Apparatus for adjusting the tracking of the blades in a rotor, especially for a rotary wing aircraft
This is a divisional of application Ser. No. 474,044, filed Mar. 10, 1983, now U.S. Pat. No. 4,545,733. 
    
    
     CLAIM TO PRIORITY 
     The present application is based on European Serial Numbers 82 102 202.7 and 82 102 203.5 filed in the European Patent Office on Mar. 18, 1982. The priority of the European filing date is claimed for the present application. 
     BACKGROUND OF THE INVENTION 
     The invention relates to an apparatus for adjusting the tracking of the blades in a rotor, especially for a rotary wing aircraft. The term &#34;tracking&#34; in this context means that all blades of a multi-blade rotor, such as a helicopter rotor, rotate in the same plane when all blades are adjusted to the same blade angle and without any cyclical blade angle change. 
     As disclosed in German Pat. Nos. 1,531,355 and 2,150,741 rotors of this type do not require any separate mechanical flapping hinges nor any separate mechanical lead-lag hinges. Avoiding such hinges has the advantage that the useful life of such rotors is substantially increased because parts that are not needed do not break down. This feature in turn results in a smaller risk of damage. Additionally, it is possible to use the rotor hub as a protective housing, for example for the control means needed for the blade angle adjustment. Reference is made in this connection to German Pat. No. 2,658,828 in which the control rods for the blade angle adjustment are driven by a swash plate and connected to the radially inner end of the respective blade root sleeve. Such a structure for the blade angle adjustment is rather simple in a kinematic sense. However, there is no possibility for adjusting the so-called tracking through an external access to the rotor hub. After the rotor blades have been mounted to the rotor hub, such tracking of the blades relative to each other or relative to one another is desirable so that all blades may rotate in the same plane. However, to assure such tracking a fine adjustment of the blades is needed independently of the collective  and uniform blade angle adjustment without regard to any cyclical blade angle adjustment. 
     The tracking adjustment involves a very fine adjustment of each blade about the longitudinal axis of a blade which extends in the radial direction relative to the rotational axis of the rotor. It must be possible to make the adjustment to the precise same angular degrees or even angular minutes for the individual rotor blades. Such adjustment must be possible after the original installation and also when bearings are required to be exchanged in the blade angle adjustment gear train. 
     German Pat. No. 3,006,088 describes a rotor with elastomeric bearings. At least one of such bearings is capable of taking up compression loads. Such rotors have the advantage that the rotor wings or blades may be tilted into a folded position. Further, such rotors also have a rotor hub functioning as a protective housing for the control mechanism used for the blade angle control. 
     OBJECTS OF THE INVENTION 
     In view of the above it is the aim of the invention to achieve the following objects singly or in combination: 
     to provide a simple always easily accessible apparatus for adjusting the blade tracking without the need, for example, of a positional adjustment of the control rods for the blade angle adjustment where such control rods are located inside the rotor hub; 
     to provide a fine adjustment which is easily performed manually to assure the required tracking adjustment of the individual rotor blades; 
     to construct the adjustment means in such a manner that they are not trouble prone; and 
     to perform the tracking adjustment at a point where it is most effective, namely directly at the blade root. 
     SUMMARY OF THE INVENTION 
     The rotor blade tracking adjustment mechanism according to the invention is characterized in that a bushing is provided with an extension reaching through the blade root sleeve, whereby the inner end of the bushing extension is rigidly connected to the blade angle adjustment means while the radially outer ends of the bushing extension has a lever arm which reaches into cooperation with the blade root sleeve through adjustment means which permit the angular adjustment of the bushing relative to the sleeve and which also permit locking the bushing into its adjusted position after the adjustment has been made so that rotation of the bushing by the blade angle adjustment levers may be transmitted to the respective rotor blades for the tracking blade angle adjustment. 
     Thus, the invention takes advantage of the bushing which normally is rigidly held in the blade root sleeve, by supporting this bushing rotatably in the blade root sleeve and by providing it with a radially outer lever arm for easy angular position adjustment from the outside, and by using the radially inner extension of the bushing in the rotor hub for connection to the respective blade angle adjustment control rod located inside the rotor hub. Since the lever arm of the bushing is directly accessible by adjustment means which are in turn accessible externally of the rotor hub, the adjustment of the bushing may be performed without disturbing the rotor hub and any components inside the rotor hub. Simple position adjustable arresting means such as screws may thus be used for said tracking adjustment of the rotor blades. 
     In a rotor with elastomeric bearings the invention constructs the bearing stud of the blade root or rather of the blade root mounting as a sleeve or bushing type extension. A control shaft connected with its radially inner end to the blade angle control means extends rotatably through said sleeve or bushing extension and has a lever arm connected to its radially outer end. This lever arm reaches adjustably into cooperative contact with the blade root or a blade root mounting for the tracking adjustment. Once the tracking adjustment has been made, the lever arm is locked in its position relative to the blade root or blade root mounting for permitting the blade angle adjustment. 
    
    
     BRIEF FIGURE DESCRIPTION 
     In order that the invention may be clearly understood, it will now be described, by way of example, with reference to the accompanying drawings, wherein: 
     FIG. 1 is a sectional view through a portion of a rotor hub with roller bearings for the blade root and showing part of the radially inner end of one rotor blade, whereby the sectional plane extends perpendicularly to the rotational axis of the rotor hub, said rotational axis extending perpendicularly to the plane of the drawing; 
     FIG. 2 is a sectional view along section line 2--2 in FIG. 1; 
     FIG. 3 is a sectional view similar to that of FIG. 1, but showing a rotor hub with elastomeric bearings for the blade root; and 
     FIG. 4 is a sectional view along section line 4--4 in FIG. 3. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BEST MODE OF THE INVENTION 
     As in the structure of the above mentioned German Pat. No. 2,658,828, the rotor hub 1 according to the invention is also constructed as a protective housing for the blade angle adjustment means (13, 14). The rotor hub 1 is provided with at least two and possibly more rotor hub arms 1.1 extending radially away from the rotor hub and being hollow for receiving a blade root sleeve 5. Such structural detail is shown in the above mentioned German Pat. No. 2,150,741. The blade root 2 is connected to the blade root sleeve 5 or rather to two legs 5.1 of the sleeve 5 by means of bolts 6. Thus, the blade root sleeve forms a mounting for the blade root 2. The blade root sleeve 5 is rotatably supported in the respective hollow root hub arm 1.1 by anti-friction bearings 3 and 4. The just mentioned blade root legs 5.1 are spaced from each other and extend substantially in parallel to each other as best seen in FIG. 2, thereby simultaneously forming a socket type of holding means for the blade root 2. Additionally, this spacing provides room for accommodating an adjustment lever 15, as will be described in more detail below. 
     The blade root sleeve 5 and the anti-friction or roller bearings 3 and 4 permit introducing any moments resulting from blade flapping movements and from blade lead-lag movements into the rotor hub arm 1.1 and thus also into the rotor hub 1. 
     According to the invention the blade angle adjustment bushing 7 is rotatably supported inside the blade root sleeve 5. This bushing 7 holds the blade root sleeve 5 against radially effective tension loads such as centrifugal forces. For this purpose the bushing 7 is secured against radially effective forces to the central body 10 of the hub 1 by a tension element 9. The radially inner end of the tension element 9 is secured to the central body 10 by a connecting bolt 11. The radially outer end of the tension element 9 is connected to the bushing 7 by a bolt 8. The tension element 9 is strong against tension loads, but capable of yielding against torque moments applied to the tension element 9 to the extent necessary for permitting the blade angle adjustment and the tracking adjustment as will be described in more detail below. Preferably, the tension element 9 is constructed as an endless belt of lamellae, for example, of fiber compound materials. The central body 10 is provided with a number of bolts 11 which correspond to the number of rotor blades. Further, the blade root sleeve 5 is provided with an inwardly reaching arresting shoulder 5.2 resting against a respective outwardly reaching arresting shoulder 5.2&#39; of the bushing 7. The arresting shoulders 5.2 and 5.2&#39; are so located that the bushing 7 with the tension element 9 restrains the blade root sleeve 5 against radial forces which are effective in the direction of the longitudinal axis of a blade more specifically against centrifugal forces. 
     According to the invention the bushing 7 is provided with an extension 7.1 reaching radially inwardly out of the hub arm 1.1 sufficiently for connection to a ring end 14&#39; of the blade angle adjustment lever 14. The ring end 14&#39; of the lever 14 and the radially inner end of the bushing extension 7.1 are preferably provided with splines 20 for transmitting torque moments from the lever 14 to the bushing 7 through the bushing extension 7.1. Additionally, the lever end 14&#39; is secured by a threaded nut 21. For the blade angle adjustment the lever 14 is movable by a control rod 13 and the movement of the control rod 13 is transmitted through the just described elements since the bushing extension 7.1 acts as a control shaft for the blade angle adjustment as long as the radially outer lever arm 15 forming preferably an integral part of the bushing 7 is held in a rigid position relative to the legs 5.1 of the blade root sleeve 5. 
     However, the bushing 7 with its extension 7.1 may also be adjusted in its angular position relative to the blade root sleeve 5 by the adjustment means shown in more detail in FIG. 2. 
     Referring to FIG. 2, the above mentioned tracking adjustment is possible due to the relative movement between the lever arm 15 of the bushing 7 and the blade root sleeve 5 when the screws 16 reaching through threaded holes in the legs 5.1 of the blade root sleeve 5 are released. The free end of the lever 15 reaches into the gap between the inner ends of the adjustment screws 16. If desired, the legs 5.1 may be provided with a downward projection 5.3 to facilitate the easy access to the heads of the adjustment screws 16. Preferably, at least one of the screws 16 is provided with an angular scale 18 arranged for cooperation with a marker 19 on the respective leg 5.1. Once the adjustment of the relative position between the lever 15 and the legs 5.1 is accomplished, the counternuts 17 are tightened on the screws 16, whereupon any blade angle adjustment movements are transmitted through the bushing extension 7.1 and the bushing 7 as well as the lever 15. 
     In view of the above it will be appreciated that the external access to the adjustment screws 16 greatly facilitates such adjustment and makes it very simple. Further, once the adjusted screws 16 are tightened by the counter nuts 17, it is assured that any movements of the control rods 13 driven by a conventional swash plate (not shown) are properly transmitted for the blade angle adjustment. 
     FIG. 3 shows a sectional view similar to that of FIG. 1, however, illustrating the invention embodied in a rotor hub 30 to which a blade root 31 is connected through elastomeric bearing means 34 and 38. The blade root 31 is provided with an aperture or hole 33. The rotor hub 30 has at least two blade root connecting means including a forked arm 32 provided with bearing support members 35 and 53. The bearing support members 35 and 53 hold the elastomeric bearing 34 and simultaneously reach through the aperture 33. 
     Simultaneously, the blade root 31 or rather its radially inner end is received between the legs 50 of a blade root mounting 39. The radially inner end of the blade root 31 is rigidly secured to the legs 50 of the blade root mounting 39 by bolts 54. The bearing holding member 35 is secured on both sides to the blade root by two bolts 37 arranged symmetrically above and below the radially extending horizontal longitudinal axis of a rotor blade. The bearing holder 53 is secured to the two hub arms 32 by a bolt 36 extending perpendicularly to and crossing the radial longitudinal axis of a rotor blade. 
     The radially inwardly directed end of the blade root mounting 39 is formed as a sleeve 40 held in the elastomeric bearing 38 which is a radial bearing. Incidentally, the elastomeric bearing 34 is an axial as well as a radial bearing capable of taking up torque moments as well as compression loads, whereby it is able to take up centrifugal forces in the blade. Blade angle adjustment means including a lever 41 and a control rod 42 are connected inside the hub 30 to an angle control shaft 43 extending rotatably through the sleeve or bushing 40. The lever 41 has a ring end 41&#39; provided with spline grooves cooperating with respective splines 51 on the radially inner end of the shaft 43. Additionally, the ring end 41&#39; is secured by a threaded nut 52 on the correspondingly threaded end of the shaft 43. 
     According to the invention the radially outer end of the shaft 43 is secured to a lever arm 44 reaching away from the radial longitudinal axis of a blade into cooperation with the blade root or preferably into cooperation with the mounting 39 providing a respective space between its mounting legs 50. 
     Tracking adjustment means in the form of screws 45 reach through threaded holes in the legs 50 as best seen in FIG. 4. The inner ends of these screws 45 cooperate with an end of the lever arm 44 for adjusting the relative angular position between the lever 44 and the blade root 31 for the above explained tracking adjustment. Once that adjustment has been made, counternuts 46 are tightened and thereafter the blade angle adjustment movements may be transmitted through the lever 44 to the blade. At least one of the screw heads may be provided with an angular or minute scale 47 arranged for cooperation with a respective marker 48 in the corresponding leg 50 of the blade root mounting 39. 
     If desired, the legs 50 may be provided with a lobe 49 in which the adjustment screws 45 are received for easy access externally of the rotor hub 30 and externally of the blade root 31. 
     Although the invention has been described with reference to specific example embodiments it will be appreciated that it is intended to cover all modifications and equivalents within the scope of the appended claims.