Figure 3-32.—Self-sealing fuel cell (standard construction).
Bladder-Type Fuel Cells
The retainer material is the next material used in fuel
cell construction. The purpose of the retainer is to
provide strength and support. It also increases the
efficiency of the mechanical action by returning the fuel
cell to its original shape when punctured. It is made of
cotton or nylon cord fabric impregnated with Buna N
rubber.
SELF-SEALING CELL (NONSTANDARD
CONSTRUCTION).—One variation from the standard
construction, self-sealing fuel cell previously discussed
is shown in figure 3-32. It has four primary layers–an
inner liner, a nylon fuel barrier, two sealant plies, and
three retainer plies.
The cords in the first retainer ply run lengthwise of
the cell. The cords in the second retainer run at a
45-degree angle to the first. The cords in the third
retainer run at a 90-degree angle to the second. The
outside is coated with Buns-Vinylite lacquer to protect
the cell from spilled fuel and weathering.
Baffles and internal bulkheads are used inside the
cell to help retain the shape of the cell and prevent
sloshing of the fuel. They are constructed of square
woven fabric impregnated with Buna N rubber.
Flapper valves are fitted to some baffles to control
the direction of fuel flow between compartments or
interconnecting cells. They are constructed of Micarta,
Bakelite, or aluminum.
These plies, baffles, internal bulkheads, and flapper
valves with the necessary fittings and combinations
make up a typical self-sealing fuel cell.
A nonself-sealing fuel cell is commonly called a
bladder cell. It is a fuel container that does not self-seal
holes or punctures. The advantage of using a bladder
fuel cell results from the saving in weight. Some of the
other advantages are the simplicity of repair techniques
and the reduced procurement costs over self-sealing fuel
cells.
Bladder-type cells are usually made of very thin
material to give minimum possible weight. They require
100-percent support from a smooth cavity. The cell is
made slightly larger than the cavity of the aircraft for
better weight and distribution throughout the aircraft’s
fuel cavity structure.
The thinner wall construction increases the fuel
capacity over the self-sealing cells, thus increasing the
range of the aircraft. Many of our aircraft that were
formerly equipped with self-sealing cells have been
changed to bladder-type cells.
There are two types of bladder fuel cells–rubber
type and nylon type.
RUBBER-TYPE BLADDER CELLS.—The
rubber-type bladder cells are made in the same manner
as self-sealing cells. They have a liner, nylon barrier,
and a retainer ply. The sealant layers are omitted. All
three plies are placed on the building form as one
material in the following order: liner, barrier, and
retainer. Figure 3-33 shows this type construction.
The inner liner may consist of Buns N rubber, Buna
N coated square-woven fabric (cotton or nylon), or Buna
N coated cord fabric. The purpose of the inner liner is
to contain the fuel and provide protection for the nylon
barrier.
3-46
Figure 3-33.—Bladder cell construction
