The first aircraft to use its own fuel for hydraulic fluid was the SR-71 Blackbird and it was called the fuel hydraulic system
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, 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, 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.
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’s 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 tank 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 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.
Fuel was the lifeblood of the world’s fastest manned aircraft.
Check out the Habubrats SR-71 and Born into the Wilde Blue Yonder Facebook pages for further Blackbird photos and stories.
Photo by NASA and U.S. Air Force