Ventilation tank of unmanned aerial vehicle fuel tank ventilation system and working method of ventilation tank

Abstract

The invention belongs to the technical field of aircraft fuel tank ventilation, and discloses a ventilation tank of an unmanned aerial vehicle fuel tank ventilation system and a working method of the ventilation tank, the ventilation tank integrates fuel collection and storage, fuel recovery and discharge and posture self-adaptive ventilation functions, and the ventilation tank comprises a ventilation tank body, a bottom floater valve, an upper floater valve assembly and a mounting structure. The ventilation box body is designed to be in a long cylinder shape, and pipeline connectors are arranged on the upper portions of the two sides of the ventilation box body and used for collecting and temporarily storing fuel oil entering from the ventilation pipeline. The bottom floater valve is automatically opened and closed according to the liquid level of the fuel tank, and fuel in the tank is recycled or backflow is prevented. The upper floater valve is arranged at the high position of the far end of the oil tank and forms redundancy with an original ventilation opening of the oil tank, and it is guaranteed that at least one ventilation channel of the airplane is unblocked in maneuvering flight such as rolling. The wing oil tank is compact in structure, does not occupy extra fuel oil space, is high in reliability and is particularly suitable for small and medium-sized unmanned aerial vehicle wing oil tanks with limited space.

Description

Technical Field

[0001] This invention belongs to the field of aircraft fuel tank venting technology, specifically relating to a venting system for aircraft fuel tanks, and more particularly to an integrated venting box and venting guarantee method suitable for small and medium-sized unmanned aerial vehicles (UAVs), especially UAVs using integral wing fuel tanks. Background Technology

[0002] During the fuel supply process to the engine, the fuel level in an aircraft fuel tank continuously decreases. If the tank were completely sealed, a negative pressure would form inside. This would not only severely affect the fuel pump's suction performance, leading to unstable or even interrupted fuel supply, but could also damage the tank structure itself due to excessive pressure difference, such as tank wall collapse or leaks at joints. Therefore, all aircraft fuel systems must be equipped with a venting system to allow the internal space of the fuel tank to communicate with the outside atmosphere, thereby maintaining the pressure difference between the inside and outside of the fuel tank within the design-allowed safe range during flight and refueling.

[0003] The design of the venting system must resolve a key contradiction: ensuring smooth gas flow while preventing liquid fuel from leaking outside the aircraft through the vents. Fuel leaks not only result in waste but also pose a serious fire risk at high temperatures or when exposed to an ignition source. For large aircraft, a separate vent box (vented fuel tank) is typically installed outside the wing fuel tanks, utilizing wing structural compartments to collect and store any spilled fuel. This solution is technically mature but requires high sealing performance and occupies additional internal wing space.

[0004] For small and medium-sized UAVs, especially those models that prioritize long endurance and large fuel capacity, the internal space of the wings is extremely valuable. Every liter of fuel space directly affects range and mission capability. Adopting the independent venting box design of large aircraft would inevitably reduce fuel capacity, contradicting the miniaturization and compactness requirements of UAVs. Therefore, there is an urgent need for a venting device that can be integrated into the fuel tank, occupying little or no effective fuel space, while reliably providing venting, fuel storage, and leak prevention functions. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a highly integrated, compact, and reliable ventilation box for a drone fuel tank ventilation system and its working method, addressing the shortcomings of existing technologies where independent ventilation boxes occupy valuable fuel tank space and are not conducive to the compact design of small and medium-sized drones.

[0006] The technical solution of this invention is implemented as follows:

[0007] Firstly, this invention provides a ventilation box for a drone fuel tank ventilation system, the core of which lies in the high integration of three major functional modules—ventilation, temporary fuel storage, and fuel recovery—into a compact unit. This ventilation box mainly includes: Vent box: As the main structure, it forms a closed cavity inside, primarily used to collect and temporarily store liquid fuel that may accidentally enter from the venting line. Preferably, the vent box is designed as a long cylindrical shape. This shape has the smallest surface area to volume ratio (relative surface area) for the same volume, meaning that less material is needed to manufacture it while meeting the same fuel storage capacity requirements, thus effectively reducing the weight of the component, which is of great significance for weight-sensitive UAVs. The volume of the vent box is generally designed to be at least 5 times the total volume of the venting line connected to it to ensure sufficient buffer capacity to accommodate fuel that may enter the system.

[0008] Bottom float valve: Integrated into the bottom of the vent box. This valve operates on the principle of buoyancy, and its core function is to achieve automatic fuel recovery and prevent backflow. Specifically, when the fuel level in the tank drops below the installation height of the valve, the float sinks under its own weight, opening the valve and allowing the fuel temporarily stored in the vent box to flow smoothly back to the main fuel tank for recycling. Conversely, when the fuel level in the tank rises and submerges the float valve, the float rises under the buoyancy of the fuel, closing the valve, thus effectively preventing fuel from the main fuel tank from flowing back into the vent box and subsequent vent lines.

[0009] Ventilation duct assembly and upper float valve: This assembly is responsible for providing the main ventilation function and redundancy safety. It includes a ventilator that communicates with the upper part of the ventilator housing, and another float valve, the upper float valve, connected to the end of the ventilator. The upper float valve is located high within the fuel tank, away from the original main vent (usually located on the opposite side of the fuel tank), for example, near the wingtip rib. These two ventilation points (the upper float valve and the original vent) are spatially separated.

[0010] Mounting Structure: This structure securely mounts the entire vent box inside the fuel tank, typically on a structural rib of the wing. A preferred embodiment involves a mounting flange on the outer wall of the vent box's central section, through which it is connected to internal structural components of the fuel tank using bolts or other fasteners. The mounting flange is preferably welded to the box to ensure connection strength and sealing.

[0011] As a further technical solution of the present invention: the venting box is provided with interfaces on the upper part of the end caps on both sides: the first interface is used to connect to the vent pipe from the vent inside the fuel tank, and the second interface is used to connect to the vent pipe leading to the outside atmosphere (usually through the vent inlet). Setting the interfaces at a high position can maximize the use of the space in the lower part of the box for fuel storage and increase the effective fuel storage volume.

[0012] As a further technical solution of the present invention: In order to facilitate maintenance and ensure installation accuracy, the bottom float valve is installed and fixed from the inside of the housing by fasteners such as screws. Specifically, a support plate nut can be pre-installed on the bottom plate inside the venting housing to achieve high-position installation of the float valve, which facilitates more thorough drainage of fuel back to the fuel tank under the action of gravity.

[0013] Secondly, based on the aforementioned ventilation box, this invention provides a fuel management and ventilation assurance method for unmanned aerial vehicle (UAV) fuel tanks, comprising the following steps: Fuel collection and storage: In cases of drastic changes in flight attitude (such as climb or dive) or overfilling of fuel tanks, a small amount of fuel may enter the vent line through the fuel tank's vent. In this case, the fuel will flow along the line into the higher vent box, where it will be collected and temporarily stored to prevent it from flowing directly out of the aircraft and causing leakage and pollution.

[0014] Automatic fuel recovery: As fuel is consumed, the fuel level in the tank drops. When the level falls below the float valve at the bottom of the vent box, the valve automatically opens, and the fuel temporarily stored in the tank flows back to the main fuel tank under gravity for reuse.

[0015] Fuel backflow prevention: During refueling or certain flight attitudes, the fuel level in the tank may rise. When the fuel level exceeds the bottom float valve, the valve automatically closes, forming a seal and blocking the passage of fuel into the vent box.

[0016] Redundant safety ventilation: During sharp turns, rolls, or other maneuvers, the fuel in the tank may slosh due to inertia, potentially causing a vent on one side of the tank to be temporarily submerged and fail. However, because the upper float valve is located at the opposite (farthest) end of the tank, it is highly unlikely to be submerged simultaneously. This float valve remains open by gravity when the fuel level is below its position, ensuring that even if one vent fails, the empty space at the top of the tank remains connected to the atmosphere through the vent box, forming a reliable redundant ventilation channel and guaranteeing uninterrupted ventilation.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. High integration and space saving: The ventilation, fuel storage, recovery and anti-backflow functions are integrated into a single container and installed directly in the high space inside the fuel tank (usually the non-full-load area on top of the fuel tank). There is no need to open up an additional independent compartment in the wing, which saves the valuable internal volume of the wing to the maximum extent, allowing the drone to carry more fuel and significantly increase its range.

[0018] 2. Simple structure and high reliability: The core functional components adopt a mature float valve mechanism, which works automatically using the principles of gravity and buoyancy. There are no complex electronic components or moving mechanisms, resulting in a low failure rate, strong environmental adaptability, and easy maintenance.

[0019] 3. High safety: By setting up an upper float valve at a remote high position, a redundant ventilation system with spatial separation is formed with the original ventilation port, ensuring that the aircraft has at least one ventilation point available in any maneuvering attitude, which greatly improves the reliability of the ventilation system and flight safety.

[0020] 4. Good economic efficiency: The cylindrical box design saves materials and reduces weight; the overall structure is simple and the processing, manufacturing and installation costs are low, making it very suitable for small and medium-sized UAV platforms that need to control costs.

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and examples. Attached Figure Description

[0022] Figure 1 This is a three-dimensional schematic diagram of the external structure of the ventilation box provided in an embodiment of the present invention.

[0023] Figure 2 This is a cross-sectional schematic diagram of the internal structure of the ventilation box provided in an embodiment of the present invention.

[0024] Figure 3 This is a schematic diagram of a typical arrangement of a venting box within the fuel tank of a UAV wing, as provided in an embodiment of the present invention.

[0025] Explanation of the reference numerals in the diagram: 1-Ventilation box; 2-Mounting flange; 3-First interface (connects to the internal ventilation line of the fuel tank); 4-Second interface (connects to the external ventilation line); 5-Bottom float valve; 6-Support plate nut / mounting seat; 7-Ventilation pipe; 8-Upper float valve; 9-Wing fuel tank wall panel; 10-Internal structural rib of the fuel tank; 11-Original vent of the fuel tank (first ventilation port); 12-Ventilation inlet to the atmosphere. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the embodiments of this invention will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are some embodiments of this invention, but not all embodiments.

[0027] The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0028] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0029] The following is in conjunction with the appendix Figure 1-3The embodiments of the present invention will be described in detail below.

[0030] Example 1 like Figures 1 to 3 As shown in the figure, this embodiment provides a venting box for the integral fuel tank of the wing of a certain type of reconnaissance and strike UAV.

[0031] The ventilation box 1 is made of aluminum alloy and is a sealed cylindrical tube with a diameter of 150mm and a length of 600mm. A mounting flange 2 with a width of 25mm is welded around the middle of the tube, and six bolt holes are evenly distributed on the flange.

[0032] At the upper part of one end cap of the ventilator housing 1, there is a first interface 3, which is connected to a section of ventilator pipe from the original vent 11 of the fuel tank via a quick-release clamp. At the symmetrical upper part of the other end cap, there is a second interface 4, which is connected to a pipe leading to the ventilator inlet 12 located at the leading edge of the wing.

[0033] A threaded, airtight support nut 6 is riveted to the center of the inner bottom plate of the ventilated housing 1. The bottom float valve 5 is secured to the support nut 6 via mounting holes on its housing using two stainless steel screws, ensuring the bottom of the valve is slightly higher than the inner bottom plate of the housing, thus creating a discharge channel. This float valve 5 is normally closed; when there is oil inside the housing and the external liquid level is low, the float falls, opening the valve; when the external liquid level rises and submerges the float, the valve closes.

[0034] At the top of the ventilator housing 1, a ventilator pipe 7, approximately 300 mm long, is connected via a right-angle bend and runs along the wing rib. The end of the ventilator pipe 7 is connected to an upper float valve 8. This valve 8 is fixed by a bracket to the highest point of the fuel tank top, near the wingtip rib, approximately 3.5 meters from the original vent 11 on the other side of the fuel tank. This upper float valve 8 is normally open, held open by the weight of the float, and closed by buoyancy when submerged in fuel.

[0035] During installation, the entire vent box assembly is fastened to a structural rib 10 in the middle of the wing fuel tank via mounting flange 2 and bolts. The installation position is higher than the maximum design full-load fuel level of the fuel tank.

[0036] In this embodiment, the venting box 1 can be integrally molded from high-strength engineering plastics (such as PEEK) to further reduce weight. The upper float valve 8 and the venting pipe 7 adopt an integrated design, with the valve housing directly serving as the pipe connector.

[0037] Working principle: During normal level flight, the air above the fuel tank is connected to the outside atmosphere through the existing vent 11, pipeline, vent housing 1, second interface 4, and subsequent pipelines. There is no fuel in vent housing 1.

[0038] When the aircraft climbs at a steep angle, fuel backflow may occur, and a small amount of fuel may seep into the vent 11. This fuel travels along pipes into the higher vent housing 1, where it is stored.

[0039] When the aircraft returns to level flight or after fuel consumption, the fuel level in the fuel tank drops. When the level is below the bottom float valve 5, the valve opens, and the fuel stored in the vent box 1 flows back to the main fuel tank.

[0040] When the aircraft performs a 60-degree roll maneuver, fuel rushes to one side, potentially completely submerging the vent 11 located on the lower side. At this time, the aforementioned float valve 8, located at the far end of the higher side, remains open due to the lack of fuel at that location, allowing fuel tank gas to communicate with the atmosphere through the vent pipe 7 and the vent box 1, ensuring uninterrupted ventilation. After leveling off, the vent 11 resumes its function.

[0041] Example 2 Applications of wing fuel tanks in medium-sized fixed-wing UAVs: This embodiment describes in detail the specific implementation of the ventilation box of the present invention in the integral fuel tank of the left wing of a certain type of medium-sized reconnaissance and strike fixed-wing UAV.

[0042] 1. Overall Layout and Integration Scheme like Figure 3 As shown, the UAV adopts a high-wing, blended wing-body configuration, with an integral fuel tank on each wing, and a maximum fuel capacity of approximately 400 liters. To meet the requirements for long endurance, the wing space needs to be fully utilized; therefore, the venting box described in this invention is integrated inside the fuel tank.

[0043] The vent box, as the core component of the ventilation system, is a structural rib installed inside the fuel tank (near the wing root) at approximately 40% of the wing chord position. Figure 3 The vent box 1 is mounted on rib 10. This installation location was carefully chosen, approximately 50mm above the theoretical maximum full-load fuel level (corresponding to 400 liters) of the fuel tank. This ensures that even when the tank is full, most of the volume of the vent box 1 remains in the vapor phase space above the fuel level, its primary function being gas flow rather than fuel storage. Simultaneously, this location avoids major accessories inside the fuel tank such as the fuel pump and fuel level sensor, facilitating installation and maintenance.

[0044] 2. Detailed design and selection of components for the ventilation box 2.1 Ventilation box 1 Materials and Processes: 6061-T6 aluminum alloy forged blanks are used, which are then milled into shape using a CNC machining center. Aluminum alloy was chosen because of its high strength-to-weight ratio, resistance to aviation fuel corrosion, mature processing technology, and controllable costs.

[0045] Structure and Dimensions: It is a long cylindrical tube with an outer diameter of Ø140mm and a length L=550mm. Both ends are flat end caps and sealed by welding. Calculations show that the internal volume of this cylindrical tube over a length of 550mm is approximately 8.5 liters. The end caps are designed with reinforcing ribs to withstand vibrations and aerodynamic loads during flight.

[0046] Key design parameter: Relative surface area (surface area / volume) is approximately 0.28 cm². - ¹, compared to a rectangular box of the same volume (approximately 0.33 cm²), - ¹), with significant weight reduction benefits. Its volume (8.5L) is approximately 13.5 times the estimated volume (approximately 0.63L) of all the ventilation pipes connected to it (inner diameter Ø10mm, total length approximately 8 meters), far exceeding the minimum requirement of 5 times, providing ample fuel storage buffer capacity.

[0047] Interface Design: Standard threaded interfaces are machined approximately 30 mm above the center line of the end caps at both ends of the cylindrical tube (based on the cylinder axis). The first interface (3) is an M22×1.5-6h external thread, used to connect the aluminum alloy hard pipe from the original vent (11) of the fuel tank. The second interface (4) is of the same specification and connects the pipe leading to the vent inlet (12) of the wing leading edge. The high-position design of the interfaces ensures that a pure oil storage space with a depth of approximately 120 mm can be formed in the lower part of the tank.

[0048] 2.2 Installation Structure Flange 2: A 25mm wide and 2.5mm thick annular boss is machined into the middle of the housing to serve as a flange. Six Ø5.2mm through holes are evenly distributed on the flange, corresponding to M5 mounting bolts. The flange and housing are machined as a single unit, resulting in high structural strength.

[0049] Installation process: Six tapped holes (M5 threaded holes) are pre-drilled at the corresponding positions on the fuel tank structural rib 10. Align the flange holes of the vent box assembly with the mounting holes on the structural rib 10, and tighten them using six A286 corrosion-resistant steel bolts with elastic washers and self-locking nuts to a tightening torque of 8 N·m. After installation, the vent box axis is basically parallel to the chord line.

[0050] 2.3 Bottom float valve assembly 5 Selection and Function: A mature aviation float-type vent valve is selected, the core of which consists of a polyurethane foam float assembly, a valve assembly, and a housing assembly. Under normal conditions (when the float is lifted by fuel), it is closed under buoyancy, and the sealing rating meets MIL standards.

[0051] Installation Details: A standard MS-type airtight support nut 6 is riveted to the geometric center of the bottom plate inside the vent box 1. The bottom float valve 5 has a mounting flange (with a sealing ring) on ​​its housing. The valve is secured by screwing the support nut upwards from the outside of the vent box using two stainless steel screws (coated with thread-locking compound). This installation method facilitates disassembly and maintenance from the tank cover without disassembling the entire vent box. The valve inlet connects to the inside of the vent box, and the outlet connects directly to the main fuel tank.

[0052] Operating point setting: The valve float is adjusted by counterweight, and its closing point (when the float just rises to close the valve) is precisely set when the fuel level in the tank reaches 25.4 mm (1.0 inch) below the bottom plate of the vent box. This means that when the fuel level in the tank is below this position, the valve automatically opens.

[0053] 2.4 Upper float valve and ventilation duct assembly (7, 8) Ventilation pipe 7: Made of Ø12x1mm 5A02 aluminum alloy pipe, with a length of 1200mm determined according to the internal space orientation of the wing. One end of the pipe is connected to the right-angle joint on the top of the ventilation box via a 37° flared connector, and the other end is connected to the upper float valve 8.

[0054] Upper float valve 8: A float valve with the same principle as the bottom valve but a normally open valve opening (i.e., open by gravity when there is no oil, and closed by buoyancy when submerged in oil). Its mounting bracket is fixed to the top structure of the end rib (one of the highest points of the fuel tank) near the wingtip using quick-release clamps. This position is approximately 3.0 meters horizontally from the original vent 11 on the other side of the fuel tank, and about 40mm lower vertically than the vent 11.

[0055] Redundancy design verification: The fuel level at the maximum design roll angle (60° in this case) of the aircraft was simulated by a three-dimensional digital prototype. It was confirmed that at any given moment, at least one of the upper float valve 8 and the original vent 11 was fully exposed to the gas phase, thus meeting the redundancy design requirements.

[0056] 3. Detailed description of system workflow 3.1 Normal Cruise Condition: Fuel tank half-full, aircraft level flight. Ventilation path: Atmosphere → Wing leading edge vent 12 → Pipeline → Second interface 4 → Gas phase space inside vent housing 1 → First interface 3 → Pipeline → Existing fuel tank vent 11 → Fuel tank gas phase space. At this time, the bottom float valve 5 is closed because the external fuel level is higher than its closing point; the upper float valve 8 is kept open by gravity because there is no fuel at its location, but it is not used as the main ventilation path (because there is already a direct path with lower drag).

[0057] 3.2 Fuel Collection and Temporary Storage Process (e.g., during aggressive maneuvers or over-refueling): Assume that a rapid climb causes fuel to surge rearward, and a small amount of fuel is forced into the vent line from vent 11. The fuel flows along the line to the higher vent box 1. Because the interfaces (3,4) are located at a higher position, fuel accumulates at the bottom of the box. This process continues until the maneuver ends or the fuel level in the box reaches a certain point.

[0058] 3.3 Automatic Fuel Recovery Process: When the aircraft transitions to level flight or as fuel is consumed, the overall fuel level in the fuel tank decreases. When the level drops below the closing point of the bottom float valve 5 (5mm below the bottom of the tank), the float inside the valve loses buoyancy due to the fuel and falls under the influence of gravity and the internal mechanism, causing the valve core to open. Fuel accumulated at the bottom of the vent box 1 flows smoothly back to the main volume area of ​​the fuel tank under the influence of gravity through the open valve 5, achieving recovery. The valve closes again when the fuel in the tank is emptied or the fuel level rises.

[0059] 3.4 Redundant Ventilation Support Process (High-Angle Roll): When the aircraft performs a continuous 60° left roll, fuel accumulates towards the right wingtip under centrifugal force. The original vent (11) located on the left side of the left wing fuel tank may be completely submerged by fuel and become ineffective. At this time, the upper float valve 8, located at a higher position on the far right side of the fuel tank, remains open under gravity because its installation position is much higher than the fuel level on the right side. The ventilation path is switched to: fuel tank vapor space → upper float valve 8 → vent pipe 7 → vent box 1 → pipeline to the atmosphere. This ensures uninterrupted ventilation and that the pressure difference between the inside and outside of the fuel tank is always controlled.

[0060] 4. Experimental verification The system described in this embodiment has completed the following bench tests and installation verifications: Functional tests: Refueling, pumping fuel, and different maneuvers were simulated on the fuel tank test bench to verify the functions of fuel collection, storage, and recovery, as well as the automatic opening and closing logic and redundant ventilation function of the two float valves.

[0061] Vibration and environmental testing: The ventilation box assembly passed the sinusoidal sweep frequency vibration, random vibration and high and low temperature cycle tests related to UAVs as specified in GJB150A. The structure is intact and the function has not failed.

[0062] Flight tests: Multiple flight tests were conducted on the actual drone, including maneuvers such as steep turns and rapid ascents and descents. The ventilation system worked normally, no fuel leak alarms occurred, and the fuel tank pressure sensor data remained within the safe range.

[0063] Applications of composite material fuel tanks for small drones: This embodiment describes a lighter and more compact implementation for composite fuel tanks in smaller electric vertical takeoff and landing (eVTOL) or fixed-wing UAVs.

[0064] 1. Overview of Differences Due to the smaller platform size, fuel capacity is typically less than 50 liters, making it extremely sensitive to weight and space constraints. Fuel tanks may be separate composite material shells (such as those made of flame-retardant nylon or carbon fiber reinforced polymer with an inner lining) rather than integral wing structures.

[0065] 2. Adaptive design of the ventilation box Box 1: Manufactured in one piece using high-strength, lightweight engineering plastic (such as 30% glass fiber reinforced PEEK) via injection molding, including the interfaces at both ends and internal mounting bosses. The shape remains cylindrical, but the dimensions are reduced to Ø80mm, with a length of 300mm and a volume of approximately 1.5 liters. Insert injection molding is used to embed threaded metal inserts in the top and bottom of the box for connecting the vent pipe and installing the float valve.

[0066] Installation method: External flanges are eliminated. Mounting lugs with through holes are designed on both the upper and lower sides of the tank. Using specially designed composite material straps or flexible clamps, the vent box is directly fixed to the pre-installed reinforcing ribs or mounting bases on the inner wall of the composite material tank to accommodate any deformation that may occur in the composite material tank.

[0067] Float valves (5,8): Miniaturized plastic-cased float valves are used to further reduce weight. The bottom float valve 5 is directly locked to the plastic interface at the bottom of the tank via a plastic snap-fit ​​mechanism, simplifying installation. The upper float valve 8 is connected to a section of flexible fluororubber tubing, facilitating adjustment of its direction and position within the limited space of the fuel tank.

[0068] Working logic: exactly the same as in Example 1, but the size, weight and installation details of each component have been optimized for a small platform.

[0069] Applications of multi-tank systems with a central vent box: For large unmanned aerial vehicles with multiple independent fuel tanks (such as left wing fuel tank, right wing fuel tank, and central fuel tank), the ventilation box concept of the present invention can be extended to other applications.

[0070] Implementation: Inside each individual fuel tank (left, right, and center), a vent box, customized to the tank's dimensions, is installed as described in this invention. The second interface 4 of each fuel tank's vent box is interconnected via a common vent manifold within the wing or fuselage, ultimately converging to one or more shared external vent inlets. This ensures balanced pressure across the fuel tanks, preventing fuel cross-flow due to pressure differences. Simultaneously, each fuel tank possesses independent fuel collection / recovery and redundant venting capabilities, enhancing system safety.

[0071] Maintenance and Troubleshooting Instructions Regular maintenance: After accumulating a certain number of flights or flight time, check the vent box for external damage, loose connections, and any abnormal fluid buildup inside by checking the fuel tank cap. The simulated float valve can be manually operated to check its smooth movement.

[0072] Failure Modes and Handling: Bottom float valve 5 is stuck in the closed position: This may prevent temporarily stored fuel in the tank from draining. The system can still ventilate, but the fuel storage buffer capacity is reduced. This valve needs to be replaced at the next maintenance.

[0073] Bottom float valve 5 is stuck in the open position: When the fuel tank is full or at a high level, a small amount of fuel may continuously seep into the tank, but this will be blocked by the upper valve and will not leak directly outside the machine. The system's ventilation function remains normal. Repair is required as soon as possible.

[0074] Upper float valve 8 malfunction: Redundant ventilation capability is lost, but the main ventilation path (original vent 11) remains operational. The aircraft should avoid extreme maneuvers that could result in continued flooding of the main vent and should plan for maintenance.

[0075] Severe blockage of the ventilator housing: Extremely rare. This will cause the entire ventilator system to fail and fuel tank pressure to become abnormal. The aircraft should have the appropriate pressure sensor to issue an alarm and execute emergency procedures.

[0076] Example 3 This invention discloses a venting box for unmanned transport aircraft, which can realize functions such as fuel tank venting, temporary storage of small amounts of fuel, and fuel discharge, while not occupying the fuel tank's fuel-carrying space. It features a simple structure and high safety and reliability. It is particularly suitable for small and medium-sized UAVs.

[0077] A drone ventilation box includes: a ventilation box body, a ventilation duct, a float valve, a flange, and other components. The ventilation box structure is as follows: Figure 1 , Figure 2 As shown.

[0078] Vent boxes are typically located high within the wing fuel tanks. This higher placement ensures that fuel stored in the vent box is drained back into the fuel tank earlier when the fuel level drops.

[0079] Ventilation boxes are elongated cylindrical in shape and typically have a smaller relative surface area (surface area / volume). When the required ventilation box volume remains constant, a cylindrical structure requires less material (metal / non-metal) and results in a lighter weight. The volume of the ventilation box is generally designed to be at least five times the volume of the ventilation piping. Ventilation piping of different specifications / diameters can be matched with ventilation boxes of different volumes.

[0080] The interfaces on both sides of the vent box are located slightly above the end caps. Interface 1 connects to the vent line inside the fuel tank, and interface 2 connects to the vent line leading to the outside of the fuel tank. The higher interface position allows the vent box to hold a larger volume of fuel, preventing fuel from overflowing directly from the tank through the vent line. The connection method for the interfaces is varied and no specific requirements are specified.

[0081] By combining two float valves with a vent box in a specific structural design, the vent box can collect and discharge fuel, as well as connect with the outside atmosphere.

[0082] A float valve 2 is installed at the bottom of the vent box. Utilizing the simple and reliable working principle of the float valve, it allows for the discharge of fuel from the vent box and prevents external fuel from flowing back into the vent box. The float valve 2 is directly fixed to the bottom of the vent box using screws and a mounting plate nut. This ensures that the float valve 2 has a high installation height, facilitating the return of fuel stored in the vent box to the fuel tank.

[0083] The upper part of the vent box is connected to float valve 1 via a vent pipe. Float valve 1 is located relatively high inside the fuel tank, near the end rib. Float valve 1 is connected to a duct, which in turn connects to a right-angle connector on the upper part of the vent box. Float valve 1 is typically located near the boundary rib of the aircraft fuel tank, away from another vent inside the tank. During maneuvers such as rolling, this design ensures that either float valve 1 or the distant vent will not be submerged in fuel, and the fuel-free space at the top of the fuel tank remains open to the atmosphere.

[0084] The vent box is welded with a mounting flange, which allows the vent box to be fixed to the structural rib inside the wing fuel tank, making installation simple.

[0085] Specific work process: Under normal circumstances, the vent, the vent pipe inside the fuel tank, the vent box, and the vent pipe outside the fuel tank form a continuous venting path to ensure that the upper part of the fuel tank is connected to the outside atmosphere for ventilation.

[0086] When a small amount of fuel in the fuel tank enters the vent pipe through the vent, the vent box will collect and temporarily store this fuel to prevent it from leaking directly out of the fuel tank.

[0087] When the fuel level in the fuel tank is lower than the height of the float valve at the bottom of the vent box, the float valve opens by gravity, and the fuel stored in the vent box is discharged back into the fuel tank.

[0088] When the fuel level in the fuel tank submerges the float valve at the bottom of the vent box, the float valve closes due to buoyancy, preventing fuel from entering the vent box.

[0089] When the aircraft's fuel tank attitude changes significantly and the vent inside the fuel tank is submerged in fuel, the float valve at the other end of the fuel tank opens because the fuel cannot submerge it, ensuring that the upper part of the fuel tank is always connected to the outside atmosphere for ventilation.

[0090] Thus, the objective of this invention has been achieved.

[0091] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A ventilation box for a drone fuel tank ventilation system, characterized in that, include: The venting box has an internal cavity for collecting and storing fuel. A bottom float valve is located at the bottom of the vent box and is used to control the discharge of fuel stored in the vent box to the fuel tank or to prevent fuel backflow into the fuel tank according to the fuel level in the fuel tank. The ventilation duct assembly includes a ventilation pipe communicating with the upper part of the ventilation box, and an upper float valve connected through the ventilation pipe, the upper float valve being arranged at a higher position inside the oil tank away from the first ventilation port. An installation structure is provided on the vent box body for fixing the vent box inside the oil tank; The ventilation box, bottom float valve, and ventilation duct assembly are integrated into one unit, enabling the ventilation box to collect and store fuel, recover emissions, and provide lateral ventilation to maintain the fuel tank's connection to the atmosphere under different flight attitudes.

2. The ventilation box according to claim 1, characterized in that, The ventilation box is in the shape of a long cylindrical tube.

3. The ventilation box according to claim 1, characterized in that, The ventilation box has interfaces on opposite sides, positioned above its bottom. These interfaces are a first interface for connecting to the ventilation pipe inside the oil tank and a second interface for connecting to the ventilation pipe leading to the outside of the oil tank.

4. The ventilation box according to claim 1, characterized in that, The bottom float valve is installed on the inner side of the bottom of the ventilation box by fasteners. Specifically, a support plate nut is provided on the bottom plate of the ventilation box, and the bottom float valve is connected and fixed to the support plate nut by screws.

5. The ventilation box according to claim 1, characterized in that, The upper float valve is installed at a higher height than the bottom float valve, and its position in the fuel tank is opposite to that of the first vent in the fuel tank; when the aircraft performs a roll maneuver, at least one of the upper float valve and the first vent is not submerged in fuel.

6. The ventilation box according to claim 1, characterized in that, The mounting structure is a mounting flange that surrounds the outer wall of the middle part of the vent box.

7. The ventilation box according to claim 1, characterized in that, The volume of the ventilation box is not less than five times the total volume of the ventilation pipeline connected to it.

8. The ventilation box according to claim 6, characterized in that, The mounting flange is welded to the vent box body.

9. A method for fuel management and ventilation assurance in a drone fuel tank, characterized in that, The method, using the ventilation box as described in any one of claims 1-8, comprises: Fuel collection and storage steps: When fuel in the fuel tank enters the vent pipe through the vent, it flows into the vent box and is collected and temporarily stored to prevent fuel from leaking directly outside the machine; Fuel recovery step: When the fuel level in the fuel tank drops below the bottom float valve at the bottom of the vent box, the bottom float valve opens under gravity, discharging the fuel stored in the vent box back into the fuel tank. Backflow prevention steps: When the fuel level in the fuel tank rises to submerge the bottom float valve, the bottom float valve closes under the action of buoyancy to prevent fuel in the fuel tank from entering the vent box; Redundant ventilation procedure: When the vent at one end of the fuel tank is submerged by fuel due to changes in flight attitude, the upper float valve located at the other end of the fuel tank opens because it is not submerged by fuel, keeping the fuel-free space of the fuel tank connected to the outside atmosphere through the vent box.

10. The method according to claim 9, characterized in that, In the redundant ventilation step, the upper float valve and the ventilation port in the fuel tank located away from its position form a redundant ventilation channel, ensuring that at least one ventilation channel remains unobstructed during the aircraft's roll maneuver.

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