTs could be produced in customer nations, says Bass. Also, they could be used in the future to house jamming systems or intelligence-collecting radars.
The tradeoff for the reduction of onboard fuel is losing about 180-200 naut. mi. of range, says Jones. Engineers are exploring whether they can section off some areas of the CFT in front of and behind the weapon bays to carry additional fuel, buying back some of that range.
Boeing's prototype of the Silent Eagle is based on the F-15E1, the Air Force test aircraft leased by Boeing for demonstration purposes. The conformal fuel tanks in the prototype were provided by the Air Force and modified for weapons carriage by Boeing. The bay doors are made of composite material.
The Air Force is not currently buying new F-15s; however, the service is interested in keeping the line alive through international sales, Boeing officials say. Any of the new F-15 models, including the Silent Eagle, could be a candidate if the Air Force is forced to buy older aircraft to build up its fleet numbers. However, the service has been focused on buying only fifth-generation fighters, which include the single-engine F-35 and the twin-engine F-22.
Also included in the Silent Eagle design is the notional addition of 15-deg. canted tail fins, a departure from the characteristic twin vertical stabilizers of the F-15 family. Though the prototype includes canted tails, they are merely for display purposes and are not structurally integrated into the airframe.
The F/A-18E/F, F-22 and F-35 all have tails canted between 15 and 18 deg., company officials say, to reduce radar cross section.
The new V-shaped vertical stabilizer design reduces the aircraft's RCS and also has the unintended consequence of generating lift at the back of the airframe, allowing engineers to reduce the amount of ballast in the front, says Jones.
The F-15E1 will begin flight tests in the first quarter of 2010 using the standard vertical-tail configuration. The testing will be dedicated to evaluating the operation of the conformal fuel tank bays only, says Jones. Through October, Boeing plans to explore the conformal tank loads, dynamics, store separation and mass properties on the ground. Needed modifications will be fitted onto the aircraft by year-end.
Stealthy coatings can be applied on straight edges around the aircraft to reduce the RCS. However, their location and application must be approved by the U.S. government, and those negotiations haven't yet taken place. The F-15E1 does not currently have the coatings. Jones says the F-15 Silent Eagle can be made as stealthy from the front aspect as an F-35 using RCS-reducing techniques incorporated into the design.
Silent Eagle will lack stealthy propulsion system features, including engine intake blockers, which are part of the F/A-18E/F design. It will also lack infrared signature suppressors on the back end of the aircraft to temper exhaust from the engines and radar blockers, says Jones. These decisions were made largely to curtail costs.
Also included in the design is a new digital electronic warfare system (DEWS), which replaces four line-replacable units with one integrated system. The radar warning receiver, jammer, countermeasures dispenser and interference blanker are better integrated to operate with the aircraft's active, electronically scanned array radar. Each tail boom contains two countermeasures dispensers as well as antennas and transmitters.
Jones says the cost of a new-build F-15 Silent Eagle is about $100 million, including spares and support for the RCS-reducing material. Though Boeing hasn't released the price of the F-15SGs sold to Singapore, officials say the cost is similar to that of the Silent Eagle. It is unclear how this compares with the price of a Joint Strike Fighter. The JSF cost is estimated to be about $70-80 million in Fiscal 2014 dollars.
Boeing is pushing new builds of the F-15 Silent Eagle. However, the conformal fuel tanks outfitted with weapons could be purchased as a kit to add on to existing F-15E variants.
With Bradley Perrett in Beijing and David A. Fulghum in Washington.
