Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PROPE~LANT GA8-GENERATION 8Y8TEM FOR CANI8TER ~JECTION
BACKGROUND
Field: This invention relates generally to
ejectable projectiles and propellants for ejecting those
projectiles from casings within which they are disposed.
Specifically, this invention is directed to solid propellant
systems for generating gases which ejeat projectiles from
canisters or casings at a controlled velocity.
State of the Art: Projectiles, such as rockets,
missiles, and the like, are well-known in the aerospace and
military industries. Propellants which are associated with
such projectiles are also well-known. Some projectiles,
such as rockets or missiles, typically comprise a warhead
and an internal motor for urging the projectile forward to
its target. Internal motors for driving the projectile may
be of a solid propellant type, a liquid propellant type, or
some other type known to those skilled in the art. Fre-
quently, rockets, missiles, and similar projectiles are dis-
posed within a closed-end casing or canister prior to fir-
ing. When fired, projectiles of this type must first be
ejected from the canister. Projectiles which have an inter-
nal motor, i.e. rockets, must first be ejected from the can-
ister before the rocket motor is ignited to prevent damage
to the canister. Projectiles which do not have internal
motors, i.e. bomblets, submunitions, flares, etc., must also
be ejected from the canister for glide or free fall to a
chosen target.
Solid propellant grains generally take many forms.
For example, some propellants are poured into the rocket
casing to fill a substantial percentage of it. Other pro-
pellant grains take the form of a carpet roll which is
placed in the rocket casing end-to-end. Examples of such
propellants are disclosed in U.S. Patent No. 3,763,787 to
Schultz, issued October 9, 1973, and U.S. Patent No.
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3,737,348 to Schultz, issued June 5, 1973, both of which
disclose a double base propellant applied to both sides of a
reinforcing material and rolled into a carpet-type roll.
The reinforcing material provides a space between the pro-
s pellant surfaces sufficient to provide a very large area of
combustion. The roll is placed within a rocket motor casing
so that the roll is in a cross-sectional orientation to the
casing. The carpet roll is bonded to the inner casing of
the rocket motor and is attached by adhesive means to a head
plate.
U.S. Patent No. 4,792,423 to Craig, et al., issued
December 20, 1988, discloses the molding together of binder,
fuel, oxidizer, and additives to form a propellant which may
then be formed into any desired shape, including filament
winding, helical roll, and carpet roll. Craig is particu-
larly directed to molding of propellant components to
achieve variable burn rates and suggests that a particular
shape may help achieve a variable burn.
These and other prior art propellant grain
configurations are typically designed to provide a geo-
metrically increasing surface area of propellant for burn-
ing. That is, as the exposed surface of the propellant
burns, it exposes an ever increasing surface area for burn-
ing, and the resulting generation of gas from the burning
propellant increases geometrically.
Consequently, there remains a need for a
propellant gas-generating system for use with ejectable pro-
jectiles which provides controlled burning of the propellant
at a rate related to the displacement of the projectile.
There i8 also a need for a propellant system which provides
controlled burning as a function of the acceleration of the
projectile.
SUMMARY OF THE INVENTION
According to the present invention, a propellant
system is provided for use in a class of projectiles which
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are disposed within an outer casing or canister and which
are ejectable from the canister. The propellant system of
the invention provides a configured propellant grain, the
burn surface of which is dependent upon the acceleration
rate of the projectile with which it is associated. That
is, the gas generated by the burning propellant is a func-
tion of the rate at which the ejectable projectile is dis-
placed from the canister. Although the invention is applic-
able to ejectable projectiles generally, this disclosure is
directed to rockets by way of example.
The propellant system of the present invention is
configured to provide a surface area which is mechanically
exposed for combustion by displacement of the exiting pro-
jectile. That is, the surface of the propellant is burned
at a rate which is directly related to the rocket displace-
ment. The propellant system of the present invention pro-
vides a rapid-burning propellant grain which generates
enough gas pressure within the canister to eject the rocket
quickly from the canister yet without over pressurizing the
canister.
Where a canister is adapted for use with different
projectiles of differing mass, the ejection acceleration as
a function of pressure will generally differ. The gas gen-
eration system of this invention compensates for such dif-
ferences, controlling the canister pressure regardless ofthe particular projectile which is ejected.
The propellant gas-generation system of the
invention generally comprises a propellant adhered to a non-
burning substrate. The propellant and substrate take the
general form of a strip having a specific width and length.
The strip is then adhesively attached to itself in a manner
which conceals part of the propellant and which will allow
the strip to peel progressively and continuously from itself
to expose concealed propellant for burning. Thus, two dif-
ferent adhesive joints, one stronger than the other, are
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formed. The substrate is a flexible material such as rubber
which is not combustible in this application.
The propellant is joined to the substrate using a
tenacious adhesive with a relatively high peel strength.
Peel strength is defined as the pounds per linear inch (pli)
required to separate one surface from another at a particu-
lar angle.
The strip of combined propellant and substrate is
then attached to itself to form a relatively weak joint.
The adhesive used to join the strip of combined propellant
and substrate to itself has a lower peel strength than the
adhesive binding the propellant to the substrate. Conse-
quently, the weaker peel strength adhesive will allow peel-
ing of the strip from itself while the stronger peel
strength will prevent peeling of the propellant from the
substrate during detachment of the strip from itself.
The gas-generation system of the present invention
is directed in one embodiment to the ejection of rockets
which are slidably disposed within an outer casing or canis-
ter. One end of the propellant/substrate strip is connectedto the rocket, e.g. to the rear end of the rocket. The
other end of the propellant/substrate strip is connected in
some manner to the closed end of the canister. One end of
the propellant/substrate strip is provided to expose a por-
tion of the propellant. Means for igniting the exposed pro-
pellant is provided within the canister, such as a pyrogen
or pyrotechnic igniter which directs hot gases on the ex-
posed surface.
Following ignition of the exposed propellant,
exhaust given off from the burning propellant causes an in-
crease in pressure within the closed end of canister and
urges the rocket to move outwardly from the canister. As
the rocket move~ outwardly, it pulls the connected end of
the propellant/substrate strip outwardly thereby causing the
strip to peel from itself to continuously and progressively
expose more propellant for burning. Thus, as more pressure
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builds, the rocket moves outwardly causing more propellant
to burn and causing more pressure to build until the rocket
has been ejected from the canister. The rocket is smoothly
ejected without a buildup of excessive pressure in the cas-
ing.
The gas-producing units are easily constructed and
provide an inexpenseive means for ejecting projectiles from
a canister. The pressure curve is easily tailored for each
application by varying the propellant strip dimensions, mass
and type of propellant, and other factors. A high batch-to-
batch uniformity is readily maintained.
The propellant system of the present invention is
also directed to use in ejecting non-motorized projectiles
such as bombsy bomblets, submunitions, flares, chaff and the
like, as well as such munitions as torpedoes from seagoing
vessels.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings, which illustrate what is
currently regarded as the best mode for carrying out the
invention,
FIG. 1 is a perspective view of the outer surface
of a partially detached propellant gas-generation system of
the invention;
FIG. 2 is a perspective view of one embodiment of
the invention ready for mounting within a canister of the
type which houses a rocket;
FIG. 3 is a partially fragmentary perspective view
of the propellant system installed within a canister;
FIG. 4 is a perspective view of the inner surface
of a partially detached propellant gas-generation system;
FIG. 5 is a pe~e~ive view of another embodiment
of the outer surface of a partially detached propellant gas-
generation system of the invention;
-FIG. 6 is a perspective view of a further
embodiment of the invention;
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FIG. 7 is a perspective view of another embodiment
of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The propellant gas-generation system, designated
generally 10 in FIG. 1, includes a substrate 12 having op-
posing surfaces and a propellant 14 adhered to at least one
opposing surface of the Rubstrate 12. The substrate 12 and
propellant 14 are generally formed into an elongated strip,
hereinafter referred to as the propellant strip 16. The
propellant 14 is depicted as being disposed on the outer
facing surface 18 of the substrate 12, but alternatively, it
may be attached to the inside surface, designated 19.
Attachment to the outside surface 18 is generally preferred
because it provides more initially exposed propellant sur-
face for generating gas pressure within the canister.
The substrate 12 of the propellant strip 16 is
preferably a resilient material such as rubber but may be
constructed of any suitable material which will adhere to
the propellant 14 and which will allow the propellant strip
16 to be formed into any desired shape.
Many different propellants are suitable for use in
the propellant gas-generation system of the present inven-
tion. Suitable propellants are those which have a suffici-
ently high strain capacity to allow the propellant strip 16
to be formed into a desired shape, such as a roll. Strain
capacity defines the amount of deformation which the pro-
pellant may undergo when subjected to forces, such as thoseexperienced when in a rolled form. The maximum strain
capacity of a propellant in a rolled form is dependent upon
the thickness of the propellant when applied to the sub-
strate and the dimensions of the propellant strip when at-
tached to itself. That is, when the propellant strip isrolled in carpet-roll fashion, for example, the maximum
strain capacity (EM) is defined by the equation
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~Do 71DI
S EM
1IDi
where Do is the diameter of the rolled propellant strip
measured from its outer circumference, and D~ is the diam-
eter of the rolled propellant strip measured from its inner
circumference at the center of the roll. Thus, the strain
capacity of a propellant will be les6 when the propellant is
applied to the substrate in a thin layer. Conversely, when
the propellant is applied more thickly to the substrate, the
candidate propellant must have a higher strain capacity, or
the propellant strip must be rolled allowing for a larger
diameter.
A particularly suitable propellant is one which
contains a carboxy-terminated polybutadiene (CTPB) binder
with trifunctional epoxy liquid. The solids of such a pro-
pellant may consist of seventy-seven percent (77%) ammonium
perchlorate (AP), five percent (5%) aluminum, and two per-
cent (2%) iron oxide. Propellants such as plastisols and
double base propellants are also suitable for use in the
invention.
The propellant 14 is adhered to the substrate 12
using a suitable adhesive. Suitable adhesives for attaching
the propellant 14 to the substrate 12 are those which have a
relatively strong peel strength and form flexible joints
immune to cracking. Peel strength is defined as the amount
of force which must be employed to separate two adhered sur-
faces at a particular angle. Peel strength is measured inpounds per linear inch (pli).
A particularly suitable adhesive for tenaciously
attaching the propellant to the substrate is TI-H-300, an
adhesive manufactured by Thiokol Corporation (Elkton, MD),
the ingredients of which include carboxy-terminated poly-
butadiene (CTPB), trifunctional epoxy liquid, chromium
octoate, and carbon black. Any flexible adhesive which ef-
fects a bond between the propellant and the substrate and
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which has a relatively stronger peel strength as compared to
the adhesive used to join the propellant strip together
(described below) is suitable for use in the invention.
The propellant strip 16 is attached to itself in a
manner which conceals propellant within the configured strip
and which allows uniform and continuously progressive expo-
sure of the concealed propellant 14 as the propellant strip
is peeled from itself. For example, as illustrated by FIG.
1, the propellant strip 16 may be rolled in carpet-roll
fashion. When the propellant strip is unrolled (i.e., de-
tached from itself), the outer surface 18 of the substrate
12 is continuously and progressively exposed, generally in
the area designated 20, thereby exposing more and more of
the propellant 14 as the unrolling continues.
lS Preferably, the opposing edges of the propellant
strip 16 are coated with a sealant for deterring combustion
from those edges. Thus, when the strip 16 is configured in
a carpet-roll fashion, the combustion proceeds primarily
from one direction only. The resulting gas production curve
is more uniform from batch to batch.
The propellant 14 may preferably, in some cases,
be applied on a grain of varying width and/or thickness to
modify the gas-generation rate. Thus, as depicted in FIG.
5, the propellant layer width 60 is decreased at point 62 to
width 64 for reducing the gas-generation rate when the pro-
~ectile is displaced distance 66. The propellant dimension
may be varied along the strip to achieve any desired pres-
sure curve. This concept is more clearly understood by the
discussion which follows.
one end 22 of the propellant strip 16 must be
connected to the end of the rocket, and the other end 24 of
the propellant strip 16 must be connected to the closed end
of the outer casing or canister within which the rocket is
disposed. One method of connecting the propellant strip 16
to the canister is to wind one end 24 of the propellant
strip 16 about a cylinder or mandrel 26. The mandrel 26 is
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then secured in some manner to the inside surface of the
canister. As illustrated by FIG. 2, one means of securing
the mandrel 26 to the inside surface of the outer casing is
to attach the mandrel securely to a ring 28 using two rods
30 and 32 interconnected between the mandrel 26 and the ring
28. The ring is secured to the canister by bolt, screw, or
other means.
FIG. 3 more fully illustrates the placement of the
propellant strip 16 in the canister 36 within which the
rocket 38 is disposed. The free end 22 of the propellant
strip 16 is attached to the bottom 40 of the rocket 38 so
that when the rocket is ejected from the canister 36, it
unrolls the propellant strip. The attachment may be by a
strong adhe~ive or other mechanical means. The ring 28 is
secured to the inside face of the bottom 42, i.e. closed
end, of the canister 34. The propellant strip 16 may be
attached in any manner to the canister 34 as long as the
propellant strip is able to peel away from itself or, as
suggested by FIGS. 1-3, is able to be unrolled.
The propellant strip may be attached to itself in
any configuration which provides the desired progressive
exposure of the concealed propellant for burning as it is
unrolled by the ejecting rocket. The desired configuration
must also be one which provides a first free end of the pro-
pellant strip for attachment to the rocket and a second free
end of the propellant strip for attachment to the canister.
Such configurations include, for example, accordion folding
or helical winding into a corkscrew shape. Rolling, fold-
ing, or winding configurations as previously described pro-
vide a type of detachment of the strip which continuously
exposes propellant for burning as the rocket is ejected from
the canister.
The propellant strip is attached to itself by use
of a weak adhesive (as compared to the relatively tenacious
adhesive used to adhere the propellant to the substrate).
As illustrated by FIG. 4, the weak adhesive 44 is applied to
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the inner facing surface 46 of the substrate 12. Any flex-
ible adhesive may be used for joining the propellant strip
together which is capable of maintaining the attachment of
the propellant strip to itself (i.e., maintained in a roll)
but which displays a sufficiently low peel strength to allow
the attached propellant strip to peel away from itself
(i.e., to unroll).
A particularly suitable adhesive for attaching the
propellant strip to itself is TI-H-300 adhesive (described
above) in admixture with Chemlok 234, an adhesive manufac-
tured by Lord Corporation (Erie, PA). The combination of
TI-H-300 adhesive with Chemlok produces an adhesive having
an approximate four-fold decrease in peel strength as com-
pared to TI-H-300 adhesive without Chemlok. The difference
in peel strengths between the adhesive used to adhere the
propellant to the substrate and the adhesive used to join
the propellant strip together allows the propellant strip to
peel away from itself without causing the propellant to dis-
lodge from the substrate. Both the weak and the strong ad-
hesives should be resilient enough to avoid cracking when
the propellant strip i8 attached to itself.
The TI-H-300 adhesive is also an excellent sealant
for coating the lateral edges of the propellant strip 16 to
deter combustion from those edges inwardly.
Means 48 for igniting the propellant is associated
with the propellant gas-generation system, as suggested by
FIG. 1. The means for igniting the propellant may be any
method or device which will initiate burning of the propel-
lant 50 exposed near end 22 of the propellant strip 16.
Types of igniters are well-known by those skilled in the art
and are typically chosen on the basis of design, resistance
to environmental effects, cost, and other factors.
The exposed propellant ignites and burns down the
length of the propellant strip until all of the exposed pro-
pellant has burned. Enough pressure is developed from the
burning of the initially eYpo~e~ propellant to urge the
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fired and directed toward a target. The mechanically
controlled increasing surface area of exposed propellant
provides smoothly increasing pressure within the casing as
the propellant burns.
FIG. 6 depicts an exemplary configuration which is
folded.
In FIG. 6, strip 70 includes a substrate 72 having
ends 74 and 76 for attachment to the canister and to the
ejectible, respectively. A layer of propellant 78 overlies
the substrate 72 and the combination folded into accordion
pleats 80 to conceal a large portion of the propellant 78.
As ends 74 and 76 are pulled apart, the pleats unfold to
permit full combustion of the propellant.
In FIG. 7, strip 84 is wound similarly to that
shown in FIG. 1, but the connections to the canister and the
ejectible are on opposite sides 86 and 88 of the ends 90 and
92 of strip 84. Thus, as the ends 90 and 92 are pulled
apart, the roll detaches helically, like the common fly
paper roll, to expose fresh propellant surface 94 for
combustion.
It should be understood that it may be desirable
to expose the propellant at a greater velocity than the
exiting velocity of the rocket. Thus, for example, the free
end 22 of the strip 16 may be connected to the rocket
through a series of pulleys which increases the velocity of
the strip relative to the rocket. A higher velocity may be
required to prevent the propellant from extinguishing with
slowly ejected projectiles. The required velocity of
unrolling or unfolding is a function of the propellant burn
rate and propellant thickness. Lower unrolling/unfolding
velocities may be used with propellants of greater thickness
and/or lower burn rate. Propellants having a high burn rate
and applied in a thin layer, e.g. 0.1 cm, may re~uire
unrolling velocities as high as 6-8 meters/sec. or more to
prevent extinguishment.
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The particular dimensions of the propellant strip,
including length and width of the strip and thickness of the
propellant on the substrate, are dependent upon many
factors. Among those factors are the size, shape and weight
of the rocket, the size of the canister, and the type of
propellant being used. The pressurization curve is readily
calculated for any projectile and propellant strip
configuration. The apparatus of the invention may be used
to eject a wide variety of objects from a casing or
canister. Thus, for example, the invention is useful for
ejecting objects from aircraft, seagoing vessels, and
stationary sites.
The invention provides a reliable gas generation
which is adaptable to the ejection of any sized object from
a canister. The apparatus is easily and inexpensively
constructed. The ejection pressure may be pre-controlled to
any desired time function.
The specific details described above as
illustrative of the present invention are by way of example
and are not intended to limit the scope of the invention as
claimed hereinafter.
