It's no secret how America's stealth warplanes primarily evade enemy radars. Their airframes are specifically sculpted to scatter radar waves rather than bouncing them back to the enemy. Somewhat less important is the application, to select areas, of Radar Absorbing Material (RAM) meant to trap sensor energy not scattered by the plane's special shape.
In short, the four most important aspects of stealth are "shape, shape, shape and materials," to quote Lockheed Martin analyst Denys Overholser, whose pioneering work resulted in the F-117 Nighthawk, the world's first operational stealth warplane.
But in addition to shaping and RAM, the Pentagon's current stealth planes -- the B-2 Spirit bomber, the F-22 Raptor fighter, the RQ-170 Sentinel drone and the in-development F-35 Joint Strike Fighter -- boast other, lesser-known qualities that help them avoid detection. (We left the Army's stealth helicopter out of the discussion owing to a lack of information.)
These other stealth enhancements include: chemicals to eliminate telltale contrails; sophisticated, untraceable sensors and radios; specially designed, hard-to-detect engine inlets; radar-canceling paint; and cooling systems for reducing a plane's heat signature. All of these evasion methods have been disclosed by the Air Force, although sometimes in scant detail.
With China and Russia both demonstrating a rapidly improving grasp of stealth shaping -- and materials to a lesser extent -- these other, possibly harder-to-master aspects of radar-evasion are arguably becoming more important to maintaining America's aerial advantage.
Smart Sensors
Radar is like long-range eyes in the sky for modern warplanes. Without this sensor, a plane is more or less flying blind. The problem is, radar works by emitting energy -- lots of it. And that can be detected by an enemy's own passive radar receptors in the same way that someone standing in a dark room can track the movements of another person carrying a flashlight.
The F-22, F-35 and B-2 work around this problem by practicing what Aviaton Week stealth guru Bill Sweetman called "emission-control principles." With the Raptor, emissions from the jet's APG-77 radar "are managed in intensity, duration and space to maintain the pilot's situational awareness while minimizing the chance that its signals will be intercepted." In other words, the plane's software is smart enough to use just enough energy to find and track targets -- and no more. The B-2 and F-35 have electronically-scanned radars that are similar to the Raptor's and probably employ the same tactics.
Plus the Raptor and Joint Strike Fighter both have non-emitting backup sensors that can fill in the gaps in the radar coverage. The F-22's ALR-94 radar-warning receptors are among the most sensitive ever designed and can accurately, and "silently," detect most radar-using targets at long range. The F-35 boasts a powerful set of cameras that achieve the same effect.
Photo: Air Force
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