Here is an interesting little Vietnam War era aircraft developed in the heat of battle that unlike many experimental aircraft, actually worked out to be perfect for the role it was intended to undertake! The Lockheed YO-3A Quiet Star was a two-seat nearly silent observation and reconnaissance aircraft designed by the Lockheed Missile and Space Division for use by the US Army at night over South Vietnam during the Vietnam War.
Its purpose was to detect enemy activity and direct artillery fire and helicopter gunship strikes upon them (they couldn’t hear the aircraft above, so this would have been a nasty surprise!). The Observer sat in the front of the cockpit and the aircraft was fitted with a downward looking Night Vision Aerial Periscope (NVAP), infra-red illuminator and a laser target designator to complete its night mission. Unarmed, silence was the only protection it carried into conflict.
The bubble canopy was large to enable all round observation capability and it is hard not to notice those long, thin wings (17.3 metre / 57 foot wingspan) which show its glider heritage (the prototypes were developed from the Schweizer SGS 2-32 glider). To keep the aircraft super quiet it was fitted with a special muffled 210-horsepower Continental Model No. IO-360D engine that powered a slow propeller to eliminate the typical sound generated by a spinning aircraft propeller (originally it was fitted with a six bladed ground-adjustable-pitch propeller but in 1971 this was changed to a 3 bladed laminated constant speed wooden propeller that was just as quiet but also more efficient at higher speeds). The engine cowling was fibreglass to help muffle engine noise and a quiet asymmetrical exhaust system was also fitted (it drew the exhaust fumes through an acoustical fairing and dissipating muffler to the rear of the fuselage and away from the aircraft).
The YO-3A flew with no night running lights, the top speed was just 166km/h or 103 mph and it could remain in the air for about 5 hours. Operationally they were intended to run quietly on missions at around 1,000 feet but apparently pilots discovered they could go much lower and remain undetected anywhere down to around 200 feet off the ground!
Only eleven were built in 1969 and nine of those were operated from the summer of 1970 to 1972 in South Vietnam. In an attest to the silent design of the aircraft, none were ever shot down or even hit by enemy fire during its time of operation in the conflict and it was proven to be very successful in its role (three did crash though in South Vietnam and a fourth in the United States)
With the 1973 end of US involvement in Vietnam though it seems the military had no further use for the YO-3A. Two (69-18006 and 69-18007) were acquired for use by the Louisiana Department of Wildlife and Fisheries in the 1970’s for locating poachers and were later used by the FBI for observation duties.
In 1978 NASA also purchased a YO-3A (69-18010) from an aircraft mechanics school and fitted it with special wing and tail microphones for flight acoustic recordings of helicopter blades, jet sonic booms and so forth (operated out of the Ames Research Center in California). It was put into flyable storage in 1997 before being returned to NASA service from 2004 until put back into storage almost two years later (it was sold in 2015 to the Vietnam Helicopters Museum in California).
The sixth aircraft built and one that was operated in South Vietnam has been restored and is on display in the Vietnam War section of the Great Gallery at the Museum of Flight in Seattle, WA (Serial Number 69-18005 features the six bladed propeller – photos taken during my visit in July 2016). Five surviving airframes are in museums and a further two are in private hands around the United States .
Museum of Flight – YO-3A
NASA – YO-3A
Vietnam Helicopters Museum – YO-3A
Western Museum of Flight – YO-3A
Wikipedia – YO-3A