Author's notes: Recently while digging around the Internet (looking for clues, contract, patents and what not) into the reported Stealth Black Hawk used in the bin Laden raid - I came across this interesting patent - complete with illustrations showing "low observable engine inlet system" for a helicopter.
Amazingly enough, one of the drawings shows the inlet as it would look on a UH-60 Black Hawk Helicopter.
Click to enlarge:
The inlet - is very similar to the low-observable inlets on the RAH-66 Comanche - the Army's first attempt to build a stealth helicopter.
In February 2004, the US Army "cancelled" further research, development and planned purchases of the RAH-66 Comanche stealth helicopter. It believed that the helicopter would not meet the requirements of changing operational environments.
The patent was filed in 1997 by United Technologies Corporation of Hartford Conn.
The Comanche RAH-66 reconnaissance and attack helicopter was being developed by Boeing and Sikorsky for the US Army. The first flight of the Comanche took place on 4 January 1996.
Production of the Comanche would have taken place at Sikorsky's site also in Connecticut.
The Boeing-Sikorsky RAH-66 Comanche was cancelled on 23 February 2004, after 22 years, 6 program restructurings, and 6.9 billion dollars.
The Army said it would use the $14.6 billion earmarked for 121 Comanches between 2004 and 2011 to buy 796 additional Black Hawk and other helicopters and to upgrade and modernize 1,400 helicopters already in the fleet.