Sunday, 8 May 2011

Stealth helicopters kept under wraps until bin Laden raid


BLACK HAWK: Aftermath of crash exposes some secrets.

By ROBERT BURNS
The Associated Press

Secret until now, stealth helicopters may have been key to the success of the Osama bin Laden raid. But the so-far-unexplained crash of one of the modified Black Hawks at the scene apparently compromised at least some of the aircraft's secrets.


The two choppers evidently used radar-evading technologies, plus noise and heat suppression devices, to slip across the Afghan-Pakistan border, avoid detection by Pakistani air defenses and deliver two dozen Navy SEALs into the al-Qaida leader's lair. Photos of the lost chopper's wrecked tail are circulating online -- proving it exists and also exposing sensitive details.



The reason one of the helicopters crash-landed at the bin Laden compound has not been disclosed, but Daniel Goure, a defense specialist at the Lexington Institute think tank, said Friday it might be explained by the unusual aerodynamics resulting from the aircraft's modifications.

"It could be much more difficult to fly, particularly at slow speed and landing, than you would expect from a typical Black Hawk," Goure said.


The U.S. military's first stealth aircraft, the now-defunct F-117 fighter jet, was notoriously difficult to handle in flight, officials have said.


FAST ROPING

The elite Army pilots who flew the daring mission are members of the 160th Special Operations Aviation Regiment, nicknamed the Night Stalkers. Night Stalker pilots also fly other, publicly acknowledged versions of the Black Hawk that are specially equipped with advanced navigation systems, plus devices allowing for low-level and all-weather flight, day or night. Those are rigged to permit occupants to "fast rope" from the helicopter as it hovers just off the ground -- a technique used in the bin Laden assault.


Also taking part in the bin Laden mission were two MH-47 Chinooks, specially modified versions of the heavy-lift Chinook helicopters that are widely used by the Army.

The MH-47s are flown by the 160th. Those aircraft are not known to have stealth capabilities, although one was summoned to the scene of the raid after one of the stealthy Black Hawks crash-landed, to help ferry the SEAL contingent out of Pakistan.

Many aspects of stealth technology have been known for decades, including the use of angled aircraft edges and composite materials to make aircraft less visible on radar. The Army began a program to build a new class of helicopter with stealth technology in 1992. Known as the RAH-66 Comanche, it was canceled in 2004, in part to speed up development of drone aircraft.

Bill Sweetman, editor in chief of Defense Technology International and a longtime student of stealth aircraft development, said the biggest secret behind the stealth helicopter is simply that it existed.

"There was obviously a fairly high risk that you were going to compromise it one way or another the minute you used it," he said in an Associated Press interview.

A HIGH-STAKES GAMBLE


The decision to use the helicopters reflected the extraordinary stakes involved in eliminating bin Laden, the world's most wanted terrorist. It is not known whether the choppers have been used in earlier Special Operations raids, but Dick Hoffman, a former Navy SEAL and now a defense analyst at the Rand Corp. think tank, said he had never before heard of their existence.

Hoffman said in a telephone interview that the apparent stealth technology on the choppers boosted the raid's chances for success.

"Getting into the target area undetected is hugely important, especially with these terrorist targets and militia targets," he said. He noted that the SEAL team did not arrive at the Abbottabad compound in complete silence, since a resident in the same town was writing on Twitter during the raid that he could hear one or more helicopters and wondered what was happening.

But the modifications that suppressed noise from the helicopters -- including the use of extra blades in the tail rotor and placement of a hubcap-like cover on the rotor -- may have been sufficient to allow the assault teams to get on the ground before bin Laden and his security guards could mount enough of a defense to slow the SEALS; only one of the defenders was said to have gotten off a shot.

KEEP IT QUIET


Noise suppression, Goure said, is "a huge advantage in these kinds of strikes."

Some elements of that suppression technology were visible in photos of the tail section that was left behind. The main body of the copter was blown up by the SEALs before they left with bin Laden's corpse, apparently in order to prevent the exposure of other secret stealth components.

A Pentagon spokesman, Marine Col. David Lapan, declined to say Friday whether Pakistan was resisting U.S. efforts to retrieve the remains of the chopper.

Sweetman said it was remarkable that the SEALs managed to swoop into the compound and catch the bin Laden party by surprise.

"They're probably expecting that someday they could get a visit from (U.S.) Special Forces," he said. "But they would also be expecting to hear helicopters for a few minutes before they arrive overhead. If your first warning is that you hear the thing and then you look up and it's right there, you've lost valuable time."

Boeing Sikorsky RAH-66 Comanche Helicopter Wallpaper

The Boeing/Sikorsky RAH-66 Comanche was an advanced U.S. Army military helicopter intended for the armed reconnaissance role, incorporating stealth technologies. It was also intended to designate targets for the AH-64 Apache. The RAH-66 program was canceled in 2004 before it was fielded.


The RAH-66 is powered by two LHTEC T800 turboshaft engines. The RAH-66’s fuselage is 43 feet (13 m) long and is made of composite material. It incorporated stealth features to avoid detection, such as retractable weapon stations and main gun, and stealth faceting and radar absorbent materials. The Comanche’s noise signature is noticeably smaller than others in its class. The U.S. Army’s current armed scout helicopter is the OH-58D Kiowa Warrior, but it is an upgraded version of a Vietnam War-era observation helicopter. The Comanche however was specifically tailored to the role of armed scout. It is smaller and lighter than the AH-64 Apache attack helicopter.



The Comanche’s very sophisticated detection and navigation systems were intended to allow it to operate at night and in bad weather. Its airframe was designed to fit more easily than the Apache into transport aircraft or onto transport ships, enabling it to be deployed to hot spots quickly. If transport assets were not available, the Comanche’s ferry range of 1,260 nautical miles (2,330 km; 1,450 mi) would allow it to fly to battlefields overseas on its own.