No story on the SR-71 would be complete without an understanding and appreciation of just how valuable the KC-135Q model tankers and their crews were to the successful and safe completion of every mission
The Lockheed A-12 and YF-12A aircraft served as the basis for the development of the SR-71, also referred to as the “Blackbird” or long-range, advanced strategic reconnaissance aircraft. The 4200th (later 9th) Strategic Reconnaissance Wing at Beale Air Force Base, California, received the first SR-71 to begin service in January 1966. The first SR-71 flight occurred on December 22, 1964. On January 26, 1990, the US Air Force retired its entire fleet of SR-71s.
For almost two decades, the SR-71 held the record for being the fastest and highest-flying operational aircraft in the world. It could cover 100,000 square miles of the Earth’s surface per hour from 80,000 feet. Two world records for its class were set on July 28, 1976, by an SR-71: an absolute speed record of 2,193.167 mph and an absolute altitude record of 85,068.997 feet.
If it weren’t for air refueling, the SR-71’s range would be relatively limited—roughly 2,000 NM. The aircraft’s range was increased by several air refuelings to the crew’s maximum endurance. Many missions have gone above 12,000 NM. The SR-71 and KC-135Q tankers’ forward basing allowed for increased overall efficiency, shorter range, shorter length missions, and faster reaction times.
There were various ways in which KC-135Q crews and their aircraft were different from other Air Force units. Actually, their boom operators were the only ones qualified to refuel the SR-71, and their aircrews were the only ones certified in Blackbird’s unique radio-silent rendezvous procedures. The Q-model tankers could move JP-4 and JP-7 fuel between different tanks because of special plumbing between the tanks.
They could use JP-4 or JP-7 fuel in their engine. If the SR-71 touched down in an area without JP-7 fuel, the Q-model tankers would fly in with the fuel and refill the aircraft using ground-based transfer hoses. One of the biggest benefits of flying Q-model tankers was that, unlike other SAC tanker crews, their personnel did not have to be on constant alert.
No story on the SR-71 would be complete without an understanding and appreciation of just how valuable the KC-135Q model tankers and their crews were to the successful and safe completion of every mission.
Most SR-71’s operational sorties started off with a refueling after takeoff.
“Many people believe we refueled after takeoff because the aircraft leaked fuel so profusely that we needed to fuel up quickly,” says Col. Richard H. Graham, a former Blackbird pilot, in his book SR-71 The Complete Illustrated History of THE BLACKBIRD The World’s Highest, Fastest Plane. “We had to refuel right after takeoff for only one reason, and it wasn’t because we leaked JP-7 fuel on the ground. Yes, the plane does leak fuel, but not enough to require refueling after takeoff.
“The JP-7 fuel reaches temperatures well over 300 degrees F. during Mach 3 cruise, making the fumes in each of the six fuel tanks very volatile and potentially explosive. The metal skin of the aircraft approaches 400 degrees F., adding to the volatility of the fuel inside the tanks. One of our aircraft limitations was a maximum speed of Mach 2.6 without an inert atmosphere inside the fuel tanks.
“The aircraft had three liquid nitrogen Dewar flasks containing 260 liters of liquid nitrogen, located in the nose wheel well. The only way to ensure 100 percent inert atmosphere in each fuel tank was to refuel the plane in flight completely full of JP-7, allowing ambient air in each fuel tank to vent overboard. Once full of fuel, gaseous nitrogen would now dominate each fuel tank’s empty space above as it burned off JP-7. The nitrogen gas pressurized each fuel tank to 1.5 psi above ambient pressure and inerts the space above the heated fuel to prevent autogenous ignition. This is why we refueled after takeoff. Then we could safely accelerate beyond Mach 2.6.”
Graham concludes:
“There was one other way of achieving tank inerting, called a “Yo-Yo,” but this was a maintenance nightmare. A few of our missions required the SR-71 to accelerate to Mach 3+ right after takeoff with a 65,000-pound fuel load. The Yo-Yo procedure had the crew chief completely refuel the plane to full tanks of 80,000 pounds of fuel. Then, with the nitrogen pressurization system working, they de-fueled 15,000 pounds of JP-7, ending up with a 65,000 pound fuel load and a plane that was capable of going immediately to Mach 3+.”
Photo by U.S. Air Force and Tony Landis Lockheed