Method for controlling at least one rotor of an air vehicle, control data providing unit for an air vehicle, and air vehicle having at least one rotor - Patents.com
Patent Information
- Application Number
- JP2024534060
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2021-12-09
- Filing Date
- 2022-10-17
- Publication Date
- 2025-10-09
AI Technical Summary
Shrouded rotors in air vehicles, such as helicopters and electric Vertical Take-Off and Landing aircraft, emit sound with discrete frequencies that are perceived as unpleasant despite reduced total acoustic energy, necessitating an alternative method to further reduce sound emissions.
A method and control data provision unit that adjust the rotational speed and angle of attack of shrouded rotors independently, using pre-flight measurements to determine optimal operating parameter pairs that minimize sound emission by exploiting frequency-dependent acoustic properties of the shroud and liner, without requiring in-flight measurements or complex equipment.
Effectively reduces the perceived unpleasantness of shrouded rotor sound emissions by minimizing tonality and total sound levels during operation, particularly in hover conditions, using a control data provision unit to implement optimal rotor control based on pre-determined sound indices.
Smart Images
Figure 00000000_0000_ABST
Abstract
Description
[Technical field]
[0001] The present invention relates to a method for controlling at least one rotor of an air vehicle, to a control data providing unit for an air vehicle having at least one rotor, and to such an air vehicle.
[0002] An example of such a flying vehicle with at least one rotor is a helicopter with a main rotor and a tail rotor. The tail rotor of a helicopter can be designed with a shroud, i.e. as an enclosed rotor. In this case, the rotor is provided in a shroud or rotor casing that radially surrounds the rotor, for example in the form of a hollow structure. This hollow structure can have various hollow chambers. The shroud also forms a flow passage that extends in the axial direction of the rotor. The shroud can reduce the sound emission, in particular in the radial direction to the rotor, in terms of the total noise level or broadband sound.
[0003] The sound emission of a shrouded rotor is generated, inter alia, by the turbulence of the medium flowing in the gap provided between the shroud and the tips of the rotor blades. The sound thus generated mainly has discrete preferred frequencies, so that the sound emission of a shrouded rotor is generally dominated by tonal components, i.e. discrete components of the sound spectrum. These individual tonal components are usually perceived as unpleasant by humans. Thus, although the total acoustic energy emitted can be reduced by a shrouded rotor compared to a non-shrouded rotor, it is still perceived as unpleasant to the human ear due to the tonal components. This also applies to the sound emission of other air vehicles with shrouded rotors, for example electric air vehicles such as aircabs, eVTOLs (electric Vertical Take-Off and Landing aircraft) or drones.
[0004] Numerical simulations of the aerodynamics and acoustics of rotor systems are disclosed, for example, in the following documents:
[0005] Stadlmair, N., Redmann, D., Hirsch, F., Zappek, V. (2021) “Four-step Simulation Toolchain to Assess the Effectiveness of Noise Reduction Measures for Shrouded Tail-Rotors” (Proceedings of the 47 th European Rotorcraft Forum (ERF), United Kingdom), and You, J., Thouault, N., Breitsamter, C., and Adams, N. (2012) “Aeroacoustic analysis of a helicopter configuration with ducted tail rotor” (28th Congress of the International Council of the Aeronautical Sciences 2012).
[0006] To reduce the sound emission of shrouded rotor systems, WO 2021 / 156077 proposes a rotor casing having an area, also referred to as a liner, that is at least partially permeable to gas on its circumferential surface facing the rotor. This configuration of the rotor casing, together with the hollow structure, can reduce at least certain frequencies of the sound spectrum.
[0007] Both any chamber of hollow structure and their combination with a liner have characteristic and frequency dependent impedances, which generally result in a complex and non-trivial relationship between the (forward) thrust generated by the rotor and the rotor's sound emissions.
[0008] For example, reducing the distance between the tips of the rotor blades and the shroud can reduce the generation of turbulence in the medium flowing through the gap between the rotor blades and the shroud, known as tip vortexes, which can reduce sound generation. For example, as the rotor rotation rate (rotational speed) decreases, the radial dimensions of the rotor blades are slightly reduced due to reduced centrifugal forces, i.e., the rotor blades are less "stretched," so the effective distance between the tips of the rotor blades and the shroud increases, which can have a negative effect on the sound generation of a shrouded rotor in a certain rotational speed range due to the enhancement of tip vortexes. Increasing the rotational speed can have the opposite effect. In addition to these effects of sound emission, there is also an impedance of the hollow structure, possibly combined with the liner, with certain preferred frequencies.
[0009] It is therefore an object of the present invention to provide an alternative or improved method for controlling at least one rotor of an aircraft, and an alternative or improved control data providing unit for an aircraft having at least one rotor, whereby a reduction in sound emission can be achieved, in particular taking into account the specific acoustic characteristics of a shrouded rotor.
[0010] This object is solved by a method according to claim 1, a control data providing unit according to claim 13 and a flying vehicle according to claim 14. Further features of the invention are given in the dependent claims, whereby the method according to the invention can also be further developed by features of the control data providing unit and / or the flying vehicle and vice versa, and features of the control data providing unit and the flying vehicle can also be used in common with each other for further development.
[0011] The method according to the invention serves to control at least one rotor of an air vehicle, the rotor being configured to compensate or at least reduce a torque acting on the air vehicle, the rotor being provided with a shroud, the rotational speed of the rotor and the angle of attack of at least one rotor blade of the rotor being adjustable for said rotor, in particular independently from further rotors provided on the air vehicle. The method comprises: (a) defining at least a first pair of operating parameter values and at least a second pair of operating parameter values for a rotor, the pairs of operating parameter values specifying different rotational speeds and angles of attack of the rotor thereby to achieve the same thrust value; (b) determining a first sound indicator of a first pair of operating parameter values and a second sound indicator of a second pair of operating parameter values, the determining step including measuring sound indicators of the rotor in a test configuration; (c) storing the first sound indicia and the second sound indicia along with their assignment to respective operational parameter value pairs; (d) controlling the rotor during operation of the air vehicle according to the first pair of operating parameter values or the second pair of operating parameter values with reference to the assignment stored in step c) and at least selectively as a function of the first or second sound indication to be achieved; Includes.
[0012] Preferably, steps a) to c) are performed in the method for three or more operational parameter value pairs and corresponding sound indicators and / or for several thrust values to be achieved.
[0013] The air vehicle may be, for example, a helicopter. Alternatively, the air vehicle may be another air vehicle, such as an air cab, an eVTOL (electric vertical take-off and landing aircraft), or a drone.
[0014] The rotors need not be used solely for torque compensation: for example, the rotors may be configured to generate dynamic lift and / or horizontal motion of the vehicle in addition to torque compensation.
[0015] Compensation or reduction of a torque acting on the flying object is understood to mean in particular counteracting a rotation of the flying object about its yaw axis (z-axis or vertical), which is in particular generated by another rotor provided on the flying object, for example the main rotor of the flying object. For this purpose, for example, a horizontal thrust is generated by the rotor, which counteracts the torque. For example, a rotor for torque compensation can be provided as a secondary rotor of the flying object, in particular a tail rotor, which is provided, for example, on the tail boom of the flying object, in particular a helicopter.
[0016] The angle of attack of at least one rotor blade of a rotor can be, for example, adjustable individually with respect to the rotor, i.e. independently of the other rotor blades of the same rotor. However, the angles of attack of all rotor blades of a rotor can also be adjustable, in particular collectively, i.e. the same angle of attack is set simultaneously for all rotor blades of the rotor. Such adjustment of the angle of attack is preferably performed separately with respect to the rotor, i.e. independently of one or more other rotors provided on the aircraft and independently of any adjustability of the angle of attack of the rotor blades of this or these other rotors.
[0017] The shroud of a rotor preferably refers to a structure surrounding the rotor in the circumferential direction. Preferably, the shroud defines an air duct of the rotor extending in the axial direction of the rotor's axis of rotation. The shroud can have, for example, a cylindrical or torus shape, and can in particular be designed as a cylindrical or torus-shaped housing. The shroud can also deviate from a cylindrical or torus shape, for example being optimized with respect to its aerodynamic properties. In general, the shroud can have any suitable shape. Such a shroud can, for example, reduce thrust losses due to turbulence at the propeller blade tips and increase safety. Alternatively or additionally, an additional, in particular non-negligible thrust can be generated by the flow through the duct or air duct formed by the shroud. Such additional thrust can, for example, be 50% or more of the total thrust.
[0018] The sound value measured in step (b) can in particular be a sound pressure. Preferably, the sound value or sound pressure is measured with time resolution, for example using a measuring device, in particular one or more microphones. The sound value can also be, for example, the tonality and / or the total level of the sound emission of the rotor. The sound index determined from the sound value can be, for example, the measured sound value itself or, for example, an index taking into account several measurements, i.e. sound values, from different sound sensors or measuring devices and / or their relative position with respect to each other or with respect to the rotor. In particular, the sound index can be determined from the measured sound values using suitable data processing routines.
[0019] The determination of the sound indicators in the described method is in particular performed by measuring sound values, in particular sound pressure, of the rotor in a test configuration. The test configuration may in particular comprise a test station, such as a component test station or an individual component test station, in which the rotor is arranged as a component together with any other components (e.g. shrouds). Such a component test station is in particular configured to perform acoustic measurements using a suitable measuring device, such as a sound measuring device. Alternatively or additionally, the test station may comprise a wind tunnel. Preferably, the measurement of the sound values of the rotor in step (b) is performed on the test station, and at least one measuring device for recording the sound values is arranged in a predefined position relative to the position of the rotor in the test station.
[0020] This means that the method, which can serve in particular to reduce the sound emission of the aircraft, is not carried out during the flight operation of the aircraft itself, but instead the respective data is recorded and evaluated in advance for the rotor, i.e. in particular on the ground. Thus, for example, characteristic maps are generated in the method offline, i.e. outside the flight operation, and thus available before the actual flight of the aircraft. Thus, the method differs in particular from adjustment-based methods for reducing sound emission, which are based on changing control data during flight based on measurements recorded during flight. This means that no complex and / or expensive equipment, such as microphones, speakers, adaptive controllers, etc., is required on the aircraft.
[0021] Furthermore, to achieve a reduction in the sound emission of the air vehicle, no complex flight measurement campaigns for reference measurements are required. Rather, the method described above can be performed using measurements, in particular easy-to-perform sweep measurements, in a test environment, such as, for example, a component test station. This also has the advantage that the control data determined in the method, which are provided for controlling the rotor during flight operation of the air vehicle, can be rechecked or updated at any time as necessary, for example to add further optimization points.
[0022] The adjustability, or individual adjustability, of the rotational speed and the angle of attack of at least one rotor blade of the rotor can for example achieve an additional degree of freedom. For example, by adjusting the angle of attack of the blade, a substantially constant thrust can be achieved for different rotational speeds, or vice versa. In particular, this means that a given thrust value can be achieved by different combinations of the angle of attack and the rotational speed of the blade, also referred to as the operational parameter value pair. The method described herein can be used to select the operational parameter value pair of the thrust value to be achieved, such that an improvement, in particular a minimization, of the sound emission by a rotor, such as a secondary rotor, in particular a tail rotor, during flight operations can be achieved. This method also makes it possible to take into account the complex acoustic properties of a shrouded rotor in a simple manner. In particular, for example, the frequency-dependent acoustic signature of a shrouded rotor can be advantageously applied by the method, such that the rotor is controlled in operation such that the frequency-dependent damping properties of the shroud are exploited. Thus, preferably, the rotor is controlled in step (d) such that frequencies of the sound emission of the rotor that are preferably not damped by the shroud are avoided. In other words, the rotor is preferably controlled in step (d) such that when the liner is used, the rotor substantially produces sound emissions having frequencies that are attenuated by the shroud.
[0023] Preferably, the control of at least one rotor according to step (d) is performed at least temporarily when the aircraft is in hover. In particular, hovering is understood to be a state of the aircraft in which it remains in a substantially unchanged horizontal and vertical position. When the aircraft is hovering, for example, an increase in rotor blade loading may be required, which may involve high tonal content, while the aircraft remains over the same position on the ground for a long time. It may therefore be particularly desirable to minimize the sound emission of the aircraft when hovering.
[0024] Preferably, in the method, the allocation in step c) comprises a graphical and / or tabular representation of the sound indicators as a function of the rotor rotational speed and / or the angle of attack and / or the thrust value achieved thereby. The graphical representation may for example be a representation of one or more functions or measurement curves. This may for example provide a simpler representation of the respective values and / or simplify the interpolation of the measurements.
[0025] Preferably, the assignment stored in step c) is complemented by further sound indicators and / or operating parameter value pairs and / or thrust values determined by numerical simulation and / or interpolation. In particular, the numerical simulation can include a simulation of the aerodynamics of the rotor system (computational fluid dynamics, cfd) and / or a simulation of the acoustic properties of the rotor system (computational aeroacoustics, caa). Such simulation and / or interpolation can, for example, reduce the measurement effort. Examples of such numerical simulations are given in the documents mentioned at the beginning.
[0026] Preferably, in step d), the sound index on which the control of the rotor is based is selected such that a reduction in the sound emission of the rotor is achieved. For this purpose, for example, the rotor can be controlled in a test environment for achieving a given thrust by different operating parameter value pairs which generate the desired thrust, and the corresponding sound index can be determined. The operating parameter value pair for which the minimum sound index has been determined is then preferably selected for the subsequent control of the rotor in flight mode. This makes it possible, for example, to reduce the sound emission in a simple manner.
[0027] Preferably, the sound indicators include the tonality and / or the total level of the rotor's sound emissions. By reducing the tonality, the sound production caused by the flying vehicle during operation can be made to appear less annoying to the human ear, for example. By reducing the total level, for example, the total volume of the sound emissions can be reduced.
[0028] The tonality of the sound emission is preferably defined as the difference between the peak sound level of the sound emission and the broadband noise level. Preferably, the peak sound level is determined at a defined frequency of the measurement frequency spectrum. For example, the defined frequency of the peak sound level can be a characteristic blade passing frequency of at least one rotor blade or rotor blades. These characteristic blade passing frequencies result, inter alia, from the number of rotor blades, their angular distance from each other and the rotational speed of the rotor. However, the tonality can also take several frequencies into account. In this case, for a number of frequencies, an arithmetic average of the differences between the respective peak sound levels and the broadband noise level is calculated. In particular, the arithmetic averaging can be limited to a predetermined frequency range.
[0029] Preferably, the method is carried out using a rotor whose shroud is formed by a circumferential hollow structure relative to the rotor's axis of rotation, the hollow structure preferably having a region that is gas-permeable at least in its section on its circumferential surface facing the rotor, the hollow structure further preferably being configured such that acoustic waves of at least one frequency penetrating into the hollow structure through the gas-permeable region are at least partially absorbed by the hollow structure. The rotor and its shroud are also referred to as rotor systems. The gas-permeable region, e.g. cross-sectional micro-perforations of the surface of the shroud, also referred to as liners, can for example allow rotor tip vortices generated by the rotation of the rotor to be introduced into the hollow structure of the shroud. In particular, this configuration of the shroud can achieve a frequency-dependent attenuation of the sound emission of the rotor. The described method has been found to be particularly advantageous for such rotor systems, since it can be used to specifically select pairs of operating parameter values whose sound generation during operation of the rotor can be particularly well attenuated by the shroud.
[0030] Preferably, the flying vehicle is designed as a helicopter and the rotor is a secondary rotor configured for torque compensation and control about the yaw axis, more preferably a tail rotor of the helicopter, more preferably the helicopter is provided with a separate drive, in particular an electric motor, configured to rotate the secondary rotor according to a predefined rotational speed. By providing a separate drive for the secondary rotor, in particular the tail rotor, the rotational speed of the rotor can for example be adjusted separately in a simple manner.
[0031] Preferably, the rotor is a first rotor of a flying body, the flying body comprising at least a second rotor configured to compensate or at least reduce a torque acting on the flying body, the second rotor being provided with a shroud, the rotational speed of the second rotor and the angle of attack of at least one rotor blade of the second rotor, preferably a uniform angle of attack of all rotor blades of the second rotor, being adjustable for the second rotor independently from the first rotor, and preferably steps a) to d) being performed separately for the first rotor and at least the second rotor or by measuring the total sound value of at least two rotors. In other words, the invention is also applicable to flying bodies with several shrouded rotors, also referred to as multi-rotor systems. The use of several shrouded rotors can provide an additional degree of freedom, for example for reducing sound emission, since there are several possibilities for combining individually controllable rotors.
[0032] According to the invention, a control data providing unit for an air vehicle having at least one rotor is provided, the rotor being configured to compensate or at least reduce a torque acting on the air vehicle, the rotor being provided with a shroud, and the rotational speed of the rotor and the angle of attack of at least one rotor blade of the rotor being adjustable for said rotor, in particular independently from further rotors provided on the air vehicle. The control data providing unit comprises: (a) a definition unit for defining at least a first pair of operating parameter values of a rotor and at least a second pair of operating parameter values of the rotor, the pairs of operating parameter values specifying different rotational speeds and angles of attack of the rotor at the same thrust value thereby to be achieved; (b) a determining unit for determining a first sound indicator of the first operating parameter value pair and a second sound indicator of the second operating parameter value pair, the determining unit including measuring sound indicators of the rotor in a test configuration; (c) a memory unit for storing the first sound indicia and the second sound indicia together with their assignment to respective operational parameter value pairs; (d) an output unit for outputting control data for controlling the rotor during operation of the air vehicle, the control data specifying control of the rotor according to the first pair of operational parameter values or the second pair of operational parameter values with reference to the assignment stored in the memory unit and as a function of at least the first sound indication or the second sound indication to be selectively obtained; and Equipped with.
[0033] By means of such a control data providing unit, for example, the same effects and advantages can be achieved as with the method described above.
[0034] The flying vehicle according to the invention comprises a rotor configured to compensate or at least reduce a torque acting on the flying vehicle, the rotor being provided with a shroud, and the rotational speed of the rotor and the angle of attack of at least one rotor blade of the rotor being adjustable for said rotor, in particular independently from further rotors provided on the flying vehicle. Furthermore, the flying vehicle has a control unit which controls the at least one rotor at least temporarily during the operation of the flying vehicle using control data provided by a control data providing unit according to the invention and / or controls it according to step (d) of the method according to the invention. Preferably, the at least one rotor is controlled at least during a hover flight of the flying vehicle using control data provided by the control data providing unit and / or according to step (d).
[0035] Further features and advantages of the invention are described below also on the basis of exemplary embodiments with reference to the drawings. [Brief description of the drawings]
[0036] [Figure 1] 1 is a schematic diagram of an air vehicle having a rotor suitable for performing the method according to the invention and for use with a control data providing unit according to the invention; [Diagram 2] FIG. 2 is a schematic perspective view of the rotor shown in FIG. [Diagram 3]FIG. 3 is a schematic perspective view, partially in section, of a portion of the shroud and rotor blade shown in FIGS. 1 and 2. [Figure 4] 4 is a schematic cross-sectional view of one section of the shroud and rotor blade shown in FIGS. 1 to 3. FIG. [Diagram 5] FIG. 5 is a schematic diagram of a method according to the present invention using the rotor shown in FIGS. 1 to 4. [Figure 6] 2 is a schematic diagram of a control data providing unit according to the present invention; [Figure 7a] 6 is an exemplary schematic graph generated by the method shown in FIG. 5. [Figure 7b] 6 is an exemplary schematic graph generated by the method shown in FIG. 5. [Figure 7c] 6 is an exemplary schematic graph generated by the method shown in FIG. 5. [Figure 8] FIG. 7 is an exemplary schematic diagram that can be used to control the flying vehicle shown in FIGS. 1-4, created based on the graphs shown in FIGS. 7a-7c. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0037] In the following, with reference to Figures 1 to 4, an air vehicle suitable for carrying out the method according to the invention and for use with the control data providing unit according to the invention is described. The air vehicle shown in the figures is a helicopter 1. The helicopter 1 shown in Figure 1 comprises 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 is provided with a shroud 15 which surrounds the tail rotor in the circumferential direction. The main rotor 3 is essentially responsible for generating the dynamic lift and possibly horizontal movement of the helicopter 1, while the tail rotor 5 is responsible for compensating at least the torque acting on the fuselage 2, in particular the counter torque generated by the main rotor 3 which rotates the fuselage 2 in the opposite direction to the rotation of the main rotor.
[0038] Furthermore, the tail rotor 5 can be driven independently from the main rotor 3, i.e. it is not coupled to the main rotor, in particular not mechanically coupled to it. For this purpose, the helicopter 1 shown in FIG. 1 comprises a drive 6, in particular an electric motor, configured to rotate the tail rotor 5 at a predefined rotational speed. In FIG. 1, the drive 6 is provided on or in the rotor hub 16 of the tail rotor 5. Alternatively, the drive 6 can also be provided at a location on the helicopter 1 other than the rotating hub, in which case the drive force from the drive 6 is transferred to the tail rotor 5. In the embodiment of FIG. 5, the helicopter 1 also comprises an energy storage 7, here in the form of a battery, which supplies energy, in particular electrical energy, to the drive 6.
[0039] The helicopter 1 also has a control unit 8 capable of controlling the individual components of the helicopter, in particular the drive 6 of the tail rotor 5 and the drive of the main rotor 3, not shown, in a coordinated manner as indicated by the arrows in FIG. 1. In particular, the control unit can specify the rotational speed of the tail rotor 5 and the angle of attack of the blades of the tail rotor 5 (see below). In the present application, the term "control unit" refers to a computer control configured to control the operation of the helicopter or one or more components of the helicopter. For this purpose, the control unit 8 can comprise, for example, a processor, a memory and an output interface. For example, the control unit 8 can be a computer. The control unit can include, for example, a central processing unit (CPU), the operation of which is controlled by a computer program (software). The computer program can be stored separately from the control unit on a storage medium or a server from which it can be loaded into the control unit 8 and / or the computer program can be loaded into the control unit 8 via a network, for example the Internet.
[0040] The tail rotor 5 will be described in more detail below with reference to Figures 2 to 4. The tail rotor 5 comprises a number of rotor blades 20 arranged around a rotor hub 16 and extending radially from the rotor hub 16 in the direction of the shroud 15. The radial extension of the rotor blades 20 is dimensioned such that the ends of the rotor blades 20 facing the shroud 15, also referred to as rotor tips 21, are provided at a certain distance from the shroud 15. A gap 22 is therefore provided between the rotor tips 21 and the shroud 15, also referred to as tip clearance. The rotor hub 16 is preferably held by a number of support struts or stators 17 and is rotatable about a rotation axis R which in Figure 2 extends perpendicular to the plane of the drawing.
[0041] The shroud 15 surrounds the tail rotor 5 in the direction of rotation relative to the axis of rotation R and defines an air duct 18 for the tail rotor 5 extending in the axial direction of the axis of rotation R. As can also be seen from Figures 3 and 4, in a rotor plane RA formed by the rotor blades 20 perpendicular to the axis of rotation R, the circumferential surface 23 of the shroud 15 facing the tail rotor 5 has a gas-permeable region 23a that intersects the rotor plane RA and extends axially on both sides of the rotor plane RA relative to the axis of rotation R. For example, the gas-permeable region 23a can be formed by a perforated plate with micro-perforations that is inserted and fixed in the shroud 15. The porosity introduced by the micro-perforations is, for example, 50% and is preferably constant in the circumferential direction and in the axial direction relative to the axis of rotation R. The gas permeable region 23a covers the radial protrusion of the rotor tip 21 of the rotor blade 20, so that the rotor tip vortex generated in the gap 22 between the rotor tip 21 and the gas permeable region 23a can be introduced into the hollow structure 25 formed by the shroud 15 through the gas permeable region 23a.
[0042] As an alternative to the above-described configuration of the shroud 15, the shroud can be designed without the gas permeable region 23a. The shroud 15 can also not form a hollow structure, and can be formed, for example, as a continuous body.
[0043] As shown diagrammatically in Fig. 4, the angle of attack of the rotor blades 20 of the tail rotor 5 is variable or adjustable. The adjustability of the angle of attack can be realized, for example, by a separately provided drive for the angle of attack of the blades (not shown) and a corresponding control by the control unit 8. The angle of attack of the rotor blades 20 is changed by rotating the rotor blades 20 about a radial axis X extending perpendicular to the axis of rotation R of the tail rotor 5. Fig. 4 diagrammatically shows the rotor blades 20 at a first angle of attack in solid lines and the same rotor blades 20 at a second angle of attack different from the first angle of attack in dashed lines.
[0044] By combining the adjustability of the blade attack angle with the rotational speed of the tail rotor 5, an additional degree of freedom can be achieved compared to a tail rotor whose motion is coupled to the rotation of the main rotor. For example, this combination can be used to achieve a substantially constant thrust for different rotational speeds by adjusting the blade attack angle, or vice versa. In other words, a given thrust value can be achieved by different combinations of the blade attack angle and the rotational speed, also referred to below as operating parameter value pairs. The selection of the operating parameter value pairs is made such that a thrust value is achieved such that an improvement, in particular a minimization, of the sound emission by the tail rotor 5 is achieved, as will be explained in more detail below.
[0045] Optionally, the hollow structure 25 formed by the shroud 15 can have reinforcing and / or hollow structure elements not shown in the figure, which can, for example, act as a cover, the dimensions and positioning of which can also influence the attenuation of acoustic waves introduced into or propagating within the hollow structure and / or form chambers within the hollow structure 25, for example to form resonator volumes that are locally different in each case and thereby influence the attenuation of the frequencies.
[0046] In the following, exemplary embodiments of the method according to the invention for controlling a tail rotor 5 according to the invention and of the control data providing unit according to the invention will be described with reference to FIGS.
[0047] The control data providing unit 100 shown in FIG. 6 is provided outside the helicopter 1 for carrying out the method shown in FIG. 5. Here, the helicopter 1 or at least its tail rotor 5 is placed in a test environment, for example on or in a test station. The test environment comprises one or more sound sensors or measuring devices for recording sound pressures within a time range, arranged at predefined positions relative to the position of the tail rotor in the test station. The sound sensors or measuring devices are configured to measure the sound pressure emitted by the tail rotor 5 in the test environment, for example as one or more microphones. The time resolution (sampling rate) of the sound pressure must be selected so that all relevant frequencies of the acoustic signal can be resolved. Using downstream data processing routines (post-processing), the desired sound indicators can subsequently be determined from the measured signals. The sound indicators can for example be the tonality or the total level of the sound emission of the tail rotor 5.
[0048] The control data providing unit 100 comprises a definition unit 101 which in a first step 51 defines at least two different operational parameter value pairs, each comprising a tail rotor blade rotational speed and an angle of attack for the same value of tail rotor thrust generated thereby. Preferably, three or more different operational parameter value pairs are defined, as well as respective operational parameter value pairs for different thrust values.
[0049] Subsequently, in a second step 52, the tail rotor 5 is controlled in a test environment according to the respective operational parameter value pairs, and the sound pressure of each operational state is measured by at least one or more sound sensors or measuring devices. A sound indicator of the tail rotor 5, e.g. the tonality or total level of sound emission, is then determined from the measured sound pressures of the respective operational parameter value pairs in the test configuration. A determination unit 102 of the control data providing unit 100 then determines a sound indicator for each operational parameter value pair based on the measured sound emission and the sound indicator derived therefrom. This can be the sound indicator itself, or an indicator taking into account, for example, several measurements from different sound sensors or measuring devices and / or their relative positions with respect to each other or with respect to the tail rotor.
[0050] For this purpose, for example, the parameters thrust, rotational speed and angle of attack of the blades of the tail rotor 5 can be investigated in a test environment and the respective sound emission measured. Such a procedure is illustrated, purely by way of example, by the measurement curves in Figures 7a to 7c.
[0051] FIG. 7a shows thrust (vertical axis of FIG. 7a) as a function of angle of attack (horizontal axis of FIG. 7a) for three different values of rotational speed. In other words, the graph shown in FIG. 7a is obtained by varying the angle of attack of the blades relative to the tail rotor at a constant rotational speed and measuring the thrust as a function of the blade angle of attack. In FIG. 7a, as in FIG. 7b and FIG. 7c, the N R,- and N R,0 and N R,+ It is labeled N R,0 corresponds to the nominal rotor speed (100%), and N R,+ corresponds to 115% of this nominal rotation speed, and N R,- corresponds to 90% of the nominal rotation speed. In Figs. 7a to 7c, the rotation speed value N R,- is shown as a dashed line, and the rotational speed value N R,0 is shown as a solid line, and the rotation speed value N R,+is shown as a dotted line. Thrust is shown in Figure 7a as a percentage of the maximum achievable thrust of the rotor. In Figures 7a-c the blade angle of attack is given in degrees (°).
[0052] The thrust force (see FIG. 7a) can be measured, for example, by a suitable force measuring device provided in contact with the rotor or its shroud and detecting the mechanical force generated by the rotor.
[0053] Simultaneously, or in a subsequent step, sound values (vertical axis in Fig. 7b, Fig. 7c) are also measured as a function of the changing angle of attack of the blades (horizontal axis in Fig. 7b, Fig. 7c) at a constant rotational speed. The graph in Fig. 7b is based on the measured tonality of the tail rotor 5 sound emission as sound indicator, while in the diagram in Fig. 7c the total sound level was measured as sound indicator. The tonality (Fig. 7b) and the total sound level (Fig. 7c) are each given in dB in this embodiment. The tonality can be defined in particular as the difference between a peak sound level and a broadband noise level, the peak sound level being determined at a predetermined frequency of the measured frequency spectrum, or as the arithmetic mean of the differences between several peak sound levels and broadband noise levels at predetermined frequencies. For example, the predetermined frequency of the peak sound level can be defined by one or more characteristic blade passing frequencies of the rotor blades. These characteristic blade passing frequencies result, inter alia, from the number of rotor blades, their angular distance from each other and the rotor speed. In particular, the arithmetic mean can be limited to a certain frequency range, for example 300 Hz to 3000 Hz.
[0054] The operating value pairs defined in the first step 51 and the sound indices assigned in the second step 52 are then stored in a third step 53 of Fig. 5, e.g. by the memory unit 103 on a storage medium or data carrier of the control data providing unit 100. In the example of Figs. 7a-c, e.g. the graph itself or the data on which the graph is based can be stored.
[0055] Subsequently, for a specified thrust value of the tail rotor 5, an operating parameter value pair is selected from the stored plurality of data in a third step 53. This selection is made based on the determined and stored sound index. For example, the operating parameter value pair for which the minimum sound index has been determined may be selected for the particular thrust value.
[0056] This is explained again below using the example graphs of Figures 7a to 7c. In Figure 7a, four different thrust values S1, S2, S3 and S4 are shown, each of which for each set rotational speed is achieved with a specific angle of attack of the blades, and in Figure 7a, each is shown by a point on the measurement curve (the intersection of the respective thrust value with the measurement curve assigned to the respective rotational speed value). By comparison with the graphs of Figures 7b and 7c, it is possible to determine whether the minimum tonality (Figure 7b) or the minimum total sound level (Figure 7c) of the tail rotor 5 sound emission is measured for a blade angle of attack or for a blade angle of attack and rotational speed pair (operational parameter value pair), which is shown in Figures 7b and 7c as points labelled with the respective thrust values S1, S2, S3 and S4. In other words, points S1, S2, S3 and S4 in Figures 7b and 7c respectively indicate blade angle of attack and rotational speed pairs (operational parameter value pairs) that have a minimum value of tonality (Figure 7b) or total sound level (Figure 7c).
[0057] Subsequently, in a fourth step 54, the output unit 104 outputs control data for controlling the tail rotor 5 during flight operation of the helicopter 1, specifying the respective operating parameter value pairs selected in step 53 for controlling the tail rotor 5 such that a thrust value for the tail rotor 5 is achieved. In the example of Figures 7a-7c, it is possible to output, for example, the operating parameter value pairs which result in a minimum tonality of the sound emission of the tail rotor 5 for the respective thrust value (Figure 7b) or a minimum total sound level (for Figure 7c).
[0058] The control data output can be stored, for example, in the form of a table. For this purpose, different sound indicators and corresponding pairs of operating parameters values can also be stored in order to define different operating modes of the helicopter 1. Figure 8 shows a purely exemplary table based on the measurements described with reference to Figures 7a to 7c. For given thrust values S1, S2, S3, S4..., the respective pairs of operating parameters values of the rotational speed N of the blades and the angle of attack Φ are determined in the above-mentioned steps 51 to 54, whereby a reduction in the tonality of the sound emission is achieved ("low tonality" mode) or a reduction in the total sound level is achieved ("low total sound level" mode) and, if necessary, other criteria of the sound characteristics are met. This defines different operating modes of the tail rotor 5 in Figure 8, for example an operating mode for reducing the tonality of the sound emission and an operating mode for reducing the total sound level. In other words, the table of Figure 8 lists blade angle of attack and rotational speed pairs (operational parameter value pairs) determined by points S1, S2, S3 and S4 with reference to Figures 7b and 7c.
[0059] During flight operation of the helicopter 1, the tail rotor 5 can be controlled according to the values stored in the table of Figure 8, i.e. to a tail rotor target thrust value depending on the operating mode according to the operating parameter value pairs stored therefor in the table, where the operating mode can be selected by the pilot or automatically, for example by the control unit 8.
[0060] For example, when the helicopter 1 is hovering, i.e. the helicopter remains in a substantially unchanged horizontal and vertical position, an increased blade loading of the tail rotor 5 is required, which is usually accompanied by a predominance of tonal components. In addition, the helicopter remains above the same ground position for a long time when hovering, so that a reduction in sound emissions is particularly desirable here. Therefore, when hovering, the tail rotor 5 is preferably operated according to the "low tonal" operating mode described above.
[0061] In the method described above with reference to Fig. 5, it is not necessary to determine all the required values, i.e. in particular the thrust values, the operating parameter value pairs and the sound indicators, by measurement. Rather, it is also possible to determine only some of these values by measurement and generate further values by interpolation and / or numerical simulation. This can reduce the amount of measurement work required.
[0062] For example, as an alternative to the above measurements based on continuously set angles of attack of the blade, the curves shown in Figures 7a-7c can also be determined based on several discrete values of the blade's angle of attack and the corresponding thrust values and sound indices, with the continuous functions shown in the figures being generated from the discrete measurements by interpolation.
[0063] Numerical simulations can also be used to generate additional values. Numerical simulations can include, for example, the simulation of the flow field of the tail rotor 5 during operation and the calculation of the acoustic sources on which this flow field is based (numerical simulation of aerodynamics, also known as computational fluid dynamics, CFD). The numerical flow simulation can be complemented by a numerical simulation of the overall system of the shrouded tail rotor 5, in particular the effect of the hollow structure 25 of the shroud and / or the liner provided on the shroud, as well as the acoustic effect (computational aerodynamics, CAA), which numerically calculates the flow around it. Examples of such numerical simulations are given in the documents mentioned at the beginning.
[0064] In the method described above with reference to Fig. 5, the respective operating parameters for controlling the tail rotor 5 are selected such that an improvement can be achieved with respect to the sound emission emitted during operation, i.e. during flight, of the helicopter 1. Now, the method can be complemented by taking into account further effects or optimization points to be achieved, i.e. the selection of the respective operating parameters for controlling the tail rotor 5 can be modified accordingly. For example, the tonality or the total sound level of the sound emission can be optimized under specific aspects such as the flight altitude of the helicopter 1, the distance to the receiver, etc. For this purpose, for example, a calculation of the sound signature on the ground can be determined using a suitable numerical model.
[0065] According to a further development of the invention, the method described above with reference to Fig. 5 and the control data providing unit described above with reference to Fig. 6 can also be applied to helicopters or more generally to flying bodies having two or more shrouded rotors. For this, the flying body comprises at least one further (hereinafter second) rotor which is provided with a shroud and the rotational speed and the angle of attack of its blades can be adjusted independently, in particular independently from the first rotor. Like the first rotor, the second rotor is at least configured to compensate or at least reduce the torque acting on the flying body. The above steps of determining the operating parameter value pairs and / or the thrust values and / or the sound indicators can be performed individually for each of the rotors or can be performed taking into account the total thrust, for example the total forward thrust, and / or the total sound value, achieved by the multiple rotors. The possibility of combining different rotors can provide a further degree of freedom for sound optimization.
[0066] The first rotor and / or the second rotor do not have to be configured as tail rotors, but can be provided at any other suitable location on the air vehicle. Thus, in general, they can also be referred to as secondary rotors, especially when they are provided in addition to the main rotor of the air vehicle, or as rotors in general. In addition to torque compensation, the first rotor and / or the second rotor can also serve to generate dynamic lift and / or horizontal motion of the air vehicle. Instead of being designed as a helicopter, the air vehicle can be another air vehicle, for example, an air cab, an eVTOL (electric vertical take-off and landing aircraft) or a drone.
Claims
1. A method for controlling at least one rotor (5) of an air vehicle (1), comprising: the rotor (5) is configured to compensate for or at least reduce torque acting on the flying vehicle (1); The rotor (5) is provided with a shroud (15), and the rotational speed of the rotor and the angle of attack of at least one rotor blade (20) of the rotor are adjustable for the rotor (5), in particular independently of a further rotor (3) provided on the aircraft (1), and the method comprises: (a) defining (51) at least a first pair of operating parameter values and at least a second pair of operating parameter values for the rotor (5), the pairs of operating parameter values specifying different rotational speeds and angles of attack of the rotor for the same thrust value to be achieved thereby; (b) determining (52) a first sound indicator for the first pair of operating parameter values and a second sound indicator for the second pair of operating parameter values, the determining step comprising measuring sound indicators of the rotor (5) in a test configuration; (c) storing (53) the first sound index and the second sound index together with their assignments to the respective operational parameter value pairs; (d) controlling (54) the rotor (5) during operation of the air vehicle (1) according to the first pair of operating parameter values or the second pair of operating parameter values, with reference to the assignment stored in step c) and at least selectively as a function of the first sound indication or the second sound indication to be achieved; A method comprising:
2. The method of claim 1 , wherein steps a) through c) are performed for three or more pairs of operational parameter values and corresponding sound indices.
3. 3. The method according to claim 1, wherein steps a) to c) are performed for several thrust values to be achieved.
4. 3. The method according to claim 1 or 2, wherein the allocation in step c) comprises a graphical and / or tabular representation of the sound index as a function of the rotational speed and / or the angle of attack of the rotor (5) and / or the thrust value achieved thereby.
5. 3. The method according to claim 1, wherein the assignment stored in step c) is complemented by further sound indicators and / or operational parameter value pairs and / or thrust values determined by numerical simulation and / or interpolation.
6. 3. The method according to claim 1 or 2, wherein in step d) the sound indicators on which the control of the rotor (5) is based are selected such that a reduction in the sound emission of the rotor (5) is achieved.
7. 3. The method according to claim 1 or 2, wherein the sound indicators comprise the tonality and / or total level of the sound emission of the rotor (5).
8. 3. The method according to claim 1, wherein the method is carried out using a rotor (5) whose shroud (15) is formed by a circumferential hollow structure (25) relative to the rotation axis (R) of the rotor, the hollow structure preferably having, on its circumferential surface (23) facing the rotor (5), an area (23a) that is gas permeable in at least a section thereof, the hollow structure being preferably further configured such that acoustic waves of at least one frequency that penetrate into the hollow structure through the gas permeable area are at least partially absorbed by the hollow structure.
9. 3. The method according to claim 1 or 2, wherein the measurement of the sound value of the rotor (5) in step (b) is performed on a test station, and at least one measuring device for detecting the sound value is arranged at a predetermined position relative to the position of the rotor (5) in the test station.
10. 3. The method according to claim 1 or 2, wherein the air vehicle is designed as a helicopter and the rotor is a secondary rotor configured for torque compensation and control about a yaw axis, preferably a tail rotor (5) of the helicopter.
11. 11. The method according to claim 10, wherein the helicopter comprises a separate drive (6), in particular an electric motor, configured to rotate the secondary rotor according to a predetermined rotational speed.
12. 3. The method according to claim 1, wherein the rotor is a first rotor of the flying body, the flying body comprising at least a second rotor configured to compensate for or at least reduce a torque acting on the flying body, the second rotor being provided with a shroud, the rotational speed of the second rotor and the angle of attack of at least one rotor blade of the second rotor, preferably a uniform angle of attack of all rotor blades of the second rotor, are adjustable for the second rotor independently from the first rotor, and preferably steps a) to d) are performed separately for the first rotor and the at least second rotor, or by measuring the total sound value of at least two of the rotors.
13. A control data providing unit for an air vehicle (1) having at least one rotor (5), comprising: the rotor (5) is configured to compensate for or at least reduce torque acting on the flying vehicle (1); The rotor (5) is provided with a shroud (15), and the rotational speed of the rotor (5) and the angle of attack of at least one rotor blade (20) of the rotor (5) are adjustable for the rotor (5), in particular independently of a further rotor (3) provided on the aircraft (1), and the control data providing unit (100) (a) a definition unit (101) for defining (51) at least a first pair of operational parameter values and at least a second pair of operational parameter values for the rotor (5), the pairs of operational parameter values specifying different rotational speeds and angles of attack of the rotor at the same thrust value thereby achieved; (b) a determination unit (102) for determining (52) a first sound indicator of the first pair of operating parameter values and a second sound indicator of the second pair of operating parameter values, the determination comprising measuring sound indicators of the rotor (5) in a test configuration; (c) a memory unit (103) for storing (53) the first sound index and the second sound index together with their assignment to the respective operational parameter value pairs; (d) an output unit (104) for outputting control data (54) for controlling the rotor (5) during operation of the air vehicle (1), the control data specifying the control of the rotor according to the first pair of operational parameter values or the second pair of operational parameter values with reference to the assignment stored in the memory unit and at least selectively as a function of the first sound indication or the second sound indication to be achieved; and A control data providing unit comprising:
14. A flying vehicle (1) comprising at least one rotor (5) configured to compensate for or at least reduce a torque acting on said flying vehicle (1), said rotor (5) being provided with a shroud (15), and the rotational speed of said rotor (5) and the angle of attack of at least one rotor blade (20) of said rotor (5) being adjustable for said rotor (5), in particular independently of a further rotor (3) provided on said flying vehicle (1), The air vehicle further comprises a control unit (8) that at least temporarily controls the at least one rotor (5) during operation of the air vehicle using control data provided by the control data providing unit of claim 13 or in accordance with step (d) of the method of claim 1.
15. 15. The air vehicle of claim 14, wherein the control of the at least one rotor (5) is performed using control data provided by the control data providing unit and / or according to step (d) at least during hover flight of the air vehicle.