“[The YO-3] was a wonderful aircraft, when it worked,” Kizaric says. Unfortunately, the Yo-Yos didn’t always work. Fuel management glitches led to a few crash landings; one unexplained crash killed the pilot and observer. Though Lockheed fixed some of the fuel problems, morale dropped at the Long Thanh North base, and with it the number of flights per week. The Army discontinued the Yo-Yo flights in August 1971, and the military’s quiet spyplane program ended five years and many evolutionary changes after it began.
How stealthy were the quiet planes? Where they flew, enemy radar was rare. They were seen by the enemy from time to time, usually when the aircraft made silhouettes against cloud layers backlit by a full moon. On moonless nights, the little planes were functionally invisible as well as practically inaudible. None of the unarmed spyplanes was ever shot down, and on a few occasions, the pilots flew less then a hundred feet above and beside enemy truck convoys at night, just to see if they could get away with it. They did.
They left behind some minor folklore: captured VC who wondered how U.S. artillery had tracked them in the dark, and U.S. soldiers who thought they’d seen ghosts when a silent shadow appeared directly overhead.
After the Vietnam war, the Louisiana Department of Wildlife and Fisheries acquired some of the YO-3As, using them for several years to catch poachers. Most of the aircraft were bought by the FBI, which used them for about a decade for suveillance. Today NASA owns one YO-3A, currently mothballed, for making acoustic measurements of other aircraft. Most are in museums, and one is in a private collection awaiting restoration.
The two original QT-2s were sent to the U.S. Naval Test Pilot School at Patuxent River, Maryland. The school had already bought some Schweizer 2-32 sailplanes and designated them X-26As, to appear to be experimental, even though they were not, in order to get around complicated procurement regulations. The QT-2s were redesignated X-26Bs, and their strange front pylons turned out to have a practical use after all, giving student pilots a chance to learn at very low speeds about yaw-roll coupling, which also affects supersonic jets.
The airplanes have a few direct descendants. Schweizer Aircraft of Elmira, New York, has produced its own quiet reconnaissance aircraft line. The Coast Guard, the CIA, the U.S. Air Force, and the governments of Mexico and Colombia have used Schweizer’s single-engine RG-8 and pusher-puller twin-tail RU-38 to spot drug smugglers at night, and to electronically eavesdrop and monitor ground events without being detected. But Schweizer’s quiet planes don’t fit the modern definition of stealth, which has come to refer to radar instead of sound.
Compared to the manned and unmanned reconnaissance aircraft of today, the QT-2s and YO-3As were primitive. Evolution has passed them by, and they seem like some exotic, long-extinct species. Their claim to history is not their effect on the Vietnam war, which was slight, but their early role in the developing stealth field and their exploitation of the physics of sound. Other means were found to accomplish the quiet birds’ purpose, and in wars fought today, U.S. military forces own the night.