H 60

The YUH-60 flight test program revealed the need for sonie changes in the aircralt s eonfiguration. The large fixed sweptback horizontal stabilizers were found to cause an excessive nose up attitude during a quick stop flarę for landing. This was caused by main rotor downwash impinging on the stabilizer. After testing a number ot alternative designs (1974 and into early 1975) a movable all flying stabilator was developed. Ihe prototype, modified with this stabilator first flewon 13 March 1975. The stabilator was depressed 40 degrees in the hover and in Iow speed flight to reduce effects of the main rotor downwash.

The taił rotor pylon area was reduced in size to lessen the effect of the taił rotor downwash. The original vertical pylon had been intended to be large enough to counteract engine torque in forward flight if taił rotor thrust was lost. The modified prototype with the smaller taił rotor pylon first flew in October of 1975.

Another change was in the main rotor head. It was found that the rotor head had to be raised due to rotor vibration caused by the proximity of the rotors to the airframe which created stress loads on the airframe. As a result, the rotor shaft was raised fifteen inches by the installation of a main rotor shaft extension. This extension was removable so that the rotor head could be lowered (not removed) for loading onto a C-130 or C-141.

Other minor changes were madę and on 17 May 1975, the production standard YUH-60 first madę its first flight. On 19 March 1976 two finał configuration prototypes were delivered to the Army at Fort Rucker, Alabama for developmental testing and one was delivered to Edwards Air Force Base, California, for engineering testing. The Fort Rucker machines were flown to Fort Campbell, Kentucky for operation testing in June of 1976 and, when the testing was completed. some 812 flight hours had been logged in all climates, from desert conditions to -65 degrees Fahrenheit.

The UTTAS competition ended on 23 December 1976 when the Army declared the Sikorsky YUH-60 as the winner. In September of 1977, the Army announced that the YUH-60 would be named the Black Hawk. following the Army tradition of naming its aireraft for Native American tribes.

This YUH-60A prototype carries a flight data sensor boom on the starboard side. The boom provided important information during the initial flight test program. The aircraft featured swept horizontal stabilizers, a short rotor mast and a wide chord taił rotor pylon. (Sikorsky via USSAM)

5

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