Born in 1952, my life was very much affected by the years immediately following WWII. This was a time of optimism, a tremendous boom in aerospace, and dreams of a push-button future. My Dad’s B-24 bomber was pretty amazing technology that helped win the War. But post-war, the B-24s were scrap and there were now screaming jet engines, electronic computers getting smaller all the time, and advanced aircraft that could fly to the edge of space itself — the stratosphere.
One of these aircraft was the KC-135 Stratotanker whose operational ceiling was 50,000 feet. Above that altitude, a pilot must wear a pressure suit, for instance, the SR-71. The first KC-135A rolled off the assembly line in 1956. They remain key assets today. I flew them from 1978 to 1982.
The KC-135 aircraft is a Boeing product and looks a great deal like the Boeing 707, which was its contemporary. Instead of people, it hauled cargo and fuel. So the KC is “C” for cargo and “K” for tanker.
The photo at the top of this blog (Randy B. Garrett, used with permission) is a KC-135Q boom refueling an SR-71 out of RAF Mildenhall.
I did fly the tanker at 50,000 feet once. The sky gets dark. The view is fantastic. And fuel mileage is miserly. But your engines are prone to flame out. And if you have any issue with your cabin pressure, you are dead in seconds. Not recommended. A better altitude for most missions is around 35,000 feet to get from one place to another, about 10,000 feet lower, 25,000 feet, for in-flight refueling operations.
The last two illustrations are from the pilot’s manual.
The fuel was hauled in the tanker aircraft in 10 tanks. These tanks are located in the wings and in the fuselage, or body of the aircraft. (See aircraft diagram above) So the tanks had names like center wing tank or forward body tank. All but one of the body tanks was below the cargo deck. This may seem very evident to some, but the KC-97 tanker (precursor to the KC-135) had a fuel tank that ran the length of the fuselage suspended above the cargo area. Baggage went below decks like in an airliner. KC-97s started being phased out in 1956 with the first KC-135s off the production line. They were completely phased out around the time I started flying 135’s with the last ones leaving the Salt Lake Air Guard in 1978. KC-97s were propeller aircraft with a couple of add-on jet engines to be able to haul enough fuel to make the in-flight refueling worthwhile. The KC-97 was 82,500 pounds dry and 175,000 pounds fully loaded with fuel. KC-135s, being a 4 engine jet aircraft, had much better performance. The KC-135 weight without fuel was about 110,000 pounds. With a typical fuel load, it was around 300,000 pounds.
There was a special panel in the cockpit just to keep an eye on the 10 fuel tanks and make sure the aircraft center of gravity stayed in a region where the aircraft remained flyable. Too much weight in the forward or aft of the aircraft and controlled flight was no longer possible. Some tanks had pumps and others had gravity feed. The panel also controlled the off-loading of fuel to the receiver aircraft; allowed for dumping of fuel in an emergency; and, in very odd circumstances, even reverse air refueling to suck fuel from the receiver aircraft to the tanker. With 2/3 of your total weight in fuel that you could off-load in minutes, it beyond important that the fuel tanks were well managed.
In my first assignment, I was specially trained to fly the KC-135Q. The Q-model had special modifications to allow it to fulfill the mission of inflight refueling the SR-71.
To understand the Q modifications, you need to know that the SR-71 was the highest flying, fastest manned jet in existence. It’s job was to acquire timely intelligence and do it with such speed that the target country could not shoot it down. Although somewhat stealthy, it was not designed to be completely invisible to radar. Stealth technology did not exist yet. So the SR-71 was designed to out-race any threat. It would fly above 50,000 feet and above Mach 3.
This speed meant that it could not burn standard jet fuel. The fuel would ignite under the heat of friction at those speeds. In fact, the modified fuel, designated JP-7, would not ignite except under the most extreme conditions. A chemical called TEB was used to ensure ignition of the SR-71 jet engines. So unlike the KC-135A, the KC-135Q had to keep this fuel separate from its standard fuel. In the A-model, the aircraft is fueled on the ground from the right landing gear wheel well. The Q-model had a refueling port in each wheel well, one for JP-4 and one for JP-7.
Clicking on THIS LINK will automatically download my latest set of PowerPoint Charts on this subject. (40 Mbytes, so make sure you have a fast connection.) I have given this presentation many times and all across the USA. It is a real crowd-pleaser. Feel free to reuse these charts, but pay attention to the copyright notes. Most of this is public usage, but there are some used with specific permission.