The Pentagon Has Figured Out How to Hunt Enemy Stealth Fighters

Infrared sensors popping up on more and more U.S. warplanes

On Feb. 11, a U.S. Navy F/A-18F Super Hornet fighter flew for the first time with a new infrared sensor fitted to its underbelly fuel tank.

And a year ago in the spring of 2013, War is Boring contributor David Cenciotti spotted the same heat sensor fitted to the air intake of an Air Force F-16 at a war game in Nevada.

Around the same time, the Air National Guard wrapped up air-to-air testing of the Sniper IR targeting pod on an F-15C.

The near-simultaneous appearance of a range of new infrared sensors on Navy and Air Force fighters is no coincidence. It’s apparently all part of the Pentagon’s preparations for the first possible stealth air war, potentially involving radar-evading jets from the U.S., Russia and China.

Japan, South Korea and India are also working on stealth fighters. The proliferation of new warplanes able to avoid radar detection—thanks to their special shaping and coatings—compels the Americans and others to find new ways to detect enemy planes.

Hence infrared. Fighter heat sensors aren’t exactly new—the Russians have been using them for decades. But they are becoming more important in the current era of stealthy air warfare.

Lockheed’s IRST. Lockheed photo

Which stealth?

Radar stealth is a fairly old art by aviation standards, dating back to the 1960s. Engineers know they can carefully craft airframes in order to avoid presenting flat surfaces and hard angles perpendicularly to a radar. That minimizes radar bounce-back.

Equally, some materials can actually absorb radar energy instead of returning it. Apply that stuff to the outside of your plane and you can shave an order of magnitude from its radar signature.

But it’s much harder to mask a plane’s heat signature. Combusting jet fuel and moving quickly through the air obviously creates huge amounts of heat. The Mach-three SR-71 spy plane—admittedly an extreme example—registered 800 degrees Fahrenheit at its nose during high speeds.

Some warplane designs try to isolate heat rather than removing it. The A-10 tank-killer, for example, keeps its engines above the fuselage and between the tail fins, blocking the view of enemy missileers on the ground—albeit imperfectly.

America’s stealth warplanes—the B-2 bomber and F-22 and F-35 fighters—reportedly use their internal fuel as heat sinks in order to keep their outside skins as cool as possible. The fuel system sucks up excess heat, conveniently using it to improve the fuel’s efficiency.

But fuel sinks pose big design and management challenges. As you burn off gas during flight, you lose the ability to absorb heat internally and must send more of it radiating out your tail pipe, where it can be more easily detected.

Air Guard F-15C with Sniper pod. Air Force photo

New eyes

All that is to say that even stealth warplanes can be hot—especially stealth planes optimized solely for radar-evasion. Relative newcomers to stealth, Russia and China might lag behind in infrared suppression.

So the Navy and Air Force are adding IR sensors to many of their planes. The Navy has begun test-flying Lockheed Martin’s Infrared Search and Track system on a Boeing F/A-18F. Adding the sensor to all 500 or so Super Hornets could cost up to $500 million.

“IRST is a passive long-range sensor system that uses infrared search and track technology to detect airborne threats and provide weapon-quality track solutions on those targets,” Lockheed explained in a release.

The sensor has the added benefit of being passive—that is, it doesn’t emit energy, only receives it. A fighter with IRST can spot enemy targets without giving away its own location. IRST works even when the enemy is jamming your radar with electronic noise.

And if a pilot is comfortable turning on his radar, he can use IRST to help tell apart two enemy planes flying close together. “Not only can IRST detect air threats, it provides increased discrimination of threat formation at longer ranges, enhancing multiple target resolution significantly compared to radar,” according to Lockheed.

“IRST will transform the way the Super Hornet conducts air-to-air operations and allows the fleet to dominate the skies in all threat environments,” said Capt. Frank Morley, the Navy’s F/A-18 manager.

The new Lockheed sensor is actually an upgrade of the much older AN/AAS-42 sensor fitted to the Navy’s F-14D, which entered service in the early 1990s and retired in 2006.

The F-14 carried the heat sensor under its nose. To ease its addition to a wide range of American and allied planes, Lockheed offers a number of IRST attachments. The Super Hornet plugs the sensor into the front tip of a modified 400-gallon drop tank. On the F-16, the IRST attaches to a pylon that fits to the air intake.

In March 2013, eagle-eyed reporter Cenciotti spotted the sensor on an F-16 belonging to the Air Force’s 64th Aggressor Squadron, which simulates the enemy in the semi-annual Red Flag war game at Nellis Air Force Base in Nevada.

F-22 and B-2 stealth planes attend most Red Flag exercises. The 64th’s F-16s need to be able to find them—not only to train the stealth crews in defensive tactics, but also to prepare U.S. fliers for a time, not long from now, when Russia, China and other countries could have stealth warplanes of their own.

The Air National Guard is ahead of the curve. In 2011, the reserve force began testing the Lockheed-made Sniper targeting pod on one of its approximately 130 Boeing F-15C fighters.

The Sniper pod, normally used to spot ground targets, includes much of the same technology as IRST and has “some pretty good air-to-air tracking capability,” according to Jon Sutter, Lockheed’s Sniper manager.

The two-year Sniper test was meant to improve the reserves’ ability to inspect suspicious aircraft at night—but the IR pod could also work against stealth planes. Northrop Grumman’s Litening pod reportedly has the same ability—especially in its new ATP-SE version.

The targeting pods’ anti-stealth skill might help explain why the active-duty Air Force cancelled the planned installation of the Lockheed IRST on its roughly 100 F-15s, an upgrade that could have cost more than $300 million. The flying branch could just use pods instead—although this begs the question why the Air Force fitted IRST to Lockheed F-16s.

Ironically, the Air Guard—having demonstrated an alternative to IRST—wants to revive efforts to fit the new Lockheed sensor to F-15s starting in 2015.

Programmatic chaos aside, the trend is clear. More American jet fighters are getting infrared sensors—and this could help them battle the Chinese- and Russian-made stealth fighters of the near future.

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