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How is fuel stored in a tanker aircraft? What arrangements are made to make the aircraft liquid tight?

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    $\begingroup$ What leads you to believe that extra arrangements are needed? It just has more fuel tanks, which are like any other fuel tank, $\endgroup$ – Simon May 26 '15 at 16:22
  • $\begingroup$ I think the first answer in this question gives you a good image: aviation.stackexchange.com/questions/9001/… $\endgroup$ – Patric Hartmann May 26 '15 at 16:28
  • $\begingroup$ How is flying boom connected to these extra tanks? $\endgroup$ – anshabhi May 26 '15 at 16:39
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    $\begingroup$ That will be a different question and you can ask that in a new post. Basically it is hose and pipe and pumps $\endgroup$ – vasin1987 May 26 '15 at 17:25
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You might be surprised to learn that most refueling tankers hold a relatively small percentage of their total fuselage volume in fuel. The reason why is simple; a plane stuffed to the gills with fuel would be so grossly overloaded it wouldn't make it off the runway. Tankers, therefore, can double as medium transports with little modification, as they have a sizable upper deck which is more or less empty space when serving as a tanker, but which can ferry troops, light vehicles or other materiel from Stateside bases to various theaters (a dedicated heavy transport like the C-5 or C-17 would be used for transporting large units or for specialized troop transport like airbornes).

Here's the layout of the KC-135 Stratotanker:

enter image description here

To my knowledge, all of this fuel is available both to power the plane and to refuel other aircraft, however the plane would likely draw primarily from the wing tanks for flight, as this is the "standard" configuration for the 707 the KC-135 is built on. Transport of the fuel from these tanks to the refueling systems would be accomplished with an integrated pump and pipe system that could move fuel from anywhere to anywhere.

The bulk of the fuel load, as you can see, is contained in four "body tanks" totaling over 144,000 pounds of fuel. For comparison, the F-15E strike fighter can carry a maximum, with CFTs and 3 droptanks, of just 35,550 pounds.

These tanks are lined with plastic bladders, which contain the fuel (so the entire fuselage doesn't have to be leak-proof which is much more difficult and expensive to ensure) and also allows the bladder to collapse as the fuel inside it is depleted, reducing the volume of air in direct contact with the fuel, thus reducing the vapor hazard. AFAIK the wing tanks do not have these bladders, but they're much smaller spaces overall and more easily accessed.

Separating the fuel into multiple tanks has several advantages:

  • The tanker is still serviceable with one or more of the tanks unable to carry fuel (leak in the bladder, pump failure, etc).

  • Sloshing of the fuel in the tanks has less effect on the weight distribution of the aircraft. Imagine trying to take off with a full Olympic swimming pool in your cargo hold; any pitch up or down will cause several tons of weight to move "downslope", unbalancing the aircraft (probably fatally).

  • Fuel can be pumped between these tanks to fine-tune or "trim" the aircraft's weight distribution and handling characteristics, a process known as "tank trimming" which is more aerodynamically efficient than elevator trimming.

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    $\begingroup$ Just a nitpick but few realize that the 707 and the KC-135 were both descendants of the Boeing 367-80 (the so-called "dash 80". Siblings of the same parents but different in many ways. $\endgroup$ – Skip Miller May 26 '15 at 21:44
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    $\begingroup$ In Vietnam the Air Force flew HC-130J's. These were modified C-130 Hercules transports that were used in Search-and-Rescue operations. Like all C-130's they had 4 turbo-prop engines, but they also had two jet engines, one under each wing. In addition, they had extensive resources for doing search-and-rescue inside the airplane. They ALSO acted as a fuel tanker for SAR helo's and fixed-wing acft - a huge fuel tank in the cargo bay fed out to a refueling hose on each wing. That hose had a basket on the end which the receiver a/c engaged, locked onto, then took a drink. $\endgroup$ – JT1000 Aug 3 '15 at 7:35

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