Description:1 Title of the Invention
Rotor Hub and Blades Assembly for Helicopter.
2 Field of the Invention
The present invention relates to Tail rotor hub and blade pair configuration for a helicopter with bearing-less Rotor Blades.
3 Background of the Invention
Conventional helicopter possesses two types of rotors. The main rotor, commonly called the main rotor blades or rotor disk, has upwards of two separate blades and provides the lift for flight. The second type is typically much smaller and mounted vertically on the end of the helicopter's tail boom. This type of blade is normally referred to as the anti-torque rotor or tail rotor blades. The function of this tail rotor is, as its technical title suggests, to counter the torque produced by the powered main set of rotors.
In general, helicopter rotor blades have to go through different types of motion during their operation. A typical single main rotor helicopter has a rotor system mounted on a rotor mast. The helicopter engine supplies power so that the helicopter can turn the mast, and thus the rotor system connected to it. When the helicopter applies torque to the mast to spin it, there is an equal-and-opposite torque reaction which tries to turn the helicopter in the opposite direction. The tail rotor is designed to provide the side thrust required to counterbalance the reaction torque of the main rotor during flight. In addition, it also provides yaw control of the helicopter.
Conventionally, for provisioning the blade angle changes, inputs are provided on the Rotor Head, along with the separate input links and attachments. The four bladed, stiff-in-plane, bearing-less tail rotor is installed on the helicopter, it is driven by Tail Gear Box which is located at the end of the tail boom.
The blades employ flexible elements of composite material, which accommodate all the blade movements namely flapping, lead-lag, and pitching thus eliminating the use of conventional mechanical hinges or bearings.
Bearing-less rotor system, in the absence of dedicated bearings makes the rotor blade design simple in construction. However, the pitch angle changes and a means of centrifugal force reaction to produce adequate thrust are still necessary at the Rotor Hub and the provision for this could increase the complexity of such rotor hub attachments. The present invention is a means to address such complexities of bearing-less rotor systems.
3.1 Prior Art
US3637321 describe the tail rotor comprising the hub with blades. Each blade can rotate about two hinges, viz, a feathering hinge which allows changing the blade angle, an da flapping hinge allowing the blade to move in the flapping plane. The blade rotation for simultaneous changing the blade angle is accomplished by a control rod whose outer end has a rigidly mounted device for blade pitch control, which will be connected by mechanical links with the blade.
Such rotor blade system, has flapping and, sometimes, drag hinges, the hinge bearings are subjected to great centrifugal forces which calls for making heavy hubs of complicated design. Therefore, it is expedient that each blade of the rotor should be connected to the hub, and integrated with dedicated hub plates. The requirement of such flapping and drag hinges would not be desirable in such rotor systems. This should be in modular construction for ease maintenance.
WO89/09164 describe the rotor system with articulated system which includes a drive mast located in an axis of rotation. Here, two, 2 bladed tail rotors are mounted to a single one-piece hub which attaches to the trail rotor drive shaft by two flapping bearings. Complex mechanical linkages are involved to achieve the blade pitch angle. Mechanical bearings which is attached in tandem arrangement and the pitch links are attached from the rotor head mast to the blade. This would not be suitable for ease installation and removal of rotor blade system and for medium helicopter configurations where the size could be limitation due to drag penalty.
4 Brief Summary of the Invention
In general, the blade pair assembly on helicopter demands torsion-elastic arrangement which will go through the bearing if such exist, that reacts to the blade pair which will generate the centrifugal force at the time of pitch angle input experience to the blade. The flapping and lead-lag motions are accommodated through the flexible portion of the blade. But with the dedicated metallic bearing arrangement, such rotor hub demand large power absorption into it. This drawback will be addressed by introducing the hub plates integration with the blade pair assembly and the construction of the blade pair assembly should be in modular. Here, the snubber bearing assembly (16) is assembled with the pitch horn and bolt-snubber bearing assembly which is placed on the shoe-snubber bearing (19). The assembled blade pair assembly-1 and 2 (2), (2A) is integrated with the Hub plate-upper (7) and Hub plate-lower (8). The entire assembly is installed to the tail rotor shaft with bolt-Tail rotor shaft (11) and nuts (5).
5 Detail Description of the Drawings
Figure 1: is a side elevation of a helicopter embodying the invention, which also depicts the major system of a helicopter.
Figure 2: depicts the tail rotor blades for a bearing-less rotor of helicopter with its blade pair assembly.
Figure 3: shows the exploded view of the bearing-less Tail rotor blade pair & hub plate assembly with the attachment to the Tail rotor shaft.
Figure 4: shows the exploded view of Tail rotor blade pairs with its hub plate attachment.
Figure 5: shows the construction of Tail rotor blade pair assembly with Pitch horn & elastomeric bearing.
Figure 6: shows the cut-section of Pitch case of Tail rotor blade with bearing attachment.
6 Detail Description of the Invention
For a conventional helicopter (HC), a Fuselage (F) main rotor (M), a tail boom (T) and tail rotor (1) and a landing gear (L) are the primary systems. The function of the tail rotor (1) is to counter the main rotor (M) torque to prevent the fuselage (F) from spinning, as shown in Figure-1. In general, it would be desirable for a rotor hub assembly to be of such a construction that permits easy assembly and disassembly in an operating environment. This requires that any complicated tooling or assembly sequence should not be present in the regular maintenance of rotor hub plate assembly. It is desirable that the construction is easy to separate out, so that it could be quickly changed over in an operating environment. In this context, the embodiment hereunder discloses a tail rotor system with all such aforementioned features. Nevertheless, proposed invention is not limited to tail rotor alone but applicable to main rotor system also with minor changes to suite such requirements.
Proposed is about a bearing-less tail rotor (1) for a helicopter, in which hub plate assembly (3) plays a vital role in the Tail rotor system assembly. The Rotor hub plate assembly (3) consists of two pair of blades (2,2A) as shown in Figure-2, is made of composite pre-preg materials and is flexible in torsional and flap directions. The two set of blade pair assembly (2) is attached to the Rotor shaft (4) using its attachment fasteners (5). The tail rotor shaft (4) is a hallow shaft in type and it has internal and external features to accommodate into the gear box. The blade pair assembly (2,2A) is pre-assembled before attaching to the rotor shaft (4). Two set of blade pair (2,2A) mention here is as an example, but it can be of single pair or more than two pair of blade sets also.
Figure -3 shows the exploded view of the Tail rotor blade pair and Hub plate assembly (3A) with the tail rotor shaft (4). The tail rotor shaft (4) is unique in construction and it has the flange (4A) portion with four holes (4B) on the flange. The rotor blade pairs and hub plate assembly (3A) is attached to the tail rotor shaft through bolts and nuts at flange (4A) area. The pre-assembled Tail rotor shaft bush (11A) on the Tail rotor blade pair assembly (2,2A) guides itself in to the Tail rotor shaft (4) by entering to the Tail rotor flange (4A) holes (4B) and fastened by bolts and nuts (5). The tail rotor (1) shaft (4) driven by the tail rotor gear box which mounted on the tail boom (T) of the helicopter (HC).
Figure-4 shows the exploded view of Tail Rotor blade pair and hub plate assembly (3). The Tail Rotor blade pair and hub plate assembly comprises of the two sets of blade pair assembly (2,2A) and two dedicated hub plates (7,8) which integrates the two sets of blade pair assembly. The blade pair assemblies (i.e.) blade pair assembly-1 (2) and blade pair assembly-2 (2A) is placed orthogonal to each other between the two hub plates (i.e.) Hub plate-upper (7) and Hub Plate-Lower (8). However, the number of blade pair assembly can be changed and also placed non-orthogonal to each other. Both the Hub plates are assembled with four hub plate bolts (9). The hub plate bolt (9) is dedicatedly made as anti-rotation scheme. Anti-rotation of hub is achieved by providing a straight portion on the circular head of the bolt (9) by which the rotation is arrested by mating with another flat projection provided on the hub plate lower (8). The hub plate bolt (9) goes through the Hub plate-lower (8), flex-beam 1 (8A), flex-beam 2 (8B) and finally gets attached to the Hub plate-upper (7) with the self-locking nuts (12). These nuts (12) finalized with split pin as secondary locking mechanism. A through bush (10) is introduced between the hub plates and blade pair assembly, which withstand against the shear force that acts along with axis of bolt installation. During installation of the Hub plates with the blade pair assembly another bush is pressed into the Hub plate-lower (8), that is called Bush-tail rotor shaft (10). The mentioned bush (10) will guide the entire Blade pair assembly into the tail rotor shaft (4) in to flange (4A) holes (4B). In the figures subsequently shown that, Tail rotor shaft bolt (11) also installed in this stage itself, so that the thread portion of the tail rotor shaft bolt (11) will be visible after the flange portion. And the entire assembly is held with these four bolts on the tail rotor shaft (4) and secured with locking nuts and split pins. The tail rotor shaft bolts have the square shaped bolt head (11), which is placed inside the pocket in square shape on the Hub plate lower (8) to prevent the possible rotation of bolt (11). This concept enables to attach the Hub plate lower (8) with the Blade pair assembly-1 (2) without any intervention. On the Hub plate lower four slots introduced to place the above said bolts (11). However, the shape of the slots on the hub plates can be altered or modified based on the requirement. Number of tail rotor shaft bolts and its placement on the hub plate lower can be modified as per design requirement.
Figure-5 shows the typical single blade pair assembly in detail. The blade consists of a Pitch case (13), Cuff region which is non lifting surface and lifting surface. Pitch case (13) acts as torque tube which will transfer the control inputs to the blade. Here the flex-beam (15) runs end to end and it connects the two-blade lifting surface. The pitch case should have the sufficient width to accommodate the snubber bearing assembly (16) into it.
Figure -6 shows the cut section of the blade pitch case (13) with the attachment of Pitch horn (6) and snubber bearing assembly (16) for illustration of its installation. Snubber bearing assembly (16) consists of plate-outer, plate-inner and elastomeric part. However, construction of the snubber bearing is not claimed as such in the present invention but the use of snubber bearing assembly in the rotor system is claimed. In Pitch horn assembly, bush-collar (24,27) is to be pressed in to the pitch horn. Before pressing the bush-collar (24,27) in to the pitch case (13), Spacer-pitch case (30) and pitch horn (6) will be placed in leading edge side and trailing edge side respectively. Position of the pitch horn assembly on the pitch case is on the trailing edge side of the blade. On the other hand, pitch horn can also be introduced in the leading edge of the blade as an alternative control link. A shim (26) will be provided between the snubber bearing assembly (16) and the pitch case flange bush to maintain the pre-compression on the snubber bearing assembly. Here, a spacer which installed between two snubber bearing assembly is referred as spacer-snubber bearing assembly (22). A spacer-snubber bearing assembly (22) is installed between two snubber bearing assemblies (16), through this bolt-snubber bearing (20) will be inserted. Length of the spacer-snubber bearing assembly is to be calculated before the installation. After measurement of the shim thickness, snubber bearing assembly will be slide on to the shoe on top and bottom side inside the pitch case. In this article, Bolt which connects the Pitch case (13) and the pitch horn (6) is referred as Bolt pitch case (14). Bolt pitch case (14) is installed from the inside the pitch case and fasten with washer and castle nut (25). A Bush pitch case (29) is installed, which runs through the Pitch horn assembly and Pitch case. After positioning the snubber bearing assembly on the shoe-snubber bearing (19) and it is to be aligned with the pitch case hole. Bolt- snubber bearing (20) is installed from cambered side of the blade, and it is fastened with the washer and castle nut (28). The same way, the bolt- snubber bearing is installed on leading edge and trailing edge side with the calculated shim thickness. A bonding braid assembly (21) is installed between the two bolt-snubber bearing before securing the bolt. After installed the bonding braid assembly, it is fastened with washer and castle nut on both the Leading edge and trailing edge sides. Shoe snubber bearing (19) is bonded to the flex-beam (15). Each blade arm has two shoe snubber bearings. After positioning the snubber bearing assembly, Shoe snubber bearing is secured with shoe snubber bearing bolts (17) along with the washer and nut. Shoe snubber bearing bush makes sure that the bolt is tightened against the bush shoe snubber bearing, not to the shoe directly.
The particulars disclosed herein above are exemplary representations, but it is also possible that proposed invention may be modified and practiced in equivalent but different ways or arrangements by one who is skilled in such art with the help of the details described in this embodiment. Therefore, all such variations are to be considered within the scope and spirit of the invention. Accordingly, the protection is sought.
, Claims:We Claim,
1. Rotor Hub and Blades Assembly for Helicopter comprising:
a hallow rotor shaft (4) with a flange (4A) with plurality of hole (4B) and a threaded (4C) on the extended shaft on first end and with splines (4D) on second end;
a hub plate-lower (8) with a central hole (8A), plurality of circular holes with non-circular pocket (11B) around said central hole to accommodate plurality of bolt (11) with non-circular head to install on to said rotor shaft (4) and plurality of circular hole (11C);
plurality of blade pair assembly (2,2A) further comprising a first blade pair (2) and a second blade pair (2A), both install on to said hub plate-lower (8), wherein both said blade pair (2,2A) spanwise axes are orthogonal to said rotor shaft (4) axis and also both said blade pair (2,2A) axes are orthogonal to each other;
a hub plate-upper (7) with a central hole (7B), with plurality of circular holes around said central hole to accommodate plurality of bolt (11); and
wherein said hub plate-upper (7), said plurality of blade pair assembly (2,2A), said hub plate-lower (8) and said rotor shaft (4) form a rotor system (1) by fasteners (9,11).
2. Rotor Hub and Blades Assembly for Helicopter as claimed in claim 1, wherein said blade pair assembly comprising:
plurality of blade (2,2A) as aerodynamic lift generating surfaces made of aerofoil (2C) in cross section;
a pitch case (13), blade extended towards the center of the rotor (1) to accommodate snubber bearing assembly (16),
a flex-beam (8A,8B) sleeved over by two blades (2,2A) along with pitch case (13) on either ends of said flex-beam (8A,8B);
plurality of snubber bearing assembly (16) install on either side of flex-beam (8A) between said flex-beam (8A,8B) and said pitch case (13);
a bolt-snubber bearing (20) attachment with the pitch horn (6) and pitch case bolt (14) and bush (29); and
a bonding braid assembly (21) and its attachment between the two bolt-snubber bearing (20).
3. Rotor Hub and Blades Assembly for Helicopter as claimed in claim 1, wherein said fasteners (9,11) are of anti-rotation fasteners with non-circular bolt head.