US2531598A - Balancing means for rotating wing - Google Patents

Description

Nov. 28, 1950 H. T. AVERY BALANCING MEANS FOR ROTATING WING 6 Sheets-Sheet 1 Filed Feb. 4, 1946 a, r S v. WM W u: WT, m I, 10 MT 0. m T Rim a 0 ,w A W 7 B i I I I. N Q3 H. T. AVERY BALANCING MEANS FOR ROTATING WING Nqv. 28, 1950 6 Sheets-Sheet 2 Filed Feb. 4, 1946 KNVENTOR W A T d l M m ATTORNEYS Nov. 28, 1950 H. T. AVERY BALANCING MEANS FOR ROTATING WING 6 Sheets-Sheet 5 Filed Feb. 4, 1946 5 RW Y O E E TV m mvf M M 0 mM H Y B Nov. 28, 1950 H; T. AVERY BALANCING MEANS FOR ROTATING WING 6 Sheets-Sheet 4 Filed Feb. 4, 1946 \w w & Qw ww W N M \Q 0 Wk WA 7 h mjuF n m Q M NR Y W 8 H 85m mm *N mm blw%jm$ Q 7 Q \wfi. H @J 2: m g :E Q Q Q R. MW mu mm WWW ATTODNEYS Nov. 28, 1950 H. T. AVERY 2,531,598

BALANCING MEANS FOR ROTATING WING Filed Feb. 4, 1946 6 Sheets-Sheecfi FLLE 9 I INVENTQR HO/"O/Q Z A very V WM ATTORNE Y5 Nov. 28, 1950 H. 'r. AVERY 2,531,598

BALANCING MEANS FOR ROTATING WING Filed Feb. 4, 1946 6 Sheets-Sheet e FLE E INVENTOR HG/fO/Q T Avery WWW ATTORNEYS Patented Nov. 28, 1950 UNITED STATES PATENT OFFICE BALANCING MEANS FOR ROTATING WING Harold T. Avery, Oakland, Calif.

Application February 4, 1946, Serial No. 645,309

12 Claims.

This invention relates to rotating wing aircraft and particularly to improvements in the sustainin rotors for such craft. It is disclosed as applied to rotors of the articulated type, that is, rotors in which the blades are hinged to a central hub member, and it is in rotors of this type that the advantages of the invention may be most fully realized.

Rotors of both the articulated type and the non-articulated type are known in the art and machines embodying each type have been constructed and flown. In rotors of the non-articulated type each blade of the rotor is free to be rocked on its own longitudinal axis to effect change in blade pitch, but except for such further slight changes in relationship as may be introduced by the bending of the blades due to their own flexibility it is otherwise fixed with respect to the rotor hub. In rotors of the articulated type, the blades ordinarily retain the same freedoms of 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 permitting the blade to be fully 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 general plane or done of rotation.

Rotors of the articulated type exhibit a number of advantages as compared to rotors of the non-articu1ated type, among which are the following:

1. The stresses in the blades, and particularly at the blade root, are minimized.

2. Because of this, much less effort is required to effect the rocking of the blades on their own longitudinal axes to introduce changes of pitch.

3. Since each blade is free to readjust itself in response to all changes or disturbances in flight conditions, instead of transmitting such disturbances to the craft itself, the articulated rotor is the most successful in smoothing out air disturbances.

' 4. This same inherent ability ofthe articulated rotor to readjust itself to all kinds of flight conditions gives greater insurance against its being forced into dangerous flight attitudes, hence providing a rotor which is inherently safer under adverse flight conditions.

5'. If used in conjunction with a pitch control arrangement in which the pitch of each blade controlled through a link pivotally attached to it forward and outboard of its flapping hinge, the rocking of the blade about its flapping hinge can be arranged to provide inherent safety against stalling of the rotor in case of engine failure, and to provide such safety in the simplest and safest manner conceivable, for slowing down of the rotor will automatically reduce blade pitch into the range of pitch settings capable of sustaining auto-rotation.

It is, therefore, not surprising that up to the present time all rotating wing aircraft (of both the Autogiro and helicopter types) which have been repetitively produced in any quantities and flown under any great variety of weather condi tions are sustained by rotors of the articulated blade type. Such rotors, however, have certain disadvantages as compared to rotors of the nonarticulated type. One of the chief disadvantages of the articulated rotor lies in the prevalence of large amounts of vibration in that type of rotor.

I have observed that such vibration is primarily due to the manner in which the center of gravity of such rotors is continually shifting, so that a rotor which is perfectly balanced un der one set of conditions will be out of balance under other conditions. These shifts are primarily due to unequal displacement of the respective blades about their respective drag hinges and/or unequal rocking of the blades about their respective flapping hinges.

One of the most troublesome sources of such the same circumstances, and hence cause that blade to continuously ride higher or lower than the track described by the other blades in their circuits. So long as all blades follow exactly the same track, and particularly if there are more than two blades in the rotor, inequalities in the flapping angles of the blades at different points in the circuit do not tend to cause very serious vibration,- for under these circumstances the center of gravity remains permanently displaced in a direction generally opposite to that part of the circuit in which the blades rock the highest, and the center 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 parts of its circuit, thus producing substantially the same efiect as an eccentrically located weight rotating with the rotor, which of course produces bad vibration. Also, if the pitch setting of a blade with such different aerodynamic shape is readjusted. relative to that of the other blades by an amount suflicient to bring it back into substantially the track described by the other blades its diiference in aerodynamic shape is very apt to cause a difference in drag which will cause that blade to be displaced differently from the others about its drag hinge, thus causing a shift in the center of gravity of the rotor in' the direction of such dilference of displacement, which again is equivalent to an eccentric weight rotating with the rotor and causes objectionable vibration. A great deal of the trouble and expense involved in the manufacture and maintenance of articulated rotors is due to the effort to secure and maintain perfect aerodynamic simi arity, as well as perfect mass balance, between all blades.

A second shortcoming which, as a rule, is more 43. from each other in the amount and distribution of mass in the respective blades.

It is an object of this invention to improve the degree of sensitiveness of the craft particularly in its pitching and rolling responses to tilting of the rotor, and especially to provide the designmarked in the articulated than the non-articue lated rotors as actually constructed is the tendency for the blades to droop low enough as the rotor is being started or stopped so that they constitute a menace to personnel in the immediate vicinity of them. As soon as the blades attain any considerable fraction of their normal rotational speed, they develop enough lift to rock 'upward v about their flapping hinges at a coning angle sufficient to remove this menace. Because the blades of an articulated rotor do not have to be constructed with sufficient strength and rigidity to transmit bending moments to the central hub, and ordinarily are not so constructed, they must be permitted to freely rock as low about their flapping hinges as there will ever be any tendency for them to rock in flight, which together with the lesser rigidity of the blad s ordinarily emploved in the articulated ro-' tor increases the tendency for this droon to reach such proportions in this type of craft as to invol e dan er to personnel or objects stand ing under the outer portion of the rotor when it is started or sto ped. Furthermore, the nonarticulated rotors have usual y been em loyed in double rotor craft, the two rotors usually being co-axial, while the articulated rotor has usually been employed in a single rotor craft, thus as a rule requiring the use of a greater rotor di ameter. and conseouentl greater droon.

A primary object of the present invention is to provide an improved sustaining rotor for rotating wing aircraft.

A further primary object of the invention is to remove the necessity for aerodynamic similarity between the various blades of a rotor,

which has been an indispensable and costly necessity in articulated blade rotors, and thus to provide a rotor which will be easy and inexpensive to manufacture and maintain.

A further primary object of the invention is to substantially reduce or completely eliminate .the vibration which has heretofore been characteris'tic particularl of the articulated rotor.

More specifically, it is an object to provide a rotor which will possess all the advantages of the articulated rotor, as above outlined, but none of the disadvantages thereof, as above described.

It is also an object of the invention to provide novel means for easily balancing a rotor even though the blades of the rotor difier considerably ers of such craft with novel means for decreasing or increasing such sensitiveness as desired.

It is also an object of this invention to avoid the droop of the rotor blades which has heretofore been characteristic of the blades when the rotor is stopped or turning slowly.

' 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 thereof, when the same is read in connection with the accompanying drawings, in which:

Figure 1 is a diagram illustrating, in accordance with the practices of descriptive geometry projection, certain of the movements of the blades, and particularly of the centers of gravity thereof, in articulated sustaining rotors characteristic of the prior art.

Figure 2 is a similar diagram of a rotor embodying my invention.

Figure 3 is a diagram illustrating in elevation the eifect of rotor tilt on resultant lifting and other controlling forces in rotors of the prior art and those involving my invention.

Figure 4 is a diagram illustrating in elevation the flapping movement of a blade and showing dimensionally the operation of the novel means I employ for stabilizing the center of gravity of the rotor and eliminating cyclic accelerations and decelerations of the blades.

Figure 5 is a plan view showing a rotor hub and the adjacent portion of one of the blades embodying m invention.

Figure 6 is a partial vertical section of a rotor embodying my invention, showing particularly in section a portion of one of the blades standing in its horizontal position and correspondingly positioning certain of the novel mechanisms with which each of the blades is equipped.

Figure 7 is a view similar to Figure 6 but showing the blade rocked upwardly about its flapping hinge, and the related mechanisms correspondingly displaced.

Figure 8 is a transverse cross-section of a blade embodying my invention.

Figure 9 illustrates in section a yieldable' link shown in Figure 5.

Figure 10 is an enlarged sectional view of certain connecting and adjusting mechanisms taken substantiall on line XX of Figure 6.

Figure 11 is an enlarged view of a portion of Figure 6 showing the piston mechanism in crosssection, and showing particularly the sub-units of which the piston and cylinder assemblies are constituted.

Figure 12 illustrates an alternative embodi ment of the invention, and als illustrates details of the mechanism pitch.

Referring to Figure 1 diagrammatically illus trating certain elements typical of prior art construction embodying articulated rotors, the diagram is drawn in accordance with the practice of descriptive geometry, wherein the mechanism is shown as projected onto two co-ordinate planes rotated into the plane of the paper. The line XY is the base line constituting the line of intersection of the two co-ordinate planes.

for controlling blade 7 accuses:

The portion oil the drawing above the line: constitutes the projection or the mechanism onto a vertical plane, and the portionbelow it the projection of the same mechanism onto a horizontal-plane. 'li'l'le'=.finedotted vertical lines are fol the purpose: of connecting one projection of each of certain: points to the other projection thereon. so as to make the relationships discussed more readily apparent.

The weight lifted by the rotor, which ordinan-1y oi the fuselage and its contents, isdiagrammatically illustrated in Figure 1 as a spherical weight [5, suspended from the-rotor hub f6. Pivotally attached to this hub by means of flapping hinges 24 are a plurality of blades ll, illustrated as two in. number in the. diagram, The center of gravity of each or these blades is located at a point t-8 -fi.xed in thebladc. When the craft is hovering stationary in the air each blade l'l'xextends outwardly and. upwardly from the hinge which attaches it to hub 16 at such an' a-ngle that the vertical projection of the blade bears to its horizontal projection the same ratiothatthe not hit contributed by theblade bears to the centrlifugal force acting on the blade, and the: surn 'of the lift forces contributed by all blades equals the weight or the craft Normally under 1 these "circumstances the axis is about. which the bladesare rotating extends vertically upward: and it the blades are accurately similar they: maize equal angles with: the-"axis, and-their centers of gravity l8 move in a truly horizontal circle 20:, and for uniform speed of the driving meansmove at uniforxmspeedi around this circle. A rotatiorrot one quarter turn, for-instance, from theip'ositions at which the blades are illustrated in. solid lines will bring their centers of gravity white the two diametrically opposite positions [811, and if the axis of hub l6 coincides substantially with vertical axis 19, the angular movementof the hub will equal the angular move ment of the bladeand n0 necessity will exist for any displacement of the blades about their drag hinges; a drag hinge as previously mentioned being a hinge (usually substantially vertical and located near the root of a blade) for permitting the blade to be advanced or retarded relative to the hub in its rotation.

[In order to impart horizontal movement to a craft which is sustained in a hovering position by an articulated rotor, as above described, it is necessary to tilt the rotor in the direction of desired movement. For instance to produce rightward acceleration of the craft the rotor would be tilted rightward into a position suchas that indicated by dotted lines in Figure 1, wherein the leftward blade I! is rocked upward through the angle F into the position Ill), and the opposite blade rocked downward-by substantially the same angle to the position l is, bringing the centersor gravity 18 of these two blades to the positions 18b and [80, respectively. Under these conditions the centers of gravity l8 rotate in the cirole 20b, concentrically located with respect to the axis 196 which is tilted rightward by the tilt angle T from the original axis of rotationl9, the tilt angle T being nearly the same as the com csponding angle F of blade displacement about flapping hinge, particularl if the diameter of hub I6 is quite small as compared with blade length. The resultant rotor force on the craft, now being directed diagonally upward toward the right, has a horizontal component which produces horizontal rightward acceleration of the craft, which in turn produces an opposing 6* drag forceon. the fuselage I5; The horizontal component of the rotor force" being vertically 011- set from the: drag force on; the: fuselage causes the craft to tilt; If the axis [19b of rotor rotation be: maintained a constant angl to the vertical (not aconstant tilt relative to the craft), then as the horizontal speed or the craft becomes greater and: consequently the drag force increases the tilt of the craft will increase while the net horizontal force producing acceleration will decrease, until finally the tilt of the craft equals the tilt of the rotor and the craft settles down to a uniform. speed or horizontal movement with the rotor maintaining substantially its ori inal normal relationship to the but not to the vertical However; during the; time that any control is being exercised on the craft to produce any horizontal accelerations or deceleration thereof the rotor must be tilted out of its normalrelati'onslrrip to the craft, and the conditions which. exist during this period of time will now be further analyzed.

In rotating: wing craft sustained by articulate rotors di'fl'erent methods have been employed to effect the tilting of the: rotor relative to the craft; In Autogiros it has hem customary to construct the blades so that they will; maintain fixed Ditch angles relative to then-respective flapping hinges during flight, "and to exercisehorizontalicontrol by tilting the rotor hub, which. tilting angularly displaces the flapping hingesand consequently roduces changes in the pitch angles of the blades such as to produce aerodynamic forces which serve to so alter the path of movement of the blades as to bring them into substantially the same positions relative to the tilted hub that they originall held relative to the hub in its original osition.

In helicopters, however; suchtilting of the hub ordinarily involves greater mechanical complications on account of the continuous power drive connection from the engine to the rotor. Also in helicopters it is possible to take advantage of the fact that it is ordinarily necessary in such a craft to provide means for independently adjusting the pitch of the blades by individually rotating them ontheir own longitudinal axes in order to exercise control for vertical climb and descent. All of this has resulted in a diiierent construction ordinarily being employed in articulated rotor helicopters, namely one in which the hub is maintained on an axis fixed relative to the craft but in which the path of blade movement may be altered by changes of blade pitch cyclicall imposed upon the blades so as to bring about a tilting of the cone of blade movement very closely comparable to that produced by tilting of the hub in an Autogiro.

Although the invention is applicable to craft embodying either of these arrangements, the following discussion of prior art construction, as well as that relating to the invention, applies particularly to the arrangement wherein the rotor hub is maintained on an axis fix-ed relative to the craft, and tilting of the rotor is brought about by changing the path of movement of the blades relative to the'hub through cyclic changes of blade pitch. A typical rior art arrangement for accomplishing this is illustrated and described in the magazine Aviation for June 1945 at pages 122 to 13c, and there is referred to as the M74272 helicop 1'.

solid line positions of the blades.

7. line l9, then if the blades'are, as previously described, caused to move in paths concentrically located relative to axis 191), each blade will rock upward about its flapping hinge as it passes from position He to position llb and downward as it passes from position ill) to position He. Also if the blades and the hub are to move with uniform rotational speed considerable displacement on the drag hinges will also be involved.

For instance when the blades occupy the position identified as 11b and He in the upper projection of Figure 1, their horizontal projections are colinear with the solid line positions labeled I1, I? in the lower projection, and the hub position is identical with that corresponding to the If the hub is then rotated one quarter turn counter-clockwise from this position without any displacement of the blades about their drag hinges, the projections of the blades will then be coincident with the vertical center-line IS in the upper projection and coincident with the extension of this line in the lower projection. The center of gravity of the right hand blade will have moved from point |8c to the point where the circle b crosses the center line H! (which point is very nearly coincident with the upper point Illa in the lower projection and with the point [8a in the upper projection), and the center of gravity of the left hand blade will have moved from point l8b to the point where circle 20b crosses back across the center line l9 (which point is very nearly coincident with the lower point [8a in the lower projection, and in the upper projection is coincident with the point to which center of gravity I80 has moved as above described). 'It is obvious that under such circumstances the center of gravity l8c of the right hand blade has travelled much further than the center of gravity I81) 01' the left hand blade. In order for the centers of gravity [8b and Me to travel equal distances from their original positions it would be necessary to have center l8c travel only to point l8d, which point is so located that its vertical projection lies on the same line as the projection of axis [9b. Similarly center l8b must travel on to point We, the vertical projection of which coincides with that of point l8d. In order to bring the centers of gravity of the two blades to positions l8d and l8e, one blade must be displaced clockwise through the angle D about its drag hinge, bringing the horizontal projection of that blade to I 1d, while the other blade is rocked counter-clockwise through the same angle about its drag hinge, bringing the horizontal projection of that blade to I la. The vertical projection of both blades coincides with that of axis I in the case of no displacement about the drag hinges, and coincides with that of axis [9b in case both blades are displaced in opposite directions through the angles D about their drag hinges as above described. Thus it is evident that it, with the rotor tilted to the right into is dotted line position, both the hub and the blades are to rotate at uniform speeds (which is necessary in order to avoid vibration of the craft due to accelerations and decelerations of the blades or of the rotor driving system) each blade must follow a pattern of movement in which (1) it is displaced in a lagging direction as its center of gravity moves counter-clockwise from point l8c until by the time it reaches point l8d this lagging displacement about the drag hinge equals angle D; (2) thereafter it starts to advance about its drag hinge until as the center of gravity reaches point 18b it is back again in its normal angular position on its drag hinge; (3) it continues to advance until by the time the center of gravity reaches point We the blade has advanced by the angle D ahead of its normal position on its drag hinge; and l) thereafter it starts lagging again until upon return to point l the blade is again back in its normal position on its. drag hinge.

This same pattern of blade displacement is also necessary in order to avoid vibratory dis-- placements of the center of gravity of the entire rotor. The center of gravity of the entire blade system of the rotor naturally lies at the center of the circle described by the centers of gravity of the blades providing these centers of gravity are always located in diametrically opposite directions from this center. When the ro-' tor is in hovering condition, as indicated by solid lines, the center of gravity of the rotor lies at point 2|, the center of circle 20. However, when the rotor is tilted as illustrated this center is displaced to 2| b, the center of circle 28b. That is,- it is evident that when the centers of gravity of the two blades lie at 812 and I80, respectively, the resultant center of gravity will be at 21b. Similarly, after the hub has rotated one quarter turn it is evident that the center of gravity of the rotor will still lie at 211) providing the centers of gravity of the blades lie at I 8d and Ne, respectively, but if no displacement of the blades about their drag hinges had been permitted to take place the projection of both blades wouldcoincide with center line l9 and the centerof gravity of the rotor would fall in a position both projections of which would fall on this center line, namely a position very nearly coinciding with the original location 2| of the rotor center of gravity.'- Hence, if no displacement of the blades about their drag hinges were permitted the center of gravity of the rotor would vibrate twice each cycle between point Zlb and a point substantially coincident with point 2|, which vibration would cause objectionable vibration of the craft. However, if the blades are displaced about their drag hinges so that when the center" of gravity of one blade lies at l Bd that of the other blades lies at I8e, not only do we attain uniform rotational velocity of the blades concurrently with uniform rotational velocity of the hub, as

previously described, but we also maintain the" center of gravity of the rotor steadily at point 2 lb instead of causing it to vibrate cyclically.

The foregoing description makes it clear why it has proved necessary to equip the articulated rotors'of the prior art with drag hinges individual to the respective blades. However, these prior art rotors have not been. equipped with any positive means to constrain the blades to move in the desired manner about their drag hinges. By locatin the drag hinges outboard of the rotational axis, centrifugal force on the blades has been made effective to yieldably resist displacement of the blades about their drag hinges, and other means have been sometimes utilized to supplement it in so doing. However, the momentum of the blades is principally responsible for producing the proper displacements about the drag hinges and if it is opposed by any of these other means in so doing the resulting displace ment is less than the proper one and vibration results. This has been generally true of the articulated blade helicopter of the prior art. Also irregular disturbances of the air may cause irregular displacement of the bladesabout their are-w drag hinges "with'consequent displacement .of the center of gravity of the rotor and correspond: ing vibration. When the craft is in close proximity to the ground a particularly aggravated form of this condition may develop, wherein an air disturbance set up by one iblade may be rehosted from the ground in such a path as to .di'r rectly engage another blade at cyclic intervals dependent upon rotor speed and craft movement. When these intervals coincide with the natural frequency of blade displacement, a condition may result known as =ground resonance which may cause very destructive vibration.

While the means, previously mentioned, for yieldably resisting displacement .of the blades is usually of a form" that will tend to return tonermal a blade that has been irregularly displaced, such centering action cannot be made very strong incomparison with the efiect of blade momentum indisplacing the blade about its drag hinge, or as previously mentioned the momentum will normally produce too small a fraction of the proper displacement to suitably minimize vibration. Il'ierefore, the arrangement must be such that blade momentum is the predominant factor in determinin the position of the blade about its drag hinge. But if this is the case the increment of-momentum imparted to the blade by an irregular displacement, such as above mentioned, will tend to cause the displacement to continue to increase after the air disturbance originating the irregular displacement has disappearedand hence the irregular displacement caused by a small disturbance may reach considerable proportions and be very slow in disappearing, and

as lqng as it persists will causea displacement of rotor center of such a nature that the displacement will rotate with the rotor and thereiore cause vibrations corresponding to those produced by an eccentrically placed weight. Hence, while it'has been necessary to provide drag hinges in the articulated rotors of the prior art, no means have been devised to positively constrain the bladesto move properly about their drag hinges, and such means as have been provided to produce the proper displacements and ;to resist and wipe out the improper displacements have conflicted with each other to a degree which has caused vibration due both to too greatly resisting the proper displacements and to not sufficiently resisting and correcting the improper displacements. That is, means must be provided to resist, at least yieldably,;improper displacements of the blades about their drag hinges, or such dis,- placernents will get completely ,outof hand and re se dest u e br t en- T Q W KJ W2 E g- 1 A a b n P Ovided f 12 .5 P '.P9 ,1 to ts inab i to d sc e b n rope nd i p d s ac men has e i t d th prope d s la em n of h blades u a mu as 'it has the improper displacements thereof. .Since lu a bad vibration il b cau ed by ie hosit on o a bla ab t d a .h ese due to its proper displacements having been rehied as b h e am u t o mis ositi mn due to the introduction of improper displace grants from extraneous sources the prior art me ns wh 1s a d s c ments have bee e apa o e mi ing v b e ien- Ea c the prio e timean o re sti g ras is lae meats-has ne essa be i v Na u e a omprom s i qun t P odu cons dera l bret on by re s ing the p nedisplac ems h heab ades i r istance to d s sal was great enough to reasonably control the proper displacements .thereof..

The primary objects of my invention are at-' tained by the provision, in a bladed rotor, of a balancing weight adjustable radially with respect to the axis of rotation of the rotor and ofdevices actuated by blade movements tending to displace the center of gravity of the rotor for directionally and quantitatively adjusting the balancing weight so as to substantially prevent any displacement the center of gravity of the rotor as a whole.-

The general manner in which this arrangement is erfectiveto attain the primary objects; of my invention in the case of an articulated rotor will be understood upon reference to Figure 2 of the drawing which is a-descriptive geometry projeotion of a rotating wing craft embodying my invention. As in Figure 1 the fuselage and its contents, diagrammatic-ah illustrated by weight 15, is supported by a rotor comprising hub 46 and blades H, the latter having centers of gravity I 8, which when the rotor is tilted by bringing the blades to positions Nb and We, respectively, assume the positions lib and We respectively.

In order to eliminate the necessity for drag hinges individual to the respective blades, and at the same time eliminate the vibration char acteristic of craft embodying such hinges, I provide in conjunction with each blade a balancing weight 25 which is arranged to be automatically adjusted longitudinally with respect to its blade in accordance with the flapping angle of said blade in such a manner as to substantially displacement of the resultant center of gravity of the entire -rotor.-

In the embodiment of the invention disclosed herein, these weights are mounted within the blades so that when the blades H are in their normal positions, as shown b solid lines, these weights will occupy the positions labe1led25 in Figure 2, under which conditions they move in the horizontal circle 26 as the rotor rotates. l f now, in the manner previously indicated the left hand blade is rocked upwardly on its flapping hinge 24 to the position lib, thereby displacing the'center of gravity of the blade itself from t8 to 181), means responsive to this change of flapping angle automatically moves the correcting weight which is incorporated in the blade from position 25 to 2519. The relative weight of the blade and of the weight 25 are such that when the center of gravity .of the blade lies at point vl-8 and that of weight 25 at the point iabelied 26; the resultant center of gravity of the combined blade and weight is located at point 2d, and the amount of shift of the weight to position 256 when the blade is rocked up is such as to bring the resultant center of gravity .of the blade and weight in their raised positions to the point labelled z lb which is located directly above point 2?! and hence the same distance from rotor axis- I9v Similarly when the right hand blade is rockeddown .to the position He, causing center of gravity to move further away from axis 19 to the position I its weight 2.5 is .causedto shift inwardly to the position ilac-so es ltoiihiiine theresultant center ,of gravity of the right hand 11 does not'alter or in any way disturb the center of gravity of the rotor, and the center of gravity remains at all times on axis l9 at substantially the point 2|. Hence when the rotor is turned through one quarter turn from the position illustrated, the blades should occupy a position which will continue to retain the rotor center of gravity on axis i9 if vibratory displacements are to be avoided, which means that all projections of the blades should coincide with center line [9 of Figure 2, as indicated at IT and Hg in the drawing, which is the condition corresponding to no displacement of the blades about their drag hinges. Since this condition applies for all possible flapping angles of the blades, drag hinges individual to the blades may be eliminated. This elimination will leave the blades always diametrically opposite each other, thus entirely avoiding the shifts in rotor center of gravity which have heretofore been incident to irregular displacement of the blades about their drag hinges.

Heretofore it has been necessary to provide the drag hinges for reasons previously described and the pattern of movement which the blades must describe about their drag hinges in order to preserve smooth operation were of such a nature and so diflicult to predict that it was not feasible to provide any mechanism capable of constraining the blades to follow such a pattern of movement. Much of the trouble with vibration in articulated rotors has been traceable to departure of the blades from such a pattern of movement. However, by introducing in each blade such a weight automatically adjusted in accordance with the flapping of the blade in the manner described, the pattern of movement of the blades about their drag hinges required to preserve smooth operation is reduced to zero movement, and it becomes practicable to provide means to constrain the blades to follow this pattern of movement, for all that is necessary in order to do so is to eliminate the drag hinges individual to the respective blades, as heretofore necessarily provided.

As I shall later describe in more detail, I consider it desirable to provide what amounts to a single master drag hinge common to all the blades, to permit some lagging or leading displacement of all blades in unison relative to the rotor driving mechanism in order to prevent transmission to the blades of any sharp irregularities in drive, and to permit them to respond to irregular air disturbances without, however, disturbing their horizontal angular relationship to each other nor disturbing the center of gravity of the rotor.

' As previously indicated, elimination'of the individual drag hinges in the prior art structures would not only cause bad vibratory displacements of the rotor center of gravity but would also cause cyclic accelerations and decelerations of the blades in a manner which would set up vibration'. It will therefore be in order to investigate the blade accelerations and decelerations with my new arrangements.

' With the rotor in its tilted condition, as indicated by the dotted line positions of the blades in the upper projection of Figure 2, the centers of gravity l8 of the blades proper will movein essentially the same eccentric path 20b (lower projection) as previously described in connection with the prior art (Figure 1) and the mass centered at I8 will be decelerated as it move from I80 through I81 to I81; and accelerated as it moves on through l8g to I again. However the counter-balancing weight 25, which under hovering conditions (with'the blades at the flapping angles indicated in solid lines) moved in the concentric circle 26, alters its path of movement when the blades are displaced to their dotted line positions and moves in the eccentric path 261), the eccentricity of which is opposite to that of path 281). The weight 25 will be accelerated as it passes from position 250 through 25f to 25b and decelerated as it passes on through 25g to 250 again. Hence the accelerations and decelerations of weight 25 will always be opposite to those of the blade proper, and since the Weight is sup ported in the blade for movement parallel to the longitudinal axis of the blade the net effect will be for these accelerations and decelerations to act toward neutralizing each other. 7

While the mass of the weight 25 will ordinarily be much less than that of the blade the amount of eccentricity of its path of movement will necessarily be correspondingly greater than that of the blade proper in order to maintain the resultant center of gravity of the weight and blade at a constant distance from the rotor axis, as previously described. In fact with the eccentricity of the path of movement of the weight such as to attain this objective, the accelerations and decelerations of each blade and its related weight exactly neutralize each other. This is necessarily true because the net accelerating or decelerating effect, if any, will be that of the resultant center of gravity of the blade and Weight which, remaining at a constant distance from the axis, moves in the path 28b which lies in the same cylindrical surface concentrically located with respect to axis I9 as does the circular path 28 described by the resultant centers of gravity 2'! of the blades under balanced hovering conditions. The horizontal projections of the path of movement of the resultant centers of gravity 2'! is the identical circle 28, regardless of the flapping an+ gles of the blades, and therefore the rotational component of velocity of these centers of gravity :7 will always be constant and no net angular accelerations or decelerations will be encountered.

Therefore, providing in conjunction with each blade a weight 25 and means for automatically adjusting it in the manner described, serves not only to prevent the displacements of rotor center of gravity heretofore caused by difierences in the flapping angles of the blades, but also eliminates the necessity for drag hinges individual to the blades, renders it feasible to automatically retain the blades at all times in their proper horizontal angular relationship to each other, and eliminates the angular accelerations and decelerations of the blades which have heretofore existed and which would become of prohibitive proportions were the individual drag hinges eliminated without the incorporation of the automatically counterbalancing weight. a I

The manner in which the tilting of the rotor produces responding movements of the craft, is affected by the introduction of the automatically adjusted weights into the blades. On the craft of the prior art, in which each blade is attached to the hub by a drag hinge and a flapping hinge about both of which it is freely displaceable, the blade cannot exert any continuing force on the craft except a tension in the direction of the blade axis. Under ideal hoverin conditions all blades are rotating about a vertical axis at a constant flapping angle. In Figure 3 the solid lines I! represent two such blades. Under these con-I the'craft, as indicated by vector R1 in Figure '3.

If now the rotor be tilted rightward by rocking the left blade up to position lib and the right blade down to position He, the rightward horizontal component of the aerodynamic force on the left blade will exceed the leftward horizontal component of theaerodynamic force on the right "blade. The resulting net rightward horizontal component of the aerodynamic forces on the two blades combined with their resultant upward component, causes the resultant force which the blades exert on the craft to be angled upward toward the right, as indicated by vector R2 (Figure 3). Also, if the two flapping hinges 24 are separated from each other, as illustrated, the raising of the left blade and lowering of the right causes the intersection of the axes of the two blades to shift leftward, the line of action of vector R2 passing throughthis new intersection.

If the amount of tilt of the prior art rotor :be increased by raisingthe left blade to position ll'm (Figure 3) and lowering'the right blade to position 7! in, both the angularity of the resultant "force and the offset of its line of action from rotor center are increased in substantially equal proportion, with the result that the new resultant force exerted on the craft by the blades, as represented by vector R3, intersects the center line of the craft at approximately the same point 132' at which vector R2 intersected it, which point is located above the rotor. Therefore the tilting of the rotor displaces the line of action of the aresultantrotor forces much further from the center of gravity l5 of the sustained craft than they are displaced in the plane of the rotor, meaning that "the turning moments tending to rotate the 'cra'ft are relatively large in comparison with the horizontal translational forces brought into play "by the tilting of the rotor.

As will be later described in more detail the :n'leans which I employ to automatically position the previously described weights 25 in the blades in accordance with the flapping angles of the blades continually exert an upward moment on ll1'l6b13d about its flapping hinge, consequently causing the blade to exert an opposite moment on the craft as indicated by the arrows M1 and'Mz inrFigure 3. The arrangement is such that the moment increases with increased flapping angle :of the blade at rates slightly greater thanproapo'rtional to the increase in flapping angle. This therefore constitutes what is known as an unstable moment, since a displacement of the blade relative tothe hub causes the moment to change in thedirection tending to produce further'such displacement. No unstable condition of the blades-actually results, however, since the mechfor producing moments M1 and M2 is-so arranged that these moments can only act when centrifugal forces are acting on the blades, under which circumstances the moments exerted onthe blades by such centrifugal forces oppose the moments M1 and M2 and stabilize the. blades.

Under hovering conditions the moments M1 and M2 balance and the resultant blade forceon "the craft coincides with the rotor axis as'represented by vector R1 justas in the prior iartcraft.

lies below the motor. "of moments M1 and M2 with flapping angle, with my mechanism as disclosed, issuch that regardless ofrotortilt the resultant force intersects the irotor axis at app-roximatelythe same point 33,

'ISpeCtlVe vectors R2 and R3. varying different factors-suchas the distance of the weights "25 from the rotor axis and the distance of the flapping hinge from the rotor forces without tilting forces. merit eliminates substantially the last vestige nowever, if in my "craft the rotor is tilted rocking the left blade to position Ho :and the right "blade to position He, the resultant .force exerted on the :craftby thelblades is tilted toiapproximately the same angle as in the prior art craft, but the counterclockwise moment M1, ex-

'ceeding'theclockwise moment 1M2, leaves a net counterclockwise moment exerted on the craft, which combined with the resultant force (which except for this unbalancedmoment would lie 'substantially along the line of actionof vectorRz) iproducesthe ne'wiresultantrforce S2 which is off- :set from the force R2 of the prior art toward'the blade oflower fiappingangle. This'force intersects the vertical axis of the rotor at point 33 The :rates of 'change the additionaltilt of the rotor to the extent represented'by blade positions l'lm and ll'nbringing the resultant blade force on the craft to the line of action indicated by vector S3, due'to'the tunstable pattern of variationsof moments M1 and M2.

- -Itwi1l b'e noted that the lines of action of vectors S2 and S3 pass less than half as farfrom center of gravity l5 as the corresponding re- By appropriately axis the point33 may be established at any chosen location within a wide range. If point 33 were established at or near center of gravity 1 5 (which ;falls well within the range of possible locations) tilting of the rotor will upro'ducetranslational Such an arrangeof vibrational'eifect from the rotor, for as previously described my proposed arrangement would eliminate all the various prior art sources of disturbances due to the various types of shiftling of center of gravity and to rotational accelerations and decelerations.

However, a blade tracking continuously higher -orlower than its mates, due to aerodynamic dissimilarity would cause a displacement of the resultant rotor force similar to that caused by tilting of the rotor except that when the displacement is due to such dissimilar tracking the resulting force will rotate with the rotor rather than. remaining substantially fixed indirection.

If slight rotor tilts produce large turning ,mo-

ments on the craft, as with forces R2 and R3 of the'prior art (Figure 3) relatively smalldisturbances can set up considerable vibration due to the rapidity with which rotational moments angularly displace the craft, butif the lift force always passes through the center of gravity,'such a displaced blade will not produce any net "mo- ,ments-on the craft, although approximately the same translational forces are cyclically exerted as that associated with the same aerodynamic disturbances in theprior art, but these forces are so small, and the craft is relatively so slow in responding to translational forces, that the eifect 'is substantially negligible.

If the point 33 is located coincident with cenzontal force component on the craft as previously Willexert less of a pitching or rolling moment, so that pitching and rolling effects of rotor disturbances and irregularities will be correspondingly minimized;

It has been characteristic of articulated blade helicopters in the past that they have been so sensitive to displacements of their pitching and rolling controls that displacements of these controls, less in amount than the vibrational displacements imparted to these controls by the rotor, would produce marked responses of the craft. My invention makes possible to not only completely eliminate the chief sources of such vibration in the prior art but to so arrange it that the craft will be slightly less sensitive in its pitching and rolling responses, although remaining substantially unchanged in translational response to its pitching and rolling controls. All of this makes for smoother and more dependable operation.

It is to be understood that while the foregogoing description, relating to Figures 1, 2, and 3, has referred to two opposite blades and to right and left directions, movements and forces, the same general effects and results as outlined apply to a rotor equipped with three blades, four blades, or any other number of blades, and the directions referred to as right and left might equally well constitute forward and back directions relative to the craft or any opposite directions in which it may be desired to investigate or exercise the control.

The amount by which the flapping movement of a blade displaces its related weight has thus far been defined only in terms of the results to be attained, namely that the displacement is to be such as to maintain the resultant center of gravity of the blade and weight at a constant distance from rotor axis $9. With the aid of Figure 4 we may now express the position that weight 25 should occupy at any given flapping position of the blade in terms of the blade flapping angle and the relative dimensions and weights of the parts involved. For this purpose:

Let

The distance of the resultant center of gravity 21h of the horizontal blade and its weight from the rotor axis as may be determined by taking the moments of the blade mass and weight mass 1'6 about the axis and dividing by the combined mass:

, The distance of the resultant center of gravity 2? of the blade standing at flapping angle A from rotor axis !9 may be determined in the same Way:

Distance from 19 to 27 If weight 25 is to move in the manner necessary to achieve its objective as previously outlined the above two distan es must be equal. E na-ting the right hand sides of Equations 1 and 2, multiplying both by the common denominator and subtracting identical terms from the two sides of the equation, we have:

Bg-l-Wa=Bg.cos A +Wa.cos A+ Wb.cos A (3) Distance from 19 to 27h Wb.cos A (Bg+Wa) (l-cos A) (4) b=(a+ secA 1) 5 b= a+% exsec A i (6) This Equation 6 indicates that the objectives previously outlined will be attained if the weight is constrained to so move that, as the blade is rocked upward from the horizontal to any flapping angle A above the horizontal, the weight Will move outward along the blade axis by a distance equal to the external secant of the angle A multiplied by the sum of the distance the weight originally stood from the flapping hinge when the blade was horizontal and the distance of the center of gravity of the blade proper from the flapping hinge increased in the ratio that the mass of the blade proper bears to themass of the weight 25. It will be noted that if the mass of the weight is decreased relative to that of the blade the required stroke of the weight is mass and stroke of the weight it is desirable in actual practice to limit the flapping .angle to not in excess of 15 or thereabouts. An average coning angle of approximately half this value is quite usual, so that by taking steps to minimize the departures therefrom the maximum flapping angle may be held well below 15. The minimizing of departures from average coning angle may be effected, without adversely affecting the desirable characteristics of the articulated rotor, by attaching each pitch control rod (rod 30 of Figure 12) at a distance well outboard of the flapping hinge 24, and connecting it by a relatively short connecting arm (arm 3! of Figure 5) to the blade spar so that changes from the flapping angle for which the pitch control rod is set will produce relatively great changes in blade pitch. With the maximum blade flapping angles thus limited the mass of weight 25 may be held as low as 20% or 25% of that of the blade proper without involving excessive stroke of the weight.

In 'theembodiment of the invention illustrated in Figures 5 to '11, inclusive, and as particularly shown in Figures 5 and '6, each blade l l comprises a skin or covering 34 integrally mounted on ribs 35, which in turnare integrallyattached to a tubular blade spar 3'5, which spar terminates inwardly in a bearing retainer 31 containing a ball thrust bearing 31a co-aiiial with the spar. This bearing serves to attachtheblade to a con necting :link 38 in a manner permitting theiblade to *be rotated about the spar axis relative to the link 38, to change "the pitch setting of the blade. Connecting link 38 is in turn attached by means of a flapping hinge 24 .toa lug 39 integral with a hub member 40. Asshown in Eigure 5, this par ticular embodiment comprises a three-bladed rotor, and there :are therefore two other lugs .38 integral with this same hub member 4.0 in addition to the one to which the blade illustratedis attached. Hub member 46 is 'in turn pivotally mounted on a'lrotor drive shaft d1 by means of roller bearings -42 and 43, and is prevented from .maving upwardly :on shaft =41 by a thrust bearing 44 which seats again-st a cap integral with the shaft M.

As also illustrated in Figure 5, cap A5 is provided-with three arms 46, each of which =carries a pin .41 to which is pivotally attached a yieldable .linkAB, the other end of which is pivotally attached to -a pin 49 mounted in one of the lugs .39 of the hub member 4!]. Cap is illustrated as having three arms 46, and pins are shown for mounting three links 58, it being assumed that the particular embodiment illustrated is equipped with three such links. However one such link or any other number of such links would serve the purpose, for the links are provided for transmitting-the drive from the shaft 41 to the hub member 40 (seeFigure 6) pin a manner which will smooth out irregularities in the drive and will permit the hub to readjust itself angulanly on the shaft MQ The assembly constitutes a master-drag hinge, whereby any irregular forces which tend to make .a blade advance or lag about its individual drag hinge in the prior art "constructions can do so, .at least in some degree, .in my present construction, the difference being that with my arrangement all other blades are forced to simultaneously advance or lag by the same amount, and displacement of the center of gravity of the rotor is avoided. I

The construction of a typical link 43 :is illustrated Figure 9. It is essentially an hydraulic shock absorber equipped with centralizing springs. It includes .a piston-rod 5!! provided at one end with a hole .51 for pivotal mounting .on the ,pin 41 and provided at theother end with a piston .52 reciprocably mounted in a closed cylinder 53 filled with hydraulic fluid. .The piston 52 has a slight amount of clearance between it and the cylinder 53 to permit the hydraulic fluid to pass from one side of the piston to the other at a rate sufficiently slow to avoid rapidreciprocation of I the piston in the cylinder. Mounted in the cylinder between the piston -52 and one head of the cylinder is a spring 5 3, while another spring is located between the piston and the opposite cylinder head. The spring 54 is considerably'longer than the spring 55 as it is the spring that is compressed by the normal driving of the rotor, spring 55 only acting to cushionthe return of the piston to its normal position. Integrally attached to the cylinder 53 is an arm 56 provided with a hole 51 for pivotally mounting on the pin Ill) 49. Movement of the piston '52 in Ethe cylinder 53 changes the effective length of the lllllk from hole 5l to hole 5?, thus changing the rotational position of the rotor hub relative to its driving shaft il. The springs E i andbfi yieldablytresist such changes, and the hydraulic fluid in the cylinder limits the rate of such changes.

In the prior artconstr-uction displacement :of any blade about itsindividualdrag hingeyunless accompanied by identical displacement of the other blades, altered the location of the center of gravity of the rotor :and because of the upward slant of the blade altered the effective tilt of the rotor. These alterations in center of gravity location and tilt might -be desired alterations required for proper operation of the craft of prior art types or they might be unwanted alterations introduced by disturbances or irregular ities o'f =one kind or another and might very adversely affect the smooth operation of the craft. Therefore, in the prior art construction the use of means for centralizing the blades on their individual drag hinges or retarding their movement about such hinges had to be provided verycaut'iously and were never very satisfactory,

for the centralizing means always prevented the desired displacements reaching their full proper values, while the retarding means; if any, tended to cause the undesired displacements to persist long enough to produce very adverse effects and to unduly delay the proper readjustment of 'de-- sired displacements. However, in my arrangement the displacement of the blades about their common drag hinge does not produce any change in the location of the center of gravity of the rotor or any change in its effective tilt, and therefore the centralizing and retarding means does 'not produce any of the adverse effects above mentioned. Therefore, the amount of centralizing and retarding action is designed to give the maximum of rotational smoothness to blade movement without having "tobe concerned with other effects, as in the prior art. In the particular embodiment illustrated in Figures 5 to 11, the adjustable weight 25 previously described is provided, not in one piece, but consists of a plurality of pieces comprising primarily two rods 60 reciprocable in two cylindersfi l integrally mounted in the ribs 35 of each blade 1-1 (see Figure 5). These rods are designed to be reciproca'ted in their cylinders by hydraulic fluid introduced into the outer end of each cylinder, which is the right hand end thereof as viewed in the drawings. Preferably each rod is provided near its outer end with an hydraulic seal and is :constructed with sufficient clearance in the cylinder over the remainder of its length so that slight flexing of the cylinder will not cause binding.

The hydraulic fluid for producing the properli controlled reciprocation of the rods Bil is introduced into the outer ends of the respective cylinders 61 through tubing 62 by a reciprocab'lehydraulic pump located in the blade spar 36 and operated by the flapping movement of the -blade. As shown particularly in Figures 6 and? this hy-' draulic pump is preferably a multiple cylinder pump comprising a plurality of pistons .64 .(four such pistons vbeing assumed in the particular showing illustrated), each piston acting in a separate cylinder 65, but all cylinders preferably being assembled together into one cylindrical unit and all pistons assembled together into a unit.

The construction of one of these cylinders is illustrated in greater detail in Figure 11. In

tegral with the inward end of each cylinder 65 is a cylinder head 66, which is provided with a hole for the piston rod 6? of the corresponding piston 64 and to which is screwed the outer end of the cylinder 65 located next further in toward the rotor hub. Each piston 54, except the outer most one, is provided with a blind tapped hole into which is screwed the end of the piston rod 6'! of the piston located next further out. The space to the left of each piston 64 is filled with hydraulic fluid and communicates with the corresponding portion of the tubing 62, while the space to the right of each piston is empty being connected to the atmosphere through bleed-hole B8. In the outermost cylinder the bleed-hole may be dispensed with and the entire outer end of the cylinder left open instead.

As will be apparent from Figures 5, 6, and 7, two of the cylinders 65 of the pump are preferably connected to one of the cylinders 6! through one set of tubing 62, and the other two to the other cylinder 6| through a separate set of tubing 62. The feeding of equal amounts of hydraulic fluid to each of the cylinders 6| may thus be assured.

The entire cylindrical assembly consisting of the plurality of cylinders 35 integrally assembled together, and the plurality of pistons 66 and the piston rods 61 integrally assembled to each other and reciprocable in cylinders 65, is concentrically mounted in blade spar 36, as indicated in Figures 6 and '7, and as will be especially clear from Figure 8, which shows a cross-section of the blade and particularly illustrates the position within the blade at which the cylinders 6| may be located, as well as the location of blade spar 36 and the hydraulic pump mechanism within it. Obviously the number of rods 6 and corresponding cylinders 6!, as well as the number of pistons 6% and cylinders 65 in the pump unit can be any number from one each up to any number of each that may prove desirable.

Means are provided for actuating the pump to feed or permit discharge of fluid from the cylinders as the flapping angle of the blade changes. The innermost or leftmost piston rod 61 (Figures 6 and 7) is pivotally attached by means of a pin 10 to a short link H, which in turn is pivotally attached to the upper end of a lever 12. Lever T2, in turn, is pivotall mounted on a pin 13, which is carried by the blade root link 38, ex-

tending between two arms 14 which extend downwardly from that link. At its lower end link 72 carries a roller 15, which roller is preferably constructed as a double roller or pair of co-axial rollers integral with each other, one located immediately adjacent each face of lever 72. So long as the rotor is in operation roller 15 will be held in firm contact with lug 76 by the centrifugal force acting on the piston assembly attached to the upper end of lever 72 and more especially by the centrifugal force on rods 60 which increases the pressure on the hydraulic fluid which tends to force pistons 64 outward. Roller 75 is designed to bear upon the face of a lug 16 which extends integrally outward from hub member 40. As the blade, during rotation of the rotor, rocks upwardly from the position in which it is shown in Figure 6 to the position in which it is shown in Figure 7, the pin 73 moves upwardly and away from the lug I6 permitting the roller 15 to move upwardly along the face of lug l5. This face is so shaped as to constitute a variable-rate cam having a flatter effective cam slope in that portion of the cam contacted by the cam follower when theblade extends at approximately right angles to the rotor axis than in that portion of the cam which is contacted by the cam follower when the blade has been rocked about its flapping hinge so as to extend upwardly at an acute angle to said axis, for the first part of this upward rocking permits lever 12 to rock slightl clockwise relative to link 38 while further upward rocking of th blade permits such clockwise rocking at an increasing rate, these rates all being such that the consequent outward movement of piston rod 51 relative to cylinders 55 will be proportional to the value of b in the previously developed formula:

b- B A a+ g) exsec (6) wherein A as previously noted is the flapping angle of the blade measured upwardly from the horizontal.

It will be noted that in the above described arrangement the rods 50, which were previously mentioned as primarily constituting the weight 25 which is longitudinally adjustable relative to the blade, are not the only parts carried by the blade which move relative to it as it flaps. The piston rod assembly including pistons (i l and rods 51 so moves, but in my preferred embodiment the movement of this assembly would be only a minor fraction of that of the rods til, but it would be exactly proportional to and in the same direction as that of these rods. Link 72 and the connecting pins would move by substantially the same amount as the piston assembly while the center of gravity of lever 12 would move b a small fraction of this amount. For instance the movement of the piston assembly and of link H and the connecting pins may, in a typical instance, be A; that of rods 69, while the movement of the center of gravity of lever 12 (including roller 75) may be that of rods 50. In such an instance the mass W of the weight 25 may be considered as made up of the mass of rods [ill plus 4 that of the piston assembly and of link H and the connecting pins plus that of lever Weight 25 of the diagrammatic disclosures is really made up, in this embodiment of the weighted sum of all the parts that move longitudinally of the blade as the blade flaps, and the proper amount of movement for rods 66 can be calculated as b in Equation 6, above, by using as the value for W in that equation the composite value of the mass arrived at in the manner above outlined. The proper piston stroke for each value of the flapping angle A would then, in the particular numerical example above suggested, be 0.252), while the movement of the center of gravity of lever 72 would be 0.1%.

The pressure which roller 15 exerts against lug 76 produces a clockwise moment on hub member 40 about hinge pin 24. This is the moment designated as M1 for one blade and M2 for the other blade in Figure 3. From Figures 6 and 7 it will be evident that, as the blade rocks upwardly, the.

amount of this moment will increase both because the consequent outward movements of rods 60 and piston assembly 64, 57 increase the centrifugal force they exert, and more especially because the direction of the pressure exerted on surface 16 by roller 75 changes so that for the higher blade positions the line of action of this pressure passes distinctly further from hinge pin 24, thus correspondingly increasing the moment set up by this pressure. The consequence is that, as previously mentioned, the resulting moment assures 21 increases more rapidly than the corresponding increase in blade napping angle.

previously indicated .if the construction is such that the various parts which constitute weight 125 are reciprocated inzsuch 1a manner as to accord with the requirements 10f Equation 6 above, changes in the flapping angle of a blade will not disturb the balance of the :rotor. Therefore the care which has heretofore been exercised in *endeavorling to secure exact aerodynamic similarity between the various blades will no longer be required for the operation will not now be adversely affected it due to .a .difierence in blade lift, one blade tracks higher for lower than the others, .nor there be any ill effect if :one blade develops more :drag than the others, .for no drag displacement of :such a blade relative to the "others can now resu'lt.

Also the new arrangement eliminates all need for the extreme care which has been heretofore exercised to secure and maintain exact mass balance and similarity in the construction of the various blades :Such care has been exercised in the past because mass iunbalancestoo small to be serious themselves were in danger of becoming the incipient cause of blade "displacements which might gradually develop under certain circumstances to troublesome proportions. Since relative drag displacements :of the blades are now prevented, and flapping displacements counterbalanced, :slight inequalities in mass balance -or distribution no longer cause the difficulty that they formerly did. Therefore, many types of blade construction which in the past would have been considered desirable except for the difiicu'lties which they present in regard to the control of mass balance and distribution, and airfoil shape, can now freely be :employed. However some \of these may involve reater mass differences between :the blades than can be tolerated even though the effect :on blade displacements is no longer of consequence. Therefore I have pro vided means 'for seasily efiecting mass balance of the rotor. Each blade is equipped with two such means either 10118 "or both of which may be employed for efiectin the desired balance in any given instance.

One of these mcans'for effectingmass balance of the 'rotor comprisesanzeccentrically adjustable connectionwbetween clink lil :and lever 12. means :is shown in greatest detail Figure 10. As there :shown alboltaflil extends through coaxial holes in the two leftwardly extending :arms :81 :of the link H. A shouldered portion "82 of this belt fits freely into :one of these holes, while a plain sleeve 83 slipped over the bolt its :in :the :other. Slipped over the bolt between the shoulder 82 and :sleeve 83 is a flat washer '8] and also an eccentric :sleeve 84 carrying integrally with "it an hexagonal flange :85. Screening down .a nut 86 2;

firmly clamps the-sleeves 8B ,and '84 the lever 12 and the washer -81 against the shoulder .82 so that they cannot beirotated relative to each other. By loosening the :nut86 thehexagonal flange may he rotated to bring the eccentric sleeve 84 into :any desired angular position, following which itmay'be locked in thatposition by tightening the nut. The outer diameter of the eccentric portion :of sleeve [84 this freely into a .hole in the top portion of lever 12, :and the length of this eccentric portion is slightly sless than. the thickness of lever 12 to insure that the eccentric sleeve M 'willzbe clamped infixed relation to thelever'when the nut 86 is screwed down. "The pivotal connection :of lever 12 to H us established by This 4 22 virtue of the fact that shoulder 82 and sleeve 83 are always free "to turn in their mating holes in arms 8L It will :be observed (that this pivotal connection is always coaxial with bolt :80 and maybe adjusted relative to the lever by rotation of the eccentric sleeve 84 By reference tolligure 6 or 7 it will be evident that, if with the blade at any given flapping angle, the eccentric connection :between link H and lever =72 be re-adjusted the piston rod "Bl-can be moved further into the cylinders '65 or brought further out without disturbing the positionof lever :12 orxthe point of contact of roller 1:5 with lug 15. Any such movement of piston :rod 6:? will, of course, result in "a corresponding and greater-movement of both rods T60, thereby increasing or decreasing the centrifugal force which the blade exerts under any given conditions. .=By thus adjusting one or more of the blades the rotor may be brought to perfect rotational balance. This may most easily hedone on a test fixture after assembly of the rotor and before mounting it on the craft, the location '(thatischoiceof blade to be readjusted), direction, and approximate .amount of the adjustments to be made :being determined by rotating therotor.

The second means provided for .effectingusimilar adjustment :of :mass balance is shown in Figure :5. It includes two cylinders 19d, one connected through one tubing system :62 to one cylinder 16L, :and the other similarly connected to the other cylinder 6!. A screw member 91 is providediin connection. with each cylinder .90, and it may be screwed any desired amount into "the cylinder and locked :by 'inut 192 The inner end of screw member 9l preferably terminates in an hydraulic-sealer in so close a :fit into 'theLmating portion of cylinder -99 as to effectively prevent leakage. Thus any inward adjustment of .screw 9| displaces a certain amount of hydraulic fluidwhich through tubin 62 causes an equal amount to flow into the respective cylinder 6| and correspondingly displaces rod fill.

This arrangement has an advantage :over the previously described means in that the :two rods.

within each blademay 'be adjusted independently of each other to-shift the center of gravity toward oraway from the leadingedge of the blade. Also the eccentric arrangement previously described, when "used alone, has the disadvantage for the purpose above outlined that the'rightward or leftward adjustment of the pivoted connection of lever 12 to link H is ordinarily also necessarily accompanied with 'an upward or downward adjustment thereof, thereby slightly alterin the efieotive length of lever 'l-Zwhich alteration might prove slightly undesirable under certain circumstances, and no such disadvantage is connected with the :use of adjustingscrews =9! When, as illustrated, 'both adjusting means are provided, a still further advantage :may be aseoured from the eccentric adjustment, however, by reference to Equation 6 developed hereinbefore it will be evident that if due to any irregularities in construction the ratio of blade weight to counterbalancing weight, or the distance of blade center of gravity from the flapping hinge differ at all from the design values, the amount of stroke of the weight for each change in flapping angle should be correspondingly increased or decreased. Therefore if the blades are constructed, :as previously suggested, without accurate control over the amount and distribution of mass therein it is desirable to have the blade counteitbalancing mechanisms equipped with ready means for adjusting the amount of stroke of plungers 60 for any given change in flapping angle; By weighing each blade and measuring the location of its center of gravity, in the manner well known in the art, the proper length of lever I2 can be computed for producing exactly the proper stroke of plungers to for that particular blade, whereupon the eccentric connection between the lever is and link II related to that blade can be adjusted and permanently locked to give this computed effective length of lever. The fact that this vertical adjustment of the connection may also adjust it horizontally causes no difficulty, for screw members 9! may thereafter be adjusted in the manner previously outlined to correct for this difference along with all other factors affecting rotational balance of the rotor, in a single operation.

In order to prevent the droop of the blades, which as previously mentioned is characteristic of prior art rotors, particularly those of the articulated type, I prefer to mount beneath each flapping hinge a spring 95 (see Figures 6 and 7) seated in a socket in hub member ill and engaging, at least when the blade is in the lower part of its range of flapping angles, a crosspiece 96 integral with the blade root link 38. This spring may, if desired, be made only strong enough to raise the blade when it is moving so slowly that its weight becomes of more consequence than the aerodynamic and centrifugal forces acting on it. Under such an arrangement the spring would exert a negligible effect as compared with the large aerodynamic and centrifugal forces acting on the blade during flight, but with a stationary or slowly rotating rotor, at which time the droop of the blades is now effective and causes the dangers and difiiculties previously mentioned, the spring is effective to rock the blades upward about their flapping hinges, thus eliminating the droop and entirely avoiding the disadvantages associated with it.

Alternatively the springs 95 may be made considerably stronger than above mentioned, and arranged to be effective over the major portion of the range of flapping angles of the blades. In

such a case they may serve the purpose of aug-' menting the moment set up by the pressure of roller I5 against lug '56. As previously noted this is an unstable moment and increases with increase of blade flapping angle at a rate in excess of the rate of increase of the flapping angle. The moment exerted by spring 95 on the other hand is a stable moment and decreases with increase of flapping angle, thus tending to offset the increase in the other moment. As previously noted the moment set up by roller '55 tends to lower the effective point of application of the resultant rotor force on the craft from a prior art position such as indicated by point 32, Figure 3, to a position such as indicated by point 33. If in any particular design this particular point of application is considered too low the methods available for raising it include, in addition to inward movement of the effective center of gravity of weight 25 and/or outward spread of drag hinges 24., the increasing of the moment exerted by spring 95 or more especially the increasing of the rate at which the moment exerted by it falls oif with increase of blade angle, for the greater the rate at which the moment set up by spring 95 thus decreases, the less the net increase of the total moment effective between the blade and the hub, and consequently the less the shift of the resultant rotor force from its prior art location. The designer is thus provided with novel means for bringing the rolling and pitching controls to the exact degree of sensitiveness desired for any particular craft.

Figure 12 illustrates an embodiment differing in certain respects from that disclosed in Figures 5 to 11, inclusive, the principal differences being in connection with the method of mounting, driving, and providing rotational yield in connection with the rotation of the hub member. The principal objects of this alternative arrangement are to provide a greater spread between the flapping hinges and to increase the rotor controlling efiect and craft stability. To this end hub member Ella, though similar in construction to the hub member 4 of first embodiment is much larger in diameter. Then instead of providing a driving shaft of correspondingly enlarged diameter, the hub member 40a is mounted by means of roller bearings 42a and 43a, generally corresponding to those similarly numbered in the first embodiment, for rotation about a fixed cylindrical frame member IOU having fixed thereto or integral therewith a cap II to which the upward thrust of hub member 46a is transmitted through thrust bearings 44a. The drive for the rotor comes from engine shaft I03 through a conventional hydraulic coupling or fluid clutch lil l to transmission shaft Hi5, mounted in flanges I E16 and I ill integral with frame member Iilfi. Integral with shaft I95 near its upper end is a gear I98 which meshes with an idler Hill, which idler is also mounted in flanges I as and Iil'l. Idler we in turn meshes with teeth IE8 cut into the inner face of hub member. 46a. Hub member dila is thus rotated upon the fixed cylindrical member Ifiil. The effect of a master drag hinge is secured since the hydraulic coupling 5 3 offers little resistance to minor angular readjustments between the engine and the rotor whether such readjustments are required to smooth out irregularities in the driving move ment transmitted by the engineor to permit the blades to respond in limited degree to irregular air conditions encountered.

Figure 12 also illustrates more fully than the preceding figures how the pitch of the blades, Which are supported just as in the first embodiment, may be controlled both cyclically and simultaneously, and it is to be understood that generally similar pitch control mechanism may be employed in connection with the first embodiment. A sleeve H2 is mounted for vertical re- 5. ciproeation on the cylindrical frame member I00.

This sleeve is raised or lowered to secure general increase or decrease in the pitch of all blades. This may be effected, for instance by a fork II3 engaging pins H4 and II 5 which extend outwardly through sleeve H2 and serve to pivotally mount a ring H5 inside member I0 3. Ring H6 is connected to a floating ring 5 I8 by two diametrically opposite links H9, one of which is shown (partly broken away) in Figure 12. Pin H5 is fixed to or integral with the ring H6 and with an arm I259 which carries a pin I2! extending through a vertical slot of a Scotch yoke I22 which may be reciprocated perpendicularly to the plane of the drawing to rock the ring II6 on its pins I If and I I5 and to thereby similarly rock floating ring lit for the exercising of cyclic control.

For exerting cyclic control at right angles to that exerted through ring I I 6 another ring I25 is provided also pivotally mounted on sleeve II2 (by means of a pin I'26 and another co-axial pin not shown). An arm I21 integral with pin I26 and ring I25 carries a pin I28 which is seated in a vertical slot I29 of a Scotch yoke I30 which may be reciprocated to the right or left to rock ring I25 on its pivot pins IZ'B, which through the two opposite links I3I serves to similarly rock floating ring IIB. Integral with ring H 8 outside of member Illll is ring I33 which through a ball and thrust bearing connection is held in a relation to ring I34 which remains at all times fixed except for relativerotati'on of the two rings, ring I34 rotating with the rotor while ring F33 does not rotate. Integral with ring I34 are a plurality of arms I35 (one for each blade), each such arm being universally connectedto vertical link 30 which is connected to the blade through arm 3| (Figure 5) as previously described".

It will be evident from the foregoing that when sleeve H2 is raised all four rods H9 and I=3,I are raised equally, raising rings I'I8, I33 and I34- parallel to themselves, causing equal increases inpitch of all blades. However if either of the" Scotch yokes I22 or I3!) is readjusted; eitherthe ring H6 or the ring I-2-5 will be tiltedand a corresponding tilting movement will. be transmitted to rings IIB, I33; and I34 causing links '33 to be raised: at one portion of the circuit for all blades and correspondingly lowered at the opposite portion, thus introducing cyclic changes of blade pitch.

I claim:

1. In a rotary wing aircraft rotor having, a hub and a blade hinged to said hub; the combination of acylinder carried by said blade, a piston. con.- stituting a weight element movable. longitudinally ofthe blade within said cylinder; said piston be ing; urged. outwardly with respect. to said hub. in response to centrifugal forces effective during rotation of said rotor, and means comprising a hydraulic pump connected to said cylinder and actuated by downward hinging movement of said blade with respect to said hub for controlling the extent of such outward piston movement and for actuating said piston to cause movement thereof in a direction toward said hub.

2. In a rotary wing aircraft rotor having a hub and a blade hinged to said hub; the combination of a plurality of cylinders carried by said blade, a piston movable longitudinally of the blade within each of said cylinders; said pistons collectively constituting a balancing weight carried by said blade and being urged outwardly with respect to said hub in response to centrifugal forces effective during rotation of said rotor, and means comprising a plurality of hydraulic pumps each of which is connected to one of said cylinders and actuated by downward hinging movement of said blade with respect to said hub for controlling the extent of such outward piston movement and for moving said pistons toward said hub.

3. In a rotary wing aircraft rotor having a hub and a blade hinged to said hub; the combination of a plurality of cylinders carried by said blade, a piston movable longitudinally of the blade within each of said cylinders; said pistons collectively constituting a balancing weight carried by said blade and being urged outwardly with respect to said hub in response to centrifugal forces effective during rotation of said rotor, and means comprising a plurality of hydraulic pumps having pumping pistons the area of which substantially exceeds the area of the respective weight pistons and each of which is connected to one of said 26 cylinders and actuated by downward hinging movement of said blade with respect to said hub for controlling the extent of such outward piston movement and for moving said pistons toward said hub.

fl. In a rotary wing aircraft rotor having a hub and a plurality of blades each connected to said hub by a flapping hinge constraining the blade to move relative to the hub in a single plane fixed relative to the hub; the combination of driving means for said hub comprising a prime mover and a yieldable driving connection between said prime mover and said hub, a plurality of balancing weights each carried by a respective one of said blades and each adjustable longitudinally of its respective blade, and means related to each respective blade and automatically responsive to h-inging displacement of said blade with respect to said hub for directionally and quantitatively adjusting said balancing weight.

5. A bladed rotor for rotary wing aircraft comprising a balancing weight adjustable with respect to the axis of rotation of said rotor, means including a lever having a first operating connection from a blade of said rotor and a second operating connection to said balancing weight; said means being automatically responsive to movement tending to displace the center of gravity of the rotor transmitted from said blade through said first operating connection, for directionally and quantitatively adjusting said balancing weight; and means'for varying the effec tive length of said lever to vary the magnitude of displacement of said weight through said second. operating connection eifected. in response to a given amount of movement of a blade as aforesaid, in combination with separate means for altering the position of said. balancing weight which corresponds to each given position of said. blade.

6. In a rotary wing aircraft having a hub and a blade hinged to said hub; the combination of a plurality of separate elements collectively constituting a balancing weight; each of said elements being adjustable with respect to the axis of rotation of said rotor, and means automatically responsive to hinging displacement of said blade with respect to said hub for directionally and quantitatively adjusting said elements; said means including a separate device associated with each of said elements for adjusting the associated element in the absence of hinging displacement of said blade with respect to said hub.

'7. In a rotary wing aircraft rotor having a hub and a blade hinged to said hub; the combination of a plurality of separate elements collectively constituting a balancing weight carried by said blade; each of said elements being adjustable longitudinally of the blade, means automatically responsive to hinging displacement of said blade with respect to said hub for directionally and quantitatively adjusting said elements to displace the resultant center of gravity of the blade and said elements collectively, and means for separately altering the position of each of a plurality of said elements longitudinally of the axis of the blade, in the absence of hinging displacement of the blade with respect to said hub.

8. In a rotary wing aircraft having a rotatable hub, a blade, and a flapping hinge connecting said blade to said hub; the combination of a balancing weight movable relative to said blade and said hub and radially adjustable with respect to the axis of rotation of said hub, a hydraulic pump having an elem nt directionally and quantita- 27 tively movable jointly by said blade and said hub during movement of said blade relative to said hub upon said flapping hinge, and a connection between said pump and said weight for selectively transmitting movement directionally and quantitatively imparted to said pump element to effect related directional and quantitative radial adjustment of said weight.

9. A rotary wing aircraft rotor according to claim 8 in which said balancing weight is enclosed within said blade and adjustable longitudinally thereof, and said pump is enclosed within said blade and said element of said pump is displaceable longitudinally of the blade.

10. In a rotary wing aircraft having a hub rotatable about a normally vertical axis, a blade, and a flapping hinge connecting said blade to said hub; the combination of a balancing weight carried by said blade and adjustable longitudb nally of the blade, and means for adjusting said weight longitudinally of said blade comprising cooperating cam and cam follower elements, one of said elements being supported by said hub and the other by said blade so as to cause the cam follower element to move along said cam element upon hinging displacement of said blade, and a connection from one of said elements to said weight, the cam element being proportioned to effect a lesser adjustment of said weight per unit of angular displacement of said blade in that portion of the cam element which is contacted by the cam follower element when the blade extends at approximately right angles to said axis than in that portion of the cam element which is contacted by the cam follower element when the blade has been rocked about said flapping hinge so as to extend upwardly at an acute angle to said 3X15;

11. In a rotary wing aircraft having a rotatable hub, a blade, and a flapping hinge connecting 28 said blade to said hub; the combination of a balancing weight enclosed within said blade, carried by said blade and adjustable longitudinally thereof, a mechanism jointly operable by said blade and said hub during movement of the blade relative to said hub upon said flapping hinge, said mechanism comprising a variable-rate cam and a cam follower, and a connection between said mechanism and said weight for transmitting movement imparted to said mechanism to efiect radial adjustment of said weight.

12. In a rotary wing aircraft having a rotatable hub, a blade, and a flapping hinge connecting said blade to said hub; the combination of a balancing weight enclosed within said blade and adjustable longitudinally thereof, a lever pivotally mounted on said blade and cooperating with a cam surface on said hub whereby said lever is jointly operable by said blade and said hub during movement of the blade relative to said hub upon said flapping hinge, and a connection between said lever and said Weight for transmitting movement imparted to said lever to efiect radial adjustment of said weight.

HAROLD T'. AVERY.

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

Stalker Aug. 12,

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