U.S. patent number 3,886,884 [Application Number 05/302,559] was granted by the patent office on 1975-06-03 for control system for hydrofoil.
This patent grant is currently assigned to The Boeing Company. Invention is credited to Irving A. Hirsch, Donald R. Stark.
United States Patent |
3,886,884 |
Stark , et al. |
June 3, 1975 |
CONTROL SYSTEM FOR HYDROFOIL
Abstract
A control system for a hydrofoil of the type having forward and
aft submerged foils for supporting the craft while foil borne. In
the preferred embodiment of the invention, separate pairs of
starboard and port control flaps are provided on the aft foil;
while the forward foil, also provided with flap means, is carried
at the lower end of a pivoted strut which acts as a rudder. The
system incorporates a high degree of redundancy for safety and
failproof operation. Craft motions are sensed by gyroscopes and
accelerometers which produce signals for controlling the flaps to
provide smooth riding characteristics and a minimum of acceleration
on passengers and crew for all seaway conditions. Turning of the
craft is achieved by initially activating the flaps to bank the
craft about its roll axis, followed by a rudder action. Pitch is
controlled by both the forward and aft flaps; motions about the
roll axis are controlled by the aft flaps only; while the height of
the craft while foil-borne is controlled by the forward flap means
only.
Inventors: |
Stark; Donald R. (Seattle,
WA), Hirsch; Irving A. (Bellevue, WA) |
Assignee: |
The Boeing Company (Seattle,
WA)
|
Family
ID: |
23168263 |
Appl.
No.: |
05/302,559 |
Filed: |
October 31, 1972 |
Current U.S.
Class: |
114/275; 318/588;
244/180 |
Current CPC
Class: |
B63B
39/06 (20130101); G05D 1/0875 (20130101); B63B
1/286 (20130101) |
Current International
Class: |
B63B
39/00 (20060101); B63B 39/06 (20060101); B63B
1/28 (20060101); B63B 1/16 (20060101); G05D
1/08 (20060101); B63b 001/28 () |
Field of
Search: |
;114/66.5H ;235/150.2
;244/77R,77D,77E,77G,77M ;318/564,584,585,588 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Blix; Trygve M.
Assistant Examiner: Kunin; Stephen G.
Attorney, Agent or Firm: Brown, Murray, Flick &
Peckham
Claims
What is claimed is:
1. In a control system for a hydrofoil craft having forward and aft
foils, the combination of separate port and starboard flap means on
at least one of said foils, rudder means associated with said
foils, means for generating a command signal for turning said
craft, means responsive to said command signal for initially
actuating said separate flap means to cause said craft to bank
about its roll axis in the direction of a desired turn, means for
sensing banking of the craft about its roll axis in response to
actuation of the separate flap means, and apparatus coupled to said
sensing means for thereafter actuating the rudder means to turn the
craft in said direction of desired turn.
2. The control system of claim 1 wherein said separate port and
starboard flap means are on the aft foil, and including control
flap means on the forward foil, the rudder means comprising a strut
extending downwardly from the bow of the craft and carrying at its
lower end said forward foil.
3. The control system of claim 1 wherein said command signal is
generated by a helm and wherein said means for sensing banking of
the craft about its roll axis comprises a gyroscope adapted to
produce an output signal which varies as a function of the roll
angle of said craft.
4. The control system of claim 3 including means for producing two
identical and redundant command signals from said helm, means for
producing two identical and redundant signals from the gyroscope,
and means for applying both roll signals and both command signals
to both of said derivative amplifiers.
5. The control system of claim 1 wherein said means for sensing
banking of the craft about its roll axis includes a gyroscope for
producing an electrical roll signal which varies as a function of
the roll angle of said craft, and including derivative amplifier
means responsive to said command signal and to said electrical
signal produced by the gyroscope for generating an electrical
signal for controlling said separate flaps.
6. The control system of claim 5 wherein said derivative amplifier
means includes two derivative amplifiers both responsive to said
command signal and to said electrical signal produced by the
gyroscope, the output of one of said derivative amplifiers being
used to control the port flap means and the output of the other
derivative amplifier being used to control the starboard flap
means.
7. The control system of claim 1 wherein said means for sensing
banking of the craft about its roll axis also senses roll of the
craft about its roll axis due to an undulating motion of the water
beneath the craft, said apparatus for actuating the rudder means
being effective to rotate the rudder means in response to such
undulating motion as well as to banking of the craft in response to
a turning command signal.
8. The control system of claim 1 including a yaw rate gyro mounted
on said craft, and means operatively connecting said yaw rate gyro
to said rudder means to limit the rate of turning of the rudder
means as a function of yaw rate.
9. The control system of claim 8 including a lateral accelerometer
mounted on said craft, and means operatively connecting said yaw
rate gyro to said rudder means to limit the rate of turning of the
rudder means as a function of lateral acceleration of the
craft.
10. The control system of claim 9 wherein the rudder means is
positioned at the bow of the ship above said forward foil.
11. In a control system for a hydrofoil craft having forward and
aft foils, the combination of control flap means on the forward
foil, flap means on the aft foil, means for sensing the height of
said craft above the surface of the water when it is foil-borne and
for producing an electrical signal proportional to said height,
means for producing an electrical signal proportional to desired
height of said craft above the water, means for comparing said
first and second electrical signals to derive an error signal when
the first and second signals are not the same, and means responsive
to said error signal for controlling the position of only the
control flap means on the forward foil to cause the hydrofoil craft
to rise or descend until said error signal is zero.
12. The control system of claim 11 including vertical accelerometer
means mounted at the bow of said craft for producing an electrical
signal proportional to vertical acceleration of the bow, and means
responsive to said last-named electrical signal for varying the
position of said control flap means on the forward foil as a
function of vertical acceleration thus sensed.
13. The control system of claim 11 including gyroscope means for
producing an electrical signal which varies as a function of the
pitch angle of said craft, and means responsive to said last-named
electrical signal for varying the position of the flap means on
said forward foil.
14. In a control system for a hydrofoil craft having forward and
aft foils, the combination of control flap means on the forward
foil, separate port and starboard flap means on the aft foil, means
including a gyroscope for producing an electrical signal which
varies as a function of both the pitch angle of said craft as well
as a function of the rate of change of said pitch angle, means
responsive to said electrical signal for controlling both the
control flap means on the forward foil as well as the flap means on
the aft foil to counteract any pitching action of the craft, an aft
port vertical accelerometer above the aft port foil, an aft
starboard vertical accelerometer above the aft starboard foil,
means operatively connecting the aft port vertical accelerometer to
the port flap means on the aft foil whereby the port flap means
will be actuated to counteract vertical acceleration forces on the
port side of the craft, and means operatively connecting the aft
starboard vertical accelerometer to the starboard flap means on the
aft foil whereby the aft starboard flap means will be actuated to
counteract vertical acceleration forces on the starboard side of
the craft.
15. In a control system for a hydrofoil craft having forward and
aft foils, the combination of flap means on the forward foil,
separate pairs of port and starboard flaps on the aft foil, a first
pair of hydraulic actuators for actuating one port and one
starboard flap of each pair, a second pair of hydraulic actuators
for actuating the other flap of each pair of port and starboard
flaps, a single hydraulic actuator for the forward flap means, a
first source of fluid under pressure for actuating the first pair
of hydraulic actuators, a second source of fluid under pressure for
actuating the second pair of hydraulic actuators, and shuttle valve
means for connecting said single actuator for the forward flap
means to either the first or second source of fluid under
pressure.
16. The control system of claim 15 including a rudder for the
hydrofoil, a single actuator for actuating said rudder, and shuttle
valve means for connecting said single rudder actuator to either
the first or second source of fluid under pressure.
17. In a control system for a hydrofoil craft having forward and
aft foils, the combination of separate port and starboard flap
means on said aft foils, each of said separate starboard and port
flap means including an inboard and an outboard flap, separate
actuators for the inboard and outboard flaps of each flap means,
separate power sources for the actuators for the inboard and
outboard flaps respectively, means for generating a command signal
for turning said craft, means responsive to said command signal for
initially actuating the actuators for said separate flap means to
cause said craft to bank about its roll axis in the direction of a
desired turn, means for sensing banking of the craft about its roll
axis in response to actuation of the actuators for the separate
flap means, and apparatus coupled to said sensing means for
thereafter actuating the rudder means to turn the craft in said
direction of desired turn.
Description
BACKGROUND OF THE INVENTION
As is known, in a hydrofoil seacraft of the submerged foil-type,
the hull of the craft is lifted out of the water by means of foils
which are carried on struts and pass through the water beneath the
surface thereof. In passing through the water, and assuming that
sufficient speed is attained, the foils create enough lift to raise
the hull above the surface and, hence, eliminate the normal
resistance encountered by a ship hull in passing through the
water.
In the usual case, there are forward and aft foils, both provided
with control flaps similar to those used on aircraft. The other
essential element is the rudder which pierces or is submerged
beneath the surface of the water and is either forward or aft of
the craft, depending upon its design. In most hydrofoils, the flaps
are used primarily to cause the craft to ascend or descend and to
control the craft about its pitch and roll axes; however they can
also be used in combination with the rudder to bank the ship about
its roll axis during a turn.
The flaps are also used to stabilize the craft during movement on
water. For example, pitching or rolling motions can be minimized by
proper counterbalancing movement of the flaps. In the past,
hydrofoils have been provided wherein a vertical gyro is employed
to sense roll and pitch, together with sensors for producing
electrical signals proportional to the height of the hull above the
surface as well as vertical and lateral acceleration of the craft.
These electrical signals are utilized in circuitry for controlling
the flaps to provide a smooth ride through the sea.
While prior art control systems of this general type are at least
partially effective, many leave something to be desired in terms of
response characteristics and smooth riding capability.
SUMMARY OF THE INVENTION
In accordance with the present invention, a new and improved
control system for a hydrofoil with submerged foils is provided
which enables a higher degree of safety than prior art control
systems while at the same time providing for smoother operation in
rough seas as well as better response characteristics.
The control system of the invention provides continuous control of
the foil-borne craft by sensing craft motions, combining the motion
signals with manual pilot commands, and converting these signals
into appropriate control surface deflections. In the hydrofoil of
the invention, the control surfaces consist of trailing edge flaps
on forward and aft foils together with a swiveled forward strut or
rubber. The port and starboard flap segments on the forward foil
operate in synchronism and are connected to a single hydraulic
actuator. The aft foil has four trailing edge flaps, two on the
port side and two on the starboard side. Each flap is driven by a
separate hydraulic actuator. The automatic control system or
computer operates upon sensed motions and manual imputs to provide
commands to the control surface servos.
The inputs to the control system are obtained from manual input
commands as well as sensed craft motions. The manual inputs to the
system consist of a foil depth command which establishes the
desired foil depth, a helm signal which provides turning commands,
and a heading hold switch which engages or disengages the automatic
heading hold function. The sensors consist of one or two vertical
gyros which sense pitch angle and roll angle, a height sensor which
can be radar or ultrasonic and which measures the distance from a
point on the bow to the water surface, a yaw rate gyro, three
vertical accelerometers, and one forward lateral accelerometer. As
mentioned above, the signals from these sensors are combined with
the manual input commands to control the flaps and maintain smooth
riding conditions while maintaining the craft on a desired
course.
One important feature of the invention resides in the fact that in
turning the craft, the trailing edge flaps on the aft foils are
initially actuated to bank the hydrofoil or cause it to roll. This
roll is then sensed to vary rudder position, which results in a
much larger roll control margin during turning.
In another aspect, the control system of the invention is such that
the height of the hydrofoil above the surface of the water is
controlled by flaps on the forward foil only; while pitch is
controlled by flaps on both the front and back foils.
Another important aspect of the invention resides in the provision
of redundant hydraulic and electrical control systems. Two
hydraulic pumping systems are provided, either of which can be
connected through shuttle valves to the forward flaps and rudder.
One aft flap on each of the starboard and port sides is connected
to one hydraulic system; while the other aft flap on each side is
connected to the other hydraulic system such that partial aft flap
effectiveness is achieved even if one hydraulic system should fail.
Similarly dual roll signals and dual helm signals are generated.
The dual roll angle signal may be derived from two separate
vertical gyros, or from two separate roll signal pickoffs on a
single vertical gyro. These roll and helm signals are both applied
to separate derivative amplifiers which control the port and
starboard aft flaps, respectively.
Another important aspect of the invention involves the generation
of acceleration signals which are used for ride smoothing. A
lateral acceleration and vertical acceleration signal are developed
at the vicinity of the forward strut base (top of strut) and are
applied to the rudder and forward flaps, respectively. The forward
vertical acceleration signal is applied to an electronic shaping
network which generates a pseudo integral of acceleration signal in
addition to the acceleration signal itself.
Finally, an important feature of the invention is the generation of
vertical acceleration signals on both the port and starboard sides
of the craft. These are applied to the respective aft port and aft
starboard flap control systems to achieve a smoother ride in a
seaway.
The above and other objects and features of the invention will
become apparent from the following detailed description taken in
connection with the accompanying drawings which form a part of this
specification, and in which:
FIG. 1 is a side view of the hydrofoil of the invention;
Fig. 2 is a bottom view of the hydrofoil of FIG. 1 showing the
positions of the flaps on the forward and aft foils of the craft as
well as the positions of the various motion sensors;
FIG. 3 is a schematic illustration of the control surface hydraulic
actuation system of the invention;
FIG. 4 is a perspective view of the hydrofoil of the invention
showing its relationship to its pitch, roll and yaw axes;
FIG. 5 is a simplified block diagram of the overall control system
for the hydrofoil of the invention; and
FIGS. 6A-6C, when placed side-by-side, comprise a detailed block
diagram of the control system of the invention for the forward and
aft flaps as well as the forward rudder.
With reference now to the drawings, and particularly to FIG. 1, the
hydrofoil shown includes a conventional hull 10 which can be
provided with a propeller or the like and an inboard motor, not
shown, in order that it can traverse the surface of water as a
conventional displacement ship. Pivotally connected to the hull is
a forward, swiveled strut or rudder 12 which is rotatable about a
vertical axis in order to steer the craft in the foil-borne mode of
operation. The rudder 12 can also be swiveled upwardly in the
direction of arrow 14 to clear the surface of the water when the
craft is operating as a conventional displacement ship. Carried on
the lower end of the rudder 12 is a forward foil 16 (FIG. 2) which
carries at its trailing edge control surfaces or flaps 18 which are
interconnected and operate in synchronism. In this respect, it can
be said that there is a single forward flap means.
In the aft portion of the craft, struts 20 and 22 are pivotally
connected to the hull 10 about an axis 21. The struts 20 and 22 can
be rotated downwardly into the solid-line position shown in FIG. 1
for foil-borne operation, or can be rotated backwardly in the
direction of arrow 24 and into the dotted-line position shown when
the craft operates as a conventional displacement ship. Extending
between the lower ends of the struts 20 and 22 is an aft foil 26
which carries, at its trailing edge, two starboard flaps 28 and 30
and two port flaps 32 and 34. As will be seen, each set of
starboard flaps and each set of port flaps normally operate in
synchronism; however each flap in the port or starboard pair is
provided with a separate hydraulic actuation system as well as a
separate electrical servo system for redundancy and safety purposes
so that one can operate even though the electrical or hydraulic
system for the other should fail.
Carried between the struts 20 and 22 and pivotally connected to the
hull 10 about axis 21 is a gas turbine - water jet propulsion
system which provides the forward thrust for the craft during
foil-borne operation. It should be understood, however, that a
propeller or other type of thrust-producing device can be used in
accordance with the invention.
With the rudder 12 and struts 20 and 22 retracted, the craft may
transit in the hull-borne mode. Assuming that the control system
about to be described is inactive, the strut-foil system in its
retracted position modifies the ship sea state response similar to
the condition of bilge boards and skegs. The struts provide roll
damping and increase the ship's directional stability. The foil
system increases damping of the ship's pitch. At higher hull-borne
speeds where the control flaps become effective, activation of the
automatic control system provides a hydrofoil ship with a sea state
response superior to a gyro-stabilized conventional ship.
In the foil-borne mode of operation, both the rudder 12 with its
foil 16 and struts 20 and 22 with their foil 26 are rotated
downwardly into the solid-line positions shown in FIG. 1 and locked
in position. In order to become foil-borne, the pilot sets the
desired foil depth in a manner hereinafter described and the
throttles are advanced. The ship, therefore, will accelerate and
the hull will clear the water and continue to rise until it
stabilizes at the commanded foil depth. The normal landing
procedure is to simply reduce the throttle setting, allowing the
ship to settle to the hull as the speed decays. During foil-borne
operation in normal water conditions, the hull does not contact the
water surface and hull impacts do not occur. At higher sea state
operations, two types of hull impacts can occasionally occur. The
first results from "cresting" higher waves. In this type of impact,
the hull contacts and furrows the wave crest without loss of foil
lift. The second type of hull impact results from "broaching" the
foil in the trough of a wave. The foil loses lift until
hydrodynamic flow is again reestablished, and the hull may or may
not impact the wave surface. The hull is designed to retain
water-tight integrity for both types of impact originating from any
flying height and for all possible ship orientations. Utilizing the
control system of the invention hereinafter described in detail,
the resulting vertical motions and accelerations are not hazardous
to the crew or passengers.
Mounted on the hull, as shown in FIG. 2, are sensors for producing
electrical signals indicative of craft motion. Thus, at the bow of
the craft is an ultrasonic height sensor 36 which produces an
electrical signal proportional to the height of the bow above the
surface of the water during foil-borne operations. Also at the bow
of the ship is a forward vertical accelerometer 35 which produces
an electrical signal proportional to vertical acceleration. Mounted
in the hull at the top of the rudder 12 is a lateral accelerometer
38 which, of course, produces an electrical signal proportional to
lateral or sideways acceleration of the craft. Mounted on the top
of the starboard strut 20 is an aft starboard vertical
accelerometer 40; and mounted at the top of the port strut 22 is an
aft port vertical accelerometer 42. A vertical gyro 44 or a pair of
vertical gyros is mounted in the craft, preferably near the center
of gravity, for producing signals proportional to the angle of the
craft with respect to vertical about its pitch and roll axes.
Finally, a yaw rate gyro 45 is provided in the forward portion of
the craft.
With reference now to FIG. 3, the hydraulic system for actuating
the forward and aft flaps is shown. The hydraulic system provides
hydraulic power from two separate hydraulic power sources or
systems A and B driven by separate prime movers to actuate the
control surfaces or flaps. The aft outboard flap and forward flap
actuators are normally driven from system A; while the aft inborad
flap and rudder actuators are normally driven from system B. A
shuttle valve 46 under the control of manual switches in the
pilothouse can transfer the forward flap actuator 48 from system A
to system B in the event of a loss of pressure in system A. A
similar shuttle valve 49 connected to the actuator 50 for rudder 12
can transfer the rudder actuator from system B to system A in the
event of loss of pressure in system B. The shuttle valves 46 and
49, as well as different hydraulic systems for inboard and outboard
aft flaps, provide the ship with a fail-safe operational capability
for any potential single hydraulic system failure.
The aft hydraulic system shown in FIG. 3 includes hydraulic
actuators 52 and 54 for the outboard aft flaps 28 and 32,
respectively. The actuators 52 and 54 are connected to hydraulic
system A. Similarly, the aft inboard flaps 30 and 34 are connected
to hydraulic actuators 56 and 58, respectively, which are powered
by hydraulic system B. Thus, even though one of the two hydraulic
systems A or B should fail, at least one of the flaps on both the
port and starboard sides will still operate. Normally, both the
inboard and outboard flaps on either side of the craft operate
simultaneously and in synchronism, the dual sets of flaps being
provided primarily for redundancy and safety purposes.
Motions of the craft about its roll, pitch and yaw axes can perhaps
best be understood by reference to FIG. 4. The roll axis is
identified by the reference numeral 60. Any movement about this
axis will be sensed by the vertical gyro 44 as well as the aft
accelerometers 40 and 42. The gyro 44 will produce an output signal
proportional to the amount of degree of roll; while the
accelerometers 40 and 42 will produce signals proportional to the
angular acceleration about the roll axis. The pitch axis in FIG. 4
is identified by the reference numeral 62. Any movement about this
axis will be sensed by the vertical gyro 44 as well as both the
forward and aft accelerometers 35, 42 and 40. Finally, the yaw axis
is identified by the reference numeral 64 in FIG. 4; and any
movement about this axis will be sensed by the yaw rate gyro 45 as
well as the lateral accelerometer 38.
In the control system of the invention, the height of the hull
above the water is controlled solely by the forward flap 18. In
order to raise the hull from the surface of the water, the forward
flap is rotated downwardly, thereby increasing the lift afforded by
the forward foil 16 and causing the hull to elevate out of the
water. In order to eliminate or minimize pitching motions about the
pitch axis 62, both the forward and aft flaps are employed.
However, the forward and aft flaps operate in opposite directions
to correct any pitch condition. For example, if the bow of the
craft should dip, the forward flap 18 will be rotated downwardly;
while the aft flaps 28-32 will be rotated upwardly to produce a
moment counterbalancing the pitching moment caused by waves or the
like. Compensation for movement about the roll axis is achieved
solely by the aft flaps 28-32; however in this case the starboard
flaps move in a direction opposite to the port flaps to correct for
undesired rolling motion. In turning the craft, the aft flaps are
initially positioned to cause the craft to bank about its roll
axis; whereupon the rudder 12 is rotated to follow through. As was
explained above, this gives a much better and smoother turning
action since the correct roll inclination is achieved before any
substantial turning of the craft occurs via the rudder.
A simplified block diagram of the control system of the invention
is shown in FIG. 5, it being understood that this is not the actual
control system but included herein to facilitate and simplify the
explanation of the manner in which the craft is controlled. The
pilothouse controls include a signal on lead 66 from a depth signal
generator 68. Additionally, a turn signal on lead 70 is derived
from the helm 72 in the pilothouse. As will be seen from the
detailed description of the system hereinafter given, the helm
signal can be derived either from the helm itself or from a heading
hold circuit. In the latter case, the signal is derived by
comparison of actual ship heading with a compass heading or the
like; and if the two are not the same, then an error signal is
derived for commanding a turn until the desired and actual headings
are the same.
As can be seen from FIG. 5, the signal from the height sensor 36
proportional to actual height is compared with the desired height
signal on lead 66 in a depth error amplifier 74. If the two signals
fed to the amplifier 74 are not the same, then a signal is
developed on lead 76 and applied to a forward flap servo system 78
which causes the forward flap 18 to rotate downwardly or upwardly,
depending upon whether the hull should rise or descend. When it is
desired to turn the craft about its yaw axis, a signal on lead 70
proportional to helm position from null is applied to a roll
derivative amplifier 80 where it is compared with a signal on lead
82 from vertical gyro 44 proportional to the roll angle about axis
60 (FIG. 4) relative to vertical.
At the beginning of a turn, and assuming that the water through
which the hydrofoil is traveling is smooth, the signal on lead 82
will be zero, or substantially zero. The roll derivative amplifier
compares the signal on lead 82 with that on lead 70; and assuming
that the two are not the same, as is the case for the conditions
just described, then an output signal appears at the output of the
amplifier 80 and is applied to inboard and outboard port flap
servos 84 and 86. At the same time, it is applied in an inverted
form to the inboard and outboard starboard flap servos 88 and 90.
The result, of course, is that one set of aft flaps will rotate
downwardly while the other set rotates upwardly to cause the craft
to bank about its roll axis. This action will continue until the
angle of roll as sensed by the gyro 44 is such as to generate a
signal which nulls out the helm signal on lead 70. However, at the
same time, the signal on lead 82 proportional to roll angle is also
applied to the rudder servo 92. This causes the rudder 12 to rotate
after the craft begins to bank about its roll axis, causing the
craft to turn in the direction to which the craft has been banked.
Thus, the craft banks to the right in response to a signal from
helm 72, the rudder 12 will thereafter rotate to steer the craft to
the right. As was explained above, this gives a much smoother turn
for all sea conditions encountered with a minimum of acceleration
forces on the passengers and crew.
Stated in other words, the system is such that the craft will
assume the correct roll angle before banking. This may not occur if
the rudder is rotated immediately as, for example, when the craft
banks to the left because of sea conditions when a right turn is
initiated.
As the ship turns, the yaw rate gyro 45 will produce a signal on
lead 94 proportional to the rate of turning about the yaw axis; and
this is utilized in the rudder servo 92 to limit the rate of
turning. The same is true of the forward lateral accelerometer 38
which produces a signal on lead 96 proportional to lateral
acceleration. This is applied to the rudder servo 92 in order to
limit the lateral acceleration. Thus, if the craft is turning into
a position where it is broadside to the direction of a strong wind
and accompanying waves, the yaw rate gyro 45 and lateral
accelerometer 38 will sense the thrust on the craft and limit the
rate of turning. Of course, after the desired turn is executed and
the helm 72 rotated back to its center or null position, the signal
on lead 70 decreases back to zero; whereupon the positions of the
aft flaps are reversed to cause the craft to come back up into a
vertical position about the roll axis. At this point, the output of
the vertical gyro 44 on lead 82 decreases to zero; the rudder 12 is
centered; and the craft is again stabilized.
The remaining control actions are primarily for the purpose of
eliminating or minimizing undesirable pitching and rolling actions.
Thus, the forward accelerometer 35 senses acceleration at the bow,
either upward or downward, and produces an electrical signal for
controlling the forward flap 18 to counteract movement about the
pitch axis 62 (FIG. 4) The output of the forward accelerometer 35,
however, is combined in integral amplifier 100 with a signal
proportional to the roll signal squared as derived from circuit 98
before the combined signal is applied to the forward flap servo 78.
This is for the reason that during a turn and while the craft is
being banked about its roll axis, and during normal rolling action
in heavy seas, the rolling movement produces a component of
vertical acceleration which must be taken into consideration.
A signal proportional to the angle of the craft about the pitch
axis is derived from vertical gyro 44 on lead 102. This is applied
to a pitch derivative amplifier 104 which produces an output signal
which varies as a function of pitch angle from horizontal and the
rate of change of pitch angle. The output of the pitch derivative
amplifier 104 is then applied to all of the flap servos and is also
applied in inverted form to the forward flap servo 78 to achieve
differential control. This signal is used for stability
augmentation, ride smoothing in a seaway, and automatic pitch trim
control.
Assuming that the craft is rolling about its roll axis 60, a signal
will be derived on lead 82 which is again applied to the roll
derivative amplifier 80. The signal on lead 82 under these
circumstances will first increase in one direction or polarity,
then recede back to zero and increase in the other direction or
other polarity and again recede back to zero as the craft rolls
from side-to-side. This again produces at the output of the roll
derivative amplifier a signal which varies as a function of both
the roll angle as well as the rate of change roll angle. The signal
is applied to the aft flap port and starboard servos so as to
achieve differential action that counteracts the rolling movement.
In other words, a signal of one polarity is applied to the port
flap servos; while a signal of inverted polarity is applied to the
starboard flap servos to achieve rotation of the respective port
and starboard flaps in opposite directions to counteract a rolling
motion.
The output of port vertical accelerometer 42 is applied to both the
inboard and outboard port flap servos 84 and 86 and acts to vary
the aft port flap positions to counteract any vertical acceleration
or heave on the port side. Similarly, the output of the starboard
vertical accelerometer 40 is applied to both the inboard and
outboard starboard flap servos 88 and 90 to achieve the same action
and counteract vertical accelerations on the starboard side of the
craft.
The complete control system is shown in FIGS. 6A-6C wherein
elements corresponding to those of FIG. 5 are identified by like
reference numerals. The control flaps and the rudder are shown
interconnected via broken line 106 and block 108 identified as
"craft motions" to complete the servo system and show that
actuation of the control flaps and rudder effect motions which, in
turn, vary the outputs of the various sensors such as the gyro, the
accelerometers, and so on.
It will be noted that the forward vertical accelerometer 35 is
connected through an amplifier-demodulator 110 to the integral
amplifier 100 where the signal is combined with a signal from
circuit 98 proportional to the absolute value of roll squared as
explained above. The output of the integral amplifier 100 is a
signal which varies as a function of both heave acceleration at the
forward strut (i.e., rudder 12) as well as heave velocity at the
forward strut. This signal is applied through a scaling network 112
to the forward flap servo 78 shown enclosed by broken lines. The
operation of the forward flap servo is identical to that of the
servos for the remaining flaps as well as the rudder 12. A detailed
explanation of operation of the servos will be given
hereinafter.
The pitch output from the vertical gyro 44 is applied through an
amplifier-demodulator 114 to the pitch derivative amplifier 104 to
produce an output signal on lead 116. This signal varies as a
function of pitch angle from horizontal as well as pitch rate. The
signal is applied through scaling network 118 to the forward flap
servo 78 and is also applied in inverted form through scaling
network 120 to each of the servos for the flaps 28-34 on the aft
foil. As was explained above, the control action is such that in
response to a pitching motion, the flap 18 on the forward foil 16
is rotated in one direction; while the aft flaps are rotated in the
opposite direction to produce a moment which counterbalances or
counteracts the pitching moment induced in the craft by rough
water, for example.
As shown in FIG. 6A, there are actually two roll outputs from the
vertical gyro 44, the two outputs being used for redundancy and
safety purposes. One output is applied through an
amplifier-demodulator 122 to two derivative amplifiers 80A and 80B;
while the other roll output is applied through an
amplifier-demodulator 124 to both the same port and starboard
derivative amplifiers 80A and 80B. An alternate implementation
would replace the two roll outputs from one vertical gyro with two
separate vertical gyros.
The helm 72 likewise has two redundant and equal outputs, one of
which is applied through an amplifier-demodulator 126 to a filter
128 and the other of which is applied through an
amplifier-demodulator 130 to a filter 132. The resulting filtered
output of filter 128 is applied through lead 134 to both derivative
amplifiers 80A and 80B. Similarly, the output of filter 132 is
applied through lead 136 to both of the derivative amplifiers 80A
and 80B. An explanation of the details and function of amplifiers
80A and 80B, capable of producing output signals which vary as a
function of both roll angle and rate of change of roll angle, can
be had by reference to Analog Computation, A. S. Jackson, 1960,
McGraw-Hill Book Company, Inc., New York.
A heading hold circuit 138 under the manual control of the pilot is
adapted to produce an output signal which is applied through an
amplifier-demodulator 140 and lead 142 to both of the derivative
amplifiers 80A and 80B. Actually, the heading hold circuit will be
disabled when the helm is activated under the control of the
operator to manually produce turning signals. On the other hand,
when it is desired to hold a certain heading of the craft, the
heading hold circuit is activated whereby if the desired heading is
directly east, for example, then the hold circuit will produce an
output signal by comparison with a compass setting to cause the
craft to turn whenever it veers off the desired course. In other
words, the output of the heading hold circuit 38 and that of the
helm 72 are used in the alternative.
The output of the port roll derivative amplifier 80A is applied
through a scaling network 144 to the outboard port flap servo 86 as
well as the inboard port flap servo 84. Similarly, the output of
the starboard roll derivative amplifier 80B is applied through
scaling network 146 to both the outboard starboard flap servo 90 as
well as the inboard starboard flap servo 88. It will be apparent,
of course, that the two circuits 80A and 80B are identical in
function and are redundant for safety purposes. Thus, if one or the
other of the circuits should fail, one set of flaps, either
starboard or port, will still be effective in controlling the
craft. Similarly, if one of the two helm or roll signal channels
should fail, both the starboard and port flaps will still be
effective to control the craft.
The output signal from the aft starboard vertical accelerometer 40
is applied through amplifier-demodulator 148 and scaling network
150 to the inboard and outboard starboard flap servos 88 and 90.
Similarly, the aft port vertical accelerometer 42 is connected
through amplifier-demodulator 152 and scaling network 154 to both
the inboard and outboard port flap servos 84 and 86. These signals
are used for ride smoothing in a seaway. That is, vertical
acceleration on the port side causes actuation of the port flaps to
counteract the acceleration. Similarly, acceleration on the
starboard side actuates the starboard flaps to counteract starboard
acceleration. The aft port and starboard accelerometers are not
used for redundancy purposes; but since both starboard and port
accelerations are sensed and used to control the flaps, a smoother
ride is achieved.
The height sensor 36 is connected to the depth error amplifier 74
as previously explained along with a signal on lead 156 from an
amplifier-demodulator 158 connected to the depth command 68. The
height sensor 36 is of the ultrasonic type. Its output is filtered
or integrated such that the actual height signal will not fluctuate
appreciably when the ship is traveling through rough water and the
actual distance between the surface and the hull is changing
rapidly due to the undulation of waves beneath it. The output of
depth error amplifier is applied through scaling network 160 to the
forward flap servo 78 as explained above. Thus, control of height
is entirely by way of the forward flap 18.
The output of the yaw rate gyro 45 is applied through an
amplifier-demodulator 162 and scaling network 166 to the rudder
servo 92. Also applied to the rudder servo, and after passing
through amplifier-demodulator 168 and scaling network 170, is a
signal proportional to forward lateral acceleration. Finally, the
outputs of both amplifier-demodulators 122 and 124, proportional to
roll angle, are applied through scaling network 172 to the rudder
servo 92. As was explained previously, the control action is such
that when the helm is turned, the aft flaps are initially actuated
to bank the craft about its roll axis; whereupon the banking action
is sensed by the vertical gyro to produce roll angle signals which
are fed to the rudder servo 92. This, in turn, causes the rudder to
turn in the direction of banking. After the craft is turned in the
proper direction and the helm returned back to its center or null
position, the aft flaps cause the craft to return to its upright
position; whereupon the roll output signals will tend to return to
zero and the rudder will return back to its center or null
position.
It is a feature of the invention that even though the helm is not
turned, rolling action of the craft will not only actuate the aft
flaps but will also actuate the rudder 12 due to the fact that the
roll outputs of the gyro 44 are connected to the rudder servo 92.
In this manner, if the craft should roll to the right due to the
action of wind or waves, for example, the rudder will be actuated
to steer the craft to the left or into the oncoming wind or wave
where the roll action is minimized.
As was mentioned above, all of the flap servos, as well as the
rudder servo, are identical. Accordingly, only the forward flap
servo 78 will be described in detail. It includes a forward flap
servo amplifier 176 which, in effect, comprises an operational
amplifier having four inputs applied to one of its two input
terminals through resistors. Preferably, the operational amplifier
is of the integrating type having a capacitive feedback path in
order to prevent rapid or abrupt response characteristics. In the
case of servo 78, the five inputs to the operational amplifier 176
comprise signals on leads 178, 180. 182, 184 and 186. The signal on
lead 178 varies as a function of both pitch angle from horizontal
as well as pitch rate. The signal on lead 180 varies as a functuion
of craft height as explained above. The signal on lead 182 is
derived through a scaling network 188 from the output of
amplifier-demodulator 114 and varies as a function of actual pitch
angle. The signal on lead 184 varies as a function of forward
acceleration; while the signal on lead 186 is a feedback signal
proportional to actual flap position. That is, the forward flap
actuator 48 (see also FIG. 3) is connected through a mechanical
linkage 190 to the flap 18. This same mechanical linkage 190 is
connected to a primary position transducer 192 which produces a
signal on lead 194 whose magnitude varies as a function of the
angular position of the forward flap 18 and whose polarity depends
upon whether the flap is rotated upwardly or downwardly from its
central or null position. This signal is applied through a feedback
demodulator 196 and scaling network 198 to the input of the servo
amplifier 176. The arrangement, of course, comprises a conventional
servo system wherein an output signal from the servo amplifier 176
will actuate the forward flap servo valve in actuator 48 to vary
the position of flap 18. When the position is varied, a feedback
signal is generated at the output of network 198; and this signal
persists until it nulls out or cancels the combined input signal on
the other input leads 178-184 which initiated the control
action.
Let us assume, for example, that it is desired to increase the
height of the craft above the surface. A signal of one polarity
(e.g., positive) will be applied to the input of amplifier 176 via
lead 180. This causes the flap 18 to rotate downwardly, thereby
producing a negative signal on lead 186 which tends to null out the
positive signal on lead 180. As the actual height increases, the
error signal on lead 180 will decrease, thereby causing a
counter-rotation of the flap 18 and a decrease in the feedback
signal on lead 186 until a null condition is again reached with the
flap centered and the new, desired height reached. The foregoing,
of course, assumes that no other signals are being applied to the
input of the servo amplifier 176. In actual practice, however, a
number of signals will be applied simultaneously from the various
inputs, some of which are additive and some of which are
subtractive depending upon forward acceleration, pitch angle, and
the like. These, when combined at the input of amplifier 176, will
effect a desired inclination of the forward flap tending to
compensate for all of the various error signals introduced into the
system.
Although the invention has been shown in connection with a certain
specific embodiment, it will be readily apparent to those skilled
in the art that various changes in form and arrangement of parts
may be made to suit requirements without departing from the spirit
and scope of the invention.
* * * * *