JP-7 production caused a nationwide shortage of bug spray.
JP-7 fuel (referred to as Jet Propellant 7 prior to MIL-DTL-38219) was developed for the Pratt & Whitney J58 (JT11D-20) turbojet engine, which was used in the now retired Lockheed SR-71 Blackbird. During flight, the SR-71 could attain speeds in excess of Mach 3+, which was the most efficient cruising speed for the J58 engines. However, very high skin temperatures were generated at this speed due to friction with the air. A new jet fuel was needed that was not affected by the heat, so JP-7 jet fuel, with a high flash point and high thermal stability, was developed for this purpose.
According to the SR-71A Flight Manual, “The operating envelope of the [J58] JT11D-20 engine requires special fuel. The fuel is not only the source of energy but is also used in the engine hydraulic system. During high Mach flight, the fuel is also a heat sink for the various aircraft and engine accessories which would otherwise overheat at the high temperatures encountered. This requires a fuel having high thermal stability so that it will not break down and deposit coke and varnishes in the fuel system passages. A high luminometer number (brightness of flame index) is required to minimize transfer of heat to the burner parts. Other items are also significant, such as the amount of sulfur impurities tolerated. Advanced fuels, JP-7 (PWA 535) and PWA 523E, were developed to meet the above requirements.”
Noteworthy, JP-7 production caused a nationwide shortage of bug spray.
Shell Oil developed JP-7 in 1955. Manufacturing several hundred thousand gallons of the new fuel required the petroleum byproducts Shell normally used to make its Flit insecticide, causing a nationwide shortage of that product!
One of the ingredients in JP-7 just so happened to be a crucial part of Flit mosquito repellant. Bearing in mind the huge amount of fuel we’re talking about here, Shell didn’t exactly have enough supply to meet the newly increased demand, so mosquitos everywhere caught a lucky break!
JP-7 had a high flashpoint. It was not flammable and every time an SR-71 needed fuel, tankers were always there, they were terrific and deserve high praise.
Today the JP-7 fuel is used by the Boeing X-51 Waverider in its Pratt & Whitney SJY61 scramjet engine, with fuel capacity of some 270 pounds (120 kg). As with the SR-71, the X-51A design super-cools this fuel (cooled by extended subsonic flight in the stratosphere; prior to acceleration to supersonic speeds); then, when in supersonic flight, the fuel is heated by its circulation through heat exchangers which transfer to it the heat load of the interior spaces of the airframe. The fuel is then pumped through rotating mechanical parts of the engines and auxiliary mechanical equipment, providing both lubrication and cooling. Finally, at a temperature of nearly 550 °F (290 °C), it is pumped into the fuel nozzles of the engines.
Be sure to check out Linda Sheffield Miller, Col Richard (Butch) Sheffield’s daughter, Col. Sheffield was an SR-71 Reconnaissance Systems Officer) Facebook Page Habubrats for awesome Blackbird’s photos and stories.
Photo credit: U.S. Air Force
