MANAGEMENT OF AN AERIAL VEHICLE

TECHNICAL FIELD

This presently disclosed subject matter relates to an aerial vehicle, and more particularly to a system and a method for controlling of an aerial vehicle in a surrounding with currents of air.

BACKGROUND

Currents of air, such as thermals, are buoyant plumes of air which are caused by convection in the lower atmosphere. These thermals are commonly used by birds and glider pilots to extend flight duration, increase cross-country speed, improve range, or simply to conserve energy. In the field of aerial vehicles novel ways are developed to improve the range, duration, or cross-country speed of the aerial vehicles by exploiting thermals. Thermals occur when the air near the ground becomes less dense than the surrounding air as a result of heating or humidity changes at the Earth's surface. Thermal height varies greatly depending on climate and season but can typically fall between 500 meter and 30,000 meter above ground level. Sailplane pilots primarily rely on thermals to travel great distances and soar for long periods of time. Large birds, such as hawks and buzzards, have been observed to soar extensively while searching for food and vary their migration path and flight times in response to thermal activity and frigatebirds are known to soar continuously day and night using thermals over tropical ocean waters.

Many aerial vehicles such as unmanned aerial vehicles (UAVs) have similar sizes and wing loadings to soaring birds and manned sailplanes. Mission profiles that could allow UAVs to take advantage of thermals include remote sensing, surveillance, atmospheric research, communications, force protection, forest-fire monitoring, land management, and border control. Studies in the field found that a UAV with a nominal endurance of 2 hours can gain up to 12 hours of flight time by using thermals.

SUMMARY OF THE PRESENTLY DISCLOSED SUBJECT MATTER

According to one aspect the presently disclosed subject matter, there is provided a method for managing an aerial vehicle at an environment having currents of air, and a system configured to execute this method. The aerial vehicle has a controlling unit configured to control the operation of the aerial vehicle and to execute steps of the method. The method comprises steps of: a) instructing the aerial vehicle to fly at a flight mode in which flight statuses of the aerial vehicle are periodically registered. The flight statuses comprise a vertical velocity of the aerial vehicle and a location of the aerial vehicle associated with the vertical velocity;

b) periodically comparing the flight statuses with at least one entrance condition, and upon fulfillment of at least said one entrance condition, entering into an analysis mode in which steps (c) - (h) are performed together with further periodic registration of the flight statuses, otherwise reverting to step (a);

c) registering the condition fulfillment location at which at least said one entrance condition has been fulfilled;

d) determining an orbiting center in accordance with the condition fulfillment location and an orbiting radius;

e) changing the flight direction of the aerial vehicle at a turning location towards a selected direction so as to complete at least one orbit around said orbiting center at said orbiting radius;

f) dividing the orbit into an array of segments, each of which being associated with a portion of the orbit and having a representative vertical velocity and a representative location, both being obtained from said flight statuses;

g) selecting at least one segment of said array of segments, in which the representative vertical velocity is maximal with respect to the vertical velocities of the other segments, and analyzing said array of segments including said selected segment for checking fulfillment of at least one escape condition, and upon fulfillment of at least said one escape condition, reverting to step (a), otherwise performing step (h); and

h) updating said orbiting center to an updated orbiting center disposed at a location being distant from said orbiting center and in a general direction towards the representative location of the selected segment and performing steps (e) to (g) with respect to the updated orbiting center.

The term "currents of air" as used herein the specification and the clams denotes movement of air from an area of high pressure to an area of low pressure, which can be caused by differences in temperature, pressure and impurity concentration. Temperature differences can cause currents of air because warmer air is less dense than cooler air, causing the warmer air to appear "lighter." Thus, if the warm air is under the cool air, air currents will form as they exchange places. The term "currents of air" can relate in particular to thermals, including, a thermal updraft and a thermal downdraft, both related to vertical movement of air created by differences in pressure of the air. In addition, the term "currents of air" can refer to updrafts which are by objects on the earth, such as power plants. The term "aerial vehicle" as used herein the specification and the claims refers to any known vehicle which can be transported in the air. For example, the aerial vehicle can be: an unmanned aerial vehicle (UAV), a glider, an airplane, and a helicopter.

The term "vertical velocity" as used herein the specification and the claims refers to a velocity or a climb rate in which the aerial vehicle moves in the upward or the downward direction. The vertical velocity of the aerial vehicle can results from propulsion of the aerial vehicle, influence of currents of air (i.e., updrafts or downdrafts), or combination thereof.

The term "location" as used herein the specification and the claims refers to a spacial location of the aerial vehicle, i.e., to the location of the aerial vehicle in a three dimensional space.

The method and the system of the presently disclosed subject matter are configured to collect information regarding currents of air at the environment of the aerial vehicle, and characterize physical parameters thereof. In particular, the method and the system of the presently disclosed subject matter can characterize the location and the strength of updrafts and downdrafts. This information can be used for providing or updating a map of the aerial vehicle's environment with indication of locations and corresponding strengths of updrafts and downdrafts detected by the aerial vehicle. This information can be later used by the aerial vehicle itself, or by other aerial vehicles or interested entities.

According to the method of the presently disclosed subject matter, the aerial vehicle can detect updrafts by being operated in two modes of operation: a flight mode and an analysis mode. In the flight mode, the aerial vehicle flies along a straight, a pre-planned or a random path in order to detect a region in which there might be a chance for an updraft. The detection of said region can be performed due to continuous analysis of the vertical velocity of the aerial vehicle and its location. The vertical velocity of the aerial vehicle is indicative of the strength of the updraft at the surrounding of the aerial vehicle. Upon detection of said region when a substantially sharp positive altitude change is detected, the aerial vehicle is switched to be operated in the analysis mode. In the analysis mode, the aerial vehicle flies along one or more orbits while changing the center of the orbit (if required), so as to find a location at which a possible updraft is maximal or has the most effective influence of the altitude of the aerial vehicle. The method of the presently disclosed subject matter can also detect downdrafts, and upon detection a downdraft, the aerial vehicle can be directed to another direction so as to eliminate the downdraft, thereby eliminating a dangerous situation of the aerial vehicle.

Below are described different details and variation of the system and the method of the presently disclosed subject matter.

The flight statuses of the aerial vehicle can be registered by using at least one of the following devices: a Global Positioning System, Inertial Navigation System, a Pitot tube, and a compass. These devices can measure and provide real-time information regarding the vertical velocity of the aerial vehicle and its location.

The at least one entrance condition can indicate a possibility for existence of an updraft at the environment of the aerial vehicle, and can include at least one of the following: the vertical velocity is above a first predetermined velocity threshold, an average of selected vertical velocities is above a first predetermined average velocity threshold, and a vertical displacement being obtained from the flight statuses is above a first predetermined displacement threshold.

The at least one escape condition can indicate that the analysis mode of the aerial vehicle should be terminated, and that the aerial vehicle should revert to its flight mode. The at least one escape condition can include at least one of the following: an vertical velocity is below a second predetermined velocity threshold, an average of selected vertical velocities is below a second predetermined average velocity threshold, an altitude of the aerial vehicle is above a predetermined altitude threshold, a time length along which the aerial vehicle is in the analysis mode, and a vertical displacement being obtained from the flight statuses is below a second predetermined displacement threshold.

The method can further comprise steps of: periodically comparing the flight statuses with at least one dangerous condition indicating a downdraft, and upon fulfillment of at least said one dangerous condition, changing the flight direction of the aerial vehicle to another direction, and reverting to step (a).

The at least one dangerous condition can indicate a possibility for existence of a downdraft at the environment of the aerial vehicle, and can include at least one of the following: a vertical velocity is below a third predetermined velocity threshold, an average of selected vertical velocities is below a third predetermined average velocity threshold, and a vertical displacement being obtained from the flight statuses is below a third predetermined displacement threshold. Detection of the at least one dangerous condition can indicate sharp reduction of altitude of the aerial vehicle, and can prevent the aerial vehicle from falling down by changing its flight direction.

The orbiting center can be determined to be identical to the condition fulfillment location. In other word, the location at which the at least one entrance condition was fulfilled, and at which there is a high chance for an updraft, can be determined by the system as the location around which the aerial vehicle should start orbiting. Alternatively, the orbiting center can be determined to be the location of the maximal registered vertical velocity at the vicinity of the condition fulfillment location.

The orbiting radius can be determined as a distance between the orbiting center and another location which is determined as one of the following: a location at which the vertical velocity is below a fourth predetermined velocity threshold; or a location at which the vertical displacement of the aerial vehicle is below a fourth predetermined displacement threshold. In other words, said another location is a location at which the influence of a possible updraft is reduced.

The steps (a) and (g) can further comprise a step of registering air-current parameters characterizing the currents of air at the location of the aerial vehicle, based on the values of the flight statuses. The air-current parameters can include at least one of the following parameters: strength of an updraft, location of an updraft, radius of an updraft, strength of a downdraft, location of a downdraft, radius of a downdraft. The method can further comprise a step of using said air-current parameters for updating a map of air-currents.

The division of an orbit into an array of segments in step (f), their analysis and the selection of at least one segment in step (g) can provide to the aerial vehicle information regarding a location around which the aerial vehicle should continue to orbit. The array of segments can include N segments, where N>2. The segments can be associated with equal portions of the orbit around the orbiting center.

The step (g) can further comprise a step of selecting the representative vertical velocity and the representative location for each of the segments.

The updated orbiting center can identical to the representative location of the selected segment. This means the aerial vehicle will continue orbiting around an updated orbiting center which is the representative location of the selected segment.

The step (h) can further comprise a step of updating the orbiting radius to an updated orbiting radius and performing said steps (e) to (g) with respect to the updated orbiting radius. This further step can allow the aerial vehicle to check whether decrease or increase of the orbiting radius increases or decreases the vertical velocity of the aerial vehicle, and to react accordingly. The updated orbiting radius can be decreased with respect to the orbiting radius in order to increase the vertical velocity of the aerial vehicle. The extent to which the orbiting radius is decreased, can be determined according to values of the flights statuses, and particularly, according to the values of the vertical velocities.

The method can further comprise a step of performing drift correction by changing the flight direction of the aerial vehicle in accordance with estimated direction and speed of a side wind at the vicinity of the aerial vehicle. This step can allow the aerial vehicle to perform the method while correcting all the measured values in accordance with the direction of the wind. This step is important since all the environment of the aerial vehicle is dynamic, and therefore should be tracked by the aerial vehicle respectively.

The representative vertical velocity can be appointed to be equal to the arithmetic mean or the maximum of the registered vertical velocities within the respective segment.

The representative location of a segment can be appointed to be the location associated with the representative vertical velocity. The distance between the orbiting center and the updated orbiting center can be equal to the orbiting radius.

The step (a) can further comprise a step of instructing the aerial vehicle to fly along a substantially straight path.

The selected direction can be the right or the left direction being determined according to at least one of the following: the side of a tilted wing of the aerial vehicle, a randomly selected direction, and the direction at which the Equator is located with respect to the aerial vehicle.

The method can further comprise a step of calculating a longitudinal axis roll of the aerial vehicle so as to estimate lift forces at both sides of the aerial vehicle and thereby to select said tilted wing as the wing on which stronger lift forces are applied.

In said step (c), the aerial vehicle can be instructed to change its flight direction in about 90° with respect to its original flight direction.

During said analysis mode, the aerial vehicle can be configured to collect an electric energy or a potential energy which is later converted to an electric energy during gliding of the aerial vehicle. The electric energy can be collected by rotation of a propeller of the aerial vehicle by the currents of air.

The method can further comprise steps of receiving environmental information regarding the environment of the aerial vehicle; and using said environmental information for navigating the aerial vehicle. The environmental information can include at least one of the following: a geographic map of the environment of the aerial vehicle, and an atmospheric map of the environment of the aerial vehicle. The atmospheric map can include known locations and other parameters of updrafts and downdrafts. This map can be used by the aerial vehicle to be navigated in step (a) to locations in which updraft should appear, so as to collect additional information about them and/or to reassure the known information.

According to another aspect of the presently disclosed subject matter, there is provided a system for managing an aerial vehicle by executing the above described method, and it different variations.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it can be carried out in practice, the embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which:

Fig. 1A is a schematic three dimensional illustration an example of an aerial vehicle being managed in an environment of currents of air, in accordance with the presently disclosed subject matter; Fig. IB is a schematic illustration of orbits being performed by the aerial vehicle of Fig. 1A;

Fig. 2 is a schematic illustration of a flow chart in which the method of the presently disclosed subject matter is presented; and

Figs. 3A to 3G are screen plots of a computer simulation of the method of the presently disclosed subject matter according to a particular example.

DETAILED DESCRIPTION OF EMBODIMENTS

Attention is first directed to Fig. 1A, IB and 2 of the drawings illustrating an example of the system and the method of the presently disclosed subject matter.

Fig. 1A schematically illustrates a three dimensional space in which an aerial vehicle 10 in the form of an unmanned aerial vehicle (UAV) is managed by a system 11 integrated therein. The aerial vehicle 10 flies in an environment 1 having currents of air (e.g., updrafts) to be detected and investigated.

Fig. IB schematically illustrates the orbits which are performed by the aerial vehicle

10.

Fig. 2 schematically illustrates a flow chart of a method 100 according to which the aerial vehicle 10 is managed by the system 11.

Reference below is made in parallel to Fig. 1 A, IB and 2 in order to explain the step of the method 100 as performed by the system 11 and its implications on the navigation of the aerial vehicle 10 in the environment 1.

The system 11 includes a controller with a memory having a computer code of the presently disclosed method embedded therein and a processor configured to execute this code. In addition to the system 11, the aerial vehicle 11 also includes a number of sensing devices (not shown) configured for providing navigation and air-pressure information to the system 11. These sensing devices can include a combination of two or more of the following devices: a Global Positioning System, Inertial Navigation System, a Pitot tube, and a compass. These devices measure and provide to the system 11 with real-time information, inter alia, regarding the vertical velocity of the aerial vehicle 10 and its location.

The method 100 executed by the system 11 allows collecting information regarding currents of air at the environment 1 of the aerial vehicle 10, and characterizing physical parameters thereof. In particular, the method 100 allows detecting and characterizing the location and the strength of an updraft 5 and a downdraft 7 of the environment 1. This information with respect to the updraft 5 and the downdraft 7 can be used for providing or updating a map (not shown) of the environment 1 with indication of locations and corresponding strengths of updrafts and downdrafts detected by the aerial vehicle 10. This information can also includes other known in the art parameters related to the updrafts and downdrafts. In should be indicated that this information can further be used by the aerial vehicle 10 itself, or by other aerial vehicles or interested entities.

By applying the method 100, the system 11 allows the aerial vehicle 10 to detect updrafts by being operated in two modes of operation: a flight mode and an analysis mode. In the flight mode, the aerial vehicle 10 flies along a straight, a pre-planned or a random path in order to detect a region in which there are high chances for an updraft. The detection of said region can be performed due to continuous analysis of the vertical velocity of the aerial vehicle 10 in conjunction with registration its spacial location. Since the aerial vehicle 10 is operated in a know propulsion speed with an expected theoretical vertical velocity, the real vertical velocity of the aerial vehicle 10 is indicative of the strength of the updraft at the surrounding of the aerial vehicle 10. When a substantially sharp positive altitude change is detected by the system 11, it concludes that the aerial vehicle 10 is located a region in which there are high chances for an updraft. Therefore, in this situation, the aerial vehicle 10 is switched to be operated in the analysis mode. In the analysis mode, the aerial vehicle 10 completes one or more orbits while changing the center of the orbit (if required), so as to find a location at which a possible updraft is maximal or has the most effective influence of the altitude of the aerial vehicle 10. The method 100 can also detect downdrafts. Upon detection of a downdraft, the aerial vehicle 10 can be directed by the system 11 to another direction so as to eliminate the downdraft, thereby prevent a high chance for the aerial vehicle to be in a dangerous situation.

In step 110 of the method 100, the aerial vehicle 10 is instructed by the system 11 to fly in its flight mode in which flight statuses thereof are periodically registered. The flight statuses include the vertical velocity and the location of the aerial vehicle 10. As shown in Fig. 1A, the aerial vehicle 10 flies in its flight mode along a straight path 80, and the flight statuses thereof are registered along this path at different locations, indicated for example, by points 81, 82 and 83. At each one of the points 81, 82 and 83, step 115 is performed. In step 115, the flight statuses of the aerial vehicle 10 are analyzed by the system 11 by being compared with one or more entrance conditions. The entrance conditions can be one of the following: the vertical velocity is above a first predetermined velocity threshold, an average of selected vertical velocities is above a first predetermined average velocity threshold, and a vertical displacement being obtained from the flight statuses is above a first predetermined displacement threshold. The value of the first predetermined velocity threshold is, for example, +2 m/sec. The value of the first predetermined average velocity threshold is, for example, +1.5 m/sec. The value of the first predetermined displacement threshold is, for example, +20 m.

One particular example of an entrance condition is the following: "is the vertical velocity is above a value of +2 m/sec?". In general, if the entrance conditions are fulfilled along the path 90, steps 120-175 are performed, and otherwise, step 110 is performed again. In the particular example of points 81, 82 and 83, the entrance conditions were not fulfilled, and therefore, the step 110 is performed.

When the aerial vehicle 10 arrives to point 84, the value of its vertical speed at this point is +3 m/sec, which is above the value of +2 m/sec, and therefore an entrance condition is fulfilled. As a result of that, in step 120, the aerial vehicle 10 is instructed to be operated in its analysis mode, and consequently steps 130-175 are performed. It should be indicated that at this stage of the method 100, the system 11 in not aware of the existence of the updraft 5 and its characteristics (e.g., its location), but only suspects that there might be an updraft in proximity thereto. The fulfillment of the entrance condition means the aerial vehicle 10 "feels" that there is a chance that an updraft is located in its proximal environment, and that this environment should be deeply investigated. In the case of point 84, the entrance condition is fulfilled due to the proximity of the aerial vehicle 10 to the updraft 5, causing the aerial vehicle 10 to gain height more than expected.

When the aerial vehicle 10 is operated by the system 11 in its analysis mode, this means that aerial vehicle 10 investigates its proximal environment in order to detect and characterize a possible updraft, and in particular to detect and characterized the updraft 5. As detailed below, in the analysis mode, the aerial vehicle 10 flies along one or more orbits while, upon necessity, changing the center of the orbit, so as to find where a possible updraft is located and at which radius the updraft has the most effective influence of the altitude of the aerial vehicle 10.

In should be indicated that during the analysis mode of the aerial vehicle 10, the system 11 continuous to periodically register flight statuses of the aerial vehicle 10 in order to collect information at least regarding its vertical velocity and location.

In step 130, the system 11 registers a condition fulfillment location being the location at which entrance condition is fulfilled. In other words, the aerial vehicle registers the location of point 84.

In step 140, the system 11 determines an orbiting center 85 and an orbiting radius Rj. The orbiting center 85 is location in the X-Y plane around which the aerial vehicle 10 should complete at least orbit, and the orbiting radius Rj is the radius of said orbit. According to the particular example of Figs. 1A and IB, the orbiting radius Rj is a distance on the X-Y plane between the point 84 and the orbiting center 85. In general, the values of the orbiting center 85 and the orbiting radius Ri can be determined by the system 11 according to various parameters and conditions. According to another particular example, the orbiting center 85 can be identical to the location of point 84, and the orbiting radius Ri has a default value which is between 90 meter and 110 meter. According to another example, the orbiting center can be determined to be identical to the condition fulfillment location. In other word, the location at which the at least one entrance condition was fulfilled, and at which there is a high chance for an updraft, can be determined by the system as the location around which the aerial vehicle should start orbiting.

According to an alternative example, the orbiting center can be determined to be the location of the maximal registered vertical velocity at the vicinity of the condition fulfillment location.

According to another particular example, the orbiting radius can be determined as a distance between the orbiting center and another location which is determined as one of the following: a location at which the vertical velocity is below a fourth predetermined velocity threshold; or a location at which the vertical displacement of the aerial vehicle is below a fourth predetermined displacement threshold. In other words, said another location is a location at which the influence of a possible updraft is reduced.

In step 150, the system 11 instructs a propulsion arrangement of the aerial vehicle 10 to change its flight direction at a turning location which is represented by a point 84', towards a selected direction, so as to complete at least one orbit around the orbiting center 85 at the orbiting radius Rj. According to the specific example of Figs. 1 A and IB, the aerial vehicle 10 completes three orbits Oi, O ₂ and O3 around the orbiting center 85 at the orbiting radius Rj. It is appreciated that the number of orbits performed by the aerial vehicle 10 is determined by the system 11 according to various parameters, such as the vertical velocity of the aerial vehicle during or after completion of each orbit.

The above mentioned selected direction can be the right or the left direction which can be determined according to at least one of the following: the side of a tilted wing of the aerial vehicle, a randomly selected direction, and the direction at which the Equator is located with respect to the aerial vehicle. According to the present example, the selected direction is the left direction since this is the direction of the aerial vehicle's upwardly tilted wing, indicating a possible location of the updraft. The selected direction according to the present example is selected by the system 11 by calculating a longitudinal axis roll of the aerial vehicle so as to estimate lift forces at both sides of the aerial vehicle. From this calculation, the system 11 selects the upwardly tilted wing as the wing on which stronger lift forces are applied and consequently the selected direction is determined.

In step 160, the system divides the performed orbit into an array of segments, each of which being associated with a portion of the orbit and having a representative vertical velocity and a representative location, both being obtained from the flight statuses. The system also performs the selection of the representative vertical velocity and the representative location for each one of the segments. According to another example, the representative vertical velocity can be appointed to be equal to the arithmetic mean or the maximum of the registered vertical velocities within the respective segment. The representative location of a segment can be appointed to be the location associated with the representative vertical velocity.

According to the present example, the step 160 is performed with respect to the orbit O3, and is schematically shown in Fig. IB. According to other examples, the step 160 can be performed with respect to each orbit that is completed by the aerial vehicle. According to still other examples, the step 160 can be performed with respect to a number of orbits at the same time.

As shown in Fig. IB the orbit O3 is divided to eight equal segments: Si, S ₂ , S3, S4, S5, S6, S7 and Ss. Each one of the segments has a representative vertical velocity and a representative location, both being obtained from the flight statuses of the aerial vehicle 10.

After performing the step 160, the system 11 performs step 170 in which at least one segment is selected from the array of segments. The selected segment is one having a representative vertical velocity which is maximal with respect to the representative vertical velocities of other segments. In addition, the parameters of all the segments are statistically analyzed for step 175. The division of the orbit into an array of segments and their analysis in step 160 and the selection of at least one segment in step 170 can provide to the aerial vehicle 10 information regarding a location around which the aerial vehicle should continue to orbit, as explained below with respect to step 180.

According to the example of Fig. IB, the segment S6 has the maximal representative vertical velocity, and therefore this segment constitutes a selected segment.

In step 175, the system 11 checks whether the analyzed segments fulfill at least one escape condition. In general, upon fulfillment of at least one escape condition, the system 11 reverts to performance of step 110, and otherwise it performs step 180. If the system 11 decides to revert to the step 110, it means the process of detecting and investigating a suspect updraft is stopped with a particular decision, and if the system 11 performs step 180, it means that the process of detecting and investigation a suspected updraft continues by performing steps 150-175. As it is described below, the method 100 also has a step 190 which can be performed instead of step 180, when specific conditions are fulfilled.

The escape conditions indicate that the analysis mode of the aerial vehicle 10 should be terminated, and that the aerial vehicle 10 should revert to its flight mode. The escape conditions, for example, include at least one of the following: an vertical velocity is below a second predetermined velocity threshold, an average of selected vertical velocities is below a second predetermined average velocity threshold, an altitude of the aerial vehicle is above a predetermined altitude threshold, a time length along which the aerial vehicle is in the analysis mode, and a vertical displacement being obtained from the flight statuses is below a second predetermined displacement threshold. The value of the second predetermined velocity threshold is, for example +1 m/sec. The value of the second predetermined average velocity threshold is, for example, 0 m/sec. The value of the predetermined altitude threshold is, for example, 10000 fit. The value of the time length is, for example, 45 minutes. The value of the second predetermined displacement threshold is, for example, 2000 fit.

According to the example of Figs. 1A and IB, after completion of the orbit (¾, the result of step 175 is "No", and therefore, step 180 is performed. According to this step, the orbiting center 85 is updated to an updated orbiting center 86 disposed at a location being distant from the location of the orbiting center 85, and in the direction of the selected segment Se. Since the selected segment S6 represents a location in which the vertical velocity of the aerial vehicle is maximal, there is a high chance that the location of a potential updraft is disposed in proximity to this segment. This can also be clearly seen in Fig. 1A, in which the updated orbiting center 86 is located substantially at the center of the updraft 5.

According to the example of Figs. 1A and IB, the distance between the orbiting center and the updated orbiting center can be equal to the orbiting radius.

According to another example, the updated orbiting center can be determined to be identical to the representative location of the selected segment. This means the aerial vehicle will continue orbiting around an updated orbiting center which is the representative location of the selected segment.

After performing step 180, the system performs step 150 by completing three orbits O4, O5 and (¾ around the updated orbiting center 86 at a radius R ₂ . It is appreciated that the number of orbits performed by the aerial vehicle 10 around the updated orbiting center 86 is determined by the system 11 according to various parameters, such as the vertical velocity of the aerial vehicle during or after completion of each orbit. After step 150, steps 160, 170 and 175 are performed with respect to orbit 0 ₆ .

As shown in Fig. IB, in step 160, the orbit 0 ₆ is divided to eight equal segments: S' i, S' ₂ , S' 3, S'4, S' 5, S'e, S'7 and S'e. Each one of the segments has a representative vertical velocity and a representative location, both being obtained from the flight statuses of the aerial vehicle 10. From step 170, in which the parameters of the segments S' ₂ , S' 3, S'4, S'5, S'e, S' 7 and S' g are analyzed, the system 11 concludes that none of these segments has a vertical velocity which is essentially higher than the other vertical velocities, and in this case, the system performs step 190. In step 190, the orbiting radius R ₂ is updated to an updated orbiting radius R ₃ and after that, steps 150-175 are performed with respect to the updated orbiting radius R ₃ around the updated orbiting center 86. In general, the performance of step 190 allows the aerial vehicle 10 to check whether increase or decrease of the orbiting radius increases or decreases the vertical velocity of the aerial vehicle, and to react accordingly.

According to the example of Figs. 1A and IB, the updated orbiting radius R3 is smaller than the orbiting radius R ₂ in order to check whether a decrease of the orbiting radius reveals to an increase of the vertical velocity of the aerial vehicle 10. The extent to which the orbiting radius is decreased can be determined according to values of the flights statuses, and particularly, according to the values of the vertical velocities.

After completing two orbits O7 and Os around the updated orbiting center 86 at the updated orbiting radius R3, step 175 is performed. The result of this step is "Yes", and this means that an escape condition is fulfilled. According to the present example, the escape condition that is fulfilled is the following: the altitude of the aerial vehicle is above a predetermined altitude threshold of 10000 fit. As a result of that, the system 11 reverts to step 110, and instructs the aerial vehicle to fly at its flight mode.

After flying in the flight mode along path 91, the aerial vehicle 10 arrives to the downdraft 7 which should be eliminated. In order to eliminate this downdraft, the method 100 further comprises a step for downdraft elimination which is not shown in Fig. 2. According to this step, the system 11 periodically compares the flight statuses of the aerial vehicle 10 with at least one dangerous condition indicating a possibility for existence of a downdraft, and upon fulfillment of the dangerous condition, the system changes the flight direction of the aerial vehicle to another direction, and reverts to step 110. Detection of the at least one dangerous condition indicates sharp reduction of altitude of the aerial vehicle, and can prevent the aerial vehicle from falling down by changing its flight direction. The at least one dangerous condition can be one of the following: a vertical velocity is below a third predetermined velocity threshold, an average of selected vertical velocities is below a third predetermined average velocity threshold, and a vertical displacement being obtained from the flight statuses is below a third predetermined displacement threshold. The value of the third predetermined velocity threshold is, for example, -3 m/sec. The value of the third predetermined average velocity threshold is, for example, -1.5 m/sec. The value of the third predetermined displacement threshold is, for example, -20 m.

During the performance of the method 100, the system 11 continuously memorizes and registers air-current parameters characterizing the currents of air at the location of the aerial vehicle 10, based on the values of the flight statuses. The air-current parameters can include at least one of the following parameters: strength of an updraft, location of an updraft, radius of an updraft, strength of a downdraft, location of a downdraft, radius of a downdraft. The system 11 also uses the air-current parameters for updating a map of air-currents.

For example, after flying around the updated orbiting center 86, with orbiting radius R ₂ and afterwards with orbiting radius R ₃ , the system registers that the updated orbiting center 86 is a location of the updraft 5, and respectively estimates the radius of the updraft by performing extrapolation on the values of the orbiting radiuses R2 and R3. In addition, after visiting point 87, the system 11 registers that this point is proximal to a downdraft. The strength of the updraft and/or the downdraft is estimated by the system in accordance with the vertical speed of the aerial vehicle. The system 11 can also receive environmental information regarding the environment of the aerial vehicle and use this environmental information for navigating the aerial vehicle. The environmental information can include at least one of the following: a geographic map of the environment of the aerial vehicle, and an atmospheric map of the environment of the aerial vehicle. The atmospheric map can include known locations and other parameters of updrafts and downdrafts. This map can be used by the aerial vehicle to be navigated in step 110 to locations in which updraft should appear, so as to collect additional information about them and/or to reassure the known information about them.

By collecting the air-current parameters and combing them with the environmental information, the system 11 and the method 100 can update known maps with updrafts and downdrafts and improve their accuracy.

It should be indicated that in view of the fact that the environment of the aerial vehicle is dynamic, this environment is tracked by the aerial vehicle during its entire operation. This tracking is done by performing drift correction of the aerial vehicle. This correction is performed by changing the flight direction of the aerial vehicle in accordance with estimated direction and speed of a side wind at the vicinity of the aerial vehicle. This step can allow the aerial vehicle to perform the method 100 while correcting all the measured values in accordance with the direction of the wind.

During the analysis mode, the aerial vehicle 10 can collect an electric energy or a potential energy which is later converted to an electric energy during gliding of the aerial vehicle. The electric energy can be collected by rotation of a propeller of the aerial vehicle by the currents of air.

Reference is now made to Figs. 3A-3Q, illustrating an example of screen plots of a computer simulation that implements the method of the presently disclosed subject matter.

Fig. 3A illustrates an environment of 12 square kilometers having currents of air and an aerial vehicle 200 flying therein for investigation purposes. The currents of air include updrafts and downdrafts indicated by black dots. The updrafts and the downdrafts cannot be distinguished from each other in Fig. 3A, but can be distinguished from each other in other drawings with a zoom-in view on the aerial vehicle 200 and its close environment. In Fig. 3A, the aerial vehicle 200 flies in its flight mode along a random path, and its flight statuses are periodically registered.

In Fig. 3B, the aerial vehicle 200 approaches a suspected updraft 300, the influence of which increases the vertical velocity of the aerial vehicle 200 and causes the aerial vehicle 200 to gain height more than expected. At this stage, the aerial vehicle 200 enters into its analysis mode in order to investigate the suspected updraft 300 and register its air-current parameters. As shown in Figs. 3C and 3D, the aerial vehicle 200 registers a condition fulfillment location 210, determines an orbiting center 211 and an orbiting radius it, and completes an orbit Qi around the orbiting center 211. Afterwards, the orbit Qi is divided to 16 equal segments, and segment Ni is selected to be the selected segment. Since none of the escape conditions is fulfilled after the completion of the orbit Qi, as shown in Fig. 3E, the aerial vehicle 200 is instructed to complete an additional orbit Q ₂ around an updated orbiting center 212 at an orbiting radius r ₂ being equal to ΐχ . Since the segment \ is associated with a maximal vertical velocity, the updated orbiting center 212 is located at the general direction of this segment. As it can clearly be seen in Fig. 3E, by implementing the method of the presently disclosed subject matter, the aerial vehicle 200 is successfully directed towards the center of the suspected updraft 300 so that the orbit Q ₂ is located almost at the center of the suspected updraft 300. After completing the orbit Q ₂ , aerial vehicle concludes that at least one escape condition is fulfilled and that the suspected updraft 300 is indeed an updraft. Therefore, after registering the air-current parameters of the updraft 300, the aerial vehicle 200 is instructed to revert to its flight mode and to leave the area of the updraft 300 for investigating other locations.

Figs. 3F-3H illustrate an example in which the aerial vehicle 200 passes in proximity to an air-current 310 which is a very weak downdraft that does not constitute any danger to the aerial vehicle 200. When the aerial vehicle 200 approaches the air-current 310, the registered values of the vertical velocity of the aerial vehicle are very close to zero, and therefore, none of the entrance conditions is fulfilled. These values are close to zero since they constitute sum of positive vertical velocity generated by the propulsion system of the aerial vehicle and negative vertical velocity generated by the air-current 310, cancelling each other. The aerial vehicle 200 thus does not continue to investigate the air-current 310, but rather continuous to fly to another area.

As shown in Figs. 31 and 3J, the aerial vehicle 200 flies is in its flight mode until it approaches a suspected updraft 320 and a suspected downdraft 330 disposed in proximity to each other. At this stage, the task of the aerial vehicle 200 is to allocate as much as possible the center of the suspected updraft 330 and to change its direction of flight as much as possible towards the center of the suspected updraft 320.

As shown in Fig. 3J, the aerial vehicle 200 is located in proximity to the suspected updraft 300, the influence of which increases the vertical velocity of the aerial vehicle 200 and causes the aerial vehicle 200 to gain height more than expected.

As shown in Fig. 3K, after passing a condition fulfillment location 213, the aerial vehicle 200 enters into its analysis mode in order to investigate the suspected updraft 320 and register its air-current parameters. According to this figure, the aerial vehicle 200 determines an orbiting center 214 and an orbiting radius 13, and completes an orbit (¾ around the orbiting center 214. After that, the orbit (¾ is divided to 16 equal segments, and segment N ₂ is selected to be the selected segment. Since none of the escape conditions is fulfilled after the completion of the orbit (¾, as shown in Fig. 3L, the aerial vehicle 200 is instructed to complete an additional orbit Q4 around an updated orbiting center 215 at an orbiting radius ¾ being equal to 13. Since the segment N ₂ is associated with a maximal vertical velocity, the updated orbiting center 215 is located at the general direction of this segment.

Since none of the escape conditions is not fulfilled also after the completion of the orbit Q ₄ , as shown in Fig. 3M, the aerial vehicle 200 is instructed to complete an additional orbit Q ₅ around an updated orbiting center 216 at an orbiting radius is being equal to 14. After that, the orbit Q5 is divided to 16 equal segments, and segment N3 is selected to be the selected segment. Since the segment N ₃ is associated with a maximal vertical velocity, the updated orbiting center 216 is located at the general direction of this segment. As it can clearly be seen in Fig. 3M, by implementing the method of the presently disclosed subject matter, the aerial vehicle 200 is successfully directed towards the center of the suspected updraft 320 so that the orbit Q ₅ is located almost at the center of the suspected updraft 320.

Figs. 3N and 30 illustrate a situation in which the suspected updraft 320 and the suspected downdraft 330 move away from each other, while the aerial vehicle 200 performs drift correction while continuing to complete additional orbits (¾ and Q7 as much as possible close to the center of the suspected updraft 320. The drift correction is performed by changing the flight direction of the aerial vehicle 200 in accordance with estimated direction and speed of a side wind at the vicinity of the aerial vehicle.

After completing the orbit Q ₇ , aerial vehicle 200 concludes that at least one escape condition is fulfilled and that the suspected updraft 320 is indeed an updraft. Therefore, as shown in Fig. 3P, after registering the air-current parameters of the updraft 320, the aerial vehicle 200 is instructed to revert to its flight mode and to leave the area of the updraft 320 for investigating other locations.

Fig. 3Q illustrates a summary of the entire path that the aerial vehicle has passed during the entire run of the simulation. This path includes the above mentioned locations.