SR-71: the Air Force’s irreplaceable Mach 3 spy plane (photos)

There was no such thing as the SR-71 – and plenty of digital ink to this day is spilled with analyzes of what might one day replace it: When the Soviet Union shot down Gary Power’s U-2 high-altitude reconnaissance plane in 1960, the United States recognized the urgent need for a more elusive spy plane. The incident, which underscored the ever-increasing sophistication of Soviet air defenses, inspired American weapons developers to create a reconnaissance airframe capable of penetrating Soviet airspace undetected or shot down.

The solution, introduced in 1966, was the fastest aircraft ever flown: the stealth SR-71 “Blackbird”.

Lockheed developed SR-71 in secret at Skunk Works, their advanced development programs division. The spy plane, which cost up to $200,000 an hour to operate, relied on speed, altitude and stealth to perform the deep-penetrating reconnaissance missions needed to monitor nuclear and military progress Soviets.

To achieve the record-breaking performance envelope of the SR-71, new technologies and procedures had to be developed.

SR-71 – The entire aircraft was custom designed to handle the heat created at Mach 3

Perhaps the most notable feature of the SR-71 is its speed.

Designed to operate at Mach 3.2, the “Blackbird” could simply outrun surface-to-air missiles (SAMs). So if a SAM was launched on an SR-71, the pilot could simply throttle forward, accelerate, and leave the SAM behind.

To travel at three times the speed of sound, the SR-71 relied on two Pratt & Whitney J-58 axial-flow turbojet engines. Each J-58 generated a jaw-dropping 32,000 pounds of thrust in afterburner mode. To put the J-58’s thrust into perspective, consider that the Redstone rocket, which launched the Mercury capsules into orbit, had a thrust of 78,000 pounds.

Initially, Pratt & Whitney struggled to create an engine with metallurgical properties capable of operating at the speed and resultant temperatures required by the SR-71. During development, the original impellers, made from conventionally cast nickel-base alloys, continued to crack due to thermal fatigue. To prevent turbines from cracking at high temperatures, Pratt & Whitney developed the Monocrystalline Turbine Blade, a technological breakthrough capable of withstanding the fiery heat needed to propel the SR-71 more than 2,000 miles per hour. hour.

Despite innovations in heat resistance, engine temperature remained the limiting factor in the SR-71’s top speed. The “Blackbird” cell could have gone faster. But Pratt & Whitney refused to guarantee or guarantee the operation of the J-58 in temperatures above 800 degrees Fahrenheit. Pratt & Whitney warned SR-71 pilots: above 800 degrees, all bets are off; “The engine could come off or you could lose turbine blades.”

The SR-71 was not just a sprinter. Remarkably, the “Blackbird” could sustain Mach 3 flight continuously, for over an hour at a time. Maintaining speeds of 2,000 miles per hour, for an hour at a time, caused the surface of the SR-71 to reach temperatures exceeding 600 degrees Fahrenheit. Conventional airframe materials were not capable of operating at such high temperatures, so the SR-71 was constructed primarily from titanium. Now the United States did not have access to the rutile ore needed to make a titanium airframe. Curiously, most of the world’s supply of rutile ore was in the Soviet Union. Obtaining the ore required a bit of cunning. The United States worked through third world countries and “fake operations” to trick the Soviets into supplying the rutile ore – a Cold War coup.

In addition to record speed, the SR-71 achieved record altitude. Capable of sustained level flight at 85,000 feet, no airframe has ever flown higher. Between speed and altitude, the SR-71 was virtually untouchable. The fastest Soviet interceptor, the MiG-25, could not catch or hit the SR-71. That is, assuming the Soviets detected the “Blackbird” in the first place.

Well, the Soviets could probably detect the SR-71. Design chief Kelly Johnson admitted that Soviet radar technology was improving faster than American stealth technology. But two decades before the F-117 debuted as the world’s first stealth fighter, Lockheed’s Skunk Works made several stealth breakthroughs while developing the SR-71. Aircraft shaping methods, radar-absorbing structural edges, radar-absorbing coatings, and other design features significantly reduced the SR-71’s radar signature.

Prohibitive costs and the development of cheaper alternatives doomed the SR-71

The SR-71 performed admirably over three decades of service with the CIA, USAF and NASA. The plane was a technological marvel, introduced well ahead of its time. But as the 21st century approached, military planners decided to decommission the spy plane.

While the SR-71 was never shot down in thirty years of service, Russian surface-to-air missile technology was advancing to the point where experts feared the SR-71 was vulnerable. The S-300 missile defense system had mostly experts concerned about the safety of the “Blackbird” crews. Likewise, the new MiG-31 was of concern. However, interception was not the only concern.

In light of the post-Cold War 1990s, the remarkable cost required to operate a fleet of SR-71s was beginning to seem untenable. Air Force Secretary Edward C. Aldridge Jr. once estimated that the money used to operate the SR-71 fleet could operate and maintain two wings of tactical fighters. That’s nearly 50 planes. One of the reasons the SR-71 was so expensive to operate was that it required so much specialized equipment and maintenance.

To illustrate the point: the SR-71 required a specialized fuel, known as JP-7. JP-7 fuel was custom-created for the SR-71 with an ultra-low flash point, which means it will not explode when exposed to the extreme heat and pressure created during normal flight operations of an SR-71. The JP-7 was so stable that you could drop a lit match into a tank and the match would go out rather than explode. But because JP-7 was so stable, a specialized engine ignition system was created, using triethylborane chemicals to cause an explosion sufficient to ignite JP-7 and start Pratt & Whitney engines. Fuel even required a specialized tanker for aerial refueling, the KC-135 “Q” variant.

SR-71 Blackbird spy plane. Image credit: Creative Commons.

SR-71

SR-71 spy planes on the tarmac. Image credit: Creative Commons.

SR-71 spy plane

SR-71 Blackbird spy plane. Image credit: Creative Commons.

SR-72 nuclear-powered aircraft

The image is of an SR-71 spy plane. Image credit: Creative Commons.

Avro 730

Image of the SR-71 spy plane. Image credit: Creative Commons.

SR-71

SR-71 Blackbird spy plane. Image credit: Creative Commons.

SR-71

SR-71 Blackbird. Image credit: Creative Commons.

Clearly, the costs of maintaining so much specialized equipment have piled up. And by the 1990s, the United States had surveillance satellites and unmanned aerial vehicles fully capable of handling the SR-71’s mission profile, making the SR-71 a forgiving redundancy. In 1998, the “Blackbird” was retired.

Although the spy plane has been out of service for nearly a quarter of a century, it remains unrivaled in terms of speed, altitude, ingenuity and ability to capture public interest.

Harrison Kass is defense editor at 19FortyFive. A lawyer, pilot, guitarist and minor professional hockey player, he joined the US Air Force as a trainee pilot, but was discharged for medical reasons. Harrison is a graduate of Lake Forest College, the University of Oregon School of Law, and the Graduate School of Arts & Sciences at New York University. He lives in Oregon and regularly listens to Dokken.