Patent Description:
Unmanned aerial vehicles (UAVs), such as a High Altitude Long Endurance aircraft, are lightweight aerial vehicles that are capable of controlled, sustained flight. UAVs may rely on solar power and at least one power source to power the aircraft. During flight, a UAV may automatically switch between the power source and the solar power. If the Sun is present, a solar array onboard the UAV may capture solar energy and propel the UAV by applying the solar power to a motor. Furthermore, the solar energy may be used to charge the power source.

<NPL>, discloses a number of optimized trajectories for a UAV to follow to improve its solar energy capture. The optimized trajectories are modelled using an offline nonlinear dynamic simulation model to optimize a UAV mission based on initial flight conditions.

Viewed from a first aspect, there is provided a system as claimed in claim <NUM>. The system includes: at least one flight control computer (FCC) associated with at least one UAV, where the at least one FCC may be configured to: determine, when the at least one UAV is flying in a flight pattern, a direction of travel of the at least one UAV relative to the Sun; adjust a UAV airspeed of the at least one UAV flying in the flight pattern to a first airspeed if the determined direction of travel may be towards the Sun; and adjust the UAV airspeed of the at least one UAV flying in the flight pattern to a second airspeed if the determined direction of travel may be away the Sun; where the first airspeed may be greater than the second airspeed to maximize solar capture of a solar array covering at least a portion of the UAV. The system also includes a battery pack system comprising: a battery for powering the UAV; and a power tracker in communication with the battery and the solar array; wherein the power tracker is configured to receive electrical energy produced by the solar array; wherein the power tracker is configured to supply electrical charge to the battery; and wherein the power tracker is configured to provide a steady voltage to the battery while the electrical energy produced by the solar array varies throughout the day as the Sun's position changes in the sky.

The at least one FCC may be further configured to: adjust a UAV angle to a first angle relative to a horizontal plane if the determined direction of travel may be towards the Sun; and adjust the UAV angle to a second angle relative to the horizontal plane if the determined direction of travel may be away the Sun; where the UAV angle may be relative to a plane of the UAV parallel to an upper surface of the UAV, and where the first angle may be less than the second angle to further maximize solar capture of the solar array covering at least a portion of the UAV.

The first angle may be substantially parallel to the horizontal plane. The second angle may cause the UAV to tilt up such that the solar array is closer to perpendicular to the Sun's rays. The solar array may be disposed on an upper surface of a wing panel of the UAV.

The system may further include: at least one computing device associated with a ground control station, where the at least one computing device may be in communication with the at least one FCC. The at least one computing device may be configured to: transmit a communication signal to the at least one FCC. The transmitted communication signal may include a command for the at least one FCC to adjust the UAV airspeed based on the direction of travel of the at least one UAV relative to the Sun. The transmitted communication signal may include a command for the at least one FCC to adjust the UAV angle based on the direction of travel of the at least one UAV relative to the Sun. The at least one FCC may be further configured to sustain flight of the UAV throughout the night via energy stored in one or more batteries when there may be no solar capture of the solar array.

Viewed from a second aspect, there is provided a method as claimed in claim <NUM>. The method includes: determining, by at least one flight control computer (FCC) associated with at least one UAV, a direction of travel of the at least one UAV relative to the Sun, when the at least one UAV is flying in a flight pattern; adjusting, by the at least one FCC, a UAV airspeed of the at least one UAV flying in the flight pattern to a first airspeed if the determined direction of travel may be towards the Sun; and adjusting, by the at least one FCC, the UAV airspeed of the at least one UAV flying in the flight pattern to a second airspeed if the determined direction of travel may be away the Sun; where the first airspeed may be greater than the second airspeed to maximize solar capture of a solar array covering at least a portion of the UAV. The method also includes: receiving, by a power tracker in communication with a battery and the solar array, electrical energy from the solar array; and supplying, by the power tracker, an electrical charge to the battery; wherein the power tracker is configured to provide a steady voltage to the battery while the electrical energy produced by the solar array varies throughout the day as the Sun's position changes in the sky.

The method may further include: adjusting, by the at least one FCC, a UAV angle to a first angle relative to a horizontal plane if the determined direction of travel may be towards the Sun; and adjusting, by the at least one FCC, the UAV angle to a second angle relative to the horizontal plane if the determined direction of travel may be away the Sun; where the UAV angle may be relative to a plane of the UAV parallel to an upper surface of the UAV, and where the first angle may be less than the second angle to further maximize solar capture of the solar array covering at least a portion of the UAV.

At least one computing device associated with a ground control station may be in communication with the at least one FCC. The method may further include: transmitting, by the at least one computing device, a communication signal to the at least one FCC. In additional method embodiments, the transmitted communication signal includes a command for the at least one FCC to adjust the UAV airspeed based on the direction of travel of the at least one UAV relative to the Sun. The transmitted communication signal may include a command for the at least one FCC to adjust the UAV angle based on the direction of travel of the at least one UAV relative to the Sun. The method may further include: sustaining, by the at least one FCC, a flight of the UAV throughout the night via energy stored in one or more batteries when there may be no solar capture of the solar array.

The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principals of the invention. Like reference numerals designate corresponding parts throughout the different views. Embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which:.

The following description is made for the purpose of illustrating the general principles of the embodiments disclosed herein and is not meant to limit the concepts disclosed herein. Further, particular features described herein can be used in combination with other described features in each of the various possible combinations and permutations. Unless otherwise specifically defined herein, all terms are to be given their broadest possible interpretation including meanings implied from the description as well as meanings understood by those skilled in the art and/or as defined in dictionaries, treatises, etc..

Near the end of the day the battery of an unmanned aerial vehicle (UAV) will become nearly fully charged since the aircraft has been exposed to solar radiation throughout the duration of the day when the Sun is above the horizon. At this point, excess energy may become available, and more batteries may be disposed on the aircraft to harness the excess energy and continue powering the aircraft to sustain flight throughout the night. However, the additional batteries are costly. Furthermore, UAV are light and batteries can account for a substantial fraction of the total weight of the UAV. Therefore, including additional batteries may result in undesired weight onboard the UAV which may hinder the performance of the UAV.

A system embodiment provides for maximizing solar capture of a solar-powered unmanned aerial vehicle (UAV) to assist in propulsion of the aircraft when solar energy is limited or no longer available to the aircraft, such as when the Sun is low on the horizon. In one embodiment, the UAV is a High Altitude Long Endurance solar-powered aircraft. The UAV may have an onboard solar array that captures solar energy. The solar energy may be used to power a motor (or motors) to propel the aircraft. The solar energy may be further used to charge at least one battery. When solar capture is limited or no longer possible, such as at night, in cloudy conditions, or when the Sun is low on the horizon the battery may be used to power the motor for propulsion of the UAV.

In one embodiment, the flight speed of the UAV is adjusted as the UAV travels to and from the Sun to maximize solar capture. The UAV may fly in a large area flight pattern, such as a "D-loop" flight pattern.

When the Sun is lower on the horizon, such as later in the day or during the winter, the UAV may mainly capture solar energy as the UAV flies away the Sun. This is because the solar array, placed on the upper surface of the wing, may be angled to the rear of the UAV due to the leading-edge-up attitude of the wing needed to create lift. Therefore, when the Sun is lower on the horizon, the solar array may capture substantial solar energy to both propel the UAV and to charge the battery as the UAV flies away from the Sun in part of the UAV's flight pattern. Slowing down when flying away from the Sun exposes more of the solar array to the Sun, particularly when the Sun is low on the horizon. This is because the nose of the UAV tilts up as the UAV slows down, causing the solar array to be more generally perpendicular to the Sun's rays as the UAV travels away from the Sun.

As the UAV travels toward the Sun, solar capture is limited or may no longer be possible; therefore, power supplied to the motors may be shifted from solar power to battery power. Thus, to sustain flight throughout the night, it is desired to maximize the time spent capturing solar energy. The UAV may slow down on the portion of the flight pattern of the UAV where the UAV travels away from the Sun as to increase the time spent capturing solar energy. This slowing down may also allow angling the wing to a steeper angle, increasing the solar energy capture. On that part of the flight pattern where the UAV is flying toward the Sun, solar energy capture decreases. Therefore, the UAV flight speed may be increased to reduce the time spent with low solar energy capture. Furthermore, flying faster may allow angling the UAV wing to a shallower angle, thereby increasing the UAV's exposure to the Sun, since the aircraft is flying toward the Sun.

With respect to <FIG>, a system <NUM> for maximizing solar capture with a solar array <NUM> of an unmanned aerial vehicle (UAV) <NUM> is depicted. UAVs are aircraft with no onboard pilot and may fly autonomously or remotely. In one embodiment, the UAV <NUM> is a High Altitude Long Endurance aircraft. The UAV <NUM> may have between one and forty motors, and a wingspan between <NUM> feet (<NUM> meters) and <NUM> feet (<NUM> meters). In one embodiment, the UAV <NUM> has a wingspan of approximately <NUM> feet (<NUM> meters) and is propelled by ten electric motors powered by the solar array <NUM> covering at least a portion of the surface of the wing, resulting in zero emissions. Flying at an altitude of approximately <NUM>,<NUM> feet (<NUM>,<NUM> meters) above sea level and above the clouds, the UAV is designed for continuous, extended missions of up to months without landing.

The UAV <NUM> functions optimally at high altitude due at least in part to the lightweight payload of the UAV. The UAV is capable of considerable periods of sustained flight without recourse to land. In one embodiment, the UAV <NUM> may weigh approximately <NUM>,<NUM> lbs (<NUM>,<NUM>) and may include wing panel sections and a center panel, providing for efficient assembly and disassembly of the UAV <NUM> due to the attachability and detachability of the wing panel sections to each other and/or to the center panel.

In one embodiment, the system <NUM> may be an automated process for maximizing solar capture, wherein a computing device <NUM> at a ground control station <NUM> may be in communication with a flight control computer (FCC) <NUM> of the UAV <NUM>. More specifically, and with respect to <FIG>, an example of a top-level functional block diagram of the computing device <NUM> is illustrated. The computing device <NUM> comprises a processor <NUM>, such as a central processing unit (CPU), addressable memory <NUM>, an external device interface <NUM>, e.g., an optional universal serial bus port and related processing, and/or an Ethernet port and related processing, and an optional user interface <NUM>, e.g., an array of status lights and one or more toggle switches, and/or a display, and/or a keyboard and/or a pointer-mouse system and/or a touch screen. Optionally, the addressable memory may, for example, be: flash memory, eprom, and/or a disk drive or other hard drive. These elements may be in communication with one another via a data bus <NUM>. In some embodiments, via an operating system <NUM> such as one supporting a web browser <NUM> and applications <NUM>, the processor <NUM> may be configured to execute steps of a process establishing a communication channel. For example, the processor <NUM> may be in communication with the FCC <NUM> onboard the UAV <NUM> to change the UAV's <NUM> heading to maximize solar capture. In another embodiment, the FCC <NUM> may be directly programmed to automatically change the heading of the UAV <NUM> to maximize solar capture. In one embodiment, the UAV <NUM> may fly west in morning because the Sun is rising in the east. In one embodiment, the UAV <NUM> may fly east in the afternoon because the Sun is setting in the west. In one embodiment, the FCC may override the fly from Sun pattern and station keep if it is desired for the UAV to station keep. In station keeping, the UAV <NUM> maintains a flight pattern relative to the ground control station <NUM>.

With respect to <FIG>, the UAV <NUM>, as shown in <FIG>, further includes at least one motor <NUM> for propulsion of the UAV <NUM>. In one embodiment, the UAV <NUM> has ten electric motors. The solar array <NUM> may be configured to capture solar energy from the Sun when the Sun is above the horizon. The solar energy, in turn, is used to power all or part of the UAV's <NUM> propulsion. In one embodiment, the UAV <NUM> includes at least one wing panel <NUM> and the solar array <NUM> is adhered to at least a portion of an upper surface <NUM> of the wing panel <NUM>, as shown in <FIG>. As the UAV <NUM> travels away from the Sun when the Sun is low on the horizon, the solar array <NUM> faces the Sun to efficiently capture the solar radiation. This is because the more area of the solar array that is exposed to the Sun, the more solar radiation will be captured by the solar array. In one embodiment, as the Sun sets below the horizon, the solar array <NUM> no longer captures solar radiation; however, the energy captured by the solar array <NUM> mainly as the UAV <NUM> headed away from the Sun may be converted to electrical energy to charge or provide power to a battery. The battery, in turn, will provide power to the motor <NUM> to propel the UAV <NUM>. More specifically, the solar array <NUM> may contain a plurality of solar array cells <NUM>. The cells <NUM> may be photovoltaic (PV) cells. In one embodiment, the cells <NUM> convert the captured solar energy into direct current (DC) electrical energy. In one embodiment, the solar array <NUM> may produce approximately one-hundred and fifty volts. The conversion of solar energy to electricity may be achieved using semiconducting materials in the PV cells which exhibit the photovoltaic effect, where light (i.e., photons) are converted to electricity (i.e., voltage).

A battery pack system <NUM> includes a battery <NUM> for powering the UAV <NUM>. In one embodiment, battery <NUM> is a lithium ion (Li-ion) battery. It is desired to maximize the life span of the battery <NUM>, such as the "cycle life" and the "calendar life". Cycle life refers to the aging of the battery <NUM> based on the overall operating, or usage, time of the battery <NUM>. More specifically, the cycle life is the number of full discharge-charge cycles of the battery <NUM>. The calendar life is the aging of the battery <NUM> which is just as a function of time. The cycle life may be decreased by a number of factors, including; (<NUM>) strain caused by operating a too high or low of a voltage state, (<NUM>) high charge rates, (<NUM>) charging at very cool temperatures, and (<NUM>) high discharge rates. The calendar life of the Li-ion battery <NUM> may lose capacity with time, and the capacity loss may be exacerbated by generally operating at very high and low temperatures, and spending too much time at high states of charge during storage. Detection of a cut-off point and terminating the charge so not too much time is spent at high states of charge is critical in preserving battery life. There may be a predetermined upper voltage limit, or "termination voltage", beyond which the charge may be terminated. This is particularly important with fast chargers where the danger of overcharging is greater. In one embodiment, the battery <NUM> may have a long life cycle, enabling the support of extended missions and can be operated in extreme environmental conditions, such as high winds and low temperatures.

The battery pack <NUM> further includes at least one power tracker <NUM>, which may be proximate the battery <NUM>. In another embodiment, the power tracker <NUM> may be located outside of the battery pack <NUM>. The power point tracker <NUM> may be configured to ensure that a maximum amount of power is obtained from the solar array <NUM>. In one embodiment, the power tracker <NUM> is in communication with the solar array <NUM>, and the power tracker <NUM> is configured to receive electrical energy produced by the solar array <NUM>. More specifically, the cells <NUM> of the solar array <NUM> convert Sunlight into electrical energy and the power tracker <NUM> receives the electricity from the solar array <NUM> from an output <NUM>, such as a bus, of the solar array <NUM>. The solar array <NUM> operates at a lower voltage than the output <NUM>. In one embodiment, the power tracker <NUM> is a maximum power point tracker (MPPT) controller configured to boost voltage from the solar array <NUM> to the output <NUM> and to adjust a boost ratio to get the maximum power from the solar array <NUM>.

The power tracker <NUM> has an output <NUM> configured for supplying electrical charge to the battery <NUM>. In one embodiment, the power tracker <NUM> is configured to maximize the power from the solar array <NUM>, and to regulate the voltage transmitted to the battery <NUM>. For example, the amount of solar radiation captured, and hence, produced by the solar array <NUM> varies throughout the day as the Sun's position changes in the sky. The power tracker <NUM> is used to provide a steady voltage to the battery <NUM>. The battery <NUM> may sustain approximately <NUM>-<NUM> Volts (as opposed to roughly <NUM> Volts coming solely from the solar array).

When the battery <NUM> becomes close to being fully charged the battery <NUM> may no longer be able to charge rapidly, requiring a slow taper off of the charge. If the battery <NUM> is fully charged, the battery <NUM> may discharge when the battery <NUM> is left unused and may lose effectiveness (e.g., the ability to charge rapidly). Additionally, over-charging of the battery <NUM> may cause the generation of heat and gasses, both of which are harmful for the battery <NUM>, or cause the battery <NUM> to overheat and even burn.

Once the battery <NUM> is fully charged, the charging current may need to be reduced as the it is desired to taper off the charging process before any damage to the battery <NUM> occurs, while at all times maintaining the battery <NUM> temperature within its pre-determined limits. In one embodiment, the battery <NUM> temperature is maintained within its pre-determined limits by adjusting the power tracker <NUM> voltage boost ratio to operate the solar array <NUM> conditions that may reduce the energy output of the solar array <NUM>. In another embodiment, the battery <NUM> temperature is maintained within its preferred limits by absorbing the extra current with the UAV <NUM> propulsion system. In another embodiment, the battery <NUM> temperature is maintained within its preferred limits the battery <NUM> temperature is maintained within its pre-determined limits in combination with the aircraft propulsion system.

The solar array <NUM> may be used to propel the UAV <NUM>, power onboard electronics, and charge the battery <NUM> with surplus energy, as described above. More specifically, the cells <NUM> of the solar array <NUM> convert Sunlight into electrical energy to provide power to the motor <NUM>. In one embodiment, the solar array <NUM> has an output <NUM> configured for supplying electrical energy to the motor <NUM>. In one embodiment, the electrical energy is a DC current.

With reference to <FIG>, the UAV <NUM> may fly in large area flight patterns, such as a "D-loop" flight pattern. Other flight patterns are possible and contemplated, such as circular, oblong, or box-shaped flight patterns. When the Sun is lower on the horizon, such as later in the day or during the winter time the UAV <NUM> mainly captures solar energy as the UAV <NUM> flies away from the Sun, as shown in <FIG>. In one embodiment, the solar array <NUM> may be placed on a portion of the upper surface <NUM> of a wing <NUM> of the UAV <NUM>. The solar array <NUM> may be angled to the rear of the UAV <NUM> due to the leading-edge-up attitude of the wing <NUM> needed to create lift. Therefore, when the Sun is lower on the horizon, the solar array <NUM> may capture substantial solar energy to both propel the UAV <NUM> and to charge the battery <NUM> as the UAV <NUM> flies away from the Sun in part of the UAV's flight pattern.

Furthermore, slowing down when heading away from the Sun exposes more of the solar array <NUM> to the Sun, particularly when the Sun is low on the horizon, as shown in <FIG>. This is because a nose <NUM> of the UAV <NUM> tilts up as the UAV <NUM> slows down, causing the solar array <NUM> to be more generally perpendicular to the Sun's rays as the UAV <NUM> travels away from the Sun. The tilting up of the nose <NUM> of the UAV <NUM> as the UAV <NUM> slows down leads to a large solar aperture <NUM>, thereby maximizing solar capture.

When the UAV <NUM> turns and maneuvers to stay close to the station, e.g., the ground control station <NUM>, solar capture may be limited as the UAV <NUM> travels toward the Sun in the UAV's <NUM> flight pattern. Furthermore, when the UAV <NUM> is not needed to stay close to the ground control station <NUM>, solar capture is limited as the UAV <NUM> turns and travels toward the Sun in the UAV's <NUM> flight pattern. Therefore, the UAV <NUM> flight speed may be increased to reduce the time spent with low solar energy capture. More specifically, flying faster may allow tilting of the UAV wing <NUM> to a shallower angle as the nose <NUM> tilts down. Traveling at a slower speed would cause the UAV <NUM> nose <NUM> to tilt up, decreasing the exposure of the solar array <NUM> to the Sun. Thus, speeding up of the UAV <NUM> as the UAV <NUM> travels toward the Sun may result in increasing the UAV's <NUM> solar aperture to the Sun. This may provide for a large solar aperture <NUM> than if the UAV <NUM> did not speed up, thereby maximizing solar capture.

In one embodiment, increasing the speed of the UAV <NUM> may be more efficient for solar capture because traveling slowly may mean that more time is spent not capturing solar energy. In one embodiment, the speed range for the UAV <NUM> as the UAV <NUM> travels toward the Sun may be <NUM> knots (<NUM> kmph) indicated airspeed, dropping to <NUM> knots (<NUM> kmph) as the UAV <NUM> travels away from the Sun. The UAV <NUM> may travel at a first airspeed <NUM> when traveling towards the Sun, such as <NUM> knots (<NUM> kmph). The UAV <NUM> may travel at a second airspeed <NUM> when traveling away from the sun, such as <NUM> knots (<NUM> kmph). The first airspeed <NUM> traveling toward the sun may be greater than a second airspeed <NUM> traveling away from the Sun. In one embodiment, if the heading of the UAV <NUM> is perpendicular to the Sun, such that the wing tip of the UAV <NUM> is pointing approximately toward the Sun. In some embodiments, the first airspeed <NUM> may be approximately <NUM>-<NUM> knots (<NUM>-<NUM> kmph). In one embodiment, at any point, or heading, on the UAV's <NUM> flight pattern, a speed of the UAV <NUM> may be determined to capture the maximum amount of solar radiation and maximize UAV <NUM> performance. A plane of the UAV <NUM> parallel to the wing panel <NUM> or an upper surface <NUM> of the wing panel <NUM> may be angled relative to a horizontal or ground plane by a first angle <NUM> when flying towards the sun, as shown in <FIG>. The first angle <NUM> may be <NUM> degrees in some embodiments. In other embodiments, the first angle <NUM> may be minimal so as to maximize solar capture by the solar array <NUM> when flying towards the Sun, as shown in <FIG>. The plane of the UAV <NUM> parallel to the wing panel <NUM> or the upper surface <NUM> of the wing panel <NUM> may be angled relative to the horizontal or the ground plane by a second angle <NUM> when flying away from the Sun, as shown in <FIG>. The second angle <NUM> may be greater than the first angle <NUM>. In other embodiments, the second angle <NUM> may be maximized so as to maximize solar capture by the solar array <NUM> when flying away the sun, as shown in <FIG>. The second angle <NUM> may produce a slower rate of speed for the UAV, i.e., the second airspeed <NUM>, as compared to the first angle <NUM>, i.e.. , the first airspeed <NUM>. In some embodiments, the airspeeds <NUM>, <NUM> of the UAV may be based on the angling <NUM>, <NUM> of the plane of the UAV <NUM>. For example, as the plane of the UAV <NUM> approaches parallel with horizontal the speed of the UAV increases, and as the plane of the UAV <NUM> approaches perpendicular with horizontal or vertical the speed of the UAV decreases. In one embodiment, adjusting the angle of the top surface relative to the horizontal plane is pitching the UAV up or down, which will change the speed of the UAV for level flight. In one embodiment, the speed may be programmed into the FCC <NUM>. Based on the location of the Sun with respect to the UAV <NUM> and the direction of travel of the UAV <NUM>, the FCC <NUM> may set a speed to capture the maximum amount of solar radiation and maximize UAV performance <NUM>.

In some embodiments, the angles <NUM>, <NUM> and/or speed <NUM>, <NUM> of the UAV <NUM> may be variable based on the time of day. For example, the angle may be less and/or the speed may be faster closer to noon when the Sun is directly overhead as compared to the beginning or end of the day where a greater angle and/or slower speed may be needed. In one embodiment, an adjustment to the angles <NUM>, <NUM> and/or speed <NUM>, <NUM> of the UAV <NUM> may be made early in the day and/or late in the day when the sun angle is low In one embodiment, angles <NUM>, <NUM> and/or speed <NUM>, <NUM> of the UAV <NUM> at noon may be such that the UAV is flown at the most optimal speed for minimum power required.

In one embodiment, the flight pattern for maximizing solar capture may be repeated until the Sun is completely below the horizon. After the Sun has set, the battery <NUM> may power the motor <NUM> throughout the night when no solar radiation is available. In one embodiment, the UAV <NUM> may transition to a different flight pattern at night or remain in the same D-loop pattern. The positioning of the loiter or D-loop pattern may be primarily dictated by wind speed and/or wind direction in one embodiment. In some embodiments, the loiter or D-pattern may be modified so as to better account for the angle of the Sun relative to the solar array of the UAV <NUM>. As the Sun begins to rise, the UAV <NUM> may execute the D-loop flight pattern for maximizing solar capture; increasing speed as the UAV <NUM> travels towards the Sun, and decreasing speed as the UAV <NUM> flies away from the Sun. When the Sun is sufficiently high above the horizon, the UAV <NUM> may travel at an approximately constant speed, since the solar array <NUM> may be continuously exposed to solar radiation from the Sun.

With respect to <FIG>, a flowchart of a method <NUM> for maximizing solar capture with a solar array of an unmanned aerial vehicle (UAV) is shown. When the Sun is lower on the horizon, such as later in the day or during the winter the UAV mainly captures solar energy as the UAV flies away from the Sun.

In one embodiment, the solar array may be placed on at least a portion of an upper surface of a wing of the UAV. The solar array may be angled to the rear of the UAV due to the leading-edge-up attitude of the wing needed to create lift. Therefore, when the Sun is lower on the horizon, the solar array may capture substantial solar energy to both propel the UAV and to charge a battery of the UAV as the UAV flies away from the Sun in part of the UAV's flight pattern. In one embodiment, a computing device at a ground control station may be in communication with a flight control computer (FCC) of the UAV. A processor of the computing device at the ground control station may execute steps to transmit a communication signal to the FCC onboard the UAV, such as when the Sun is lower on the horizon (step <NUM>). In some embodiments, the FCC may take steps to adjust a speed and angle of the UAV to maximize solar capture autonomously, semi-autonomously, and/or in response to an input from a processor at a ground control station. In some embodiments, the FCC may adjust an angle and/or speed of the UAV based on the UAV heading autonomously. The FCC may receive the communication signal (step <NUM>). The FCC may change the UAV's heading based on the communication signal to fly away from the Sun to maximize solar capture with the solar array (step <NUM>). In another embodiment, the FCC may be directly programmed to automatically change the heading of the UAV to maximize solar capture. The FCC may decrease the UAV's speed based on the communication signal to exposes more of the solar array to the Sun, particularly when the Sun is low on the horizon (step <NUM>). The nose of the UAV tilts up as the UAV slows down, causing the solar array to be more generally perpendicular to the Sun's rays, e.g., at a greater angle than as compared to level flight, as the UAV travels away from the Sun. The tilting up of the nose of the UAV as the UAV slows down leads to a large solar aperture, thereby maximizing solar capture. In one embodiment, increasing the speed of the UAV may be more efficient for solar capture because traveling slowly may mean that more time is spent not capturing solar energy.

When the UAV turns and maneuvers to stay close to a ground control station, solar capture may be limited as the UAV travels toward the Sun in the UAV's flight pattern. Furthermore, when the UAV is not needed to stay close to the ground control station, solar capture is limited as the UAV turns and travels toward the Sun in the UAV's flight pattern. The UAV flight speed may be increased based on a communication signal received at the FCC from the computing device to maximize solar capture (step <NUM>). The increased speed reduces the time spent with low solar energy capture, and flying faster may allow tilting of the UAV wing to a shallower angle as the nose tilts down, exposing more of the solar array to the Sun. Speeding up of the UAV as the UAV travels toward the Sun may result in increasing the UAV's solar aperture to the Sun. This may provide for a large solar aperture than if the UAV did not speed up, thereby maximizing solar capture.

<FIG> depicts a high-level flowchart of a method <NUM> embodiment for maximizing solar capture with a solar array of an unmanned aerial vehicle (UAV), according to one embodiment. The method <NUM> may include determining if it is daytime, i.e., whether it is between sunrise and sunset when a solar array <NUM> of the UAV <NUM> can capture solar energy (step <NUM>). Determining the time of day may be done by a computing device <NUM> at a ground control station <NUM> and/or a flight control computer (FCC) <NUM> of the UAV <NUM>, as shown in <FIG>. If it is not daytime, the UAV may continue in a flight path to conserve energy until solar energy can be captured again, such as after sunrise. The computing device <NUM> at the ground control station <NUM> and/or the FCC <NUM> of the UAV <NUM> may then determine a direction of travel of the UAV <NUM>, as shown in <FIG> (step <NUM>). The UAV may fly in a stating keeping pattern to stay within a set distance of a ground control station. In some embodiments, the UAV may fly in a large area flight pattern, such as a "D-loop" flight pattern. This flight pattern may have a portion that is towards the Sun and a portion that is away from the Sun. Away from the Sun and towards the Sun are relative to a position of the Sun in the sky. For example, the Sun rises in the east and sets in the west. In the morning, if the UAV is flying east it will be flying towards the Sun and if the UAV if flying west it will be flying away from the Sun.

If the UAV is flying toward the Sun, the computing device <NUM> at the ground control station <NUM> and/or the FCC <NUM> of the UAV <NUM>, as shown in <FIG>, may adjust a UAV airspeed to a first UAV airspeed (step <NUM>). The computing device <NUM> at the ground control station <NUM> and/or the FCC <NUM> of the UAV <NUM>, as shown in <FIG>, may also adjust a UAV angle to a first angle (step <NUM>).

If the UAV is flying away from the Sun, the computing device <NUM> at the ground control station <NUM> and/or the FCC <NUM> of the UAV <NUM>, as shown in <FIG>, may adjust a UAV airspeed to a second UAV airspeed (step <NUM>). The computing device <NUM> at the ground control station <NUM> and/or the FCC <NUM> of the UAV <NUM>, as shown in <FIG>, may also adjust a UAV angle to a second angle (step <NUM>). In some embodiments, the angle and airspeed of the UAV may be related. For example, an angle closer to horizontal may result in a faster airspeed and an angle closer to vertical may result in a slower airspeed. In some embodiments, the FCC may change the angle of the UAV and the speed may change accordingly. In some embodiments, the FCC may change the speed of the UAV and the angle may change accordingly.

The first airspeed may be greater than the second airspeed. The first angle may be less than the second angle. The first airspeed is greater than the second airspeed to minimize the amount of time that the UAV is flying towards the Sun as less solar energy is captured by the solar array of the UAV when the UAV is flying towards the Sun. By flying at a faster first airspeed, the UAV can get to a portion of the flightpath of the UAV where the UAV is flying away from the sun sooner. The first angle is closer to parallel with a ground or horizontal plane in order to increase and/or maximize solar energy captured by the solar array of the UAV when the UAV is flying towards the Sun. The second airspeed is slower than the first airspeed to maximize the amount of time that the UAV is flying away from the Sun as more solar energy is captured by the solar array of the UAV when the UAV is flying away from the Sun. The second angle is closer to perpendicular with a ground or horizontal plane in order to increase and/or maximize solar energy captured by the solar array of the UAV when the UAV is flying away from the Sun.

<FIG> is a high-level block diagram <NUM> showing a computing system comprising a computer system useful for implementing an embodiment of the system and process, disclosed herein. Embodiments of the system may be implemented in different computing environments. The computer system includes one or more processors <NUM>, and can further include an electronic display device <NUM> (e.g., for displaying graphics, text, and other data), a main memory <NUM> (e.g., random access memory (RAM)), storage device <NUM>, a removable storage device <NUM> (e.g., removable storage drive, a removable memory module, a magnetic tape drive, an optical disk drive, a computer readable medium having stored therein computer software and/or data), user interface device <NUM> (e.g., keyboard, touch screen, keypad, pointing device), and a communication interface <NUM> (e.g., modem, a network interface (such as an Ethernet card), a communications port, or a PCMCIA slot and card). The communication interface <NUM> allows software and data to be transferred between the computer system and external devices. The system further includes a communications infrastructure <NUM> (e.g., a communications bus, cross-over bar, or network) to which the aforementioned devices/modules are connected as shown.

Information transferred via communications interface <NUM> may be in the form of signals such as electronic, electromagnetic, optical, or other signals capable of being received by communications interface <NUM>, via a communication link <NUM> that carries signals and may be implemented using wire or cable, fiber optics, a phone line, a cellular/mobile phone link, an radio frequency (RF) link, and/or other communication channels. Computer program instructions representing the block diagram and/or flowcharts herein may be loaded onto a computer, programmable data processing apparatus, or processing devices to cause a series of operations performed thereon to produce a computer implemented process.

Embodiments have been described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments. Each block of such illustrations/diagrams, or combinations thereof, can be implemented by computer program instructions. The computer program instructions when provided to a processor produce a machine, such that the instructions, which execute via the processor, create means for implementing the functions/operations specified in the flowchart and/or block diagram. Each block in the flowchart/block diagrams may represent a hardware and/or software module or logic, implementing embodiments. In alternative implementations, the functions noted in the blocks may occur out of the order noted in the figures, concurrently, etc..

Computer programs (i.e., computer control logic) are stored in main memory and/or secondary memory. Computer programs may also be received via a communications interface <NUM>. Such computer programs, when executed, enable the computer system to perform the features of the embodiments as discussed herein. In particular, the computer programs, when executed, enable the processor and/or multi-core processor to perform the features of the computer system. Such computer programs represent controllers of the computer system.

<FIG> shows a block diagram of an example system <NUM> in which an embodiment may be implemented. The system <NUM> includes one or more client devices <NUM> such as consumer electronics devices, connected to one or more server computing systems <NUM>. A server <NUM> includes a bus <NUM> or other communication mechanism for communicating information, and a processor (CPU) <NUM> coupled with the bus <NUM> for processing information. The server <NUM> also includes a main memory <NUM>, such as a random access memory (RAM) or other dynamic storage device, coupled to the bus <NUM> for storing information and instructions to be executed by the processor <NUM>. The main memory <NUM> also may be used for storing temporary variables or other intermediate information during execution or instructions to be executed by the processor <NUM>. The server computer system <NUM> further includes a read only memory (ROM) <NUM> or other static storage device coupled to the bus <NUM> for storing static information and instructions for the processor <NUM>. A storage device <NUM>, such as a magnetic disk or optical disk, is provided and coupled to the bus <NUM> for storing information and instructions. The bus <NUM> may contain, for example, thirty-two address lines for addressing video memory or main memory <NUM>. The bus <NUM> can also include, for example, a <NUM>-bit data bus for transferring data between and among the components, such as the CPU <NUM>, the main memory <NUM>, video memory and the storage <NUM>. Alternatively, multiplex data/address lines may be used instead of separate data and address lines.

The server <NUM> may be coupled via the bus <NUM> to a display <NUM> for displaying information to a computer user. An input device <NUM>, including alphanumeric and other keys, is coupled to the bus <NUM> for communicating information and command selections to the processor <NUM>. Another type or user input device comprises cursor control <NUM>, such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to the processor <NUM> and for controlling cursor movement on the display <NUM>.

According to one embodiment, the functions are performed by the processor <NUM> executing one or more sequences of one or more instructions contained in the main memory <NUM>. Such instructions may be read into the main memory <NUM> from another computer-readable medium, such as the storage device <NUM>. Execution of the sequences of instructions contained in the main memory <NUM> causes the processor <NUM> to perform the process steps described herein. One or more processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in the main memory <NUM>. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement the embodiments. Thus, embodiments are not limited to any specific combination of hardware circuitry and software.

The terms "computer program medium," "computer usable medium," "computer readable medium", and "computer program product," are used to generally refer to media such as main memory, secondary memory, removable storage drive, a hard disk installed in hard disk drive, and signals. These computer program products are means for providing software to the computer system. The computer readable medium allows the computer system to read data, instructions, messages or message packets, and other computer readable information from the computer readable medium. The computer readable medium, for example, may include non-volatile memory, such as a floppy disk, ROM, flash memory, disk drive memory, a CD-ROM, and other permanent storage. It is useful, for example, for transporting information, such as data and computer instructions, between computer systems. Furthermore, the computer readable medium may comprise computer readable information in a transitory state medium such as a network link and/or a network interface, including a wired network or a wireless network that allow a computer to read such computer readable information. Computer programs (also called computer control logic) are stored in main memory and/or secondary memory. Computer programs may also be received via a communications interface. Such computer programs, when executed, enable the computer system to perform the features of the embodiments as discussed herein. In particular, the computer programs, when executed, enable the processor multi-core processor to perform the features of the computer system. Accordingly, such computer programs represent controllers of the computer system.

Generally, the term "computer-readable medium" as used herein refers to any medium that participated in providing instructions to the processor <NUM> for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media includes, for example, optical or magnetic disks, such as the storage device <NUM>. Volatile media includes dynamic memory, such as the main memory <NUM>. Transmission media includes coaxial cables, copper wire and fiber optics, including the wires that comprise the bus <NUM>. Transmission media can also take the form of acoustic or light waves, such as those generated during radio wave and infrared data communications.

Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, or any other magnetic medium, a CD-ROM, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, an EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave as described hereinafter, or any other medium from which a computer can read.

Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to the processor <NUM> for execution. For example, the instructions may initially be carried on a magnetic disk of a remote computer. A modem local to the server <NUM> can receive the data on the telephone line and use an infrared transmitter to convert the data to an infrared signal. An infrared detector coupled to the bus <NUM> can receive the data carried in the infrared signal and place the data on the bus <NUM>. The bus <NUM> carries the data to the main memory <NUM>, from which the processor <NUM> retrieves and executes the instructions. The instructions received from the main memory <NUM> may optionally be stored on the storage device <NUM> either before or after execution by the processor <NUM>.

The server <NUM> also includes a communication interface <NUM> coupled to the bus <NUM>. The communication interface <NUM> provides a two-way data communication coupling to a network link <NUM> that is connected to the world wide packet data communication network now commonly referred to as the Internet <NUM>. The Internet <NUM> uses electrical, electromagnetic or optical signals that carry digital data streams. The signals through the various networks and the signals on the network link <NUM> and through the communication interface <NUM>, which carry the digital data to and from the server <NUM>, are exemplary forms or carrier waves transporting the information.

In another embodiment of the server <NUM>, interface <NUM> is connected to a network <NUM> via a communication link <NUM>. For example, the communication interface <NUM> may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line, which can comprise part of the network link <NUM>. As another example, the communication interface <NUM> may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. In any such implementation, the communication interface <NUM> sends and receives electrical electromagnetic or optical signals that carry digital data streams representing various types of information.

The network link <NUM> typically provides data communication through one or more networks to other data devices. For example, the network link <NUM> may provide a connection through the local network <NUM> to a host computer <NUM> or to data equipment operated by an Internet Service Provider (ISP). The ISP in turn provides data communication services through the Internet <NUM>. The local network <NUM> and the Internet <NUM> both use electrical, electromagnetic or optical signals that carry digital data streams. The signals through the various networks and the signals on the network link <NUM> and through the communication interface <NUM>, which carry the digital data to and from the server <NUM>, are exemplary forms or carrier waves transporting the information.

The server <NUM> can send/receive messages and data, including e-mail, program code, through the network, the network link <NUM> and the communication interface <NUM>. Further, the communication interface <NUM> can comprise a USB/Tuner and the network link <NUM> may be an antenna or cable for connecting the server <NUM> to a cable provider, satellite provider or other terrestrial transmission system for receiving messages, data and program code from another source.

The example versions of the embodiments described herein may be implemented as logical operations in a distributed processing system such as the system <NUM> including the servers <NUM>. The logical operations of the embodiments may be implemented as a sequence of steps executing in the server <NUM>, and as interconnected machine modules within the system <NUM>. The implementation is a matter of choice and can depend on performance of the system <NUM> implementing the embodiments. As such, the logical operations constituting said example versions of the embodiments are referred to for e.g., as operations, steps or modules.

Similar to a server <NUM> described above, a client device <NUM> can include a processor, memory, storage device, display, input device and communication interface (e.g., e-mail interface) for connecting the client device to the Internet <NUM>, the ISP, or LAN <NUM>, for communication with the servers <NUM>.

The system <NUM> can further include computers (e.g., personal computers, computing nodes) <NUM> operating in the same manner as client devices <NUM>, where a user can utilize one or more computers <NUM> to manage data in the server <NUM>.

As shown, cloud computing environment <NUM> comprises one or more cloud computing nodes <NUM> with which local computing devices used by cloud consumers, such as, for example, personal digital assistant (PDA), smartphone, smart watch, set-top box, video game system, tablet, mobile computing device, or cellular telephone 54A, desktop computer 54B, laptop computer 54C, and/or automobile computer system 54N may communicate.

Claim 1:
A system, comprising:
at least one flight control computer, FCC, (<NUM>) associated with at least one UAV (<NUM>), wherein the at least one FCC is configured to:
determine, when the at least one UAV is flying in a flight pattern, a direction of travel of the at least one UAV (<NUM>) relative to the Sun;
adjust a UAV airspeed of the at least one UAV flying in the flight pattern to a first airspeed (<NUM>) if the determined direction of travel is towards the Sun; and
adjust the UAV airspeed of the at least one UAV flying in the flight pattern to a second airspeed (<NUM>) if the determined direction of travel is away the Sun;
wherein the first airspeed is greater than the second airspeed to maximize solar capture of a solar array (<NUM>) covering at least a portion of the UAV (<NUM>);
a battery pack system (<NUM>) comprising:
a battery (<NUM>) for powering the UAV (<NUM>); and
a power tracker (<NUM>) in communication with the battery (<NUM>) and the solar array (<NUM>);
wherein the power tracker (<NUM>) is configured to receive electrical energy produced by the solar array (<NUM>);
wherein the power tracker (<NUM>) is configured to supply electrical charge to the battery (<NUM>); and
wherein the power tracker (<NUM>) is configured to provide a steady voltage to the battery (<NUM>) while the electrical energy produced by the solar array (<NUM>) varies throughout the day as the Sun's position changes in the sky.