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SR-71 Blackbird: Why Only America Built This Mach 3 Monster Spy Plane

SR-71 History
SR-71 Blackbird Spy Plane. Image Credit: Creative Commons.

In the late 1960s, there is no question that Western nations—particularly the United States—immediately took notice when the MiG-25 Foxbat first emerged out of the Soviet Union during the peak of the Cold War.

Designed by the Soviet Union’s Mikoyan-Gurevich bureau, the Foxbat is a supersonic interceptor and reconnaissance plane that is among the fastest military aircraft ever to take to the skies—as it boasted a top speed of Mach 3.2.

According to the Aviation Geek Club, “this aircraft could outrun any fighter in the air, and indeed any military aircraft other than the SR-71 Blackbird. The MiG-25’s development has been attributed at various times to the threat posed by either the B-70 Valkyrie, or to the SR-71.”

The writer also pointed out that Lou Drendel, in his book SR-71 Blackbird In Action, noted that the SR-71 “posed a much more formidable threat, with its demonstrated ability to sustain cruise speeds above Mach 3 at over eighty thousand feet.”

A Soviet Blackbird?

Given these facts, some aviation experts have often wondered why the Soviets didn’t just come up with their own version of the SR-71.

“The J58 engine in the SR-71 was the first engine to use directionally solidified turbine blades, which were able to resist creep at higher temperatures than any blades before them. This is a critical technology. Without high temperature turbine blades, you cannot make a jet engine fast,” one such expert Iain McClatchie wrote on Quora.

“In fact, the SR-71 and MiG-25 are both thermally rather than power limited. Both have reserve power to climb (rapidly) at full speed. Their speed is limited by the temperature of their turbines, and not by power. These days, most turbine engines have hollow turbine blades, with ‘cooler’ air from the compressor blown through them and out tiny holes in their leading edges. The air forms a film over the blade, insulating it from the heat of the surrounding gas. Neither the SR-71 nor the MiG-25 had these blades. Neither had the ceramic coatings we use today. These changes would have enabled an operating speed increase, but probably not more than Mach 3.6 or so,” he continued.

Down to Technology

“As it turns out, the Soviets did not have the technology to make blades that could tolerate as high temperatures as the J58 turbine. As a result, the MiG-25 flew slower than the SR-71, and its engine did not last the four hundred hours between overhauls that the J58 managed. That speed limit … is a very abrupt speed limit. NASA squeezed a tiny performance increase out of the SR-71 by reducing engine life from four hundred to fifty hours. A MiG-25 was tracked at Mach 3.2 over the Sinai in March 1971. That speed excursion would have only lasted minutes and the engines were scrapped after the flight,” he concluded.

Ethen Kim Lieser is a Washington state-based Science and Tech Editor who has held posts at Google, The Korea Herald, Lincoln Journal Star, AsianWeek, and Arirang TV. Follow or contact him on LinkedIn.

Written By

Ethen Kim Lieser is a Washington state-based Science and Tech Editor who has held posts at Google, The Korea Herald, Lincoln Journal Star, AsianWeek, and Arirang TV.



  1. Steve

    November 21, 2021 at 7:22 pm

    The SR-71.
    A class unto itself.
    Pick your hyperbole, and it’s not big enough; simply the BEST.
    The sexiest craft ever flown.

  2. Jim Bagge

    November 22, 2021 at 11:33 am

    With it’s existing technology the SR-71 could and did exceed 3.5 Mach for a short period of time, if SR-71 pilot Brian Shul can be believed. Shul claims to have exceeded 3.5 Mach while being pursued by a SAM on a recon mission over Libya in 1986. And Shul flew his SR-71 thousands of miles back to his home base at Beale AFB outside Sacramento CA.
    As the writer says, SR-71’s (and the top secret CIA A-12 Oxcart spy plane from which the SR-71 was derived) were thermally limited as to how fast the pilot could push the aircraft, not engine thrust limited. The writer choses to focus on the engine technology that allowed the P&W J-58 to survive hour after hour at 3.2 Mach, but the actual thermal limit that set the speed limit for how fast an SR-71 could be pushed was something called Compressor Inlet Temperature, CIT.
    All Flight Manuals, for the SR-71, the CIA A-12, and the Air Force YF-12A, in the section, Maximum Mach, all specify that the pilot must NOT exceed a CIT of 427 degrees C. There is no maximum Mach number, instead a maximum CIT temperature. Depending on the ambient temperature of the air at 85,000 feet a CIT of 427 C would usually be reached at around 3.35 Mach. But Lockheed chief engineer Kelly Johnson is on record saying that if a pilot found himself in some unusually cold air at cruise altitude he could fly the plane faster before he hit the CIT limit of 427 C.

  3. Tony Maddox

    November 22, 2021 at 6:07 pm

    Because only the US had the know-how, the tools, the people and the drive to do it. Communism eradicates most of those attributes.

  4. Charles Jones

    November 22, 2021 at 9:56 pm

    The question was never answered.

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