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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 (AFB), Calif., in January 1966.
The US Air Force (USAF) retired its fleet of SR-71s on Jan. 26, 1990, because of a decreasing defense budget and high costs of operation.
Throughout its nearly 24-year career, the SR-71 remained the world’s highest-flying and fastest operational aircraft. From 80,000 feet, it could survey 100,000 square miles of Earth’s surface per hour.
Today there are many rumors about just how fast the SR-71 could go. The J58 engine temperature limited the top speed. The speed limit for the airplane ironically had nothing to do with the airframe; it had to do with the engines. Right in front of the engine compressor was a temperature probe that reported the temperature to the pilot; when the temperature was around 427°C, 800°Fahrenheit, that’s as fast as they were allowed to go.
However, as revealed by Paul Crickmore in his new book Lockheed Blackbird: Beyond the Secret Missions The missing chapters, during bomb damage assessment (BDA) flights of Libya in support of Operation El Dorado Canyon in April 1986, the SR-71 could go faster because the 427°C limitation was removed.
As already explained, SR-71 pilots could not exceed 427°C, which was the usual inlet max temperature. That was because the compressor inlets govern the speed limits. However, a WARTIME EMERGENCY limit was established for Operation El Dorado Canyon: instead of the usual 427°C, the max was PUSHED UP to 450°C.
In other words, for the crew’s safety, they could push the airplane faster than normal. This required extensive inspection of the first-stage compressor afterward (the mechanics would be looking for damage to the engines).
It is known from flight test experience that at Mach 3.4 the unstable air in the SR-71 Blackbird inlet reaches the engine and can cause a flame out. There were quite a few flameouts during the SR-71 career.
As we have already reported, SR-71 pilot Brian Shul claimed to have reached Mach 3.5 during a BDA flight in support of Operation El Dorado Canyon (CLICK HERE to read the full story). According to the information featured Paul Crickmore’s new book, that speed was totally feasible with the inlet max temperature pushed up to 450°C.
Also, during the speed run of the SR-71 #972 from California to Virginia, a Skunk Works engineer said that the limitation of 427°C could be lifted for the final flight. Sure, it might damage the engines, but it would be the last flight! The USAF refused because they didn’t want to draw attention to the fact that they were kicking out of their inventory the SR-71 Blackbird and her incredible range and speed.
Noteworthy, for the final flight a speed run could’ve been done in less than 68 minutes. My Dad Butch Sheffield, who was working for the Skunk Works Washington DC division, was in charge of the final 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 Page Habubrats SR-71 and Facebook Page Born into the Wilde Blue Yonder for awesome Blackbird’s photos and stories.
Photo credit: David Peters and U.S. Air Force
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