Unmanned aircraft

Provided is an unmanned aircraft which is capable of stably taking off. In one example, the unmanned aircraft has an aircraft body which includes an information acquisition device, a plurality of rotary wings, and a protective member disposed around the rotary wings. Each of the rotary wings has a rotation axis which is tilted with respect to a vertical direction by a given angle, such that the rotary wings generate a forward thrust force. The aircraft body has a lower edge which includes a middle lower edge and a forward lower edge, wherein the protective member has a lower edge including the forward lower edge. The forward lower edge is located above the middle lower edge, and the forward lower edge has a rear end located backward of a rear end of the rotary wing.

RELATED DISCLOSURE

The present application is a U.S. National Phase Application under 35 U.S.C. § 371 of International Application No. PCT/JP2021/029899 filed Aug. 16, 2021, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to an unmanned aircraft configured to fly based on a manipulation signal received from the outside.

BACKGROUND ART

As a method of inspecting the inside of a sewage pipe, there have been known a method in which an inspector moves inside a sewage pipe to visually inspect the inside of the sewage pipe, and a method in which a wheeled vehicle equipped with a camera is driven to travel inside a sewage pipe to image the inside of the sewage pipe. In these inspection methods, the inspector is likely to be exposed to danger due to toxic gas generated in the sewage pipe, or control of the wheeled vehicle is likely to become difficult due to rise in the water level in the sewage pipe.

Therefore, the below-mentioned Patent Document 1 proposes an inspection method using an unmanned aircraft. An aircraft body of this unmanned aircraft is configured such that a dimension in a width direction thereof is less than a dimension thereof in a front-rear direction thereof, and is provided with a plurality of rotary wings, so as to allow the unmanned aircraft to easily move along a direction in which a sewage pipe extends. The rotary wings are configured to blow air downwardly and backwardly, thereby generating a lift force and a thrust force. An inspector can remotely manipulate this unmanned aircraft to image the inside of the sewage pipe, so that it becomes possible to perform the inspection while ensuring safety of the inspector, and mitigating the influence of the water level in the sewage pipe

However, the unmanned aircraft described in the Patent Document 1 is equipped with rotary wings mainly for generating a lift force, and a rotary wing mainly for generating a thrust force, separately, so that it is apt to increase in size. Thus, the unmanned aircraft is likely to have difficulty in flying inside a sewage pipe having a relatively small inner diameter.

Therefore, the present inventors carried out a study on employing a rotary wing capable of simultaneously generating a lift force and a thrust force. Specifically, the present inventors conducted research on a configuration in which a rotation axis of a rotary wing is tilted with respect to a vertical direction by a given angle such that the rotary wing blows air downwardly and backwardly. This configuration makes it possible to obtain a lift force and a thrust force without providing separate rotary wings as in the unmanned aircraft described in Patent Document 1, and thereby achieving a more compact configuration.

CITATION LIST

Patent Document 1: PCT International Publication No. WO2019/198155

SUMMARY OF INVENTION

However, when employing the rotary wing configured to blow air downwardly and backwardly, an airflow is likely to become unstable during takeoff of the unmanned aircraft, causing the aircraft body to suddenly largely tilt forwardly. This gives rise to a problem that a forward part of a lower end of the aircraft body interferes with an inner bottom surface of the sewage pipe, and therefore the unmanned aircraft becomes failing to stably take off.

As used in this specification, the term “takeoff” means that an unmanned aircraft which remains stationary on a given surface (e.g., inner bottom surface of a sewage pipe) is lifted upwardly. Further, the term “forward-tilt” means that an unmanned aircraft is in a posture where it is tilted forwardly with respect to a posture where the unmanned aircraft which remains stationary on a horizontal surface.

The present invention has been made to solve the above problem, and an object thereof is to provide an unmanned aircraft capable of stably taking off.

[Solution to Technical Problem]

In order to achieve the above object, the present invention provides an unmanned aircraft configured to fly based on a manipulation signal received from outside. The unmanned aircraft comprises an aircraft body which comprises: an information acquisition device for acquiring information regarding an object around the aircraft body; a rotary wing for blowing air downwardly to generate a lift force; and a protective member disposed around the rotary wing to protect the rotary wing, the aircraft body being configured such that a dimension in a width direction thereof is less than a dimension in a front-rear direction thereof, wherein: the rotary wing has a rotation axis which is tilted with respect to a vertical direction by a given angle, such that the rotary wing generates a forward thrust force; and the aircraft body has a lower edge which comprises a middle lower edge located in a middle of the aircraft body in the front-rear direction, and a forward lower edge located forward of the middle lower edge, and wherein: the protective member has a lower edge comprising the forward lower edge; the forward lower edge is located above the middle lower edge; and the forward lower edge has a rear end located backward of a rear end of the rotary wing.

Preferably, in the unmanned aircraft of the present invention, the forward lower edge is formed to linearly extend forwardly and upwardly from the side of the middle lower edge.

Preferably, in the unmanned aircraft of the present invention, the protective member is formed with an opening which opens, to outside, a space lateral to the rotary wing in the width direction.

More preferably, in the above unmanned aircraft, the rotary wing is disposed in a position corresponding to the forward lower edge in the front-rear direction.

The present invention makes it possible to provide an unmanned aircraft capable of stably taking off.

DESCRIPTION OF EMBODIMENTS

With reference toFIGS.1to6, the configuration of an unmanned aircraft1(hereinafter referred to as “aircraft1”) according to one embodiment of the present invention will be described. As used in this specification, in the aircraft1which is positioned such that a width direction and a front-rear direction thereof orthogonal to each other is coincident with a horizontal direction, the left side when looking forward of the aircraft1is referred to as “left”, and the right side when looking forward of the aircraft1is referred to as “right”. That is, a right-left direction is coincident with the width direction of the aircraft1. Further, the upper side of a vertical direction is referred to as “up”, and the lower side of the vertical direction is referred to as “down”.

FIG.1is a perspective view showing the aircraft1as viewed from thereabove, andFIG.2is a perspective view showing the aircraft1as viewed from therebelow.FIG.3is a side view showing the aircraft1as viewed from the left side thereof.FIG.4is a front view showing the aircraft1, andFIG.5is a top plan view showing the aircraft1.FIG.6is a perspective view showing the after-mentioned main unit2and protective member8which are separated from each other, as viewed from thereabove.

The aircraft1is used to acquire information regarding the inside of a non-illustrated sewage pipe. An aircraft body11of the aircraft1has a longitudinally-long shape to allow the aircraft1to easily move along a direction in which the sewage pipe extends. Specifically, the aircraft body11illustrated inFIG.2is configured such that a dimension W thereof between opposed lower edges11ain the width direction is less than a dimension L of each of the lower edges11ain the front-rear direction. Each of the lower edges11acomprises a middle lower edge91a, a forward lower edge85f, and a backward lower edge85reach of which will be described in detail later.

The aircraft body11comprises a main unit2, and a protective member8. As shown inFIG.6, the main unit2comprises a casing3, four motors41to44, and four rotary wings51to54. As shown inFIG.3, the main unit2further comprises an information acquisition device6.

As shown inFIG.6, the casing3comprises a casing body31and a lid member32. Each of the casing body31and the lid member32is formed of a lightweight and high-rigidity material (e.g., carbon fiber-reinforced plastic). A non-illustrated housing space is formed inside the casing body31. The housing space has an opening on top thereof. Four arms33to36are provided on an outer surface of the casing body31. Specifically, two arms33,34extend forwardly from a front surface of the casing body31, and two arms35,36extend backwardly from a rear surface of the casing body31. The arms33,34extent approximately parallel to each other while being spaced apart from each other in the right-left direction. The arms35,36also extent approximately parallel to each other while being spaced apart from each other in the right-left direction.

Electrical components such as a battery, a control device and a wireless communication device are housed in the housing space of the casing body31. The lid member32closes the opening of the housing space to form a watertight seal with respect to a peripheral edge of the casing body31, thereby preventing water from entering the housing space.

Each of the motors41to44is an actuator configured such that an output shaft thereof is rotated in response to receiving electric power. Each of the motors41to44is attached to a lower surface of a corresponding one of the arms33to36, such that the output shaft thereof extends downwardly. A non-illustrated signal line is provided to penetrate through each of the arms33to36, and each of the motors41to44is electrically connected to the control device housed in the housing space of the casing body31.

Each of the rotary wings51to54has a plurality of blades around a corresponding one of four rotation axes51ato54a, and is fixed to the output shaft of a corresponding one of the motors41to44. As shown inFIG.3, each of the rotation axes51ato54ais positioned such that it is tilted backwardly with respect to a straight line N extending in the vertical direction, by a given angle θ1. The angle θ1 is about 10°. Further, as shown inFIG.4, each of the rotation axes51ato54ais positioned such that it is tilted toward the outside of the aircraft body11with respect to the straight line N by a given angle θ2.

The information acquisition device6is provided to acquire information regarding an object around the aircraft body11. As shown inFIG.3, the information acquisition device6comprises a forward camera61, a backward camera63, and a central camera65. The forward camera61and the backward camera63are provided, respectively, at a front end and a rear end of the lid member32of the casing body31. The central camera65is fixed to the lid member32at a position between the forward camera61and the backward camera63. Each of the forward camera61, the backward camera63and the central camera65is electrically connected to the control device housed in the housing space of the casing body31. For example, an infrared camera may be used as the central camera65. Further, for example, a measurement device such as LiDAR (Light Detection And Ranging) may be used in place of the central camera65.

The protective member8is formed of a material having a specific gravity less than water and high impact absorption performance (e.g., polypropylene foam). The protective member8is formed to be approximately symmetrical in the front-rear direction and in the width direction. As shown inFIG.6, the protective member8comprises: a main unit setup part81located in the middle thereof; a front cover82located at a position spaced apart forwardly from the main unit setup part81; and a rear cover83located at a position spaced apart backwardly from the main unit setup part81.

As shown inFIG.2, a plurality of cushions91are fixed onto a bottom surface81aof the main unit setup part81. Each of the cushions91is made of a rubber material harder than a material forming the protective member8, and formed in a rod shape linearly extending along the front-rear direction. As shown inFIG.3, a lower edge of each of the cushions91fixed onto the bottom surface81acorresponds to the middle lower edge91awhich is located in the middle of the aircraft body11. Further, two illuminators92,93are fixed, respectively, onto outer surfaces of the front cover82and the rear cover83. Each of illuminator92,93is composed of a tape-shaped LED. The rear cover83is further provided with a wire connection part89to which a non-illustrated wire (e.g., piano wire).

As shown inFIG.6, the main unit setup part81, the front cover82and the rear cover83are connected together by four pairs of upper and lower bars84,85. Each of the pairs of upper and lower bars84,85are spaced apart from each other in the vertical direction. Thus, four openings881to884are formed between respective pairs of upper and lower bars84,85(i.e., in opposed sidewalls of the protective member8). Each of the forward lower edge85fand the backward lower edge85rcorresponds to a lower edge of a corresponding one of the lower bars85.

As shown inFIG.3, the forward lower edge85fis formed to linearly extend forwardly and upwardly from the side of the middle lower edge91a. On the other hand, the backward lower edge85ris formed to linearly extend backwardly and upwardly from the side of the middle lower edge91a. Specifically, each of the forward lower edge85fand the backward lower edge85ris formed to extend obliquely upwardly by an angle θ3 with respect to the middle lower edge91a, so that it is located above the middle lower edge91a. The angle θ3 is about 8°. It should be noted here that each of the forward lower edge85fand the backward lower edge85rneeds not necessarily be entirely located above the middle lower edge91a. For example, a rear end85faof the forward lower edge85fand a front end85raof the backward lower edge85rmay be located at the same height as that of the middle lower edge91a.

The forward lower edge85fis formed to occupy a sufficiently large region in the entirety of the lower edge11aof the aircraft body11. Specifically, the rear end85faof the forward lower edge85fis located backward of a rear end51b(52b) of the rotary wing51(52), in the front-rear direction. In order words, the rear end85faof the forward lower edge85fis spaced apart backwardly from the rear end51b(52b) of the rotary wing51(52) by a dimension Lfa. Further, a dimension Lf of the forward lower edge85fin the front-rear direction is greater than L/4. As mentioned above, L means a dimension of the entire lower edge11aof the aircraft body11of the aircraft1in the front-rear direction. Although the rear end of the rotary wing51(52) varies according to rotation of the rotary wing51(52), the term “rear end51a(52b)” here means the rear end of the rotary wing51(52) when it is located at the backwardmost position.

On the other hand, the front end85raof the backward lower edge85ris located forward of a front ends53b(54b) of the rotary wing53(54), in the front-rear direction. In order words, the front end85raof the backward lower edge85ris spaced apart forwardly from the front end53b(54b) of the rotary wing53(54) by a dimension Lrb. Although the front end of the rotary wing53(54) varies according to rotation of the rotary wing53(54), the term “front end53a(53b)” here means the front end of the rotary wing53(54) when it is located at the forwardmost position.

As shown inFIG.6, a plurality of fixing holes8ais formed in an upper end portion of the main unit setup part81of the protective member8, and a non-illustrated fastener is placed in each of the fixing holes8a. When the protective member8is attached to the main unit2, the main unit2is set up in the main unit setup part81, and a bottom surface and right and left surfaces of the main units2are covered by the main unit setup part81, as shown inFIGS.1and2. Further, the protective member8is disposed around the rotary wings51to54.

Further, when the protective member8is attached to the main unit2, a space surrounded by the main unit setup part81, the front cover82, the rear cover83, the upper bars84and the lower bars85is divided into a forward space80fand a backward space80r, as shown inFIG.1. The forward space80fhas an upper opening86fand a lower opening87f, and the backward space80rhas an upper opening86rand a lower opening87r. The rotary wings51,52are arranged in the forward space80f, and the rotary wings53,54are arranged in the backward space80r. The opening881is located on the right side of the forward space80f, and the opening882is located on the left side of the forward space80f. On the other hand, the opening883is located on the right side of the backward space80r, and the opening884is located on the left side of the backward space80r.

Further, when the protective member8is attached to the main unit2, the rotary wings52,54are arranged at positions overlapping the openings882,884, respectively, in side view, as shown inFIG.3. In other words, the opening882,884are arranged to open respective spaces on the left side of the rotary wings52,54to the outside. Although not illustrated, the rotary wings51,53are arranged at positions overlapping the openings881,883, respectively, in side view, and respective spaces on the right side of the rotary wings51,53are opened to the outside through the openings881,883, in a similar manner.

The rotary wings51,53are also arranged in a position corresponding to the forward lower edge85f. In other words, the rotary wings51,53are arranged within the range of the dimension Lf of the forward lower edge85f, as shown inFIG.3.

<Imaging of Inside of Sewage Pipe using Unmanned Aircraft>

Next, imaging of the inside of a sewage pipe using the unmanned aircraft1will be described. Upon being subjected to manipulation of an inspector, a non-illustrated remote controller transmits a manipulation signal corresponding to the manipulation to the outside. In the aircraft1, the wireless communication device receives the manipulation signal, and, based on the received manipulation signal, the control device transmits control signals, respectively, to the motors41to44.

The motors41to44rotate their output shafts at respective rotational speeds according to the control signals. Thus, the rotary wings51to54rotate about the rotation axes51ato54a, respectively. The rotary wings51,52draw air into the forward space80fthrough the upper opening86f, and simultaneously blow air out from the lower opening87f. The rotary wings53,54draw air into the backward space80rthrough the upper opening86r, and simultaneously blow air out from the lower opening87r.

As mentioned above, each of the rotational axes51ato54aof the rotary wings51to54is tilted backwardly with respect to the straight line N extending in the vertical direction by the angle θ1 (seeFIG.3), and further tilted toward the outside of the aircraft body11with respect to the straight line N by the angle θ2 (seeFIG.4). Thus, the rotary wings51to54blow air downwardly, backwardly, and outwardly as indicated by the arrowed lines A31, A32inFIG.3and the arrowed lines A41, A42inFIG.4.

As a result, a force oriented upwardly, forwardly, and inwardly (i.e., in a direction opposite to a direction in which the rotary wings51to73blow out air) is applied to the rotary wings51to54. This force becomes a lift force that lifts the aircraft body11upwardly, and a thrust force that drives the aircraft body11forwardly, to allow the aircraft1to fly. Thus, the aircraft1does not need to be equipped with a rotary wing mainly for generating a lift force and a rotary wing mainly for generating a thrust force, separately, so that it becomes possible to achieve a more compact configuration. The aircraft1moves along a direction in which the sewage pipe extends, while flying. One end of the non-illustrated wire is connected to the wire connection part89of the protective member8, and the wire is fed along with the movement of the aircraft1.

During flight of the aircraft1, the illuminators92,93emit light to illuminate an area of the sewage pipe around the aircraft body11, and each of the forward camera61, the backward camera63and the central camera65images the illuminated area of the sewage pipe. Videos of the sewage pipe imaged by the forward camera61and the backward camera63are converted to a signal and transmitted to the inspector through the wireless communication device, in real time. The inspector manipulates the remote controller while checking videos displayed on a display based on the signal.

During flight of the aircraft1, the protective member8protects the rotary wings51to54from interference with the sewage pipe. Further, the protective member8is formed of a material having a specific gravity less than water. Thus, even in a situation where the aircraft1lands on water, it generates a buoyant force to prevent submergence of the aircraft1.

After completion of the flight, the aircraft1stops the rotation of the rotary wings51to54, and lands on water inside the sewage pipe or on the inner bottom surface of the sewage pipe. The inspector pulls the wire to move the aircraft1toward the inspector and collect the aircraft1.

<Behavior of Unmanned Aircraft during Takeoff>

Next, with reference toFIGS.7to10, the behavior of the aircraft1during takeoff will be described.FIGS.7to10are explanatory diagrams showing the aircraft1during takeoff. For facilitating understanding of the explanation, only the protective member8is shown in cross-section taken along the line VII-VII inFIG.5.FIG.7shows a state in which the aircraft1remains stationary on an inner bottom surface B of a sewage pipe.FIG.8shows a state in which the aircraft1is tilted forwardly during takeoff, andFIG.9shows a state in which the aircraft1is more largely tilted forwardly during takeoff.FIG.10enlargedly shows the vicinity of a front end11bof the aircraft body11inFIG.8.

InFIG.7, the aircraft1is placed on the inner bottom surface B of the sewage pipe in the middle lower edge91a. As mentioned above, the middle lower edge91acorresponds to the lower edge of each of the cushions91fixed to the bottom surface81aof the protective member8(seeFIG.2). Thus, the cushions91come into contact with the inner bottom surface B of the sewage pipe, to suppress interference between the bottom surface81aof the protective member8and the inner bottom surface B and thus suppress abrasion of protective member8.

When the output shafts of the motors41to44start rotating for takeoff, air is blown downwardly, backwardly, and outwardly from the rotary wings51to54, as indicated by the arrowed lines A71, A72. Most of this air is blown onto the inner bottom surface B through the lower openings87f,87rof the protective member8.

In this process, due to changes in airflow caused by a curved shape of the inner bottom surface B of the sewage pipe, a lift force generated by the rotary wings51,52arranged closer to the front end11bof the aircraft body11can become less than a lift force generated by the rotary wings53,54located closer to a rear end11cof the aircraft body11. In this case, the aircraft body11can be tilted forwardly (i.e., the aircraft1takes a posture wherein it is tilted forwardly with respect to a posture where it remains stationary on a horizontal surface), as shown inFIG.8.

As mentioned above, in the aircraft1which is positioned such that the width direction thereof is coincident with the horizontal direction, the forward lower edge85fof the protective member8is formed to extend obliquely upwardly with respect to the middle lower edge91a, and is located above the middle lower edge91a(seeFIG.3). Thus, even when the aircraft body11is tilted forwardly as shown inFIG.8, a gap C is maintained between the forward lower edge85fand the inner bottom surface B. This prevents interference between the forward lower edge85fand the inner bottom surface B.

Here, when the aircraft body11is tilted forwardly, backward directivity of air blown out by the rotary wings51,52is increased, so that air flows between the bottom surface81aof the protective member8and the inner bottom surface B of the sewage pipe, as indicated by the arrowed line A101inFIG.10. As a result, when the pressure of air on the bottom surface81abecomes lower than the pressure of air on an upper surface2aof the main unit2, a force F10acts to press the aircraft body11against the inner bottom B. This force F10is likely to hinder stable takeoff of the aircraft1.

However, part of air blown out by the rotary wings51,52is discharged outside the protective member8through the opening881, as indicated by the arrowed line A102. Although not illustrated, the opening882also allows part of air blown out by the rotary wings51,52to be discharged outside the protective member8therethrough.

Further, part of air blown out by the rotary wings51,52is discharged outside the protective member8through the gap C between the forward lower edge85fand the inner bottom surface B. Specifically, the air is discharged from the gap C leftwardly and rightwardly with respect to the protective member8, as indicated by the arrowed line A103, and further discharged from gap C forwardly with respect to the protective member8, as indicated by the arrowed line A104.

This reduces an increase in the flow rate of air flowing as indicated by the arrowed line A101. As a result, a difference between the air pressure on the bottom surface81aand the air pressure on the upper surface2aof the main unit2is also reduced.

When the aircraft body11is more largely tilted forwardly on a sudden, the forward lower edge85fof the protective member8is brought into contact the inner bottom surface B of the sewage pipe, as shown inFIG.9. As mentioned above, the forward lower edge85fis formed to linearly extend forwardly and upwardly from the side of the middle lower edge91a. Thus, the forward lower edge85fis brought into contact with the inner bottom surface B over its entire length, and receives a force F9from the inner bottom surface B. This inhibits the aircraft body11from being further tilted forwardly.

Next, functions/effects based on the aircraft1will be described.

In the aircraft1configured as above, a lift force and a forward thrust force are simultaneously generated by the rotary wings51to54whose rotation axes51ato54aare tilted with respect to the vertical direction by a given angle. When the aircraft1takes off from a posture where the middle lower edge91aof the aircraft body11thereof is in contact with the inner bottom of the sewage pipe B, the aircraft body11is likely to be tilted forwardly. However, since the forward lower edge85fin the lower edge11aof the aircraft body11is located above the middle lower edge91a, it is possible to suppress interference between the forward lower edge85fand the inner bottom surface B, even when the aircraft body11is tilted forwardly.

In the above embodiment, the rear end85faof the forward lower edge85fis located backward of the rear end51b(52b) of the rotary wing51(52) in the front-rear direction. According to this feature, during takeoff of the aircraft1, part of air blown out by the rotary wings51,52can be efficiently discharged outside the protective member8through the gap C between the forward lower edge85fand the inner bottom surface B. This makes it possible to reduce an increase in the flow rate of air flowing between the bottom surface81aof the protective member8and the inner bottom surface B of the sewage pipe, while protecting the rotary wings51,52by the protective member8. It is also possible to reduce the difference between the air pressure on the bottom surface81aand the air pressure on the upper surface2aof the main unit2, and thus reduce the force F10based on this pressure difference. As a result, it becomes possible to further suppress interference between the forward lower edge85fand the inner bottom surface B, thereby allowing the aircraft1to stably taking off.

In the above embodiment, the forward lower edge85fis formed to linearly extend forwardly and upward from the middle lower edge91a.

According to this feature, when the aircraft body11is largely tilted forwardly on a sudden during takeoff of the aircraft1, the linearly-extending forward lower edge85fis brought into contact with the inner bottom surface B over a wide range thereof, so that it is possible to inhibit the aircraft body11from being further tilted forwardly. As a result, it becomes possible to allow the aircraft to more stably take off.

In the above embodiment, the protective member8is formed with the openings881,882which open, to outside, spaces lateral to the rotary wings51,52in the width direction.

According to this feature, when the aircraft body11is tilted forwardly during takeoff of the aircraft1, part of air blown out by the rotary wings51,52can be discharged outside the protective member8through the openings881,882. As a result, it becomes possible to reduce an increase in the flow rate of air flowing below the aircraft body11, and the resulting difference between air pressures above and below the aircraft body11. It also becomes possible to reduce the force F10acting to press the aircraft body11against the inner bottom surface B, and thus further suppress the interference between the forward lower edge85fof the aircraft body11and the inner bottom surface B, thereby allowing the aircraft1to more stably take off.

In the above embodiment, the rotary wings51,52are arranged in a position corresponding to the forward lower edge85fin the front-rear direction.

According to this feature, when the aircraft body11is tilted forwardly during takeoff of the aircraft1, part of air blown out by the rotary wings51,52can be discharged outside the protective member8through the gap C formed between the inner bottom surface B and the forward lower edge85f. As a result, it becomes possible to reduce an increase in the flow rate of air flowing below the aircraft body11, and the resulting difference between air pressures above and below the aircraft body11. It also becomes possible to reduce the force F10acting to press the aircraft body11against the inner bottom surface B, and thus further suppress the interference between the forward lower edge85fof the aircraft body11and the inner bottom surface B, thereby allowing the aircraft1to more stably take off.

The embodiment described above is intended to facilitate understanding of the present invention, but is not intended to be construed as limiting the present invention. The elements equipped in the embodiment, and arrangements, materials, conditions, shapes and sizes, etc., thereof are not limited to those exemplified therein, but it should be understood that various changes and modifications may be appropriately made therein.

INDUSTRIAL APPLICABILITY

The present invention can be used in a water supply pipe, a sewage pipe, a drainage pipe, a tunnel, a duct, a pipe shafts, a gas pipe, etc.

LIST OF REFERENCE SIGNS