Lockheed YO-3

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 hours of darkness.

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 at night. Lockheed was approached to produce such a design. In 1966, the company built a prototype QT1 "Quiet Thrust", also known as X-26B, using a modified Schweizer SGS 2-32 glider. This was abandoned for two prototypes of a two-seat version called the QT-2 "Prize Crew". The QT had a silenced engine and a propeller operating at subsonic tip speed for quiet operation.

Following operation trials with the QT-2 in Vietnam, 1968, a production version, designated the YO-3A was ordered by the Army. Based on the QT2's SGS 2-32 platform, the YO-3A was highly modified. It had a low-mounted wing, retractable main-wheel landing gear and a modified fuselage with tandem seating for a pilot in back and an observer in the front seat using a NVAP (Night Vision Aerial Periscope) and infrared illuminator. The YO-3A was powered by a 210 hp IO-360 engine driving a six-bladed, fixed-pitch propeller; the propeller was later changed to a wooden three-bladed constant-speed version.

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.

Vietnam War
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 and two to Binh Thuy. The aircraft were used at night, at low altitudes. Observations were initially made visually (80%), later followed on with a Night Vision Aerial Periscope developed by Xerox Electro-Optical of Pasadena, California. The YO-3A had a specially designed propeller operated by 12 belts, an exhaust system that ran the length of the aircraft and other sound quieting technologies. The mission equipment on the YO-3A was a Night Vision Aerial Periscope with infrared illuminator. One YO-3A was equipped with a laser target designator. The laser system was never used.

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.

Postwar usage
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 FBI eventually acquired the aircraft, and operated the type for several years, assisting the apprehension of kidnappers and extortionists.

NASA took possession of one YO-3A, 69-18010, in the late 1970s. The aircraft was used in rotorcraft research. Most recently, it was in operation at Moffett Field, California. This aircraft was to be returned to NASA's Dryden research facility at Edwards AFB, California in early 2009.

Variants

 * QT-1 Quiet Thrust
 * Prototype single-seat glider conversion


 * QT-2
 * Two-seat version, two built for combat evaluation


 * Q-Star
 * One-aircraft for propeller development


 * YO-3A
 * Production aircraft for the United States Army, 11 built

Military operators

 * United States Army
 * United States Army

Civil operators

 * FBI
 * Louisiana Department of Fish and Game
 * NASA
 * NASA

Survivors

 * 18000 is on display at the Army Collection at Fort Rucker, Alabama.
 * 18001 is on display at the Hiller Aviation Museum in San Carlos, California.
 * 18005 is on display at the Museum of Flight. at Boeing Field in Seattle, Washington.
 * 18006 is at the Pima Air & Space Museum, Arizona.
 * 18007 is at the Western Museum of Flight in Torrance, California.
 * 18010 belongs to NASA and is currently based at Dryden Flight Research Center, California.

Specifications
General characteristics

 Crew: Two Length: 30 ft 0 in (9.14 m)  Wingspan: 57 ft 0 in (17.37 m)  Wing Area: 180 sq. ft. (16.70 sq. m) Powerplant: 1 × Continental six-cylinder horizonally-opposed, 210 hp 

NOTES: Weight and Data listed as Classified - Data from Bombers in Service, Patrol and Transport Aircraft Since 1960