Manufacturing method for flight propeller

Abstract

To provide a flight propeller and a manufacturing method therefor in which: the bonding portion of the periphery of the hull of the propeller is made small or minimized; especially the leading edge has no bonding portion; the propeller has sufficient strength as a propeller, with weight reduced with a hollow portion provided inside; and the manufacturing cost is reduced.SOLUTION: A flight propeller is constituted of a main girder, ribs, and a hull. An interior covered with the hull is constituted of one main girder and a plurality of ribs connected to the main girder, with the other parts being hollow. The hull is formed of one or more sheets of carbon fiber reinforced plastic laminated together. A leading edge of the propeller has no bonding portions with each of the upper and lower hulls. Meanwhile, a part or whole of a trailing edge of the propeller has bonding portions with each of the upper and lower hulls.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a flight propeller and a method for manufacturing the same. [Background technology]

[0002] A propeller is a device used in airplanes and the like to convert the output from a power source into thrust through the rotation of the propeller to move the aircraft forward. Propellers are not limited to those used in aircraft powered by engines, but are also important devices in human-powered airplanes for sports and human-powered airplanes with auxiliary power. Furthermore, in recent years, various propellers have been developed for drones (unmanned aerial vehicles) and flying cars (amphibious vehicles).

[0003] In particular, small flying devices such as human-powered airplanes and drones require propellers that are lightweight in addition to structural and strength. Below, we will explain using the propeller of a human-powered airplane as an example. The power source of a human-powered airplane is a person, and the rotation of the pedal shaft obtained by the person stepping on the pedal is transmitted to the propeller by a power transmission mechanism, and the propeller rotates to fly.

[0004] For example, a competition called the "Birdman Contest Championship," sponsored by a commercial broadcasting station, is held every year to compete in the flight distance and flight time of human-powered airplanes, and improvements to the aircraft and propellers are a hot topic every year. For the propellers of human-powered airplanes, it is important to design a propeller to match the aircraft and make it as strong and light as possible.

[0005] Generally, the propellers of human-powered aircraft are made by using wood or foamed resin as a core material and attaching CFRP, which has a carbon fiber base, or GFRP, which has a glass fiber base, to the surface. However, there is a problem with this type of propeller in that it is difficult to reduce its weight because of the core material inside.

[0006] Therefore, a method of manufacturing a propeller has been developed in which as much hollow space as possible is provided inside the propeller to reduce its weight. For example, the following Non-Patent Documents 1 and 2 describe the structure and manufacturing method of a propeller for a human-powered aircraft. In these methods, the outer skin of the designed propeller is divided into two outer skins, an upper and lower skin, and each is manufactured separately.

[0007] Specifically, 3D data is created for two molds for the two outer skins on the top and bottom. Next, materials such as chemical wood are cut on a CNC lathe to create the molds for the top and bottom skins. The surface of each mold is given a release treatment, and balsa wood is covered and CFRP prepreg sheets are laminated. In this state, it is vacuumed and then heated in an oven to harden the resin in the prepreg sheets. This completes the two outer skins on the top and bottom.

[0008] Next, the main spars and ribs are placed and fixed inside the skin, and the periphery of the top and bottom skins are fixed with epoxy adhesives. The surface of the propeller with the top and bottom skins fixed is then painted to complete the propeller for human-powered aircraft. Even in this state, the propeller skin is strong due to the laminated CFRP and balsa wood, and has a hollow interior to reduce weight. However, this method requires the production of two molds, one for the top and one for the bottom, which increases the production costs.

[0009] Furthermore, because the outer skin is made up of two pieces, the top and bottom, and the adhesive between them is located around the entire circumference of the propeller, there was a problem that the adhesive at the leading edge of the outer skin, which is directly exposed to air resistance during flight, would peel off during flight. To prevent this peeling, the adhesive at the leading edge could be increased to reduce the problem, but it was not possible to eliminate the peeling at the leading edge. Also, there was a problem that excessive adhesive at the leading edge would increase the weight of the propeller. [Prior art documents] [Non-patent literature]

[0010] [Non-Patent Document 1] Daiichi Institute of Technology Research Report No. 22 (2010) pp.31-39 [Non-Patent Document 2] Dobonkai Human Powered Aircraft Production Diary (2011 / 08 / 09) (URL:http: / / dobonkai.blog99.fc2.com / blog-entry-77.html) Summary of the Invention [Problem to be solved by the invention]

[0011] Therefore, the present invention addresses the above-mentioned problems by minimizing or reducing the adhesive area around the periphery of the propeller skin, particularly at the leading edge, and aims to provide a flight propeller and a manufacturing method thereof that has sufficient strength as a propeller, is lightweight due to the provision of a hollow area inside, and has low manufacturing costs. [Means for solving the problem]

[0012] In order to solve the above problems, the inventors conducted extensive research and discovered that the above objects could be achieved by using a propeller-shaped core, not dividing the outer skin into two pieces, an upper and lower, and not providing an adhesive joint at the leading edge, and removing the core when the outer skin is completed, or by melting and removing the core with a minimum of openings, which led to the completion of the present invention.

[0013] That is, the flight propeller according to the present invention, according to claim 1, A propeller consisting of a main spar, a rib, and a skin, The inside covered with the outer skin is composed of one main girder and a plurality of ribs connected thereto, and the other parts are hollow, The outer skin is made of carbon fiber reinforced plastic in one or more laminated sheets, and is characterized in that the leading edge of the propeller does not have an adhesion area between the upper skin and the lower skin, and part or all of the trailing edge of the propeller has an adhesion area between the upper skin and the lower skin.

[0014] According to claim 2, the method for manufacturing a flight propeller according to the present invention further comprises the steps of: Producing a core having a designed propeller shape; applying a release sheet or a release agent to a part or all of a portion of the core corresponding to the trailing edge of the propeller; A step of attaching one or more laminated carbon fiber reinforced plastic prepreg sheets to the upper and lower surfaces of the core to which the release sheet or release agent has been applied; A step of hardening the matrix resin of the prepreg sheet to form a propeller-shaped outer skin; removing the core from inside the outer skin made of the carbon fiber reinforced plastic molded into a propeller shape through a portion where the release sheet or release agent is applied and where the upper outer skin and the lower outer skin are not bonded; a step of inserting a propeller skeleton consisting of one main girder and a plurality of ribs connected thereto into the inside of the skin from which the core has been removed, via a portion where the upper skin and the lower skin are not bonded; a step of bonding an unbonded portion of the upper surface skin and the lower surface skin of the skin into which the propeller skeleton is inserted; The present invention is characterized by having the following.

[0015] According to claim 3, the present invention provides a method for manufacturing the flight propeller according to claim 2, In the step of removing the core from inside the outer shell, The core is removed in the propeller shape or after being divided.

[0016] According to claim 4, the present invention provides a method for manufacturing the flight propeller according to claim 2, In the step of removing the core from inside the outer shell, The core is removed in a dissolved or swollen state in a solvent.

[0017] According to claim 5, the present invention provides a method for manufacturing the flight propeller according to claim 4, The core is made of a water-soluble resin, the solvent is water, The core is removed from inside the shell in a dissolved or swollen state with water.

[0018] According to claim 6, the flight propeller of the present invention comprises: A propeller consisting of a main spar, a rib, and a skin, The inside covered with the outer skin is composed of one main girder and a plurality of ribs connected thereto, and the other parts are hollow, The outer skin is made of one or more laminated carbon fiber reinforced plastic sheets, and is characterized in that there are no adhesion sites between the upper and lower outer skins at the leading and trailing edges of the propeller.

[0019] According to claim 7, the method for manufacturing a flight propeller according to the present invention comprises the steps of: A step of preparing a propeller skeleton including one main spar and a plurality of ribs connected thereto; producing a propeller-shaped core containing the propeller skeleton therein using a solvent-soluble resin; a step of attaching one or more laminated carbon fiber reinforced plastic prepreg sheets to both upper and lower surfaces of the core; A step of hardening the matrix resin of the prepreg sheet to form a propeller-shaped outer skin; a step of opening a portion of the outer shell and removing the core in a state where the core is dissolved or swollen with a solvent; repairing the open portion of the shell from which the core was removed; The present invention is characterized by having the following.

[0020] According to claim 8, the present invention provides a method for manufacturing the flight propeller according to claim 7, The core is made of a resin that is soluble in an organic solvent, and the solvent is the organic solvent, The core is removed from inside the shell in a state where it is dissolved or swollen with the organic solvent.

[0021] According to claim 9, the present invention provides a method for manufacturing the flight propeller according to claim 7, The core is made of a water-soluble resin, the solvent is water, The core is removed from inside the shell in a dissolved or swollen state with water. Effect of the Invention

[0022] According to the above configuration, the flight propeller is composed of a main spar, a rib, and an outer skin. The interior covered by the outer skin is composed of one main spar and multiple ribs connected to it, and the remaining portion is hollow. The outer skin is made of carbon fiber reinforced plastic in which one or multiple sheets are laminated. The leading edge of the propeller does not have an adhesion area between the upper skin and the lower skin. Meanwhile, a part or all of the trailing edge of the propeller has an adhesion area between the upper skin and the lower skin.

[0023] This makes it possible to provide a flight propeller that has a small adhesive area around the periphery of the propeller skin, with no adhesive area at the leading edge in particular, that has sufficient strength as a propeller, is lightweight due to the provision of a hollow area inside, and has low manufacturing costs.

[0024] Also, according to the above configuration, the manufacturing method for a flight propeller has a first step of producing a core having a designed propeller shape. The next step is to apply a release sheet or a release agent to a part or all of the portion of the core that corresponds to the trailing edge of the propeller. The next step is to attach one or more laminated carbon fiber reinforced plastic prepreg sheets to both the top and bottom surfaces of the core to which the release sheet or release agent has been applied. The next step is to harden the matrix resin of the prepreg sheets to form an outer skin in the shape of a propeller.

[0025] In the next step, the core is removed from inside the skin made of carbon fiber reinforced plastic molded into a propeller shape, through a portion where a release sheet has been applied and where the upper and lower skins are not bonded. In the next step, a propeller skeleton consisting of one main girder and multiple ribs connected to it is inserted into the skin from which the core has been removed, through the portion where the upper and lower skins are not bonded. In the next step, the portion of the skin into which the propeller skeleton has been inserted, where the upper and lower skins are not bonded, is bonded.

[0026] This makes it possible to provide a manufacturing method for an flight propeller that has small adhesive joints around the periphery of the propeller skin, particularly no adhesive joints at the leading edge, has sufficient strength as a propeller, is lightweight due to the provision of a hollow section inside, and has reduced manufacturing costs.

[0027] Furthermore, according to the above configuration, in the step of removing the core from inside the outer shell, the core may be removed in the propeller shape or divided. The core may also be removed in a state dissolved or swollen with a solvent. In this case, the core may be made of a water-soluble resin and removed in a state dissolved or swollen with water. By doing so, the above-mentioned action and effect can be concretely and effectively exhibited.

[0028] Also, according to the above configuration, the flight propeller is composed of a main spar, a rib, and an outer skin. The inside covered by the outer skin is composed of one main spar and multiple ribs connected to it, and the other parts are hollow. The outer skin is made of carbon fiber reinforced plastic, with one or multiple sheets laminated. The leading edge and trailing edge of the propeller do not have any bonding area between the upper skin and the lower skin.

[0029] This makes it possible to provide an aircraft propeller that has sufficient strength as a propeller by minimizing the adhesive around the periphery of the propeller skin, while having a hollow interior to reduce weight and keep manufacturing costs down.

[0030] Also, according to the above configuration, the manufacturing method for a flight propeller includes, in the first step, preparing a propeller skeleton consisting of one main spar and a number of ribs connected thereto. In the next step, using a solvent-soluble resin, a core having a propeller shape that contains the propeller skeleton inside is produced. In the next step, one or more laminated carbon fiber reinforced plastic prepreg sheets are attached to both the top and bottom surfaces of the core. In the next step, the matrix resin of the prepreg sheets is hardened to form a propeller-shaped outer skin. In the next step, a part of the outer skin is opened, and the core is removed in a state dissolved or swollen with a solvent. In the next step, the opened portion of the outer skin from which the core was removed is repaired.

[0031] This makes it possible to provide a manufacturing method for an flight propeller that minimizes the adhesive around the peripheral edge of the propeller skin, has sufficient strength as a propeller, is lightweight due to the provision of a hollow section inside, and keeps manufacturing costs down.

[0032] According to the above configuration, the core may be made of a resin soluble in an organic solvent and removed from inside the outer shell in a state where it is dissolved or swollen with the organic solvent. Also, the core may be made of a water-soluble resin and removed from inside the outer shell in a state where it is dissolved or swollen with water. By these means, the above-mentioned operational effects can be concretely and effectively exhibited. [Brief description of the drawings]

[0033] [Figure 1] FIG. 2 is a schematic plan view showing a core used in the first embodiment. [Diagram 2] FIG. 2 is a schematic plan view showing the state in which a release sheet is attached to the rear edge of the core of FIG. 1. [Diagram 3] FIG. 3 is a schematic plan view showing a state in which a CFRP or CFRTP prepreg sheet is attached to the surface of the core of FIG. 2. [Figure 4] FIG. 4 is a schematic plan view showing a state in which the entire surface of the core in FIG. 3 is covered with a CFRP or CFRTP prepreg sheet. [Diagram 5]FIG. 5 is a schematic plan view showing the state in which the core in FIG. 4 is removed from inside the outer shell of the propeller after the matrix resin of CFRP or CFRTP attached to the entire surface of the core is hardened. [Figure 6] FIG. 6 is a schematic plan view showing a state in which a propeller skeleton is inserted into the inside of the outer skin of the propeller from which the core in FIG. 5 has been removed. [Figure 7] FIG. 7 is a schematic plan view showing the propeller of the first embodiment completed by inserting a propeller skeleton inside the outer skin of the propeller in FIG. 6 and bonding an upper skin and a lower skin together. [Figure 8] FIG. 11 is a schematic plan view showing a core used in the second embodiment. [Figure 9] FIG. 9 is a schematic plan view showing a state in which the entire surface of the core in FIG. 8 is covered with a CFRP or CFRTP prepreg sheet. [Figure 10] FIG. 10 is a schematic plan view showing a state in which the core in FIG. 9 is dissolved and removed from inside the outer shell of the propeller after the CFRP or CFRTP matrix resin attached to the entire surface of the core is hardened. [Figure 11] 11 is a schematic plan view showing a propeller according to a second embodiment completed after the core has been removed from inside the outer shell of the propeller in FIG. 10 and the removed open portion has been repaired. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] Here, we will specifically explain the flight propeller (hereinafter simply referred to as "propeller") according to the present invention. The use of the propeller according to the present invention is not limited to human-powered airplanes, but can also be used in human-powered helicopters, human-powered airplanes with auxiliary power, drones (unmanned aerial vehicles), flying cars (amphibious vehicles), model airplanes and helicopters, and various other flying devices.

[0035] Furthermore, the propeller according to the present invention is characterized by its light weight so that it can be used with flying devices with low output power sources, such as human-powered aircraft. In other words, even if the internal hollow portion is made large to reduce weight, the design strength of the propeller can be maintained. Specifically, the interior covered by the propeller skin is composed of only one main girder and the necessary number of ribs to maintain strength. Note that a minimum number of other structures (such as auxiliary girder and auxiliary ribs) may be added as necessary.

[0036] The outer skin is made of one or more laminated carbon fiber reinforced plastic sheets to reduce weight, and may be made of a minimum of other laminates (such as glass fiber GFRP) if necessary.

[0037] In the present invention, carbon fiber reinforced plastics includes both CFRP (Carbon Fiber Reinforced Plastics) in the narrow sense, which uses a thermosetting resin as the matrix resin, and CFRTP (Carbon Fiber Reinforced Thermo Plastics), which uses a thermoplastic resin as the matrix resin.

[0038] Furthermore, according to the first embodiment, the propeller of the present invention does not have an adhesion area between the upper and lower skins at the leading edge of the propeller, but has an adhesion area between the upper and lower skins at part or all of the trailing edge of the propeller. This adhesion area at the trailing edge of the propeller is an open area for removing a propeller-shaped mold (called a "core" in this invention) used in the manufacturing stage of the propeller. This open area becomes the area where the upper and lower skins are adhered after the core is removed (details will be described later).

[0039] On the other hand, according to the second embodiment, the leading and trailing edges of the propeller do not have any adhesion areas between the upper and lower skins. This is because in the second embodiment, the propeller-shaped mold (core) used in the propeller manufacturing stage is mainly dissolved and extracted (details will be described later). Note that the term "core" originally refers to a sand mold that is fitted into a casting mold as the part that corresponds to the cavity when manufacturing a casting that has a cavity inside. In this invention, the term "core" is used to refer to the internal mold that is fitted into a propeller when manufacturing the propeller.

[0040] In this way, the propeller according to the present invention uses a core in the manufacturing stage, and by removing the core after use, the inside of the propeller can be made hollow, making it lighter. Also, by not having an adhesive site at the leading edge, which receives the most wind pressure during flight, damage during flight can be prevented and the design strength can be maintained. Furthermore, by using a core in the manufacturing stage, two dies for the two outer skins on the top and bottom surfaces, as in the above-mentioned conventional technology, are not used. This not only improves the strength of the propeller, but also reduces manufacturing costs.

[0041] Next, a method for manufacturing a propeller according to the present invention will be described with reference to first and second embodiments. In the present invention, as described above, a mold (core) in the shape of a propeller is used.

[0042] First Embodiment In the first embodiment, a core is removed from inside a shell made of carbon fiber reinforced plastic molded into a propeller shape, and a propeller skeleton made of one main beam and multiple ribs is inserted. Each step of the first embodiment is specifically described below.

[0043] (1) Creation of a propeller-shaped core A propeller has a complex three-dimensional shape in order to obtain thrust in a flow that combines the speed of the rotational motion of the propeller itself and the forward speed of the aircraft. In the present invention, the design method is not limited, and a mold (core) in the shape of a propeller designed by any method is used.

[0044] First, a core is produced based on the design data of the propeller. Fig. 1 is a schematic plan view showing a core 10 used in the first embodiment. In Fig. 1, one edge of the core 10 corresponds to the propeller leading edge that receives a large wind pressure during flight, and is designated as a core leading edge 11. The other edge of the core 10 corresponds to the propeller trailing edge through which air flows through the propeller, and is designated as a core trailing edge 12. Note that in Fig. 1, the three-dimensional shape of each part of the propeller, such as the inclination and thickness, is omitted.

[0045] The material for making the core 10 is not particularly limited, and may be any material, such as wood, resin, or foam material such as polystyrene foam. Based on the design data of the propeller, a block of such material may be cut using a CNC lathe or the like. Alternatively, various resins may be ejected using a 3D printer to make the core 10 in a three-dimensional shape.

[0046] (2) Apply a release sheet to part or all of the part of the core that corresponds to the trailing edge of the propeller (rear edge of the core). As will be described later, a CFRP or CFRTP prepreg sheet is used as the material for the propeller skin. Therefore, a release sheet 13 that does not adhere to the matrix resin is attached to the core trailing edge 12. Figure 2 is a schematic plan view showing the state in which the release sheet 13 has been attached to the core trailing edge 12 of the core 10. This is to prevent the upper and lower skins from adhering to each other at the area of ​​this release sheet 13 when the propeller skin is molded.

[0047] It is preferable to use a material to which the matrix resin of CFRP or CFRTP cannot adhere, such as a film or tape of silicone rubber, polypropylene, polyethylene, polyacetal, fluororesin, etc., for the release sheet 13. Also, to prevent the matrix resin of the prepreg sheet from adhering to areas not covered with the release sheet 13, a release sheet may be affixed to the entire surface of the core 10, or a fluorine-based or silicone-based release agent may be applied.

[0048] (3) Carbon fiber reinforced plastic prepreg sheets are attached to the top and bottom of the core. A release sheet 13 is attached to the core trailing edge 12, and a release sheet is attached or a release agent is applied to the entire surface of the core 10, and a CFRP or CFRTP prepreg sheet is attached to the entire surface of the core 10. Figure 3 is a schematic plan view showing the state in which a CFRP or CFRTP prepreg sheet 14 is attached to the surface of the core 10. There are no particular limitations on the combination of carbon fiber and matrix resin that make up the prepreg sheet 14.

[0049] The carbon fiber may be a UD prepreg sheet in which a large number of carbon fiber bundles are aligned in one direction to form a sheet, or a woven prepreg sheet made of woven carbon fiber. For example, 3K plain weave carbon may be used as the woven carbon fiber. For example, epoxy resin, phenol resin, unsaturated polyester resin, vinyl ester resin, etc. may be used as the matrix resin (thermosetting resin) of the CFRP. On the other hand, for example, polyamide, polycarbonate, polybutylene terephthalate, polyphenylene sulfide, polyether ether ketone, etc. may be used as the matrix resin (thermoplastic resin) of the CFRTP.

[0050] In Fig. 3, when the prepreg sheets 14 are applied, they are applied to the entire upper and lower surfaces of the core 10 before the matrix resin of the CFRP is cured or in a melted state. In the present invention, the prepreg sheets 14 are applied to the upper and lower surfaces so as to straddle the leading edge 11 of the core. On the other hand, the prepreg sheets 14 are applied to the upper and lower surfaces without straddling the trailing edge 12 of the core (see Fig. 3). In Fig. 3, multiple prepreg sheets 14 are laminated, but the present invention is not limited to this, and one large prepreg sheet may be applied to the entire upper and lower surfaces of the core 10.

[0051] It is preferable that the prepreg sheets 14 are attached to required locations in consideration of the propeller structure, and are attached by changing the orientation direction of the carbon fibers, etc. By doing so, the completed propeller maintains the designed strength, does not have an adhesion site between the upper and lower skins at the leading edge of the propeller, and can have an adhesion site between the upper and lower skins formed at part or all of the trailing edge of the propeller.

[0052] (4) The matrix resin of the prepreg sheet is hardened to form the propeller-shaped outer skin. Fig. 4 is a schematic plan view showing the entire surface of the core covered with a CFRP or CFRTP prepreg sheet. In Fig. 4, the entire surface of the core 10 is covered with a prepreg sheet 14, and a propeller-shaped outer skin 20 is formed before the resin hardens.

[0053] One edge of the skin 20 (the portion covering the core leading edge 11) corresponds to the propeller leading edge where the propeller receives large wind pressure during flight, and is referred to as the skin leading edge 21. The other edge of the skin 20 (the portion covering the core trailing edge 12) corresponds to the propeller trailing edge where air flows through the propeller, and is referred to as the skin trailing edge 22. At the skin trailing edge 22, the upper skin 23 (front surface in the figure) and the lower skin 24 (reverse surface in the figure) of the skin 20 are not bonded with the release sheet 13 sandwiched therebetween.

[0054] In this state, the matrix resin of the CFRP has not yet hardened. Therefore, the outer shell 20 holding the core 10 therein is sealed, and the inside is evacuated and degassed. In this way, the outer shell 20 is placed in a heating furnace while conforming to the shape of the core 10, and the curing reaction of the matrix resin (thermosetting resin) is completed. On the other hand, in the case of CFRTP, before the matrix resin (thermoplastic resin) hardens, the outer shell 20 holding the core 10 therein is sealed, and the inside is evacuated and degassed. In this way, the outer shell 20 is cooled while conforming to the shape of the core 10, and the thermoplastic resin is hardened.

[0055] Thus, in the present invention, "hardening" includes both the reaction and hardening of the thermosetting resin of the CFRP, as well as the hardening of the thermoplastic resin of the CFRTP from a high-temperature softened state to a low-temperature crystalline state, etc. Through these operations, the outer skin 20 can fix the designed propeller shape.

[0056] (5) The core is removed from inside the outer shell, which has been molded into a propeller shape. Figure 5 is a schematic plan view showing the state in which core 10 is removed from inside the outer skin 20 of a propeller after the CFRP or CFRTP matrix resin affixed to the entire surface of core 10 has been cured. In Figure 5, core 10 can be removed from the portion of the outer skin trailing edge 22 where the upper outer skin 23 and the lower outer skin 24 are not bonded. The outer skin 20 from which core 10 has been removed has the shape of a propeller and is hollow inside.

[0057] In FIG. 5, the core 10 can be removed while still in the shape of a propeller. Therefore, the removed core 10 can be reused to manufacture propellers. This can further reduce the manufacturing costs of the propeller. On the other hand, if the core 10 is divided into a plurality of pieces inside the outer skin 20, it becomes easier to remove it. In this case, the release sheet 13 is shortened to narrow the non-bonded area between the upper skin 23 and the lower skin 24 of the skin trailing edge 22. This can reduce the bonded area at the trailing edge of the propeller, further improving the strength of the propeller.

[0058] On the other hand, when the core 10 is made of a resin that dissolves in a solvent, preferably a water-soluble resin, the resin can be taken out in a dissolved or swollen state inside the shell 20. When making the core 10 from a water-soluble resin, it may be made using a 3D printer. The water-soluble resin is not limited to a resin that dissolves completely, but may be one that swells in water. Examples include polyvinyl alcohol (PVA), polyacrylamide (PAA), carboxymethyl cellulose (CMC), butenediol vinyl alcohol copolymer (PVOH), etc.

[0059] (6) The main spars and ribs are inserted into the outer skin formed into the shape of a propeller. Next, to ensure the strength of the propeller, a propeller skeleton consisting of one main girder and multiple ribs connected to it is inserted inside the hollow outer skin 20. Fig. 6 is a schematic plan view showing the state in which the propeller skeleton is inserted inside the outer skin 20 from which the core 10 has been removed. Multiple ribs 32 are fixed to the main girder 31, which can maintain and reinforce the propeller shape. It is preferable to use CFRP rods or the like for the main girder 31 in consideration of strength and weight reduction. It is also preferable to use CFRP boards or the like for the ribs 32.

[0060] (7) Glue the upper and lower outer skins together at the untouched portions. 7 is a schematic plan view showing a completed propeller 40 in which a propeller skeleton is inserted inside the outer skin 20 and the upper skin 23 and the lower skin 24 are bonded. The upper and lower surfaces of this propeller 40 are covered with the outer skin 20, and the propeller leading edge 41 does not have a bonding area between the upper skin 23 and the lower skin 24. On the other hand, the propeller trailing edge 42 has a bonding area between the upper skin 23 and the lower skin 24. The inside of the outer skin 20 is composed of only one main girder 31 and multiple ribs 32 connected thereto, and the rest of the interior is hollow. One end of the main girder 31 protrudes outside the outer skin 20, and a connection terminal 33 is provided at this part and connected to a power transmission mechanism that transmits the rotation of the pedal shaft.

[0061] Next, the propeller according to the first embodiment will be described with reference to examples. Note that the present invention is not limited to the examples described below. EXAMPLES

[0062] In this Example 1, the core is produced by a 3D printer, and the outer skin of the propeller is produced by CFRP consisting of carbon fiber fabric and thermosetting resin as a matrix resin. The following is a detailed description.

[0063] First, a core 10 was produced using a 3D printer based on the design data of the propeller (see FIG. 1). In this Example 1, the core was produced from ABS resin (a copolymer of acrylonitrile, butadiene, and styrene). Next, a release sheet 13 was applied to the core trailing edge 12 of the core 10. In this Example 1, OPP tape (an adhesive tape made of a stretched polypropylene film coated with an adhesive) was used (see FIG. 2). In addition, OPP tape was also applied to the entire surface of the core 10 where the release sheet 13 was not applied.

[0064] Next, a CFRP prepreg sheet 14 was attached to the entire surface of the core 10. In this Example 1, only the prepreg sheet 14 was used, which was made by impregnating a carbon fiber fabric (3K plain weave carbon) with epoxy resin, which is a thermosetting resin. As described above, the prepreg sheet 14 was attached to the top and bottom surfaces of the core 10 so as to straddle the core leading edge 11. On the other hand, the prepreg sheet 14 was attached to the top and bottom surfaces without straddling the core trailing edge 12 (see FIG. 3). In order to reinforce the strength of the propeller, the prepreg sheet 14 was laminated in the necessary parts, and the fiber direction was changed as necessary. In this way, the prepreg sheet 14 was attached to the surface of the core 10, and a propeller-shaped outer skin was formed (see FIG. 4).

[0065] Next, the thermosetting resin of the CFRP was reacted and cured, and the skin 20 with the designed propeller shape was fixed. First, the core 10 with the prepreg sheet 14 attached was placed in a bag, sealed, and the inside was evacuated. Next, the core 10 in this state was placed in a heating furnace, and the temperature was raised to 80°C to complete the curing reaction of the epoxy resin of the skin 20. In this state, the skin 20 was fixed in the designed propeller shape, and the skin trailing edge 22 was in an open state.

[0066] Next, the core 10 was removed from the inside of the skin 20 fixed in a propeller shape through the opened skin trailing edge 22 (see FIG. 5). Next, a propeller skeleton consisting of a main girder 31 and ribs 32 was inserted into the hollow inside of the skin 20 through the opened skin trailing edge 22. In this Example 1, a CFRP rod was used for the main girder 31, and a CFRP board was used for the rib 32. The main girder 31 and the rib 32 were inserted into the inside of the skin 20 as a propeller skeleton in a pre-assembled state, and the outer edge of the rib 32 was adhesively fixed inside the skin 20 (see FIG. 6).

[0067] Next, the open skin trailing edge 22 of the skin 20 into which the propeller skeleton was inserted was sealed. In this embodiment 1, the upper skin 23 and the lower skin 24 were bonded with an epoxy adhesive. In this way, the propeller 40 of this embodiment 1 was completed (see FIG. 7). A connection terminal 33 of the main girder 31 is provided at one end of the propeller 40, and is connected to a power transmission mechanism that transmits the rotation of the pedal shaft. EXAMPLES

[0068] In this Example 2, a core similar to that in the above Example 1 is created by a 3D printer, and the outer skin of the propeller is made of CFRTP, which is composed of carbon fiber fabric and thermoplastic resin as a matrix resin. The details will be explained below.

[0069] First, a core 10 was produced using a 3D printer based on the design data of the propeller. In this Example 2, the core was produced from the same ABS resin as in Example 1 above. Next, a release sheet 13 was applied to the core trailing edge 12 of the core 10 using the same OPP tape as in Example 1 above. In addition, OPP tape was also applied to the entire surface of the core 10 where the release sheet 13 was not applied.

[0070] Next, a CFRTP prepreg sheet 14 was attached to the entire surface of the core 10. In this Example 2, only a prepreg sheet 14 was used, which was made by impregnating a carbon fiber fabric (3K plain weave carbon) similar to that in Example 1 with a polyamide resin (nylon 66), which is a thermoplastic resin. Since CFRTP was used in this Example 2, the prepreg sheet 14 was heated to the melting point of nylon 66, 265°C, and attachment was performed while maintaining the glass transition point of nylon 66 at or above 75°C.

[0071] Next, the thermoplastic resin of the CFRTP was cooled and hardened, and the skin 20 with the designed propeller shape was fixed. First, the core 10 with the prepreg sheet 14 attached was placed in a bag and sealed, and the inside was evacuated to make the prepreg sheet 14 adhere to the core 10 and to degas it. Next, the core 10 in this state was cooled to crystallize the nylon 66. In this state, the skin 20 was fixed in the designed propeller shape, and the skin trailing edge 22 was left open.

[0072] Next, the core 10 was removed from the inside of the outer skin 20 fixed in a propeller shape via the opened outer skin trailing edge 22. Next, a propeller skeleton was inserted into the hollow inside of the outer skin 20 via the opened outer skin trailing edge 22, and the outer edges of the ribs 32 were adhesively fixed to the inside of the outer skin 20. In this Example 2, a propeller skeleton similar to that in the above Example 1 was used.

[0073] Next, the open skin trailing edge 22 of the skin 20 into which the propeller skeleton was inserted was sealed. In this Example 2, the upper skin 23 and the lower skin 24 were bonded with an epoxy adhesive in the same manner as in Example 1. In this manner, the propeller 40 of this Example 2 was completed. EXAMPLES

[0074] In this Example 3, the core is made by a 3D printer using a water-soluble resin, and the outer skin of the propeller is made of CFRP that uses a thermosetting resin as a matrix resin, similar to the above Example 1. The following is a detailed description.

[0075] First, a core 10 was produced using a 3D printer based on the design data of the propeller. In this Example 3, the core was produced using polyvinyl alcohol (PVA) as the water-soluble resin. Next, a release sheet 13 was applied to the core trailing edge 12 of the core 10 using the same OPP tape as in Example 1 above. In this Example 3, the core made of the water-soluble resin was dissolved and removed, so OPP tape was not applied to the entire surface of the core 10.

[0076] Next, a CFRP prepreg sheet 14 was attached to the entire surface of the core 10. In this Example 3, only a prepreg sheet 14 was used, which was made of a carbon fiber fabric (3K plain weave carbon) similar to that in Example 1 above, impregnated with epoxy resin, which is a thermosetting resin. In this way, the prepreg sheet 14 was attached to the surface of the core 10, and a propeller-shaped outer skin was formed.

[0077] Next, the CFRP thermosetting resin was reacted and cured to fix the skin 20 in the designed propeller shape. In this Example 3, the curing reaction of the epoxy resin of the skin 20 was completed by the same operation as in Example 1. In this state, the skin 20 was fixed in the designed propeller shape, and the skin trailing edge 22 was in an open state.

[0078] Next, the core 10 was removed from inside the skin 20 fixed in the propeller shape through the opened skin trailing edge 22. In this Example 3, the core 10 was made of polyvinyl alcohol, which is a water-soluble resin. Therefore, when removing the core 10 from inside the skin 20, the core 10 could be dissolved in hot water and removed, making the removal operation easy. Furthermore, the open area of ​​the skin trailing edge 22 can be made smaller, improving the strength of the propeller.

[0079] Next, the propeller skeleton was inserted into the hollow interior of the skin 20 via the opened skin trailing edge 22, and the outer edge of the rib 32 was adhesively fixed to the interior of the skin 20. In this Example 3, the same propeller skeleton as in Example 1 was used. Next, the opened skin trailing edge 22 of the skin 20 into which the propeller skeleton was inserted was sealed. In this Example 3, the upper skin 23 and the lower skin 24 were adhered with an epoxy adhesive in the same manner as in Example 1. In this manner, the propeller 40 of this Example 3 was completed.

[0080] As described above, in the first embodiment, it is possible to provide a flight propeller and a manufacturing method thereof, in which the adhesive portion around the periphery of the propeller skin is small, and in particular there is no adhesive portion at the leading edge, so that the propeller has sufficient strength, is lightweight due to the provision of a hollow portion inside, and has low manufacturing costs.

[0081] Second Embodiment The second embodiment is a method in which a core that contains a propeller skeleton consisting of one main girder and multiple ribs is used, and the core is removed in a dissolved or swollen state from inside an outer shell made of carbon fiber reinforced plastic molded into a propeller shape. Each step of the second embodiment is specifically described below.

[0082] (1) Prepare a propeller skeleton consisting of one main girder and multiple ribs connected to it. In this second embodiment, first, a propeller skeleton (one main girder and multiple ribs connected to it) is prepared to be placed inside the hollow outer skin in order to ensure the strength of the propeller. The structure of the propeller skeleton is the same as that of the first embodiment, and it is preferable to use CFRP rods or the like for the main girder in consideration of strength and weight reduction. It is also preferable to use CFRP boards or the like for the ribs.

[0083] (2) Using a solvent-soluble resin, a core having a propeller shape and containing the propeller skeleton therein is produced. In this second embodiment, a core having a propeller shape that contains a propeller skeleton therein is used. Fig. 8 is a schematic plan view showing a core 110 used in the second embodiment. In Fig. 8, one edge of the core 110 corresponds to the propeller leading edge that receives large wind pressure during flight of the propeller, and this is referred to as a core leading edge 111. The other edge of the core 110 corresponds to the propeller trailing edge through which air flows through the propeller, and this is referred to as a core trailing edge 112. Note that in Fig. 1, the three-dimensional shape of each portion of the propeller, such as the inclination and thickness, is omitted.

[0084] In Fig. 8, a propeller skeleton is contained within core 110, to which one main girder 131 and a number of ribs 132 (six in Fig. 8) connected to the main girder are fixed. Note that while main girder 131 is embedded within core 110, the outer edges of ribs 132 are not embedded within core 110 and are exposed on the surface of core 110. This exposed surface of core 110 is bonded to the inside of the outer shell of the propeller, which will be described later, to reinforce the strength of the propeller. Also, since the propeller skeleton is contained within core 110, core 110 is divided into a number of blocks a to f by ribs 132 (six blocks in Fig. 8).

[0085] In the second embodiment, a solvent-soluble resin is used as the material for producing the core 110. The solvent-soluble resin is not particularly limited, but it is necessary that it is soluble in a solvent that does not affect the matrix resin of the CFRP or CFRTP that constitutes the outer skin, which will be described later. For example, limonene, which is extracted from citrus fruits and has attracted attention as a safe solvent, can be used. Examples of resins that are soluble in limonene include polystyrene and polystyrene foam, and high impact polystyrene (HiPS) can also be used.

[0086] In the present invention, the solvent-soluble resin includes a water-soluble resin, and it is preferable to use a water-soluble resin that uses water as a solvent. Examples of the water-soluble resin include polyvinyl alcohol (PVA), polyacrylamide (PAA), carboxymethyl cellulose (CMC), butenediol vinyl alcohol copolymer (PVOH), etc. When producing core 110 using a solvent-soluble resin including a water-soluble resin, it is preferable to use a 3D printer since it may include a propeller skeleton.

[0087] (3) One or more laminated carbon fiber reinforced plastic prepreg sheets are attached to the top and bottom surfaces of the core. A CFRP or CFRTP prepreg sheet is applied to the entire surface of the core 110. Fig. 9 is a schematic plan view showing a state in which the entire surface of the core 110 is covered with a CFRP or CFRTP prepreg sheet. In Fig. 9, the core 110 containing the propeller skeleton is contained inside the outer skin 120. Note that in this second embodiment, unlike the above-mentioned first embodiment, prepreg sheets are applied to the top and bottom surfaces so as to straddle both the core leading edge 111 and the core trailing edge 112. As a result, in Fig. 9, there are no open areas not only on the outer skin leading edge 121 but also on the outer skin trailing edge 122, and the design strength of the propeller can be further improved.

[0088] The combination of the carbon fibers and matrix resin constituting the prepreg sheet is not particularly limited. As in the first embodiment, UD prepreg sheets and woven prepreg sheets can be used as the carbon fibers. Also, the matrix resin (thermosetting resin) of the CFRP and the matrix resin (thermoplastic resin) of the CFRTP can be various resins similar to those in the first embodiment.

[0089] (4) The matrix resin of the prepreg sheet is hardened to form the propeller-shaped outer skin. In Fig. 9, the entire surface of the core 110 is covered with a prepreg sheet, and the matrix resin of the propeller-shaped outer shell 120 is in an uncured state. Therefore, the matrix resin of the outer shell 120 that holds the core 110 containing the propeller skeleton inside is cured. The curing operation of the CFRP and CFRTP resins is the same as in the first embodiment, and will not be described here.

[0090] (5) A part of the outer shell is opened, and the core is taken out in a dissolved or swollen state with a solvent. In the second embodiment, the core 110 is made of a solvent-soluble resin. The core 110 also includes the propeller skeleton. Therefore, in the second embodiment, a part of the outer skin 120 is opened, and the core 110 is taken out in a state in which it is dissolved or swollen with a solvent. It is preferable to keep the open area to a minimum and not provide it at the outer skin leading edge 121 and the outer skin trailing edge 122 of the outer skin 120. Fig. 10 is a schematic plan view showing the state in which the core 110 is dissolved and taken out from inside the outer skin 120 of the propeller after the CFRP or CFRTP matrix resin attached to the entire surface of the core 110 is hardened.

[0091] In FIG. 10, the core 110 includes a propeller skeleton and is divided into six blocks (a to f in FIG. 8). Small open sections a1 to f1 are provided corresponding to the blocks a to f. This allows a solvent to be poured into the inside of the outer shell 120 from each of the open sections a1 to f1 to dissolve or swell the resin of each of the blocks a to f and remove it to the outside. The outer shell 120 removed by dissolving or swelling the core 110 has the propeller skeleton inside, has a propeller shape, and is hollow inside. The ribs 132 of the propeller skeleton are bonded and fixed to the inside of the outer shell 120 by a matrix resin of CFRP or CFRTP.

[0092] (6) Repair the open area of ​​the shell from which the core was removed. Finally, each of the open portions a1-f1 that have been taken out by dissolving or swelling the core 110 is repaired by gluing, etc. Fig. 11 is a schematic plan view showing the propeller of the second embodiment that has been completed after the core has been taken out from inside the outer skin 120 of the propeller 140 and the taken-out open portions a1-f1 have been repaired.

[0093] The upper and lower surfaces of this propeller 140 are covered with an outer skin 120, and the propeller leading edge 141 and the propeller trailing edge 142 do not have any bonding sites between the upper and lower outer skins. The inside of the outer skin 120 is composed only of one main girder 131 and multiple ribs 132 connected to it, and the rest of the body is hollow. One end of the main girder 131 protrudes outside the outer skin 120, and a connection terminal 133 is provided at this part, which is connected to a power transmission mechanism that transmits the rotation of the pedal shaft.

[0094] Next, the propeller according to the second embodiment will be described using examples. Note that the present invention is not limited to only the examples described below. EXAMPLES

[0095] In this Example 4, the core containing the propeller skeleton is made of water-soluble resin using a 3D printer, and the outer skin of the propeller is made of CFRP consisting of carbon fiber fabric and thermosetting resin as the matrix resin. The details will be explained below.

[0096] First, a propeller skeleton was prepared by assembling six ribs 132 fixed to the main girders 131. In this Example 4, as in the above Example 1, CFRP rods were used for the main girders 131, and CFRP boards were used for the ribs 132. Next, based on the design data for the propeller, a 3D printer was used to create a core 110 that encompasses the propeller skeleton (see FIG. 8). In this Example 4, the core 110 was created using polyvinyl alcohol (PVA), which is a water-soluble resin.

[0097] Next, a CFRP prepreg sheet was attached to the entire surface of the core 110. In this Example 4, similar to the above Example 1, only a prepreg sheet made of carbon fiber fabric (3K plain weave carbon) impregnated with epoxy resin, which is a thermosetting resin, was used. As described above, the prepreg sheets were attached to the top and bottom surfaces of the core 110 so as to straddle both the core leading edge 111 and the core trailing edge 112 (see FIG. 9). As a result, there are no open areas not only on the outer skin leading edge 121 but also on the outer skin trailing edge 122.

[0098] Next, the thermosetting resin of the CFRP was reacted and cured, and the skin 120 with the designed propeller shape was fixed. First, the core 110 with the prepreg sheet attached was put into a bag, sealed, and the inside was evacuated. Next, the core 110 in this state was put into a heating furnace, and the temperature was raised to 80°C to complete the curing reaction of the epoxy resin of the skin 120. In this state, the skin 120 was fixed in the designed propeller shape, and there were no open areas on the skin leading edge 121 and the skin trailing edge 122.

[0099] Next, small holes were provided as small open sections a1 to f1 at positions corresponding to each of the blocks a to f in a portion of the skin 120 fixed in a propeller shape near the skin trailing edge 22. Next, hot water was poured into the skin 120 from each of the open sections a1 to f1 to dissolve the PVA resin in each of the blocks a to f and remove it to the outside (see FIG. 10). The skin 120 from which the PVA resin was removed had a propeller skeleton inside, was propeller-shaped, and was hollow inside. Also, each rib 132 of the propeller skeleton was adhesively fixed to the inside of the skin 120 by the matrix resin of CFRP.

[0100] Next, the small holes in each of the open parts a1 to f1 from which the PVA resin had been taken out were repaired with adhesive. In this way, the propeller 140 of this Example 4 was completed (see FIG. 11). A connection terminal 133 of the main girder 131 is provided at one end of the propeller 140, and is connected to a power transmission mechanism that transmits the rotation of the pedal shaft.

[0101] As described above, in the second embodiment, it is possible to provide a flight propeller and a manufacturing method thereof that minimizes the adhesive around the periphery of the propeller skin, has sufficient strength as a propeller, is lightweight due to the provision of a hollow space inside, and has low manufacturing costs. [Explanation of symbols]

[0102] 10,110...core, 11,111...core leading edge, 12,112...core trailing edge, 13... release sheet, 14... prepreg sheet, 20,120...Integument, 21,121...Integument anterior edge, 22,122...Integument rear edge, 23...Top skin, 24...Bottom skin, 31,131...Main beam, 32,132...Rib, 33,133...Connection terminal, 40,140…propeller, 41,141…propeller leading edge, 42,142…propeller trailing edge, a~f...blocks, a1~f1...release sections.

Claims

1. A propeller consisting of a main spar, a rib, and a skin, The inside covered with the outer skin is composed of one main girder and a plurality of ribs connected thereto, and the other parts are hollow, The skin is made of carbon fiber reinforced plastic, one or more of which are laminated, and the leading edge of the propeller does not have an adhesion area between the upper skin and the lower skin, while part or all of the trailing edge of the propeller has an adhesion area between the upper skin and the lower skin.

2. Producing a core having a designed propeller shape; applying a release sheet or a release agent to a part or all of a portion of the core corresponding to the trailing edge of the propeller; A step of attaching one or more laminated carbon fiber reinforced plastic prepreg sheets to the upper and lower surfaces of the core to which the release sheet or release agent has been applied; A step of hardening the matrix resin of the prepreg sheet to form a propeller-shaped outer skin; removing the core from inside the outer skin made of the carbon fiber reinforced plastic molded into a propeller shape through a portion where the release sheet or release agent is applied and where the upper outer skin and the lower outer skin are not bonded; a step of inserting a propeller skeleton including one main girder and a plurality of ribs connected thereto into the skin from which the core has been removed, via a portion where the upper skin and the lower skin are not bonded; a step of bonding an unbonded portion of the upper surface skin and the lower surface skin of the skin into which the propeller skeleton is inserted; A method for manufacturing a flight propeller, comprising the steps of:

3. In the step of removing the core from inside the outer shell, 3. The method for manufacturing a flight propeller according to claim 2, wherein the core is taken out in the shape of a propeller or in a divided form.

4. In the step of removing the core from inside the outer shell, 3. The method for manufacturing a flight propeller according to claim 2, wherein the core is taken out in a dissolved or swollen state with a solvent.

5. The core is made of a water-soluble resin, the solvent is water, 5. The method for manufacturing a flight propeller according to claim 4, wherein the core is taken out from inside the outer shell in a dissolved or swollen state with water.

6. A propeller consisting of a main spar, a rib, and a skin, The inside covered with the outer skin is composed of one main girder and a plurality of ribs connected thereto, and the other parts are hollow, a propeller for flight, the propeller being characterized in that the skin is made of one or more laminated carbon fiber reinforced plastic sheets, and that there are no adhesive sites between the upper skin and the lower skin at the leading edge and the trailing edge of the propeller.

7. A step of preparing a propeller skeleton including one main spar and a plurality of ribs connected thereto; producing a propeller-shaped core containing the propeller skeleton therein using a solvent-soluble resin; a step of attaching one or more laminated carbon fiber reinforced plastic prepreg sheets to both upper and lower surfaces of the core; A step of hardening the matrix resin of the prepreg sheet to form a propeller-shaped outer skin; a step of opening a portion of the outer shell and removing the core in a state where the core is dissolved or swollen with a solvent; repairing the open portion of the shell from which the core was removed; A method for manufacturing a flight propeller, comprising the steps of:

8. The core is made of a resin that is soluble in an organic solvent, and the solvent is the organic solvent, 8. The method for manufacturing a flight propeller according to claim 7, wherein the core is taken out from inside the outer shell in a state where it is dissolved or swollen with the organic solvent.

9. The core is made of a water-soluble resin, the solvent is water, 8. The method for manufacturing a flight propeller according to claim 7, wherein the core is taken out from inside the outer shell in a dissolved or swollen state with water.

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