超能老豆粤语13:Stealth Black Hawk : Radar-evading Version is...

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Stealth Black Hawk : Radar-evading Version is Vulnerable?

Profile: “radar-evading” version of Black Hawk

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Black Hawk

A previously undisclosed, classified stealth helicopter apparently was part of the U.S. task force that killed Osama bin Laden in Pakistan on May 1.

The exact type of helicopter is unknown but it appears to be a highly modified version of an H-60 Blackhawk. Photos disseminated via the European PressPhoto agency and attributed to an anonymous stringer show that the helicopter’s tail features stealth-configured shapes on the boom and the tail rotor hub fairings, swept stabilizers and a “dishpan” cover over a five-or-six-blade tail rotor. It has a silver-loaded infrared suppression finish similar to that seen on V-22s.

Stealth helicopter technology is not new and was applied extensively to the Boeing/Sikorsky RAH-66 Comanche, cancelled in 2004. Compared with fixed-wing stealth, more emphasis is usually placed on noise and infrared signatures.

Noise can be reduced and made less conspicuous by adding blades to the main and tail rotors. It can also be reduced by aerodynamic modifications and flight control changes that make it possible to reduce rotor rpm, particularly in forward flight below maximum speed. Infrared reduction measures are crucial – the Comanche had an elaborate system of exhaust ducts and fresh-air ejectors in its tailboom.

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V-22s

Radar cross-section (RCS) reduction measures include flattened and canted body sides, making landing gear and other features retractable, and adding fairings over the rotor hubs. It usually is not possible to achieve the same – you can’t make a helo as radar-stealthy as a fixed-wing airplane, but helicopters generally operate at low altitude in ground clutter. Reducing RCS also makes jamming more effective, whether from the aircraft itself or from a standoff jammer.

It’s Damaged Now, but not an unusual case

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Part of a damaged helicopter is seen lying near the compound after U.S. Navy SEAL commandos killed al-Qaida leader Osama bin Laden in Abbottabad, Pakistan, on May 2. (Reuters via Newscom)

The loss of a U.S. Black Hawk helicopter during the mission that killed Osama bin Laden reveals the vulnerability of such aircraft, but also reflects important lessons learned from earlier helicopter accidents.

U.S. government officials say the helicopter destroyed during the mission in Pakistan was a newer version of the two Sikorsky UH-60 Black Hawks that were shot down during a raid in Somalia in October 1993 that killed 18 soldiers.

In Pakistan, the helicopter packed with soldiers made a "controlled but hard landing" after encountering higher-than-expected temperatures at bin Laden's compound near Islamabad, Senator Dianne Feinstein told reporters on Tuesday.

The accident was not unusual, military experts said.

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Sikorsky UH-60 Black Hawks

Dozens of U.S. helicopters have crashed or been shot down in Afghanistan and Iraq, challenged by sandstorms and high temperatures that reduce the lifting capability of aircraft powered by rotors. In mountainous Afghanistan, there is the added challenge of flying at high altitudes.

The Pentagon is still investigating the problem in the bin Laden raid, but the helicopter was not damaged by enemy fire, said one defense official, who was not authorized to speak on the record. Officials said it suffered mechanical failure.

Although Not New Technology...

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F-117

The helicopter's low-observable technology is similar to that of the F-117 Stealth Fighter the retired special operations aviator said. "It really didn't look like a traditional Black Hawk," he said. It had "hard edges, sort of like an … F-117, you know how they have those distinctive edges and angles - that's what they had on this one."

The low-observable MH-60s were armed with the same sort of door mini-guns as standard MH-60s, "There was not a DAP conversion," he added, referring to the MH-60 variant known as the Direct Action Penetrator, which is equipped with stub wings upon which can be fitted a variety of armaments.

The early versions of the low-observable Black Hawks were not fitted with air-to-air refueling probes, the retired special operations aviator said. "The probe would disrupt the ability to reduce the radar cross-section," he added. "There was no way to put some kind of a hub or cowling over the probe that would make it stealthy." However, he said he did not know whether the models that flew the bin Laden mission had been equipped with such probes.

In addition, "in order to keep the radar cross-section down, you have to do something to treat the windshield," he said. If a special coating was applied to the windshield it is "very plausible" that would make the helicopter more difficult to fly for pilots wearing night-vision goggles, he said. The helicopters carrying the SEALs arrived over the bin Laden compound at about 1 a.m. local time on May 2. One crash-landed in the courtyard and was so badly damaged it was unable to take off again.

"It's hard to settle with power in a Black Hawk, but then again, if they were using one of these [low-observable helicopters], working at max gross weight, it's certainly plausible that they could have because they would have been flying so heavy," the retired special operations aviator said, noting that low-observable modifications added "several hundred pounds" to the weight of the MH-60, which already weighs about 500 to 1000 pounds more than a regular UH-60 Black Hawk.

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RAH-66

The low-observable program started with AH-6 Little Bird special operations attack helicopters in the 1980s, said the aviator. During the 1990s U.S. Special Operations Command worked with the Lockheed-Martin Skunk Works division, which also designed the F-117, to refine the radar-evading technology and apply it to the 160th Special Operations Aviation Regiment's MH-60s, he said. USSOCOM awarded a contract to Boeing to modify several MH-60s to the low-observable design "in the '99 to 2000 timeframe," he said.

Initial plans called for the low-observable Black Hawks to be formed into a new unit commanded by a lieutenant colonel and located at a military facility in Nevada, the retired special operations aviator said. "The intent was always to move it out west where it could be kept in a covered capability," he said. (Aviation week/Defense/Reuters)

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