US3717317A - Method and devices for improving the longitudinal stability of helicopters - Google Patents

Abstract

The technical province of this invention is that of aeronautical engineering. The invention relates to a method and to devices for improving the longitudinal stability of helicopters, in which an incipient tendency for the nose of the helicopter to pull up is compensated by generating a diving moment responsively to a hinged stabilizer actuated as a result of the inertia of a weight attached thereto. The principal industrial applications of the invention are to be found in the realm of rigid-rotor helicopters.

Description

United States Patent Certain 51 Feb. 20, 1973 [54] METHOD AND DEVICES FOR IMPROVING THE LONGITUDINAL STABILITY OF HELICOPTERS [75] inventor: Bernard Maurlce Certain, Aix-en- Provence, France [73] Assigncc: Societe Nationale lndustrielle Aerospatiale, Paris (Seine), France 221 Filed: Nov.25, 1970 [21] Appl. No.: 92,631

[30] Foreign Application Priority Data Nov. 27, 1969 France ..6940879 [52] US. Cl. ..244/l7.l3, 244/l7.19, 244/87 [51] Int. Cl ..B64c 5/10 [58] Field of Search..244/17.13, 17.19, 17.11, 17.17, 244/17.15, 87-90 [56] References Cited UNITED STATES PATENTS Goland et a1. ..244/17.l3 X

2,630,985 3/1953 Sherry ..244/17.l9 2,941,792 6/1960 Stutz 3,081,052 3/1963 Michel ..244/l7.l9

Primary ExaminerTrygve M. Blix Assistant Examiner-Paul E. Saubercr AtlomeyWatcrs, Roditi, Schwartz and Nisscn [57] ABSTRACT The technical province of this invention is that of aeronautical engineering.

The invention relates to a method and to devices for improving the longitudinal stability of helicopters, in which an incipient tendency for the nose of the helicopter to pull up is compensated by generating a diving moment responsively to a hinged stabilizer actuated as a result of the inertia of a weight attached thereto.

The principal industrial applications of the invention are to be found in the realm of rigid-rot0r helicopters.

5 Claims, 13 Drawing Figures PATENTED FEB 2 01975 SHEET 10F 4 PATENTED FEB 2 0 I975 SHEET 30F 4 METHOD AND DEVICES FOR IMPROVING THE LONGITUDINAL STABILITY OF HELICOPTERS The technical province of this invention is that of aeronautical engineering.

Conventional rotary-wing aircraft with their rotor blades hinged to the hub are affected by longitudinal instability. In forward flight, the resultant of the pulling forces, which is exerted through the aerodynamic center of the rotor, in conjunction with the drag applied to the fuselage, give rise to an unstable diving moment about the center of gravity of the machine that increases with increasing flight speed. This diving moment is countered by an opposing moment which, inter alia, may be generated by a negative-lift horizontal stabilizer positioned at the rear end of the fuselage.

A similar phenomenon of instability in the longitudinal attitude is to be observed in helicopters having flexible rotor blades. At high speeds a sudden increase in this instability may occur as the result of a gust or a change in cyclic pitch. Thus, in level flight, if the machine were to be left to itself it would tend to pull up, resulting in positive load factors which could reach high values.

This phenomenon of instability, which is commonplace on rotorcraft equipped with such so called rigid rotors, is attributed to a coupling effect between the motions of the blades due to .drag and to blade twist.

Inasmuch as the design of rotors of this kind already raises delicate problems to solve, modifications to such rotors have not been contemplated.

It is the object of the present invention to overcome this longitudinal instability of helicopters and to accordingly provide a stabilization method whereby any tendency to diverge from the longitudinal attitude is compensated by engendering a reverse moment on the machine responsively to an inertiaoperated stabilizer.

Thus an incipient pulling-up moment instantly gives rise to a diving moment.

In a preferred embodiment of the method of this invention, said diving moment is generated by the inertia of a pendular weight, the action of which is thus proportional to the increase in the load factor but independent of the aerodynamic forces.

The invention further relates to devices for performing such method that include in particular a horizontal stabilizer positioned at the rear end of a helicopter fuselage, which stabilizer is pivotally mounted about a horizontal shaft and is fast with a weight the inertia of which deflects said stabilizer in response to incipient longitudinal divergence from the flight path, such deflection being appropriate to counter said divergence.

In a preferred embodiment, said weight is supported on the end of a lever arm substantially parallel to the chord of the stabilizer airfoil, said lever being directly or indirectly connected to a return spring which, by acting with respect to the instantaneous fulcrum of said stabilizer together with the aerodynamic forces exerted against the latter, balances the moment generated by said weight, the rating of the spring being determined by the maximum stabilizer deflection setting at which stability is desired.

In accordance with a first alternative embodiment in which a horizontal stabilizer of this kind is mounted on top of a vertical stabilizer, the lever arm and its pivotal elements are arranged to form a support for said horizontal stabilizer on an intermediate part pivotally mounted on top of the vertical stabilizer, said intermediate part being rigid with means for setting it angularly with respect to the upper edge of the vertical stabilizer, which angular setting means permit adjustment of the balancing position of the horizontal stabilizer, the latter being set to provide negative lift in normal flight.

The horizontal stabilizer support is formed by an inverted channel section which caps the intermediate part, which part is formed in turn by braced flanges.

The liaison between the horizontal stabilizer support and said flanges is provided by two divergent links which are mounted, on the one hand, on two upper shafts fast with the upper parts of the inner flanges and, on the other, on two subjacent shafts which are more widely spaced than said upper shafts and are rigid with said support. This balancing pendular articulation system permits stable pivotal motion of the horizontal stabilizer, which is normally at negative incidence, about the first-mentioned two shafts which are connected to the vertical stabilizer, the other two articulation shafts rigid with the horizontal stabilizer support being preferably included in a plane parallel to the plane containing the chord of said horizontal stabilizer airfoil.

One of the flanges is fast with a balancing-positionsetting bellcrank which is attached to a tie rod formed by a bracket supported on the vertical stabilizer.

In order to obtain, from the aerodynamic standpoint, sufficient damping of the horizontal stabilizer motion subsequent to actuation thereof, the corresponding articulation is associated to a damper possibly positioned between the two flanges and having its body portion fast with one thereof, the other flange being equipped with an arrangement of adjustable stops positioned in registry with contacting surfaces formed on the side of the horizontal stabilizer support.

With such an arrangement, the instantaneous fulcrum about which the horizontal stabilizer rotates and which is at all times located at the intersection of two planes defined respectively by the shafts rigid with the flanges and by the shafts rigid with the supports, is caused to shift rearwardly along a locus which is a circular arc as the motions required to achieve the desired stabilization take place.

The position at which the instantaneous fulcrum coincides with the aerodynamic center is the position at which the system is in a state of equilibrium.

In an arrangement as hereinbefore described, when the load factor increases, the moment developed by said weight increases and tends to cause the horizontal stabilizer which the weight is rigid assume positivegoing incidence, whereby a modified lift value is produced that generates a diving moment for the helicopter about its center of gravity, which diving moment counters the pull-up moment due to the longitudinal divergence and thereby ensures the required stabilization of the helicopter about its pitch axis.

In a second alternative embodiment likewise designed to improve longitudinal stability, the rear end and, mounted thereon, a weight secured to the rear ofa formed section rigid with the root of each stabilizer element. A spring connected between the forward part of this element and an associated end of a horizontal rocker arm fast with the tail boom balances the moment generated mainly by said weight.

Pivotal motion of the said formed sections responsively to the inertia of the associated weights, in order to cause the horizontal stabilizer to react at the onset of a pitch-up divergence by the machine, takes place about the axis of a tube carrying the two horizontal stabilizer elements and is limited by two stops.

With such an arrangement there is likewise provided a damper the body portion of which may be disposed within said formed section.

Possible industrial applications of the invention are to be found in the field of helicopters, and more particularly helicopters having rotors with flexible blades devoid of hinges.

The description which follows of a number of nonlimitative exemplary embodiments of devices for improving the longitudinal stability of helicopters, given with reference to the accompanying drawings, will give a clear understanding of how the invention can be cartied into practice.

In the drawings:

FIG. 1 schematically illustrates the location of the subject device of the invention on top of a vertical stabilizer on a helicopter FIG. 2 shows in side elevation a horizontal stabilizer equipped with a deflecting system according to the invention FIG. 3 is a section taken through the line III--III of FIG. 2

FIG. 4 is a section taken along the line IV-IV of FIG. 2

FIG. 5 is a section taken along the line V-V of FIG.

FIG. 6 is a section taken along the dash line VIVI of FIG. 2

FIG. 7 is a section taken through the line VII-VII of FIGS. 2 and 8 FIG. 8 is a side elevation view which is the reverse of that of FIG. 2;

FIG. 9 is a section taken through the line IX-IX of FIG. 8

FIG. 10 is a fragmental showing, in corresponding fashion to FIG. 1, of an alternative arrangement for a stabilizing device according to this invention FIG. 11 shows in side elevation on an enlarged scale a control arrangement applicable to the embodiment of FIG. 10

FIG. 12 is a plan view corresponding to FIG. 11, with partial cutaway and FIG. I3 is a section taken through the line XIII-XIII of FIG. 11.

As shown in FIG. 1, the vertical stabilizer D of a helicopter l-I having a rotor R carries at its top a horizontal stabilizer E for stabilizing the longitudinal attitude of the helicopter, more particularly when said attitude tends to be disturbed by gusts or sudden changes in the cyclic pitch of the rotor blades.

Reference is next had to FIG. 2, in which the top 1 of the helicopters vertical stabilizer D receives an element 2 forming a horizontal stabilizer E. This arrangement is effected by means of a support 4 formed by an inverted channel section having its web applied against the lower surface 3 of element 2 and secured thereto by screws 5 and 6 and blocks 7 and 8 permitting precise mutual positioning of support 4 and airfoil 2. The web and flanges of support 4 are suitably cut to shape. and there is secured to the rear end of support web 9, by means of bolts 10 and 11, a weight 12 made of heavy alloy and of size appropriately adjusted'thickness-wise.

The flanges l3 and 14 of support 4 are form'edwith corresponding openings 15 and 16 shaped substantially as trapeziums having their longer bases respectively forming the upper edges of said openings.

Attached to the upper edge 1 of the vertical stabilizer are two vertical flanges l7 and 18 which jointly form an intermediate part and which embody circular openings 19 and 20 respectively, in registry with each other. The spacing between flanges 17 and I8 is maintained by spacer means, one of which is secured by a bolt and nut 24.

In respect of these two flanges, such attachment is effected, on the one hand, upon a shaft 21 extending through one of said spacer means and restrained in lugs 22 of said flanges and in the sides of a clevis 23 fixed to the top of stabilizer D, in the forward region thereof. The attachment system is completed, on the other hand, by having flange l8 bear at its rear a bellcrankforming extension 25 which is bolted at 26 and 27 to rear lugs on flange 18.

The tapering end of bellcrank 25 is secured by a bolt and nut 28 to a slotted portion 29 of a bracket 30 secured by bolts and nuts 31 to a clevis 32 likewise carried on the crest line 1 of vertical stabilizer D. Bolt 28 is movable along slot 33 of bracket 30 in order to enable the equilibrium position of horizontal stabilizer E to be set, the need for which setting will become apparent hereinafter.

Adjacent the rear end of its crest line 1, vertical stabilizer D carries a bracket 35 from which extends a threaded rod 34 associated to a nut and locknut, said rod terminating in an eye 36 into which is hooked the end of a spring 37.

The rating of spring 37 is determined by the maximum angular setting of the horizontal stabilizer for which stability is desired, and the other end of spring 37 engages in a groove 38 formed in the middle region of a spacer pin 39 extending through the flanges 13 and 14 of horizontal stabilizer support 4 (FIGS. 6 and 9). The lower part 40 of bracket 30 (FIG. 5) forms a yoke between the arms of which spring 37 freely extends, each yoke arm being provided with a bolt and nut 31.

The hinge coupling between stabilizer E and stabilizer D, which is an indirect coupling, is accomplished through the agency of the intermediate member formed by flanges 17 and 18, the angular positions of which are adjustable about shaft 21 and which are associated to two links 41 and 42 (see FIGS. 2, 3 and 4). Links 41 and 42 are hingedly connected to the forward upper ends respectively of flanges 17 and 18 through the medium of spacer pins 43 and 44.

Links 41 and 42 splay out downwardly from pins 43 and 44 and are interconnected in corresponding pairs by pins 45 and 46 supported in bearings 47 and 48, the latter being fast with lower portions of the side plates or flanges l3 and 14 of support 4 by means of securing lugs 49. Pivotal motion of links 41, 42 about upper pins 43 and 44 is facilitated by needle-bearings 50 and bores 51 in the link ends, said needle-bearings being spaced as required by central cylindrical distance-pieces 52 and flanged washers 53 and 54 pivotal motion of said links about the lower pins 45 and 46 is likewise facilitated by identical needle-bearings driven into bores in the other ends 55 of said links and maintained in spaced relationship by a central distance-piece 52 and two flanged bushes 56 and 57.

A peg 58 (FIG. 3) equipped with a flag marker may be inserted through aligned holes 59 in flanges l3 and 14 of support 4 and in the lugs 49 of bearings 47 and 48, and thereafter in the link 42, these last holes lying in the plane containing pins 44 and 46. Peg 58, shown in the engaged position in FIG. 3, is designed to restrain the stabilizer support 4 in relation to flanges 17 and 18 when the resting position of equilibrium of the horizontal stabilizer has been set subsequent to suitable adjustment of the mass of material required to form the weight referred to precedingly.

Fitting and removal of pins 43 and 44 with respect to flanges 17 and 18 are possible by the access provided through openings and 16 of unequal size formed in the sides 13 and 14 of support 4 and through a marginal opening 16 (FIG. 1) associated-to openings 60a in the sides 13 and 14 respectively for permitting engagement and disengagement of pin 24. The cutaway formed in the lower portion of sides 13 and 14 likewise provides access to pins 45 and 46 and to pin 21.

In order to provide damping of the motion of horizontal stabilizer E during variations in the load factor, a damper (not shown) is positioned between the two flanges 17 and 18, the body portion of the damper being screwed through the medium of a base to flange 18 (shown in dash lines in FIG. 2). The facing opening 19 in flange 17 provides passage for the hinge-pin of such pivotal damper, which hinge-pin is made fast with a crank to which is hingedly connected a link having its other end pivotally connected to an appropriately configured end of one of pins 45 or 46. A linkage system of this kind is shown in dot-dash lines in FIG. 2.

Associated to said damper is a system of lengthwiseadjustable stops 61 and 62 (FIG. 8) screwed into and restrained by nuts and locknuts in a bracket 63 fast with flange 18, which bracket and stops project into the cutout 16 above the lower edge thereof, which edge bears a bracket 64 carried internally on the facing flange 14 of support 4. That surface of bracket 64 which faces the tips of stops 61 and 62 bears linings cooperating with said tips.

The theory of operation of the system described hereinabove is as follows:

While the helicopter is on the ground, peg 58 is removed after setting the equilibrium position of horizontal stabilizer E that is required in stable flight (by setting a degree of negative lift on said stabilizer to balance the diving moment which is generated by the component of pull exerted at the aerodynamic center of the rotor and by the drag exerted against the fuselage) having regard for the reciprocal actions of weight 12 and spring 37.

Since in stable flight it is required to have a zero angular setting of the horizontal stabilizer, the sum of the moments acting about the instantaneous fulcrum of said stabilizer must be zero, whereby the need for the action of spring 37 to counter the moment generated by weight 12. Horizontal stabilizer E consequently remains motionless.

In response to a gust or an abrupt change in the cyclic pitch at high forward speeds, the helicopter experiences incipient pitch-up, thereby causing an increase in the load factor. This increase in turn causes the moment generated by weight 12 to increase and to thereby cause horizontal stabilizer E to assume positive-going incidence. Two moments oppose this motion, one of which is due to the spring 37 and the other to the aerodynamic forces acting downwardly on stabilizer E.

The equilibration of the moment due to weight 12, to spring 37 and to said aerodynamic forces determines a different angular setting of horizontal stabilizer E and hence a different lift value therefor, whereby a force is caused to act upwardly and to engender a diving moment about the center of gravity of the helicopter. This diving moment opposes the pitchup moment which accompanies the incipient longitudinal divergence referred to precedingly, whereby the required stabilization of the longitudinal attitude of the helicopter is achieved automatically.

In the alternative embodiment depicted in FIGS. 10 to 13, the longitudinal stability improving device is mounted on the helicopter tail boom P in the form of two horizontal half-stabilizers E, projecting from either side of boom P. In FIGS. 11 and 12, only one horizontal stabilizer element 66 is shown in addition to the tail boom skin 65.

Secured to the root 67 of element 66 is a tapering channel-section 68 having its open side facing skin 65. Attached to the rear end of channel section 68 is a weight 69 made of heavy alloy. Forward thereof is disposed, on the web of section 68, a damper 70 the axle of which carries a crank 72 pivotally connected to a link 73 which is in turn pivotally connected to a hinge-pin 71 fixed to skin 65.

The forward end of section 68 is provided with means for attaching the looped end of a spring 69a, through the agency of retention means threaded over a bolt 75. The other end of spring 69a (FIG. 13) is attached to a metal strip welded to a threaded rod 76 which is secured by a nut and locknut to one end of a substantially horizontal transverse arm 77 which is fulcrumed by means of a hinge-pin in a clevis 78 rigid with the undersurface of tail boom skin 65. Arm 77 accordingly forms a rocker arm interconnecting the two stabilizer elements.

Additionally fixed to the sides of the tail boom are T- sections 79 the webs 80 of which are cut to match the shape of skin 65 and welded over their entire lengths thereto, and the flanges 81 of which have bolted into slots therein two brackets 82 and 83 faced with elastic linings 84 against which the sides of channel section 68 bear alternately.

The positioning of these abutment brackets and the spacing imparted thereto are determined, on the one hand, according to the resting position which it is desired for stabilizer element 66 to assume, and on the other according to the maximum deflection of which said element is to be capable in the event of longitudinal divergence of the helicopter due to pitch-up caused by a gust and/or a sudden variation in cyclic pitch.

The two stabilizer elements 66 are fast with a common tubular spar 85 which is carried in antiafriction bearings 86 supported in associated housings in the tail boom and by means of which said elements are capable of pivotal motion.

As stated precedingly, the two horizontal stabilizer halves are identically devised and are positioned symmetrically with respect to the helicopter fore-aft axis.

In the event of incipient pitch-up by the helicopter, the two stabilizer elements react by pivoting about the spar axis in response to any increase in the load factor causing the weights 69 to react. Such reaction determines a modified angle of incidence of the horizontal stabilizer and a consequently modified lift value thereof. With the arrangements described hereinabove, this results in the generation of a diving moment which stabilizes the helicopter about its center of gravity.

It goes without saying that changes and substitutions may be made to the specific forms of embodiment hereinbefore described without departing from the scope of the invention. By way of example, the stabilizer elements could be provided with aerodynamic control surfaces known as tabs, capable of being deflected with respect to the chord line of the airfoil section of such stabilizer in order to cancel the effect of an aerodynamic pitching-up moment about the instantaneous fulcrum of said stabilizer element.

What I claim is:

1. In a device for improving the longitudinal stability of a helicopter having a rotor provided with flexible blades deprived of articulations for flapping and leadlag oscillations, in which at least one horizontal stabilizer element is hingedly mounted on said helicopter on a first axis parallel to pitch axis of said helicopter and is rigid with a weight, said weight being situated at one extremity of a lever arm nearly parallel to the airfoil chord of said stabilizer element said lever being attached to a return spring, an intermediate member being interposed between helicopter body and hinge of said stabilizer element, said intermediate member being itself hingedly mounted on a second axis parallel to said first axis, the improvement according to which said lever is forming a horizontal stabilizer Supporting element straddling said intermediate member constituted of cross-braced flanges, supported by said second axis on the first hand and attached, on the other hand, by an interconnecting arm to a slotted bracket, said second axis and said bracket being affixed to crest line of a vertical stabilizer of a fuselage of said helicopter, said horizontal stabilizer over-lying said crest line.

2. In a device according to claim 1, a flange supporting a damper body and adjustable stop means situated in front of contact surfaces formed in said lever, said damper having a movable part mechanically connected to said lever.

3. In a device for improving longitudinal stability of a helicopter having a rotor provided with flexible blades deprived of articulations for flapping and lead-lag oscillations, in which at least one horizontal stabilizer element is hingedly mounted on said helicopter on a first axis, parallel to pitch axis of said helicopter, said horizontal stabilizer element being fast with a weight situated at one end of a lever arm nearly parallel to airfoil chord of said stabilizer element, said lever arm being attached to a return spring, the improvement according to which said stabilizer element is supported by a spar carried as an axle in a bearing housing inserted in a helicopter tail boom, said stabilizer element having a root portion fast with a lever supporting at its rear end a high-density weight and attached at its forward end to a spring itself attached at one extremity of an arm hingedly fixed to said tail-boom, said forward end being rockable between two adjustable abutment means rigid with said tail boom.

4. In a device as claimed in claim 3, an arrangement, symmetrical with respect to the longitudinal centerplane of said tail boom, of empennage elements, of levers, of weights, of springs and of said arm, the latter being supported for rocking motion about an axis lying in said longitudinal plane.

5. In a device as claimed in claim 3, damper means having its stationary portion supported by said lever and its movable portion attached to pivot means rigid with said tail boom.

Claims (5)

1. In a device for improving the longitudinal stability of a helicopter having a rotor provided with flexible blades deprived of articulations for flapping and lead-lag oscillations, in which at least one horizontal stabilizer element is hingedly mounted on said helicopter on a first axis parallel to pitch axis of said helicopter and is rigid with a weight, said weight being situated at one extremity of a lever arm nearly parallel to the airfoil chord of said stabilizer element said lever being attached to a return spring, an intermediate member being interposed between helicopter body and hinge of said stabilizer element, said intermediate member being itself hingedly mounted on a second axis parallel to said first axis, the improvement according to which said lever is forming a horizontal stabilizer supporting element straddling said intermediate member constituted of crossbraced flanges, supported by said second axis on the first hand and attached, on the other hand, by an interconnecting arm to a slotted bracket, said second axis and said bracket being affixed to crest line of a vertical stabilizer of a fuselage of said helicopter, said horizontal stabilizer over-lying said crest line.

1. In a device for improving the longitudinal stability of a helicopter having a rotor provided with flexible blades deprived of articulations for flapping and lead-lag oscillations, in which at least one horizontal stabilizer element is hingedly mounted on said helicopter on a first axis parallel to pitch axis of said helicopter and is rigid with a weight, said weight being situated at one extremity of a lever arm nearly parallel to the airfoil chord of said stabilizer element said lever being attached to a return spring, an intermediate member being interposed between helicopter body and hinge of said stabilizer element, said intermediate member being itself hingedly mounted on a second axis parallel to said first axis, the improvement according to which said lever is forming a horizontal stabilizer supporting element straddling said intermediate member constituted of cross-braced flanges, supported by said second axis on the first hand and attached, on the other hand, by an interconnecting arm to a slotted bracket, said second axis and said bracket being affixed to crest line of a vertical stabilizer of a fuselage of said helicopter, said horizontal stabilizer over-lying said crest line.

2. In a device according to claim 1, a flange supporting a damper body and adjustable stop means situated in front of contact surfaces formed in said lever, said damper having a movable part mechanically connected to said lever.

3. In a device for improving longitudinal stability of a helicopter having a rotor provided with flexible blades deprived of articulations for flapping and lead-lag oscillations, in which at least one horizontal stabilizer element is hingedly mounted on said helicoPter on a first axis, parallel to pitch axis of said helicopter, said horizontal stabilizer element being fast with a weight situated at one end of a lever arm nearly parallel to airfoil chord of said stabilizer element, said lever arm being attached to a return spring, the improvement according to which said stabilizer element is supported by a spar carried as an axle in a bearing housing inserted in a helicopter tail boom, said stabilizer element having a root portion fast with a lever supporting at its rear end a high-density weight and attached at its forward end to a spring itself attached at one extremity of an arm hingedly fixed to said tail-boom, said forward end being rockable between two adjustable abutment means rigid with said tail boom.

4. In a device as claimed in claim 3, an arrangement, symmetrical with respect to the longitudinal centerplane of said tail boom, of empennage elements, of levers, of weights, of springs and of said arm, the latter being supported for rocking motion about an axis lying in said longitudinal plane.

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