SR-71 Top Speed

Not only JP-7: the SR-71 could use JP-4 and JP-5 as emergency fuels but they both limited the Blackbird top speed to Mach 1.5

The SR-71 Blackbird was the first aircraft to use its own fuel for hydraulic fluid. It was called the fuel hydraulic system.

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The legendary SR-71 Blackbird Mach 3+ spy plane was powered by two 34,000 lbf (151,240 N) thrust-class J58 afterburning turbojet engines. Each engine contained a nine-stage compressor driven by a two-stage turbine. The main burner used an eight-can combustor and the afterburner is fully modulating. The primary nozzle area was variable. Above Mach 2.2, some of the airflow was bled from the fourth stage of the compressor and dumped into the augmentor inlet through six bleed-bypass tubes, circumventing the core of the engine and transitioning the propulsive cycle from a pure turbojet to a turbo-ramjet.

The SR-71 was the first aircraft to use its own fuel for hydraulic fluid. It was called the fuel hydraulic system.

An engine-driven pump provided 1800 psi of recirculating fuel to accurate various engine components and then returned it back to the aircraft fuel system to be burned. Fuel was used in the actuators to control the afterburner nozzles, which maintain the proper exhaust gas temperature and control the thrust output. The fuel was also used in the engine actuators to shift the two-position inlet guide veins from their axial position to the cambered position and back again. This was just another of the many first-ever inventions of the-SR-71.

The J58 engine was hydromechanically controlled and burned a special low volatility jet fuel mixture known as JP-7.

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

Emergency fuels could be used in the SR-71 if the crew was low on fuel and had to use ANY tanker (as already explained the Blackbird relied on KC-135Q tankers [that could simultaneously carry a maximum of 74,490lb of JP-7 and 110,000lb of JP-4 for their own engines] but the SR-71 could also be refueled by standard Stratotankers in the event KC-135Qs were not available or if the Blackbird crew had to deal with an emergency situation) they could find to avoid the loss of the aircraft. The emergency fuels were JP-4 or JP-5 but they limited the Blackbird top speed to Mach 1.5. There were six main fuselage tanks. All 80,285 pounds of JP-7 fuel were carried in six main fuselage tanks. The tanks numbered one through six moved forward to aft (back) tank 6B It could hold 7,020 pounds of gravity-fed fuel and two tanks sumps. This was also called the “doghouse” and was located in the extreme back portion of the fuselage.

These are just a few interesting facts that I found by reading Rich Graham’s “SR 71 Revealed the inside story.” This book was published in 1996 before some of the facts about the SR-71 became unclassified. Last year when I was visiting SR-71 #972 one of my Grandson’s friends asked me “Why is this airplane so big? My immediate answer was… they needed the room to hold as much fuel as possible.

Fuel was the lifeblood of this fastest-manned airplane in the world.

Be sure to check out Linda Sheffield Miller (Col Richard (Butch) Sheffield’s daughter, Col. Sheffield was an SR-71 Reconnaissance Systems Officer) Facebook Pages Habubrats SR-71 and Born into the Wilde Blue Yonder for awesome Blackbird’s photos and stories.

This model is available in multiple sizes from AirModels – CLICK HERE TO GET YOURS.

Photo credit: NASA and U.S. Air Force

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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