Middle fuselage structure of large-size low-speed wind tunnel turboprop aircraft test model and design method thereof

Abstract

The invention belongs to the technical field of airplane wind tunnel test model design, and discloses a middle fuselage structure of a large-size low-speed wind tunnel turboprop airplane test model and a design method thereof, the middle fuselage structure adopts a composite design of combining an internal steel skeleton and an external aluminum alloy cover plate, and the internal steel skeleton is made of 30CrMnSiA alloy steel and serves as a main bearing structure; the outer aluminum alloy cover plate is made of 7075 aluminum alloy, and the aerodynamic shape of the middle fuselage is formed. A structure for installing wind tunnel test equipment such as a slip flow test air bridge is arranged on the internal steel framework, and the problems that the internal space of a traditional large-size middle fuselage is small, and the equipment is difficult to install are solved. Meanwhile, the method further comprises the optimal design of detachable upper and lower cover plates, a balance, a supporting rod connecting piece, a split type transition rectification bag and the like, and on the premise that the structural rigidity and strength and the test precision are guaranteed, the machining difficulty is greatly reduced, and the machining period and cost are greatly reduced. The method is suitable for manufacturing and testing the large-size low-speed wind tunnel turboprop aircraft test model.

Description

Technical Field

[0001] This invention belongs to the technical field of large-size low-speed wind tunnel aircraft test model design, specifically relating to the mid-fuselage structure and design method of a large-size low-speed wind tunnel turboprop aircraft test model. Background Technology

[0002] In conventional large-scale wind tunnel aircraft model design, the fuselage model is usually divided into the nose, mid-fuselage, and tail section. The mid-fuselage is mostly made of aluminum bars or thick plates, manufactured by machining the exterior to conform to the aerodynamic shape and hollowing out the interior to reduce weight. However, in the largest wind tunnel test section in China (8m×6m), the fuselage length of the aircraft model can reach 2m, and the maximum diameter is 0.6m to 0.8m. There is a lack of aluminum raw materials on the market that meet these dimensions, and special casting is often required to obtain the blanks, resulting in high processing difficulty, long cycle, and high cost.

[0003] In addition, as a load-bearing component, the mid-fuselage needs to have sufficient wall thickness to transmit the load between the nose and tail sections. This further results in a small internal space, making it difficult to install wind tunnel testing equipment such as air bridges required for slipstream testing, which limits the conduct of test projects and the integrity of data.

[0004] Therefore, there is an urgent need for a new mid-fuselage design method that can ensure structural strength, reduce weight, and improve test accuracy, while also being compatible with the installation of test equipment and reducing processing difficulty and cost. Summary of the Invention

[0005] The purpose of this invention is to provide a mid-fuselage structure and its design method for a large-size, low-speed wind tunnel turboprop aircraft test model, so as to solve the problems of difficult processing, long cycle, high cost and insufficient internal space in the prior art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a mid-fuselage structure for a large-size, low-speed wind tunnel turboprop aircraft test model, comprising: The internal steel frame is made of 30CrMnSiA alloy steel and serves as the main load-bearing structure of the mid-fuselage. The external aluminum alloy cover, made of 7075 aluminum alloy, covers the outside of the internal steel frame, forming the aerodynamic shape of the mid-fuselage. The internal steel frame is equipped with structures for mounting wind tunnel testing equipment, particularly air bridges for slipstream testing.

[0007] As a further technical solution of the present invention: the internal steel frame includes a front connecting piece for the balance, a rear mounting stop for the middle fuselage, and connecting steel plates on both sides of the middle fuselage connecting the two. The front connecting piece for the balance has round stops at both ends for docking with the front and rear fuselage. Weight-reduction slots are provided on the connecting steel plates on both sides.

[0008] As a further technical solution of the present invention: the external aluminum alloy cover plate includes left and right side cover plates of the middle fuselage, a front cover plate, and upper side cover plates. The left and right side cover plates are 10mm thick, and reinforcing ribs are provided in the middle to prevent deformation.

[0009] As a further technical solution of the present invention, the structure also includes: The detachable upper and lower cover plates are located near the support rods on the middle of the machine body, with a gap reserved between their inner holes and the support rods to avoid interference; A holeless cover plate, used to replace a perforated cover plate, to close the opening when not supported; The balance and support rod connector is a rectangular alloy steel part that connects the fixed end of the balance to the web support rod, and can also connect the diagonal support rod and the mirror support rod at the same time. The transition fairing is located between the wing and the mid-fuselage and is composed of four detachable cover plates: front, rear, left, and right.

[0010] As a further technical solution of the present invention: the left and right sides of the front rectifier cover plate are fixed to the connecting steel plates on both sides of the middle fuselage; The left and right sides of the rear rectifier cover are fixed to the upper cover of the middle fuselage; The left and right rectifier cover plates are fixed to the wing, and their mounting surfaces fit the shape of the wing.

[0011] Secondly, the present invention provides a mid-fuselage design method for a large-size low-speed wind tunnel turboprop aircraft test model, comprising the following steps: Design and construct the internal steel frame using 30CrMnSiA alloy steel, and plan the installation locations for the wind tunnel testing equipment; Design and manufacture the external aluminum alloy cover plate, using 7075 aluminum alloy, to form an aerodynamic shape; Install and fix the outer cover plate onto the internal steel frame; Design and install the balance and strut connectors, removable upper and lower cover plates, and transition rectifier package; Simulation software was used to verify the stiffness and strength of the structure to ensure compliance with GJB 180A-2006 "Design Guidelines for Low-Speed ​​Wind Tunnel Aircraft Models".

[0012] As a further technical solution of the present invention: a balance and a support rod connector are designed and installed between the fixed end of the balance and the abdominal support rod; Design and install detachable upper and lower cover plates in the area near the support rod on the middle body, and leave a gap between the inner hole of the cover plate and the support rod; Design and install a transition fairing in the connection area between the wing and mid-fuselage.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention adopts a composite structure of steel frame and aluminum cover plate, which reduces weight and improves test accuracy while ensuring strength; 2. The invention has ample internal space, allowing for the installation of testing equipment such as air bridges, thus expanding testing capabilities; 3. The modular and split design of this invention significantly reduces processing difficulty, shortens the cycle time, and saves costs; 4. The structural rigidity of this invention has been verified by simulation and meets the safety standards for wind tunnel testing.

[0014] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall assembly of the fuselage components in this invention; Figure 2 This is a schematic diagram of the internal steel frame structure; Figure 3 This is a schematic diagram of the external aluminum alloy cover plate structure; Figure 4 This is a schematic diagram of the upper and lower cover plates of the fuselage. Figure 5 A schematic diagram of the connection between the balance and the support rod; Figure 6 This is a schematic diagram of the transition rectifier package structure; Figure 7 A schematic diagram of the structure for installing an air bridge in the middle fuselage. Detailed Implementation

[0016] 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.

[0017] 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.

[0018] 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.

[0019] The following is in conjunction with the appendix Figure 1-7 The embodiments of the present invention will be described in detail below.

[0020] Example 1 like Figure 1 As shown, the fuselage assembly of this invention adopts a composite structure of an internal steel frame and an external aluminum alloy cover plate. The internal steel frame is made of 30CrMnSiA alloy steel and includes a front connecting part for the balance, a rear mounting stop for the fuselage, and connecting steel plates on both sides. Figure 2 The connecting steel plates on both sides have weight-reduction slots to reduce weight.

[0021] The external aluminum alloy cover is made of 7075 aluminum alloy and includes left and right side covers, a front cover, and top side covers. Figure 3 The left and right cover plates are 10mm thick, with reinforcing ribs in the middle, and screw holes for connection to the steel frame are arranged on the surface.

[0022] To accommodate the downward-sloping abdominal support strut, removable upper and lower cover plates are installed near the strut on the middle of the machine body. Figure 4 The inner hole and the support rod are reserved with a 7mm gap, and a holeless cover plate is provided for sealing.

[0023] The fixed end of the balance is connected to the balance and the support rod ( Figure 5 It is connected to the support rod. The connector is a rectangular alloy steel block and can connect both the diagonal brace and the mirror support rod.

[0024] A transition fairing is provided between the wing and the mid-fuselage. Figure 6 It is divided into four parts: front, back, left, and right, which facilitates installation and maintenance.

[0025] This invention features a pre-installed mounting structure on the internal steel frame of the fuselage, allowing for the installation of wind tunnel testing equipment such as air bridges. Figure 7 This meets the requirements of slipstream testing.

[0026] Finally, the overall structure was subjected to a stiffness and strength analysis using simulation software to ensure that its safety factor met the requirements of GJB 180A-2006.

[0027] Example 2 This embodiment uses the mid-fuselage design of a certain type of turboprop aircraft wind tunnel test model as an example, but the application of the present invention is not limited to this specific model.

[0028] I. Overall Structural Design Reference Figure 1 The fuselage assembly of this invention adopts a composite structure of "internal load-bearing frame + external aerodynamic skin". The overall structure is approximately 2.0 meters long and has a maximum diameter of approximately 0.7 meters, making it suitable for 8m×6m large low-speed wind tunnel test sections.

[0029] The internal load-bearing frame (i.e., the internal steel frame) is made of 30CrMnSiA high-strength alloy steel and serves as the main load-bearing frame of the entire mid-fuselage, responsible for transmitting test loads from the nose, wings, and tail section. The external aerodynamic skin (i.e., the external aluminum alloy cover) is made of 7075-T6 aviation aluminum alloy, accurately replicating the theoretical aerodynamic shape of the aircraft's mid-fuselage, with a surface roughness of Ra1.6 or less, meeting the requirements of wind tunnel testing for model surface quality.

[0030] II. Detailed Structure of the Internal Steel Frame like Figure 2 As shown, the internal steel frame is welded together from the following main components: The front connector of the balance is located at the very front of the frame and is a ring-shaped forging structure. Its front end is machined with a precision circular stop of Φ400H7 / g6 for positioning and connection with the head section model; the rear end is also machined with a circular stop of the same precision for connection with the middle part of the frame.

[0031] The rear mounting stop of the middle body is located at the rear end of the frame. Its structure is similar to that of the front connector. The rear mounting stop is used to connect with the tail section model.

[0032] Two steel plates are connected to the sides of the fuselage, symmetrically arranged on the left and right sides of the frame. Each steel plate measures approximately 1800mm × 500mm × 15mm (length × height × thickness), and is laser-cut and then milled to the final dimensions. The upper part of the steel plate is connected to the front connector of the balance, and the lower part is connected to the rear mounting stop through bevel welds, forming a stable frame structure.

[0033] To reduce the weight of the frame while maintaining rigidity, regularly arranged weight-reducing slots were designed in the non-critical load-bearing areas (middle and lower parts) of the two connecting steel plates. The slots are oblong in shape, 30mm wide, and a 50mm wide reinforcing rib is retained between adjacent slots. Finite element analysis verified that this weight-reduction design can reduce the frame weight by approximately 25%, while the overall bending stiffness decreases by less than 5%.

[0034] On the inner side of the connecting steel plate on the right (the side facing the center of the frame), there is a specially designed area for the installation interface of wind tunnel testing equipment. This area includes: Two rows of M8 threaded mounting holes, 50mm apart, are used to install the support rails for the air bridge; Four Φ12 locating pin holes are used for precise initial positioning of the air bridge; A set of aviation socket mounting plates for centralized routing and connection of test cables.

[0035] III. Detailed Design of External Aluminum Alloy Cover Plate External aluminum alloy cover assembly such as Figure 3 As shown, it includes the following blocks: Left and right side covers of the mid-fuselage: Each cover plate is milled from a single piece of 7075-T6 aluminum alloy sheet, with a thickness of 10mm, and its shape is CNC machined according to the theoretical profile.

[0036] The inner side of the cover plate (the surface in contact with the steel frame) is provided with a crisscrossing grid of reinforcing ribs, with ribs 8mm high and 5mm wide, and the grid size is approximately 150mm × 150mm. This design effectively suppresses deformation during processing and testing while ensuring the rigidity of the cover plate.

[0037] The cover plate has Φ6.6 through holes spaced 80mm apart around its perimeter. These holes are used to mate with threaded holes on the steel frame and are connected using M6×1.0 grade 12.9 high-strength screws. All connection holes are designed with countersunk recesses to ensure that the screw heads do not protrude from the pneumatic surface.

[0038] Front cover of mid-fuselage: It is an arc-shaped curved surface component that covers the outside of the front connector of the balance.

[0039] It is fixed to the front connector of the balance by 24 M5 screws evenly distributed in a circular direction.

[0040] The front end is equipped with a positioning step and a sealing groove for docking with the head model.

[0041] Top two side covers of the fuselage: One piece on each side, symmetrically placed, covering the upper part of the skeleton.

[0042] The inner side has an installation edge, which is connected to the steel frame and the left and right side cover plates by screws.

[0043] An opening is provided in the rear area for the installation of the transition rectifier package.

[0044] All the joints between the cover plates are designed with a stepped overlap structure, with the front plate covering the rear plate to ensure unidirectional airflow and reduce interference with the test flow field. The gap between the plates is controlled within 0.1 mm.

[0045] IV. Design of a dedicated cover plate for the support pole area For the model which uses a downward-sloping bracing method (with the support rod at a 45° angle to the vertical), a cover plate assembly was specifically designed for the support rod area, such as... Figure 4 As shown.

[0046] Perforated upper cover plate and perforated lower cover plate: It is installed in the area where the support rod passes through the middle fuselage.

[0047] The cover plate has a Φ120mm through hole machined in the center for the support rod to pass through.

[0048] The single-sided gap between the inner wall of the through hole and the outer surface of the support rod is designed to be 7mm. This value has been verified by wind tunnel tests, which can ensure the freedom of movement of the support rod without causing significant airflow leakage due to excessive gap.

[0049] The cover plate is connected to the surrounding cover plates by eight quick-release latches, which facilitates quick operation when installing and removing the support rod.

[0050] Hole-free top cover and hole-free bottom cover: The dimensions are exactly the same as the perforated cover, but there is no central through hole.

[0051] Used to replace perforated covers, it can maintain the integrity and aerodynamic smoothness of the fuselage shape when the test does not use the ventral support method or when certain specific tests are conducted.

[0052] V. Balance and Support Rod Connection System like Figure 5 As shown, a special balance and support rod connector is provided between the balance and the support rod. This part is made of 30CrMnSiA alloy steel through integral forging and machining.

[0053] Its main functions and features are as follows: Structural form: It is a cuboid structure with dimensions of approximately 300mm×150mm×100mm, and has complex weight-reducing cavities and reinforcing ribs inside.

[0054] Connection interface: The upper surface is equipped with an interface for connection to the fixed end flange of the balance, which is fixed with 12 M10 screws and coaxiality is ensured with Φ16 locating pins.

[0055] The lower surface is provided with a tapered sleeve interface for connection with the 45° diagonal brace, with a taper of 1:10.

[0056] Rear side: Features a flat flange interface for connection to a vertical mirror support (used to simulate a tail brace).

[0057] Load transfer: This connector has been optimized by finite element design and can effectively decompose and transfer the pneumatic load measured by the balance to the two rods. It can withstand a load combination of axial force of 50kN and bending moment of 2kN·m.

[0058] VI. Wing-Fuselage Transition and Rectification Structure To address the airflow separation issue at the wing-fuselage junction, a separate transition fairing was specifically designed, such as... Figure 6 As shown.

[0059] The rectifier pack consists of four independent components: Front fairing cover: one on each side, with the front end fitting flush with the leading edge of the wing and the rear end fixed to the mounting brackets at the front of the connecting steel plates on both sides of the mid-fuselage by screws. The cover surface smoothly transitions with the wing and fuselage surfaces.

[0060] Aft fairing cover: one on each side, the front end is fixed to the rear of the wing, and the rear end is fixed to the rear edge of the cover above the mid-fuselage with screws. The cover has sufficient space inside to hide protrusions such as wing mounting bolts.

[0061] Left and right fairing cover plates: one each, located below the junction of the wing and fuselage. Their mounting surfaces are CNC machined to precisely fit the lower surface of the wing and connected to the wing structure via multiple rows of screws.

[0062] All fairing covers are made of 7075 aluminum alloy, 3mm thick, and have reinforcing ribs on the inside. This modular design allows for a more rational installation sequence, facilitates wing assembly and disassembly, and reduces the machining difficulty of individual parts.

[0063] VII. Wind Tunnel Testing Equipment Integration like Figure 7 As shown, a slipstream test air bridge system is specifically integrated on the right side of the internal steel frame: Support structure: Two high-strength aluminum alloy guide rails are fixed to the mounting interface of the steel frame by bolts. The guide rails are 1.5 meters long and have T-slots on the upper surface.

[0064] Air bridge body: A hollow bridge structure made of composite materials, allowing for airflow as required for the test. The air bridge is connected to the guide rail via a slider, and its position can be adjusted along the fuselage axis.

[0065] Drive and measurement system: It integrates a small electric actuator for angle of attack adjustment and a built-in micro pressure sensor array for airflow parameter measurement.

[0066] Cable Management: All power and control cables are routed centrally through cable trays inside the steel frame and eventually converge at the multi-core aviation connector at the front of the mid-fuselage to achieve rapid connection with the wind tunnel data acquisition system.

[0067] This integrated design increases the utilization rate of the internal space of the fuselage by about 40%, providing ample installation space for various testing equipment.

[0068] VIII. Structural Strength Verification and Testing After completing the detailed design, the overall structure was checked for stiffness and strength using finite element analysis software. Load conditions: Based on GJB 180A-2006 "Design Criteria for Low-Speed ​​Wind Tunnel Aircraft Models", aerodynamic loads at a maximum test wind speed of 80 m / s and a safety factor of 2.0 were considered.

[0069] Analysis results: The maximum stress occurs in the area where the steel frame connects to the support rod, with a value of 285 MPa, which is lower than the yield strength of 30CrMnSiA material (≥835 MPa). The maximum deformation of the fuselage under maximum load is 0.8 mm, which is located in the middle section and meets the stiffness requirements of the aeroelastic test. The first natural frequency is 126Hz, which is much higher than the excitation frequency that may be caused by the wind tunnel, thus avoiding the risk of resonance.

[0070] Experimental verification: A static test was conducted on a 1:1 verification specimen. When the load was increased to 1.5 times the design load, no permanent deformation occurred in the structure. The measured deformation was within 10% of the finite element prediction.

[0071] IX. Manufacturing and Assembly Process The manufacturing and assembly of the fuselage of this invention are carried out according to the following main steps: Steel frame manufacturing: blanking → milling connecting steel plates → machining balance connecting parts → welding assembly → heat treatment to relieve stress → precision machining of all mating surfaces and stops → surface rust prevention treatment.

[0072] Aluminum alloy cover plate manufacturing: Thick plate pre-stretching treatment → CNC rough machining → Aging treatment → CNC precision machining → Hand grinding and polishing → Anodizing treatment (hard anodizing, thickness 25μm).

[0073] Component assembly: Install the steel frame onto a dedicated assembly frame; Install testing equipment such as air bridge guide rails; Assemble the left and right side covers, front and rear covers, and top cover in sequence; Cover plate for the support rod installation area; Install a transition rectifier package; Install the balance connector and support rod interface.

[0074] Final inspection: Coordinate measuring machine to check the outline (deviation ±0.1mm); laser tracker to check the positional accuracy of each interface; airtightness check (for cavities that need to be sealed).

[0075] X. Summary of Technological Advantages Compared with the prior art, the design solution provided in this embodiment has the following significant advantages: The problem of obtaining large-sized raw materials has been solved: the split design avoids the use of hard-to-obtain ultra-large aluminum billets.

[0076] Achieving a balance between lightweight and high rigidity: the steel-aluminum composite structure reduces weight by about 30% and increases rigidity by about 15% compared to integral aluminum parts.

[0077] It expands testing capabilities: ample internal space supports the integration of various testing equipment such as air bridges, meeting the complex needs of modern wind tunnel testing.

[0078] Improved manufacturing economics: modular processing reduces the need for large CNC equipment, shortens the processing cycle by about 40%, and reduces manufacturing costs by about 35%.

[0079] Easy to maintain and modify: The modular design allows for individual replacement when parts are damaged, and also makes it easy to adjust the layout of internal equipment according to test requirements.

[0080] Example 3 This invention discloses a new design method for a mid-fuselage model to solve the problems of high difficulty, long cycle and high cost in the manufacturing of fuselage in large-size wind tunnel aircraft test models. At the same time, it can meet the installation requirements of wind tunnel test equipment such as air bridges required for turboprop aircraft slipstream tests.

[0081] The technical solution of this invention is: The fuselage components of the model employ an internal steel frame and an external aluminum alloy cover structure. The internal steel frame, made of 30CrMnSiA alloy steel, serves as the primary load-bearing structure. The external aluminum alloy cover, made of 7075 aluminum alloy, reflects the aerodynamic shape of the fuselage. Wind tunnel testing equipment, such as air bridges, is installed within the internal steel frame. Upper and lower cover plates are designed near the struts on the fuselage to meet the model's support requirements. A balance and strut connector is designed between the balance and the struts. A transition rectifier package is also added between the wing and the mid-fuselage. For ease of installation and fabrication, the rectifier package is divided into four parts: front, rear, left, and right.

[0082] The advantages of this invention are: The purpose of this invention is to provide a novel design method for large-scale aircraft fuselage models, addressing the challenges of complex manufacturing processes, long lead times, high costs, limited internal space within the fuselage, and the inability to install wind tunnel testing equipment such as air bridges required for slipstream testing. Furthermore, this method reduces model weight and improves the accuracy of experimental data measurement while maintaining the fuselage's rigidity and strength.

[0083] The following is in conjunction with the attached diagram. Figures 1 to 7 The embodiments of the present invention will be described in detail below.

[0084] The fuselage assembly of a certain turboprop aircraft model adopts an internal steel frame and an external aluminum alloy cover structure. The internal steel frame is the main load-bearing structure and is made of 30CrMnSiA alloy steel. The surface of the external aluminum alloy cover reflects the aerodynamic shape of the fuselage and is made of 7075 aluminum alloy. This design ensures the rigidity and strength of the fuselage while reducing the model's weight and improving the measurement accuracy of experimental data. The internal steel frame structure of the fuselage includes the front connector of the balance, the rear mounting stop of the fuselage, and the connecting steel plates on both sides of the fuselage. The overall design of the fuselage assembly in the model is as follows: Figure 1 As shown.

[0085] The front connector of the balance has a pre-drilled circular stop for installation with the front fuselage components, and a similar circular stop is provided at the rear for installation with the rear fuselage components. The front connector and the rear mounting stop of the balance are connected by connecting steel plates on both sides of the middle fuselage. To reduce the overall weight of the middle fuselage steel frame structure, the connecting steel plates on both sides are slotted to reduce weight. Figure 2 As shown.

[0086] The model's external aluminum alloy cover structure includes left and right side covers of the central fuselage, a front cover of the central fuselage, and two upper side covers of the central fuselage. The left and right side covers are 10mm thick. To prevent deformation during manufacturing, reinforcing ribs are designed in the middle of the covers. Screw holes for connection to the internal steel frame of the central fuselage are located on the left and right side covers. Similarly, the front cover and the upper side covers are connected to the front connector of the balance and the rear mounting brackets of the central fuselage, respectively. The model's external aluminum alloy cover structure is as follows: Figure 3 As shown.

[0087] To meet the requirement of using a downward-sloping strut support for the model, upper and lower cover plates are designed near the struts on the fuselage. These cover plates must be removed before installing the struts to ensure no collision between the struts and cover plates during installation. The cover plates are then installed to the fuselage after the struts are installed. To avoid interference during testing due to insufficient clearance between the cover plates and struts, a 7mm gap is reserved around the inner holes of the upper and lower cover plates on the fuselage and the struts. Additionally, a non-perforated cover plate is designed to replace the perforated cover plate; this non-perforated cover plate eliminates the inner hole, such as... Figure 4 As shown.

[0088] The fixed end of the balance needs to connect to the support rod. The transition connector designed between the balance and the support rod is called the balance-support rod connector. This part is a rectangular alloy steel component. The connecting flange at the fixed end of the balance connects to the rear balance-support rod connector. The balance-support rod connector can simultaneously connect to the lower diagonal support rod and the upper mirror support rod. Figure 5 As shown.

[0089] In addition, a transition fairing component was designed between the wing and the mid-fuselage. For ease of installation and fabrication, the fairing is divided into four parts: front, rear, left, and right. The left and right sides of the front fairing cover are directly fixed to the connecting steel plates on both sides of the mid-fuselage. The left and right sides of the rear fairing cover are directly fixed to the cover plate on top of the mid-fuselage. The left and right fairing covers need to be fixed to the wing. The mounting surfaces of the screw holes fit snugly against the shape of the wing sides. The transition fairing between the fuselage and the wing is as follows: Figure 6 As shown.

[0090] This invention proposes a design method for a mid-fuselage model. Through the described process, the mid-fuselage model is designed in sections, reducing processing costs and improving efficiency compared to traditional sheet metal milling. It also solves the problems of limited internal space and difficulty in installing wind tunnel testing equipment within the mid-fuselage. A diagram of the air bridge structure for installing the mid-fuselage is shown below. Figure 7 Simulation software was used to verify the stiffness and strength of the model design, ensuring that the safety factor of the model design meets the requirements of GJB 180A-2006 "Design Guidelines for Low-Speed ​​Wind Tunnel Aircraft Models".

[0091] Thus, the objective of this invention has been achieved.

[0092] 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 mid-fuselage structure for a large-size, low-speed wind tunnel turboprop aircraft test model, characterized in that, include: The internal steel frame, which serves as the main load-bearing structure of the fuselage, is made of 30CrMnSiA alloy steel. An external aluminum alloy cover plate covers the outside of the internal steel frame, forming the aerodynamic shape of the fuselage. Its material is 7075 aluminum alloy. The internal steel frame is provided with an installation structure for mounting wind tunnel testing equipment, which includes an air bridge for slipstream testing.

2. The mid-fuselage structure according to claim 1, characterized in that: The internal steel frame includes a front connector for the balance, a rear mounting stop for the middle fuselage, and connecting steel plates on both sides of the middle fuselage connecting the two. The front and rear ends of the balance front connector are respectively provided with circular stops for docking with the front fuselage component and the rear fuselage component.

3. The mid-fuselage structure according to claim 2, characterized in that: Weight reduction slots are provided on the connecting steel plates on both sides of the fuselage.

4. The mid-fuselage structure according to claim 1, characterized in that: The external aluminum alloy cover plate includes the left and right side cover plates of the middle fuselage, the front cover plate of the middle fuselage, and the two side cover plates above the middle fuselage; The thickness of the left and right side cover plates is 10mm, and a reinforcing rib is provided in the middle of them.

5. The mid-fuselage structure according to claim 1, characterized in that, Also includes: An upper cover plate and a lower cover plate are disposed in the area near the support rod on the middle body, and the upper cover plate and the lower cover plate are detachably installed on the middle body; A gap is reserved between the inner hole of the upper and lower cover plates and the support rod.

6. The mid-fuselage structure according to claim 5, characterized in that: It also includes a holeless cover plate for replacing the upper or lower cover plate to close the inner hole in a non-supported state.

7. The mid-fuselage structure according to claim 1, characterized in that, Also includes: The balance and support rod connector is located between the fixed end of the balance and the web support rod. It has a rectangular structure and is made of alloy steel. The balance and support rod connector can be connected to both the diagonal brace and the mirror support rod simultaneously.

8. The mid-fuselage structure according to claim 1, characterized in that, Also includes: A transition rectifier is located in the connection area between the wing and the mid-fuselage; The transition rectifier is composed of four detachable parts: a front rectifier cover, a rear rectifier cover, a left rectifier cover, and a right rectifier cover.

9. The mid-fuselage structure according to claim 8, characterized in that: The left and right sides of the front rectifier cover are fixed to the connecting steel plates on both sides of the middle fuselage; The left and right sides of the rear rectifier cover are fixed to the upper cover of the middle fuselage; The left and right rectifier cover plates are fixed to the wing, and their mounting surfaces fit the shape of the wing.

10. A method for designing the mid-fuselage of a large-size, low-speed wind tunnel turboprop aircraft test model, characterized in that, Includes the following steps: The internal steel frame was designed and constructed. The internal steel frame was made of 30CrMnSiA alloy steel and served as the main load-bearing structure of the middle fuselage. The structure for installing wind tunnel testing equipment was planned on it. Design and manufacture an external aluminum alloy cover plate made of 7075 aluminum alloy to cover the internal steel frame and form the aerodynamic shape of the fuselage. The external aluminum alloy cover plate is installed and fixed onto the internal steel frame; Design and install the balance and support rod connector between the fixed end of the balance and the belly support rod; Design and install detachable upper and lower cover plates in the area near the support rod on the middle body, and leave a gap between the inner hole of the cover plate and the support rod; Design and install a transition fairing in the connection area between the wing and the mid-fuselage; Simulation software was used to verify the stiffness and strength of the mid-fuselage structure to ensure that its safety factor meets the requirements of GJB 180A-2006 "Design Guidelines for Low-Speed ​​Wind Tunnel Aircraft Models"; The wind tunnel testing equipment includes an air bridge for slipstream testing.

Images