Rotor hub for a tail rotor of a rotary wing aircraft and rotary aircraft with a rotor hub

Abstract

The present application relates to a rotor hub (10) for a tail rotor (6) of a rotary wing aircraft (1) comprising a plurality of tail rotor blades (11) as well as a central mounting (12) for fastening the plurality of tail rotor blades. The central mounting is designed to be driven by means of a tail rotor drive. The rotor hub further includes a plurality of blade holders (30), each of which connects a tail rotor blade (11) to the central mounting (12). The rotor hub comprises a cup-shaped hub body (13) including at least an annular outer structure (14) and an annular inner structure (15), both the annular outer structure and the annular inner structure including a plurality of first openings (16) and second openings (17), respectively. Each of the plurality of first and second openings is configured for receiving a blade holder (30), wherein at least the first openings of the annular outer structure each comprise a first reinforcing element (18) for increasing the rigidity of the rotor hub (10).

Description

[0001] Rotor hub for a tail rotor of a rotary wing aircraft and rotary aircraft with a rotor hub

[0002] Technical field

[0003] The present invention relates to a rotor hub for a tail rotor of a rotary wing aircraft comprising a plurality of tail rotor blades. The rotor hub comprises a central mounting, a plurality of blade holders and a cup-shaped hub body. The cup-shaped hub body includes an annular outer structure and an annular inner structure, each of the structures comprising a plurality of openings configured for receiving a blade holder. At least the openings of the annular outer structure each include a reinforcing element for increasing the stiffness and rigidity of the rotor hub. The present invention further relates to a rotary wing aircraft including such a rotor hub.

[0004] Background art

[0005] Rotor hubs for tail rotors of rotary wing aircraft are subjected to much strain, and forces and friction wear especially in the areas of the openings receiving the blade holder. Due to the friction wear these areas of the rotor hub may suffer damages which often leads to repair activities or the need of replacing the rotor hub and / or the blade holder entirely, which leads to high maintenance costs and prolonged down-time of the rotary wing aircraft.

[0006] Summary of the invention

[0007] It is thus the object of the present invention to provide a rotor hub with a reduced friction wear and reduced maintenance costs.

[0008] The solution of the invention is specified by the features of claim 1. The rotor hub comprises a plurality of tail rotor blades as well as a central mounting for fastening the plurality of tail rotor blades. The central mounting is designed to be driven by means of a tail rotor drive. The rotor hub further includes a plurality of blade holders, each of which connects a tail rotor blade to the central mounting. The rotor hub comprises a cup-shaped hub body including at least an annular outer structure and an annular inner structure, both the annular outer structure and the annular inner structure including a plurality of first openings and second openings, respectively. Each of the plurality of first and second openings is configured for receiving a blade holder, wherein at least the first openings of the annular outer structure each comprise a first reinforcing element for increasing the rigidity of the rotor hub.

[0009] By providing the first reinforcing elements at least on the first openings of the annular outer structure the stiffness and rigidity of the whole rotor hub can be significantly increased. The increased stiffness prevents ovalisation of the openings. Hence, the rotor hub exhibits a higher stability and is more resistant to friction wear. Furthermore, no varnish or coating needs to be applied to the blade holder, which reduces the need for replacement or repair activities.

[0010] The rotor hub provides a central attachment point for the tail rotor blades as well as a drive means to entrain the tail rotor blades into a rotating motion. The rotor hub is usually located on a tail boom of a rotary wing aircraft. In certain embodiments, the rotor hub may be located on a tail rotor pylon located at the end of a tail boom. The rotor hub is thereby rotatably connected to the tail boom or tail rotor pylon. The rotor hub according to the present invention may be for a tail rotor with exposed tail rotors blades or in connection with a so-called fantail, where the tail rotor is configured as an enclosure ducted fan.

[0011] The rotor hub includes a plurality of tail rotor blades, i.e. more than one tail rotor blade, such as, for example, two, three, four, five, six, seven, eight or more tail rotor blades. The rotary wing aircraft preferably is a helicopter.

[0012] The central mounting is designed to be driven in rotation by means of a tail rotor drive, i.e. the central mounting is in an active connection with the tail rotor drive. For example, the central mounting may be mechanically connected to an output of the tail rotor drive by means of a shaft or the like. The tail rotor drive may be a combustion engine, e.g. a turbine or piston engine, an electric motor or a hybrid engine. For example, the tail rotor drive is separate from a main drive used to entrain a main rotor of the rotary wing aircraft into rotary motion. However, in certain embodiments, the tail rotor drive may be configured as gear connected to the main drive, so that the tail rotor is entrained in a rotary motion by means of the main drive. The number of blade holders corresponds to the number of tail rotor blades of the rotor hub. Preferably, one tail rotor blade is connected to each blade holder. The connection is preferably a releasable connection, such as e.g. a connection by means of at least one bolt or the like. Alternatively, however, the tail rotor blade is permanently affixed to the blade holder, for example by means of an adhesive bond, such as a weld. In a further alternative, the blade holder and tail rotor blade may be unitary, i.e. made as a single piece.

[0013] The blade holder preferably has a generally cylindrical shape. Preferably, the blade holder has a connection structure for connecting the blade holder to a tail rotor blade at one of its ends. The connection structure preferably comprises a longitudinal groove in which a part of a tail rotor blade may be inserted. Further preferably, the connection structure comprises at least one bore through which a connection element, such as a bold, may be inserted to releasably secure a tail rotor blade to the blade holder. Alternatively, the connection structure may comprise a surface to which a tail rotor blade may be adhesively attached to, for example by means of welding. The blade holder preferably comprises at least one coupling with which the blade holder may be connected to a control rod, for example a control rod which allows to rotate the blade holder around its length axis to a certain degree, i.e. in order to alter a tilt angle of a tail rotor blade connected to the blade holder.

[0014] The hub body is cup shaped, i.e. comprises a circular base wall with an annular outer circumference. The annular outer structure is configured as an annular wall which protrudes from a first side of the base wall around the entire circumference of the base wall. The annular inner structure is configured as an annular wall which protrudes from the first side of the base wall and which is arranged at a defined distance from the annular outer structure in the direction of the centre of the circular base wall . As such, the annular outer structure and the annular inner structure are concentric one to another.

[0015] For each first opening of the annular outer structure the annular inner structure includes a corresponding second opening which is arranged radially relative to the respective first opening. This means that, when viewed in a radial direction of the cup-shaped hub body, each second opening lies beneath the corresponding first opening. In certain embodiments, each second opening is congruent with the corresponding second opening. However, preferably, the second openings may have different dimensions and / or a different shape as the first openings. Preferably, all first opening of the annular outer structure have the same shape and the same dimensions. Further preferably, all second openings of the annular inner structure have the same shape and the same dimensions.

[0016] Preferably, the first and / or the second openings are circular. In an alternative embodiment, the first openings and / or the second openings are polygonal, preferably hexagonal or octagonal. In the case that the first openings and / or the second openings are polygonal, the comers of the polygon are preferably rounded such that the polygon does not include and sharp angles at its comer. This allows a more even force distribution in the area of the comers, thus reducing the wear in the area of the comers.

[0017] One blade holder may be inserted through a first opening and subsequently through the corresponding second opening. As such, each of the blade holders is thereby securely hold at least around its circumference both by a first and a second opening. Preferably, each blade holder is thereby still rotatable around its length axis when inserted through the first and second opening, respectively. This allows to alter a tilt angle of a tail rotor blade connected to a blade holder by rotating the respective blade holder within the openings.

[0018] Preferably, the first reinforcing elements span around the entire circumference of each of the first openings of the annular outer structure. As such, the first reinforcing elements increase the rigidity of the annular outer structure at least locally in the area of each of the first openings, thereby increasing the rigidity of the entire rotor hub. Preferably, the first reinforcing elements are configured to at least partially cover the edge surface of the first openings. Thereby, the first reinforcing elements are at least partially lodged between the edge surface of each first opening and an outer surface of a blade holder inserted through said first opening.

[0019] Preferably, each of the second openings of the inner annular structure comprise a second reinforcing element for increasing the rigidity of the rotor hub. Provision of the second reinforcing elements on each of the second openings further increases the rigidity of the rotor hub.

[0020] Preferably, the second reinforcing elements span around the entire circumference of each of the second openings of the annular inner stmcture. As such, the second reinforcing elements increase the rigidity of the annular inner stmcture at least locally in the area of each of the second openings, thereby increasing the rigidity of the entire rotor hub. Preferably, the second reinforcing elements are configured to at least partially cover the edge surface of the second openings. Thereby, the second reinforcing elements are at least partially lodged between the edge surface of each second opening and an outer surface of a blade holder inserted through said second opening. In addition, the functional gap between the blade holder and the reinforcing elements can be optimized because an increased degree of tolerance can be achieved.

[0021] In a preferred embodiment the first reinforcing elements and preferably the second reinforcing elements are designed as a sleeve, preferably a metallic sleeve, in particular as a steel sleeve. In this embodiment, the sleeve shaped first reinforcing elements may be inserted into the first openings of the annular outer structure. Thereby, an outer contour of the first reinforcing elements corresponds to a contour of the first openings. Preferably, an inner contour of the sleeve shaped first reinforcing elements is circular, i.e. the sleeve shaped first reinforcing elements comprise an inner surface which is cylindrical. If the outer contour of the sleeve-shaped first reinforcing elements is circular, the sleeve-shaped first reinforcing elements have the general shape of a hollow cylinder.

[0022] If the rotor hub comprises sleeve-shaped second reinforcing elements, the sleeve shaped second reinforcing elements may be inserted into the second openings of the annular inner structure. Thereby, an outer contour of the second reinforcing elements corresponds to a contour of the second openings. Preferably, an inner contour of the sleeve shaped second reinforcing elements is circular, i.e. the sleeve shaped second reinforcing elements comprise an inner surface which is cylindrical. If the outer contour of the sleeve-shaped second reinforcing elements is circular, the sleeve-shaped second reinforcing elements have the general shape of a hollow cylinder.

[0023] Preferably, the first reinforcing elements of the annular outer structure have a first inner diameter and the second reinforcing elements of the annular inner structure have a second inner diameter, wherein the first inner diameter is larger than the second inner diameter.

[0024] As the annular outer structure spans the outer edge of the cup-shaped hub body, it is considerably longer than the annular inner structure. Hence, the first openings of the annular outer structure may have bigger dimensions than the second openings of the annular inner structure, as there are less size constraints. Concurrently, the first inner diameter of the first reinforcing elements may be larger than the second inner diameter of the second reinforcing elements. Hence, the first reinforcing elements may absorb a higher load as the second reinforcing elements. Accordingly, in this embodiment, the blade holders are configured such as to tight fitting into both the first reinforcing elements and the second reinforcing elements by caving different diameters essentially corresponding to the first inner diameter and to the second inner diameter in areas which lie within the first and second openings during use of the rotor hub, i.e. in the assembled state thereof. Preferably, the blade holders are thereby generally shaped like the letter T, i.e. having an enlarged area on one end thereof. This enlarged area has a diameter which essentially corresponds to the first inner diameter, while the remainder of the blade holders have a diameter which essentially corresponds to the second inner diameter. The enlarged area preferably includes the connection means for a tail rotor blade.

[0025] Preferably, the first reinforcing elements and preferably also the second reinforcing elements comprise a flange. The flange is preferably configured to engage with an inner surface, i.e. a surface facing towards the centre of the cup-shaped hub body, of the annular outer structure and of the annular inner structure, in the case that the second openings comprise second reinforcing elements. Hence, the flange protrudes away of the outer contour of the first and preferably second reinforcing element in the area of an end thereof which is facing towards the centre of the cupshaped hub body. The flange thereby secures the first reinforcing elements and preferably the second reinforcing elements from being dislodged out of the first openings or the second openings, respectively, by the centrifugal force when the rotor hub is rotated.

[0026] Preferably, the flange is in the form of a wedge. In the case of sleeve-shaped first reinforcing elements with a circular outer contour, the flange hence provides the end of the first reinforcing elements which face towards the centre of the cup-shaped hub body with a frusto-conical outer surface. In the case that the rotor hub comprises second reinforcing elements and said second reinforcing elements are sleeve-shaped and comprise a circular outer contour, the flange provides the end of the second reinforcing elements which face towards the centre of the cup-shaped hub body with a frusto-conical outer surface.

[0027] Preferably, the first reinforcing elements and preferably the second reinforcing elements are each designed as plain bearings for the blade holders. Hence, the first reinforcing elements and preferably the second reinforcing elements provide a bearing structure for the blade holders allowing a rotation of the blade holders around their length axis within the openings. Therefore, the first reinforcing elements and preferably the second reinforcing elements serve the dual purpose of reinforcing the rotor hub on one hand and providing a bearing structure for the blade holders on the other hand.

[0028] Preferably, the first reinforcing elements of the annular outer structure have a first plain bearing surface and wherein preferably the second reinforcing elements of the annular inner structure have a second plain bearing surface.

[0029] The first plain bearing surface and preferably the second plain bearing surface are facing towards the blade holder and are in contact therewith.

[0030] The bearing surfaces are preferably configured such as to take up radial forces only. This means that the bearing surfaces are configured to not take up any force acting parallel to the length axis of the blade holders.

[0031] Preferably, the blade holders each have a first bearing area and preferably a second bearing area, wherein the first bearing area is assigned to the first plain bearing surface of the first reinforcing elements and preferably the second bearing area is assigned to the second plain bearing surface of the second reinforcing elements. Provision of the first bearing area and preferably of the second bearing area on the blade holders decreases the friction between the first reinforcing elements and the second reinforcing elements with the rotor holders.

[0032] The first bearing area and preferably the second bearing area are preferably plain areas, preferably polished areas.

[0033] Preferably, the first bearing area comprises a first bearing sleeve and preferably the second bearing area comprises a second bearing sleeve. This additionally decreases the friction between the first reinforcing elements and the second reinforcing elements and the blade holders. No varnish or coating needs to be applied to the blade holder, which reduces the need for replacement or repair activities. The bearing sleeves are preferably slipped or heat shrunk onto the rotor holders. Provision of bearing sleeves allows for an easy and cost effective repair of the gearing between the cup-shaped hub body and the blade holders, as worn or damaged bearing sleeves may be simply replaced with new bearing sleeves.

[0034] Preferably, the first bearing sleeve and preferably the second bearing sleeve are each designed as a metallic sleeve, in particular as a steel sleeve. By using a metal, especially steel, for the sleeve increases the wear resistance of the gearing between the cup-shaped hub body and the blade holders.

[0035] Preferably, a first annular insert element is arranged between each first bearing sleeve and the first plain bearing surface.

[0036] Preferably, a second annular insert element is arranged between each second bearing sleeve and the second plain bearing surface.

[0037] The first annular insert element and / or the second annular insert element is hence lodged between the first bearing sleeve and the first plain bearing surface and / or between the second bearing sleeve and the second plain bearing surface, respectively. The first annular insert element and / or the second annular insert element may serve a dual purpose by reducing wear and by increasing the dynamic friction between the first bearing sleeve and the first plain bearing surface and / or the second bearing sleeve and the second plain bearing surface. As a worn down first annular insert or second annular insert may be more easily replaced than the first or second bearing sleeve or the first or second reinforcing element (which includes the first or second bearing surface, respectively), the repair of signs of wear between the blade holder and the cup-shaped hub body may be more efficiently and cost effectively performed when a first annular insert element and / or second annular insert element is present.

[0038] Preferably, the first and / or second annular insert element is made of a polymeric material, preferably of a fibre reinforced polymeric material. Alternatively, the first and / or second annular insert element is made of a metallic material.

[0039] Preferably, the first and / or second annular insert element has a U-shaped cross-section. The first and / or second annular insert element is configured such that the legs of the U are oriented outwards of the outer circumference, such that the edge surface of a first or second opening may be at least partially inserted between the legs of the U. In the case that a first or second reinforcing element is present, the first or second reinforcing element is likewise positioned between the legs of the U in this case.

[0040] Preferably, the first and / or second annular insert element is configured as a snap ring, especially preferably when the first and / or second annular insert element is U-shaped. Provision of the first and / or second annular insert element as snap ring facilitates the arrangement thereof in a first or second opening.

[0041] Preferably, the number of tail rotor blades is at least four, in particular at least eight, in particular at least ten. Accordingly, the rotor hub preferably comprises a matching number of blade holders to which the tail rotor blades are attached to, preferably in a releasable manner.

[0042] The present invention further relates to a rotary wing aircraft with a rotor hub according to the description above. The rotary wing aircraft preferably is a helicopter.

[0043] The present invention further relates to a rotor hub for a rotary wing aircraft. The rotor hub comprises a plurality of tail rotor blades as well as a central mounting for fastening the plurality of tail rotor blades. The central mounting is designed to be driven by means of a tail rotor drive. The rotor hub further includes a plurality of blade holders, each of which connects a tail rotor blade to the central mounting. The rotor hub comprises a cup-shaped hub body including at least an annular outer structure and an annular inner structure, both the annular outer structure and the annular inner structure including a plurality of first openings and second openings, respectively. Each of the plurality of first and second openings is configured for receiving a blade holder, wherein at least the first openings of the annular outer structure each comprise an insert element for increasing the wear resistance arranged between an edge surface of the first openings and the blade holder.

[0044] Provision of an insert element for increasing the wear resistance has the advantage that said element is easily replaceable during normal maintenance of the rotary wing aircraft. Compared to wear resistance coatings applied on blade holders as known in the art, replacement of an insert requires less time and is simpler to implement, thus reducing the time and cost required for maintenance of a rotary wing aircraft.

[0045] Further advantageous embodiments and combinations of features of the invention may be derived from the following detailed description and the entirety of the patent claims.

[0046] Short description of the drawings

[0047] The drawings used to illustrate the embodiments of the invention example show: Fig. 1 an exemplary embodiment of a helicopter as an example of a rotary wing aircraft comprising a tail rotor with a rotor hub according to the present invention;

[0048] Fig. 2 a partial detail view of a first embodiment of a rotor hub according to the present invention as a perspective drawing;

[0049] Fig. 3 a longitudinal sectional view of a pair of openings with a blade holder inserted therein;

[0050] Fig. 4, 5 a partial detail view of the cup-shaped hub body without blade holder and without the annular insert elements;

[0051] Fig. 6 the view of Fig. 6 without blade holders and annular insert elements;

[0052] Fig. 7 a blade holder in a perspective representation;

[0053] Fig. 8 a second exemplary embodiment of a rotor hub with a cup-shaped hub body having octagonal first openings and octagonal second openings;

[0054] Fig. 9 a first reinforcing element of the second embodiment as shown in Fig. 8 in detail;

[0055] Fig. 10 a third embodiment of an inventive rotor hub, where the blade holder and the tail rotor blade are a unitary piece.

[0056] In principle, identical parts are labelled with identical reference signs in the figures.

[0057] Exemplary embodiments to implement the invention

[0058] Fig. 1 shows an exemplary embodiment of a helicopter 1 as an example of a rotary wing aircraft comprising a tail rotor 6 with a rotor hub 10 according to the present invention. Multiple tail rotor blades 11 are connected to the rotor hub 10. As known in the art, a helicopter comprises a fuselage 2 enclosing a passenger compartment and a cockpit. A main rotor 3 is arranged on top of the fuselage 2, the main rotor 3 being coupled to a main drive (not shown) arranged in the fuselage 2. The helicopter includes a tail boom 4 with horizontal stabilizers 5 connected thereto. The tail rotor 6 is arranged at the end of the tail boom 4. Further, above the tail rotor 6 the helicopter 1 comprises a rudder 7. In the embodiment shown, the tail rotor 6 is configured as a so-called fantail. Fig. 2 shows a partial detail view of a first embodiment of a rotor hub 10 according to the present invention as a perspective drawing. The rotor hub 10 includes a central mounting 12 with a cupshaped hub body 13. The cup-shaped hub body 13 includes a circular base wall 24. A first annular outer structure 14 is arranged around the outer edge of the circular base wall 24. The annular outer structure 14 is configured as a wall which extends essentially perpendicular from the circular base wall 24 on one side thereof. An annular inner structure 15 is further arranged on the circular base wall 24 at a defined distance from the annular outer structure 14. The annular outer structure 14 and the annular inner structure 15 are concentric relative to each other.

[0059] A plurality of first openings 16 are arranged on the annular outer structure 14. The annular inner structure 15 also comprises a plurality of second openings 17. The central mounting 12 comprises the same number of first openings 16 and second openings 17. One first opening 16 and one second opening 17 thereby form a pair of openings 16, 17 which are arranged radially relative to each other. This means that a center of the outer opening 16 and a center of the inner opening 17 are arranged on a radial line of the circular base wall 24 of the cup-shaped hub body 13. As may be seen on Fig. 2, both the first openings 16 and the second openings 17 are circular, but differ in their diameter, the second openings 17 having a smaller diameter than the first openings 16.

[0060] An edge surface of each of the first openings 16 and of the second openings 17 comprise a first reinforcing element 18 and a second reinforcing element 19, respectively (not visible on Fig. 2, see Figs. 3 and 4). The first reinforcing elements 18 and the second reinforcing elements 19 reinforce the cup-shaped hub body 13 in the areas of the first openings 16 and of the second openings 17. As a multitude of reinforcing elements are present, the reinforcing elements reinforce the entire structure of the rotor hub 10.

[0061] A blade holder 30 is inserted through each pair of first openings 16 and second openings 17. The blade holders 30 include an essentially cylindrical main body 31 with an enlarged area 40 at one end. The enlarged area 40 includes a first bearing area 32 which cooperates with the first reinforcing element to form a first frictional bearing between the cup-shaped hub body 13 and the blade holder 30. Further, the main body 31 of the blade holder 30 includes a second bearing area 33 which cooperates with the second reinforcing element to form a second frictional bearing between the cup-shaped hub body 13 and the blade holder 30. In order to reduce the wear of the blade holder 30, a first bearing sleeve 34 is arranged on the first bearing area 32 and a second bearing sleeve 35 is arranged on the second bearing area 33. To further reduce the wear, a first annular insert element 50 and a second annular insert element 51 are arranged between the first reinforcing element and the first bearing sleeve 34 as well as between the second reinforcing element and the second bearing sleeve 35, respectively. The annular insert elements 50, 51 are thereby arranged on a plain bearing surface of the first reinforcing element and second reinforcing element, respectively (not visible on Fig. 2, see Fig. 3). As may be seen, both the first annular insert element 50 and the second annular insert element 51 are configured like snap rings to allow an easier insertion thereof.

[0062] The main body 31 of the blade holders 30 have a diameter which is chosen such that the main body 31 may be inserted through and snuggly fitted within a second opening 17 fitted with a second reinforcing element and with a second annular insert element 51. Likewise, the enlarged area 40 has a diameter which is chosen such that the enlarged area 40 may be inserted through and snuggly fitted within a first opening 16 fitted with a first reinforcing element and with a first annular insert element 50.

[0063] By means of the first frictional bearing and the second frictional bearing the blade holders 30 are rotatably hold within a pair of openings 16, 17. It is to be noted that the first frictional bearing and the second frictional bearing only bear radial loads of the blade holders 30, but no axial loads.

[0064] The blade holders further comprise a connection structure 36 which is arranged on the enlarged area 40. A tail rotor blade (not shown in Fig. 2) may be releasably attached to the blade holder 30 by means of the connection structure 36. The connection structure 36 includes a groove 37 flanked by two side walls 38.1, 38.2. A plurality of bores 39 are provided pairwise on the side walls 38.1, 38.2 such as to affix a tail rotor blade inserted into the groove 37 by means of bolts or the like.

[0065] Fig. 3 shows a longitudinal sectional view of a pair of openings 16, 17 with a blade holder 30 inserted therein, according to the embodiment as shown in Fig. 2. It is noted that the figure shows a cut along a plane through a longitudinal axis of the blade holder 30 and parallel to the circular base wall 24 of the cup-shaped hub body 13.

[0066] The arrangement of the reinforcing elements 18, 19 within the openings 16, 17 is well recognizable in Fig. 3. As may be seen, the first reinforcing element 18 is inserted within the first opening 16. the first reinforcing element 18 is sleeve shaped and includes an first inner diameter D 1. The outer diameter of the first reinforcing element 18 corresponds to the diameter of the first opening 16. The first reinforcing element 18 includes a flange 20 on one edge thereof. The flange 20 of the first reinforcing element 18 is in the form of a wedge in the embodiment shown. As the first reinforcing element 18 is in the form of a sleeve, the wedge shaped flange 20 provides the first reinforcing element 18 with a frusto-conical outer surface. The flange 20 of the first reinforcing element 18 is arranged on a side of the first opening 16 which is oriented towards the center of the cup-shaped hub body 13. Hence, the flange 20 secures the first reinforcing element 18 from being dislodged out of the first opening 16 by centrifugal forces when the rotor hub 10 is rotated.

[0067] The first annular insert element 50 has a U-shaped cross-section, as may readily be seen on Fig. 3. The legs of the U are arranged on the outer circumference of the first annular insert element 50 and overlap with an outer and inner surface of the annular outer structure 14.

[0068] The second reinforcing element 19 is substantially configured like the first reinforcing element 18, albeit having smaller dimensions such as to fit into the smaller second opening 17. As such, the second reinforcing element 19 has a second inner diameter D2 which is smaller than the first inner diameter DI. The same applies to the second reinforcing element 19 which also includes a flange 21 which is in the shape of a wedge in the embodiment shown. The second annular insert element 51 is likewise configured similar to the first annular insert element 50.

[0069] As may be seen on Fig. 3, the blade holder 30 also includes a coupling 41 which may be coupled to a control rod (not shown) or the like. By means of the coupling 41 the blade holder 30 may be rotated around its length axis, e.g. such as to alter the tilt angle of a tail rotor blade (not shown) connected to the connection structure 36 provided on the enlarged area 41 of the blade holder 30.

[0070] Fig. 4 shows a partial detail view of the cup-shaped hub body 13 according to the embodiment shown in Fig. 3 without blade holder 30 and without the annular insert elements 50, 51. As may be seen, the first reinforcing element 18 comprises a first plain bearing surface 22 and the second reinforcing element 19 a second plain bearing surface 23. The dashed line shown in Fig. 4 exemplifies the arrangement of each second opening 17 radially relative to a first opening 16. Further, the arrangement of the annular outer structure 14 and of the annular inner structure 15 as walls which are essentially perpendicular to the circular base wall 24 of the cup-shaped hub body 13 may also be readily recognize in said figure.

[0071] Fig. 5 shows essentially the same situation like Fig. 4, albeit from the other side of the annular outer structure 14. Fig. 6 shows essentially the same situation as Fig. 3, albeit without blade holder 30 and annular insert elements 50, 51. In this figure, the first plain bearing surface 22 of the first reinforcing element 18 and the second plain bearing surface 23 of the second reinforcing element 19 are well recognizable. Further, the securing of the first reinforcing element 18 and of the second reinforcing element 19 by means of the respective flanges 20, 21 is also readily recognizable.

[0072] Fig. 7 shows an exemplary embodiment of a blade holder 30 according to the present invention in a perspective representation. As already mentioned in connection with Fig. 3, the blade holder 30 includes a substantially cylindrical main body 31 with an enlarged area 40 at one end thereof. On a circumferential surface of the enlarged area 41, the blade holder 30 includes the first bearing area 32 on which the first bearing sleeve 34 is arranged. On the other end of the blade holder 30, the main body 31 includes the second bearing area 33 onto which the second bearing sleeve 35 is arranged. As may be seen on the figure, the coupling 41 is in the form of a protrusion with a bore, to which e.g. a control rod may be attached by means of a bolt. Also well recognizable is the connection structure 36 with the groove 37 flanked by the two side walls 38.1, 38.2. As mentioned above, a tail rotor blade (not shown) may be releasably coupled to the blade holder 30 by means of the connection structure 36. Thereby, an end of the tail rotor blade may be inserted into the groove 37 and affixed to the blade holder 30 by means of bolts or the like passed through the pairwise arranged bores 39 on the two side walls 38.1, 38.2.

[0073] Fig. 8 shows a second exemplary embodiment of a rotor hub 10 with a cup-shaped hub body 13 having octagonal first openings 16 and octagonal second openings 17 on the annular outer structure 14 and the annular inner structure 15, respectively. It is noted that the first reinforcing elements 16 and the second reinforcing elements 17, which are shown inserted into the first openings 16 and the second openings 17, respectively, in the figure have an outer contour which is octagonal and matching the shape and dimensions of the first openings 16 and the second openings 17, respectively, while an inner contour is circular and forms the respective plain bearing surface.

[0074] Fig. 9 shows a first reinforcing element 18 of the second embodiment as shown in Fig. 8 in detail. As may readily be seen on this figure, the outer contour 25 of the first reinforcing element 18 is octagonal, while the inner contour, which forms the first plain bearing surface 22 is circular. While only the first reinforcing element 18 of the second embodiment is shown, it is to be noted that the second reinforcing element 19 of the second embodiment is analogously shaped and configured, albeit having smaller dimensions.

[0075] Fig. 10 shows a third embodiment of an inventive rotor hub 10, where the blade holder 30 comprises a tail rotor blade 11, i.e. the blade holder 30 and the tail rotor blade 11 are a unitary piece. Otherwise, the third embodiment is configured essentially the same as the first embodiment as shown in Fig. 2.

[0076] Reference sign list

Claims

Patent Claims1. A rotor hub (10) for a tail rotor (6) of a rotary wing aircraft (1) comprising a plurality of tail rotor blades (11), the rotor hub (10) comprising: a central mounting (12) for fastening the plurality of tail rotor blades (11), wherein the central mounting (12) is designed to be driven by means of a tail rotor drive, a plurality of blade holders (30), each of which connects a tail rotor blade (11) to the central mounting (12), a cup-shaped hub body (13) comprising at least an annular outer structure (14) and an annular inner structure (15), wherein the annular outer structure (14) includes a plurality of first openings (16) and the annular inner structure (15) include a plurality of second openings (17), each of the plurality of first openings (16) and second openings (17) being configured for receiving a blade holder (30), and wherein at least the first openings (16) of the annular outer structure (14) each comprise a first reinforcing element (18) for increasing the rigidity of the rotor hub (10).

2. The rotor hub (10) according to claim 1, wherein the second openings (17) of the annular inner structure (15) each comprise a second reinforcing element (19) for increasing the rigidity of the rotor hub (10).

3. Rotor hub (10) according to claim 1 or 2, wherein the first reinforcing elements (18) and preferably the second reinforcing elements (19) are designed as a sleeve, preferably a metallic sleeve, in particular as a steel sleeve.

4. The rotor hub (10) according to claim 3, wherein the first reinforcing elements (18) of the annular outer structure (14) have a first inner diameter (DI) and the second reinforcing elements (19) of the annular inner structure (15) have a second inner diameter (D2), wherein the first inner diameter (DI) is larger than the second inner diameter (D2).

5. Rotor hub (10) according to one of the preceding claims, wherein the first reinforcing elements (18) and preferably the second reinforcing elements (19) comprise a flange (20, 21).

6. Rotor hub (10) according to one of the preceding claims, wherein the first reinforcing elements (18) and preferably the second reinforcing elements (19) are each designed as plain bearings for the blade holders (30).

7. The rotor hub (10) according to claim 6, wherein the first reinforcing elements (18) of the annular outer structure (14) have a first plain bearing surface (22) and wherein preferably the second reinforcing elements (19) of the annular inner structure (15) have a second plain bearing surface (23).

8. Rotor hub (10) according to claim 7, wherein the blade holders (30) each have a first bearing area (32) and preferably a second bearing area (33), wherein the first bearing area (32) is assigned to the first plain bearing surface (22) of the first reinforcing elements (18) and preferably the second bearing area (32) is assigned to the second plain bearing surface (22) of the second reinforcing elements (19).

9. The rotor hub (10) according to claim 8, wherein the first bearing area (32) comprises a first bearing sleeve (34) and preferably the second bearing area (33) comprises a second bearing sleeve (35).

10. Rotor hub (10) according to claim 9, wherein the first bearing sleeve (34) and preferably the second bearing sleeve (35) are each designed as a metallic sleeve, in particular as a steel sleeve.

11. Rotor hub (10) according to claim 9 or 10, wherein a first annular insert element (50) is arranged between the first bearing sleeve (34) and the first plain bearing surface (22).

12. The rotor hub (10) according to any one of claims 9 to 11, wherein a second annular insert element (51) is arranged between each second bearing sleeve (35) and the second plain bearing surface (23).

13. Rotor hub (10) according to claim 11 or 12, wherein the first annular insert element (50) and / or the second annular insert element (51) has a U-shaped cross-section.

14. Rotor hub (10) according to one of the preceding claims, wherein the number of tail rotor blades (11) is at least four, in particular at least eight, in particular at least ten.

15. Rotary wing aircraft (1) with a rotor hub (10) according to any one of claims 1 to 14.

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