This application claims priority to European patent application 09 400025.4 filed May 27, 2009, the contents of which is incorporated in its entirety by reference herein.
1. Field of the Invention
The invention relates to a rotor blade, in particular of a main rotor of a rotary-wing aircraft or helicopter, made of fibre-reinforced plastic. This comprises a blade section and a connecting section for fastening the rotor blade to a drive device. The connecting section comprises a sleeve-shaped connecting device and lies at the end of the rotor blade opposite to the blade tip and therefore facing a drive axis. It connects the rotor blade at least indirectly to the drive device. For this it comprises at least one sleeve-shaped connecting device, for example, for a bolt connection. The rotor blade more favourably has two sleeve-shaped connecting devices which are disposed adjacent to one another in the plane of rotation of the blade since tilting moments of the blade from its forward travel or as a result of its inertia can be absorbed.
2. Description of Related Art
Nowadays rotor blades are usually manufactured using the wet or prepreg method of construction. This offers a low degree of automation and is associated with a large amount of manual work and is as a result very cost-intensive and liable to error. Even small improvements of the rotor blade or its method of manufacture can therefore have a cost-reducing or quality-enhancing effect. The development of new rotor blade systems is primarily directed towards reducing the power requirement, the weight and the maintenance expenditure as well as towards increasing the lifetime and reducing the manufacturing costs. The lifetime is substantially determined by the introduction of forces and the transmission of forces between the rotor blade and the drive device. The introduction of forces into the rotor blade is usually effected via loop and bolt connections which are dynamically highly loaded. Loop connections are regarded as solutions appropriate to fibres. It is found, however, that their operating strength is determined by the resin properties. As a result, additional structural-2-elements can be required to increase the dynamic strength. Bolt connections have provided useful as detachable connections. They make it possible, inter alia, to form a folding hinge which is used primarily in the military area.
GB-A 2 131 373 discloses a rotor blade for a main rotor of a rotary-wing aircraft, made of fibre-reinforced plastic comprising a blade section and a connecting section for fastening the rotor blade to a drive device which comprises a sleeve-shaped connecting device with flat fibre layers running substantially in the plane of extension of the connection section. An axial-radial elastomeric bearing is incorporated in the blade root for connection of the rotor blade.
It is therefore the object of the invention to further simplify the manufacture of a rotor blade of the type specified initially.
This object is achieved in a rotor blade of the type specified initially in that the connection device comprises flat fibre layers running substantially in the plane of extension of the connecting section or consists thereof. The connecting section of the rotor blade extends substantially in its plane of rotation. According to the invention, said section is formed from fibre layers likewise extending in the plane of rotation or from a corresponding fibre package. The invention therefore goes away from forming a loop-shaped connecting device by a so-called standing loop in which the fibre layers forming the loop stand perpendicularly to the plane of rotation of the rotor blade. Rather, when forming the loop- or sleeve-shaped connecting device, it follows the principle of the bearing stress connection of fibre layers located in the plane of rotation. This therefore makes it possible to achieve a very flat connecting section having only a small overall height. Thus, the connecting section has a lower aerodynamic resistance.
According to an advantageous embodiment of the invention, the fibre layers forming the connecting section comprise both unidirectional layers and also additional fibre layers running pivoted at an angle with respect to these. The alignment of the fibres in the unidirectional fibre layers corresponds to the longitudinal direction of the rotor blade. The unidirectional fibre layers can therefore in particular transmit the centrifugal forces of the rotor blade optimally and in a material-saving manner. The fibres of the additional layers can run as additional reinforcing layers between the unidirectional fibre layers at an almost arbitrary angle, for example of +/−30, +/−45, +/−60 or 0/90 degrees. They can comprise approximately 50-60% unidirectional fibre layers, 35-45% of +/−45 degree fibre layers and about 5-10% of 0/90 fibre layers. These additional layers can also be formed with biaxial or triaxial scrims or fabrics. The additional fibre layers can be provided in the connecting section in the same or different fractions to the unidirectional fibres between them. Thus, the entire cross-section in the connection zone can be filled with fibre material.
According to a further advantageous embodiment of the invention, the unidirectional layers run into the blade section of the rotor blade. They thus form a component both of the connecting section and of the blade section. There they can run continuously to the blade tip. In particular, they can form spars of the blade section which run in the longitudinal direction of the blade and form the leading edge of the blade. They thereby ensure a good connection of the blade section to the connecting section. The additional layers can also run at least partly into the blade section and contribute to its formation. Layers of the blade skin can also be tied into the connecting section. However, the continuous course of the unidirectional layers has the advantage compared to this that they run in accordance with the force flow and the direction of the centrifugal force and consequently transmit this with minimal usage of material into the connecting section in the best possible manner.
According to a further advantageous embodiment of the invention, the unidirectional fibre layers which tie into the blade section of the rotor blade, are predominantly disposed in a near-surface region of the connecting device. They therefore surround the additional or reinforcing layers, with the result that the connecting section experiences an increase in its bending stiffness and an improvement in its strength properties.
According to a further advantageous embodiment of the invention, the connecting section comprises additional reinforcing layers running at an angle of substantially 90 degrees with respect to the longitudinal axis of the rotor blade. The strength of the connecting sections can also be further improved by this means.
According to a further advantageous embodiment of the invention, all the fibre layers comprise fabric or scrim having a glass fibre and a carbon fibre component. The rotor blade and in particular its connecting section are therefore constructed in a mixed design of glass and carbon fibres which combined the advantages of both materials.
The sleeve-shaped connecting device is therefore formed according to the invention according to the principle of a bearing-stress connection. This means that the fibre layers in the area of bolt connection are interrupted by a sleeve-shaped gap. The gap can, as in the prior art, be omitted by incorporating the fibre layers of the rotor blade in the connecting section. According to an advantageous embodiment of the invention, the sleeve-shaped connecting device is formed by holes substantially perpendicular to the plane of extension of the connecting section. The hole leads to a bearing-stress connection which loads the fibre layers of the connecting section during operation more or less exclusively in their plane of extension and therefore optimally appropriate to the fibres. When a force is introduced via a bolt, as a result of the bearing stress connection, instead of a standing loop according to the prior art, there is no longer any deflection of forces into the fibre layers which could lead to delaminations and cracks in the loop. Rather, the loaded fibre layers run almost free from deflection between the connecting section and the rotor blade. As a result, a maximum load-bearing capacity is in turn possible with minimal material usage. This favours cost-effective production, long lifetime, small thickness dimension of the connecting section and a low weight of the rotor blade.
According to a further advantageous embodiment of the invention, the connecting device has a liner-shaped metal reinforcement. As a result, on the one hand, the introduction of force into the connecting section in fibre composite design can be improved and made more uniform and on the other hand, the wear of the connecting device can be reduced.
According to a further advantageous embodiment of the invention, the edge distances of the sleeve-shaped connecting device in and at right angles to the longitudinal axis of the rotor blade are different. Thus, the different cases of failure of the bearing stress connection can be countered. In the longitudinal direction of the blade, by dimensioning the edge distance of the connecting device at the front side, a sufficient shear strength can be achieved to prevent tearing out of the connecting device due to shear failure. The edge distance of the connecting device to the side edge running in the longitudinal direction of the blade possibly together with a distance from one another, determines its tensile strength in order to eliminate cheek rupture. The lateral edge distance can be kept somewhat lower by a somewhat higher fraction of unidirectional fibre layers.
The principle of the invention will be described in further detail hereinafter with reference to a drawing as an example. In the drawings:
b shows a sectional view according to
Comparable views are shown in
b shows a sectional view according to
The holes 16 are only drilled subsequently in the connecting section 12. This results in a very uniform and homogeneous formation of the regular cylindrical bearing stress of the holes 16 whereon their subsequent production can be identified without any doubts. Due to the undisturbed reveal formation, the remaining cross-section of the connecting section 12 is fully loadable as far as the edges of the bores 16, resulting in an optimal utilisation of the cross-section and therefore minimal dimensions of the connecting section 12. The holes 16 pass through the fibre layers S1 to S18 of the connecting section 12 perpendicularly to their plane of extension and therefore load these optimally in a manner appropriate to the fibres. During introduction of force via the bolts 20, due to the bearing stress connection of the holes 16, there is no deflection of force into the fibre layers S1 to S18 which could lead to delaminations in the connecting section 12. As a result, a maximum load-bearing capacity can be achieved with minimal material usage. This favours cost-effective production, long lifetime, small external dimension and a low weight of the rotor blade 1.
In the plan view of the connecting section 12 according to
A failure of the connecting section 12 in the direction transverse to the longitudinal direction of the blade through the two holes 16, i.e. a “cheek rupture” would correspond to a tensile failure. The cross-section thereby loaded is calculated from the width of the connecting section 12 multiplied by its height h minus the loaded bearing stress surfaces of the holes 16. Since sufficiently loadable cross section is available between the holes 16, the edge distance R1 can be smaller. The tensile loading is substantially absorbed by the unidirectional layers S2, S3, S5, S7 and S8 (cf.
The side views or sectional views according to
In the plan views according to
The layer S4 is a reinforcing layer consisting of a triaxial fabric. This no longer fills the entire connecting section 12 as shown by a comparison with the layer S3.
The following layer S5 again consists of unidirectional fibre material. This extends through the entire blade section 10 and expands in the connecting section 12 on its width. This likewise forms a part of the spar in the rotor blade 1. This also no longer fills the entire length of the connecting section 12 in the longitudinal direction of the rotor blade 1. This is followed by the layers S6 to S8 correspondingly.
Unlike the previous principle, the layer S10 forms a reinforcing layer consisting of unidirectional fibre material. In contrast to the previous layers S2, S3, S5, S7 and S8 of unidirectional fibre material, this is not involved in forming the spar in the rotor blade 1. The following layers S11 to S18 are also reinforcing layers which, with the exception of the last layer S18, no longer fill the complete connecting section 12.
The layers S1 to S3 as well as S5, S7 and S8 form a lower shell of the blade section 10 and are guided further in the connecting region 12 of the rotor blade 1. There they are, as it were, fanned out by providing the reinforcing layers S4, S6, S9 to S18 in between and to this end.
The edges L are also like the edges K (cf.
Since the preceding rotor wing which has been described in detail comprises an exemplary embodiment, it can be broadly modified in the usual manner by the person skilled in the art without departing from the scope of the invention. In particular, the specific cut of the fibre layers and the sequence of their arrangement can be effected in a different form to that described here. Likewise, the mechanical coupling to the connecting section can be configured in a different form if this is necessary for reasons of space or design reasons. Furthermore, the use of the indefinite article “a” or “an” does not exclude the fact that the relevant features can also be multiply present.
Number | Date | Country | Kind |
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09400025 | May 2009 | EP | regional |
Number | Name | Date | Kind |
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3321019 | Dmitroff et al. | May 1967 | A |
4110056 | Stevenson | Aug 1978 | A |
4304525 | Mouille | Dec 1981 | A |
4352632 | Schwarz et al. | Oct 1982 | A |
5439353 | Cook et al. | Aug 1995 | A |
Number | Date | Country |
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2 131 373 | Jun 1984 | GB |
2131373 | Jun 1984 | GB |
Entry |
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European Search Report dated Dec. 10, 2009, from corresponding European application. |
Number | Date | Country | |
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20100303628 A1 | Dec 2010 | US |