A ducted screw and method of manufacture

Abstract

This invention belongs to the technical field of aviation electric propulsion systems, particularly the field of aircraft technology, and specifically relates to a ducted propeller and its manufacturing method. It addresses the problems of insufficient passive lift, redundant structural weight, and insufficient stiffness in existing ducted propellers. The invention includes a ducted shell, which is a thin-walled rotary structure. The inner wall of the ducted shell has airfoil-shaped passive lift surfaces in at least two different pressure zones. These airfoil-shaped passive lift surfaces are airfoil-shaped curved surfaces formed by or attached to the wall of the ducted shell. The inner wall of the ducted shell has multiple axial reinforcing ribs, and the outer wall of the ducted shell has multiple annular reinforcing ribs. At least some of the axial reinforcing ribs simultaneously form a support frame for the airfoil-shaped passive lift surfaces. The cross-sectional dimension of the support frame at the installation position of the airfoil-shaped passive lift surface is larger than the cross-sectional dimension of the support frame at other positions.

Description

Technical Field

[0001] This invention belongs to the field of aviation electric propulsion system technology, and in particular relates to the field of aircraft technology, specifically to a ducted propeller and its manufacturing method. Background Technology

[0002] Ducted rotors are widely used in electric vertical takeoff and landing (eVTOL) aircraft, large cargo drones, and special aircraft power plants due to their high safety, low noise, and superior aerodynamic efficiency compared to open rotors.

[0003] Traditional ducted propellers suffer from the following technical defects: First, insufficient passive lift exploitation. The duct is primarily used as a protective cover for the blades and a flow field straightening device. Areas that could generate significant lift, such as the lip and diffuser walls, are not designed with airfoil characteristics. Passive lift typically accounts for only 10%-20% of the total lift. Second, redundant structural weight and insufficient stiffness. Traditional designs employ thick-walled homogeneous duct shells, and the aerodynamic surfaces require independent support frames, resulting in a large number of structural components and high weight. Furthermore, there is a lack of effective longitudinal and circumferential stiffness transfer paths, making it difficult to support asymmetric two-point connection methods. Summary of the Invention

[0004] This invention provides a ducted propeller and its manufacturing method, which solves the problems of insufficient passive lift, redundant structural weight, and insufficient rigidity of existing ducted propellers. By setting at least two airfoil-shaped passive lift surfaces in different pressure zones on the inner wall of the duct, and using at least some of the multiple axial reinforcing ribs on the inner wall of the duct shell as the supporting frame for the passive lift surfaces, and by setting multiple annular reinforcing ribs on the outer wall of the duct shell, the duct as a whole becomes a lift generating device and improves the overall rigidity.

[0005] This invention is achieved through the following technical solution: A ducted rotor includes a ducted shell, wherein the ducted shell is a thin-walled rotary structure; The inner wall of the duct shell is provided with airfoil-shaped passive lift surfaces in at least two different pressure zones. The airfoil-shaped passive lift surfaces are airfoil-shaped curved surfaces formed by or attached to the wall of the duct shell. The inner wall of the duct shell is provided with multiple axial reinforcing ribs, and the outer wall of the duct shell is provided with multiple annular reinforcing ribs. At least some of the axial stiffeners simultaneously form the support frame of the airfoilized passive lifting surface, and the cross-sectional dimension of the support frame at the installation position of the airfoilized passive lifting surface is larger than the cross-sectional dimension of the support frame at other positions.

[0006] Furthermore, the airfoil-shaped passive lifting surface includes an upper airfoil located in the negative pressure zone above the duct and a lower airfoil located in the positive pressure zone below the duct; the upper airfoil is located in the negative pressure zone inside the upper lip of the duct, and its angle of attack is 3°-10°; the lower airfoil is located in the positive pressure zone of the lower diffuser section of the duct, and it has an S-shaped curve profile, an expansion ratio of 1.2-1.5, and a static pressure recovery coefficient greater than 0.80.

[0007] Furthermore, it also includes multiple upper guide vanes and multiple lower guide vanes. The upper and lower guide vanes are airfoil plates independent of the upper and lower airfoil surfaces. Both the upper and lower guide vanes have airfoil sections and generate passive lift under the action of airflow in the duct. Multiple upper guide vanes are distributed circumferentially and pass through the center of the duct, with each upper guide vane fixed at both ends to the upper airfoil; multiple lower guide vanes are distributed circumferentially and pass through the center of the duct, with each lower guide vane fixed at both ends to the lower airfoil; the upper guide vanes, lower guide vanes, axial reinforcing ribs, and annular reinforcing ribs together constitute the spatial stiffness frame of the duct, which is used to improve the overall stiffness of the duct propeller.

[0008] Furthermore, the duct shell is a thin-walled cylinder made of fiber-reinforced composite material with a wall thickness of 0.8-2.0 mm; Multiple axial reinforcing ribs are evenly distributed circumferentially on the inner wall of the duct shell, and multiple annular reinforcing ribs are evenly distributed axially on the outer wall of the duct shell; wherein at least one axial reinforcing rib is located at the same position as the installation position of the airfoil passive lifting surface, and the height of the axial reinforcing rib at the overlapping position is greater than the height of the axial reinforcing rib at the non-overlapping position.

[0009] Furthermore, it also includes a rotor ring disposed within the duct housing and a stator fixed to the duct housing; The rotor ring is fixed with blades, the root of which extends toward the center, forming a non-blocking flow zone with a diameter of not less than 50 mm in the central region. The stator is a coreless stator with a non-metallic composite material frame and a Halbach array permanent magnet outer rotor to maintain the air gap magnetic flux density.

[0010] Furthermore, it also includes two connection interfaces disposed on the outer wall of the duct shell. The two connection interfaces are asymmetrically distributed along the circumferential direction, and the central angle between adjacent connection interfaces is 60°-120°. The connection interfaces are used to transfer the entire load of the rotor to the external load-bearing body. The culvert has an inner diameter of 800-3500mm, a rated lift-to-weight ratio greater than 4, and a rated force efficiency greater than 7g / W.

[0011] A method for increasing the passive lift of a ducted propeller and reducing the system's weight includes the following steps: S01. At least two airfoil-shaped passive lifting surfaces are constructed in different pressure zones on the inner wall of the duct of the ducted rotor. The airfoil-shaped passive lifting surfaces are designed in coordination according to the aerodynamic load at the rated operating speed, so that the duct as a whole acts as a lift generating device, and the passive lift accounts for more than 30% of the total lift. S02. Multiple axial reinforcing ribs are provided on the inner wall of the duct shell and multiple annular reinforcing ribs are provided on the outer wall of the duct shell. At least some of the axial reinforcing ribs are used simultaneously as the support frame of the airfoil passive lifting surface, and the cross-sectional dimension of the support frame at the installation position of the airfoil passive lifting surface is larger than the cross-sectional dimension at other positions.

[0012] Furthermore, in step S01, the airfoilized passive lifting surface includes an upper airfoil located in the negative pressure zone above the duct and a lower airfoil located in the positive pressure zone below the duct. It also includes multiple upper guide vanes and multiple lower guide vanes. The upper and lower guide vanes have airfoil sections and generate passive lift under the action of airflow in the duct. The multiple upper guide vanes pass through the center of the duct and are fixed at both ends to the upper airfoil. The multiple lower guide vanes pass through the center of the duct and are fixed at both ends to the lower airfoil. The upper and lower guide vanes, together with the axial reinforcing ribs and the annular reinforcing ribs, constitute the spatial stiffness frame of the duct to support the fixed connection with the external load-bearing body through two connection interfaces arranged asymmetrically in the circumferential direction.

[0013] The beneficial effects achieved by this invention compared with the prior art are as follows: 1. In the ducted propeller of the present invention, airfoil-shaped passive lifting surfaces are provided on the inner wall of the duct shell in at least two different pressure zones, which can generate aerodynamic lift under the action of airflow inside the duct; at least a portion of the axial reinforcing ribs simultaneously constitute the support frame of the airfoil-shaped passive lifting surfaces, and the cross-sectional dimension of the support frame at the installation position of the airfoil-shaped passive lifting surfaces is larger than the cross-sectional dimension of the support frame at other positions. The airfoil-shaped passive lifting surfaces are designed in coordination according to the aerodynamic load at the rated operating speed, so that the entire duct acts as a lift generating device, and the passive lift accounts for more than 30% of the total lift; The passive lift of the ducted rotor is greatly improved by the manufacturing method described in this invention. Through the coordinated configuration of multiple passive lift surfaces, the passive lift can reach 30%-45% of the total lift, which is 2-4 times higher than that of the traditional ducted rotor. 2. The upper and lower air deflectors are airfoil plates independent of the airfoil surface. They are arranged radially, pass through the center of the duct, and are fixed at both ends to the upper and lower airfoil surfaces respectively. They generate passive lift in the airflow and also serve as reinforcements to improve the stiffness of the fixed airfoil surfaces. 3. The upper and lower guide vanes, along with the axial reinforcing ribs on the inner wall and the annular reinforcing ribs on the outer wall of the duct shell, are at the same structural level, together forming the spatial stiffness frame of the duct, improving the overall stiffness of the duct rotor, and supporting the fixed connection with the external load-bearing body through two asymmetrically arranged connection interfaces in the circumferential direction. 4. Significantly improved structural stiffness, supporting asymmetric two-point connections. The upper and lower guide vanes are fixed to the upper and lower airfoil surfaces at both ends through the duct center, forming a tensioned beam-type reinforcement structure, which significantly improves the local bending stiffness of the airfoil surface; at the same time, together with the axial reinforcing ribs and the annular reinforcing ribs, they form a radial-longitudinal-circumferential spatial stiffness frame, making the two-point connection scheme structurally feasible; 5. The aerodynamic-structural integration is highly efficient, with the axial reinforcing ribs serving as the supporting framework for the airfoil-shaped passive lifting surface, achieving "one material for two purposes"; the upper and lower guide vanes serve as both airfoil aerodynamic surfaces and airfoil reinforcement components, eliminating the weight redundancy of independent reinforcement structures. Attached Figure Description

[0014] Figure 1 This is a three-dimensional schematic diagram of the upper side of the ducted propeller described in this invention; Figure 2 This is a three-dimensional schematic diagram of the lower side of the ducted propeller described in this invention; Figure 3 A schematic diagram of the assembly of the blades and the variable diameter rotor ring; Figure 4 Radial cross-sectional view of the coreless stator and ducted air-cooled heat dissipation system; Figure 5 Schematic diagram for titanium alloy bolt installation; Figure 6 This is a schematic diagram of the distribution of asymmetric two-point connection interfaces; Figure 7 This is a passive lift-rotation speed characteristic curve; In the diagram: 1-Upper guide vane; 2-Lower guide vane; 3-Thin-walled inner curved section; 4-Small hub; 5-Microscale eddy current generator; 6-CFRP thin-walled cylinder; 7-Axial reinforcing rib; 8-Annular reinforcing rib; 9-Blade; 10-Variable diameter rotor ring; 11-Elastic sealing brush; 12-Coreless stator; 13-Stator frame; 14-Winding slot; 15-Radial aluminum heat pipe; 16-Connection interface; 17-Titanium alloy bolt; 18-CFRP transition section; 19-Upper airfoil; 20-Lower airfoil. Detailed Implementation

[0015] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0016] In the description of the invention, it should be understood that the terms "front", "rear", "up", "down", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the invention.

[0017] Example 1 Reference Figure 1 , Figure 2 and Figure 7 This embodiment provides a ducted propeller with an inner diameter of 1300mm, mainly comprising a duct shell, which is a thin-walled rotating structure. The inner wall of the duct shell has airfoil-shaped passive lift surfaces in at least two different pressure zones. These airfoil-shaped passive lift surfaces are airfoil-shaped curved surfaces formed by or attached to the duct shell wall. The airfoil-shaped passive lift surfaces include an upper airfoil located in the upper negative pressure zone of the duct and a lower airfoil located in the lower positive pressure zone of the duct.

[0018] In this embodiment, an upper airfoil 19 is arranged in the negative pressure zone inside the upper lip of the duct. This airfoil is a continuous annular airfoil-shaped curved surface formed by the duct shell wall, using a NACA4412 airfoil section with a chord length of 130mm, an installation angle of attack of 6°, and an unfolded area of ​​0.436 square meters. It is integrally formed with the duct shell and uses carbon fiber / epoxy prepreg, which is cyclically laid in a [45 / 0 / -45 / 90] layup sequence, with a total of 8 layers, followed by hot pressing. The total thickness is 1.0mm, generating 17.7kg of lift at a rated speed of 1650rpm. The lower airfoil 20 is arranged in the positive pressure zone of the duct diffuser section. It is an S-shaped curved airfoil formed by the duct shell wall. The inlet diameter is 1300mm, the outlet diameter is 1482mm, the axial length is about 520mm, the expansion ratio is 1.30, the half angle is 10 degrees, the static pressure recovery coefficient is 0.85, the unfolded area is 0.714 square meters, it generates 23.9kg lift, and the wall thickness is 1.5mm.

[0019] In this embodiment, the layup designation [45 / 0 / -45 / 90] is a common and standardized layup representation in the field of composite materials. Each set of numbers corresponds to the angle between the fiber orientation of a single layer of prepreg and the axis of the main load-bearing reference of the component. The parameters are defined as follows: 0: Prepreg fibers are laid along the axial direction of the main load-bearing reference of the component; 90: The prepreg fibers are laid perpendicular to the main load-bearing axis of the component; +45 (abbreviated as 45): The prepreg fibers are laid at a 45° angle to the main load-bearing reference axis of the component; -45: The prepreg fibers are laid at a -45° (i.e., 135°) angle with the main load-bearing reference axis of the component; [45 / 0 / -45 / 90] is the basic quaternary layup unit, and the layup sequence is 45° single layer, 0° single layer, -45° single layer, and 90° single layer. In this embodiment, the total number of layup layers is set to 8 layers, that is, the above quaternary layup unit is used to lay up the layers twice in a cycle. After the layup is completed, it is cured and formed by conventional hot pressing process.

[0020] The thin-walled inner curved section of the duct adopts a medium-camber airfoil equivalent design with a camber of 6%, equivalent to NACA6412, an unfolded area of ​​0.789 square meters, generating 20.7 kg of lift, and a wall thickness of 1.2 mm. Several micro-scale vortex generators 5 are arranged on the diffuser wall. The cross-section of the micro-scale vortex generator 5 is a triangular fin, 2 mm high, with a base length of 4 mm, a spacing of 15 mm, and an angle of 15 degrees with the flow direction. This increases the static pressure recovery coefficient from 0.80 to 0.85, resulting in an overall efficiency improvement of 5.8%, equivalent to an additional lift of 3.8 kg.

[0021] The aforementioned airfoil-shaped passive lifting surfaces work together to generate 64.9 kg of passive lift at the rated speed of 1650 rpm, accounting for 40.6% of the total lift of 160 kg.

[0022] The main body of the duct shell is a CFRP thin-walled cylinder 6 with an inner diameter of 1300 mm, a wall thickness of 1.2 mm, and an axial length of 676 mm. Forty-eight axial reinforcing ribs 7 are evenly distributed circumferentially on the inner wall of the duct shell, spaced 7.5 degrees apart; eight annular reinforcing ribs 8 are evenly distributed axially on the outer wall of the duct shell, spaced approximately 84.5 mm apart. At least some of the axial reinforcing ribs simultaneously form the support frame of the airfoil-shaped passive lifting surface. The cross-sectional dimension of the support frame at the installation position of the airfoil-shaped passive lifting surface is larger than the cross-sectional dimension of the support frame at other positions. In this embodiment, the sixth of every eight axial reinforcing ribs, spaced 45° apart, coincides with the installation position of the upper airfoil 19 and the lower airfoil 20. These eight ribs are increased in height to 12 mm and also serve as the main load-bearing frame; the remaining 40 axial ribs are 8 mm high.

[0023] The outer annular reinforcing rib 8 provides circumferential stiffness constraint, preventing the thin wall from undergoing elliptical deformation under negative pressure; the inner axial reinforcing rib 7 provides longitudinal stiffness and transfers the aerodynamic loads of the airfoil lifting surface to the duct shell. This integrated design eliminates approximately 0.8 kg of weight from the independent support frame, while allowing a smooth transition between the root of the airfoil lifting surface and the duct wall, reducing aerodynamic interference. The 48 axial reinforcing ribs increase the overall structural stiffness by approximately 80%, raising the first natural frequency from 86 Hz to 142 Hz.

[0024] This embodiment also discloses a method for increasing the passive lift of a ducted propeller and reducing the system's weight, including the following steps: S01. At least two airfoil-shaped passive lifting surfaces are constructed in different pressure zones on the inner wall of the duct of the ducted rotor. The airfoil-shaped passive lifting surfaces are designed in coordination according to the aerodynamic load at the rated operating speed, so that the duct as a whole acts as a lift generating device, and the passive lift accounts for more than 30% of the total lift. In this step, the airfoilized passive lifting surface includes an upper airfoil located in the negative pressure zone above the duct and a lower airfoil located in the positive pressure zone below the duct. It also includes multiple upper guide vanes and multiple lower guide vanes. The upper and lower guide vanes have airfoil sections and generate passive lift under the action of airflow in the duct. The multiple upper guide vanes pass through the small hub 4 at the center of the duct and are fixed at both ends to the upper airfoil. The multiple lower guide vanes pass through the center of the duct and are fixed at both ends to the lower airfoil. The upper and lower guide vanes, together with the axial reinforcing ribs and the annular reinforcing ribs, constitute the spatial stiffness frame of the duct to support the fixed connection with the external load-bearing body through two connection interfaces arranged asymmetrically in the circumferential direction. S02. Multiple axial reinforcing ribs are provided on the inner wall of the duct shell and multiple annular reinforcing ribs are provided on the outer wall of the duct shell. At least some of the axial reinforcing ribs are used simultaneously as the support frame of the airfoil passive lifting surface, and the cross-sectional dimension of the support frame at the installation position of the airfoil passive lifting surface is larger than the cross-sectional dimension at other positions.

[0025] The ducted propeller manufactured using the above method has a total system weight of 29.25 kg, a rated operating speed of 1650 RPM, a rated force efficiency of 11.99 g / W at a lift of 160 kg, a rated lift-to-weight ratio of 5.47, and a maximum lift-to-weight ratio of 10.94 at a maximum lift of 320 kg.

[0026] Example 2 This embodiment provides a ducted propeller with an inner diameter of 1300mm. Based on embodiment 1, a further optimization is made by setting multiple upper guide vanes 1 and multiple lower guide vanes 2. The upper airfoil surface 19 and the lower airfoil surface 20 are continuous annular airfoilized curved surfaces formed by the duct shell wall, and the upper guide vanes 1 and the lower guide vanes 2 are independent airfoil plates.

[0027] Reference Figure 1-2 The upper deflector 1 consists of eight pieces, evenly distributed at 45 degrees circumferentially. Each piece extends radially and passes through the center of the duct. Both ends of the upper deflector 1 are fixed to the upper airfoil 19, forming a tensioned beam-type reinforcement structure for the upper airfoil, reducing the maximum deflection of the upper airfoil under negative pressure load by approximately 70%. The lower deflector 2 also consists of eight pieces, similarly evenly distributed at 45 degrees circumferentially and passing through the center of the duct. Both ends of the lower deflector 2 are fixed to the lower airfoil 20. Both the upper deflector 1 and the lower deflector 2 adopt the NACA0012 symmetrical airfoil section with a chord length of 60 mm. They are hot-pressed from carbon fiber / epoxy prepreg and provide a total of approximately 6.5 kg of additional passive lift in the airflow within the duct at a rated speed of 1650 rpm.

[0028] Reference Figure 5-6 The propeller and the UAV fuselage are connected by two asymmetrical connection interfaces 16, located at 0° and 90° respectively. The connection interface material is TC4 titanium alloy, with an outer diameter of 120mm, an inner diameter of 80mm, and a thickness of 15mm. It is connected by eight M10 titanium alloy bolts 17 evenly distributed, with a preload of 4.0kN. The connection interface is connected to the duct body through a CFRP transition section 18, with 12 layers of [45 / 0 / -45 / 90]s and a length of 80mm. The upper and lower guide vanes, together with 48 axial reinforcing ribs and 8 annular reinforcing ribs, form a radial-longitudinal-circumferential spatial stiffness frame, which is equivalent to forming two tensioned beam-type reinforcing layers inside the duct. When the propeller is connected to the external load-bearing body through the two asymmetrical connection interfaces, such as the 0° and 90° flanges, the bending moment and torque generated by the lift are transmitted to the connection interface through the duct shell. Without this spatial stiffening frame, relying solely on the thin-walled shell to transmit bending moments would result in angular deformation exceeding 0.5° at the connection interface under a rated lift of 160 kg, leading to uneven air gaps and sealing failure. With the addition of this frame, the angular deformation is reduced to below 0.08°, meeting design requirements. This design also eliminates approximately 1.2 kg of weight from the independent airfoil reinforcement structure.

[0029] Reference Figure 3The blade 9 employs a hubless design, with eight blades directly fixed to the inner side of the rotor ring 10, extending towards the center. The blade root is located at 650mm of the rotor ring's inner diameter, and the blade tip terminates 100mm from the center, with an actual span of 550mm. The blade root chord length is 90mm, the blade tip chord length is 45mm, with a linear taper, a solidity of 0.982, and an aspect ratio of 6.11. A non-obstructive flow passage with a diameter of approximately 200mm is formed in the central region. The hubless design eliminates the obstruction of the central flow field by the traditional hub, reducing hub losses by approximately 25%, while also reducing the hub structure weight by approximately 0.5kg.

[0030] The rotor ring 10 is a variable-diameter CFRP integral wound structure with a wall thickness of 6mm. The upper inner diameter is 1300mm, the lower inner diameter is 1380mm, and there is a transition section in between, approximately 80mm in length. The transition section features a V-groove eddy current control structure with a depth of 0.5mm. A 3mm thick carbon fiber bristle elastic sealing brush 11 is installed at the inlet of the lower large gap area, reducing leakage to 0.15%.

[0031] Reference Figure 4 The stator 12 adopts a coreless design, and the stator frame 13 is made of carbon fiber / epoxy winding with an outer diameter of 1296mm and 288 winding slots 14. The windings use rectangular aluminum busbars in parallel with 12 turns per slot, in an 8-way parallel star connection. It is equipped with a Halbach magnet array of 192 N48SH neodymium iron boron magnets, with an air gap magnetic flux density of 0.55T and a stator efficiency of 99.57%. The stator frame contains 12 radial aluminum heat pipes 15, each 6mm in diameter, evenly distributed at 15-degree intervals around the circumference. Under rated operating conditions, the duct wind speed exceeds 80m / s, the convective heat transfer coefficient is 250W / (m²·K), and the maximum winding temperature is 53℃.

[0032] With the above scheme, the ducted propeller system described in this embodiment has a total weight of 29.25 kg, a rated lift-to-weight ratio of 5.47, and a rated force efficiency of 11.99 g / W.

[0033] Example 3 This embodiment provides a ducted propeller with an inner diameter of 1500mm and a rated lift of 225kg. The difference between this embodiment and Embodiment 1 is that the duct inner diameter is 1500mm, the wall thickness is 1.3mm, and there are 56 inner axial reinforcing ribs, 8 of which coincide with the installation positions of the upper and lower airfoils, with a rib height of 14mm and the remaining ribs having a height of 9mm. There are also 10 outer annular reinforcing ribs. The upper airfoil uses a NACA4415 airfoil section with a chord length of 150mm and an angle of attack of 5 degrees. The lower airfoil has an expansion ratio of 1.35. There are 10 upper and 10 lower guide vanes, evenly distributed at 36-degree angles around the circumference, passing through the center of the duct and fixed at both ends to the upper and lower airfoils respectively. Passive lift accounts for 38% of the total lift, and the rated lift-to-weight ratio is 5.2.

[0034] Example 4 This embodiment provides a ducted propeller with an inner diameter of 900mm and a rated lift of 80kg. The difference between this embodiment and Embodiment 1 is that the duct inner diameter is 900mm, the wall thickness is 1.0mm, and there are 32 inner axial reinforcing ribs, 6 of which coincide with the installation positions of the upper and lower airfoil surfaces. There are also 6 outer annular reinforcing ribs. Six upper and six lower guide vanes are evenly distributed circumferentially at 60-degree angles, passing through the center of the duct and fixed at both ends to the upper and lower airfoil surfaces respectively. Passive lift accounts for 35% of the total lift, and the rated lift-to-weight ratio is 4.8.

[0035] Comparative Examples Comparative Test A: Weight and stiffness comparison between an independent support frame and an integrated reinforcing member using the present invention. Under the premise of maintaining a duct diameter of 1300mm, a thin-wall thickness of 1.2mm, and consistent upper and lower airfoil parameters, the results are compared between the present invention's "axial reinforcing ribs also serving as upper and lower airfoil support frames + upper and lower guide vanes fixed through the center and also serving as airfoil reinforcing members" technical solution and the traditional technical solution of "independent support frame + ordinary reinforcing ribs + independent bulkhead". Conclusion: The independent frame design adds 1.64 kg to the weight, and due to the lack of a baffle-reinforcing rib spatial stiffness frame, the angular deformation at the two-point connection interface reaches 0.52°, exceeding the design allowable value of 0.1°, thus failing to meet the structural requirements of asymmetric two-point connections. In contrast, the angular deformation at the two-point connection interface of the present invention is only 0.08°, which does not exceed the design allowable value, thus meeting the structural requirements of asymmetric two-point connections.

[0036] Comparative Test B: Performance comparison between the hubed design and the hubless design using this invention. While maintaining the same duct diameter of 1300mm, 8 blades, duct airfoil-shaped passive lifting surface configuration, and connection method, the only difference was changing the hubless layout to a traditional hubed layout with a hub outer diameter of 120mm. The results are as follows: Conclusion: Due to central flow field obstruction and increased hub weight, the rated lift-to-weight ratio of the hub-based design drops to 5.05, and the rated force efficiency drops to 10.85 g / W. In contrast, the rated lift-to-weight ratio of this invention is 5.47, and the rated force efficiency drops to 11.99 g / W.

Claims

1. A ducted propeller, characterized in that, It includes a duct shell, wherein the duct shell is a thin-walled rotary structure; The inner wall of the duct shell is provided with an airfoil-shaped passive lift surface in at least two different pressure zones. The airfoil-shaped passive lift surface is an airfoil-shaped curved surface formed by or attached to the wall of the duct shell. The inner wall of the duct shell is provided with multiple axial reinforcing ribs, and the outer wall of the duct shell is provided with multiple annular reinforcing ribs. At least some of the axial stiffeners simultaneously form the support frame of the airfoilized passive lifting surface, and the cross-sectional dimension of the support frame at the installation position of the airfoilized passive lifting surface is larger than the cross-sectional dimension of the support frame at other positions.

2. The ducted propeller according to claim 1, characterized in that, The airfoil-shaped passive lifting surface includes an upper airfoil located in the negative pressure zone above the duct and a lower airfoil located in the positive pressure zone below the duct. The upper airfoil is located in the negative pressure zone inside the upper lip of the duct, and its angle of attack is 3°-10°. The lower airfoil is located in the positive pressure zone of the lower diffuser section of the duct, and it has an S-shaped curve profile, an expansion ratio of 1.2-1.5, and a static pressure recovery coefficient greater than 0.

80.

3. The ducted propeller according to claim 2, characterized in that, It also includes multiple upper guide vanes and multiple lower guide vanes. The upper and lower guide vanes are airfoil plates independent of the upper and lower airfoil surfaces. Both the upper and lower guide vanes have airfoil sections and generate passive lift under the action of airflow in the duct. Multiple upper guide vanes are distributed circumferentially and pass through the center of the duct, with each upper guide vane fixed at both ends to the upper airfoil; multiple lower guide vanes are distributed circumferentially and pass through the center of the duct, with each lower guide vane fixed at both ends to the lower airfoil; the upper guide vanes, lower guide vanes, axial reinforcing ribs, and annular reinforcing ribs together constitute the spatial stiffness frame of the duct, which is used to improve the overall stiffness of the duct propeller.

4. The ducted propeller according to claim 1, characterized in that, The duct shell is a thin-walled cylinder made of fiber-reinforced composite material with a wall thickness of 0.8-2.0 mm; Multiple axial reinforcing ribs are evenly distributed circumferentially on the inner wall of the duct shell, and multiple annular reinforcing ribs are evenly distributed axially on the outer wall of the duct shell; wherein at least one axial reinforcing rib is located at the same position as the installation position of the airfoil passive lifting surface, and the height of the axial reinforcing rib at the overlapping position is greater than the height of the axial reinforcing rib at the non-overlapping position.

5. The ducted propeller according to claim 1, characterized in that, It also includes a rotor ring disposed within the duct housing and a stator fixed to the duct housing; The rotor ring is fixed with blades, the root of which extends toward the center, forming a non-blocking flow zone with a diameter of not less than 50 mm in the central region. The stator is a coreless stator with a non-metallic composite material frame and a Halbach array permanent magnet outer rotor to maintain the air gap magnetic flux density.

6. The ducted propeller according to any one of claims 1-5, characterized in that, It also includes two connection interfaces disposed on the outer wall of the duct shell. The two connection interfaces are asymmetrically distributed along the circumferential direction, and the central angle between adjacent connection interfaces is 60°-120°. The connection interfaces are used to transfer the entire load of the rotor to the external load-bearing body. The culvert has an inner diameter of 800-3500mm, a rated lift-to-weight ratio greater than 4, and a rated force efficiency greater than 7g / W.

7. A method for manufacturing a ducted propeller to increase passive lift and reduce system weight, characterized in that, Includes the following steps: S01. At least two airfoil-shaped passive lifting surfaces are constructed in different pressure zones on the inner wall of the duct of the ducted rotor. The airfoil-shaped passive lifting surfaces are designed in coordination according to the aerodynamic load at the rated operating speed, so that the duct as a whole acts as a lift generating device, and the passive lift accounts for more than 30% of the total lift. S02. Multiple axial reinforcing ribs are provided on the inner wall of the duct shell and multiple annular reinforcing ribs are provided on the outer wall of the duct shell. At least some of the axial reinforcing ribs are used simultaneously as the support frame of the airfoil passive lifting surface, and the cross-sectional dimension of the support frame at the installation position of the airfoil passive lifting surface is larger than the cross-sectional dimension at other positions.

8. The manufacturing method according to claim 7, characterized in that, In step S01, the airfoil-shaped passive lifting surface includes an upper airfoil located in the negative pressure zone above the duct and a lower airfoil located in the positive pressure zone below the duct. It also includes multiple upper guide vanes and multiple lower guide vanes. The upper and lower guide vanes have airfoil sections and generate passive lift under the action of airflow in the duct. The multiple upper guide vanes pass through the center of the duct and are fixed at both ends to the upper airfoil. The multiple lower guide vanes pass through the center of the duct and are fixed at both ends to the lower airfoil. The upper and lower guide vanes, together with the axial reinforcing ribs and the annular reinforcing ribs, constitute the spatial stiffness frame of the duct to support the fixed connection with the external load-bearing body through two connection interfaces arranged asymmetrically in the circumferential direction.

Images