Stealth Blackhawk (Silent hawk) in pictures...

When compared to recent revelations of Chinese Stealth technologies it should be of no surprise that the American military was capable of creating a stealth Blackhawk.

 Of course the real shock is that they have been able to kept it secret.

Silent hawk? (from the Sun)

The Chinese have had rapid development in Stealth technology with the revelation of two working test beds of their new Stealth Fighter earlier this year.

J20 with variable fins and stealth technology

They have also developed a helicopter that incorporates some stealth technologies from shaped airframes to radar limiting coverings and paint.  Compare the Chinese designs on airframes in service to the Blackhawk drawings and the wreckage.

Chinese Attack helicopter WZ 10 (operational in 2010) 

WZ 10 with radar avoiding features

Stealth Helos Used In Osama Raid

Posted by Bill Sweetman

Well, now we know why all of us had trouble ID'ing the helicopter that crashed, or was brought down, in the Osama raid.

tail rotor recovered in Abbottababd raid

It was a secretly developed stealth helicopter, probably a highly modified version of an H-60 Blackhawk. Photos published in the Daily Mail and on the Secret Projects board show that the helicopter's tail features stealth-configured shapes on the boom and tip fairings, swept stabilizers and a "dishpan" cover over a non-standard five-or-six-blade tail rotor. It has a silver-loaded infra-red suppression finish similar to that seen on some V-22s. 

A graphic of a so called Silent hawk

No wonder the team tried to destroy it. The photos show that they did a thorough job - except for the end of the tailboom, which ended up outside the compound wall. (It almost looks as if the helo's tail hit the wall on landing.)

http://www.aviationgraphic.com/sparta/

Aviation Graphic's version of the Stealth Blackhawk compared to a typical Special Forces helicopter

Stealth helicopter technology in itself is not new and was applied extensively to the RAH-66 Comanche. Priorities are usually different versus fixed-wing aircraft. Reducing noise and making it less conspicuous is the first job (more main and tail blades reduce the classic whop-whop signature). Listen here. 

Noise can also be reduced by aerodynamic modifications and flight control changes that make it possible to slow the rotor down, particularly in forward flight below maximum speed. Infra-red reduction measures are crucial -- the Comanche had an elaborate system of exhaust ducts and fresh-air mixers in its tailboom.

Comanche cancelled in 2004 (stealth gunship)

Radar cross-section reduction is also possible - you can't make a helo as radar-stealthy as a fixed-wing airplane, because of all its moving parts, but on the other hand it is generally operating at low altitude in ground clutter, and is not an easy target. Reducing RCS also makes jamming more effective, whether from the aircraft itself or from a standoff jammer.

The willingness to compromise this technology shows the importance of the mission in the eyes of US commanders -- and what we're seeing here also explains why Pakistani defenses didn't see the first wave (at least) coming in.