Description:1 Title of invention
Apparatus to Assist Rigging of Rotor Blades of Rotorcraft
2 Field of invention
The present invention relates to an apparatus to verify the pitch angle of a rotor blade for limited rigging of the rotor system, in particular, the main rotor system of a rotorcraft which is embarked in a ship deck.
3 Background of Invention
In rotorcraft, the thrust, lift and control forces required for the flight are achieved through rotor by altering the blade pitch angle according to the flight condition. Generally the blade pitch angle is altered by the pilot through his control input, which transfers to the rotor blades through flight control linkages and a hydraulic actuator. It is paramount important to achieve the required range of blade angle to maintain the given flight condition, hence rotor control rigging is carried out to set a reference and further to verify whether the required range of blade pitch is achieved in the rotor blade. The rigging of rotor system has to be carried out after the initial built-up of rotorcraft and subsequently, after the change of any components in the flight control circuit, generally control rods, actuators and rotor blades etc. The general procedure followed to measure and correct (if required) the blade angles during the rigging is as follows. First, the rotorcraft need to be levelled in the ground using the screw-jacks to establish the horizontal reference, and then the blade angles are measured using digital clinometer and necessary corrections are given through the provisions in the flight control linkage to minimize the error within the specified limits. But in case of rotorcrafts operating from ships, it is difficult to carry out rigging by normal procedure, since the operating condition with high sea state, makes it challenging to level the rotorcraft and further measuring the blade angles using digital clinometer in the ship deck. Hence a rigging tool is designed to eliminate the jacking requirement and measuring the blade angle with local reference, i.e at rotor hub reference. The objective of the rigging tool described in the current embodiment is to carryout limited rigging of rotor system of rotorcraft to ensure safe flight for one hop from the ship to the nearest shore, and normal rigging procedure will be followed in the shore, otherwise the rotorcraft needs to be moved with crane and shifted to shore using another ship, which is a difficult procedure. Further the said rigging tool can also be used for limited rigging of rotor system in the ground, when full rigging is not required, which reduces the effort required to jack the rotorcraft and carryout the rigging using clinometer.
Patent number 5564655, titled “Rigging of a aircraft wing flaps” invented by Philip H. Garland, Michael J. Corner and Peter R Gill, explains about rigging of trailing edge flaps for aircraft wings. Patent number WO 84/01426 titled “Flap position measuring tool”, invented by CHAU and Albert et al. describes about a flap position measuring system for a aircraft using electrical means. Patent number EP 3543147A3 titled “Optical systems and methods for aircraft flight control rigging” invented by FARNER et. al. describes a laser based method for aircraft flight control rigging.
The said patents are explain about the rigging of flaps in fixed wing aircraft, whereas the current invention focus on the rigging of rotor system of a rotorcraft which is different from the procedure followed for fixed wing aircraft.
4 Summary of Present Invention
The present invention describes about an apparatus for measuring the blade pitch angle and method of mounting said apparatus on a composite rotor hub, for limited rigging of main rotor system. The main object of the current invention is to provide a optimum method for limited rigging of a rotor system of a rotorcraft embarked on a ship deck, which can highly reduce the maintenance effort on-board ship. It is a further object of the present invention to arrive at a method for setting reference for blade angle measurement without jacking the rotorcraft on ground. It is further object of the present invention to incorporate an existing tool which is used to measure the azimuthal position of the blade with respect to the reference axis of rotorcraft, in the said apparatus.
5 Brief Description of Drawings
Figure-1 is a layout of rotorcraft (1) with reference axis (101) consists of main rotor head (2) with plurality of rotor blades (3).
Figure-2 is a layout of main rotor head (2) which is equipped with said apparatus (4) to measure and verify the pitch angle for a range of angle (102) to (103) of rotor blade (3) (only the root segment (3a) of said rotor blade (3) is shown in this Figure) about the pitch axis (104) of rotor blade (3) and it shows the method of mounting the said apparatus (4) on the main rotor head (2) particularly on main bolt (5) in hub plate (2a). Further Figure-2 shows the method of incorporating an existing azimuth pointer (6) with tip (6a) for measurement of azimuthal location of the blade with reference to the rotorcraft axis (101), using an existing azimuth scale (7) which consists of two halves (7a) and (7b) which are having the center (105) on the axis of rotation (106) and mounted on the fixed structure (not shown in this Figure) of the rotorcraft (1).
Figure-3 is a schematic layout of said apparatus (4) with a fixture assembly (8) along with existing azimuth pointer (6) which is having a step (6b) to locate the said azimuth pointer (6) inside the hole feature (5a) in the said main bolt (5) (as shown in Figure-2) , a pointer assembly (9) and an angular scale (10). Further this figure shows the method of mounting angular scale (10) to the fixture (11) by means of bracket (12) and holder (13).
Figure-4 is a partial section view of fixture assembly (8) consisting of a locking arrangement (14) which comprises base plate (15) which is mounted on fixture (11) by fastening means (16), taper bolt (17), set of split bush (18) at one end of the said fixture (11) and further it shows the method of incorporating the existing azimuth pointer (6) at the other end of the said fixture (11) for measurement of azimuth of rotor blade (3) by locating the said azimuth pointer (6) in the hole feature (11c) and positioning the said tip (6a) of the said azimuth pointer (6) in the required height (as shown in Figure-2) by rotating of lock nut (20) over thread feature (6c).
Figure-5 is an exploded view of said locking arrangement (14) for quickly lock and unlock the fixture assembly (8) on the said hub plate (2a) which is made up of composite material. The figure shows the split bush (18-1) and (18-2) with internal taper (18-1a) in the said split bush (18-1) and corresponding taper surface (17a) on the taper bolt (17). Similar taper surface (18-2a) is provided on the split bush (18-2) which is not shown in the figure.
Figure-6 is a layout of pointer assembly (9) comprising pointer (23), pointer holder (24), lock screw (25), dowel pin (26) and fastening means (27) to lock the said holder (24) on bracket (28). Further it shows the method of locking said bracket (28) with clamp (29) by means of two shear bolts (30).
Figure-7 is a partial section view showing the method of mounting the said pointer (23) in holder (24) and locking of said pointer (23) by means of lock screw (25). Further it shows the clearance (108) maintained between the bracket (28) and clamp (29) to lock the entire assembly with said root segment (3a) of rotor blade (3) by means of two shear bolts (30).
Figure-8 is an alternate method of measuring the pitch angle of rotor blade (3) by means of a Vernier scale (31) which is assembled in place of pointer (23) to achieve the better least count of measurement using angular scale (10), compared to measurement using said pointer (23).
6 Detailed Description of Invention
The embodiment described hereunder discloses about an apparatus (4) to measure the pitch angle of rotor blade (3) in the main rotor head (2) for limited rigging of main rotor system of rotorcraft (1). This artifact also discloses the method of mounting the said apparatus (4) on the main rotor head (2) for measurement of pitch angle of rotor blade (3), further it discloses the method of incorporating an existing azimuth pointer (6) in the said apparatus (4), for measurement of azimuthal position of rotor blade (3) with respect to the reference axis (101) of rotorcraft (1). The current embodiment also describes the method of achieving the geometric controls of said apparatus (4) such as perpendicularity and parallelity by defining the appropriate reference surfaces and features, to achieve the best measuring accuracy using the said apparatus (4).
The rotorcraft (1) consists of main rotor head (2) having plurality of rotor blades (3) is shown in Figure-1. With reference to Figure-2, the said apparatus (4), to measure the pitch angle of rotor blade (3) is mounted on the said main rotor head (2), particularly on hub plate (2a) and root segment (3a) of the said rotor blade (3). The blade pitch angle from negative pitch (102) to positive pitch (103) for different flight conditions is achieved by tilting the rotor blade (3) about the pitch axis (104) at pitching/feathering hinge, which is a laminated bearing (2c), by means of pilot input received through flight control linkages which is connected to blade fork (2d) in the main rotor head (2) as shown in Figure-2. The range of said pitch angle from (102) to (103) is verified using said apparatus (4) to achieve the required flight condition. The said apparatus (4) comprises a fixture assembly (8) and a pointer assembly (9) as shown in Figure-3. Fixture assembly (8) is mounted on hub plate (2a) of said main rotor head (2) and said pointer assembly is mounted on root segment (3a) of said rotor blade (3) as shown in Figure-2 and the pointer assembly (9) reads ‘zero’ degree in an angular scale (10) corresponding to the ‘zero’ pitch angle of rotor blade as shown in this Figure.
With reference to Figure-3 said fixture assembly (8) consists of said angular scale (10), a fixture (11), a bracket (12), a holder (13) and a locking arrangement (14) to lock the said fixture assembly (8) on the hub plate (2a). With reference to Figure-2 and Figure-4, the reference for fixing the fixture (11) over the hub plate (2a) for pitch angle measurement of rotor blade (3) is achieved by means locating the cylindrical feature (11a) in the hole feature (5a) of the main bolt (5) by a sliding fit and further butting the reference surface (11b) provided in the fixture (11) over the machined surface (5b) in the main bolt (5) as shown in Figure-2, further the reference axis (5c) of the said hole feature (5a) is perpendicular to the pitch axis (104). The said method of mounting the fixture (11) in the hub plate (2a) ensures the parallelity of the fixture (10) with respect to the hub plate (2a) which is one of the critical reference to ensure correct measurement of pitch angle of rotor blade (3), further it constraints lateral degree of freedom of the said fixture.
Further, with reference to Figure-4, a hole feature (11c) is made concentric to the cylindrical feature (11a) in fixture (11) to incorporate an existing azimuth pointer (6) for measurement of azimuthal position of rotor blade (3) with respect to the reference axis (101), by rotating the main rotor head (2) about the rotor axis (106) as shown in Figure-2. The said azimuthal rotation of rotor blade about the rotor axis (106) is carried out during the rigging of said main rotor system, to verify whether the pitch angle of plurality rotor blades (3), both collective (same amount of pitch angle in plurality of blades) and cyclic (Varying pitch angle in plurality of blades with repect to position of the rotor blade in the plane of rotation) are achieved as desired with respect to different azimuth of the rotor blade (3) with respect to reference axis (101). A lock nut (20) along with washer (21) are engaged with thread feature (6c) as shown in Figure-4 to position the azimuth pointer (6) in the required height such that the tip (6a) of the azimuth pointer (6) moves closely over azimuth scale (7) which consists two halves (7a) and (7b) as shown in Figure-2, for reading the angle. The said azimuth scale (7) is mounted on a horizontal plane in fixed structure of rotorcraft (1), which is parallel to the plane of rotation of main rotor head (2). The cylindrical feature (6b) as shown in Figure-3 is located inside the hole feature (5a) of the main bolt (5), hence ensures the alignment of azimuth pointer (6) parallel to pitch axis (106) of main rotor head (2).
With reference to Figure-3, the said angular scale (10) is mounted to the fixture (11) by means of a bracket (12) and a holder (13). The angular scale (10) is set to ‘zero’ with respect to pointer assembly (9), corresponding to zero pitch angle of rotor blade (3) as shown in Figure-2, by adjusting the angular scale (10) vertically over the slot feature (10a) along the fastening means (10b); the said ‘zero’ reference to be set during the first time rigging of the rotor system and will be used as reference for further riggings. The perpendicularity of the angular scale (10) with respect to fixture (11) is achieved by means of butting the angular scale (10) against the reference surface (12a) of bracket (12), further locating the bracket (12) with slot feature (13a) in holder (13) and mounting the said holder (13) perpendicular to the reference surface (11d) of fixture (11) as shown in Figure-3.
Further the fixture assembly (8) is locked at the other end of the fixture (11) to ensure that all degrees of freedom of the fixture assembly (8) with respect to the hub plate (2a), is constrained, so that the angular scale (10) does not move, once the ‘zero’ reference is set. For said purpose, the fixture assembly (8) is mounted on the hub plate (2a) by means of locking arrangement (14) in the said fixture (11) as shown in Figure 4 and 5. The said locking arrangement (14) consists of a base plate (15) having internal thread feature (15a) to receive threaded portion (17b) of a taper bolt (17), set of split bushes (18-1) and (18-2) , a lock nut (19) as shown in Figure-5. The said base plate (15) with locater (15b) is located concentrically in the hole feature (11f) and further fastened to fixture (11) through bolts (16) and washer (22) as shown in Figure-4 and Figure-5.
With reference to Figure-2 and Figure-4, locking of fixture (11) with hub plate (2a) is achieved by rotating the taper bolt (17) by means of a hexagonal head feature (17c) provided in the said taper bolt (17) through an appropriate tool. The rotation of taper bolt (17) by anti-clockwise direction makes it to move upward and hence the split bushes (18-1) and (18-2) expands diametrically by means of sliding motion between the taper surface (17a) in the taper bolt (17) over the corresponding taper surface (18-1a) and (18-2a) provided in the split bush (18-1) and (18-2) respectively as shown in Figure-5, hence the split bushes (18-1) and (18-2) make contact with hole feature (2b) in hub plate (2a) and locks. Similarly the unlocking of the tool from the hub plate (2a) can be done vice-versa. The said means of locking have an advantage of quick assembly and dis-assembly of said apparatus (4) from the hub plate (2a), which is an operational requirement when using this device in the rotorcraft (1) embarked in a ship.
To ensure the proper locking of the split bush (18) in the hole feature (2b) of the hub plate (2a), the diameter of the hole feature (11e) provided in the fixture (11) as shown in Figure-4, is designed larger than the diameter of the hole feature (2b) in the hub plate (2a) so that the split bush makes contact only with hole feature (2b) during locking, hence the proper locking of fixture is ensured with said hub plate (2a). The main advantage of the said locking arrangement (14) is that the hole dimension of the said hole feature (2b) provided in the said composite hub plate (2a) has a wide range of tolerance say +/- 2 mm, hence by means of said locking arrangement (14), the said apparatus is assembled in the hub plate (2a) without any clearance, for the range of dimensions of the said hole feature (2b) for the given tolerance, as desired; further said locking arrangement (14) constraints the vertical and rotational degrees of freedom of the said fixture assembly (9). The another feature that is provided in the locking arrangement (14) is that the split bushes (18-1) and (18-2) are made of Teflon material which is softer than the hub plate (2a) which is made of composite material, hence it avoids any damage by contact forces between hole feature (2b) in hub plate (2a) and split bush (18) during locking, since hub plate (2a) is one of the critical part of the rotorcraft (1).
The pointer assembly (9) mounted on the root segment (3a) of the rotor blade (3) as shown in Figure-2, moves over the angular scale (10) while blade pitch is altered through the flight control linkage which are connected to the blade fork (2d) as shown in Figure-2. With reference to Figure-6, the said pointer assembly (9) consists of a pointer (23), a pointer holder (24), a bracket (28) and a clamp (29). The apex of the pointer is aligned with pitch axis (104) of rotor blade (3) by means of following methods. For said purpose, the pointer (23) is mounted in the holder (24) in a sliding fit and locked with a lock screw (25) which butts on the flat surface (23a) provided on the pointer (23) hence prevents the rotation of the said pointer (23) as shown in Figure-7, further the pointer holder (24) is fastened to the bracket (28) by means of two diagonally mounted dowel pins (26) and screws (27) as shown in Figure-6. The said bracket (28) is assembled with clamp (29) which is mounted on the root segment (3a) of blade (3) through two shear bolts (30) to avoid any clearance and play. The said arrangement ensures the alignment of the pointer (23) with respect to the pitch axis (104). To ensure proper locking of said pointer assembly (9) with root segment (3a) of rotor blade (3), a small clearance (108) of around 2 mm is provided between bracket (28) and clamp (29) in the locked condition as shown in Figure-7.
With reference to Figure-6, the said bracket (28) and clamp (29) are having reliefs (28a) and (29a) respectively to avoid any damage to the conductive strip (3b) (as shown in Figure-2) passing over the surface of the root segment (3a) of rotor blade (3) for the purpose of lightening protection of the said blade. The further feature provided in the said bracket (28) and clamp (29) are the corresponding inner surfaces (28b) and (29b) are bonded with flexible strip, particularly made of rubber material, to avoid any potential damage to the composite skin of said blade root segment (3a) of rotor blade (3) which is made of composite material, during mounting and dis-mounting of said pointer assembly (9), since the rotor blade (3) is a critical part of rotorcraft (1).
With reference to Figure-2, when the pilot moves the control stick between the extreme positions, which causes the blade (3) to tilt about the said feathering hinge (2c) through the flight control linkages (not shown in figure) which are connected to blade fork (2d), hence the pointer (23) moves over the angular scale (10) for a range, from (102) to (103) which corresponds to the combined blade angle (collective and cyclic) of around -15° to +30°, by said means it can be verified that whether the required blade angle is achieved or not, which confirms the satisfactory functioning of flight control linkages, and if not, necessary corrections will be given with the provisions in the main rotor system which is well known to the people in this art. The said apparatus (4) can be mounted in all four rotor blades (3) of said rotorcraft (1) or plurality of blades to measure the corresponding blade angles at different azimuthal position with respect to reference axis (101) of rotorcraft (1).
The particulars disclosed above are representations of the invention, it is also possible that the invention may be modified and practiced in equivalent but different ways or arrangements by one who is skilled in the art with the help of the details described in this manuscript, one such alternate method of measuring the angle using a Vernier scale (31) is disclosed in Figure-8. The main objective of using a Vernier scale (31) is to improve the least count of the measurement which is one of the key specifications of the said apparatus (4). The least count of the said apparatus (4) is dictated by the minimum pitch distance of the angular divisions (10c) in the angular scale (10) which is 0.5 degree or 30’, which can be read using the pointer (23). Whereas by incorporating the Vernier scale, a least count of 0.1 degree or 6’ can be achieved, which provides more accurate reading compared to the earlier case using pointer (23), since the pitch distance (109) in the Vernier scale is 0.9 degree. The least count of the said apparatus with Vernier scale can be defined as, the difference between the pitch distance (107) of main scale (10) (which is 1 degree) and pitch distance (109) of the Vernier scale (31) division (which is 0.9 degree). Hence the accuracy of the said Vernier scale can be improved by changing the pitch distance (109) of Vernier scale (31) in a suitable manner. Therefore, all such variations are considered within the scope and spirit of the invention. Accordingly, the protection is sought. , Claims:I/We claim;
1. An apparatus (4) to verify the pitch angle of rotor blade (3) mounted on main rotor head (2) of a rotorcraft (1) comprising:
a fixture assembly (8) consisting of a fixture (11), a locking arrangement (14) at one end, an azimuth pointer (6) at other end and an angular scale (10);
wherein locating cylindrical feature (11a) of said fixture (11) of one end insert in to hallow portion (5a) of main bolt (5) and locating cylindrical feature (18) inserts in to a hole (2b) on said hub plate (2a) to arrest degrees of freedom of said fixture (11) while connecting axis of said cylindrical features (11a,18) orientation is parallel to pitch axis (104);
wherein said angular scale (10) installed on to said fixture (11) through an extended arm comprising a holder (13) and a bracket (12) in such a way that said angular scale (10) orientation is perpendicular to pitch axis (104);
an azimuth pointer (6) inserted through said locating cylindrical feature (11a) to read azimuthal angle (7a,7b) of rotor blade (3) on an angular scale (7) with respect to reference axis (101) of rotorcraft (1); and
a pointer assembly (9) installed on to said root segment (3a) of said rotor blade (3) by means of clamps (28,29) on one side and a pointer (23) provisioned in parallel alignment to said pitch axis (104) on a base (24) on other side to read the angle (10c) on said angular scale (10).
2. The apparatus (4) as claimed in claim 1, wherein said fixture assembly (8) is constraints for all degree of freedom with respect to said root segment (3a) thereby to said rotor blade (3).
3. The apparatus (4) as claimed in claim 1, wherein said locking arrangement (14) locks said fixture assembly (8) with said hub plate (2a) by rotating a taper bolt (17) in anti-clockwise direction to move upward and hence the split bushes (18-1 & 18-2) expand diametrically on the taper surface (17a) of said taper bolt (17), and by rotating said taper bolt (17) in clockwise direction unlocks said fixture assembly (8) from the hub plate.
4. The apparatus (4) as claimed in claim 1, wherein said split bushes (18-1) and (18-2) are made of soft material, particularly using Teflon material to avoid any damage during locking and unlocking.
5. The apparatus (4) as claimed in claim 1, wherein said pointer assembly (9) is locked in the root segment (3a) of rotor blade (3) by means of fastening said bracket (28) and clamp (29) through shear bolts (30) and maintaining a clearance (108) of around 2 mm between the said bracket (28) and clamp (29).
6. The apparatus (4) as claimed in claim 1, wherein surfaces (28b) and (29b) of respective clamps ((28,29) are bonded with a soft material to avoid damage to rotor blade (3).
7. The apparatus (4) as claimed in claim 1, measure a range of pitch angle from negative pitch (102) angle to positive pitch angle (103) between a angles ranging from -15° to +30°.
8. The apparatus (4) as claimed in claim 1, wherein said angular scale (10) comprises a main scale with 0.5° (or) 30’ angular (10c) divisions and an angular Vernier scale (31) to achieve a least count of 0.1° (or) 6’ or less.