Blade having an integral cuff, and a rotorcraft rotor provided with such a blade

A rotorcraft blade is provided having at least one spar and an outer covering. At the root of the blade, the spar is subdivided into at least one bottom tape and at least one top tape. The blade further includes a hollow cuff whose outer wall includes the outer covering secured to the bottom and top tapes.

The present invention relates to a blade including an integral cuff, and to the rotor of a rotorcraft on which the blade is arranged.

BACKGROUND OF THE INVENTION

A rotorcraft is provided with at least one engine that drives a main rotor for providing the aircraft with lift and even with propulsion. The rotor comprises a hub that is driven by a rotor shaft, in turn driven by the engine, and a plurality of blades are arranged on the hub.

While rotating, the blades are subjected to a torsor of forces, and consequently they are subjected to centrifugal force as well as to multiple effects due to flapping, due to drag, and due to twisting, where twisting is caused in particular by the changes in pitch that serve to change the inclination of the blades relative to the plane of the hub.

In addition, the hub generally includes a plurality of arms, that are preferably flexible in flapping, with the blades being arranged at the ends of those arms. The forces due in particular to centrifugal force are then transmitted to the non-flexible central zone of the hub.

Under such conditions, a first fastener device is known for fastening each blade to the hub that makes use of external means, in particular a sleeve. For example, it may be constituted by the configuration known to the person skilled in the art by the name “Starflex” as implemented in particular on “Ecureuil” helicopters, where the terms “Starflex” and “Ecureuil” are trademarks registered in the name of Eurocopter.

Under such circumstances, the hub has a solid and rigid central portion that is extended radially by as many arms that are flexible in flapping as there are blades, thus forming an assembly with the appearance of a star when seen from above.

At its root, each blade is rigidly secured, via its spar(s), to radially outer, first ends of two straps forming a sleeve, those straps being disposed on either side of the blade and the flexible arm. In addition, the inner, second radial ends of the two straps are secured to a laminated spherical abutment which is also secured to the flexible arm by being arranged in an opening present at the base of the flexible arm.

Consequently, the centrifugal force on each blade is taken up via the corresponding sleeve by the associated laminated spherical abutment, which transmits said force to the solid and rigid central portion of the hub.

Flapping, drag, and twisting are taken up firstly via the laminated spherical abutment, and secondly by adding a joint. The joint then comprises a self-lubricating ball joint fastened to the end of the flexible arm and secured to two viscoelastic elastomer soleplates, each connected to one of the two straps.

Although very effective, it will be understood that that first device is not necessarily optimized from an aerodynamic point of view, because of the presence of the straps which can lead to aerodynamic disturbances.

Document EP 0 448 685 discloses a second device for fastening a blade to a hub that implements external means, namely a cuff. A cuff merely constitutes a sleeve that is faired and a priori hollow. This definition for the term “cuff” is explained below.

The hub then has a passage at the base of each arm, with a laminated elastomer support secured to the hub being arranged in the passage. Similarly, the end of each arm is provided with a joint provided with an elastomer support.

Each blade is then fastened to one end of the cuff via its root, said cuff itself being secured to the joint and to the laminated elastomer support. In addition, the cuff surrounds the arm of the hub, thereby increasing the aerodynamic performance of the assembly because of the fairing of the blade-cuff assembly.

Nevertheless, since the cuff is then constituted by means on the outside of the blade, the use of a cuff requires an interface enabling the blade to be secured to the cuff.

Unfortunately, such an interface is penalizing in terms of weight. This has multiple consequences. Since the blade-and-cuff assembly is naturally heavier, the forces to which it the assembly is subjected and that are transmitted to the hub are greater, thus implying that the hub needs to be reinforced. Consequently, the hub is more voluminous and not very streamlined. It can thus be understood that the hub becomes particularly bulky, and overall the performance of the rotor is diminished.

To remedy the above drawbacks, document EP 0 085 129 discloses a third device in which the cuff is integral with the blade.

The cuff is then constituted by a casing that is rigid in twisting and that extends the casing of the blade. In addition, the cuff surrounds, without touching, a segment of the neck of the blade that is fastened to the hub of the rotor.

Consequently, the cuff forms part of the blade, in particular by being constituted by the covering thereof. It is also connected to a rod so as to be able to control the pitch of the blade.

By integrating the cuff in the blade, that third device eliminates the system for fastening the blade to the cuff that is provided in the second device, thereby achieving a corresponding overall saving in weight.

However, it is found that the cuff presents a section that is circular, or even nearly rectangular, which is not suitable for obtaining good aerodynamic performance. Similarly, the cuff is used ultimately only for transmitting twisting to the blade (controlling pitch), with the flapping, drag, and centrifugal forces being taken up by the neck segment of the blade. It can be understood that that cuff constitutes weight that is practically dead since its use is confined to controlling the pitch of the blade.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the present invention is thus to propose a blade having an integral cuff, and also a rotorcraft rotor provided with such a blade, enabling the limitations of the above-mentioned rotors to be overcome so as to optimize the weight of the rotor and thus its aerodynamic and mechanical performance.

According to the invention, a rotorcraft blade is provided with at least one spar and an outer covering. The blade is remarkable in that, at the root of the blade, the spar is subdivided into at least one bottom tape and at least one top tape, the blade including a hollow and faired cuff whose outer wall is at least provided with said outer covering secured to said bottom and top tapes.

It should be observed that the bottom and top tapes are elongate structural elements made of a material that is capable of taking up forces and transmitting them to the hub of the rotorcraft rotor. The spar is then advantageously made of longitudinal and unidirectional glass fibers referred to as “roving” by the person skilled in the art.

Thus, the flapping and drag forces, and also centrifugal force, are transmitted essentially to the spar of the blade, which, as explained below, ends up by being fastened to the hub of a rotorcraft rotor. The bottom and top tapes making up the spar in the cuff are secured to said cuff by being fastened to its covering. Consequently, the cuff is necessarily a working component, and under the effect of the bottom and top tapes, it participates fully in transmitting forces by means of its own structural architecture.

This result constitutes a major technical advance, since the function of the cuff is no longer limited to transmitting a twisting force or merely acting as fairing. Its utility and its presence are thus completely justified. In addition, since the cuff is integral with the blade, there is no fastening to be provided between those two elements, thereby optimizing the weight of the assembly.

Furthermore, in order to obtain aerodynamic results that are as satisfactory as possible, the cuff is advantageously a body that is aerodynamically streamlined. In other words, the three-dimensional aerodynamic shape of said cuff provides geometrical and thus surface continuity with the three-dimensional aerodynamic shape of the blade.

As a result, seen from the outside, the blade then presents an overall appearance that is smooth, and a three-dimensional shape that is aerodynamic, enabling maximum fineness to be obtained, i.e. a maximum ratio of lift to drag. Since the cuff is streamlined so as to present an aerodynamic three-dimensional shape that matches the aerodynamic shape of the blade, the cuff and the remainder of the blade constitute a single streamlined body of drag that is minimized in order to optimize fineness, the cuff thus actively contributing to the aerodynamic performance of the blade.

Geometrically, the cuff comprises in succession a first zone at the end of the cuff that is closer to the tip of the blade, an intermediate zone, and a second zone at the end of the cuff that is further from said tip.

In a first embodiment, for sections of the bottom and top tapes each having a longitudinal dimension along the chord axis of the blade and an elevation dimension along the thickness direction of the blade, said sections of the bottom and top tapes present, in the first zone, a longitudinal dimension that is greater than their dimension in elevation, whereas, in the second zone, said sections of the bottom and top tapes have a longitudinal dimension that is less than their dimension in elevation. Consequently, the bottom and top tapes are flattened in the intermediate zone. In this way, it is possible to ensure that the intermediate or transition zone is located in the desired position. This technique is much more effective than a technique that involves twisting the fiberglass tapes, since twisting can lead to shapes and also to mechanical vibratory characteristics that are poorly reproducible from one blade to another.

In a second embodiment, the longitudinal dimension of the bottom and top tapes is greater than their dimension in elevation in the first zone, in the intermediate zone, and in the second zone. This embodiment makes it possible to preserve the physical integrity of the tapes by avoiding any flattening or twisting thereto. This embodiment is also easier to implement.

Finally, for a cuff having a plurality of bottom tapes, the cuff is advantageously provided with bottom reinforcement that surrounds at least two adjacent bottom tapes. Thus, the bottom reinforcement is constituted by a reinforcing tape that surrounds the bottom tape so as to improve the mechanical performance of the assembly, where necessary.

Similarly, for a cuff having a plurality of top tapes, the cuff is advantageously provided with top reinforcement that surrounds at least two adjacent top tapes.

The present invention also provides a rotorcraft rotor having a hub provided with a plurality of arms, a blade being arranged at a first end of each arm and being provided with at least one spar and with an outer covering. At the root of the blade, the spar is subdivided into at least one bottom tape and at least one top tape, the blade further including a hollow cuff whose outer wall is provided with said outer covering secured to said bottom and top tapes, a base of said arm being provided with a passage, and the bottom and top tapes being connected together via a support passing through the passage, said support being secured to the hub by connection means.

Advantageously, the support comprises a high platform and a low platform interconnected by a central portion secured to the connection means. Consequently, each bottom tape surrounds a pin passing through the low platform and each top tape passes round a pin passing through the high platform, the bottom tape thus being fastened to the low platform by a pin passing therethrough and the top tape thus being fastened to the high platform by another pin passing therethrough.

In the first embodiment, the bottom and top tapes are wound substantially vertically around the pins, these pins thus extending in an elevation direction, i.e. in the thickness direction of the blade.

In contrast, in a second embodiment, the bottom and top tapes are wound substantially horizontally about the pins, the pins then extending in a longitudinal direction, i.e. along the chord of the blade.

It is also appropriate to specify how the bottom and top tapes are arranged on the support secured to the hub.

In a first variant of the above embodiments and relating to said arrangement, the high and low platforms are perpendicular to said central portion, the bottom and top tapes being substantially parallel to the high and low platforms, respectively.

In a second variant of said arrangement, the high and low platforms are perpendicular to the central portion, with the bottom and top tapes presenting, relative to the low and high platforms respectively, a first angle lying in the range 5° to 15°.

In a third variant relating to said arrangement, the low and high platforms present, relative to the central portion of the support, a second angle lying substantially in the range 75° to 85°, the bottom and top tapes being substantially parallel to the low and high platforms, respectively.

Furthermore, the first end of the arm is provided with a ball joint that includes an outer ring, the ball joint being arranged inside said cuff.

Consequently, the blade is fastened to the arm of the hub via a support secured to a connection means, and also via an additional bearing point located at the first end of the arm. Thus, with the connection means preferably being constituted by a laminated abutment, the blade can move under the effects of the flapping and drag forces while continuing to be properly held to the hub.

For adjusting the pitch of the blade, a pitch control rod is secured to the support, itself fastened to the cuff. Under the action of the rod, and since the cuff is rigid in twisting, the blade tilts substantially about an axis passing through the connection means and the bearing point so as to present the desired inclination relative to the plane of the hub.

In addition, said additional bearing point is implemented in the form of a ball joint arranged inside the cuff and at the first end of the arm of the hub, being secured to the blade by fastener means.

In a first variant of the above-mentioned fastener means, the fastener means comprise at least one screw enabling the outer ring of the ball joint to be connected to a shoulder present inside the blade.

Similarly, it is possible to use a plurality of screws, e.g. four screws placed at equal distances around the circumference of the outer ring of the ball joint.

A second variant of the fastener means uses two fastener means, firstly a screw and secondly fastener means relying on friction, e.g. a flat. The outer ring of the ball joint then has a flat and is inserted inside a shoulder in the cuff, the shoulder presenting an inside shape that accurately matches the shape of the outer ring. Thus, because of friction, any turning of the blade will lead to turning of the outer ring of the ball joint.

In addition, in this variant, the outer ring is secured to a shoulder of the cuff via at least one screw.

In a third variant of the fastener means, the fastener means comprise adhesive serving to bond the outer ring to a shoulder present inside the blade.

In a fourth variant of the fastener means, the fastener means comprises a bayonet system.

MORE DETAILED DESCRIPTION

Elements that are shown in more than one figure are given the same reference in each of them.

FIGS. 1,2, and3are respectively an isometric view, a plan view, and a rear view of a blade1of the invention.

The blade1is provided with a tip2at its free end and with a cuff10at its root. In addition, the blade1is fitted along its span with at least one spar and it has an outer covering4,4′.

The cuff10is integrated in the blade1. It is naturally hollow, its outer wall including top and bottom tapes31and32coming from the spar(s) of the blade1and secured to the outer covering4′.

Consequently, the cuff10is constituted firstly by an outer covering4′ which thus extends the outer covering4of the remainder of the blade1, and secondly by top and bottom tapes31and32that are secured to the outer covering4′ of the cuff10and that extend the spar(s) of the blade1.

Consequently, the cuff10is a working component, i.e. because of its own structural architecture it transmits to the hub40for driving the blade1the forces that are exerted on the blade1, and in particular forces associated with the centrifugal effect.

It can also be seen that the cuff10is a streamlined body, with the outer three-dimensional shape of the cuff10being aerodynamic and providing geometrical, and thus surface, continuity with the three-dimensional aerodynamic shape of the blade1. This continuity can be seen particularly clearly inFIGS. 1 and 3.

FIG. 4is a detailed view of the top and bottom tapes31and32of the cuff10.

The blade1has a fiberglass spar, and more precisely a main spar3arranged substantially at the leading edge of the blade1, and secondary spars3′ and3″ arranged close to the pressure side and the suction side of the blade1.

In the cuff10, the glass fibers constituting the main spar3, and the secondary spars3′ and3″, become redistributed between at least one bottom tape32and at least one top tape31. With reference toFIG. 4, the cuff10has two top tapes31,31′ and two bottom tapes32,32′.

A first top tape31extends from a point A of the secondary spar3″ situated at the suction side of the blade1, describes a loop311, and finally returns to the secondary spar3″ at a point B adjacent to the point A. A second top tape31′ extends from a point C of the secondary spar3″ adjacent to the point B, describes a loop312, and finally returns to the main spar3.

The same path is followed from the secondary spar3′ situated at the pressure side of the blade so as to obtain two bottom tapes32and32′ which describe two loops321and322.

In addition, the cuff10comprises in succession, going from the tip2of the blade1towards the hub40, a first zone11, an intermediate zone12, and a second zone13.

In a first embodiment, in the first zone11of the sleeve, located beside the tip2of the blade1, i.e. at its outer end, the top and bottom tapes31,31′ and32,32′ are disposed in a plane that is substantially parallel to the hub40on which the blade1is arranged. Thus, the longitudinal dimension of the sections of the bottom and top tapes32,32′ and31,31′, i.e. their dimension in the X direction extending along the chord of the blade, is greater than their dimension in elevation, i.e. their dimension in a Z direction extending substantially across the thickness of the blade1.

At the opposite end, in order to secure the blade to a support60at the second zone13situated beside the hub40, the top and bottom tapes31,31′ and32,32′ are disposed in a plane substantially perpendicular to the plane of the hub40on which the blade1is arranged. The bottom and top tapes32,32′ and31,31′ then have a longitudinal dimension that is less than their dimension in elevation.

Consequently, in the intermediate zone12, the top and bottom tapes31,31′ and32,32′ are progressively flattened perpendicularly to the plane of the hub40, their longitudinal dimension decreasing as their dimension in elevation increases, and vice versa. This operation has the result of changing the orientation of the bottom and top tapes while avoiding seeking to obtain the same result by twisting the tapes, which would be harmful.

It should be observed that in a second embodiment (not shown in a figure), the sections of the bottom and top tapes have a longitudinal dimension that is greater than their dimension in elevation, whatever the zone under consideration.

Furthermore, in a variant of the first embodiment as shown inFIG. 11, the cuff has a plurality of bottom tapes32,32′ and is advantageously provided with bottom reinforcement32′″ which surrounds at least the two adjacent bottom tapes32,32′.

Similarly, the cuff having a plurality of top tapes is advantageously provided with top reinforcement that surrounds at least the two adjacent top tapes.

In addition, although the present invention does indeed provide the above-described blade, it also provides a rotorcraft rotor, and in particular the hub40for driving the blade1in rotation.

With reference toFIGS. 5 and 6, the rotorcraft rotor is thus provided with a hub40having a plurality of arms41, each arm enabling a blade1to be installed.

Consequently, the base of an arm41is provided with a passage42, and a support60passes through the passage42. In addition, the support60comprises a high platform61and a low platform62interconnected by a central portion63. The central portion63is then secured to the hub40via connection means, specifically a laminated spherical abutment64.

In addition, the cuff10of the blade is secured to the support60. Thus, the top and bottom tapes31,31′ and32,32′ are secured respectively to the high and low platforms61and62, the top and bottom tapes31,31′ and32,32′ surrounding pins61′ that pass through the high and low platforms61and62. The loops311,312,321,322of the top and bottom tapes31,31′ and32,32′ then demonstrate their importance since each surrounds a pin61′ in the vicinity of the high and low platforms61and62so as to attach the cuff10of the blade1effectively to the support60, possibly with interposition of intermediate rings that are secured to the loops311,312,321, and322. Furthermore, it is recalled that the bottom and top tapes32,32′ and31,31′ are secured to the outer coating4′ of the cuff and naturally to the remainder of the blade.

In order to allow the pins61′ to pass through the loops311,312,321,322, the outer covering4′ of the cuff10may locally include orifices. In order to avoid the presence of such an orifice, it is nevertheless possible to envisage covering the loops311,312,321, and322of the top and bottom tapes31,31′ and32,32′ in part only so as to leave an opening enabling the pins61′ to be put into place.

Finally, the central portion63of the support60is secured to a pitch control rod65, which thus continuously adjusts the pitch of the blade1to the appropriate value.

In conclusion, because of its arrangement on the connection means64, the support60enables the blade1to perform movements under the effect of flapping, drag, and twisting forces, while transmitting centrifugal forces to the hub40, the connection means64being rigid in compression.

Nevertheless, a single fastening point does not suffice for the blade to be fastened correctly. Consequently, the hub40includes an additional bearing point that serves to define the axis of rotation for pitch movements, which axis passes through the additional bearing point and the connection means64, thus enabling pitch to be adjusted accurately by means of the control rod65.

This bearing point is embodied by a self-lubricating ball joint50mounted at the first end41′ of each arm41of the hub40. This ball joint50comprises an outer ring52and an inner ring51that is secured to the first end41′ by being held by conventional means such as a circlip or a nut53, for example.

Since the cuff10of the blade1is hollow, the arm41and the ball joint50are located inside the cuff10. Consequently, the ball joint50is secured to the blade1with the help of fastener means, and in fact it is secured inside the cuff10of the blade1. Thus, the ball joint50constitutes a bearing point for the blade1.

Depending on which variant of the invention is selected, the fastener means may comprise adhesive or at least one screw enabling the outer ring52, optionally provided with a flat, to be connected to the ball joint50via a shoulder present inside the blade, or they may even comprise a bayonet system or any other equivalent means.

Furthermore,FIGS. 7 to 10are diagrams showing how the bottom and top tapes32,32′ and31,31′ are arranged on the support60, in several variants.

In a first variant of the first embodiment, shown inFIG. 7, the low and high platforms62and61are perpendicular to the central portion63of the support60. In addition, in the second zone13, the bottom and top tapes32,32′ and31,31′ are respectively parallel to the low and high platforms62and61in the transverse direction Y. Furthermore, the bottom and top tapes32,32′ and31,31′ are wound substantially vertically around the pins61′, these pins thus extending in an elevation direction Z, i.e. in the thickness direction of the blade.

In a second variant of the first embodiment, shown inFIG. 8, the low and high platforms62and61are perpendicular to the central portion63of the support60. Nevertheless, the bottom and top tapes32,32′ and31,31′ present, relative to the high and low platforms62and61respectively, a first angle α lying in the range 5° to 15°. This variant limits folding in each tape, and if necessary eliminates a zone of curvature relative to the above-described variant.

In a third variant of the first embodiment, the low and high platforms62and61present, relative to the central portion63of the support60respectively, a second angle β substantially lying in the range 75° to 85°, the bottom and top tapes32,32′ and31,31′ being respectively parallel to the low and high platforms62and61. This third variant presents the same advantages as the second variant, while limiting the size of the assembly comprising the blade1and the support60.

It should also be understood that the three variants shown inFIGS. 7 to 9have bottom and top tapes arranged respectively below and above the low and high platforms. It will readily be understood that the arrangement could be different without thereby going beyond the ambit of the invention, while maintaining the values of the first and second angles α and β identical, in particular if the bottom or top tapes are arranged respectively above and below the low and high platforms.

The same applies for the variant shown inFIG. 10, which corresponds to the second variant shown diagrammatically inFIG. 8.

In this example, the pins61′ are disposed at the free ends of the low and high platforms62and61. Nevertheless, it can be considered that the bottom and top tapes32,32′ and31,31′, or rather virtual extensions32″,31″ of said tape, still present a first angle α lying in the range 5° to 15° relative to the low and high platforms62and61.

Naturally, it will be understood that the variants shown inFIGS. 7 to 10apply equally well to the first embodiment and to the second embodiment of the invention. Nevertheless, it should be observed that in the second embodiment (not shown in a figure), the pins61′ extend in a longitudinal direction X, i.e. in the chord direction of the blade, the winding then being made substantially horizontally.

Naturally, the present invention can be subjected to numerous variant implementations. Although several embodiments are described above, it will readily be understood that it is not possible to identify exhaustively all possible embodiments. It is naturally possible to envisage replacing any of the means described by equivalent means without going beyond the ambit of the present invention.

For example, the additional bearing point of the blade against the first end of the arm of the hub is embodied in the above-described variant by a ball joint.

However this need not be so. In another variant of the invention, the first end41′ of the arm has a Teflon finger engaged in a Teflon bearing secured to the cuff, said bearing being constituted, for example, by a Teflon ring arranged inside the cuff. This arrangement allows the blade to make the necessary movements while simplifying assembly of the blade on the hub.