TAIL ROTOR OF A TURNTABLE AND BLADE HOLDER

Description

TECHNICAL FIELD

[0001] The present invention describes a tail rotor head of a shrouded tail rotor of a rotary wing aircraft, comprising at least a pitch control unit and a tail rotor hub, wherein a multiplicity of tail rotor blade holder is connectable reaching through openings in the tail rotor hub and the pitch control unit at the tail rotor head, such as a tail rotor blade is detachable connected at a first side of the tail rotor blade holder and a tension torsion strap is detachable mounted at a second side of the tail rotor blade holder, wherein the tension torsion strap is running from the tail rotor head at least partly through the tail rotor blade holder radially outward in direction of the tail rotor blade, as well as a blade holder for detachable fixing of a tail rotor blade in a tail rotor hub on a first side and holding a tension torsion strap and connected to a pitch control unit on a second side.STATE OF THE ART

[0002] From EP3315403 a tail rotor blade attachment device or blade holder is known, comprising a blade holder with an essentially tube-like shape. A tail rotor blade is attached directly at one connection eye of a tension torsion strap, wherein the tension torsion strap partially protrudes through the blade holder. The tail rotor blade and the blade holder are connected with the second connection eye of the tension torsion strap at a rotor hub in which a pitch control unit is inserted, wherein the parts are covered by a hub cap. The tube-like blade holder shows a pitch horn or control lever, connected to a part of the pitch control unit and the blade holder is flanged in the inside of the hub.

[0003] Accordingly the blade holder, the tension torsion strap and the whole tail rotor blade can be deflected while the rotary wing aircraft is operating. The tube-like blade holder and the tension torsion strap are at least partly inserted in the hub and additionally internally mounted for stability reasons. An overview of the prior art is shown in Figure 6, showing Figure 9 of EP3315403. A compact structure is reached, showing highest stability but maintenance was no issue, while designing the tail rotor head. The prior art was not focused on easy blade replacement and the flexibility to select freely the most suitable material for both parts.

[0004] The tube-like blade holder, the connected tension torsion strap and the tail rotor blades can only be removed from the tail rotor head, after removing a cover of the tail rotor hub and disassembling of almost all components mentioned.

[0005] Due to the complicated structure and the concealed or hidden attachment of the components at the tail rotor head, which is usually covered, maintenance work is difficult in practice. The known tail rotor blade attachment device is always covered in a rotor hub under a rotor hub cap, when connection of the tail rotor blade, blade holder and tension torsion strap are completed. The maintenance and especially the replacement of a single tail rotor blade is only possible after many work steps have been carried out.

[0006] Another tail rotor of a helicopter is described in WO 93 / 02918 A1 of The Boeing Company. This rotor includes a rotor shaft, a rotor hub, a rotating control shaft, a stationary control shaft, and an actuator for moving the rotating control shaft axially along the rotor shaft. The rotor hub includes rotor arms, each supporting a pitch shaft for pivotable movement about a pitch axis. Each pitch shaft is adapted to support a rotor blade whose angle of attack changes with movement of the pitch shafts. A rotor blade is attached to each pitch shaft.

[0007] Yet another rotor for a rotorcraft is described in EP 0 680 876 A1 of Eurocopter France. Each rotor blade comprises a blade root with a sleeve and two coaxial carriers. The sleeve mounted rotatably about an inclination axis in two coaxial bearings, which are mounted in one of two walls of a hub body of a hub. Thereby, the rotor blade is connected to the hub by a flexible arm that can be rotated about the tilt axis.1 DESCRIPTION OF THE INVENTION

[0008] The object of the present invention is to create a shrouded tail rotor head of a rotary wing aircraft with a multiplicity of tail rotor blade attachment devices and a tail rotor blade attachment device, allowing easy replacement of single rotor blades, a more simplified maintenance of the tail rotor head and therewith of the rotary wing aircraft.

[0009] The solution of the invention is provided by a tail rotor head and multiplicity of tail rotor blade holders of a shrouded tail rotor of a rotary wing aircraft. The tail rotor head comprises at least a pitch control unit, a tail rotor hub and tension torsion straps. The multiplicity of tail rotor blade holders is connectable to reach through openings in the tail rotor hub and the pitch control unit at the tail rotor head, such as a tail rotor blade is detachably connectable at a first side of one of the multiplicity of tail rotor blade holders and the tension torsion strap is detachably mounted at a second side of the one of the multiplicity of the tail rotor blade holders, wherein the tension torsion strap is running from the tail rotor head at least partly through the tail rotor blade holder radially outward in direction of the tail rotor blade. The blade holders comprise a strap holding part and a moulded blade holding part, wherein the blade holding part comprises a flange with disc-like shape and an integrally formed mounting bracket with two parallel bracket arms, wherein the tension torsion strap is fixed in the tube-like strap holding part by a strap holding bolt with one connection eye in a connection bore, while one end of the tail rotor blade is detachably fixable independently and spaced apart from the tension torsion strap in a bracket interior of the mounting bracket with at least one blade bolt passing a bore in the blade holding part, wherein the blade holding part is located outside of the tail rotor hub, wherein a circumference of the flange is adapted to the opening in the tail rotor hub. The pitch control unit is placed inside the tail rotor hub, the strap holding part is lying completely inside the tail rotor hub and the blade holding part is protruding completely out of the tail rotor hub.

[0010] No further components, such as hub caps, rotor hubs or control spiders have to be removed or disassembled to replace a single tail rotor blade individually, by using simplified fastening means. Thereby the maintenance effort will be significantly reduced.

[0011] Furthermore, the disposed position of the blade attachment and the extension of one of the blade bolts allows easy balancing of the rotor head respectively the tail rotor.

[0012] Parts of the tail rotor blade attachment device are accessible at any time from the outside of the tail rotor head respectively the tail rotor hub, wherein also a possibility is given, to connect at least one balancing weight to the blade holder to balance the tail rotor after installation of all tail rotor blades at the tail rotor hub.

[0013] Our split design of the blade holder is more focused on easy blade replacement and the flexibility to select freely the most suitable material for both parts, e.g. composite fibre reinforced plastics for the blades and metals, e.g aluminium, for the blade holder.2 BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Further understanding of various aspects of the invention can be obtained by reference to the following detailed description in conjunction with the associated drawings, which are described briefly below.

[0015] A preferred exemplary embodiment of the subject matter of the invention with some additional optional features is described below in conjunction with the attached drawings. Figure 1shows a perspective view of a tail rotor of a rotary wing aircraft partly covered by a shroud. Figure 2ais an explosive view of a tail rotor with partly deconstructed tail rotor head, a tail rotor blade and a tail rotor blade attachment device, while Figure 2bshows a detailed view of a part of a tail rotor blade the tail rotor blade attachment device according figure 2a. Figure 3ashows an explosion view of a blade before connection to the tail rotor blade attachment device, while Figure 3bshows a connected tail rotor blade in a side view. Figure 4shows a tail rotor blade attachment device in a side view, wherein balancing with appropriate means is shown. Figure 5shows prior art Figure 9 from EP3315403. DESCRIPTION

[0016] A shrouded tail rotor 1 of a rotary wing aircraft is shown in Figure 1, which here shows a circumferential shroud 4 enveloped spaced apart from the axis of rotation L. In the centre of the tail rotor 1 a tail rotor head 3 comprising a multiplicity of parts is shown, here only a hub 8 and a covering hub cap 9 are visible. A multiplicity of tail rotor blade attachment devices 6 or blade holders 6 is attached to the tail rotor head 3. Tail rotor blades 2 are directly attached to the blade holders 6 and therewith indirectly with the tail rotor head 3. The shape of the blade holder 6 and the location of the blade holder 6 guarantees the advantageous features of the here described invention.

[0017] The exploded view Figure 2a shows the components in more detail, whereby only the attachment of one rotor blade 2 by means of one blade holder 6 over a tension torsion strap TT on the tail rotor hub 8 and a pitch control unit 5 of the tail rotor head 3 is shown here as an example. A signal from a control system of the rotary wing aircraft is transferred via the pitch control unit 5 to the tail rotor blades 2.

[0018] The tail rotor head 3 is at least formed by the hub cap 9, the pitch control unit 5, the tail rotor hub 8 and a number of tension torsion straps TT, according to the later attached blade holder / tail rotor blade attachment devices 6 and tail rotor blades 2.

[0019] The tension torsion straps TT are fixed with one connection eye at the hub 8, each protruding through an assigned hole in the hub 8. The hub 8 provides support for the blade holder 6.

[0020] The pitch control unit 5 is placed inside the hub 8, showing connecting links for connecting a part of the tail rotor blade attachment devices or blade holder 6. The pitch control unit 5 also shows openings or recesses, such that the blade holder 6 can protrude in radial direction.

[0021] Each blade holder 6 is connectable at an assigned tension torsion strap TT and an assigned link at the pitch control unit 5. After attachment of the blade holder 6 indirectly at the hub 8, the hub cap 9 is covering the hub 8. A part of the blade holder 6 protrudes from the hub 8. With two bolts 7 the tail rotor blade 2 is fixed at their assigned blade holder 6. At least one bolt 7 is necessary.

[0022] The blade holder 6 comprises a strap holding part 60 and a blade holding part 61, which are moulded together at a linear distance from one another. The strap holding part 60 has a tube-like shape and on a first side a connection bore 600 is recessed, which allows a strap holding bolt 601 to be passed through. In practice, the strap holding part 60 is put over the tension torsion strap TT, not depicted in figure 2b. With the strap holding bolt 601, the tension torsion strap TT is detachably connected to the blade holder 6. With a pitch horn 602 at the strap holding part 60, the blade holder 6 is detachably connected to the pitch control unit 5, allowing transmission of rotary movements from the pitch control unit 5 to the blade holder 6. Also this connection can also be achieved by a screw connection.

[0023] As depicted in figure 2b, the wall of the hub 8 shows an opening 80, through which the blade holder 6 is fed. While the strap holding part 60 is lying completely inside the tail rotor hub 8, the blade holding part 61 is protruding completely out of the hub 8. The blade holding part 61, comprises a flange 610 with a disc-like shape and an integrally formed mounting bracket 611 with two parallel bracket arms 6110. The flange 610 is moulded to the strap holding part 60 and forms part of the blade holding part 61, merging into the strap holding part 60. The circumference of the flange 610 is adapted to the opening 80 in the tail rotor hub 8.

[0024] In the mounting bracket 611 of the blade holding part 61, fully traversing bores 612 are arranged, through which the blade bolts 7 can reach. Of course, corresponding through holes 20 must be arranged on each tail rotor blade 2. By using two blade bolts 7, an anti-twist connection is possible, because the tail rotor blade 2 cannot rotate relative to the blade holder 6 and therewith relative to the hub 8, the connection between blade 2 and blade holder 6 is fixed. The blade holder 6 itself can rotate around its longitudinal axis, aligned with centrifugal force direction. Relatively to the tail rotor hub 8, the tail rotor blade 2 can and must rotate in blade pitch for thrust control of the rotary wing aircraft.

[0025] In Figure 3a the connection of the tail rotor blade 2 with the blade holder 6 and therewith, indirectly with the tail rotor hub 8 is shown. Even with connected hub cap 9, the blade holding part 61 of the tail rotor blade holder 6 is reachable outside of the tail rotor hub 8 and a blade 2 can be easily replaced by simply removing the two blade bolts 7. Beside the bolt and nut connection by the two blade bolts 7, a plug connection with a split pin 72 at each blade bolt 7 can additionally be fixed. Accordingly, a suitable blade bolt 7 with a bore 70 and a suitable split pin receptacle 71 must be used, if the additional securing split pin connection is used.

[0026] Each blade bolt 7 is inserted between the bracket arms 6110 of the mounting bracket 611, reaching through a bracket interior 6111.

[0027] The connected and securely attached tail rotor blade 2 at a blade holder 6 and indirectly connected at the tail rotor hub 8 is shown in figure 3b in more detail. The tail rotor blade 2 is formed in such a way that it is fully inserted into tan interior 6111 of the mounting bracket 611 of the blade holding part 61 and held there by the at least one blade bolt 7 and / or the additional detachable split pin connection with at least one blade bolt 7. Most preferred two blade bolts 7 should be used.

[0028] Optionally the at least one blade bolt 7 can be equipped with weight attachment means 11, to connect a balancing weight 12. Such balancing weights 12 are used to balance the tail rotor head 3 respectively the tail rotor 1 after installation of all tail rotor blades 2 at the tail rotor hub 8.

[0029] The weight attachment means 11 can be for example an extension at the blade bolt 7 that allows installation of at least one balancing weight 12. Usually one or more symmetrical bodies with concentric through-hole are used as weights 12. Such a balancing weight 12 could be a washer. Here the blade bolt 7 has a prolonged cylindrical section, at which again with a detachable split pin connection one or more balancing weights 12 can be attached. The balancing weights 12 can also be attached with a nut.

[0030] The tail rotor blade attachment device 6 or blade holder 6 is to be formed, that the blade holding part 61 can hold the tail rotor blade 2 independently from the strap holding part 60, which holds the tension torsion strap TT. Therewith a removal of the tail rotor blade 2 independently from the rest of the parts, without removing many other parts is possible. The stick out of the blade holding part 61 from the tail rotor hub 8 leads to a very easy access. An optimized fast coupling of the at least one blade bolt 7 to the blade holder 6 is useful, just as the creation of a simple balancing method. Of course, sufficient stability and strength of connections especially in the helicopter area must be provided.LIST OF REFERENCE NUMERALS

[0031] 1 tail rotor 2 tail rotor blade 20 through hole 3 tail rotor head 4 shroud 5 Pitch Control Unit 6 tail rotor blade attachment device / blade holder 60 strap holding part / tube like part 600 connection bore 601 strap holding bolt 602 pitch horn 61 blade holding part 610 flange 611 mounting bracket 6110 bracket arms 6111 bracket interior 612 bore 7 blade bolt 70 bore (in blade bolt) 71 split pin receptacle 72 split pin 8 tail rotor hub 80 opening 9 rotor hub cap 10 assembling / disassembling direction 11 weight attachment means 12 balancing weight the detachable split pin connection TT tension torsion strap

Claims

1. Tail rotor head (3) and multiplicity of tail rotor blade holders (6) of a shrouded tail rotor (1) of a rotary wing aircraft, the tail rotor head (3) comprising at least a pitch control unit (5), a tail rotor hub (8) and tension torsion straps (TT), wherein the multiplicity of tail rotor blade holders (6) is connectable to reach through openings (80) in the tail rotor hub (8) and the pitch control unit (5) at the tail rotor head (3), such as a tail rotor blade (2) is detachably connectable at a first side of one of the multiplicity of tail rotor blade holders (6) and the tension torsion strap (TT) is detachably mounted at a second side of the one of the multiplicity of the tail rotor blade holders (6), wherein the tension torsion strap (TT) is running from the tail rotor head (3) at least partly through the tail rotor blade holder (6) radially outward in direction of the tail rotor blade (2), wherein the blade holders (6) comprise a strap holding part (60) and a moulded blade holding part (61), wherein the blade holding part (61) comprises a flange (610) with disc-like shape and an integrally formed mounting bracket (611) with two parallel bracket arms (6110), wherein the tension torsion strap (TT) is fixed in the tube-like strap holding part (60) by a strap holding bolt (601) with one connection eye in a connection bore (600), while one end of the tail rotor blade (2) is detachably fixable independently and spaced apart from the tension torsion strap (TT) in a bracket interior (6111) of the mounting bracket (611) with at least one blade bolt (7) passing a bore (612) in the blade holding part (61), wherein the blade holding part (61) is located outside of the tail rotor hub (8), wherein a circumference of the flange (610) is adapted to the opening (80) in the tail rotor hub (8) and wherein the strap holding part (60) is lying completely inside the tail rotor hub (8) and the blade holding part (61) is protruding completely out of the tail rotor hub (8), characterised in that the pitch control unit (5) is placed inside the tail rotor hub (8).

2. Tail rotor head (3) and multiplicity of tail rotor blade holders (6) according claim 1, wherein the blade (2) is fixable at the mounting bracket (611) by means of the at least one blade bolt (7) comprising a bore (70), a split pin receptacle (71) and a split pin (72), forming a detachable split pin connection, independent of the fixing of the tension torsion strap (TT) at the strap holding part (60) from outside of the tail rotor hub (8).

3. Tail rotor head (3) and multiplicity of tail rotor blade holders (6) according to one of the preceding claims, wherein two blade bolts (7) are used for an attachment of the blade (2) secured against twisting relatively to the tail rotor blade holder (6).

4. Tail rotor head (3) and multiplicity of tail rotor blade holders (6) according to one of the preceding claims, wherein each blade bolt (7) comprises weight attachment means (11) and at least one balancing weight (12) for easy balancing the tail rotor hub (8) after installation of the tail rotor blades (2) at the tail rotor hub (8).

5. Tail rotor head (3) and multiplicity of tail rotor blade holders (6) according to claim 4, wherein the weight attachment means (11) is a prolonged cylindrical section at the blade bolt (7).

6. Tail rotor head (3) and multiplicity of tail rotor blade holders (6) according to one of the claims 4 or 5, wherein the at least one balancing weight (12) is secured by a detachable split pin connection at the blade bolt (7).

7. Tail rotor head (3) and multiplicity of tail rotor blade holders (6) according to one of the preceding claims, wherein the strap holding part (60) comprises a tube-like formed cover for the tension torsion strap (TT) to be inserted, the blade holder (6) comprises a pitch horn (602) to be attached to pitch control unit (5), the blade holding part (61) is moulded to the strap holding part (60), and the mounting bracket (611) of the holding part (61) comprises bracket arms (6110) through which the one bore (612) is cut out.

8. Tail rotor head (3) and multiplicity of tail rotor blade holders (6) according to claim 7, wherein the blade holding part (61) shows a moulded flange (610) before merging into the strap holding part (60), which circumference is adapted to a opening in the tail rotor hub (8).

9. Tail rotor head (3) and multiplicity of tail rotor blade holders (6) according to one of the preceding claims, wherein with a pitch horn (602) at the strap holding part (60), the blade holder (6) is detachably connected to the pitch control unit (5), allowing transmission of rotatory movements from the pitch control unit (5) to the blade holder (6).