Abstract:
A propelled cable fairing system for towing objects underwater having a plurality of cable fairings, which are individually propelled by motorized propulsion to avoid the thrust of propellers to overcome normally encountered drag heretofore utilized, which required use of longer and thicker cables resulting in a loss of control over the position of the towed object. In addition, the relative position of the propelled cable fairing system is maintained through a set of serially linked motor controllers that sense the relative position of each propelled cable fairing relative to it adjacent propelled cable fairing. Variation in position of the propelled cable fairing from a target, causes increase in speed of the motor or alters its angle of attack in order to keep the propelled cable fairings in predetermined alignment with the adjacent cable fairing. By use of a plurality of rudders, the propelled cable fairing system allows the operator to maintain the towed object at desired horizontal and vertical positions.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without payment of any royalties thereon or therefor. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the field of overcoming drag caused by the relative underwater flow of fluid past a cable. Specifically, this invention relates to the field of using improved tow cables to better control a submerged object. 
     2. Description of the Related Art 
     This invention relates to the towing of submerged objects, commonly called “fish.” These fish can be sonar devices, deep-sea exploration vehicles, or other underwater vehicles that are towed underwater. These fish are often towed behind a towing vehicle, such as a ship or submarine. In addition, they can be tethered to a stationary object. The typical arrangement is for the towing vehicle to be a ship, which will be attached to the fish by a cable. In order to submerge the fish, the cable will be played out until the fish sinks to the desired depth. 
     The foregoing described arrangement is generally satisfactory either where a ship is moving relatively slowly, or where the current is minimal, or where the cable length is relatively short. However, depending on both the relative speed of the water flowing past the cable and the length of the cable, this arrangement can result in significant drag produced by the water on the cable. Because of such increased drag, more cable is required to maintain the fish at a given depth. As the length of the cable is increased, the weight of the entire towing apparatus increases. Furthermore, as the length of the cable increases, the operator&#39;s ability to control the fish decreases. Thus there has been a long felt need to find a way to reduce the effect of this drag in order to both reduce the amount of cable used, and to increase the operator&#39;s control over the fish at a desired depth. 
     To date, the prior art has focused on attempts to passively reduce drag on the cable, which generally consisted of improved fairing shapes. These fairings are airfoil-shaped coverings that are designed to streamline the profile of the cable in order to reduce drag on the cable. There are many types of such fairings. Examples are disclosed in U.S. Pat. No. 5,050,445, which describes a fairing that completely covers the cable, and in U.S. Pat. No. 4,829,929, which describe a fairing that only partially covers the cable. In a variation on the fairing system, systems utilizing ribbons to additionally reduce drag are shown in U.S. Pat. No. 4,843,996. Lastly, where a fish requires the use of electricity, other cables were designed that enclose both the cable and the electrical lines. Examples of the latter referred to systems are disclosed in U.S. Pat. Nos. 3,379,161 and 3,343,516. While these systems typically did reduce drag, they were unable to eliminate it totally since such systems all lacked the capacity to produce thrust. Since the production of thrust is the only way to truly overcome drag, such attempts to passively reduce drag prove only to be partially effective. 
     As previously noted, where cable lengths are lengthened, the capability to control the fish became more difficult. Since certain towing applications required greater control over the fish, attempts were made to devise systems that provided such control. The systems shown in U.S. Pat. Nos. 3,987,745 and 4,843,996 dealt with this problem by creating two fish: one that maintained a general base position, and a second that could explore out from the base position under its own power. However, such solution is not practicable in all towing situations. 
     Another technique has been largely confined to the field of towed hydrophone arrays where the cable needs to extend horizontally over great distances. In those situations, systems such as those disclosed in U.S. Pat. Nos. 3,605,674 and 4,290,124 use controllable wings attached to the cables. These wings maintain the cable horizontally at a predetermined depth as the entire array is towed. In other towing arrangements, such as that shown in U.S. Pat. No. 4,709,355, a closed loop feedback system is utilized where the controller is located on a ship and automatically maintains the wings at a desired angle to maintain or alter its depth based on sensor readings. However, such technology was never applied to the cable fairings used in towing fish, since without some means of providing thrust to the cable there was no way to correct a fairing segment to keep it in desired alignment. 
     Thus, prior to the present invention, there was no active means to overcome the drag on cable fairings, and no effective way to control the cable, resulting in the use of longer and thicker cables than those utilized in the system of the present invention. 
     SUMMARY OF THE INVENTION 
     Accordingly, pursuant to the present invention an active means is provided to overcome drag on cables used in the towing of submerged objects. Also according to the present invention, sufficient thrust is provided along the length of a cable used in the towing of submerged objects to allow a reduction in both the thickness and amount of cable used. Furthermore, a means is provided to increase the control over the towed object by decreasing the amount of cable that needs to be used in the towing of underwater objects. Still further, a propelled cable fairing is created that has the internal capability to maintain a relative position between adjacent fairings. Such propelled cable fairing also has the capability to maintain the cable at an angular position as it is towing a submerged object. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     A more complete appreciation of the invention and many of its attendant advantages will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing herein: 
     FIG. 1 is a side view of propelled cable fairing system showing the relative position of towing body, towed body, cable, and propelled cable fairings arrayed along the cable according to the present invention. 
     FIG. 2 a top view of the interior of an individual propelled cable fairing according to the present invention. 
     FIG. 3 is a side view of the interior of an individual propelled cable according to the present invention. 
     FIG. 4 is a front view of an individual propelled cable according to the present invention showing the placement of the propeller and the propeller duct. 
     FIG. 5 is a section view of a swage having grooves for use according to the present invention. 
     FIG. 6 is a front view of the swage shown with the cable according to the present invention. 
     FIG. 7 is a top view of the laser diode control system showing the laser beams linking the receiving propelled cable fairing to its adjacent propelled cable fairing according to the present invention. 
     FIG. 8 is a top view of the interior of an individual propelled cable fairing showing the laser diode control system embodiment of the propelled cable fairing feedback control system according to the present invention. 
     FIG. 9 is a top view of the metallic rod embodiment according to the present invention showing the metallic rods linking the receiving propelled cable fairing to its adjacent propelled cable fairing according to the present invention. 
     FIG. 10 is a top view of the interior of an individual propelled cable fairing showing the metal bar embodiment of the propelled cable fairing feedback control system according to the present invention. 
     FIG. 11 is a side view of the propelled cable fairing according to the present invention showing the alternative embodiment employing a rudder. 
     FIG. 12 is a view from the rear of the propelled cable fairing system showing the controller and the capacity of the system to maintain the cable at an angular position where the system further includes a rudder according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in FIG. 1, the propelled cable fairing system  1  includes the towing body  5 , a towed body  10 , a cable  20  connecting the towing body  5  to the towed body  10 , and a set of propelled cable fairings  100  attached to the cable  20 . Located on the towing body  5  is a power source  240 , which provides power to the propelled cable fairings  100  by means of a power cable  260 . The cable  20  is conventional in nature, but is untwisted in the preferred embodiment. 
     In the preferred embodiment, the towing body  5  is a ship, and the towed body  10  is a fish. However, the towing body  5  and the towed body  10  can be any two objects between which the cable  20  is strung so long as the cable  20  is exposed to a water flow, such as a current. In addition, the power source  240  shown provides electrical power. However, it is recognized that a power source  240  could also provide hydraulic or pneumatic forms of power to the propelled cable fairings  100  along with or instead of electric power, depending on the design chosen. 
     FIGS. 2,  3 , and  4  provide a side, top, and front view of an individual propelled cable fairing  100 . As shown in FIG. 2, the external structure of the propelled cable fairing  100  comprises a housing  160 . As shown in FIG. 3, the housing  160  is in the shape of an airfoil having a maximum thickness  170  of between 10%-30%. In addition, the cable  20  extends through the width of the propelled cable fairing  100  near the point of maximum thickness  170 . As shown in FIG. 2, the housing  160  is attached to the cable  20  through bearings  110 . 
     In the preferred embodiment, the propulsion for the propelled cable fairing  100  is provided by a propeller  220 . The propeller  220  is attached to a propeller shaft  200  such that the propeller  220  is flush with and behind the leading edge  175  of the housing  160 . In order to flush mount the propeller  220 , the housing  160  includes a propeller duct  230 . The propeller duct  230  allows the wash produced by the propeller  220  to flow over the housing  160  in an aerodynamic fashion. However, it is recognized, but not shown, that the propeller  220  may also be mounted in front of the leading edge  175  of the housing  160 . Whether mounted flush or in front of the leading edge  175 , as shown in FIG. 4, the propeller is mounted in the center of the leading edge  175 . It is recognized that other forms of propulsion may be used instead of the propeller  220 , such as those using jets of water, gas or other similar means to produce thrust. 
     As shown in FIG. 2, in the preferred embodiment, the motor  180  is located behind the cable  20 . As such, the propeller shaft  200 , which transmits the power from the motor  180  to the propeller  220 , extends through the cable  20 . In order to extend through the cable  20 , the preferred embodiment employs a swage  120 , as shown in FIGS. 5 and 6. The swage  120  has grooves  26  and as shown in FIG. 6 is in the cable  20 , separating the strands  25  thereof to allow the propeller shaft  200  to pass through the cable  20 . The grooves  26  allow the strands  25  to pass around the swage  120  in spaced relation to the propeller shaft  200  to prevent interference therewith. In order to attach the swage  120 , the strands  25  are exposed by removing a portion of covering  27  from the cable  20 . Above and below the swage  120 , the cable  20  is bound by bands  130 . Thus, as shown in FIG. 2, using the swage  120  to define a passageway through the cable  20 , the propeller shaft  200  is able to extend from the motor  180  to the propeller  220 . The swage  120  is preferably of a hard material, such as metal or a hard plastic. 
     It is recognized that there are other means to transmit power from the motor  180  to the propeller  220  which might not require the use of the swage  120 . Other possible mechanisms include flexible shafts, placing the motor  180  in front of the cable  20 , or even directly connecting the motor to the propeller as is done in radial engines. If the propeller is banded, the band may be driven electromagnetically. 
     In the preferred embodiment shown in FIG. 2, the motor  180  is an electric motor. The motor  180  is attached through controller cables  270  to a motor controller  280 . The motor controller  280  provides input to the motor  180 , which determines the speed at which the propeller  220  turns, thus controlling the thrust of the individual propelled cable fairing  100 . The motor controller  280  is electrically attached to the power cable  260  through power cables  275 . 
     In its simplest embodiment, the motor controller  280  would keep the thrust constant or respond to signals from the towing body  5  or the towed body  10 . However, where there is a need for each propelled cable fairing  100  to control its alignment with its adjacent propelled cable fairing, each propelled cable fairing  100  would have a closed loop feedback system which would provide an automatic relative position control between these propelled cable fairings. This propelled cable fairing feedback control system would control the motor controller  280  and vary the thrust according to the relative position of the propelled cable fairing  100  to its adjacent propelled cable fairing. 
     A preferred embodiment of the propelled cable fairing feedback control system is shown in FIG.  7 . According to this preferred embodiment, the propelled cable fairing feedback control system comprises a series of linked propelled cable fairings  100 . Each link is a laser beam  340  that extends between adjacent propelled cable fairings. Specifically, the laser beam  340  extends from a first propelled cable fairing  305  to a second propelled cable fairing  310 . The laser beam  340  is produced by the fixed laser diode  320  in the first propelled cable fairing  305 . The laser diode  320  is aimed at a target  400  on a position sensitive device  380  located on the second propelled cable fairing  310 . This target  400  is normally the center of the position sensitive device  380 . Since the output of position sensitive device  380  is dependent on the position of the laser beam  340  relative to the target  400 , the motor controller  280  is able to sense the relative position of the first propelled cable fairing  305 . Where the laser beam  340  is not on the target  400 , the motor controller  280  will accordingly adjust the speed of the motor  180  to move the second propelled cable fairing  310  such that the laser beam  340  is brought onto the target  400 . 
     As shown in FIG. 8, this embodiment of the propelled cable fairing feedback control system requires that each propelled cable fairing  100  includes a laser diode  300 , which receives power from the power source  240  by being electrically connected to the power cable  260  via power cables  330 . This laser diode  300  generates a laser beam  340  that will communicate its position to an adjacent propelled cable fairing  100  (not shown). In addition, each propelled cable fairing  100  includes a position sensitive device  380 , which is electrically connected to the motor controller  280  via sensor cables  390 . Such position sensitive device  380  receives a laser beam  340  from an adjacent propelled cable fairing  100  (not shown), and produces an output indicating the position of the laser beam  340 . Through these sensor cables  390 , the motor controller  280  is able to sense the output of the position sensitive device  380 , evaluate this output as compared to the output received when the laser beam  340  is received at the target  400  (not shown), and adjust the speed of the motor  180  according to this output. Such control may be proportional, proportionally derivative or proportional derivative integral. As shown in FIG. 7, by linking the propelled cable fairings  100  in this way, each propelled cable fairing  100  can communicate its relative position to one adjacent propelled cable fairing  100 , while simultaneously being able to automatically maintain its relative position relative to another adjacent propelled cable fairing  100 . 
     In FIG. 9, an alternative linking mechanism is shown to keep the propelled cable fairing system  1  in alignment. In this embodiment, the propelled cable fairing feedback control system utilizes metallic rods  440 , which extend from a first propelled cable fairing  305  into a second propelled cable fairing  310  where the metallic rod  440  is received by the metal sensing magnets  420 . Each metallic rod  440  contains sufficient metallic content to allow it to be sensed by these metal sensing magnets  420 , and is stiffer than the cable  20 . These metal sensing magnets  420  have a target area  430  (not shown), which represents an ideal position for the metallic rod  420 . Through the sensor cables  390 , the motor controller  280  in the second propelled cable fairing  310  senses the position of the metallic rod  440 , evaluates this position relative to the target area  430  of the metal sensing magnets  420 , and adjusts the speed of its motor  180  to move the metallic bar  440  onto the target are  430 . In this way, the position of the first propelled cable fairing  305  is communicated to the second propelled cable fairing  310 , so that the motor controller and the second propelled cable fairing  310  can align with the first propelled cable fairing  305 . 
     As shown in FIG. 10, the motor controller  280  is electrically attached to the metal sensing magnets  420  through sensor cables  390 . Both the metal sensing magnets  420  and the metallic rod  440  are attached to the housing  160 . It is the metallic rod  440  which will communicate the position of the propelled cable fairing  100  to an adjacent propelled cable fairing  100  (not shown). By linking the propelled cable fairings  100  in this way, each propelled cable fairing  100  can communicate its relative position to one adjacent propelled cable fairing  100 , while at the same time automatically maintaining its relative position relative to another adjacent propelled cable fairing  100 . 
     In another embodiment shown in FIG. 11, the propelled cable fairing  100  can be adjusted to maintain a desired angle of attack/attitude relative to the free flow of the water  507 . The embodiment shown uses a rudder  460  that is attached to the housing  160  of the propelled cable fairing  100  by a hinge  480 . The rotation of the rudder  460  about the hinge  480  is controlled by an actuator  500 , which is also attached to the housing  160 . The actuator  500  is connected to the rudder  460  by a gear  505 . Gear  505  engages the rudder teeth  506  to allow the actuator to control the movement of rudder  460 . Since other conventional connections between actuators and rudders are available, such as the electrical or hydraulic systems, they may also be utilized between servos and rudders on aircraft. 
     In the preferred embodiment, the actuator  500  is electrically connected to the motor controller  280  through power cables  510 . The actuator  500  is controlled by the motor controller  280  to control both the speed of the motor  180  and the actuator  500  so as to automatically maintain and adjust both the relative speed and the attitude of the propelled cable fairing  100 . It is understood, that the actuator  500  might be controlled by a separate control system existing outside of the motor controller  280  so long as this separate control system relies upon the input from the propelled cable fairing feedback control system that indicates the relative position of adjacent propelled cable fairing  100 . Although not shown, it is also understood that the rudder  460  might be replaced by a plurality of rudders, and that these rudders may be positioned along the fairing close to its maximum thickness so long as the rudders can provide the attitudinal control desired for a given application. 
     Where an embodiment includes a rudder  460 , there is an additional advantage: the entire propelled cable fairing system  1  can be made to pivot about the towing body  5  as shown in FIG.  12 . In such preferred embodiment as shown, this pivot is accomplished by controlling the attitude of the primary propelled cable fairing  540 , whose position determines the relative position of the other propelled cable fairings  100 . In the laser diode embodiment for the propelled cable fairing feedback control system, the primary propelled cable fairing  540  is the propelled cable fairing  100  that has a laser beam  340  extending from it into an adjacent propelled cable fairing, but does not receive a laser beam  340  from an adjacent propelled cable fairing. Where the metallic rod embodiment of the propelled cable fairing feedback control system is employed, the primary propelled cable fairing  540  is the propelled cable fairing  100  that extends its metallic rod  440  into an adjacent propelled cable fairing, but which receives no metallic rod  440  from an adjacent propelled cable fairing. Whichever propelled cable fairing feedback system is employed, by controlling this primary propelled cable fairing  540 , all other propelled cable fairings  100  can be rotated, manipulated, or otherwise controlled by merely controlling the primary propelled cable fairing  540 . 
     In order to control the primary propelled cable fairing  540 , the embodiment shown in FIG. 12 uses the controller  520  to both communicate a position command to the primary propelled cable fairing  540  through system control cables  550 , and to maintain this position command. These system control cables  550  are connected to the motor controller  280  of the primary propelled cable fairing  540 . It is understood that communication need not be through a hardwired system such as heretofore described, but may be through other conventional means such as radio waves, or, depending on the propelled cable fairing feedback control system used, linking the controller  520  to the primary propelled cable fairing  540  using either metallic rods and laser beams as appropriate. 
     However communicated, communication provides the motor controller  280  for the primary propelled cable fairing  540  with a desired attitude for the propelled cable fairing system  1 . The motor controller  280  adjusts the motor  180  and rudder  460  of the primary propelled cable fairing  540  to reach the desired attitude. Since the relative position of the propelled cable fairings  100  are dependent on the position of the primary propelled cable fairing  540 , the use of the controller  520  allows the operator to manipulate the attitude of the entire propelled cable fairing system  1  as shown in FIG.  12 . 
     Obviously, other modifications and variations of the present invention may be possible in light of the foregoing teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.