JP7465026B1 - How to make a flight propeller - Google Patents

Abstract

[Problem] To provide a flight propeller and its manufacturing method, in which the adhesive parts around the periphery of the propeller skin are kept small or to a minimum, particularly at the leading edge, and which has sufficient strength as a propeller while being lightweight due to a hollow part provided inside and which keeps manufacturing costs down. [Solution] The flight propeller is made up of a main spar, ribs, and skin. The interior covered by the skin is made up of one main spar and multiple ribs connected to it, and the rest of the propeller is hollow. The skin is made of carbon fiber reinforced plastic, with one or multiple sheets laminated together. The leading edge of the propeller does not have an adhesive part between the upper skin and the lower skin. Meanwhile, part or all of the trailing edge of the propeller has an adhesive part between the upper skin and the lower skin. [Selected Figure] Figure 5

Description

The present invention relates to a flight propeller and a method for manufacturing the same.

Propellers are devices used in airplanes and the like to convert the power output from the power source into thrust through the rotation of the propeller, propelling the aircraft forward. Propellers are not limited to those used in engine-powered aircraft, but are also important devices in human-powered sports aircraft and human-powered aircraft with auxiliary power. Furthermore, various propellers have been developed in recent years for drones (unmanned aerial vehicles) and flying cars (two-wheeled vehicles).

In particular, small flying devices such as human-powered airplanes and drones require propellers that are lightweight in addition to having good structure and strength. Below, we will explain using the propeller of a human-powered airplane as an example. A human-powered airplane is powered by a person, and the rotation of the pedal shaft obtained by the person stepping on the pedals is transmitted to the propeller by a power transmission mechanism, rotating the propeller and allowing the airplane to fly.

For example, a competition called the Birdman Contest Championship is held every year, sponsored by a commercial broadcasting station, in which participants compete to see who can fly the longest and longest human-powered aircraft. Improvements to the aircraft and propellers are a hot topic every year. When it comes to the propellers of human-powered aircraft, it is important to design them to match the aircraft and make them as strong and light as possible.

Typically, the propellers of human-powered aircraft are made by using wood or foamed resin as a core material, and then attaching CFRP, which has a carbon fiber base, or GFRP, which has a glass fiber base, to the surface. However, the problem with such propellers is that the core material is inside, making it difficult to reduce their weight.

As a result, methods of manufacturing propellers have been developed that aim to reduce weight by creating as much hollow space as possible inside the propeller. For example, the following non-patent literature 1 and non-patent literature 2 describe the structure and manufacturing methods of propellers for human-powered aircraft. These methods involve dividing the outer skin of the designed propeller into two outer skins, one for the top and one for the bottom, and then manufacturing each separately.

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, the mold is vacuumed and then heated in an oven to harden the resin in the prepreg sheets. This completes the two outer skins for the top and bottom.

Next, the main girders and ribs are placed and fixed inside the skin, and the periphery of the top and bottom skins are fixed with epoxy adhesive or similar. The surface of the propeller with the top and bottom outer peripheries fixed is then painted, and the propeller for a human-powered aircraft is complete. Even in this state, the propeller skin is strong as it is made of laminated CFRP or 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.

Furthermore, because the outer skin is made up of two pieces, an upper and lower surface, and the adhesive joint between them is located around the entire circumference of the propeller, there was a problem that the adhesive joint at the leading edge of the outer skin, which is directly subjected to air resistance during flight, would peel off during flight. In order to prevent such peeling, the amount of adhesive used at the leading edge could be increased, which reduced the problem, but it was not possible to eliminate peeling at the leading edge. Another problem was that excessive adhesive use at the leading edge would increase the weight of the propeller.

Daiichi Institute of Technology Research Report No. 22 (2010) pp.31-39 Dobonkai Human-Powered Airplane Construction Diary (2011/08/09) (URL: http://dobonkai.blog99.fc2.com/blog-entry-77.html)

The present invention aims to address the above problems by providing a flight propeller and a manufacturing method thereof that has a small or minimal adhesive area around the periphery of the propeller skin, particularly no adhesive area at the leading edge, that has sufficient strength as a propeller, is lightweight due to the provision of a hollow area inside, and has low manufacturing costs.

In order to solve the above problems, the inventors conducted extensive research and discovered that the above objectives could be achieved by using a propeller-shaped core, not dividing the outer skin into two pieces, an upper and lower, not providing an adhesive 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.

According to a first aspect of the present invention, there is provided a method for manufacturing a flight propeller, comprising the steps of:
A method for manufacturing a flight propeller, which is covered with an outer skin made of carbon fiber reinforced plastic, and the inside of the outer skin is hollow except for the main beams and ribs that constitute the propeller skeleton, comprising:
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 , straddling a leading edge of the core but not straddling a trailing edge of the core ;
A step of hardening the matrix resin of the prepreg sheet to form a propeller-shaped outer skin;
a step of removing the core from inside the outer skin made of the carbon fiber reinforced plastic molded into a propeller shape through a portion of the core where the release sheet or release agent is applied to a portion corresponding to the trailing edge of the propeller and where the prepreg sheet is attached without straddling the trailing edge of the core, so that the upper outer skin and the lower outer skin are not bonded to each other;
a step of inserting the propeller skeleton, which is composed 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;
By carrying out a process of adhering the unadhered portions of the upper and lower skins of the skin into which the propeller skeleton is inserted,
The manufactured flight propeller is characterized in that the leading edge of the propeller does not have an adhesion area between the upper and lower outer skins, and part or all of the trailing edge of the propeller has an adhesion area between the upper and lower outer skins.

According to a second aspect of the present invention, there is provided a method for manufacturing the flight propeller according to the first aspect, comprising the steps of:
In the step of removing the core from inside the outer shell,
The core is removed in the propeller shape or after being divided.

According to a third aspect of the present invention, there is provided a method for manufacturing the flight propeller according to the first aspect, comprising the steps of:
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.

According to a fourth aspect of the present invention, there is provided a method for manufacturing the flight propeller according to the third aspect, comprising the steps of:
The core is made of a water-soluble resin, the solvent is water,
The core is removed from inside the shell in a state where it is dissolved or swollen with water.

According to a fifth aspect of the present invention, there is provided a method for manufacturing a flight propeller, comprising the steps of:
A method for manufacturing a flight propeller that is covered with an outer skin made of carbon fiber reinforced plastic, and a portion inside the outer skin other than the main beams and ribs that constitute the propeller skeleton is hollow, comprising:
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 the upper and lower surfaces of the core so as to straddle both the leading edge and the trailing edge of the core ;
A step of hardening the matrix resin of the prepreg sheet to form a propeller-shaped skin having no bonding site between the upper skin and the lower skin at the propeller leading edge and the propeller trailing edge ;
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;
and repairing the open portion of the shell from which the core was removed.
The manufactured flight propeller is characterized in that a portion of the outer skin has the repaired open area .

According to a sixth aspect of the present invention, there is provided a method for manufacturing the flight propeller according to the fifth aspect, comprising the steps of:
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.

According to a seventh aspect of the present invention, there is provided a method for manufacturing the flight propeller according to the fifth aspect, comprising the steps of:
The core is made of a water-soluble resin, the solvent is water,
The core is removed from inside the shell in a state where it is dissolved or swollen with water.

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 rest of the skin is hollow. The outer skin is made of carbon fiber reinforced plastic, with one or multiple sheets laminated together. The leading edge of the propeller does not have an adhesion area between the upper skin and the lower skin. On the other hand, part or all of the trailing edge of the propeller has an adhesion area between the upper skin and the lower skin.

This allows us to provide a flight propeller with 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 hollow area inside, and has low manufacturing costs.

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, straddling the leading edge of the core but not straddling the trailing edge of the core . The next step is to harden the matrix resin of the prepreg sheets to form an outer skin in the shape of a propeller.

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 the upper and lower skins are not bonded because a release sheet or release agent has been applied to the portion of the core corresponding to the propeller trailing edge and the prepreg sheet has been attached without straddling the trailing edge of the core. 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 where the upper and lower skins of the skin into which the propeller skeleton has been inserted are bonded.

This makes it possible to provide a method for manufacturing an aircraft propeller that has a small adhesive around the periphery of the propeller skin, and in particular has no adhesive at the leading edge, while still having sufficient strength as a propeller and a hollow interior for reduced weight and manufacturing costs.

Furthermore, according to the above configuration, in the process 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 from 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 achieved.

Furthermore, 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 rest of the part is hollow. The outer skin is made of one or multiple laminated carbon fiber reinforced plastic sheets. The leading edge and trailing edge of the propeller do not have any adhesion areas between the upper and lower skins.

This allows us to provide a flight propeller that has a minimum amount of adhesive around the periphery of the propeller's outer skin, is strong enough to function as a propeller, has a hollow interior to reduce weight, and has low manufacturing costs.

According to the above configuration, the manufacturing method of a flight propeller includes, in the first step, preparing a propeller skeleton consisting of one main spar and a plurality 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 manufactured. In the next step, one or a plurality of laminated carbon fiber reinforced plastic prepreg sheets are attached to both the upper and lower surfaces of the core so as to straddle both the leading edge and the trailing edge of the core . In the next step, the matrix resin of the prepreg sheets is hardened to form a propeller-shaped outer skin that does not have an adhesive portion between the upper skin and the lower skin at the leading edge and the trailing edge of the propeller . In the next step, a part of the outer skin is opened, and the core is taken out in a state dissolved or swollen with a solvent. In the next step, the open portion of the outer skin from which the core was taken out is repaired.

This makes it possible to provide a manufacturing method for an aircraft propeller that minimizes the repaired open areas on the propeller's outer skin, has sufficient strength as a propeller, is lightweight due to the provision of a hollow section inside, and keeps manufacturing costs down.

Furthermore, according to the above configuration, the core may be made of a resin soluble in an organic solvent, and the core may be 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 the core may be removed from inside the outer shell in a state where it is dissolved or swollen with water. By doing so, the above-mentioned action and effect can be concretely and effectively exhibited.

FIG. 2 is a schematic plan view showing a core used in the first embodiment. FIG. 2 is a schematic plan view showing a state in which a release sheet is applied to the rear edge of the core of FIG. 1 . 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 . FIG. 4 is a schematic plan view showing a state in which the entire surface of the core of FIG. 3 is covered with a CFRP or CFRTP prepreg sheet. 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 CFRP or CFRTP matrix resin affixed to the entire surface of the core has been hardened. 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 of FIG. 5 has been removed. FIG. 7 is a schematic plan view showing the propeller of the first embodiment completed by inserting a propeller skeleton into the inside of the outer skin of the propeller in FIG. 6 and bonding an upper skin and a lower skin together. FIG. 11 is a schematic plan view showing a core used in the second embodiment. FIG. 9 is a schematic plan view showing a state in which the entire surface of the core of FIG. 8 is covered with a CFRP or CFRTP prepreg sheet. 10 is a schematic plan view showing the 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 affixed to the entire surface of the core is hardened. 11 is a schematic plan view showing a propeller of the second embodiment that has been 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.

Here, we will specifically explain the flight propeller (hereinafter simply referred to as "propeller") of the present invention. The use of the propeller of 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.

The propeller of the present invention is also 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.

The outer skin is made of one or more laminated carbon fiber reinforced plastic layers to reduce weight. If necessary, a minimum of other laminates (such as glass fiber GFRP) may be added.

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.

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 the propeller-shaped mold (called the "core" in this invention) used in the propeller manufacturing stage. This open area becomes the area where the upper and lower skins are adhered after the core is removed (details will be described later).

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 when manufacturing a propeller.

In this way, the propeller of the present invention uses a core during 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 during the manufacturing stage, two molds for the two outer skins on the top and bottom surfaces, as in the prior art described above, are not used. This not only improves the strength of the propeller, but also reduces manufacturing costs.

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

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 into the shell. Each step of the first embodiment will be described in detail below.

(1) Fabrication of a core having a propeller shape A propeller has a complex three-dimensional shape in order to obtain thrust in a flow in which the speed due to the rotational motion of the propeller itself and the forward speed of the aircraft are combined. In the present invention, the design method is not limited, and a mold (core) having a propeller shape designed by any method is used.

First, a core is created based on the design data for the propeller. Figure 1 is a schematic plan view showing a core 10 used in the first embodiment. In Figure 1, one edge of the core 10 corresponds to the propeller leading edge, which receives large wind pressure during flight, and is designated as the 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 the core trailing edge 12. Note that in Figure 1, the three-dimensional shape of each part of the propeller, such as the slope and thickness, is omitted.

The material from which the core 10 is made 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 for the propeller, blocks of these materials may be cut using a CNC lathe or the like. Alternatively, various resins may be ejected using a 3D printer to create the three-dimensional shape of the core 10.

(2) A release sheet is applied to part or all of the portion of the core corresponding to the propeller trailing edge (core trailing edge) 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 applied to the core trailing edge 12. Figure 2 is a schematic plan view showing the state in which the release sheet 13 has been applied 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 portion of this release sheet 13 when the propeller skin is molded.

It is preferable to use a material for the release sheet 13 to which the matrix resin of the CFRP or CFRTP cannot adhere, such as a film or tape of silicone rubber, polypropylene, polyethylene, polyacetal, or fluororesin. 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 release agent such as a fluorine-based or silicone-based agent may be applied.

(3) Affixing carbon fiber reinforced plastic prepreg sheets to the top and bottom surfaces of the core A release sheet 13 is attached to the core trailing edge 12, and a release sheet is attached to the entire surface of the core 10, or a release agent is applied thereto, and then 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.

The carbon fiber may be a UD prepreg sheet in which a 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, phenolic 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.

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 when the matrix resin of the CFRTP is melted. 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 stacked, but this is not limiting, and one large prepreg sheet may be applied to the entire upper and lower surfaces of the core 10.

The prepreg sheets 14 are preferably attached in the necessary locations, taking into consideration the structure of the propeller, and are attached by changing the orientation direction of the carbon fibers. As a result, the completed propeller maintains the designed strength, does not have an adhesion area between the upper and lower skins at the leading edge of the propeller, and can have an adhesion area between the upper and lower skins formed at part or all of the trailing edge of the propeller.

(4) Forming a propeller-shaped outer skin by curing the matrix resin of the prepreg sheet Fig. 4 is a schematic plan view showing a state in which the entire surface of the core is 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 is cured.

One edge of the skin 20 (the portion covering the core leading edge 11) corresponds to the propeller leading edge where the propeller receives strong wind pressure during flight, and is designated 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 designated as the skin trailing edge 22. At the skin trailing edge 22, the upper skin 23 (front side in the figure) and the lower skin 24 (back side in the figure) of the skin 20 are not bonded together with the release sheet 13 sandwiched between them.

In this state, the matrix resin of the CFRP has not yet hardened. Therefore, the outer shell 20 holding the core 10 inside is sealed, and the inside is vacuum-suctioned 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 inside is sealed, and the inside is vacuum-suctioned 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.

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

(5) Removing the core from inside the outer skin molded into a propeller shape Figure 5 is a schematic plan view showing the state in which the 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 the core 10 has been cured. In Figure 5, the core 10 can be removed from the portion of the skin trailing edge 22 where the upper skin 23 and the lower skin 24 are not bonded. The outer skin 20 from which the core 10 has been removed has the shape of a propeller and is hollow inside.

In FIG. 5, the core 10 can be removed while still in the propeller shape. 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 multiple pieces inside the outer skin 20, it becomes easier to remove. In this case, the release sheet 13 is shortened to narrow the non-adhesive area between the upper outer skin 23 and the lower outer skin 24 of the outer skin trailing edge 22. This can reduce the adhesive area at the trailing edge of the propeller, further improving the strength of the propeller.

On the other hand, if 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 outer shell 20. If the core 10 is made of a water-soluble resin, it may be made using a 3D printer. The water-soluble resin is not limited to resins that dissolve completely, and may be one that swells in water. Examples include polyvinyl alcohol (PVA), polyacrylamide (PAA), carboxymethyl cellulose (CMC), butenediol vinyl alcohol copolymer (PVOH), etc.

(6) Inserting the main girder and ribs inside the outer skin molded into the propeller shape Next, in order 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. Figure 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, so that the propeller shape can be maintained and reinforced. 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.

(7) Bonding of Unbonded Parts of the Upper Skin and the Lower Skin of the Skin Fig. 7 is a schematic plan view showing a propeller 40 completed by inserting a propeller skeleton inside the skin 20 and bonding the upper skin 23 and the lower skin 24. The upper and lower surfaces of this propeller 40 are covered with the skin 20, and the propeller leading edge 41 does not have a bonding part between the upper skin 23 and the lower skin 24. On the other hand, the propeller trailing edge 42 has a bonding part between the upper skin 23 and the lower skin 24. The inside of the skin 20 is composed of only one main spar 31 and a plurality of ribs 32 connected thereto, and the other parts are hollow. One end of the main spar 31 protrudes outside the skin 20, and a connection terminal 33 is provided on this part and is connected to a power transmission mechanism that transmits the rotation of the pedal shaft.

Next, the propeller according to the first embodiment will be described using examples. Note that the present invention is not limited to the examples described below.

In this Example 1, the core is made using a 3D printer, and the outer skin of the propeller is made from CFRP, which is made of woven carbon fiber and a thermosetting resin as the matrix resin. The details are explained below.

First, a core 10 was created using a 3D printer based on the design data for the propeller (see Figure 1). In this Example 1, the core was created using ABS resin (a copolymer of acrylonitrile, butadiene, and styrene). Next, a release sheet 13 was applied to the 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 Figure 2). In addition, OPP tape was also applied to the entire surface of the core 10 that did not have the release sheet 13 applied.

Next, a CFRP prepreg sheet 14 was attached to the entire surface of the core 10. In this Example 1, only a prepreg sheet 14 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 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 Figure 3). In order to reinforce the strength of the propeller, the prepreg sheet 14 was laminated where necessary, 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 Figure 4).

Then, the thermosetting resin of the CFRP was reacted 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, 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 hardening 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 left open.

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

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 Figure 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.

In this second embodiment, a core similar to that in the first embodiment is created using a 3D printer, and the outer skin of the propeller is made using CFRTP, which is made of carbon fiber fabric and thermoplastic resin as the matrix resin. The details are explained below.

First, the core 10 was created using a 3D printer based on the design data of the propeller. In this Example 2, the core was created using 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.

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 of carbon fiber fabric (3K plain weave carbon) similar to that in Example 1 above, impregnated with 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.

Then, the thermoplastic resin of the CFRTP was cooled and hardened, and the skin 20 in 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 adhere the prepreg sheet 14 to the core 10 and degassed. 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.

Next, the core 10 was removed from the inside of the outer skin 20, which had been fixed in a propeller shape, via the open outer skin trailing edge 22. Next, a propeller skeleton was inserted into the hollow inside of the outer skin 20 via the open outer skin trailing edge 22, and the outer edge of the rib 32 was adhesively fixed to the inside of the outer skin 20. In this Example 2, a propeller skeleton similar to that in Example 1 was used.

Next, the open skin trailing edge 22 of the skin 20 into which the propeller skeleton was inserted was sealed. In this second embodiment, the upper skin 23 and the lower skin 24 were bonded together with an epoxy adhesive in the same manner as in the first embodiment. In this manner, the propeller 40 of this second embodiment was completed.

In this third embodiment, the core is made with a 3D printer using a water-soluble resin, and the outer shell of the propeller is made of CFRP using a thermosetting resin as the matrix resin, similar to that of the first embodiment. The details are explained below.

First, the core 10 was created using a 3D printer based on the design data of the propeller. In this Example 3, the core was created 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 water-soluble resin was dissolved and removed, so OPP tape was not applied to the entire surface of the core 10.

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 carbon fiber fabric (3K plain weave carbon) similar to that in Example 1 above, impregnated with epoxy resin, 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.

Next, the thermosetting resin of the CFRP was reacted and cured, and the skin 20 was fixed 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 above. In this state, the skin 20 was fixed in the designed propeller shape, and the skin trailing edge 22 was in an open state.

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

Next, the propeller skeleton was inserted into the hollow skin 20 via the open skin trailing edge 22, and the outer edge of the rib 32 was glued and fixed to the inside of the skin 20. In this Example 3, the same propeller skeleton as in Example 1 above was used. Next, the open 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 glued together with an epoxy adhesive in the same manner as in Example 1 above. In this manner, the propeller 40 of this Example 3 was completed.

As described above, in the first embodiment, the adhesive portion around the periphery of the propeller skin is small, and there is no adhesive portion at the leading edge in particular, making it possible 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 portion inside, and has low manufacturing costs.

Second Embodiment
In the second embodiment, 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 a shell made of carbon fiber reinforced plastic molded into a propeller shape. Each step of the second embodiment will be specifically described below.

(1) Preparing a propeller skeleton consisting of one main girder and multiple ribs connected to it In this second embodiment, first, in order to ensure the strength of the propeller, a propeller skeleton (one main girder and multiple ribs connected to it) is prepared, which is placed inside the hollow outer skin. The structure of the propeller skeleton is the same as in 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.

(2) Using a solvent-soluble resin to fabricate a propeller-shaped core that contains the propeller skeleton inside In this second embodiment, a propeller-shaped core that contains the propeller skeleton inside 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 a 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 the propeller, such as the inclination and thickness at each portion, is omitted.

In FIG. 8, the inside of the core 110 contains a propeller skeleton with one main girder 131 and multiple ribs 132 (six in FIG. 8) connected to it. The main girder 131 is embedded inside the core 110, but the outer edges of the ribs 132 are not embedded inside the core 110 and are exposed on the surface of the core 110. This exposed surface of the core 110 is bonded to the inside of the propeller skin, which will be described later, to reinforce the strength of the propeller. Also, because the propeller skeleton is contained inside the core 110, the core 110 is divided into multiple blocks a-f by the ribs 132 (six blocks in FIG. 8).

In this second embodiment, a solvent-soluble resin is used as the material for producing the core 110. There are no particular limitations on the solvent-soluble resin, but it is necessary that the resin 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.

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 water-soluble resins include polyvinyl alcohol (PVA), polyacrylamide (PAA), carboxymethyl cellulose (CMC), butenediol vinyl alcohol copolymer (PVOH), etc. When producing the core 110 using a solvent-soluble resin that includes a water-soluble resin, it is preferable to use a 3D printer, as it may include a propeller skeleton.

(3) Affixing one or more laminated carbon fiber reinforced plastic prepreg sheets to the upper and lower surfaces of the core A CFRP or CFRTP prepreg sheet is affixed 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 included inside the outer shell 120. In the second embodiment, unlike the first embodiment, prepreg sheets are affixed to the upper and lower 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 shell leading edge 121 but also on the outer shell trailing edge 122, which can further improve the design strength of the propeller.

The combination of carbon fiber and matrix resin that constitute 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 fiber. 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.

(4) Forming a propeller-shaped outer skin by curing the matrix resin of the prepreg sheet 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 skin 120 is in an uncured state. Then, the matrix resin of the outer skin 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.

(5) Part of the outer shell is opened, and the core 110 is taken out in a state of being dissolved or swollen 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. In the second embodiment, therefore, part of the outer shell 120 is opened, and the core 110 is taken out in a state of being dissolved or swollen with a solvent. It is preferable to keep the open area to a minimum, and not to provide the open area at the outer shell leading edge 121 and the outer shell trailing edge 122 of the outer shell 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 shell 120 of the propeller after the CFRP or CFRTP matrix resin attached to the entire surface of the core 110 is hardened.

In FIG. 10, the core 110 contains the propeller skeleton and is divided into six blocks (a-f in FIG. 8). Small open sections a1-f1 are provided for each block a-f. This allows a solvent to be poured into the inside of the outer shell 120 from each open section a1-f1, dissolving or swelling the resin of each block a-f and removing it to the outside. The outer shell 120 removed by dissolving or swelling the core 110 has the propeller skeleton inside, is propeller-shaped, and is hollow inside. The ribs 132 of the propeller skeleton are adhesively fixed to the inside of the outer shell 120 by a matrix resin of CFRP or CFRTP.

(6) Repairing the opened portions of the outer shell from which the cores were removed Finally, each of the opened portions a1 to f1 that were removed by dissolving or swelling the cores 110 is repaired by gluing, etc. Figure 11 is a schematic plan view showing the propeller of the second embodiment that has been completed after the cores have been removed from inside the outer shell 120 of the propeller 140 and the removed open portions a1 to f1 have been repaired.

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 adhesive areas 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 skin 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.

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

In this fourth embodiment, the core containing the propeller skeleton is made from water-soluble resin using a 3D printer, and the outer skin of the propeller is made from CFRP, which is made of carbon fiber fabric and a thermosetting resin as the matrix resin. The details are explained below.

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 propeller design data, a 3D printer was used to create a core 110 that contains the propeller skeleton (see Figure 8). In this Example 4, the core 110 was created using polyvinyl alcohol (PVA), a water-soluble resin.

Next, a CFRP prepreg sheet was attached to the entire surface of the core 110. In this Example 4, as in Example 1 above, only a prepreg sheet made of carbon fiber fabric (3K plain weave carbon) impregnated with epoxy resin, a thermosetting resin, was used. As described above, the prepreg sheet was 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 Figure 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.

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

Next, small holes were made as small open sections a1 to f1 in the area of the skin 120 near the rear edge 22, which was fixed into the propeller shape, at positions corresponding to each of the blocks a to f. Next, hot water was poured into the skin 120 from each of the open sections a1 to f1, and the PVA resin in each of the blocks a to f was dissolved and removed to the outside (see Figure 10). The skin 120 from which the PVA resin was removed had a propeller skeleton inside, was propeller shaped, and was hollow inside. Additionally, each rib 132 of the propeller skeleton was adhesively fixed to the inside of the skin 120 by the matrix resin of the CFRP.

Next, the small holes in each of the open sections a1 to f1 from which the PVA resin had been removed were repaired with glue. In this way, the propeller 140 of this embodiment 4 was completed (see Figure 11). A connection terminal 133 of the main girder 131 is provided at one end of the propeller 140, and is connected to the power transmission mechanism that transmits the rotation of the pedal shaft.

As described above, in the second embodiment, it is possible to provide a flight propeller and its manufacturing method 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 section inside, and keeps manufacturing costs down.

10, 110 ... core, 11, 111 ... core front edge, 12, 112 ... core rear edge,
13... release sheet, 14... prepreg sheet,
20, 120 ... skin, 21, 121 ... skin front edge, 22, 122 ... skin rear edge,
23...upper surface outer skin, 24...lower surface outer 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 to f: blocks, a1 to f1: open portions.

Claims (7)

A method for manufacturing a flight propeller, which is covered with an outer skin made of carbon fiber reinforced plastic, and the inside of the outer skin is hollow except for the main beams and ribs that constitute the propeller skeleton, comprising:
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 , straddling a leading edge of the core but not straddling a trailing edge of the core ;
A step of hardening the matrix resin of the prepreg sheet to form a propeller-shaped outer skin;
a step of removing the core from inside the outer skin made of the carbon fiber reinforced plastic molded into a propeller shape through a portion of the core where the release sheet or release agent is applied to a portion corresponding to the trailing edge of the propeller and where the prepreg sheet is attached without straddling the trailing edge of the core, so that the upper outer skin and the lower outer skin are not bonded to each other;
a step of inserting the propeller skeleton, which is composed 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;
By carrying out a process of adhering the unadhered portions of the upper and lower skins of the skin into which the propeller skeleton is inserted,
A method for manufacturing a flight propeller, characterized in that the leading edge of the manufactured flight 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. In the step of removing the core from inside the outer shell,
2. The method for manufacturing a flight propeller according to claim 1 , wherein the core is taken out in the shape of a propeller or in a divided form. In the step of removing the core from inside the outer shell,
2. The method for manufacturing a flight propeller according to claim 1 , wherein the core is taken out in a dissolved or swollen state with a solvent. The core is made of a water-soluble resin, the solvent is water,
4. The method for manufacturing a flight propeller according to claim 3 , wherein the core is taken out from inside the outer shell in a dissolved or swollen state with water. A method for manufacturing a flight propeller, which is covered with an outer skin made of carbon fiber reinforced plastic, and the inside of the outer skin is hollow except for the main beams and ribs that constitute the propeller skeleton, comprising:
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 the upper and lower surfaces of the core so as to straddle both the leading edge and the trailing edge of the core ;
A step of hardening the matrix resin of the prepreg sheet to form a propeller-shaped skin having no bonding site between the upper skin and the lower skin at the propeller leading edge and the propeller trailing edge ;
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;
and repairing the open portion of the shell from which the core was removed.
A method for manufacturing a flight propeller, comprising the step of repairing the open area on a portion of the outer skin of the manufactured flight propeller. The core is made of a resin that is soluble in an organic solvent, and the solvent is the organic solvent,
6. The method for manufacturing a flight propeller according to claim 5 , wherein the core is taken out from inside the outer shell in a state where it is dissolved or swollen with the organic solvent. The core is made of a water-soluble resin, the solvent is water,
6. The method for manufacturing a flight propeller according to claim 5 , wherein the core is taken out from inside the outer shell in a dissolved or swollen state with water.