Being modified sailplanes, the QTs had a single main wheel mounted in the center of the belly, two tiny wheels under each wingtip to keep the tips from dragging, and a small nosewheel. When the test pilot, Quint Burden, started the engine, he taxied down the runway listing to port until, at around 15 knots (about 17 mph), he had enough speed to level the wings.
After he took off, he circled the field, the big wooden propeller turning at a leisurely 800 rpm, about a third the speed of a normal prop for an engine of that size. “This was a really quiet airplane, I tell you,” recalls Hall, who was there for the test flights “We could fly it at 250 feet and barely hear it at all. At 800 feet it was completely silent” to ground observers.
There had been a few studies of techniques for quieting airplanes, but for the most part the Lockheed team had to figure out acoustic stealth for itself. There was ground-level masking noise, to start with—crickets and frogs in the countryside, or the background sounds of a small town late at night, which Lockheed pegged at 50 decibels. Lockheed found the QT’s overall sound level was 70 decibels at 1,000 feet.
Then there was the QT’s acoustic signature, which was different from other aircraft. And it was so close to the threshhold of hearing that it was perceived in very different ways. Hall thought it was “the gentle rushing sound of the ocean surf” while Burden, the test pilot, described it as an almost subliminal thub…thub…thub. Others were reminded of tires on a distant highway, the whirring of an electric fan, or a flock of birds overhead. The heart of acoustic stealth, the Lockheed guys discovered, is a widely observed but imperfectly understood relationship between detecting noise and perceiving and identifying its source. If you didn’t suspect an airplane was above you or notice that a few stars were being blocked and then reappearing, you might not be aware of anything at all—even if a QT-2 were only a couple hundred feet overhead.
Further tests revealed the QT was best flown cautiously, straight and level. A yaw, or turn on the vertical axis, could develop into a larger yaw than expected because the area around the nose pylon was so large it counteracted the stabilizing effect of the vertical tail. A banked turn could lead to a phenomenon called yaw-roll coupling; in a slow roll, which nobody ever tried, once upside down the wings would probably fall off. “It was a very tender aircraft,” says Les Horn, who notes that the original Schweizer has an 8-G rating, while the QT-2, weighed down by an engine and other gear, had a rating of barely 2.4 G.
They needed a long runway for takeoff, then the airplanes could slowly climb to 5,000 feet and cruise at 110 knots. For minimum noise, though, the best speed was down around 70 knots, which was just one knot over the stall speed. In this so-called quiet mode, the craft required only 17 horsepower to stay aloft, according to the tests.
Toward the end of August 1967, the brass arrived at Tracy for a night demonstration. Asked to find the airplane, they peered upward and strained to hear something. Suddenly a bright light appeared directly above them, and the pilot boomed into his mike a single word, “Gotcha!”—amplified, of course, through strategically placed loudspeakers on the ground. Members of the delegation were suitably impressed.
Further modifications were made—portholes in the sides to improve visibility for the backseat observers, a bigger vertical tail to offset the effect of the nose pylon, self-sealing fuel tanks, and military avionics. They received a couple of Starlight Scopes, and training began. Then the QT-2PCs, as the new models were called, were disassembled, put on trailers, and loaded onto C-130s. They were flown to Soc Trang, in the Mekong delta, and the trailers were unloaded and wheeled into a secure hangar, with other trailers encircling them like covered wagons to keep them safe from prying eyes. It was January 1968, and as enemy activity picked up, sandbags were being stacked up around the base.
Within a day the funky little airplanes were operational. Under the command of Horn, newly promoted to lieutenant commander, there were briefings in the late afternoon, first flights after sunset, refuelling around midnight, and second flights with a change of pilots until shortly before dawn. They got in 10 hours of flight time every night.
On January 30, 1968, communist forces launched a countrywide offensive during the Vietnamese new year, or Tet. Soon enemy rockets and mortar shells were landing in Soc Trang. “I was supposed to get a little green card saying I was a noncombatant,” recalls a laconic Dale Ross Stith, a Lockheed avionics specialist. “What I actually got was an M-14 and 200 rounds.” With Soc Trang under fire, the QT-2s were flown to Vung Tau, which was a little more secure, and the missions continued.