JP7576750B2 - Propeller Guard - Google Patents

Description

This disclosure relates to a propeller guard that protects the propellers of an aircraft.

In recent years, aircraft that fly by rotating multiple propellers (e.g., drones, multicopters, etc.) have been used to inspect infrastructure structures.

Non-Patent Document 1 discloses a method of using an aircraft to inspect underground pipeline facilities. When an aircraft flies in such a space surrounded by walls, if the aircraft collides with an object such as a wall, the propeller may be damaged and the aircraft may crash. Therefore, a propeller guard to protect the propeller may be attached to the aircraft.

Non-Patent Document 2 proposes a propeller guard to protect the propeller when the aircraft collides with an object and to prevent the aircraft from losing its balance and becoming uncontrollable even if it collides with an object.

Yoshihiko Tanito and 1 other, "Development of drones capable of operating in enclosed spaces such as sewer pipes," 29th Trenchless Technology Research Symposium, 2.1, 2018. Tokuyuki Kanehira and 3 others, "Development of a bridge inspection system using drones," Kawada Technical Report, vol. 38, 2019

However, when an aircraft moves vertically in a space surrounded by walls, the propeller guard proposed in Non-Patent Document 2 has the risk that the guard frame will come into contact with protrusions, preventing the aircraft from moving, and that the aircraft will lose balance and fall.

Fig. 16 is a cross-sectional view of a manhole. As shown in Fig. 16, when a manhole cover installed on the ground is opened and closed, a cylindrical or rectangular structure 51 (e.g., a reinforced concrete pipe) extends vertically underground, and a step 52 is installed midway so that a worker can go down underground or go up to the ground.

Figure 17 is a diagram showing the problems that arise when an aircraft with a propeller guard moves through a space surrounded by walls, such as a manhole 50. As shown in Figure 17A, when an attempt is made to raise an aircraft 100 equipped with a propeller guard within a structure, the propeller guard may get caught on a protruding object such as a step 52 or a manhole cover receiving frame 53, preventing it from ascending. Similarly, as shown in Figure 17B, when the aircraft is descending, there is a problem with step 52.
In some cases, the propeller guard may get caught on a protruding object such as the manhole cover receiving frame 53, preventing it from moving.

In consideration of the above circumstances, an object of the present disclosure is to provide a propeller guard that can prevent a flying object moving vertically from stopping flight when it collides with an object.

A propeller guard according to one embodiment is configured to surround a propeller of an aircraft, and includes an upper frame provided on the top surface of the propeller guard, an intermediate frame provided below the upper frame, a lower frame provided below the intermediate frame, a base frame provided on the bottom surface of the propeller guard, a connecting frame connecting the upper frame, the intermediate frame, the lower frame, and the base frame, and a curved frame provided outside the connecting frame between the intermediate frame and the lower frame and configured to curve horizontally outward , wherein the outer edge of the intermediate frame is located outside the outer edge of the upper frame, and the outer edge of the lower frame is located outside the outer edge of the base frame.

According to the present disclosure, a propeller guard can be provided that can prevent a flying object moving vertically from stopping flight when it collides with an object.

1 is an example of a side view of an aircraft equipped with a propeller guard according to a first embodiment. FIG. 1 is an example of a side view of an aircraft equipped with a propeller guard according to a first embodiment. FIG. 1 is an example of a perspective view of an aircraft equipped with a propeller guard according to a first embodiment and a top view of a frame. FIG. 1 is a diagram showing an example in which the shape of the frame of the propeller guard according to the first embodiment is a regular square. FIG. 5 is a diagram showing an example in which the shape of the frame of the propeller guard according to the first embodiment is a regular octagon. FIG. 1 is a diagram showing an example in which the shape of the frame of the propeller guard according to the first embodiment is an arc shape relative to the circumference of the propeller. FIG. FIG. 2 is a diagram for explaining the conditions of the distance T0 shown in FIG. 1 . FIG. 2 is a diagram for explaining the conditions of the distance B0 shown in FIG. 1 . FIG. 2 is a diagram for explaining the conditions of the distance H0 shown in FIG. 1 . 1 is a diagram showing a state in which the flying object according to the first embodiment comes into contact with a wall surface while moving vertically upward. FIG. FIG. 11 is an example of a side view of an aircraft equipped with a propeller guard according to a second embodiment. 13 is a diagram showing a state in which an aircraft equipped with a propeller guard according to a second embodiment comes into contact with a wall surface while moving vertically upward. FIG. FIG. 13 is an example of a side view of an aircraft equipped with a propeller guard according to a third embodiment. FIG. 13 is an example of a side view of an aircraft equipped with a propeller guard according to a fourth embodiment. 13A and 13B are diagrams showing a state in which an aircraft equipped with a propeller guard according to a fourth embodiment comes into contact with a wall surface while moving vertically upward. FIG. 13 is an example of a side view of an aircraft equipped with a propeller guard according to a modified example of the fourth embodiment. FIG. 13 is an example of a side view of an aircraft equipped with a propeller guard according to a fifth embodiment. 13 is a diagram showing a state in which an aircraft equipped with a propeller guard according to a fifth embodiment comes into contact with a wall surface while moving vertically upward. FIG. 1 is an example of a cross-sectional view of a manhole. 1 is a diagram showing a problem with a conventional aircraft equipped with a propeller guard. 1 is a diagram showing a problem with a conventional aircraft equipped with a propeller guard.

Hereinafter, the embodiments will be described in detail with reference to the drawings. Note that each drawing is merely a schematic illustration to allow a sufficient understanding of the present invention. Therefore, the present invention is not limited to the illustrated examples. Also, for convenience of illustration, the scales in each drawing may differ from the actual scales, or may not match between drawings.

(First embodiment)
FIG. 1 is an example of a side view of an aircraft equipped with a propeller guard according to a first embodiment.
The aircraft with a propeller guard (hereinafter simply referred to as the "aircraft") 1 shown in FIG. 1 includes a propeller guard 10, an aircraft body 20, and one or more propellers 30. The aircraft 1 includes:
It flies by using one or more propellers with a vertical axis of rotation.

The propeller guard 10 is configured to surround the propeller 30 and protect the propeller 30. The propeller guard 10 is configured to protect not only the propeller 30 but also the aircraft body 20 as shown in FIG. 1A.
1B , the propeller guard 10 may be configured to surround the entire aircraft body 20, or may be configured to surround only a portion of the aircraft body 20 as shown in FIG. 1B. In the following drawings, the propeller guard 10 that surrounds the entire aircraft body 20 is shown.

In the example shown in Fig. 1, the propeller guard 10 includes a connecting frame 11, an upper frame 12, an intermediate frame 13, a lower frame 14, and a base frame 15. The number of connecting frames 11 and intermediate frames 13 is not limited to one, but can be determined arbitrarily. The number of connecting frames 11 and intermediate frames 13 affects the strength of the propeller guard when the aircraft 1 comes into contact with an object. Therefore, for example, when it is expected that the aircraft 1 will move at a high speed, the number of connecting frames 11 and the number of intermediate frames 13 may be increased to increase the strength of the propeller guard 10.

The upper frame 12 is a frame provided on the top surface of the propeller guard 10.

The intermediate frame 13 is a frame that is provided below the upper frame 12 and approximately parallel to the upper frame 12. The intermediate frame 13 is a frame that is provided below the upper frame 12 and the lower frame 14.
It is possible to provide the sensor at any height between these.

The lower frame 14 is a frame that is provided below the intermediate frame 13 and approximately parallel to the upper frame 12. A motor 31 for a propeller 30 is mounted on the lower frame 14.

The base frame 15 is installed below the lower frame 14 (at the bottom surface of the propeller guard 10) and approximately parallel to the upper frame 12, and is a frame that comes into contact with an object such as the ground when the aircraft 1 lands. The base frame 15 ensures stability when the aircraft 1 lands and protects the bottom of the aircraft 1. In order to maintain balance during flight, it is desirable to position the center points of the upper frame 12, intermediate frame 13, lower frame 14, and base frame 15 on the central axis of the aircraft body 20.

The connecting frame 11 is a frame that connects the upper frame 12, the intermediate frame 13, the lower frame 14, and the base frame 15.
and a first connecting portion 111 connecting the intermediate frame 13 to the lower frame 14, a second connecting portion 112 connecting the intermediate frame 13 to the lower frame 14, and a third connecting portion 113 connecting the lower frame 14 to the base frame 15.

Figure 2 shows a perspective view of the aircraft 1 shown in Figure 1A and a top view of each frame. The intermediate frame 13 and the lower frame 14 are annular in shape, but the upper frame 12 does not have to be annular in shape. The base frame 15 may also be annular in shape. In this specification, the "outer edge" of a frame means a line along the annular shape if the frame is annular, and means a line connecting the outer end points if the frame is not annular.

In the example shown in Fig. 2, the outer edges of the upper frame 12, the middle frame 13, and the lower frame 14 are regular octagonal, but as long as these frames can be positioned on the outer periphery of the propeller 30, they can be various shapes such as circular or any polygonal shape. In order to achieve balance during horizontal movement, it is desirable for the shape of the outer edges of the frames to be a point-symmetric structure. For example,
A circular shape or a shape that is line-symmetrical with respect to the front, back, left and right is desirable. In this specification, the term "horizontal direction" refers to a direction that is approximately perpendicular to the vertical direction.

For example, the shape of the outer edge of the frame is preferably a regular even-numbered polygon shape that is balanced in all directions, such as a regular square shape shown in Fig. 3A or a regular octagon shape shown in Fig. 3B. The shape of the outer edge of the frame may also be a shape that draws an arc around the circumference of the multiple propellers 30 (a shape that follows the outer edges of the multiple propellers 30), as shown in Fig. 3C. In this case, the diameter of the aircraft body 20 can be minimized.

The outer edge of the intermediate frame 13 is located outside the outer edge of the upper frame 12. That is, the area of the outer edge of the intermediate frame 13 is larger than the area of the outer edge of the upper frame 12. Moreover, the outer edge of the lower frame 14 is located outside the outer edge of the base frame 15. That is, the area of the outer edge of the lower frame 14 is larger than the area of the outer edge of the base frame 15.

Referring again to Fig. 1, the intermediate frame 13 and the lower frame 14 are the same size, but may be different sizes. Distance T0 is the distance between the outer edge of the upper frame 12 and the outer edge of the intermediate frame 13 and the outer edge of the lower frame 14 that is located on the outside. Distance B0 is the distance between the outer edge of the base frame 15 and the outer edge of the intermediate frame 13 and the outer edge of the lower frame 14 that is located on the outside. Distance H0 is the distance between the outer edge of the upper frame 12 and the outer edge of the base frame 15.

4 is a diagram for explaining the condition of the distance T0 shown in FIG. 1. The distance T0 is set to be greater than the maximum length S of a protruding object protruding in a direction perpendicular to the traveling direction in the flight space when the flying object 1 moves (ascends) vertically upward. When the protruding object is a step 52 installed on the wall surface of a structure 51, the maximum length S is generally standardized as 8 cm. By setting T0≧S, even if the propeller guard 10 comes into contact with the protruding object when the flying object 1 moves vertically upward, the propeller guard 10 slides in the D1 direction along the first connecting part 111 relative to the protruding object, so that the flying object 1 itself can proceed in the traveling direction without stopping.

5 is a diagram for explaining the condition of the distance B0 shown in FIG. 1. The distance B0 is set to be greater than the maximum length S of a protruding object protruding in a direction perpendicular to the traveling direction in the flight space when the flying object 1 moves (descends) vertically downward. When the protruding object is a step 52 installed on the wall surface of a structure 51, the maximum length S is generally standardized as 8 cm. By setting B0≧S, even if the propeller guard 10 comes into contact with the protruding object when the flying object 1 moves vertically downward, the propeller guard 10 slides in the D2 direction along the third connecting part 113 relative to the protruding object, so that the flying object 1 itself can proceed in the traveling direction without stopping.

6 is a diagram for explaining the conditions of the distance H0 shown in FIG. 1. The distance H0 is set so as to be greater than the maximum interval L1 between adjacent protruding objects such as steps 52 protruding in a direction perpendicular to the traveling direction in the flight space when the flying object 1 moves (ascends or descends) vertically upward or downward.
In this case, the maximum distance L1 is generally standardized as 20 cm. In the example shown in Fig. 6, the distance L1 of the step 52 is greater than the distance L2 between the manhole cover receiving frame 53 and the step 52. L2 is generally 16 cm or less. By making H0 ≥ L1, it is possible to prevent the flying object 1 from being caught between the protruding objects even if it shakes horizontally during flight.

Thus, according to this embodiment, when the aircraft 1 is used to inspect a space surrounded by walls, such as a manhole, if the propeller guard 10 collides with a protruding object such as a projection on the wall, it is possible to prevent the aircraft from stopping flight or losing balance and falling.

Next, let us consider contact between the propeller guard 10 and a wall surface. The flying object 1 may shake horizontally during flight and come into contact with an object such as a wall surface. If the structure 51 is made of reinforced concrete or the like, the surface is not uniformly smooth, and irregularities occur due to fine aggregate and the like. If the propeller guard 10 comes into contact with such an object that is not smooth, there is a risk that the propeller guard 10 will get caught. If the flying object 1 comes into contact with a wall surface while moving vertically downward, the horizontally outermost edge of the propeller guard 10 will become a fulcrum and the flying object 1 will move in the direction of travel (
As the aircraft 1 rotates in a downward direction, the aircraft 1 loses its balance, but the aircraft 1 is automatically controlled to return to horizontal, and the wind is blown out from the bottom of the propeller 30, so there is little chance of the aircraft sticking to the wall and losing its balance.

7 is a diagram showing a state in which the flying object 1 according to the first embodiment comes into contact with a wall surface while moving vertically upward. When the flying object 1 comes into contact with a wall surface while moving vertically upward, since the flying object 1 is in motion in the direction of travel (ascending direction), as shown in FIG. 7, the flying object 1 rotates in the R direction with the horizontally outermost edge P1 of the propeller guard 10 as a fulcrum, and there is a risk of losing flight balance and falling. Furthermore, since the flying object 1 sucks in wind from the top of the propeller 30 and expels it from the bottom in order to float the aircraft in the air, when the top of the flying object 1 approaches the wall surface, there is a risk that the flying object 1 will be stuck to the vertical wall surface due to the wind generated by the propeller 30. Therefore, in the following embodiment, a propeller guard that can also solve this problem will be described.

Second Embodiment
FIG. 8 is an example of a side view of an aircraft equipped with a propeller guard according to the second embodiment.
8 includes a propeller guard 10a, an aircraft body 20, and one or more propellers 30. The propeller guard 10a includes a connecting frame 11, an upper frame 12, an intermediate frame 13, a lower frame 14, and a base frame 15. The connecting frame 11 includes a first connecting portion 111 that connects the upper frame 12 and the intermediate frame 13,
It has a second connecting portion 112 that connects the intermediate frame 13 and the lower frame 14 , and a third connecting portion 113 that connects the lower frame 14 and the base frame 15 .

The propeller guard 10a differs from the propeller guard 10 according to the first embodiment in that the intermediate frame 13 and the lower frame 14 are substantially the same in size, and the second connecting portion 112 that connects the intermediate frame 13 and the lower frame 14 is configured to extend linearly in the vertical direction. Furthermore, the length of the second connecting portion 112 is configured to be a length that generates a reaction force equal to or greater than the rotational moment when the second connecting portion 112 comes into contact with an object.

9 is a diagram showing a state in which the flying object 2 comes into contact with a wall surface while moving vertically upward. When the second connecting part 112 comes into contact with the wall surface, the second connecting part 112 becomes a fulcrum, and a rotational force is applied to the flying object 2 in the direction R. However, since a reaction force F1 equal to or greater than the rotational moment is applied to the second connecting part 112, the flying object 2 does not rotate in the direction R. Therefore, according to this embodiment, even if the flying object 2 comes into contact with an object such as a wall surface, it is possible to prevent the flying object 2 from rotating and sticking to the wall surface.

Third Embodiment
Fig. 10 is an example of a side view of an aircraft equipped with a propeller guard according to the third embodiment. The aircraft 3 shown in Fig. 10 includes a propeller guard 10b, an aircraft body 20, and one or more propellers 30. The propeller guard 10b includes a connecting frame 11 and an upper frame 1
2, an intermediate frame 13, a lower frame 14, a base frame 15, and a curved frame 1
The connecting frame 11 includes a first connecting portion 111 that connects the upper frame 12 and the intermediate frame 13, a second connecting portion 112 that connects the intermediate frame 13 and the lower frame 14, and a third connecting portion 113 that connects the lower frame 14 and the base frame 15.
has.

The propeller guard 10b differs from the propeller guard 10 according to the first embodiment in that the propeller guard 10b further includes a curved frame 18. The curved frame 18 is
This frame is provided on the outside of the connecting frame 11 and has a structure (shape) that is curved horizontally outward (in the direction in which the aircraft body 20 does not exist when viewed from the propeller guard 10b).

The curved frame 18 is configured to be curved horizontally outwardly in a convex shape between the intermediate frame 13 and the lower frame 14, for example, as shown in Fig. 10. By providing the curved frame 18, it is possible to eliminate corners (edges) that occur at the connection point between the first connecting part 111 and the second connecting part 112 (the connection point between the connecting frame 11 and the intermediate frame 13) and the connection point between the second connecting part 112 and the third connecting part 113 (the connection point between the connecting frame 11 and the lower frame 14). Therefore, according to this embodiment, even if the flying object 3 comes into contact with an object such as a wall surface, it is possible to prevent the flying object 3 from being caught by the corners and to prevent the flying object 3 from rotating and losing flight balance.

(Fourth embodiment)
Fig. 11 is an example of a side view of an aircraft equipped with a propeller guard according to the fourth embodiment. The aircraft 4 shown in Fig. 11 includes a propeller guard 10c, an aircraft body 20, and one or more propellers 30. The propeller guard 10c includes a connecting frame 11 and an upper frame 1
The connecting frame 11 includes a first connecting portion 111 that connects the upper frame 12 and the intermediate frame 13, a second connecting portion 112 that connects the intermediate frame 13 and the lower frame 14, and a third connecting portion 113 that connects the lower frame 14 and the base frame 15.
3 and has.

The propeller guard 10c differs from the propeller guard 10 according to the first embodiment in that it further includes a first protruding frame 16. The first protruding frame 16 is a frame that protrudes between the upper frame 12 and the intermediate frame 13 and has a structure (shape) that protrudes horizontally outward. The outer edge of the first protruding frame 16 is located outside the outer edge of the upper frame 12, and is located inside the outer edge that is located outside of the outer edge of the intermediate frame 13 and the outer edge of the lower frame 14. In the example shown in FIG. 11, the first protruding frame 16 is connected to the upper frame 12.

The distance T0 is the distance between the outer edge of the upper frame 12, the outer edge of the intermediate frame 13, and the outer edge of the lower frame 1
T1 is the distance between the outer edge of the first protruding frame 1 and the outer edge of the second protruding frame 2.
6 and the outer edge that is located on the outside of the outer edge of the intermediate frame 13 and the outer edge of the lower frame 14. As explained in the first embodiment, T0 ≧ S, in the present embodiment, T1 ≧ S is similarly set. By setting T1 ≧ S, even if the propeller guard 10c comes into contact with a protruding object when the flying object 4 moves vertically upward, the propeller guard 10c slides along the first connecting part 111 relative to the protruding object, so that the flying object 4 itself can proceed in the direction of travel without stopping.

12 is a diagram showing a state in which the flying object 4 comes into contact with a wall surface when moving vertically upward. When the flying object 4 comes into contact with a wall surface when moving vertically upward, as shown in FIG. 12, the outer edge of the intermediate frame 13 or the lower frame 14 first becomes a fulcrum (first contact point) P1, and the flying object 4 rotates in the R direction. Next, the outer edge of the first protruding frame 16 becomes a second contact point P2, and a repulsive force F2 is generated when the flying object 4 comes into contact with the wall surface while moving vertically upward. Therefore, according to this embodiment, even if the flying object 4 comes into contact with the wall surface while moving vertically upward, the flying object 4 can be moved away from the wall surface, and it is possible to prevent the flying object 4 from being stuck to the wall surface and becoming unable to move.

Fig. 13 is an example of a side view of an aircraft equipped with a propeller guard according to a modification of the fourth embodiment. As shown in Fig. 13, the first protruding frame 16 may have an elastic member 161 such as a spring at the tip of the protrusion. Alternatively, the entire first protruding frame 16 may be made of an elastic member. That is, a part or the whole of the first protruding frame 16 may be made of an elastic member. By having the first protruding frame 16 have an elastic member, it is possible to increase the repulsive force when contacting the wall surface at the second contact point P2 in Fig. 12.

Fifth Embodiment
Fig. 14 is an example of a side view of an aircraft equipped with a propeller guard according to the fifth embodiment. The aircraft 5 shown in Fig. 14 includes a propeller guard 10d, an aircraft body 20, and one or more propellers 30. The propeller guard 10d includes a connecting frame 11 and an upper frame 1
The connecting frame 11 includes a first connecting portion 111 that connects the upper frame 12 and the intermediate frame 13, a second connecting portion 112 that connects the intermediate frame 13 and the lower frame 14, and a third connecting portion 113 that connects the lower frame 14 and the base frame 15.
3 and has.

The propeller guard 10d differs from the propeller guard 10 according to the first embodiment in that it further includes a second protruding frame 17. The second protruding frame 17 is a frame that is protruding between the upper frame 12 and the intermediate frame 13, protrudes outward in the horizontal direction, and has a curved structure (shape).
14, the second protruding frame 17 is located outside the outer edge of the second frame 2, and is located inside the outer edge of the outer edge of the intermediate frame 13 and the outer edge of the lower frame 14 that is located outside.
It is connected to the upper frame 12 .

The distance T0 is the distance between the outer edge of the upper frame 12, the outer edge of the intermediate frame 13, and the outer edge of the lower frame 1
4. Distance T2 is the distance between the outer edge of the second protruding frame 17 and the outer edge that is located on the outside among the outer edges of the intermediate frame 13 and the lower frame 14. Although it has been described that T0 ≧ S in the first embodiment, in this embodiment, T0 ≧ S is satisfied if at least T2 ≧ S is satisfied. In addition, since the second protruding frame 17 is curved, it is sufficient that T0 ≧ S is satisfied even if T2 ≧ S is not satisfied.

FIG. 15 is a diagram showing a state in which the flying object 5 comes into contact with a wall surface while moving vertically upward.
15, the protruding frame 17 is curved even when it comes into contact with an object such as the step 52, so that if T0≧S, the flying body 5 can slide in the D3 direction. Also, since it is sufficient that T0≧S, it is possible to lower the height H0 of the flying body 5 compared to the flying body 4 according to the fourth embodiment. By lowering the height H0 of the flying body 5, the ratio of the horizontal direction to the vertical direction of the flying body 5 increases, thereby improving the stability during flight.

Although the above-mentioned embodiment has been described as a representative example, it is obvious to those skilled in the art that many modifications and substitutions can be made within the spirit and scope of the present disclosure. Therefore, the present invention should not be interpreted as being limited by the above-mentioned embodiment, and the present invention can be modified without departing from the scope of the claims.
Various modifications and variations are possible. For example, the propeller guard 10b described in the third embodiment
However, the first protruding frame 16 described in the fourth embodiment or the second protruding frame 17 described in the fifth embodiment may be used.
The first protruding frame 16 of the fourth embodiment may have a curved shape like the second protruding frame 17 of the fifth embodiment.

REFERENCE SIGNS LIST 1, 2, 3, 4, 5 Aircraft 10, 10a, 10b, 10c, 10d Propeller guard 11 Connecting frame 12 Upper frame 13 Middle frame 14 Lower frame 15 Base frame 16 First protruding frame 17 Second protruding frame 18 Curved frame 20 Aircraft body 30 Propeller 31 Motor 50 Manhole 51 Structure 52 Step 53 Manhole cover receiving frame 111 First connecting part 112 Second connecting part 113 Third connecting part

Claims (9)

A propeller guard configured to surround a propeller of an aircraft,
An upper frame provided on the top surface of the propeller guard;
an intermediate frame provided below the upper frame;
a lower frame provided below the intermediate frame;
A base frame provided on the bottom surface of the propeller guard;
a connecting frame that connects the upper frame, the intermediate frame, the lower frame, and the base frame;
a curved frame provided outside the connecting frame between the intermediate frame and the lower frame and configured to curve outward in a horizontal direction ;
A propeller guard, wherein an outer edge of the intermediate frame is positioned outside an outer edge of the upper frame, and an outer edge of the lower frame is positioned outside an outer edge of the base frame. 2. The propeller guard of claim 1, wherein a vertical distance between an outer edge of the upper frame and an outer edge of the base frame is greater than 20 cm . The propeller guard according to claim 1 or 2, wherein the shape of the outer edge of the upper frame, the intermediate frame, or the lower frame is a circle, a regular even-numbered polygon, or a shape that follows the outer edge of the propeller. The difference between the distance from the center to the outer edge of the upper frame and the distance from the outer edge located outside the outer edge of the intermediate frame and the outer edge of the lower frame to the center of the outer edge is greater than 8 cm ;
4. The propeller guard according to claim 1, wherein a difference between a distance from a center of the base frame to an outer edge and a distance from an outer edge located outside one of the outer edges of the intermediate frame and the lower frame to a center of the outer edge is greater than 8 cm . The propeller guard according to any one of claims 1 to 4, wherein the connecting portion of the connecting frame that connects the intermediate frame and the lower frame is configured to extend linearly in the vertical direction. The propeller guard according to any one of claims 1 to 5, further comprising a protruding frame protruding between the upper frame and the intermediate frame. The propeller guard according to claim 6, wherein the outer edge of the protruding frame is located outside the outer edge of the upper frame and inside the outer edge of the outer edge of the intermediate frame and the outer edge of the lower frame that is located on the outside. The propeller guard according to claim 6 or 7, in which part or all of the protruding frame is an elastic member. The propeller guard according to any one of claims 6 to 8, wherein the protruding frame has an outwardly curved shape.

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