Air America's Black Helicopter
The secret aircraft that helped the CIA tap phones in North Vietnam.
- By James R. Chiles
- Air & Space magazine, March 2008
(Page 2 of 7)
Disturbing the peace
The Hughes Tool Aircraft Division had started working on such a helicopter in 1968; that year an affluent suburb of Los Angeles had bought two piston-powered Hughes 269 helicopters for police patrols. Citizens soon called to complain about the noise of the low-flying patrols, and the city told
Hughes to either make them quieter or take them back. An emerging market for police patrols was at stake. Engineers at Hughes identified one of the worst of the noisemakers: the tail rotor. By doubling the number of blades to four, Hughes was able to cut the speed of the rotor in half, which reduced the
Coincidentally, the Advanced Research Projects Agency was hunting for contractors who could cut noise from military helicopters of all sizes. After hearing about Hughes' work on the police helicopters, ARPA offered the company $200,000 in 1968 to work similar magic on a Hughes OH-6A light helicopter. Hughes Tool made a short movie about the modifications, which included a new set of gears to slow the tail rotor, and showed it to ARPA. "ARPA came back and offered a blank check to do a Phase Two of the program with no holds barred," recalls Taylor, the project engineer. "Each and every noise source in the helicopter was to be addressed in an attempt to reduce the signature to an absolute minimum." ARPA gave the project the code name Mainstreet. Even before work was fully under way, the CIA ordered two (later registered as N351X and N352X) for use in the field. Test flights began at Culver City, California, in 1971, followed by a brisk training program for the U.S. instructor-pilots who would later train mission pilots.
Flights of the Quiet One included low-level work at the secret Air Force base Area 51 in Nevada and touchdowns on peaks in California to familiarize pilots with close-quarters maneuvering and landing in darkness. Pilots needed at least eight hours to get comfortable with steering by sole reference to the comparatively narrow view of the forward-looking infrared (FLIR) camera, which was mounted just above the skids. Says Allen Cates, an Air America pilot who flew one in 1973: "When you saw a person, it was like looking at a photo negative. Or you'd see just the hood of a car, glowing from heat off the engine block…. And when you were landing, a blade of grass looked as big as a tree."
The slapping noise that some helicopters produce, which can be heard two miles away or more, is caused by "blade vortex interaction," in which the tip of each whirling rotor blade makes tiny tornadoes that are then struck by oncoming blades. The Quiet One's modifications included an extra main rotor blade, changes to the tips on the main blades, and engine adjustments that allowed the pilot to slow the main rotor speed, making the blades quieter (see "How To Hush a Helicopter," p. 68). The helicopter also had extra fuel tanks in the rear passenger compartment, an alcohol-water injection system to boost the Allison engine's power output for short periods, an engine exhaust muffler, lead-vinyl pads to deaden skin noise, and even a baffle to block noise slipping out the air intake.
The extensive alterations did not blank out all noise, Taylor says. Rather, they damped the kinds of noise that people associate with a helicopter. "Noise is very subjective," he says. "You can reduce the overall noise signature and an observer will still say, 'I can hear it as well as before.' It's related to the human ability to discriminate different sounds. You don't hear the lawnmower next door, but a model airplane is easily heard. It has a higher frequency and seems irritating."
Hughes shipped the two Quiet Ones to Taiwan in October 1971. Under the CIA's original plans, the Vinh wiretap mission would be flown by pilots from the Taiwanese air force's 34th Squadron. This would offer the United States some deniability, however flimsy, if any of the helicopters were captured. The pilots' U.S. instructors included two veteran helicopter pilots with experience flying low-level missions in Vietnam: Lloyd George Anthony Lamothe Jr. and Daniel H. Smith. The two had joined Air America six months earlier for that purpose.