U.S. patent application number 11/606763 was filed with the patent office on 2010-09-02 for detachable aerodynamic missile stabilizing system.
This patent application is currently assigned to Raytheon Company. Invention is credited to Andrew B. Facciano, Richard A. McClain, Robert T. Moore, Craig D. Seasly, Raymond J. Spall.
Application Number | 20100219285 11/606763 |
Document ID | / |
Family ID | 40094328 |
Filed Date | 2010-09-02 |
United States Patent
Application |
20100219285 |
Kind Code |
A1 |
Facciano; Andrew B. ; et
al. |
September 2, 2010 |
DETACHABLE AERODYNAMIC MISSILE STABILIZING SYSTEM
Abstract
Provided is a detachable aerodynamic missile stabilizing system
for a missile flying at low flight speeds. The system includes a
housing adapted to couple to couple to the missile. Extending
outward from the housing is at least one grid fin. Specifically the
grid fin extends from the housing such that it is transverse to a
longitudinal axis of the housing and the missile. The grid fin
provides a plurality of apertures. The apertures are parallel to
the longitudinal axis of the housing and the missile. A coupler is
adapted to detachably couple the housing to the missile. A method
of use is also provided.
Inventors: |
Facciano; Andrew B.;
(Tucson, AZ) ; Moore; Robert T.; (Tucson, AZ)
; Seasly; Craig D.; (Tucson, AZ) ; McClain;
Richard A.; (Tucson, AZ) ; Spall; Raymond J.;
(Tucson, AZ) |
Correspondence
Address: |
POLSINELLI SHUGHART PC
700 West 47th Street, Suite 1000
KANSAS CITY
MO
64112
US
|
Assignee: |
Raytheon Company
|
Family ID: |
40094328 |
Appl. No.: |
11/606763 |
Filed: |
November 30, 2006 |
Current U.S.
Class: |
244/3.25 |
Current CPC
Class: |
F42B 10/143 20130101;
F42B 10/64 20130101 |
Class at
Publication: |
244/3.25 |
International
Class: |
F42B 10/14 20060101
F42B010/14 |
Claims
1. A detachable aerodynamic missile stabilizing system for
stabilizing a missile at subsonic speeds, the missile having a
forward portion and an aft portion, comprising: a grid fin
interstage assembly including a housing configured to be coupled to
the aft portion, a plurality of grid fins disposed on an exterior
of the housing and movable between a stowed position and a deployed
position extending transversely from a longitudinal axis of the
housing, the grid fins having a plurality of apertures, and an
articulation control system configured to control an orientation of
the grid fins and to link with a missile control system; and at
least one coupler configured to attach the grid fin interstage
assembly to the missile at the aft portion and further configured
to release the grid fin interstage assembly from the aft portion to
dispose of the grid fin interstage assembly at subsonic speeds.
2. The aerodynamic stabilizing system of claim 1, wherein the
apertures are arranged in a grid pattern, the apertures parallel to
a longitudinal axis of the housing.
3. (canceled)
4. (canceled)
5. A detachable aerodynamic missile stabilizing system for
stabilizing a missile at subsonic speeds, the missile having a
forward portion and an aft portion, comprising: a grid fin
interstage assembly including a housing configured to be coupled to
the aft portion, and a grid fin disposed on an exterior of the
housing, the grid fin having a plurality of apertures and the grid
fin being a single grid fin extending circumferentially and
annularly about the housing; and at least one coupler configured to
attach the grid fin interstage assembly to the missile at the aft
portion and further configured to release the grid fin interstage
assembly from the aft portion to dispose of the grid fin interstage
assembly at subsonic speeds.
6. The aerodynamic stabilizing system of claim 1, wherein the grid
fins are symmetrically disposed about the housing.
7. (canceled)
8. The aerodynamic stabilizing system of claim 6, wherein the grid
fins are operable to articulate.
9. The aerodynamic stabilizing system of claim 6, wherein the
coupler couples the grid fins to a control system disposed within
the missile.
10. The aerodynamic stabilizing system of claim 6, wherein the grid
fins are aligned between the tail fins.
11. (canceled)
12. The aerodynamic stabilizing system of claim 1, wherein the grid
fins provide control surfaces operable to provide lift.
13. (canceled)
14. The aerodynamic stabilizing system of claim 1, wherein the grid
fins include mesh.
15. The aerodynamic stabilizing system of claim 1, wherein each
grid fin includes two primary opposing sides transverse to the
longitudinal axis, and the plurality of apertures are disposed
between the opposing sides and are parallel to the longitudinal
axis.
16.-27. (canceled)
Description
FIELD
[0001] This invention relates generally to the field of missile
control system, and more specifically to a detachable aerodynamic
missile stabilizing system for use during launch to cause the
missile to pitch over rapidly while maintaining roll stability.
BACKGROUND
[0002] Offensive missiles such as any number of cruise missiles,
are constructed to fly at low altitudes (i.e., just above tree tops
or water surfaces) so as to avoid detection by the targeted party's
radar. In such a situation a targeted ship, for example, may have
just a few seconds to first identify the thread and then take
countermeasures, such as the launching of one of its defensive
missiles.
[0003] Typically, a land or ship born defensive missile is launched
from a canister or missile launcher in a generally vertical
direction. Such a defensive missile must attain a sufficient
velocity before its airfoil surfaces are able to perform any
substantial maneuvers. This generally translates into having the
missile reach an altitude of thousands of feet before it is able to
pitch over and begin seeking the incoming missile threat. For long
range threats this high altitude pitch over is a common design
characteristic and is therefore a common element in existing
defense missile systems.
[0004] Given the low altitudes of threat missiles and the
consequential small window for identification and reaction, such a
high altitude for pitch over is problematic. More specifically,
given the limited timeframe to successfully determine an intercept
solution and the high speeds of the threat missiles, it may not be
possible to optimize the intercept trajectory due to the lack of
launch maneuverability and stability. There exists a very real
possibility of overshooting the target or expending too much time
and fuel with large arching course corrections resulting in missed
intercept opportunities.
[0005] Common missile control systems incorporate a number of
different technologies by which guidance control and vehicle
stability are provided to a missile, however attempts to adapt
these systems to address this low speed guidance control and
stability problem have not been complete.
[0006] Control surfaces such as wings and canards that are actuated
during flight essentially interrupt the airflow around the missile
body for high speed control authority. If sized for high speed use
they are ineffective at low speeds. If sized for low speed they are
large, heavy and likely not to fit within the launch frame or
canister.
[0007] Movable nozzle systems are heavy and complicated. As they
are not detachable they add to the overall vehicle weight and
degrade overall performance after they have fulfilled their purpose
at low speed. In addition, nozzle systems frequently do not provide
sufficient thrust vector angles as are required for low speed
guidance control and vehicle stability to meet a rapidly
approaching low altitude threat that has been detected only a short
time period away from impact.
[0008] Thrust vector control ("TVC") systems typically incorporate
movable nozzles, jet tabs, or jet vanes, the latter offering roll
control but substantially degrading rocket motor kinematic
performance by impinging propellant flow. TVC thrust redirection
systems steer the missile from the aft rocket nozzles. These
systems are ineffective after motor burn-out and again are often
heavy and costly devices resulting in significant vehicle weight
increase and subsequent overall missile performance
degradation.
[0009] Missile jet vane control systems have been shown to be
effective at providing low speed guidance control and stability.
However, as the jet vanes are placed in the flow of the missile
exhaust they do impact missile motor performance. In addition, jet
vane control systems require the use of low smoke, low energy
propellant grains to enable the jet vanes to survive the nozzle
plasma flow environments and are therefore not suitable for use
with many currently existing and intended rocket motor designs.
[0010] Moreover, despite various prior art attempts, missile
control at launch and within the period after launch before the
missile obtains sufficient high speed velocity to utilize its
traditional control surfaces has remained problematic and elusive.
Given the large variety of currently existing defensive missile
inventories, individualized customization and/or modification is
undesirable. The redesign of motors is both costly and time
intensive and may in many cases lead to additional disposal costs
of hazardous materials as fuel systems are replaced.
[0011] Hence, there is a need for a missile stabilization system
that overcomes one or more of the issues and problems identified
above.
SUMMARY
[0012] This invention provides a detachable missile stabilization
system and associated method.
[0013] In particular, and by way of example only, according to one
embodiment of the present invention, provided is a detachable
aerodynamic missile stabilizing system for stabilizing a missile at
low flight speeds, the missile having a forward portion and an aft
portion, including: a housing adapted to couple to the missile; at
least one grid fin extending transversely from the housing, the
grid fin providing a plurality of apertures; and a coupler adapted
to detachably couple the housing to the missile.
[0014] In yet another embodiment, provided is a method of providing
aerodynamic missile stability at low flight speed, the missile
having a forward portion, an aft portion, a longitudinal center
portion therebetween, and a flight control system, including:
providing a grid fin interstage assembly having a housing with a
central axis and at least one grid fin extending from the housing
transverse to the central axis, the grid fin providing a plurality
of apertures parallel to the center portion; coupling the grid fin
interstage assembly to the aft portion of the missile, the central
axis of the grid fin interstage assembly imposed upon a central
axis of the missile; in response to missile launch, the grid fin
interstage assembly establishing increased lift and drag at low
flight speed; detaching the grid fin interstage assembly as the
missile transitions from low flight speed to high flight speed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a perspective view of a missile provided with a
detachable aerodynamic missile stabilizing system according to an
embodiment;
[0016] FIG. 2 is an enlarged view of the detachable aerodynamic
missile stabilizing system shown in FIG. 1;
[0017] FIG. 3 is an enlarged view of the detachable aerodynamic
missile stabilizing system of FIG. 2 showing the grid fins in a
stowed orientation according to an embodiment;
[0018] FIG. 4 is a face view of the detachable aerodynamic missile
stabilizing system shown in FIG. 3;
[0019] FIG. 5 is a perspective view of an alternative embodiment of
the detachable aerodynamic missile stabilizing system;
[0020] FIG. 6 is a face view of the detachable aerodynamic missile
stabilizing system shown in FIG. 5;
[0021] FIG. 7 is a side view of a missile with a detachable
aerodynamic missile stabilizing system according to an embodiment
within a canister;
[0022] FIG. 8 is a side view of the missile with a detachable
aerodynamic missile stabilizing system as shown in FIG. 7, now
launched from the canister with the grid fins deployed; and
[0023] FIG. 9 is a high level flow diagram illustrating the method
of using a detachable aerodynamic missile stabilizing system in
accordance with at least one embodiment.
DETAILED DESCRIPTION
[0024] Before proceeding with the detailed description, it is to be
appreciated that the present teaching is by way of example only,
not by limitation. The concepts herein are not limited to use or
application with a specific system or method for route planning
whether in a maritime environment or other environment. Thus,
although the instrumentalities described herein are for the
convenience of explanation, shown and described with respect to
exemplary embodiments, it will be appreciated that the principles
herein may be applied equally in other types of systems and methods
involving missile and/or rocket stabilization at low speeds.
[0025] Turning now to the figures, and more specifically to FIG. 1,
there is shown a missile 100 having a body 102 with a forward
portion 104 and an aft portion 106 and a longitudinal center
portion 108 therebetween, the longitudinal center portion generally
circumferential about longitudinal axis 110. The missile also has
tail fins 112 which are aligned to extend substantially parallel to
longitudinal axis 110. Moreover, as the longitudinal axis 110 is
parallel to the Z-axis, each tail fin 112 is also aligned parallel
to the Z-axis, the alignment represented by dotted line 120 which
is clearly parallel to the longitudinal axis 110. As such the
opposing sides 114, 116 of each tail fin 112 provide aerodynamic
control surfaces for articulation and missile flight control at
high velocity.
[0026] Missile 100 has been fitted with detachable aerodynamic
missile control system 130. In at least one embodiment, the
detachable aerodynamic missile control system 130 includes a grid
fin interstage assembly ("GFIA") 132, having a housing 134 and at
least one grid fin 136. As shown in the illustrations, at least one
grid fin 136 extends outwardly from the housing 134. The housing
134 and at least one grid fin 136 as the GFIA 132 are detachably
coupled in at least one embodiment to the aft portion 106 of the
missile 100 by a coupler 138.
[0027] In at least one alternative embodiment, not shown, GFIA 132
is coupled to the missile between the forward portion 104 and the
aft portion 106 of the missile 100. In such an embodiment the
housing of GFIA 132 may clamp around the exterior of the missile
100 rather than fitting in line with it as shown in the
accompanying figures.
[0028] At least one purpose of the GFIA 132 is to provided drag
upon the missile shortly after launch, i.e., while the missile 100
has a low velocity. At least one additional purpose of the GFIA 132
is to provide additional lift and control surfaces to further
missile stability while the missile 100 has a low velocity. As in
the absence of the FGIA 132 the missile is subject to pitch
instability, coupling to the aft portion 106 is generally
preferred. This lift and drag increase permits missile
stabilization and pitch-over to occur more rapidly. Where the GFIA
132 employs grid fins 136 that are operable to articulate, the
imparted lift and drag may be controlled to further reduce the time
to missile pitch over.
[0029] As noted above, for a typical missile the tail fins 112 are
intended to provide control at high speed. In addition to imparting
drag upon the missile 112 to induce pitch over more rapidly, the
grid fins 136 may also impart lift and thus provide additional
stability when the orientation of the missile 100 is such to
present an angle of attack to the component surfaces of the grid
fin 136.
[0030] As shown in FIG. 1, in at least one embodiment there are at
least four grid fins of which 136A.about.136D are exemplary.
Whereas the tail fins 112 are substantially parallel to the
longitudinal axis 110, the grid fins 136 are transverse to the
housing 134, and more specifically transverse to the longitudinal
axis 110. Specifically, the primary opposing sides 140, 142 are
transverse to longitudinal axis 110 as they are parallel to the
X-axis. See dotted lines 150, 152 representing the alignment of
opposing sides 140, 142.
[0031] Each grid fin 136 provides a plurality of apertures 144,
between opposing sides 140 and 142. In at least one embodiment
these apertures 144 are arranged in a grid pattern. Whereas the
grid fin 136 itself is transverse to the longitudinal axis 110, the
apertures 144 are generally parallel to the longitudinal axis 110.
In other words the grid fin 136 is a lattice structure, i.e. a
non-solid surface which disrupts the air flow about the missile 100
and induces lift and drag upon the missile 100 and in at least one
embodiment, at the aft of the missil
[0032] In at least one embodiment, GFIA 132 also provides an
articulation control system 132 operable to permit articulation of
the grid fins 136A-136D. When GFIA 132 is coupled to the missile
100 by coupler 138, articulation control system 132 is also coupled
to the missile control system 132. As such, missile control system
132 may articulate each grid fin 136 to further enhance and achieve
low speed stability and orientation. Such articulation is
illustrated by arrow 148A with respect to grid fin 136A and arrow
148B with respect to grid fin 136B.
[0033] An embodiment of the detachable aerodynamic missile control
system 130 is shown separately and enlarged in the perspective
views of FIGS. 2 and 3, and the face view of FIG. 4. An alternative
embodiment of the detachable aerodynamic missile control system 130
wherein the grid fin is a single grid fin extending
circumferentially about the housing is shown in the perspective
view of FIG. 5 and the face view of FIG. 6.
[0034] With respect to FIGS. 1-8 it is appreciated that GFIA 132 is
constructed to be retrofit to existing missiles, such as for
example SM6 MR (Standard Missile 6 Medium Range), ESSM (Evolve Seas
Sparrow Missile), RAM (Rolling Airframe Missile), SM3 (Standard
Missile 3), SDB (Small Diameter Bomb), AMRAAM (Advanced Medium
Range Air to Air Missile), AIM-9X (Air Intercept Missile 9X), and
HARM (High Speed Anti-Radiation Missile), where low speed control
authority is desirable. The GFIA 132 may also be coupled to new
missile systems.
[0035] As may be appreciated in FIG. 2, each grid fin
136A.about.136D has side surfaces, of which surface 220 is
exemplary. In addition each aperture 144 has at least one side
surface, of which side surfaces 222 and 224 are exemplary. For each
grid fin, these surfaces 220, 222, 224 provide additional surface
area that collectively may provide increased lift when the angle of
the missile 100 is such that one or more of these surfaces present
an angle of attack.
[0036] With respect to FIG. 2, for embodiments wherein the GFIA 132
is attached to the aft portion 106 of a missile, the housing is
appreciated to have a hollow passage 200 such that the rocket plume
will pass through without impingement. In at least one embodiment,
the internal passage 200 is a nozzle extension cone that receives
and further directs the plume through the GFIA 132. As the grid
fins 136 are disposed about the outside of the housing 134 and
therefore are not subjected to the plume, modifications to the
propellant and/or fabrication of the grid fins 136 from plume
resistant materials is not required.
[0037] Gimbals, gear train assemblies, articulation devices and/or
drive train devices are commonly used to control the orientation of
missile tail fins and are commercially available. In at least one
embodiment, a commercially available drive train device
conventionally employed to control tail fins is adapted to control
the grid fins 136. In at least one embodiment the drive train is an
integral component to the supports 202 connecting each grid fin 136
to the housing 134. A communication link, such as articulation
control system 146 provides a point of connection to link the drive
train for each grid fin 136 with the missile control system.
[0038] As GFIA 132 is intended to provide lift and drag induced
attitude and pitch stability for the missile 100 at low velocity,
it will also impinge upon missile performance at high velocity. As
such, GFIA 132 is constructed as an interstage element to be
released from the missile 100. More specifically, once stability of
the missile has been reached at high subsonic speeds on the
established flight trajectory where the traditional missile
guidance system and components are capable of effectuating missile
stability and control, the coupler 138 is released and the GFIA 132
is released for separation and disposal.
[0039] In at least one embodiment, the coupler 138 is a V-band
clamp. More specifically, in at least one embodiment the coupler
138 is a Marman clamp engagement system as is known and used in the
missile arts. It is further understood and appreciated that GFIA
132 may provide a second coupler (not shown) at the aft section of
the GFIA 132 such that a nozzle extension cone or other interstage
assembly may be coupled to the aft portion of GFIA 132 opposite
from the missile 100.
[0040] As may be appreciated with respect to FIG. 2, whereas a
solid control surface would redirect air and/or block the flow of
air, air, represented as arrows 210 is permitted to pass through
the apertures 144 of the grid fins 136. By utilizing a grid of
apertures 144 a known and generally consistent lift coefficient is
provided. The size and configuration of the apertures 144 is
selected based on design parameters so as to provide desired drag
and lift coefficients less and more than a solid surface
respectively.
[0041] As shown with respect to both FIGS. 2 and 3, in at least one
embodiment the grid fins are selectively movable between a first
stowed position (shown in FIG. 3) and a second deployed position
(shown in FIG. 2). As shown in FIG. 3, in at least one embodiment
this first stowed position is lying down and extending forward
along the housing 134. When the missile is launched, the forward
inertia and passage of air may help to deploy the grid fins 136
from their stowed position to their deployed position. Spring
mechanisms within or adjacent to the supports 202 may also be
employed to assist with the deployment of the grid fins 136.
[0042] As the grid fins 136 permit air to pass through them, there
is a relatively small hinge moment involved given the relative
apparent size of each grid fin 136. As such supports 202 should not
require elaborate measures or design characteristics to support the
grid fins during the low velocity period of travel wherein the grid
fins 136 are employed.
[0043] FIG. 4 provides a face on view of the GFIA 132 which further
permits appreciation of the relative simplicity of the GFIA 132 as
an element of the detachable aerodynamic missile control system
130. In at least one embodiment, the grid fins 136 are composed of
metal or composite materials as are typically utilized in missile
design and fabrication.
[0044] With respect to the above descriptions and discussion
regarding FIGS. 1 through 4 it is appreciated that GFIA 132
provides a plurality of grid fins 136. As shown in FIGS. 5 and 6,
in at least one embodiment, the grid fin is a single grid fin 136E
extending circumferentially about the housing 134. As in the case
of the plurality of grid fins, e.g. 136A.about.136D discussed
above, the circumferential grid fin 136E extends transversely from
the housing 134, and more specifically transversely to the
longitudinal axis 110 of the housing 134, see FIG. 5.
[0045] More specifically, circumferential grid fin 136E has primary
opposing sides 500, 502 transverse to longitudinal axis 110 as they
are parallel to the X-axis. Again, as described above with respect
to grid fins 136A.about.136D, the circumferential grid fin 136E
provides a plurality of apertures 144 and as such does not provide
a substantial solid surface when viewed face on as in FIG. 6.
[0046] As in an embodiment providing multiple grid finds
136A.about.136D, the apertures 144 of circumferential grid fin 136E
enable the circumferential grid fin 136E to provide additional lift
and drag. This lift and drag permits improved missile stability at
low velocity and permits pitch over to advantageously occur quickly
after launch.
[0047] As many conventional missiles are launched from a canister,
it is not uncommon for the typical flight control surfaces such as
tail fins to fold against the body of the missile 100 when the
missile 100 is within such a canister or otherwise in storage. As
shown and described above with respect to FIGS. 2 and 3, for at
least one embodiment utilizing a plurality of grid fins 136, the
grid fins 136 are selectively movable between a stowed position and
a deployed position. In FIG. 1, GFIA 132 is shown coupled to
missile 100 such that the grid fins 136A.about.136D are aligned
between deployed tail fins 112.
[0048] FIG. 7 provides a side illustration of missile 100 disposed
within a canister 700. Tail fins 112 are shown folded against the
body 102, and grid fins 136 are shown folded over the tail fins
112. Upon launch, as soon as the missile 100 clears the canister
700, the grid fins 136A.about.136D will deploy as shown in FIG. 8.
As shown in FIG. 8, in at least one embodiment, the tail fins 112
may remain against the body 102 as missile velocity is sub-optimum
for their effectiveness. In an alternative embodiment, the tail
fins 112 may deploy as well. Having discussed the structural
embodiments of the detachable aerodynamic missile stabilizing
system 130, the method of use will now be described with reference
to the above figures and the flow diagram of FIG. 9. It will be
appreciated that the described events and method of use need not be
performed in the order in which it is herein described, but that
this description is merely exemplary of one method of operation in
accordance with the present invention.
[0049] In at least one embodiment, the method of providing
detachable aerodynamic missile stabilization commences with the
providing of a GFIA 132 as discussed above, block 900. In at least
one embodiment the GFIA 132 is as described with respect to FIGS.
2, 3, 4, 7 and 8 in that it has four grid fins 136A.about.136B. In
at least one alternative embodiment, the GFIA 132 is as described
with respect to FIGS. 5 and 6 in that it has a single
circumferential grid fin 136E.
[0050] The provided GFIA 132 is coupled to the aft portion of the
missile, as in block 902. It is appreciated that GFIA 132 is
intended to be retrofit to existing missiles and does not require
modification of the existing missile for the coupling to be
performed. It is further appreciated that the providing of the GFIA
132 and coupling to the missile 100 may be performed well in
advance of the missile being placed in the canister or other launch
environment. Indeed, GFIA 132 coupling may be performed in the
field when and as deemed necessary to respond to perceived local
threats, or it may be performed at a factory before deployment.
[0051] In at least one embodiment, the coupling is accomplished
with the use of a Marman clamp engagement system. In at least on
optional embodiment, wherein the grid fins are operable to
articulate, the coupling of the GFIA 132 to the missile also
couples the grid fin articulation system to the missile flight
control system, optional block 904.
[0052] Following the missile launch, the grid fins 136 deploy and
impart lift and drag to the missile. The grid fins 136 thereby
stabilize the missile and permit accelerated pitch over and flight
path alignment for target acquisition before the missile has
reached high flight speed, block 906. When an embodiment of GFIA
132 providing at least four grid fins 136 is utilized, upon launch
the grid fins will deploy from the stowed position shown in FIG. 7
to the operable position shown in FIG. 8.
[0053] For the optional embodiment utilizing articulating grid
fins, the missile control system is operable to articulate the grid
fins 136 and thereby further control the induced lift and drag so
as to provide enhanced low speed aerodynamic stabilization. In at
least one embodiment the grid fins are slaved to the traditional
tail fins 112, which is to say that they move in coordinated
harmony. In at least one alternative embodiment, the missile
control system is operable to articulate the grid fins independent
from the tail fins.
[0054] When the missile has performed the desired pitch over and is
transitioning to high speed flight, the GFIA 132 is released, block
908. By releasing GFIA 132, missile 100 is able to reduce weight
and utilize its intended high speed flight capabilities without
encumbrance.
[0055] As GFIA 132 does not impede the plume, it is understood and
appreciated that if desired, an additional interstage unit could be
attached to the aft end of the GFIA 132, such as for example an
additional booster motor or a jet vain control system.
[0056] With respect to FIGS. 1-8, it is understood and appreciated
that GFIA 132, and specifically the grid fin(s) 136 are not
necessarily rendered to scale with respect to missile 100. Rather,
especially in the case of FIG. 1 the relative size of the grid fins
136 may be viewed as exaggerated for ease of illustration and
discussion.
[0057] Changes may be made in the above methods, systems and
structures without departing from the scope hereof. It should thus
be noted that the matter contained in the above description and/or
shown in the accompanying drawings should be interpreted as
illustrative and not in a limiting sense. The following claims are
intended to cover all generic and specific features described
herein, as well as all statements of the scope of the present
method, system and structure, which, as a matter of language, might
be said to fall therebetween.
* * * * *