Fluid tank for integration into the structure of an unmanned aircraft

Description

TECHNICAL AREA

[0001] The invention relates to a fluid tank for integration into a structure of an unmanned aircraft and to an unmanned aircraft with such a fluid tank. BACKGROUND OF THE INVENTION

[0002] Unmanned aerial vehicles (UAVs) can be used for a wide variety of tasks and can have suitable designs and sizes for these purposes. For example, it is known to perform surveillance tasks from high altitudes using aircraft with a large wingspan, a high aspect ratio, and a very slender fuselage. It is particularly advantageous if long flight durations can be achieved along with the altitude. These durations can be extended, among other things, by using solar cells as an energy source. It is known to convert solar energy into another form of energy when there is sufficient sunlight and to store this energy on board the aircraft. In darkness, the stored energy can then be used to propel the aircraft.

[0003] One possible approach is the so-called regenerative fuel cell system. In this system, water is split into hydrogen and oxygen through solar-powered electrolysis and stored in suitable tanks on board the aircraft. As the hydrogen is consumed, water is produced and stored on board. For this purpose, a fluid tank located near the aircraft's center of gravity is used, for example.

[0004] To perform electrolysis continuously, a constant flow of water must be supplied to the electrolyzer. However, a continuous outflow of water is also necessary in unexpected flight conditions, such as vertical gusts of wind.

[0005] GB 580 006 A shows a fuel tank system with an auxiliary tank inside a main tank, which enables a reliable fuel supply even in the event of strong changes in position or reversal of gravity.

[0006] US 2015 / 210162 A1 discloses a tank system with an inner and at least one outer chamber which, by means of controllable flow openings, influences the position of the fluid's center of gravity in order to prevent exceeding the vehicle's center of gravity limit.

[0007] US 1 364 770 A1 shows aircraft, particularly those with oil tanks that serve both as storage for hydrocarbon fluids and as a reservoir for lubricating oil in the engine crankcase.

[0008] FR 2 756 255 A1 shows a fuel tank with a suction opening and at least one filler neck outside the tank. A storage tank mounted inside the main tank is connected to the main tank, allowing liquid to transfer into the storage tank. The suction opening of the filler neck opens into the storage tank, the volume of which is dimensioned such that the suction opening remains continuously supplied with liquid even under negative or zero load factors or for a predetermined tilting duration.

[0009] FR 3 071 817 A1 shows a drone with at least one electric motor for propulsion and an electrical energy source in the form of a fuel cell.

[0010] This includes a tank for storing the fuel and at least one basic cell with two electrodes separated by an electrolyte, which can generate electrical energy electrochemically.

[0011] EP 3 524 526 A1 shows a system with a pressure vessel serving as a fuel tank inside the aircraft fuselage, extending over most of its length and with its center of gravity essentially coinciding with that of the fuselage. The tank can either bear a partial load of the fuselage or be decoupled from its loads. In some embodiments, the tank consists of a fiber-wound pressure vessel.

[0012] US 2013 / 105628 A1 shows an aircraft frame system with two side walls, a propulsion platform to accommodate the propulsion system and two structural struts that secure the side walls parallel to each other and support a camera mount. SUMMARY OF THE INVENTION

[0013] It is an object of the invention to propose a particularly advantageous fluid tank for integration into a structure of an unmanned aircraft, which has a desired storage capacity, especially for water, and at the same time allows a continuous release of water, even during abrupt movements of the aircraft in flight.

[0014] The problem is solved by a fluid tank having the features of independent claim 1. Advantageous embodiments and further developments can be found in the dependent claims and the following description.

[0015] A fluid tank for integration into the structure of an unmanned aerial vehicle is proposed, comprising a shell with a first axial wall, a second axial wall arranged oppositely, a top surface, a bottom surface, and an enclosed interior, at least one receiving chamber in the interior for storing fluid, and a collection chamber arranged at the bottom, which is in fluid communication with the at least one receiving chamber. The collection chamber has a bottom surface through which a drain extends, with a cover surface arranged above the bottom surface and covering at least a section of the collection chamber.

[0016] The outer shape of the fluid tank is defined by its shell. It is conceivable that the fluid tank has an elongated shape. This means that its extent in one spatial direction significantly exceeds its extent in the other two spatial directions. However, this can be determined by the desired shape of the structure of the unmanned aerial vehicle into which the fluid tank is to be integrated. The shell has two opposing axial walls, the first and second. These can also be referred to as the tank end caps or end caps, and each represents an axial boundary of the fluid tank. The interior enclosed by the shell is therefore located between the two axial walls.

[0017] The at least one receiving chamber serves to store the fluid. It is therefore dimensioned to accommodate the desired or required quantity of fluid. In the aforementioned case of using the fluid tank in conjunction with a renewable fuel cell system, the at least one receiving chamber could, for example, be designed so that its volume corresponds at least to the volume of water produced during a predetermined operating time of the fuel cell. This operating time could, for example, be in the range of 12 to 48 hours.

[0018] The collection chamber is located at the bottom of the fluid tank, allowing fluid to be drawn off via the drain in the collection chamber regardless of the fluid level in the tank. The drain extends through the base and into the collection chamber. It is conceivable that the drain extends straight through the base and terminates at an inward-facing edge of the base. Alternatively, the drain could extend a certain distance into the collection chamber, with an inlet cross-section located at a distance from the base and directed inwards.

[0019] The surface above the base serves to form a partially enclosed collection chamber. During gusts of wind that cause the aircraft to accelerate downwards along its z-axis, the surface largely prevents any upward, inertial movement of the fluid within the collection chamber. Consequently, regardless of the fluid level in the remaining volume of the interior, a nearly constant amount of fluid remains in the collection chamber and can be reliably removed through the drain. To ensure the continuous removal of fluid from the collection chamber, a constant flow of fluid from the at least one receiving chamber into the collection chamber is necessary. This is achieved through the fluid connection between the collection chamber and the at least one receiving chamber.The fluid connection should be dimensioned to allow for continuous flow. However, the flow cross-sections should remain as small as possible. Furthermore, it is preferable to locate the fluid connection near the bottom surface or the underside of the fluid tank, so that fluid escapes from the collection chamber during load changes caused by vertically directed gusts.

[0020] In summary, the discussed measures result in a fluid tank that integrates very well into the structure of an unmanned aerial vehicle and offers several advantages. Different load directions acting on the fluid tank and the fluid it contains do not lead to a substantial emptying of the collection chamber, thus ensuring that fluid can always be extracted.

[0021] It should also be noted that the fluid tank could be designed like a pressure tank. The first and second axial walls could, for example, have a convex, outward-facing bulge. A hollow cylindrical section could be located between the two axial walls. The fluid can be introduced into the fluid tank at various points and from different directions. When implemented as a pressure tank, the primary consideration is the pressure extraction of the fluid. For example, compressed air could be applied to the fluid tank, creating a specific pressure differential between the surrounding environment and the interior. The resulting outlet could then act as a pressure sink from which the fluid flows out. This significantly simplifies the extraction process and eliminates the need for a pump.This could be particularly useful if the aircraft already has a source of compressed air, for example in connection with an engine.

[0022] However, the fluid tank could only be pressurized for short periods. For other, and predominant, periods, the fluid tank could also be operated without pressure.

[0023] It should also be noted that, for the purposes of the invention, the term "fluid" refers in particular to a substance that, in its stored state within the fluid tank, is in a liquid state. Water or a water-containing mixture is particularly preferred as the fluid. However, it is not excluded that other substances may also be stored in this fluid tank.

[0024] According to the invention, both lateral receiving chambers each have a bottom that slopes slightly downwards vertically from the respective axial wall or in the direction of the collecting chamber.

[0025] In a preferred embodiment, at least one flow opening is arranged on the upper side of the collection chamber, allowing gas bubbles to escape towards the top of the fluid tank. The accumulation of gas bubbles in the collection chamber should be prevented as much as possible, since otherwise, in the event of unfavorable movement of the aircraft, the fluid in the collection chamber could move into the space occupied by the gas bubbles. This can be prevented by allowing any gas bubbles to escape from the collection chamber through flow openings. However, the flow openings also allow the fluid itself to flow through them. It is therefore preferred that the flow openings are dimensioned such that, during downward acceleration of the aircraft along the z-axis, the fluid flows from the collection chamber into the adjacent areas of the interior only with a very limited volume flow.The size of the flow opening must therefore also be adapted to the viscosity of the fluid.

[0026] Preferably, the collection chamber has at least one collection chamber wall extending from the underside of the fluid tank to the top surface, defining the collection chamber, and wherein the at least one collection chamber wall is at least partially separated from an outer collection chamber wall. This would allow for a further improved device for storing a small volume of fluid that can be easily extracted. For example, the collection chamber wall could be located at a relatively small distance from the outer collection chamber wall, thus enabling the inflow or outflow of fluid or air, while the residual volume in the collection chamber is retained by the top surface and the collection chamber wall.The flow opening could then be located, for example, at an edge of the deck surface, at a transition between the collection chamber wall and the deck surface, on the top side of the deck surface or on an upper edge of the collection chamber wall.

[0027] In an advantageous embodiment, the collecting chamber wall encloses a collecting chamber gap with the outer collecting chamber wall. The gap is to be understood as an intermediate space that preferably has a constant or largely constant extent in one direction. Depending on the shape of the collecting chamber, the collecting chamber gap could extend outwards from a center point of the collecting chamber at least along one spatial direction. In some embodiments, the collecting chamber gap could also take the form of two separate gaps arranged axially or laterally in front of, behind, or beside the collecting chamber. A combination of lateral and axial gaps would also be conceivable. The collecting chamber gap serves to establish the fluid connection between the collecting chamber and the at least one receiving chamber.

[0028] It is advantageous if the collection chamber is in fluid communication with the at least one receiving chamber via an opening located on its underside. For fluid to flow into the collection chamber, an open flow cross-section is necessary at least at one point, preferably located in the region of the bottom surface. This prevents the fluid from escaping the collection chamber through such flow cross-sections during negative acceleration in the Z-direction of the aircraft. The opening could, for example, be implemented as a gap beneath a collection chamber wall. Alternatively, it might be suitable to provide a collection chamber wall with openings located on its underside, extending radially or transversely through the wall.

[0029] Preferably, the top surface has a radially central area that is further away from the bottom surface than radially outer areas. Gas bubbles could then be directed to radially inner areas for escape. It is advantageous to provide corresponding flow openings in these areas. The radially central area could, for example, have a convex bulge. The sufficiently large distance allows gas bubbles to accumulate in this area. The placement of at least one flow opening in the top surface allows the gas bubbles to flow into the fluid tank.

[0030] The surface could preferably have a conical or ramped shape. The shape can be designed with a more or less steep slope to improve the guidance of gas bubbles to the intended flow openings. However, a relatively flat shape might be advantageous to reduce the pressure exerted by the fluid on the at least one flow opening during negative accelerations.

[0031] It is advantageous to position the collection chamber centrally along a longitudinal axis between the first and second axial walls. The entire fluid tank could therefore be optimized to be located in a center-of-gravity region or symmetrically to an axis of the aircraft encompassing the center of gravity. The fluid is always drawn from near the center of gravity. The longitudinal axis refers to a principal axis of extension of the fluid tank.

[0032] Preferably, a first receiving chamber connects axially to the first axial wall, with a second receiving chamber connecting axially to the second axial wall. Using two receiving chambers allows for a somewhat better distribution of the fluid mass within the interior. Depending on the type of aircraft and the required interior size, it may be advantageous to use one or more additional receiving chambers.

[0033] Preferably, the collection chamber is arranged symmetrically between the axial walls. If the fluid tank has two outer receiving chambers and one central receiving chamber, the collection chamber can be located axially between the two outer receiving chambers and below the central receiving chamber.

[0034] The at least one receiving chamber can have a bottom that slopes down towards the underside in a ramp-like manner. This ramped shape allows the fluid in the receiving chamber to be guided to the collecting chamber by gravity. The ramped shape can be symmetrical to the collecting chamber and extend laterally across the bottom of the fluid tank towards the collecting chamber.

[0035] The fluid tank according to the invention further comprises at least one baffle plate extending transversely to an axial direction of the fluid tank. The baffle plate can, in particular, dampen sloshing of the fluid. It is conceivable that a baffle plate has several cutouts that allow the fluid to pass through. However, it would also be conceivable to completely close the baffles except for one side facing the collection chamber, thus enabling a division of the interior into two or more chambers.

[0036] The at least one baffle plate can be attached, in particular vertically above or to the side of the collection chamber, and at the same time act as a stiffening of the shell.

[0037] Preferably, the fluid tank is designed as a water tank. This means that the surfaces of the fluid tank facing the interior are waterproof and preferably corrosion-resistant. The material selection for the fluid tank is suitable for storing water or fluids with similar properties, for example, mixtures containing water. The flow opening for the gas bubbles to escape should be dimensioned as small as possible to minimize the escape of water from the collection chamber into the rest of the interior, without preventing the escape of gas bubbles. It may be advantageous to design the at least one flow opening with an opening width of a few millimeters. All other openings, flow cross-sections, and the like should be adapted to the viscosity of the water to ensure that the continuous flow of water between different areas of the interior is not prevented or excessively restricted.

[0038] The invention further relates to an unmanned aerial vehicle (UAV) comprising at least one wing and at least one fluid tank, as previously described and integrated into the UAV. For an UAV intended particularly for high altitudes, at least one elongated fuselage could be provided. However, flying wing aircraft or aircraft with multiple fuselages are also conceivable. In particular, for the previously described embodiment of a solar-powered UAV for extended stays at higher altitudes, a streamlined design with an elongated fuselage could be advantageous.

[0039] The fluid tank is specifically designed to bear loads. To minimize the weight of the aircraft, the fluid tank according to the invention could therefore be designed to bear loads. The arrangement of the individual chambers formed within the interior, as well as the walls between them, can be optimized to assume load-bearing functions. For example, a baffle plate could be used to stiffen the fluid tank in one direction. By using several baffles arranged parallel and / or perpendicular to each other, a kind of three-dimensional truss structure could be achieved, giving the fluid tank particularly high stiffness and strength. This would allow the area of ​​the aircraft housing the fluid tank to be formed by the fluid tank itself or to be limited to a non-load-bearing skin or the like.

[0040] Finally, the aircraft could have at least one regenerative fuel cell connected to the fluid tank. The water produced during the operation of the regenerative fuel cell could then be fed into the interior of the fluid tank. The aircraft preferably also includes an electrolyzer that can be connected to the fluid outlet to extract water from the fluid tank and split it into hydrogen and oxygen via electrolysis. At least the hydrogen could then be stored to power the fuel cell. BRIEF DESCRIPTION OF THE FIGURES

[0041] Further features, advantages and possible applications of the present invention will become apparent from the following description of the exemplary embodiments and the figures.

[0042] The figures continue to use the same reference symbols for identical or similar objects. Fig. 1a und 1b show a fluid tank according to the invention in several different views. Fig. 2a und 2b show a detail of a collection chamber of the fluid tank. Fig. 3 shows a detail of the collection chamber in a cross-sectional view. Fig. 4 schematically depicts an unmanned aerial vehicle. DETAILED PRESENTATION OF EXEMPLARY EXECUTION FORMS

[0043] Fig. 1a Figure 1 shows a fluid tank 2 integrated into a structure 4 of an unmanned aerial vehicle. The structure 4 is represented by an exemplary skin, fuselage skin, or spar skin. The invention is not limited to this. Rather, it may be advantageous to integrate the fluid tank, in particular, into a streamlined structure of an aircraft.

[0044] The fluid tank 2 has a shell 6 with a first axial wall 8, a second axial wall 10 arranged oppositely, a top surface 12, a bottom surface 14, and an enclosed interior space 16. The interior space 16 has a first lateral receiving chamber 18, which is axially connected to the first axial wall 8. A second lateral receiving chamber 20 is connected to the second axial wall 10. Both receiving chambers 18 and 20 are designed to store fluid in the interior space 16. They therefore form individual tank segments. While the structure 4 could be made of a carbon fiber reinforced plastic, the shell 6 could be made of an aluminum alloy.

[0045] Centrally located is a central receiving chamber 22, which is in fluid communication with both lateral receiving chambers 18 and 20. The central receiving chamber 22 has a floor surface 24 with a collection chamber 28 into which a drain 26 extends.

[0046] Both lateral receiving chambers 18 and 20 each have a bottom 32 that slopes slightly downwards in the vertical (z-direction) from the respective axial wall 8 or 10 towards the collecting chamber 28. However, the receiving chambers 18, 20, and 22 can also have a conical shape without a bottom. This allows a fluid, especially water, to flow by gravity from the respective lateral receiving chamber 18 or 20 to the collecting chamber 28. To create a fluid connection, lower inlet openings 34 are arranged in baffles 36. These baffles connect directly to the respective bottom 32. The baffles 36 can extend essentially vertically upwards from the respective bottom 32 to the top surface 12 of the fluid tank 2. In addition to preventing excessive fluid movement, the baffle plates 36 can also contribute to stiffening and, in particular, to increasing the bending and torsional stiffness of the fluid tank 2.On their upper surface, they may have upper inlet openings 35, which serve, for example, to allow the passage of air or other gaseous fluids. A thermal insulation 30 is provided below the receiving chambers 18, 20 and 22, which is designed, for example, as a foam, in particular as a closed-cell foam, or as an aerogel.

[0047] In Fig. 1b A three-sided view of fluid tank 2 is presented. The elongated, tubular shape of fluid tank 2 is particularly evident here. The axial walls 8 and 10 are strongly convex and can also form fluid tank 2 as a pressure tank. Fluid can be introduced into fluid tank 2 at relatively arbitrary points. A first fluid inlet 38 and a second fluid inlet 39 are shown as examples. The first fluid inlet 38 could be used to introduce water. It is conceivable that a pressurized gas, such as oxygen, hydrogen, or air, could be introduced at least temporarily through the second fluid inlet 39, so that a controlled release of fluid from the outlet 26 can occur due to the overpressure prevailing in fluid tank 2. A valve (not shown) could, for example, be connected there, which is opened to withdraw fluid and closed after withdrawal.Fluid, especially water, could then be fed into an electrolyzer, for example. It may be advisable not to pressurize fluid tank 2 for a significant portion of the time.

[0048] In the Figuren 2a, 2b and 3 The collection chamber 28 is shown in sectional views. The collection chamber 28 has two lateral walls 42 extending from the underside of the fluid tank 2 to a top surface 44, thus defining the collection chamber 28. The top surface 44 is provided here with a rounded, shallowly conical, or ramp-shaped form, and, for example, a convex upward curve, such that it has a greater distance to the bottom surface 24 in a radially central region 46 than in radially outer regions.

[0049] Flow openings 50 are arranged in the radially central region 46, allowing gas bubbles to be discharged. This is facilitated by the shape of the top surface 44, as gas bubbles can rise towards the top surface 44 in a steady flight condition of the aircraft and then migrate along the slope into the central region 46 towards the flow openings 50. The drain 26 has an inlet cross-section 52 that is clearly spaced from the bottom surface 24 and terminates below the radially central region 46. Fluid can be drawn from the collection chamber 28 through the drain 26. In steady flight, it can be assumed that the collection chamber 28 is always filled with the fluid to be drawn.

[0050] Based on Fig. 2b The figure illustrates how, during a vertical downward acceleration of the aircraft, indicated by the vertical upward load factor Nz, fluid in the collection chamber 28 is forced towards the top surface 44 due to inertia. The fluid can only exit the collection chamber 28 through the top surface 44 via the flow openings 50. If the flow openings 50 are sufficiently small, the fluid can only escape in the form of droplets 48. To equalize the pressure in the collection chamber 28, air 55 can enter through a collection chamber gap 56 surrounding the chamber 28. However, in steady-state operation, the passage of gas bubbles is not prevented. This applies both in the steady state in Fig. 2a as well as in the case of gust loads or descent in Fig. 2b The inlet cross-section 52 is completely connected to the fluid, so that reliable fluid extraction is possible in both cases.

[0051] Furthermore, it is shown here that flow openings 34 are made of Fig. 1a Fluid is in contact with the collection chamber 28 via a gap 54 above the bottom surface 24 and below the collection chamber walls 42, in conjunction with the collection chamber gap 56 between the collection chamber walls 42 and the outer collection chamber walls 57. With a conical design of the receiving chambers 18 and 20, the collection chamber walls 57 could also be designed as the outer wall of the fluid tank 2. In the steady state, fluid can flow into the collection chamber 28 via a flow path formed by this. In the Fig. 2b In the illustrated load case, air or another gas flows through this flow path into the collection chamber 28. Due to the openings 50 being dimensioned as small as possible and the inlet cross-section 52 being located far from the bottom surface 24, it would theoretically take a considerable amount of time for the fluid to be displaced and for the air to even reach the inlet cross-section 52. Therefore, with a sufficiently large collection chamber 28, it can be ensured that in no conceivable load case would such a vertical acceleration persist long enough for this condition to occur. The maximum volume of the collection chamber 28 is defined by the upper edge of the gap 54.

[0052] As in Fig. 3 The outlet 26 can be connected to a suction line 29 that extends under the fluid tank 2. Depending on the design, the suction line 29 can extend beyond the axial wall 8 or 10 or be bent in another direction along its course.

[0053] Finally, it shows Fig. 4 A very schematic representation of an unmanned aerial vehicle 58, into which a fluid tank 2 is integrated, is shown. This illustration is merely exemplary and is not intended to limit the subject matter to such an aircraft. For example, the fluid tank 2 is arranged transversely on, in, or below wings 60. Alternatively, the fluid tank 2 could also be arranged in a tail assembly 62. Another alternative is that the fluid tank 2 could also be arranged in a fuselage 64. Further embodiments of aircraft without a fuselage, with multiple fuselages, and with or without a separate tail assembly are conceivable.

[0054] It should be further noted that "having" does not exclude any other elements or steps, and "a" or "an" does not exclude a plurality. It should also be noted that features described with reference to one of the above embodiments may also be used in combination with other features of other embodiments described above. Reference numerals in the claims are not to be considered as a limitation. REFERENCE MARK

[0055] 2 Fluid tank 4 Structure 6 Hull 8 First axial wall 10 Second axial wall 12 Top 14 Bottom 16 Interior 18 First intake chamber 20 Second intake chamber 22 Central intake chamber 24 Bottom surface 26 Drain 28 Collection chamber 30 Thermal insulation 32 Bottom 34 Lower inlet opening 35 Upper inlet opening 36 Baffle plate 38 First fluid inlet 40 Second fluid inlet 42 Collection chamber wall 44 Top surface 46 Radially central area 48 Droplet 50 Flow opening 52 Inlet cross-section 54 Gap / radial opening 55 Air 56 Collection chamber gap 57 Outer collection chamber wall 58 Aircraft 60 Wing 62 Tail unit 64 Fuselage

Claims

1. Fluid tank (2) for integration into a structure of an unmanned aircraft (58), comprising: - a shell (6) having a first axial wall (8), an oppositely arranged second axial wall (10), an upper side (12), a lower side (14) and an enclosed interior (16), - at least one receiving chamber (18, 20, 22) in the interior (16) for storing fluid, and - a collecting chamber (28) arranged at the lower side (14), which is in fluid communication with the at least one receiving chamber (18, 20, 22), wherein the collecting chamber (28) has a bottom surface (24) through which an outlet (26) extends, wherein a top surface (44) is arranged above the bottom surface (24) and covers at least a section of the collecting chamber (28), wherein a first receiving chamber (18) axially adjoins the first axial wall (8) and wherein a second receiving chamber (20) axially adjoins the second axial wall (10), and wherein the collecting chamber (28) is arranged centrally in a longitudinal axial direction between the first axial wall (8) and the second axial wall (10) and between the first receiving chamber (18) and the second receiving chamber (20) and below a central receiving chamber (22), further comprising at least one baffle plate (36) extending transversely to an axial direction of the fluid tank (2), wherein both lateral receiving chambers (18) and (20) each have a floor which slopes slightly in the vertical direction from the respective axial wall (8) or (10) towards the collecting chamber.

2. Fluid tank (2) according to claim 1, wherein at least one flow opening (50) is arranged at an upper side of the collecting chamber (28), which allows gas bubbles to escape towards the upper side of the fluid tank (2).

3. Fluid tank (2) according to claim 1 or 2, wherein the collecting chamber (28) has at least one collecting chamber wall (42) which extends from the lower side (14) of the fluid tank (2) to the top surface (44) and defines the collecting chamber (28), and wherein the at least one collecting chamber wall (42) is spaced, at least in regions, from an outer collecting chamber wall (57).

4. Fluid tank (2) according to claim 3, wherein the collecting chamber wall (42) encloses a collecting chamber gap (56) with the outer collecting chamber wall (57).

5. Fluid tank (2) according to any one of the preceding claims 3 or 4, wherein the collecting chamber (28) is in fluid communication with the at least one receiving chamber (18, 20, 22) through an opening (54) arranged at the lower side (14).

6. Fluid tank (2) according to any one of the preceding claims, wherein the top surface (44) has a radially central region (46) which has a greater distance from the bottom surface (24) than radially outer regions.

7. Fluid tank (2) according to any one of the preceding claims, wherein the at least one receiving chamber (18, 20, 22) has a floor (32) which slopes down in a ramp-like manner towards the collecting chamber (28) in the direction of the lower side (14).

8. Fluid tank (2) according to claim 1, wherein the at least one baffle plate (36) is arranged vertically above or to the side of the collecting chamber (28).

9. Fluid tank (2) according to any one of the preceding claims, wherein the fluid tank (2) is configured as a water tank.

10. Unmanned aircraft (58), comprising at least one wing (60) and at least one fluid tank (2) according to any one of the preceding claims integrated into the aircraft (58).

11. Aircraft according to claim 10, wherein the fluid tank (2) is configured to be load-bearing.

12. Aircraft according to claim 10 or 11, further comprising at least one regenerative fuel cell which is in fluid communication with the fluid tank (2), and an electrolyzer which can be brought into fluid communication with the outlet in order to take water from the fluid tank (2) and decompose it into hydrogen and oxygen by an electrolysis process.