Method for detecting deformation states of an aerodynamic structure of an aircraft

Abstract

The invention relates to a method for detecting deformation states of at least one aerodynamic structure of an aircraft, in particular of a rotor blade (7, 9) of a rotor (3, 5) and / or of an airfoil and / or of a tail unit of an aircraft, in particular of a helicopter (1), the aerodynamic structure having at least one strain sensor (11). The method has the following steps: (a) detecting deformation states by means of the at least one strain sensor (11) and detecting temperature measurement values by means of at least one temperature sensor (12) in a plurality of different temperature states of the aerodynamic structure, and (b) determining a relationship between the deformation states detected by the at least one strain sensor (11) and the temperature measurement values detected by the at least one temperature sensor (12).

Description

[0001] Method for detecting deformation states of an aerodynamic structure of an aircraft

[0002] The present invention relates to a method for detecting deformation states of at least one aerodynamic structure of an aircraft, an arrangement with an aerodynamic structure, in particular a rotor blade arrangement, and an aircraft.

[0003] Deformation measurements, e.g., in the form of strain measurements, on helicopter rotor blades are carried out, for example, in flight tests to determine the mechanical loads acting on the rotor blades, such as aerodynamic forces. For this purpose, the respective rotor blade can be equipped with strain sensors, e.g., strain gauges or fiber Bragg sensors, which measure local strains of the rotor blade at the location of the respective strain sensor.

[0004] Deformations, e.g., elongations, of the rotor blade can occur not only due to the mechanical stress on the rotor blade, but also due to changing ambient temperatures or temperatures of the rotor blade itself.

[0005] Temperature changes and fluctuations occur particularly during flight due to changing environmental conditions, such as solar radiation, wind, weather, the day-night cycle, and altitude, as well as due to the airflow around the rotor blade. Such temperature changes can cause local dimensional changes and thus local deformations of the rotor blade. These deformations are measured by strain gauges mounted on the rotor blade by converting the detected signal, such as an electrical voltage or reflected wavelength of light, into strain or deformation measurements. Furthermore, mechanical loads acting on the rotor blade during operation, such as tensile, compressive, and / or shear forces, as well as torsional and / or bending moments, also occur. These loads are likewise measured by the strain gauges as strain or deformation values.

[0006] Thus, strain sensors attached to the rotor blade output a total strain as the measured value, which includes both a thermally induced component and a mechanically induced component, making it difficult to draw conclusions about the mechanical loads acting on the rotor blade.

[0007] It is therefore an object of the present invention to provide an improved method for detecting deformation states of at least one aerodynamic structure, for example a rotor blade of a rotor of an aircraft, as well as an improved arrangement with an aerodynamic structure and an improved aircraft.

[0008] The problem is solved by a method for detecting deformation states of at least one aerodynamic structure according to claim 1, an arrangement according to claim 13, and an aircraft according to claim 16. Further features of the invention are specified in the dependent claims. The method according to the invention can also be further developed by the features of the arrangement and / or the aircraft, and vice versa, and features of the arrangement and the aircraft can also be used mutually for further development.

[0009] A method according to the invention for detecting deformation states of at least one aerodynamic structure of an aircraft, in particular a rotor blade of a rotor and / or a wing and / or a tail assembly of an aircraft, in particular a helicopter, wherein the aerodynamic structure has at least one strain sensor, comprises at least the steps of: (a) detecting deformation states by the at least one strain sensor and detecting temperature measurements by at least one temperature sensor, at a plurality of different temperature states of the aerodynamic structure, and

[0010] (b) Determining a relationship between the deformation states detected by the at least one strain sensor and the temperature measurements detected by the at least one temperature sensor.

[0011] The deformation state detected by the at least one strain sensor can be a deformation state of the aerodynamic structure, describing a deformation occurring locally at the location of the strain sensor. Such a local deformation is preferably a deformation state detected by a single strain sensor, e.g., a (point) strain value determined or detected by a single strain sensor. Alternatively or additionally, the deformation state detected by the at least one strain sensor can be a deformation state of the aerodynamic structure, describing a deformation occurring regionally or sectionally, i.e., in a region of the aerodynamic structure that includes the location of the at least one strain sensor, or it can include a characteristic value for such a regional or sectional deformation.Preferably, a regional or sectional deformation is a deformation detected or determined by a plurality of strain sensors. A regional or sectional deformation state can, for example, be a deformation state associated with a section or cross-section of the aerodynamic structure. For this purpose, the aerodynamic structure, in particular a rotor blade, preferably has several sections or cross-sections, which are preferably spaced apart from one another in the radial direction of the aerodynamic structure, in particular the rotor blade, wherein each section or cross-section has at least one strain sensor which detects or determines a deformation state attributable to the respective section or cross-section.

[0012] Particularly when using multiple strain gauges, a regional, e.g., sectional, deformation state of the aerodynamic structure can be detected using a predetermined number of strain gauges arranged in a defined measurement configuration on the aerodynamic structure. This defined measurement configuration can include a defined positioning and / or orientation of the respective strain gauges relative to each other and / or to the aerodynamic structure, and / or a defined electrical connection between the strain gauges, for example, in the form of a Wheatstone bridge. A regional deformation state of the aerodynamic structure can also be determined by measuring multiple local deformation states of the aerodynamic structure using individual strain gauges.

[0013] Preferably, in step b) of the method, the determination of a relationship between the deformation states detected by the at least one strain sensor and the temperature measurements detected by the at least one temperature sensor is carried out using regional deformation states.

[0014] A deformation state is preferably a value determined by one or more strain sensors, which includes a local or regional deformation of the aerodynamic structure, such as strain and / or curvature and / or compression and / or displacement and / or torsion and / or shear, etc., or a measured value from which, for example, at least one of these values ​​can be determined, such as a Wheatstone bridge deflection, an electrical voltage, a reflected wavelength of light, etc. For example, a deformation state can be a strain measurement.

[0015] Preferably, the at least one strain sensor is a thermally and mechanically calibrated strain sensor. Preferably, the at least one strain sensor is calibrated such that an effect on the strain sensor itself caused by changing temperatures, for example, a temperature-related change in the length of an optical fiber or a temperature-related change in the refractive index of an optical fiber when using a fiber optic Bragg grating sensor, is already compensated. The at least one temperature sensor is preferably a thermally calibrated temperature sensor. An aerodynamic structure is understood to be, in particular, a structural element of an aircraft which, during operation of the aircraft, has a lift-generating effect and / or a flow-guiding effect, especially a control effect.For example, an aerodynamic structure can be one or more rotor blades of an aircraft's rotor, and / or one or more wings or airfoils of an aircraft, and / or one or more empennages of an aircraft. The aircraft can be, for example, a helicopter and / or an airplane and / or an unmanned aerial vehicle (UAV) or a drone.

[0016] By determining the relationship between the deformation states detected by at least one strain sensor, also referred to as measured values ​​of aerodynamic structure distortion, and the temperature measurements detected by at least one temperature sensor, it is possible, for example, to obtain a temperature-dependent behavior of the aerodynamic structure with respect to the measured deformation states. This allows the temperature-related components of the deformation states, e.g., strain measurements, to be taken into account in subsequent strain or distortion measurements, particularly during rotor or aircraft operation, in order to calculate, for example, a purely mechanical component of the aerodynamic structure's deformation states. Based on a mechanical component of the deformation states, a mechanical load on the aerodynamic structure can, for instance, be determined.Overall, the method can achieve improved measurement accuracy of deformation states of at least one aerodynamic structure.

[0017] The method according to the invention makes it possible, for example, to determine deformations of the aerodynamic structure that occur due to mechanical stress, whereby thermally induced components of the deformations, e.g., due to temperature fluctuations, can be factored out or compensated for. It is not necessary to know or consider the exact geometry and structure of the aerodynamic structure. Typically, an aerodynamic structure, such as a rotor blade, wing, or tail assembly, exhibits anisotropic structure, which can lead to anisotropic deformation or strain behavior. Therefore, this must be taken into account when theoretically determining mechanically induced deformations and compensating for thermally induced deformations, e.g., through simulation or mathematics.Rather, in the method according to the invention, the determination of the thermally and mechanically induced deformation components of the aerodynamic structure can be carried out in a purely experimental manner, so that, for example, it is not necessary to explicitly consider or know the anisotropic behavior of the aerodynamic structure. Likewise, it is not necessary, for example, to explicitly know or consider an occurring, and usually inhomogeneous, temperature distribution on or within the aerodynamic structure, which can also lead to anisotropic deformation behavior of the aerodynamic structure. An inhomogeneous temperature distribution can be caused, for example, by solar radiation on the aerodynamic structure, which can result in a higher temperature on the upper side of the aerodynamic structure than on its lower side, as well as by the anisotropic structure of the aerodynamic structure itself.Locally varying coefficients of thermal expansion exist. However, measuring the temperature distribution, for example by providing multiple temperature sensors and / or attaching them to suitable locations on the aerodynamic structure, can lead to a more accurate determination of thermally induced deformations of the aerodynamic structure. Preferably, the at least one temperature sensor is designed to detect an inhomogeneous temperature distribution of the aerodynamic structure, at least partially, and particularly in conjunction with other provided temperature sensors.

[0018] Preferably, the aerodynamic structure is a rotor blade having at least one first end connected to the aircraft rotor, for example, at a hub or axle of the rotor. The rotor blade can extend from the first end to a second end in the radial direction of the rotor. Preferably, the second end of the rotor blade is a free end. The free end is preferably not connected to the rotor or other components of the aircraft, or only connected via the rotor blade itself. Preferably, determining the relationship between the deformation states and the temperature measurements includes determining a functional relationship, in particular performing a regression analysis to obtain a regression function that represents thermally induced deformation states as a function of the recorded temperature measurements.Preferably, this results in a functional dependence of the measured strain values ​​on a temperature, particularly a local temperature, of the aerodynamic structure. Such a functional relationship, especially a regression function, can, for example, provide a mathematical correlation between the measured strains and the temperatures, which can simplify, for example, the compensation of thermally induced strains, in particular the calibration of the determined regional deformation states with respect to temperature effects, and / or a comparison between different measurements. Such a regression function is preferably a function that assigns a thermally induced deformation state or a thermally induced deformation of the aerodynamic structure to each temperature or temperature state of the at least one aerodynamic structure, at least within a specific temperature interval.A temperature state of at least one aerodynamic structure can, for example, be a temperature vector or temperature field, which is determined by a plurality of temperature sensors. The method described above can, for example, serve to determine this functional relationship. This can also be referred to as training the measurement system consisting of the various sensors associated with the aerodynamic structure. Applying the relationship or regression function thus determined, deformation states occurring during the operation of the aircraft, e.g., a helicopter, can be detected by the at least one strain sensor. These deformation states include mechanically and thermally induced components. The thermally induced deformation components can then be calculated based on the previously determined relationship and the temperature measurements occurring during operation, in order to, for example,The mechanically induced deformation components of the aerodynamic structure are subtracted from the recorded deformation states. Preferably, the at least one temperature sensor is provided on the aerodynamic structure. This can, for example, improve the accuracy of the method described above. Alternatively, the at least one temperature sensor can also be provided independently of the aerodynamic structure, particularly in the vicinity of the aerodynamic structure.

[0019] Preferably, the deformation states and temperature measurements are recorded at different temperature states of the aerodynamic structure under a reproducible mechanical condition and / or substantially constant mechanical load on the at least one aerodynamic structure, particularly when a rotor on which the aerodynamic structure is mounted is at rest, and / or in a substantially windless condition, and / or the aerodynamic structure is arranged in a test rig. The different temperature states of the at least one aerodynamic structure are preferably caused by natural environmental conditions, in particular by varying solar radiation and / or the day-night cycle and / or weather-related temperature fluctuations.Alternatively, the different temperature states of at least one aerodynamic structure can be specifically controlled, for example, by temperature-controlled (i.e., heated and / or cooled) the aerodynamic structure or its environment in a hangar. This allows, for example, consistent and / or reproducible mechanical loads to be applied to the aerodynamic structure, and in particular, minimizes variance or disturbances, which can facilitate the determination or compensation of thermally induced strains in the aerodynamic structure. Alternatively or additionally, data points (e.g., represented by temperature-deformation state pairs) that deviate significantly from other data points can be filtered out through appropriate data or signal processing. Such significantly deviating data points can occur, for example, due to wind gusts, and so on.This can be detected by observing that significantly different deformation states are recorded at essentially identical temperature measurements. For this purpose, a filter can be incorporated into a preceding signal processing stage. Alternatively, the method can be performed in a test environment that provides a substantially constant mechanical state for the aerodynamic structure. This makes it possible, for example, to keep the mechanical loads acting on the aerodynamic structure essentially constant. Thus, the deformation behavior of the aerodynamic structure caused solely by temperature fluctuations or thermal influences can be determined under the assumption of substantially constant mechanical influences.Preferably, in the method according to the invention, no simulated or theoretical or mathematically calculated deformation states of the aerodynamic structure are used to obtain the strain behavior or deformation of the aerodynamic structure.

[0020] Preferably, the method further comprises a step of deriving calibration information based on the determined relationship between the deformation states and the temperature measurements, such that temperature-dependent deformation or strain of the aerodynamic structure is essentially compensated. More preferably, the method further comprises a step of calibrating the at least one strain sensor and / or the determined deformation states based on the derived calibration information. This allows the at least one strain sensor to be used, for example, to measure purely mechanically induced strains of the aerodynamic structure, particularly during the operation of the aircraft, e.g., during the operation of a rotor on which the aerodynamic structure is mounted, in order to determine, for example, the mechanical loads on the aerodynamic structure based on the mechanically induced strains, independent of any temperature fluctuations.

[0021] Preferably, the aerodynamic structure comprises a plurality of strain sensors for detecting deformation states, wherein the strain sensors are provided at different positions, more preferably at different radial positions, of the aerodynamic structure, in particular of a rotor blade, and / or in different spatial orientations. More preferably, the aerodynamic structure, in particular the rotor blade, preferably comprises at least two distinct sections, and at least one strain sensor is provided in each section. Preferably, the distinct sections of the aerodynamic structure or rotor blade are separated from each other in the radial direction of the aerodynamic structure or rotor blade.Alternatively or additionally, a plurality of temperature sensors are preferably provided, more preferably on the aerodynamic structure, for acquiring temperature measurements, wherein the temperature sensors are provided at different positions, more preferably at different radial positions of the aerodynamic structure, in particular the rotor blade, and / or on different sides, in particular a top and bottom of the aerodynamic structure, and / or wherein different temperature sensors are more preferably assigned to different strain sensors. More preferably, the aerodynamic structure, in particular the rotor blade, has at least two different sections, and at least one temperature sensor is provided in each section. Preferably, each section of the aerodynamic structure or rotor blade has at least one strain sensor and at least one temperature sensor.The at least one strain sensor and / or the at least one temperature sensor can be provided on a surface, e.g., a top and / or bottom surface, of the aerodynamic structure or rotor blade, or embedded within the aerodynamic structure or rotor blade. By providing different strain and / or temperature sensors at different positions and / or with different orientations, i.e., spatial orientations, spatially resolved measurement data can be achieved, for example.

[0022] Preferably, the at least one strain sensor comprises a strain gauge and / or a fiber optic Bragg grating sensor, or is configured as a strain gauge and / or a fiber optic Bragg grating sensor. Alternatively or additionally, the at least one strain sensor can be a sensor suitable for use in an optical method for measuring deformation states, for example, an optical sensor, e.g., a camera that detects an optical marker, for example, a stochastic pattern and / or an optically detectable marking. The optical marker is preferably attached to the aerodynamic structure. The strain sensors mentioned above can, for example, be provided that are easily attached to the aerodynamic structure and / or that are robust and durable.

[0023] Preferably, in the method, steps (a) and (b) are repeated at different times, preferably under substantially the same mechanical load on the at least one aerodynamic structure and / or using the same temperature conditions, and if information derived from step (b) about the relationship between the deformation states and the temperature measurements at at least a first time point differs from the information derived at at least a second time point, it is concluded that there is a structural change in the aerodynamic structure and / or a change in at least one strain and / or temperature sensor.Alternatively or additionally, an overdetermination of a measuring system consisting of at least one strain sensor and / or at least one temperature sensor is preferably provided, and based on the overdetermination of the measuring system, a structural change in the aerodynamic structure and / or a change in at least one strain sensor and / or temperature sensor can be inferred. This makes it possible, for example, to monitor and determine the condition of the aerodynamic structure and / or at least one of the sensors. Preferably, the method is carried out at predetermined (time) intervals. In this procedure, which is also referred to as "health monitoring," a characteristic value is preferably determined in a first step as the information derived from step (b), e.g., a characteristic value determined by the regression analysis described above, and a deviation of this characteristic value is used to determine whether a change has occurred.In a second step, a location of the damage in the aerodynamic structure is preferably determined, or it is determined which of the sensors shows a change, whereby the localization of the damage can be carried out, for example, via redundant measured values ​​that may be available based on the overdetermination of the measuring system.

[0024] An arrangement according to the invention, in particular a rotor blade arrangement, comprises at least one aerodynamic structure of an aircraft, in particular at least one rotor blade of a rotor and / or a wing and / or a tail assembly of an aircraft, in particular a helicopter, wherein the aerodynamic structure has at least one strain sensor for detecting deformation states, and wherein the arrangement further comprises at least one temperature sensor for detecting temperature measurements, and at least one evaluation unit configured to perform at least steps (a) and (b) of the method described above.Preferably, the at least one aerodynamic structure is provided in a reproducible mechanical state and / or under a substantially constant mechanical load, wherein preferably the aerodynamic structure is a rotor blade of a rotor and the rotor is provided in a resting state and / or in a substantially windless state and / or wherein the aerodynamic structure, in particular the rotor blade, is arranged in a test rig. Alternatively or additionally, the aerodynamic structure preferably has a plurality of strain sensors and / or a plurality of temperature sensors, wherein the strain sensors and / or temperature sensors are provided at different positions, preferably different radial positions, of the aerodynamic structure, in particular of the rotor blade, and / or in different spatial orientations, wherein the aerodynamic structure orthe rotor blade preferably has at least two different sections and at least one strain sensor and / or at least one temperature sensor is provided in each section.

[0025] The evaluation unit can be integrated with the aerodynamic structure, e.g., provided on the aerodynamic structure itself, or provided on or in the aircraft, or external to the aircraft and / or external to an aircraft rotor. For example, the evaluation unit can also reside on a computer system at any location. The evaluation unit can be connected to the strain and temperature sensors via a data transmission unit, e.g., a data cable or wirelessly, to receive the sensor readings. The evaluation unit can comprise a hardware and / or software component, e.g., be provided in the form of a computer program. For example, the evaluation unit can be provided on a computer system that is independent of the aircraft. This arrangement offers, for example, the same advantages as the deformation state detection method described above.

[0026] An aircraft according to the invention comprising at least the arrangement described above, in particular a rotor blade arrangement. The aircraft can in particular be a helicopter.

[0027] Further features and advantages of the invention are described below with reference to an exemplary embodiment and the drawings.

[0028] Fig. 1 shows a schematic view of an aircraft in the form of a helicopter with rotors, which is suitable for carrying out a method according to the invention;

[0029] Fig. 2a shows a schematic view of a rotor blade of one of the rotors of the aircraft shown in Fig. 1, with the rotor blade shown in a top view from above;

[0030] Figs. 2b and 2c each show schematic views of the rotor blade shown in Fig. 2a in section along line AA (Fig. 2b) and line BB (Fig. 2c), respectively, with views of the top and bottom of the rotor blade in the area of ​​the cross-section and an exemplary arrangement of sensors on the rotor blade;

[0031] Fig. 3 shows a diagram schematically illustrating the steps of a method according to the invention for detecting deformation states in the form of strain measurements for at least one rotor blade of a rotor shown with reference to Figs. 1 to 2c and for calibrating the strain measurements determined by the at least one sensor; Fig. 4 schematically shows exemplary diagrams obtained by temperature and strain measurements on the rotor blade shown in Figures 2b-2c using the method described with reference to Fig. 3; and

[0032] Fig. 5 shows a diagram schematically illustrating the steps for determining the presence of a change occurring on the rotor blade shown in Figs. 1 to 2c and / or a sensor provided thereon, using the method described with reference to Fig. 3.

[0033] The following describes, with reference to Fig. 1, an aircraft suitable for carrying out a method according to the invention. The aircraft shown in Fig. 1 is a helicopter 1, which has a fuselage 2 with a main rotor 3, and a tail boom 4 on which a tail rotor 5 is provided. The tail rotor 5 can be provided with a shroud 6 that completely surrounds the tail rotor 5.

[0034] The main rotor 3 essentially serves to generate dynamic lift and, if necessary, horizontal movement of the helicopter 1, and the tail rotor 5 can at least serve to counteract a torque acting on the fuselage 2, in particular to counteract a counter-torque generated by the main rotor 3, which would cause a rotation of the fuselage 2 in the opposite direction to the rotation of the main rotor.

[0035] The main rotor 3 has several rotor blades 7 as aerodynamic structures, with two rotor blades 7 shown in the view of the helicopter 1 in Fig. 1. The rotor blades 7 of the main rotor 3 are rotatable about a vertical axis 8 of the helicopter 1. The tail rotor 5 also has several rotor blades 9, which are rotatably arranged about a rotor hub 10 with a horizontal axis (in Fig. 1, the horizontal axis of the rotor hub 10 extends into the plane of the drawing).

[0036] Optionally, the pitch angle of the rotor blades 20 of the tail rotor 5 and / or the rotor blades 7 of the main rotor 3 can be adjusted. To perform strain measurements on at least one rotor blade of the helicopter 1, this rotor blade is equipped with at least one strain sensor. This is explained in more detail below with reference to Figures 2a to 2c. In the following, reference is made to a rotor blade 7 of the main rotor 3 in Fig. 1; however, the rotor blade could also be a rotor blade 9 of the tail rotor 5.

[0037] Fig. 2a shows a schematic view of the rotor blade 7, which has a plurality of strain gauges 11 and at least one temperature sensor 12. The rotor blade 7 extends from a first end 13, which is located at the hub or axis of the main rotor 3 (not shown in Fig. 2a; the axis of the main rotor 3 corresponds to the z-direction in Fig. 2a), to a second, free end 14 in the radial direction of the respective rotor, corresponding to the x-direction in Fig. 2a. The rotor blade 7 has a top surface 15, which is visible in the view of Fig. 2a, and a bottom surface 16, which is hidden in the view of Fig. 2a (see Figs. 2b, 2c). Perpendicular to the radial x- and z-directions, the rotor blade extends between a leading edge 17 and a trailing edge 18 in a lateral direction y.

[0038] In Figures 2a to 2c, strain gauges 11 are provided on the upper surface 15 and the lower surface 16 of the rotor blade 7 in sections of the rotor blade 7 spaced apart from each other in the radial direction x. The individual sections are represented in Figure 2a by the cross-sections AA, BB, CC, DD, and EE, of which cross-section AA is shown in Figure 2b and cross-section BB in Figure 2c. The cross-sections CC, DD, and EE are not shown in detail in the figures and may have arrangements of strain gauges 11 similar to the arrangement shown in Figure 2b or Figure 2c.

[0039] In Figures 2b and 2c, the same number of strain sensors 11 are provided on the upper surface 15 and the lower surface 16 of the rotor blade 7 in each section (cross-section AA and cross-section BB, respectively). However, the number of strain sensors 11 on the upper surface 15 and the lower surface 16 of the rotor blade 7 can also differ. The strain sensors on the upper surface 15 and the lower surface 16 of a section (cross-section AA and cross-section BB) each have strain sensors 11 spaced apart in the lateral direction y and aligned in the radial direction x, as well as strain sensors 11 oriented transversely to this. That is, the strain sensors 11 of a section (a cross-section) are provided with different spatial orientations on the upper surface 15 and the lower surface 16 of the rotor blade.

[0040] Thus, the strain sensors 11 of different sections or cross-sections shown in Figures 2a to 2c are spaced apart from each other at least in the radial direction x of the rotor blade, and the strain sensors of the same section or cross-section differ at least in their arrangement along the lateral direction y and / or their spatial orientation.

[0041] The number and arrangement of strain sensors 11 shown in Figures 2a to 2c are purely exemplary. The strain sensors can be arranged in any configuration on the upper and / or lower surface of the rotor blade. The number of strain sensors can also differ from that shown in the figures. According to a further embodiment not shown in the figures, one or more of the strain sensors are located inside the rotor blade, i.e., in the area between the lower surface 16 and the upper surface 15 of the rotor blade. In other words, the strain sensors can also be at least partially embedded in the rotor blade.

[0042] Figure 2a further shows a temperature sensor 12, which is provided between the sections represented by cross-sections DD and EE on the upper surface 15 of the rotor blade 7. Similarly, another temperature sensor, not shown in the figures, can be provided on the lower surface 16 of the rotor blade 7 and / or further temperature sensors can be provided on other sections of the rotor blade. For example, each of the sections shown in Figure 2a can be provided with at least one temperature sensor. According to a further embodiment not shown in the figures, the at least one temperature sensor, instead of being provided on the upper and / or lower surface of the rotor blade, can also be at least partially embedded in the rotor blade. It is also possible to provide the at least one temperature sensor independently of the rotor blade, in particular in the vicinity of the rotor blade.Each of the strain sensors 11 is configured to detect at least one local deformation of the rotor blade 7 in the area where the respective strain sensor is located, as a deformation state of the rotor blade in the form of a strain measurement. Instead of detecting a strain measurement, the strain sensor 11 can also be configured to detect another measurement that characterizes a local or regional deformation state of the rotor blade. The at least one temperature sensor 12 is configured to detect a local temperature of the rotor blade 7 and / or the surrounding area of ​​the rotor blade in the area where the temperature sensor 12 is located, as a temperature measurement.

[0043] Strain gauges and / or fiber optic Bragg grating sensors, or any other sensor suitable for detecting a strain measurement of the rotor blade, can be used as strain sensors 11. The strain sensors 11 are preferably calibrated such that any effect on the strain sensor itself caused by changing temperatures, for example, a temperature-related change in the length of an optical fiber when using a fiber optic Bragg grating sensor, is already compensated for.

[0044] The at least one temperature sensor 12 can, for example, also be a fiber optic Bragg grating sensor or any other suitable temperature sensor.

[0045] The strain gauges and temperature sensors are connected to an evaluation unit (not shown in the figures), for example via a data cable and / or a wireless data transmission device. The evaluation unit can be located on the rotor blade itself, or on or in the helicopter 1, or externally, separate from the helicopter 1 and / or the rotor 3 or 15.

[0046] The following describes, with reference to Figure 3, an embodiment of a method according to the invention for acquiring strain measurements using the rotor blade 7 described in relation to Figures 2a to 2c. For this purpose, the rotor blade can be provided in a test environment in which a suitable, preferably substantially constant, mechanical load acts on the rotor blade 7. The test environment preferably provides a repeatable and / or static mechanical state of the rotor blade 7. Preferably, the test environment is selected such that the mechanical forces acting on the rotor blade are substantially constant. For example, the rotor blade 7 can be in an operating configuration (i.e., provided on the rotor 3 or 5, and / or provided on the helicopter 1) with the engines switched off.The test environment should be, for example, outdoors, and / or essentially without wind and / or gusts, and with a defined rotor control state that specifies, for example, a blade pitch angle. The test environment can be, for example, outdoors, and / or in a building, particularly a hangar. For example, the rotor blade can be arranged in a test rig that preferably ensures constant mechanical loads on the rotor blade.

[0047] In the next step of the process, strain measurements are then acquired by the strain sensors 11 and temperature measurements are acquired by the at least one temperature sensor 12. The acquisition of strain and temperature measurements is carried out under a plurality of different temperature conditions of the rotor blade 7. These different temperature conditions of the rotor blade 7 are preferably achieved due to changing natural or environmental conditions, for example, by varying solar radiation and / or the day-night cycle and / or weather-related temperature fluctuations, and / or are achieved or set in a hangar.

[0048] The process then checks whether sufficient data in the form of strain and temperature measurements are available to perform a regression analysis. If insufficient data is available, the acquisition of strain and temperature measurements continues, and / or a larger number of previously acquired data points are used for the regression analysis. In particular, the number of previously acquired strain and temperature measurements may be greater than the number of data points used for the regression analysis. The data from the dataset not used for the regression analysis can then be used, for example, for a test set. If sufficient data is available, or if...For the regression analysis, a relationship between the strain measurements recorded by the strain sensors 11 and the temperature measurements recorded by the at least one temperature sensor 12 is determined in a next step. This is done by performing a regression analysis, which yields a regression function that represents the recorded strain measurements as a function of the recorded temperature measurements. In other words, temperature-related strain values ​​are determined for the rotor blade 7, which are essentially independent of mechanically induced strain values ​​of the rotor blade. This can be done as follows:

[0049] To determine the regression function, the recorded temperature measurements are used as input parameters, particularly regarding their spatial distribution with respect to the rotor blade and / or their temporal gradients. The recorded strain measurements, representing thermally induced strain values, are used as outputs of the regression function. Based on these input parameters and results, the regression function is determined, for example, using the following equation:

[0050] Where £ Ci therm^ e The thermally induced component of the strain measurements taken by the strain sensors 11 is,

[0051] Ti, T2 are the temperature measurements taken by two different temperature sensors 12 at the same time,

[0052] — and — the time gradients of the temperature measurements Ti and T2 are, respectively, and dt dt r

[0053] — a spatial temperature distribution based on the values ​​Ti, T2. The dots in the equation above indicate that 12 temperature readings from more than two temperature sensors can be included at the same time, i.e., temperature readings from more than two temperature sensors can be included.

[0054] Based on the determined regression function f, and assuming constant mechanical load on the rotor blade, i.e., assuming that the mechanically induced component of the measured strain values ​​is essentially constant in the above measurements, the mechanically induced component of the strains is then calculated. c>mech , by subtracting the thermally induced component of the strains, s Citherm , of the measured total strain, E C , calculated, i.e.

[0055] The regression function can be linear or nonlinear. Software employing artificial intelligence (AI), such as decision trees, random forests, or neural networks, can be used to determine the regression function. These models can be implemented, for example, using the Python module scikit-learn.

[0056] The regression analysis can be performed for each strain sensor 11 separately, or for several, preferably for all strain sensors 11 of the rotor blade together.

[0057] Based on the regression function determined in the procedure, the sectional strain measurements determined using the strain sensors 11 of the rotor blade 7 can then be calibrated in a further step of the procedure shown in Fig. 3 so that, in subsequent measurements of the strain measurements by the strain sensors 11 under varying mechanical loads of the rotor blade, the temperature-dependent strain of the rotor blade 7, i.e. s Citherm , is essentially compensated. In Fig. 3, this step is labelled as thermal calibration. Thus, the strain sensors 11 can be used to detect the strain of the rotor blade 7 caused by purely mechanical influences, for example during rotor operation or helicopter flight.

[0058] The determination of the regression function can then be carried out for different mechanical load conditions of the rotor blade, for example for a rotor blade 7 rotating at a constant speed, and / or for different rotor control conditions, for example at different blade pitch angles of the rotor blade.

[0059] Preferably, in the thermal calibration method described above with reference to Fig. 3, data, i.e., temperature and strain measurements, are acquired for a wide range of thermal conditions under substantially constant mechanical conditions. Alternatively or additionally, the data can be extrapolated. This also allows a wide range of thermal conditions to be covered.

[0060] Fig. 4 shows an exemplary diagram graphically representing temperatures measured by two temperature sensors 12 provided on the rotor blade and strain values ​​determined based on strain measurements of the strain gauges 11 (see Figs. 2a-2c). The upper diagram in Fig. 4 shows the time course of the temperature measurements of a first temperature sensor, which is provided on the upper surface 15 of the rotor blade in Figs. 2a-2c (e.g., the temperature sensor 12 shown in Fig. 2a), represented in Fig. 4 by the solid line labeled "top", and the time course of the temperature measurements of a second temperature sensor, which is provided on the lower surface 16 of the rotor blade in Figs. 2a-2c (not shown in the figures), represented in Fig. 4 by the dashed line labeled "bottom".

[0061] The diagrams in Fig. 4 show three time periods: a first period in which a rotor, to which the rotor blade equipped with the temperature and strain sensors is attached, is in a resting state ("not rotating"), a subsequent second period in which the rotor rotates ("operation"), and a subsequent third period in which the rotor is again in a resting state ("not rotating").

[0062] The lower diagram in Fig. 4 shows the time course of the strain values ​​calculated based on the strain measurements obtained from the strain sensors 11 provided on the rotor blade and based on the method described above with reference to Fig. 3. In detail, the lower diagram in Fig. 4 shows a total strain value measured by the strain sensors. c, represented as a solid line, as well as the mechanically induced component of the strains c.mech and the thermally induced component of the strains Sc, therm each represented as dashed lines.

[0063] The diagram in Fig. 4 can be used, for example, to determine the mechanically induced component of the rotor blade strains acting during operation, and based on this, conclusions can be drawn about the mechanical loads acting during operation.

[0064] Preferably, for a comparison between different calibration procedures described with reference to Fig. 3, the temperature and strain measurements are recorded under reproducible conditions and / or defined thermal conditions, for example in a hangar. A data comparison of the calibration function between different calibration procedures performed at different times can, for example, provide information about the condition of the rotor blade and / or at least one of the strain sensors 11 or temperature sensor 12, hereinafter also referred to as "health monitoring".

[0065] For this purpose, as schematically illustrated in Fig. 5, the regression analysis described in relation to Fig. 3 is performed at least at two different times, preferably in the same test environment and / or using the same temperature conditions of the rotor blade. If information derived from this analysis regarding the relationship between the strain and temperature measurements, for example, the determined regression function, differs at at least a first time point from the information derived at at least a second time point, i.e., if changes occur in the regression function or in the determined relationship over time, it can be concluded that there is a structural change in the rotor blade and / or a change or measurement deviation in at least one strain and / or temperature sensor, up to and including sensor failure.

[0066] For example, the overdetermination of the measurement system formed by the strain gauges and / or temperature sensors can differentiate between a change, such as a deterioration in measurement behavior and / or a failure, of one of the strain gauges or a temperature sensor, and a local or global structural change of the rotor blade itself, such as material fatigue, the occurrence of a crack, water ingress, etc. The overdetermination of the measurement system can, for example, enable the localization of damage occurring in the rotor blade. Appropriate maintenance measures, such as the maintenance or repair of the rotor blade and / or the replacement of a strain gauge or a temperature sensor, can then be initiated.

[0067] In general, the occurrence of changes in the regression function or in the determined relationship over time and / or an overdetermination of the measuring system can indicate the occurrence of a structural change in the rotor blade and / or a change in at least one strain and / or temperature sensor.

[0068] Although the invention has been described using one or more rotor blades of a helicopter rotor, it is not limited thereto. Rather, the invention can also be applied to other aircraft, such as airplanes and / or unmanned aerial vehicles (UAVs) or drones, or to any other aerodynamic structure of such an aircraft. An aerodynamic structure of the aircraft can, in particular, be a structural element of the aircraft which, during operation of the aircraft, has a lift-generating effect and / or a flow-guiding effect, especially a control effect, such as a rotor blade and / or a wing and / or an airfoil and / or a tail assembly of the aircraft.

Claims

Claims 1. Method for detecting deformation states of at least one aerodynamic structure of an aircraft, in particular a rotor blade (7, 9) of a rotor (3, 5) and / or a wing and / or a tail assembly of an aircraft, in particular a helicopter (1), wherein the aerodynamic structure has at least one strain sensor (11), and the method comprises at least the steps: (a) Detection of deformation states by the at least one strain sensor (11) and detection of temperature measurements by at least one temperature sensor (12), under a plurality of different temperature states of the aerodynamic structure, and (b) Determining a relationship between the deformation states detected by the at least one strain sensor (11) and the temperature measurements detected by the at least one temperature sensor (12).

2. Method according to claim 1, wherein determining the relationship between the deformation states and the temperature measurements includes determining a functional relationship, in particular performing a regression analysis to obtain a regression function that represents thermally induced deformation states as a function of the recorded temperature measurements.

3. Method according to claim 1 or 2, wherein the at least one temperature sensor is provided on the aerodynamic structure.

4. Method according to any one of claims 1 to 3, wherein the detection of the deformation states and temperature measurements at different temperature states of the aerodynamic structure is carried out under a reproducible mechanical condition and / or substantially constant mechanical load of the at least one aerodynamic structure (7, 9), in particular in a rest state of a rotor on which the aerodynamic structure is provided, and / or in a essentially in windless conditions and / or where the aerodynamic structure is arranged in a test rig.

5. Method according to any one of claims 1 to 4, wherein the different temperature states of the at least one aerodynamic structure (7, 9) are caused by natural environmental conditions, in particular by changing solar radiation and / or by the day-night rhythm and / or by weather-related temperature fluctuations.

6. Method according to one of claims 1 to 5, further comprising a step of deriving calibration information based on the determined relationship between the deformation states and the temperature measurements, such that a temperature-dependent strain of the aerodynamic structure (7, 9) is substantially compensated.

7. Method according to claim 6, further comprising a step of calibrating the at least one strain sensor (11) and / or the determined deformation states based on the derived calibration information.

8. Method according to any one of claims 1 to 7, wherein the aerodynamic structure (7, 9) has a plurality of strain sensors (11) for detecting deformation states, wherein the strain sensors are provided at different positions, preferably different radial positions, of the aerodynamic structure, in particular of a rotor blade, and / or in different spatial orientations, wherein the aerodynamic structure, in particular the rotor blade, preferably has at least two different sections and at least one strain sensor is provided in each section.

9. A method according to any one of claims 1 to 8, wherein a plurality of temperature sensors (12) are provided, preferably on the aerodynamic structure (7, 9), wherein the temperature sensors are further preferably provided at different positions, preferably different radial positions, of the aerodynamic structure, in particular of a rotor blade, and / or wherein Different temperature sensors are assigned to different strain sensors.

10. Method according to any one of claims 1 to 9, wherein the at least one strain sensor (11) comprises a strain gauge and / or a fiber optic Bragg grating sensor and / or is a sensor suitable for use in an optical method for measuring deformation states, for example an optical sensor.

11. Method according to any one of claims 1 to 10, wherein steps (a) and (b) are repeated at different times, preferably under substantially the same mechanical load on the at least one aerodynamic structure (7, 9) and / or using the same temperature conditions, and if information derived from step (b) about the relationship between the deformation states and the temperature measurements at at least a first time differs from the information derived at at least a second time, it is concluded that there is a structural change in the aerodynamic structure and / or a change in at least one strain and / or temperature sensor.

12. Method according to one of claims 1 to 11, wherein an overdetermination of a measuring system formed from the at least one strain sensor (11) and / or the at least one temperature sensor (12) is provided, and based on the overdetermination of the measuring system, a structural change of the aerodynamic structure and / or a change of at least one strain and / or temperature sensor can be inferred.

13. Arrangement, in particular rotor blade arrangement, comprising at least one aerodynamic structure of an aircraft, in particular at least one rotor blade (7, 9) of a rotor (3, 5) and / or a wing and / or a tail assembly of an aircraft, in particular of a helicopter (1), wherein the aerodynamic structure (7, 9) has at least one strain sensor (11) for detecting deformation states, and wherein the arrangement further comprises at least one temperature sensor (12) for detecting temperature measurements, and at least one evaluation unit configured to perform steps (a) and (b) of a method according to any one of claims 1 to 12.

14. Arrangement according to claim 13, wherein the at least one aerodynamic structure (7, 9) is provided in a reproducible mechanical state and / or under a substantially constant mechanical load, wherein preferably the aerodynamic structure is a rotor blade of a rotor, and the rotor is provided in a rest state and / or in a substantially windless state and / or wherein the aerodynamic structure, in particular the rotor blade, is arranged in a test stand.

15. Arrangement according to claim 13 or 14, wherein the aerodynamic structure (7, 9) comprises a plurality of strain sensors (11) and / or a plurality of temperature sensors (12), wherein the strain sensors and / or temperature sensors are provided at different positions, preferably different radial positions, of the aerodynamic structure, in particular the rotor blade, and / or in different spatial orientations, wherein the aerodynamic structure, in particular the rotor blade, preferably comprises at least two different sections and at least one strain sensor and / or at least one temperature sensor is provided in each section.

16. Aircraft, in particular helicopter (1) comprising at least one arrangement, in particular a rotor blade arrangement, according to any one of claims 13 to 15.

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