Ameer Randolph
The SR-71 Blackbird is a retired long-range, high-altitude, Mach 3+ strategic reconnaissance aircraft that was developed and manufactured by the American aerospace company Lockheed Corporation. The aircraft was revealed to the public in July 1964 and entered service in the United States Air Force (USAF) in January 1966. The SR-71 was designed to operate at high speeds and altitudes, allowing it to evade or outrace threats such as surface-to-air missiles. To support these high-performance capabilities, the SR-71 consumed a significant amount of fuel. In this article, we will explore the fuel usage, specifications, and unique characteristics of the SR-71 Blackbird's fuel system.
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What You'll Learn
- The SR-71 Blackbird uses 44,000 pounds of fuel per hour
- The Blackbird's fuel is three times more expensive than airliner fuel
- The Blackbird uses a vintage military specification called MIL-T 38219, or Jet Propellant 7 (JP-7)
- The Blackbird's six main tanks form its exterior skin
- The Blackbird's fuel is extra-slippery after rainfall
The SR-71 Blackbird uses 44,000 pounds of fuel per hour
The SR-71 Blackbird is a retired long-range, high-altitude strategic reconnaissance aircraft developed and manufactured by the American aerospace company Lockheed Corporation. It was developed in the 1960s by Lockheed's Skunk Works division, with American aerospace engineer Clarence "Kelly" Johnson responsible for many of the aircraft's innovative concepts. The SR-71 was based on the Lockheed A-12, a pioneer in stealth technology, but was longer and heavier to carry more fuel and a crew of two in tandem cockpits.
The SR-71 Blackbird's fuel demands are quite remarkable. It uses 44,000 pounds of fuel per hour, which equates to about 12,000 gallons. This fuel, known as JP-7, is three times as expensive as the type used in airliners. It was designed to meet exacting specifications, including a non-irritating odour and a water-white, clean and bright colour at room temperature. To meet these specifications, Shell Oil invented a compound blend of kerosene distillates and hundreds of hydrocarbons.
The JP-7 blend offers high thermal oxidative stability, which means it remains predictable at high temperatures. This stability is crucial as the heat generated on the SR-71's skin as it flies at Mach 3.2 radiates inward. The fuel also has a high flash point to prevent unintended combustion, as the fuel serves as the primary heat sink to dissipate the high temperatures during flight. The SR-71's six main fuel tanks form its exterior skin and are not fully sealed against leaks, allowing for expansion during high-speed flight.
The SR-71's fuel requirements presented unique challenges. For example, a traditional fuel tank liner would dissolve in JP-7, and the fuel's slipperiness after rainfall could make taxiing dangerous. Additionally, the fuel leaked on the ground before takeoff due to the lack of a fuel-sealing system that could withstand extreme temperature cycles during flight. Despite these challenges, the SR-71 Blackbird's fuel consumption and performance characteristics made it a remarkable aircraft, capable of evading or outracing threats during its operational lifespan.
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The Blackbird's fuel is three times more expensive than airliner fuel
The SR-71 Blackbird, also known as the "Strategic Reconnaissance", is a retired long-range, high-altitude aircraft. It was developed and manufactured by the American aerospace company Lockheed Corporation in the 1960s. The Blackbird is the fastest plane on the planet, with a top speed of Mach 3.2 at 85,000 ft or 26,000 m. To achieve these incredible speeds, the Blackbird required a special type of fuel known as MIL-T 38219 or Jet Propellant 7 (JP-7).
The Blackbird's fuel, JP-7, is three times more expensive than the type of fuel used by airliners. This is because JP-7 is a highly specialized military specification fuel designed to meet the Blackbird's unique requirements. JP-7 has "high thermal oxidative stability," meaning it performs predictably at high temperatures. The Blackbird's skin can reach temperatures of over 300 degrees F during Mach 3 cruise, and the fuel itself can reach temperatures of 400 degrees F, making it extremely volatile.
The high cost of JP-7 is also due to the fact that it is a compound blend of various hydrocarbons, including paraffins, cycloparaffins or naphthenes, and olefins. All but five percent of the aromatics are removed during processing, resulting in a clean mixture with low levels of impurities such as sulfur, nitrogen, and oxygen. Additionally, an agent known as PWA-536 is added to the fuel to make it more slippery and reduce wear on the fuel pump.
The Blackbird's fuel system was not sealed because there were no seals flexible and durable enough to handle the extreme temperatures and expansion-contraction cycles the aircraft experienced during flight. This meant that the Blackbird would often leak fuel on the ground before takeoff, causing annoyance to ground crews. The fuel tanks themselves formed the exterior skin of the aircraft and were not fully sealed, allowing for expansion during high-speed flight.
The SR-71 Blackbird's performance and capabilities were groundbreaking, but they came at a cost. The specialized fuel it required was a significant expense, but it was necessary to enable the Blackbird to achieve its record-breaking speeds and altitudes.
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The Blackbird uses a vintage military specification called MIL-T 38219, or Jet Propellant 7 (JP-7)
The Lockheed SR-71 Blackbird is a retired long-range, high-altitude, Mach 3+ strategic reconnaissance aircraft. It was developed in the 1960s by Lockheed's Skunk Works division and entered service in the United States Air Force (USAF) in January 1966. The SR-71 was designed to operate at high speeds and altitudes, Mach 3.2 at 85,000 ft or 26,000 m, allowing it to evade or outpace threats such as surface-to-air missiles. To support these high-performance capabilities, the Blackbird required a significant amount of fuel, consuming up to 44,000 pounds of fuel per hour.
The Blackbird's fuel demands were met by a specialised type of jet fuel known as MIL-T 38219 or Jet Propellant 7 (JP-7). This fuel was specifically developed in 1955 by master chemist Clarence Brown CB Eichman at Pratt and Whitney for the Central Intelligence Agency (CIA) for use in high-speed reconnaissance aircraft. The SR-71, with its design speed of Mach 3.2, experienced very high skin temperatures due to aerodynamic heating. To address this challenge, JP-7 fuel was formulated with a high flash point and high thermal stability, enabling it to serve as an effective heat sink for the aircraft's severe high-temperature environment.
JP-7 fuel is characterised by its high thermal oxidative stability, maintaining predictability even at elevated temperatures. Its composition includes a blend of kerosene distillates and various hydrocarbons, including paraffins, cycloparaffins or naphthenes, and olefins. Notably, JP-7 has low levels of aromatics, resulting in a cleaner mixture with reduced impurities such as sulfur, nitrogen, and oxygen. To compensate for the poor lubrication properties of low-aromatic fuel, an agent known as PWA-536 was added to the blend to enhance its lubricity and reduce wear on the fuel pump.
The unique specifications of JP-7 fuel also included aesthetic considerations. According to the military standard, the odour of the fuel "shall not be nauseating or irritating," and its colour should be "water-white, clean, and bright" at room temperature. These requirements further distinguished the specialised nature of the fuel used by the Blackbird.
The high-performance capabilities of the SR-71 Blackbird and its reliance on the specialised JP-7 fuel contributed to its operational success as a strategic reconnaissance aircraft. The combination of advanced aerodynamics, high-speed capabilities, and the unique fuel specifications of the SR-71 made it a formidable asset in the sky during its service in the United States Air Force.
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The Blackbird's six main tanks form its exterior skin
The Lockheed SR-71 "Blackbird" is a retired long-range, high-altitude, Mach 3+ strategic reconnaissance aircraft. It was developed in the 1960s by the American aerospace company Lockheed Corporation and revealed to the public in July 1964. The SR-71 was designed to carry more fuel than its predecessor, the Lockheed A-12, and it could operate at high speeds and altitudes (Mach 3.2 at 85,000 ft or 26,000 m).
The Blackbird's fuel demands were particularly high. It could consume 44,000 pounds of fuel in an hour, and it required a specific type of fuel known as MIL-T 38219 or Jet Propellant 7 ("JP-7"). This fuel was three times more expensive than the type used in airliners and had to meet exacting specifications. It needed to have a high flash point to avoid unintended combustion, as the Blackbird's skin could heat up to 600 °F (320 °C) during a mission, and the fuel was used as the primary heat sink.
The six main fuel tanks of the Blackbird formed its exterior skin. They were not fully sealed against leaks, which allowed for the expansion of the tanks from heat during high-speed flight. This design choice was necessary because a traditional fuel tank liner would dissolve in JP-7. Photos of the Blackbird at low altitude often show fuel on its fuselage due to the leaks. Before takeoff, the ground crews would count the drips per minute with a stopwatch and a chart to mark the location and clean the hangar floor.
The JP-7 fuel played a critical role in the Blackbird's performance and safety. As each pound of JP-7 was burned during flight, the cavity was filled with inert nitrogen gas pumped from the nose wheel well. This prevented the empty tanks from caving in as the Blackbird descended into higher air pressure. Additionally, the fuel's low aromatic content resulted in a clean mixture with low levels of impurities, contributing to the overall stability and performance of the aircraft.
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The Blackbird's fuel is extra-slippery after rainfall
The SR-71 Blackbird is a retired long-range, high-altitude, Mach 3+ strategic reconnaissance aircraft developed in the 1960s by Lockheed's Skunk Works division. The aircraft was designed by American aerospace engineer Clarence "Kelly" Johnson, who was responsible for many of the SR-71's innovative concepts. The SR-71 is a thirsty aircraft, consuming 44,000 pounds of fuel per hour, which is three times more expensive than the type used in airliners. To meet the specifications, Shell Oil developed a compound blend of kerosene distillates with hundreds of hydrocarbons, resulting in Jet Propellant 7 (JP-7).
The SR-71's fuel, JP-7, is extra-slippery after rainfall. This caused a unique challenge for ground crews, as the wet tires of the SR-71 would often slide while taxiing, requiring hangar crews to scramble to prevent accidents. The slipperiness of JP-7 is attributed to its low aromatic content, which, while resulting in a cleaner mixture, also makes it a poor lubricant. To address this issue, Shell added an agent (PWA-536) at a concentration of at least 200 parts per million to increase the fuel's lubricity and reduce wear on the fuel pump.
The SR-71's fuel system and tank design also contributed to its unique characteristics. The aircraft's six main fuel tanks formed its exterior skin and were not fully sealed against leaks. This design allowed for the expansion of the tanks during high-speed flight due to extreme temperature cycles. As a result, the SR-71 was known to leak fuel, with steady streams of fuel dripping onto the hangar floor before takeoff. The fuel leaks were so significant that it was common practice to add 400 to 700 pounds of extra JP-7 fuel to compensate for the expected leakage.
The slipperiness of the JP-7 fuel after rainfall presented a challenge for ground operations, but it was a necessary trade-off for the aircraft's performance and stability at high speeds and altitudes. The fuel's high thermal oxidative stability and flash point made it suitable for the SR-71's unique operational requirements, allowing it to operate at Mach 3.2 at 85,000 feet.
The SR-71 Blackbird's fuel system and the unique characteristics of its JP-7 fuel are a testament to the innovative engineering that went into the development of this aircraft. The ground crews' experiences with the extra-slippery fuel after rainfall highlight the complexities of working with such advanced technology.
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Frequently asked questions
The SR-71 used around 44,000 pounds of fuel per hour.
The SR-71 used a vintage 1970 military specification called MIL-T 38219, or Jet Propellant 7 (JP-7).
The fuel specifications required that its odour "shall not be nauseating or irritating", and its colour should be "water-white, clean and bright" at room temperature. The fuel also needed to have high thermal oxidative stability and a high flash point to avoid unintended combustion.
The SR-71 was a long-range, high-altitude, Mach 3+ strategic reconnaissance aircraft that operated at high speeds and altitudes. It required a large amount of fuel to support these operations.
