Aero-engine average preventive maintenance time assessment feasibility demonstration method

Abstract

The invention discloses a feasibility demonstration method for evaluating average preventive maintenance time of an aero-engine. The feasibility demonstration method comprises the following steps: acquiring quantitative index parameters and evaluation requirements determined during project approval demonstration of the aero-engine; the method comprises the following steps: acquiring preventive maintenance time sample distribution characteristics and preventive maintenance time observation samples according to aircraft engine preventive maintenance working characteristics and influence factors, and estimating a standard deviation S and an allowable error E of the preventive maintenance time samples; determining a confidence coefficient beta corresponding to the sample distribution characteristic mean value, and calculating a minimum sample size N of the average preventive maintenance time MPT assessment; the resources needing to be put into the flight test are calculated; when the resources needing to be put into the flight test are acceptable, it is demonstrated that quantitative index parameter evaluation determined during aeroengine project establishment demonstration is feasible, whether specified related quantitative indexes are matched with planned flight test resources or not can be determined, the flight test resources are accurately matched, and the flight test efficiency is improved. Therefore, the model identification test cost of the aero-engine is controlled.

Description

Technical Field

[0001] This invention belongs to the field of preventive maintenance technology for aero engines, specifically relating to a feasibility study method for assessing the mean preventive maintenance time (MTBG) of aero engines. Background Technology

[0002] Preventive maintenance for aircraft engines refers to all work performed to identify and eliminate potential fault signs in the engine through online inspections and manual checks, ensuring it remains in a specified condition. Maintenance work typically employs a periodic maintenance approach, with maintenance cycles including 50-hour and 100-hour intervals. To control labor costs associated with the in-service use of aircraft engines, the maintenance quantitative indicators affecting in-service labor costs, such as the mean time to preventive maintenance (MTBG), must be evaluated during the aircraft engine model development process.

[0003] The lack of quantitative indicators and feasibility assessment methods in existing national standards, military standards, and technical documents leads to a mismatch between the planned flight test resources during the identification phase and the inability to accumulate sufficient evaluation samples. This results in the inability to provide quantitative assessment conclusions, causing increased costs, delays, or unresolved issues in the identification testing of aero-engine models.

[0004] Therefore, there is an urgent need to design a technical solution to demonstrate whether the relevant quantitative indicators specified when the aero-engine project is initiated match the planned flight test resources, so as to accurately match the flight test resources, control the cost of aero-engine model identification tests, and fill the technical gaps in this field. Summary of the Invention

[0005] To address the above technical problems, this application provides a feasibility study method for assessing the mean preventive maintenance time (MTBG) of an aircraft engine, comprising the following steps:

[0006] Obtain the quantitative indicator parameters and evaluation requirements determined during the project approval and demonstration of the aero-engine, including the specified preventive maintenance cycle T. BMP The mean preventive maintenance time M under the specified preventive maintenance cycle PT and the prescribed overhaul life T of aircraft engines L The evaluation requirement is as follows: set a confidence level β and calculate the mean preventive maintenance time M. PT Interval assessment;

[0007] Based on the characteristics and influencing factors of preventive maintenance work for aero engines, the distribution characteristics of preventive maintenance time samples and the observed samples of preventive maintenance time are obtained, and the standard deviation S and permissible error E of the preventive maintenance time samples are estimated; the observed samples of preventive maintenance time are preventive maintenance time samples statistically collected during the in-service use of other similar aero engines.

[0008] Based on the sample distribution characteristics of the preventive maintenance time, determine the confidence level β corresponding to the mean of the sample distribution characteristics, and calculate the average preventive maintenance time M. PT The minimum sample size N for evaluation;

[0009] According to the specified preventive maintenance cycle T BMP The specified overhaul life T of aircraft engines L and mean preventive maintenance time M PT The minimum sample size N for evaluation is used to calculate the resources required for flight testing.

[0010] When the resources required for flight testing are acceptable, it means that the quantitative indicator parameters determined during the feasibility evaluation of the aero-engine project are feasible.

[0011] Furthermore, the confidence level β ranges from 60% to 80%, so that the mean preventive maintenance time M... PT The probability of exceeding the upper limit requirement is no more than 10%.

[0012] Furthermore, the preventive maintenance time sample distribution characteristic is that the preventive maintenance time sample follows a normal distribution.

[0013] Furthermore, the standard deviation S of the preventive maintenance time sample is estimated using the following formula:

[0014]

[0015] Among them, X i —The i-th preventive maintenance time observation sample value, i = 1, 2, 3, ..., n, where n is the total number of observation samples; —The average value of the preventive maintenance time observation sample.

[0016] Furthermore, when the total number of observed samples n is less than 30, the t-distribution approximation is used, and the formula for calculating the allowable error E is:

[0017]

[0018] Among them, t (1-β) / 2，df —The quantile of the t-distribution with confidence level β and degrees of freedom df of n-1, where n is the total number of observation samples for preventive maintenance time;

[0019] Furthermore, when the total number of observed samples n is greater than or equal to 30, the Z-normal distribution approximation is adopted, and the formula for calculating the allowable error E is:

[0020]

[0021] Among them, Z (1-β) / 2—The standard normal distribution quantile corresponding to the confidence level β.

[0022] Furthermore, the mean preventive maintenance time M PT The formula for calculating the minimum sample size N for evaluation is:

[0023]

[0024] Wherein, σ—specifies the standard deviation of the population. When σ is unknown, the standard deviation S of the preventive maintenance time sample is used as an approximation.

[0025] Furthermore, the resources required for flight testing include the minimum total flight test hours (T) for aero-engines. MIN And the number of aero engines that need to be put into flight testing, Q.

[0026] Furthermore, the minimum total flight test time T for the aero-engine MIN The calculation formula is:

[0027] Furthermore, the formula for calculating the number Q of aero engines that need to be put into flight testing is as follows:

[0028] The beneficial effects of this invention are as follows: By obtaining the quantitative indicator parameters and evaluation requirements determined during the project approval and demonstration of aero-engines, as well as the characteristics and influencing factors of preventive maintenance work for aero-engines, the distribution characteristics of preventive maintenance time samples are obtained. Based on this, preventive maintenance time observation samples are selected, and the minimum total flight test time T of the aero-engine is calculated. MIN The number of aero-engines required for flight testing, Q, reveals the relationship between quantitative indicators of preventive maintenance time, assessment confidence requirements, and assessment time and resource needs. This can be used to support feasibility studies for assessing the average preventive maintenance time of aero-engines and to demonstrate the planning of test resources. It can also determine whether the relevant quantitative indicators stipulated when aero-engine projects are initiated match the planned flight test resources, enabling precise matching of flight test resources and control of aero-engine type qualification test costs. Attached Figure Description

[0029] Figure 1 This is a flowchart of the feasibility study method for assessing the mean preventive maintenance time of aero engines provided by this invention.

[0030] Figure 2 This is a typical preventive maintenance workflow diagram for aero engines provided by the present invention. Detailed Implementation

[0031] The technical solution of the present invention is further described below, but the scope of protection is not limited to what is described.

[0032] This invention provides a method for assessing the feasibility of mean preventive maintenance time (MTBG) for aero engines, such as... Figure 1 As shown, it includes the following steps:

[0033] Step S100: Obtain the quantitative indicator parameters and evaluation requirements determined during the project initiation and demonstration of the aero-engine. The quantitative indicator parameters include the specified preventive maintenance cycle T. BMP The mean preventive maintenance time M under the specified preventive maintenance cycle PT and the prescribed overhaul life T of aircraft engines L The evaluation requirement is as follows: set a confidence level β and calculate the mean preventive maintenance time M. PT Interval assessment;

[0034] The confidence level β ranges from 60% to 80% to ensure that the mean preventive maintenance time M... PT The probability of exceeding the upper limit requirement is no more than 10%.

[0035] The higher the confidence level β requirement, the longer the mean preventive maintenance time M will be after the aero-engine is put into service. PT The lower the probability of non-compliance with the requirements, the larger the sample size required for the assessment, the more flight test resources needed, and the higher the development costs. To balance user risk and development costs, an interval assessment is generally conducted with a confidence level of 60% to 80%. When the confidence level β is 80%, the user bears a 10% risk, meaning the probability of the upper limit of the mean preventive maintenance time exceeding the requirements is 10%.

[0036] Step S200: Based on the characteristics and influencing factors of preventive maintenance work for aero engines, obtain the distribution characteristics of preventive maintenance time samples and preventive maintenance time observation samples, and estimate the standard deviation S and permissible error E of the preventive maintenance time samples;

[0037] The preventive maintenance time sample distribution characteristics are that the preventive maintenance time sample follows a normal distribution.

[0038] The scheduled preventative maintenance intervals depend primarily on the preventative maintenance tasks and their content. Typical preventative maintenance tasks and procedures for aircraft engines are as follows: Figure 2 As shown.

[0039] Preventive maintenance work for aircraft engines generally includes three main categories: maintenance, visual inspection, and functional characteristic inspection. Once the design status is determined, the work items, workflows, operating procedures, interfaces, tools, and equipment are basically fixed. At this point, the main factors affecting the preventive maintenance time are the skill level of ground maintenance personnel and weather conditions.

[0040] The factors mentioned above can cause fluctuations in the time data for each preventive maintenance operation, exhibiting the following characteristics in a large sample:

[0041] a. Symmetrically distributed within a certain range with the mean as the center;

[0042] b. The closer to the mean, the denser the data; the farther from the mean, the sparser the data.

[0043] c. The mean, median, and mode of the data basically overlap;

[0044] Based on the above characteristics, it can be inferred that the time for preventive maintenance work follows a normal distribution.

[0045] The preventive maintenance time observation sample is a sample of preventive maintenance time collected during the service life of other similar types of aircraft engines.

[0046] Using observational samples of preventive maintenance time for other similar aircraft engines, the standard deviation s and permissible error E of the samples are estimated.

[0047] The standard deviation S of the preventive maintenance time sample is estimated using the following formula:

[0048]

[0049] Among them, X i —The i-th preventive maintenance time observation sample value, i = 1, 2, 3, ..., n, where n is the total number of observation samples;

[0050] —The average value of the preventive maintenance time observation sample.

[0051] When the total number of observed samples n is less than 30, which is considered a small sample case, the t-distribution can be used as an approximation. The formula for estimating the allowable error E is as follows:

[0052]

[0053] Among them, t (1-β) / 2，df —Quantiles of the t-distribution with confidence level β and degrees of freedom df of n-1;

[0054] n—The total number of preventive maintenance time observation samples.

[0055] When the total number of observed samples n is greater than or equal to 30, the Z-normal distribution is used as an approximation, and the formula for estimating the allowable error E is:

[0056]

[0057] Among them, Z (1-β) / 2 —The standard normal distribution quantile corresponding to the confidence level β.

[0058] Step S300: Based on the sample distribution characteristics of the preventive maintenance time, determine the confidence level β corresponding to the mean of the sample distribution characteristics, and calculate the average preventive maintenance time M. PT The minimum sample size N for evaluation;

[0059] Since the preventive maintenance time of aero-engines follows a normal distribution, the average preventive maintenance time M is given by the confidence interval of the mean of the normal distribution. PT The formula for calculating the minimum sample size N for evaluation is:

[0060]

[0061] Wherein, σ—specifies the standard deviation of the population. When σ is unknown, the standard deviation S of the preventive maintenance time sample is used as an approximation.

[0062] Step S400, according to the specified preventive maintenance cycle T BMP The specified overhaul life T of aircraft engines L and mean preventive maintenance time M PT The minimum sample size N for evaluation is used to calculate the resources required for flight testing.

[0063] The resources required for flight testing include the minimum total flight test time (T) for aero-engines. MIN And the number of aero engines that need to be put into flight testing, Q.

[0064] A single aircraft engine reaches a single overhaul lifespan (T). L At that time, the number of times preventive maintenance work is triggered is N. L for:

[0065]

[0066] Several aircraft engines, after accumulating working time T W The minimum number of preventative maintenance operations N required to trigger this time. MIN for:

[0067]

[0068] Among them, the cumulative working time for TW-type aircraft engine flight test is included.

[0069] Based on equation (6), and according to the assessment requirements of the minimum sample size N for the mean preventive maintenance time assessment of aero-engines, it is estimated that at least T hours of total flight test time for aero-engines must be invested. MIN .

[0070] The minimum total flight test time T for the aero-engine MINThe calculation formula is:

[0071]

[0072] Considering the overhaul life T of the aircraft engine participating in the test L Due to limitations, it is generally necessary to plan for several engines to complete flight tests.

[0073] The formula for calculating the number Q of aero engines that need to be put into flight testing is as follows:

[0074]

[0075] Step S500: When the resources required for flight testing are acceptable, the quantitative indicator parameters determined during the feasibility evaluation of the aero-engine project are demonstrated.

[0076] Taking the process of estimating flight test resources during the project initiation and demonstration of a certain turbofan engine as an example:

[0077] 1. Obtaining the quantitative indicators and evaluation requirements determined during the project initiation and feasibility study of a certain turbofan engine: The mean preventive maintenance time indicator determined during the project initiation and feasibility study of a certain turbofan engine is as follows:

[0078] The preventive maintenance cycle is 100 hours, and the average preventive maintenance time is no more than 6 hours.

[0079] The requirement is to conduct interval assessments based on natural samples of preventative maintenance generated from flight tests, with a confidence level of 80%.

[0080] Refurbishment life T L It is 500 hours.

[0081] The estimated flight test resources are as follows:

[0082] 2. Based on the characteristics and influencing factors of preventive maintenance work for aircraft engines, obtain the distribution characteristics of preventive maintenance time samples and preventive maintenance time observation samples, and estimate the standard deviation S and permissible error E of the preventive maintenance time samples;

[0083] Based on the characteristics and influencing factors of preventive maintenance for aircraft engines, it is inferred that the overall preventive maintenance time follows a normal distribution.

[0084] Table 1 shows a sample of preventive maintenance times based on statistics from the in-service use of similar turbofan engines.

[0085] Table 1. Preventive Maintenance Time Record of a Certain Turbofan Engine

[0086] Serial Number Engine number Engine operating time Preventive maintenance time Xi 1 WS16130022 100h 6.01h 2 WS16141101 400h 6.22h 3 WS16150001 300h 5.93h 4 WS16130022 200h 6.15h 5 WS16160201 200h 5.84h 6 WS16170053 100h 5.79h 7 WS16180001 400h 6.19h 8 WS16150001 400h 6.05h 9 WS16130022 300h 5.89h 10 WS16170053 200h 6.09h 11 WS16160201 300h 5.81h 12 WS16170053 300h 5.86h

[0087] Estimate the standard deviation s of the sample according to equation (1):

[0088]

[0089] Since the total sample size is 12, which is less than 30, a small sample is used, and the t-distribution is used as an approximation. The allowable error E is estimated according to equation (2):

[0090]

[0091] 3. Based on the sample distribution characteristics of the preventive maintenance time, determine the confidence level β corresponding to the mean of the sample distribution characteristics, and calculate the average preventive maintenance time M. PT The minimum sample size N for evaluation.

[0092] With a confidence level of 80%, the minimum sample size N for evaluating the mean preventive maintenance time is calculated according to equation (4):

[0093]

[0094] 4. According to the specified preventive maintenance cycle T BMP The specified overhaul life T of aircraft engines L and mean preventive maintenance time M PT The minimum sample size N for evaluation is used to calculate the resources required for flight testing.

[0095] Based on overhaul life T L The minimum total flight test time T for an aero-engine is 500 hours, calculated according to formula (7). MIN :

[0096]

[0097] The number of aero engines Q to be put into flight testing is calculated according to formula (8):

[0098]

[0099] 5. When the resources required for flight testing are acceptable, it demonstrates that the quantitative indicator parameters determined during the feasibility study of the aero-engine project are feasible.

[0100] If the minimum total flight test time T for an aero-engine MIN If the flight time is 1375 hours and the number of aero-engines Q to be put into flight testing is 3, then the quantitative indicator parameters determined during the project establishment and demonstration of the turbofan engine are feasible.

[0101] The above-disclosed embodiments are merely specific examples of the present invention. However, the present invention is not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for assessing the feasibility of mean preventive maintenance time (MTBG) for aero-engines, characterized in that, Includes the following steps: Obtain the quantitative indicator parameters and evaluation requirements determined during the project approval and demonstration of the aero-engine, including the specified preventive maintenance cycle T. BMP The mean preventive maintenance time M under the specified preventive maintenance cycle PT and the prescribed overhaul life T of aircraft engines L The evaluation requirement is as follows: set a confidence level β and calculate the mean preventive maintenance time M. PT Interval assessment; Based on the characteristics and influencing factors of preventive maintenance work for aero engines, the distribution characteristics of preventive maintenance time samples and the observed samples of preventive maintenance time are obtained, and the standard deviation S and permissible error E of the preventive maintenance time samples are estimated; the observed samples of preventive maintenance time are preventive maintenance time samples statistically collected during the in-service use of other similar aero engines. Based on the sample distribution characteristics of the preventive maintenance time, determine the confidence level β corresponding to the mean of the sample distribution characteristics, and calculate the average preventive maintenance time M. PT The minimum sample size N for evaluation; According to the specified preventive maintenance cycle T BMP The specified overhaul life T of aircraft engines L and mean preventive maintenance time M PT The minimum sample size N for evaluation is used to calculate the resources required for flight testing. When the resources required for flight testing are acceptable, it means that the quantitative indicator parameters determined during the feasibility evaluation of the aero-engine project are feasible.

2. The feasibility study method for assessing the mean preventive maintenance time of an aero-engine as described in claim 1, characterized in that, The confidence level β ranges from 60% to 80% to ensure that the mean preventive maintenance time M... PT The probability of exceeding the upper limit requirement is no more than 10%.

3. The feasibility study method for assessing the mean preventive maintenance time of an aero-engine as described in claim 1, characterized in that, The preventive maintenance time sample distribution characteristics are that the preventive maintenance time sample follows a normal distribution.

4. The feasibility study method for assessing the mean preventive maintenance time of an aero-engine as described in claim 1, characterized in that, The standard deviation S of the preventive maintenance time sample is estimated using the following formula: Among them, X i —The i-th preventive maintenance time observation sample value, i = 1, 2, 3, ..., n, where n is the total number of observation samples; —The average value of the preventive maintenance time observation sample.

5. The feasibility study method for assessing the mean preventive maintenance time of an aero-engine as described in claim 4, characterized in that, When the total number of observed samples n is less than 30, the t-distribution approximation is used, and the formula for calculating the allowable error E is: Among them, t (1-β) / 2，df —The quantile of the t-distribution with confidence level β and degrees of freedom df of n-1, where n is the total number of observation samples for preventive maintenance time.

6. The feasibility study method for assessing the mean preventive maintenance time of an aero-engine as described in claim 5, characterized in that, When the total number of observed samples n is greater than or equal to 30, the Z-normal distribution approximation is used, and the formula for calculating the allowable error E is: Where Z(1-β) / 2 — the standard normal distribution quantile corresponding to the confidence level β.

7. The feasibility study method for assessing the mean preventive maintenance time of an aero-engine as described in claim 6, characterized in that, The mean preventive maintenance time M PT The formula for calculating the minimum sample size N for evaluation is: Wherein, σ—specifies the standard deviation of the population. When σ is unknown, the standard deviation S of the preventive maintenance time sample is used as an approximation.

8. The feasibility study method for assessing the mean preventive maintenance time of an aero-engine as described in claim 1, characterized in that, The resources required for flight testing include the minimum total flight test time (T) for aero-engines. MIN And the number of aero engines that need to be put into flight testing, Q.

9. The feasibility study method for assessing the mean preventive maintenance time of an aero-engine as described in claim 8, characterized in that, The minimum total flight test time T for the aero-engine MIN The calculation formula is:

10. The feasibility study method for assessing the mean preventive maintenance time of an aero-engine as described in claim 8, characterized in that, The formula for calculating the number Q of aero engines that need to be put into flight testing is as follows:

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