US3476484A - Rotor blade construction - Google Patents

Description

Nbv. 4, 1969 K. BRUNSCH 3,476,484

ROTOR BLADE CONSTRUCTION 4 Filed July 25, 1968 INVENTDR Klaus Brunsch WWW by ATTORNEYS United States Patent 01 3,476,484 ROTOR BLADE CONSTRUCTION Klaus Brunsch, Weidach, Germany, assiguor to Bolkow Gesellschaft mit beschrankter Haftung, Postabhalfach, Ottobruun, near Munich, Germany Filed July 23, 1968, Ser. No. 746,810 Claims priority, applicatign 4G1tgrmany, Sept. 12, 1967,

Int. 01. B63h 1/06, 5/12, 5/14 US. Cl. 416-230 6 Claims ABSTRACT OF THE DISCLOSURE SUMMARY OF THE INVENTION This invention relates in general to the construction of rotor blades, and in particular, to a new and useful rotor blade of a fiber-reinforced plastic material having fiber strands which extend in the longitudinal direction of the blade and are formed into a plurality of loopchanges at the blade root region.

It is known to arrange fiber strands of a rotor blade element into loops which are wound about a separate securing bolt for supporting the rotor blade on a rotor head. Such a construction is a multiple statically undefined form of fastening and it is practically impossible to form the loops so that the loops of the blade and the bolts which secure the blade are stressed equally.

In another known solution all fiber strands of the blade element are combined into a single loop. This loop is stressed substantially by the centrifugal forces which appear during the operation of the rotor. The bending moments are absorbed by a blade root sleeve which surrounds the blade root. The reaction forces produced by the bending moments in the blade root sleeves act perpendicularly to the longitudinal direction of the blade and thus perpendicularly to the direction of the fiber strands. The size of the reaction forces depends on the span or length of the blade root sleeves. Since the reaction forces alternate periodically corresponding to the bending moments to which the blade is subjected during operation and in addition, since these reaction forces act in a direction which is unfavorable for the fiber reinforced plastic, that is in a direction perpendicular to the fiber direction, it is desirable to keep them as small as possible in order to prevent premature fatigue of the material. To do this it is necessary to provide long and heavy blade root sleeves. In addition, the harmful relative movement between the fitting and the blade root increases with increasing fitting length.

In accordance with the present invention there is provided a rotor blade construction having a root region formed in a manner so that a heavy root sleeve is not required and the reaction forces caused by the bending moments are absorbed from the blade root in a manner which is adapted to the type of material employed.

The inventive construction includes a rotor blade having reinforcing fiber strands which are divided in the blade root region approximately in the plane of the determinant bending moments into at least two flanges which are formed two loops at their ends. Such a division of the fiber strands into two flanges which extend in the plane of the moments makes it possible to split the bending moment into two forces which extend in the direction of the fibers. By proper selection of the spacing between the flange formation it is possible to influence the size of the bending forces. With a greater spacing the forces caused by the bending of the blade will diminish.

The two determinant load cases for a rotor blade of a helicopter appear, for example, in high speed maneuvers, and during transportation of the vehicle on the ground with the rotor standing still. In the former case the bending moments and centrifugal forces act on each blade. Due to the division of the total fibers into two flanges for each bending plane the bending forces may be kept very small. By selecting a suflicient spacing between the flanges the bending forces will be out weighed by the centrifugal forces. This results in a particularly favorable arrangement for the fiber reinforced plastic since only tensile forces will appear in the flanges.

When the rotor blades are subjected to substantially only bending forces which will occur when a rotor is standing still and the bending is produced by the weight of the rotor blades, the top flange portion of the root of the blade which is divided into two spaced flange elements is stressed by tensile forces. The bottom flange which may be reinforced by rigid material would be stressed by compressive forces. The tensile and compressive forces are transmitted through the fiber loops formed at the root blade portion. These loops are placed about securing bolts for securing the blade to the rotor head. With such a construction blade root sleeves are not required so that the total weight of the rotor is considerably reduced. However, in some instances it is possible or even desirable to provide short and light weight blade root sleeves which are constructed to absorb the bending moments acting on the blades when the rotors are standing still. In this manner the compressive forces which are less favorable for fiber reinforced plastics can be avoided, but the advantage of the fiber construction can be maintained without any undesirable stressing effects.

In many instances, it is suflicient if the blade is formed into a number of loops which are sized and spaced to provide for the greatest bending moment which would appear during operation. In many instances the pivotal bending moments considerably exceed the impact bending moments. But with the inventive arrangement the total number of fiber strands is divided in the pivotal bending plane into two juxtaposed flanges each formed with two loops at their ends. In this manner the lower impact bending moment can be absorbed by using a short blade root sleeve, for example, or the height of the loop which must have a certain dimension for manufacturing purposes as well as for reasons of surface pressure can be used as the basis for absorbing this bending moment.

In the case where the impact bending moment is of the order of the pivotal bending moment then the two flanges are arranged side by side in the pivotal bending plane and the loops are divided according to another feature of the invention into superimposed flanges and loops. With such a construction above advantages are also obtained in the impact bending plane. In the preferred arrangement the flanges and the loops are bordered by a single common fitting and the fitting fixes the position of the loops relative to each other and provides an underlining flange below each loop.

Accordingly, it is an object of the invention to provide a helicopter rotor blade construction which includes a fiber reinforced plastic body having fibers extending in the longitudinal direction of the blade and forming loops in the region of the root of the blade, the fiber strands being divided in the root region approximately in the plane of the determinant blade bending moment into at least two flanges which are formed into loops at their ends.

A further object of the invention is to provide a rotor blade structure which includes a fiber reinforced plastic blade body having fibers extending in the longitudinal direction and formed into an upper portion having two spaced apart loops and a bottom flange portion for reinforcing the area below the loops and forming eyelets and holding members for the loops.

A further object of the invention is to provide a blade construction for a rotor which includes a fiber reinforced plastic body having fibers extending in longitudinal directions and formed into at least two sets of loops at the blade inner or root portion, the loops being spaced apart in a direction perpendicular to the fibers with corresponding upper and lower loops being aligned for receiving securing bolts to aflix the blade to a rotor.

A further object of the invention is to provide a rotor blade for a helicopter which is simple in design, rugged in construction, and economical to manufacture.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a partial elevational and partial sectional view of the inner portion of a rotor blade constructed in accordance with the invention; and

FIG. 2 is a view similar to FIG. 1 of another embodiment of the invention and on a slightly enlarged scale.

k GENERAL DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of rotor blades made of fiber reinforced plastic is as a rule such that a plurality of rovings or strands which comprise a great number of individual glass threads are combined into fiber strand elements and impregnated with synthetic resin. These fiber strand elements are inserted into a mold which corresponds to the outside contour of the finished rotor blade and are hardened therein. The fiber strands which form at the blade root of the blade structure may be fastened with one or more loops by means of which the blade can be secured to the rotor head.

In FIG. 1 there is indicated a rotor blade generally designated 1 having a blade body constructed of a fi-ber reinforced plastic wherein the fiber strands in accordance with the invention is divided into two flange elements 2 and 3. The flange elements 2 and 3 are arranged side by side in the pivotal bending plane which corresponds approximately to the plane of rotation of the blade. The two flanges 2 and 3 each form a loop 4 and 5, respectively. The distance a between the centers of the loops is so selected that the forces caused by the pivotal bending which appear in one flange as a tensile force and in the other flange, as a compressive force is exceeded in each flange by the centrifugal force portion. In this manner only tensile force appears in the two flanges under normal operating conditions and fiber reinforced plastics are particularly suited for absorbing such forces.

The two loops 4 and 5 are bordered by a single two part fitting generally designated 6. The fitting 6 comprises a lower flange forming part 7 and an upper covering and guide part 8. Each of the parts 7 and 8 carry a through eyelet or bushing 9 which extends through the loops 4 and 5 respectively. The fitting 6 fixes the loops 4 and 5 in their respective positions and also protects the stress blade root against damage by erosion etc. The bushings 9 which extend through the loops serve to receive the securing bolts which are not represented and which are provided for fastening the blades to the rotor head (not shown).

In the construction indicated in FIG. 2, there is indicated a rotor blade body generally designated 20 having fiber strands which are divided at the blade root portion into four flanges; two in a top plane 21, 22, and two in a bottom plane 22 and 24. The distance 17 between the center lines of corresponding flanges of the top and bottom portions is chosen to provide for the absorption of the pivotal bending moment corresponding to the spacing provided in FIG. 1. In addition the bottom flanges are spaced from the top flanges by an amount to provide an adequate absorption of impact bending forces which are liable to act on the blade structure. This spacing is represented by the distance indicated 0.

A fitting of the same general type as the fitting 6 of FIG. 1 should be applied to the construction of FIG. 2, but it would have an adequate interior or central section to provide for the spacing in a vertical direction c between the upper loops 21 and 22 and the lower loops 23 and '24. The fittings in each instance can be made very short since they no longer have to absorb any moment loads which would appear during operation because of the division of the fibers into the spaced loops.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

l. A rotor blade construction for rotors of rotary aircraft which have a. fixed blade root mounting and a bendable blade subject principally to bending and centrifugal forces which act in substantially a horizontal plane during rotation of the rotor, comprising a blade body of a fiber reinforced material having fiber strands in said blade body extending in the longitudinal direction of the blade body and having an inner root portion which is adapted to be mounted on the rotor, all of said fiber strands being divided at said root portion into a plurality of loops forming at least two flanges arranged in spaced relationship in substantially a horizontal plane, the plane of the acting blade bending moments.

2. A rotor blade construction according to claim 1, wherein said fiber strands of said blade are divided in a substantially vertical pivotal bending plane into two juxtaposed ones of said flanges.

3. A rotor blade construction according to claim 1, wherein there are at least two said flanges arranged in an upper horizontal plane and at least two additional ones of said flanges arranged in a horizontal plane beneath said upper plane flanges.

4. A rotor blade construction according to claim 1, including a fitting of a rigid material bordering said flanges.

5. A rotor blade construction according to claim 1, wherein the number of said flanges comprises two flanges spaced apart in a horizontal plane of rotation of the rotor blade and including a fitting of a rigid material disposed beneath and corresponding to the outline of each of said flanges and covering the top thereof, said fitting also having a journal portion extending through the loops of said flanges to provide a mounting bearing for a securing bolt.

6. A rotor blade construction according to claim 1, wherein said blade body is divided into two upper hori- 5 6 zontal flanges and two lower flanges which are spaced FOREIGN PATENTS apart in a. direction transverse to the longitudinally ex- 1,334,446 7/1963 France tending fibers and with corresponding lower loops of said flanges being aligned with the corresponding loops EVERETTE POWELL JR p i Examiner of said upper flanges.

US. Cl. X.R. References Cited

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