Patent Publication Number: US-11643204-B2

Title: Unmanned aerial vehicle for low-pressure hydrogen transport

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional patent application 62/945,688, filed Dec. 9, 2019 titled “Unmanned Aerial Vehicle for Low-Pressure Hydrogen Transport,” the entirety of the disclosure of which is hereby incorporated by this reference. 
    
    
     TECHNICAL FIELD 
     Aspects of this document relate generally to an unmanned aerial vehicle for low-pressure hydrogen transport. 
     BACKGROUND 
     Although technologies that make use of hydrogen, such as fuel cells, continue to advance, and the appetite for energy sources continues to grow, the use of hydrogen is not widespread. One reason for the slow adoption of hydrogen as a fuel source is economics. Conventional methods of transporting hydrogen come with constraints that significantly increase the cost, making hydrogen too expensive for many applications. 
     Hydrogen transmission and delivery is largely limited to relatively short distances in the petroleum and chemical industries. Longer distance transport is still not well-developed. Present research efforts in this area are primarily focused on improvements in conventional modes of transport: pipelines, and gas or liquid tube trailer transport by truck or ship. Efforts are also being made in the area of converting hydrogen to a liquid carrier chemical for transport using these methods or liquefied shipping, and then reconverting to hydrogen at the destination. 
     The common approach in traditional hydrogen transportation methods is to take hydrogen, the least dense of all gasses, and to substantially densify it so it can economically fit into existing transportation modes. Densification is achieved by compression (e.g. compression to 70-700 bar), by liquefaction (e.g. cooling below −253° C.), and/or by chemical conversion. 
     This often means a substantial investment in infrastructure is required. Not only does the transport require construction of a pipeline or the existence of a highway, the endpoints of a traditional hydrogen transport chain require specialized facilities at one or both endpoints, to compress, liquefy, and/or chemically convert the hydrogen before and/or after transport. This represents an additional cost above and beyond the investment required for conventional petroleum-based combustible fuel, or other alternatives that hydrogen competes against. These infrastructure requirements mean that establishing a new hydrogen supply chain can require a large investment in time and resources. 
     SUMMARY 
     According to one aspect, an unmanned aerial vehicle (UAV) for gas transport includes an airframe having a fuselage and a box wing. The fuselage is an airfoil enclosing a volume, wider than long, pointed upward while the UAV is on the ground, and pointed forward when the UAV is flying. The UAV also includes a gas reservoir having a plurality of tanks in fluid communication and enclosed within the fuselage, filling at least a majority of the volume. The gas reservoir is configured to receive and store a gas at a pressure no greater than 30 bar. The gas is hydrogen gas. The UAV also includes a propulsion system including a power generator and at least one engine, each of the at least one engines coupled to a prop that is driven by the at least one engine using electricity generated by the power generator from the gas stored in the gas reservoir. The power generator is in fluid communication with the gas reservoir and communicatively coupled to the at least one engine. Each prop has a rotational axis. The UAV further includes a control system communicatively coupled to the propulsion system and configured to operate the unmanned aerial vehicle to autonomously transport the hydrogen gas. The UAV is a vertical take-off and landing (VTOL) aircraft. The UAV has a footprint, while on the ground, that is no larger than three standard parking spaces. The box wing serves as the undercarriage of the UAV when the UAV is on the ground. All prop rotational axes are parallel and fixed with respect to the fuselage. 
     Particular embodiments may comprise one or more of the following features. The UAV may further include a gas interface for placing the gas reservoir in fluid communication with at least one of a user-end equipment and an on-site storage while the UAV is on the ground. The power generator may be communicatively coupled to an external electrical interface configured to provide electricity generated from the gas within the gas reservoir while the UAV is on the ground. The power generator may be a hydrogen-powered fuel cell. The gas reservoir may fill at least 85% of the volume of the fuselage. 
     According to another aspect of the disclosure, an unmanned aerial vehicle (UAV) for gas transport includes an airframe having a fuselage enclosing a volume, and a gas reservoir enclosed within the fuselage, filling at least a majority of the volume. The gas reservoir is configured to receive and store a gas at a pressure no greater than 100 bar. The UAV also includes a propulsion system having at least one engine, each of the at least one engine coupled to a prop that is driven by the at least one engine using energy derived from the gas stored in the gas reservoir. Each prop has a rotational axis. The UAV further includes a control system communicatively coupled to the propulsion system and configured to operate the unmanned aerial vehicle to autonomously transport the gas. 
     Particular embodiments may comprise one or more of the following features. The UAV may further include a gas interface for placing the gas reservoir in fluid communication with at least one of a user-end equipment and an on-site storage while the UAV is on the ground. The UAV may further include a power generator in fluid communication with the gas reservoir and communicatively coupled to the at least one engine, the power generator providing electricity generated from the gas to the at least one engine. The power generator may be communicatively coupled to an external electrical interface configured to provide electricity generated from the gas within the gas reservoir while the UAV is on the ground. The power generator may be a hydrogen-powered fuel cell. The pressure of the gas within the gas reservoir may be no greater than 30 bar. The gas reservoir may include a plurality of tanks in fluid communication. The gas reservoir may fill at least 85% of the volume of the fuselage. The gas reservoir may have the capacity to hold at least 100 kg of hydrogen gas. The UAV may be a vertical take-off and landing (VTOL) aircraft. The UAV may have a footprint while on the ground, and the footprint of the UAV may be no larger than three standard parking spaces. All prop rotational axes may be parallel and/or fixed with respect to the fuselage. The fuselage may be an airfoil. The fuselage may be pointed upward while the UAV is on the ground, and may be pointed forward when the UAV is flying. The fuselage may be wider than it is long. The airframe may further include a box wing, and the box wing may serve as the undercarriage of the UAV when the UAV is on the ground. 
     Aspects and applications of the disclosure presented here are described below in the drawings and detailed description. Unless specifically noted, it is intended that the words and phrases in the specification and the claims be given their plain, ordinary, and accustomed meaning to those of ordinary skill in the applicable arts. The inventors are fully aware that they can be their own lexicographers if desired. The inventors expressly elect, as their own lexicographers, to use only the plain and ordinary meaning of terms in the specification and claims unless they clearly state otherwise and then further, expressly set forth the “special” definition of that term and explain how it differs from the plain and ordinary meaning. Absent such clear statements of intent to apply a “special” definition, it is the inventors&#39; intent and desire that the simple, plain and ordinary meaning to the terms be applied to the interpretation of the specification and claims. 
     The inventors are also aware of the normal precepts of English grammar. Thus, if a noun, term, or phrase is intended to be further characterized, specified, or narrowed in some way, then such noun, term, or phrase will expressly include additional adjectives, descriptive terms, or other modifiers in accordance with the normal precepts of English grammar. Absent the use of such adjectives, descriptive terms, or modifiers, it is the intent that such nouns, terms, or phrases be given their plain, and ordinary English meaning to those skilled in the applicable arts as set forth above. 
     Further, the inventors are fully informed of the standards and application of the special provisions of 35 U.S.C. § 112(f). Thus, the use of the words “function,” “means” or “step” in the Detailed Description or Description of the Drawings or claims is not intended to somehow indicate a desire to invoke the special provisions of 35 U.S.C. § 112(f), to define the invention. To the contrary, if the provisions of 35 U.S.C. § 112(f) are sought to be invoked to define the inventions, the claims will specifically and expressly state the exact phrases “means for” or “step for”, and will also recite the word “function” (i.e., will state “means for performing the function of [insert function]”), without also reciting in such phrases any structure, material or act in support of the function. Thus, even when the claims recite a “means for performing the function of . . . ” or “step for performing the function of . . . ,” if the claims also recite any structure, material or acts in support of that means or step, or that perform the recited function, then it is the clear intention of the inventors not to invoke the provisions of 35 U.S.C. § 112(f). Moreover, even if the provisions of 35 U.S.C. § 112(f) are invoked to define the claimed aspects, it is intended that these aspects not be limited only to the specific structure, material or acts that are described in the preferred embodiments, but in addition, include any and all structures, materials or acts that perform the claimed function as described in alternative embodiments or forms of the disclosure, or that are well known present or later-developed, equivalent structures, material or acts for performing the claimed function. 
     The foregoing and other aspects, features, and advantages will be apparent to those artisans of ordinary skill in the art from the DESCRIPTION and DRAWINGS, and from the CLAIMS. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will hereinafter be described in conjunction with the appended drawings, where like designations denote like elements, and: 
         FIG.  1    is a perspective view of a H 2 UAV  100  in flight; 
         FIG.  2    is a perspective view of the H 2 UAV  100  of  FIG.  1   , on the ground; 
         FIG.  3    is a schematic view of a H 2 UAV  100 ; 
         FIG.  4    is a top view of the H 2 UAV  100  of  FIG.  1   , in flight; 
         FIG.  5    is a cross-sectional view of the H 2 UAV  100  of  FIG.  4    along A-A; 
         FIG.  6    is a perspective view of another embodiment of a H 2 UAV  100 ; 
         FIG.  7    is a cross-sectional view of the H 2 UAV  100  of  FIG.  6    along B-B; and 
         FIG.  8    is a bottom view of yet another embodiment of a H 2 UAV  100 . 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure, its aspects and implementations, are not limited to the specific material types, components, methods, or other examples disclosed herein. Many additional material types, components, methods, and procedures known in the art are contemplated for use with particular implementations from this disclosure. Accordingly, for example, although particular implementations are disclosed, such implementations and implementing components may comprise any components, models, types, materials, versions, quantities, and/or the like as is known in the art for such systems and implementing components, consistent with the intended operation. 
     The word “exemplary,” “example,” or various forms thereof are used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “exemplary” or as an “example” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Furthermore, examples are provided solely for purposes of clarity and understanding and are not meant to limit or restrict the disclosed subject matter or relevant portions of this disclosure in any manner. It is to be appreciated that a myriad of additional or alternate examples of varying scope could have been presented, but have been omitted for purposes of brevity. 
     While this disclosure includes a number of embodiments in many different forms, there is shown in the drawings and will herein be described in detail particular embodiments with the understanding that the present disclosure is to be considered as an exemplification of the principles of the disclosed methods and systems, and is not intended to limit the broad aspect of the disclosed concepts to the embodiments illustrated. 
     Although technologies that make use of hydrogen, such as fuel cells, continue to advance, and the appetite for energy sources continues to grow, the use of hydrogen is not widespread. One reason for the slow adoption of hydrogen as a fuel source is economics. Conventional methods of transporting hydrogen come with constraints that significantly increase the cost, making hydrogen too expensive for many applications. 
     Hydrogen transmission and delivery is largely limited to relatively short distances in the petroleum and chemical industries. Longer distance transport is still not well-developed. Present research efforts in this area are primarily focused on improvements in conventional modes of transport: pipelines, and gas or liquid tube trailer transport by truck or ship. Efforts are also being made in the area of converting hydrogen to a liquid carrier chemical for transport using these methods or liquefied shipping, and then reconverting to hydrogen at the destination. 
     The common approach in traditional hydrogen transportation methods is to take hydrogen, the least dense of all gasses, and to substantially densify it so it can economically fit into existing transportation modes. Densification is achieved by compression (e.g. compression to 70-700 bar), by liquefaction (e.g. cooling below −253° C.), and/or by chemical conversion. 
     This often means a substantial investment in infrastructure is required. Not only does the transport require construction of a pipeline or the existence of a highway, the endpoints of a traditional hydrogen transport chain require specialized facilities at one or both endpoints, to compress, liquefy, and/or chemically convert the hydrogen before and/or after transport. This represents an additional cost above and beyond the investment required for conventional petroleum-based combustible fuel, or other alternatives that hydrogen competes against. These infrastructure requirements mean that establishing a new hydrogen supply chain can require a large investment in time and resources. 
     Contemplated herein is an unmanned aerial vehicle for transporting comparatively low-pressure hydrogen. The unmanned aerial vehicle for hydrogen transport (hereinafter H 2 UAV) disclosed herein transports hydrogen by air, with much less densification, which stands in contrast to conventional methods of ground-based transport of highly densified hydrogen. The H 2 UAV facilitates the transportation of hydrogen at a lower cost than conventional methods, without facing the barriers that have held back hydrogen adoption in the past. For example, unlike conventional methods that are constrained to transportation endpoints dictated by the location of ports, depots, roads, and/or pipelines, a H 2 UAV can be redirected for use in virtually any location, including locations that are not realistically feasible with conventional methods. This flexibility also means the H 2 UAV does not require a costly and slow infrastructure to operate. Additionally, the H 2 UAV  100  can easily be redirected to a new destination, providing a flexibility impossible using conventional systems. If a sudden need arose (e.g. natural disaster has disrupted normal supply lines or infrastructure, etc.), the H 2 UAV  100  can be used to quickly provide needed resources, as will be discussed in greater detail, below. 
     Transporting hydrogen in a relatively low-pressure, gaseous state using a UAV is advantageous over the transport of hydrogen using manned aircraft while in states common to conventional transport (e.g. high pressure, liquefied, as a liquid carrier chemical, etc.) for a number of reasons. The unmanned, autonomous nature of the H 2 UAV reduces the cost of operation, and makes it easier to scale than a manned aircraft-based operation. Additionally, transport of hydrogen at low-pressure does not present the complications of transporting high pressure tanks at flight altitudes, nor the inefficiencies inherent to solutions that prevent dangerous weight shifts when transporting a liquid, particularly cryogenic liquid, in an aircraft. 
     The H 2 UAV substantially reduces the infrastructure and other capital costs related to hydrogen transport, as well as operational costs, via decreased labor requirements and high payload ratios. Unlike pipelines and road trailers, the H 2 UAV requires infrastructure only at the origin and destination. Depending on the chosen H 2 UAV size, even endpoint infrastructure can be modest or minimal. A H 2 UAV-based supply chain can be put into operation quickly compared to conventional systems, deploying as individual vehicles are built and put into service. Additionally, compared with chemically bound hydrogen for overseas shipping, H 2 UAV eliminates the need for two chemical conversions (at origin and destination), the associated infrastructure, and additional energy requirements. 
     The H 2 UAV&#39;s minimal infrastructure requirements can open up otherwise non-existing markets for hydrogen. For example, long distance or overseas transport, or transport from/to temporary or remote locations using conventional methods is not readily made economically efficient. The use of the H 2 UAV contemplated herein, on the other hand, is not constrained to coastal operation or existing roads, and essentially eliminates any right-of-way issues. According to various embodiments, the operation of the H 2 UAV is effectively unlimited, geographically. 
     The H 2 UAV is also advantageous over conventional transport methods because it has a high payload ratio. Depending on the operating pressure, the H 2 UAV payload fraction (i.e. the weight of the payload divided by the takeoff weight of the aircraft) can be between 25% and 50%. This is in stark contrast to compressed gas and liquefied gas trailers, which are expected to eventually achieve a 5% and 15% payload ratio, but are currently at roughly 2% and 12%, respectively. Some embodiments of the H 2 UAV may be implemented with much lower capital costs than trailers, per unit carrying capacity. Furthermore, unlike large capital/infrastructure projects, H 2 UAV can benefit from economies of mass production, where relatively small units are produced in large numbers, and also where units of different sizes are produced from the same set of basic parts. 
     It should be noted that while this disclosure is focused on the use of the H 2 UAV  100  for the transportation of hydrogen, those skilled in the art will recognize that it may be adapted for use in transporting other gases. Furthermore, while some embodiments of the H 2 UAV  100  are fueled by the very gas that is being transported, other embodiments may be adapted for use in transporting gases that are not viable fuels, either physically or economically. Alternative power sources will be discussed below. 
       FIGS.  1  and  2    are perspective views of a non-limiting example of a H 2 UAV  100 , in flight and on the ground, respectively. As shown, the H 2 UAV  100  comprises an airframe  102  that includes a fuselage  104  enclosing a volume, and at least one wing  106 . The non-limiting example shown in  FIG.  1    is propelled by a plurality of props  110 , driven by engines. The engines will be discussed further with respect to  FIG.  4   , below. 
     The shape of the fuselage  104  and overall architecture of the H 2 UAV  100  will vary from embodiment to embodiment, depending on the intended application. For example, an embodiment intended for use in transporting hydrogen to be delivered in an urban area may be a vertical take-off and landing (VTOL) aircraft  200 . The use of a VTOL aircraft  200  is advantageous in an urban environment, where a traditional, horizontal landing might not be possible at a location close to the final destination. Some embodiments intended for urban delivery may resemble a ground vehicle more than a traditional airplane, at least with respect to the footprint  202 , allowing the H 2 UAV  100  to go places originally intended for automobiles. 
     On the other hand, embodiments intended for long distance transportation, where having to land a distance from the ultimate destination does not introduce so great an expense to render the endeavor impractical, the H 2 UAV  100  may more closely resemble a traditional aircraft, which tends to be more efficient. For example, in some embodiments, a H 2 UAV  100  intended for overseas journeys may have a blended wing geometry. Some long distance embodiments may be VTOL  200  aircraft, while others may land horizontally on a runway or other long stretch of space. Those skilled in the art will recognize that a wide range of fuselage  104  geometries may be used, depending on the circumstances (e.g. stability in inclement weather for use in certain climates, etc.). 
     The shape of the fuselage  104  of the non-limiting example shown in  FIGS.  1  and  2    is geared towards an efficient use of space in a VTOL aircraft  200  intended for use in a cramped urban area originally designed for ground vehicles and the like, rather than traditional runways used by fixed wing aircraft. According to various embodiments, the fuselage  104  is an airfoil, meaning it has a cross-sectional shape of a wing or blade that results in the production of an aerodynamic force when moving through a fluid. As shown, in some embodiments, the fuselage  104  may comprise one or more control surfaces  112 . By maximizing the number of elements on the H 2 UAV  100  that act as lifting surfaces, the H 2 UAV  100  is able to carry meaningful payloads without requiring a great deal of space. 
     Most VTOL aircraft  200  tend to maintain (roughly) their orientation with respect to gravity, whether in flight or while on the ground. While this makes for a much more comfortable ride for a pilot or passengers, and minimizes the shift of solid payloads, it is a feature that is not necessary when the payload is a gas. According to various embodiments, the fuselage  104  is pointed upward while the H 2 UAV  100  is on the ground, and is pointed forward when the H 2 UAV  100  is flying. In the context of the present description and the claims that follow, the direction of the fuselage  104  is the direction of motion after the aircraft has taken off, and before it has begun landing. Put differently, the direction of the fuselage  104  may be thought of as roughly the same direction of the average vector pointing from the trailing edge to the leading edge of the wings  106  (e.g. tail to nose, etc.). 
     In some embodiments, including the non-limiting example shown in  FIGS.  1  and  2   , the H 2 UAV  100  may have a tail-sitting triplane geometry, having a fuselage  104  that is an airfoil, and employing a structure at the aft end of the aircraft on which the H 2 UAV  100  sits when on the ground. As shown, in some embodiments, the H 2 UAV  100  may comprise a box wing  108 , which serves as the undercarriage (i.e. the part of the aircraft that is underneath the main body when at rest, such as landing gear of an airplane or landing skids of a helicopter) of the H 2 UAV  100  when the H 2 UAV  100  is on the ground. This results in a H 2 UAV  100  that has a small footprint  202 , without sacrificing lifting power or payload capacity. As a specific example, in one embodiment, the H 2 UAV  100  may be sized and shaped such that it can deliver a 100 kg payload of hydrogen gas at 100 bar delivery pressure, within a 100 mile range moving at up to 100 kn airspeed, and then land vertically, taking up a footprint  202  no bigger than three standard parking spaces  204 . Such an embodiment would be well adapted for delivery of hydrogen to gas stations in urban areas, for use in hydrogen-powered vehicles, without requiring a drastic restructuring of the premises. The delivery could be made using the preexisting parking lot of the station, with less disruption than is caused when gasoline deliveries are made using tanker semitrucks. 
     Taking off, the H 2 UAV  100  would follow a trajectory closer to a rocket than a helicopter, being thrust upward by the props  110  and then gradually tilting towards horizontal to use that same thrust for forward motion and the resulting lifting force. Since the payload is a gas that is always evenly distributed, such a drastic reorientation is not problematic as it would be if the gas was being transported in a cryogenic or chemical liquid state. 
     Other embodiments of the H 2 UAV  100  may resemble more traditional VTOL aircraft  200 , with sources of thrust that are movable and/or directed in different directions (e.g. pusher props combined with lift props, etc.). This will be discussed further with respect to  FIGS.  6  and  7   , below. 
       FIG.  3    is a schematic view of a non-limiting example of a H 2 UAV  100 . As shown, the H 2 UAV  100  comprises a control system  300 , a propulsion system  302 , and a gas reservoir  310 . In some embodiments, the gas reservoir  310  is enclosed within the fuselage  104 , while in other embodiments, some or all of the gas reservoir  310  may be outside the fuselage  104  (e.g. attached to the wings  106 , etc.). 
     The H 2 UAV  100  may be implemented using various propulsion methods. For example, in some embodiments, including the non-limiting example shown in  FIGS.  1  and  2   , the H 2 UAV  100  may be propelled using props  110  driven by engines  304 . Those skilled in the art will recognize that the H 2 UAV  100  may be implemented in a number of different aircraft styles, using various propulsion methods known in the art, some of which may be advantageous over others depending on the needs and limits of particular use cases. 
     According to various embodiments, the H 2 UAV  100  may be powered by drawing fuel from the gas reservoir  310 . In some embodiments, the gas  312  may be used directly as fuel within the engines  304 . In other embodiments, including the non-limiting example depicted in  FIG.  3   , the gas  312  may be converted into energy (e.g. electricity) by a power generator  306 . The energy is then sent to the engines  304 . As shown, the power generator  306  is in fluid communication with the gas reservoir  310  and communicatively coupled to the engines  304  as well as the control system  300 . As a specific example, the hydrogen may be used in conjunction with one or more hydrogen fuel cells  308 . In still other embodiments, the hydrogen may be utilized in any other method known in the art. 
     In other embodiments, the H 2 UAV  100  may be powered by batteries, which may be charged from one or more sources including, but not limited to, charging from a ground station, on-board photovoltaics, one or more hydrogen or other type of fuel cells, thermoelectric generators, and the like. In still other embodiments, the H 2 UAV  100  may be combustion driven. Also, some embodiments may make use of multiple propulsion and or power systems. 
     The H 2 UAV  100  is unmanned, and comprises a control system  300  that is communicatively coupled to the propulsion system  302 . In some embodiments, the H 2 UAV  100  may piloted remotely by a human operator. In other embodiments, the H 2 UAV  100  may be configured to operate semi-autonomously, relying on the intervention of a human operator for piloting during particular events (e.g. takeoff, landing, equipment failure, inclement weather, etc.) or when in certain locations, as dictated by the limitations of automation technology and/or regulations regarding operation of unmanned aerial vehicles (e.g. flying over residential areas vs. operating over wilderness, etc.). In still other embodiments, the H 2 UAV  100  may operate entirely autonomously. As an option, in some embodiments, the acquisition and/or delivery of the hydrogen payload may also be performed autonomously, using appropriate sensors and a standardized or predictable gas interface at the source and destination. The control system  300  may also include other devices common to UAVs or other aircraft including, but not limited to, transponders, recorders, sensors (e.g. sensors to monitor the operation of the aircraft, sensors to monitor the gas reservoir  310  in transit and while transacting with an external gas source or receiver, etc.), satellite navigation receivers, telemetry equipment, and other avionics known in the art. 
     The H 2 UAV  100  comprises a gas reservoir  310 . In the context of the present description and the claims that follow, a gas reservoir  310  is a structure capable of storing a gas  312  during transit. In some embodiments, the gas reservoir  310  may be a single, enclosed void (e.g. a large tank, the sealed interior of the fuselage, etc.), while in other embodiments the gas reservoir  310  may comprise a plurality of vessels able to contain the gas  312  during transit, which may be in fluid communication with each other. As a specific example, some embodiments of H 2 UAV  100  employ a plurality of tanks that operate together as a gas reservoir  310 , as will be discussed with respect to  FIG.  5   , below. 
     In the context of the present description, low-pressure hydrogen refers to low pressure as compared to the pressures used in conventional transportation methods. For example, conventional gas tube trailers presently operate at roughly 250 bar, and are targeted to be up to 500 bar in the Department of Energy&#39;s FCTO Multi-Year Research, Development, and Demonstration Plan. According to some embodiments, the H 2 UAV  100  is configured to transport hydrogen at pressures an order of magnitude lower. In some embodiments, the transport pressure of a H 2 UAV  100  does not exceed 30 bar. It should be noted that the use of the term “low-pressure” to describe hydrogen in the present disclosure should not be interpreted to describe a pressure lower than atmospheric pressure. The hydrogen transported by the various embodiments of the H 2 UAV  100  is still a pressurized gas. 
     In some embodiments, the pressure  314  within the gas reservoir  310  may be 30 bar or lower. However, in use cases where overall volume and size of the H 2 UAV  100  are a concern (e.g. urban deliveries, etc.), the pressure  314  may be higher. For example, in one embodiment, the pressure  314  of the gas  312  may be 100 bar. In another embodiment, the pressure  314  may be as high as 120 bar. However, in these embodiments, the pressure  314  of the gas reservoir  310  is still much lower than the pressures employed in conventional systems, and are kept outside the regime where expensive (e.g. monetary, energy, time, etc.) processes are required to prepare the gas  312  for transit, and then prepare it for use. This is one of the numerous advantages the H 2 UAV  100  contemplated herein has over conventional gas transportation technologies. 
     As shown, the H 2 UAV  100  comprises at least one gas interface  316 . In the context of the present description and the claims that follow, a gas interface  316  is a mechanism through which gas  312  may be stored within and extracted from, the gas reservoir  310 . As shown, it is in fluid communication with the gas reservoir  310 . In some embodiments, the gas interface  316  may be as simple as a valve or a standardized attachment point where hoses can be coupled to connect the gas reservoir  310  to a source or a destination. In other embodiments, the gas interface  316  may be a complicated mechanism comprising elements that allow the H 2 UAV  100  to autonomously, or semi-autonomously, couple with a gas supply to receive and/or dispense gas  312  with little to no human interaction. The gas interface  316  may include articulated arms, cameras, LIDAR, machine vision processors, and the like. 
     According to various embodiments, the H 2 UAV  100  may be applied in a wide range of use cases. In many of the contemplated use cases, the H 2 UAV  100  may couple with on-site storage  322  through the gas interface  316  to either refuel the storage or receive a gas payload to be delivered to another location. In some embodiments, the gas interface  316  may directly refuel end-user equipment such as on-site equipment, power generators, vehicles, and the like, without having to pass the delivered gas  312  through an on-site storage  322 . In some embodiments, the same gas interface  316  may be used to couple with on-site storage  322  as well as end-user equipment  320 , while in other embodiments, the H 2 UAV  100  may comprise multiple gas interfaces  316  which may be configured for different uses or integrations. 
     In some embodiments, the H 2 UAV  100  may comprise an external electrical interface  318 . One of the many use cases contemplated is the use of the H 2 UAV  100  to provide needed hydrogen fuel in response to a natural disaster or other devastating event. The H 2 UAV  100  can rapidly respond to emergency needs. In some embodiments, the H 2 UAV  100  not only is able to deliver needed fuel gas to locations in need, it may operate as a temporary on-site hydrogen storage, creating a piece of needed infrastructure the moment it drops down from the sky. In some embodiments, the H 2 UAV  100  may also provide electricity generated using the on-board power generator  306  (e.g. hydrogen fuel cells, etc.). That electricity may be dispensed through the external electrical interface  318 . In some embodiments, the external electrical interface may be as simple as one or more plugs adapted for use with consumer level devices such as lights, refrigerators, medical equipment, and the like. In other embodiments, an external electrical interface  318  may be more robust, able to patch the H 2 UAV  100  into a pre-existing power infrastructure (e.g. the wiring of a hospital, a power grid, etc.) and provide electricity on a larger scale. 
     The H 2 UAV  100  contemplated herein presents a safer alternative to both hydrogen trailers and pipelines. The H 2 UAV  100  utilizes comparatively low-pressure tanks at ambient temperature, can mostly be operated at a distance from objects and people, and can employ time-tested safe practices and designs from the airline industry. 
     Many examples can be envisioned for using the H 2 UAV  100  for the transport of hydrogen from points of generation, which tend to be away from urban centers, to points of use, which tend to be where the people are. One example would be the transport of hydrogen, or hydrogen containing gas mixtures, from a point of generation to a processing plant, such as from a remote biomass gasification unit to a central collection/processing plant. 
     Not only can the H 2 UAV  100  operate efficiently in replacing conventional transport methods as presently used, the H 2 UAV  100  is able to be used for applications that are inefficient or even impossible for conventional methods. One such application would be to deliver hydrogen to remote operations (e.g. mining, construction, off-grid houses or communities, etc.) to be used as a fuel, replacing or augmenting fuels more typically used in these applications, such as diesel. Another application would be in military installations, particularly in areas in which the risks and costs associated with surface fuel transport are significant. In this application, H 2 UAV  100  can also offer risk mitigation by enabling the delivery of many relatively small hydrogen payloads, such that the loss of some of them can be tolerated. 
     On a larger and broader scale, applications might include the transportation of hydrogen from large production regions to large consumption regions. One such example would be transporting solar energy derived hydrogen from the solar rich regions of the U.S. southwest, to large population or industrial centers elsewhere in the U.S. or overseas (e.g. Japan or Europe). Another example would be the (relatively) local delivery of hydrogen from points of production or storage, to dispensing points, such as hydrogen fueling stations. 
     According to various embodiments, the H 2 UAV  100  enables hydrogen delivery under currently technically impossible or uneconomical scenarios, significantly expanding the markets where hydrogen may potentially be used. These scenarios include ad-hoc or remote origins and destinations, high-risk locations and routes, as well as in quantities that are either too small or too variable to be realistically served by current hydrogen transport technologies. In some embodiments, payloads ranging from a few kilograms to hundreds of metric tons are feasible, so H 2 UAVs  100  can be built to optimally match many different market needs. In comparison, trailer capacities are typically 1.1-5.3 metric tons. 
     H 2 UAV  100  can serve a wide range of roles—from local/distribution, to global/transmission. Origins, destinations, and routes can be adapted quickly to fit evolving market needs, strategic shifts, or unexpected events. The H 2 UAV  100  can make deliveries to remote areas more practical than conventional solutions. 
       FIG.  4    is a top view of the H 2 UAV  100  of  FIG.  1   , in flight. It should be noted that this could also be called a side view of the H 2 UAV  100  while on the ground, if the concepts of “top” and “up” are defined relative to gravity. According to various embodiments, the fuselage  104  may have a width  400  (e.g. “wing tip to wing tip” direction) that is greater than its length  402  (e.g. “tail to nose” direction). 
     As previously mentioned, in some embodiments the H 2 UAV  100  may be a VTOL aircraft  200 . In some of these embodiments, the engines  304  and props  110  (or whatever is providing thrust) may be able to move, changing the orientation of the thrust they provide with respect to the fuselage  104 . In other embodiments, they may remain fixed with respect to the fuselage  104 . In some embodiments, these fixed sources of thrust may be fixedly pointing in different directions, with respect to the fuselage  104 . For example, in some embodiments, the H 2 UAV  100  may comprise a plurality of props  110 , some providing lift, others pushing the H 2 UAV  100  forward. In other embodiments, all of the thrust sources may be pointed in essentially the same direction. See, for example, the non-limiting embodiments of  FIGS.  1 ,  2 , and  4   . Specifically, each prop  110  (or other thrust source) has a central rotational axis  404  about which the prop or other airfoil rotates. In some embodiments, all prop rotational axes  404  are parallel and fixed in orientation with respect to the fuselage, simplifying the construction and maintenance of the H 2 UAV  100  (e.g. fewer moving parts, etc.). 
       FIG.  5    is a cross-sectional view of the H 2 UAV  100  of  FIG.  4    taken along A-A. As shown, the fuselage  104  encloses a volume  502 . According to various embodiments, the H 2 UAV  100  has a fuselage  104  configured such that a large fraction (e.g. at least a majority) of the enclosed volume  502  is taken up by the gas reservoir  310 . In some embodiments, at least 85% of the volume  502  of the fuselage  104  is filled with the gas reservoir  310 . 
     In some embodiments, a large fraction of the volume  502  is filled with low-pressure hydrogen tanks  500 . In other embodiments, a large fraction of the aircraft fuselage  104  is sealed such that it may act as a vessel and contain the low-pressure hydrogen. For example, some embodiments may comprise a fuselage  104  designed to take advantage of the reduced design constraints inherent to transporting a low-pressure gas, whose weight always remains evenly distributed and which can take advantage of even the smallest, oddly shaped crevice of a containing volume. Using the fuselage  104  as a storage reservoir is advantageous, as it can be designed for greater storage volume and aerodynamic efficiency because it is not required to hold the shapes of gas tanks or cargo containers. In other embodiments, the airframe may be designed for use with low-pressure hydrogen tanks. In still other embodiments, the H 2 UAV  100  may comprise a commercially available, off-the-shelf airframe, fitted with storage tanks  500 , which may be located within the fuselage  104 , or outside of the H 2 UAV  100  (e.g. attached to the wings, etc.). 
       FIG.  6    is a perspective view of a non-limiting example of a H 2 UAV  600 , according to another embodiment. This non-limiting example of an H 2 UAV  600  is a VTOL aircraft  200  having a slightly more traditional design. As shown, the wings  106  may each comprise a wing hinge  602 , reducing the footprint  202  of the H 2 UAV  600  while on the ground. The wings  106  may be extended once the H 2 UAV  600  is in the air, providing stability and lift for forward flight. The lift may be provided by rotatable engines, or, in some embodiments, rotating wings. Those skilled in the art will recognize that other folded-wing plane designs may be adapted for use with the H 2 UAV  600  contemplated herein. 
       FIG.  7    is a cross-sectional view of the H 2 UAV  600  of  FIG.  6   , taken along B-B. As shown, this fuselage  104  does not have a conventional cross-section, which typically is ovoid. This allows the tanks  500  to make more efficient use of the volume  502  within the fuselage  104 . In some embodiments, the skin on the fuselage  104  is simply reducing drag, with the tanks  500 , which may be coupled to each other, providing the structural stability. 
       FIG.  8    is a bottom view of a non-limiting example of yet another embodiment of a H 2 UAV  800 . In some embodiments, the airframe  102  may be a simple, off-the-shelf UAV design, which may be adapted for use as a H 2 UAV  800 . As shown, a number of drop tanks  802  may be releasably coupled to the bottom of the H 2 UAV  800  on under-wing pylons (not shown). While not as efficient for use in low-pressure hydrogen gas transport, adapting conventional UAVs to operate as a H 2 UAV  800  contemplated herein is advantageous as it allows for the initiation of a supply line without the delay of manufacturing custom aircraft. Furthermore, conventional UAVs may be less expensive to create due to the economy of scale. This may ease the cost of the reduced efficiency in using such a design. This is another example of the potential low startup costs that will facilitate the adoption of hydrogen as a fuel source in more use cases. 
     Where the above examples, embodiments and implementations reference examples, it should be understood by those of ordinary skill in the art that other UAV and gas transportation devices and examples could be intermixed or substituted with those provided. In places where the description above refers to particular embodiments of a UAV for transporting low-pressure hydrogen, it should be readily apparent that a number of modifications may be made without departing from the spirit thereof and that these embodiments and implementations may be applied to other gas transportation technologies as well. Accordingly, the disclosed subject matter is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the disclosure and the knowledge of one of ordinary skill in the art.