The LOCKHEED YO-3 "QUIET STAR" was an American single-engined, propeller-driven aircraft that was developed for battlefield observation during the Vietnam War. It was designed to be as quiet as possible, and was intended to observe troop movements in near-silence during the hours of darkness.
* 1 Design and development
* 2 Operational history
* 2.1 Vietnam War * 2.2 Postwar usage
* 3 Variants
* 4 Operators
* 4.1 Military operators * 4.2 Civil operators
* 5 Survivors * 6 Specifications * 7 See also
* 8 References
* 8.1 Notes * 8.2 Bibliography
* 9 External links
DESIGN AND DEVELOPMENT
The YO-3A was designed to a U.S. Army specification of 1968, which called for an observation aircraft that would be acoustically undetectable from the ground when flying at an altitude of 1,200 feet (355 m) at night.
Lockheed Missiles and Space Company located in Sunnyvale, California was contracted to produce two prototype aircraft. In 1966, the company built two QT-2 "Quiet Thrusters", using modified Schweizer SGS 2-32 gliders . The prototype QT-2s were then modified to the QT-2PC "PRIZE CREW" configuration. The QT-2PC had a silenced engine and a slow turning propeller for quiet operation.
Following operational trials with the QT-2PC in Vietnam, a production
aircraft, designated the YO-3A was ordered. This aircraft's design was
also based on the
Schweizer SGS 2-32
The YO-3A was powered by an air-cooled, six-cylinder, horizontally opposed, fuel injected, Continental Model No. IO-360D engine. The engine is coupled to a slow turning propeller through a belt pulley-drive system. The propeller reduction ratio is 3.33:1. Originally equipped with a six bladed ground-adjustable-pitch propeller, this was replaced in March 1971 with a three bladed laminated constant speed wooden propeller produced by Ole Fahlin . The engine cowling and firewall were lined with fiberglass material to dampen and contain engine noise.
The YO-3A is equipped with an Asymmetrical Exhaust System. A crossover exhaust pipe is used to remove exhaust from the left bank of engine cylinders to the right side of the engine compartment. This crossover joins the right bank exhaust pipe and exits along the lower right side of the engine compartment. The exhaust gases are then moved through an acoustical fairing into a dissipating and resonating muffler continuing to the aft end of the fuselage.
Nine of the 11 YO-3As produced operated in South Vietnam, at night, from 1970 to 1971 (14 months) and never took a round or were shot down. The YO-3A was very successful in spotting movement by the North Vietnamese, but its deployment late in the American involvement in Vietnam reduced its value in that war. By early 1973 all American troops were out of Vietnam.
Following combat evaluation of the QT-2s in Vietnam by the Army, nine
production YO-3As were sent to Long Thanh North , Vietnam, in 1970.
Three were sent to
Phu Bai Combat Base and two to
Binh Thuy Air Base
The YO-3A operated silently at 1,000 feet, or lower, depending on terrestrial background noise. Some pilots were known to have gone unobserved over the enemy at 200 feet. Occasionally, daylight flights were made over the rivers. Crew chiefs would monitor the YO-3A flying over the maintenance section prior to deployment, listening for rattles, whistles or other noises. The propeller, even at 500 feet over the maintenance area, made only a light flutter, heard just as it approached. This was followed by a light rushing of wind over the wings. There was no audible sound once the aircraft had passed over. If any abnormal noises were heard, the aircraft returned to the runway, where duct tape and other measures were employed to quiet noticeable sounds.
After Vietnam, two YO-3As, 69-18006 and 69-18007, were used by the
Louisiana Department of Fish and Game . The aircraft was effective at
catching poachers . The
QT-2PC in 1968 QT-1 Quiet Thruster Proposed single-seat
powered glider based on the
Schweizer SGS 2-32
* 18000 is on display at the
United States Army Aviation Museum