A method for evaluating the minimum flight weight of a civil helicopter to have a steady autorotation capability
Patent Information
- Application Number
- CN202510418152.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-03
- Publication Date
- 2026-10-16
AI Technical Summary
但在试验过程中，自转下滑作为高风险科目，机上必须加装测试设备以监控实时情况，和留有安全余油，因此试验重量难以达到适航取证目标的最小飞行重量，试飞过程中留有离地安全试验高度，便于高风险科目试飞处置，保障试飞安全性
[0035]本发明提出的一种评估民用直升机最小飞行重量具备稳定自转能力的方法，考虑了飞行重量、大气温度、气压高度变化因素的影响，可在确保安全的前提下，利用现有实际条件开展尽可能小的飞行重量、低温和低高度环境的飞行试验，通过采用上述不同低距位置稳定自转下滑试飞方法和建立的换算重量和旋翼转速换算关系的试飞数据处理方法，可减少试飞风险科目架次，只需保证2次不同总距低距位置有效试验即可具备试飞数据插值条件，即可获得目标取证飞行包线和转速范围限制的稳定自转的最小飞行重量，表明适航条款的符合性，突破了无法达到最小飞行重量、最小密度高度试验环境表明符合性的瓶颈。
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of helicopter design technology, and in particular relates to a method for evaluating the stable autorotation capability of a civil helicopter at its minimum flight weight. Background Technology
[0002] The Civil Helicopter Airworthiness Regulations for Transport Category Rotorcraft (CCAR-29-R2), specifically CCAR29.33, require autorotation checks to be performed at various extreme points of the flight envelope and under various environmental conditions during normal testing. Under low-weight conditions combined with low altitude and extremely cold temperatures, normal low-pitch adjustments should maintain the autorotator speed within the limits. This verifies that the rotor speed remains within the minimum speed range during autorotation flight at the lowest pressure altitude and lowest temperature within the flight envelope, thus verifying stable autorotation capability at the minimum flight weight. However, autorotation descent is a high-risk maneuver during testing, requiring onboard testing equipment for real-time monitoring and the maintenance of a safety margin of fuel. Therefore, it is difficult to achieve the minimum flight weight required for airworthiness certification. A safe test altitude is maintained during flight testing to facilitate handling of high-risk maneuvers and ensure flight safety. The selected test airport and low-temperature conditions, influenced by the actual flight testing environment, make it difficult to simultaneously achieve the designed minimum pressure altitude and lowest temperature. Therefore, it is necessary not only to combine flight testing and verification, but also to combine calculation and analysis to demonstrate compliance with airworthiness regulations. Summary of the Invention
[0003] The technical solution of this invention proposes a method for evaluating the stable autorotation capability of a civil helicopter at its minimum flight weight. In line with the requirements for airworthiness certification, it clarifies the stable autorotation gliding test flight method and test flight data processing method at different low-altitude positions to demonstrate compliance with the provisions, thus breaking through the bottleneck of not being able to demonstrate compliance with airworthiness provisions in the minimum flight weight and minimum density altitude test environment.
[0004] To achieve the above objectives, the present invention employs the following technical solution.
[0005] A method for assessing the stable autorotation capability of a civil helicopter at its minimum flight weight, the method comprising:
[0006] S1, move the helicopter collective pitch control stick to the low position;
[0007] S2, during the helicopter's autorotation and descent, acquire test flight data at this collective pitch position;
[0008] S3, process the flight test data to obtain the relationship between rotor speed and converted weight;
[0009] S4, based on the relationship in S3 and the target pressure altitude, target atmospheric temperature and target minimum weight, obtains the rotor speed at the current collective pitch position;
[0010] S5, increase the helicopter collective pitch control stick to multiple preset collective pitch positions, and repeat S2-S4; obtain multiple sets of rotor speeds at different collective pitch positions under target pressure altitude, target atmospheric temperature, and target minimum weight;
[0011] S6. Interpolate the multiple sets of data obtained in S5 to obtain the rotor speed corresponding to the target low collective pitch position;
[0012] S7 determines whether the rotor speed obtained in S6 is within the specified rotor speed range. If it is, the helicopter has stable autorotation capability at its minimum flight weight.
[0013] Otherwise, increase the target minimum weight in S5 by the preset weight increase step size, and repeat S5-S6 until the rotor speed obtained in S6 is within the specified rotor speed range.
[0014] Furthermore, in S3, the relationship between rotor speed and converted weight is obtained, specifically:
[0015]
[0016] GwN is the converted weight, N R Let k be the rotor speed, k be the slope, and b be the intercept.
[0017] Furthermore, in S3, the flight test data is processed, specifically as follows:
[0018] The flight test data was processed to obtain the relationship between rotor speed and converted weight:
[0019]
[0020] Where Gw is the actual flight weight, N R δ is the rotor speed, δ is the ratio of the atmospheric density of the current flight environment to the standard atmospheric density, and GwN is the converted weight.
[0021] Furthermore, the ratio δ between the current atmospheric density and the standard atmospheric density in the flight environment is specifically:
[0022]
[0023] The pressure ratio Δ between the current flight altitude and the standard altitude
[0024]
[0025] The temperature ratio θ between the current atmospheric temperature during flight and the standard atmospheric temperature
[0026]
[0027] Hp represents the measured atmospheric pressure altitude, and OAT represents the measured atmospheric temperature.
[0028] Furthermore, in S5, the preset total distance positions are:
[0029] Increase the helicopter collective pitch stick to the 10%, 15%, or 20% position.
[0030] Furthermore, prior to S1, the method further includes:
[0031] The design of the helicopter's autorotation descent speed and test target altitude, as well as the safe ground clearance for safety, were determined.
[0032] Furthermore, firstly, determine the range of stable autorotation test altitudes, considering the safe altitude above the ground, and adjust the speed to the minimum descent rate before entering autorotation.
[0033] Furthermore, S1 specifically refers to:
[0034] With the engine in ground slowdown mode and the collective pitch at its lowest setting, the rotor speed should be kept below the maximum continuous speed in the unpowered state during the test. If it does, the collective pitch should be increased until the rotor speed is within the normal unpowered speed range. Then, the test should be repeated with the current collective pitch maintained. Otherwise, the collective pitch should be kept at its lowest setting, and the rotor should be kept at the selected minimum descent rate to rotate steadily until the selected minimum safe takeoff altitude is reached. After completion, the test should be resumed in powered flight.
[0035] This invention proposes a method for evaluating the minimum flight weight of a civil helicopter to ensure stable autorotation capability. It considers the influence of flight weight, atmospheric temperature, and changes in air pressure and altitude. Under the premise of ensuring safety, it allows for flight tests in the smallest possible flight weight, low temperature, and low altitude environments using existing practical conditions. By employing the aforementioned stable autorotation glide flight test method at different low-distance positions and the established conversion relationship between calculated weight and rotor speed for flight test data processing, the number of risky flight test subjects can be reduced. Only two effective tests at different collective pitch and low-distance positions are required to meet the conditions for flight test data interpolation. This allows for obtaining the minimum flight weight for stable autorotation within the target certification flight envelope and rotor speed range limits, demonstrating compliance with airworthiness regulations. This method overcomes the bottleneck of not being able to demonstrate compliance in the minimum flight weight and minimum density altitude test environment. Detailed Implementation
[0036] The technical solution of the present invention will be described in detail below.
[0037] This invention provides a method for evaluating the stable autorotation capability of a civil helicopter at its minimum flight weight. The method includes: 1) defining the autorotation glide flight test method for helicopters at different low-altitude positions; 2) proposing a conversion method between autorotation glide flight weight and rotor speed and processing the flight test data, calculating the rotor speed corresponding to the target weight and density altitude based on the flight test results; 3) determining an interpolation method for stable autorotation glide flight test data at different low-altitude positions, interpolating the rotor speed at the minimum flight weight, minimum temperature of the flight envelope, and pressure altitude combination (minimum density altitude) around the certification target value and considering the collective pitch tolerance range, and comparing it with the minimum speed range limit of the certification target to indicate whether compliance with the requirements is met; 4) if the calculation and analysis results do not meet the requirements, the target minimum flight weight can be adjusted to obtain the minimum flight weight that meets the rotor speed range conditions for unpowered autorotation glide.
[0038] Specifically,
[0039] 1) Defining the method for obtaining rotor speed test data at different low-pitch positions: Taking a twin-engine civil helicopter as an example, first determine the stable autorotation test altitude range (e.g., 1500m→500m). Considering the safe altitude above the ground, adjust the speed to the long-flight speed before entering autorotation. Place both engines in ground slowdown mode and set the collective pitch to the minimum (do not increase the collective pitch unless the rotor speed exceeds the maximum continuous speed). Then, maintain this collective pitch and speed throughout the required altitude range for a stable descent. After completion, resume powered flight. Then, select low pitches of 10%, 15%, or 20% (different from the minimum collective pitch position) and maintain stability, repeating the above steps. This will obtain at least one set of test data at different low-pitch positions.
[0040] 2) Based on the flight test data obtained above, the following methods were used for processing and analysis. The rotor speed corresponding to the target weight and density altitude was calculated based on the flight test results. Where Hp(ft) is the measured pressure altitude, OAT(°C) is the measured atmospheric temperature, Gw is the actual flight weight, and N... R This represents the rotor speed.
[0041] Pressure ratio Δ
[0042]
[0043] Temperature ratio θ
[0044]
[0045] Density ratio δ
[0046]
[0047] GwN is the converted weight:
[0048]
[0049] Based on autorotation flight test data with a small weight and constant collective pitch, the rotor speed corresponding to the minimum collective pitch was analyzed, and the conversion method between rotor speed and equivalent weight under the same collective pitch was established as shown in the following formula:
[0050]
[0051] Linear fitting was performed on the above flight test data points to obtain the slope k and intercept b. Then, the rotational speed NR at the current low-altitude position was obtained based on the target pressure altitude, atmospheric temperature, and minimum target weight.
[0052] 3) Determine the interpolation method for stable autorotation glide flight test data at different low altitude positions; Based on the flight test data corresponding to different low altitudes obtained in 1) and the rotor speed corresponding to different low altitude positions after processing in 2), linear or polynomial fitting interpolation methods can be used to calculate the rotor speed under the combination of minimum flight weight, minimum temperature of flight envelope, and pressure altitude (minimum density altitude) around the certification target value and considering the collective pitch tolerance range. Compare this with the minimum speed range limit of the certification target to indicate whether the compliance with the clause is met.
[0053] 4) If the calculation and analysis results in 3) do not meet the requirements, the minimum target flight weight in 2) can be adjusted, and the interpolation method in 3) can be repeated until the minimum flight weight that meets the conditions of the unpowered autorotating glide rotor speed range is obtained.
[0054] This invention proposes a method for evaluating the minimum flight weight of a civil helicopter to ensure stable autorotation capability. The method itself considers the influence of flight weight, atmospheric temperature, and changes in air pressure and altitude. Under the premise of ensuring safety, it can conduct flight tests in the smallest possible flight weight, low temperature, and low altitude environment using existing actual conditions. By adopting the above-mentioned stable autorotation glide flight test method at different low distance positions and the flight test data processing method that establishes the conversion relationship between converted weight and rotor speed, the number of risky flight test subjects can be reduced. Only two effective tests at different collective pitch and low distance positions are required to meet the conditions for flight test data interpolation. The minimum flight weight for stable autorotation within the target certification flight envelope and speed range limits can be obtained, indicating compliance with airworthiness provisions. This method overcomes the bottleneck of not being able to demonstrate compliance in the minimum flight weight and minimum density altitude test environment.
Claims
1. A method for evaluating the stable autorotation capability of a civil helicopter at its minimum flight weight, characterized in that, The method includes: S1, set the helicopter collective pitch stick position to below 5%; S2, during the helicopter's autorotation descent, acquires test flight data at this collective pitch position, including: barometric altitude, atmospheric temperature, rotor speed, and flight weight; S3, process the flight test data described in S2 to obtain the relationship between rotor speed and converted weight; S4, based on S3 and the target pressure altitude, target atmospheric temperature and target minimum weight, obtains the rotor speed at the current collective pitch position; S5, increase the position of the helicopter collective pitch control stick to multiple preset collective pitch positions, and repeat S2-S4; obtain multiple sets of rotor speeds at different collective pitch positions under target air pressure altitude, target atmospheric temperature and target minimum weight; S6. Interpolate the multiple sets of data obtained in S5 to obtain the rotor speed corresponding to the target low collective pitch position; S7 determines whether the rotor speed obtained in S6 is within the specified rotor speed range. If it is, the helicopter has stable autorotation capability at its minimum flight weight. Otherwise, increase the target minimum weight in S4 by the preset weight increase step size, and repeat S4-S6 until the rotor speed obtained in S6 is within the specified rotor speed range.
2. The method for evaluating the stable autorotation capability of a civil helicopter at its minimum flight weight according to claim 1, characterized in that, In S3, the flight test data is processed, specifically as follows: The flight test data was processed to obtain the relationship between rotor speed and converted weight: Where Gw is the actual flight weight, N R δ is the rotor speed, δ is the ratio of the atmospheric density of the current flight environment to the standard atmospheric density, and GwN is the converted weight.
3. The method for evaluating the stable autorotation capability of a civil helicopter at its minimum flight weight according to claim 1, characterized in that, S3, a linear fit is performed on the rotor speed and the equivalent weight, and the resulting relationship between rotor speed and equivalent weight is as follows: GwN is the converted weight, N R Let be the rotor speed, k be the slope, and b be the intercept.
4. The method for evaluating the stable autorotation capability of a civil helicopter at its minimum flight weight according to claim 3, characterized in that, In S5, the preset total distance positions are: Increase the helicopter collective pitch control stick to the 10%, 15%, or 20% collective pitch position.
5. The method for evaluating the stable autorotation capability of a civil helicopter at its minimum flight weight according to claim 1, characterized in that, Prior to S1, the method further includes: Design the helicopter's autorotation descent speed, the target test altitude, and the safe ground clearance.
6. The method for evaluating the stable autorotation capability of a civil helicopter at its minimum flight weight according to claim 5, characterized in that, First, determine the stable autorotation test altitude range, consider the safe altitude off the ground, and adjust the speed to the minimum descent rate before entering the autorotation phase.
7. The method for evaluating the stable autorotation capability of a civil helicopter at its minimum flight weight according to claim 1, characterized in that, S1 specifically refers to: With the engine in ground slowdown mode and the collective pitch at its lowest setting, the rotor speed should be kept below the maximum continuous speed in the unpowered state during the test. If it does, the collective pitch should be increased until the rotor speed is within the normal unpowered speed range. Then, the test should be repeated with the current collective pitch maintained. Otherwise, the collective pitch should be kept at its lowest setting, and the rotor should be kept at the selected minimum descent rate to rotate steadily until the selected minimum safe takeoff altitude is reached. After completion, the test should be resumed in powered flight.
8. A device for evaluating the stable autorotation capability of a civil helicopter at its minimum flight weight, characterized in that, The apparatus is used to perform the method as described in any one of claims 1-7.