In 1968, U.S. forces in South Vietnam sought to halt the nighttime infiltration of Viet Cong into the Mekong Delta area using helicopters and Cessna O-1 “Bird Dog” aircraft to detect the enemy. But, according to one account, “The Bad Guys could almost always hear approaching forces, whether from the air or on the river, and seek cover prior to detection.”1
The problem already was being worked on back in the United States. As early as 1965, the director of Defense Research and Engineering, John F. Foster, was challenging the aerospace industry to develop a “quiet” surveillance aircraft. Funded through the Defense Advanced Research Projects Agency (DARPA), the Lockheed Missiles and Space Company proposed such a platform—which soon was designated the QT-2.2
Some “recollections” contend the designation QT was a play on the 19th-century abbreviation for “quiet.” Some engineers claim it was derived from “Quiet Thruster.” The official U.S. aircraft designation scheme of the time implied that QT was an unmanned drone (Q prefix) trainer (T). So much for following regulations.
As DARPA was sponsoring this effort through Lockheed, the Navy was developing an operational requirement for such an aircraft. At Lockheed, commercial off-the-shelf parts were used with “minimal inspection, documentation, and reporting.” Two Schweizer X-26A sport gliders were diverted from a Navy order to the QT program. Those aircraft were fabricated with thicker wings and with spars that could accommodate the weight of the engine. A long belt-drive shaft connected the 57-horsepower engine to a slow-turning propeller with blade tips that did not go supersonic. The engine was mounted behind the one-man cockpit with the drive shaft above the cockpit, supported by a pylon mounted on the aircraft’s nose. The aircraft retained the two-wheel (bicycle) landing gear of gliders.
The first QT flew in August 1967 and the second soon after. They were quiet and, with proper paint color, difficult to see.
After being fitted with sensors, in January 1968, the aircraft were disassembled, crated, and flown by C-130 Hercules to South Vietnam. Given the codename Prize Crew (PC), the aircraft reached the Army airfield at Soc Trang in the Delta area on 22 January and began surveillance operations almost immediately—flown by the Army. They were designated QT-2PC.
The Viet Cong–North Vietnamese Tet Offensive began on the 30th. The two “quiet” aircraft flew 591 hours of night surveillance from 24 January through 24 March. A short time later the two aircraft were returned to the United States and delivered to the Patuxent River naval air station in Maryland. One aircraft was cannibalized to provide spare parts for the other, which was flown by the Naval Test Pilots School with the designation X-26B.3
Meanwhile, Lockheed extensively modified another Schweizer glider—this one referred to as the “Q-Star” and given the commercial registration N57135. With funding from the Navy, Lockheed, and Curtiss-Wright—and undoubtedly other government agencies—this aircraft was fitted with a conventional, fixed undercarriage and was employed to test various engines and propellers, the latter including a six-blade affair. The engines included a Wright liquid-cooled, Wankel rotary combustion engine; it was cooled by an automobile radiator fitted in the nose.
The success of the QT-2PCs in Vietnam led to the Army awarding a contract to Lockheed for 14 YO-3A production aircraft in July 1968. The major difference in configuration was that these production planes had a nose-mounted, 210-horsepower Continental, six-cylinder, air-cooled engine. Initially, they were fitted with a six-blade, fixed-pitch propeller, but this later was replaced by a three-blade, variable-pitch unit. While retaining the Schweizer all-metal sailplane structure, the YO-3A provided for a conventional, retractable undercarriage and an upward-hinged canopy and windshield over the two-man cockpit. All performance criteria were increased over the QT-2PC aircraft.
One YO-3A was retained in the United States for test and evaluation, with the 13 other aircraft shipped to Vietnam in early 1970 for operation by the 1st Army Security Agency Company at Long Binh. After successful employment, the planes were returned to the United States when the unit was deactivated in April 1972.
With no further interest by the Army (or the Navy), the aircraft were distributed to various state and private parties, with two flown by the Federal Bureau of Investigation and one flown by the National Air and Space Administration—in a helicopter research program.
The “very quiet” QT-PC/YO-3A effort was a short-lived but interesting aircraft program and a model of interservice and industry cooperation.
1. Dale Ross Smith, “Prize Crew Takes Back the Night,” Naval Intelligence Professionals Quarterly (Fall 2008), 42. This column is based primarily on that article, which was derived from a presentation by Smith at Texas Tech University, Lubbock, Texas, on 15 March 2008, and Rene J. Francillon, Lockheed Aircraft since 1913 (Annapolis, MD: Naval Institute Press, 1987), 442-447.
2. Smith, 42.
3. That aircraft later was placed on display in the Army Aviation Museum at Fort Rucker, Alabama.
Schweizer QT-2PC
Type: Surveillance
Crew: Pilot
Max. weight: 2,182 pounds
Engines: 1 Continental O-400-A four-cylinder, air-cooled; 100 hp
Length: 30 feet, 10 inches
Wingspan: 57 feet, 1 inch
Wing area: 180 square feet
Height: 9 feet, 3 inches
Max. speed: 115 mph
Range: 350 miles
Ceiling: 18,500 feet
Armament: nil