The KC-135Q tanker
It’s impossible to overemphasise the essential role played by the KC-135Q tanker crews, without whom successful prosecution of the SR-71 Blackbird mission would have been impossible. As told by Paul F Crickmore in his book Lockheed Blackbird: Beyond the Secret Missions (Revised Edition), it became apparent to Strategic Air Command (SAC) that the tanker force dedicated to supporting SR-71 operations would need to be expanded beyond the original 21 Q-model aircraft and in 1967 the decision was made to modify an additional 35 aircraft. Some 20 KC-135As from the 70th AREFS, 43rd BW at Little Rock AFB, Arkansas, and 15 from the 306th AREFS, 306th BW at McCoy AFB, Florida were therefore converted.
As told by 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, KC-135Q crews and their aircraft were unique from the rest of the Air Force in several ways. Their aircrews in fact were the only one certified in Blackbird’s specific radio-silent rendezvous procedures, and their boom operators were the only ones qualified to refuel the SR-71.
SR-71 Blackbird air refueling
The Q-model tankers had special plumbing between their fuel tanks, allowing them to transfer JP-4 and JP-7 fuel between various tanks. Their engine could burn transfer JP-4 or JP-7 fuel. If the SR-71 landed somewhere JP-7 fuel was not available, the Q-model tankers flew in with the fuel and, through the use of transfer hoses on the ground, were able to refuel the SR-71. One of the best advantages of flying the Q-model tankers is that their crews did not have to be on twenty-four-hour alert status like the rest of the SAC’s tankers’ crew members.
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 SR-71, needed to be refueled approximately every hour. Refueling was tricky, but SR-71 pilots were always up to the challenge.
Usually, refueling was the first thing that they did after takeoff. Under some circumstances, while flying from Kadena Air Force Base in Okinawa, they would take off with enough fuel for the entire mission.
“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+.”
SR-71 Blackbird air refueling special problems
As explained by Aloysius G. Casey and Patrick A. Casey in their book Velocity Speed with Direction The Professional Career of Gen Jerome F. O’Malley, refueling presented special problems: visibility was poor due to the triangular forward window, and the helmet associated with the pressure suit caused undesired reflections. The receptacle (which received the fuel) was aft of the cockpit; therefore, the SR-71 had to fly underneath the tanker. Normally, one would take on about 70,000 pounds or 11,000 gallons of JP7 fuel.
Typically, refueling took place at about 25,000 feet. As the weight increased and the air speed had to be held down to accommodate the slower tanker, the aircraft became thrust-limited; that is, drag increased as it approached the stall speed for this unique aircraft (there was no additional thrust available without afterburner). At that point, the pilot had to move one throttle slightly into the afterburner range to hold position.
The left afterburner technique
Using one afterburner required the pilot to counter the asymmetry with rudder or just tolerate some sideways flight. Interestingly, the pilots developed the left afterburner technique so the aircraft would yaw slightly to the right. This way, only the left quarter panel had defogged air, and one could get that benefit if needed. Refueling was an intense effort for the pilot and was required two to four times for each mission.
Be sure to check out Linda Sheffield Miller (Col Richard (Butch) Sheffield’s daughter, Col. Sheffield was an SR-71 Reconnaissance Systems Officer) Twitter X Page Habubrats SR-71 and Facebook Page Born into the Wilde Blue Yonder for awesome Blackbird’s photos and stories.
Photo credit: U.S. Air Force