CA1235680A - Hubless, hingeless and bearingless helicopter rotor system - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A helicopter rotor system in which a plurality of rotor blades are attached to the rotor mast. Each blade has a spar formed of fibers bundled and bonded together inside a skin. These fibers are divided into two bundles, each of which has a bight with a bend and two arms that double back into the spar. The bights are joined to the mast by spaced-apart attachments. The attachments may be plate-like, and can be shaped to pro-vide initial coning and camber angles.

Description

5~i80 This invention relates to a helicopter rotor system, in particular a rotor system which is hubless, hingeless and bearingless.
Helicopter rotor systems constitute a highly developed art. Especially for the larger rotor systems, and also for the smaller, lighter rotor systems, the mounting of the blades for their necessary motions is relatively complicated. Attempts are being made to provide hingeless, hubless and bearingless rotor systems, but these are presently quite complicated and extremely critical in their construction. It is an object of this invention to provide a hubless, hingeless and bearingless rotor system for a light helicopter which can readily be manuEactured with the use of conventional fiberglass fabrication techniques and simple, strong and expedient metal components without many of the intermediate elements between the blade and the mast which are common in existing rotor systems.
Summary of the Invention The invention provides a helicopter rotor system com-prising: a rotary mast having an upright axis; three or more rotor blades mounted to said rotary mast to be turned by said mast, each said blade having a respective longitudinal axis directed away from said mast, all of said rotor blades being substantially identical to one another, and being angularly spaced apart around said mast, each said blade comprising a skin forming an airfoil and an internal region, a counterweight rod and a spar extending longitudinally inside said region, said spar comprising a bundle of aligned fibers which, inside said region are bonded to each other, to said skin, and to said counterweight rod, said bundle ~k 1 35~8[) being doubled and divided so as to form inboard of said skin a pair of U-shaped bight portions, each with a bend and a pair of arms, said arms being stiffly flexi~le, said fibers inside said region constituting continuations of the fibers in said bight portions, said fibers in bight portions being bonded together, whereby the total cross-section area of said fibers is substant-ially constant from the inboard end of said arms through the major portion of the length of the spar; attachment means attaching each of said bight portions to said mast at locations spaced apart from one another and substantially spaced from the center of said shaft, both on the same side of the center of the mast; a long-itudinally-extending torque tube rigidly attached to said counter-weight rod at a first end of each said torque tube, and a first bearing member adjacent to the other end of said torque tube, said torque tube having an axis; and a second bearing member mounted to said attachment means and to said first bearing member, whereby said torque tube is rotatable around its own axis, and can move in any angular direction away from said longitudinal axis around the center of said second bearing means, whereby to enable ~0 lead/lag, feathering and flapping movements.
The two bearing members are not intended to transfer any appreciable centrifugal load from the blade to the mast. In-stead, they function to stabilize the torque tube so it can rotate around its own axis . . ~, ~ .
~ 2 -i~35680 for feathering motion, and angularly in any direction from the torque tube axis, around the center of the first bearing member for lead/lag and flapping motion. Pitch horn means is attached to the torque tube to rotate the torque tube around the axis of the torque tube.
According to a preferred but optional feature of this invention, the attachment means comprises a mounting flange member, which can provide ~or an initial coning angle and for an initial camber angle, whereby to minimize flexure of the arms in normal operations.
According to yet another preferred but optional feature of the invention, the flexing portions of the arms are disposed outboard from the attachment means, whereby to minimize such flexures as tend to destroy the integrity of the bonded structure.
The above and other features of the invention will be fully under-stood rom the following detailed description and the accompanying drawings, in which:
Figure 1 is a partial top view of an embodiment of the invention;
Figure 2 is a side view partly in cutaway cross-section of the system shown in Figure l;
Figures 3, 4, 5, 6 and 7 are cross-sections taken at lines 3-3, ~0 4-4, 5-5, 6-6 and 7-7, respectively, in Figure l;
Figure 8 is an enlarged view of a portion of Figure 1, partially in cutaway cross-section;
Figure 9 is a view taken at line 9-9 in Figure 8;
Figure 10 is a fragmentary plan view showing the presently-prefer_ red embodiment of the invention;
Figures 11, 12 and 13 are cross-sections taken at lines 11-11, 12-12 and 13-13, reapectively, in Figure lO;

-~ lZ~S68~1 Figure 14 is a fragmentary plan view showing other features of the embodiment of Figure 10~
Figure 15 is a partial view taken at line 15~15 in Figure 14;
Figures 16 and 17 are top and side views, respectively, of the torque tube used in Figures lO and 14; and Figures 18 - 25 are cross-sections ta~en at lines 18-18, 19-19, 20-20, 21-21, 22-22, 23-23, 24-24, and 25-25, respectively in Figure 14.
One embodiment of a helicopter rotor system 10 according to this invention is shown in the Figures, It includes a mast 11 mounted to a fuse-lage and driven by a fuselage-mounted engine (both not shown). The mast has an upright axis of rotati.on 12 around which it turns to drive a plurality of rotor blades of which two are shown, blades 13 and 14. In the example shown, ive identical and identically mounted blades will be provided, spaced equal-ly angularly apart from one another around axis 12. Because all of them are identical, only blade 13 will be described in detail.
Especially in Figures 1 and 2, the size of the parts near the mast are shown disproportionately large, the blade itself having been reduced in size to fit it on the "sheet".
The airfoil portion 20 of blade 13 is foreshortened in the draw-ings. It will be made of any appropriate length and dimensions, extending asfar to the left as desired, generally shaped to NACA profiles, and is driven by the mast to exert a lifting force on the craft. The airfoil portion and its method of manufacture are shown in detail in my United States patent No.
4,316,700. The airfoil portion includes a skin 21 which is preferably made of a composite material, and shaped to an appropriate configuration. The skin may be made in two parts 22, 23 (Figure 3) which can be mirror images of one " ~23~68C) another when the blade is symr,letrical, or can be of different shapes when the blade is asymmetrical. 'Ihe parts meet at the leading edge 24 and trail-ing edge 25. Bonding and joinder in this blade can readily be accomplished with adhesives. The trailing edges could be joined together by adhesives or fasteners.
The skin forms an internal region 26 which contains a longitudinally-extending spacer 27 that is U-shaped so that its flanges 28, 29 abut and are fastened to the parts 22, 23 respectively. Inside the region at the leading edge there is a ~r~etal counterweight rod 30 which extends parallel to the 10 longitudinal axis 31 of the blade. A spar 32 is formed inside the region. It comprises a plurality of fibers joined together in a bundle by a bonding material to be described, and the skin, the fibers and the counten~eight member are all mutually bonded to one another to form a monolithic construc-tion adjacent to the leading edge. The spar is made of bundles of lengths of fibers as ~1ill be further described below.
The skin, spar, spacer and counterweight rod are assembled in accordance with the techniques described in more detail in the said United States patent No. 4,316,700. Persons skilled in the art will recognize that the bundles of fibers can be appropriately formed while the bonding material ~û is still liquid. Instead of building up the airfoil by bonding together a group of prefabricated parts, the skin itself could be used as a mold, and the counterweight rod, fibers and bonding material laid inside the skin, and the skin then closed and held in a fixture so it will have the proper contour during the curing operation. Also, the system can use the well-known 'pre-preg" process for building up the structure.

lZ35680 At the inboard end of the counterweight member there is attached a torque tube 35 (Figure 1). This torque tube is a strong metal tube which has a flattened portion 36 that is attached to the counterweight rod by a weld-ment 37 so that the torque tube can rotate (feather) the airfoil portion around its pitching axis. The fibers which form the spar continue inboard from the airfoil portion to form a bight portion 40. When the airoil construction is made, the bight portion will be made at the same time, and the spar consti-tutes an extension of the bight portion itself. The purpose of the bight portion is to mount the airfoil portion directly to the mast so as to trans-c~.~trl f u~ I
A 1~ fer the ~e~i}gag&~ load directly to the mast, without the interposition of bearings and clevises as are customarily used in the prior art.
The bight portion includes a flat portion 41 bent around the mast and fitted closely thereto. When this portion is manufactured, tooling pins ~not shown) will be inserted so that the fibers do not cut across holes 42 through which bolts will later pass. In the example, because there are five blades there are five such holes.
The bight portion includes a pair of arms 43, 44 which extend from the 1at portion toward the airfoil portion, and are progressively shaped at flrst to provide a pair of channels 45, 46 on opposite sides of the torque tube (Figures 4 and 5). The channels are identical so that only channel 45 will be discussed in detail. It has a flat bottom member 47 and a pair of flanges 4~, 49. The flanges are directed away from the torque tube, which passes between the channels. These channels progressively change their shape as shown in the drawings and finally merge to form a bundle 50, parts of which pass on each side of the flattened portion of the torque tube and then continue into the region to form the spar.

- 6 =

~ 56~(~

At least arms 43 and 44 are stiffly flexible, as would be expected of a bundle of glass fibers bonded together. They have substantial tensile strength to resist centrifugal forces, and sufficient flexibility to accom-modate feathering, lead/lag and flapping movements.
The torque tube extends inboard toward the mast and has a pitch horn 51 connected thereto. The torque tube of each of the blades will have its own respective pitch horn. The pitch horns are connected to a swash plate (not shown) to control the angle of attack of the blades. Turning the pitch horn will rotate the blade around its axis 31 for feathering motion.

A first bearing member 52 (Figure 8~ is formed inside the torque l-~;s t~be at its inward end. ~ bearing member includes a cylindrical passage adapted to receive a second bearing member 53 in the shape of a bàll which closely fits inside bearing member 52. Thus the torque tube can be rotated aro~md its own axis, and can be angularly moved in any direction from its axis around the center of bearing member 53. It also has limited freedon for longitudinal movement, as limited by the bight portion and by arms 43 and 44.
The bearing comprising members 52 and 53 is not intended to transfer any appreciable centrifugal load. The centrifugal load is transferred by flat portion 41 which constitutes a flexible continuation of the spar itself.
~0 Instead, the bearing acts to stabilize the inboard end of the blade at the torque tube. It enables the blade (and torque tube) to move angularly in any direction from axis 31 of the blade, around bearing member 53 as a center.
This enables lead/lag and flapping movement.
Second bearing member 53 is mounted to a mounting plate 54 which fits between the two arms of the bight portion, and has a hole 55 to pass attachment means yet to be described.

~Z~S680 As best shown in Figure 2, a small angle 60 (perhaps

2 up from the horizontal) is formed in the arms in the bight portion to give a built-ln coning angle to the structure.
Attachment means 65 is provided to mount the flat portions of the bight portions to the mast. The attachment means includes an upper plate 66 which is attached near the top of the mast and is connected thereto by a cross bolt 67. It behaves as a flange on the mast. Five attachment bolts 68 extend downwardly through holes in a bottom plate 69, below which nuts 70 are applied to compress the flat portions and the mounting plates in a stack and to hold them to the mast. Attachment means 65 comprises plates 66 and 69, and bolts 67 and 68. It will now be seen that upward forces exerted by the blades on the mast when the mast is turned will be exerted through the attachment means, and that centrifugal loads will be transmitted directly to the mast by the bights of the blades.
As to materials of construction, the skin section will usuallybeof glass fibre orcomposite type construction.The fibers will usually be S-glass or some other form of glass fibers, with the correct cross-section area and in a sufficient number to provide the properties required for the blade. The bonding material is preferably an initialIy liquid curable resin.
Preferably it is a vinyl ester resin rather than a thermal setting epoxy. When glass fiber is used, polyester resin can be used.
While polyester resin will mix well, it has relatively poor ~ -8-` 1~35680 strength. However ! vinyl ester has the strength of epoxy and the workability of polyester. A wet layup procedure can be utilized, which is very convenient. One can squeeze and pat out excess resins to room temperatures while shaping the material to the desired configuration. Instead, a ~'pre-preg" system can be used, which is well-known ~8a-`" ~Z356Z~0 in the art. In all of the processes, the bonding material (the resin) fills out the structure to a smooth and continuous configuration by seepage and by abutment with a mold surface, or by mechanical smoothing The term "bonding material" is used for the resin, even though it provides much or most of the structure, and the materials in it act primarily as structure elements or reinforcement. However, it does adhere to the other material and joins them to form unitary constructions. For this reason, the term "bonding" is used, although it is not intended to e~clude the meaning of "structure'~ The bonding layers which join the sub-elements may be the same or a different material. Using the same bonding material has the advantage of avoiding points of discontinuity of structural properties. The techniques of constructing the various portions will be understood by persons skilled in the glass fiber and resin epoxy arts and require no further discussion here.
However, a more complete disclosure will be found in the aforesaid United States patent No. 4,316,700.
In order to provide some streamlining for the system inboard of the airfoil portion, a shroud 75 is provided which preferably has an airfoil configuration It covers most of the bight portion of the blades. It, and the skin in Figures 1 and 2, are shown in dashed lines in order to reduce the ~0 complexity of the drawings.
It will now be seen that the blades and the bight portions can readily be manufactured, uniformly and quickly, using conventional molds, fixtures, and techniques After assembly and curing, they can simply be mounted to the mast by the attachment means, and the system is ready to operate iZ35680 The system flexes and twists in the arms near the mast.
The blade bends to lead and lag primarily just outboard from the point of joinder of the torque tube to the counterweight rod.
The bearing means is forgiving of movements in directions lateral to the blade axis (:which constitute these motions). Rotating the pitch horn will rotate the blade to vary its angle of attack.
As many or as few blades as necessary will be provided and will be joined in the stack at the mast. Only two are shown for purposes of simplicity of drawings, although in the illustrated example, three more will be provided.
It will thereby be seen that a simple, unitary rotor system is provided which can reliably and readily be manufactured utilizing simple metal forming techniques and glass fiber layup techniques, resulting in a relatively inexpensive blade of a very high quality. The construction provides for all necessary blade motions, without requiring conventional hubs, hinges and bearings.
The blade is in effect a single, monolithic structure without interposition of conventional elements such as clevises and hinges.
The embodiment of Figures 10-25 overcomes some of the shortcomings in the embodiment of Figures 1-9, Principal among these is the fact that in the embodiment of Figures 1-9, the bights of the individual blades must be stacked one atop the other so that the height of the stack at the mast is determined by the number of blades, and this of course, can limit the number of blades. Furthermore, it would be advantageous to have the mount-ings of all the blades in or close to the s~me plane. This advantage is attained in the embodiment of Figures 10-25.

~lZ3~ 80 In addition, by utilizing different attachment means for the blades, it is possible to provide camber and coning angles at the attachment means rather than as part of the structure of the blade itself.
It is a further advantage that lead/lag stresses can be taken up in the arms themselves, distant from the attachment means so that there is less tendency to loosening of the fabric arrangement.
This embodiment also provides means for reducing static blade droop, and also means for obtaining more useful lift from the inboard 25% of the rotor blade~
ln In Figure 10 there is shown rotor mast 100 which has a flange 101 to which is attached a stack of attachment plates 102. In the illustration, there are eight of these plates in stacks of four each, which are held to the central flange by bolts 103. All of the attachment plates are identical to one c~mother.
The embodiment shows five rotor blades, all of which are identical, so that only rotor blade 105 will be described in detail. Each of them has a similar attachment and a similar pitch horn 106.
~ he blades are constructed identically to the blades in Figures 1-9, especially in the active region best shown in Figures 18 and 19, where the skln 107 is shol~n wrapped around a counterweight member 108, and spar 109 constructed of fibers and bonding material as aforesaid. An alternate spacer member 110 can be placed between the surfaces of the skin near the ~ s )r~ Fi~u~e, Iq trailing edge if desired~ It is unnecessary to repeat the details of con-struction of this blade because they have been thoroughly described above.
~y extending the "wings" of the spar, the skin can be stiffened enough that the spacer member is unnecessary.

1~35~80 A torque tube lOOa is attached to the pitch horn. It is also welded to the counterweight member. Turning the pitch horn therefore varies the pitch of the blade.
In figure 20, there is shown an optional stiffener member 111 welded to the counterweight member. It extends for a short distance along the counterweight member and is welded thereto.
There is a substantial difference in the blade, as shown progressively from Figures 21-25. The skin, it will be noted, begins to have a camber at its trailing end, and as can be seen, the lower rear edge 112 beginstodroop fartherand fartherbelow the horizontal axis 113. This gives a greater angle of attack, the closer the skin approaches to the horizontal axis 113. This provides an increase angle of attack closer to the mast, which with the enhanced stiffness of the llp will give some lift in this area which usuall~v does not provide any substantial lift. Also, the chord of the blade can increase as it extends toward the mast, also increasing the lift at the inboard section. While the increase might seem small, still in a machine weighing perhaps 2,000 pounds, even 125 pounds of lift can be a considerable assistance and can lift the weight of the blades themselves.
To attain certain of the advantages of this invention, the fibers of the spar are taken from the spar in two bundles instead of one. As before, each bundle 115, 116 is doubled so as to form a bight portion 117, 118 with a pair of arms 119, 120, ~ -12-" 12356~3~

121, 122 and a respective bend 123~ 124c These bends are wrapped around respective bolts 125, 126 on the attachment plates whereby to mount the b.lade to the mast, The fibers wrapped around the bend return the full len~th of the blade. Because the fibers are bonded together, and so are the arms, they appear to be simple bundles.

-12a--` lZ3568(~
25g9-138 It should be recognized hexe that the attachment plates are intended to be quite rigid and take no part in ~lexure or control of the attitude of the blade. They are intended to constitute an extension of the rotor mast and constitute direct attachment means for the blade, Each blade has a respective counterweight member as aforesaid, which extends to a first hearing member 127 (Figure 12 in the nature of a hollow longitudinal tube fitting over a second bearing 128 mounted to the attachment means, i~e., to the attachment plates~ This enables longitudinal motion and rotary motion around the center of the ball-like second bearing member as has already been described.
It will now be seen that each blade has two points of attachment to the attachment plates instead of only one,and thatit is attached to the plate rather than being directly wrapped around the mast. Therefore, all attachments can be at the same elevation.
The bundles are shown as they progress from adjacent to the plate, to adjacent to the a-ttachment means in Figures 21-25.
It will be seen that they progress from a pair of relatively squat, constructions through U-shaped constructions and then to modified hat-shaped constructions, the most significant of which are shown in Figures 24 and 25 to include stiffener lip 130, which e~tends normally to the horizontal axis It will be appreciated that this can give substantial rigidity against droop. ~t the bolts, the fibers have been bent to form the bend.

~ -13-123S~i80 In the use of these blades, it transpires that the lead/
lag effects occur at approximately sections 20~20 through 22-22.
It will be observed that at this point it is quite distant from the attachment means and that there is no discontinuity at this location which could work to destroy or degrade the -13a-:~LZ35680 bonded structure, In conventional structures, attachment means are provided at this location, which is disadvantageous.
The use of attachment plates enables substantial advantages to be attained because these plates can be shaped to provide various angles. For example, in Figure 12 the plates are shown with a coning angle 131 stamped into them at the center so as to reduce the excursion required of the bight itself to achieve this angle, Similarly, the plates can be stamped with a ` ~3 2 /~ ~
air of joggles~ to establish a positive basic pitch angle for the blades with the same objective and advantage. Thus, by merely shaping the plates, it is possible to reduce cyclic stresses on the blades themselves.
Again, it is emphasized that the attachment plates form merely an extension of the mast itself and take no part in the flexure of the blades during operation, neither as to feathering, nor flapping, nor lead/lag motion.
Another advantage of this class of blade is that wider cross-sections of the blade 44~ can be provided at its root than at its tip so as to take greater advantage of the inboard portion of the blade, and that the total cross-section of the fibers is constant throughout the entire blade and its attachment, thereby avoiding discontinuities of transition points between the various shapes. This is a tremendous assistance in lay up of the device in manufacture, Although each blade is attached to two points instead of one, it is hubless in the same sense as the embodiment of Figures 1-9. A rotor hub is a mechanism which provides not only for retention of the blade, but also for movement of the blade lead/lag, flapping and feathering modes.
Because the at~achment plates do not provide for any of this, they are hubless in the same sense as before, ~ 14 -~3S68Q

This invention is not to limited by the embodiments shown in the drawings and described in the description, which are given by way of example and not of limitation, but only in accordance with the scope of the appended claims.

Claims (19)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A helicopter rotor system comprising:
a rotary mast having an upright axis;
three or more rotor blades mounted to said rotary mast to be turned by said mast, each said blade having a respective longi-tudinal axis directed away from said mast, all of said rotor blades being substantially identical to one another, and being angularly spaced apart around said mast, each said blade comprising a skin forming an airfoil and an internal region, a counterweight rod and a spar extending longitudinally inside said region, said spar comprising a bundle of aligned fibers which, inside said region are bonded to each other, to said skin, and to said counterweight rod, said bundle being doubled and divided so as to form inboard of said skin a pair of U-shaped bight portions, each with a bend and a pair of arms, said arms being stiffly flexible, said fibers inside said region constituting continuations of the fibers in said bight portions, said fibers in bight portions being bonded together, whereby the total cross-section area of said fibers is substantially constant from the inboard end of said arms through the major portion of the length of the spar;
attachment means attaching each of said bight portions to said mast at locations spaced apart from one another and substantially spaced from the center of said shaft, both on the same side of the center of the mast;
a longitudinally-extending torque tube rigidly attached to said counterweight rod at a first end of each said torque tube, and a first bearing member adjacent to the other end of said torque tube, said torque tube having an axis; and a second bearing member mounted to said attachment means and to said first bearing member, whereby said torque tube is rotatable around its own axis, and can move in any angular direction away from said longitudinal axis around the center of said second bear-ing means, whereby to enable lead/lag, feathering and flapping movements.

2. A helicopter rotor system according to claim 1 in which said attachment means comprises a substantially rigid flange on said mast, each said bight being attached at its bend to said flange.

3. A helicopter system according to claim 2 in which said attachment means includes a plurality of bolt means, each bend extending around a respective said bolt means.

4. A helicopter system according to claim 3 in which said flange is formed to mount the bight portion at an initial coning angle.

5. A helicopter system according to claim 3 in which said flange is formed to mount the bight portion at an initial camber angle.

6. A helicopter system according to claim 5 in which said flange is formed to mount the bight portion at an initial coning angle.

7. A helicopter system according to claim 2 in which said flange comprises a plurality of plates rigidly mounted to said shaft, one on each side of the bend, whereby to sandwich at least part of the bend between them.

8. A helicopter system according to claim 7 in which said plates have aligned apertures to pass bolts through them and through the bight portion inside the bend to attach the blade to said plates.

9. A helicopter system according to claim 8 in which said plates are formed to mount the bight portion at an initial coning angle.

10. A helicopter system according to claim 8 in which said plates are formed to mount the bight portion at an initial camber angle.

11. A helicopter system according to claim 10 in which said plates are formed to mount the bight portion at an initial coning angle.

12. A helicopter system according to claim 7 in which each of said pluralities comprises a stack of similar plates.

13. A helicopter system according to claim 1 in which said arms are shaped to form a stiffener lip extending generally up-wardly for at least part of their length to resist static droop of the blade.

14. A helicopter system according to claim 1 in which the major portion of flexure in lead/lag motion occurs at a sub-stantial distance from the point of attachment of the bight portion to the mast, between said attachment means and said spar.

15. A helicopter system according to claim 1 in which the length of the forwardly extending chord of the blade lengthens as it approaches the bight portion.

16. A helicopter system according to claim 1 in which a substantial skin area enfolds the bight portion, out of contact therewith.

17. A helicopter rotor system according to claim 1 in which said skin has a camber in a region adjacent to the end of the rotor blade having said bights, which camber increases as it approaches said end.

18. A helicopter rotor system according to claim 1 in which the number of said blades is an odd number.

19. A helicopter rotor system according to claim 1 in which pitch horn means is attached to each torque tube to rotate said torque tube around the axis of said torque tube.