Skunk Works

There was simply no way to cut any corners. We discovered that there was no off-the-shelf, readily available electronics—none of the standard wires, plugs, and transducers commonly used by the aviation industry could function at our extreme temperatures. There were no hydraulics or pumps, oils or greases that could take our kind of heat. There were no escape parachutes, drag chutes, rocket-eject propellants, or other safety equipment that could withstand our temperature ranges, and no engine fuel available for safe operation at such high temperatures. There was no obvious way to avoid camera lens distortions from fuselage heat flows, and no existing pilot life-support systems that could cope with such a hostile, dangerous environment. We would even be forced to manufacture our own titanium screws and rivets. By the time the project ended, we had manufactured on our own thirteen million separate parts.

Cannibalization had been a house specialty at the Skunk Works on every airplane we had ever built before this one. To save cost and avoid delays, whenever possible we would use engines, avionics, and flight controls from other aircraft and cleverly modify them to fit ours. But now we would even have to reinvent the wheel—literally. Our fear was that the rubber tires and folded landing gears might explode as the heat built in flight. We took our problem to B. F. Goodrich, which developed a special rubber mixed with aluminum particles that gave our wheels a distinctive silver color and provided radiant cooling. The wheels were filled with nitrogen, which was less explosive than air.

The airplane was essentially a flying fuel tank carrying 85,000 pounds of fuel—more than 13,000 gallons—in five noninsulated fuselage and wing tanks that would heat up during supersonic flight to about 350 degrees; we turned to Shell to develop a special, safe, high-flash-point fuel that would not vaporize or blow up under tremendous heat and pressure. A lighted match dropped on a spill would not set it ablaze. The fuel remained stable at enormous temperature ranges: the minus 90 degrees experienced when a KC-135 tanker pumped fuel into the Blackbird at 35,000 feet, and the 350 degrees by the time the fuel fed the engines. As an added safety precaution, nitrogen was added to the fuel tanks to pressurize them and prevent an explosive vapor ignition.

The fuel acted as an internal coolant. All the heat built up inside the aircraft was transferred to the fuel by heat exchangers. We designed a smart valve—a special valve that could sense temperature changes—to supply only the hottest fuel to the engines and keep the cooler fuel to cool the retracted landing gear and the avionics.

One day Kelly Johnson came to me looking as happy as a little kid who had just received a free World Series ticket. “I found a guy in Texas who claims to have developed a special oil product that can withstand nine hundred degrees,” he said. “He’s sending a sample overnight.”

Poor Kelly. A big canvas sack of crystal powder arrived the next day. The powder changed into a lubricant at 900 degrees. Oiling our engines with a blowtorch just wouldn’t make it for us, so we turned to Penn State’s excellent petroleum research department to develop a special oil, which they eventually did, but at a price that made it imperative that not one drop be wasted. A quart of our oil was more expensive than the best scotch malt whiskey. We use 10–40 motor oil in our cars when wide temperature ranges are anticipated; our oil was more like 10–400.

Slowly, but expensively, we began to problem-solve. Kelly offered a hundred-dollar reward for any idea that saved us ten pounds of weight. No one collected. He offered five hundred bucks to anyone who could come up with an effective high-temperature fuel-tank sealant. No one collected that dough either, and our airplane would sit on the tarmac leaking fuel from every pore. But fortunately the tanks sealed themselves in flight from the heat generated by supersonic speeds.

Our crown of thorns was designing and building the powerful engine’s inlets—the key to the engine’s thrust and its ability to reach blistering speeds. This became the single most complex and vexing engineering problem of the entire project. Our engines needed tremendous volumes of air at very high pressures to be efficient, so Dave Campbell and I invented movable cones that controlled the velocity and pressure of the air as it entered the engines. These spike-shaped cones acted as an air throttle and actually produced 70 percent of the airplane’s total thrust. Getting those cones to function properly took about twenty of the best years off my life.