At least two of the helicopters used in the raid on Osama bin Laden's compound seems to have been a new stealth design, according to several reports emerging from the scene. The use of such helicopters may have been key to the success of the operation that resulted in bin Laden's death.
A huge part of the operation was crossing the border between Afghanistan and Pakistan to avoid detection by the Pakistani military and get the Navy SEALs into Osama bin Laden's compound.
In the attack, 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. The purpose is not only to reduce the cross-section visible to radar, but to cut down the noise the helicopter makes. One must also reduce the amount of heat the engines generate.
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.