JPS6013880B2 - Rotor blade outer skin structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of a rotor blade of a wind turbine for helicopter L wind power generation, a propeller for a blower, or the like.

The center of gravity of the rotor blade is 2 points from the leading edge of the blade airfoil.
It is preferable to position the vane in the vicinity of 0 to 25% of the chord length, and for this reason, it is required to reduce the weight on the trailing edge side of the blade as much as possible.

Therefore, various improvements have been made to the blade rear structure.
For example, a rib structure in which a thin plate outer skin is supported by ribs arranged in the direction of the blade, and a sandwich structure in which a light material such as honeycomb or foamed plastic is filled between the blade outer skins are known.

However, in the rib structure, the ribs are installed at certain intervals in the longitudinal direction of the blade, so the outer skin between the ribs needs to maintain rigidity and strength, and the outer skin needs to be thicker, which increases the weight. In addition, it required high precision and labor to align the ribs, skin, and main girder with each other, and it was expensive.Also, the precision of the blade outline was not good.On the other hand, in the sandwich structure, Because the outer dimensions of the blade are determined by the core (core material) to be filled, high-precision curved surface cutting is required to form the core.
There is a drawback that the cost of cutting the core increases especially when the cross-sectional shape of the blade changes in the blade longitudinal direction, the thickness or inside changes, or the weeping is large.

In particular, at the connection between the main girder and the sandwich part, there is a problem that bonding is impossible unless the dimensional difference between the main girder and the core is made extremely small, and an expensive special adhesive is required. Therefore, each outer skin on the upper and lower surfaces that form the rear part of the blade is constructed with a sandwich structure filled with honeycomb core, etc., and each outer skin is configured to be adhesively bonded at only two places, the rear part of the main spar and the rear twill part of the blade, so that the aerodynamic force If it is configured so that it is transmitted to the main girder as a drum structure of the upper and lower skins and the main girder, cutting of the curved surface of the honeycomb core is not necessary, and the required precision of the main girder and the skin plate is reduced, and the parts It should have the effect that the number of points is extremely small and it is inexpensive. However, such attempts have not been successful. The reason for this is that an external air force applied to the rear part of the blade causes a large bending moment to act on the joint with the main girder, which cannot be withstood by adhesives or iron. In addition, it is necessary to apply a separate reinforcing member to the joint between the main girder and the outer plate from the inner surface of the blade, which increases the assembly effort and number of parts.
This is because there was a problem that the reliability of adhesion decreased. An object of the present invention is to provide a sandwich-structure rotor blade skin structure that solves these problems.

According to the present invention, the sandwich structure upper skin is connected to the upper part of the trailing edge of the main spar and forms an airfoil-shaped upper surface from the main spar to the trailing edge of the blade; A rotor blade outer skin structure comprising a sandwich structure lower skin forming an airfoil-shaped lower surface up to a rear green, and the rear ends of the upper skin and the lower skin are joined by a blade rear green. A thin plate portion is provided in the vicinity of the main spar joint of each of the outer skin and the lower skin, the outer skin thickness is thinner, and the bending rigidity is 4.0 mm higher than that of the other skin parts, and the length in the chord direction of the thin plate portion is set to the above-mentioned above. and approximately 3 of the mid-chord dimension of the lower skin.
A rotor blade skin structure characterized in that the rotor blade has a thickness of 15%.

In this case, it is preferable that the upper and lower outer skins have a sandwich structure with a lightweight core village such as foamed plastic or honeycomb structure interposed between fiber-reinforced plastic plates to reduce the weight as much as possible relative to the required strength. .

Furthermore, if an airfoil-shaped front part from the upper and lower skins to the blade front green is formed by the main spar, the structure of the blade can be simplified.

Further, the thin plate part may have a plate material structure with the core village of the sandwich structure removed, and the rear ends of the upper and lower skins may be directly connected to each other to form the blade rear twill part with the skin itself. By doing so, it is possible to obtain a rotor blade that has a simple structure, is easy to manufacture, and is lightweight.

Next, a detailed explanation will be given according to the drawings.

Figure i shows an embodiment of the present invention applied to a rotor blade of a helicopter, and Figure 2 is an enlarged sectional view of the airfoil shape of the blade in Figure 1 to Figure 3 is a partial enlarged view showing the external part. be.

In the illustrated case, the main girder 2 is a main structural member in which the front edge of the blade is integrally formed and is responsible for the main loads such as centrifugal force, bending moment load, and tear load applied to the blade.
A lug 3 is formed on the root side for attachment to a support mechanism for the rotor blade. Hanekawa front green section 5 and back green section 6
including. At the upper and lower ends of the rear edge of the main girder 2 are upper and lower outer skins 8? A connecting portion 7 with 9 is provided. The main spar 2, upper skin 8, and lower skin 9 form one airfoil. Here, the upper skin 8 and the lower skin 9 are joined to the main girder joining part 7 of each L, and are directly joined to each other by adhesive or rivets at the rear plan joining part 01 to form a trailing edge part. ing. However, if desired, other suitable members may be used to which the trailing ends of the upper and lower skins are connected to form the trailing twill. The upper skin 8 and the lower skin 9 have covers 11 at the root and tip of the rotor blades,
Except for the part connected to 12, "the two connecting parts 7,
No combination other than 10. The upper outer skin 8 and the lower outer skin 9 have a sandwich structure in which, for example, a glass fiber reinforced plastic skin 1, G5 is adhesively bonded to the upper and lower surfaces of a core material 13 of a honeycomb core.

The core material 13 has only a portion on its front edge side and rear edge side cut off diagonally. In this configuration, the thickness of the honeycomb core 3 may be thin, so it can be easily made to follow the curved surface without cutting into the curved surface.
Cutting can be done by simply cutting a flat surface. Moreover, precision is required only on the surfaces of the outer skins 8 and 9 that are exposed to airflow, and the other surfaces may have irregularities, so a molding jig is used to form the airfoil shape between the honeycomb core 13 and the end-hardened RP sheet. It can be manufactured by heating and curing once. For this reason, the upper and lower outer skins 8, 9 are manufactured at low cost. The upper and lower skins 8
, 9, the main girder joint part 7 and the honeycomb core diagonal processing part 17
A thin plate portion 16 having no honeycomb core 13 is formed between the two.

The length of the thin plate portion 16 in the chord direction is the middle C(
(see Figure 2), preferably 3% to 15%
selected to be. By providing such a thin slope portion 16 and selecting the thinnest portion 16 within the above range, a practical rotary blade outer skin structure capable of resisting the following external air force was obtained.

In other words, in a rotor blade having a conventional sandwich machine skin, in which there is no portion corresponding to the thin plate portion 16 or the portion is extremely short, the outer air force acting on the upper and lower skins 8 and 9 A bending moment load acts on the joint 7 with the main girder, and bonding or mirror joining of the joint 7 could not withstand the large bending moment load.

When the thin plate part 16 is provided near the connecting part with the main girder as in the present invention, since the thin plate part has lower rigidity than the honeycomb core insertion part, this part has an effect like a pin joint, and therefore the connecting part 7 It is possible to reduce the moment load acting on the To explain this point in more detail, the upper skin 8 and the lower skin 9 are each connected to the rear edge side of the main girder 2 by a pin joint, and the rear edge of the upper skin 8 and the rear green of the lower skin 9 are rigidly connected to each other. It can be seen as a composite structure of a triangular rigid frame structure and a truss structure. From another point of view, since the joint at the trailing edge of the upper skin 8 and the lower skin 9 undergoes some degree of rotation when subjected to a load, this rear green joint is also similar to a pin joint and has a triangular rigid frame structure. You can also think that. In the case of this triangular rigid frame or truss structure, the displacement of the trailing edge joint is extremely small compared to the bending displacement, so when considering the upper skin 8 and the lower skin 9 separately, each of them is It can be treated as Therefore, for example, considering the upper skin 8, this skin 8 may be considered as a beam whose leading edge is pin-coupled to the main girder 2 and whose rear edge is supported by a pin joint or by a rigid connection. For example, when a uniform upwardly distributed aerodynamic force is applied to the outer skin 8, the bending moment generated in the outer skin 8, assuming that both ends are pin joints, is maximum at the center in the chord direction, becomes 0 at both ends, and at the rear. When the edge is considered as a fixed support, it is 0 in the front green and increases in a quadratic curve shape toward the rear. In any case, if the connection between the upper skin 8 and the main girder is considered to be a pin joint, the moment becomes 0. In reality, the thin plate part 16 is not a perfect pin joint, but has properties intermediate between a rigid joint and a pin joint, so a certain amount of moment is generated at the joint between the upper skin 8 and the main girder. , its size is significantly reduced compared to the case where the thin slope portion 16 is not provided. This thing is
This is also clear from the schematic diagrams shown in FIGS. 4 and 5.

That is, when a uniformly distributed load is applied to a member fixedly supported at both ends, the moment at the fixed end is W12/12 if the member has uniform rigidity. Here, W is the distributed load, and 1 is the length of the material. Therefore, if a configuration is adopted in which a portion adjacent to the fixed end has a lower rigidity than other portions, the fixed rudder will have a small and false illusion. As an example, if the stiffness ratio is 1
The value of the fixed end moment in the case of 0 is set to 11/1 (
11 The length of the portion with low rigidity (1: total length) is shown in Figure 5.

As is clear from this, there is an optimum value of 11/1 that minimizes the fixed end moment in the vicinity of 11/1≠0.1, and in that case the fixed end moment is reduced to about 1'2. The rate of decrease in this moment and the optimal value of 11/1 vary depending on the rigidity ratio; the larger the rigidity ratio, the greater the reduction in the fixed end moment, and the optimal value of 11/1 is 4.
・It becomes thinner.

In order to increase the rigidity ratio, the thickness of the thin plate portion 16 may be made sufficiently thin, but there is a limit to this.

In other words, there is a limit to reducing the thickness of the plate in order to meet the requirements of not buckling due to the compressive force generated by the outer skin functioning as a truss, and there is a limit to the rigidity that can be obtained in practice. Optimal 1 for the ratio
1/] is between 3% and 15%. How the moment of the coupling portion is reduced when actually applied to a rotary blade will be explained in further detail with examples shown in FIGS. 6 to 8.

FIG. 6 shows the lift force distribution of a wing with a thin slope section according to the present invention, and FIGS. ) and the distribution of the moment of the upper skin and the trout shearing force when there is no such thing.The distribution of this moment and the deep shearing force can be easily obtained as follows. The distribution of shearing force is based on the assumption that the upper epithelium is a beam with both ends fixed and supported.
It is calculated assuming that a distributed lift force that decreases uniformly from the front end to the rear end acts on it. It is considered to be divided into a beam, a front slope section, a honeycomb section, a sandwich section, and a rear thin plate section, each of which has a different bending rigidity depending on its structure.
Based on these assumptions, the distribution of bending moment and shear force can be determined using the beam theory of mechanics of materials.
An example of this is shown in FIGS. 7 and 8. It should be noted that most of the lifting force is carried by the upper skin, and the load on the lower skin is small. When there is a thin plate part, the bending moment acting on the joint part is reduced to about 1/2 by providing the thin plate part, and the effect is clear.

On the other hand, in the sandwich structure section at the center of the upper outer skin, the moment increases by providing a thin plate section, but
The sandwich structure has sufficient strength and does not diminish the effects of the present invention. Further, the strength of the thin plate part itself is not a problem. This is because, generally, the strength of a structure including such a joint is controlled by the strength of the joint, and the strength of the parts other than the joint is usually numerically higher than the strength of the joint. Furthermore, even if there is a problem in areas other than the joint, the strength can be easily improved by increasing the thickness of the plate. On the other hand, even if the thickness of the joint is increased, the strength of the joint is only slightly improved. A more specific example is as follows. The rotor blade has a chord length of 750, a diameter of 10, and a rotation speed of 2.
It is assumed that the maximum lift force is generated at 0 pm.

As shown in Figure 3, the outer skin is composed of glass fiber reinforced plastics and a honeycomb core, and the thickness of the thin plate part is 3.
The ribs and sandwich structure have a core thickness of 1 and a skin of 0.
．． There should be 5 ribs. In this case, the load acting on the thin plate part is bending moment per unit width (1 fence) 14.1 x 9.
Rudder trout shearing force 0.22k per unit width (1 sail)
g Compressive force 0.31kg per unit width (1 fence)
The stress due to each is tensile and compressive stress due to bending moment 9.4k9 / chick shear stress due to rudder's 2 deep shear force
Compressive stress due to 2 compressive force of 0.11k9/0.10k9/bar Here, the compressive force is determined from the scale shearing force generated at the joint at the rear end of the blade out of the deep shearing force determined by the above calculation.

In other words, the upper skin and the lower skin are considered to constitute a triangular truss in which the front end is supported and the rear end is connected to each other. and find the compressive force of. The tensile and compressive stress due to the bending moment can be calculated by dividing the bending moment by 1'6 x [plate thickness]2, and the stress due to the trout shearing force can be calculated by dividing the number shearing force by 2/3.
× [Plate thickness] The stress due to tensile force can be calculated by dividing the tensile force by the plate thickness. The strength of the glass fiber reinforced plastics is approximately 40k9/2 fences for tensile compression and 10k9/2 ribs for deep cutting, and it is clear that the strength is sufficient.

In addition, regarding fatigue strength, the strength of glass fiber reinforced plastics after 107 cycles is 18[
9/side 2, there is about 3k9/skin 2 for the piece cutting, and there is plenty of room even when the maximum load is repeated.

However, stress concentration occurs at the transition between the thin slope and the honeycomb sandwich structure, but this can be easily avoided by reducing the gradient in the thickness direction of the honeycomb core and by making the layers of glass fiber reinforced plastics continuous. Can be lowered.

For example, when the gradient of the thickness of a honeycomb core is 30 degrees, the stress concentration is estimated to be 1.9 degrees at maximum, by analogy with the stress concentration of a solid metal structure. It has sufficient strength. The stress shown above can be easily reduced by increasing the plate thickness.

For example, if the plate thickness is increased by 1.2 times, the stress due to bending moment can be reduced to 1/1.44. The loads and stresses in each part can be determined more accurately by the finite element method using an electronic computer. In this way, by creating a thin plate part, there is no problem with the outer skin structure itself, including the thin slope part, and by changing the plate thickness, etc., it is possible to easily meet various rotor blades and practical requirements. .

In this embodiment, as shown in FIG. 3, three layers of glass fiber cloth are laminated on each side of the core in the sandwich structure part, and four additional layers are added to the thin plate part 16 as a neck layer, making a total of 10 layers. The required strength has been obtained.

From the concept of the present invention, the most suitable material for the thin plate portion 16 is a material having a low modulus of longitudinal elasticity and high tensile strength, such as glass fiber, but carbon fiber or Keplerian fiber may also be used. In particular, the advantages of the present invention can be further emphasized by combining carbon fibers or Keplerian fibers with high rigidity for the sandwich structure requiring rigidity, and using glass fibers with low rigidity near the thin slope section 16. I can do it.
Since the present invention is configured as described above, the following effects can be obtained. That is, it is not necessary to cut the curved surface of the core 13 at all, and it is sufficient to simply cut the end portion 17 diagonally, and it is not necessary to require severe cutting precision for the core, so it can be manufactured at a very low cost.

Furthermore, since precision is required only on one side (outer surface) of the outer skins 8 and 9, and the other side can be completely uneven, we adopted a method of heating and curing the honeycomb core and uncured FRP sheet at one time. The outer skin can be manufactured very easily and inexpensively, and a rear structure with a practical degree of rotation that has sufficient strength against aerodynamic forces can be obtained. In addition, conventional honeycomb sandwich structures and rib structures are extremely expensive and impractical for rotor blades with complex shapes, for example, when the cross-sectional shape of the airfoil changes in the longitudinal direction of the blade or when the blade thickness changes. Even in the case where the deflection or runout increases significantly, the outer shell structure of the present invention has the advantageous effect of being able to be implemented at low cost without any change in manufacturing costs or equipment processes.

In this way, it has become possible to easily and inexpensively provide a high-performance rotor blade with an aerodynamically optimal blade shape. In addition, when adhesive bonding is used for the connecting portion 7 of the main girder portion 2, since the connecting portion is provided continuously on the thin slope portion 16, the rigidity is low, and even with a small adhesive pressure, the bonding portions are in close contact with each other.
Adhesive thickness is sufficiently uniform and adhesive strength is highly reliable.

Furthermore, since there are only two joining parts per outer skin, pressure is always applied to the adhesive parts, and there is no adhesion failure, so assembly can be completed in one time, and assembly costs are extremely low. The effect of improving reliability can also be obtained. The method of the present invention is applicable not only to the present embodiment, but also to various modifications without departing from the concept thereof, and can be widely applied to rotor blades of various propellers, fans, etc.

[Brief explanation of drawings]

FIG. 1 is a plan view of a helicopter rotor blade having the skin structure of the present invention, FIG. 2 is an enlarged cross-sectional view taken along line 01D' in FIG. 1, and FIG. 3 is a portion m of FIG. 2. FIG. 4 is a schematic diagram showing the bending moment distribution of the conventional skin structure, FIG. 5 is a schematic diagram showing an example of the bending moment distribution of the skin structure of the present invention, and FIG. Fig. 2 is a schematic diagram showing the lift force distribution on the rotor blade, and Figs. 2 is a graph showing the moment distribution of the upper skin and the sea bream shearing force distribution. 1...Rotor blade, 2...King digit, 7...
・Joining part of outer skin to main girder, 8... Upper outer skin, 9...
...Lower integument, 10... Posterior green joint of integument, 16...
...Thin plate part. Sokancho Zui 2, Figure 3, Figure 4, Teikan 5, Book 6, *7, Box 8,

Claims (1)

[Scope of Claims] 1. A sanderch structure upper skin that forms an airfoil upper surface from the main spar to the trailing edge of the blade, which is connected to the upper part of the trailing edge of the main spar, and an upper skin that is connected to the lower part of the trailing edge of the main spar, In a rotor blade skin structure, the rotor blade has a sanderch structure lower skin forming an airfoil-shaped lower surface from to the blade trailing edge, and is configured by joining the rear ends of the upper skin and the lower skin at the blade trailing edge, A thin plate portion having a thinner outer skin thickness and lower bending rigidity than other outer skin portions is provided in the vicinity of the main spar joint of each of the upper skin and the lower skin, and the length in the chord direction of the thin plate portion is set to the above-mentioned upper skin. and an outer skin structure for a rotor blade, characterized in that the width of the lower outer skin in the chord direction is about 3 to 15%. 2. The rotating device according to claim 1, wherein the upper and lower outer skins have a sandwich structure formed by interposing a lightweight core member such as foamed plastic or a honeycomb structure between fiber-reinforced plastic plates. The outer skin structure of the wing blade. 3. The skin structure of a rotor blade according to claim 1, wherein the main spar forms an airfoil-shaped front part from the upper and lower skins to the leading edge of the blade. 4. The outer skin structure of a rotor blade according to claim 1, wherein the thin plate portion has a plate structure by removing the core material of the sanderch structure. 5. The outer skin structure of a rotor blade according to claim 1, wherein the rear ends of the upper and lower outer skins are directly connected to each other to form a blade trailing edge.