A unique design
The SR-71 is renowned for its record-breaking speed, much of which was achieved without reaching the aircraft’s full potential. Flying at an altitude of 80,000 feet, it could survey approximately 100,000 square miles of the Earth’s surface every hour. Its distinctive design sets it apart from every other aircraft in the gallery. With its unusual, spaceship-like shape, the Blackbird could achieve the astonishing speeds for which it became famous.
The aircraft’s technology was so advanced that even the tools required to build it had to be created from the ground up.
The SR-71 Blackbird fuel
In fact, the Blackbird’s Mach 3.2 cruising speed generated so much heat that conventional jet fuel was unsuitable. The aircraft required a fuel with a high flash point and exceptional thermal stability, prompting Shell to develop a specialized blend known as JP-7.
JP-7, designated Jet Propellant 7 before the introduction of MIL-DTL-38219, was created specifically for the Pratt & Whitney J58 (JT11D-20) turbojet engines. The SR-71’s most efficient cruising speed was above Mach 3, but the intense friction with the atmosphere produced extreme skin temperatures. JP-7 was therefore formulated to withstand the heat without breaking down, making it ideal for the Blackbird’s demanding flight conditions.
Nationwide shortage of bug spray
According to the SR-71A Flight Manual, the J58 JT11D-20 engine required a specialized fuel that served several functions beyond providing power. It also operated the engine’s hydraulic system and acted as a heat sink during high-Mach flight, absorbing heat from aircraft and engine components that would otherwise overheat.
To perform these roles effectively, the fuel needed exceptional thermal stability to prevent the formation of coke and varnish deposits in the fuel-system passages. It also required a high luminometer rating, indicating a bright flame that minimized heat transfer to the burner components, along with strict limits on sulfur impurities. To satisfy these demands, engineers developed the advanced fuels JP-7 (PWA 535) and PWA 523E.
Flit mosquito repellent
Remarkably, the production of JP-7 led to a nationwide shortage of insect repellent.
Shell Oil developed JP-7 in 1955 and, in producing several hundred thousand gallons of the specialized fuel, consumed petroleum byproducts that the company normally used to manufacture its Flit insecticide. As a result, supplies of the popular bug spray became scarce.
One of the compounds used in JP-7 was also an essential ingredient in Flit mosquito repellent. Because the Blackbird program required such enormous quantities of fuel, Shell could not produce enough of the ingredient to satisfy the increased demand for both products, giving mosquitoes an unexpected advantage.
JP-7 also had a high flash point, making it highly resistant to ignition. Whenever an SR-71 needed to refuel, tanker crews were on hand to support the aircraft, and their role deserves recognition.
SR-71 Blackbird fuel used by the Boeing X-51 Waverider
Today, JP-7 fuel powers the Boeing X-51 Waverider’s Pratt & Whitney SJY61 scramjet engine, which carries approximately 270 pounds (120 kilograms) of fuel. Like the SR-71, the X-51A uses its design to super-cool the fuel during prolonged subsonic flight in the stratosphere before accelerating to supersonic speeds.
Once the aircraft reaches supersonic velocity, the fuel circulates through heat exchangers that transfer heat from the airframe’s internal components. It then passes through the engines’ rotating parts and auxiliary machinery, serving as both a lubricant and a coolant. Finally, after reaching nearly 550°F (290°C), the fuel is delivered to the engine nozzles.
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Photos by U.S. Air Force
