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The Blackbird
The SR-71, unofficially known as the “Blackbird,” is a long-range, advanced, strategic reconnaissance aircraft developed from the Lockheed A-12 and YF-12A aircraft. The first flight of an SR-71 took place on Dec. 22, 1964, and the first SR-71 to enter service was delivered to the 4200th (later 9th) Strategic Reconnaissance Wing at Beale Air Force Base, Calif., in January 1966. The U.S. Air Force retired its fleet of SR-71s on Jan. 26, 1990.
Throughout its nearly 24-year career, the SR-71 remained the world’s fastest and highest-flying operational aircraft. From 80,000 feet, it could survey 100,000 square miles of Earth’s surface per hour.
The Blackbird’s performance and operational achievements placed it at the pinnacle of aviation technology developments during the Cold War.
The reason why Soviets never developed their own SR-71
Why didn’t the Soviets come up with their own “SR-71” and build a counterpart warplane to the Blackbird?
‘The Soviets built the MiG-25,’ says Iain McClatchie, an aviation expert, on Quora.
‘Notice how huge those air intakes are? Compare that against a Mach 2 airplane:
‘Dynamic pressure is what holds the aircraft up and causes drag. It scales with air density linearly, and with velocity SQUARED.
‘Air mass flow rate through the engines is what is needed for thrust. It scales with air density linearly, and with velocity LINEARLY.
‘Since the wing works with dynamic pressure, dynamic pressure can’t vary more than a factor of 5 or so during the flight. So, if you want to go fast, you have to go high, where the air is less dense. For mass flow to keep up with drag, you’ll need big fat intakes. These aren’t going to work well at lower speeds.
‘The moment we saw the MiG-25, we knew it was designed to go fast like an SR-71/A-12, whose intakes are each nearly the size of the fuselage.
‘The other problem that a high and fast jet faces is hidden. The engine intake slows the air to subsonic flow before it goes into the compressor. The air’s kinetic energy turns into heat… the temperature rise goes as the SQUARE of velocity. The engine then has to compress that air (heating it more), and then add lots of heat before expanding it through the turbine. The turbine has to survive air heated in all three ways.’
The first engine to use directionally solidified turbine blades
McClatchie continues;
‘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.
‘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).
Soviets never developed their own SR-71. Here’s why.
‘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 (Mach 2.83 rather than Mach 3.4), and its engine did not last the 400 hours between overhauls that the J58 managed.’
McClatchie concludes;
‘That speed limit, btw, is a very abrupt speed limit. NASA squeezed a tiny performance increase out of the SR-71 by reducing engine life from 400 to 50 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.’
Be sure to check out Linda Sheffield Miller (Col Richard (Butch) Sheffield’s daughter, Col. Sheffield was an SR-71 Reconnaissance Systems Officer) Twitter X Page Habubrats SR-71, Instagram Page SR71Habubrats and Facebook Page Born into the Wilde Blue Yonder Habubrats for awesome Blackbird’s photos and stories.
Top SR-71 Blackbird photo: Stuart Freer
Photo credit: NASA, U.S. Navy, Alex Beltyukov and Dmitriy Pichugin via Wikipedia
