The SR-71 needed to be refueled approximately every hour. Refueling was tricky, but Blackbird pilots were always up to the challenge
The SR-71 Blackbird would have been a very short-range aircraft without air refueling, with only about 2,000 nautical miles of range. Repeated refuelings pushed its range to the edge of crew endurance, and many missions covered more than 12,000 nautical miles. Forward basing the SR-71 and KC-135Q tankers improved response time, reduced flight distance and mission length, cut the number of refuelings, and made operations more efficient.
According to 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, the KC-135Q crews and aircraft were unlike the rest of the Air Force in several important ways. They were the only crews qualified in the Blackbird’s radio-silent rendezvous procedures, and their boom operators were the only ones trained to refuel the SR-71. The Q-model tankers also had special fuel-transfer plumbing that allowed them to move JP-4 and JP-7 between tanks, and their engines could burn either fuel. If the SR-71 landed where JP-7 was unavailable, the tankers could bring it in and refuel the aircraft on the ground using transfer hoses. Another major benefit was that Q-model tanker crews were not kept on the same 24-hour alert schedule as the other SAC tanker crews.
Any story of the SR-71 is incomplete without recognizing how essential the KC-135Q tankers and their crews were to the safe and successful completion of every mission.
The SR-71 had to be refueled about once an hour, and although the process was demanding, Blackbird pilots handled it with confidence. In most cases, refueling was the first task after takeoff. On some missions from Kadena Air Force Base in Okinawa, however, the aircraft could depart with enough fuel to complete the entire flight.
Graham recalls,
“No refueling necessary; it was 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+.”
As Aloysius G. Casey and Patrick A. Casey explain in Velocity: Speed with Direction: The Professional Career of Gen. Jerome F. O’Malley, refueling posed several challenges. Visibility was limited by the triangular forward window, and the pressure-suit helmet created unwanted reflections. Because the receptacle was aft of the cockpit, the SR-71 had to fly beneath the tanker. A normal refueling took on about 70,000 pounds, or 11,000 gallons, of JP-7 fuel.
Refueling usually took place at around 25,000 feet. As the aircraft got heavier and had to slow to match the tanker, it became thrust-limited. Drag increased as it approached stall speed, and no extra thrust was available without afterburner. At that point, the pilot had to advance one throttle slightly into the afterburner range to hold position.
Using a single afterburner meant the pilot had to correct the imbalance with the rudder or accept some sideways drift. Over time, crews developed the left afterburner technique, which caused the aircraft to yaw slightly to the right. That kept defogged airflow over only the left quarter panel, providing that advantage when needed. Refueling was a demanding task for the pilot and had to be done two to four times on each mission.
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Photo by U.S. Air Force
