Note: Descriptions are shown in the official language in which they were submitted.
CA 02202980 1997-04-17
W/D 96/12641 PCTIUS95/07072
EXPENDABLE UNDERWATER VEHICLE
Statement Reqarding Federally Sponsored Research
5This invention was made with government support
under Contract No. N00024-91-C-6127 awarded by the
Department of the Navy. The government has certain
rights in the invention.
10Field of the Invention
This invention relates to expendable underwater
vehicles, and more particularly, expendable underwater
vehicles adapted for operation in relatively shallow
water.
Backqround of the Invention
An expendable underwater vehicle, such as the
Expendable Mobile ASW tAnti-Submarine Warfare) Training
Target (EMATT) which is available from Sippican, Inc.
of Marion, Massachusetts, is used to train naval forces
in the detection, localization, tracking, and/or
attacking of a submarine in the ocean (i.e., to train
naval forces in anti-submarine warfare). After being
launched into the ocean, the expendable underwater
vehicle "swims" a pre-programmed underwater course as
it acoustically simulates a submarine. The naval
forces use acoustics to detect, localize, track, and/or
attack the simulated submarine. After a specified
time, currently about three hours, the internal
batteries of the expendable underwater vehicle become
exhausted, and the vehicle drops to the bottom of the
ocean. If the water is relatively shallow (e.g., less
than about 100 feet), the expended vehicle at the ocean
CA 02202980 1997-04-17
PCT/US95/07072
WO 96/126~1
bottom can be washed onto the shore by the action of
the tide and currents.
The expenda~le underwater vehicle can be launched
into the ocean from either a surface ship or an
aircraft. When launched by a surface ship, the
expendable underwater vehicle is dropped into the water
from a short distance thereabove such that the impact
is ~;nim~l and no damage results. In an aircraft
launch, the expendable underwater vehicle cannot simply
be dropped into the water because the impact with the
water typically will damage the vehicle. Additional
hardware is used in an aircraft launch to help the
vehicle survive the impact with the water. The
additional hardware, known as the air launch assembly,
includes a two-piece nose cup assembly, a windflap, a
harness, and a parachute.
To air launch the expendable underwater vehicle, it
is fitted with the air launch assembly. The two-piece
nose cup goes over the nose of the vehicle and is held
in place by straps of the harness which also attach to
the parachute. The parachute is packaged underneath
the windflap and the entire vehicle is packaged in a
sonobuoy launch container. The vehicle can be launched
from the aircraft either using a launching tube that
accepts the sonobuoy launch container and
automatically, upon comm~n~, ejects the vehicle from
the container, or by manually removing the vehicle from
the sonobuoy launch container and dropping (launching
the unit through a launching tube or other opening in
the aircraft. After the vehicle is launched from the
aircraft, the windflap separates from the vehicle and
deploys the parachute. The parachute opens and
decelerates the vehicle such that the vehicle enters
the water nose-first and along its longitudinal axis.
=
CA 02202980 l997-04-l7
PCTIUS95107072
WO ~96/12641
At or just after water impact, the force causes the
two-piece nose cup assembly to separate into its two
halves, each of which is forced away from the vehicle
as the vehicle continues to descend into the water.
The two-piece nose cup assembly: (i) serves as a
packaging spacer to contain the vehicle properly in the
sonobuoy launch container prior to launch; (ii) keeps
the parachute attached to the vehicle after air launch
and until or just after water impact; (iii) impacts the
]0 water first and thereby helps to protect the vehicle
from damage which can be caused by the impact of water
entry; and (iv) separates into its two halves at or
just after water impact.
After separation of the two halves of the two-piece
nose cup, which occurs at or relatively soon after
water impact, the vehicle continues to dive into the
water at a relatively fast speed such that it can ~each
a depth of about 100 feet or more before it stops
diving. One or both of the halves of the nose cup can
contact the rear section (shroud) of the vehicle as the
vehicle dives past the separated halves. Because the
vehicle is traveling at a high speed as it enters the
water (e.g., about 60 miles per hour), the contact can
cause serious damage to the shroud which can result in
poor performance or even an inoperable vehicle.
The two-piece nose cup assembly can be useful when
air launching the vehicle for deep water (e.g., from
about 150 to 600 feet) operation. For shallow water
(e.g., from about 50 to 150 feet) operation, the
vehicle typically must be launched by a surface ship
and cannot be air launched with the two-piece nose cup
assembly due to the depth to which the vehicle
typically descends when air launched with the two-piece
nose cup assembly.
CA 02202980 1997-04-17
WO 961126~1 PCT/US95/07072
Training and practice in the detection,
localization, tracking, and/or attacking of a submarine
in the ocean (i.e., training and practice in anti-
submarine warfare) in relatively shallow waters (e.g.,
about 150 feet deep or less) can be important to naval
~orces.
- ~ -
CA 02202980 1997-04-17
PCT/ US95/07072
WO 96/12641
Summary of the Invention
The invention relates to an expendable underwater
vehicle for use in training naval forces in anti-
submarine warfare in ocean waters, including shallow
waters. The vehicle is between about three to five
feet in length and about five inches in diameter, and
it includes various improvements which make successful
operation in the ocean waters possible.
In one aspect, the invention features a one-piece
:L~ nose cup assembly which allows the expendable
underwater vehicle to be air launched into and operated
in relatively shallow waters such as water less than
about 150 feet deep and, more particularly, water about
100 feet deep or less. It also generally allows for a
more reliable air launch in all water depths. The one-
piece nose cup assembly, like the vehicle, is
expendable.
In another aspect, the invention involves a scuttle
plug which allows water to fill the expendable
underwater vehicle after the vehicle is expended and
drops to the ocean bottom. When filled with water, the
expended vehicle typically will not wash onto the shore
by the action of the tide and currents, thereby
reducing the likelihood of recovery of the expended
vehicle and resultant exposure to the hazards
associated with a partially discharged lithium battery.
In addition, once the sea water is within the expended
vehicle, the water depletes the energy of the battery,
thereby further reducing the hazard associated with a
partially discharged lithium battery in the event the
expended vehicle is inadvertently recovered.
In still another aspect of the invention, the
expendable underwater vehicle has rudders and elevators
of larger surface area to improve controllability of
CA 02202980 1997-04-17
WO 96/12641 PCT/US95/07072
the vehicle in the water by overcoming any out-of-
straightness condition of the vehicle which can result
from the shock of an air launch and/or hydrostatic
pressures.
The foregoing and other objects, aspects, features,
and advantages of the invention will become more
apparent from the following description and from the
claims.
CA 02202980 1997-04-17
PCTrUS95/07072
W O 96/12641
Brief Description of the Drawings
In the drawings, like reference characters
generally refer to the same parts throughout the
different views. Also, the drawings are not
necessarily to scale, emphasis instead generally being
placed upon illustrating the principles of the
invention.
FIG. 1 is a perspective view of an expendable
underwater vehicle.
LO FIG. 2 is an exploded perspective view of the
expendable underwater vehicle of FIG. 1 and a two-piece
nose cup for use therewith.
FIG. 3A is a top view o a one-piece nose cup for
use with the expendable underwater vehicle of FIG. 1
]5 according to the invention.
FIG. 3B is a side view in cross-section of the one-
piece nose cup of FIG. 3A taken along line B-B.
FIG. 3C is a bottom view of the one-piece nose cup
of FIG. 3A.
FIG. 3D iS a partial side view of the one-piece
nose cup of FIG. 3A taken along line D-D.
FIG. 3E is a side view in partial cross-section of
the one-piece nose cup of FIG. 3A taken along line E-E,
the side view including an air launch harness and a
release band.
FIG. 3F is a side view in partial cross-section of
the one-piece nose cup of FIG. 3A taken along line F-F,
the side view including a plunger and a hook.
FIG. 4 is a diagram of the release band for use
with the one-piece nose cup of FIGS. 3A-3F.
FIG. 5 is a diagram of a spring for use with the
one-piece nose cup of FIGS. 3A-3F.
FIG. 6 is a side view in cross-section of a scuttle
plug for use with the expendable underwater vehicle of
CA 02202980 1997-04-17
WO96/12641 PCT~S95/07072
FIG. 1 according to the invention.
FIG. 7A is a side view in partial cross-section of
rudders used in the expendable underwater vehicle of
FIG. 1.
FIG. 7B is a side view in partial cross-section of
an improved rudder for use in the expendable underwater
vehicle of FIG. 1 according to the invention.
CA 02202980 1997-04-17
PCTrUS95/07072
W OS\6/12641
Description
Referring to FIGS. 1 and 2, an expendable
underwater vehicle 10, such as an Expendable Mobile ASW
(Anti-Submarine Warfare) Training Target (EMATT) which
5 is available from Sippican, Inc. of Marion,
Massachusetts, is a battery-powered, self-propelled
unit which is about three feet long, about five inches
in diameter at its thickest point, and about twenty-
five pounds in weight. It can range up to about five
lO feet in length. In ASW training exercises, the
vehicle 10 is used to simulate a submarine, and it
performs a three-hour pattern with varying headings and
depths. After being launched into the water, the
vehicle 10 turns on and "swims" when a pressure
1!~ sensor 12 mounted on the hull confirms that the
negatively buoyant vehicle 10 is below a specified
depth, currently thirty feet.
The vehicle lO includes a nose 24 at a front end
and a shroud 26 at a rear end. Between the nose 24 and
20 the shroud 26 is a generally watertight compartment
which houses a DC motor 30 for driving a propeller 32,
a guidance and control subsystem for implementing a
preprogrammed course for the vehicle in the ocean by
controlling the motor 30 and solenoids 34 to cause the
25 vehicle to follow the course, a signal processing
subsystem, and a battery pack 36 for supplying power to
the signal processing subsystem, the guidance and
control subsystem, the motor 30, and the solenoids 34.
The battery pack 36 preferably includes one or more
30 lithium batteries, although in general o~her power
g sources can be used. The solenoids 34 are actuators
which move elevators 38 and rudders 40 at the co~m~n~
of the guidance and control subsystem. The guidance
and control subsystem includes a fluxgate compass 42,
CA 02202980 l997-04-l7
WO 96/126~1 PCTIUS95/07072
-- 10 --
the pressure sensor 12, the solenoids 34, and
electronics 44. The signal processing subsystem
simulates a submarine by generating signals
representative of the submarine and causing
5 corresponding acoustic signals to be transmitted into
the ocean. The signal processing subsystem includes
the electronics 44, a forebody projector 46, and at
least one midbody projector 48. The forebody
projector 46 is an acoustic transducer which, under the
10 control of the electronics 44, receives acoustic
interrogations from an external source (e.g., from a
sonobuoy) and then transmits acoustic signals
representative of echoes which the submarine would
return. The forebody projector 46 thus is an active
15 echo receiver/repeater. The midbody projectors 48 are
acoustic transducers which, under the control of the
electronics 44, generates "noise" which simulates the
sound of the running submarine. The midbody
projectors 48 thus generate a passive acoustic
20 signature of the simulated submarine.
The vehicle 10 can be launched either from a
surface ship by manually dropping it into the water or
from an aircraft by using additional hardware. In a
conventional configuration, the additional hardware
25 used in an air launch includes a windflap 14, a
parachute 16, a harness 18, and a two-piece nose cup
assembly 20. In accordance with one aspect of the
invention, the two-piece nose cup assembly 20 is
replaced with a one-piece nose cup 22 (FIGS. 3A-3F) for
30 air launching into relatively shallow waters such as
water about 150 feet or less in depth and, more t
particularly, water about 100 feet or less in depth.
The one-piece nose cup 22 also improves the reliability
of air launches in all water depths.
CA 02202980 1997-04-17
W O 96/12641 PCTrUS95/07072
-- 11 --
With either the two-piece nose cup assembly 20 or
the one-piece nose cup 22, the vehicle 10 is air
launched from an aircraft by loading it into and then
firing it out of a sonobuoy launcher or from a gravity
tube on the aircraft. Prior to loading the vehicle 10
into the sonobuoy launch container, the cup 20 or 22 is
placed over the nose 24, and the harness 18 is
releasably secured to the cup and extends on either
side of the vehicle 10 along its length to th~
shroud 26. The parachute 16 is tucked in around the
shroud 26 and then the windflap 14 is put in place such
that the entire assembly fits into the sonobuoy launch
container. Once the vehicle 10 is launched out of the
sonobuoy launch container and into the air, the
windflap 14 deploys the the parachute 16 and, in so
doing, the windflap 14 separates from the vehicle 10
while the vehicle 10 is in flight. The deployed
parachute 16 then decelerates the vehicle 10 and causes
it to enter the water nose-first and along its
longitll~;nAl axis 28.
In the conventional air launch configuration which
uses the two-piece nose cup assembly 20, while the
vehicle 10 is in flight, the two halves of the two-
piece nose cup assembly 20 are held together over the
nose 24 by a release band. This release band also
helps to secure the harness 18 to the cup assembly 20
while the vehicle 10 is in flight. Upon water impact,
a plunger in the face of the cup assembly 20 is
depressed by the force of the impact, and the release
band is thereby released allowing the two halves of the
cup assembly 20 to separate. The cup assembly 20 bears
the brunt of the impact, which impact typically is
strong enough to damage the nose 24 if the nose 24 is
unprotected (e.g., if the cup assembly 20 is not fitted
CA 02202980 1997-04-17
WO 96/12641 PCT~S95/07072
- 12 -
over the nose 24) . After water impact, the vehicle 10
continues to drive into the water and the two halves of
the cup assembly 20 are shed alongside the vehicle 10
and left behind. As the two-piece nose cup assembly 20
separates and is left behind, the harness 18 and the
parachute 16 also are left behind.
Referring to FIGS. 3A-3F, 4, and 5, when the one-
piece nose cup 22 according to the invention is used in
an air launch, the vehicle 10 enters the water with the
same orientation as described previously but the cup 22
remains on the nose 24 for a longer period of time
after water impact. Because the cup 22 iS formed of a
single piece of material, it does not separate into
halves upon impact with the water. By staying fitted
over the nose 24 for a longer period of time after
water impact as compared to the two-piece nose cup
assembly 20, the one-piece nose cup 22 causes the
vehicle 10 to decelerate ~uicker and then stop driving
into the water at a depth less than about 150 feet and,
more particularly, at a depth about 100 feet or less
and, even more particularly, at a depth between about
20 to 30 feet. Because the cup 22 inhibits the
vehicle 10 from driving beyond about 50 feet into the
water, use of the cup 22 allows the vehicle 10 to be
25 air launched into and operated in relatively shallow
waters such as water less than about 150 feet deep and,
more particularly, water about 100 feet deep or less.
Upon water impact, a plunger in the face 50 of the
one-piece nose cup 22 depresses due to the force of the
30 water on the face 50, and a release band 52 ( FIGS . 3E
and 4), which is releasably secured around the cup 22
to hold the harness 18 thereto while the vehicle 10 is
in flight in the air, is thereby released allowing the
harness 18 and the parachute 16 to fall away from the
CA 02202980 1997-04-17
WO 96/12641 PCTIUS95107072
-- 13 --
cup 22 and the vehicle 10. The one-piece nose cup 22
remains on the nose 24 of the vehicle lO through water
entry and initial deceleration in the water. After the
vehicle 10 has slowed (e.g., to about five to ten miles
per hour), well past the mos~ dynamic stages of the air
launch, the cup 22 falls away from the nose 24. The
one-piece nose cup 22 is expendable (i.e., it typically
is left in the ocean and not recovered or reused). The
various components associated and used with the cup 22
also are expendable. In the disclosed embodiment, the
cup 22 is in fact pushed off of the nose 24 by an
ejector spring 54 (FIGS. 3B and 5) after the vehicle 10
has slowed sufficiently to allow the force of the
spring 54, together with the weight of the nose cup 22,
to overcome the hydrodynamic force of the water against
the face 50 of the cup 220 The speed of the vehicle 10
in the water at which the spring force together with
the cup weight exceed the water force is about five to
ten miles per hour. The one-piece nose cup 22 is made
of a material which gives it sufficient weight such
that it separates from the nose 24 at the proper water
depth (i.e., at about 50 feet or less below the surface
of the water and, more particularly, at a depth between
about 20 to 30 feet) to allow air launching of the
vehicle 10 into shallow water such as water less than
about 150 feet deep and, more particularly, water about
100 feet deep or less. The material from which the
cup 22 is made also must be sufficiently rigid to
withstand the impact of the water on the face 50 of the
cup 22 as the vehicle enters the water at about sixty
miles per hour. In the disclosed embodiment, the
cup 22 is made of aluminum, although any material which
meets the above-stated weight and structural integrity
requirements may be used.
CA 02202980 1997-04-17
WO96/12641 PCT~S95/07072
- 14 -
After the one-piece nose cup 22 comes off of the
nose 24 of the vehicle lO, the vehicle lO typically is
vertical (i.e., its longitudinal axis 28 typically is
perpendicular to the surface of the water). In the
disclosed embodiment, the guidance and control
subsystem of the vehicle lO will not start the motor 30
to begin the preprogrammed course until the vehicle lO
has reached a predetermined depth such as about sixty
feet. The pressure sensor 12 informs the guidance and
control subsystem when the predetermined depth has been
reached. In general, once the vehicle lO reaches the
predetermined depth, the vehicle lO is horizontal
(i.e., its longitudinal axis 28 is parallel to the
surface of the water). The danger of starting the
motor 30 when the vehicle lO is not horizontal or
substantially horizontal is that the vehicle lO will
spin out of control.
The one-piece nose cup 22 eliminates many problems
associated with the conventional two-piece nose cup
assembly 20. For example, the one-piece nose cup 22
does not travel the length of the vehicle lO as the
vehicle lO drives into the water, and therefore the
cup 22 cannot and does not ever damage the shroud 26
when it separates from the nose 24. In fact, when the
25 cup 22 separates from the nose 24, the cup 22 falls
down towards the ocean floor in the opposite direction
of the shroud 26. Also, with the use of the cup 22,
the vehicle lO can be air launched into and operated in
shallow water.
The bottom of the one-piece cup 22 includes a
recess 56 (FIG. 3C) for receiving the spring 54 when
the cup 22 is held tight against the nose 24. The
cup 22 is held tight against the nose 24: (i) prior to
air launch while in the sonobuoy launch container and
CA 02202980 1997-04-17
W~ 96/12641 PCT/US9~/07072
during flight after the air launch but before water
impact by the harness 18 which attaches to the
shroud 26 at the rear end of the vehicle 10 and to the
cup 22 at the front end of the vehicle 10 and
(ii) after water impact by the force o~ the water
against the face 50 of the cup 22 until the force of
the spring 54 together with the weight of the cup 22
exceed the hydrodynamic force of the water on the
cup 22 as the vehicle slows down and the cup 22 is
pushed off of the nose 24. The recess 56 includes two
holes 58, 60 for receiving two pins 62, 64 at the end
of the spring 54.
Referring to FIGS. 3A and 3E, the harness 18
attaches to the one-piece cup 22 as follows. A pin 66
at the end of each half of the harness 18 (only one
half is shown in FIG. 3E ) rests on a chamfered shelf 68
of the cup 22 and is held securely against a side 80 of
the cup 22 by the release band 52. When the release
band 52 is released from the cup 22, the pinned end of
the harness 18 also releases and slides off of the
chamfered shelf 68 and falls away (the other pinned end
does the same thing) so that the harness 18 is no
longer attached to the nose cup 22.
Referring to FIGS. 3A, 3D, and 3F, the release
band 52 is released from the one-piece cup 22 as
follows. A plunger 51 is slidable in a plunger hole 70
formed in the cup 22. When the plunger is depressed
(e.g., due to the force of the water on the face 50 of
the cup 22 when the cup 22 impacts the water), a
hook 72 coupled to the plunger 51 moves in the same
direction as the plunger 51 (the direction indicated by
an arrow 74 in FIGS. 3D and 3E) and releases from two
notches 76, 78 (FIG. 4) in the release band 52 thereby
allowing the release band to spring away from the
=
CA 02202980 1997-04-17
WO 96/12641 PCT/US95/07072
-- 16 --
cup 22. The release band 52 is initially put in place
by wrapping it around the cup 22 and overlapping the
two ends of the release band 52 such that the
notches 76, 78 line up at the location of the hook 72
and the plunger 51. The plunger 51 is then moved up
(in the direction opposite of the direction indicated
by the arrow 74), and the hook 72 enters the
overlapping notches 76, 78 to hold the release band 52
releasably in place around the cup 22. In FIG. 3F, the
plunger 51 and the hook 72 are shown in the non-
depressed position in which the hook 72 is holding the
release band 52 (not shown in FIG. 3F) in place. A
ball and spring arrangement holds the plunger 51 in the
non-depressed position of FIG. 3F. In this
arrangement, a spring 53 pushes on a ball 55 and forces
the ball 55 into a recess 57 in the cup 22 which holds
the plunger 51 in the non-depressed position until,
upon water impact, the force of the water on the
face 50 of the cup 22 causes the plunger 51 to descend
in the direction of the arrow 74.
The release band 52 preferably is made of spring
steel although other strong, resilient materials also
can be used. The face 50 of the cup 22 includes
recessed slits 82, 84 for receiving a safety crossbar.
The plu~ger 51 also includes a recessed slit on its top
face, and this slit aligns with the slits 82, 84 in the
cup 22 so that the safety crossbar lies flat across the
face 50 of the cup 22 when in place. When installed in
the slits 82, 84, the crossbar helps to prevent the
plunger from being accidentally depressed by a person
handling the cup 22 to prepare the vehicle 10 for an
air or surface launch. A person cannot depress the
plunger easily when the safety crossbar is in place.
The safety crossbar does not, however, prevent or
CA 02202980 l997-04-l7
WO 96/12641 PCTIUS95/07072
-- 17 --
inhibit the plunger from being depressed when the
face 50 of the cup 22 impacts the water.
As seen in FIGS. 3A and 3C, the cup 22 includes
three water flow-through holes 86, 88, 90 in the
disclosed embodiment. These holes, like the plunger
hole 70, extend from the face 50 of the cup 22 through
to the inside of the cup 22 where the nose 24 fits.
The water flow-through holes allow water to flow freely
through the cup 22, thus reducing any tendency for the
cup 22 to "stick" to or stay attached to the nose 24
after the vehicle 10 has completed its initial entry
dive and slowed to about five to ten miles per hour.
Referring to FIGS. 1, 2, and 6, another aspect of
the invention which makes the vehicle 10 useful in
shallow ocean water operations involves a scuttle
plug 100. The watertight compartment of the vehicle 10
which houses the motor 30, the guidance and control
subsystem, the signal processing subsystem, and the
battery pack 36 has a passage 102 thereinto via an
existing vent plug. The passage 102 is formed in a
bulkhead 105 located at approximately the center of the
vehicle 10. The passage 102 is sealed with the scuttle
plug 100 which includes a new vent plug 104 which
incorporates a corrodible disk 101. The corrodible
disk 101 fits into a recess 106 formed in the bottom of
the vent plug 104 as indicated by an arrow 108~ Once
the corrodible disk 101 is placed into the recess 106,
the combination of the corrodible disk 101 and the vent
plug 104 (i.e., the scuttle plug 100) is inserted into
the passage 102 to seal the compartment and make it
watertight. The vent plug 104 has a central
passage 110 therethrough. When the corrodible disk 101
is fitted into the recess 106 of the vent plug 104, the
central passage 110 is blocked with an O-ring face
CA 02202980 1997-04-17
WO 96/12641 PCT/US95/07072
-- 18 --
seal 107 installed on the inner surface of the
corrodible disk 101. When the vehicle 10 is in ocean
water, the corrodible disk 101 corrodes away as a
function of time, salinity, temperature, and pressure
thereby allowing a hole through the disk 101 to form
which allows the water to travel down the central
passage 110 of the vent plug 104 and into the
vehicle 10.
The vent plug 104 can be made from a variety of
noble materials including aluminum, copper, and
stainless steel (preferred). The corrodible disk 101
is made of an active material which corrodes after
prolonged exposure to ocean water. Magnesium is the
preferred material for the disk 101 although other
materials are possible. In the disclosed embodiment,
the thinnest portion of the disk 101 has a thickness,
t, of 0.030 inches. In the disclosed embodiment, the
disk 101 corrodes enough to allow water to enter and
fill the formerly watertight compartment after an
exposure period of between about six to seventy-two
hours and, more particularly, after about twenty-four
hours of exposure to the water. For a runtime (i.e.,
battery pack 36 life) of about three hours, the
vehicle 10 will flood with water about twenty-one hours
after the expended vehicle 10 drops to the bottom of
the ocean. The exact time it takes for the disk 101 to
corrode is a function of a number of factors including
the type of corrodible material, the salinity of the
water, the temperature of the water, and the pressure
on the disk.
Use of the scuttle plug 100 with the vehicle 10
makes the vehicle 10 suitable for shallow water
operations (i.e., operations in water having a depth of
about 100 ~eet or less) because an expended vehicle
CA 02202980 1997-04-17
WO 96/12641 PCTIUS9~;/07072
-- 19 --
filled with water is not likely to be washed onto the
shore by the action of the tide and currents. An
expended vehicle that is not filled with water and that
is at the bottom of shallow ocean waters can be moved
and washed onto the shore by the action of the tide and
currents. Use of the scuttle plug 100 thereby reduces
the likelihood of recovery of the expended vehicle and
resultant exposure to the hazards associated with a
partially discharged lithium battery. In addition,
once the sea water is within the expended vehicle, the
water depletes the energy of the battery, thereby
further reducing the hazard associated with a partially
discharged lithium battery in the event the expended
vehicle is inadvertently recovered.
Referring to FIGS. 7A and 7B, another aspect of the
invention which makes the vehicle 10 useful in shallow
ocean water operations involves rudders and elevators
with enlarged surface areas as compared to the surface
areas of the rudders and elevators of a conventional
EMATT. The rudders 40 of a conventional EMATT are
shown in FIG. 7A. Each fin 41, 43 of the rudder 40 has
a surface area of about 0.63 square inches, and thus
the total rudder surface area is about 1.26 square
inches. Note that this is the total rudder surface
area for the surface shown and that the rudders 40 have
opposite sides with the same total rudder surface area,
making the overall surface area of the rudders 40 equal
to about 2.52 square inches. While the elevators 38 of
the conventional EMATT are not shown in FIG. 7A, they
are similar in shape to the rudders 40, and thus the
total elevator surface area (on one side thereof) also
is about 1.26 square inches. Improved rudders 120 are
shown in FIG. 7B. The improved rudders 120 take
advantage of some unused space 118 in the conventional
CA 02202980 lgg7-o4-l7
WO96/12641 PCT~S95/07072
- 20 -
EMATT design by enlarging each of the fins such that it
now extends into the unused space 118. The enlarged
rudders 120 have a surface area which is about 24%
greater than the surface area of the rudders 40 used in
the conventional EMATT. More specifically, the total
improved rudder surface area is about 1.56 square
inches (on one side thereof), making the overall
surface area of the enlarged rudders 120 equal to about
3.12. While the improved elevators are not shown in
FIG. 7B, it should be understood that they are similar
in shape to the improved rudders 120, and thus the
total improved elevator surface area also is about 1.56
square inches (on one side thereof).
With the enlarged rudders and elevators, the
controllability of the vehicle 10 in the water is
greatly improved. In fact, when the enlarged rudders
and elevators are used in the vehicle 10, they
generally are able to overcome any out-of-straightness
condition of the vehicle 10 which can result from air
launch shocks and hydrostatic pressures. With the
conventional rudders 40 and elevators 38 of FIG. 7A,
the vehicle lO cannot always overcome an out-of-
straightness condition of the vehicle 10 thereby
resulting in a loss of heading and/or depth control of
the vehicle 10. These out-of-straightness conditions
which can result from shocks due to air launching
and/or hydrostatic pressures generally relate to the
shape of the vehicle 10 along its longitudinal axis 28.
That is, the out-of-straightness conditions are
conditions where the shape of the vehicle 10 deviates
from straight along its longitll~;n~l axis 28. In
general, the greater the deviation (i.e., the more
severe the out-of-straightness condition), the less
likely it is that the guidance and control subsystem of
CA 02202980 1997-04-17
WO96/12641 PCT~S95107072
. - 21 -
t the vehicle 10 can keep the vehicle 10 on the
preprogrammed course.
Variations, modifications, and other
implementations of what is described herein will occur
to those of ordinary skill in the art without departing
from the spirit and the scope of the invention as
claimed. Accordingly, the invention is to be defined
- not by the preceding illustrative description but
~ instead by the following claims.
What is claimed is:
-'1;
~.
.
.
~r~
,
. ~ ~
. .
