Did you know the SR-71 Blackbird had a Smart Valve that allowed to use JP-7 fuel as internal coolant?

The SR-71 Blackbird had a Smart Valve that allowed to use JP-7 fuel as internal coolant. Here’s how it worked.

By Linda Sheffield Miller
Aug 20 2023
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The SR-71 Blackbird smart valve supplied only the hottest fuel to the engines and sent cooler fuel to retracted landing gear and avionics.

SR-71 T-Shirts
CLICK HERE to see The Aviation Geek Club contributor Linda Sheffield’s T-shirt designs! Linda has a personal relationship with the SR-71 because her father Butch Sheffield flew the Blackbird from test flight in 1965 until 1973. Butch’s Granddaughter’s Lisa Burroughs and Susan Miller are graphic designers. They designed most of the merchandise that is for sale on Threadless. A percentage of the profits go to Flight Test Museum at Edwards Air Force Base. This nonprofit charity is personal to the Sheffield family because they are raising money to house SR-71, #955. This was the first Blackbird that Butch Sheffield flew on Oct. 4, 1965.

The SR-71, unofficially known as the “Blackbird,” was a long-range, Mach 3+, 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.

Throughout its nearly 24-year career, the SR-71 Blackbird spy plane remained the world’s fastest and highest-flying operational aircraft. Flying at Mach 3+ from 80,000 feet, it could survey 100,000 square miles of Earth’s surface per hour. And in the off chance an enemy tried to shoot it down with a missile, all the Blackbird had to do was speed up and outrun it.

SR-71 Blackbird pilot tells the hilarious story behind his famed L.A. ground speed check

The Blackbird was in a different category from anything that had come before. “Everything had to be invented. Everything,” Skunk Works legendary aircraft designer and Skunk Works founder Kelly Johnson recalled in an interesting article appeared on Lockheed Martin website.

Ben Rich (the second Director of Lockheed’s Skunk Works from 1975 to 1991, succeeding Johnson) explains in book Skunk Works: A Personal Memoir of My Years of Lockheed, that the design team headed by him and Johnson turned to Shell Gas to develop a fuel having high thermal stability so that it will not break down and deposit coke and varnishes in the fuel system passages.

Rich says that “We needed the fuel to remain stable at enormous temperature ranges. The JP-7 (as it was later known), was at -60° when a KC-135 tanker pumped fuel into the SR-71. The fuel acted as an internal coolant. All the heat built up inside the aircraft was transferred to the fuel by heat exchanges. They designed a smart valve that could sense temperature change. It supplied only the hottest fuel to the engines. The smart valve sent cooler fuel to the retracted landing gear and avionics.”

As already explained, the fuel also cooled the cockpit.

SR-71 print
This print is available in multiple sizes from AircraftProfilePrints.com – CLICK HERE TO GET YOURS. SR-71A Blackbird 61-7972 “Skunkworks”

The air conditioning bled off the engine compressor, dumped it through a fuel cooler, then through an expansion turbo into the cabin at a fridged -40°.

My Dad, Butch Sheffield (RSO’s for eight years in the SR-71), told me he was always happy when they refueled as it would cool off the cockpit. The cockpit would become increasingly uncomfortable as it ran low on fuel.

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: U.S. Air Force

Lockheed SR-71 Blackbird model
This model is available in multiple sizes from AirModels – CLICK HERE TO GET YOURS.

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Linda Sheffield Miller

Linda Sheffield Miller

Grew up at Beale Air Force Base, California. I am a Habubrat. Graduated from North Dakota State University. Former Public School Substitute Teacher, (all subjects all grades). Member of the DAR (Daughters of the Revolutionary War). I am interested in History, especially the history of SR-71. Married, Mother of three wonderful daughters and four extremely handsome grandsons. I live near Washington, DC.
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