Monocoque type rotor blade

The present rotor blade is constructed as a so-called monocoque or shell type blade for use in large fans and windmill rotors. For this purpose the blade is made of fiber reinforced synthetic material with a differnt orientation of the fibers in different sections of the blade. The transition between the blade proper and the connecting end of the blade is formed by a blade root section which has a connecting end of circular or elliptical cross-section and a wing facing end corresponding in cross-section to the blade cross-section. The blade root section has three zones. In the main leading edge zone including the leading edge and adjacent sides of the blade root section the reinforcing fibers extend in parallel to one another. The fibers also extend unidirectionally in a rear zone forming the trailing edge of the blade root section and in this trailing edge zone the fibers also extend in parallel to one another but at an angle relative to the fibers in the leading edge zone. An intermediate zone is located between the leading and trailing edge zones. The fibers in the intermediate zone are arranged in a cross-over relationship relative to one another. The connecting end is formed only by unidirectionally extending fibers.

CROSS-REFERENCE TO RELATED APPLICATION 
The present application corresponds to German patent application No. P 31 
03 710.0, filed in the Federal Republic of Germany on Feb. 4, 1981. The 
priority of said German filing date is hereby claimed for the present 
application. 
BACKGROUND OF THE INVENTION 
The present invention relates to a monocoque type rotor blade which 
comprises a shell manufactured of fiber reinforced synthetic material. The 
reinforcing fibers extend at least in the zone of the leading edge of the 
blade unidirectionally in the longitudinal direction of the blade. The 
fiber strands extend out of the blade proper and into the blade root. 
Rotor blades of this type, for example, as disclosed in German patent 
publication (DE-OS) No. 30 14 347 are preferably connected to a rotor hub 
in a hingeless manner by means of so-called tension bolts which are 
subject to tension loads only. However, heretofore, it has been necessary 
to limit the monocoque type construction to the blade shell proper if it 
was desired to avoid additional hardware for the blade root. Thus, the 
blade shell proper was constructed to comprise a support core between two 
cover skins which support core is soft relative to tension forces or 
loads. The cover skins were constructed of fiber reinforced synthetic 
material. In this connection reference is made to German Patent 
Publication (DE-OS) No. 2,832,098. Additionally, it is necessary to employ 
for the rotors of large scale wind energy collecting windmills a flange 
type bearing adapter which must conform to the blade angle bearing. Such 
adapter is necessary because the blades for such large scale rotors 
require an adjustability of the pitch angle of the rotor blades and 
because of the wing profile of the blade root section. Besides, this type 
of prior art construction is rather heavy which is undesirable for 
lightweight structures. 
OBJECTS OF THE INVENTION 
In view of the above it is the aim of the invention to achieve the 
following objects singly or in combination: 
to provide a rotor blade of the type mentioned above for a hingeless 
connection to the rotor hub, whereby the rotor blade is to be constructed 
in such a manner that a direct connection may be accomplished between the 
blade or shell root and a blade angle bearing directly by means of a 
tension bolt connection; 
to simplify the construction of rotor blades for use in large scale fans 
and windmills while simultaneously satisfying the requirement of an 
aerodynamic construction even of the blade root section; and 
to connect each blade root section with its connecting end to a respective 
rotor hub flange by means of a plurality of tension loaded bolts for 
increased safety. 
SUMMARY OF THE INVENTION 
According to the invention there is provided a monocoque rotor blade 
especially for large scale fans and windmills, wherein the blade root 
section has a radially inner connecting end having a circular or 
elliptical shape which is constructed of unidirectionally extending fiber 
strands. The strands of the leading and trailing edges are so located that 
they come together substantially at the connecting end of the blade root 
section while a gusset type zone in which the reinforcing fibers are 
arranged in a cross-over relationship is located between the leading and 
trailing edge zones. Thus, the connecting end is formed by fiber strands 
which in turn form exclusively supporting blade zones subject to tension 
forces. This type of structure assures that the transition formed by the 
blade root between the wing section of the blade and the connecting end of 
the blade root section has a bending stiffness which is undiminished 
relative to the strength of the wing section of the blade. 
The stiffness of the rotor blade relative to lead-lag movements may even be 
increased by merely extending the unidirectionally running fiber strands 
forming the curved surface of the trailing edge of the blade root section, 
into the trailing edge of the wing section proper of the blade. 
Preferably, the trailing edge zone of the blade root section has a width 
which increases from the interface between the root section and the wing 
section to the connecting end of the root section. In other words, the 
fiber strands forming the trailing edge zone of the blade root taper 
toward the trailing edge of the wing section in the radial, outward 
direction. Due to this tapering it is possible to splice certain 
unidirectional fiber strands of the trailing edge zone with the fiber 
strands of the intermediate zone, whereby longitudinal forces resulting 
due to the blade connection may be introduced through the intermediate 
zone having a crosswise fiber orientation, into the unidirectionally 
extending fibers which form the leading edge of the blade shell 
construction. Thus, the intermediate zone with its crosswise fiber 
orientation is subjected to shearing loads which are taken up as 
longitudinal loads by the leading edge of the rotor blade which leading 
edge performs the function of a support spar. 
The present rotor blade is simple in its structure and satisfies 
simultaneously the requirement that the blade root section has a flow 
dynamically advantageous contour. This flow dynamically advantageous 
contour is achieved due to the width of the curved surface of the trailing 
edge zone of the blade root section which width is relatively large 
compared to the profile depth of the wing section. The contour of the 
blade root section may be further improved in a flow dynamic sense by 
providing edge type transitions between the intermediate zones and the 
zone forming the trailing edge of the blade root section. 
Another advantage of the invention is seen in that the fibers are utilized 
so as to exploit the fiber characteristics in an optimal manner. Another 
advantage is seen in that the connecting bolts for the blade connection 
may be subjected to a biasing without any problems to assure a uniform 
minimum stiffness of the blade connection during its operation. By 
providing a substantial number of tension loaded connecting bolts for each 
blade it is possible to provide a substantial safety factor.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BEST MODE 
OF THE INVENTION 
FIG. 1 shows a partial, perspective view of a rotor blade according to the 
invention having a wing or blade section 1 and a root section 2. Both 
sections are constructed of fiber reinforced synthetic material. The wing 
section 1 has a leading edge zone 1.1 forming a support spar 3, two 
intermediate zones 1.2 and a trailing edge 1.3. The fibers in the leading 
edge zone 1.1 and in the trailing edge zone 1.3 extend unidirectionally 
substantially in parallel to the longitudinal direction of the blades. The 
fibers in the intermediate zones 1.2 extend in a cross-over relationship. 
The wing section 1 has a radially inner end 1.5 having a given 
cross-sectional profile or area. Similarly, the root section 2 has a 
radially outer end 2.5 with the same cross-sectional area so that both 
sections may merge smoothly into each other. The root section 2 also has a 
leading edge zone 2.1, two intermediate zones 2.2 and a trailing edge zone 
2.3. Further, the root section 2 has a connecting end 2.4 which is secured 
to a rotor hub member 4 as will be explained in more detail below with 
reference to FIG. 2. 
Referring further to FIG. 1, the connecting end 2.4 has a circular or 
elliptical configuration and the zones 2.1, 2.2, and 2.3 are so shaped 
that the contour surface of the root section 2 may be projected into a 
flat or two-dimensional plane when the contour surface of the root section 
2 is unrolled. This feature of the invention has the advantage that the 
manufacturing is simplified because the laminating molds may be assembled 
from a plurality of individual mold surface components, for example, the 
mold surface components may comprise one component for the leading edge 
zone 2.1, another component for the two intermediate zones 2.2 and still 
another component for the trailing edge zone 2.3. 
The fiber orientation in the root section 2 is the same as the fiber 
orientation in the wing section 1. To illustrate the fiber orientation the 
longitudinal lines in the leading edge zones 1.1 and 2.1 indicate the 
unidirectional extension of the reinforcing fibers in these zones. The 
same applies to the unidirectional extension of the fibers in the trailing 
edge zones 1.3 and 2.3. The fibers in the intermediate zones 2.2 also 
extend in a crossover relationship as in the zones 1.2 of the wing 
section. The intermediate section 2.2 form gussets between the leading and 
trailing edge zones. Further, the flow dynamic characteristics of the 
roots and wing section may be improved by providing an edge type 
transition 1.6 and another edge type transition 2.6 between the 
intermediate zones 1.2, 2.2 on the one hand and the respective trailing 
edge zones 1.3 and 2.3 on the other hand. 
Due to the arrangement of the unidirectionally extending fibers in the zone 
2.1 these fibers form approximately two thirds of the circumference 
constituting the connecting end 2.4 of the root section 2. The remaining 
one third is formed by the curved extensions 2.3' of the trailing edge 
zone 2.3 reaching with its extensions 2.3' substantially to the leading 
edge zone 2.1 at the connecting end 2.4 so that the gussets 2.2 of fibers 
arranged in a crosswise formation do not reach into the connecting end 
2.4. Thus, the connecting end 2.4 itself is completely formed by 
unidirectionally and hence homogeneously extending fiber strands. 
The intermediate zones 2.2 may be formed as part of an outer blade envelope 
only partly shown at the zones 2.2. In other words, the outer blade 
envelope and the intermediate gussets 2.2 will have the above mentioned 
crosswise fiber orientation which is very effective for a force 
transmission from the trailing edge zone 2.3 into the leading edge zone 
2.1 forming the supporting spar of the blade structure. The force 
transmission subjects the gussets 2.2 to shearing loads which are taken up 
well by the crosswise fiber orientation. The outer envelope of which the 
gussets 2.2 form a part, will enclose the leading and trailing edges of 
the entire blade structure. 
Since the trailing edge zones 2.3 have a curved shape with extensions 2.3', 
the width of the trailing edge zone 2.3 increases from the radially outer 
end 2.5 to the connecting end 2.4. Thus, the fiber strands of the trailing 
edge zone 2.3 which end at points radially inwardly of the root end 2.5 
are spliced into the gussets 2.2, thereby improving the force transmission 
from the trailing edge zones 2.3 into the leading edge zones 2.1. 
Additionally, the fibers which extend unidirectionally along the entire 
length of the trailing edge zone 2.3 and thus into the trailing edge zone 
1.3 of the wing section 1, contribute to the overall blade stiffness in 
the lead-lag direction of the blade. 
Incidentally, the above mentioned subdivision of the blade root into 
several zones as described does not depend on the particular number of 
zones for its operability. Thus, the number of zones may be larger or 
smaller and the teaching of the invention will be satisfied as long as 
longitudinally extending, unidirectional fiber strands form the connecting 
end 2.4 substantially entirely. 
FIG. 2 shows a sectional view along section line 2--2 in FIG. 1. The flange 
4 may have the shape of a circular ring or disk and it may form a radially 
outer portion of a bearing. The connecting end 2.4 of the root section 2 
is connected to the flange 4 by a plurality of tension bolts 5, only one 
of which is shown in FIG. 2. Each bolt extends in an opening 9 which is 
formed by a respective spacing between two fiber strand layers 6 arranged 
one above the other. Preferably, each layer 6 has the same thickness. The 
radially outer ends of the fiber layers 6 merge into each other in a zone 
10' and the wedge shaped spacing is filled with a filler member core 7, 
for example, made of a foam synthetic material. The tension bolts 5 are 
secured in threaded holes of respective locking members 11 extending 
through cross-bores 8. The longitudinal axis of these cross-bores 8 
extends substantially perpendicularly to the longitudinal axis of the 
tension bolts 5. The openings 9 may be formed as longitudinally extending 
bores in the filler cores 7. 
Due to the cross-bores 8 it is desirable to reinforce the root section 2 in 
the zone of the layers 6 by cover layers 10 having a crosswise fiber 
orientation. The cover layers 10 preferably end in the zone 10' outside 
the core 7. The cover layers 10 have a cross-over fiber orientation. If 
necessary, a plurality of such fiber layers may be used as reinforcements, 
whereby layers with a unidirectional fiber orientation may alternate with 
layers of a crosswise fiber orientation. The fiber orientation in the 
unidirectional layers may extend in the longitudinal direction of the 
blade or in a direction extending across the longitudinal blade direction. 
By a proper combination of these reinforcing layers 10 with glass fibers 
and carbon fibers the root section 2 may be provided with a thermal 
expansion coefficient or characteristic corresponding to that of the 
connecting flange 4 which is normally made of metal. Providing the root 
section 6 and the flange 4 with the same thermal expansion characteristic 
has the advantage that a uniform stiffness of the blade connection is 
assured in operation. 
The connection between the connecting end 2.4 of the root section 2 and the 
flange 4 by means of the locking members 11 in the cross-bores 8 and by 
means of the respective tension bolts 5 has the advantage that the tension 
bolts 5 may be biased by adjusting the respective nut 12. For this purpose 
it is preferable to use tension bolts 5 of the so-called necked-down type 
with a reduced diameter section intermediate the threaded ends as shown in 
FIG. 2. Thus, the locking members 11 merely require a threaded hole 
without any need for further locking means. 
Although the invention has been described with reference to specific 
example embodiments, it will be appreciated, that it is intended, to cover 
all modifications and equivalents within the scope of the appended claims.