Stealth Engine Advances Revealed in JSF Designs

Several aviation companies are competing for the ultimate in stealth propulsion in the Joint Strike Fighter (JSF) program. Stealth aircraft avoid radar signatures from designs that keep radar beams from striking the engine or radar-absorbing materials (RAM). The Pentagon, by extending the JSF competition, allowed more opportunities for stealth technology and engine design leaks. Industry's concerns about their competition-sensitive technology are justified with much already known about recent JSF improvements and the two distinct designs of Boeing and Lockheed Martin.
Engine faces are sources of large, distinct radar reflections that identify the engine and aircraft. Boeing and Pratt & Whitney, two engine manufacturers that cooperated, added stealth to the inlet guide by masking inlet vanes. Lockheed Martin and McDonnell Douglas diverted radar beams using air duct surfaces coated with RAM. Radar blockers in the latest JSF designs are an integral part of the engines. In contrast, radar blockers for the Boeing's F/A-18E/F and F-22 are separate add-on devices. The Lockheed F-117 has inlet screens that divert radar waves around the aircraft. The tradeoff in new stealth technology is one between costs and aerodynamic performance. Smaller aircraft use integrated serpentine ducts rather than large inlets in their stealth designs. In larger aircraft, a larger radar blocker is sometimes more efficient. A large complex inlet has integration costs and will put demand on power systems.
The Pentagon will have choices between short takeoff and vertical landings (STOVL) systems, inlet designs, weapon bays positioning, and sensor arrays in the two Boeing and Lockheed Martin designs. Infrared and optical sensors are used in newer antiaircraft missiles. Hiding hot elements and weapon systems are critical in addition to radar concealment. The Pentagon wants a stealth technology with radar and infrared blockers that are simple, inexpensive, and sturdy.