A method and system for measuring the distance between the blades of upper and lower rotors based on measured bending moment

Abstract

The present application belongs to the technical field of helicopter dynamics test, and relates to a method and system for measuring the distance between blades of upper and lower rotors based on measured bending moment. The measured bending moment data in flight is used, and the existing blade measurement system is used. Without additional measurement equipment, the relationship between bending moment and deformation is used to establish the calibration relationship between the test bending moment and the deformation of different profiles of the blade, so as to obtain the distance between the blades of the upper and lower rotors in the real-time flight state. The method can relatively real-time monitor the distance between the blades of the upper and lower rotors in the full flight spectrum state without additional measurement equipment, and ensure flight safety. The method has the advantages of simplifying the measurement method of the blade tip distance, shorter feedback time compared with the light ray sensor and radar wave measurement, and better real-time effect.

Description

Technical Field

[0001] This invention belongs to the field of helicopter dynamics testing technology, and relates to a method and system for measuring the distance between the upper and lower rotor blades based on measured bending moment. Background Technology

[0002] This invention relates to the measurement of the vertical distance between the upper and lower rotor blades on the same rotor shaft in a dual-rotor aircraft, used for the rapid determination of whether the blades of the upper and lower rotors on the same rotor shaft are in close proximity during flight. Currently, methods for measuring the distance between the upper and lower rotors include optical sensors or radar measurement, utilizing light source positioning, electromagnetic waves, and ultrasonic waves for measurement. Various measuring instruments need to be installed to provide relatively real-time feedback on the distance between the blades under different flight conditions, achieving the goal of real-time monitoring of the blade distance during flight and ensuring that the blades of the upper and lower rotors do not collide during flight.

[0003] Current measurement methods, while providing relatively real-time feedback on the distance between propeller blades under various flight conditions, require additional equipment installation and are often affected by factors such as installation location, space, and factors like light, weather, and electromagnetic interference during flight. This results in high measurement costs and limited data, making it impossible to guarantee the monitoring of the distance between propeller blades under all flight conditions. Summary of the Invention

[0004] Purpose of the invention

[0005] By utilizing measured bending moment data during flight and existing blade measurement systems, without adding additional measurement equipment, the relationship between bending moment and deformation is established to calibrate the test bending moment and the deformation of different blade profiles, thereby obtaining the blade distance between the upper and lower rotors in real-time flight.

[0006] Technical solution

[0007] A method and system for measuring the distance between upper and lower rotor blades based on measured bending moment is proposed, and the scheme is as follows:

[0008] 1. Through calculation and analysis, the vertical bending moment and vertical displacement of different blade profiles are obtained;

[0009] 2. Establish the relationship between vertical bending moment and vertical displacement;

[0010] 3. Obtain the measured vertical displacement based on the measured bending moment;

[0011] 4. Obtain the blade distance between the rotors based on the vertical displacement of the upper and lower rotors.

[0012] The specific steps are as follows:

[0013] 1. Establish a computational analysis model and verify it through experimental bending moments to obtain the vertical bending moment and vertical displacement of different blade profiles under flight conditions.

[0014] 2. Using the calculation results, the relationship between vertical bending moment and vertical displacement of the blade at different cross sections is calibrated. Based on the calculation results obtained in step (1), the relationship between flapping bending moment and flapping displacement at the corresponding blade root spanwise position under different states is established. The linearity of the relationship is used as the benchmark, and the blade root spanwise position with good linearity is selected. Then, the relationship between the displacement at the blade root position and the blade tip displacement is established, and finally, the relationship between the blade root bending moment and the blade tip vertical displacement is determined. Establishing the relationship between vertical bending moment and vertical displacement is the key point of this method. In the process of establishing the linear relationship, the linear relationship analysis of flapping bending moment and flapping displacement at multiple states and multiple spanwise positions should be carried out, and the average value should be selected.

[0015] 3. Based on the measured bending moment results during flight, the vertical bending moment and vertical displacement relationship expression in (2) are used to obtain the displacement of the blade at different spanwise positions. Based on the measured flapping moment at the root of the blade, the relationship a obtained in step (2) is used to convert it into the vertical displacement result of the blade tip, thereby obtaining the measured vertical displacement b of the blade tip in the flight state of a rotor (b1 for the upper rotor and b2 for the lower rotor to distinguish).

[0016] 4. Based on the rotor configuration and the static blade spacing between the upper and lower rotors, correct the result of step (3) to finally obtain the vertical distance between the upper and lower rotor blades in flight. In step (3), the flapping displacements b1 and b2 of the upper and lower rotors were obtained respectively. Based on the shaft spacing c of the upper and lower rotors in the rotor configuration, through geometric transformation, the vertical distance d at the same spanwise position of the upper and lower rotor blades was finally obtained.

[0017] d = b1 + c - b2

[0018] In step 1, the theoretical calculations of blade bending moment and aeroelastic response under flight conditions are first performed. The structural model of the calculation model adopts the moderately deformable beam theory, the blade is an elastically deformable beam, and the aerodynamic model airfoil adopts the second-order lift line theory, using a free wake model. The focus of this method is on establishing the relationship between blade flapping bending moment and vertical displacement. Therefore, the calculation methods for blade flapping bending moment and aeroelastic response in the calculation model are not described in detail. The calculation result is considered usable if the error of the first harmonic quantity is within 15% when comparing the calculated bending moment with the experimental bending moment.

[0019] In step 2, the main influence in this relationship is the blade structural stiffness. There is a certain aerodynamic bending moment effect, but its proportion is small and can be ignored in rapid calculations. Finally, the relationship between the blade root flapping moment and the blade tip flapping displacement in forward flight is determined as equation a. The reason for not directly formulating the relationship between the blade tip flapping moment and flapping displacement is that in forward flight, the flapping moment has significant periodicity, resulting in poor linearity with the blade tip displacement and causing a large error. In the specific example, the selection of the specific spanwise section at the blade root is based on the quality of linearity, while the spanwise position at the blade tip is selected as close as possible to the blade tip.

[0020] The linear relationship between blade flapping moment and vertical displacement established in this method has certain errors compared to the nonlinear relationship between actual blade flapping moment and vertical displacement. Analysis suggests these errors arise from the difference between the blade root displacement and the blade tip displacement, i.e., caused by the elastic deformation of the blade. Under a rigid blade structure, and with identical structural parameters for both rotor blades, the relative tip-to-blade distance error caused by the elastic deformation of the blades is relatively small and within an acceptable range.

[0021] If the rotor configuration is a bearingless rotor configuration or the blades are flexible with large elastic deformation, or the upper and lower rotor blade structures are significantly different, then the error of this method cannot be ignored and it is no longer applicable.

[0022] Furthermore, the calculated bending moment is compared with the experimental bending moment, and the error of the first harmonic component should be less than 15%. This method assumes a one-to-one correspondence between the bending moment and displacement results. Only when the calculated errors of the bending moment and the experiment are within this range can the accuracy of the established relationship between bending moment and vertical displacement be guaranteed, thus ensuring the accuracy of the final displacement result.

[0023] Furthermore, the method can be applied to the measurement of vertical displacement of blades in a single rotor.

[0024] Furthermore, in establishing the relationship between bending moment and displacement, a blade root profile with a linearity R² greater than 0.99 should be selected. The linearity R² of both the blade root and tip profiles should be greater than 0.99. Because the magnitudes of bending moment and displacement differ significantly, maintaining a linearity of 0.99 for both is crucial to ensuring the accuracy of the converted displacement. Similarly, maintaining a linearity of 0.99 for the blade tip and root displacements is essential to meet the accuracy requirements for rapid estimation.

[0025] Furthermore, the upper and lower rotor blades should have a greater than 90% consistency in shape. The difference in shape between the upper and lower rotors mainly causes the difference in aerodynamic load, which can be reflected by measured loads. Therefore, a 90% consistency requirement for the upper and lower rotor shapes is sufficient.

[0026] Furthermore, the structural characteristics of the upper and lower rotor blades should have a consistency of more than 95%. The structural characteristics of the upper and lower rotor blades directly affect the calibration relationship between bending moment and displacement. If the two differ significantly, separate bending moment-displacement relationships should be established for the upper and lower rotor blades. The same bending moment-displacement relationship formula cannot be used, otherwise the accuracy of the final result will be affected.

[0027] Furthermore, in the first round of analysis, the calculation model was modified based on the measured bending moment results of the blades. When the two were in high agreement, the calculation model was fixed, and then the blade bending moment and vertical displacement were calculated in the forward flight state.

[0028] Furthermore, in step 3, during actual flight testing, the flapping moment at different spanwise positions of the propeller blades will be measured under normal circumstances, and the flapping moment at different spanwise positions of the propeller blades will be output in real time. The beneficial effects of this application are:

[0029] This method enables relatively real-time monitoring of the blade distance between the upper and lower rotors across the entire flight spectrum without requiring additional measuring equipment, ensuring flight safety. The advantages of this method include simplified tip distance measurement, shorter feedback time, and better real-time performance compared to methods using light sensors or radar waves with installed equipment; it utilizes existing strain gauges for bending moment measurement, eliminating the need for additional measuring equipment, thus avoiding difficulties related to equipment installation location and space constraints, reducing testing costs, and improving testing efficiency; furthermore, strain gauge load measurement technology has long been used in flight bending moment testing, is mature and reliable, and is not limited by flight lighting, flight attitude, electromagnetic interference, or other flight environmental factors, enabling the measurement of the blade distance between the upper and lower rotors under various flight attitudes, including high-speed forward flight, horizontal turns, and spiral turns.

[0030] This method can also be applied to the measurement of vertical displacement in the rotating state of a traditional single rotor rigid blade, as well as the measurement of vertical displacement at different spanwise positions in motion states such as the rotation of a rigid beam. Attached Figure Description

[0031] Figure 1 This is a schematic diagram showing the vertical distance between the upper and lower rotor blades. Detailed Implementation

[0032] The present invention will be further described below with reference to embodiments. The following description represents only a portion of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0033] 1. Utilize computational modeling to obtain the blade flapping moment and flapping displacement.

[0034] Comparing the calculated and experimental bending moments of the blade flapping under the same forward flight conditions, this example selects two positions at the blade root for comparison with the experimental measurement results. The error of the first harmonic load between the two is less than 15%, indicating that the calculation model is usable.

[0035] After determining the computational model, a flight condition identical to the experimental condition was calculated, and the blade flapping moment and vertical displacement results for one revolution of the blade were extracted. The root flapping moment, vertical displacement, and tip vertical displacement results extracted in this example are as follows:

[0036] Table 1 shows the calculated flapping moments and vertical displacements at the blade root and tip.

[0037] Azimuth Blade root flapping moment (NM) Vertical displacement of the propeller root (mm) Vertical displacement of propeller tip (mm) 0 -2414.88 27.54259 184.6336 30 -5409.13 29.78532 224.0379 60 -7593.71 31.44265 270.4046 90 -7946.73 31.80318 288.7174 120 -6267.66 30.6921 265.2893 150 -3495.06 28.84309 208.0817 180 95.1056 26.37941 136.1726 210 3186.05 24.17566 80.27528 240 3933.69 23.59604 61.29138 270 3181.81 23.91335 83.198 300 784.767 25.50387 123.4536 330 -979.616 26.63594 156.9351 360 -2414.88 27.54259 184.6336

[0038] Note: This example is for demonstration purposes only. The data points have been simplified. The more points selected, the easier it is to establish the relation.

[0039] 2. Using the calculation results, establish the relationship between the blade flapping moment and flapping displacement.

[0040] First, using the data in Table 1, a relationship between the blade root bending moment and vertical displacement is fitted. An R² value greater than 0.99 indicates that this relationship is valid. Then, a relationship between the blade root and tip vertical displacements is fitted; an R² value greater than 0.99 indicates that this relationship is valid. Using these two fitted relationships, relationship a between the blade root bending moment and tip vertical displacement is established. The established relationship is as follows:

[0041] Relationship a: Tip displacement = -0.0186 * root moment + 112.479

[0042] 3. Using the relationship between blade flapping moment and flapping displacement, the vertical displacement of a rotor blade is obtained by measuring the bending moment.

[0043] The flapping moments at the root of the upper and lower rotor blades under actual flight conditions were obtained using strain gauge load measurement. The flapping displacements at the tips of the upper and lower rotor blades were then obtained using the preceding relationship a. The results are as follows:

[0044] Table 2. Measured bending moment (NM) at the blade root and obtained vertical displacement at the blade tip (mm)

[0045]

[0046] 4. The distance between the upper and lower rotor blades is obtained using the vertical displacements of the upper and lower rotor blades. Based on the obtained vertical displacements b1 and b2 at the rotor tips, the shaft spacing c of the upper and lower rotors in this example is 500 mm. According to the formula:

[0047] d = b1 + c - b2

[0048] The final vertical distance between the upper and lower rotor tips is as follows:

[0049] Table 3 Vertical distance between the tips of the upper and lower rotor blades (mm)

[0050]

[0051] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the meaning consistent with their meaning in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein. The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for measuring the distance between upper and lower rotor blades based on measured bending moment, characterized in that, Using measured bending moment data during flight and existing blade measurement systems, without adding additional measurement equipment, a calibration relationship between the test bending moment and the deformation of different blade profiles is established through the relationship between bending moment and deformation. This allows for the acquisition of the blade distance between the upper and lower rotors in real-time flight conditions, including the following steps: (1) Through calculation and analysis, the vertical bending moment and vertical displacement of different blade profiles are obtained; (2) Establish the relationship between vertical bending moment and vertical displacement; (3) Obtain the measured vertical displacement based on the measured bending moment; (4) Obtain the blade distance between the rotors based on the vertical displacement of the upper and lower rotors; The specific steps are as follows: Step (1) Establish a calculation and analysis model, and verify it through experimental bending moment to obtain the vertical bending moment and vertical displacement of different blade profiles under flight conditions; Step (2) Use the calculation results to calibrate the relationship between vertical bending moment and vertical displacement of different blade profiles; establish the relationship between vertical bending moment and vertical displacement at the corresponding blade root spanwise position under different states based on the calculation results obtained in step (1), and select the blade root spanwise position with good linearity as the benchmark based on the linearity of the relationship; then establish the relationship between the displacement at the blade root position and the blade tip displacement, and finally determine the blade root bending moment and blade tip vertical displacement relationship a; establishing the relationship between vertical bending moment and vertical displacement is the key point of this method. In the process of establishing the linear relationship, the linear relationship analysis of vertical bending moment and vertical displacement at multiple states and multiple spanwise positions should be carried out, and the average value should be selected. Step (3) Based on the measured bending moment results during flight, use the vertical bending moment and vertical displacement relationship expression from step (2) to obtain the displacement of the blade at different spanwise positions; based on the measured vertical bending moment at the blade root, use the relationship a obtained in step (2) to convert it into the vertical displacement result at the blade tip, thereby obtaining the measured vertical displacement b of the blade tip under the flight state of a rotor. The result for the upper rotor is b1, and the result for the lower rotor is b2, to distinguish them. Step (4) Based on the rotor configuration and the static blade spacing between the upper and lower rotors, correct the result of step (3) to finally obtain the vertical distance between the upper and lower rotor blades in flight; in step (3), the vertical displacements b1 and b2 of the upper and lower rotors were obtained respectively; then, based on the shaft spacing c of the upper and lower rotors in the rotor configuration, through geometric transformation, the vertical distance d at the same spanwise position of the upper and lower rotor blades was finally obtained; d = b1 + c - b2.

2. The method according to claim 1, characterized in that, In step (1), the blade bending moment and aeroelastic response theoretical calculations under flight conditions are performed first. In the calculation model, the structural model adopts the medium deformation beam theory, the blade is an elastic deformation beam, the aerodynamic model airfoil adopts the second-order lift line theory, and the free wake model is adopted.

3. The method according to claim 2, characterized in that, In step (2), the main influence in this relationship is the blade structure stiffness. There is an aerodynamic bending moment effect, which accounts for a small proportion and is ignored in the rapid calculation. Finally, the relationship between the vertical bending moment at the blade root and the vertical displacement at the blade tip in the forward flight state is determined. The reason for not directly formulating the relationship between the vertical bending moment and the vertical displacement at the blade tip is that in the forward flight state, the vertical bending moment is significantly periodic and has poor linearity with the blade tip displacement, resulting in a large error.

4. The method according to claim 3, characterized in that, The calculation of bending moment and the experimental bending moment show that the error of the first harmonic component is less than 15%. The bending moment and displacement results correspond one-to-one. Only when the calculation error of the bending moment and the experiment is within this range can the accuracy of the established relationship between bending moment and vertical displacement be guaranteed, thus ensuring the accuracy of the final displacement result.

5. The method according to claim 4, characterized in that, The method can be applied to the measurement of vertical displacement of blades in a single rotor.

6. The method according to claim 5, characterized in that, In the process of establishing the relationship between bending moment and displacement, the blade root profile with a linearity R2 greater than 0.99 is selected. The linearity R2 of the blade root profile and the blade tip profile is also greater than 0.

99. Because the magnitude of bending moment and displacement differs greatly, the linearity of bending moment and displacement is kept at 0.99 to ensure the accuracy of the displacement after conversion. The linearity of the blade tip and blade root displacement is kept at 0.99 to meet the accuracy requirements of rapid estimation.

7. The method according to claim 6, characterized in that, The upper and lower rotor blades have a greater than 90% consistency in shape; the difference in shape between the upper and lower rotors causes aerodynamic load differences, which are reflected by the measured load, so the consistency of the upper and lower rotor shapes is required to be 90%.

8. The method according to claim 7, characterized in that, The structural characteristics of the upper and lower rotor blades are more than 95% consistent; the structural characteristics of the upper and lower rotor blades directly affect the calibration relationship of bending moment and displacement. If the difference between the two is large, separate bending moment and displacement relationships should be established for the upper and lower rotor blades respectively. The same bending moment and displacement relationship formula should not be used, otherwise the accuracy of the final result will be affected; in the first round of analysis, the calculation model is corrected according to the measured bending moment results of the blades. When the two have a high degree of consistency, the calculation model is fixed, and the blade bending moment and vertical displacement are calculated in the forward flight state; in step (3), in the actual flight test, the vertical bending moment of the blades at different spanwise positions will be measured under normal circumstances, and the vertical bending moment of the blades at different spanwise positions will be output in real time.

9. A system employing the method according to any one of claims 1-8.

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