Boeing F-15SE Silent Eagle

The Boeing F-15SE Silent Eagle, an upgraded version of the McDonnell Douglas F-15E Strike Eagle aircraft, was first unveiled in March 2009 as a prototype. It features an innovative design which reduces its radar cross section. The F-15SE flight demonstrator aircraft, F-15E1, completed its first flight in July 2010.

Design

F-15SE is 63.6ft (19.4m) long, 18.5ft (5.6m) high and has a wingspan of 42.8ft (13m). The basic design of the F-15SE is similar to that of the F-15 Strike Eagle aircraft with new components added. The new components include the conformal weapons bay (CWB) instead of the standard conformal fuel tanks.

The CWB significantly increases the internal carriage capacity of the aircraft and also reduces its radar signature. Two additional weapons stations have been included to enable the aircraft to carry an additional four air-to-air missiles.

The Silent Eagle also features twin vertical tails canted 15° outward. Canted tails provide rear lift to the aircraft and reduce ballast usage, while increasing the range by 75 to 100 nautical miles. Coatings were also applied to various areas of the aircraft to minimize the radar signature.

The F-15SE has also been designed to function as a non-stealthy, multirole aircraft. The CWBs can be removed and the aircraft can be reconfigured to include conformal fuel tanks based on mission requirements.

Development program

Boeing began developing the F-15SE as an evolution to the F-15 family of aircraft. The company signed a Memorandum of Understanding with Korea Aerospace Industries in November 2010 for development of the F-15SE’s CWB.

Boeing successfully completed the weapons launch from the left CWB of the F-15E1 flight demonstrator aircraft in November 2010. The F-15E1 launched an inert AIM-120 demonstrating the aircraft’s ability to deploy a missile in flight.

“The F-15SE can carry air-to-air missiles, such as AIM-120 and AIM-9, and air-to-ground weapons.”

Wind tunnel tests on the CWB of the Silent Eagle were completed in June 2012. A scale model of the aircraft was used to test the aerodynamics of the CWB design.

Boeing offered the aircraft for the F-X III competition launched by South Korea’s Defense Acquisition and Procurement Agency to obtain 60 new fighter aircraft for the Republic of Korea Air Force. The F-15SE is competing for the $7.3 billion order with the Eurofighter Typhoon and Lockheed Martin’s F-35.

The three companies submitted their formal bids in June 2012. South Korea was scheduled to decide the winner of the competition in October 2012 but postponed the decision to mid-2013.

New orders from Saudi Arabia and Japan are also the driving forces behind the development of the next generation of F-15 aircraft. The development cost of F-15SE is estimated at $100 million each. Boeing plans to offer the aircraft to five foreign customers with an estimated market for 190 orders. Flight testing of the F-15SE was planned for 2013.

Aircraft engines, cockpit and avionics

The F-15SE will be fitted with two General Electric F110-GE-129 turbofan engines providing thrust of 29,000lbs, or two Pratt & Whitney F 100-PW-229 engines providing thrust of 29,000lbs.

The F-15SE will feature next-generation Joint Helmet Mounted Cueing System produced by Vision Systems International, Elbit 11in x 19in Large Area Display (LAD) system on the front and rear cockpits, digital fly-by-wire flight control system, Link-16 Fighter Data Link and infrared search and track (IRST) system. An advanced targeting pod provides the aircraft with target identification and autonomous tracking capabilities. A navigation pod will also be fitted to the aircraft providing it with all-weather and night-attack capabilities.

The aircraft will also feature advanced electronic equipment including BAE Systems digital electronic warfare system (DEWS) and active electronically scanned array (AESA) radar. The F-15SE Silent Eagle also incorporated a change to the vertical stabilizers. Whereas all preceding F-15s had featured twin vertical stabilizers, standing perfectly parallel to each other, the Silent Eagle’s stabilizers were canted outward at 15 degrees. The change reduced the Silent Eagle’s RCS and provided a bit more lift. The additional lift granted the Silent Eagle a 75-to-100 mile range increase over its predecessor.   

In addition to the structural modifications, the Silent Eagle was also coated in radar-absorbent materials, or RAM, to further reduce the jet’s RCS. “RAM is used on modern stealth fighters to minimize the radar return created by the facets of their designs that couldn’t be adjusted to deflect radar waves – things like ramjet inlets, the fighter’s nose, and the leading edges of its wings,” Hollings wrote.

Weapons and performance

The F-15SE can carry air-to-air missiles, such as AIM-120 and AIM-9, and air-to-ground weapons including precision-guided weapons, JDAM and globules admire. The F-15SE can fly at a maximum speed of 2,655km/h. It can climb at the rate of 15,240m/min.

The aircraft will have a range of 3,900km and a service ceiling of 18,200m. The empty weight of the aircraft will be 14,300kg and the maximum takeoff weight will be 36,741kg. The aircraft can carry a payload of 11,748kg.

The Silent Eagle featured a conformal weapons bay and fuel tanks, which served to reduce the jet’s radar cross-section, or RCS. The conformal weapons bay also allowed the Silent Eagle to carry four additional air-to-air missiles. The aircraft was qualified to carry a variety of weapons, including “AIM-9 Sidewinder and AIM-120 AMRAAM air-to-air missiles, JDAM satellite-guided bombs, and Small Diameter Bombs, among others,” as Alex Hollings reported in Sandboxx.

Most notably, the Silent Eagle could also carry “Raytheon AGM-88 high-speed anti-radiation missile (HARM) commonly leveraged by Wild Weasel aircraft hunting for enemy radar systems, making the Silent Eagle a viable and even potent option for SEAD (Suppression of Enemy Air Defenses) operations.” To further decrease the jet’s RCS, external missiles and fuel tanks were removed.

F-15SE Silent Eagle: An Interesting Idea

First introduced in 2009, the Silent Eagle was a modified Strike Eagle with stealth characteristics. Boeing developed the Silent Eagle especially for the export market, hoping to siphon business away from Lockheed Martin and their stealthy F-35 Lightning II. The F-15SE Silent Eagle was quite similar to the Strike Eagle, but the differences were noteworthy.

Why Did the F-15SE Fail?

Despite the Silent Eagle’s various RCS-lowering modifications, the F-22 and F-35 are still exceedingly more stealthy airframes – which contributed to the Silent Eagle failing to gain traction on the export market.

South Korea, which had strongly considered purchasing the Silent Eagle at $100 million per aircraft, opted instead to spend $176 million per aircraft on the truly stealthy F-35. Saudi Arabia, on the other hand, who had also considered purchasing the Silent Eagle, opted instead to purchase C, D, and Strike Eagle-variant F-15s.

The examples of South Korea and Saudi Arabia show the failure of the F-15 SE Silent Eagle to establish a niche market. Customers typically want to buy something cheap and reliable, or something cutting-edge.

The Silent Eagle fell somewhere in between – an expensive modification of a proven fourth-generation fighter, without true stealth capabilities.