At least one of the helicopters used in the raid on Osama bin Laden's compound might have been a new stealth design, according to several reports emerging from the scene.

In an attack on the compound where Osama bin Laden was in hiding, one of the helicopters was forced to land, and was destroyed by the U.S. Navy SEAL team that eventually killed bin Laden. The tail section was separated and soon photos of it were making the rounds on the Internet.

According to an unnamed source quoted by the Army Times, the tail doesn't look like any of the acknowledged helicopters in use by the U.S. military. One feature is the large disc covering part of the rotor. Another is the edges on the surface that lend it a somewhat different shape. Such sharp angles are similar to those used in older models of stealth aircraft such as the F-117.

The Army Times source noted that there are several trade-offs in building a stealth helicopter. Unlike a stealth fighter jet or bomber, the purpose is not necessarily to reduce the cross-section visible to radar, but to cut down the noise the helicopter makes.

To do that, one can increase the number of rotor blades and reduce the speed at which they turn. The problem is that reduces the lift they can produce.

The crash landing might have been caused by settling with power, which occurs when a helicopter descends too quickly. The turbulence below the craft, generated by the rotors' downwash, prevents them from getting the lift they need. The Army Times' source, a retired special operations aviator, noted that modifying a typical Blackhawk helicopter to be stealthier adds a lot of weight and make them more difficult to fly.

The U.S. military has requested that the Pakistani government return the tail section. Analysts say that may take some time as the Pakistanis may want to examine it closely to see what technologies are used.

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