Suspension Of Rotor Blades On The Rotor Head Of A Rotorcraft Without The Use Of Flapping Or Drag Hinges

Abstract

Vibration-free and wobble-free suspension of rotor blades in the rotor head of a helicopter. The invention is applicable to blade suspensions wherein the blades are received into a blade-base holding sleeve and same is then mounted on a central member in the rotor head through a compact bundle of elastic lamellae which are arranged parallel to the rotating plane of the rotor and whose radially inner ends are connected to a pin fixed in the central member and coaxially with the rotor axis. In the present invention there is additionally provided bands of stiffly resilient material encircling the central member and further similar bands are arranged around the holding sleeve. Thus, in case of breakage of the central member the rotor blade will not only be temporarily held in operational position but will be permitted to move radially outwardly sufficiently to slightly unbalance the rotor and thereby give the pilot warning of the occurrence of damage. On the sleeves holding the base of the blade, the resilient bands will in the event of breakage hold the parts in operating relationship for a sufficient period of time to maintain the rotor operational until the break is presumably discovered on a routine inspection.

Description

BACKGROUND OF THE INVENTION

For the suspension of the rotor blades of a helicopter on the rotor head, it is known to use torsion-elastic, package-like, combined, tension lamellae which are arranged parallel to the rotating plane of the rotor. In such a known rotor (German Pat. No. 1,531,355) the ends of the tension lamellae facing the rotor axis are supported on a pin which is arranged coaxially with the rotor axis on the rotor head. This manner of support has the advantage that the centrifugal forces originating in the individual rotor blades can be balanced out by the pin.

If for each individual rotor blade a separate lamellae bundle is to be used, then these can also be secured on a common central member which is supported on the aforementioned pin. Also in this case the forces which engage the pin are in equilibrium so that it does not transmit forces onto the rotor head. Such an arrangement, however, fails to provide for the safety of the lamellae packages in case of a breakage of the central member in the zone of its connections, for example, due to defects in material, mechanical damage or a temporary overstress (as at an excessive rotational speed). This then results in loss of the aircraft.

The same is true in case of breakage of other overstressed parts, for example, the blade-base sleeves through which in known rotor blades are rotatably received in blade-angle-bearing sleeves provided on the rotor head. Also in this arrangement in which the respective connections for the blade-base or the blade-base sleeve are provided by a pin, no precaution is taken for the case of a breakage of the blade-base sleeves in the zone of the pins.

The purpose of the invention is to provide simple means by which the central member and the blade-base sleeves can be made operatively redundant in case of a breakdown resulting from a break in the zone of the fastening means thereof.

By means of torsion-elastic, unitary, combined tension lamellae which are arranged parallel to the rotating plane of the rotor and are secured on a central member which is arranged coaxially to the rotor axis on the rotor head, it is provided by the invention that the central member be enclosed on its periphery at least by one "bandage winding", as a band. Further, if each one blade-base sleeve which is associated with each rotor blade and is fixedly connected to same by at least one pin is rotatably connected to each one blade-angle-bearing sleeve which is provided on the rotor head, it is additionally provided that the pin be supported in openings in the blade-base sleeves which are each peripherally enclosed by at least one bandage winding, as a band. Upon the occurrence of a break of the central member and/or the blade-base sleeves in the general zone of the pin receiving openings, the centrifugal forces which originate in the rotor blades are received by the bands and if necessary are transmitted thereby. Such damage is then noticed in a simple manner if the bands consist of a fiber-reinforced, particularly glass-fiber-reinforced plastic. Upon the stressing of such stretchable bands an unbalance is created by a radially outward movement of the fastening means for the tension lamellae or the pin for the blade-base sleeves at the rotor hub. Such unbalance cannot be withstood for any extended period of operation and thus is an indication to the pilot that a break has occurred in the central member and/or one, or possibly more, of the blade-base sleeves. The pilot will then land immediately.

The bands may also consist of steel wire or boron fibers. In this case it is conceivable that in case of damage to the central member and/or the blade-base sleeves, the unbalance at the rotor hub may be so small that it is not noticed by the pilot. Therefore one can so design such bands that they can be loaded over a longer period of time and damage thereto is perhaps recognized only during an inspection of the aircraft.

The invention and further developments of same are discussed more in detail hereinafter in connection with one exemplary embodiment, as illustrated in the drawing, in which:

FIG. 1 is a side view of the central portion of a rotor, wherein one rotor arm is illustrated in a cross-sectional view and another in a longitudinal sectional view;

FIG. 2 illustrates a detail of FIG. 1 on an enlarged scale;

FIG. 3 is a sectional view along the line III--III of FIG. 2 and

FIG. 4 is an also enlarged sectional view along the line IV--IV of FIG. 1.

Detailed Description

In FIG. 1 a rotor head 1 of a four-blade rotor is fixedly connected to a rotor shaft 3 by screws 2. The rotor head 1 consists substantially of four radially outwardly extending rotor arms which comprise housings 4 for the blade-angle-bearings. A blade-base sleeve 7 is rotatably supported in each of the blade-angle-bearing housings 4 through roller bearings 5 and 6, said blade-base sleeve 7 serving at the same time as a mounting for the associated rotor blade 8. The pivotal and bending moments which act on the rotor blades 8 are conducted to the rotor head 1 through the blade-base sleeves and the roller bearings 5 and 6.

To receive the centrifugal forces which develop in the rotor blades 8 there are provided sleeve holding devices 9 arranged in the blade-base sleeves. Said sleeve holding devices are each supported on their sides toward the rotor axis against a shoulder 10 and are each connected to a pin 12 through package-like, combined, continuous tension or nonextensible, torsionally and elastically deformable lamellae 11 in the form of a continuous lamellae strip. Said pin 12 is supported in the rotor housing 1 coaxially with the rotor axis. The connection between the tension lamellae 11 and the associated sleeve holding devices 9 is provided by a connecting pin 13 which is guided through an opening 14 in the tension lamellae and is supported in the sleeve holding device.

To connect the tension lamellae 11 to the central pin 12, there is provided a pair of central disklike members 15 supported on said pin and having a number of connecting pins 16 which corresponds to the number of lamellae strips. Said pins 16 are supported in openings 17 of both central members, and are secured against axial shifting by retaining disks 18 which are arranged in the rotor head 1. The connection of the connecting pins 16 to the associated tension lamellae 11, or the lamellae strips, is again each provided by an opening 19.

As can further be seen from FIG. 1, both of the central members 15 are provided each with one band 20 on their peripheries. The bands 20 are constructed as endless turns or bands (FIG. 3) and are each embedded in a groove 21 on the periphery of the associated central member part (FIG. 2 illustrates the lower one of the two central member parts). They are made of any appropriate material, such as a glass-fiber-reinforced plastic. Such bands 20 will stretch upon a breakage of the central member 15 in the zone of one or more of its openings 17 under the effect of the centrifugal forces caused by the respective rotor blades 8. A slight radially outward movement of the connecting pin 16 then takes place at the breakage point in question and results in an unbalance at the rotor hub. This gives the pilot an immediate indication of damage.

In order to prevent damage to the elastic bands 20 by a break in the central member 15 adjacent the pin receiving openings therein transmitting the centrifugal forces through sharp broken edges, each central member part is provided on its periphery near each opening 17 with two concave recesses 22 which extend approximately parallel to the rotor axis (FIG. 3). Thus in the opening zone as a practical matter only such breaks will occur as are illustrated by lines 23 extending from the respective opening 17 to the nearest recess 22. Since the bands 20 will not touch these break points, damage to the bands by the broken edges is impossible.

In place of bands 20 of fiber-reinforced plastic, bands made of steel wire or boron fibers can also be used which can be secured against mechanical damage or splitting by a further band or an elastomer on a silicone or polyurethane base. The use of such bands has the advantage that the individual strands of the bands which secure the central member (which bands are steel wire or boron fiber bands) can move with respect to one another when under load.

The safety of the central member 15 against breakdown is enhanced in a simple manner by the bands 20. The same is true for the blade-base sleeves 7 with which each associated rotor blade 8 is connected through a pin 24. As is illustrated in FIG. 1, said bolt 24 is supported in the associated blade-base sleeve 7 in openings 25 provided therein and further supported by bands 26 of glass-fiber-reinforced plastic. The bands 26 are secured in place by suitable collars on sleeves 27. Each of openings 25 is further provided with two concave recesses 28 (FIG. 4). Thus, again, in case of breakage of a blade-base sleeve 7 in the zone of the openings 25 it is assured that the base will remain fully functional and damage to the bands 26 by broken edges is practically impossible.

It is noted in addition that for protecting all bands 20 and 26 against damage by friction on the central member 15 or the openings 25, same can be provided on their peripheries with a coating which resists mechanical abrasion. Such a coating may be made of lacquer or a plastic, as polytetrafluoroethylene or the like. With reference to the central member, same can also be constructed as a single piece. Further a rectangular form of the central member is not essential for, for example, by utilizing an uneven number of lamellae bands it can also be constructed triangularly or in other polygonal shapes.

Claims

The embodiments of the invention in which exclusive property or privilege is claimed are defined as follows:

1. In a suspension device for a plurality of rotor blades on rotor head means of a rotorcraft which is devoid or flapping and drag hinges in the connection between said rotor blades and said rotor head means, said suspension device having a rotatable rotor shaft supporting said rotor head means for rotation therewith, said plurality of elongated blades being mounted on said rotor head means and extending radially outwardly therefrom, support means for supporting each of said plurality of elongated rotor blades for rotational movement about an axis parallel to the longitudinal axis of said rotor blades and a plurality of nonextensible, torsionally and elastically deformable members for securing said rotor head means to each of said rotor blades, the improvement comprising:

at least one central dislike member mounted on said rotor head means coaxial with the axis of rotation thereof and being rotatable therewith, said central member including means for permitting a connection to each of said nonextensible, torsionally and elastically deformable members; and

elastic band means encircling said central dislike member to retain said central dislike member in an operating condition if said central dislike member should break during usage thereof, said broken central dislike member, and said elastic band means, during a rotation thereof, imparting one of a purposeful imbalance to said suspension device to thereby warn a pilot of the occurrence of a broken component in said suspension device and an insignificant amount of imbalance so that said breakage will be detected during inspection of said rotorcraft.

2. The improvement according to claim 1, wherein said support means for each of said elongated rotor blades includes means defining an opening therein spaced radially outwardly from said rotor head means, said rotor blade having a pin thereon adapted to be received in said opening and further elastic band means encircling said means defining said opening to retain said means in an operating condition if said means should break during usage thereof, said means, when broken, and said further elastic band means imparting one of a purposeful imbalance to said suspension device to thereby warn a pilot of the occurrence of a broken component in said suspension device and an insignificant amount of imbalance so that said breakage will be detected during inspection of said rotorcraft.

3. The improvement according to claim 2, wherein said means defining said opening has a plurality of recesses in the periphery thereof to encourage breakage to occur at the location of said recesses to isolate the breakage from said further elastic band means.

4. The improvement according to claim 2, wherein said further elastic band means consists of a fiber-reinforced plastic.

5. The improvement according to claim 2, wherein said further elastic band means consist of steel wire or boron fibers.

6. The improvement according to claim 5, wherein each of said elastic bands is secured by a further band of an elastomer on a silicone or polyurethane base.

7. The improvement according to claim 1, wherein said central disklike member has a plurality of recesses in the periphery thereof to encourage breakage to occur at the location of said recesses to isolate the breakage from said elastic band means.

8. The improvement according to claim 1, wherein said further elastic band means consists of a fiber-reinforced plastic.

9. The improvement according to claim 1, wherein said further elastic band means consist of steel wire or boron fibers.

10. In a suspension device for a plurality of rotor blades on rotor head means of a rotorcraft which is devoid of flapping and drag hinges in the connection between said rotor blades and said rotor head means, said suspension device having a rotatable rotor shaft supporting said rotor head means for rotation therewith, said plurality of elongated blades being mounted on said rotor head means and extending radially outwardly therefrom, support means for supporting each of said plurality of elongated rotor blades for rotational movement about an axis parallel to the longitudinal axis of said rotor blades and a plurality of nonextensible, torsionally and elastically deformable members for securing said rotor head means to each of said rotor blades, the improvement comprising:

means defining an opening in said support means for each of said elongated rotor blades, said rotor blades each having pin means thereon adapted to be received in said opening and elastic band means encircling said means defining said opening to retain said means in an operating condition if said means should break during usage thereof, said means, when broken, and said elastic band means imparting one of a purposeful imbalance to said suspension device to thereby warn a pilot of the occurrence of a broken component in each suspension device and an insignificant amount of imbalance so that said breakage will be detected during inspection of said rotorcraft.

11. The improvement according to claim 10, wherein said elastic band is secured by a further band of an elastomer on a silicone or polyurethane base.