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
4.1 Military operators
4.2 Civil operators
7 See also
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
Schweizer SGS 2-32 glider. Like the QT-2PC, the
YO-3A has a large wingspan and a larger canopy area for observation.
Two crew members (a pilot and an observer) are seated in tandem. The
observer is located at the front of the cockpit. The YO-3 is an
all-metal low-wing monoplane of semi-monocoque construction. The
control surfaces of the YO-3 including the ailerons and rudder are
fabric covered. The engine cover, canopy, engine exhaust shroud,
wing-root fairings, and wheel-well fairings were constructed of
fiberglass. The YO-3 has retractable tailwheel-type landing gear.
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.
Observations were initially made visually (80%), later followed on
with a Night Vision Aerial
Periscope developed by Xerox
Electro-Optical of Pasadena, California. 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
designator 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
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. Following service with
the U.S. Army this aircraft was transferred to an airframe and
powerplant mechanics school. NASA's
Ames Research Center
Ames Research Center located at
Moffett Federal Airfield
Moffett Federal Airfield in
California acquired the YO-3A from the
school in 1977.
NASA equipped the aircraft with wing-tip and
tail-mounted microphones. These microphones were used to record the
in-flight acoustic signatures of a variety of U.S. Army helicopters
Tiltrotor aircraft. The YO-3 was also used to measure sonic booms
from the Lockheed SR-71 Blackbird. In 1997, the
NASA YO-3A was
transferred to the Dryden Flight Research Center (now Armstrong Flight
Research Center) at Edwards Air Force Base, in California. The YO-3A
remained in a flyable storage state until October 2004. Then the YO-3A
was flown back to Ames to support rotorcraft research again for nearly
two years before once again returning to Dryden. In 2015, the aircraft
was retired by
NASA and sold by the
General Services Administration
General Services Administration at
auction to the Vietnam Helicopters Museum.
QT-2PC in 1968
QT-1 Quiet Thruster
Proposed single-seat powered glider based on the Schweizer SGS 2-32,
Two modified Schweizer X-26 two-seat sailplanes for evaluation, later
modified with sensor packages as the QT-2PC.
QT-2PC PRIZE CREW
Two QT-2s with combat sensor packages for evaluation in Vietnam
theatre, one reduced to spares and the other returned to the United
States Navy as the Schweizer X-26B.
Schweizer SGS 2-32
Schweizer SGS 2-32 for engine/propeller development.
Production aircraft for the
United States Army, 11 built
United States Army
Louisiana Department of Fish and Game
18000 is on display at the
United States Army
United States Army Aviation Museum located
at Fort Rucker, Alabama.
18001 is on display at the
Hiller Aviation Museum
Hiller Aviation Museum located in San
Carlos, California.
18005 is on display at the
Museum of Flight
Museum of Flight at
Boeing Field in
Seattle, Washington.
18006 is on display at the Pima Air & Space Museum, located in
Tucson, Arizona.
18007 is currently in storage at the Western
Museum of Flight
Museum of Flight in
Torrance, California.
18010 is currently in storage at the Vietnam
Helicopters Museum located in Concord, California.
Length: 29 ft 4 in (9.093 m)
Wingspan: 57 ft (17.374 m)
Wing area: 213.1 ft2 (19.797 m2)
Aspect ratio: 1:7 at 80kts IAS
Max. takeoff weight: 3800 lb (1,723.653 kg)
Maximum speed: 103 mph (165.762 km/h)
Cruise speed: 80.6 mph (126.64 km/h)
Stall speed: 64.4 mph (103.62 km/h)
Aircraft of comparable role, configuration and era
^ "QT-2PC PRIZE CREW". Retrieved 2015-05-03.
^ a b c "YO-3A "Quiet Star" Silent Stealth Airplane". Vietnam
Helicopters Museum. Retrieved 2015-05-02.
^ Andrade 1979, p. 140.
^ Peter Merlin, Public Affairs
NASA Armstrong Flight Research Center.
"Quiet Research Aircraft Retires to
Flight Research Center Website. Retrieved 2015-05-02.
^ a b c d Francillon 1982, pp. 434-439
^ YO-3A "Quiet Star" Silent Stealth Airplane
Andrade, John. U.S. Military Aircraft Designations and Serials since
1909. Hinckley, UK: Midland Counties Publications, 1979.
Francillon, René J. (1982). :Lockheed Aircraft since 1913. London:
Putnam & Company. ISBN 0-370-30329-6.
The Illustrated Encyclopedia of Aircraft (Part Work 1982-1985).
London: Orbis Publishing, 1985.
Munson, Kenneth. Bombers in Service, Patrol and Transport Aircraft
Since 1960. London: The Macmillan Co., 1972.
Wikimedia Commons has media related to Lockheed YO-3.
Lockheed's Combined Sailplane & Slow-Turning Propeller at
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QT-2PC PRIZE CREW
Lockheed QT-2 / Q-Star / YO-3A 1971 at the Virtual Aircraft Museum
Lockheed YO-3A Quiet Start: The Original Stealth Aircraft of the
YO-3A Acoustic Research Aircraft Image Gallery
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