by Ben R Rich
We were being funded to build five A-12 spy planes over the next two years at a quoted price of $96.6 million.
God help us, we were in business.
The CIA code-named the project Oxcart, an oxymoron to end all: at Mach 3, our spy plane would zip across the skies faster than a high-velocity rifle bullet.
Kelly had sold the idea brilliantly, but now it was up to us peons to deliver the goods. One of the great strengths of the place was the combined experience of Kelly’s most senior and trusted engineers and designers, who, among other attributes, were walking parts catalogs. But suddenly we were all operating in the dark, struggling by trial and error, like Cro-Magnons trying to look beyond the cooking fire to the first steam engine.
All the fundamentals of building a conventional airplane were suddenly obsolete. Even the standard aluminum airframe was now useless. Aluminum lost its strength at 300 degrees F, which for our Mach 3 airplane was barely breaking a sweat. At the nose the heat would be 800 degrees—hotter than a soldering iron—1,200 degrees on the engine cowlings, and 620 degrees on the cockpit windshield, which was hot enough to melt lead. About the only material capable of sustaining that kind of ferocious heat was stainless steel.
For security and convenience, Kelly kept those of us working on his airplane jammed together in one corner of our old Building 82, a remnant of the bomber factory from World War II, in which we had built the U-2 and the F-104 Starfighter before it. From the original four he had approached on this project, we had now grown to a modest fifty or so, seated at back-to-back desks, where, like the early U-2 days, privacy surrendered to incessant kibitzing, teasing, brainstorming, and harassment. Some wag hung the sign PRIVACY SUCKS. My three-man thermodynamics and propulsion group now shared space with the performance and stability control people. Through a connecting door was the eight-man structures group, who designed the strength and load characteristics of the airplane. Their “dean” was that irascible genius Henry Combs, who had been with Kelly since World War II and helped him build the classic two-engine P-38 Lightning interceptor. Henry and I could have reached through the doorway and shaken hands. And, of course, he relished offering his unsolicited advice and opinions to the young whippersnapper running thermodynamics and propulsion.
“Ben Rich,” he teased, “how in hell do you propose getting our stainless-steel monstrosity up to speed at Mach 3? You’ll need inlets the size of the Holland Tunnel.” Then he chuckled sardonically.
Of course, Henry was no happier with the prospect of building a steel airplane than I was. More weight meant more internal support structure, more fuel, less range, and less altitude. Back in 1951 he had recommended to Kelly that we use a rare alloy called titanium for the white-hot exhaust nozzles on the afterburner of the supersonic F-104 Starfighter. So Henry Combs now was mulling the pluses and minuses of building the world’s first titanium airplane. It would be a huge risk. On the positive side, titanium was as strong as stainless steel but only half its weight and could withstand blast-furnace heat and tremendous pressures. Titanium’s tensile strength would allow us to make our wings and fuselage paper-thin. But to build a high-performance aircraft out of such an unproven exotic material was inviting potential disaster. “Unpredictability is a guarantee that we’ll be in the soup on this one from start to finish,” Henry predicted dourly. I knew he was right. Meanwhile, Kelly was already pondering the titanium idea himself. “Any material that can cut our gross weight nearly in half is damned tempting,” Kelly told Combs, “even if it will drive us nuts in the bargain.”
Only one small U.S. company milled titanium, but sold it in sheets of wildly varying quality. We had no idea how to extrude it, push it through into various shapes, or weld or rivet or drill it. Drilling bits used for aluminum simply broke into pieces trying to pierce titanium’s unyielding hide. This exotic alloy would undoubtedly break our tools as well as our spirits. At one of our daily seven a.m. planning sessions in Kelly’s office, I volunteered some unsolicited advice about how we could use a softer titanium that began to lose its strength at 550 degrees. My idea was to paint the airplane black. From my college days I remembered that a good heat absorber was also a good heat emitter and would actually radiate away more heat than it would absorb through friction. I calculated that black paint would lower the wing temperatures 35 degrees by radiation. But Kelly snorted impatiently and shook his head. “Goddam it, Rich, you’re asking me to add weight—at least a hundred pounds of black paint—when I’m desperately struggling to lose even an extra ounce. The weight of your black paint will cost me about eighty pounds of fuel.” I said, “But, Kelly, think of how much easier it will be to build the airplane using a softer titanium, which we can do if we lower the heat friction temperatures on the surface. Adding a hundred pounds is nothing compared to that.”
“Well, I’m not betting this airplane on any damned textbook theories you’ve dredged up. Unless I got bad wax buildup, I’m only hearing you suggest a way to add weight.”
Overnight, however, he apparently had second thoughts, or did some textbook reading on his own, and at the next meeting he turned to me as the first order of business. “On the black paint,” he said, “you were right about the advantages and I was wrong.” He handed me a quarter. It was a rare win. So Kelly approved my idea of painting the airplane black, and by the time our first prototype rolled out the airplane became known as the Blackbird.
Our supplier, Titanium Metals Corporation, had only limited reserves of the precious alloy, so the CIA conducted a worldwide search and, using third parties and dummy companies, managed to unobtrusively purchase the base metal from one of the world’s leading exporters—the Soviet Union. The Russians never had an inkling of how they were actually contributing to the creation of the airplane being rushed into construction to spy on their homeland.
Even before the first titanium shipment arrived, many of us were already worrying that building this particular airplane might just prove too difficult, even for the Skunk Works. Wind tunnel tests of our mock-up amazed us all by indicating that, at Mach 3, intense friction heating on the fuselage would actually stretch the entire airframe a couple of inches! The structures people struggled like medieval alchemists to find rare and exotic metals that could withstand such blowtorch temperatures. They recommended that the hydraulic lines be of stainless steel; for the ejector flaps they found a special alloy called Hastelloy X; and they recommended making our control cables out of Elgiloy, the material used in watch springs. Plumbing lines would be gold-plated since gold retains its conductivity at high temperatures better than silver or copper. Kelly just fumed watching our materials costs rocket into the stratosphere.
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.
I had a staff of three (by Skunk Works standards that was almost an empire). On the air-conditioning team, I had two engineers to help design the internal cooling system to safeguard the camera bays and the avionics and landing gear systems. The cockpit environment also presented a unique problem: without effective and fail-safe cooling the pilot could bake a cake in his lap. And as head thermodynamicist, that problem fell in my lap.
We designed the cockpit air-conditioning to bleed air off the engine compressor and dump it through a fuel air cooler, then through an expansion turbine, into the cabin at a frigid minus 40 degrees F, which lowered the ovenlike 200-degree cockpit to a balmy Southern California beach day. Developing these systems took us a year of frustrating trial and error.
Our engines were the only items off the shelf, so to speak. Kelly agreed with me that if we started from scratch to invent our engines, we would be hopelessly late in delivering the first Blackbird. We chose two Pratt & Whitney J-58 afterburning bypass turbojets, designed in 1956 for a Navy Mach 2 fighter-interceptor that had been canceled before the start of production. But the engine, which would need major modifications for our purposes, had already undergone about seven hundred hours of testing before the government cut off its funding. Each of these engines was Godzilla, producing the total output of the Queen Mary’s four huge turbines, which churned out 160,000 shaft horsepower. Using afterburners at Mach 3, the exhaust-gas temperatures would reach an incredible 3,400 degrees.
This propulsion system would not only be the most powerful air-breathing engine ever devised but also the first ever to fly continuously on its afterburners, using about eight thousand gallons of fuel an hour. To build this system to our needs and specifications, P & W’s chief designer, Bill Brown, who had worked closely with us on the U-2, agreed to construct a separate plant at their Florida manufacturing complex exclusively for developing this extraordinary engine. The CIA unhappily swallowed the enormous development costs of $600 million. Brown preached teamwork and pledged an unprecedented degree of partnership with the Skunk Works in general, and with me and my team in particular, to design their compressor to match my airflow inlet. This close partnership between the engine builder and the airplane manufacturer was unusual in an industry where the engine people and the airplane manufacturers often used each other as scapegoats if an airplane failed to live up to its potential. Abandoning this kind of adversarial posturing led to achieving the most powerful engine system coupled to the highest-performance inlets at these high Mach numbers that has ever been attained.
Bill Brown also offered us access to one of the largest and costliest computer systems of the day, the IBM 710. The system was state-of-the-art for its time and about as sophisticated as today’s commonly used handheld calculators. But, like us, the Pratt & Whitney team would problem-solve mostly by what Kelly jokingly referred to as “my Michigan computer”—the battered old slide rule he had been using since his university days at Michigan.
Despite the unprecedented power of those two massive engines, they supplied only 25 percent of the Blackbird’s thrust at Mach 3, a fact Bill Brown hated to admit. The inlets produced most of the propulsive thrust by supplying the air required by the engine at the highest pressure recovery and with the lowest drag. At supersonic cruising speed, each of our two inlets swallowed 100,000 cubic feet of air per second—the equivalent of two million people inhaling in unison. Hydrocarbon fuels like kerosene burn at high pressure, but at 80,000 feet, the air density is only one-sixteenth the density at sea level, so we used the inlets to pump up compression, before burning the air-fuel mixture inside the engine and then expanding it through a turbine and finally refiring it with tremendous thrust through the afterburner.
The only way to get energy out of the air is to pump pressure into it or to burn it. Our unique movable inlet cone, shaped like a spike, acted as an air throttle by regulating the airflow into the inlet across the spectrum of speeds from takeoff to climb to maximum cruise speed. Operated by our revolutionary electronic measuring sensors, which recorded speed and angle of attack to position the spikes precisely, the movable spikes were fully extended about eight feet out from the inlets on takeoff and gradually retracted by as much as two feet into the inlet interior as the airplane gained maximum supersonic speed.
At 80,000 feet, the outside air temperature was about minus 65 degrees F. As the inlet sucked in the air at Mach 3 through narrowed openings that compressed it, the air heated to 800 degrees. The bypass turbojet engines took the heated and high-pressure air (40 psi) and squeezed it further in a compressor, heating it to about 1,400 degrees F. At that point fuel was added to heat the air inside the burner to 2,300 degrees F. This supercharged air was then expanded through the turbine, before being fed into the roaring afterburners, superheating the combustible mix of gas and air to 3,400 degrees F, just 200 degrees below the maximum temperature for burning hydrocarbon fuels. The white-hot steel nozzle spit out its fiery plume in the form of diamond-shaped supersonic shock waves. Even in th
e frigid upper atmosphere, the air boiled at 200 degrees F for a thousand yards behind those booming engines. This unprecedented propulsive power sped the Blackbird at an unbelievable two-thirds of a mile a second.
About six months into our wind tunnel testing, I went to Kelly with joyful results: the inlets produced 64 percent of the airplane’s full-throttled power. The precise shaping of the inlets and our unique movable air throttle cones, or spikes, allowed us to achieve an astounding 84 percent propulsion efficiency at Mach 3, which was 20 percent more than that of any other supersonic propulsion system ever built.
Developing this air-inlet control system was the most exhausting, difficult, and nerve-racking work of my professional life. The design phase took more than a year. I borrowed a few people from the main plant, but my little team and I did most of the work. In fact the entire Skunk Works design group for the Blackbird totaled seventy-five, which was amazing. Nowadays, there would be more than twice that number just pushing papers around on any typical aerospace project.
Having today’s high-speed computers would have accelerated the design process and simplified much of our testing, but perfection was seldom a Skunk Works goal. If we were off in our calculations by a pound or a degree, it didn’t particularly concern us. We aimed to achieve a Chevrolet’s functional reliability rather than a Mercedes’s supposed perfection. Eighty percent efficiency would get the job done, so why strain resources and bust deadlines to achieve that extra 20 percent, which would cost as much as 50 percent more in overtime and delays and have little real impact on the overall performance of the aircraft itself?