The Lockheed YO-3A was a very quiet surveillance aircraft, designed to fly low and silently over Vietnam in an attempt to locate hidden Communist troops.
The YO-3 emerged from an attempt to produce a very quiet aircraft that could be used to carry sensors over the Vietnamese jungle without being detected by the Communists.
The project was carried out by the Lockheed Missiles & Space Company, and was the only even partly standard aircraft produced by that Lockheed division. The original idea was to fit a very quiet motor in an aerodynamically efficient airframe. This would power a slowly rotating propeller, which would further reduce the amount of noise produced.
The LMSC suggested fitting a 57hp engine in a Schwieizer SGS 2-32 two or three seat glider. The engine would be mounted behind the cockpit and would drive a tractor propeller that was mounted above the fuselage and driven by a long extension shaft. The Army approved a two-seat version of the design as the QT-2 (Quiet Thruster, two-seat), and provided two Schweizer X-26A sailplanes (a version of the SGS 2-32 used by the Naval Test Pilot School). These were given a 100hp Continental O-200-A four cylinder engine, which was given larger than normal mufflers. An extension shaft ran above the cockpit and drove a four blade wooden propeller. Otherwise very few modifications were made.
Tests of the first QT-2 began in July 1967 ad it lived up to expectations. Both prototypes were equipped with sensors and sent to Vietnam for evaluation. They arrived in December 1967, just in time to see action during the Tet offensive of January 1968. They performed well, but after a few months were returned to the United States, where one was used to provide spares for the other. They were then used at the Naval Test Pilot School, under the designation X-26B.
Lockheed then moved onto a more advanced version, the Q-Star. This was given a fixed under carriage, and was originally built with the same engine and propeller setup as the QT-2. It was later used to test a series of different propeller types. In 1969 it was given a Wright RC2-60 liquid cooled Wankel type rotary engine, which required a car radiator I to be mounted in the nose. This version of the Q-Star made its maiden flight in September 1969, when it became the first Wankel powered aircraft.
In July 1968 the US Army’s Aviation Systems Command gave Lockheed a $2 million contract to produce fourteen YO-3A production aircraft. These were rather more conventional looking than the QT-2. The rather cumbersome rear-mounted engine and extension shaft powered propeller were replaced with a standard nose mounted engine, in this case a 210hp Continental IO-360D six-cylinder air cooled engine, driving a six blade fixed pitch propeller (later replaced with a three blade variable pitch propeller). The wings were moved from their fairly high position into a low mounted position, and the cockpit was moved back. A large glazed canopy was added, hinged at the back. A standard retractable undercarriage was installed.
The first YO-3A was kept by the army, while the other thirteen went to Vietnam early in 1970, where they were tested by the Army Security Agency, based at Long Binh. This was the Army’s signals intelligence branch, and the aircraft were used to try and monitor Communist activities. The aircraft were shipped back to the United States in the spring of 1972.
Some of these aircraft ended up in civil hands. Two were used by the State of Louisiana Department of Wildlife and Fisheries and were used to track poachers, another good use of their quiet running. Another one was used by NASA as a microphone carrying vehicle to measure rotor-blade noise from helicopters. At least six of the aircraft still exist, with four on public display.
Engines: Continental IO-360D six-cylinder air cooled engine
Wing span: 57ft
Length: 29ft 4in
Height: 9ft 1in
Empty weight: 3,129lb
Loaded weight: 3,519lb
Maximum weight: 3,800lb
Maximum speed: 138mph at sea level
Cruising speed: 110mph
Rate of climb: 615ft/ min
Service ceiling: 14,000ft
Endurance: 4.4 hours at sea level