Patent Description:
A UAV can be equipped with vertical-lift rotors, which the UAV can use for taking off, hovering, and landing vertically. This can be referred to as a vertical take-off and landing (VTOL) capability for a UAV. Such UAVs are typically controlled autonomously or with a degree of remote operator guidance. In some situations, a UAV can lose functionality during flight, such as a loss of power to the UAV's engine. A safe landing is desired in these situations, and existing solutions typically involve computing various trajectories to potential emergency landing sites.

What is needed is an improved control system for a VTOL-capable UAV that takes into account various factors in facilitating safe navigation of the UAV to a desired landing site, while also utilizing both glide capabilities and VTOL capabilities of the UAV.

<NPL>, in accordance with its abstract, states challenges to creating practical autonomous air-taxis and personal aerial transportation systems.

<NPL>, in accordance with its abstract, states that Advanced Air Mobility is quickly developing as a new air transportation system with increasing autonomy levels to support low-cost on-demand passenger and package transport. Advanced Air Mobility must operate safely despite the potential to encounter hazards and experience anomalies and failures inflight. It becomes especially important to have systematic auto mitigation strategies to perform safe contingency actions in Advanced Air Mobility flight operations, as pilots have limited Situational Awareness and limited time to make decisions when encountering failures/anomalies in complex airspace and terrain. "Assured Contingency Landing Management for Advanced Air Mobility" presents Assured Contingency Landing Management with an online landing strategy selection capability to decide between the following three options when a contingency landing is required: (<NUM>) Return-to-launch landing, (<NUM>) Land immediately at a nearby clear but unprepared site, and (<NUM>) Land at a prepared landing site within the aircraft's reachable footprint. The presented algorithm shows a real-time auto-mitigation loop with multiple threads that run simultaneously to check controllability, reachability, and intermediate decisions to hold/loiter or continue the flight plan as the landing strategy solution is being computed.

According to a first aspect, there is provided a unmanned aerial vehicle (UAV) as defined in claim <NUM>.

According to a second aspect, there is provided a method for controlling an unmanned aerial vehicle (UAV) as defined in claim <NUM>.

The features, functions, and advantages that have been discussed can be achieved independently in various examples or may be combined in yet other examples. Further details of the examples can be seen with reference to the following description and drawings.

The novel features believed characteristic of the illustrative examples are set forth in the appended claims. The illustrative examples, however, as well as a preferred mode of use, further objectives and descriptions thereof, will best be understood by reference to the following detailed description of an illustrative example of the present disclosure when read in conjunction with the accompanying drawings, wherein:.

Disclosed examples will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all of the disclosed examples are shown. Indeed, several different examples may be described and should not be construed as limited to the examples set forth herein. Rather, these examples are described so that this disclosure will be thorough and complete and will fully convey the scope of the disclosure to those skilled in the art.

Unless otherwise specifically noted, elements depicted in the drawings are not necessarily drawn to scale.

Within examples, described herein is a UAV, system, and a corresponding method for controlling the UAV, particularly to manage the power consumption of a vertical-lift-equipped UAV and assist the UAV with landing in the event of a loss of operation of a propulsion system of the UAV.

The disclosed UAV, for example, includes an avionics system, a propulsion system, vertical-lift rotors, and a controller. In the event the controller detects a loss of operation of the propulsion system (e.g., engine failure), the controller responsively determines energy and time constraints based on (i) a remaining avionics battery life of the avionics system and (ii) a remaining rotor battery life of the vertical-lift rotors. The controller then uses a rotor edgewise inflow model stored on the controller to evaluate parameters (e.g., a path of the UAV, as well as speed profile of the UAV's speed over time) for a glide descent trajectory and subsequent rotor-powered flight trajectory to a candidate landing site, to thereby determine whether, based on evaluation of the parameters, an estimated energy consumption during the rotor-powered flight trajectory and time needed for the UAV to land at the candidate landing site exceed the energy and time constraints. And in response to determining that the estimated energy consumption and time needed for the UAV to land at the candidate landing site exceed the energy and time constraints, the controller selects an alternative candidate landing site. The controller then evaluates parameters for the alternative candidate landing site to determine whether the alternative candidate landing site is suitable for landing.

Within examples, the UAV receives the candidate landing sites from a ground control computing system. The ground control computing system can be configured to perform the same operations as the controller of the UAV, so that the ground control computing system can assist other UAVs with finding suitable landing sites in the event of engine failure, such as vertical-lift rotor-equipped UAVs that do not have the same landing site evaluation capabilities as the disclosed UAV.

Accordingly, a controller onboard a UAV and/or a controller of a ground control computing system is able to evaluate multiple candidate landing sites and determine a desired flight trajectory for safely landing at a given one of those landing sites, particularly in a manner that meets the energy and time constraints placed on the avionics and rotor systems of the UAV.

These and other improvements are described in more detail below. Implementations described below are for purposes of example. The implementations described below, as well as other implementations, may provide other improvements as well.

Referring now to the figures, <FIG> depicts a system <NUM> for controlling one or more UAVs. The system <NUM> includes the one or more UAVs, of which UAV <NUM> is representative. The system <NUM> also includes a communications network <NUM> that is configured to communicate various information to the one or more UAVs. And the system <NUM> also includes a ground control computing system <NUM> that is configured to engage in communication with each of the one or more UAVs via the communications network <NUM>.

Each UAV, as represented by UAV <NUM>, includes an avionics system <NUM>, a propulsion system <NUM> (e.g., a main engine), vertical-lift rotors <NUM> (e.g., propeller blades), and a controller <NUM>. The controller <NUM> includes one or more processors <NUM>, as well as memory <NUM> storing instructions <NUM>. The UAV <NUM> also includes batteries <NUM> configured to power the avionics system <NUM>, the propulsion system <NUM>, the vertical-lift rotors <NUM>, and the controller <NUM>. Although not explicitly shown, the UAV <NUM> can include other components as well, such as flaps or other drag devices, or wings, which can include such flaps or other drag devices. Within examples, the UAV <NUM> and/or at least one other UAV of the one or more UAVs is a fixed-wing UAV.

Within examples, the propulsion system <NUM> can take the form of an internal combustion engine or a hybrid engine such as an electric-internal combustion engine. Using the vertical-lift rotors <NUM>, the UAV <NUM> is capable of taking off, hovering, and landing vertically.

The one or more processors <NUM> can be a general-purpose processor or special purpose processor (e.g., a digital signal processor, application specific integrated circuit, etc.). The one or more processors <NUM> are configured to execute the instructions <NUM> (e.g., computer-readable program instructions including computer executable code) that are stored in the memory <NUM> and are executable to provide various operations described herein. At least some of the operations described herein as being performed by the controller <NUM> can be performed by the one or more processors <NUM>.

The memory <NUM> can take the form of one or more computer-readable storage media that can be read or accessed by the one or more processors <NUM>. The computer-readable storage media can include volatile and/or non-volatile storage components, such as optical, magnetic, organic or other memory or disc storage, which can be integrated in whole or in part with the one or more processors <NUM>. The memory <NUM> is considered computer readable media. The memory <NUM> may be considered non-transitory computer readable media. In some examples, the memory <NUM> can be implemented using a single physical device (e.g., one optical, magnetic, organic or other memory or disc storage unit), while in other examples, the memory <NUM> can be implemented using two or more physical devices.

The controller <NUM> can take the form of a computing device configured to manage and control operations of at least a portion of the other components of the UAV <NUM>, including but not limited to the avionics system <NUM>, the propulsion system <NUM>, and the vertical-lift rotors <NUM>. The controller <NUM> is also coupled to the batteries <NUM> and configured to monitor a battery life (e.g., energy level) of each such battery.

Within examples, such as the example shown and described with respect to <FIG>, and as primarily discussed herein, the controller <NUM> is located onboard the UAV <NUM>. Within other examples, however, at least a portion the operations described herein are performed by a separate controller of the ground control computing system <NUM> that is in communication with the controller <NUM> of the UAV <NUM>.

Within examples, the avionics system <NUM> and the vertical-lift rotors <NUM> are powered by respective different batteries. As such, the batteries <NUM> can include a first battery configured to power the avionics system <NUM> and a second, different battery configured to power the vertical-lift rotors <NUM>. Within other examples, the avionics system <NUM> and the vertical-lift rotors <NUM> are powered by the same battery.

As further shown, the ground control computing system <NUM> is also configured to engage in communication with at least one other UAV <NUM>, different from the one or more UAVs, via the communications network <NUM>. A representative UAV of the at least one other UAV <NUM> can take the form of a UAV that does not include a respective controller configured to perform the disclosed operations. As such, the ground control computing system <NUM> can be configured to perform the disclosed operations on behalf of the at least one other UAV <NUM> and send that/those UAV(s) instructions for landing. To facilitate this, the ground control computing system <NUM> can include a controller <NUM> configured to perform the disclosed operations.

The disclosed operations will now be described in more detail. In operation, there may be a situation in which the controller <NUM> detects a loss of operation of the propulsion system <NUM>, such as due to a power outage of the propulsion system <NUM>. With this loss of operation, the UAV <NUM> must rely on the avionics system <NUM> and the vertical-lift rotors <NUM> to navigate to a landing site. As such, it is desired to land the UAV <NUM> safely, at a landing site that is not within nolanding zone, and in a manner that does not exceed any time or energy constraints defined by the remaining battery life of the one or more of the batteries <NUM> that power the avionics system <NUM> and the vertical-lift rotors <NUM>.

Thus, in response to detecting loss of operation of the propulsion system <NUM>, and in order to help manage both avionics power and VTOL power, the controller <NUM> determines energy and time constraints based on (i) a remaining avionics battery life of the avionics system <NUM> and (ii) a remaining rotor battery life of the vertical-lift rotors <NUM>. In other words, these constraints represent a remaining amount of avionics battery life and rotor battery life for the controller <NUM> to set aside for the UAV <NUM> to safely land.

When the propulsion system <NUM> loses power, the descent of the UAV <NUM> is defined by three phases. <FIG> depicts these three phases - a rapid descent phase <NUM>, a transition phase <NUM>, and a VTOL phase <NUM> - as well as a trajectory <NUM> of the UAV <NUM>, according to an example implementation. <FIG> then depicts the trajectory <NUM> in a three-dimensional view, according to an example implementation. Within examples, the avionics system <NUM> is used during all three phases, and thus power is drawn during these phases. Whereas, the vertical-lift rotors <NUM> are used only during the VTOL phase <NUM>. Within other examples, the avionics system <NUM> can be used for less time. In either case, the corresponding batteries for these subsystems have respective energy and time constraints to take into account.

The first phase is referred to herein as the rapid descent phase <NUM>, in which the UAV <NUM> relies on gliding to descent to a particular altitude and/or speed. And UAV <NUM> might fly at minimum airspeed.

Once a desired altitude and/or speed is reached, plus or minus a predefined margin, the controller <NUM> instructs the UAV <NUM> to pull up its nose and slow down, and then, once another desired altitude and/or speed is reached, the controller <NUM> activates the vertical-lift rotors <NUM> and the UAV <NUM> quickly decelerates. The time during which this occurs is referred to herein as the transition phase <NUM> and, for the sake of example, the end of the transition phase <NUM> can be defined as a time-point at which the vertical-lift rotors <NUM> are turned on, thus beginning the VTOL phase <NUM>.

Subsequent rotor-powered flight then occurs, which is referred to herein as the VTOL phase <NUM>. During the VTOL phase <NUM>, the UAV <NUM> uses the vertical-lift rotors <NUM> to navigate the trajectory <NUM> and then land. In addition, landing in the no-land zone <NUM> is not desired. Rather, the disclosed operations aim to control the UAV <NUM> to travel into safe airspace <NUM> and land at a desired landing site <NUM> within a safe landing zone (e.g., within safe landing region <NUM>).

Also shown in <FIG> are one or more safe landing regions <NUM> and a maximum range <NUM>. The safe landing region <NUM> is a region within which the UAV <NUM> can also safely land within the energy and time constraints, based on the evaluation performed by the controller <NUM>, as described in more detail below. The maximum range <NUM> is a maximum range from a current location of the UAV <NUM> within which the UAV <NUM> is capable of landing at a landing site. The controller <NUM> determines the maximum range <NUM> based at least in part on of the remaining avionics battery life and the remaining rotor battery life of the vertical-lift rotors needed to reach the desired landing site <NUM> with a sufficient amount of rotor battery life set aside for the UAV <NUM> to vertically descend and safely land upon reaching the desired landing site <NUM>. Since conditions and the location of the UAV <NUM> change while the UAV <NUM> is in flight, the controller <NUM> can be configured to periodically reevaluate the parameters described herein and recalculate the maximum range <NUM> as needed.

Further, as will be discussed later herein, the controller <NUM> is configured to evaluate multiple different candidate landing sites to assess their viability for safe landing. For example, the controller <NUM> could determine that the desired landing site <NUM> is not viable, in which case the controller <NUM> select another candidate landing site to evaluate, such as landing site <NUM> shown in <FIG> and <FIG>.

As an example of the time (and corresponding energy) constraints the controller <NUM> determines, consider a situation in which, at the time the propulsion system <NUM> loses power, the controller <NUM> determines that the remaining avionics battery life is <NUM> minutes and that the remaining rotor battery life is <NUM> minutes. Thus, the UAV <NUM> must be safely landed at a particular landing site within <NUM>, while also allowing for a maximum of <NUM> minutes of rotor-powered flight. In other words, the energy and time constraints are determined based at least in part on a lesser of the remaining avionics battery life and the remaining rotor battery life. Other examples are possible as well.

Within examples, the energy and time constraints allow for use of an entirety of the remaining rotor battery life and/or the remaining avionics battery life. Within other examples, the energy and time constraints allow for use of a portion of the remaining rotor battery life and/or the remaining avionics battery life. For instance, the controller <NUM> can be configured such that, in evaluating how best to land the UAV <NUM> as described in more detail below, the controller <NUM> will not allow consumption of the remaining rotor battery life and/or the remaining avionics battery life to fall below a predetermined energy threshold, such as <NUM>% capacity, or to exceed a predetermined time threshold, such as <NUM>% of the total time remaining. As an example of the latter, even if the remaining rotor battery life is determined to be <NUM> minutes, the controller <NUM> can be configured to land the UAV <NUM> in a manner that requires the vertical-lift rotors <NUM> to be turned on for no more than <NUM> minutes.

Further, in some situations, the avionics system <NUM> has a constant power draw during flight after the power loss, whereas VTOL power draw by the vertical-lift rotors <NUM> is a function of airspeed, with the highest VTOL power draw occurring at approximately zero airspeed when the UAV <NUM> is hovering.

Referring back to the disclosed operations, the controller <NUM>, using a rotor edgewise inflow model stored on the controller <NUM> (e.g., in memory <NUM>), evaluates parameters for a glide descent trajectory and subsequent rotor-powered flight trajectory to a candidate landing site (e.g., landing site <NUM>). The controller <NUM> performs this evaluation to determine whether, based on evaluation of the parameters, an estimated energy consumption during the rotor-powered flight trajectory and time needed for the UAV <NUM> to land at the candidate landing site exceed the energy and time constraints.

Herein, and in line with the three phases of descent described above, the glide descent trajectory refers to UAV operation using the avionics system <NUM>, but without using the propulsion system <NUM> and the vertical-lift rotors <NUM>. In addition, the rotor-powered flight trajectory refers to UAV operation using the vertical-lift rotors <NUM> and the avionics system <NUM>, but without using the propulsion system <NUM>.

To facilitate evaluation of a candidate landing site, the controller <NUM> stores, or otherwise has access to, a set of predetermined landing sites. The set of predetermined landing sites includes the candidate landing site and can also include alternative candidate landing sites as well. Within examples, the set of predetermined landing sites are identified by an off-board system, located remote from the one or more UAVs, and either pre-loaded into memory of the one or more UAVs (e.g., memory <NUM> of UAV <NUM>) before takeoff or later communicated by the communications network <NUM> to the one or more UAVs. In the later example, the communications network <NUM> is configured to communicate the set of predetermined landing sites to the one or more UAVs. More particularly, the ground control computing system <NUM> is configured to transmit the set of predetermined landing sites to the one or more UAVs via the communications network <NUM>.

Within examples, the set of predetermined landing sites are a set of predetermined landing sites that are within the maximum range <NUM> of the UAV <NUM>. The controller <NUM> or the ground control computing system <NUM> thus selects, from that set of predetermined landing sites, a particular predetermined landing site as the candidate landing site for evaluation.

Within examples, for a given candidate landing site, the evaluation of the parameters involves determining whether, based on a first set of parameters for the glide descent trajectory and the rotor-powered flight trajectory to the candidate landing site, the estimated energy consumption of the remaining rotor battery life during the rotor-powered flight trajectory and the time needed for the UAV to land at the candidate landing site exceed the energy and time constraints. And in response to determining that the estimated energy consumption of the remaining rotor battery life during the rotor-powered flight trajectory and the time needed for the UAV to land at the candidate landing site exceed the energy and time constraints, determining whether, based on a second, different set of parameters for the glide descent trajectory and the rotor-powered flight trajectory to the candidate landing site, the estimated energy consumption of the remaining rotor battery life during the rotor-powered flight trajectory and the time needed for the UAV to land at the candidate landing site exceed the energy and time constraints. Phrased another way, if one set of parameters does not help meet the energy and time constraints, the controller <NUM> can evaluate a different set of parameters that define a different glide trajectory and/or rotor-powered flight trajectory.

The parameters for the glide descent trajectory and the subsequent rotor-powered flight trajectory to the candidate landing site can take various forms. Within examples, the parameters include a path, as well as a speed profile associated with that path, for reaching the candidate landing site. In particular, the parameters can include a path and speed profile for the glide descent trajectory, the rotor-powered flight trajectory, or a combination of the two. The parameters dictate the glide descent trajectory and the rotor-powered flight trajectory. As such, the controller <NUM> can evaluate various different glide descent trajectories, rotor-powered trajectories, and corresponding parameters for landing at the candidate landing site to determine whether one or more of those approaches will meet the energy and time constraints.

With respect to the glide descent trajectory, other example parameters that the controller <NUM> can evaluate include (i) an indicated airspeed of the UAV <NUM> (e.g., an airspeed commanded by a flight operator, automatically selected as a conservative minimum speed, or optimized via hodograph and wind estimates), (ii) a lift over drag ratio (which varies with airspeed), (iii) a roll-angle, or angle of bank of the UAV <NUM>, and (iv) a rate of descent. The rate of descent can be manipulated using flaps or drag devices of the UAV <NUM> and controlling the roll-angle. Equation <NUM>, for instance, indicates how the rate of descent, RoD, can be approximated as a function of the indicated airspeed, V_glide, the lift over drag ratio, LoD, and the roll-angle, ϕ.

Consider, for instance, a scenario in which the propulsion system <NUM> fails when the UAV <NUM> is at an altitude of <NUM>,<NUM> feet above ground level (AGL), and the UAV <NUM> has <NUM> minutes of remaining avionics battery life and <NUM> minutes of remaining rotor battery life. The UAV <NUM> must then land safely within those <NUM> minutes and without using more than <NUM> minutes of rotor power. If the UAV <NUM> was to glide in a straight line from <NUM>,<NUM> feet at a lift over drag ratio of <NUM>, the UAV <NUM> might be able to fly approximately <NUM> nautical miles in a no-wind situation. However, if the UAV <NUM> is commanded to fly at an indicated airspeed of <NUM> meters per second (m/s), this would require approximately <NUM> minutes, and thus the UAV <NUM> would run out of avionics power before this point. As such, an operator would need to consider increasing the indicated airspeed, as well as using flaps and/or spiraling, for a higher rate of descent.

Continuing the scenario above, the operator might elect to fly the UAV <NUM> directly towards a desired landing zone having multiple candidate landing sites instead of spending descent time in spiraling flight. To accomplish this, the operator sets a higher indicated airspeed of <NUM>/s and deploys flaps to lose additional altitude. As such, a rate of descent of approximately <NUM>/s is achieved, which would require approximately <NUM> minutes of flight to sea level, and is thus a valid choice for a landing, given the <NUM> minutes of remaining avionics battery life. In addition, this allows for up to <NUM> minutes of rotor-powered flight without exceeding the <NUM> minutes of remaining avionics battery life.

In any event, the controller <NUM> can use flight parameters that define a particular glide descent trajectory that result in the UAV <NUM> arriving at a particular altitude (e.g., <NUM> AGL) and a particular distance away from the candidate landing site (e.g., <NUM> meters horizontally from the candidate landing site). Given that glide descent trajectory, the controller <NUM> evaluates parameters for the rotor-powered flight trajectory that continues flight from that particular altitude and distance. If, as a result of the evaluation and in line with the discussion above, the controller <NUM> determines that the energy and time constraints are exceeded, the controller <NUM> then attempts to evaluate parameters for an alternative glide descent trajectory and/or parameters for an alternative rotor-powered flight trajectory, or selects an alternative candidate landing site.

With respect to the rotor-powered flight trajectory, other example parameters that the controller <NUM> can evaluate include rotor inflow velocity, required thrust (approximately equal to one quarter of the UAV's weight), air density, rotor disk area, vehicle air speed (i.e., speed of the unperturbed airflow), resultant air speed, and unperturbed airflow angle relative to rotor disk (nominally equal to vehicle pitch angle).

An example process for evaluating these and other parameters using the rotor edgewise inflow model stored on the controller <NUM> will now be described. The controller <NUM> selects a particular procedure for the rotor-powered flight trajectory to the candidate landing site. This procedure can take various forms, including, for instance, a minimum jerk trajectory that minimizes changes in deceleration, a maximum braking trajectory, or a constant deceleration trajectory (e.g., constant deceleration in horizontal flight to ground speed, followed by a constant vertical descent rate). Given the selected procedure, the controller <NUM> determines an associated speed profile such that the total time in the glide descent trajectory and the total time in the rotor-powered flight trajectory is less than the remaining time that the remaining avionics battery life will allow.

The controller <NUM> then models the vertical-lift rotors <NUM> as momentum generating disks that are flying edgewise. Based on the associated speed profile, the controller <NUM> determines a resulting edgewise inflow by iteratively solving Equation <NUM> and Equation <NUM> for each rotor, where vi is the rotor inflow velocity, T is the required thrust, ρ is the air density, A is the rotor disk area, Vinfty is the vehicle air speed, vres is the resultant air speed, and α is the unperturbed airflow angle relative to rotor disk. <MAT> <MAT>.

Increased accuracy can be obtained when down flow is accounted for in vehicle air speed and unperturbed airflow angle at the rear rotors. This adjustment can be obtained from known wind tunnel data or from straightforward estimates based on flow from the front rotors.

Using predetermined rotor and electric motor efficiencies, the controller <NUM> estimates the total energy required for the rotor-powered flight trajectory approach to the candidate landing site. The required rotor power as a function of time, Preq(t), is obtained from the inflow velocity solution and is depicted in Equation <NUM>. The energy used as a function of time, E(t), starting from time t<NUM> is depicted in Equation <NUM>, where µ is the predetermined combined efficiency of the rotor and electric motor. <MAT> <MAT>.

The controller <NUM> then compares the resulting energy from Equation <NUM> against the determined energy constraint. If the controller <NUM> determines that the energy and time constraints are met, the controller <NUM> navigates the UAV <NUM> in accordance with the evaluated parameters. Whereas, if the energy constraint is not met, the controller <NUM> can evaluate another set of parameters as described above, such as by reducing the length of the rotor-powered approach procedure or selecting a speed profile that favors higher translation speeds.

Continuing the scenario above even further, the UAV <NUM> might navigate the glide descent trajectory from <NUM>,<NUM> feet to <NUM> feet AGL, at which point almost <NUM> minutes will have passed since the loss of operation of the propulsion system <NUM> and at which point the UAV <NUM> will begin decelerating to approximately <NUM>/s and will transition to using the vertical-lift rotors <NUM> at <NUM> feet AGL. The transition might take within one minute to complete, thus giving the UAV <NUM> approximately <NUM> to <NUM> minutes left of time to safely land.

When the controller <NUM> has evaluated the parameters (e.g., different sets of parameters) relative to the candidate landing site and determines that the estimated energy consumption and time needed for the UAV <NUM> to land at the candidate landing site exceed the energy and time constraints, the controller <NUM> responsively selects an alternative candidate landing site. Within examples, the act of selecting the alternative candidate landing site involves selecting, from the set of predetermined landing sites, a next closest landing site to the candidate landing site, such as landing site <NUM> shown in <FIG> and <FIG>.

Once an alternative candidate landing site has been selected, the controller <NUM> then uses the rotor edgewise inflow model to evaluate alternative parameters for a glide descent trajectory and subsequent rotor-powered flight trajectory to the alternative candidate landing site, to determine whether, based on evaluation of the alternative parameters, an estimated energy consumption during the rotor-powered flight trajectory and time needed for the UAV <NUM> to land at the alternative candidate landing site exceed the energy and time constraints. And, in response to determining that the estimated energy consumption and time needed for the UAV <NUM> to land at the alternative candidate landing site do not exceed the energy and time constraints, the controller <NUM> selects the alternative candidate landing site to be a target landing site at which to land the UAV <NUM>.

Once the alternative candidate landing site has been evaluated and selected as a target landing site for the UAV <NUM>, the controller <NUM> controls the UAV <NUM> to navigate the glide descent trajectory and the rotor-powered flight trajectory to the alternative candidate landing site. To facilitate this, the controller <NUM> is configured to monitor various flight parameters while the UAV <NUM> is navigating the glide descent trajectory and, in response to detecting that at least one predefined condition has been met relative to one or more of such flight parameters, control the UAV <NUM> to (i) switch from the glide descent trajectory to the rotor-powered flight trajectory and then (ii) navigate in accordance with the rotor-powered flight trajectory to the target landing site. Within examples, the at least one predefined condition includes a condition that a speed of the UAV <NUM> has fallen below a predefined threshold speed (e.g., <NUM>/s) and/or a condition that an altitude of the UAV <NUM> has fallen below a predefined threshold altitude (e.g., <NUM> feet). Within additional examples, the controller <NUM> is configured to initiate the transition phase <NUM> and begin slowing down upon detecting that an altitude of the UAV <NUM> has fallen below a predefined threshold altitude and to then turn on the vertical-lift rotors <NUM> upon detecting that a speed of the UAV <NUM> has fallen below a predefined threshold speed. Other conditions and examples are possible as well.

<FIG> depicts a graph of remaining avionics battery life <NUM> and remaining rotor battery life <NUM> as a function of time during the three phases described above, according to an example implementation. In particular, the graph depicts the remaining avionics battery life <NUM> and the remaining rotor battery life <NUM> in a scenario where the controller <NUM> has selected landing site <NUM> to be an alternative candidate landing site after evaluating landing site <NUM> and is able to safely land the UAV <NUM> at landing site <NUM> with at least <NUM>% left of the battery life of both the avionics system <NUM> and the vertical-lift rotors <NUM>. As shown, the power draw by the avionics system <NUM> is constant, whereas the power draw of the vertical-lift rotors <NUM> does not begin until the transition phase <NUM>.

Furthermore, as noted above, the ground control computing system <NUM> can perform the disclosed operations for the at least one other UAV <NUM> that do not comprise a respective controller configured to perform the disclosed operations. As such, the ground control computing system <NUM> performs the disclosed operations until the ground control computing system <NUM> determines that respective estimated energy consumption and time needed for the at least one other UAV <NUM> to land at a particular predetermined landing site of the set of predetermined landing sites do not exceed respective energy and time constraints determined for the at least one other UAV <NUM>. The ground control computing system <NUM> then transmits, to the at least one other UAV <NUM> via the communications network <NUM>, data identifying the particular predetermined landing site. In addition, the ground control computing system <NUM> additionally transmits, to the at least one other UAV <NUM> , the parameters (e.g., direction, speed, etc.) according to which the at least one other UAV <NUM> should navigate the three phases of descent in order to land at the particular predetermined landing site.

<FIG> shows a flowchart of an example of a method <NUM> for controlling a UAV, such as UAV <NUM>. Method <NUM> could be used with the system <NUM> and components thereof shown in <FIG> and in the scenarios shown and described with respect to <FIG>, <FIG>, and <FIG>. Method <NUM> may include one or more operations, functions, or actions as illustrated by one or more of blocks <NUM>-<NUM>.

At block <NUM>, the method <NUM> includes, in response to detecting loss of operation of a propulsion system of the UAV, determining energy and time constraints based on (i) a remaining avionics battery life of an avionics system of the UAV and (ii) a remaining rotor battery life of vertical-lift rotors of the UAV.

At block <NUM>, the method <NUM> includes using a rotor edgewise inflow model, evaluate parameters for a glide descent trajectory and subsequent rotor-powered flight trajectory to a candidate landing site, to determine whether, based on evaluation of the parameters, an estimated energy consumption during the rotor-powered flight trajectory and time needed for the UAV to land at the candidate landing site exceed the energy and time constraints.

At block <NUM>, the method <NUM> includes in response to determining that the estimated energy consumption and time needed for the UAV to land at the candidate landing site exceed the energy and time constraints, selecting an alternative candidate landing site.

In some embodiments, the evaluating of block <NUM> includes determining whether, based on a first set of parameters for the glide descent trajectory and the rotor-powered flight trajectory to the candidate landing site, the estimated energy consumption of the remaining rotor battery life during the rotor-powered flight trajectory and the time needed for the UAV to land at the candidate landing site exceed the energy and time constraints. The evaluating of block <NUM> also includes, in response to determining that the estimated energy consumption of the remaining rotor battery life during the rotor-powered flight trajectory and the time needed for the UAV to land at the candidate landing site exceed the energy and time constraints, determining whether, based on a second, different set of parameters for the glide descent trajectory and the rotor-powered flight trajectory to the candidate landing site, the estimated energy consumption of the remaining rotor battery life during the rotor-powered flight trajectory and the time needed for the UAV to land at the candidate landing site exceed the energy and time constraints.

In some embodiments, the method <NUM> also includes using the rotor edgewise inflow model to evaluate alternative parameters for a glide descent trajectory and subsequent rotor-powered flight trajectory to the alternative candidate landing site, to determine whether, based on evaluation of the alternative parameters, an estimated energy consumption during the rotor-powered flight trajectory and time needed for the UAV to land at the alternative candidate landing site exceed the energy and time constraints. The method <NUM> also includes, in response to determining that the estimated energy consumption and time needed for the UAV to land at the alternative candidate landing site do not exceed the energy and time constraints, selecting the alternative candidate landing site to be a target landing site at which to land the UAV. And the method <NUM> also includes controlling the UAV to navigate the glide descent trajectory and the rotor-powered flight trajectory to the alternative candidate landing site. In such embodiments, the method <NUM> is performed by a controller onboard the UAV and/or by a ground computing system, located remote from the UAV.

Different examples of the system(s), device(s), and method(s) disclosed herein include a variety of components, features, and functionalities. It should be understood that the various examples of the system(s), device(s), and method(s) disclosed herein may include any of the components, features, and functionalities of any of the other examples of the system(s), device(s), and method(s) disclosed herein in any combination or any sub-combination, and all of such possibilities are intended to be within the scope of the disclosure.

Claim 1:
An unmanned aerial vehicle, UAV, (<NUM>) comprising:
an avionics system (<NUM>);
a propulsion system (<NUM>);
vertical-lift rotors (<NUM>);
a controller (<NUM>);
batteries (<NUM>) configured to power the avionics system (<NUM>), the propulsion system (<NUM>), the vertical-lift rotors (<NUM>) and the controller (<NUM>); and
wings,
wherein the controller (<NUM>) comprises one or more processors (<NUM>) configured to execute instructions (<NUM>) stored in memory (<NUM>) to perform operations comprising:
in response to detecting loss of operation of the propulsion system (<NUM>), determining energy and time constraints based on (i) a remaining avionics battery life (<NUM>) of the avionics system (<NUM>) and (ii) a remaining rotor battery life (<NUM>) of the vertical-lift rotors;
using a rotor edgewise inflow model stored on the controller (<NUM>), evaluate parameters for a glide descent trajectory and subsequent rotor-powered flight trajectory to a candidate landing site (<NUM>), to determine whether, based on evaluation of the parameters, an estimated energy consumption during the rotor-powered flight trajectory and time needed for the UAV (<NUM>) to land at the candidate landing site (<NUM>) exceed the energy and time constraints, wherein:
the glide descent trajectory comprises UAV (<NUM>) operation using the avionics system (<NUM>), but without using the propulsion system (<NUM>) and the vertical-lift rotors; and
the rotor-powered flight trajectory comprises UAV (<NUM>) operation using the vertical-lift rotors and the avionics system (<NUM>), but without using the propulsion system (<NUM>); and the operations further comprising:
in response to determining that the estimated energy consumption and time needed for the UAV (<NUM>) to land at the candidate landing site (<NUM>) exceed the energy and time constraints, selecting an alternative candidate landing site (<NUM>).