Aircraft and electric power systems for aircraft

Abstract

Aircraft and electric power systems for aircraft are disclosed. An aircraft as disclosed comprises a wing structure, a propulsion system mounted to the wing structure, a first power system configured to supply electric power to the propulsion system, and a second power system configured to supply electric power to the propulsion system. Each of the first and second power systems is distributed on the wing structure.

Description

TECHNICAL FIELD [1] The present invention relates to aircraft and to electric power systems for aircraft. BACKGROUND [2] Aircraft are required to meet high safety standards. For example, an aircraft might be required to sustain no more than one catastrophic failure for every billion flight-hours. These safety standards are especially difficult to meet in the case of electrically-powered aircraft, because the size and weight of electrical devices (e.g. batteries) mean that safety improvements often necessitate large compromises in the performance of the aircraft. [3] Any increase in the weight of the aircraft typically reduces the maximum payload, which in turn results in a reduction in the number of people or the weight of cargo that can be transported. [4] Battery-powered aircraft face specific challenges that are not applicable to battery-powered cars. In particular, an aircraft has vastly differing power consumption requirements at different stages of flight, with proportionally more power being required for take-off and landing, as opposed to the lower power requirements for cruising flight. [5] It is desired to address or ameliorate one or more disadvantages or limitations associated with the prior art, or to at least provide a useful alternative. [6] Any reference in this specification to prior art or matter which is said to be known is not to be taken as an acknowledgement or admission that such prior art or matter forms part of the common general knowledge in the field of invention to which this specification relates. SUMMARY [7] According to an example aspect, there is provided an aircraft comprising: a wing structure; a propulsion system mounted to the wing structure; a first power system configured to supply electric power to the propulsion system; and a second power system configured to supply electric power to the propulsion system. Each of the first and second power systems is distributed on the wing structure. [8] In some examples, each of the first and second power systems comprises: a power generation system configured to generate electric power; and a power distribution network electrically connecting the power generation system to the propulsion system. In some examples, the power generation system comprises two or more source devices configured to generate electrical energy. In some examples, the power generation system comprises a hydrogen fuel cell system. In some examples, the power generation system comprises two or more energy storage devices. In some examples, each of the energy storage devices comprises an electric battery. [9] In some examples, each of the first and second power systems is distributed between two complementary wings of the wing structure. In some examples, the wing structure comprises two forward wings and two rearward wings, and each of the first and second power systems is distributed on the two forward wings and on the two rearward wings. In some examples, the weight of the first power system balances the weight of the second power system.

[10] In some examples, the aircraft further comprises two or more housings mounted to the wing structure, wherein each housing stores at least one first device and one second device configured to perform the same function, the first device being part of the first power system, and the second device being part of the second power system. In some examples, each of the first device and the second device comprises an energy storage device.

[11] In some examples, the first device comprises a first electric battery and the second device comprises a second electric battery, each of the first and second electric batteries comprising an array of electrochemical cells in which each electrochemical cell is adjacent to at least one void in the array, and wherein the first electric battery and the second electric battery are stored in the housing in a stacked configuration.

[12] In some examples, each of the housings further stores a first propulsion unit controller of the first power system and a second propulsion unit controller of the second power system, the first and second propulsion unit controllers being configured to control the operation of a propulsion unit of the propulsion system.

[13] In some examples, a first housing of the housings further stores a first fuel tank, and a second housing of the housings further stores a second fuel tank, the first and second fuel tanks being connected to respective first and second fuel cell systems. In some examples, the first and second fuel tanks are configured to store a liquid fuel. In some examples, wherein the first and second fuel tanks are configured to store hydrogen. In some examples, the first housing further stores the first fuel cell system, and the second housing further stores the second fuel cell system. In some examples, the first and second housings are mounted to opposite ends of the wing structure.

[14] In some examples, the propulsion system comprises two or more propulsion units mounted to the wing structure at two or more mounting locations, and the housings are supported by the wing structure at the mounting locations of the propulsion units. In some examples, each of the housings is positioned in the wake of one of the propulsion units. In some examples, the aircraft further comprises two or more mounting assemblies connecting each of the propulsion units to the wing structure, wherein each of the mounting assemblies comprises one of the housings.

[15] In some examples, the aircraft is a vertical take-off and landing aircraft. BRIEF DESCRIPTION OF THE DRAWINGS

[16] Examples of the present invention are described next with reference to the accompanying drawings, in which:

[17] Figure 1 shows a perspective view of an example aircraft;

[18] Figure 2 shows a block diagram of an example redundant power system for an aircraft;

[19] Figure 3 shows a block diagram of example auxiliary systems for operating a hydrogen fuel cell system;

[20] Figure 4 shows an example spatial configuration of a redundant power system within the aircraft of Figure 1;

[21] Figure 5 shows another example spatial configuration of a redundant power system within the aircraft of Figure 1; and

[22] Figure 6 shows a perspective view of an example energy storage assembly. DETAILED DESCRIPTION

[23] Examples of the invention provide aircraft comprising two or more separate power systems configured to supply (including generate and / or deliver) electric power to the aircraft’s electrically powered propulsion system and, in some examples, to other electrical systems of the aircraft. Each power system duplicates one or more or all functions of the other power systems.

[24] The redundancy resulting from the provision of multiple power systems to power the same propulsion system of the aircraft reduces the risk of catastrophic failure of the aircraft in the event of failure of one or more components of any of the power systems.

[25] Moreover, each power system may be spatially distributed or divided on a wing structure of the aircraft, so that components of the power system are positioned or secured at two or more different locations on the wing structure. In some examples, each power system is distributed between complementary or symmetrically arranged wings of the wing structure, so that one or more components of the power system are positioned or secured at one or more locations on a left side or port wing, and one or more other components of the power system are positioned or secured at one or more locations on a right side or starboard wing.

[26] The physical separation of different components of each power system increases the aircraft’s tolerance to damage, for example, from a bird strike or thermal runaway of a battery of one of the power systems.

[27] In some examples, each power system is a powertrain (i.e. an electric powertrain) configured to generate and deliver electric power to the propulsion system of the aircraft. Each power system may comprise hybrid power generation systems configured to generate power through different electricity generation means, such as hydrogen storage and electrical storage systems, to benefit from the advantages of different energy-generation technologies and achieve an improved range, payload, and performance.

[28] An example aircraft 100, which is a box wing aircraft, is shown in Figure 1. Aircraft 100 comprises a central fuselage 110 and a box wing structure comprising two forward wings 120, 122, fixed to a front section of fuselage 110, and two rearward wings 130, 132, having a continuous wingspan, fixed to a rear section of fuselage 110. Forward wing 120 is connected to rearward wing 130 by a first wing connecting member 136 on a first side of aircraft 100, and, likewise, forward wing 122 is connected to rearward wing 132 by a second wing connecting member 138 on a second side of aircraft 100, opposite to the first side of aircraft 100.

[29] Aircraft 100 further comprises a propulsion system comprising eight electrically powered propulsion units 140, two of which are mounted to each of wings 120, 122, 130, and 132. Each propulsion unit 140 comprises an electric motor and a propeller or rotor. In other examples, propulsion units 140 may comprise any other device or engine configured to generate thrust. Moreover, in other examples, aircraft 100 may have any number of wings and propulsion units, including one or more.

[30] Aircraft 100 may be configured for vertical take-off and landing. Accordingly, the components of aircraft 100 may be structured and / or operate similarly to the components described in International Application No. PCT / AU2018 / 050962, filed on 6 September 2018, International Application No. PCT / AU2018 / 050963, filed on 6 September 2018, International Application No. PCT / AU2020 / 050261, filed on 19 March 2020, and International Application No. PCT / AU2021 / 051078, filed on 17 September 2021, which are incorporated by reference herein in their entirety.

[31] An example power system assembly or redundant power system 200 for aircraft 100 is shown in Figure 2. Redundant power system 200 comprises a first and a second power systems 210 and 220, each of which is configured to supply electric power to propulsion units 140 and, in some examples, to other electrical systems 202 of aircraft 100 performing nonpropulsion functions, such as avionics and ancillary functions.

[32] Power system 210 comprises a power generation system 230 configured to generate electric power, and a power distribution network electrically connecting power generation system 230 to propulsion units 140.

[33] Power generation system 230 comprises a plurality of source or energy-supply devices configured to generate or supply electrical energy. The source devices comprise eight energy storage devices 232 and one fuel cell system, or fuel cell, 234. The number of electric energy storage devices 232 equals the number of propulsion units 140 because, as described below, the energy storage devices 232 may be spatially distributed to the same locations as propulsion units 140, but, in other examples, power generation system 230 may comprise any number of energy storage devices 232, including one or more, and any number of fuel cells 234, including one or more. In other examples, power generation system 230 comprises a turbogenerator instead of fuel cell 234.

[34] Each energy storage device 232 comprises a battery pack. In other examples, each energy storage device 232 may comprise any device configured to store energy in any form and release electrical energy, including any type of electrochemical energy storage device (e.g. a battery), an electrostatic energy storage device (e.g. a capacitor or supercapacitor), a combination electrochemical and electrostatic storage device (e.g. a hybrid capacitor or supercapacitor), or a mechanical energy storage device (e.g. a flywheel or compressed gas tank).

[35] Fuel cell 234 comprises a hydrogen fuel cell. In other examples, fuel cell 234 may comprise any device configured to generate electrical energy from the reaction between a fuel and an oxidising agent.

[36] Every energy storage device 232 and fuel cell 234 is connected to an electric power distribution channel or high-voltage bus 250 of the power distribution network. In this way, the power generated by energy storage devices 232 and fuel cell 234 is aggregated or pooled before being distributed, so that each electrical device (e.g. any propulsion unit 140) connected to the power distribution network can draw power from any, including all, power sources of power generation system 230.

[37] Power system 210 further comprises eight propulsion unit controllers 252, each of which is electrically connected to power distribution channel 250 and to one of propulsion units 140 for controlling operational characteristics of the propulsion unit’s motor, such as start, stop, and speed. In other examples, there may be any number of propulsion unit controllers 252, including one or more, and any propulsion unit controller 252 may be configured to control operational characteristics of one or more propulsion units 140.

[38] Power system 210 further comprises first and second power converters 254 and 256, which are bi-directional DC-to-DC converters. In other examples, power converters 254 and 256 may any other types of power converters. Power converter 254 electrically connects fuel cell 234 to power distribution channel 250, and power converter 256 electrically connects non-propulsion electrical systems 202 to power distribution channel 250.

[39] Power system 220, like power system 210, also comprises a power generation system 240, comprising energy storage devices 242 and a fuel cell 244, a power distribution network comprising an electric power distribution channel 260, propulsion unit controllers 262, and power converters 264 and 266. The components of power system 220 are arranged like and perform the same functions as the components of power system 210, so that the foregoing description of power system 210 likewise applies to power system 220.

[40] When propulsion units 140 are motors, each motor may comprise two armatures, one being electrically connected to a propulsion unit controller 252, and the other being electrically connected to a propulsion unit controller 262.

[41] In some examples, fuel cells 234 and 244 are configured to supply a majority or all of the power that aircraft 100 needs to cruise (in flight), and energy storage devices 232 and 242 are configured to supply a majority or all of the power that aircraft 100 needs to take off and land. Thus, by reducing the amount of energy they need to supply, energy storage devices 232 and 242 can have a lower minimum energy capacity, for a fixed minimum power rating, than they would otherwise need if they had to supply most of the energy for cruising, in addition to take-off and landing.

[42] Redundant power system 200 may further comprise a controller (not shown) comprising one or more processing systems configured to control the operation of power systems 210 and 220. The controller may be configured to coordinate the operation of power systems 210 and 220 so that the power systems, in combination, concurrently supply the total power demanded by the propulsion system and electrical systems 202, without negatively interfering with each other. For example, power systems 210 and 220 may be required to supply equal powers or unequal powers with a predetermined ratio to the two armatures of any propulsion unit 140. At any given time, each of power systems 210 and 220 may supply a portion of the total power demanded by aircraft 100. The portions of total power supplied by power systems 210 and 220 may be equal or, when one power system has to compensate for a failure in the other power system, different.

[43] Each of power systems 210 and 220 further comprises auxiliary systems for operating fuel cells 234 and 244. Example auxiliary systems, shown in Figure 3, may include an air intake system, an air filtration system, fuel storage or a fuel tank, a pressure regulation system, a heat rejection system, a high-temperature and low-temperature coolant pumping system, a muffler and exhaust system, and a control system.

[44] An example spatial configuration of redundant power system 200 within aircraft 100 is shown in Figure 4, in which components of power systems 210 and 220 are distributed on the wing structure of aircraft 100.

[45] A first housing 150 is provided on each forward wing 120 and 122, and two first housings 150 are provided on each of rearward wings 130 and 132. Each first housing 150 stores or holds an energy storage device 232 of power system 210 and an energy storage device 242 of power system 220. A second housing 152 is provided in connecting member 136 and is therefore supported by both wings 120 and 130 on one side or end of the wing structure. Second housing 152 stores or holds an energy storage device 232, an energy storage device 242, fuel cell 234, and a fuel tank 236. A third housing 154 is provided in connecting member 138 and is therefore supported by both wings 122 and 132 on the opposite side or end of the wing structure. Third housing 154 stores or holds an energy storage device 232, an energy storage device 242, fuel cell 244, and a fuel tank 246. Housings 152 and 154 are larger than housings 150 to provide space for the fuel cell and the fuel tank.

[46] Fuel tanks 236 and 246, located in wing connecting members 136 and 138, are configured to store fuel for fuel cells 234 and 244, respectively. In some examples, fuel tanks 236 and 246 are configured to store a liquid fuel, such as liquid hydrogen. Tanks for storing liquid hydrogen are generally smaller and lighter than tanks for storing hydrogen gas. In other examples, fuel tanks 236 and 246 are configured to store a gas fuel, such as hydrogen gas, or any other type of fuel for fuel cells 234 and 244, such as cryo-compressed hydrogen. In other examples, such as when redundant power system 200 comprises a turbogenerator instead of a fuel cell, fuel tanks 236 and 246 may be configured to store kerosene or any other fuel for the turbogenerator. Tanks 236 and 246 may be configured to be refilled or removed and swapped.

[47] Housings 150, 152, and 154 form part of mounting assemblies or wing pods for mounting propulsion units 140 to the wing structure. In this way, housings 150, 152, and 154 are supported by the wing structure at the same locations as propulsion units 140. In addition, each of housings 150, 152, and 154 is positioned and oriented in the wake of one of propulsion units 140 (i.e. on a thrust axis, upstream of the propulsion unit relative to the direction of thrust) to reduce or minimise aerodynamic drag and blockage on aircraft 100. Each of housings 150, 152, and 154 may also carry or store a pair of propulsion unit controllers 252 and 262 configured to control the operation of the propulsion unit 140 supported by the mounting assembly containing the housing.

[48] The spatial configuration of the components of power systems 210 and 220 is symmetrical about a longitudinal axis (or a plane of symmetry) of aircraft 100, so that the weight of the components on one side of the longitudinal axis balances the weight of the components on the other side of the axis. In other examples, the spatial configuration of power systems 210 and 220 is a weight-balanced configuration without being symmetrical.

[49] The box wing structure of aircraft 100 therefore allows the formation of two concentric power loops by power systems 210 and 220, and, in some examples, further allows the formation of concentric data loops for sending and receiving data (e.g. control data and sensor data) to different parts of the aircraft. This redundancy, in combination with the redundancy obtained by employing multiple propulsion units 140, may enhance the safety of aircraft 100.

[50] Another example spatial configuration of power system 200 is shown in Figure 5, which differs from Figure 4 in that fuel cells 234 and 244 are located within fuselage 110, fore and aft of a passenger cabin.

[51] The spatial distribution of power storage devices 232 and 242 may provide several advantages. First, it may increase the signal-to-noise ratio on power distribution channels 250 and 260, improving the reliability of power systems 210 and 220. Second, it may reduce the distance electricity has to travel to reach propulsion units 140 on account of each of power storage devices 232 and 242 being placed near to a propulsion unit, reducing the length (and weight) of the required electrical conductors and the corresponding electrical losses, thus diminishing the effects of electrical noise and reducing the amount of filtering required; these factors may contribute to lowering the weight, cost, and complexity of the aircraft’s power systems. Third, it may counteract the increase in angular momentum caused by the location of fuel cells 234 and 244 and fuel tanks 236 and 246 at the extremities of the wing structure, reducing inertias in roll, pitch, and yaw, and improving the controllability of aircraft 100. Fourth, it may address issues related to aeroelasticity (i.e. natural structural frequencies corresponding with natural aerodynamic frequencies) caused by the increased weight load on the wing structure.

[52] An example energy storage assembly 300, suitable to be stored in any one of housings 150, 152, and 154, is shown in Figure 6.

[53] Energy storage assembly 300 comprises a first energy storage device 310, which may be one of energy storage devices 232, and a second energy storage device 320, which may be one of energy storage devices 242.

[54] Each of energy storage devices 310 and 320 is a battery pack, which comprises a plurality of electrochemical cells 312 and 322 arranged in an array or grid formation, such as a two-dimensional grid formation, with empty spaces or voids next to each cell 312 and 322 to assist cooling and to reduce the risk of total failure if one of the cells suffers a thermal runaway. In other examples, the electrochemical cells in the array are separated by a material configured to assist cooling or to reduce the risk of total failure.

[55] Energy storage devices 310 and 320 are adjacently disposed, or positioned next to each other in a pancake or stacked configuration, so that a major surface of energy storage device 310 faces or is aligned with, but spaced apart from, a major surface of energy storage device 320. Energy storage assembly 300 therefore provides two battery packs arranged in a way that facilitates cooling in a size or configuration that reduces or minimises aerodynamic drag.

[56] The power systems described herein may allow aircraft 100 to achieve a maximum total range of about 1,000 km at an average speed of about 300 km / h (about 160 knots). In some examples, aircraft 100 is suitable for passenger transportation, aeromedical evacuation, freight movement, and for providing support to emergency services. In some examples, aircraft 100 can carry up to five people (the pilot plus four passengers) or 500 kg of cargo.

[57] Optional embodiments may also be said to broadly include the parts, elements, steps and / or features referred to or indicated herein, individually or in any combination of two or more of the parts, elements, steps and / or features, and where specific integers are mentioned which have known equivalents in the art to which the invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

[58] Throughout this specification, unless the context requires otherwise, the word “comprise” and any variations thereof, such as “comprises” or “comprising”, are to be interpreted in a non-exhaustive sense.

Claims

1. An aircraft comprising: awing structure;a propulsion system mounted to the wing structure;a first power system configured to supply electric power to the propulsion system; and a second power system configured to supply electric power to the propulsion system; wherein each of the first and second power systems is distributed on the wing structure.

2. The aircraft of claim 1, wherein each of the first and second power systems comprises:a power generation system configured to generate electric power; anda power distribution network electrically connecting the power generation system to the propulsion system.

3. The aircraft of claim 2, wherein the power generation system comprises two or more source devices configured to generate electrical energy.

4. The aircraft of claim 2, wherein the power generation system comprises a hydrogen fuel cell system.

5. The aircraft of claim 2 or 4, wherein the power generation system comprises two or more energy storage devices.

6. The aircraft of claim 5, wherein each of the energy storage devices comprises an electric battery.

7. The aircraft of any one of claims 1 to 6, wherein each of the first and second power systems is distributed between two complementary wings of the wing structure.

8. The aircraft of claim 7, wherein the wing structure comprises two forward wings and two rearward wings, and wherein each of the first and second power systems is distributed on the two forward wings and on the two rearward wings.

9. The aircraft of claim 7 or 8, wherein the weight of the first power system balances the weight of the second power system.

10. The aircraft of any one of claims 1 to 9, further comprising two or more housings mounted to the wing structure, wherein each housing stores at least one first device and one second device configured to perform the same function, the first device being part of the first power system, and the second device being part of the second power system.

11. The aircraft of claim 10, wherein each of the first device and the second device comprises an energy storage device.

12. The aircraft of claim 10, wherein the first device comprises a first electric battery and the second device comprises a second electric battery, each of the first and second electric batteries comprising an array of electrochemical cells in which each electrochemical cell is adjacent to at least one void in the array, and wherein the first electric battery and the second electric battery are stored in the housing in a stacked configuration.

13. The aircraft of claim 11 or 12, wherein each of the housings further stores a first propulsion unit controller of the first power system and a second propulsion unit controller of the second power system, the first and second propulsion unit controllers being configured to control the operation of a propulsion unit of the propulsion system.

14. The aircraft of any one of claims 10 to 13, wherein a first housing of the housings further stores a first fuel tank, and wherein a second housing of the housings further stores a second fuel tank, the first and second fuel tanks being connected to respective first and second fuel cell systems.

15. The aircraft of claim 14, wherein the first and second fuel tanks are configured to store a liquid fuel.

16. The aircraft of claim 14 or 15, wherein the first and second fuel tanks are configured to store hydrogen.

17. The aircraft of any one of claims 14 to 16, wherein the first housing further stores the first fuel cell system, and wherein the second housing further stores the second fuel cell system.

18. The aircraft of any one of claims 14 to 17, wherein the first and second housings are mounted to opposite ends of the wing structure.

19. The aircraft of any one of claims 10 to 18, wherein the propulsion system comprises two or more propulsion units mounted to the wing structure at two or more mounting locations, and wherein the housings are supported by the wing structure at the mounting locations of the propulsion units.

20. The aircraft of claim 19, wherein each of the housings is positioned in the wake of one of the propulsion units.

21. The aircraft of claim 19 or 20, further comprising two or more mounting assemblies connecting each of the propulsion units to the wing structure, wherein each of the mounting assemblies comprises one of the housings.

22. The aircraft of any one of claims 1 to 21, wherein the aircraft is a vertical take-off and landing aircraft.

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