Stealth Helicopter used in Osama Raid

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

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.)

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.



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.

Update: Quellish at Secret Projects mentions an ancestor system.

Read the Aviation Week article: Bin Laden Raid May Have Exposed Stealth Helicopter.