Measuring device for determining the velocity of a fluid

Abstract

A measurement device (200) for determining a velocity of a fluid relative to a vehicle (100) is disclosed. The measurement device (200) includes a processing system (610) and a sensor device (224) mounted to the vehicle (100). The sensor device includes a bendable rod (210) and sensors (224a, 224b, 224c, 224d). The bendable rod (210) is attached to the vehicle (100) and has a predetermined shape and stiffness. The sensors are associated with the bendable rod (210) and generate signals indicative of a force or moment (230) exerted on the bendable rod (210) by the fluid. The processing system (610) receives the signals (620) from the sensors, determines the velocity of the fluid relative to the vehicle (100) based on the signals (620) from the sensors (224a, 224b, 224c, 224d) and the predetermined shape and stiffness of the bendable rod (210).

Description

Technical Field

[0001] This technology relates to a measuring device for determining the velocity of a fluid relative to a vehicle. This technology also relates to a rotary-wing aircraft having such a measuring device. Background Technology

[0002] Measuring fluid velocity is used in many fields, including climatology, oceanography, weather forecasting, construction, and power generation. Other applications of measuring fluid velocity include measuring the velocity of fluids relative to vehicles, such as ships (e.g., the velocity of water relative to a submarine or the velocity of water and / or air relative to a sailboat), aircraft (e.g., airplanes, drones, or helicopters), spacecraft, and ground vehicles (e.g., cars, buses, trucks, or trains).

[0003] As an example, measuring the velocity of air relative to an aircraft allows the pilot to operate the aircraft within its optimal performance parameters, including lift, drag, stress on the fuselage, critical stall speed, fuel management, and so on.

[0004] A pitot tube, also known as a Prandtl tube, is typically used on aircraft to determine the relative velocity of the air around the aircraft. This type of pitot tube is usually mounted to the aircraft fuselage and is based on measurements of static pressure and total pressure.

[0005] For example, documents US3407655A, CA2279246, and CA2325023 describe Pitot tube anemometers based on the measurement of static pressure and total pressure. For instance, document CA2325023 describes a Pitot tube comprising a support column, an axisymmetric body fastened to the support column, a pneumatic path arranged within the axisymmetric body and the support column, an electrically heated element arranged within the axisymmetric body and the support column, and three sets of orifices for determining total pressure, static pressure, and angle of attack. This Pitot tube is characterized in that the orifices for measuring static pressure are arranged on a plate upstream of the support column.

[0006] However, pitot tubes cannot provide reliable pressure measurements at low air speeds relative to the aircraft. These low speeds are typically encountered during hovering or slow movement relative to the ground.

[0007] Document US10,877,060B2 describes an omnidirectional anemometer comprising a housing, a cavity, and multiple ports in fluid communication with the atmosphere. The ports may include at least one sensor configured to measure air pressure. The robust housing may be formed by additive manufacturing, casting, machining, or molding. The anemometer may include a controller configured to determine wind speed and wind direction using barometric pressure measurements from at least one sensor.

[0008] However, the described anemometer is constructed using relatively heavy materials, such as steel or other robust, high-strength materials. It also includes multiple barometric pressure sensors, which typically have slow response times, are susceptible to environmental factors including mechanical shock, vibration, dust, humidity, and temperature, and are expensive. Furthermore, the barometric pressure sensors are not sensitive enough at low speeds.

[0009] Document EP4163643 A1 describes a wind estimation system for an aircraft, comprising: a first sensor configured to sense a first position associated with aircraft control components under wind conditions; a second sensor configured to sense a first configuration associated with the aircraft's rotor system under wind conditions; and at least one controller communicating with at least one of the first or second sensors. The at least one controller is configured to determine the aircraft's end-path plane angle based on the first position and the first configuration, and to determine at least one of current wind speed or current wind direction based on the end-path plane angle.

[0010] Document US6,419,186B1 describes a support arm and probe assembly for a helicopter, having a support mounting arm extending outward from the helicopter body in a selected direction, preferably forward. The support arm has an outer end for mounting a low lateral velocity sensing probe, positioned with its axis substantially parallel to the axis of the helicopter rotor and within the downwash region of the airflow caused by the rotor. The low lateral velocity sensing probe has ports arranged annularly around the probe, and measures the pressure sensed at selected annular or peripheral locations on the probe to determine low air velocity.

[0011] Both documents place the sensor used to sense low air speeds within the downwash region caused by the rotor's air movement, which in turn disrupts the airflow. The rotor downwash also makes it difficult to obtain the crosswind component of the airflow.

[0012] However, none of the above solutions provide a lightweight, low-cost, and high-precision measurement device capable of determining low airspeeds relative to an aircraft. Document WO2014124646A1 describes a wind turbine component with an optical fiber sensor for detecting wind speed on the component surface, where optical loss allows some light transmitted in the fiber to escape, such that the amount of fiber bending reflects a measure of the airflow velocity around the wind turbine. Documents such as “The Design, Development and Performance Characteristics of a Fiber Optic Dragforce Flow Sensor” by Philip-Chandy R. et al., Measurement Science and Technology, IOP, Bristol, UK, Vol. 11, No. 3, 2000, US5117687A and US2004174542A1 are also known. Summary of the Invention

[0013] Based on the limitations and shortcomings of existing technologies, the aim is to provide a measuring device for determining the velocity of a fluid relative to a vehicle. The measuring device should have low fault sensitivity relative to environmental conditions such as temperature, vibration, and oscillation; be relatively simple and lightweight; and have low purchase and maintenance costs. The measuring device should be readily available and replaceable, and perform accurate measurements at low speeds.

[0014] These objectives are addressed by a measuring device including the features of claim 1. More specifically, a measuring device for determining the vector velocity of a fluid relative to a vehicle includes a sensor device mounted to the vehicle and a processing system. The sensor device includes a flexible rod and a sensor. The flexible rod is attached to the vehicle and has a predetermined shape and stiffness. The sensor is associated with the flexible rod and generates a signal indicating the force or torque exerted by the fluid on the flexible rod. The processing system receives the signal from the sensor and determines the velocity of the fluid relative to the vehicle based on the signal from the sensor and the predetermined shape and stiffness of the flexible rod.

[0015] The flexible rod can be several centimeters long. It can be positioned perpendicular to the direction of interest in the fluid flow. For example, the flexible rod can have the shape of a rod antenna mounted on the surface of a vehicle.

[0016] In examples of rotary-wing aircraft with a main rotor, tail rotor, tail fin, and / or T-tail, a flexible rod can be attached to the rotary-wing aircraft, pointing upwards on the tail fin or T-tail. Therefore, the bending of the flexible rod is largely independent of the rotor downwash of the main rotor. Consequently, this measuring device can also be used at low speeds.

[0017] The sensor device includes a sensor. The sensor can be adapted to determine the deformation of a bendable rod. Examples of such sensors include electrical strain gauges, piezoelectric sensors, fiber optic measurement techniques based on fiber Bragg gratings (FBGs), or fiber optic techniques based on fiber segment interferometry (FSI). The sensor can extend along the longitudinal axis in the outer region of the bendable rod.

[0018] FSI-based techniques allow for the direct determination of the deformation of a bendable rod. In contrast, the material properties of the bendable rod are considered in conjunction with other sensor technology solutions to arrive at conclusions about its deformation. For example, knowledge of the cross-sectional characteristics of the bendable rod and the sensor's placement on it (e.g., bending stiffness and the distance between the sensor and the neutral fiber of the bendable rod) can be used. Appropriate calibration methods can be employed for the electrical measurement sensor.

[0019] In the case of directly measuring the deformation of a bendable rod using FSI, several glass fibers can be embedded in grooves of the bendable rod and extend along the outer region of the cross-section of the bendable rod. The sensor device may include at least two (e.g., two, three, four, five, six, etc.) such glass fibers distributed around the circumference of the bendable rod. Fiber-based reflectors can be integrated at intervals into these glass fibers along the longitudinal axis of the bendable rod; these reflectors reflect light introduced at the fiber base. When the glass fibers are stretched or compressed, the propagation time of the reflected light changes, and therefore the propagation time in the relative fibers also changes when the rod bends. Fibers attached to the outside of the rod in the bending direction are compressed, while the opposite fibers are stretched.

[0020] The strength of the bend can be determined by both the compression and tension of the fibers. Tension and compression can be determined not only at a single point along the longitudinal axis of the bendable rod, but also at all sections defined by the reflector along the longitudinal axis of the bendable rod, making it possible to reconstruct even complex bend lines. A bendable rod attached to a vehicle perpendicular to the fluid flow is subjected to the force or torque of the fluid flow and thus bends.

[0021] If the geometry and structural data of the bendable rod (e.g., its diameter, shape, and stiffness) are known, a processing system connected to the sensor via cable or wirelessly can directly correlate the bend line of the bendable rod with the flow velocity through calculation, simulation, reference measurement, or any combination thereof. Therefore, the velocity of the fluid relative to the vehicle can be determined by measuring the bend line of the bendable rod.

[0022] This measuring device enables the determination of low fluid speeds (e.g., the speed of liquids and / or gases) relative to vehicles (e.g., ships such as submarines or sailboats, aircraft such as airplanes, drones or helicopters, rockets, spacecraft, or ground vehicles such as cars, buses, trucks, or trains). For example, this measuring device allows the determination of speeds in the range between zero and 20 knots.

[0023] Furthermore, this measuring device is very robust and insensitive to electromagnetic waves and harsh environmental conditions such as rain, ice, snow, hail, high and low temperatures.

[0024] The measuring device allows for very high sampling rates while providing high accuracy, including omnidirectional information of the measured velocity, even though the sensor is small and very lightweight.

[0025] The processing system of the measuring device can be located near the sensor device or at a predetermined distance from the sensor device. For example, the distance between the processing system and the sensor device can be between zero and 50 meters.

[0026] The sensor device can be constructed without electrical or electronic equipment. Therefore, no power source is required at the sensor device. However, a power source is needed in cases where the flexible rod is electrically heated to prevent icing.

[0027] According to one aspect, a force or torque causes deformation of the bendable rod, and a sensor measures the strain in the form of compression or tension caused by the deformation of the bendable rod.

[0028] For example, the sensor includes at least one of an electrical strain gauge, a piezoelectric sensor, or an optical sensor.

[0029] By way of example, the bendable rod has a neutral axis, and the sensor also includes at least one series of alignment sensors arranged parallel to the neutral axis at a predetermined distance from the neutral axis.

[0030] According to one aspect, at least one series of alignment sensors includes at least three series of alignment sensors, and the processing system determines the magnitude and direction of the fluid velocity in a plane perpendicular to the bendable rod.

[0031] In some embodiments, at least one series of alignment sensors includes an even number of series of alignment sensors, wherein any two of the even number of series of alignment sensors arranged on opposite sides of the neutral axis are connected to the distal end of the flexible rod away from the vehicle.

[0032] For example, at least one series of alignment sensors includes fiber optic cables and optical reflectors embedded in the fiber optic cables at predetermined distances from each other.

[0033] For example, the processing system determines the tilt angle of the bendable rod based on the change in distance between adjacent pairs of optical reflectors of the measured optical reflector.

[0034] According to one aspect, the bendable rod also includes a body material comprising a composite material having a fiber orientation forming a predetermined angle with the neutral axis, wherein the predetermined angle is selected between 30 degrees and 60 degrees to prevent torsional movement of the bendable rod.

[0035] In some implementations, the thickness and / or stiffness of the bendable rod varies along the neutral axis.

[0036] As an example, the sensor device further includes: an additional bendable rod attached perpendicular to the bendable rod to the vehicle and having an additional predetermined shape and stiffness; and an additional sensor associated with the additional bendable rod, generating an additional signal indicating an additional force or torque exerted by the fluid on the additional bendable rod, and transmitting the additional signal to a processing system, wherein the processing system determines a three-dimensional representation of the fluid’s velocity relative to the vehicle based on the signal and the additional signal.

[0037] For example, the measuring device also includes an additional sensor device having an additional sensor associated with an additional flexible rod attached to the vehicle at a location free from fluid influence, and wherein the processing system uses a measurement related to another force or torque acting on the additional sensor to filter out parasitic forces or torques acting on the sensor.

[0038] In some embodiments, the bendable rod also includes a heating device adapted to prevent the bendable rod from freezing; and a cable connected to and supplying power to the heating device.

[0039] In addition, a rotary-wing aircraft includes the aforementioned measuring device, wherein the rotary-wing aircraft further includes at least a main rotor adapted to generate lift during operation, the main rotor including at least two rotor blades, the at least two rotor blades generating a downwash flow affecting a predetermined surface area of ​​the rotary-wing aircraft during rotation of the main rotor, and wherein a flexible rod is attached to the rotary-wing aircraft outside the predetermined surface area.

[0040] Furthermore, a method for operating a measuring device for determining the velocity of a fluid relative to a vehicle, the measuring device including a bendable rod attached to the vehicle, the method comprising: using a sensor associated with the bendable rod to measure strain in the bendable rod caused by a force or torque exerted on the bendable rod by the fluid; using the sensor to generate a signal indicating the force or torque; receiving the signal from the sensor using a processing system; using the processing system to determine the bending of the bendable rod based on the signal from the sensor; using the processing system to determine the force or torque based on the bending of the bendable rod and predetermined material properties of the bendable rod; and using the processing system to determine the velocity of the fluid relative to the vehicle based on the force or torque and geometric properties of the bendable rod.

[0041] Preferably, the predetermined material properties may include at least the stiffness of the bendable rod. In some embodiments, the processing system may receive data related to the temperature and ambient pressure near the bendable rod, determine the density of the fluid near the bendable rod, and determine the velocity of the fluid relative to the vehicle based on the force or torque, the geometry of the bendable rod, and the density of the fluid near the bendable rod. Attached Figure Description

[0042] The embodiments are summarized by way of example in the following description with reference to the accompanying drawings. In these drawings, parts or elements that are the same or have the same function are labeled with the same reference numerals and characters, and are therefore described only once in the following description.

[0043] Figure 1 This is a diagram of an exemplary rotary-wing aircraft having an exemplary measuring device for determining air velocity relative to the rotary-wing aircraft;

[0044] Figure 2A This is a diagram of an exemplary sensor device with a bendable rod and a sensor;

[0045] Figure 2B When a fluid applies a force or torque to a bendable rod Figure 2A A diagram of an exemplary sensor device;

[0046] Figure 3A This is a diagram of an exemplary bending rod with a series of alignment sensors attached to the bending rod parallel to its neutral axis.

[0047] Figure 3B yes Figure 3A A cross-sectional view of an exemplary bendable rod with a series of alignment sensors;

[0048] Figure 4 This is a diagram of an exemplary sensor device having two bendable rods arranged perpendicularly to each other;

[0049] Figure 5A This is a diagram of an exemplary sensor device having three bendable rods arranged perpendicularly to each other at the same base;

[0050] Figure 5B This is a diagram of an exemplary sensor device having three bendable rods arranged in series and perpendicular to each other;

[0051] Figure 5C This is a diagram of an exemplary sensor device with three bendable rods arranged perpendicularly to each other at the same base and having a spherical shape at the distal end of the base, wherein two series of alignment sensors are connected to each other in a spherical shape; and

[0052] Figure 6 This is a diagram of an exemplary processing system of an exemplary measurement system, which receives signals from sensors and provides a magnitude of velocity and an angle of velocity to a display and an alarm system. Detailed Implementation

[0053] Figure 1 This is a diagram of an exemplary rotary-wing aircraft 100 having at least one rotor 110 with a rotor shaft 115. Figure 1 As shown, the rotorcraft 100, sometimes referred to as rotorcraft 100, is exemplarily shown as a helicopter. Therefore, for the purposes of simplicity and clarity, rotorcraft 100 is referred to as "helicopter" 100 hereinafter.

[0054] For example, helicopter 100 may have a fuselage 120 forming the fuselage of helicopter 100. The fuselage 120 is connected to appropriate landing gear and, for example, forms a cabin 123 and a rear fuselage 127. The rear fuselage 127 is connected to a tail boom 130.

[0055] As an example, helicopter 100 may include at least one anti-torque device 140 configured to provide anti-torque during operation, i.e., to counteract the torque generated by the rotation of at least one rotor 110 in order to balance the helicopter 100 in terms of yaw. The anti-torque device 140 may be covered if desired. At least one anti-torque device 140 is exemplary disposed in the rear section of tail boom 130 and may have a tail rotor 145. The rear section of tail boom 130 may include a tail fin 150. Exemplarily, tail boom 130 may be provided with a suitable horizontal stabilizer 135.

[0056] Exemplarily, the helicopter 100 may have at least one rotor 110, which is exemplary configured as a multi-bladed rotor 110 for providing lift and forward or rearward thrust during operation. The at least one multi-bladed rotor 110 includes a plurality of rotor blades 112 mounted at an associated rotor head 114 to a rotor shaft 115, sometimes also referred to as a rotor mast 115. During operation of the helicopter 100, the rotor shaft 115 rotates in a rotor plane 119 about an associated rotor shaft 117, thereby generating a downwash flow affecting a predetermined surface region 160 of the rotorcraft 100 during the rotation of the multi-bladed rotor 110.

[0057] The rotary-wing aircraft 100 includes a measuring device 200 for determining the velocity of air relative to the rotary-wing aircraft 100. The measuring device 200 includes a processing system and a sensor device 224 mounted to the rotary-wing aircraft 100. The sensor device 224 includes a flexible rod attached to the rotary-wing aircraft 100. The flexible rod has a predetermined shape and stiffness.

[0058] The flexible rod can be positioned on the rotary-wing aircraft 100 such that the rotary-wing aircraft has almost no impact on the flow of fluid (i.e., air). In the case of the rotary-wing aircraft 100, the flow of fluid may be affected by the surfaces of the rotary-wing aircraft 100 (such as the fuselage 120, tail boom 130, anti-torque device 140, or tail fin 150). The flow of fluid may also be affected by the fluid flow generated by moving parts such as the multi-bladed rotor 110 or the tail rotor.

[0059] Exemplarily, a flexible rod is attached to the outside of a predetermined surface region 160 of the rotorcraft 100, which is affected by the downwash during rotation of the multi-bladed rotor 110. Mounting the flexible rod outside the predetermined downwash-affected surface region 160 of the rotorcraft 100 is useful for measuring low airspeeds relative to the rotorcraft 100. Existing interferences due to the interaction with the main rotor downwash, such as interference with the ground or in quarter-flight, can be filtered out by a correction factor in conjunction with the measured altitude above the ground. Such a correction factor can be determined during a reference flight.

[0060] As an example, the flexible rod can be attached to the tail fin 150. As another example, the flexible rod can be attached to the nose boom outside a predetermined surface area 160 affected by the downwash, which is attached to the fuselage forward of the nacelle 123.

[0061] The sensor device 224 also includes a sensor associated with the bendable rod and that generates a signal indicating the force or torque exerted by the air on the bendable rod.

[0062] The processing system receives signals from sensors and determines the air velocity relative to the rotary-wing aircraft 100 based on the signals from the sensors and the predetermined shape and stiffness of the bendable rod.

[0063] The processing system can be installed anywhere on the rotary-wing aircraft 100. As an example, the processing system can be installed near the sensor device 224 (e.g., in the tail boom 130). As another example, the processing system can be installed away from the sensor device 224 in the fuselage 120 (e.g., in the cabin 123).

[0064] Independent of the positioning of each part of the processing system 610, signals from sensor device 224 can be transmitted to the processing system via a wired connection. If needed, signals from sensor device 224 can be transmitted to the processing system wirelessly. (Reference) Figure 6 Describe the processing system in more detail.

[0065] If needed, the measuring device 200 may include an additional sensor device 201. The additional sensor device 201 may include an additional sensor associated with an additional flexible rod attached to the rotorcraft 100 at a location near the sensor device 224 and protected from fluid influences. For example, the additional flexible rod of the additional sensor device 201 may be attached to the rotorcraft 100 inside the tail fin 150.

[0066] The processing system can use measurements related to another force or torque acting on the additional sensor to filter out parasitic forces or torques, such as vibrations of the structure of the rotary-wing aircraft 100 acting on the sensor. In some embodiments, a notch filter can be used to filter out parasitic forces or torques acting on the sensor.

[0067] The measuring device 200 is not limited to determining the speed of air relative to a rotary-wing aircraft, and can also be mounted on any other vehicle to determine the speed of any fluid relative to that vehicle. As an example, the measuring device can determine the speed of a liquid such as water relative to a vessel such as a submarine or ship. As another example, the measuring device can determine the speed of a gas (such as air) relative to an aircraft (such as an airplane or drone), relative to a rocket or spacecraft, or relative to a ground vehicle (such as a car, bus, truck, or train). If desired, the measuring device 200 can be used to determine the speed of a fluid relative to a wind turbine, weather measurement system, building, or in a wind tunnel.

[0068] For example, the measuring device 200 can be used as an accelerometer, since the sensor will also respond to the bending of the bendable rod, which is caused by the inertia of the bendable rod and by external acceleration induced by the bendable rod. The interference in the measurement of fluid velocity caused by the external acceleration induced by the bendable rod can be compensated, for example, by utilizing parallel measurements of the acceleration of a pure accelerometer near the bendable rod.

[0069] Figure 2A This is a diagram of an exemplary sensor device 224 for a measuring device 200 used to determine the velocity of a fluid relative to a vehicle. The sensor device 224 is mounted to the vehicle and includes a flexible rod 210 and sensors 224a, 224b, 224c, and 224d.

[0070] Exemplarily, the flexible rod 210 is attached to a vehicle via a base 280. The flexible rod 210 has a predetermined shape and stiffness. As an example, the flexible rod 210 may have a cylindrical shape, wherein the ratio between its height (i.e., the length of the flexible rod 210) and its diameter (i.e., the thickness of the flexible rod 210) is in the range of 5 to 40. As another example, the flexible rod 210 may have a conical shape, with or without a tip (i.e., a whole cone or a truncated cone), wherein the ratio between its height (i.e., the length of the flexible rod 210) and its diameter at the base (i.e., the thickness of the flexible rod 210) is in the range of 5 to 40.

[0071] If desired, the thickness and / or stiffness of the bendable rod 210 can vary along its length. For example, the bendable rod 210 can have one or more cylindrical shapes with different diameters, optionally combined with a conical truncated section. Multiple cylindrical shapes of the bendable rod 210 with different diameters can result in different bending sensitivities along the length of the bendable rod 210 via variable stiffness.

[0072] In some embodiments, the flexible rod 210 may include additional elements, such as a sphere or cylinder, at its tip to focus measurements on the flow region further away from the flow-affected surface to which the flexible rod 210 is attached. Figure 5C An exemplary embodiment of this flexible rod is shown in the figure.

[0073] When a force or torque is applied to the bendable rod 210 by a fluid, the bendable rod 210 is adapted to bend along a bending line. Thus, the force or torque causes deformation of the bendable rod 210, wherein a portion of the bendable rod 210 is compressed and another portion of the bendable rod 210 is stretched.

[0074] The neutral axis 240 separates the compressed portion of the bendable rod 210 from the stretched portion. Therefore, the neutral axis 240 is the portion of the bendable rod 210 that is neither stretched nor compressed. Figure 2A As shown, the neutral axis extends along the length of the flexible rod 210.

[0075] For example, the bendable rod 210 may include a body material 260. The body material 260 may include any bendable material. For example, the body material 260 may include metal, plastic, rubber, wood, fabric, foam, or any combination thereof. For instance, the bendable rod 210 may include different body materials 260 along its length to provide variable stiffness along the length of the bendable rod 210.

[0076] If desired, the bendable rod 210 may comprise a composite material. In some embodiments, the composite material may be a fiber-reinforced composite material. In these embodiments, the composite material may have a fiber orientation forming a predetermined angle 270 with respect to the neutral axis 240. Exemplarily, the predetermined angle 270 may be selected between 30 degrees and 60 degrees to prevent torsional movement of the bendable rod 210.

[0077] If necessary, measurement errors caused by the torsional movement of the bendable rod 210 can be eliminated by means of compensation measurements, either additionally or alternatively.

[0078] Sensors 224a, 224b, 224c, and 224d are associated with the flexible rod 210 and generate signals indicating the force or torque 230 applied to the flexible rod 210 by the fluid. Exemplarily, sensors 224a, 224b, 224c, and 224d are fixedly disposed at the flexible rod 210. As an example, sensors 224a, 224b, 224c, and 224d may be attached to the surface of the flexible rod 210. As another example, sensors 224a, 224b, 224c, and 224d may be embedded in a groove extending along the outer region of the flexible rod 210. As yet another example, sensors 224a, 224b, 224c, and 224d may be embedded within the body material 260. Therefore, sensors 224a, 224b, 224c, and 224d can be protected from environmental influences.

[0079] For example, force or torque 230 causes deformation of the bendable rod 210, resulting in a so-called bend line. Sensors 224a, 224b, 224c, 224d can measure the strain in the form of compression or tension caused by the deformation of the bendable rod 210 along the bend line.

[0080] Such as reference Figure 6The processing system 610 described herein can use simulation and reference measurements to directly correlate the curved line determined by sensors 224a, 224b, 224c, and 224d with the incident velocity of the fluid. Therefore, the measuring device 200 can determine the fluid velocity by measuring the curved line.

[0081] For example, sensors 224a, 224b, 224c, and 224d include at least one of an electrical strain gauge, a piezoelectric sensor, or an optical sensor. For instance, sensors 224a, 224b, 224c, and 224d can be implemented using a plurality of fiber Bragg gratings (FBGs) in fiber optic cable 222.

[0082] Fiber optic cables 222 containing FBG are very lightweight, relatively small in size, immune to electromagnetic interference, flexible, robust, compatible with composite materials, and require no power per sensor. For example, fiber optic cables 222 can have a fiber optic cable diameter of 80 μm.

[0083] For example, the fiber optic cable 222 may include an optical fiber core (e.g., a glass fiber cable) for transmitting light. The optical fiber core may be surrounded by an optical fiber cladding, such that light is reflected from the optical fiber cladding back into the optical fiber core, which ensures minimal transmission loss. In practice, the optical fiber core may have a higher refractive index η than the optical fiber cladding, resulting in total internal reflection at the boundary between the optical fiber core and the optical fiber cladding.

[0084] If required, the fiber optic cable 222 may include a protective sheath (e.g., a coating). The protective sheath can protect the fiber cladding and fiber core from external conditions and physical damage.

[0085] Characteristics of a fiber Bragg grating modulated propagation light source. The interrogator in the processing system may include a light source and send light with a first predetermined wavelength distribution to the FBG. The FBG can reflect light with a second wavelength distribution back to the processing system as a signal. All other wavelengths of the input signal can be transmitted unaffected via fiber optic cable 222.

[0086] For example, a fiber Bragg grating acts as a wavelength selective mirror, reflecting back to a predetermined wavelength distribution via fiber optic cable 222. Perturbations to the grating (e.g., by strain or temperature) cause changes in the reflected wavelength distribution, which is the basis of the sensing method. Therefore, changes in the force or torque exerted by a fluid on the bendable rod 210 cause a change in a second wavelength distribution. If desired, multiple optical sensors with a center wavelength are distributed in a specific nm wavelength band to ensure proper signal monitoring.

[0087] If needed, sensors 224a, 224b, 224c, and 224d can perform strain measurements using fiber segment interferometry (FSI). In FSI, sensors 224a, 224b, 224c, and 224d include optical reflectors embedded at predetermined distances into fiber optic cable 222, and the change in distance between pairs of adjacent optical reflectors is measured to determine the tilt angle of the bending rod 210. (Refer to...) Figure 3A and Figure 3B Further description of strain measurement via FSI.

[0088] For example, sensors 224a, 224b, 224c, 224d may include at least one series of alignment sensors 250a, 250b disposed at the bendable rod 210, preferably parallel to the neutral axis 240 at a predetermined distance from the neutral axis 240.

[0089] Preferably, the sensor includes at least three series of alignment sensors 250a, 250b, 250c, and 250d, and the processing system (e.g., Figure 6 The processing system 610) determines the magnitude and direction of the fluid velocity in a plane perpendicular to the bendable rod 210.

[0090] Figure 2B When the fluid applies a force or torque 230 to the bendable rod 210 Figure 2A A figure of an exemplary sensor device 224 of the measuring device 200.

[0091] like Figure 2B As shown, force or torque 230 causes the bendable rod 210 to deform along the bending line. Sensors 224a, 224b, 224c, and 224d generate signals indicating the force or torque 230 applied to the bendable rod 210 by the fluid. For example, sensors 224a, 224b, 224c, and 224d measure the strain along the bending line in the form of compression or tension caused by the deformation of the bendable rod 210.

[0092] Cable 222 can be connected to sensors 224a, 224b, 224c, and 224d, and transmits a signal associated with a measured force or torque acting on the bendable rod 210. In some embodiments, cable 222 can be a cable for transmitting electrical signals, and sensors 224a, 224b, 224c, and 224d can include strain gauges that generate electrical signals. In other embodiments, cable 222 can be an optical fiber cable for transmitting optical signals, and sensors 224a, 224b, 224c, and 224d can include optical sensors.

[0093] The measuring device 200 may include, for example, in Figure 6The processing system is described in more detail below. Exemplarily, the processing system is connected to cable 222 and receives signals from sensors 224a, 224b, 224c, and 224d via cable 222. The processing system determines the velocity of the fluid relative to the vehicle based on the signals from sensors 224a, 224b, 224c, and 224d, as well as the predetermined shape and stiffness of the flexible rod 210.

[0094] Figure 3A The diagram shows an exemplary bending rod 210 having a series of alignment sensors 250a, 250b attached to the bending rod 210 at a predetermined distance from the neutral axis 240 parallel to the neutral axis 240.

[0095] For example, the alignment sensors 250a and 250b in the series can perform strain measurements via fiber optic segment interferometry (FSI). Figure 3A As shown, each series of alignment sensors 250a, 250b may include an optical fiber cable 222 and optical reflectors 324a, 324b, 324c, 324d embedded in the optical fiber cable 222 at predetermined distances from each other. Therefore, the series of alignment sensors 250a, 250b form a continuous sensor chain.

[0096] In FSI, the strain on the bending rod 210 is measured as the change in light propagation time through measurement segments 350a, 350b, 350c, and 350d. Optical reflectors 324a, 324b, 324c, and 324d are used to measure the fiber length between two adjacent optical reflectors (e.g., adjacent optical reflectors 324c and 324d), which is calculated as the difference between the optical path distances between the optical reflectors. The processing system can convert the resulting stage changes in the measurement segments (e.g., measurement segment 350c) into measurements of interest, such as strain and temperature. Therefore, the processing system determines the tilt angle of the bending rod 210 based on measuring the distance changes between pairs of adjacent optical reflectors 324c and 324d.

[0097] For example, the sensor may include a preferred even number of alignment sensors 250a, 250b, 250c, 250d. If desired, any two alignment sensors (e.g., series 250a, 250b or series 250c, 250d) arranged on opposite sides of the neutral axis 240 may be connected to the distal end 215 of the flexible rod 210, away from the vehicle.

[0098] Figure 3B It features four series of alignment sensors: 250a, 250b, 250c, and 250d. Figure 3AA cross-sectional view of an exemplary flexible rod 210. (See example...) Figure 3B As shown, the four series of alignment sensors 250a, 250b, 250c, and 250d can be evenly distributed around the neutral axis 240.

[0099] As an example, appropriate additional processing of the different strains experienced by corresponding fiber segments in the processing system allows for vertical shape change measurement via differential strain changes obtained from two opposing series of alignment sensors (e.g., alignment sensors 250a and 250b). For horizontal shape change measurement, sensors 250c and 250d arranged perpendicular to 250a and 250b can be used in the same manner, enabling direct and independent measurement of the bending of the rod in both the vertical and horizontal directions. When the bendable rod 210 bends along the target plane, one segment of the alignment sensors (e.g., alignment sensor 250a) extends, and the corresponding segment of another series of alignment sensors (e.g., alignment sensor 250b) on the opposite side of the bendable rod 210 shortens. The inclination of the bendable rod 210 can be measured via the measuring segment (e.g., Figure 3A The bending line of the bendable rod 210 can be determined directly by the measurement segment 350c, and by the integration over several segments (e.g., measurement segments 350a, 350b, 350c, 350d). The processing system (e.g., Figure 6 The processing system 610 can determine the magnitude and direction of the fluid velocity in a plane perpendicular to the bendable rod 210.

[0100] Therefore, in Figure 1 In the example of the rotary-wing aircraft 100, the use of four series of alignment sensors arranged perpendicularly to each other provides valuable additional information for determining wind direction during hovering. The pilot may be able to use this additional information to avoid dangerous vortex ring conditions. Furthermore, the pilot will have reliable speed information in flight directions other than forward flight, which will significantly increase situational awareness in a wide range of operational missions.

[0101] have Figure 2A , Figure 2B , Figure 3A and Figure 3B The measuring device 200 of the sensor device 224 described herein can determine the velocity in a plane perpendicular to the longitudinal direction of the flexible rod 210 (i.e., perpendicular to the neutral axis 240). However, by adding another flexible rod with an additional sensor to the measuring device in a plane perpendicular to the neutral axis 240, the measuring device can determine the three-dimensional fluid flow direction.

[0102] Figure 4 This is a diagram of an exemplary sensor device 224 having two flexible rods 210, 410 arranged perpendicularly to each other. Figure 4 As shown, in addition to the bendable rod 210 and sensors 224a, 224b, 224c, and 224d, the sensor device 224 also includes an additional bendable rod 410 and an additional sensor 424. The additional bendable rod 410 may have an additional predetermined shape and stiffness, and is attached to a vehicle perpendicular to the bendable rod 210 via a base 280 identical to that of the bendable rod 210 (e.g., [missing information]). Figure 1 Rotary-wing aircraft 100).

[0103] An additional sensor 424 associated with the additional flexible rod 410 generates an additional signal indicating the additional force or torque exerted by the fluid on the additional flexible rod 410. The additional sensor 424 can transmit the additional signal to a processing system (e.g., via an additional cable 422). Figure 6 Processing system 610).

[0104] The processing system can determine a three-dimensional representation of the fluid's velocity relative to a vehicle based on the signal and additional signals.

[0105] like Figure 4 As shown, two series of alignment sensors 250a and 250b can be associated with the flexible rod 210 and connected to the processing system via cable 222, and two separate series of alignment sensors 460a and 460b can be associated with the flexible rod 410 and connected to the processing system via cable 422. If needed, Figure 4 The sensor device 224 may include a single series of alignment sensors (i.e., a series of alignment sensors 250a, 250b, 460a, 460b are coupled and connected in series with the processing system via a single cable or wirelessly).

[0106] In some embodiments, the bendable rods 210, 410 may include a heating device 450 adapted to prevent the bendable rods 210, 410 from freezing. A cable 440 may be connected to the heating device 450 to supply power to the heating device 450.

[0107] If needed, the second unheated sensor device can potentially be used as an icing detector by comparing the bending line of the bent rod of the unheated sensor device with the bending line of the bent rod of the heated sensor device.

[0108] Figure 4 The sensor device 224 shown can increase the robustness and redundancy of the measurement because the velocity of the fluid relative to the sensor device 224 is captured by the sensor associated with the two bending rods 210 and 410, as long as the flow direction of the fluid is not parallel to the plane formed by the bending rods 210 and 410.

[0109] By arranging flexible rods with sensors in all three coordinate directions (i.e., perpendicular to each other), further increases in redundancy and robustness in determining the velocity of fluid relative to a vehicle can be achieved.

[0110] Figure 5A This is a diagram of an exemplary sensor device having three bendable rods 210, 410, 510 arranged perpendicularly to each other and attached to the same base 280, and associated sensors. The bendable rods 210, 410, 510 may each have a predetermined shape and stiffness. The sensors may include a separate series of alignment sensors associated with the different bendable rods 210, 410, 510 and connected to a processing system via cables. In a scenario where the series of alignment sensors are connected in pairs from the base 280 at the distal ends 215 of the respective bendable rods (e.g., as shown in the diagram),... Figure 3A As shown), a tight radius at the distal end 215 may cause difficulties. In this case, the individual flexible rods 210, 410, 510 can be arranged in series.

[0111] Figure 5B This is a diagram of an exemplary sensor device 224 having three bendable rods 210, 410, and 510 arranged in series and perpendicular to each other. Thus, the first end of bendable rod 210 is attached to the base 280, the first end of bendable rod 410 is attached to the second end of bendable rod 210, and the first end of bendable rod 510 is attached to the second end of bendable rod 410.

[0112] For example, Figure 5B The sensor device 224 may include a single series of alignment sensors connected to the processing system via a single cable or wirelessly. If desired, this can be achieved, for example, through... Figure 5A The difficulty of the tight radius at the distal end 215 of the flexible rod is solved by using a ball-shaped or ball-shaped form.

[0113] Figure 5C The figure shows an exemplary sensor device 224 having three flexible rods 210, 410, 510, which are arranged perpendicularly to each other at the same base 280 and have a spherical shape at the distal end 215 of the base 280, wherein two series of alignment sensors are connected to each other in a spherical shape. Figure 5C A three-dimensional representation of the bendable rods 410 and 510 and a cross-section of the bendable rod 210 having an embedded sensor arranged in a single series of alignment sensors are shown. Exemplarily, the bendable rods 410 and 510 may both include a similar series of alignment sensors.

[0114] In some embodiments, the flexible rods 210, 410, and 510 may include a shape different from the sphere at the distal end 215 of each flexible rod. For example, the flexible rods 210, 410, and 510 may each include an ellipsoid or an oval shape at the distal end 215.

[0115] Figure 6 This is a diagram of an exemplary processing system 610 for an exemplary measuring device. The processing system 610 receives data from a sensor device 224 (such as...). Figure 2B The sensor device 224, which has a sensor associated with the bendable rod, receives the signal 620. The processing system 610 determines the velocity of the fluid relative to the vehicle based on the signal 620 from the sensor device 224 and the predetermined shape and stiffness of the bendable rod.

[0116] like Figure 6 As shown, the processing system 610 provides the display 650 and the alarm system 655 with the speed relative to the size 670 and direction 680 of the vehicle.

[0117] For example, the display 650 can display the magnitude 670 and direction 680 of the fluid's velocity relative to the vehicle, thus making the information visually available (e.g., for...). Figure 1 (Pilot of a rotary-wing aircraft 100).

[0118] If needed, the alarm system 655 can provide at least one of a visual or audible alarm when the magnitude 670 and / or direction of the fluid velocity may put the vehicle in a dangerous situation. As an example, the vehicle could be a helicopter, and the handling system 610 could detect the risk of a vortex ring state. As another example, the vehicle could be a truck, and the handling system 610 could detect the risk of the truck overturning due to strong crosswinds.

[0119] For example, alarm system 655 can issue an alarm or make a clear voice announcement. As another example, alarm system 655 can flash the screen or display a message on the screen.

[0120] For example, sensor device 224 (e.g., Figure 2A , Figure 2B , Figure 3A or Figure 3B The sensor device 224, which has a bendable rod 210 and sensors 224a, 224b, 224c, 224d, can measure the strain of the bendable rod in the form of compression or tension caused by a force or torque applied to it by a fluid (e.g., as shown in the image). Figure 2B (As shown). In response, sensor device 224 can generate a signal 620 indicating the force or torque associated with strain, and transmit the signal 620 to processing system 610 via cable or wirelessly.

[0121] For example, the processing system 610 includes an interrogator. The interrogator may include a light source. For instance, the interrogator may transmit light to an optical fiber sensor device, such as a reference sensor, of the sensor device 224. Figure 2A , Figure 2B , Figure 3A , Figure 3B The sensor device described.

[0122] The processing system 610 may include a storage circuit 630. The storage circuit 630 may store information about the shape and stiffness of the bendable rod, information about the bending of the bendable rod in relation to the velocity of the fluid, information about the stiffness of the bendable rod depending on the ambient temperature, etc.

[0123] For example, the processing system 610 may include a processing unit 640. For instance, the processing unit 640 may obtain data from the storage circuitry 630, such as information about the shape and stiffness of the bendable rod.

[0124] If needed, the processing unit 640 may include an arithmetic logic unit (ALU) 645. The arithmetic logic unit 645 may determine the magnitude 670 and direction of the fluid flow 680 based on information obtained from the storage circuit 630 and signals 620 received from the sensor device.

[0125] As an example, the storage circuit 630 can store a lookup table having a magnitude 670 and a direction 680 depending on the speed of the measured force or torque acting on the bendable rod, and the processing unit 640 can use the lookup table to obtain the magnitude 670 and direction 680 of the speed corresponding to the measured force or torque acting on the bendable rod.

[0126] As another example, the processing unit 640 can use the arithmetic logic unit 645 to calculate the magnitude 670 and direction 680 of the velocity based on the functional relationship between the bending moment and the force or moment acting on the bendable rod being measured (e.g., a functional relationship determined during the calibration of the measuring device).

[0127] As yet another example, the processing unit 640 can query a trained machine learning engine to determine the magnitude 670 and direction 680 of the velocity based on the measured force or torque acting on the bendable rod.

[0128] If necessary, the processing unit 640 may record information for further processing and analysis of the recorded information (e.g., by storing the information in the storage circuit 630). For example, the processing unit 640 may sample the magnitude 670 and / or direction 680 of the fluid velocity within a predetermined range over a duration (e.g., between two maintenance intervals).

[0129] If needed, the processing system 610 can provide the recorded information from the storage circuit 630 for further processing. As an example, the processing system 610 can provide the recorded information to the maintenance device during maintenance. As another example, the processing system 610 can provide a graph showing the size and orientation of the recorded information depending on time.

[0130] If necessary, the processing unit 640 may include at least one of a system self-test function, a calibration function adapted to set a zero-point reference or signal scaling factor, or an output function adapted to select between providing analog or digital output signals.

[0131] The processing system 610 can be implemented using different discrete components. For example... Figure 6 As shown, the discrete components may include a storage circuit 630, a processing unit 640, a display 650, and an alarm system 655.

[0132] If needed, Figure 6 Some or all of the discrete components can be combined and integrated into a single component. As an example, the alarm system 655 can be integrated with a speaker into the display 650. As another example, the processing unit 640 can have embedded memory circuitry, thereby combining the processing unit 640 and the storage circuitry 630.

[0133] It should be noted that the above embodiments are described merely to illustrate possible embodiments of the invention and are not intended to limit the invention thereto. On the contrary, various modifications and variations of the above embodiments are possible and should therefore be considered part of the invention.

[0134] For example, above Figure 6 The measuring device described herein presents the display 650 and alarm system 655 as the sole recipients of the magnitude 670 and direction 680 of the fluid velocity. However, the storage circuit 630 may receive and store the magnitude and / or direction of the fluid velocity under certain predetermined conditions, such as whenever the magnitude and / or direction of the fluid velocity exceeds a predetermined threshold, including duration and timestamp if desired. Alternatively, any other component of the alarm system or measuring device may include additional storage circuitry that stores the timestamps under the predetermined conditions, as well as the magnitude and / or direction of the fluid velocity.

[0135] In addition, sensors 224a, 224b, 224c, and 224d can be obtained from Figure 2A and Figure 2B The measuring device 200 is omitted. Instead, the camera can observe the bendable rod 210, and Figure 6The processing system 610 can analyze the images transmitted by the camera to determine the force or torque exerted by the fluid on the bendable rod 210, and use the results of the analysis to determine the size and direction of the fluid relative to the vehicle based on the images from the camera and the predetermined shape and stiffness of the bendable rod 210.

[0136] List of reference numerals

[0137] 100 Rotary-wing aircraft, rotorcraft, helicopters

[0138] 110 Multi-bladed Rotor

[0139] 112 rotor blades

[0140] 114 Rotor Head

[0141] 115 rotor shaft

[0142] 117 Rotor axis

[0143] 119 Rotor Plane

[0144] 120 fuselage

[0145] Cabin 123

[0146] 127 rear fuselage

[0147] 130 tail boom

[0148] 135 Horizontal Stabilizer

[0149] 140 Anti-torque device

[0150] 145 Tail Rotor

[0151] 150 Caudal Fin

[0152] 160 Predetermined surface area affected by the downwash flow

[0153] 200 Measuring Device

[0154] 201 Sensor Device

[0155] 210 Bendable Rod

[0156] 215 Remote

[0157] 222 Fiber Optic Cable

[0158] 224 Sensor Device

[0159] Sensors 224a, 224b, 224c, and 224d

[0160] 230 Force or torque

[0161] 240 Neutral axis

[0162] A series of alignment sensors: 250a, 250b, 250c, 250d.

[0163] 260 Main materials

[0164] 270 degrees

[0165] 280 base

[0166] 324a, 324b, 324c, 324d optical reflectors

[0167] Measurement sections 350a, 350b, 350c, and 350d

[0168] 410 Bendable Rod

[0169] 422 Additional Cables

[0170] 424 Additional Sensors

[0171] 440 cable

[0172] 450 heating equipment

[0173] Alignment sensors of the 460a and 460b series

[0174] 510 Bendable Rod

[0175] 610 Processing System

[0176] 620 signal

[0177] 630 storage circuit

[0178] 640 processing units

[0179] 645 Arithmetic Logic Units

[0180] 650 monitor

[0181] 655 Alarm System

[0182] Data obtained from 660

[0183] 670 speed size

[0184] 680 speed direction.

Claims

1. A measuring device (200) for determining the velocity of a fluid relative to a vehicle (100), the measuring device (200) comprising a sensor device (224) and a processing system (610): The sensor device (224) is configured to be installed on the vehicle (100) and includes: A bendable rod (210), the bendable rod being configured to be attached to the vehicle (100) and having a predetermined shape and stiffness, and Sensors (224a, 224b, 224c, 224d), said sensors (224a, 224b, 224c, 224d) are associated with the flexible rod (210) and configured to generate signals indicating the force or torque (230) exerted by the fluid on the flexible rod (210); and The processing system (610) is configured to receive the signal (620) from the sensors (224a, 224b, 224c, 224d) and determine the velocity of the fluid relative to the vehicle (100) based on the signal (620) from the sensors (224a, 224b, 224c, 224d) and the predetermined shape and stiffness of the flexible rod (210).

2. The measuring device (200) according to claim 1, wherein, The force or torque (230) causes deformation of the bendable rod (210), and the sensors (224a, 224b, 224c, 224d) are configured to measure the strain in the form of compression or tension caused by the deformation of the bendable rod (210).

3. The measuring device (200) according to claim 1 or 2, wherein, The sensors (224a, 224b, 224c, 224d) include at least one of an electrical strain gauge, a piezoelectric sensor, or an optical sensor.

4. The measuring device (200) according to claim 1 or 2, wherein, The flexible rod (210) has a neutral axis (240), and the sensors (224a, 224b, 224c, 224d) further include: At least one series of alignment sensors (250a, 250b) are disposed at the bendable rod (210), preferably parallel to the neutral axis (240) and at a predetermined distance from the neutral axis (240).

5. The measuring device (200) according to claim 4, wherein, The at least one series of alignment sensors (250a, 250b) includes: A predetermined number of alignment sensors (250a, 250b, 250c, 250d) are provided, and the processing system (610) is further configured to determine the magnitude and direction of the velocity of the fluid in a plane perpendicular to the bendable rod (210).

6. The measuring device (200) according to claim 4, wherein, The at least one series of alignment sensors (250a, 250b) includes: A predetermined number of alignment sensors (250a, 250b, 250c, 250d) of a series, wherein any two of the even-numbered alignment sensors (250a, 250b) (250c, 250d) arranged on opposite sides of the neutral axis (240) are connected to the distal end (215) of the flexible rod (210) away from the vehicle (100).

7. The measuring device (200) according to any one of claims 4 to 6, wherein, One of the at least one series of alignment sensors (250a, 250b) includes: Fiber optic cable (222); and Optical reflectors (324a, 324b, 324c, 324d) are embedded in the optical fiber cable (222) at a predetermined distance from each other.

8. The measuring device (200) according to claim 7, wherein, The processing system (610) is further configured to determine the tilt angle of the flexible rod (210) based on measuring the distance change between adjacent optical reflector pairs (324c, 324d) of the optical reflectors (324a, 324b, 324c, 324d).

9. The measuring device (200) according to any one of claims 4 to 8, wherein, The flexible rod (210) also includes: The main material (260) includes a composite material having a fiber orientation forming a predetermined angle (270) with the neutral axis (240), wherein the predetermined angle (270) is selected between 30 degrees and 60 degrees to prevent torsional movement of the bendable rod (210).

10. The measuring device (200) according to any one of claims 4 to 9, wherein, The thickness and / or stiffness of the bendable rod (210) varies along the neutral axis (240).

11. The measuring device (200) according to any one of the preceding claims, wherein, The sensor device (224) further includes: An additional flexible rod (410) is provided, which is configured to be attached to the vehicle (100) perpendicular to the flexible rod (210) and has an additional predetermined shape and stiffness; and An additional sensor (424), associated with the additional flexible rod (410), is configured to generate an additional signal indicating an additional force or torque exerted by the fluid on the additional flexible rod (410), and is configured to send the additional signal to the processing system (610), wherein the processing system (610) is further configured to determine a three-dimensional representation of the velocity of the fluid relative to the vehicle (100) based on the signal (620) and the additional signal.

12. The measuring device (200) according to any one of claims 1 to 10, further comprising: An additional sensor device (201) having an additional sensor associated with an additional flexible rod attached to the vehicle (100) at a location free from fluid influence, and wherein the processing system (610) uses a measurement related to another force or torque acting on the additional sensor to filter out parasitic forces or torques acting on the sensors (224a, 224b, 224c, 224d).

13. The measuring device (200) according to any one of claims 1 to 10, wherein, The flexible rod (210) also includes: Heating device (450), said heating device (450) being adapted to prevent the bendable rod (210) from freezing; and A cable (440) is connected to the heating device (450) and supplies power to the heating device (450).

14. An aircraft (100) comprising a measuring device (200) according to any one of the preceding claims, wherein, The flexible rod (210) is attached to the aircraft (100) at a predetermined surface area (160).

15. The aircraft (100) according to claim 14, wherein the aircraft (100) is a rotary-wing aircraft (100), comprising: A multi-bladed rotor (110) is at least adapted to generate lift during operation, the multi-bladed rotor (110) comprising at least two rotor blades (112) that generate a downwash flow affecting a predetermined surface area (160) of the rotorcraft (100) during rotation of the main rotor (120), and wherein the flexible rod (210) is attached to the rotorcraft (100) outside the predetermined surface area (160).

16. A method of operating a measuring device (200) for determining the velocity of a fluid relative to a vehicle (100), the measuring device (200) comprising a flexible rod (210) attached to the vehicle (100), the method comprising: The strain in the bendable rod (210) caused by the force or torque (230) applied to the bendable rod (210) by the fluid is measured using sensors (224a, 224b, 224c, 224d) associated with the bendable rod (210); The sensors (224a, 224b, 224c, 224d) are used to generate signals indicating the force or torque (230); The signal (620) is received from the sensors (224a, 224b, 224c, 224d) using the processing system (610). Using the processing system (610), the bending of the bendable rod (210) is determined based on the signals (620) from the sensors (224a, 224b, 224c, 224d); Using the processing system (610), the force or torque (230) is determined based on the bending of the bendable rod (210) and predetermined material properties of the bendable rod (210); and Using the processing system (610), the velocity of the fluid relative to the vehicle (100) is determined based on the force or torque (230) and the geometry of the flexible rod (210).

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