Propulsion system and associated method

Abstract

The present invention relates to a propulsion system for an electrically powered aircraft, the system comprising: a first cryogenic fuel propulsion system; and, a second cryogenic fuel propulsion system; the first cryogenic fuel propulsion system comprising: a first cryogenic fuel source; a first propulsion source arranged to generate propulsion from a cryogenic fuel; a first conduit for transporting cryogen from the first cryogenic fuel source; the second cryogenic fuel propulsion system comprising a second cryogenic fuel source; a second propulsion source arranged to generate propulsion from a cryogenic fuel; a second conduit for transporting cryogen from the second cryogenic fuel source; wherein the first conduit is arranged to transport cryogen from the first cryogenic fuel propulsion system to the second cryogenic fuel propulsion system; and wherein the second conduit is arranged to transport cryogen from the second cryogenic fuel propulsion system to the first cryogenic fuel propulsion system, the system further comprising: a third conduit, arranged to transport a liquid cryogen from the first cryogenic fuel propulsion system to the second cryogenic fuel propulsion system, wherein the third conduit is in thermal communication with the first conduit, a fourth conduit, arranged to transport a liquid cryogen from the second cryogenic fuel propulsion system to the first cryogenic fuel propulsion system, wherein the fourth conduit is in thermal communication with the second conduit.

Description

[0001] PROPULSION SYSTEM AND ASSOCIATED METHOD

[0002] Technical Field

[0003] The present invention is concerned with electrical propulsion systems and the configuration and arrangement of fuel provision for electrical propulsion systems within aircrafts.

[0004] There are several alternative power sources options (that are much more environmentally friendly than typical combustion of fossil fuels) but these are not widespread. Moreover, such systems are not at present used in commercial-sized aircraft (e.g. 48 or 96 passenger aircraft and / or CS-25 related aircraft). The system used herein is directed toward use of green energy options within commercial-sized aircraft.

[0005] Power systems in aircraft are designed to include fault mitigation. In particular, for developing technologies high levels of safety are to be shown prior to widespread use. As such, the system disclosed herein is directed towards improved safety of operation for fuel provision for electrical propulsion systems within aircrafts. The system herein is safe, robust and more environmentally-friendly than modern systems.

[0006] Electrical propulsion systems have many benefits over combustion propulsion systems, particularly in relation to chemical emissions and the like. It is widely seen that electrical propulsion systems may render transport as more viable in a long term perspective.

[0007] Summary of the Invention

[0008] Aspects of the invention are set out in the accompanying claims.

[0009] In accordance with some embodiments described herein, there is provided a propulsion system for an electrically powered aircraft, the system comprising: a first cryogenic fuel propulsion system; and, a second cryogenic fuel propulsion system; the first cryogenic fuel propulsion system comprising: a first cryogenic fuel source; a first propulsion source arranged to generate propulsion from a cryogenic fuel; a first conduit for transporting cryogen from the first cryogenic fuel source; the second cryogenic fuel propulsion system comprising a second cryogenic fuel source; a second propulsion source arranged to generate propulsion from a cryogenic fuel; a second conduit for transporting cryogen from the second cryogenic fuel source; wherein the first conduit is arranged to transport cryogen from the first cryogenic fuel propulsion system to the second cryogenic fuel propulsion system; and wherein the second conduit is arranged to transport cryogen from the second cryogenic fuel propulsion system to the first cryogenic fuel propulsion system, the system further comprising: a third conduit, arranged to transport a liquid cryogen from the first cryogenic fuel propulsion system to the second cryogenic fuel propulsion system, wherein the third conduit is in thermal communication with the first conduit, a fourth conduit, arranged to transport a liquid cryogen from the second cryogenic fuel propulsion system to the first cryogenic fuel propulsion system, wherein the fourth conduit is in thermal communication with the second conduit.

[0010] The present propulsion system provides excellent redundancy in response to a need for providing cryogenic fuel around the system. For example, this may occur in response to a fault or during a safety event or the like. In particular, the present system provides multiple pathways from one cryogenic fuel propulsion system to another. That the system has two cryogenic fuel propulsion systems provides some form of redundancy, however the present system takes this advantage further by introducing redundant pathways from one cryogenic fuel propulsion system to the other cryogenic fuel propulsion system.

[0011] In particular, there are conduits from each cryogenic fuel propulsion system to the other. In particular, two conduits are in thermal communication such that cryogen through one of the conduit pair cools the other conduit. In the above, the first and third conduits are arranged so that cryogenic fuel through one cools the other, and the same for the second and fourth conduits. In this way, transport of cryogen through certain conduits maintains other conduits in a suitable condition for further transportation of cryogenic fuel. In modern systems, redundant conduits are not used. Where conduits are used (we are not aware that they are) this thermal maintenance is not provided, and as such rapid delivery of cryogen via the redundancy conduits is interrupted due to boil off of cryogen cooling the conduits, or vapour lock in the conduits due to cryogen that has previously boiled off within the conduit. In contrast, the present system advantageously maintains the redundant conduits for use. As a result, the system is quicker to react in safety events and is able to conduct fuels more quickly to desired elements within the system.

[0012] The present system provides an improved response speed to providing solutions to faults or the like and has therefore a significantly increased safety over modern systems. The present system also may be used with environmentally friendly fuels (e.g. liquid hydrogen or the like).

[0013] In examples, the third conduit is arranged, in use, to transport a liquid cryogen during all stages of flight.

[0014] In the present system it is advantageous that the third conduit transport liquid cryogen at all stages of flight to provide a cooling effect to the first conduit (they are linked in thermal communication). This means that the first conduit, while not necessarily carrying cryogen, is maintained at a temperature that is suitable for transporting cryogen such that, if the first conduit is to be used in transport of cryogen, the first conduit does not need to be cooled before effectively conducting cryogen.

[0015] This removes the likelihood that the first portion of cryogen provided to the first conduit is boiled off in the process of cooling the conduit. In turn, this improves the response time of the successful delivery of cryogen through the first conduit (as cryogen delivered to the first cryogen is transported to the desired location without a boiling off period). The system used herein is therefore highly responsive in moments of need for cryogen. The system used herein is also improved in terms of safety as there is a reduced chance for thermal shock of the first conduit and overproduction of gaseous cryogen (from the boiling off process discussed above).

[0016] In examples, the fourth conduit is arranged, in use, to transport a liquid cryogen during all stages of flight.

[0017] As per the above, in providing liquid cryogen through the fourth conduit throughout flight, the second conduit is maintained at a temperature suitable for conducting liquid cryogen. Therefore, the advantages as explained for the third and first conduits are carried over to the fourth and second.

[0018] The system disclosed herein has excellent redundancy in terms of accounting for fuel faults as the one cryogenic fuel propulsion system has, at all times, two conduits for providing fuel to the other cryogenic fuel propulsion system. Moreover, these conduits are either already active or available to become active immediately. As such, the response to faults for this system is excellent and highly reliable.

[0019] In examples, the first conduit is arranged, in use, to transport a liquid cryogen during predetermined stages of flight. In examples, the second conduit is arranged, in use, to transport a liquid cryogen during predetermined stages of flight.

[0020] The system is able to note predetermined stages of flight and provide liquid cryogen through the first and second conduits. This may be during fuel faults or during redistribution of weight or the like for additional thrust or stability or, in general, improved flight characteristics. Other predetermined stages of flight may be failure of a propulsor or any failure that leads to a need for transfer of fuel. This may include a liquid tank being faulty or the like.

[0021] These stages of flight may be detected by a controller arrangement or may be detected by a change in flight characteristics or the like. Flight characteristics may include operational thrust, flight speed, flight altitude or the like.

[0022] In examples, the first conduit, the second conduit, the third conduit and the fourth conduit are arranged within a vacuum.

[0023] The present system maintains conduits at low temperatures such that cryogens can be transported through the system if needed (for the first and second conduits). As such, use of vacuums maintains the low temperatures desirable in the present system for less energy / cryogen fuels. Vacuums therefore render the arrangement cheaper to maintain and more energy efficient.

[0024] In examples, the first conduit and the third conduit are arranged within the same vacuum.

[0025] It may be spatially advantageous for the first and third to be maintained in the same vacuum. As the first and third are in thermal communication with one another, surrounding these two conduits with a vacuum reduces the impact of parasitic thermal energy from the environment in warming up the first conduit. As such, the arrangement with the same vacuum tor the first and third conduit is spatially and, in terms of energy usage, advantageous.

[0026] In examples, the first conduit and the third conduit are connected via a thermally conductive element. By connecting the first conduit and the third conduit, the third conduit can thermally influence the first conduit by conduction, convection and radiation. As such, this provides an improved ease of thermal conduction from the cold third conduit to the first conduit. Of course, radiation applies when vacuums are provided between the first conduit and the third conduit, however an arrangement is envisaged wherein the first conduit and third conduit are arranged in a material and that material allows conduction, convection and radiation, with the larger structure being within a vacuum for additional prevention against incoming thermal energy.

[0027] In examples, the second conduit and the fourth conduit are arranged within the same vacuum. In examples, the second conduit and the fourth conduit are connected via a thermally conductive element.

[0028] The same advantages as explained above for the first conduit and third conduit apply for the second and fourth conduits.

[0029] In examples, the first conduit and the third conduit are contained within a fifth conduit, the fifth conduit arranged to carry a low temperature gas. In examples, the fifth conduit is arranged to carry gaseous helium.

[0030] This arrangement is further advantageous for maintenance of the first and third conduits at a low temperature. This further reduces the energy and resources required to maintain the first conduit in a low temperature state and therefore reduces the cost of maintenance of the overall system. The low temperature gas further protects the first and third conduits from thermal energy incident on the system from the external environment. The helium may in particular play the role of an efficient conductor of cold energy from the cold third conduit to the first conduit. Any other suitably good thermally conductive low temperature gases may be used.

[0031] In examples, the second conduit and the fourth conduit are contained within a sixth conduit, the sixth conduit arranged to carry a low temperature gas. In examples, the sixth conduit is arranged to carry gaseous helium.

[0032] The same advantages as explained above for the first conduit and third conduit apply for the second and fourth conduits. In examples, at least a portion of the first conduit is arranged within the third conduit. This arrangement further protects the first conduit from incident parasitic heat from the external environment and more easily maintains the first conduit at a cold temperature.

[0033] In examples, at least a portion of the second conduit is arranged within the fourth conduit. This arrangement further protects the second conduit from incident parasitic heat from the external environment and more easily maintains the second conduit at a cold temperature.

[0034] In examples, the system further comprises at least one of: a first valve arranged to control movement of a fluid through the first conduit; a second valve arranged to control movement of a fluid through the second conduit; a third valve arranged to control movement of a fluid through the third conduit; a first pump arranged to control movement of a fluid from the first cryogenic fuel source; and, a second pump arranged to control movement of a fluid from the second cryogenic fuel source.

[0035] In accordance with some embodiments described herein, there is provided an at least partially electrically powered aircraft comprising the propulsion system of any of the above embodiments and examples.

[0036] Such an aircraft may comprise fuel cells as well as e.g. a gas turbine power generator. Combined power propulsion may be advantageous for power redundancy. Similarly, combined power propulsion may provide advantageous thrust benefits considering differing requirements of thrust at different stages of flight.

[0037] The propulsion system disclosed herein is particularly advantageous within an aircraft, however the propulsion system may be used in any vehicle.

[0038] In accordance with some embodiments described herein, there is provided a method of power management system in an aircraft, the method comprising: i) provide a first conduit for carrying a cryogen from a first cryogenic fuel source at predetermined stages of flight; ii) provide a second conduit for carrying a cryogen from a first cryogenic fuel source at predetermined stages of flight; and, iii) provide a cryogen through a third conduit; iv) maintain at least one of the first conduit and second conduit at a predetermined temperature by virtue of the presence of the cryogen in the third conduit. With this use, the method provides a robust and proactive approach tor fault mitigation. I his method provides improvement over previous systems as per the above discussion particularly in light of the ability to respond quickly in fault mitigation. This therefore improves the overall safety of the system and the methods disclosed over modern versions.

[0039] Brief Description of the Drawings

[0040] One or more embodiments of the invention will now be described, by way of example only, and with reference to the following figures in which:

[0041] Figure 1 shows a schematic view of a propulsion system according to an example of the present disclosure;

[0042] Figure 2 shows a schematic view of a portion of a propulsion system according to an example of the present disclosure;

[0043] Figures 3a, 3b and 3c show schematic views of arrangements of conduits according to examples of the present disclosure; and,

[0044] Figure 4 shows a flow diagram of a method according to an example of the present disclosure.

[0045] Any reference to prior art documents in this specification is not to be considered an admission that such prior art is widely known or forms part of the common general knowledge in the field. As used in this specification, the words “comprises”, “comprising”, and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean “including, but not limited to”. The invention is further described with reference to the following examples. It will be appreciated that the invention as claimed is not intended to be limited in any way by these examples. It will also be recognised that the invention covers not only individual embodiments but also combination of the embodiments described herein.

[0046] The various embodiments described herein are presented only to assist in understanding and teaching the claimed features. These embodiments are provided as a representative sample of embodiments only, and are not exhaustive and / or exclusive. It is to be understood that advantages, embodiments, examples, functions, features, structures, and / or other aspects described herein are not to be considered limitations on the scope of the invention as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the spirit and scope of the claimed invention. Various embodiments of the invention may suitably comprise, consist of, or consist essentially of, appropriate combinations of the disclosed elements, components, features, parts, steps, means, etc, other than those specifically described herein. In addition, this disclosure may include other inventions not presently claimed, but which may be claimed in future. Detailed Description

[0047] An invention described herein relates to propulsion system for an electrical powered aircraft. A particular use for this invention may be in an aircraft with an electrically drivable motor or a drivable motor that is at least partially electrically driven. For example, a propulsion source in the arrangements discussed may be fully or partially electrically powered. Partially powered aircraft may use thrust provided in part by electrical means and in part by combustion means. The electrical and combustion aspects may be provided by one or by a few fuels.

[0048] Figure 1 shows a simple schematic view of a propulsion system 100. The propulsion system 100 may be for an electrically powered aircraft. The system 100 comprises a first cryogenic fuel propulsion system 110 and a second cryogenic fuel propulsion system 120.

[0049] The first cryogenic fuel propulsion system 110 comprises a first cryogenic fuel source 112. The cryogenic fuel source 112 may be tank holding liquid cryogen or the like. The liquid cryogen may be liquid hydrogen, liquid natural gas and / or liquid methane to name only a few.

[0050] The first cryogenic fuel propulsion system 110 comprises a first propulsion source 114 arranged to generate propulsion from a cryogenic fuel. The propulsion source 114 may be a converter of chemical energy to kinetic energy. The propulsion source 114 may be a fuel cell and propulsor arrangement that is capable of providing electrical energy from chemical energy for conversion into kinetic energy. The propulsion source 114 may be a gas turbine and propulsor arrangement that combusts chemical energy into kinetic energy.

[0051] The first cryogenic fuel propulsion system 110 comprises a first conduit 131 for transporting cryogen from the first cryogenic fuel source 112 and / or the first cryogenic fuel propulsion system 110. The conduit 131 is able to transport cryogen from the first cryogenic fuel propulsion system 110 to the second cryogenic fuel propulsion system 120.

[0052] The second cryogenic fuel propulsion system 120 comprises a second cryogenic fuel source 122 and a second propulsion source 124 arranged to generate propulsion from a cryogenic fuel. These may be similar to the fuel source 112 and propulsion source 114. These elements perform the same function at the least. In that, the fuel sources provide a source of fuel for conversion into propulsion by the propulsion sources.

[0053] That the system 100 has two cryogenic fuel propulsion systems provides good redundancy from a safety perspective. If one cryogenic fuel propulsion system fails, the other can be used. This system 100 goes further than that however and provides for cross linking of the two systems 110, 120 for a more intricate sharing of resources. This allows better use of the fuel from one system if the other requires additional fuel or if the first system can no longer use the fuel due to faults or the like.

[0054] The propulsion system 100 further comprises a third conduit 133 and a fourth conduit 134. The third conduit 133 is arranged to transport a liquid cryogen from the first cryogenic fuel propulsion system 110 to the second cryogenic fuel propulsion system 120, wherein the third conduit 133 is in thermal communication with the first conduit 131. As shown, the third conduit 133 is physically close to the first conduit 131. By physically close, it is intended that there is reasonable thermal transfer between the two conduits. Reasonable in this sense relates to the function provided, that of maintenance of low temperature for the first conduit from the cryogen being transported in the third conduit. This allows for the cryogen being provided through the third conduit 133 to be cooling on the first conduit 131.

[0055] The fourth conduit 134 is arranged to transport a liquid cryogen from the second cryogenic fuel propulsion system 120 to the first cryogenic fuel propulsion system 110, wherein the fourth conduit 134 is in thermal communication with the second conduit 132. As shown, the fourth conduit 134 is physically close to the second conduit 132. This allows for the cryogen being provided through the fourth conduit 134 to be cooling on the second conduit 132.

[0056] In use, the system 100 provides a cryogen through the third 133 and fourth 134 conduits continuously. This allows these conduits to be maintained in a low temperature state suitable for transporting cryogen. The location of these proximally to the other conduits, (specifically the first and second conduits), maintains these other conduits - that are not used continuously - in a low temperature suitable for handling cryogens.

[0057] In aircraft, there are a number of parasitic thermal heat sources. These negatively impact elements that are preferentially maintained in a cold temperature. Therefore the present system provides both low temperature maintenance and a high level of redundancy by the arrangement provided.

[0058] The third conduit may carry cryogen from the first cryogenic fuel propulsion system 110 to anywhere in the second cryogenic fuel propulsion system 120 as is deemed useful. This may be into the tank 122 of the second cryogenic fuel propulsion system 120. This allows the cryogen to be redistributed from tank to tank where this may be beneficial for weight reasons. This may also be robust against a tank fault in the first cryogenic fuel propulsion system 110. If the tank has an issue that would lose the fuel therein, the fuel can be preferentially moved and stored in the tank 122 of the second cryogenic fuel propulsion system 120. In this way, there is not a great loss of fuel when one of the e.g. storage tanks for cryogenic fuel experiences a fault.

[0059] The same applies to the fourth conduit 134.

[0060] While the first 131 and second 132 conduits are not always transporting cryogen, they are maintained at a temperature where if a cryogen is needed to be transported, the conduits do not require initial cooling to receive cryogen. As such, when transport of cryogen is desired (e.g. during a fault), this can be provided immediately without need to initially cool the conduit. As such, the present system 100 has excellent response time to a desire to transport cryogen via conduits 131 , 132.

[0061] The first and second conduits may be larger than the third and fourth conduits, such that a small amount of cryogen can be used (in the third and fourth conduits) to maintain the main transportation links as cold. Then, in response to a desire to move cryogen, a large amount can be transported via the first and / or second conduits.

[0062] In this way, and in other words, there are live and redundant conduits provided. The first and second are controllably active or not active, while the third and fourth are always on and with a low level amount of cryogen passing through them. The live (third and fourth) conduits can transport very small cryogen loads as there is only sufficient required to balance the heat loads incident on the cross feed pipes. This is likely a small fraction of the total cryogenic heat considerations.

[0063] As noted above, cryogen may be provided through the first and second conduits at predetermined stages of flight, such as during fault mitigation or during weight redistribution. Other examples include where there has been a failure in one of the cryogenic fuel propulsion systems. When a full propulsion systems fails, there is a need to move cryogenic fuel into the other system for propulsion. Where a failure is partial, there may be a redistribution of fuel and operation of the propulsion sources that accounts for the partial failure. For example, whereas while in normal operation both cryogenic fuel propulsion systems provide 50% propulsion of the total propulsion, in partial failure the partially-failed system may provide 40% while the fully operational system may provide 60% propulsion or the like. Referring now to Figure 2, there is shown a portion of a propulsion system 200 according to an example of the present disclosure. The portion does not show the whole of the second cryogenic fuel propulsion system (as shown in Figure 1).

[0064] The portion of the system 200 shows a first cryogenic fuel source 212, a first conduit 231 , a second conduit 232, a third conduit 233 in thermal communication with the first conduit 231 , a fourth conduit 234 in thermal communication with the second conduit 232, a cryogenic fuel 225 that has been provided to the first cryogenic fuel source 212 from the second cryogenic fuel source (not shown). This in use is illustrating an example of when fuel may be transported from tank to tank. The fuel may be provided as a mist or a spray but is in liquid form and maintained at a cold temperature. The fuel may be provided via a spray bar of a diffuser at the top of the tank.

[0065] Figure 2 also shows a series of valves and pumps for assistance in controlling fluid flow within the system 200. The pumps and valves are shown as elements 252, 254, 256, 258. The role of the various pumps and valves are to assist in control over the movement of the fluid flowing in the system 200. For example, the “double arrowhead” valves are two way valves. One such two-wat valve is valve 254. A pump 252 is shown for generating a differential pressure and improving movement through the system 200 for fluids. A one way valve 258 is shown. The one way valve 258 allows provision of liquid from the first tank 212 to the second tank (not shown). The valve is one way as it is not expected that the conduit would receive liquid from the other tank along the conduits 231 , 233. Instead, the tank 212 receives liquid along conduits

[0066] 232, 234 (as shown).

[0067] In particular, the yellow conduit 234 shows the fourth conduit with cryogen present in the conduit 234. The green conduit 233 shows the third conduit with cryogen present in the conduit

[0068] 233. The first and second conduits are shown as red line conduits 231 , 232. These do not have conduit in them but can have where desired.

[0069] Portions of the first conduit 231 are close to the third conduit 233 and therefore are maintained in a cold state. Portions of the second conduit 232 are close to the fourth conduit 234 and therefore are maintained in a cold state.

[0070] While only a portion of the full system 200 is shown, the arrangement is the same as per Figure 1 and cross feeding of liquid cryogen is shown in both. Referring now to Figures 3a, 3b, and 3c, there are shown a series of conduit arrangements according to examples of the present disclosure. While the numerals for first and third conduits will be used, the examples apply equally to the second and fourth conduits.

[0071] Figure 3a shows a first conduit 331 and a third conduit 333. The example of Figure 3a also shows a linking 336. The linking 336 may be a thermally conductive member 336 to allow third conduit 333 to cool first conduit 331 . The element 336 may be a strap that may be a conduction link made from laminations, braids of high purity aluminium or the like.

[0072] Figure 3b shows a first conduit 331 and a third conduit 333 within an outer conduit 337. The outer conduit 337 may be referred to as a fifth conduit 337. The fifth conduit 337 may be arranged to carry a low temperature gas. Use of a low temperature gas allows cooling from the third conduit 333 to the first conduit 331 via convection as a well as radiation. This therefore improves the cooling from the third conduit 333 to the first conduit 331. The fifth conduit 337 may be arranged to carry gaseous helium or the like. This may form a closed system of helium as helium is a very good thermal conductor for efficient transfer of heat between the conduits.

[0073] Figure 3c shows a first conduit 331 and a third conduit 333. In Figure 3c, the first conduit 331 is located outside and around the third conduit 333. In this way, the first conduit 331 is cooled from the centre and in this way very little cooling is lost to the environment without cooling the first conduit 331. In practice, some portion or all of the third conduit 333 may be within the first or vice versa.

[0074] In each of these examples, the conduits may be surrounded (not shown) by a vacuum or the like. This improves the prevention of external warming thermal energy from impinging on the conduits which are being maintained in a low temperature.

[0075] In the proposed system, there is a maintenance of low temperature of a conduit that is used when needed. The calculation of the time when this is needed may be performed via a controller arrangement and sensors or the like. This controller may ascertain that a change in performance or output has occurred and provide signals to fuel sources to transport cryogen through the relevant conduit or conduits. This may be via a series of valves or pumps or the like to generate sufficient differential pressure.

[0076] The proposed system may be located within an aircraft as noted above, however may be effective with any vehicle. The present system may be highly advantageous in aircraft where redundancy, weight and size of system are of high importance. Referring now to Figure 4, a method 400 according to an example of the present disclosure is shown as a flow diagram. The method 400 has four steps 405, 410, 415, 420.

[0077] In a first step 405, a first conduit is provided for carrying a cryogen from a first cryogenic fuel source at predetermined stages of flight. As noted above, this may be during fault stages or during weight distribution or the like.

[0078] In a second step 410, a second conduit is provided for carrying a cryogen from a second cryogenic fuel source at predetermined stages of flight. As noted above, this may be during fault stages or during weight distribution or the like.

[0079] These two steps together provide a great level of redundancy for the vehicle. This is useful in many vehicles but is particularly advantageous in aircraft.

[0080] In a third step 415, a cryogen is provided through a third conduit. This may be provided throughout the process of a flight. This may be used to maintain temperatures for other conduits in the overall system.

[0081] In a fourth step 420, at least one of the first conduit and second conduit is maintained at a predetermined temperature by virtue of the presence of the cryogen in the third conduit. In this way, the first conduit and / or second conduit are ready to receive cryogen in a moment of requirement. In this method therefore there is high redundancy and high responsiveness to a fault or the like where cryogen is advantageously moved throughout a propulsion system.

[0082] In the above, the cryogenic sources may be tanks containing liquid cryogen or the like. These may be double walled fuel tanks with outer vacuum enclosures and inner hydrogen vessels in liquid fill and feed lines. These may have gas vent lines. These may have burst disks provided for vacuum space protection or the like.

[0083] In the above, there may be pressure relief valves as well as flow control valves. These may have specific conduits (not discussed above) to allow for release or redistribution of gaseous cryogen or the like.

Claims

AMENDED CLAIMS received by the International Bureau on 27 March 2025 (27.03.2025)1 . A propulsion system for an electrically powered aircraft, the system comprising: a first cryogenic fuel propulsion system; and, a second cryogenic fuel propulsion system; the first cryogenic fuel propulsion system comprising: a first cryogenic fuel source; a first propulsion source arranged to generate propulsion from a cryogenic fuel; a first conduit for transporting cryogen from the first cryogenic fuel source; the second cryogenic fuel propulsion system comprising: a second cryogenic fuel source; a second propulsion source arranged to generate propulsion from a cryogenic fuel; a second conduit for transporting cryogen from the second cryogenic fuel source; wherein the first conduit is arranged to transport cryogen from the first cryogenic fuel propulsion system to the second cryogenic fuel propulsion system; and wherein the second conduit is arranged to transport cryogen from the second cryogenic fuel propulsion system to the first cryogenic fuel propulsion system, the system further comprising: a third conduit, arranged to transport a liquid cryogen from the first cryogenic fuel propulsion system to the second cryogenic fuel propulsion system, wherein the third conduit is in thermal communication with the first conduit, a fourth conduit, arranged to transport a liquid cryogen from the second cryogenic fuel propulsion system to the first cryogenic fuel propulsion system, wherein the fourth conduit is in thermal communication with the second conduit.

2. A propulsion system according to claim 1 , wherein the third conduit is arranged, in use, to transport a liquid cryogen during all stages of flight.

3. A propulsion system according to claim 1 or 2, wherein the fourth conduit is arranged, in use, to transport a liquid cryogen during all stages of flight.

4. A propulsion system according to any preceding claim, wherein the first conduit is arranged, in use, to transport a liquid cryogen during predetermined stages of flight.

5. A propulsion system according to any preceding claim, wherein the second conduit is arranged, in use, to transport a liquid cryogen during predetermined stages of flight.

6. A propulsion system according to any preceding claim, wherein the first conduit, the second conduit, the third conduit and the fourth conduit are arranged within a vacuum.

7. A propulsion system according to any preceding claim, wherein the first conduit and the third conduit are arranged within the same vacuum.

8. A propulsion system according to claim 7, wherein the first conduit and the third conduit are connected via a thermally conductive element.

9. A propulsion system according to any preceding claim, wherein the second conduit and the fourth conduit are arranged within the same vacuum.

10. A propulsion system according to claim 9, wherein the second conduit and the fourth conduit are connected via a thermally conductive element.

11. A propulsion system according to any preceding claim, wherein the first conduit and the third conduit are contained within a fifth conduit, the fifth conduit arranged to carry a low temperature gas.

12. A propulsion system according to claim 11 , wherein the fifth conduit is arranged to carry gaseous helium.

13. A propulsion system according to any preceding claim, wherein the second conduit and the fourth conduit are contained within a sixth conduit, the sixth conduit arranged to carry a low temperature gas.

14. A propulsion system according to claim 13, wherein the sixth conduit is arranged to carry gaseous helium.

15. A propulsion system according to any preceding claim, wherein at least a portion of the third conduit is arranged within the first conduit.

16. A propulsion system according to any preceding claim, wherein at least a portion of the fourth conduit is arranged within the second conduit.

17. A propulsion system according to any preceding claim, further comprising at least one of: a first valve arranged to control movement of a fluid through the first conduit; a second valve arranged to control movement of a fluid through the second conduit; a third valve arranged to control movement of a fluid through the third conduit; a first pump arranged to control movement of a fluid from the first cryogenic fuel source; and, a second pump arranged to control movement of a fluid from the second cryogenic fuel source.

18. An at least partially electrically powered aircraft comprising the propulsion system of any of claims 1-17.

19. A method of power management system in an aircraft, the method comprising: i) provide a first conduit for carrying a cryogen from a first cryogenic fuel source at predetermined stages of flight; ii) provide a second conduit for carrying a cryogen from a second cryogenic fuel source at predetermined stages of flight; and, iii) provide a cryogen through a third conduit; iv) maintain at least one of the first conduit and second conduit at a predetermined temperature by virtue of the presence of the cryogen in the third conduit, the third conduit being arranged in thermal communication with the first conduit and / or the second conduit.

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