Aerodynamic parameter identification method suitable for small aircraft

Abstract

The invention belongs to the technical field of aircraft design and research and development, and particularly relates to an aerodynamic parameter identification method suitable for a small aircraft, which comprises the following steps: acquiring ground test parameters, and acquiring measurement parameters in flight; and calculating aerodynamic parameters of the aircraft based on the acquired ground test parameters and the measured parameters in flight.

Description

Technical Field

[0001] The present invention belongs to the technical field of aircraft design and development, and particularly relates to an aerodynamic parameter identification method suitable for small aircraft. Background Art

[0002] In the field of aircraft design and development, accurately obtaining aerodynamic parameters is crucial, directly impacting aircraft performance, safety, and overall design quality. Currently, the main technical approaches for obtaining aircraft aerodynamic parameters include CFD simulation, wind tunnel testing, component assembly, flight test modeling, and other theoretical calculations. CFD simulations, based on the fundamental principles of computational fluid dynamics and utilizing numerical methods based on differential equations, can determine aerodynamic parameters and flow field characteristics under various operating conditions. However, these methods require simplified, three-dimensional simulation models. Wind tunnel testing simulates wind conditions within a specific flight speed range and uses scaled models for wind testing. While the physical testing environment approximates actual flight conditions, it requires wind tunnel facilities and a physical prototype or scaled model of the aircraft. Component assembly methods use extensive engineering data and the characteristics of the aircraft's aerodynamic layout to divide components. After fitting component aerodynamic parameters, an overall aerodynamic data calculation model is derived. This requires a high degree of similarity between the calculated model and existing models in the database. Flight test modeling, using data collected from actual flight tests and parameter identification based on aerodynamic and flight control principles, can better reflect actual flight conditions. However, the aircraft must meet basic flight function and performance requirements and possess appropriate data acquisition equipment. Other theoretical calculations, based on fundamental aerodynamic principles, calculate aerodynamic parameters for specific aerodynamic shapes and are suitable for situations that meet theoretical simplified conditions.

[0003] In actual small aircraft engineering, aerodynamic design implementation presents unique characteristics. When carrying out design work, engineers will draw on basic aerodynamic principles and engineering experience, develop innovative designs based on actual needs, attempting to break through the typical characteristics of existing aerodynamic layouts. The rationality of the design is then verified through flight tests. At the same time, existing aircraft are also partially modified, and the effectiveness of the modifications is also verified through flight tests. This process exhibits low engineering costs and short turnaround times, with a high reliance on experience, relatively less theoretical analysis, and greater reliance on engineering verification. However, this design model also brings some problems. Although the aircraft can meet basic flight conditions, it lacks sufficient theoretical or data foundation to support the design of complex missions and complex aircraft control methods based on this aircraft.

[0004] Existing methods for obtaining aerodynamic parameters often present numerous challenges when applied to small aircraft. For one thing, when engineers creatively design an aircraft whose aerodynamic layout differs significantly from conventional aircraft, it can be difficult to find a suitable design model for component assembly calculations. Furthermore, for aircraft obtained through modification, complete drawings are often lacking, which hinders the use of CFD for aerodynamic parameter calculations and also hinders the availability of suitable design models for component assembly calculations. Furthermore, using simplified models for CFD calculations requires not only a 3D model but also often simplification. Simulation parameter setting and meshing also rely on experience, often leading to inaccurate results. Wind tunnel testing methods, however, are subject to high infrastructure and technical coordination costs in the small aircraft sector, hindering their widespread application. Flight test methods, however, often follow the experimental design of large aircraft, resulting in complex test designs and demanding data identification and application methods, making them unsuitable for small aircraft. These issues hinder the accuracy and efficiency of obtaining aerodynamic parameters for small aircraft, necessitating an urgent need for more effective solutions. Summary of the Invention

[0005] In order to overcome the problems in the prior art, the present invention proposes an aerodynamic parameter identification method suitable for small aircraft.

[0006] The technical solution of the present invention to solve the above technical problems is as follows: The present invention provides an aerodynamic parameter identification method applicable to a small aircraft, comprising the following steps: Obtain ground test parameters and in-flight measurement parameters; The aerodynamic parameters of the aircraft are calculated based on the acquired ground test parameters and the parameters measured during flight.

[0007] Furthermore, the actual flight data includes aircraft x-axis acceleration, aircraft z-axis acceleration, flight speed, flight altitude, aileron control value, elevator control value, and thrust control value.

[0008] Furthermore, parameters obtained from ground testing include wing area, vehicle mass, elevator control coefficient, aileron control coefficient, and thrust control coefficient.

[0009] Furthermore, the elevator control coefficient , aileron control coefficient and thrust control coefficient , calculated as follows: ; In the above formula, Indicates the aileron angle; Indicates the elevator angle; Indicates thrust; Indicates the elevator control amount; Indicates the aileron control trim value; Indicates the aileron control amount; Indicates the elevator control trim value; Indicates the thrust control amount.

[0010] Furthermore, the aerodynamic parameters of the aircraft include a total lift coefficient constant term and an elevator lift coefficient.

[0011] Furthermore, the total lift coefficient constant term and the elevator lift coefficient are solved, including: Based on the elevator control coefficient , Elevator control amount trim value , calculate A L matrix: ; Based on flight altitude , using the standard atmospheric model to calculate air density : ; Based on the aircraft mass m and air density , aircraft z-axis acceleration , flight speed and wing area ,calculate matrix: ; Based on the AL matrix and Matrix, calculate the lift coefficient: ; Also because ; Calculate the corresponding aerodynamic parameters , the total lift coefficient constant term , elevator lift coefficient .

[0012] Furthermore, the aerodynamic parameters of the aircraft include a total drag coefficient constant term, an aileron drag coefficient, and an elevator drag coefficient.

[0013] Furthermore, the drag coefficient constant term, aileron drag coefficient, and elevator drag coefficient are solved, including: Based on the elevator control coefficient , aileron control coefficient , Elevator control amount trim value , Aileron control amount trim value , elevator control amount and aileron control amount, calculate A D matrix: ; Based on flight altitude , using the standard atmospheric model to calculate air density : ; According to the thrust control coefficient , thrust control amount , aircraft x-axis acceleration , flight speed , wing area , air density and the vehicle mass m, the bD matrix is ​​calculated: ; Calculate the drag coefficient: ; Also because ; Calculate the corresponding aerodynamic parameters , represents the constant term of the total drag coefficient, represents the aileron drag coefficient, Indicates the elevator drag coefficient.

[0014] Compared with the prior art, the present invention has the following technical effects: The aerodynamic parameter identification method provided by the present invention has many significant beneficial effects: its theoretical basis and calculation model are concise and easy to understand, making it easy for engineering and technical personnel to quickly master and promote their application in actual projects; the model is constructed by a component combination method, which can be flexibly adapted to different and novel aerodynamic layouts and has strong scalability; the method has a short preparation cycle, which meets the time efficiency requirements of small aircraft engineering applications; at the same time, the system cost is low, which effectively reduces the economic burden in the research and development process of small aircraft; the reproducible operation is simple, which is conducive to carrying out multiple tests, which can not only detect errors in a timely manner, but also help to improve the accuracy of parameter identification; in addition, the method can also be coordinated with the aircraft aerodynamic and structural design optimization work, providing strong support for the engineering design optimization process and promoting the improvement of the overall performance of the aircraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions and advantages of the embodiments of the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 It is a schematic diagram of the process of the present invention; Figure 2 Schematic diagram of different wing shape features of the present invention; Figure 3 The logical relationship between the measurement and calculation of aerodynamic parameters (total lift coefficient constant term, aileron lift coefficient) of the present invention; Figure 4 The present invention provides a logical relationship between the measurement and calculation of aerodynamic parameters (elevator lift coefficient, total drag coefficient constant term, aileron drag coefficient, and elevator drag coefficient). DETAILED DESCRIPTION

[0017] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose of the invention, the following, in conjunction with the accompanying drawings and preferred embodiments, describes in detail the specific implementation methods, structures, features, and effects of the technical solutions proposed by the present invention. Specific features, structures, or characteristics in one or more embodiments may be combined in any suitable form. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0018] The basic principle equations include: the force equation of the aircraft, the aerodynamic force calculation equation and the aerodynamic parameter equation.

[0019] Among them, (1) force equation: The aircraft is subject to multiple forces during flight. According to Newton's second law, the force equations in the x-axis and z-axis directions are established respectively: (1); In the above formula, m Indicates the mass of the aircraft; represents the acceleration due to gravity; Indicates thrust; represents the total resistance; represents the total lift; Indicates aircraft x Axis acceleration; Indicates aircraft z Axis acceleration.

[0020] (2) Aerodynamic calculation equation: Aerodynamic forces (lift and drag) are related to flight speed, aerodynamic coefficient, and wing area, and their calculation equation is: (2); In the above formula, Indicates the air density; Indicates flight speed; represents the total lift coefficient; represents the total drag coefficient; Represents the wing area.

[0021] (3) Aerodynamic parameter equations.

[0022] In a stable flight state, it can be approximately considered that the three-axis angular velocity of the aircraft is 0, and the rate of change of the angle of attack and sideslip angle is 0. Therefore, the generation of aerodynamic force at this time is only related to the aerodynamic shape and control surface angle of the aircraft.

[0023] From the perspective of the source of aerodynamic force, any aircraft can be divided into three main components: fuselage, wings, and tail. Therefore, the aerodynamic lift coefficient and aerodynamic drag coefficient of the entire aircraft can be expressed as: (3); In the above formula, represents the lift coefficient of the wing; represents the fuselage lift coefficient; represents the tail lift coefficient; represents the wing drag coefficient; represents the fuselage drag coefficient; represents the tail wing drag coefficient.

[0024] Since the wings are equipped with ailerons and the tail is equipped with elevators, the coefficients related to the wings and tail in the above expression can be further expressed as: (4); In the above formula, represents the constant term of the total lift coefficient; represents the constant term of the total lift coefficient; represents the elevator lift coefficient; represents the constant term of the total drag coefficient; represents the aileron drag coefficient; represents the constant term of the tail wing drag coefficient; represents the elevator drag coefficient; Indicates the aileron angle; Indicates the elevator angle.

[0025] Therefore, the above formula can be expressed as: (5); remember (6); Then there is (7); In the above formula, represents the total lift coefficient; Represents the total drag coefficient.

[0026] Reference Figure 1 ,A method for identifying aerodynamic parameters of small aircraft includes the following steps: ,acquiring actual flight data in a stable flight state, and ,combining the parameters obtained from ground tests to solve the aerodynamic parameters of the aircraft, ,providing an important basis for the performance analysis and control ,design of the aircraft.

[0027] As an example, this step specifically includes: Step 100: Obtain ground test parameters, including wing area , aircraft mass m, elevator control coefficient , aileron control coefficient and thrust control coefficient .

[0028] Given a set of aileron control values, elevator control values, and thrust control values, the aileron angle, elevator angle, and thrust are measured to calculate the elevator control coefficient. , aileron control coefficient and thrust control coefficient : (8); In the above formula, Indicates the aileron angle; Indicates the elevator angle; Indicates thrust; Indicates the elevator control amount; Indicates the aileron control trim value; Indicates the aileron control amount; Indicates the elevator control trim value; Indicates the thrust control amount.

[0029] The balance is used to measure the mass m of the aircraft, and the ruler is used to measure the wing area of ​​the aircraft. , the protractor is used to measure the deflection angles of the elevator and aileron, and the dynamometer is used to measure the thrust of the aircraft power system.

[0030] Step 200: Obtaining measurement parameters during flight, including aircraft x-axis acceleration, aircraft z-axis acceleration, flight speed, flight altitude, aileron control value, elevator control value, and thrust control value.

[0031] Design a balanced working state that requires calculation of aerodynamic parameters, implement flight tests, and use specific equipment to measure and store the "parameters measured in flight" during stable flight. The data stored at each moment is recorded as a group of data, and the data storage capacity required is no less than 3 groups.

[0032] Among them, the airspeed meter measures flight speed; the altimeter measures flight altitude; the accelerometer measures aircraft acceleration; the flight controller outputs aileron control quantity, elevator control quantity, and thrust control quantity for flight control; the data storage device is used to save the collected data; and the aerodynamic parameter calculator is used to calculate aerodynamic parameters.

[0033] Step 300: Based on the acquired ground test parameters and the parameters measured in flight, calculate the total lift coefficient constant term, the aileron lift coefficient, the elevator lift coefficient, the total drag coefficient constant term, the aileron drag coefficient and the elevator drag coefficient.

[0034] Step 300 may include: Step 3100: Calculating lift-related aerodynamic parameters, which includes: Step 3101: Based on the elevator control coefficient , Elevator control amount trim value , calculate A L matrix: (9); in, It is a defined 2X2 matrix used to conveniently represent related calculation parameters.

[0035] Step 3102: Based on the flight altitude , using the standard atmospheric model to calculate air density : (10); Based on the aircraft mass m and air density , aircraft z-axis acceleration, flight speed and wing area ,calculate: (11); Step 3103: Based on and , calculate the lift coefficient; (12); in, is a defined two-dimensional vector used to conveniently represent the lift coefficient.

[0036] Also because (13); The corresponding aerodynamic parameters can be calculated , the total lift coefficient constant term , elevator lift coefficient .

[0037] Step 320: Regarding the drag coefficient.

[0038] Step 3201: Based on the elevator control coefficient , aileron control coefficient , Aileron control amount trim value , elevator control amount and aileron control amount, calculate A D matrix: (14); Step 3202: Calculate the air density using the standard atmospheric model, where H is the flight altitude: ; Step 3203: According to the thrust control coefficient , thrust control quantity, aircraft x-axis acceleration, flight speed, wing area and aircraft mass m, calculate the bD matrix: (15); Step 3204: Calculate the drag coefficient: (16); Also because (17); The corresponding aerodynamic parameters can be calculated , represents the constant term of the total drag coefficient, represents the aileron drag coefficient, Indicates the elevator drag coefficient.

[0039] Table 1 is a summary of relevant parameters, and Table 2 is a grouping of parameters involved in the present invention: Table 1 Summary of relevant parameters

[0040] Table 2 Parameter grouping involved

[0041] The specific implementation is given below: Step 100: Obtain ground test parameters, including wing area , aircraft mass m, elevator control coefficient , aileron control coefficient and thrust control coefficient .

[0042] (1) Obtain the vehicle mass m.

[0043] Before the aircraft takes off, a weighing device is used to test the weight of the entire aircraft, which is recorded as m. For example, after testing, the total weight of a certain type of small UAV is m=2.8kg.

[0044] (2) Elevator control trim value : Just record it according to the flight controller settings. In this example: ; (3) Aileron control amount trim value : Just record it according to the flight controller settings. In this example: ; (4) Calculate the thrust control coefficient .

[0045] According to the formula: (18); Given a control signal value, a fixed tension T can be obtained, where is the control system setting or output value, which can be regarded as a known quantity. Therefore, by measuring The corresponding pulling force T can be used to calculate the thrust control coefficient. .

[0046] For example, when testing The value is 1600, corresponding to a measured tensile force of 9N. At this time, the tensile coefficient can be calculated as: (19).

[0047] (5) Calculate the elevator control coefficient .

[0048] According to the formula: (20); Given a control signal value , a fixed elevator deflection angle can be obtained, where is the control system setting or output value, which can be regarded as a known quantity. Therefore, by measuring The corresponding elevator deflection angle can be used to inversely calculate the elevator control coefficient .

[0049] For example, when testing The value is 1800, which corresponds to a measured elevator deflection angle of 30°. At this time, the elevator control coefficient can be calculated as: (twenty one).

[0050] (6) Calculate the aileron control coefficient .

[0051] According to formula (8): ; Given a control signal value, a fixed aileron deflection angle can be obtained, where is the control system setting or output value, which can be regarded as a known quantity. Therefore, by measuring The corresponding aileron deflection angle can be used to inversely calculate the aileron control coefficient .

[0052] For example, when testing The value is 1700, corresponding to the measured aileron deflection angle of 20°. At this time, the aileron control coefficient can be calculated as: .

[0053] (7) Obtain the wing area.

[0054] The wing area of ​​a simple shape can be calculated using the basic area formula. The wing area of ​​an irregular shape can be divided into several simple shapes and calculated separately before summing them up. Figure 2 As shown, simple shapes include rectangles, triangles, trapezoids, ellipses, semicircles, chords, etc.

[0055] Based on the specific shape of the wing, basic data such as side length, height, and radius are measured, and then the wing area is calculated. Assuming that the aircraft wing is right-sided and the left wing is symmetrical to the right wing, the characteristic parameter measurement results are shown in the figure. The wing area of ​​aircraft B can be calculated as: (twenty two).

[0056] Step 200: Obtaining parameters measured during flight, including aircraft x-axis acceleration, aircraft z-axis acceleration, flight speed, flight altitude, aileron control value, elevator control value, and thrust control value.

[0057] (1) The relationship between the main equipment in flight test and the required test data.

[0058] The data required for testing and saving during flight are shown in Table 3, and the equipment used during flight are shown in Figure 2 .

[0059] Table 3 Correspondence between in-flight test equipment and test data

[0060] Step 300: Based on the acquired ground test parameters and the parameters measured during flight, calculate the total lift coefficient constant term, aileron lift coefficient, elevator lift coefficient, total drag coefficient constant term, aileron drag coefficient and elevator drag coefficient, refer to Figure 3 and Figure 4 . Given formula (1) and formula (2), we can L Substituting the expression into formula (1) we get: (twenty three); After finishing, we can get: (twenty four); Right now: (25); It is known that formula (7) is substituted into formula (25) to obtain: (26); Since formula (8) is known, we can substitute formula (8) into formula (26) to obtain: (27); Since there are two unknowns in formula (27), two sets of data are needed to solve it. Assume that these two sets of data are and , then: (28); Written in matrix form: (29); Assume formulas (9), (11), and (13): ; ; ; According to formula (29), and the definitions of (9), (11), and (13), we have: ; Then we can know that Contains two unknowns, in order to calculate , at least 2 groups of data need to be collected; in addition, according to different specific situations, it is necessary to set a suitable sampling frequency. Here, it is assumed that the sampling frequency is 50Hz.

[0061] Sampling of data required for drag coefficient calculation: ; ; ; but ; Then we can know that X D Contains 3 unknowns, in order to calculate X D , at least 3 groups of data need to be collected; in addition, according to different specific situations, it is necessary to set a suitable sampling frequency. Here, it is assumed that the sampling frequency is 50Hz.

[0062] The flight test was conducted uniformly according to the three groups of sampling requirements. In one flight test, the data obtained are shown in Table 4: Table 4 Examples of specific data collected during flight tests

[0063] According to the above steps, we can obtain the specific data of ground testing and the data collected in real time during flight.

[0064] (1) Based on the above data, the lift coefficient can be calculated X L : Air density calculation: ; b L Matrix calculations: ; A L Matrix calculations: ; X L calculate: ; Right now ; (2) Calculation of resistance coefficient: Air density calculation: ; b D Matrix calculations: ; A D Matrix calculations: ; X D calculate: ; Right now .

[0065] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A method for identifying aerodynamic parameters of a small aircraft, characterized in that: The following steps are involved: Obtain ground test parameters and in-flight measurement parameters; The aerodynamic parameters of the aircraft are calculated based on the acquired ground test parameters and the parameters measured during flight.

2. The aerodynamic parameter identification method for small aircraft according to claim 1, characterized in that: The actual flight data includes aircraft x-axis acceleration, aircraft z-axis acceleration, flight speed, flight altitude, aileron control amount, elevator control amount, and thrust control amount.

3. The aerodynamic parameter identification method for small aircraft according to claim 1, characterized in that: The parameters obtained from the ground test include wing area, aircraft mass, elevator control coefficient, aileron control coefficient and thrust control coefficient.

4. The aerodynamic parameter identification method for small aircraft according to claim 3, characterized in that: Elevator control coefficient , aileron control coefficient and thrust control coefficient , calculated as follows: ； In the above formula, Indicates the aileron angle; Indicates the elevator angle; Indicates thrust; Indicates the elevator control amount; Indicates the aileron control trim value; Indicates the aileron control amount; Indicates the elevator control trim value; Indicates the thrust control amount.

5. The aerodynamic parameter identification method for small aircraft according to claim 4, characterized in that: The aerodynamic parameters of the aircraft include a total lift coefficient constant term and an elevator lift coefficient.

6. A method for identifying aerodynamic parameters of a small aircraft according to claim 5, characterized in that: Solve for the total lift coefficient constant term and the elevator lift coefficient, including: Based on the elevator control coefficient , Elevator control amount trim value , calculate A L matrix: ； Based on flight altitude , using the standard atmospheric model to calculate air density : ； Based on the aircraft mass m and air density , aircraft z-axis acceleration , flight speed and wing area ,calculate matrix: ； Based on the AL matrix and Matrix, calculate the lift coefficient: ； Also because ； Calculate the corresponding aerodynamic parameters , the total lift coefficient constant term , elevator lift coefficient .

7. The aerodynamic parameter identification method for small aircraft according to claim 1, characterized in that: The aerodynamic parameters of the aircraft include a total drag coefficient constant, an aileron drag coefficient, and an elevator drag coefficient.

8. The aerodynamic parameter identification method for small aircraft according to claim 7, characterized in that: Solve for the drag coefficient constant term, aileron drag coefficient, and elevator drag coefficient, including: Based on the elevator control coefficient , aileron control coefficient , Elevator control amount trim value , Aileron control amount trim value , elevator control amount and aileron control amount, calculate A D matrix: ； Based on flight altitude , using the standard atmospheric model to calculate air density : ； According to the thrust control coefficient , thrust control amount , aircraft x-axis acceleration , flight speed , wing area , air density And the mass of the aircraft m, calculate the bD matrix: ； Calculate the drag coefficient: ； Also because ； Calculate the corresponding aerodynamic parameters , represents the constant term of the total drag coefficient, represents the aileron drag coefficient, Indicates the elevator drag coefficient.

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