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All embodiments of the subject means prevent the passage or spread of flame
between compartments of the enclosure without otherwise substantially
restricting or preventing the circulation of the contents. As indicated,
the subject devices operate to arrest and/or quench flame and at the same
time attenuate and minimize the effects of an accompanying explosion by
distributing the isolated combustion forces thereof over a larger volume
than the volume of the container portion in which it was produced. The
invention contemplates use of layers, blocks, hollow members, and other
forms of the subject open-celled or porous material geometrically
configured to reduce their weight and to minimize volume loss, and it is
contemplated to position such layers or members at various suitable
locations in a chamber or compartment such as in a single compartment or
multi-compartment fuel tank. The geometry and other structural
characteristics including pore size of the open-called members are
important to the operation while the geometry and other structural
features of the containers or tanks in which they are installed are
relatively unimportant. Many possible embodiments of the present
open-celled members are possible and some few of these are disclosed in
this specification.
This invention relates in general to certain new and useful improvements in
flame arresting and explosion attenuating systems, and more particularly
to such systems that use open cellular members or devices of low weight
and volume displacement which permit relatively unrestricted circulation
of the contents and do not prevent normal use and operation of a fuel tank
or other container. The term "flame arresting" as used in this
specification is given a fairly broad meaning to include "flame
attenuation" as well as "flame quenching".
There are a number of available inerting or flame arresting systems
presently known and in use including some that are used in fuel systems
such as in fuel tanks and other structural enclosures for the storage of
highly inflammable fluids such as fuels or the like. For the most part,
the known inerting and extinguishing systems are designed to prevent
ignition of the flammable fluid or to eliminate flame propagation. These
include various inert dilutents or flame extinguishing or suppression
means such as means for introducing a non-flammable liquid or gas such as
nitrogen into the container, or introducing a substance such as a halogen
fire extinguishing material into the tank or enclosure under certain
conditions such as in response to the detection of a predetermined
pressure, radiation or excessively high temperature, and they include
other forms of manual and automatic means usually involving fairly
complicated devices having movable parts. Plastic or metal foams, felts,
screens, honeycomb and like devices introduced into and filling the tank
with these flame arrestor materials have been found to be moderately
effective in some applications in that they serve only to prevent the
spread of the flame but not as explosion attenuators. These same material
configurations have been used as flame barriers for apertures on vent
systems. However, all known systems either prevent or extinguish the flame
propagation, while not attenuating explosions or they have other
undesirable aspects in that they make the tank and/or the contents thereof
unusable and inoperative, and/or they impose large weight, displacement,
maintenance and reliability penalties, and this cannot be permitted in
certain cases such for example as in aircraft fuel tanks.
Some prior art constructions having also included tanks which are
subdivided into a plurality of cells certain of which are allocated for
containing fuel and others for containing flame inhibitor substances of
some kind. In the event of an explosion in such a structure, a partition
or other member that normally prevents communication between the different
types of cells will rupture to permit the flame inhibitor material to
enter fuel cells rendering the latter non-flammable or otherwise unusable.
While such systems are moderately effective for extinguishing flame and
preventing the spread thereof they add considerably to the weight and
complexity of the container and they are subject to leakage, accidental or
otherwise, as well as other failures and there is a high risk that they
may destroy the fuel system accidentally. They also substantially reduce
the fuel carrying capacity of a given space. For these and other reasons,
such systems have not enjoyed wide usage.
Many of the known systems that use inerting means have been designed for
use in aircraft and particularly military aircraft where there is a fairly
high risk of fuel tank fires. These systems are designed to protect
aircraft against accidental and other forms of fuel ignition including
protection against the resulting explosions. There is considerable
interest in improving the safety of fuel tanks including also fuel tanks
on commercial aircraft as well as fuel tanks used for other purposes such
as automobile fuel tanks, and other tanks used for storing highly
flammable substances. Aircraft fuel tanks present special problems,
however, because they are usually divided into a plurality of
communicating compartments or cells distributed throughout the plane
including the wings and some of the compartments are separated from each
other and by internal structural partitions with transference aperatures
and other communication means that permit intercommunication and fuel
circulation therebetween. Many military aircraft have single compartment
fuselage fuel tanks and multi-compartment or partitioned wing tanks while
most commercial aircraft have compartmentalized wing tanks only. The known
inerting systems, however, impose serious structural, operational, design,
weight, capacity and expense limitations on such fuel systems and they
also add considerably to the complexity of the tanks they seek to protect.
For these and other reasons they are unsatisfactory. Furthermore, the
known systems not only reduce fuel storage capacity but they may cause a
fuel tank to become inoperative at a critical time and they may prevent
the free flow circulation of fuel between the various compartments and
between the inlets and outlets of the tank. These conditions obviously
cannot be tolerated in certain applications such as in airborne situations
as well as many others.
It is therefore a principal object of the present invention to provide
means for making fuel tanks and other inflammable liquid storage means
safer.
Another object is to confine fires in fuel tanks and like strutures to
relatively small regions and to prevent their spread.
Another object is to compartmentalize the inside of a fuel storage
container with means capable of preventing the spread of flame but which
do not interfere with normal container operations including normal fuel
circulation.
Another object is to confine fires in fuel tanks and like structure to
relatively small regions and to prevent their spread while attenuating the
combustion overpressure eliminating structural damage.
It is another object to provide a flame arresting system for fuel tanks and
other structural enclosures which includes porous means which are wetted
by the fuel to form a flame arresting barrier between different portions
of the tanks.
It is another object to teach the construction and operation of a flame
arresting system using open-celled foam-type arresting materials which are
relatively lightweight and do not displace much fluid capacity, usually
less than about 2% of the capacity.
Another object is to provide a compressible open pore foam or foam-like
structure which can be installed in almost any size and shape opening or
chamber without requiring separate fastener means, and which will operate
to quench a flame that tries to pass through it and attenuate the
accompanying explosion.
Another object is to provide a porous flame barrier which when wetted also
acts as a heat sink.
It is a further object of the present invention to provide a flame
arresting system which is relatively simple to install and can be
installed in new as well as in existing fuel tanks and other structural
enclosures without requiring separate sealing and fastener means.
It is an additional object to provide a flame arresting system for fuel
tanks and the like which does not materially restrict the normal flow of
fluids contained therein.
Another object is to provide means to efficiently arrest the propagation of
flame in highly combustible environments and which means can be used to
compartmentalize single chamber container structures as well as being used
on or in conjunction with the partition means in multi-cell enclosures
with and without cell-to-cell communication.
It is another object to teach the use of flame arresting members or devices
in all or in some of the cells of a multi-cell enclosure such as a
multi-cell fuel tank to prevent the spread of flame.
Another object is to minimize the chances for structural damage to fuel
tanks as a result of explosions produced therein.
Another object is to confine the area of flame and prevent its spread in an
enclosed structure while permitting the forces of an explosion produced in
a portion only of the structure to be dissipated throughout the structure.
These and other objects and advantages of the present invention will become
apparent after considering the following detailed specification of several
practical embodiments of the subject system in conjunction with the
accompanying drawings, wherein:
FIG. 1 is a perspective view showing a multi-compartment fuel tank in which
the compartments are in free flow communication, said tank including means
to prevent the spread of flame from one compartment to another and to
attenuate the forces of an explosion produced therein;
FIG. 2 is a cross-sectional view taken along line 2--2 of FIG. 1;
FIG. 3 is a cross-sectional view similar to FIG. 2 but showing a modified
form of the fuel tank wherein the flame arrestor or flame quenching
material is positioned only adjacent to apertures in partitions between
adjacent tank compartments;
FIG. 4 is a fragmentary cross-sectional view taken along line 4--4 of FIG.
3;
FIG. 5 is a cross-sectional view similar to FIG. 2 showing another tank
construction wherein portions only of each of the tank compartments are
provided with flame arresting voided blocks;
FIG. 6 is a fragmentary cross-sectional view taken on line 6--6 of FIG. 5;
FIG. 7 is a cross-sectional view similar to FIG. 2 showing another modified
form of the subject flame arresting system;
FIG. 8 is a fragmentary cross-sectional view taken along line 8--8 of FIG.
7;
FIG. 9 is a perspective view partially broken away and in section showing
another compartmentalized tank structure wherein the compartments are
formed by strips of flame arresting material;
FIG. 10 is a side elevational view of an automobile fuel tank equipped with
flame arresting means constructed according to another embodiment of the
present invention;
FIG. 11 is a cross-sectional view showing the interior of the modified fuel
tank of FIG. 10 wherein the tank is compartmentalized using hollow porous
spheres;
FIG. 12 is a perspective view of another single compartment enclosure or
tank illustrating a method for introducing hollow spheres of flame
quenching material therein;
FIG. 13 is a fragmentary perspective view showing the structural details of
another fuel tank embodiment having flame arresting means therein;
FIG. 14 is a perspective view showing a foam wall honeycomb embodiment of
flame arresting structure for use in fuel tanks and the like; and,
FIGS. 15-18 are perspective views showing other possible forms of porous
flame arresting materials for use in fuel tanks and like structures.
Referring more in detail and by reference characters to the drawings which
illustrate some of the many possible practical embodiments of the present
invention, the number 20 designates a fuel tank or similar structural
enclosure of a type such as might be used in the wing of an aircraft or
the like. The tank 20 may be constructed as an individual self-contained
unit inserted into a recess or other area allocated for this purpose in a
host structure such as an aircraft wing, or the tank may be constructed as
an integral part of the host structure. In either case, the tank 20 may be
constructed as a single or as a multiple compartmented structure. If a
multi-compartment structure is to be used, then at least some of the
different compartments should be in flow communication with each other so
that the tank can be filled and emptied expeditiously and fuel can
circulate without difficulty and as desired.
FIGS. 1 and 2 show the multi-compartmented fuel tank 20 constructed as an
integral part of the wing structure of an aircraft. The tank comprises
spaced front and rear side walls 22 and 24 connected by transverse ribs
26, opposite end walls 27 and 28, and top and bottom walls 29 and 30,
respectively, which may be the upper and lower skins of the wing itself.
Whether the tank is formed as an integral unit unto itself or as part of
the host or wing structure it is divided structurally or compartmentalized
into a plurality of individual compartments of fuel cells. This can be
done structurally by means of the ribs 26 and/or by means of one or more
longitudinally extending partitions or "spars" 32 as required. The ribs 26
and spars 32 in the case of an airplane wing may be the regular structural
ribs and spars that form the wing.
Each of the compartments or cells communicates with the others through
various openings formed by the structural members through specially
constructed openings such as the openings 34 and 36 sometimes called
"lightning holes" provided to lighten the weight of the wing structure.
These openings 34 and 36 should be constructed and located to permit
substantially uninterrupted fluid flow communication and fuel transfer
between all of the various cells or compartments in the tank. The number
and size of the cells and of the openings therebetween will vary from tank
to tank depending on the intended application and the environment in which
the tank is used. In most cases, the spars and ribs are located to provide
the desired rigidity and strength and to otherwise enhance the structural
integrity, and their designs and shapes are governed by aerodynamic
considerations. The number of transfer openings 34 and 36 and their
relative positions are also determined by various considerations including
the type of fuel or other material which is to flow, the desired flow
rates to be maintained and to prevent trapping fuel in portions of the
tank. The structural members are usually also constructed of a metal
material such as steel, aluminum, magnesium, and alloys of these and other
metals, and they may be provided with protective linings or coatings to
minimize corrosion and for other reasons. Fuel tanks having these and
other similar structural characteristics are well known.
Fuel tanks of the type illustrated in FIGS. 1 and 2 are generally also
provided with one or several inlets, such as one or more fuel inlet ports
or ducts 37 for filling the tank, and with one or several outlets for fuel
delivery to the engines as illustrated by fuel line 38. Various control
means (not shown) may also be provided at suitable locations in or
adjacent to one or more of the cells to be operated by means controlled by
the pilot or by some form of automatic control means that control the flow
of fuel as well as the environment in the tank and for other purposes.
The subject flame arresting means can be designed to have many forms and
shapes so that they may be used in either single-cell or multi-cell tanks
and other structural enclosures for containing ignitable and flammable
liquids and/or gases. In all cases, the flame arresting means are either
associated with partitions which subdivide the structure into
communicating chambers or compartments or they serve themselves to divide
the tank into compartments which are isolated from each other to prevent
the propagation of flame from compartment to compartment but not to
otherwise prevent the free flow of fuel throughout. The subject flame
arresting means are porous structures made of materials such as plastics
that are relatively uneffected by the fuel but serve to prevent the
passage of flame therethrough. When a flame tries to pass through the
subject porous members it will in so doing be arrested and quenched, while
at the same time, the pressure forces produced by the flame or explosion
in one or more of the compartments are free to pass through the arrestor
material and to dissipate themselves throughout the entire internal
confines of the tank. The advantages of being able to prevent the spread
of combustion thus neutralizing or minimizing the effects of explosion
with a minimum of displacement, and without interrupting normal tank
operation, are at the heart of the present invention.
When used in multi-cell enclosures of tanks, such as the wing tank
illustrated in FIGS. 1 and 2, layers of the subject porous flame arresting
material are located at or attached to the partitions between the
compartments and over all of the openings 34 and 36 therein. The arrestor
materials and the devices made therefrom as already explained, may have a
wide variety of forms, shapes, sizes and thicknesses depending on how and
where they are to be installed. In the embodiment of FIG. 2 they are shown
as layers 40 and 42 of foam arrestor material located adjacent to the ribs
26 and the spar 32. The foam material used in the construction of the
layers 40 and 42 is porous and relatively lightweight, and the size or
diameter of the pores in the material is selected to produce the desired
quenching action. The pores are also constructed to permit full
communication and circulation of the contents of the tank throughout. The
desired quenching action produced by the subject layers refers to the
ability of the said members or layers to extinguish flames that come in
contact therewith and try to pass through. The action of the foam material
in quenching or extinguishing a flame is somewhat similar to the action
produced by a screen placed over an open flame such as the flame of a
Bunsen burner. In the Bunsen burner case, the flame striking the underside
of the screen will spread out and try to pass around the edges of the
screen but will not pass directly through it. The same is true of the
present device, except that with the present device the pores may be
larger than the screen openings as a screen is made up of a single layer
of material whereas the porous member simulates many layers, thus
providing a length or distance to the quenching action and they may also
be filled and blocked by being wetted by the fuel. The wetting of the
pores is caused by capillary action and has little effect on the quenching
action particularly at the higher pressures such as when an explosion
occurs in one of the compartments and blows outwardly through the pores.
The inability of a flame to pass through a screen or porous structure is
at the heart of the present invention. Certain foam or foam-like
materials, and certain pore sizes give the best results in each case
depending on many factors including the tank pressure and the type of
fuel, and the porous material should be selected to be able to withstand
the temperature and other environmental conditions encountered including
the heat produced during an explosion. In some cases, it may be sufficient
or even preferred to use perforated barriers or grids other than those
formed of foam including perforated metal structural members although this
has not been found necessary for most purposes and such members are
usually too expensive and too difficult to make and install as compared to
simple plastic foam members. Also, metal screens or grids may present
undesirable weight factors. Even so, metal screens or grids could be used
and are contemplated as being within the scope of the invention.
Referring again to FIG. 2, the layers of flame arrestor material 40 and 42
are disposed in surface-to-surface engagement with the ribs 26 and spars
32 between the adjacent tank compartments and in this way isolate the
compartments from each other as far as flame propagation is concerned.
This therefore provides maximum protection against the spread of flame in
the tanks.
In some cases it may also be desirable to apply porous layers to all or
more of the interior surfaces of the structural walls, including the top
and bottom walls 29 and 30 as well as to the front and rear walls 22 and
24 which may also be spars in a wing construction. The layers may be
retentively held against their respective walls by suitable clamps or
other mechanical or adhesive fasteners (not shown) or by a suitable
bonding agent such as an epoxy resin or the like. In most cases, where the
layers are to be anchored or attached, a bonding agent is preferred
because of the ease of application and the fact that bonding agents do not
add substantial additional weight and volume to the structure. The
selection of a bonding agent, however, must take into account its possible
effect or reaction with the fuel or other substances to be contained
within the tank. Epoxy bonding resins and similar bonding agents have been
found to be effective securing means for most plastic type arresting
materials since such agents are relatively chemically inert and do not
react with most petroleum fuels and similar products.
The structure and placement of the arresting material are important. The
material itself as explained is preferably an open-celled porous material
such as a reticulated polyurethane foam and essentially almost any plastic
foam or foam-like material which can stand up to the environment
conditions can be used. Examples of other substances that can be used for
the subject porous structures include Teflon, rubber derivatives,
cellulose compositions, Nylon compositions and other plastic or
plastic-like compositions, whether flexible or rigid, and the selection
will depend upon the particular characteristics desired. In some cases,
for code or specification compliance, the selected substance may be
required to be treated with flame retardants or flame inhibitors, such as
with the various known organophosphorous compounds for added protection.
Essentially any open-celled material which is capable of permitting
relatively unrestricted liquid and gas flow therethrough, and which has a
relatively high ignition temperature may be used. Regarding ignition
characteristics, the flame arrestor material should preferably have an
ignition temperature that is as high as possible. The expected time of
exposure to the flame should also be taken into account. Porous and foamed
metals such as porous and foamed steel, aluminum, nickel, copper and
alloys of these and other materials may also be used for the construction
of the flame arrestor member but are not usually preferred. It is also
contemplated as in the case of plastic members to coat a metal substrate
as well as the tank wall with a coating of a plastic or other similar
porous material such as with one of the cellulosic foam plastics in order
to provide the desired flame arresting protection.
It is important to recognize that the subject porous material can be
operated to produce the desired flame quenching and explosion attenuation
while in either a wet or a dry condition. This is true even though it is
recognized that in some cases there may be some, usually relatively small,
advantages in having the material wetted by the fuel so that a heat sink
effect will be produced. This is true regardless of whether the porous
material extends across a liquid-gaseous interface in the tank. However,
since a flame can only exist in a gaseous phase portion of the tank, the
porous member or members should be so constructed and located in the tank
that they subdivide the tank interior into distinct chamber portions as
already described. Furthermore, if it is desired to increase the wetting
characteristics of the porous member chemical introfiers may be
incorporated in the flame arresting material or added to the fuel.
The pore size of the open-celled material will vary with many factors
including the density of the material, and as a general rule a lower
density material usually has a smaller pore size and/or a larger pore
density in order to produce the same flame arresting properties. In any
case, however, the pore size of the arrestor material should be large
enough to permit relatively unrestricted liquid and gas flow or
circulation between compartments with no more than a slight pressure
differential ever appearing between adjacent compartments. Thus the
arrestor material should not interfere with normal movement of the fuel in
the tank except as it may minimize the amount of sloshing that can occur.
The pore density in a typical case may be as low as ten pores per lineal
inch and even lower, and it may be as high as forty or more pores per
lineal inch. For most fuels, a pore density in the range of from about
fifteen to about twenty-eight pores per lineal inch produces satisfactory
results. In a preferred embodiment using a reticulated polyurethane foam,
a pore density of about twenty-five pores per lineal inch provides very
satisfactory results.
The selected arrestor material may be deposited or otherwise attached and
it can be used in one or more layers over the entire wall surface or only
those portions where the adjacent compartments communicate. The thickness
of the layer or layers of arrestor material will depend on a number of
factors including the volume or capacity of the compartments, the surface
areas of the layer or layers which may be exposed to flame or explosion,
the shape of the space in which material is installed, the composition of
the explosive mixture, and the anticipated forces generated by an
explosion. The magnitude and force of an explosive wave which is generated
and its effect on the subject structure may also be a factor in
determining the structural characteristics including the most desirable
pore size and layer thickness. This in turn should take into account the
fact that the liquid to gas ratio in the tank will vary substantially as
the tank goes from a full to an empty condition. Usually, however, the
larger the volume of an enclosure the thicker will be the required layer
or layers of flame arrestor material. As can be expected, the pore size of
the selected arrestor material may also be an important factor in
determining the best layer thickness. As a general rule, arrestor
materials having relatively large pore sizes, and hence low pore
densities, must be made or applied in thicker layers than those with
smaller pore sizes. For example, in one case a polyurethane foam arrestor
material having a pore density of about ten pores per lineal inch and a
material density of 1.86 lbs/ft.sup.3, required a layer thickness of
approximately eight inches to satisfactorily arrest flame propagation. In
another case, using a polyurethane foam having a pore density of about
twenty pores per lineal inch with a foam density of 1.36 lbs/ft.sup.3, a
layer thickness of only about one inch was needed to provide the same
flame arresting properties. The pore size and pore density should, as far
as possible, be selected to permit as free a flow or circulation of fuel
as possible while at the same time it must be recognized that some slight
flow reduction may be produced but this is usually not objectionable.
It should be recognized that in liquid fuel containers such as in fuel
tanks, most of the fuel is usually in a liquid state and the space above
the liquid fuel is occupied by a gas, usually air, with some amount of the
liquid fuel evaporated therein. Obviously, it is only possible to sustain
combustion in the gaseous phase which means that the fuller the tank, the
less space is available to support combustion. A full tank therefore
theoretically has no space in it to support combustion. It is important,
however, to have the subject flame quencher action regardless of how full
the tank is and therefore the quencher material should preferably extend
from as near to the bottom of the tank to as near to the top as possible.
The portion of the quenching material that is submerged in the liquid
phase will therefore be completely wetted and the portion extending above
the liquid surface will be wetted by the capillary action of the member
and the liquid.
It is important to recognize that the forces and pressures associated with
an explosion in one compartment are able to pass through the subject
porous members blowing any flame that may be present through the pores and
quenching them in the process while at the same time causing the forces of
the explosion to be dissipated or attenuated throughout the entire
interior of the tank and not just in that portion or portions where the
explosion occurred. This is highly desirable since it is this fact that
minimizes the possibility for structural or other damage to the tank and
therefore also minimizes the possibility that the tank will become
inoperative. These actions, namely the flame quenching action, the action
of dissipating the forces of explosion over a large area, the limited
action of the heat sink produced by the wetting of the porous member, and
the free flow communication available at all times, combine to minimize
fire and structural damage and substantially reduce the possibility that
the tank will be completely knocked out of service or that the flame will
spread to other nearby parts.
In many cases, it may not be necessary to completely cover or enclose the
inner surface of a compartment to provide adequate protection and several
such constructions are disclosed herein. FIGS. 3 and 4 illustrate another
construction wherein the flame arresting system is formed by a plurality
of porous flame arresting plugs 50 inserted in or adjacent to transfer
apertures 52 formed in the partitions 54 between adjacent compartments 56.
The plugs 50 are shown for illustrative purposes as being round plugs and
are formed to be somewhat thicker than the partitions 54 on which they are
installed. The plugs 50 may be made of relatively resilient material for
ease and convenience of installation, and they may have an outside
diameter that is greater than the diameter of the transfer apertures 52 so
that they must be squeezed or compressed to be installed. When installed
in this way each member entirely fills and closes its aperture and the
peripheral or flange portions 58 thereof engage opposite surfaces of the
partitions to hold them in place. Plugs similar to the plugs 50 can also
be secured in place by other types of means including clamp means,
adhesives, fastener devices and so forth.
The plugs 50 operate in substantially the same way as the layers described
above to confine and quench flame and to distribute the forces of an
explosion throughout all communicating cells of the tank. The plugs 50
preferably are located so that they will be at least partially submerged
in the liquid phase of the fuel and will become sufficiently surface
wetted to obtain the benefits of acting as heat sinks. The plugs 50, as
with the other forms of the device, are constructed to permit relatively
unrestricted fluid flow therethrough and to prevent excessive pressure
differentials from existing thereacross. They should also be installed so
that they cannot be blown out of their installed positions by the forces
of explosion.
The present invention includes other forms of the subject flame arresting
devices for locating in fuel tanks and some examples of these will be
described including some for use in single compartment tanks and some for
use in multiple compartment tanks. These may be constructed in a wide
variety of forms, shapes and sizes depending on the type and structure of
the tank, the type of fluid or fuel to be placed in the tank, the
dimensions of the tank and other considerations. Some tank embodimnts may
also have a plurality of the present elements in each compartment and some
only one. Some typical examples of these possibilities will be described.
The shape and geometry of the particular structural enclosure or tank in
which the subject devices are used are relatively unimportant to the
invention so long as the devices can be properly installed and located.
The geometric construction and shape of the devices themselves, however,
as already stated may be of considerable importance to their operation in
a particular application. The important thing is that they and/or the
partitions or walls with which they are used, divide the inside of the
enclosure into a plurality of communicating compartments each separated
from the adjacent compartments at least in part by the subject porous
flame arresting devices. The subject devices must be constructed with
sufficient surface area and pore size to permit rapid flame quenching and
yet permit relatively unrestricted flow communication. As already stated,
the subject devices may be secured to one or more of the partitions or
walls and they may be held in place by various means such as by clamps,
adhesives, or other forms of fasteners, they can be suspended or supported
by guy wires or like members, and they can be held in place simply by
being compressed between two or more surfaces. Some forms of the present
devices can also be made as hollow members or members having portions
removed to define chambers or cavities in them. These may be referred to
as voided embodiments and have the advantages of minimizing the amount of
fuel they displace. The gross-voided configuration, using hollow forms
also weigh less which is advantageous in most cases.
The size and positions of the subject flame arresting devices as mentioned
above, also enable them to function effectively as anti-slosh devices to
reduce or minimize undesired and sudden movements of the fuel. This can be
especially desirable in aircraft where sudden fuel movements can cause
unstable dangerous flying conditions especially during changes in the
altitude of the aircraft and under turbulent and other flight conditions.
For these and other reasons, certain forms of the present devices may be
preferred over others.
The multi-cell wing fuel tank embodiment 60 illustrated in FIGS. 5 and 6 is
very similar in tank structure to the tank 20 described above. For
example, the tank 60 includes spaced front and rear spars or walls 62 and
64, opposite end walls 66 and 68, the wall 66 being adjacent to the
fuselage of the aircraft, a plurality of spaced ribs 70 and 72, and a
central longitudinally extending spar 74. The ribs and spars divide the
tank 60 into a plurality of compartments 76 which extend between the top
and bottom walls or skins 78 and 80 of the wing. The ribs 70 and 72 and
the spar 74 each have a plurality of openings such as openings 82 and 84
which provide communication between the adjacent compartments. Flame
arresting devices 86, of which one is in each of the six compartments, are
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