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YO-3A parked on ramp YO-3A parked on ramp

Photo Number: EC97-44128-1
Photo Date: June 27, 1997

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NASA's YO-3A parked on the Dryden ramp.


The YO-3A aircraft was originally a Schweizer SGS-2-32 sailplane. During the late 1960s Lockheed modified over a dozen of these sailplanes to create ultra-quiet observation aircraft for use over South Vietnam. This particular YO-3A flew combat missions and was later sold to an airframe and powerplant mechanics school.

NASA's Ames Research Center at Mountain View, California, acquired the aircraft from the school in 1978. It restored the YO-3A to flight status and fitted it with wing- and tail-mounted microphones as an acoustic research aircraft. Ames operated it at Edwards Air Force Base for noise measurements of helicopters and tilt rotor aircraft. One set of tests in December 1995 obtained free-flight noise data on the XV-15 tilt rotor.

NASA also used the YO-3A for sonic boom measurements of a NASA SR-71 assigned to the Dryden Flight Research Center. NASA transferred the YO-3A to Dryden in December 1997 and the aircraft was placed in flyable storage for nearly seven years. It was then restored to flight status in mid-2004. This involved replacing the old hoses, belts, and tires on the aircraft. The YO-3A was then returned to Ames in October 2004, where it will be used for acoustic measurements of helicopters and rotorcraft.

The designation YO-3A indicates that this aircraft was a pre-production (Y) observation (O) aircraft. Even though the YO-3A saw operational use, the Y designation was never removed. Its 210-horsepower Continental V-6 was modified to reduce noise. The engine was connected to a propeller through a belt-driven reduction system. This reduced the propeller's rotation speed. The propeller blades themselves were made of birch plywood and were wider than standard propellers. The result of these modifications was an aircraft so quiet that its noise was drowned out by the background sounds.

NASA Photo by: Tony Landis

Keywords: YO-3A; Schweizer SGS-2-32; sailplane; observation; microphones; acoustic research; Ames Research Center; NASA; Dryden Flight Research Center; XV-15; SR-71

Last Modified: December 22, 2004
Responsible NASA Official: Marty Curry
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