flying object

Abstract

To provide an air vehicle with rotors which can inhibit rapid increase of a thrust force.SOLUTION: An air vehicle (a small unmanned aircraft 1) includes one or more rotors 7. Each rotor 7 includes: a hub 13 which is attached to a rotary shaft 11 of the rotor 7 and rotates with rotation of the rotary shaft 11; an annular body 15 which encloses the hub 13 and is centered on the rotary shaft 11 and arranged concentrically with the hub; a connection part 17 which connects the hub 13 with the annular body 15; and multiple blades 19 extending from a peripheral wall part of the annular body 15 in a direction orthogonal to the rotary shaft 11. Pressure recovery holes 21 which are through holes are formed between the hub 13 and the annular body 15.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a flying object.

Background Art

[0002] Unmanned small flying objects (drones) have come to be used for inspecting structures. A drone controls the rotation of its rotary wings (propellers) to control ascent / descent and the direction of travel. When the rotary wings rotate, lift is generated, creating thrust on the flying object. "Thrust" is obtained by subtracting drag (the force due to friction between the surface of the rotary wing and the fluid air) from the lift generated by the rotary wing. When the flying object is in flight, a downward airflow occurs where the upper side of the rotary wing is the inlet and the lower side is the outlet.

[0003] It is known that when the rotary wing of a flying object approaches an upper wall, the thrust generated by the rotary wing rapidly increases. This phenomenon is called the "Ceiling Effect". The "Ceiling Effect" occurs when the rotary wing of a flying object approaches an upper wall and the airflow is drawn into the rotary wing at an angle close to perpendicular to the rotary wing axis direction, causing the axial velocity component of the rotary wing (induced velocity) to decrease. As a result, (i) the angle of attack with respect to the rotary wing increases, the lift increases, the torque decreases, and the drag of the downward component of the rotary wing decreases, and (ii) a pressure difference is considered to occur between the upper wall and the rotary wing (negative pressure side) and the downstream of the rotary wing (static pressure side) (for example, Non-Patent Documents 1, 2, and 3). If the thrust rapidly increases, there is a risk that the rotary wing will collide with the upper wall.

[0004] Therefore, conventionally, as in Patent Document 1, there are some drones as flying objects that have a frame structure to prevent the rotary wing from colliding with the upper wall.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Non-Patent Documents

[0006] [Non-Patent Document 1] T. Nishio et al., "Stable Control in Climbing and Descending Flight under Upper Walls using Ceiling Effect Model based on Aerodynamics," 2020 IEEE International Conference on Robotics and Automation (ICRA), 2020, pp. 172-178, doi: 10.1109 / ICRA40945.2020.9197137. [Non-Patent Document 2] YH Hsiao and P. Chirarattanon, "Ceiling Effects for Surface Locomotion of Small Rotorcraft," 2018 IEEE / RSJ International Conference on Intelligent Robots and Systems (IROS), 2018, pp. 6214-6219, doi: 10.1109 / IROS.2018.8593726. [Non-Patent Document 3] Yasutada Tanabe, Masahiko Sugiura, Takashi Aoyama, Hideaki Sugawara, Shigeru Sunada, Koichi Yonezawa, and Hiroshi Tokutake, “Multiple Rotors Hovering Near an Upper or a Side Wall,” J. Robot. Mechatron., Vol.30, No.3, pp. 344-353, 2018, DOI: 10.20965 / jrm.2018.p0344 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, in the example of Patent Document 1, since the aircraft has a frame structure, there is a problem that the number of parts increases and the overall weight of the aircraft increases.

[0008] The object of the present invention is to provide an aircraft equipped with rotor blades that can suppress a rapid increase in thrust. [Means for solving the problem]

[0009] To achieve the above objective, the aircraft of the present disclosure is an aircraft equipped with one or more rotors, wherein the rotors include a hub attached to the rotation axis of the rotor and rotating together with the rotation axis, an annular body surrounding the hub, centered on the rotation axis and concentric with the hub, a connecting portion connecting the hub and the annular body, and a plurality of blades extending from the peripheral wall of the annular body in a direction perpendicular to the rotation axis, and a pressure recovery hole, which is a through hole, is formed between the hub and the annular body. [Effects of the Invention]

[0010] When the rotor blade approaches the upper wall, a pressure difference is created between the upper wall and the rotor blade (negative pressure side) and downstream of the rotor blade (static pressure side). However, in the aircraft of this disclosure, air is supplied between the upper wall and the rotor blade (negative pressure side) by the pressure recovery hole, reducing the pressure difference. As a result, a rapid increase in thrust can be suppressed compared to the case of conventional rotor blades. [Brief explanation of the drawing]

[0011] [Figure 1] This is a perspective view of a small unmanned aerial vehicle (drone), which is an example of an aircraft. [Figure 2] This is a plan view of the rotor blade. [Figure 3] This is a plan view of a rotor blade (conventional blade) with a hub diameter of 0.1D and no pressure recovery hole. [Figure 4] This is a conceptual diagram of an experimental apparatus (single wing) used for effectiveness verification experiments. [Figure 5]It is a graph showing the relationship between the height dimension g [mm] from the upper surface of the rotating wing to the upper wall surface and the thrust [N] in the case of a single wing, and it is a comparison diagram of the rotating wing when the diameter dimension x of the conventional wing and the annular body is 0.2D. [Figure 6] It is a graph showing the relationship between the height dimension g [mm] from the upper surface of the rotating wing to the upper wall surface and the thrust [N] in the case of a single wing, and it is a comparison diagram of the rotating wing when the diameter dimension x of the conventional wing and the annular body is 0.5D. [Figure 7] It is a graph showing the relationship between the height dimension g [mm] from the upper surface of the rotating wing to the upper wall surface and the thrust [N] in the case of a single wing, and it is a comparison diagram of the rotating wing when the diameter dimension x of the conventional wing and the annular body is 0.6D. [Figure 8] It is a graph showing the relationship between the height dimension g [mm] from the upper surface of the rotating wing to the upper wall surface and the thrust [N] in the case of a single wing, and it is a comparison diagram of the rotating wing when the diameter dimension x of the conventional wing and the annular body is 0.7D. [Figure 9] It is a graph showing the thrust change rate α when the diameter dimension x [mm] of the conventional wing and the annular body of the rotating wing in the case of a single wing is changed from 0.2D to 0.7D. [Figure 10] It is a graph showing the relationship between the height dimension g [mm] from the upper surface of the rotating wing to the upper wall surface and the thrust [N] when the thrust is made to match when the rotating wing is located infinitely far away where the influence of the ceiling effect by the upper wall can be ignored. [Figure 11] It is a conceptual diagram of an experimental device (four blades) for the effect confirmation experiment. [Figure 12] It is a graph showing the relationship between the height dimension g [mm] from the upper surface of the rotating wing to the upper wall surface and the thrust [N] in the case of four blades, and it is a comparison diagram of the rotating wing when the diameter dimension x of the conventional wing and the annular body is 0.2D. [Figure 13] It is a graph showing the relationship between the height dimension g [mm] from the upper surface of the rotating wing to the upper wall surface and the thrust [N] in the case of four blades, and it is a comparison diagram of the rotating wing when the diameter dimension x of the conventional wing and the annular body is 0.5D. [Figure 14] It is a graph showing the relationship between the height dimension g [mm] from the upper surface of the rotating wing to the upper wall surface and the thrust [N] in the case of four blades, and it is a comparison diagram of the rotating wing when the diameter dimension x of the conventional wing and the annular body is 0.6D. [Figure 15] It is a graph showing the relationship between the height dimension g [mm] from the upper surface of the rotary wing to the upper wall surface and the thrust [N] in the case of four wings, and is a comparison diagram of the rotary wing when the diameter dimension x of the conventional wing and the annular body is 0.7D. [Figure 16] It is a graph showing the thrust change rate α when the diameter dimension x [mm] of the annular bodies of the conventional wing and the rotary wing in the case of four wings is changed from 0.2D to 0.7D. [Figure 17] It is a graph showing the relationship between the height dimension g [mm] from the upper surface of the rotary wing to the upper wall surface and the thrust [N] when the thrusts are made to coincide when the rotary wing is located infinitely far away where the influence of the ceiling effect by the upper wall can be ignored.

Mode for Carrying Out the Invention

[0012] Hereinafter, with reference to the drawings, embodiments of the flying object of the present invention will be described in detail.

[0013] FIG. 1 is a perspective view of a small unmanned aircraft (drone), which is an example of a flying object.

[0014] The small unmanned aircraft 1 is a so-called quadcopter type drone including a main body part 3, four arm parts 5A to 5D, and four rotary wings 7A to 7D.

[0015] The main body part 3 incorporates a battery (not shown) and a control part (not shown) for controlling the rotation of the rotary wings 7A to 7D, and can incorporate and mount various sensors, cameras, etc. depending on the application.

[0016] The four arm parts 5A to 5D extend radially from the main body part 3, and motors 9A to 9D that are electrically connected to the battery and rotate the rotary wings are attached to the respective tip parts. The rotary wings 7A to 7D are fixed to the rotation shafts 11A to 11D of the respective motors 9A to 9D. Hereinafter, unless otherwise particularly distinguished, the arm parts 5A to 5D are referred to as "arm part 5", the motors 9A to 9D are referred to as "motor 9", and the rotation shafts 11A to 11D are referred to as "rotation shaft 11".

[0017] The four rotors 7A through 7D are also called propellers or rotors. Rotor blades 7A and 7C, which are arranged diagonally across the main body 3, are identical in shape and dimensions, while rotor blades 7B and 7D have blade angles that are opposite to those of rotor blades 7A and 7C. The aircraft is able to fly because rotor blades 7A and 7C rotate in the same direction, and rotor blades 7B and 7D rotate in the opposite direction to rotor blades 7A and 7C. Hereafter, unless otherwise specified, rotor blades 7A through 7D will be referred to as "rotor blade 7".

[0018] In this embodiment, in a plan view, the distance between the rotation axes of adjacent rotor blades 7 (for example, rotation axis 11A and rotation axis 11B) is 178 mm, and the distance between the rotation axes of rotor blades 7 that are arranged diagonally across the main body 3 (for example, rotation axis 11A and rotation axis 11C) is set to 252 mm.

[0019] Figure 2 is a plan view of the rotor blade 7. As shown in Figure 2, the rotor blade 7 comprises a hub 13, an annular body 15, a connecting portion 17, a blade 19, and a pressure recovery hole 21.

[0020] The hub 13 is attached to the rotation axis 11 of the motor 9, which is the rotation axis of the rotor blade 7, and rotates together with the rotation of the rotation axis 11.

[0021] The annular body 15 surrounds the hub 13 and is a circular member concentric with the hub 13, with the rotation axis 11 as its center. In this embodiment, the thickness dimension of the annular body 15 (thickness dimension between the outer and inner surfaces) is 3 mm, and the height dimension is 7 mm.

[0022] The hub 13 and the annular body 15 are connected by a connecting portion 17. In this embodiment, the connecting portion 17 is composed of a first connecting portion 17a and a second connecting portion 17b that extend from the hub 13 to the annular body 15. The first connecting portion 17a and the second connecting portion 17b are arranged in a straight line with respect to the hub 13. In this embodiment, the thickness dimension of the connecting portion 17 (the thickness dimension between the first pressure recovery hole 21a and the second pressure recovery hole 21b) is 3 [mm], and the height dimension is 7 [mm].

[0023] The blade 19 extends from the peripheral wall portion 15a of the annular body 15 in a direction perpendicular to the rotation axis 11. In this embodiment, the first blade 19a extends along the extension line of the first connecting portion 17a, and the second blade 19b extends along the extension line of the second connecting portion 17b.

[0024] The pressure recovery hole 21 is a through hole formed between the hub 13 and the annular body 15. More specifically in this embodiment, the pressure recovery hole 21 is a first pressure recovery hole 21a and a second pressure recovery hole 21b surrounded by the hub 13, the inner circumferential surface 15b of the annular body 15, the first connecting portion 17a, and the second connecting portion 17b. The presence of the pressure recovery hole 21 allows air to be supplied between the upper wall and the rotor blade when the rotor blade 7 approaches the upper wall, reducing the pressure difference and thus suppressing a rapid increase in thrust.

[0025] As shown in Figure 2, the diameter of the circle passing through the tips of the first blade 19a and the second blade 19b is D [mm] (127 [mm]), and the diameter of the annular body 15 (circumferential wall portion 15a of the annular body 15) is x. In this embodiment, as will be described later, D is set to a fixed value, and the diameter of the annular body 15 x [mm] is changed relative to D (x = 0.2D to 0.7D) to change the size of the pressure recovery hole 21, and the effect of suppressing a rapid increase in thrust has been confirmed.

[0026] <Effect Verification Experiment> To confirm the effect of the pressure recovery hole 21 in suppressing a rapid increase in thrust, an effect verification experiment was conducted using the apparatus shown in Figures 4 and 11, with a rotor blade without a pressure recovery hole and a hub diameter of 0.1D (hereinafter referred to as "conventional blade") as shown in Figure 3 as a comparison target.

[0027] The experimental apparatus ED shown in Figures 4 and 11 consists of a simulation device SM that mimics the small unmanned aerial vehicle 1, a load cell LC, and a support stand SS. The experimental apparatus shown in Figure 4 measures the thrust when there is one rotor blade (hereinafter referred to as "single wing"), while the experimental apparatus shown in Figure 11 measures the thrust when there are four rotor blades (hereinafter referred to as "quad-wing"), similar to the small unmanned aerial vehicle 1. The single wing is assumed to be a single-rotor drone equipped with one rotor blade, and the quad-wing is assumed to be a quad-rotor drone equipped with four rotor blades.

[0028] Since the simulation device SM is modeled after the small unmanned aerial vehicle 1, the same symbols used for the small unmanned aerial vehicle 1 will be used for the simulation device SM below, and the explanation of each component will be omitted. In addition, the simulation device SM differs from the small unmanned aerial vehicle 1 in that a motor 9 is built into the main body 3, and the rotational force of the motor 9 is transmitted via the arm 5 to a rotating shaft 11 provided at the tip of the arm 5, causing the rotor blade 7 to rotate.

[0029] For the rotor blades 7 attached to the simulation device SM, we prepared two types: one with a diameter dimension x [mm] of the annular body 15 of x = 0.2D to 0.7D (hereinafter, rotor blades may be indicated by the value of the diameter dimension x to distinguish them) and a conventional rotor blade.

[0030] The load cell LC is a force detection sensor, which in this example is fixed to the support base SS and detects the force exerted vertically by the simulated device SM as "thrust". In this experiment, "thrust" is defined as the vertical component of the lift generated by the rotor blades minus the vertical component of the drag force (force due to friction between the rotor blade surface and the air fluid).

[0031] The experimental apparatus ED was installed in a laboratory with an upper wall. The height from the laboratory floor to the upper wall was 976 mm. The thrust was measured when the height from the ground to the upper surface of the rotor blade 7 was h mm, and the height from the upper surface of the rotor blade 7 to the upper wall was g mm, and g was varied from infinity (where the ceiling effect of the upper wall can be ignored) to 3 mm.

[0032] [In the case of a single wing] The motor speed was standardized to 4000 rpm, and the experiment was conducted using the experimental apparatus ED shown in Figure 4. The experiment was performed at least five times, and the results are displayed using error bars; the plotted points represent the average values.

[0033] Figures 5 to 8 are graphs showing the relationship between the height dimension g [mm] from the top surface to the top wall surface of a rotor blade and the thrust [N] in the case of a single blade. The horizontal axis shows g / D and the vertical axis shows the thrust [N]. Figure 5 is a comparison diagram of a conventional blade and a rotor blade when the diameter dimension x of the annular body 15 is 0.2D, Figure 6 is a comparison diagram of a conventional blade and a rotor blade when the diameter dimension x of the annular body 15 is 0.5D, Figure 7 is a comparison diagram of a conventional blade and a rotor blade when the diameter dimension x of the annular body 15 is 0.6D, and Figure 8 is a comparison diagram of a conventional blade and a rotor blade when the diameter dimension x of the annular body 15 is 0.7D.

[0034] Table 1 shows the results from Figures 5 to 8, and T max (Thrust [N] when the rotor blade is closest to the upper wall (g=3 [mm]) and T ∞ This summarizes the thrust [N] when the rotor blades are located at infinity, where the ceiling effect from the upper wall can be ignored.

[0035] [Table 1] Figure 9 is a graph showing the thrust change rate α when the diameter dimension x [mm] of the annular body 15 of the conventional wing and rotor blade 7 is changed from 0.2D to 0.7D in the case of a single wing. The horizontal axis shows x / D, and the vertical axis shows the thrust change rate α.

[0036] The "thrust rate of change α" is calculated using the following formula: Thrust force change rate α=T max / T ∞ However, T max This is the thrust [N] when the rotor blade is closest to the upper wall (g=3 [mm]), and T ∞ This is the thrust [N] when the rotor blade is located at infinity, where the ceiling effect from the upper wall can be ignored.

[0037] This experiment revealed the following: (1) For all rotor blades, the thrust increase becomes significant at around g / D = 0.1 (g = approximately 12 [mm]). (2) The effect of suppressing thrust rise was confirmed across the entire range of rotor blades with a diameter dimension x of 0.2D to 0.7D of the ring-shaped body 15. (3) When the diameter dimension x of the ring-shaped body 15 is 0.6D to 0.7D, the effect of suppressing thrust rise becomes greater. (4) Considering the relationship between the effect of suppressing thrust rise and the thrust change rate α, and the ease of control during flight, such as approaching the ceiling from infinity, it is considered that a rotor blade with a diameter dimension x of the ring body 15 of 0.5D or more and 0.6D or less is a suitable shape for a single wing.

[0038] In this embodiment, as the diameter dimension x of the annular body 15 increases, the length dimension of the blade 19 decreases. As is clear from Figures 5 to 8, as the diameter dimension x of the annular body 15 increases, there is a tendency for the thrust obtained when the motor speed is matched to decrease. For reference, Figure 10 shows a graph illustrating the relationship between the height dimension g [mm] from the top surface of the rotor blade to the top wall surface and the thrust [N] when the rotor blade is positioned at infinity, where the ceiling effect due to the top wall can be ignored, and the thrust is matched. Figure 10 is a comparison of a conventional rotor blade and a rotor blade with an annular body 15 diameter dimension x of 0.6D. To obtain the thrust (T=0.13 [N]) obtained when the conventional rotor blade is at 4000 rpm, 4500 rpm was required for a rotor blade with an annular body 15 diameter dimension x of 0.6D. Therefore, it is expected that power consumption will increase to obtain a similar amount of thrust, but even in that case, it can be seen that the effect of suppressing the increase in thrust can be obtained.

[0039] [In the case of a four-wing design] The motor speed was standardized to 4000 rpm, and the experiment was conducted using the experimental apparatus ED shown in Figure 11. The experiment was performed at least five times, and the results are displayed using error bars; the plotted points represent the average values.

[0040] Figures 12 to 15 are graphs showing the relationship between the height dimension g [mm] from the top surface to the top wall surface of a rotor blade and the thrust [N] in the case of a four-bladed rotor. The horizontal axis shows g / D and the vertical axis shows the thrust [N]. Figure 12 is a comparison diagram of a rotor blade when the diameter dimension x of the annular body 15 is 0.2D, Figure 13 is a comparison diagram of a rotor blade when the diameter dimension x of the annular body 15 is 0.5D, Figure 14 is a comparison diagram of a rotor blade when the diameter dimension x of the annular body 15 is 0.6D, and Figure 15 is a comparison diagram of a rotor blade when the diameter dimension x of the annular body 15 is 0.7D.

[0041] Table 2 shows the results from Figures 12 to 15, and T max (Thrust [N] when the rotor blade is closest to the upper wall (g=3 [mm]) and T ∞This summarizes the thrust [N] when the rotor blades are located at infinity, where the ceiling effect from the upper wall can be ignored.

[0042] [Table 2] Figure 16 is a graph showing the thrust change rate α when the diameter dimension x [mm] of the annular body 15 of the rotor blade 7 is changed from 0.2D to 0.7D in the case of a four-bladed rotor. The horizontal axis shows x / D, and the vertical axis shows the thrust change rate α.

[0043] This experiment revealed the following: (1) For all rotor blades, the thrust increase becomes significant at around g / D = 0.1 (g = approximately 12 [mm]). (2) The effect of suppressing thrust rise was confirmed across the entire range of rotor blades with a diameter dimension x of 0.2D to 0.7D of the ring-shaped body 15. (3) When the diameter dimension x of the ring-shaped body 15 is 0.5D to 0.7D, the effect of suppressing thrust rise becomes greater. The reason why the result differs from that of a single wing is thought to be due to the mutual influence of the airflow from the four wings. (4) Considering the relationship between the effect of suppressing thrust rise and the thrust change rate α, and the ease of control during flight, such as approaching the ceiling from infinity, it is considered that even in the case of four wings, a rotor blade with a diameter dimension x of the ring body 15 of 0.5D or more and 0.6D or less is an appropriate shape.

[0044] Similar to the case of a single wing, Figure 17 shows a graph illustrating the relationship between the height dimension g [mm] from the top surface of the rotor blade to the top wall surface and the thrust [N] when the thrust is matched when the rotor blade is located at infinity, where the ceiling effect of the top wall can be ignored. Figure 17 compares a conventional wing with a rotor blade when the diameter dimension x of the annular body 15 is 0.5D. To obtain the thrust (T=0.48 [N]) obtained when the conventional wing is at 4000 rpm, the rotor blade with a diameter dimension x of the annular body 15 of 0.5D required 4160 rpm. Therefore, it is expected that power consumption will increase to obtain a similar amount of thrust, but even in that case, it can be seen that the effect of suppressing the increase in thrust can be obtained.

[0045] Although embodiments of the present invention have been specifically described above, the present invention is not limited to these embodiments, and modifications are, of course, possible within the scope of the technical idea of ​​the present invention.

[0046] For example, the shape and dimensions of the rotor blades are not limited to those described above. The shape of the annular body is not limited to a circular shape; it can also be polygonal. Furthermore, the number of blades is not limited to two; three or more blades can be arranged at equal intervals around the annular body to increase thrust. Similarly, the number of connecting parts is not limited to two; three or more connecting parts can be arranged at equal intervals around the annular body to increase strength. In this case, since the number of connecting parts increases and the area of ​​the pressure recovery holes decreases, it is desirable to design the rotor blades to balance strength with the thrust-suppressing effect. Note that because the rotor blades have an annular body, the number of blades and the number of connecting parts do not need to match. For example, the number of blades can be increased to three or more while keeping the number of connecting parts at two, or the number of blades can be increased to three or more while keeping the number of connecting parts at two. [Explanation of Symbols]

[0047] 1 Small unmanned aerial vehicle (flying object) 3. Main body 5 (5A to 5D) Arm section 7 (7A to 7D) Rotary blades 9 (9A to 9D) motor 11 (11A to 11D) Rotation axis 13 Hubs 15 Ring-shaped bodies 17 (17a and 17b) Connecting section 19 (19a and 19b) Blades 21 (21a and 21b) Pressure recovery holes

Claims

[Claim 1] An aircraft equipped with one or more rotors that performs flight close to an upper wall such that a ceiling effect occurs, causing the thrust from the rotors to increase rapidly, The aforementioned rotor blade is A hub attached to the rotation axis of the rotor blade and rotating together with the rotation of the rotation axis, Surrounding the hub, with the axis of rotation at its center, is a circular annular body concentric with the hub, A connecting portion that connects the hub and the annular body, It comprises a plurality of blades extending from the peripheral wall portion of the annular body in a direction perpendicular to the rotation axis, A pressure recovery hole, which is a through hole, is formed between the hub and the annular body. When the diameter of the circle passing through all the tips of the aforementioned multiple blades is D, the diameter of the annular body is set to be between 0.5D and 0.6D, The thrust T when the rotor blade is located at infinity, where the ceiling effect can be ignored. ∞ The thrust T when the rotor blade is closest to the upper wall. max The thrust change rate α, which is the ratio of , was set to 2.2 or less. An aircraft characterized by the following features.

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