Skunk Works

“Ben, this guy has shown us how to accurately calculate radar cross sections across the surface of the wing and at the edge of the wing and put together these two calculations for an accurate total.”

Denys saw my blank stare. Radar cross section calculations were a branch of medieval alchemy as far as the non-initiated were concerned. Making big objects appear tiny on a radar screen was probably the most complicated, frustrating, and difficult part of modern warplane designing. A radar beam is an electromagnetic field, and the amount of energy reflected back from the target determines its visibility on radar. For example, our B-52, the mainstay long-range bomber of the Strategic Air Command for more than a generation, was the equivalent of a flying dairy barn when viewed from the side on radar. Our F-15 tactical fighter was as big as a two-story Cape Cod house with a carport. It was questionable whether the F-15 or the newer B-70 bomber would be able to survive the ever-improving Soviet defensive net. The F-111 tactical fighter-bomber, using terrain-following radar to fly close to the deck and “hide” in ground clutter, wouldn’t survive either. Operating mostly at night, the airplane’s radar kept it from hitting mountains, but as we discovered in Vietnam, it also acted like a four-alarm siren to enemy defenses that picked up the F-111 radar from two hundred miles away. We desperately needed new answers, and Ufimtsev had provided us with an “industrial-strength” theory that now made it possible to accurately calculate the lowest possible radar cross section and achieve levels of stealthiness never before imagined.

“Ufimtsev has shown us how to create computer software to accurately calculate the radar cross section of a given configuration, as long as it’s in two dimensions,” Denys told me. “We can break down an airplane into thousands of flat triangular shapes, add up their individual radar signatures, and get a precise total of the radar cross section.”

Why only two dimensions and why only flat plates? Simply because, as Denys later noted, it was 1975 and computers weren’t yet sufficiently powerful in storage and memory capacity to allow for three-dimensional designs, or rounded shapes, which demanded enormous numbers of additional calculations. The new generation of supercomputers, which can compute a billion bits of information in a second, is the reason why the B-2 bomber, with its rounded surfaces, was designed entirely by computer computations.

Denys’s idea was to compute the radar cross section of an airplane by dividing it into a series of flat triangles. Each triangle had three separate points and required individual calculations for each point by utilizing Ufimtsev’s calculations. The result we called “faceting”—creating a three-dimensional airplane design out of a collection of flat sheets or panels, similar to cutting a diamond into sharp-edged slices.

As his boss, I had to show Denys Overholser that I was at least as intellectual and theoretical as Ufimtsev,[1]

so I strummed on my desk importantly and said, “If I understand you, the shape of the airplane would not be too different from the airplane gliders we folded from looseleaf paper and sailed around the classroom behind the teacher’s back.”

Denys awarded me a “C+” for that try.

The Skunk Works would be the first to try to design an airplane composed entirely of flat, angular surfaces. I tried not to anticipate what some of our crusty old aerodynamicists might say. Denys thought he would need six months to create his computer software based on Ufimtsev’s formula. I gave him three months. We code-named the program Echo I. Denys and his old mentor, Bill Schroeder, who had come out of retirement in his eighties to help him after serving as our peerless mathematician and radar specialist for many years, delivered the goods in only five weeks. The game plan was for Denys to design the optimum low observable shape on his computer, then we’d build the model he designed and test his calculations on a radar range.