“Kelly,” Wheelon recalls responding, “you’re the world’s greatest aeronautical engineer. But this program is going to stop unless you put an electronic servo on that thing. Now take your pick.”
Wheelon says that Johnson went to Washington, apparently to go to someone in the agency over Wheelon’s head. When he came back he told Wheelon that he had decided to go to the electric servo. But that may have been sheer guile, because hydraulic actuators are still used in the few SR-71s still flying. The number of unstarts was greatly reduced when the system’s analog computers were replaced in 1983 by far faster and more sensitive digital ones as a result of the development of a Digital Automatic Flight and Inlet Control System. The DAFICS computer, working closely with the spikes and other inlet components, reverses unstarts in fractions of a second.
Pratt & Whitney’s Arnold Gunderson has thought a lot about his supremely powerful but high-strung engine. The J-58 is complex, and each of its systems is coupled in some obscure way with other systems, which meant that all these relationships had to be learned.
“Every time you make an improvement, you’ve ruined or degraded something else,” Gunderson observes. “If you optimize something here, you’ve made it significantly less optimal somewhere else. Now, you’ve got an engine, which is a highly complex thing, with its own internal subsystems. You’ve got a completely self-contained afterburner control system, a self-contained main engine control system. You’ve got the spike going back and forth along its 26-inch path. You’ve got the four bypass doors that regulate the static pressure inside the duct. When they’re closed, it’s maximum ram recovery. When they’re open, you create drag. All of these things affect the entire propulsion system. Now, that’s just the main features.... Every time we made a minor change in how the engine worked,” he adds, “it had to go back into an integrated engineering approach with the entire propulsion system.”
The problems plaguing the engine in the beginning caused delays of months and would have financially broken the program had the Navy not bailed it out with $38 million. Every serious problem that afflicted the J-58 was given a number, and the list eventually reached more than 270. “ENC—Exhaust Nozzle Control instability—was problem number 6,” Gunderson says. “It was still an active problem in 1974. Even then we were trying to figure ways to keep the engine stable. As you can imagine, it goes back a long, long way.”
Some J-58s, like a couple of the airplanes they powered, absolutely refused to work properly no matter what was done to them. Gunderson says that any J-58 whose parts were fundamentally unhappy with one another for no apparent reason was disassembled and their parts saved to repair other engines.
The SR-71s also had marked differences. Thomas maintains that each Blackbird had a distinct personality and that careful records documented them as clearly as diary entries. “I could tell you something different about each one of those airplanes,” he says. Number 974, which perished in the South China Sea near Luzon after a catastrophic engine failure, gave its crews all it had. Justin Murphy agrees, and says the same about 971. Author and former SR-71 pilot Richard Graham swears that 962 “never let us down.” But 959 was a hangar queen, an absolute “lemon,” according to Thomas. “You could never get everything to work at the same time. The Air Force said, ‘Come and get it. We don’t want it.’ ” There were also problems with the defensive system, but they were philosophical, not technical. Johnson believed so strongly that his supersonic spyplanes would be adequately protected above 80,000 feet at Mach 3.2 that he vigorously resisted equipping them with electronic countermeasures.
Wheelon recalls that he tangled with the always weight-conscious Johnson over ECM too. Wheelon won, and as a result, the A-12 and SR-71 were equipped with the newest defensive systems.
And the opposition never gave up the notion of trying to bag one, as it had Francis Gary Powers’ U-2. He can’t recall the precise designation but Gunderson remembers a Soviet missile that had the theoretical capability of flying up in front of an SR-71, then plunging down and hitting it at Mach 6—a nearly impossible feat because there was almost no warning that the airplane was coming. Still, there was always the possibility that one would get hit by a “golden BB.”
It was certainly in the back of the Air Force’s collective mind. The airmen were concerned that if the airplane went down carrying ECM hardware all of the fighters and bombers that carried the same equipment would be compromised. Yet not installing it could have hastened the day when one of the high fliers was shot down.