US2520268A - Sustaining rotor for rotating wing aircraft - Google Patents

Description

Aug. 29, 1950 H. T. AVERY 2,520,268

SUSTAINING ROTOR FOR ROTATING WING AIRCRAFT Filed Feb. 17, 1947 ATTORNEYS Patented Aug. 29, 1950 UNITED STATES PATENT OFFICE SUSTAINING' ROTOR FOR ROTATING'WING- AIRCRAFT HaroldT. Avery, Oakland, Calif.

ApplicationlFebrua-ry' 17, 1945-7, Serial No. 729,071

5 Claims. (Cl. Fill-160.5)

This invention relates to rotating wing, aircraft and: particularly to improvements in the. sustainingrotorsfor such craft. As isv well known such rotorsmaybe. of either: the articulated or. the non-articulated type. Inrotors' of the non-,- articulated type eachblade of. the rotor is con-- structed in fixed; relationship to the rotor hubexcent; for freedom of the blade to; berockedon its own. longitudinal axis; to efiect change. in blade pitch, andtor-such further changes inrelation.- ship as; maybeintroduced by the bending of the blades; due. to their own flexibility. In rotors oi the. articulated; type, the. blades; ordinarily retain, the same: freedoms; ofv movement relative to the hub as in rotors of the non-articulated type plus: (1) the freedom; provided by introducing a so called flapping hinge at the root of each blade (or in some cases such a hinge common to more. than one blade). permitting. the blade, to be rocked up and. down in response to. the. forces acting on it in flight, and. usually also. (2.) the freedom provided by additionally introducing near the. root of each blade a so. called drag.

hinge. permitting, it. to, be angularly displaced, in its generalplane or come. of. rotation.

All such rotors, and more particularly rotors oi the articulated type, are, more or less subject to undersirable. amounts. of vibration.v Such vibrations are largely due to the manner in which the-center of gravity of'suchrotorslis continually shifting, so that a'rotor which isperfectly: balanced under one setof conditions-Will be out of balance under other conditions. These shifts-are primarily due to unequal displacement ditherespective-bladesabout their respective dragchinges, and/or unequal rocking of the bladesabout their respective flapping hinges; andyor (particularly in the case of non-articulated rotors). unequal flexing'oftheiblades.

One of themost. troublesome seurcestofi such unequal displacement. and. rocking to; be. found aerodynamic dissimilaritybetween the; respective blades. Very slight. amounts at twist: or: warp, or imperfection; in part of: the. airfoil, surface will veryreadily cause: one: blade. to produce more; or less liit; than the other bladesdo underv thesame circumstances. and hence, cause that blade tocon- .tinuously ride; higher or lower. than thetrack. de-

scribed bythe. other blades in their circuits. So long asallnblades follow exactly the same track, and particularly if there are more than twoxbl'ades in the rotor, inequalities in the flapping angles of the blades: at difierentpointsin-the circuit do not tend to cause very serious vibration for under these circumstancesthecenter oi, gravity remains 5:5

permanently displaced in adirecti'ongenerall'y opposite. to that part of the. circuit in which the bladesrock the highest. and. thecenter of gravity remains very nearly fixed relative to, the craft. However, if the aerodynamic characteristics of one blade cause it to. permanently track any higher or lower than the others. it will cause. the center of gravity of, the rotor to. be. shifted away from. or toward that blade in all partsoi. its cincu-it, thus producing substantially the same effect as an eccentrically located. weight rotating with the. rotor, whichof course-producesbad vibration. Also, if the pitch. setting of a. blade withsuchdifferent aerodynamic slmpe is readjusted. relative to; that of, the other blades, by an amount sufilcient to bring, it backinto substantially thetrack described by the other blades its, difference. in aerodynamic shape is very apt to cause-a difierence in drag which will cause that blade' tobe displaced .difl'erently' from the others, about its draghinge, thus causing, a shift in the. center of gravity of the rotor in. the direction of such difference of displacement, which. again isequivalent to an eccentric weight rotating; with the. rotor and causes bad vibration A. great. dealoi thetrouble and expense involved in the manufacture and maintenance of articulated rotorsv is-due to the effort to secure and. maintain perfect aerodynamic similarity, as. well. as perfectmass balance, between all blades.

As long as arotor is sustaining, a craft the lift exerted along the blades cause. them to cone up;- wardly, or inthe caseoi. a noni-articulatednotor at least flex upwardly, so. that the centers of mass of the blades normally describe circlesabout the rotor axis olisetverticallyabove the plane of the blade hinges or blade roots. It, is usual in rotating Wing; craft-toexertcontroloi the craft-in the various horizontal directions by imposing, cyclic changes of pitch. upon the; blades, thuscaus ing them to travel higher in certain. parts.- of their circuits than others, thereby tilting thecone described by the, rotor blades. about theblade hinges, or the equivalent points of flexure in a non-articulated rotor, anclcausing; the centersof mass. of. the blades to. describea circle. Whit-hunder these circumstances. will be eccentrically lo cated, relative to; the rotor axis. The momentof inertiav of each blade about the. rotorv axis will then cyclically increase. and decrease causing. cyclic changes in the angular momentumandthe'rerfore, vibration unless. each. blade. is permitted to be. freely displaced on its drag hihgesoastoang ularly accelerate. anddecelerate sufficiently to maintain constancy. of. angular. momentum. .How-

ever if a blade is perfectly freelto thus readjust itself in the plane of rotation it will readily become displaced from its proper angular relation to other blades, thus causing a bad disturbance in the location of the center of gravity of the rotor. To whatever extent a blade is restrained from thus readjusting itself while the blade is undergoing cyclic changes in its moment of inertia, changes in angular momentum will be introduced thereby introducing both vibration and increase in blade root stresses.

My copending applications Serial No. 645,309, filed February 4, 1946, and Serial No. 665,653, filed April 29, 1946, disclose means for automatically compensating for flapping displacements of a blade so as to stabilize the resultant center of gravity. However, in order to avoid changes in angular momentum in spite of the presence of some degree of restraint of the blade in the leadlag direction it would be necessary to stabilize the resultant moment of inertia. If this stabilization of the resultant moment of inertia be accomplished by stabilizing the moment of inertia of each blade it will further avoid the increas in blade stresses which would otherwise be introduced by restraining the blade in the lead-lag direction. Stabilizing the center of gravity of the rotor or of the individual blades in the manner disclosed in the above mentioned co-pending applications does not, in general, effect stabilization of the moment of inertia, and it is desirable that both should be stabilized, for blade displacements will, in general, produce either radial displacements of the center of gravity or changes in angular momentum, or both, unless both the center of gravity and moment of inertia of each blade are stabilized. Furthermore if the moment of inertia of each blade be stabilized, the drag hinge ma be eliminated and the blade completely restrained in the lead-lag direction without any increase in blad stress under normal flight conditions, and in fact with some decrease from the stresses inherent in the usual arrangement wherein each blade is partially restrained in its movement about the drag hinge.

It is an object of the invention to provide improved means for eliminating vibration in sustaining rotors, and particularly in rotors of articulated construction.

It is an object to render means for automatically'stabilizing rotors and/or the blades thereof responsive to blade flexure so as to correct for disturbances in moment of inertia and/or center of gravity produced by such flexure.

It is an object to minimize the forces required to operate such an automatic stabilizing means, and it is a further object to minimize the weight of such means.

More broadly it is the object of the present invention to provide an improved sustaining rotor for rotating wing aircraft.

It is also an object of the invention to provide a rotor which will be particularly asy and inexpensive to manufacture and maintain.

More specifically, it is an object of the invention to remove by particularly improved means the necessity for aerodynamic similarity between the various blades of a rotor, which necessity has been paramount and costly in articulated blade rotors.

The novel features of the invention are set forth with particularity in the appended claims. The invention itself, however, together with additional' objects and advantages thereof will be best understood from the following description of a specific example of an embodiment thereof.

My copending applications hereinabove referred to disclose the use of movable compensating weights located in the blades or on the hub of a sustaining rotor together with means for automatically positioning such weights to stabilize the center of gravity of the rotor and/or the individual blades. t would be possible to alter the form of the positioning means therein disclosed so as to effect stabilization of the moment of inertia of the rotor and/or the blades about the rotor axis, if that were desired, but the specific requirements for positioning such weights to stabilize moment of inertia are, in general, so much at varianc with those for pcsitioning them to stabilize center of gravity, that it would be impossible to position weights located as therein disciosed in a manner that would stabilize both the moment of inertia and the center of gravity.

I have discovered, however, that it is possible to arrange a compensating weight in such a manner that it will satisfactorily stabilize both the moment of inertia and the center of gravity of a blade with respect to the axis of rotation of the rotor, and that such dual compensation is dependent upon locating the compensating weight near the center of gravity of the blade and so arranging the displacing means that, as set forth in my copending application Serial No. 645,309, the displacement of the weight with change of flapping angle should be approximately proportional to the value of the expression (g%+a) exsec A (1) wherein:

g=distance from flapping hinge to center of gravity of blade, measured along blade B=mass of uncompensated blade W=mass of compensating weight a=the distance from the flapping hinge to the center of gravity of the compensating weight with the blade horizontal, that is perpendicular to the rotor axis, and

A=the effective flapping angle of the blade measured up from the horizontal.

In view of the fact that a compensating weight which is so located becomes subject to relatively large centrifugal forces under flight conditions, I prefer to provide means which will substantially counterbalance these centrifugal forces, thereby minimizing the operating forces which must be exerted by the weight positioning system. Also preferably this counter-balancing means is arranged to automatically readjust its counterbalancing force substantially in proportion to the changes in centrifugal force introduced by radial repositioning of the compensating weight.

The following is a description of my preferred embodiment of the invention as shown in th accompanying drawings, in which:

Figure 1 is a vertical section of the rotor hub and one blade, including the automatic stabilizing mechanism, the section being substantially on line ll of Figure 2, and Figure 2 is an enlarged sectional view of the automatic stabilizing mechanism taken substantially on line 2-4 of Figure l.

Rotor construction and drive The invention as illustrated in Figures 1 and 2 can be applied to a rotor of any number of 5 blades. As shown in Figure 1, each blade l ll comprises a, skin or covering H integrally mounted on ribs l2, which in turn are integrally attached to the tubular blade spar I 3, which spar terminates inwardly in a bearing retainer [4 containing a ball thrust bearing I-5 co-axial with. the spar. This bearing serves to attach the blade to the connecting link 16 in a manner'permitting ofthe blade being rotated about the spar axis relative to link 16-, to effect changes in the pitch setting of the blade. Connecting link I6 is in turn attached by means of flapping hinge l! to lugs l8 integral with hub member 19-. Hub member i9- is in turn pivotally mounted by means of: rollerbearings 28 and 21, for rotation about cylindrical member 22 fixed in the framework of the craft, and about the co-axial cylindrical member 23 which is attached to member 22 by means of a plurality of bolts 24. Attached to the bottom of hub member l-9 by means of a plurality of bolts 30- is aring 3! having downwe rdly extending lugs 3-2 for receiving the roller bearing 20. The spherical roller thrust bearing 33 is interposed between ring 31 and cylindrical member 23, thus serving to transmit to the framework of the craft, the upward thrust of hub; member l9, which is primarily the force which sustains the craft in flight. Attached to thetop or hub member l9 by means of a plurality of bolts 34 is a plate 35. Interposed between this plate and a flange 36- of cylindrical frame member 23 is ball thrust bearing 31, which servesto sustain the rotor when it is not exerting an upward lift on the craft.

The drive for the rotor comes from the engine- (not shown) through transmission shaft 40, which shaft is guided in the upper surface 4| of cylindrical frame member 22. Integral with the upper end of shaft 40 is gear 42 which meshes with idler 43-, which idler is rotatably mounted on Stud 44 which is integrally mounted in member 22'. Idler &3 in turn meshes with teeth 45 cut into the inner face of hub member I9. Hub member t9 isthus-rotated upon the fixed cylindrical member-22-,;23.

Mechanism responsive to blade flexure Because of the fact that rotor blades are ordinarily constructed of relatively slight vertical dimension. and sustain relatively great aerody-- namic. loads of uneven and cyclically changing distribution along the length of the blade, such blades are ordinarily subjected. to considerable flexing in flight, particularly in a vertical direction. If. a blade which is attached to'the rotor hubby a. flapping hinge. is appreciably flexed, the efiective flappingpositionof the blade, and therefore its tracking of the other blades, is dependent uponthe direction and. amount of the flexing of the blade as well as upon the vertical angular displacement of the root section of the blade about the flapping hinge. In, order to take both of these factors into account I provide mechanism which is quantitatively responsive to blade flexure as well as to displacement of the blade about the flapping hinge. This mechanism consists. essentially of an element displaceable relative to the hub for measuring blade displacement and a flexible member connecting the element to the outer part of. the blade, the flexible member form illustrated this mechanism includes a lever 51 (IE-lg. 1 which constitutes the. element above referred to and which is angularly positioned about flapping hinge ll inresponse toboth verticalflexing of theblade and angular displace-- ment. of the blade on flapping hinge. I]. This angular positioning of lever 51- isefiected. bythe. following mechanism:

Lugs 50 are integrally. attached totubular blade, spar l3. Flexible cables-or rods 5.l are. attached. to;- these lugs by means oi pins 52 andare led, through guides 53, each of which guidesmay con: sist of a pair of rollers mounted on. aiug. integral with spar [3. Guides. 53 are so located as. to guide one of the cables! along a. path located. above .the neutral axis of thebl'ade, and theother along a path located below the neutr-alaxis, and hence. are located in portions. of the blade which. are compressed or extended by vertical flexing of the blade. Near the root of. the. blade. each. cable 5| is attached, to a connecting linkf54'by means of a. connecting pin 55 Connecting links. 54 are pivotally attached by means of pins 56' to, lever 51. Plus 56 are placed considerably fur.- ther apartthan are thepins 5.2 at, the outer ends of cables 5|, so. that the angular displacement of lever 51 will be correspondingly less than that of lugs 50. The reasonfor this is so thatlever 51 will be angularly displaced in proportion to. the. average effective angular displacement. of the. blade relative tothe hub due to blade flexing, as. measured at the flapping hinge. This angular displacement is substantially that of a lineconnectingthe flapping hinge toa pointon. the blade. somewhere in the vicinity of the. average eiT'ectivecenter of lift of the blade, andis many case. veryconsiderably less in. amountthan the. angle. through which the outer tip portion of th blade. hasbeen flexed. Therefore, if lugs 50,. are located rather close to the blade tip, pins 56. should be. about three times asZ far apartas pins 52 so that, lever: 51 will be rocked. through about one-third. the angle through which lugs 50. are deflected, while if lugs 50 are located further in on. the blade the ratio ofthe distance between pins 59 to thatbetween pins. 52 shouldv be correspondingly decreased, so that in any case, whether the spacing is determined by theory or by test, the. flexing of the blade in flightshall displace lever 5.1 through. an angle equalto that through which the-.unflexed blade would havetobe rocked around flapping. hinge II in order to, produce substantial'ly the same amount of change in the radius of gyration of the blade or in. the location of its center of gravity- These same connections to lever .51 will also. cause that lever torock about flapping hinge L1 in unison with the blade, for any given condition of blade flexure. Hence lever'51: is angularly positioned about hinge IT in accordance with the average effective blade position taking into accountboth blade flexureand, rocking of the blade upon the flapping hinge.

In case of a blade construction in which'there is no flapping hinge'the flexure ofthe blade will nevertheless ordinarily be sufiicient to producea Vertical flapping movement of the blade, and the average. axis about which such movement takes place constitutes an effective flapping hinge. The flexure responsive mechanism, therefore, makes it possible to apply the principles of the invention. to non-articulated rotors as well as making it possible to apply themgmore satisfactorily to articulated rotorsthan would otherwise be possible.

- Stabilizing mechanism The mechanism for stabilizing the location of the center of gravity of the rotor and of each blade thereof, and for stabilizing the value of the radius of gyration of each blade comprises a compensating weight 85 slidably mounted within the tubular spam [3 of each blade, and means for automatically positioning the weight in response to blade flapping and flexure substantially in accordance with the criteria hereinbefore set forth and especially in accordance with expression (1) set forth above.

As previously described lever 51 is rotatably positioned on flapping hinge pin ll directly in accordance with the rocking of the blade on the flapping hinge plus the amount of flexing of the blade reduced to an equivalent amount of change in blade flapping angle. Each lever 51 therefore occupies at each instant an angular position corresponding to the equivalent eifective flapping angular position of the blade at that instant and it is therefore used as a source of control for positioning the compensating weight. For this purpose a slot 65 is cutinto the lower part of lever 51 of the proper shape to produce movement in accordance. with expression (1) hereinabove. This slot 65 is arranged to embrace a roller 66 which is rotatably mounted on a stud 6 8 integrally mounted in segment 61 which is rockably mounted on pin 69 integrally supported inlugs l integral with hub member [9. Cut into the outer face of segment 61 are gear teeth H which mesh with spur gear 12 which is rotatably mounted on flapping hinge pin I1. Integrally attached to spur gear 12 is planetary carrier 13 at the extremities of which are mounted studs 15 carrying planetary pinions 14. These planetary pinions mesh with internal gear 16 which'is mounted on studs 56 so as to remain in fixed relation to lever 57. The planetary pinions also mesh with sun gear 18 which is integrally attached to drum 1 l and both the drum and sun gear are rotatably mounted on flapping hinge pin l1.

As previously mentioned, the compensating weight 85 is slidably mounted in the interior of tubular blade spar I3. Attached to the inboard end of the weight 85 is tension spring 86, the inboard end of which is attached to the tubular blade spar. This spring is provided for the purpose of counterbalancing as nearly as possible the centrifugal force of the compensating weight. For a given angular velocity the centrifugal force of a weight is directly proportional to the distance from the weight to the center of rotation. Therefore, for a given angular velocity, the change in centrifugal force of a weight, due to a radial movement of the weight, is proportional to the distance that the weight has been shifted radially. Spring 86 has a spring force gradient such that the change in force of the spring for a radial movement of the weight is equal, at a selected angular velocity corresponding substantially to the normal rotor speed, to the change in centrifugal force of the weight for the same radial movement of the weight. With such an arrangement the weight positioning means need only exert a force great enough to overcome frictions plus the amount that centrifugal force may change due to the rotor speed departing from that at which the spring force equals centrifugal force. With compensating weight 85 located at as a great a radial distance from the rotor axis as required to stabilize both moment of inertia, and

center of gravity; the adjustment of the weight would set up prohibitively great moments between the hub and the blade were it not for the effect of spring 86.

Attached to each end of movable weight is positioning cable 81, the purpose of which is to position the movable weight. Cable 81 passes from the inward end of movable weight 86 through the interior of tension spring 86, thence inwardly through tubular blade spar l3 and through a central hole in connecting link I6. It then passes over pulley 88, which is attached to connecting link [6, and around cable drum TI to which it is firmly attached and from which it derives its motion. From the outward end of movable weight 85, cable 81 extends outwardly through tubular blade spar l3. It then passes over pulley 89, which is attached to tubular blade spar l3, at which point it passes through the wall of tubular blade spar l3 and extends inwardly optionally being guided by pulleys c0- axial with the previously mentioned pulleys 58. Near the root of the blade, cable 81 is guided into the interior of tubular blade spar I3 by means of pulleys 90 which are attached to the tubular blade spar. The cable then passes inwardly through the previously mentioned hole in connecting link l6, over pulley 9|, which is attached to connecting link l6, and thence around cable drum H to which it is attached.

The operation of this mechanism for automatically positioning the compensating weight 85 may be summarized as follows: Lever 51 is rotatably positioned on hinge pin I! in accordance with the current effective flapping position of the blade. Cam slot 65 in this lever 51 embraces roller 66 and thereby angularly positions segment 67 on its support pin 69. This motion is transmitted through the previously described planetary gear system and multiplied by it to rotate drum l! at a faster rate. This rotation of the drum causes displacement of compensating weight 85 along the blade by means of positioning cable 87, so as to position the weight in accordance with expression (1) hereinabove, thus serving to simultaneously and continuously stabilize the center of gravity and radius of gyration of each blade.

By thus stabilizing the effective center of gravity and moment of inertia of each blade it is no longer necessary to endeavor to secure a high degree of aerodynamic similarity or mechanical balance between the blades, for failure of a blade to properly track or otherwise act like the other blades will not disturb rotor operation or cause vibration. Also with the moment of inertia of each blade about the rotor axis maintained constant, the drag hinge may be entirely eliminated, as shown in the accompanying drawings, without causing vibratory cyclic disturbances and without setting up any blade root stresses due to cyclic variations in blade movement, for with constant radius of gyration each blade will tend to maintain constant angular velocity regardless of its cyclic changes of path.

I claim:

1. In an aircraft having a sustaining rotor comprising a hub and a flexible blade attached thereto; means selectively positioned in response to the effective angular position of the blade relativeto the hub produced by vertical flexure of the blade, comprising an element supported by the hub and displaceable relative thereto, a flexible member connected at one end to the element for displacing same and connected at the other end to the blade in the outer portion thereof, and means for guiding said member relative to said blade at a plurality of points along the length of the member, each of said points being vertically removed from the neutral axis of the blade.

2. In an aircraft having a sustaining rotor comprising a hub, a flexible blade, and a hinge connecting the blade to the hub; means selectively positioned in response to the effective angular position of the blade relative to the hub, including both the changes due to vertical flexing of the blade and those due to rocking of the blade on its hinge, comprising an element supported by the hub and displaoeable relative thereto, a flexible member connected at one end to said element at a point remote from said hinge and connected at the other end to the blade in the outer portion thereof, and means for guiding said member relative to said blade at a plurality of points along the length of the member, each of said points being vertically removed from the neutral axis of the blade.

3. In an aircraft having a sustaining rotor comprising a hub and a blade mounted for flapping movement relative to the hub; the combination with a mass movable longitudinally of the blade, of means for moving the mass longitudinally of the blade in response to flapping movement of the blade relative to the hub, means for minimizing the force necessary to move said mass along said blade under normal rotor operating conditions, said means comprising a spring biased between the blade and the mass to exert an inward force on the mass substantially equal to the centrifugal force exerted on the mass by the rotation of the rotor at a normal operating speed of rotation, said spring being constructed with a spring force gradient substantially equal to the change in the centrifugal force on said mass per unit change in the position of said mass relative to said blade with said rotor rotating at said normal operating speed of rotation.

4. In an aircraft having a sustaining rotor comprising a hub and a flexible blade attached thereto; the combination of an element supported by the hub and displaoeable relative thereto, a flexible member connected at one end to the element for displacing same in response to blade flexure and connected at the other end to the blade in the outer portion thereof, means for guiding said member relative to said blade at a plurality of points along the length of the member, a weight displaoeable relative to the blade, and means connecting the element to the weight to displace the weight relative to the blade in amounts quantitatively responsive to the amount of fiexure of the blade.

5. In an aircraft having a sustaining rotor comprising a hub, a flexible blade, and a hinge connecting the blade to the hub; the combination of an element supported by the hub and displaoeable relative thereto, a flexible member connected at one end to said element at a point remote from said hinge for displacing said element relative to the hub in response to displacements of the blade relative to the hub, including both the displacements due to flexing of the blade and those due to rocking of the blade on its hinge, said flexible member being connected at its other end to the blade in the outer portion thereof, means for guiding said member relative to said blade at a plurality of points along the length of the member, a weight displaoeable relative to the blade, and means connecting the element to the weight to displace the weight relative to the blade in amounts quantitatively responsive to the combined amounts of flexure of the blade and rock of the blade on its hinge relative to the hub.

HAROLD T. AVERY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,139,982 Smith Dec. 13, 1938 2,203,012 Campbell June 4, 1940 2,237,030 Gathmann Apr. 1, 1941 2,423,733 Stalker July 8, 1947 2,425,650 Stalker Aug. 12, 1947 2,455,866 Kaman Dec. 7, 1948

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