Composite landing gear for a vertical take-off and landing aircraft and method of forming the same

Abstract

The application discloses a composite landing gear for a vertical take-off and landing aircraft and a forming method thereof; the method comprises the following steps: S1, according to the structural shape of the landing gear, a hollow-structure metal frame 1 is made through 3D printing profiling; the surface of the metal frame is cleaned and is ready for use; S2, the two end openings of the metal frame are sealed, and a composite material prepreg is laid on the surface of the metal frame; meanwhile, cold extraction pre-compaction and hot pre-compaction are carried out during the laying process of the composite material prepreg; S3, after the laying of the composite material prepreg is completed, vacuum extraction is carried out for compaction, and then the metal frame is put into a hot pressing tank for solidification; S4, after the solidification, the material used for compaction is removed, the sealing material at the two ends of the metal frame is removed, and a plurality of connecting holes used for being connected with the aircraft body are processed at one end, so that the composite material landing gear is obtained. The forming method provided by the application adopts integral forming of the internal metal frame and the composite material part with an external special-shaped structure, so that the risk of assembly is reduced, and the assembly difficulty is reduced.

Description

Technical Field

[0001] This invention relates to the field of composite material molding technology, specifically to a composite material landing gear for vertical takeoff and landing aircraft and its molding method. Background Technology

[0002] Landing gear is a critical component of aircraft, used to support the aircraft's weight, withstand corresponding loads, and ensure safe flight during ground operations, takeoff, and landing. Statistics show that landing gear-related accidents account for more than two-thirds of all civil aircraft structural accidents. Improving the material properties of landing gear and developing new manufacturing technologies will extend its service life, making it one of the fundamental, common, and key technologies in the aviation industry. With technological innovation, aviation companies are demanding increasingly higher specific strength from aircraft materials. Composite materials and titanium alloys, due to their high specific strength, are in greater demand in the aviation industry, leading to continuous changes in the selection of landing gear materials.

[0003] Currently, landing gear is mainly divided into three types: leaf spring landing gear, strut rocker arm landing gear, and skid landing gear. Among them, leaf spring landing gear has the advantages of high stability, strong integrity, and ease of layout, conversion, and maintenance, making it an ideal structural form for lightweight UAVs. However, current leaf spring landing gear development uses a glass fiber and carbon fiber hybrid layup design, which has low interlayer strength and poor impact resistance; the cross-section of leaf spring landing gear often adopts a hollow, runway-shaped design, resulting in low longitudinal displacement and limited load-bearing capacity.

[0004] The strut-rocker landing gear structure is relatively complex, with joints subjected to significant stress, resulting in substantial wear during loading and inconvenient maintenance. Skid-type landing gear is commonly used on light helicopters. It mainly consists of two slides and two arched beams. It cannot move on the ground and requires trolleys for towing. Due to its inherent structural limitations, to ensure lightweight characteristics, the slides and arched beams are typically manufactured separately and connected using metal components, thus posing a significant risk of damage from impact loads. Summary of the Invention

[0005] The purpose of this invention is to address the current problems faced by landing gear by providing a novel composite material landing gear for vertical take-off and landing aircraft and its molding method.

[0006] This invention is achieved through the following technical solution:

[0007] A method for molding a composite material landing gear for a vertical takeoff and landing aircraft, characterized in that the method includes the following steps:

[0008] S1. Tooling preparation: Based on the structural shape of the landing gear, a hollow metal frame 1 is fabricated using 3D printing; the surface of the metal frame is cleaned and ready for use.

[0009] S2. Prepreg laying: Seal the openings at both ends of the metal frame, and then lay composite prepreg on the surface of the metal frame; at the same time, cold pre-compacting and hot pre-compacting are carried out during the laying process of composite prepreg.

[0010] S3. After all the prepregs of the composite materials have been laid, vacuum compaction is performed, and the materials are then placed in an autoclave for curing.

[0011] S4. After curing, remove the material used for compaction, remove the sealing material at both ends of the metal frame, and machine several connection holes at one end for connection with the aircraft fuselage to obtain the composite material landing gear.

[0012] Specifically, the composite material landing gear of this invention is manufactured using a one-piece molding method. It is mainly used in vertical takeoff and landing aircraft and can consist of three composite material landing gears connected to the aircraft fuselage to provide support for the aircraft on the ground (the three landing gears form a three-point support). The internal structure of the composite material landing gear uses a metal frame (aluminum alloy) for support.

[0013] In this invention, the metal frame acts as a core mold. After molding, the metal frame serves as the internal support frame for the composite landing gear and does not require demolding.

[0014] The composite material landing gear of the present invention is an irregularly shaped structural component, and the corresponding metal frame is also an irregularly shaped structural component.

[0015] Unlike the composite material molding method of ordinary parts, the composite material landing gear of this invention adopts an internal aluminum alloy frame and an external composite material integrally molded, and the internal aluminum alloy frame is a cavity structure.

[0016] Furthermore, a method for forming a composite landing gear for a vertical takeoff and landing (VTOL) aircraft: the metal frame in step S1 is made of 7-series aluminum alloy, and the metal frame is manufactured by 3D printing; the surface of the metal frame is cleaned with acetone. The metal frame is manufactured using 3D printing, ensuring that the print itself is airtight, and then the mounting operation is performed on the basis of this metal frame.

[0017] Furthermore, a method for forming a composite landing gear for a vertical takeoff and landing aircraft: the wall thickness of the metal frame in step S1 is 1.0 to 2.0 mm.

[0018] Furthermore, a method for molding a composite landing gear for a vertical takeoff and landing aircraft: Step S2, a baffle is provided at one end of the metal frame to seal its opening, and the opening at the other end is sealed by a sealing strip.

[0019] Specifically, in order to facilitate the bag making of vacuum bags during the subsequent vacuum compaction process, the metal frame of the part itself is used as a tooling. At the same time, in order to ensure the bag making area of ​​the part's vacuum bags, a baffle is added to the end of the metal frame (the size of the baffle is larger than the cross-sectional area of ​​the end of the metal frame). The baffle serves as both the bag making area and the positioning reference required for processing and making the connecting holes.

[0020] Furthermore, a method for forming a composite landing gear for a vertical takeoff and landing aircraft: Step S2, after every 3 to 5 layers of composite prepreg are laid, a vacuum bag is placed on the outside of it for cold pre-compaction (cold pre-compaction means vacuuming at room temperature).

[0021] Wherein: the pressure of cold pre-compaction is 0.06 to 0.1 MPa; when setting up the vacuum bag, flexible material is set at the corners of the metal frame along the length direction of the metal frame.

[0022] Specifically, when manufacturing vacuum bags, flexible material is placed at the rounded corners of the metal frame. This flexible material allows for uniform pressure distribution during vacuum compaction, ensuring even pressure distribution and preventing wrinkles. Sealing strips or similar materials can be used as the flexible material.

[0023] Furthermore, a method for forming a composite material landing gear for a vertical takeoff and landing aircraft: Step S2, hot pre-compacting is performed every 15 to 20 layers of composite material prepreg;

[0024] The pressure for hot precompaction is 0.6±0.05MPa. The hot precompaction process is as follows: a vacuum bag is used to draw a vacuum, and the sample is placed in a hot autoclave with a vacuum degree of not less than 85KPa. The temperature is raised to 55-65℃ at a heating rate of 1-2℃ / min and held for 30-35min. Then, the temperature is lowered to no more than 30℃ at a cooling rate of no more than 2℃ / min, and the sample is depressurized and removed from the autoclave.

[0025] Specifically, the pressure here is provided by vacuum bags and autoclaves.

[0026] Furthermore, a method for molding composite landing gear for vertical takeoff and landing aircraft: Step S3, after all the composite prepreg is laid, a vacuum bag is used to evacuate the material, and it is simultaneously placed in an autoclave with a vacuum degree of not less than 85 kPa. The temperature is increased to 75-85°C at a heating rate of 1-2°C / min, held for 60-65 min, and then increased to 115-125°C and held for 90-95 min. Then, the temperature is decreased to not more than 60°C at a cooling rate of not more than 2°C / min, the pressure is released from the autoclave, and curing is completed. The curing pressure is 0.6 ± 0.05 MPa.

[0027] Furthermore, a method for molding a composite material landing gear for a vertical takeoff and landing aircraft: Step S4, after curing, remove the vacuum bag used for compaction, remove the baffles and sealing strips at both ends of the metal frame respectively, and process a connection hole for connection with the aircraft fuselage at the end near the baffle, perform non-destructive testing, and obtain the composite material landing gear.

[0028] The difficulties in the molding process of this invention are: (1) The internal metal frame is made of 7-series aluminum alloy, which is difficult to manufacture. This invention is completed by 3D printing and welding. After welding, it is necessary to ensure that the weld is undamaged and airtight to make vacuum bags possible; (2) The aluminum alloy metal frame with a wall thickness of 1-2mm needs to be verified. For this kind of irregular structure, it is necessary to verify that the aluminum alloy will not deform under cold pre-compaction; (3) It is necessary to verify a similar bag making method. By using the metal frame as a tool, the pressure of the autoclave inside and outside the metal frame is offset, thereby ensuring that the product does not deform during the curing process; (4) During the curing process of similar columnar structural parts, stress concentration points are prone to wrinkles. Therefore, this invention sets flexible materials when making vacuum bags to ensure uniform pressure transmission at the corresponding stress concentration points, avoid wrinkles, and ensure good part molding quality.

[0029] A composite material landing gear for a vertical takeoff and landing aircraft, characterized in that it is formed using the above-described molding method.

[0030] Furthermore, a composite material landing gear for a vertical takeoff and landing aircraft: the composite material landing gear includes: a hollow metal frame and a composite material wrapped around the outside of the metal frame; one end of the composite material landing gear is provided with a plurality of connection holes for connecting with the aircraft fuselage.

[0031] The beneficial effects of this invention are:

[0032] (1) The composite material landing gear manufactured by the present invention has composite material design for its parts, which ensures the required strength of the product while reducing the weight of the landing gear structure itself.

[0033] (2) The molding method provided by the present invention uses an internal metal frame and an external irregular structure composite material parts to be integrally molded, which reduces the risk of assembly and reduces the difficulty of assembly.

[0034] (3) The composite material landing gear formed by the present invention is an irregular structure. The molding process of the present invention solves the problem of difficult product molding. At the same time, the molding method of the present invention is simple and easy to operate. The present invention uses the original metal support frame in the composite material landing gear as the laying tool, which further reduces the required work, saves tooling costs, and is economical and convenient. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the composite material landing gear manufactured according to the present invention;

[0037] Figure 2 This is a schematic diagram of a baffle plate provided at the end of a metal frame in Embodiment 1 of the present invention;

[0038] Figure 3 This is a schematic diagram of the vacuum bag making process in the molding process of this invention.

[0039] The markings in the diagram are: 1. Metal frame, 2. Connecting hole, 3. Composite landing gear, 4. Baffle, 5. Flexible material, 6. Vacuum bag. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0041] In the description of this invention, it should be understood that the terms "upper," "lower," "left," "right," "top," and "bottom," etc., indicating orientation or positional relationships, are merely 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, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" and "second" may explicitly or implicitly include one or more of that feature. Moreover, the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein.

[0042] like Figure 1 As shown, the composite landing gear 3 is curved in two directions, resulting in a complex shape. Its total length is approximately 770mm. Internally, it uses a 1-2mm thick 7075 aluminum alloy frame 1 for auxiliary support, while externally, it is covered with composite material, which is then cured. Two connecting holes 2, approximately 30mm in diameter, are provided at one end of the composite landing gear for pins to pass through, supporting the overall fuselage weight. Metal holes at the other end of the landing gear are used to connect to the bottom metal boot, reducing wear on the composite landing gear.

[0043] Example 1

[0044] A method for molding a composite material landing gear for a vertical takeoff and landing aircraft, characterized in that the method includes the following steps:

[0045] S1. Tooling preparation: Based on the structural shape of the landing gear, design a hollow metal frame 1 (the metal frame is made of 7075 aluminum alloy); clean the surface of the metal frame 1 with acetone and set it aside; wherein: the wall thickness of the metal frame 1 is 1.0mm.

[0046] S2. Prepreg Laying: A baffle 4 is installed at one end of the frame 1 to seal the opening at this end. The opening at the other end is sealed with a sealing strip (e.g., Figure 2 As shown, the baffle 4 can serve as both the bag-making area when setting up the vacuum bag 6 and the positioning reference required for subsequent processing and making the connecting hole 2; then composite material (carbon fiber) prepreg is laid on the surface of the metal frame 1 (a total of 50 layers of prepreg are laid);

[0047] Note: When laying 5 layers of composite prepreg, a vacuum bag 6 should be placed outside the prepreg. When placing the vacuum bag 6, flexible material 5 (such as...) should be placed along the length of the metal frame 1 at the corners of the metal frame 1 (i.e., at the R-corner between the top and bottom surfaces of the metal frame). Figure 3 (As shown), then a vacuum is drawn to a pressure of 0.06 MPa at room temperature for cold pre-compaction; then the above cold pre-compaction process is repeated every 5 layers of prepreg; when the prepreg is laid to 20 layers, cold pre-compaction is performed first; then, ensuring that the vacuum bag form remains unchanged during the above cold pre-compaction process, a vacuum is drawn and the whole thing is sent into a thermostatic precipitator with a vacuum degree of not less than 85 kPa, at a pressure of 0.55 MPa, and at a heating rate of 2℃ / min, the temperature is raised to 65℃, held for 30 min, and then cooled to 30℃ at a cooling rate of 1℃ / min, and the pressure is released from the precipitator. After being removed from the precipitator, one hot pre-compaction is completed; then the above hot pre-compaction process is repeated every 20 layers of prepreg.

[0048] After all the S3 and 50-layer composite prepregs have been laid, a vacuum bag is used to evacuate the material, which is then placed in an autoclave with a vacuum of not less than 85 kPa. The temperature is increased to 85°C at a rate of 2°C / min under 0.55 MPa and held for 60 min. The temperature is then increased to 125°C and held for 90 min. Finally, the temperature is decreased to 60°C at a rate of 1°C / min, and the material is depressurized and removed from the autoclave to complete the curing process.

[0049] S4. After curing, remove the vacuum bag and flexible material used for compaction. 5. Remove the baffles 4 and sealing strips at both ends of the metal frame 1, and machine two connection holes 2 for connection with the aircraft fuselage at the end near the baffles 4. Perform non-destructive testing to obtain the composite landing gear 3 (the structure of the composite landing gear 3 is as follows). Figure 1 (As shown).

[0050] Example 2

[0051] A method for molding a composite material landing gear for a vertical takeoff and landing aircraft, characterized in that the method includes the following steps:

[0052] S1. Tooling preparation: Based on the structural shape of the landing gear, design a hollow metal frame 1 (the metal frame is made of 7075 aluminum alloy); clean the surface of the metal frame 1 with acetone and set it aside; wherein: the wall thickness of the metal frame 1 is 2.0mm;

[0053] S2. Prepreg Laying: A baffle 4 is installed at one end of the metal frame 1 to seal the opening at this end. The opening at the other end is sealed with a sealing strip (e.g., Figure 2As shown, the baffle 4 can serve as both the bag-making area when setting up the vacuum bag 6 and the positioning reference required for subsequent processing and making the connecting hole 2; then composite material (carbon fiber) prepreg is laid on the surface of the metal frame 1 (a total of 45 layers of prepreg are laid);

[0054] Note: When laying every 3 layers of composite prepreg, a vacuum bag 6 should be placed outside the prepreg. When placing the vacuum bag 6, flexible material 5 (such as...) should be placed along the length of the metal frame 1 at the corners of the metal frame 1 (i.e., the R-corner between the top and surface of the metal frame). Figure 3 (As shown), then a vacuum is drawn to a pressure of 0.1 MPa at room temperature for cold pre-compaction; then the above cold pre-compaction process is repeated every 3 layers of prepreg; when the prepreg is laid to 15 layers, cold pre-compaction is performed first; then, ensuring that the vacuum bag form remains unchanged during the above cold pre-compaction process, a vacuum is drawn and the whole thing is sent into a thermostatic precipitator with a vacuum degree of not less than 85 kPa, at a pressure of 0.65 MPa, and at a heating rate of 1 °C / min, the temperature is raised to 55 °C, held for 35 min, and then cooled to 25 °C at a cooling rate of 2 °C / min. The pressure is released and the material is removed from the precipitator, thus completing one hot pre-compaction; then the above hot pre-compaction process is repeated every 15 layers of prepreg.

[0055] After all the S3 and 45-layer composite prepregs have been laid, a vacuum bag is used to evacuate the material, and it is simultaneously placed in an autoclave with a vacuum degree of not less than 85 kPa. The temperature is increased to 75°C at a rate of 1°C / min under 0.65 MPa, and held for 65 min. Then the temperature is increased to 115°C and held for 95 min. Finally, the temperature is decreased to 50°C at a rate of 2°C / min, and the pressure is released from the autoclave to complete the curing process.

[0056] S4. After curing, remove the vacuum bag and flexible material used for compaction. 5. Remove the baffles 4 and sealing strips at both ends of the metal frame 1, and machine two connection holes 2 for connection with the aircraft fuselage at the end near the baffles 4. Perform non-destructive testing to obtain the composite landing gear 3 (the structure of the composite landing gear 3 is as follows). Figure 1 (As shown).

[0057] The above-described preferred embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of the invention. Any obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for molding composite material landing gear for vertical takeoff and landing aircraft, characterized in that, The method includes the following steps: S1. Tooling preparation: Based on the structural shape of the landing gear, design a hollow metal frame (1); clean the surface of the metal frame (1) and set it aside for use; S2, Prepreg laying: A baffle (4) is set at one end of the metal frame (1) to seal its opening, and the other end is sealed with a sealing strip. Then, composite material prepreg is laid on the surface of the metal frame (1). At the same time, cold pre-compaction and hot pre-compaction are carried out during the laying process of composite material prepreg. For every 3 to 5 layers of composite prepreg, a vacuum bag is placed on the outside for cold pre-compaction; the pressure of cold pre-compaction is 0.06 to 0.1 MPa; when setting the vacuum bag, flexible material (5) is placed at the corner of the metal frame (1) along the length direction of the metal frame (1). The process involves hot precompaction after every 15 to 20 layers of composite prepreg. The pressure for hot precompaction is 0.6 ± 0.05 MPa. The hot precompaction process is as follows: a vacuum bag is used to create an autoclave with a vacuum level of not less than 85 kPa. The temperature is increased to 55 to 65°C at a heating rate of 1 to 2°C / min and held for 30 to 35 minutes. Then, the temperature is reduced to no more than 30°C at a cooling rate of no more than 2°C / min, and the pressure is released before removing the material from the autoclave. S3. After all the prepregs of the composite material have been laid, a vacuum bag is used to evacuate the material, which is then placed in an autoclave with a vacuum level of not less than 85 kPa. The temperature is increased to 75–85°C at a rate of 1–2°C / min and held for 60–65 min. Then the temperature is increased to 115–125°C and held for 90–95 min. Finally, the temperature is decreased to no more than 60°C at a rate of no more than 2°C / min. The material is then depressurized and removed from the autoclave to complete the curing process. The curing pressure is 0.6 ± 0.05 MPa. S4. After curing, remove the material used for compaction, remove the sealing material at both ends of the metal frame (1), and process several connection holes (2) at one end for connection with the aircraft fuselage to obtain the composite landing gear (3).

2. The molding method for a composite material landing gear for a vertical takeoff and landing aircraft according to claim 1, characterized in that, The metal frame (1) mentioned in step S1 is made of 7-series aluminum alloy and is manufactured by 3D printing; the surface of the metal frame (1) is cleaned with acetone.

3. A method for molding a composite material landing gear for a vertical takeoff and landing aircraft according to claim 1 or 2, characterized in that, The wall thickness of the metal frame (1) mentioned in step S1 is 1.0 to 2.0 mm.

4. The molding method for a composite material landing gear for a vertical takeoff and landing aircraft according to claim 1, characterized in that, Step S4: After curing, remove the vacuum bag used for compaction, remove the baffles (4) and sealing strips at both ends of the metal frame (1), and process a connection hole (2) for connection with the aircraft fuselage at one end near the baffle (4). Perform non-destructive testing to obtain the composite material landing gear (3).

5. A composite material landing gear for a vertical takeoff and landing aircraft, characterized in that, It is formed by the molding method described in any one of claims 1 to 4.

6. A composite material landing gear for a vertical takeoff and landing aircraft according to claim 5, characterized in that, The composite landing gear (3) includes: a hollow metal frame (1) and a composite material wrapped around the outside of the metal frame (1); one end of the composite landing gear (3) is provided with a plurality of connection holes (2) for connecting with the aircraft fuselage.

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