Method for calculating aerodynamic characteristics of fuselage of modified helicopter

Abstract

The invention belongs to the field of aerodynamic design of helicopters, and provides a method for calculating aerodynamic characteristic data of a fuselage of a modified helicopter. The method comprises the following steps: emphatically paying attention to the aerodynamic configuration of a part with relatively large influence on a resistance coefficient, a pitching moment coefficient and a yaw moment coefficient in aerodynamic characteristic data of a helicopter fuselage; comparing the similarity between the aerodynamic configuration of each focused component and the aerodynamic configuration of the existing helicopter component one by one; according to similar analysis results of the components, preliminarily selecting a remodeling design helicopter fuselage aerodynamic characteristic data combination calculation mode and component aerodynamic characteristic calculation requirements; according to the similarity analysis result of the component and the aerodynamic characteristic calculation requirement of the component, the fuselage force measurement wind tunnel test result before modification is carded and analyzed; and correcting the calculation result of the fuselage force measurement wind tunnel test according to the difference of the components of the modified helicopter.

Description

Technical Field

[0001] The invention belongs to the field of helicopter aerodynamic design and proposes a method for calculating aerodynamic characteristic data of a modified helicopter fuselage. Background Art

[0002] During helicopter development, fuselage aerodynamic data serves as a design input for calculations of flight performance, flying qualities, flight loads, and rotor loads. Therefore, rapid and accurate data is essential in the early stages of helicopter model development. Currently, CFD and wind tunnel testing are the primary methods used to obtain this data. While CFD is relatively fast and can provide timely data based on design changes, it can only calculate a limited range of angles of attack and sideslip, resulting in relatively low accuracy and reliability. While wind tunnel testing can provide relatively accurate data for a wide range of angles of attack and sideslip, the design, fabrication, and assembly of the wind tunnel test model, followed by testing in the wind tunnel, are time-consuming. Summary of the Invention

[0003] Purpose of the Invention: This method, which uses a modified helicopter fuselage aerodynamic characteristics calculation method to obtain modified helicopter fuselage aerodynamic characteristics data, can save 95% of time and 85% of development costs compared to fuselage force measurement wind tunnel testing. It can also save 60% of time and 50% of development costs compared to fuselage aerodynamic characteristics CFD calculation methods. This will accelerate the development of modified helicopters and save helicopter development costs.

[0004] Technical solution:

[0005] A method for calculating aerodynamic characteristic data of a modified helicopter fuselage is provided, comprising:

[0006] Focus on the aerodynamic shape of the components that have the greatest impact on the drag coefficient, pitching moment coefficient and yaw moment coefficient in the aerodynamic characteristics data of the helicopter fuselage;

[0007] Compare the similarity of each focused component to the aerodynamic shape of existing helicopter components one by one;

[0008] Based on the similarity analysis results of components, the calculation method of the aerodynamic characteristics data combination of the modified helicopter fuselage and the calculation requirements of the aerodynamic characteristics of the components are preliminarily selected;

[0009] Based on the similarity analysis results of the components and the calculation requirements of the aerodynamic characteristics of the components, the wind tunnel test results of the fuselage before the modification were sorted out and analyzed;

[0010] Correct the calculation results of the fuselage force wind tunnel test according to the differences of various components of the modified helicopter;

[0011] The aerodynamic characteristic data of the fuselage of the modified design helicopter in the selected state are obtained by combined calculation based on the combined calculation method of the fuselage aerodynamic characteristic data and the revised calculation results of the fuselage force measurement wind tunnel test;

[0012] The aerodynamic characteristic data of each component are respectively subtracted from the aerodynamic characteristic data of the fuselage in the selected state of the modified design helicopter to obtain the aerodynamic characteristic data of the fuselage in each component-removed state.

[0013] The key components include: isolated fuselage, main rotor hub, power compartment, landing gear, horizontal tail, vertical tail, short wings, tail rotor hub and some external attachments that have a relatively large impact on the aerodynamic characteristics of the fuselage; among them, some models of helicopters do not have short wings.

[0014] Compare the similarity of each component of focus to the aerodynamic shape of existing helicopter components, including:

[0015] First, compare them with the components of the basic configuration platform helicopter. If they are not similar, compare them with the components of other models of helicopters that have been successfully developed; other models of helicopters that have been successfully developed must have fuselage force measurement wind tunnel test results.

[0016] The main parameters and key areas of concern for each component during the comparison are as follows:

[0017] a. For the isolated fuselage, focus on the nose shape, cockpit shape, engine compartment shape, maximum frontal area, and the shape of the transition section between the fuselage and the tail boom. The maximum frontal area of ​​the fuselage is the frontal area of ​​the fuselage below the rotor shaft.

[0018] The isolated fuselage part has a greater influence on the drag coefficient in the fuselage aerodynamic characteristics data, and the influencing parameter is the maximum frontal area;

[0019] b. Main propeller hub: Focus on the hub configuration, number of blades, and installation position; hub configuration refers to single-rotor and coaxial twin-rotor configurations;

[0020] The drag coefficient of the coaxial twin-hub is twice that of the single-rotor hub;

[0021] c. Tail rotor hub: Pay attention to the installation position, number of tail rotor blades, and whether to retain the tail rotor blades;

[0022] The tail rotor hub focuses on the drag coefficient, and whether to retain the tail rotor blades has a certain impact on the side force coefficient and yaw moment coefficient;

[0023] d. For the horizontal tail, pay attention to the installation position, airfoil shape, area, and installation angle;

[0024] The horizontal tail has the greatest influence on the change of the pitching moment coefficient in the aerodynamic characteristics data of the fuselage;

[0025] Pitching moment coefficient = horizontal tail lift coefficient * lever arm length;

[0026] The length of the lever arm is the fore-aft distance from the aerodynamic center of the horizontal tail to the center of the rotor axis;

[0027] The installation position of the horizontal tail of the modified helicopter will not change, and the length of the lever arm will not change;

[0028] If the horizontal tail installation position changes, simply measure the distance from the horizontal tail aerodynamic center to the rotor shaft center;

[0029] The area of ​​the horizontal tail has the greatest impact on the horizontal tail lift coefficient; if the horizontal tail area increases by 10%, the horizontal tail lift coefficient increases by 10%;

[0030] e. Pay attention to the installation position and area of ​​the vertical tail;

[0031] The vertical tail has the greatest influence on the change of the yaw moment coefficient in the aerodynamic characteristics data of the fuselage;

[0032] Yawing moment coefficient = vertical tail side force coefficient * lever arm length;

[0033] The length of the lever arm is the fore-aft distance from the aerodynamic center of the vertical tail to the center of the rotor axis;

[0034] The installation position of the vertical tail of the modified helicopter will not change, and the length of the lever arm will not change. If the installation position of the vertical tail is changed, the distance from the aerodynamic center of the vertical tail to the center of the rotor shaft can be directly measured.

[0035] The area of ​​the vertical tail has the greatest impact on the vertical tail side force coefficient; if the vertical tail area increases by 10%, the vertical tail side force coefficient increases by 10%;

[0036] f. Landing gear: Pay attention to the layout of the landing gear and the size of the windward area;

[0037] There are two main landing gear arrangements: 1. Skid type, 2. Wheel type;

[0038] The landing gear focuses on the aerodynamic drag coefficient, which is positively correlated with the maximum frontal area of ​​the landing gear;

[0039] g. Pay attention to the installation position, length, width, height and cross-sectional shape of the short wing;

[0040] The short wings of an armed helicopter affect the lift coefficient of the helicopter; the length and width of the short wings have a great influence on the lift coefficient;

[0041] The short wing of a transport helicopter affects the drag coefficient and pitching moment coefficient; the drag coefficient is affected by the height and width, and the pitching moment coefficient is affected by the length of the short wing;

[0042] h. For external stores, pay attention to the change in frontal area caused by the installation, the number of stores installed, the installation location, and the protrusion on the outside of the fuselage;

[0043] External attachments affect the drag coefficient in the aerodynamic characteristics of the fuselage, focusing on the change in the frontal area. The fuselage drag coefficient is positively correlated with the frontal area.

[0044] The calculation method for the aerodynamic characteristics data combination of the modified helicopter fuselage was preliminarily selected, including:

[0045] Based on the similarity analysis results of the components, and taking the isolated fuselage as the basis, the similarities of the main rotor hub, power nacelle, landing gear, horizontal tail, vertical tail, short wing, and tail rotor hub connected to the isolated fuselage are sorted out;

[0046] The fuselage before and after modification is disassembled into several components and parts; the disassembly methods and results are consistent before and after modification; during the disassembly process, the above-mentioned parts are combined with the isolated fuselage as much as possible, or other parts with physical connections are combined together, so as to reduce the number of combined parts and parts obtained by disassembly and reduce the time for subsequent calculation of the fuselage aerodynamic characteristics data;

[0047] The combined calculation method for determining subsequent fuselage aerodynamic characteristic data is the method of addition and subtraction.

[0048] Based on the similarity analysis results of the components and the calculation requirements of the aerodynamic characteristics of the components, the wind tunnel test results of the fuselage before the modification were sorted out and analyzed, including:

[0049] Based on the wind tunnel test results of the basic configuration platform and other successfully developed fuselage models, the aerodynamic characteristics of similar components are obtained, thereby obtaining the aerodynamic characteristics of the isolated fuselage and the combination of connected components. During the calculation process, pay attention to the wind tunnel test model status, included components, quantity and installation location parameters in the test records.

[0050] For the aerodynamic characteristics data of the newly added external stores, the wind tunnel test results of the two helicopter fuselages before the modification were selected and subtracted to obtain the preliminary aerodynamic characteristics data of the external stores.

[0051] Correct the calculation results of the fuselage force wind tunnel test based on the differences in various components of the modified helicopter, including:

[0052] For components with a drag coefficient greater than 0.05, the drag coefficient is corrected: the drag coefficient is corrected according to the change ratio k1 of the maximum frontal area;

[0053] For planar components that have a significant impact on the pitching moment coefficient, the lift coefficient and pitching moment coefficient are corrected according to the proportion of area change k1;

[0054] For planar components that have a greater impact on the yaw moment coefficient, the side force coefficient and yaw moment coefficient are corrected according to the proportion of area change k3;

[0055] For the short wings of armed helicopters, the lift coefficient is corrected according to the top-view area ratio k4 of the short wings;

[0056] For transport helicopter short wings, the drag coefficient is corrected according to the proportion of the short wing's frontal area k5; the pitching moment coefficient is corrected according to the proportion of the short wing's frontal area k6;

[0057] For external attachments, the drag coefficient is corrected according to the windward area ratio k5.

[0058] The aerodynamic characteristic data of the fuselage in the hub-less state = the aerodynamic characteristic data of the fuselage in the selected state - the aerodynamic characteristic data of the main hub.

[0059] The aerodynamic characteristic data of the fuselage in the state without the horizontal tail = the aerodynamic characteristic data of the fuselage in the selected state - the aerodynamic characteristic data of the horizontal tail.

[0060] Beneficial effects:

[0061] With the accelerating pace of helicopter development and the urgent need for low-cost designs, many helicopter models are currently being developed using a retrofit design approach. This involves modifying components such as the nose, rotor, horizontal tail, tail rotor, and stub wings on a base platform helicopter to meet specific mission requirements. With helicopters of various tonnages already successfully developed, the number of subsequent retrofit designs is expected to increase. Typically, the aerodynamic shapes of components that significantly impact the aerodynamic characteristics of the retrofit helicopter's fuselage will be inherited from the corresponding components on the base platform helicopter (typically, a model with a similar isolated fuselage is designated as the base platform), or from components on previously developed helicopter models, such as the isolated fuselage, main rotor hub, power nacelle, landing gear, horizontal tail, and vertical tail. Based on this design approach, the aerodynamic characteristics of the retrofit helicopter's fuselage can be calculated using the results of wind tunnel tests on the fuselage of previous models. Since the accuracy of the fuselage force measurement wind tunnel test results is relatively high, the method of integrating previous fuselage force measurement wind tunnel test results can obtain relatively accurate fuselage aerodynamic characteristics data results. At the same time, since the time spent on splitting and combining the wind tunnel test results of each component is relatively short, the fuselage aerodynamic characteristics data of the modified helicopter model can be obtained relatively quickly, thereby providing design input for subsequent design and calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 This is a flow chart of a method for calculating the aerodynamic characteristics of a modified helicopter fuselage. DETAILED DESCRIPTION

[0063] In order to make the purpose, technical solutions and advantages of the implementation of this application clearer, the technical solutions in the implementation of this application will be described in more detail below in conjunction with the drawings in the implementation of this application. In the drawings, the same or similar numbers throughout represent the same or similar elements or elements with the same or similar functions. The described implementation is a part of the implementation of this application, not all of the implementations. The implementation described below with reference to the drawings is exemplary and is intended to be used to explain this application, and should not be understood as a limitation on this application. Based on the implementation in this application, all other implementations obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. The implementation of this application is described in detail below in conjunction with the drawings.

[0064] In the description of the present invention, it should be understood that the terms "center", "axial", "vertical", "up", "down", "upper end", "bottom end", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the scope of protection of the present invention.

[0065] The present invention proposes a method for calculating the aerodynamic characteristics of a modified helicopter fuselage, such as Figure 1 As shown, the main steps are as follows:

[0066] 1. Preliminary review of the aerodynamic design schemes for various components of the modified helicopter fuselage.

[0067] The aerodynamic shapes of the modified helicopter's isolated fuselage, main rotor hub, engine nacelle, landing gear, horizontal stabilizer, vertical stabilizer, stub wings (some models do not have them), tail rotor hub, and some external attachments that have a significant impact on the fuselage's aerodynamic characteristics were reviewed. Special attention was paid to the aerodynamic shapes of components that have a significant impact on the drag coefficient, pitching moment coefficient, and yaw moment coefficient in the fuselage's aerodynamic characteristics data.

[0068] The following is added:

[0069] This is conducted using a pre-modification helicopter fuselage force measurement wind tunnel test model. Often, the differences between the pre-modification and post-modification models need to be separated. For example, a component was absent before the modification but added afterward, or a component was present before the modification but removed afterward.

[0070] Since only the components on the outside of the fuselage will affect the aerodynamic characteristics data of the fuselage, changes in components inside the fuselage do not need to be considered.

[0071] The drag coefficient of the isolated fuselage, main rotor hub (including the main rotor blade root), engine compartment, and landing gear accounts for more than 10% of the total aircraft drag coefficient. The total aircraft drag coefficient here refers to the total aircraft drag coefficient of the fuselage force measurement wind tunnel test model, which usually only includes the main rotor blade root and not the main rotor blade.

[0072] The isolated fuselage and horizontal tail determine the variation characteristics of the pitch moment coefficient.

[0073] The isolated fuselage and vertical tail determine the changing characteristics of the yaw moment coefficient.

[0074] 2. Compare and analyze the similarity of the aerodynamic shapes of each component.

[0075] Based on the aerodynamic shapes of the components identified in step 1, the aerodynamic shapes of the isolated fuselage and other components are compared one by one in 3D graphics processing software. First, the aerodynamic shapes are compared with the components of the basic configuration platform helicopter. If there is a dissimilarity, the aerodynamic shapes are compared with the components of other successfully developed models (for which fuselage force measurement wind tunnel test results are available). The main parameters and key areas of concern for each component during the comparison process are as follows:

[0076] a. The isolated fuselage mainly focuses on the nose shape, cockpit shape, engine compartment shape, maximum windward area, and the shape of the transition section between the fuselage and the tail boom. The maximum windward area of ​​the fuselage is usually the windward area of ​​the fuselage below the rotor shaft.

[0077] The isolated fuselage part has a great influence on the drag coefficient in the fuselage aerodynamic characteristics data, and the main influencing parameter is the maximum frontal area.

[0078] b. The main propeller hub mainly focuses on the hub configuration, number of blades, and installation position. The hub configuration refers to single rotor, coaxial twin rotor, etc.

[0079] Usually the drag coefficient of a coaxial twin-hub is twice that of a conventional single-rotor hub.

[0080] c. The tail rotor hub mainly focuses on the installation position, the number of tail rotor blades and whether to retain the tail rotor blades;

[0081] The tail rotor hub usually focuses on the drag coefficient, and whether to retain the tail rotor blades has a certain impact on the side force coefficient and yaw moment coefficient.

[0082] d. For the horizontal tail, the main focus is on the installation position, airfoil shape, area, installation angle, etc.

[0083] The horizontal tail has the greatest impact on the change of the pitch moment coefficient in the fuselage aerodynamic characteristics data.

[0084] Pitching moment coefficient = horizontal tail lift coefficient * lever arm length

[0085] The lever arm length is the fore-aft distance from the aerodynamic center of the horizontal tail to the center of the rotor axis.

[0086] Typically, the tailplane mounting position of a modified helicopter remains unchanged, so the lever arm length does not change. If the tailplane mounting position is changed, simply measure the distance from the tailplane's aerodynamic center to the rotor axis center.

[0087] The area of ​​the horizontal tail has the greatest impact on the tail's lift coefficient. Generally, a 10% increase in tail area results in a 10% increase in the tail's lift coefficient, and similarly for other increases or decreases.

[0088] e. The vertical tail mainly focuses on the installation position and area;

[0089] The vertical tail has the greatest impact on the change of the yaw moment coefficient in the fuselage aerodynamic characteristics data.

[0090] Yawing moment coefficient = vertical tail side force coefficient * lever arm length

[0091] The lever arm length is the fore-aft distance from the aerodynamic center of the vertical tail to the center of the rotor axis.

[0092] Typically, the vertical tail mounting position of a modified helicopter remains unchanged, so the lever arm length does not change. If the vertical tail mounting position is changed, simply measure the distance from the vertical tail aerodynamic center to the rotor axis center.

[0093] The area of ​​the vertical tail has the greatest impact on the vertical tail side force coefficient. Generally, a 10% increase in the vertical tail area will increase the vertical tail side force coefficient by 10%, and the same applies to other increases or decreases.

[0094] f. Landing gear: mainly focus on the layout of the landing gear, the size of the windward area, etc.

[0095] There are two main landing gear arrangements: 1. Skid type, 2. Wheel type

[0096] The landing gear mainly focuses on the aerodynamic drag coefficient, which is positively correlated with the maximum frontal area of ​​the landing gear.

[0097] g. Short wing mainly focuses on installation position, length, width, height and cross-sectional shape;

[0098] The stub wings of attack helicopters are typically attached to the left and right sides of the fuselage, positioned forward and backward near the rotor axis. Therefore, they primarily influence the helicopter's lift coefficient. The stub's overhead area (roughly equal to the product of its length and width) is directly proportional to its lift coefficient.

[0099] The short wing of a transport helicopter mainly affects the drag coefficient and pitching moment coefficient. The drag coefficient is mainly affected by the height and width (frontal area), while the pitching moment coefficient is mainly affected by the length of the short wing.

[0100] h. For external stores, the main focus should be on the change in windward area caused by installation, the number of stores installed, the installation location, and the protruding shape on the outside of the fuselage.

[0101] External attachments mainly affect the drag coefficient in the aerodynamic characteristics of the fuselage, and focus on the change in the frontal area. The fuselage drag coefficient is positively correlated with the frontal area.

[0102] At the same time, it is important to note that the tail turbulence of external stores should not affect the horizontal tail. In a three-dimensional numerical model, you can use lines to preliminarily determine whether the tail turbulence of external stores affects the aerodynamic characteristics of the horizontal tail.

[0103] 3. Preliminarily select the calculation method for the aerodynamic characteristics data combination of the modified helicopter fuselage.

[0104] Based on the results of similar components sorted out in step 2, with the isolated fuselage as the basis, sort out the similarities of the main rotor hub, power compartment, landing gear, horizontal tail (some models), vertical tail, short wings (some models do not have), tail rotor hub, etc. connected to the isolated fuselage. Split the fuselage before and after the modification into several components and parts. The splitting method and splitting results before and after the modification are consistent. During the splitting process, try to combine the above components with the isolated fuselage as much as possible, or combine other components with a physical connection relationship, so as to reduce the number of combined parts and components obtained by splitting and reduce the calculation time of the subsequent fuselage aerodynamic characteristics data.

[0105] The subsequent calculation of fuselage aerodynamic characteristics primarily utilizes addition and subtraction. Based on the disassembled components and subassemblies, the aerodynamic characteristics of each component and subassembly before the modification are first calculated based on the pre-modification force-measuring wind tunnel test results. This calculation is performed using addition or subtraction. The calculated aerodynamic characteristics of each component and subassembly are then corrected. Finally, the aerodynamic characteristics of each component and subassembly are summed to obtain preliminary aerodynamic characteristics data for the modified fuselage.

[0106] 4. Preliminary review and calculation of wind tunnel test results of aerodynamic characteristics of similar components (before modification).

[0107] Based on the aerodynamic shape similarity analysis results from step 2 and the aerodynamic characteristics of the components identified in step 3, the aerodynamic characteristics of the various components and parts obtained after the fuselage is disassembled are calculated, including the fuselage before and after the modification. For example, the fuselage + main rotor hub + landing gear, external equipment, horizontal tail, short wings, vertical tail + tail rotor hub, etc.

[0108] The results of previous fuselage dynamometric wind tunnel tests (before modification) were reviewed and analyzed. Because the incremental method is used to obtain aerodynamic characteristics data for individual components during helicopter fuselage dynamometric wind tunnel tests, the aerodynamic characteristics wind tunnel test results for similar components can be obtained based on the results of the basic configuration platform and the fuselage dynamometric wind tunnel tests of other successfully developed models. Furthermore, aerodynamic characteristics wind tunnel test results for the combination of an isolated fuselage and connected components can be obtained. During the calculation process, pay attention to the wind tunnel test model status, included components, quantity, and installation location parameters in the test records.

[0109] For the aerodynamic characteristic data of the newly added external attachments, the force measurement wind tunnel test results of two helicopter fuselages before the modification can be selected and subtracted to obtain the preliminary aerodynamic characteristic data of the external attachments.

[0110] 5. Based on the differences between the various components of the modified helicopter, the aerodynamic characteristics data of similar components are corrected. Corrections are made according to the following three categories:

[0111] a. For components with a drag coefficient greater than 0.05, such as the isolated fuselage, main rotor hub, tail rotor hub, and landing gear, the drag coefficient is mainly corrected. The drag coefficient is corrected according to the change ratio k1 of the maximum frontal area. Taking the drag coefficient of the isolated fuselage as an example:

[0112] Drag coefficient of isolated fuselage after modification = Drag coefficient of isolated fuselage before modification * k1

[0113] k1 = Maximum frontal area of ​​isolated fuselage after modification / Maximum frontal area of ​​isolated fuselage before modification

[0114] b. Planar components such as the horizontal tail basically determine the change trend of the pitching moment coefficient. The lift coefficient and pitching moment coefficient are corrected according to the proportion of the area change k1. Take the horizontal tail pitching moment coefficient as an example:

[0115] The pitching moment coefficient of the horizontal tail after modification = the pitching moment coefficient of the horizontal tail before modification * k1

[0116] k1 = area of ​​horizontal tail after modification / area of ​​horizontal tail before modification

[0117] c. Planar components such as the vertical tail basically determine the changing trend of the yaw moment coefficient. The side force coefficient and yaw moment coefficient are corrected according to the proportion of the area change k3. Take the vertical tail yaw moment coefficient as an example:

[0118] Yaw moment coefficient of vertical tail after modification = Yaw moment coefficient of vertical tail before modification * k3

[0119] k3 = area of ​​vertical tail after modification / area of ​​vertical tail before modification

[0120] d. Short wings are divided into weapon-mounted short wings of armed helicopters and short wings of transport helicopters (usually with fuel tanks inside).

[0121] Since the lift coefficient of the helicopter fuselage is very small except for the short wings, the lift coefficient of the armed helicopter fuselage is basically proportional to the short wing's overhead area (basically equal to the product of length and width). The lift coefficient is corrected according to the short wing's overhead area ratio k4:

[0122] The lift coefficient of the short wing after modification = the lift coefficient of the short wing before modification * k4

[0123] k4 = short wing top-view area after modification / short wing top-view area before modification

[0124] The short wings of transport helicopters have a certain influence on the drag coefficient and pitching moment coefficient.

[0125] The drag coefficient is corrected according to the proportion of the short wing's frontal area k5:

[0126] The drag coefficient of the short wing after modification = the drag coefficient of the short wing before modification * k5

[0127] k5 = frontal area of ​​the short wing after modification / frontal area of ​​the short wing before modification

[0128] The pitching moment coefficient is corrected according to the proportion of the short wing's frontal area k6:

[0129] Short wing pitching moment coefficient after modification = Short wing pitching moment coefficient before modification * k6

[0130] k6 = short wing top-view area after modification / short wing top-view area before modification

[0131] d. External attachments have a significant impact on the drag coefficient of the fuselage's aerodynamic characteristics. The drag coefficient can be corrected based on the frontal area ratio k5:

[0132] The drag coefficient of the external load after modification = the drag coefficient of the external load before modification * k5

[0133] k5 = windward area of ​​external stores after modification / windward area of ​​external stores before modification

[0134] 6. Preliminary calculation of the aerodynamic characteristics of the modified helicopter fuselage.

[0135] The fuselage aerodynamic characteristic data for the selected state of the modified design helicopter are calculated using a combined calculation method based on the fuselage aerodynamic characteristic data obtained in step 3 (described in step 3) and the corrected calculation results of the fuselage force wind tunnel tests of the isolated fuselage assembly and each component obtained in step 5.

[0136] 7. Subtract the aerodynamic characteristic data of each component from the obtained fuselage aerodynamic characteristic data of the selected state of the modified design helicopter to obtain the fuselage aerodynamic characteristic data of each component-removed state. The calculation method for the fuselage aerodynamic characteristic data of the state without the hub and horizontal tail is as follows. The calculation method for the fuselage aerodynamic characteristic data of the other component-removed states is similar. Due to the limitations of the assembly characteristics of some components, the aerodynamic characteristic data of the fuselage in some component-removed states may be the aerodynamic characteristic data of the fuselage after removing multiple components. For example, if the horizontal tail of some helicopters is installed on the vertical tail, the aerodynamic characteristic data of the fuselage in the state without the vertical tail is actually the aerodynamic characteristic data of the fuselage in the state without the vertical tail and the horizontal tail.

[0137] a. Aerodynamic characteristic data of fuselage in hub-less state = aerodynamic characteristic data of fuselage in selected state - aerodynamic characteristic data of main hub.

[0138] b. Aerodynamic characteristic data of fuselage in the state without horizontal tail = aerodynamic characteristic data of fuselage in the selected state - aerodynamic characteristic data of horizontal tail.

[0139] Other embodiments of the present disclosure will readily occur to those skilled in the art after considering the specification and practicing the disclosure herein. This application is intended to cover any variations, uses, or adaptations of the present disclosure that follow the general principles of the present disclosure and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only, with the true scope and spirit of the present disclosure being indicated by the following claims.

[0140] It should be understood that the present disclosure is not limited to the exact structures that have been described above and shown in the drawings, and that various modifications and changes can be made without departing from the scope thereof. The scope of the present disclosure is limited only by the appended claims.

Claims

1. A method for calculating the aerodynamic characteristics data of a modified helicopter fuselage, characterized in that: include: Focus on the aerodynamic shape of the components that have a greater impact on the drag coefficient, pitching moment coefficient and yaw moment coefficient in the aerodynamic characteristics data of the helicopter fuselage; Compare the similarity of each focused component to the aerodynamic shape of existing helicopter components one by one; Based on the similarity analysis results of components, the calculation method of the aerodynamic characteristics data combination of the modified helicopter fuselage and the calculation requirements of the aerodynamic characteristics of the components are preliminarily selected; Based on the similarity analysis results of the components and the calculation requirements of the aerodynamic characteristics of the components, the wind tunnel test results of the fuselage before the modification were sorted out and analyzed; Correct the calculation results of the fuselage force wind tunnel test according to the differences of various components of the modified helicopter; The aerodynamic characteristic data of the fuselage of the modified design helicopter in the selected state are obtained by combined calculation based on the combined calculation method of the fuselage aerodynamic characteristic data and the revised calculation results of the fuselage force measurement wind tunnel test; The aerodynamic characteristic data of each component are respectively subtracted from the aerodynamic characteristic data of the fuselage in the selected state of the modified design helicopter to obtain the aerodynamic characteristic data of the fuselage in each component-removed state.

2. The method according to claim 1, characterized in that The key components include: isolated fuselage, main rotor hub, power compartment, landing gear, horizontal tail, vertical tail, short wings, tail rotor hub and some external attachments that have a relatively large impact on the aerodynamic characteristics of the fuselage; among them, some models of helicopters do not have short wings.

3. The method according to claim 2, characterized in that Compare the similarity of each component of focus to the aerodynamic shape of existing helicopter components, including: First, compare them with the components of the basic configuration platform helicopter. If they are not similar, compare them with the components of other models of helicopters that have been successfully developed; other models of helicopters that have been successfully developed must have fuselage force measurement wind tunnel test results.

4. The method according to claim 3, characterized in that The main parameters and key areas of concern for each component during the comparison are as follows: a. For the isolated fuselage, focus on the nose shape, cockpit shape, engine compartment shape, maximum frontal area, and the shape of the transition section between the fuselage and the tail boom. The maximum frontal area of ​​the fuselage is the frontal area of ​​the fuselage below the rotor shaft. The isolated fuselage part has the greatest influence on the drag coefficient in the fuselage aerodynamic characteristics data, and the influencing parameter is the maximum frontal area; b. Main propeller hub: Focus on the hub configuration, number of blades, and installation position; hub configuration refers to single-rotor and coaxial twin-rotor configurations; The drag coefficient of the coaxial twin-hub is twice that of the single-rotor hub; c. Pay attention to the installation position of the tail rotor hub, the number of tail rotor blades, and whether to retain the tail rotor blades; The tail rotor hub focuses on the drag coefficient, and whether to retain the tail rotor blades has a certain impact on the side force coefficient and yaw moment coefficient; d. For the horizontal tail, pay attention to the installation position, airfoil shape, area, and installation angle; The horizontal tail has the greatest influence on the change of the pitching moment coefficient in the aerodynamic characteristics data of the fuselage; Pitching moment coefficient = horizontal tail lift coefficient * lever arm length; The length of the lever arm is the fore-aft distance from the aerodynamic center of the horizontal tail to the center of the rotor axis; The installation position of the horizontal tail of the modified helicopter will not change, and the length of the lever arm will not change; If the horizontal tail installation position changes, simply measure the distance from the horizontal tail aerodynamic center to the rotor shaft center; The area of ​​the horizontal tail has the greatest impact on the horizontal tail lift coefficient; if the horizontal tail area increases by 10%, the horizontal tail lift coefficient increases by 10%; e. Pay attention to the installation position and area of ​​the vertical tail; The vertical tail has the greatest influence on the change of the yaw moment coefficient in the aerodynamic characteristics data of the fuselage; Yawing moment coefficient = vertical tail side force coefficient * lever arm length; The length of the lever arm is the fore-aft distance from the aerodynamic center of the vertical tail to the center of the rotor axis; The installation position of the vertical tail of the modified helicopter will not change, and the length of the lever arm will not change. If the installation position of the vertical tail is changed, the distance from the aerodynamic center of the vertical tail to the center of the rotor shaft can be directly measured. The area of ​​the vertical tail has the greatest impact on the vertical tail side force coefficient; if the vertical tail area increases by 10%, the vertical tail side force coefficient increases by 10%; f. Landing gear: Pay attention to the layout of the landing gear and the size of the windward area; There are two main landing gear arrangements:

1. Skid type, 2. Wheel type; The landing gear focuses on the aerodynamic drag coefficient, which is positively correlated with the maximum frontal area of ​​the landing gear; g. Pay attention to the installation position, length, width, height and cross-sectional shape of the short wing; The short wings of an armed helicopter affect the lift coefficient of the helicopter; the length and width of the short wings have a great influence on the lift coefficient; The short wing of a transport helicopter affects the drag coefficient and pitching moment coefficient; the drag coefficient is affected by the height and width, and the pitching moment coefficient is affected by the length of the short wing; h. For external stores, pay attention to the change in frontal area caused by the installation, the number of stores installed, the installation location, and the protrusion on the outside of the fuselage; External attachments affect the drag coefficient in the aerodynamic characteristics of the fuselage, focusing on the change in the frontal area. The fuselage drag coefficient is positively correlated with the frontal area.

5. The method according to claim 4, characterized in that The calculation method for the aerodynamic characteristics data combination of the modified helicopter fuselage was preliminarily selected, including: Based on the similarity analysis results of the components, and taking the isolated fuselage as the basis, the similarities of the main rotor hub, power nacelle, landing gear, horizontal tail, vertical tail, short wing, and tail rotor hub connected to the isolated fuselage are sorted out; The fuselage before and after modification is disassembled into several components and parts; the disassembly methods and results are consistent before and after modification; during the disassembly process, the above-mentioned parts are combined with the isolated fuselage as much as possible, or other parts with physical connections are combined together, so as to reduce the number of combined parts and parts obtained by disassembly and reduce the time for subsequent calculation of the fuselage aerodynamic characteristics data; The combined calculation method for determining subsequent fuselage aerodynamic characteristic data is the method of addition and subtraction.

6. The method according to claim 5, characterized in that Based on the similarity analysis results of the components and the calculation requirements of the aerodynamic characteristics of the components, the wind tunnel test results of the fuselage before the modification were sorted out and analyzed, including: Based on the wind tunnel test results of the basic configuration platform and other successfully developed fuselage models, the aerodynamic characteristics of similar components are obtained, thereby obtaining the aerodynamic characteristics of the isolated fuselage and the combination of connected components. During the calculation process, pay attention to the wind tunnel test model status, included components, quantity and installation location parameters in the test records. For the aerodynamic characteristic data of the newly added external attachments, the force measurement wind tunnel test results of two helicopter fuselages before the modification were selected and subtracted to obtain the preliminary aerodynamic characteristic data of the external attachments.

7. The method according to claim 6, characterized in that Correct the calculation results of the fuselage force wind tunnel test based on the differences in various components of the modified helicopter, including: For components with a drag coefficient greater than 0.05, the drag coefficient is corrected: the drag coefficient is corrected according to the change ratio k1 of the maximum frontal area; For the planar components that have the greatest impact on the pitching moment coefficient, the lift coefficient and pitching moment coefficient are corrected according to the proportion of area change k1; For the planar components that have the greatest impact on the yaw moment coefficient, the side force coefficient and yaw moment coefficient are corrected according to the proportion of area change k3; For the short wings of armed helicopters, the lift coefficient is corrected according to the top-view area ratio k4 of the short wings; For transport helicopter short wings, the drag coefficient is corrected according to the proportion of the short wing's frontal area k5; the pitching moment coefficient is corrected according to the proportion of the short wing's frontal area k6; For external attachments, the drag coefficient is corrected according to the windward area ratio k5.

8. The method according to claim 7, characterized in that The aerodynamic characteristic data of the fuselage in the hub-less state = the aerodynamic characteristic data of the fuselage in the selected state - the aerodynamic characteristic data of the main hub.

9. The method according to claim 8, characterized in that The aerodynamic characteristic data of the fuselage in the state without the horizontal tail = the aerodynamic characteristic data of the fuselage in the selected state - the aerodynamic characteristic data of the horizontal tail.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 9 is implemented.

Images