“The fine art of pulling the throttle ever so slightly up and just into the minimum burner range was handed down from one generation of SR pilots to the next. The SR is the only airplane I know that required the use of afterburner to stay on the boom,” Brian Shul, former SR-71 Pilot.
The Lockheed SR-71 Blackbird would be a very short-ranged aircraft were it not for air refueling, limited to around 2,000 NM. Multiple air refuelings extended the range of the aircraft to the limits of crew endurance. Many missions have exceeded 12,000 NM. Forward basing of the SR-71 and tankers permitted faster response, shorter range, shorter duration missions, fewer air refuelings, and greater overall efficiency.
But at 100% thrust the SR-71’s J58 turbo-ramjets could not produce enough thrust to stay with the tanker once the fuel load became too heavy. To allow it to stay connected and receive all 80,000 lbs of fuel, the pilot had to light one afterburner, the asymmetric thrust of which made the plane fly slightly sideways.
As told by Brian Shul in his book Sled Driver, that was standard operating procedure. The J58 engine in fact did not appreciate subsonic flight.
“I was accustomed to being on the boom for just a few minutes to top off in fighters. In contrast, SR-71 refuelings took fifteen minutes or more which could seem like an eternity. This time was needed because the airplane took on an incredible amount of fuel. During a normal refueling we usually received over 11,000 gallons. This changed our gross weight by 70,000 pounds and caused a corresponding change in the center of gravity of our aircraft. At the slow 300 knot range in which we were flying to refuel, the feel of the jet became sluggish as the SR filled with fuel. At these gross weights and slower airspeeds, the SR-71 became thrust limited during the last few minutes of refueling.
“In military power, we would start to fall off the boom. A disconnect was highly undesirable since the jet was less responsive now and to reconnect was more difficult. It also meant wasting time on the refueling track and this could affect our overall mission timing. The solution was to light one afterburner with careful finesse. The fine art of pulling the throttle ever so slightly up and just into the minimum burner range was handed down from one generation of SR pilots to the next. The SR is the only airplane I know that required the use of afterburner to stay on the boom.
“Using one afterburner caused another problem: asymmetrical thrust. Some pilots used a little rudder to handle the yaw. Others left the rudders alone, flew sideways, and looked out the front quarter panel to see forward. The quarter panels were located on either side of the windshield. Only the left quarter panel was wired for defogging so we always lit the left burner to yaw right so we could use this feature if needed.
“The most exciting moments on the refueling track were normally reserved for those final few minutes in afterburner on the boom with a very heavy jet. Once I selected min AB and the TEB dumped in, there was a pause, then the airplane lunged sideways and started to charge up the boom. With the left burner stabilized in min AB, I controlled our fore and aft position with right throttle.
“With this method, the pilot controlled the airplane by leading the power inputs. It was like flying a freight train because the airplane’s inertia caused a lag between throttle input and aircraft response. It wasn’t uncommon at this point for the director lights to resemble a pinball game, flashing from end to end as the fore and aft movements of the jet caused continual changes in relative position. I had to ignore the director lights, grit my teeth, and call on every bit of my experience to get to the end of the refueling track with a full tank.”
Photo credit: U.S. Air Force and Tony Landis Lockheed