Unmanned aerial vehicle electronics

Abstract

An unmanned aerial vehicle 200 comprises: a primary altimeter (202) configured to indicate an altitude of the vehicle in flight based on time taken for an electromagnetic signal emitted from the vehic

Description

Technical Field The present invention relates to unmanned aerial vehicles, more particularly to control and sensing electronics for such vehicles, and their methods of use. Background Unmanned aerial vehicles (UAVs) are increasingly being used in a variety of different contexts. For example, UAVs may be used for reconnaissance purposes, or the delivery of cargo or a payload to a desired location. UAVs typically include a variety of electronic hardware (avionics), including (but not limited to) communication, navigation and sensor systems. These can include certain components that are used to determine the altitude of the aircraft. This information can be used to control the aircraft in flight and / or may be relayed to a user on the ground. Although satellite positioning data can be used to obtain a measure of altitude, such data is often imprecise. Barometric pressure sensors, which use a measurement of the atmospheric pressure to determine altitude, have also been used as altimeters,. However, this technique may also provide inaccurate readings, due for example to changes in ambient air pressure and calibration errors. Radar altimeters have also been used in aircraft to determine altitude. This technique measures altitude above terrain beneath the aircraft based on the time it takes for radio waves to travel to ground, reflect, and return to the aircraft. However, these signals may be subject to interference and may be affected by movement or changes in the orientation of the aircraft. UAVs typically include communications systems for communicating with a remote device on the ground. However, in some environments it may be desirable to switch off such communications whilst continuing on a flight path. Summary of Invention Embodiments of the present invention aim to address the above problems and others. Aspects of the disclosure are set out in the independent claims and optional features are set out in the dependent claims. Aspects of the disclosure may be provided in conjunction with each other, and features of one aspect may be applied to other aspects. In an aspect there is provided an unmanned aerial vehicle (UAV) comprising: a primary altimeter configured to provide an indication of an altitude of the vehicle in flight based on the time taken for an electromagnetic signal emitted from the vehicle to return to the vehicle; a secondary altimeter configured to measure the ambient pressure and provide an indication of an altitude of the vehicle in flight based on the measured ambient pressure; a controller configured to obtain one or more altitude signals from each of the primary altimeter and the secondary altimeter, and in a first mode, select the altitude of the vehicle based on the signals from the primary altimeter; in a second mode, select the altitude of the vehicle based on the signals from the secondary altimeter; wherein the controller is configured to switch from the first mode to the second mode in response to a change in the orientation or trajectory of the vehicle. The UAV may be configured to switch from the first mode to the second mode in response to the vehicle rotating about its longitudinal axis (rolling), for example from a non-turning configuration into a turning configuration. The UAV may further comprise at least one wing, wherein, in the turning configuration, the wing is arranged transverse, i.e. not parallel, to the ground above which the UAV is flying. For example the wing may be angled about its roll axis at approximately 90° to the plane of the ground, or above a selected threshold angle between 0° and 90°. In the non-turning configuration, the wing may be arranged substantially parallel to the ground plane. The UAV may be configured to switch from the first mode to the second mode in response to the UAV transitioning from the non-turning to the turning configuration, e.g. at a predetermined roll angle between 0° and 90°. The primary altimeter may be flush mounted on a surface of the vehicle. The UAV may further comprise a nosecone, wherein the primary altimeter is flush mounted on the nosecone. The primary altimeter may comprise a radar altimeter, and / or it may comprise a Lidar altimeter. The radar altimeter may comprise a radio transceiver configured to transmit radio waves towards the ground above which the UAV is flying, and to detect radio waves reflected off the ground. The lidar altimeter may comprise a laser emitter configured to transmit laser light towards the ground above which the UAV is flying, and a detector configured to detect laser light reflected off the ground. The UAV may further comprise a satellite navigation receiver, e.g. a GPS receiver, wherein the receiver is configured to provide data indicating the global position of the vehicle to the controller. The data may include altitude data, and the controller may be configured to determine / select altitude of the UAV based on the global position data. The controller may be configured to switch from the second mode to the first mode in response to a change in the orientation or trajectory of the vehicle, e.g. a second rotation I roll of the vehicle. The rotation may be a rotation from the turning configuration into the non-turning configuration, e.g. the second rotation of the vehicle may be the reverse of the first rotation. The UAV may further comprise an engine control unit, wherein the controller is configured to provide data indicating the determined altitude of the vehicle to the engine control unit, and wherein the engine control unit is configured to control an engine of the unmanned aerial vehicle based on the determined altitude data. The controller may be configured to modify operation of the UAV in response to the determined altitude, e.g. to modify the pitch, roll or yaw of the UAV. The UAV may be configured to wirelessly transmit data indicating the altitude to a remote user device. The UAV may comprise a wireless transceiver, e.g. a radio antenna, configured to wirelessly transmit the data, and to receive control signals from the remote device, e.g. to control operation of the UAV. The UAV may further comprise a switching unit configured to disconnect at least one of: the primary altimeter; the secondary altimeter; the controller and the wireless receiver from a power source of the UAV. The controller may be configured to provide auto-pilot control of the UAV. In another aspect there is provided a method of determining the altitude of an unmanned aerial vehicle, the method comprising: obtaining a first altitude signal based on the time taken for an electromagnetic signal emitted from the vehicle to return to the vehicle; in a first mode, determining the altitude of the vehicle based on the first altitude signal; switching from the first mode to a second mode in response to change in the orientation or trajectory of the vehicle; obtaining a second altitude signal based on the pressure surrounding the vehicle; in the second mode, determining the altitude of the vehicle based on the second signal. The method may further comprise switching from the first mode to the second mode to the vehicle rotating about its longitudinal axis (rolling), e.g. from a non-turning configuration into a turning configuration. The method may further comprise switching from the second mode to the first mode in response to a change in the orientation or trajectory of the vehicle. The method may further comprise obtaining satellite navigation data indicating the global position of the vehicle. The method may further comprise providing data indicating a determined altitude of the vehicle to an engine control unit. In another aspect there is provided an unmanned aerial vehicle comprising a power source, a communications unit, and a switching unit, wherein the switching unit is configured to disconnect the communications unit from the power unit in flight. The communications unit may be configured to communicate with a remote user device, e.g. to transmit data about the UAV and / or to receive control signals for controlling the UAV. The switching unit may be configured, e.g. actuated, to physically sever a link between the power source and the communications unit. For example, the switching unit may be configured to irreversibly sever the link between the power source and the communications unit, and / or to inhibit reconnection between the power source and the communications unit. The switching unit may comprise a mechanical switch, which may be configured to latch into an open position. The UAV may comprise a controller, and the switching unit may be configured to disconnect the communications unit from the power source in response to a command signal from the controller. The communications unit may comprise the controller, e.g. such that the controller is disconnected from the power source upon actuation of the switching unit. Disconnecting may comprise breaking an electrical link by mechanical force, for example by deforming the link to failure. The controller may be configured to provide the command signal in response to a wireless signal received by the vehicle in flight. The controller may be pre-programmed to provide the signal at a selected time in flight. The vehicle is configured to fly in a first mode in which the vehicle is in wireless communication with a remote device, and in response to the switching unit switching off power to the communications unit, to fly in a second mode in which the wireless communication is disabled. In the second mode UAV may be controlled according to a pre-programmed flight path I route, e.g. by a controller. In another aspect there is provided an unmanned aerial vehicle comprising: a power source; a controller; an engine fuel pump; an altimeter; a satellite navigation receiver; and an actuating device configured to release the UAV from a launching device and / or to activate a device carried by the UAV; and a power distribution board configured to distribute the power from the power source between the controller, the engine fuel pump, the primary altimeter, the satellite navigation receiver and the actuating device. The altimeter may be configured to provide an indication of an altitude of the vehicle in flight based on the time taken for an electromagnetic signal emitted from the vehicle to return to the vehicle, e.g. a radar or lidar altimeter. The unmanned aerial vehicle may further comprise an engine fuel pump, and the power distribution board may be additionally configured to distribute power to the engine fuel pump. The unmanned aerial vehicle may further comprise an engine starter, and the power distribution board may be additionally configured to distribute power to the engine starter. The unmanned aerial vehicle may further comprise an engine control unit, and the power distribution board may be additionally configured to distribute power to the engine control unit. The unmanned aerial vehicle may further comprise a secondary altimeter, and the power distribution board may be additionally configured to distribute power to the secondary altimeter. The secondary altimeter may be configured to measure the ambient pressure and provide an indication of an altitude of the vehicle in flight based on the measured ambient pressure. The unmanned aerial vehicle may further comprise a GPU connector, and the power distribution board may be additionally configured to distribute power to the GPU connector. The unmanned aerial vehicle may further comprise a switch, e.g. a microswitch, operable to adjust the voltage provided to the power distribution board. The actuating device may be configured to launch the UAV from the launching device. The actuating device may comprise at least one of a solenoid, a squib and a detonator configured to release, e.g. launch, the UAV from the launching device. Additionally or alternatively, the actuating device may be configured to activate a component or device that is carried by the UAV. Brief Description of Figures Some examples of the present disclosure will now be described with reference to the figures, in which: Figure 1a shows a schematic view of an example unmanned aerial vehicle (UAV); Figure 1b shows another schematic view of the example UAV; Figure 2 illustrates an example electronic system used in a UAV; Figure 3 illustrates an example method performed by a controller of a UAV; Figure 4 illustrates another example electronic system used in a UAV; Figure 5 illustrates another example electronic system used in a UAV. In the drawings like reference numerals are used to indicate like elements. Specific Description The present disclosure relates to unmanned aerial vehicles (UAVs) and in particular, to electronic control and sensor systems for UAVs. The UAV includes multiple altimeters which measure the altitude of the UAV in flight, and are used at different points in the UAV’s flight. A radar or lidar altimeter is predominantly used to determine the altitude when the UAV is flying normally, e.g. when not turning. However, when the UAV is executing a turn, the radar / lidar altimeter may be inaccurate and so a pressure-based altimeter is instead used to determine the altitude. A controller of the UAV is configured to switch between the two altimeters as appropriate. Additionally, the UAV may include a kill switch to disconnect certain electronic components of the UAV from power at a particular point during the UAVs flight path. Figure 1a shows an example of a UAV 100 in a first in-flight configuration. The first configuration is a stable non-turning configuration of the UAV, e.g. such that the UAV is flying in substantially a straight line. The UAV 100 comprises a nose cone 102 and at least one wing 104. In this configuration the wing is substantially parallel to the ground below. Aviation electronics 200 such as communication, navigation and / or sensor components are provided in the nose cone 102, and are described in more detail below. Figure 1b shows the UAV 100 in a second in flight-configuration. The second configuration is a turning configuration, in which the UAV 100 has rotated 90° about its longitudinal axis (i.e. it has rolled 90°). In this configuration the wing 104 is substantially perpendicular to the ground below. Figure 2 shows a schematic view of an example aviation electronics system 200, which may be used in the UAV 100, e.g. provided in the nose cone 102. The electronics system 200 comprises a controller 210 which is electrically connected to a primary altimeter 202, a secondary altimeter 204 and a satellite navigation receiver 206. Each of the primary altimeter 202, the secondary altimeter 204 and the satellite navigation receiver 206 are configured to communicate with the controller 210, in particular to provide signals to the controller 210. The electronics 200 further comprises an engine control unit 220, that is electrically connected to the controller 210. The controller 210 is configured to provide control signals and / or data to the engine control unit 220. The engine control unit 220 is configured to control an engine (not shown) of the unmanned aerial vehicle 100 based on data provided by the controller 210. The controller is also connected to a communications unit 212, which is configured to send and receive signals from a remote user device, e.g. on the ground. For example, the communications unit 212 may be able to provide data from the UAV 100 to the remote device, and may be able to receive control signals from the remote device for controlling operation of the UAV 100, and provide these to the controller 210. The primary altimeter 202 may be a radar or Lidar altimeter, and is arranged determine the altitude of the UAV in flight based on the time taken for an electromagnetic signal emitted from the aircraft to return to the aircraft, and to provide an indication of the determined altitude of the vehicle to the controller 210. In the case of a radar altimeter, the altimeter 202 comprises an antenna configured to transmit radio waves toward the ground beneath the UAV 100 and to detect said waves after they have been reflected back to the UAV 100. In the case of a Lidar altimeter, laser light is correspondingly transmitted and detected from the ground below. The primary altimeter 202 may be flush mounted onto the surface of the nose cone 102 shown in Figure 1a. The secondary altimeter 204 comprises a barometer and is configured to sense the ambient air pressure surrounding the UAV 100 (the barometric pressure) and provide a barometric reading to the controller 210. The controller 210 may then determine an altitude of the UAV based on the barometric reading. Alternatively, the secondary altimeter 204 may determine the altitude of the UAV based on the barometric reading and provide an indication of the determined altitude to the controller 210. The controller 210 is configured to determine and / or select an altitude of the vehicle based either on the signals from the primary altimeter 202 (a first mode) or the signals from the secondary altimeter 204 (a second mode). Which mode is used in dependent on the configuration of the UAV 100. For example, in a stable non-stable flying configuration, e.g. the first configuration shown in Fig. 1a, the controller 210 may be configured to select the altitude based on the primary altimeter 202 data. However, when the UAV 100 is performing a turn, it may roll (rotate about its longitudinal axis) up to 90°, such that it is at least partially transverse to the ground above which it is flying. In this scenario the UAV 100 is in a turning configuration e.g. as shown in Figure 1b. In such a configuration the altitude as determined using the primary altimeter 202 may be less accurate, e.g. because the primary altimeter 202 does not have a direct line of sight to the ground below. In the turning configuration it may therefore be desirable to use the secondary altimeter 204 to determine the altitude of the UAV 100. The controller 210 is configured to switch from the use of the primary altimeter 202 to the use of the secondary altimeter 204 in response to the UAV 100 rotating from its non-turning configuration into its turning configuration. Similarly, the controller 210 is configured to switch from the use of the secondary altimeter 204 to the use of the primary altimeter 202 in response to the UAV 100 rotating from its turning configuration into its non-turning configuration. The satellite navigation receiver 206 (e.g. GPS) is configured to receive signals from a plurality of satellites to determine the global position of the UAV 100, and to provide information indicating the global position of the UAV 100 to the controller 202. This information may include altitude data, and so in certain modes of operation the controller 202 may be configured to select or determine the altitude of the UAV 100 based on the satellite navigation data. The controller 210 is configured to switch from the first mode to the second mode above in response to an indication of a change in the UAV’s trajectory, e.g. that the UAV 100 is in its turning configuration or is transitioning from its non-turning configuration into its turning configuration. Such an indication may be provided by an accelerometer. Alternatively, the indication may be obtained from a remote control signal that instructs the UAV to perform the turn. Alternatively, the indication may be provided by the obtained satellite positioning data, which may indicate that the UAV 100 is performing the turn. Alternatively, controller 210 may be pre-programmed to switch to the second mode at a given flight time of the UAV, e.g. based on a pre-programmed route of the UAV 100. Similarly, the controller 210 is configured to switch from the second mode to the first mode above in response to an indication that the UAV 100 is in its non-turning configuration or is transitioning from its turning configuration into its non-turning configuration. The controller 210 is also configured to control operation the UAV 100, e.g. its movement, roll, pitch, yaw, and / or thrust, based on the selected altitude. For example, the controller 210 may provide a command signal to the engine control unit 220 that is based on the selected altitude. The controller 210 is also configured to communicate with a remote device, via communication unit 212. The altitude data selected by the controller may thereby be communicated to a user. Figure 3 is a flow chart illustrating an example method 30 of the aviation electronics, e.g. a method performed by a controller such as controller 210. In particular, Figure 3 illustrates a method 30 of determining the altitude of an unmanned aerial vehicle. The method 30 comprises obtaining 32 a first signal based on the time taken for an electromagnetic signal emitted from the vehicle to return to the vehicle, e.g. the radar or lidar data described above. The method 30 further comprises in a first mode, determining 34 the altitude of the vehicle based on the first signal. A further step 36 comprises switching from the first mode to a second mode in response to a change in the orientation or trajectory of the vehicle, e.g. as described above. The method further comprises obtaining 38 a second signal based on the pressure surrounding the UAV, e.g. the barometric measurement described above. Finally, in the second mode, determining 40 the altitude of the vehicle based on the second signal is performed. It will be understood that the order of steps shown in Figure 3 is merely exemplary. For example, the obtaining of the first signal and the second signal may be performed concurrently. For example, the step 38 of obtaining of the second signal may be performed before the switching step 36. Figure 4 illustrates another example of an aviation electronics system 300 which may be used in the UAV 100. The system 300 comprises a controller 210, which may be the same as controller 210 described above. The system further comprises a power source 302, such as a LiPO battery. The power source 302 is arranged to power the electronics of the UAV 100. The system 300 further comprises a communications unit 212, which is electrically connected to the controller 210. The communications unit 212 may be configured to send and receive signals from a remote user device, e.g. it may be a radio transceiver. For example, the communications unit 212 may be configured to receive control signals from the remote device to control operation of the UAV 100. The communications unit 212 may also comprise a radar unit, and / or a lidar unit,. The unit 212 may provide any or all of these functions in combination. The system 300 further comprises a switching unit 306, arranged between the power source 302 and the communications unit 212. The switching unit is configured to physically disconnect the communications unit 212 from the power source 302 in flight. The switching unit may be actuated in response to a control signal from the controller 210. For example, the control signal may be provided in response to an instruction from a remote user device and / or the controller 210 may be pre-programmed to provide the control signal at a certain point in the flight path of the UAV 100, e.g. at a certain time. Additionally or alternatively, the switching unit 306 may itself be pre-programmed to physically disconnect the communications unit 212 from the power source 302 at a certain point in the flight path of the UAV 100, e.g. at a certain time. In other examples, the switching unit 306 is provided between the power source 302 and all of the electronics of the UAV, e.g. including the controller and / or other electronic components such as those described above with reference to Figure 1, such that upon actuation of the switching unit, all of said electronics are physically disconnected from the power source 302. Upon actuation, the switching unit 306 is configured to sever the link between the power source and the electronics physically and irreversibly, such that the electronic components switch off. The UAV may be configured to continue flying on a predetermined flight path after the switching unit 306 has been actuated. As such, the UAV 100 can be configured to fly in a first mode in which it is in wireless communication with a remote device, and in a second mode after the wireless communication has been disabled. In the second mode, once the communications unit 212 has been disconnected from the power source 302, the controller 210 is configured to control the flight of the UAV according to a pre-programmed flight path I route. Figure 5 illustrates another example of an aviation electronics system 500 which may be used in the UAV 100. The electronics system 500 may comprise some or all of the components of the systems 200 and 300 described above. The system 500 comprises a power source 302 configured to power the other components of the system 500. The power source is electrically connected to a power distribution I relay board 510, which is configured to distribute, e.g. divide, the power from the power source 302 between the other components of the system 500. The system further comprises an engine starter 502, an engine fuel pump 504, a primary altimeter 202 a secondary altimeter 204, a controller 210, satellite navigation receiver 206, an actuating device 506, an engine control unit 220, and a GPU connector 508, all electrically coupled either directly or indirectly, to the power distribution board 510. The power distribution board 510 comprises a plurality of output ports for connection to the downstream components. The engine starter 502 and engine fuel pump 504 share a connection to the power distribution board 510. The engine control unit 220 and / or the secondary altimeter 204 may be connected to the power distribution board 510 via the controller 210. The primary altimeter 202, secondary altimeter 204, satellite navigation receiver 206, controller 210 and engine control unit 220 substantially correspond to those components as described above with reference to the earlier figures. As shown, the satellite navigation receiver 206 is configured to receive four satellite signals E1-E4 in order to determine the global position of the UAV. The actuating device 506 may be electrically activated. The actuating device 506 may configured to release, e.g. launch, the UAV from a launching device. The actuating device 506 comprises an actuating element, e.g a solenoid, a squib or a detonator which are configured to launch, the UAV from the launching device. A switch 514 is arranged between the actuating device 506 and the power distribution board 510, which may be switched to cause actuation of the actuating device 506. Additionally or alternatively, the actuating device 506 may be configured to activate, e.g. switch on, a device carried by the UAV 100. In the example shown in Figure 5, the power source 302 is a battery, such as a LiPo battery which provides a 22.2 V DC voltage. The power distribution board 510 is configured to provide different voltage levels to the different downstream components according to their power needs. The power distribution board 510 is configured to provide: 5V to the actuating device 506 I actuating device switch 514, 12V to the shared engine starter 502 and engine fuel pump 504 output, 6V to the satellite navigation receiver 206, 3V to the controller 210 and 8 or 4V to the primary altimeter 202. The system 500 further comprises a microswitch 512 arranged between the power source 302 and the power distribution board 510. The switch 512 is operable to adjust the voltage provided to the power distribution board. For example, the switch 512 may be operable to switch on the power supply from the power source 302 to the power distribution board 510. The power distribution board 510 is configured to switch a control voltage to switch in / out the DC voltage from the power source 502. It will be appreciated from the discussion above that the examples shown in the figures are merely exemplary, and include features which may be generalised, removed or replaced as described herein and as set out in the claims. With reference to the drawings in general, it will be appreciated that schematic functional block diagrams are used to indicate functionality of systems and apparatus described herein. As will be appreciated by the skilled reader in the context of the present disclosure, each of the examples described herein may be implemented in a variety of different ways. Any feature of any aspects of the disclosure may be combined with any of the other aspects of the disclosure. For example, method aspects may be combined with apparatus aspects, and features described with reference to the operation of particular elements of apparatus may be provided in methods which do not use those particular types of apparatus. In addition, each of the features of each of the examples is intended to be separable from the features which it is described in combination with, unless it is expressly stated that some other feature is essential to its operation. Each of these separable features may of course be combined with any of the other features of the examples in which it is described, or with any of the other features or combination of features of any of the other examples described herein. Furthermore, equivalents and modifications not described above may also be employed without departing from the invention. Certain features of the methods described herein may be implemented in hardware, and one or more functions of the apparatus may be implemented in method steps. It will also be appreciated in the context of the present disclosure that the methods described herein need not be performed in the order in which they are described, nor necessarily in the order in which they are depicted in the drawings. Accordingly, aspects of the disclosure which are described with reference to products or apparatus are also intended to be implemented as methods and vice versa. The methods described herein may be implemented in computer programs, or in hardware or in any combination thereof. Computer programs include software, middleware, firmware, and any combination thereof. Such programs may be provided as signals or network messages and may be recorded on computer readable media such as tangible computer readable media which may store the computer programs in non-transitory form. Hardware includes computers, handheld devices, programmable processors, general purpose processors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), and arrays of logic gates. Other examples and variations of the disclosure will be apparent to the skilled addressee in the context of the present disclosure. 16 05 25

Claims

1. An unmanned aerial vehicle comprising:a primary altimeter configured to provide an indication of an altitude of the5 vehicle in flight based on the time taken for an electromagnetic signal emitted from the vehicle to return to the vehicle;a secondary altimeter configured to measure the ambient pressure and provide an indication of an altitude of the vehicle in flight based on the measured ambient pressure;10 a controller configured to obtain one or more altitude signals from each ofthe primary altimeter and the secondary altimeter, andin a first mode, select the altitude of the vehicle based on the signals from the primary altimeter;in a second mode, select the altitude of the vehicle based on the 15 signals from the secondary altimeter;wherein the controller is configured to switch from the first mode to the second mode in response to a change in the orientation or trajectory of the vehicle.

2. The unmanned aerial vehicle of claim 1, wherein the controller is configured to 20 switch from the first mode to the second mode in response to the vehicle rolling about its longitudinal axis, for example from a non-turning configuration into a turning configuration.

3. The unmanned aerial vehicle of claim 2, further comprising at least one wing, 25 wherein, in the turning configuration, the wing is arranged transverse to the ground above which the UAV is flying.

4. The unmanned aerial vehicle of any preceding claim, wherein the primary altimeter is flush mounted on a surface of the vehicle.

305. The unmanned aerial vehicle of claim 4, further comprising a nosecone, wherein the primary altimeter is flush mounted on the nosecone.

6. The unmanned aerial vehicle of any preceding claim, wherein the primary16 05 25altimeter comprises a radar altimeter.

7. The unmanned aerial vehicle of any preceding claim, wherein the primary altimeter comprises a Lidar altimeter.

58. The unmanned aerial vehicle of any preceding claim, further comprising a satellite navigation receiver, wherein the receiver is configured to provide data indicating the global position of the vehicle to the controller.10 9. The unmanned aerial vehicle of any preceding claim, wherein the controller is configured to switch from the second mode to the first mode in response to a change in the orientation or trajectory of the vehicle.

10. The unmanned aerial vehicle of any preceding claim, further comprising an 15 engine control unit, wherein the controller is configured to provide data indicating the determined altitude of the vehicle to the engine control unit, and wherein the engine control unit is configured to control an engine of the unmanned aerial vehicle based on the determined altitude data.20 11. The unmanned aerial vehicle of any preceding claim, wherein the vehicle comprises a communications unit configured to wirelessly transmit data indicating the altitude to a remote user device.

12. The unmanned aerial vehicle of claim 11, further comprising a switching unit 25 configured to disconnect at least one of: the primary altimeter and the communications unit from a power source of the vehicle.

13. A method of determining the altitude of an unmanned aerial vehicle, the method comprising:30 obtaining a first altitude signal based on the time taken for an electromagnetic signal emitted from the vehicle to return to the vehicle;in a first mode, determining the altitude of the vehicle based on the first altitude signal;switching from the first mode to a second mode in response to a change in theLO CXIorientation or trajectory of the vehicle;obtaining a second altitude signal based on the pressure surrounding the vehicle;in the second mode, determining the altitude of the vehicle based on the second signal.

514. The method of claim 13, further comprising switching from the first mode to the second mode in response to the vehicle rolling about its longitudinal axis, for example rotating from a non-turning configuration into a turning configuration.10 15. The method of claim 13 or 14, further comprising switching from the second mode to the first mode in response to a change in the orientation or trajectory of the vehicle.

16. The method of claim 13 to 15 further comprising providing data indicating a determined altitude of the vehicle to an engine control unit.

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