Method for reducing noise from coaxial counter-rotating propeller by using initial phase difference control, and aircraft comprising same

Abstract

The present invention relates to an aircraft with the function of reducing noise from a coaxial counter-rotating propeller and a noise reduction method therefor, and the aircraft comprising a first propeller rotating in one direction, a second propeller rotating in a direction opposite to the first propeller, and a rotary shaft provided to allow the first propeller and the second propeller to rotate about one shaft, wherein an initial phase angle formed by the first propeller and the second propeller before rotating forms a certain angle.

Description

Method for reducing noise of a coaxial counter-rotating propeller using initial phase difference control and aircraft including the same

[0001] This invention claims the benefit of Korean Patent Application No. 10-2023-0158557 filed with the Korean Intellectual Property Office on November 15, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to an aircraft having a coaxial contra-rotating propeller, in which the initial phase angle of the propeller is set to a predetermined angle in order to reduce noise generated from the aircraft, and to a noise reduction method thereof.

[0003] Coaxial contra-rotating propellers use the lift generated by propellers rotating in opposite directions around the same axis to create lift. Coaxial contra-rotating propellers offer the advantage of increasing thrust with a limited rotational surface area, making them widely used in helicopters, multicopter drones, and urban air mobility (UAM).

[0004] These coaxial contra-rotating propellers have the advantage of generating high thrust per unit rotational area because they can generate lift with two rotors. Furthermore, helicopters equipped with coaxial contra-rotating propellers eliminate the need for a separate tail rotor, thereby enhancing helicopter stability and reducing the risk of accidents.

[0005] However, as the number of blades in a coaxial contra-rotating propeller increases, additional noise is generated due to interference between the propeller and the airframe. Generally, technologies to reduce noise generated from propellers are divided into active and passive methods, but passive methods are preferred over active methods that require additional systems considering the aircraft's weight penalty. Such passive techniques include modifying the propeller platform shape and arranging propeller blades at unequal intervals. However, these technologies are applied to single propellers and have limitations in applying them to coaxial contra-rotating propellers.

[0006] The background technology described above is technical information that the inventor possessed for the purpose of deriving embodiments of the present invention or acquired during the derivation process, and cannot necessarily be said to be publicly known technology disclosed to the general public prior to the filing of the embodiments of the present invention.

[0007] In order to solve the above problem, the present invention provides an aircraft and a noise reduction method thereof that reduces aerodynamic noise generated between propellers and / or between a propeller and a frame by differentiating the phase angle of coaxial counter-rotating propellers by a predetermined angle.

[0008] An aircraft having a noise reduction function of a coaxial counter-rotating propeller according to one embodiment of the present invention includes a first propeller rotating in one direction, a second propeller rotating in an opposite direction to the first propeller, and a rotation axis for rotating the first propeller and the second propeller around one axis, wherein an initial phase angle formed before the first propeller and the second propeller rotate can form a predetermined angle.

[0009] According to one embodiment of the present invention, the predetermined angle of the initial phase angle formed by the first propeller and the second propeller may be 90 degrees or more and 135 degrees or less.

[0010] According to one embodiment of the present invention, the aircraft may further include a frame extending from the fuselage so that a rotational axis can be connected by penetrating between the first propeller and the second propeller.

[0011] According to one embodiment of the present invention, the distance between the frame and the first propeller and the second propeller may be a distance of 0.1 to 0.5 times the radius of the first propeller or the second propeller.

[0012] According to one embodiment of the present invention, the radii of the first propeller and the second propeller may be different.

[0013] According to one embodiment of the present invention, the device may further include a first motor for rotating the first propeller in one direction through the rotational axis, and a second motor for rotating the second propeller in the opposite direction of the first propeller through the rotational axis.

[0014] According to one embodiment of the present invention, a phase angle measuring sensor for measuring a phase angle formed by the first propeller and the second propeller may be further included.

[0015] According to one embodiment of the present invention, a control unit may further be included that receives a measured phase angle measured by a phase angle measuring sensor during rotation of the first motor and the second motor, and inputs a PWM signal to at least one of the first motor and the second motor according to the rotation speed of the first motor and the second motor to control the first motor and the second motor in order to maintain an initial phase angle set for the first propeller and the second propeller.

[0016] According to one embodiment of the present invention, the control unit can control the rotational speed and torque of at least one of the first motor and the second motor according to the frequency and magnitude of the current according to the PWM signal.

[0017] According to one embodiment of the present invention, the radii of the first propeller and the second propeller may be different.

[0018] A noise reduction method of a coaxial contra-rotating propeller according to one embodiment of the present invention may include a step of forming an initial phase angle at a predetermined angle before a first propeller, to which a first motor is connected and which rotates in one direction around a rotational axis as a center, and a second propeller, to which a second motor is connected and which rotates in an opposite direction to the first propeller, rotate, are rotated, a step of measuring the phase angle formed by the first propeller and the second propeller when the first propeller and the second propeller rotate, through a phase angle measuring sensor, and a step of controlling by inputting a PWM signal to at least one of the first motor and the second motor according to the rotational speed of the first motor and the second motor in order to maintain the initial phase angle set for the first propeller and the second propeller when the first propeller and the second propeller rotate.

[0019] According to one embodiment of the present invention, the predetermined angle of the initial phase angle formed by the first propeller and the second propeller may be 90 degrees or more and 135 degrees or less.

[0020] According to one embodiment of the present invention, the method may further include a step of setting a distance between a frame through which a rotation axis is connected between the first propeller and the second propeller and the first propeller and the second propeller to be 0.1 to 0.5 times the radius of the first propeller or the second propeller.

[0021] According to one embodiment of the present invention, the controlling step may adjust the rotational speed and torque of at least one of the first motor and the second motor according to the frequency and magnitude of the current according to the PWM signal.

[0022] An aircraft having a noise reduction function of a coaxial counter-rotating propeller according to one embodiment of the present invention and a noise reduction method are economically superior because they can be easily applied to existing platforms.

[0023] Additionally, it has the advantage of being applicable to a wide range of applications, from large-scale helicopters to small-scale drones.

[0024] The effects that can be obtained from the invention are not limited to the effects mentioned above, and other effects not mentioned can be clearly understood by a person having ordinary skill in the art to which the present invention pertains from the description below.

[0025] FIG. 1 is a perspective view of a portion of an aircraft having a noise reduction function of a coaxial counter-rotating propeller according to one embodiment of the present invention.

[0026] FIG. 2 illustrates a top view of a portion of an aircraft having a noise reduction function of a coaxial counter-rotating propeller according to one embodiment of the present invention.

[0027] FIG. 3 is a side view of a portion of an aircraft having a noise reduction function of a coaxial counter-rotating propeller according to one embodiment of the present invention.

[0028] FIG. 4 illustrates a block diagram of an aircraft having a noise reduction function of a coaxial counter-rotating propeller according to one embodiment of the present invention.

[0029] FIG. 5 is a flowchart illustrating a noise reduction method of an aircraft having a noise reduction function of a coaxial counter-rotating propeller according to an embodiment of the present invention.

[0030] ※ Explanation of symbols

[0031] 1: Aircraft with noise reduction function of coaxial contra-rotating propeller

[0032] 10: No. 1 propeller

[0033] 20: Second propeller

[0034] 30: Rotation axis

[0035] 40: Frame

[0036] α: initial phase angle

[0037] β: Measurement phase angle

[0038] R: Radius of the propeller

[0039] △: Distance between frame and propeller

[0040] 100: 1st motor

[0041] 200: Second motor

[0042] 300: Phase angle measurement sensor

[0043] 400: Control Unit

[0044] The present invention will become clearer with reference to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms. These embodiments are provided only to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention. The present invention is defined solely by the scope of the claims. Meanwhile, the terminology used in this specification is for the purpose of describing the embodiments and is not intended to limit the present invention.

[0045] Throughout this specification, singular forms also include plural forms unless specifically stated otherwise in the text.

[0046] Throughout this specification, the terms "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components, steps, operations and / or elements, and do not exclude other components unless specifically stated to the contrary, but rather include other components.

[0047] Terms such as “first” or “second” used throughout this specification may be used simply to distinguish the corresponding component from other corresponding components and do not limit the corresponding components in any other respect (e.g., importance or order).

[0048] Additionally, terms such as “unit” described throughout this specification mean a unit that processes at least one function or operation, which may be implemented as hardware or software, or a combination of hardware and software.

[0049] Additionally, when it is said throughout this specification that a part is "connected" to another part, this includes not only cases where it is "directly connected" but also cases where it is connected "with another structure in between."

[0050] Hereinafter, the present invention will be described in more detail.

[0051] FIG. 1 is a perspective view of a part of an aircraft (1) having a noise reduction function of a coaxial contra-rotating propeller according to an embodiment of the present invention, FIG. 2 is a top view of a part of an aircraft (1) having a noise reduction function of a coaxial contra-rotating propeller according to an embodiment of the present invention, and FIG. 3 is a side view of a part of an aircraft (1) having a noise reduction function of a coaxial contra-rotating propeller according to an embodiment of the present invention.

[0052] Referring to FIGS. 1, 2 and 3, an aircraft (1) having a noise reduction function of a coaxial counter-rotating propeller according to one embodiment of the present invention may include a plurality of propellers and a rotation shaft (30).

[0053] In particular, the present invention relates to an aircraft having multiple propellers rotating around a single rotation axis (30), wherein the propellers rotate in different directions. More specifically, when a first propeller (10) among the multiple propellers rotates in one direction, a second propeller (20) rotates in the opposite direction to the direction in which the first propeller (10) rotates. In this case, noise generation may be a problem due to interference between aircraft caused by the rotation of each propeller.

[0054] Accordingly, in the case of the present invention, the phase angle of the first propeller (10) and the second propeller (20) can be set to reduce such noise generation. Here, the 'phase angle' is the angle formed by the blades of the propeller, and when a plurality of propellers manufactured with the same blade shape maintain the same blade position, the phase angle is 0°.

[0055] Referring to (a) of FIG. 2, in the case of the present invention, a technical feature is that when the initial phase angle (α) formed by each blade of the first propeller (10) and the second propeller (20), i.e. the phase angle formed before the first propeller (10) and the second propeller (20) rotate, forms a predetermined angle, noise in the coaxial contra-rotating propeller can be reduced.

[0056] Here, the initial phase angle (α) formed by the first propeller (10) and the second propeller (20) can be set to a predetermined angle of 90° or more and 135° or less. The effect within this phase angle range will be specifically described with reference to the following examples and comparative examples.

[0057] Meanwhile, an aircraft (1) having a noise reduction function of a coaxial counter-rotating propeller according to an embodiment of the present invention may further include a frame (40). The frame (40) is a part of the fuselage of the aircraft, and a rotation shaft (30) may be disposed to penetrate the frame (40), and a first propeller (10) and a second propeller (20) may be disposed at both ends of the rotation shaft (30).

[0058] The frame (40) may be a part of a body that connects a propeller of a device such as a drone, for example. The frame (40) is not limited to a specific embodiment, and may be a part of a part of an aircraft that is connected to the rotation axis (30) of a coaxial counter-rotating propeller.

[0059] In particular, when a frame (40) is formed between the first propeller (10) and the second propeller (20), the amount of noise generated may vary depending on the gap between the propellers. In order to minimize interference between propellers, noise is reduced as the gap between the propellers is increased, but this poses the problem of making it difficult to miniaturize the aircraft.

[0060] Accordingly, referring to FIG. 3, when the distance (△) between the frame (40) and the first propeller (10) and the second propeller (20) is 0.1 to 0.5 times the radius (R) of the first propeller (10) or the second propeller (20), aerodynamic noise generated between propellers and / or between the propeller and the frame (40) in the coaxial contra-rotating propeller can be reduced.

[0061] Here, the radii (R) of the first propeller (10) and the second propeller (20) may be the same or may be formed differently. In this case, the distance (△) between them may be formed to be 0.1 to 0.5 times the radius (R) of the first propeller (10), or 0.1 to 0.5 times the radius (R) of the second propeller (20). Alternatively, the distance (△) between them may be formed within an overlapping range within a range of 0.1 to 0.5 times the radius (R) of each of the first propeller (10) and the second propeller (20). Consequently, it can be easily adjusted depending on the size of the aircraft and the sizes and radii (R) of the first propeller (10) and the second propeller (20).

[0062] A motor can be used as a power source to rotate the first propeller (10) and the second propeller (20). There are no special restrictions on the type and specifications of the motor.

[0063] Additionally, the number of motors that rotate the first propeller (10) and the second propeller (20) is not limited, but the first propeller (10) and the second propeller (20) can be rotated by one motor or two motors.

[0064] In particular, when rotating the first propeller (10) and the second propeller (20) with one motor, the initial phase angle (α) of the first propeller (10) and the second propeller (20) can be installed by setting them to a predetermined angle, more preferably 90° or more and 135° or less.

[0065] FIG. 4 illustrates a block diagram of an aircraft (1) having a noise reduction function of a coaxial counter-rotating propeller according to one embodiment of the present invention.

[0066] Referring to FIG. 4, when formed with two motors, that is, a first motor (100) that rotates a first propeller (10) in one direction through a rotation shaft (30) and a second motor (200) that rotates a second propeller (20) in the opposite direction of the first propeller (10) through a rotation shaft (30), each motor can be controlled to rotate the first propeller (10) and the second propeller (20) by maintaining the initial phase angle (α) of the first propeller (10) and the second propeller (20) at a predetermined angle, more preferably, 90° or more and 135° or less. Here, the rotation shaft (30) may be formed in multiple pieces, but may be arranged so that the axis on which the first propeller (10) and the second propeller (20) rotate are formed as one.

[0067] Therefore, in order to control the initial phase angle (α) of the first propeller (10) and the second propeller (20) through the first motor (100) and the second motor (200), a phase angle measuring sensor (300) may be included.

[0068] The phase angle measuring sensor (300) is a device that measures the phase angle formed by the first propeller (10) and the second propeller (20), and can measure the initial phase angle (α) formed before the first propeller (10) and the second propeller (20) rotate and the phase angle formed when the first propeller (10) and the second propeller (20) rotate.

[0069] In particular, referring to (a) and (b) of FIG. 2, a control unit (400) may be further included to control a difference between the initial phase angle (α) and the measured phase angle (β), which is the phase angle measured when the first propeller (10) and the second propeller (20) rotate.

[0070] More specifically, when the initial phase angle (α) is not maintained as the first propeller (10) and the second propeller (20) individually rotate through the first motor (100) and the second motor (200), it is necessary to adjust it to the value of the measured phase value. Accordingly, the control unit (400) receives data of the measured phase angle (β) and data of the rotational speed at which the first motor (100) and the second motor (200) rotate, and transmits a PWM (Pulse Width Modulation) signal to at least one of the first motor (100) and the second motor (200) to control them in order to maintain the initially set initial phase angle (α). This can adjust the rotational speed and torque of the first motor (100) and / or the second motor (200) with the frequency and magnitude of the current according to the signal transmitted from the control unit (400).

[0071] FIG. 5 is a flowchart illustrating a noise reduction method (S1) of an aircraft (1) having a noise reduction function of a coaxial counter-rotating propeller according to one embodiment of the present invention.

[0072] Referring to FIG. 5, a noise reduction method (S1) of a coaxial counter-propeller according to an embodiment of the present invention may include a step (S10) of forming an initial phase angle (α) at ​​a predetermined angle, a step (S20) of measuring the phase angle through a phase angle measuring sensor (300), and a step (S30) of inputting a PWM signal for control.

[0073] The step (S10) of forming the initial phase angle (α) at ​​a predetermined angle is a step of setting the initial phase angle (α) of the first propeller (10) and the second propeller (20) connected around a single axis, that is, a rotation axis (30). In this case, the first propeller (10) may be connected to a first motor (100) that rotates in one direction, and the second propeller (20) may be connected to a second motor (200) that rotates in the opposite direction to the first propeller (10). Therefore, before each propeller rotates, the initial phase angle (α), which is the phase angle of the first propeller (10) and the second propeller (20), may be formed at a predetermined angle through the first motor (100) and the second motor (200).

[0074] Here, the predetermined angle of the initial phase angle (α) formed by the first propeller (10) and the second propeller (20) can be formed to be 90° or more and 135° or less as described above.

[0075] In addition, the noise reduction method (S1) of a coaxial counter-rotating propeller according to one embodiment of the present invention may further include a step (S11) of setting a distance (△) between the frame (40) and the first propeller (10) and the second propeller (20).

[0076] In more detail, when the first propeller (10) and the second propeller (20) are installed in a frame (40) that is part of the aircraft body, the rotation shaft (30) is arranged to penetrate the frame (40), and the first propeller (10) and the second propeller (20) are arranged at both ends of the rotation shaft (30), and the distance (△) between the frame (40) and the first propeller (10) and the second propeller (20) can be set to be 0.1 times or more and 0.5 times or less of the radius (R) of the first propeller (10) or the second propeller (20).

[0077] The step (S20) of measuring the phase angle through the phase angle measuring sensor (300) is a step of measuring the phase angle formed when the first propeller (10) and the second propeller (20) rotate. As described above, when the first propeller (10) and the second propeller (20) are connected to separate motors and rotate, the measured phase angle (β), which is the phase angle measured during rotation, may differ from the initial phase angle (α). This is a step of producing data of the measured phase angle (β).

[0078] The step (S30) of controlling by inputting a PWM signal is a step of controlling to maintain the initial phase angle (α) of the first propeller (10) and the second propeller (20) by transmitting a PWM signal to the first motor (100) and the second motor (200). As described above, by receiving data of the measured phase angle (β) and data of the rotational speed at which the first motor (100) and the second motor (200) rotate, a PWM (Pulse Width Modulation) signal can be transmitted to at least one of the first motor (100) and the second motor (200) to maintain the initially set initial phase value.

[0079] A noise reduction method (S1) of a coaxial counter-rotating propeller according to an embodiment of the present invention may include all of the features of an aircraft (1) having a noise reduction function of a coaxial counter-rotating propeller according to an embodiment of the present invention described above.

[0080] Hereinafter, examples and comparative examples of an aircraft (1) having a noise reduction function of a coaxial counter-rotating propeller according to an embodiment of the present invention are reviewed.

[0081] Examples and Comparative Examples

[0082] An aircraft (1) having a noise reduction function of a coaxial counter-rotating propeller according to an embodiment of the present invention and an aircraft according to a comparative example both include a coaxial counter-rotating propeller. The aircraft is configured as a small multicopter drone, and the number of blades of the propeller is set to two per propeller. In the embodiment and the comparative example, the radius (R) of the first propeller (10) and the second propeller (20) is set to 120 mm, the thickness (d) of the frame (40) is set to 16 mm, and the gap between the first propeller (10) and the frame (40) and the gap between the second propeller (20) and the frame (40) are set to 12 mm, which is 0.1 times the radius (R).

[0083] However, in the case of the comparative example, the initial phase angle (α) was set to 0°, and in the case of the embodiment, the initial phase angle (α) was set to 45°, 90°, and 135°, respectively, and noise according to the difference in the initial phase angle (α) was measured.

[0084] Table 1 shows the results of noise generated by the difference in the initial phase angle (α) of an aircraft (1) having a noise reduction function of a coaxial contra-rotating propeller according to an embodiment of the present invention and an aircraft according to a comparative example. The noise intensity described in Table 1 is a value measured in a direction parallel to the first propeller rotational plane and at a distance of 16 times the propeller radius (1.920 m) from the propeller rotational axis.

[0085] Initial phase angle (°) Noise (dB) Comparison Example 056 Example 14554 Example 29043 Example 313539

[0086] Referring to Table 1, it can be confirmed that noise is reduced compared to the aircraft according to the comparative example when the initial phase angle (α) formed before the first propeller (10) and the second propeller (20) rotate is formed at a predetermined angle, such as in the aircraft (1) having the noise reduction function of the coaxial counter-rotating propeller according to the embodiment of the present invention.

[0087] In particular, it can be confirmed that when the initial phase angle (α) is formed as 90° as in Example 2, a noise reduction effect of 13 dB can be obtained compared to the comparative example, and when the initial phase angle (α) is formed as 135° as in Example 3, a noise reduction effect of 17 dB can be obtained compared to the comparative example.

[0088] Although the present invention has been described above with reference to limited embodiments, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical idea of ​​the present invention and the equivalent scope of the patent claims to be described below by a person having ordinary skill in the art to which the present invention pertains.

Claims

1. A first propeller rotating in one direction; a second propeller rotating in the opposite direction to the first propeller; and The first propeller and the second propeller include a rotation shaft for rotating around one axis; An aircraft having a noise reduction function of a coaxial contra-rotating propeller, characterized in that the initial phase angle formed before the first propeller and the second propeller rotate forms a predetermined angle.

2. In paragraph 1, The predetermined angle of the initial phase angle formed by the first propeller and the second propeller is, An aircraft having a noise reduction function of a coaxial contra-rotating propeller characterized by an angle of 90 degrees or more and 135 degrees or less.

3. In paragraph 1, An aircraft having a noise reduction function of a coaxial contra-rotating propeller, further comprising a frame extending from the fuselage of the aircraft such that the rotational shaft can penetrate and be connected between the first propeller and the second propeller.

4. In paragraph 3, The distance between the above frame and the first and second propellers is, An aircraft having a noise reduction function of a coaxial contra-rotating propeller, characterized in that the distance is 0.1 to 0.5 times the radius of the first propeller or the second propeller.

5. In paragraph 4, An aircraft having a noise reduction function of a coaxial contra-rotating propeller, characterized in that the distance between the frame and the first propeller and the distance between the frame and the second propeller are different.

6. In paragraph 1, A first motor that rotates the first propeller in one direction through the rotation axis, An aircraft having a noise reduction function of a coaxial contra-rotating propeller, further comprising a second motor for rotating the second propeller in the opposite direction of the first propeller through the rotational axis.

7. In paragraph 6, An aircraft having a noise reduction function of a coaxial contra-rotating propeller, further comprising a phase angle measuring sensor that measures a phase angle formed by the first propeller and the second propeller.

8. In paragraph 7, An aircraft having a noise reduction function of a coaxial contra-rotating propeller, further comprising a control unit that receives a measured phase angle measured by the phase angle measuring sensor when the first motor and the second motor rotate, and controls at least one of the first motor and the second motor by inputting a PWM signal according to the rotation speed of the first motor and the second motor to maintain the initial phase angle set for the first propeller and the second propeller.

9. In paragraph 8, The above control unit, An aircraft having a noise reduction function of a coaxial contra-rotating propeller, characterized in that the rotation speed and torque of at least one of the first motor and the second motor are controlled by the frequency and size of the current according to the PWM signal.

10. In paragraph 1, An aircraft having a noise reduction function of a coaxial contra-rotating propeller, characterized in that the radii of the first propeller and the second propeller are different.

11. A step of forming an initial phase angle at a predetermined angle before a first propeller, to which a first motor is connected and which rotates in one direction around a single axis, and a second propeller, to which a second motor is connected and which rotates in the opposite direction to the first propeller, rotate; A step of measuring a phase angle formed by the first propeller and the second propeller when the first propeller and the second propeller rotate using a phase angle measuring sensor; and A method for reducing noise of a coaxial contra-rotating propeller, comprising: a step of controlling at least one of the first motor and the second motor by inputting a PWM signal according to the rotation speed of the first motor and the second motor so as to maintain the initial phase angle set for the first propeller and the second propeller when the first propeller and the second propeller rotate; 12. In paragraph 11, The predetermined angle of the initial phase angle formed by the first propeller and the second propeller is, A method for reducing noise of a coaxial counter-rotating propeller, characterized in that the angle is 90 degrees or more and 135 degrees or less.

13. In paragraph 11, A method for reducing noise of a coaxial contra-rotating propeller, further comprising the step of setting a distance between a frame through which the rotational shaft penetrates and is connected between the first propeller and the second propeller and the first propeller and the second propeller to 0.1 to 0.5 times the radius of the first propeller or the second propeller.

14. In paragraph 11, The above controlling step is, A method for reducing noise of a coaxial contra-rotating propeller, characterized in that the rotation speed and torque of at least one of the first motor and the second motor are controlled by the frequency and size of the current according to the PWM signal.

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