Calculation Method of Fighter Structural Life

Abstract

The present invention discloses a method for calculating the structural life of a fighter jet, comprising: obtaining flight parameters, fuel consumption, and mounting status information of the fighter jet to be evaluated; preprocessing the overload data of the fighter jet to be evaluated to obtain effective overload data; obtaining equivalent weight information, equivalent overload information, and equivalent load information of the fighter jet to be evaluated based on at least one of the flight parameters, fuel consumption, mounting status information, and effective overload data; converting the equivalent load information into a structural load spectrum and correcting the structural load spectrum; and calculating the fatigue life of the fighter jet to be evaluated using a fatigue damage criterion based on the corrected structural load spectrum. An embodiment of the present invention proposes a method for calculating the structural life of a fighter jet based on tactical missions, utilizing flight parameter data to monitor the structural life of the fighter jet during tactical missions, thereby providing support for fighter airframe structural risk assessment and rational use planning.

Description

Technical Field

[0001] The present invention relates to the technical field of aircraft structure health monitoring, and in particular to a method for calculating the structural life of a fighter jet. Background Art

[0002] Fighter jets are military aircraft used to gain air superiority and destroy the enemy's ability to use it during wartime. They are characterized by excellent flight performance, maneuverability, and powerful firepower. Due to the demands of tactical missions, fighter jets are often required to perform high-G maneuvers during tactical training. These maneuvers subject the airframe to loads exceeding 7g, exacerbating fatigue damage to key load-bearing structures such as the wing. Furthermore, to maximize combat effectiveness during tactical missions, fighter jets often need to take off with full fuel and ammunition. A certain domestically produced heavy fighter can carry approximately ten tons of fuel and several tons of ammunition, adding tens of tons to the aircraft's weight. Combined with high-G maneuvers, these maneuvers place even greater stress on the airframe, significantly reducing its lifespan. Due to frequent high-G maneuvering tactical training missions, a certain domestically produced aircraft developed extensive cracks in its wing structure, resulting in the aircraft's operational restrictions and severely hampering the military's flight training.

[0003] Currently, the traditional method for monitoring the service life of our military aircraft still relies on fleet-based life calculations. This fleet life calculation method is based on the expected usage intensity of the fleet, but the usage intensity of each aircraft during its service life is not uniform. Using aircraft flight parameter data for individual aircraft life monitoring is an economically feasible method. Flight parameter data records the changes in the aircraft's center of gravity during flight, including information such as aircraft position, altitude, speed, overload, and attitude. This information can be used to determine the aircraft's mission load. Based on this mission load information, the aircraft structure is treated as a whole. By introducing an equivalent damage index, a relationship can be established between the aircraft's flight load history and the severity of the baseline spectrum. As our military's combat-oriented training continues to deepen, the intensity of tactical training and flight time of fighter units have continued to increase, and the unit's combat effectiveness has also continued to improve. However, at the same time, the high-intensity tactical training missions have also placed a significant burden on the equipment, resulting in rapid depletion of fighter service life and the emergence of previously unseen structural strength issues.

[0004] Therefore, how to improve the accuracy of structural life assessment results for fighter jets performing high-overload maneuvering tactical missions has become an urgent problem to be solved. Summary of the Invention

[0005] In view of this, an embodiment of the present invention provides a method for calculating the structural life of a fighter jet to solve the problem in the prior art of using a traditional calculation method based on the life of a fleet of aircraft, which results in insufficient accuracy in the structural life assessment of fighter jets performing high-overload maneuvering tactical missions.

[0006] An embodiment of the present invention provides a method for calculating the structural life of a fighter aircraft, comprising:

[0007] Obtain flight parameters, fuel consumption, and mount status information of the fighter to be evaluated;

[0008] Pre-process the overload data of the fighter to be evaluated to obtain effective overload data;

[0009] Obtaining equivalent weight information, equivalent overload information, and equivalent load information of the fighter to be evaluated based on at least one of flight parameters, fuel consumption, load status information, and effective overload data;

[0010] Convert the equivalent load information into a structural load spectrum and modify the structural load spectrum;

[0011] According to the modified structural load spectrum, the fatigue life of the fighter to be evaluated is calculated using the fatigue damage criterion.

[0012] Optionally, the flight parameters include overload, remaining fuel, flight time and external hardpoint position.

[0013] Optionally, before pre-processing the overload data of the fighter to be evaluated to obtain effective overload data, the method further includes:

[0014] Obtain the center of gravity overload history and fuel consumption history of the fighter to be evaluated.

[0015] Optionally, the overload data of the fighter to be evaluated is preprocessed to obtain effective overload data, including:

[0016] Interpret the flight parameter data of the fighter to be evaluated to eliminate distorted and lost data;

[0017] The rain flow counting method is used to count the overload spectrum of the fighter aircraft to be evaluated, and the overload peak-valley curve is obtained by removing the middle point.

[0018] According to the preset filtering threshold, the small overload cycle data in the overload peak-valley history curve is filtered out.

[0019] Optionally, the setting of the preset filtering threshold includes:

[0020] Select at least three typical overload cycles;

[0021] Calculate structural fatigue damage based on typical overload cycles;

[0022] The threshold range is determined based on the calculated damage ratio.

[0023] Optionally, obtaining equivalent weight information of the fighter to be evaluated includes:

[0024] Obtain the distances of each fuel tank and hardpoint relative to the center of gravity of the fighter to be evaluated, calculate the corresponding loads based on the bending moments of the fuel tanks and hardpoints, and convert the weight of the fighter to be evaluated into an equivalent weight at standard takeoff weight.

[0025] According to the fuel consumption of each internal tank and the external mount situation of the fighter to be evaluated, the remaining fuel weight and external mount weight are converted into the remaining fuel equivalent weight and external mount equivalent weight respectively.

[0026] Optionally, the equivalent overload information of the fighter to be evaluated is calculated based on the measured instantaneous overload, the equivalent weight of the fighter to be evaluated and the standard take-off weight.

[0027] Optionally, the equivalent load information of the fighter to be evaluated is calculated based on the structural load and equivalent overload information at the standard take-off weight.

[0028] Optionally, the Miner criterion is used to calculate the fatigue life of the fighter aircraft to be evaluated.

[0029] Optionally, the Goodman model is used to modify the structural load spectrum.

[0030] Beneficial effects of the embodiments of the present invention:

[0031] To address the issue of fighter aircraft airframe structural life consumption caused by high-G maneuvering flights during tactical missions, an embodiment of the present invention proposes a fighter aircraft structural life calculation method based on tactical missions. This method uses flight parameter data to monitor the fighter aircraft structural life during tactical missions, providing support for fighter aircraft airframe structural risk assessment and reasonable usage planning arrangements. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the present invention in any way. In the accompanying drawings:

[0033] Figure 1 A flowchart of a method for calculating the structural life of a fighter jet in Example 1 of the present invention is shown;

[0034] Figure 2 The diagram shows the center of gravity overload process of a certain type of fighter during a certain tactical mission in Example 2 of the present invention;

[0035] Figure 3 A simplified overload cycle in embodiment 2 of the present invention is shown. DETAILED DESCRIPTION

[0036] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making any creative efforts shall fall within the scope of protection of the present invention.

[0037] Example 1

[0038] The embodiment of the present invention provides a method for calculating the life of a fighter aircraft structure. Figure 1 As shown, including:

[0039] Step S1, obtaining the flight parameters, fuel consumption and mounting status information of the fighter to be evaluated.

[0040] In this embodiment, fighter flight parameter data is filtered to calculate the fighter's structural lifespan. Parameters such as overload, remaining fuel, flight time, and external hardpoints are selected, and the aircraft's center-of-gravity overload history and fuel consumption history are recorded. The aircraft's fuel weight can be calculated by calculating the remaining fuel weight for each overload cycle in the filtered overload spectrum based on the flight time corresponding to each overload cycle. While the flight parameter data does not record parameters for aircraft payload weight, it does record the presence or absence of payloads at each external hardpoint. The payload type and weight can then be determined based on the flight training subject.

[0041] Step S2: pre-processing the overload data of the fighter to be evaluated to obtain effective overload data.

[0042] Step S3, obtaining the equivalent weight information, equivalent overload information, and equivalent load information of the fighter to be evaluated based on at least one of the flight parameters, fuel consumption, mounting status information, and effective overload data.

[0043] In this embodiment, the weight of the fighter jet in flight is composed of the aircraft empty weight, pilot weight, remaining fuel weight, and payload weight. The aircraft empty weight and pilot weight can be considered as known fixed values, while the remaining fuel weight and payload weight are obtained based on the flight parameters, fuel consumption, and payload status information in step S1.

[0044] To increase range and combat effectiveness, modern fighter jets are increasingly carrying more fuel and ammunition. To accommodate this increased fuel, fuel tanks are located throughout the fuselage, including on the wings and vertical tail. Externally, there are typically several to dozens of hardpoints. Obviously, different fuel tank and hardpoint locations will cause varying levels of fatigue damage to the airframe structure. The farther from the aircraft's center of gravity, the greater the load. Based on flight parameters, fuel consumption, and load status information, the weight of the aircraft's internal fuel tanks and the remaining fuel weight in externally mounted tanks can be determined.

[0045] In order to calculate the structural life more accurately, the load is calculated based on the distance of each fuel tank and external attachment point relative to the center of gravity of the aircraft and the bending moment, and the aircraft weight is converted into an equivalent weight under the standard takeoff weight.

[0046] In a specific embodiment, obtaining the equivalent weight information of the fighter to be evaluated includes:

[0047] Obtain the distances of each fuel tank and hardpoint relative to the center of gravity of the fighter to be evaluated, calculate the corresponding loads based on the bending moments of the fuel tanks and hardpoints, and convert the weight of the fighter to be evaluated into an equivalent weight at standard takeoff weight.

[0048] According to the fuel consumption of each internal tank and the external mount situation of the fighter to be evaluated, the remaining fuel weight and external mount weight are converted into the remaining fuel equivalent weight and external mount equivalent weight respectively.

[0049] In a specific embodiment, the equivalent overload information of the fighter to be evaluated is calculated based on the measured instantaneous overload, the equivalent weight of the fighter to be evaluated, and the standard take-off weight.

[0050] In a specific embodiment, the equivalent load information of the fighter to be evaluated is calculated based on the structural load and equivalent overload information at a standard take-off weight.

[0051] In a specific embodiment, the remaining fuel weight of the aircraft and the external load weight are converted into the remaining fuel equivalent weight and the external load equivalent weight, respectively, based on the fuel consumption of each fuel tank inside the aircraft and the external load situation.

[0052] The remaining fuel equivalent weight is:

[0053] W y '=∑W y ×l y (1)

[0054] Where W y ' is the remaining fuel equivalent weight; W y is the weight of the remaining fuel in the tank; l y is the position of the fuel tank relative to the aircraft's center of gravity.

[0055] The equivalent weight of external stores is:

[0056] W g '=∑W g ×l g (2)

[0057] Where W g ' is the external load equivalent weight; W g The external hanging point mounting weight; l g The position of the attachment point relative to the aircraft's center of gravity.

[0058] The equivalent weight of the aircraft is:

[0059] W'=W0+W y '+W g ' (3)

[0060] Where W' is the equivalent weight of the aircraft; W0 is the empty weight of the aircraft.

[0061] For the airframe structure related to the fighter's center of gravity overload, its structural fatigue damage under large overload can be quantified and converted to the equivalent overload under the standard takeoff weight. The fighter's overload under different tactical missions is quantified and converted to the overload under the standard takeoff weight:

[0062] G'=G0×W' / W1 (4)

[0063] Where G' is the equivalent overload; G0 is the measured instantaneous overload; W1 is the standard takeoff weight.

[0064] After obtaining the equivalent overload of the fighter under different tactical missions, the equivalent load of the fighter structure can be calculated by the structural load under the standard takeoff weight:

[0065] P'=P0×G' (5)

[0066] Where P' is the equivalent load; P0 is the structural load at standard takeoff weight.

[0067] Step S4: converting the equivalent load information into a structural load spectrum and correcting the structural load spectrum.

[0068] The overload spectrum obtained from the flight data of the fighter to be evaluated is converted into a structural load spectrum. However, the stress ratio R of each load cycle in the converted load spectrum is inconsistent, which is not conducive to fatigue life calculation. In addition, the mean stress also affects the fatigue life of the structure. In this embodiment, the structural load spectrum is corrected using a mean stress correction model.

[0069] Step S5: Calculate the fatigue life of the fighter to be evaluated according to the corrected structural load spectrum and the fatigue damage criterion.

[0070] To address the issue of high-overload maneuvering during tactical missions consuming the fighter's airframe structure life, the embodiments of the present invention utilize flight parameter data to monitor the fighter's structural life during tactical missions. The flight parameter data is used to obtain the fighter's overload history, and the fighter's overloads under different tactical missions are converted into equivalent overloads, thereby achieving accurate calculation of the fighter's structural life after executing the tactical mission. This can provide support for fighter airframe structure risk assessment and reasonable usage planning arrangements.

[0071] As an optional implementation, preprocessing the overload data of the fighter to be evaluated to obtain effective overload data includes:

[0072] Interpret the flight parameter data of the fighter to be evaluated to eliminate distorted and lost data;

[0073] In this embodiment, due to the influence of electronic interference, noise, etc., there may be data errors, data loss, etc. in the flight parameter data. It is necessary to first interpret the flight parameter data and pre-process the distorted and lost data.

[0074] The rain flow counting method is used to count the aircraft overload spectrum of the fighter to be evaluated, and the overload peak-valley history curve is obtained by removing the middle point.

[0075] In this embodiment, the sampling rate of flight parameter data also plays a significant role in calculating the fighter's structural lifespan. The higher the sampling rate, the more accurately it reflects the aircraft's true state. Especially for aircraft overload conditions, a low sampling rate may miss peaks and valleys in the aircraft's overload, affecting the accuracy of the structural lifespan calculation. However, an excessively high sampling rate can result in a significant increase in the amount of data. In fatigue life calculations, only peaks and valleys in the load are considered. Therefore, to simplify the overload spectrum, the midpoints of the spectrum can be removed, retaining only the peaks and valleys.

[0076] The rainflow counting method is a commonly used structural load spectrum screening method. It can convert random load spectra obtained from field measurements into multiple cyclic load spectra to facilitate fatigue life calculation of structures. This embodiment uses the rainflow counting method to count the measured aircraft overload spectrum, obtaining an overload peak-valley history curve with the intermediate points removed.

[0077] According to the preset filtering threshold, the small overload cycle data in the overload peak-valley history curve is filtered out.

[0078] In this embodiment, the overload peak-valley history curve obtained by counting the aircraft's overload spectrum using the rainflow counting method serves as the basis for calculating the structural fatigue life. However, structural fatigue life is primarily affected by high-overload cycles, while the impact of low-overload cycles on airframe structural fatigue damage is almost negligible. Therefore, to reduce the complexity of structural life calculations, an appropriate filtering threshold is selected to filter out low-overload cycles from the overload spectrum.

[0079] As an optional implementation, the setting of the preset filtering threshold includes:

[0080] Select at least three typical overload cycles;

[0081] Calculate structural fatigue damage based on typical overload cycles;

[0082] The threshold range is determined based on the calculated damage ratio.

[0083] In this embodiment, the selection of the threshold for overload spectrum filtering is crucial. While filtering out small overload cycles that have little impact on structural fatigue damage, it is also crucial to ensure that the cumulative damage of the filtered overload spectrum is substantially consistent with the original overload spectrum. To ensure the effectiveness of the filtering threshold, several typical overload cycles can be selected, and the structural fatigue damage can be calculated. An effective threshold can then be selected based on the calculated damage ratio.

[0084] As an optional implementation, the Miner criterion is used to calculate the fatigue life of the fighter aircraft to be evaluated.

[0085] After obtaining the corrected load spectrum of the fighter structure, the fatigue life of the structure can be calculated using the fatigue damage criterion. The Miner fatigue damage criterion is a fatigue life calculation method widely used in engineering. It has the characteristics of simple form and convenient engineering calculation. This embodiment uses the Miner criterion to calculate the fatigue life of the fighter structure. The form of the Miner criterion is:

[0086]

[0087] Where n i is the number of cycles at each stress level in the load spectrum; N i is the number of failure cycles under each stress level; D is the total damage of the structure; k represents the level of the load spectrum stress level.

[0088] As an optional implementation, the Goodman model is used to correct the structural load spectrum.

[0089] In this embodiment, the Goodman model is used to correct the load spectrum. The calculation formula of the Goodman model is:

[0090]

[0091] Where, σ a is the stress amplitude; σ m is the stress mean; σ ae is the equivalent stress amplitude; σ b is the tensile strength of the material.

[0092] Example 2

[0093] A certain fighter jet has an empty weight of 14 tons, a maximum takeoff weight of 30 tons, a maximum internal fuel capacity of 6.5 tons, and nine external hardpoints. This example uses this fighter jet as an example. Based on its structural characteristics and tactical missions, flight parameter data is used to calculate its structural fatigue life. This calculation verifies the tactical mission-based fighter jet structural life calculation method proposed in Example 1.

[0094] 1. Equivalent weight calculation

[0095] This fighter has nine external attachment points, and the distances from each attachment point to the aircraft's centerline are shown in Table 1. The tactical missions performed by this fighter include combat patrol, interception, ground suppression, close air support, anti-ship, anti-runway, anti-armor, and bombing. High-overload maneuvers are performed during combat patrol and interception missions. Therefore, three typical tactical missions, combat patrol, combat patrol / intercept, and interception, were selected to calculate the structural life of this fighter. The attachment schemes for these three typical tactical missions are shown in Table 2. Equation (2) was used to convert the attachment weights for each attachment scheme into equivalent attachment weights.

[0096] Table 1. Position of mounting points on a certain fighter jet (unit: m)

[0097]

[0098] Table 2 Equivalent payload weight under different mounting schemes (unit: kg)

[0099]

[0100] Table 3 Internal fuel tank position of a certain fighter (unit: m)

[0101]

[0102] Table 4 Internal fuel equivalent weight (unit: t)

[0103]

[0104] The internal fuel of this fighter is mainly stored in the fuselage, wings and vertical tail structure. The position of each internal fuel tank from the center of gravity of the aircraft is shown in Table 3. The fuel weight is converted into equivalent fuel weight using formula (1), as shown in Table 4.

[0105] 2. Equivalent weight calculation

[0106] The structural life of this fighter jet was calculated for three typical tactical missions, and the results are shown in Table 5. As can be seen in the table, under a high overload of 7g, the structural fatigue damage of the fighter jet with full fuel and ammunition is significantly higher than that with no ammunition. The structural damage under maximum load reached 15.02 times that of the no ammunition state. However, in actual missions, fighter jets typically do not perform high-overload maneuvers with full fuel. Instead, they consume a certain amount of fuel and reach the designated area before commencing tactical training. Conditions 5 and 6 in Table 5 more closely reflect this reality. In these two cases, the structural fatigue damage of the fighter jet reached 3.22 and 1.80 times that of the full fuel and no ammunition state, respectively.

[0107] Table 5 Structural damage of fighter jets under different tactical missions

[0108]

[0109] 3. Structural life calculation based on tactical missions

[0110] According to the overload spectrum recorded in the flight parameter system of this type of fighter, its structural fatigue cumulative damage during a tactical mission can be calculated. The overload spectrum of this type of fighter obtained by the flight parameter system during a tactical mission is as follows: Figure 2 shown.

[0111] The obtained overload spectrum is preprocessed by interpretation, simplification, filtering, etc., and the overload spectrum is counted using the rain flow counting method. The overload cycles after counting are as follows: Figure 3 shown. Figure 3 As can be seen from the figure, after the rain flow counting method is used, the overload spectrum is simplified to 7 overload cycles. The fatigue damage of the airframe structure under each level of overload cycle is calculated, and the results are shown in Table 6. It can be seen from Table 6 that the fatigue cumulative damage of the airframe structure in this flight mission is 9.51×10 -5 Based on the load of this flight mission, the fatigue life of the airframe structure is 10,515 times.

[0112] Table 6 Fatigue damage at various levels of overload cycles

[0113]

[0114] Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention. Such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A method for calculating the structural life of a fighter aircraft, characterized in that: include: Obtain flight parameters, fuel consumption, and mount status information of the fighter to be evaluated; Preprocessing the overload data of the fighter to be evaluated to obtain effective overload data; acquiring, based on at least one of the flight parameters, the fuel consumption, the load status information, and the effective overload data, equivalent weight information, equivalent overload information, and equivalent load information of the fighter to be evaluated; converting the equivalent load information into a structural load spectrum, and correcting the structural load spectrum; performing fatigue life calculation on the fighter to be evaluated according to the modified structural load spectrum and using fatigue damage criteria; The flight parameters include the overload data, remaining fuel, flight time and external hardpoint position; Obtaining the equivalent weight information of the fighter to be evaluated includes: Obtaining the distance between each fuel tank and external hardpoint and the center of gravity of the fighter to be evaluated, calculating the corresponding load based on the bending moment of the fuel tank and the external hardpoint, and converting the weight of the fighter to be evaluated into an equivalent weight at a standard takeoff weight; Based on the fuel consumption of each internal tank and the external load situation of the fighter to be evaluated, the remaining fuel weight and the external load weight are converted into the remaining fuel equivalent weight and the external load equivalent weight respectively; Calculating equivalent overload information of the fighter to be evaluated based on the measured instantaneous overload, the equivalent weight of the fighter to be evaluated, and the standard takeoff weight; The equivalent load information of the fighter to be evaluated is calculated based on the structural load at the standard take-off weight and the equivalent overload information.

2. The method for calculating the structural life of a fighter aircraft according to claim 1, characterized in that: Before pre-processing the overload data of the fighter to be evaluated to obtain effective overload data, the method further includes: Obtain the center of gravity overload history and fuel consumption history of the fighter to be evaluated.

3. The method for calculating the structural life of a fighter aircraft according to claim 1, characterized in that: Preprocessing the overload data of the fighter to be evaluated to obtain effective overload data includes: Interpreting the flight parameter data of the fighter to be evaluated to eliminate distorted data and lost data; The aircraft overload spectrum of the fighter to be evaluated is counted using a rain flow counting method to obtain an overload peak-valley history curve excluding the middle point; According to a preset filtering threshold, small overload cycle data in the overload peak-valley history curve is filtered out.

4. The method for calculating the structural life of a fighter jet according to claim 3, characterized in that: The setting of the preset filtering threshold includes: Select at least three typical overload cycles; Calculate the structural fatigue damage based on the typical overload cycles; The threshold range is determined based on the calculated damage ratio.

5. The method for calculating the structural life of a fighter aircraft according to claim 1, characterized in that: The Miner criterion is used to calculate the fatigue life of the fighter to be evaluated.

6. The method for calculating the structural life of a fighter aircraft according to claim 1, characterized in that: The Goodman model is used to correct the structural load spectrum.

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