IN 1966, THE U.S. NAVY SENT A YOUNG LIEUTENANT named Leslie J. Horn to South Vietnam to evaluate the use of night-vision devices in combat. Horn, a pilot and physicist, soon found himself in a patrol boat looking for Viet Cong in the canals and waterways of the Mekong Delta in the southern end of the country. With his Starlight scope, a handheld light amplifying device, he could see in the dark, but not through the thick foliage that lined the waterways.
One night, rounding a river bend, Horn had a surprise encounter with an armored junk. A firefight erupted, and Horn began wondering if there wasn’t a better way to locate the enemy. What about a spy in the sky, some kind of aircraft that could find the VC without being seen or heard?
“Being a physicist,” Horn recalls today, “I figured, Let’s see, noise is energy, so how do you build a plane with low energy? I started running some equations, and what fell out was a glider.” An airframe with a high lift-to-drag ratio wouldn’t need much power, so the engine could be smaller and therefore quieter. He sent the Office of Naval Research a detailed proposal for a glider—a sailplane, technically—with a muffled engine and a propeller turning slowly enough to avoid generating a buzz from the blade tips. Crewed by fliers equipped with Starlight scopes, the result would be a night reconnaissance airplane that was very nearly silent.
Americans believe that if we invent gadget X, we can get result Y and change situation Z for the better. So it’s no surprise that even before Horn had drawn up his proposal, others had visited the very same turf. The Department of Defense had been asking for new technologies to counter communist infiltration in Vietnam. Before being asked, the big thinkers at Lockheed Missiles & Space had started running analyses and brainstorming.
Lockheed Missiles & Space, based in Sunnyvale, California, had never built an airplane before. The division had produced the Polaris missile, designed for launch by nuclear submarines, and the first generation of spy satellites. But there was a war on, and Sunnyvale’s advanced programs group decided to take on the problem of detecting the Viet Cong.
The group began by analyzing the available sensors and their ranges, and then the ranges at which various aircraft could be heard by the enemy. They discovered the problem: The VC could always hear an aircraft coming before the crew on the aircraft could hear or see the VC. What was needed, the Lockheed guys decided, was a super-quiet airborne sensor platform. They studied balloons, sailplanes, and conventional airplanes with mufflers, but found them all lacking. Then Don Galbraith, head of advanced design, suggested a powered sailplane, one with a muffler and an oversize, slow-turning propeller. Halfway around the world from young Lieutenant Horn, and about half a year earlier, Lockheed Missiles & Space had reached the same conclusion.
Lockheed project manager Stanley Hall, the designer of several sailplanes and known in the national soaring community, was pulled off a satellite project to supervise the quiet airplane. DARPA, the Defense Advanced Research Projects Agency, tossed in a meager $100,000 to build two proof-of-concept aircraft and sent Les Horn to be its representative at Lockheed. Horn arrived when construction was already under way; he thought he’d died and gone to R&D heaven.
The tiny budget turned out to be an advantage. Because the project was so small, the military and corporate bureaucracies didn’t bother with oversight. The team set up shop behind a plywood partition in the back of the Lockheed executive hangar at the San Jose airport. Engineers and mechanics came from all over Lockheed, including the famed Skunk Works, where the exotic U-2 and SR-71 spyplanes had been designed and built. But this spyplane was going to be a different: simple, designed to fly low and slow, and built and tested on the cheap.
For the airframe, Hall chose a well-known commercial sailplane, the Schweizer 2-32. His team took an ordinary 100-horsepower Continental O-200 engine and mounted it behind and slightly above the cockpit, so it made a bulge in the top of the airframe, like a camel’s hump. The propeller shaft ran above the canopy, outside the airplane, to a vertical pylon attached to the nose. They tested several propellers and chose an eight-foot-diameter model with four wooden blades. To quiet the engine further, the Sunnyvale team lined the inside of the cowling with fiberglass batting and ran the exhaust through a muffler from a 1958 Buick. Instead of using noisy gears, they connected the engine to the propeller shaft with V-belts, similar to fan belts. Les Horn recalls that it was the “only aircraft flying that was powered by rubber bands.” But the engineering and workmanship were first-rate.
The prototype aircraft were designated QT-2: “2” for two-seater, and “QT” for “Quiet Thruster,” officially, though everybody knew it also stood for “on the Q.T.” (on the sly). The first flight was set for August 15, 1967, at an isolated municipal airport in Tracy, California, about 50 miles from San Jose.