Abstract:
An energy kite may be coupled to a tether and ground station via an electro-mechanical bridle. The energy kite may generate a significant amount of lift during power generation and may need to transfer this load to a tether that is anchored at the ground. Transferring the load at a single point would place a substantial bending moment on the energy kite. To mitigate this bending moment, the load may be divided between multiple locations with a bridle system. The bridle system may have a plurality of electrical conductors to conduct electrical power and signals.

Description:
BACKGROUND 
       [0001]    Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. 
         [0002]    Power generation systems may convert chemical and/or mechanical energy (e.g., kinetic energy) to electrical energy for various applications, s as utility systems. As one example, a wind energy system may convert kinetic wind energy to electrical energy. 
       SUMMARY 
       [0003]    Electro-mechanical bridles are described herein. The high-aspect ratio wing of an energy kite generates a significant amount of lift during power generation and needs to transfer this load to a tether that is anchored at or near the ground. Although a single tether may be closer to ideal for aerodynamics and efficiency, transferring the load from the wing to the tether at a single point would cause the long wing to experience a substantial bending moment. This substantial bending moment would require a very large and expensive structure. This bending moment and the need for a large and expensive structure can be mitigated by dividing the load transfer between the tether and the wing between multiple locations using one or more electro-mechanical bridles. Beneficially, embodiments of bridles described herein can be strong, fatigue resistant, aerodynamic, cost effective, and may allow for pitch and roll degrees of freedom of the energy kite. 
         [0004]    In one aspect, an electro-mechanical bridle includes a structural member comprising wrapped fiber filaments. The electro-mechanical bridle includes a tether thimble coupled to a first end of the structural member that is configured to couple a tether to the electro-mechanical bridle. The electro-mechanical bridle includes a wing thimble coupled to a second end of the structural member. The wing thimble is configured to couple an aerial vehicle to the bridle. The electro-mechanical bridle also includes a plurality of electrical conductors coupled to the structural member and extending from the first end to the second end. 
         [0005]    In another aspect, an electro-mechanical bridle system includes a first bridle comprising: a first structural member comprising a wrapped fiber; a first tether thimble coupled to a first end of the first structural member; and a first wing thimble coupled to a second end of the first structural member, wherein the first wing thimble is configured to couple an aerial vehicle to the first bridle. The electro-mechanical bridle system further includes a second bridle comprising: a second structural member comprising a wrapped fiber; a second tether thimble coupled to a first end of the second structural member; and a second wing thimble coupled to a second end of the second structural member, wherein the second wing thimble is configured to couple an aerial vehicle to the second bridle. The first tether thimble and the second tether thimble are configured to couple the first bridle and the second bridle to a tether. The electro-mechanical bridle also includes a plurality of electrical conductors coupled to the first bridle and extending the length of the first structural member. 
         [0006]    In yet another aspect, an energy kite system includes a ground station coupled to an electrically conductive tether. The energy kite system includes a plurality of bridles, each bridle comprising: a structural member comprising a wrapped fiber; a tether thimble coupled to a first end of the structural member; and a wing thimble coupled to a second end of the structural member; wherein each tether thimble is coupled to the electrically conductive tether. The energy kite system also includes a plurality of electrical conductors extending the length of at least one of the plurality of bridles and electrically coupled to an aerial vehicle. The energy kite system also includes a power transfer loop configured to transfer electrical power or signals between the electrically conductive tether and the electro-mechanical bridle system. The wing thimbles are each coupled to the aerial vehicle. 
         [0007]    These as well as other aspects, advantages, and alternatives, will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0008]      FIG. 1  depicts an Airborne Wind Turbine (AWT), according to an example embodiment. 
           [0009]      FIG. 2  is a simplified block diagram illustrating components of an AWT, according to an example embodiment. 
           [0010]      FIG. 3  depicts an aerial vehicle, according to an example embodiment. 
           [0011]      FIG. 4  depicts an aerial vehicle coupled to a ground station via a tether, according to an example embodiment. 
           [0012]      FIG. 5  depicts the aerial vehicle  330  coupled to the tether  120  via a bridle system  500 , according to an example embodiment. 
           [0013]      FIG. 6  depicts a bridle  600  in a first orientation and in a second orientation where the bridle  600  is turned 90 degrees from the first orientation, according to an example embodiment. 
           [0014]      FIG. 6A  depicts a bridle in cross-section, according to an example embodiment. 
           [0015]      FIG. 6B  depicts a bridle in cross-section, according to an example embodiment. 
           [0016]      FIG. 7A  depicts a bridle in cross-section, according to an example embodiment. 
           [0017]      FIG. 7B  depicts a bridle in cross-section, according to an example embodiment. 
           [0018]      FIG. 7C  depicts a bridle in cross-section, according to an example embodiment. 
           [0019]      FIG. 7D  depicts a bridle, according to an example embodiment. 
           [0020]      FIG. 8A  depicts a bridle  800 , according to an example embodiment. 
           [0021]      FIG. 8B  depicts the bridle  800  in cross-section along line AA, according to an example embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Exemplary systems and methods are described herein. It should be understood that the word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or feature described herein as “exemplary” or “illustrative” is not necessarily to be construed as preferred or advantageous over other embodiments or features. More generally, the embodiments described herein are not meant to be limiting. It will be readily understood that certain aspects of the disclosed systems can be arranged and combined in a wide variety of different configurations, all of which are contemplated herein. 
       I. Overview 
       [0023]    Illustrative embodiments relate to aerial vehicles, which may be used in a wind energy system, such as an energy kite, which may also be called an Airborne Wind Turbine (AWT). In particular, illustrative embodiments may relate to or take the form of bridles that may be used in AWTs. 
         [0024]    By way of background, an AWT may include an aerial vehicle that flies in a closed path, such as a substantially circular path, to convert kinetic wind energy to electrical energy. In an illustrative implementation, the aerial vehicle may be connected to a ground station via a tether. While tethered, the aerial vehicle can: (i) fly at a range of elevations and substantially along the path, and return to the ground, and (ii) transmit electrical energy to the ground station via the tether, (In some implementations, the ground station may transmit electricity to the aerial vehicle for take-off and/or landing.) 
         [0025]    In an AWT, an aerial vehicle may rest in and/or on a ground station (or perch) when the wind is not conducive to power generation. When the wind is conducive to power generation, such as when a wind speed may be 3.5 meters per second (m/s) at an altitude of 200 meters (m), the ground station may deploy (or launch) the aerial vehicle. In addition, when the aerial vehicle is deployed and the wind is not conducive to power generation, the aerial vehicle may return to the ground station. 
         [0026]    Moreover, in an AWT, an aerial vehicle may be configured for hover flight and crosswind flight. Crosswind flight may be used to travel in a motion, such as a substantially circular motion, and thus may be the primary technique that is used to generate electrical energy. Hover flight in turn may be used by the aerial vehicle to prepare and position itself for crosswind flight. In particular, the aerial vehicle could ascend to a location for crosswind flight based at least in part on hover flight. Further, the aerial vehicle could take-off and/or land via hover flight. 
         [0027]    In hover flight, a span of a main wing of the aerial vehicle may be oriented substantially parallel to the ground, and one or more propellers of the aerial vehicle may cause the aerial vehicle to hover over the ground. In some implementations, the aerial vehicle may vertically ascend or descend in hover flight. Moreover, in crosswind flight, the aerial vehicle may be oriented, such that the aerial vehicle may be propelled by the wind substantially along a closed path, which as noted above, may convert kinetic wind energy to electrical energy. In some implementations, one or more rotors of the aerial vehicle may generate electrical energy by slowing down the incident wind. 
         [0028]    Embodiments described herein may relate to or take the form of an electro-mechanical bridle. In an illustrative implementation, the electro-mechanical bridle system may link together to form a “Y”-shaped system that is used to divide a load transfer between the tether and the aerial vehicle between multiple locations. 
       II. Illustrative Systems 
     A. Airborne Wind Turbine (AWT) 
       [0029]      FIG. 1  depicts an AWT  100 , according to an example embodiment. In particular, the AWT  100  includes a ground station  110 , a tether  120 , and an aerial vehicle  130 . As shown in  FIG. 1 , the tether  120  may be connected to the aerial vehicle on a first end and may be connected to the ground station  110  on a second end. In this example, the tether  120  may be attached to the ground station  110  at one location on the ground station  110 , and attached to the aerial vehicle  130  at three locations on the aerial vehicle  130 . However, in other examples, the tether  120  may be attached at multiple locations to any part of the ground station  110  and/or the aerial vehicle  130 . 
         [0030]    The ground station  110  may be used to hold and/or support the aerial vehicle  130  until it is in an operational mode. The ground station  110  may also be configured to allow for the repositioning of the aerial vehicle  130  such that deploying of the device is possible. Further, the ground station  110  may be further configured to receive the aerial vehicle  130  during a landing. The ground station  110  may be formed of any material that can suitably keep the aerial vehicle  130  attached and/or anchored to the ground while in hover flight, crosswind flight, and other flight modes, such as forward flight (which may be referred to as airplane-like flight). In some implementations, a ground station  110  may be configured for use on land. However, a ground station  110  may also be implemented on a body of water, such as a lake, river, sea, or ocean. For example, a ground station could include or be arranged on a floating off-shore platform or a boat, among other possibilities. Further, a ground station  110  may be configured to remain stationary or to move relative to the ground or the surface of a body of water. 
         [0031]    In addition, the ground station  110  may include one or more components (not shown), such as a winch, that may vary a length of the tether  120 . For example, when the aerial vehicle  130  is deployed, the one or more components may be configured to pay out and/or reel out the tether  120 . In some implementations, the one or more components may be configured to pay out and/or reel out the tether  120  to a predetermined length. As examples, the predetermined length could be equal to or less than a maximum length of the tether  120 . Further, when the aerial vehicle  130  lands in the ground station  110 , the one or more components may be configured to reel in the tether  120 . 
         [0032]    The tether  120  may transmit electrical energy generated by the aerial vehicle  130  to the ground station  110 . In addition, the tether  120  may transmit electricity to the aerial vehicle  130  in order to power the aerial vehicle  130  for takeoff, landing, hover flight, and/or forward flight. The tether  120  may be constructed in any form and using any material which may allow for the transmission, delivery, and/or harnessing of electrical energy generated by the aerial vehicle  130  and/or transmission of electricity to the aerial vehicle  130 . The tether  120  may also be configured to withstand one or more forces of the aerial vehicle  130  when the aerial vehicle  130  is in an operational mode. For example, the tether  120  may include a core configured to withstand one or more forces of the aerial vehicle  130  when the aerial vehicle  130  is in hover flight, forward flight, and/or crosswind flight. In some examples, the tether  120  may have a fixed length and/or a variable length. For instance, in at least one such example, the tether  120  may have a length of 140 meters. 
         [0033]    The aerial vehicle  130  may be configured to fly substantially along a closed path  150  to generate electrical energy. The term “substantially along,” as used in this disclosure, refers to exactly along and/or one or more deviations from exactly along that do not significantly impact generation of electrical energy. 
         [0034]    The aerial vehicle  130  may include or take the form of various types of devices, such as a kite, a helicopter, a wing and/or an airplane, among other possibilities. The aerial vehicle  130  may be formed of solid structures of metal, plastic and/or other polymers. The aerial vehicle  130  may be formed of any material which allows for a high thrust-to-weight ratio and generation of electrical energy which may be used in utility applications. Additionally, the materials may be chosen to allow for a lightning hardened, redundant and/or fault tolerant design which may be capable of handling large and/or sudden shifts in wind speed and wind direction. 
         [0035]    The closed path  150  may be various different shapes in various different embodiments. For example, the closed path  150  may be substantially circular. And in at least one such example, the closed path  150  may have a radius of up to 265 meters. The term “substantially circular,” as used in this disclosure, refers to exactly circular and/or one or more deviations from exactly circular that do not significantly impact generation of electrical energy as described herein. Other shapes for the closed path  150  may be an oval, such as an ellipse, the shape of a jelly bean, the shape of the number of 8, etc. 
         [0036]    The aerial vehicle  130  may be operated to travel along one or more revolutions of the closed path  150 . 
       B. Illustrative Components of an AWT 
       [0037]      FIG. 2  is a simplified block diagram illustrating components of the AWT  200 . The AWT  100  may take the form of or be similar in form to the AWT  200 . In particular, the AWT  200  includes a ground station  210 , a tether  220 , and an aerial vehicle  230 . The ground station  110  may take the form of or be similar in form to the ground station  210 , the tether  120  may take the form of or be similar in form to the tether  220 , and the aerial vehicle  130  may take the form of or be similar in form to the aerial vehicle  230 . 
         [0038]    As shown in  FIG. 2 , the ground station  210  may include one or more processors  212 , data storage  214 , and program instructions  216 . A processor  212  may be a general-purpose processor or a special purpose processor (e.g., digital signal processors, application specific integrated circuits, etc.). The one or more processors  212  can be configured to execute computer-readable program instructions  216  that are stored in a data storage  214  and are executable to provide at least part of the functionality described herein. 
         [0039]    The data storage  214  may include or take the form of one or more computer-readable storage media that may be read or accessed by at least one processor  212 . The one or more computer-readable storage media can include volatile and/or non-volatile storage components, such as optical, magnetic, organic or other memory or disc storage, which may be integrated in whole or in part with at least one of the one or more processors  212 . In some embodiments, the data storage  214  may be implemented using a single physical device (e.g., one optical, magnetic, organic or other memory or disc storage unit), while in other embodiments, the data storage  214  can be implemented using two or more physical devices. 
         [0040]    As noted, the data storage  214  may include computer-readable program instructions  216  and perhaps additional data, such as diagnostic data of the ground station  210 . As such, the data storage  214  may include program instructions to perform or facilitate some or all of the functionality described herein. 
         [0041]    In a further respect, the ground station  210  may include a communication system  218 . The communication system  218  may include one or more wireless interfaces and/or one or more wireline interfaces, which allow the ground station  210  to communicate via one or more networks. Such wireless interfaces may provide for communication under one or more wireless communication protocols, such as Bluetooth, WiFi (e.g., an IEEE 802.11 protocol), Long-Term Evolution (LTE), WiMAX (e.g., an IEEE 802.16 standard), a radio-frequency ID (RFID) protocol, near-field communication (NFC), and/or other wireless communication protocols. Such wireline interfaces may include an Ethernet interface, a Universal Serial Bus (USB) interface, or similar interface to communicate via a wire, a twisted pair of wires, a coaxial cable, an optical link, a fiber-optic link, or other physical connection to a wireline network. The ground station  210  may communicate with the aerial vehicle  230 , other ground stations, and/or other entities (e.g., a command center) via the communication system  218 . 
         [0042]    In an example embodiment, the ground station  210  may include communication systems  218  that allows for both short-range communication and long-range communication. For example, the ground station  210  may be configured for short-range communications using Bluetooth and for long-range communications under a CDMA protocol. In such an embodiment, the ground station  210  may be configured to function as a “hot spot”; or in other words, as a gateway or proxy between a remote support device (e.g., the tether  220  the aerial vehicle  230 , and other ground stations) and one or more data networks, such as cellular network and/or the Internet. Configured as such, the ground station  210  may facilitate data communications that the remote support device would otherwise be unable to perform by itself. 
         [0043]    For example, the ground station  210  may provide a WiFi connection to the remote device, and serve as a proxy or gateway to a cellular service provider&#39;s data network, which the ground station  210  might connect to under an LTE or a 3G protocol, for instance. The ground station  210  could also serve as a proxy or gateway to other ground stations or a command center, which the remote device might not be able to otherwise access. 
         [0044]    Moreover, as shown in  FIG. 2 , the tether  220  may include transmission components  222  and a communication link  224 . The transmission components  222  may be configured to transmit electrical energy from the aerial vehicle  230  to the ground station  210  and/or transmit electrical energy from the ground station  210  to the aerial vehicle  230 . The transmission components  222  may take various different forms in various differ embodiments. For example, the transmission components  222  may include one or more conductors that are configured to transmit electricity. And in at least one such example, the one or more conductors may include aluminum and/or any other material which allows for the conduction of electric current. Moreover, in some implementations, the transmission components  222  may surround a core of the tether  220  (not shown). 
         [0045]    The ground station  210  could communicate with the aerial vehicle  230  via the communication link  224 . The communication link  224  may be bidirectional and may include one or more wired and/or wireless interfaces. Also, there could be one or more routers, switches, and/or other devices or networks making up at least a part of the communication link  224 . 
         [0046]    Further, as shown in  FIG. 2 , the aerial vehicle  230  may include one or more sensors  232 , a power system  234 , power generation/conversion components  236 , communication system  238 , one or more processors  242 , data storage  244 , program instructions  246 , and a control system  248 . 
         [0047]    The sensors  232  could include various different sensors in various different embodiments. For example, the sensors  232  may include a global positioning system (GPS) receiver. The GPS receiver may be configured to provide data that is typical of well-known GPS systems (which may be referred to as a global navigation satellite system (GNNS)), such as the GPS coordinates of the aerial vehicle  230 . Such GPS data may be utilized by the AWT  200  to provide various functions described herein. 
         [0048]    As another example, the sensors  232  may include one or more wind sensors, such as one or more pitot tubes. The one or more wind sensors may be configured to detect apparent and/or relative wind. Such wind data may be utilized by the AWT  200  to provide various functions described herein. 
         [0049]    Still as another example, the sensors  232  may include an inertial measurement unit (IMU). The IMU may include both an accelerometer and a gyroscope, which may be used together to determine the orientation of the aerial vehicle  230 . In particular, the accelerometer can measure the orientation of the aerial vehicle  230  with respect to earth, while the gyroscope measures the rate of rotation around an axis, such as a centerline of the aerial vehicle  230 . IMUs are commercially available in low-cost, low-power packages. For instance, the IMU may take the form of or include a miniaturized MicroElectroMechanical System (MEWS) or a NanoElectroMechanical System (NEMS). Other types of IMUs may also be utilized. The IMU may include other sensors, in addition to accelerometers and gyroscopes, which may help to better determine position. Two examples of such sensors are magnetometers and pressure sensors. Other examples are also possible. 
         [0050]    While an accelerometer and gyroscope may be effective at determining the orientation of the aerial vehicle  230 , slight errors in measurement may compound over time and result in a more significant error. However, an example aerial vehicle  230  may be able mitigate or reduce such errors by using a magnetometer to measure direction. One example of a magnetometer is a low-power, digital 3-axis magnetometer, which may be used to realize an orientation independent electronic compass for accurate heading information. However, other types of magnetometers may be utilized as well. 
         [0051]    The aerial vehicle  230  may also include a pressure sensor or barometer, which can be used to determine the altitude of the aerial vehicle  230 . Alternatively, other sensors, such as sonic altimeters or radar altimeters, can be used to provide an indication of altitude, which may help to improve the accuracy of and/or prevent drift of the IMU. In addition, the aerial vehicle  230  may include one or more load cells configured to detect forces distributed between a connection of the tether  220  to the aerial vehicle  230 . 
         [0052]    As noted, the aerial vehicle  230  may include the power system  234 . The power system  234  could take various different forms in various different embodiments. For example, the power system  234  may include one or more batteries for providing power to the aerial vehicle  230 . In some implementations, the one or more batteries may be rechargeable and each battery may be recharged via a wired connection between the battery and a power supply and/or via a wireless charging system, such as an inductive charging system that applies an external time-varying magnetic field to an internal battery and/or charging system that uses energy collected from one or more solar panels. 
         [0053]    As another example, the power system  234  may include one or more motors or engines for providing power to the aerial vehicle  230 . In some implementations, the one or more motors or engines may be powered by a fuel, such as a hydrocarbon-based fuel. And in such implementations, the fuel could be stored on the aerial vehicle  230  and delivered to the one or more motors or engines via one or more fluid conduits, such as piping. In some implementations, the power system  234  may be implemented in whole or in part on the ground station  210 . 
         [0054]    As noted, the aerial vehicle  230  may include the power generation/conversion components  236 . The power generation/conversion components  236  could take various different forms in various different embodiments. For example, the power generation/conversion components  236  may include one or more generators, such as high-speed, direct-drive generators. With this arrangement, the one or more generators may be driven by one or more rotors. And in at least one such example, the one or more generators may operate at full rated power wind speeds of 11.5 meters per second at a capacity factor which may exceed 60 percent, and the one or more generators may generate electrical power from 40 kilowatts to 600 kilowatts. 
         [0055]    Moreover, as noted, the aerial vehicle  230  may include a communication system  238 . The communication system  238  may take the form of or be similar in form to the communication system  218 . The aerial vehicle  230  may communicate with the ground station  210 , other aerial vehicles, and/or other entities (e.g., a command center) via the communication system  238 . 
         [0056]    In some implementations, the aerial vehicle  230  may be configured to function as a “hot spot”; or in other words, as a gateway or proxy between a remote support device (e.g., the ground station  210 , the tether  220 , other aerial vehicles) and one or more data networks, such as cellular network and/or the Internet. Configured as such, the aerial vehicle  230  may facilitate data communications that the remote support device would otherwise be unable to perform by itself. 
         [0057]    For example, the aerial vehicle  230  may provide a WiFi connection to the remote device, and serve as a proxy or gateway to a cellular service provider&#39;s data network, which the aerial vehicle  230  might connect to under an LIE or a 3G protocol, for instance. The aerial vehicle  230  could also serve as a proxy or gateway to other aerial vehicles or a command station, which the remote device might not be able to otherwise access. 
         [0058]    As noted, the aerial vehicle  230  may include the one or more processors  242 , the program instructions  246 , and the data storage  244 . The one or more processors  242  can be configured to execute computer-readable program instructions  246  that are stored in the data storage  244  and are executable to provide at least part of the functionality described herein. The one or more processors  242  may take the form of or be similar in form to the one or more processors  212 , the data storage  244  may take the form of or be similar in form to the data storage  214 , and the program instructions  246  may take the form of or be similar in form to the program instructions  216 . 
         [0059]    Moreover, as noted, the aerial vehicle  230  may include the control system  248 . In some implementations, the control system  248  may be configured to perform one or more functions described herein. The control system  248  may be implemented with mechanical systems and/or with hardware, firmware, and/or software. As one example, the control system  248  may take the form of program instructions stored on a non-transitory computer readable medium and a processor that executes the instructions. The control system  248  may be implemented in whole or in part on the aerial vehicle  230  and/or at least one entity remotely located from the aerial vehicle  230 , such as the ground station  210 . Generally, the manner in which the control system  248  is implemented may vary, depending upon the particular application. 
         [0060]    While the aerial vehicle  230  has been described above, it should be understood that the methods and systems described herein could involve any suitable aerial vehicle that is connected to a tether, such as the tether  220  and/or the tether  120 . 
       C. Illustrative Aerial Vehicle 
       [0061]      FIG. 3  depicts an aerial vehicle  330 , according to an example embodiment. The aerial vehicle  130  and/or the aerial vehicle  230  may take the form of or be similar in form to the aerial vehicle  330 . In particular, the aerial vehicle  330  may include a main wing  331 , pylons  332   a ,  332   b , rotors  334   a ,  334   b ,  334   c ,  334   d , a tail boom  335 , and a tail wing assembly  336 . Any of these components may be shaped in any form which allows for the use of components of lift to resist gravity and/or move the aerial vehicle  330  forward. 
         [0062]    The main wing  331  may provide a primary lift force for the aerial vehicle  330 . The main wing  331  may be one or more rigid or flexible airfoils, and may include various control surfaces, such as winglets, flaps (e.g., Fowler flaps, Hoerner flaps, split flaps, and the like), rudders, elevators, spoilers, dive brakes, etc. The control surfaces may be used to stabilize the aerial vehicle  330  and/or reduce drag on the aerial vehicle  330  during hover flight, forward flight, and/or crosswind flight. 
         [0063]    The main wing  331  and pylons  332   a ,  332   b  may be any suitable material for the aerial vehicle  330  to engage in hover flight, forward flight, and/or crosswind flight. For example, the main wing  331  and pylons  332   a ,  332   b  may include carbon fiber and/or e-glass, and include internal supporting spars or other structures. Moreover, the main wing  331  and pylons  332   a ,  332   b  may have a variety of dimensions. For example, the main wing  331  may have one or more dimensions that correspond with a conventional wind turbine blade. As another example, the main wing  331  may have a span of 8 meters, an area of 4 meters squared, and an aspect ratio of 15. 
         [0064]    The pylons  332   a ,  332   b  may connect the rotors  334   a ,  334   b ,  334   c , and  334   d  to the main wing  331 . In some examples, the pylons  332   a ,  332   b  may take the form of, or be similar in form to, a lifting body airfoil (e.g., a wing). In some examples, a vertical spacing between corresponding rotors rotor  334   a  and rotor  334   b  on pylon  332   a ) may be 0.9 meters. 
         [0065]    The rotors  334   a ,  334   b ,  334   c , and  334   d  may be configured to drive one or more generators for the purpose of generating electrical energy. In this example, the rotors  334   a ,  334   b ,  334   c , and  334   d  may each include one or more blades, such as three blades or four blades. The rotor blades may rotate via interactions with the wind and be used to drive the one or more generators. In addition, the rotors  334   a ,  334   b ,  334   c , and  334   d  may also be configured to provide thrust to the aerial vehicle  330  during flight. With this arrangement, the rotors  334   a ,  334   b ,  334   c , and  334   d  may function as one or more propulsion units, such as a propeller. Although the rotors  334   a ,  334   b ,  334   c , and  334   d  are depicted as four rotors in this example, in other examples the aerial vehicle  330  may include any number of rotors, such as less than four rotors or more than four rotors (e.g., eight rotors). 
         [0066]    A tail boom  335  may connect the main wing  331  to the tail wing assembly  336 , which may include a tail wing  336   a  and a vertical stabilizer  336   b . The tail boom  335  may have a variety of dimensions. For example, the tail boom  335  may have a length of 2 meters. Moreover, in some implementations, the tail boom  335  could take the form of a body and/or fuselage of the aerial vehicle  330 . In such implementations, the tail boom  335  may carry a payload. 
         [0067]    The tail wing  336   a  and/or the vertical stabilizer  336   b  may be used to stabilize the aerial vehicle  330  and/or reduce drag on the aerial vehicle  330  during hover flight, forward flight, and/or crosswind flight. For example, the tail wing  336   a  and/or the vertical stabilizer  336   b  may be used to maintain a pitch of the aerial vehicle  130  during hover flight, forward flight, and/or crosswind flight. The tail wing  336   a  and the vertical stabilizer  336   b  may have a variety of dimensions. For example, the tail wing  336   a  may have a length of 2 meters. Moreover, in some examples, the tail wing  336   a  may have a surface area of 0.45 meters squared. Further, in some examples, the tail wing  336   a  may be located 1 meter above a center of mass of the aerial vehicle  130 . 
         [0068]    While the aerial vehicle  330  has been described above, it should be understood that the systems described herein could involve any suitable aerial vehicle that is connected to an airborne wind turbine tether, such as the tether  120  and/or the tether  220 . 
       D. Aerial Vehicle Coupled to a Ground Station Via a Tether 
       [0069]      FIG. 4  depicts the aerial vehicle  330  coupled to a ground station  510  via the tether  120 . Referring to  FIG. 4 , the ground station  410  may include a winch drum  412  and a platform  414 . The ground station  110  and/or the ground station  210  may take the form of or be similar in form to the ground station  410 .  FIG. 4  is for illustrative purposes only and may not reflect all components or connections. 
         [0070]    As shown in  FIG. 4 , the tether  120  may be coupled to a tether gimbal assembly  442  at a proximate tether end  122  and to the aerial vehicle  330  at a distal tether end  124 . Additionally or alternatively, at least a portion of the tether  120  (e.g., the at least one insulated electrical conductor) may pass through the tether gimbal assembly  442 . In some embodiments, the tether  120  may terminate at the tether gimbal assembly  442 . Moreover, as shown in  FIG. 4 , the tether gimbal assembly  442  may also be coupled to the winch drum  412  which in turn may be coupled to the platform  414 . In some embodiments, the tether gimbal assembly  442  may be configured to rotate about one or more axes, such as an altitude axis and an azimuth axis, in order to allow the proximate tether end  122  to move in those axes in response to movement of the aerial vehicle  330 . 
         [0071]    A rotational component  444  located between the tether  120  and the tether gimbal assembly  442  may allow the tether  120  to rotate about the long axis of the tether  120 . The long axis is defined as extending between the proximate tether end  122  and the distal tether end  124 . In some embodiments, at least a portion of the tether  120  may pass through the rotational component  444 . Moreover, in some embodiments, the tether  120  may pass through the rotational component  444 . Further, in some embodiments, the rotational component  444  may include a fixed portion  444   a  and a rotatable portion  444   b , for example, in the form of one or more bearings and/or slip rings. The fixed portion  444   a  may be coupled to the tether gimbal assembly  442 . The rotatable portion  444   b  may be coupled to the tether  120 . 
         [0072]    The use of the word fixed in the fixed portion  444   a  of the rotational component  444  is not intended to limit fixed portion  444   a  to a stationary configuration. In this example, the fixed portion  444   a  may move in axes described by the tether gimbal assembly  442  (e.g., altitude and azimuth), and may rotate about the ground station  410  as the winch drum  412  rotates, but the fixed portion  444   a  will not rotate about the tether  120 , i.e., with respect to the long axis of the tether  120 . Moreover, in this example, the rotatable portion  444   b  of the rotational component  444  may be coupled to the tether  120  and configured to substantially rotate with the rotation of tether  120 . 
         [0073]    Via the rotational component  444 , the tether  120  may rotate about its centerline along the long axis as the aerial vehicle  330  orbits. The distal tether end  124  may rotate a different amount than the proximate tether end  122 , resulting in an amount of twist along the length of the tether  420 . With this arrangement, the amount of twist in the tether  420  may vary based on a number of parameters during crosswind flight of the aerial vehicle  330 . 
       E. Illustrative Bridles and Bridle Systems 
       [0074]      FIG. 5  depicts the aerial vehicle  330  coupled to the tether  120  via a bridle system  500 .  FIG. 5  and the remaining Figures depicting bridles and bridle systems are for illustrative purposes only and may not reflect all components or connections. Further, as illustrations, the Figures may not reflect actual operating conditions but are merely to illustrate the embodiments described. For example, while a perfectly straight figure may be used to illustrate the described bridle components, during orbiting crosswind flight the tether and/or bridle(s) may in practice exhibit some level of droop between the ground station and the aerial vehicle. Further still, the relative dimensions in the Figures may not be to scale but are merely to illustrate the embodiments described. 
         [0075]    As shown in  FIG. 5 , the bridle system  500  includes a first bridle  510  and a second bridle  520 , according to an example embodiment. The bridle system  500  includes a first bridle-to-tether interface  510 A and a second bridle-to-tether interface  520 A. The bridle system  500  includes a first bridle-to-wing interface  510 B and a second bridle-to-wing interface  520 B. The bridle system  500  includes a tether termination component  502 . 
         [0076]    In some implementations, the tether  120  terminates at the tether termination component  502 . A double clevis, 2-pin connector may be used as the bridle-to-tether interface for interfaces  510 A and  510 B. This interface transfers mechanical load from the tether to the bridles, allows for a roll degree-of-freedom, and allows the transfer of power and signal conductors from the tether to the bridles. Other connectors may be used as well (e.g., a double clevis and single pin connector and a 3 pin configuration). In some embodiments, the pins may use wear-resistant and low-friction journal bearings to achieve good roll motion. For example, a journal bearing with a polytetrafluoroethylene (“PTFE”) embedded fabric on a stainless steel backing may be used. In some embodiments, a spherical bearing may be used at the bridle-to-tether interface. Other connectors and examples are possible. 
         [0077]    The power and signal transfer may occur, for example, by way of a power transfer loop, cable, or system such as a full or partial service loop that allows roll motion without generating bending fatigue on the conductors. The first bridle  510  and the second bridle  520  may have a structural member composed of wrapping fiber filaments around thimbles (e.g., the clevis pin at the tether-to-bridle interface may go through the bridle thimble). The wrapped fiber filaments may be consolidated and cured into a solid, stiff, and strong link. 
         [0078]    As shown in  FIG. 5 , the length of the bridles may be different. For example, the length of the second bridle  520  from the bridle-to-tether interface  520 A to the bridle-to-wing interface  520 B may be shorter than the length of the first bridle  510  from the bridle-to-tether interface  510 A to the bridle-to-wing interface  510 B in order to balance the load during power generation (since the aerial vehicle may be flying in a one-directional path). The electrical conductors (not shown in  FIG. 5 ) may take advantage of this shorter distance (and the nominally smaller loads experienced along the second bridle  520  compared to the loads along the first bridle  510 ) and only extend along the second bridle  520 . 
         [0079]    The bridle-to-wing interfaces  510 B and  520 B may use a spherical bearing to allow low-friction and high-cycle pitch movement. A metal plate installed on the aerial vehicle may act as a clevis and capture the bearing to transfer load in the aerial vehicle (e.g., into the wing spar of the aerial vehicle). In some embodiments, the bridle-to-wing interface may not comprise a spherical bearing. For example, the bridle-to-wing interface may be a saddle-type bearing surface (e.g., links in a chain), a combination of journal and thrust bearings; or two journal bearings joints that serve as a universal joint. Other examples are possible. 
         [0080]      FIG. 6  depicts a bridle  600  in a first orientation and in a second orientation where the bridle  600  is turned 90 degrees from the first orientation, according to an example embodiment. The bridle  600  includes one or more sensors (not shown), bridle-to-tether interface  610 A, a tether thimble  612 , a bridle-to-wing interface  620 A, a wing thimble  620 , and a structural member  630 . As shown in  FIG. 6 , the wing thimble and the tether thimble are rotated ninety degrees. In some implementations, the wing thimble and the tether thimble may be rotated more or less than ninety degrees, or may be in phase and not rotated at all. 
         [0081]    The structural member  630  may comprise wrapped fiber filaments or a variety of materials. For instance, in some embodiments, the structural member  630  may comprise carbon fiber, glass fiber, dry strength fiber (e.g., aramid, poly(p-phenylene-2,6-benzobisoxazole) (“PBO”), or ultra-high-molecular-weight polyethylene (“UHMW-PE”)), metallic wire, or any other suitable material. 
         [0082]    Portions of the bridle that may experience higher loads may be more reinforced than others. For example, as depicted in  FIG. 6 , the portion of the bridle-to-tether interface  610 A that is closest to the tether thimble  612  may have more reinforcement (e.g., a higher number of wrapped fiber filaments) in comparison to the center of the structural member  630 . Similarly, the portion of the bridle-to-wing interface  620 A that is closest to the wing thimble  622  may have more reinforcement (e.g., a higher number of wrapped fiber filaments) in comparison to the center of the structural member  630 . 
         [0083]    The dimensions of the bridles and bridle components may be selected based at least in part on a predicted loading of the bridle  600 , such as a predicted tensile loading of the bridle  600 . For use with AWTs, a first bridle may have a length L of about 7100 millimeters (e.g., the distance from the center of the tether thimble  612  to the center of the wing thimble  622 ). On the first bridle, the tether thimble  612  may have an inside diameter D 2  of about 62 millimeters and a width W 2  of about 57 millimeters. On the first bridle, the wing thimble  622  may have an inside diameter D 1  of about 120 millimeters and a width W 1  of about 45 millimeters. A second bridle may have a length L of about 7880 millimeters. The second bridle may have a tether thimble  612  with an inside diameter D 2  of about 62 millimeters and a width W 2  of about 57 millimeters. The second bridle may have a wing thimble  622  with an inside diameter D 1  of about 120 millimeters and a width W 1  of about 45 millimeters. 
         [0084]    The bridle system  600  may include one or more sensors (not shown). The sensors may be placed on the terminations (e.g., the bridle-to-tether interface  610 A and the bridle-to-wing interface  620 A), or the sensors could be placed elsewhere in the bridle  600 , in the tether  120 , or the aerial vehicle  330 . In some embodiments, the bridle system  600  may be designed to measure loads or positions. For example, the bridle system  600  may include a sensor such as an embedded fiber-bragg strain-sensing fiber optic, a one-directional load pin at a bridle end, a bidirectional load pin at a bridle end, or a direct strain gage coupled to the bridle-to-wing interface  620 A. 
         [0085]      FIGS. 6A and 6B  depict the bridle  600  in cross-section along the lines AA and BB in  FIG. 6 , according to an example embodiment. As shown in  FIGS. 6A and 6B , the structural member  630  may have an approximately elliptical shape in cross-section. In some implementations, the oval aspect ratio is about 2:1. As shown in  FIG. 6A , the structural member  630  cross-section is in phase with the wing thimble  622 . As shown in  FIG. 6B , the structural member  630  is still in phase with the wing thimble, but is 90 degrees out of phase with the tether thimble  612 . By providing a 90 degree phase difference between the tether thimble  612  and the wing thimble  622 , the tether thimble  612  may be aligned with a roll axis to allow for roll motions, and the wing thimble  622  may be aligned with a pitch axis to allow for pitch motions. Further, having the cross-section of the structural member  630  in phase with the wing thimble  622  minimizes drag on the bridle  600 . While  FIGS. 6A and 6B  depict an elliptical cross-section of the structural member  630 , the cross-section may have various shapes, such as a circle or an aerofoil shape, among others. 
         [0086]      FIGS. 7A, 7B, 7C, and 7D  depict example implementations for placing conductors in or around the bridle, according to some embodiments.  FIG. 7A  depicts a bridle  700  with a structural member  730 , two hollow tubes  740 , and conductors  750 . The conductors  750  may be insulated or bare. In some implementations, one or more hollow tubes may be configured inside of the structural member  730 . Conductors  750  may run through the hollow tubes  740  and extend throughout the bridle  700 . 
         [0087]    In other implementations, the conductors  750  may be connected in other ways. For example, the conductors  750  may be connected to the wing along a path that is separate from the bridles. In some embodiments, the conductors (and other components) may run on the only one bridle. In other embodiments, the conductors (and other components) may be split between two or more bridles. In some embodiments, the conductors are run on the outside of the bridle in a straight line. In some embodiments, the conductors are helically wrapped around the structural member of the bridle. In some embodiments, the conductors are tacked to the structural member in several places but have slack between those spots so the structural member can be loaded without straining the conductors. In some embodiments, each conductor on a bridle is matched with a conductor on the tether. In other embodiments, conductors on the bridle may be combined such that the bridle has fewer conductors than the tether (e.g., conductors within a phase may be combined). 
         [0088]      FIG. 7B  depicts a bridle  700  with an elliptically shaped structural member  730 , a fairing component  735 , and conductors  750 . As shown in  FIG. 7B , the bridle  700  may include a fairing component  735  that couples to the structural member  730  to provide a more aerodynamic shape for the structural member  730  and conductors  750 . The structural member  730  may be surrounded by a layer of compliant material  732  with an elastic modulus higher than that of the structural member  730 . The compliant material  732  may protect the conductors  750  from abrasion caused by friction against the structural member  730  and from the full axial strains of the structural member  730 . A bridle may be faired in some or all parts, including along the main length of the structural member  730  and at the terminations (e.g., the bridle-to-wing interface and the bridle-to-tether interface). The fairing could comprise a “V” shape that is added to a round or elliptical main cross-section, or the main section itself may be molded into an aerodynamic shape. Fairing design includes a proper positioning of the center of gravity, elastic center, and the aerodynamic center such that the bridle will be stable at all flights speeds and not flutter. 
         [0089]    To mitigate flutter, the conductors  750  may run along the leading edge of the bridle  700  so that the center of mass of the bridle  700  is placed in such a way that the faired bridle is stable. The fairing component  735  may be a non-structural component that is added around all or part of the bridle  700  to lower the drag and/or pull back the aerodynamic center of the bridle  700  cross-section for stability and to resist flutter. The cross-section of the structural core may be elliptically shaped where the minor axis is aligned with the airflow. This alignment provides more width to fit the conductors  750  neatly in front of the structural member  730  and shortens the amount of total fairing needed, which in turn allows the bridle  700  to be more tolerant of high angles between the oncoming air or relative wind and a reference line on the bridle  700 . The fairing component  735  may be designed to fit around the bridle  700  such that it can rotate and “vane” into the wind to help achieve a proper orientation. In some embodiments, where wind direction is expected to remain substantially constant along the length of the bridle  700 , the fairing component  735  may be affixed to the structural member  730  in alignment with the airflow such that it cannot rotate or “vane.” 
         [0090]    In some implementations, the fairing may have a profile that not only reduces drag (e.g., via boundary tripping features) in one direction, but has a low drag and/or low lift when the angle of attack is at higher angles. The major axis of the fairing may be angled slightly to help match the typical direction of the local relative airflow (instead of being aligned perpendicular to the wing axis). In some implementations, the angle of the major axis of the fairing may vary along the length of the bridle  700 . 
         [0091]    In some implementations, bridle  700  may have surface features that trips the boundary layer for lower overall drag. For example, the bridle  700  may have riblets, grooves, vortex generators, dibbles, or other boundary layer tripping features. In some implementations, bridle  700  may have surface features that provide leading edge protection, such as a polyurethane elastomer or any other material that may provide leading edge wind protection. 
         [0092]      FIG. 7C  depicts a bridle  700  with a circular structural member  730 , a fairing component  735 , and conductors  750 . As shown in  FIG. 7C , the bridle  700  may include a fairing component  735  that couples to the structural member  730  to provide a more aerodynamic shape for the structural member  730  and conductors  750 . The conductors  750  may run along the leading edge of the bridle  700  so that the center of mass of the bridle  700  is placed in such a way that the faired bridle is stable and won&#39;t flutter. The fairing component  735  may be a non-structural component that is added around all or part of the bridle  700  to lower the drag and/or pull the aerodynamic center of the bridle  700  cross-section for stability and to resist flutter. 
         [0093]      FIG. 7D  depicts conductors  750  helically wrapped about a structural member  730  of a bridle  700 . As shown in  FIG. 7D , the bridle  700  may include a structural member  730 , a plurality of electrical conductors  750 , and a jacket  760 . The bridle  700  may have a long axis  702 . For purposes of illustration only, the bridle  700  in  FIG. 7D  is shown with a portion of some components removed (e.g., the jacket  760  and the plurality of electrical conductors  750 ) to illustrate the arrangement of components in the bridle  700 . Accordingly,  FIG. 7D  may be referred to as a partial cutaway view of the bridle  700 . 
         [0094]    The structural member  730  may be wrapped fiber filaments that have been consolidated and cured as described herein. In some embodiments, the structural member  730  may provide a significant contribution to the tensile strength and/or shear strength of the bridle  700 . Beneficially, the structural member  730  may improve resistance of the bridle  700  to fatigue loads while an AWT (e.g., the AWT  100  and/or AWT  200 ) is in operation. Further, the structural member  730  may improve resistance of various components of the bridle  700  to fatigue or tensile loads, such as the plurality of electrical conductors  750 . 
         [0095]    The structural member  730  may take various different forms in various different embodiments. For example, in some embodiments, the structural member  730  may comprise pultruded fiber rod, carbon fiber rod, fiberglass, one or more metals (e.g., aluminum), a combination of carbon fiber, fiberglass, and/or one or more metals, and/or resins or thermoplastics. As one example, the structural member  730  may comprise a combination of fibers, such as a first carbon fiber having a first modulus and second carbon fiber having a second modulus that is greater than the first modulus. As another example, the structural member  730  may comprise carbon fiber and fiberglass. Further, the structural member  730  may comprise a matrix composite and/or carbon fiber and/or fiberglass, such as a metal matrix composite (e.g., aluminum matrix composite). 
         [0096]    In some embodiments, the structural member  730  may have a circular cross-section shape or may comprise other cross-section shapes. For example, in some embodiments, the structural member  730  may have an elliptical shape (e.g., with an aspect ratio of about 2:1), a trapezoidal cross-section shape, a pie-wedge cross-section shape, a rectangular cross-section shape, a triangular cross-section shape, etc. In some embodiments, the structural member  730  may comprise a plurality of smaller structural members with various cross-section shapes. In addition, in some embodiments, the structural member  730  may have a cross-section shape that varies along the long axis  702  of the bridle  700 . 
         [0097]    Further, the plurality of electrical conductors  750  may be configured to transmit electricity. For example, the plurality of electrical conductors  750  may be configured for high-voltage AC or DC power transmission e.g., greater than 1,000 volts). For instance, the plurality of electrical conductors  750  may be configured to carry an AC or DC voltage of between 1 kilovolt and 5 kilovolts, or higher, and an associated power transmission current of between 50 amperes to 250 amperes. 
         [0098]    In some embodiments, as shown in  FIG. 7D , the plurality of electrical conductors  750  may be helically wound around the outer surface of the structural member  730 . The plurality of electrical conductors  750  may be wound in other ways. For example, in some embodiments, electrical conductors in the plurality of electrical conductors  750  may have an alternating arrangement around the outer surface of the structural member  730 , or a reverse oscillating lay around the outer surface of the structural member  730 . 
         [0099]    In some embodiments, the plurality of electrical conductors  750  may include groups of electrical conductors that define separate electrical paths. Further, in some embodiments, the groups of electrical conductors may be configured to operate differently. For instance, in an AC power transmission arrangement, a first group of electrical conductors may be configured to carry a first phase of electrical power along a first electrical path, a second group of electrical conductors may be configured to carry a second phase of electrical power along a second electrical path that is different from the first phase of electrical power, and so on. Moreover, in a DC power transmission arrangement, a first group of electrical conductors may be configured to operate at a first potential along a first electrical path, a second group of electrical conductors may be configured to operate at a second potential along a second electrical path that is different from the first potential, and so on. As one example, the first potential may be +2000 volts relative to ground, and the second potential may be −2000 volts relative to ground. As another example, the first potential may be a high voltage, and the second potential may be near ground potential. 
         [0100]    In some embodiments, each electrical conductor of the plurality of electrical conductors  750  may comprise the same material and have the same thickness. However, in some embodiments, at least two electrical conductors of the plurality of electrical conductors  750  may comprise different materials and/or have different thicknesses. For example, in some embodiments, an electrical conductor in the first group of electrical conductors that is adjacent to an electrical conductor in the second group of electrical conductors may have a different thickness than an electrical conductor in the first group of electrical conductors that is adjacent to two electrical conductors in the first group of electrical conductors. 
         [0101]    In some embodiments, the electrical conductors  750  may be relieved of strain by winding at a helical angle that is steep or far from the bridle axis. The electrical conductors  750  may additionally be relieved of strain by inclusion of a low bulk modulus layer within the winding radius of the electrical conductors  750 , such that the low bulk modulus layer compresses under the tension of the electrical conductors  750 , allowing some inward radial travel of the electrical conductors  750 , and thus reduces the required free length of the electrical conductors  750 . 
         [0102]    Moreover, in some embodiments, each electrical conductor of the plurality of electrical conductors  750  may include an insulating layer  752 . However, in other embodiments, at least one electrical conductor of the plurality of electrical conductors  750  may not include an insulating layer. 
         [0103]    In some embodiments, the bridle  700  may further include a fill material  790  located between the conductors  750  and the jacket  760 , such that the fill material  790  fills the interstices. With this arrangement, the fill material  790  may block moisture from the plurality of electrical conductors  750 . For instance, in some embodiments, the fill material  790  may block moisture from diffusing inside of the bridle  700  along the plurality of electrical conductors  750 . 
         [0104]    Fill material  790  may take various different forms in various different embodiments. For instance, in some embodiments, the fill material  790  may include a vulcanizing rubber on silicone, such as a room-temperature vulcanizing rubber. In addition, the fill material  790  may include mylar. Further, in some such embodiments, the fill material  790  may comprise one or more filler rods, fibers, and/or tapes. 
         [0105]    The jacket  760  may take various different forms in various different embodiments. For instance, the jacket  760  may include a thermoplastic polyurethane (“TPU”), polypropylene, hytrel, and/or nylon (e.g., nylon 11). In some embodiments, the jacket  760  may be extruded over the plurality of electrical conductors  750 . Moreover, in some embodiments, when the bridle  700  includes the fill material  790 , the jacket  760  may be extruded over the fill material  790 . Further, in some embodiments, the jacket  760  may have a preferred thickness of 1.2 or 1.5 millimeters. Other thicknesses are possible as well. 
         [0106]    In some embodiments, one or more materials of the jacket  760  may be selected to increase the visibility of the bridle  700  to humans and/or animals. For instance, in some embodiments, the jacket  760  may include materials that have a white or bright color, or a contrasting color pattern. Further, in some embodiments, the jacket  760  may include a material or coating that reflects ultra-violet (UV) light, glows, or a combination of UV reflection and glowing. 
         [0107]    Further, in some examples, the bridle  700  may further include at least one fiber optic cable and/or a coaxial conductor (not shown). The fiber optic cable or coaxial conductor may be configured for communication between an aerial vehicle (e.g., the aerial vehicle  330 ) and a ground station (e.g., the ground station  410  via the tether  120 ). In some embodiments, the fiber optic cable or coaxial cable may be wound around the outer surface structural member  730  in the same or similar way as the plurality of electrical conductors  750  are wound. Yet further, in some examples, the bridle  700  may further include conductors configured to communicate via Ethernet over power (“EOP”). 
         [0108]    In some implementations, a bridle may include a jacket that has a plurality of drag-affecting surface features (e.g., features that trip the boundary layer).  FIG. 8A  depicts a bridle  800 , according to an example embodiment. Further,  FIG. 8B  depicts the bridle  800  in cross-section along line AA, according to an example embodiment. For purposes of illustration only, the bridle  800  in  FIG. 8A  is shown with a portion of some components removed in the same way as the bridle  700  in  FIG. 7D . 
         [0109]    As shown in  FIG. 8A , the bridle  800  may include, among other components, a structural member  830 , a plurality of electrical conductors  850 , a jacket  860 , and a fill material  890 . Components in  FIGS. 8A and 8B  similar to those in  FIG. 7D  may be of the same configuration and function in a similar manner. 
         [0110]    The jacket  860  may include an inner surface  842  that covers at least a portion of the plurality of electrical conductors  830  and an outer surface  844  opposite the inner surface  842 . The outer surface  844  of the jacket  860  may comprise a plurality of drag-affecting surface features  846 . The plurality of drag-affecting surface features  846  may be configured to affect drag of the bridle  800 . As one example, the plurality of drag-affecting surface features  846  may reduce the drag of the bridle  800 . As another example, the plurality of drag-affecting surface features  846  may increase the drag of the bridle  800 . 
         [0111]    The plurality of drag-affecting surface features  846  may take various different forms in various different embodiments. In some embodiments, the plurality of drag-affecting surface features  846  may comprise a plurality of flutes  847  (e.g., grooves) in the outer surface  844  of the jacket  860 . As shown in  FIG. 8B , in some embodiments, the plurality of flutes  847  may include sixteen flutes having a pitch of 500 millimeters (flute  847   a  of the plurality of flutes  847  labeled in  FIG. 8B ). However, in other embodiments, the plurality of flutes  847  may include more or less than sixteen flutes and/or the plurality of flutes  847  may have a different pitch. In addition, in some embodiments, each flute of the plurality of flutes  847  may have the same depth and same radius. However, in other embodiments, at least two flutes of the plurality of flutes  847  may have a different depth and/or a different radius. As one example, flute  847   a  may have a depth of 0.6 millimeters and a radius of 0.8 millimeters. 
         [0112]    Moreover, in some embodiments, the plurality of drag-affecting surface features  846  may include a plurality of strakes (e.g., ridges) protruding from the outer surface  844  of the jacket  860 , a plurality of dimples, tape with riblets, or any other textured shape/material that can affect drag of the bridle  800 . In addition, the plurality of surface features  846  may include one or more of flutes, strakes, dimples, and tape with riblets. With this arrangement, the plurality of surface features  846  may comprise a combination of flutes, strakes, dimples and/or tape with riblets. 
         [0113]    The plurality of drag-affecting surface features  846  may be arranged on the outer surface  844  of the jacket  840  in a variety of ways. For instance, in some embodiments, the plurality of drag-affecting surface features  846  may be disposed on the outer surface  844  along the long axis  802  of the bridle  800 . Further, in some embodiments, the plurality of drag-affecting surface features  846  may be disposed on the outer surface  844  in a helical pattern. In some such embodiments, the helical pattern a be based on a fixed helical angle and/or a varying helical angle. Further still, in some embodiments, the plurality of drag-affecting surface features  846  may be disposed on the outer surface  844  in an oscillating path. Moreover, in some embodiments, at least a portion of the plurality of drag-affecting surface features  846  may be disposed on the outer surface  844  along the long axis  802  of the bridle  800 , in a helical pattern with a fixed or varying helical angle, or in an oscillating path. With this arrangement, the plurality of drag-affecting surface features  846  may comprise surface features arranged on the outer surface  844  in a combination of being disposed along the long axis  802  of the tether  800 , in a helical pattern with a fixed or varying helical angle, and/or in an oscillating path. 
         [0114]    Although example bridles described above may be used in AWTs, in other examples, bridles described herein may be used for other applications, including overhead transmission, aerostats, subsea and marine applications, including offshore drilling and remotely operated underwater vehicles (ROVs), towing, mining, and/or bridges, among other possibilities. 
       III. Conclusion 
       [0115]    The particular arrangements shown in the Figures should not be viewed as limiting. It should be understood that other embodiments may include more or less of each element shown in a given Figure. Further, some of the illustrated elements may be combined or omitted. Yet further, an exemplary embodiment may include elements that are not illustrated in the Figures. 
         [0116]    Additionally, while various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the Figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are contemplated herein.