Stealth uses 'invisibility' to sneak up on Iraqis WAR IN THE GULF

January 22, 1991|By Ted Shelsby

It had to be frustrating for Iraqi air force officials: A plane that they couldn't "see" or hear flew over their headquarters building in Baghdad and dropped a 2,000-pound bomb down the building's air shaft.

The plane delivering the one-ton explosive, the F-117A fighter, "is not really magic or invisible," according to Hugh P. Burns, a spokesman for Lockheed Corp., which manufactured the plane.

"Only Wonder Woman has an invisible plane."

Technically, Mr. Burns is correct. A person on the ground can look up and see the F-117A streaking through the sky. But that same plane is not nearly as visible on radar, which replaced the human eye as the surest way of detecting enemy aircraft in World War II.

The secret of Stealth technology, explained Mr. Burns, is to reduce greatly a plane's "radar cross section" -- its electronic image on a radar screen.

In the case of the F-117As flying over Iraq, Mr. Burns said, their radar images "are smaller than a bird. They are almost bug-like. They are almost lost on the screen."

The F-117A is the only Stealth plane in operation with the U.S. military. Its manufacturer says it is hard to "see" because of a combination of design factors.

The plane's diamond shape eliminates many of the flat surfaces of other fighter planes in favor of angled panels that scatter radar beams.

The F-117A's outer skin is made of materials that absorb a radar signal in much the same way that a sponge absorbs coffee spilled on a counter, so that the signal is not bounced back for radar screens to detect.

Mr. Burns said materials used in building the plane are secret, but analysts have said Stealth construction makes wide use of ceramics.

According to the Massachusetts Institute of Technology, there also could be some salts that absorb radar frequencies dissolved in the materials used for the F-117A's wings and fuselage.

Another difference between the F-117A and the other fighter planes operating in the Persian Gulf, including the F-15, F-18 and A-16, is that the Stealth jet carries its weapons inside its body.

"Weapons hanging on the outside of the plane are very radar-reflective," Mr. Burns said. in explaining why the F-117A is made with a smooth exterior profile.

"One of the biggest radar reflectives," the Lockheed spokesman said, "is the jet engine fans."

For that reason, the engines on the Stealth fighter are built inside the body of the plane and are designed to give off less exhaust heat that can be detected by infrared sensors.

The F-117A that dropped the "smart bomb" down the air shaft of the Iraqi air force headquarters and blew it apart was also flying much more slowly than most of the other allied planes used in the bombing raids on Baghdad.

It would seem that the faster a plane zips through the sky, the more difficult it would be to see, but Lockheed engineers say that is not the case. The metal skin of a supersonic fighter gets hotter the faster the plane travels, and that heat gives off a "signature" that can be picked up by the enemy's electronic equipment.

Mr. Burns said the Stealth jet is also much quieter than most others.

"You don't want to be able to hear it," he said. "You want it to be as quiet as possible."

The engines and the exhaust system of the F-117A were designed with sound reduction in mind. "People often say they don't hear it until it's past," he said.

"I think this is what was happening in Baghdad, he said, "when the CNN guys were reporting that they could see bombs falling from the sky but couldn't [see] any planes."

The plane is painted black, Mr. Burns said, so that "it's hard as hell to see at night."

Secrecy has surrounded the F-117A most of its life. The Air Force unveiled the plane to the public in 1988 after it had been flying for nearly five years. Its development dates to 1978.

"We don't want to give people the wrong impression," Mr. Burns said. "This plane is not invisible; it's just real hard to see."

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