An aerodynamic fairing whose floor has absolutely no contact with respect to the lateral panels over the entire length of the fairing along the longitudinal axis. A free space e is provided between the floor and the lower edge of each panel. There is a longitudinal mechanical gap between the floor and each of the lateral panels. The absence of any rigid mechanical connection between the floor and the lateral panels allows the transfer of the thermomechanical stresses from the floor to the lateral panels and therefore preventing the deformation of the fairing.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of the French patent application No. 1361555 filed on Nov. 25, 2013, the entire disclosures of which are incorporated herein by way of reference.

BACKGROUND OF THE INVENTION

The present invention relates to an aerodynamic fairing of the rear portion of an aircraft pylon which is also referred to as an “aft pylon fairing” or APF.

Such an aerodynamic fairing is known in particular from the document U.S. Pat. No. 4,712,750. In this document, the aerodynamic fairing is in the form of a casing which comprises two lateral panels which are assembled together by means of frames or transverse inner reinforcement ribs which are spaced apart from each other along the longitudinal axis of the fairing, and a thermal protection floor which is fixed, on the one hand, to the lateral panels and, on the other hand, to the transverse inner ribs with which the floor is in contact.

In a position for use, such a fairing is subjected to very high temperatures which originate from the engine unit of the aircraft. These temperatures bring about deformations as a result of thermal expansions of the fairing, thus disrupting the aerodynamic qualities thereof. In particular, the thermal protection floor is subjected to a primary flow of the turbo engine at high temperature (in the order of 600° C.) while the lateral panels are subjected to a secondary flow of the turbo engine at a relatively low temperature (in the order of 150° C.) in relation to that of the primary flow. These temperature differences bring about significant thermomechanical stresses on the casing.

SUMMARY OF THE INVENTION

An object of the invention is to at least partially overcome the deformation of the structure of the aerodynamic fairing.

The subject-matter of the invention is thus an aerodynamic fairing of a pylon of a turbo engine, the fairing being in the form of a casing which extends along a longitudinal axis and which comprises, on the one hand, a floor and, on the other hand, a first lateral panel and a second lateral panel which are substantially parallel with the longitudinal axis and which are distributed at one side and the other of a plane of symmetry of the fairing, the fairing comprising at least two frames which are spaced apart from each other along the longitudinal axis and which are orientated transversely relative to this axis, each frame having, in a position for use, an upper edge, a lower edge which is fixed to an inner face of the floor and a first lateral edge and a second lateral edge to which the first lateral panel and the second lateral panel are fixed, respectively, each lateral panel having, in a position for use, an edge which is referred to as the lower edge, the floor has a width such that it is substantially less than a distance d defined between the lower edges of the lateral panels so that each lateral panel has the lower edge thereof spaced by a distance e from the inner face of the floor, and the fairing comprises at least one longitudinal reinforcement member which is associated, on the one hand, with the floor and, on the other hand, with the frame.

Each longitudinal reinforcement member comprisesa first face which is fixed to a face of a frame, the face of the frame extending transversely to the longitudinal axis, and;a second face, which is substantially perpendicular to the first face and which is fixed to the inner face of the floor.

Preferably, the fairing further comprises at least one transverse reinforcement member which is fixed to the inner face of the floor and which extends in a plane perpendicular to the longitudinal axis.

The distance e is such that 0<e<5 cm, with e preferably being from 0.3 mm to 1 cm.

Advantageously, each lateral panel comprises an aerodynamic extension which extends each of the lateral panels beyond the lower edge thereof.

A joint may be arranged between the inner face of the floor and each of the lateral panels, the joint extending between two successive frames of the fairing.

Furthermore, each lateral panel may be formed by a plurality of lateral panel portions which are fixedly attached to each other.

Other advantages and features of the invention will be appreciated from the non-limiting detailed description set out below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference toFIG. 1, an engine unit1which is fixed below a wing2of an aircraft is illustrated. The engine unit comprises a pylon4and a turbo engine6, for example, a turbo reactor, which is secured to the wing2via the pylon4.

The pylon4comprises in known manner a rigid structure8, which is also called a primary structure, which allows the turbo reactor6to be supported via known means.

Furthermore, the pylon4comprises secondary structures of the fairing type. The secondary structures of the pylon4include in particular a front aerodynamic structure24, a rear aerodynamic structure26and a rear aerodynamic fairing30, which is also called an APF or thermal shield. The terms “front” and “rear” are intended to be considered relative to a direction of advance of the aircraft encountered following the thrust applied by the turbo reactor6, this direction being illustrated schematically by the arrow7.

As illustrated inFIGS. 2 to 4, the rear aerodynamic fairing30is in the form of a casing which is open in an upward direction, that is to say, in the direction of the other structures of the securing device on which the casing is intended to be mounted, that is to say, the rear aerodynamic structure26and the rigid structure8.

Conventionally, the longitudinal axis of the rear aerodynamic fairing30is called X. On the other hand, Y is used to refer to the axis which is orientated transversely relative to the turbo reactor6and the rear aerodynamic fairing, and Z to refer to the vertical axis or height, these three axes X, Y and Z being mutually orthogonal.

A thermal protection floor31forms the lower portion of the casing while the two sides (in the longitudinal axis X) of the casing are formed by two lateral panels44. The rear aerodynamic fairing30further comprises a reinforcement member, described in the remainder of the description, which allows the lateral panels44and the floor31to be held together.

It should be noted that, as illustrated inFIG. 2, the rear aerodynamic fairing30is not planar in the plane XZ and is substantially in the form of an arrow (whose tip is orientated toward the rear) in the plane XY. This is because the rear aerodynamic fairing30is shaped so as to assume the shape of the pylon4to which it is intended to be fixed. The rear aerodynamic fairing30is closed by a frame32at the front end thereof and, at the rear end thereof, it is closed by the floor31which is inclined in the plane YZ.

On the other hand, it should be noted that, in the plane YZ, the floor31has a curved shape which opens toward the outer side or a shape which is concave with respect to the rear aerodynamic fairing30.

One of the specific features of the present invention is that the floor31of the fairing has absolutely no contact with respect to the lateral panels44over the entire length of the rear aerodynamic fairing30along the longitudinal axis X. This is because, in the plane YZ, a distance (space) e which is not equal to zero is provided between the floor31and the lower edge44eof each lateral panel44(the lower edge of each panel44being extended in the manner of the edge of the lateral panel closest to the floor31). In other words, this is equivalent to ensuring that there is a longitudinal mechanical gap between the floor31and each of the lateral panels44.

As illustrated more specifically inFIG. 4, in the YZ plane, the width L of the floor31is less, for example, by a distance equal to 2×e (two times e) than the distance d between the lower edges44eof the lateral panels. The distance e is such that 0<e<5 cm, with e preferably being from 0.3 mm to 1 cm (these two values being inclusive).

It should be noted inFIGS. 2 to 4that the rear aerodynamic fairing30has a plane of symmetry P which corresponds to a plane XZ. The floor31is provided with an outer face which is designated70inFIG. 4, this face being intended to be followed by the primary flow36which it partially delimits radially at the outer side. In order to withstand the thermal stresses, the floor31is preferably produced from Inconel®, or an equivalent titanium alloy.

As illustrated inFIGS. 2 and 3, the armature of the rear aerodynamic fairing30comprises frames32and longitudinal reinforcement members35which are fixed to the frames32. There are as many frames and longitudinal reinforcement members as necessary in order to form the rear aerodynamic fairing30according to desired dimensions. In the example illustrated inFIG. 2, four frames32and four longitudinal reinforcement members35are illustrated.

A frame32is in the form of a structural panel, which is preferably produced from titanium and which extends in the plane YZ and which comprises four edges. In the example illustrated inFIGS. 2 to 4, the frame32is in the form of an isosceles trapezium in the plane YZ. The two lateral edges32bof the frame32are each intended to receive a lateral panel44as will be described in greater detail below. The upper edge32aof some frames32(in the case where only some frames are fixed to structures of the pylon) or of all the frames32(in the case where all the frames are fixed to structures of the pylon) is arranged so as to correspond to another structure of the pylon4to which it is fixed, that is to say, for example, the rear aerodynamic structure26or the rigid structure8. The lower edge32cof each frame is fixed to the inner face71of the floor31, for example, by means of splicing connection. The lower edge32cof a frame32corresponds to the floor31and therefore has, as illustrated inFIG. 4, in a cross-section of the rear aerodynamic fairing30, a curved shape which opens toward the outer side relative to the rear aerodynamic fairing30. In order to withstand the thermal stresses, a frame32is preferably produced from Inconel® or from an equivalent titanium alloy.

In the example illustrated inFIGS. 2 and 3, a longitudinal reinforcement member35of the rear aerodynamic fairing (along the longitudinal axis X) is in the form of an angled member35. As illustrated inFIG. 3, this angled member35comprises a first face in the plane YZ and a second face in the plane XY. The first face of the angled member35is fixed to a frame32, for example, by means of screwing, while the second face is fixed to the inner face71of the floor31, for example, also by means of screwing or welding.

With reference more specifically toFIGS. 2 and 4, each lateral panel44of the rear aerodynamic fairing30extends substantially in the plane XZ and the two lateral panels44are distributed at one side and the other of the plane of symmetry P of the casing. Each lateral panel44is fixedly mounted with respect to the lateral edges32b(located at the same side of the plane P) of the successive frames32. To this end, each lateral panel44is fixed to a lateral edge32bof a frame32by means of screwing directly to the lateral edge32b, or is screwed to an intermediate component (not illustrated in the Figures) which is itself screwed to the lateral edge32b. It is possible to size the intermediate component in order to increase the distance e.

During use, the lateral panels44are provided so as to be followed externally by the secondary flow38.

The lateral panels44are, for example, produced from titanium and have a thickness in the order of from 1 mm to 7 mm. In the example illustrated inFIG. 2, the lateral panels44extend, each in one piece, from the front to the rear of the rear aerodynamic fairing30. In this configuration, the panels44allow the rear aerodynamic fairing30to be reinforced since they are fixed to each of the frames32of the fairing30.

In order to maintain efficient separation between the primary flow36which flows below the floor31and the air contained in the fairing30, that is to say, in order to prevent the primary flow36having a temperature close to 600° C. from rising and propagating within the fairing30, joints61are provided between the floor31and each lateral panel44. With reference toFIG. 4, each joint61has a first face which is fixed to the inner face71of the floor31and a second face which is fixed to the lateral panel44. Each joint61extends over the entire length, along the longitudinal axis X, between two successive frames32of the fairing30.

When the turbo reactor6is operational, the rear aerodynamic fairing30ensures the formation of a thermal barrier which serves to protect the structure8and the wing2of the aircraft from the heat released by the primary flow36, and the formation of thermal continuity between the outlet of the turbo reactor6and the pylon4. According to the invention, the hot portion of the rear aerodynamic fairing30, that is to say, the floor31, is completely mechanically insulated from the cold portions44, that is to say, the lateral panels44.

In this manner, the absence of fixing between the floor31and the lateral panels44enables the transfer of the thermomechanical stresses of the floor31to the lateral panels44to be prevented. The lateral panels44are immersed in the relatively cold secondary flow38so that they are subjected to only a very small amount of deformation owing to thermal expansion. In this manner, the general level of deformation of the aerodynamic fairing30is therefore kept relatively low, which brings about a very satisfactory aerodynamic quality, which contributes to the reduction of the effects of parasitic drag and the improvement of the performance/consumption ratio of the aircraft.

The absence of fixing between the floor31and the lateral panels44is compensated for by means of the angled members35which allow reinforcement of the structure of the fairing30and in particular the connection between the floor and the frames32in order to better withstand the mechanical stresses, in particular sound vibrations, to which the floor31is subjected.

In a first variant of the embodiment which has been described, and with reference toFIG. 5, each lateral panel44is provided with an aerodynamic extension60. An aerodynamic extension60has a thickness of a few millimeters, extending each lateral panel44beyond the lower edge44ethereof. In the plane YZ, an aerodynamic extension60has a curved shape and extends the curve formed by the floor31.

This aerodynamic extension60is fixed to a panel44, for example, by means of screwing or welding, and is produced from a material, for example, a titanium alloy, which has a strength which is different from that of the titanium used to produce the panels44. This is because it is advantageous to use different materials and thicknesses in order to produce the panels44and the aerodynamic extensions60in order to optimize the thermal and acoustic functions of the casing.

The advantage afforded by this variant is to protect the rigid structure8, the rear aerodynamic structure26and the wing2of the aircraft from the heat released by the primary flow36by preventing the flow from rising above the floor31.

In a second variant (not illustrated) of the embodiment which has been described above, the lateral panels44are formed by a plurality of lateral panel portions which are fixedly attached to each other. A portion of lateral panel being fixed to a first frame and a second frame which is directly or indirectly consecutive with the first frame.

This second variant has the advantage of simplifying the assembly of the rear aerodynamic fairing30.

It should be noted that, in the example ofFIG. 3, each angled member35is arranged so that the second face thereof is substantially in the plane of symmetry P in order to allow better distribution of the stresses to which the rear aerodynamic fairing30is subjected.

However, in a third variant (not illustrated) of the embodiment described above, a plurality of angled members35are fixed both to each of the frames32and to the floor31in order to form supplementary longitudinal reinforcement members of the rear aerodynamic fairing30along the longitudinal axis X.

In a fourth variant (not illustrated in the Figures) of the embodiment which has been described above, the angled member(s)35are positioned at variable distances from the plane of symmetry P. The advantage afforded by this variant is to reduce the extents of potential vibrations, which are capable of bringing about noise disruptions.

Furthermore, in a fifth variant (not illustrated in the Figures) of the embodiment which has been described above, at least one frame/floor assembly of the rear aerodynamic fairing30is not reinforced by one or more angled members. The advantage afforded by this variant is a saving of weight.

With reference toFIG. 3, and in a sixth variant of the embodiment which has been described above, the floor31comprises at least one transverse reinforcement member37(only 1 illustrated inFIG. 3) which is in the form of a metal profile-member which extends transversely relative to the floor31, that is to say, in the plane YZ. A metal profile-member is fixed, for example, by means of screwing, to the inner face71of the floor31. A metal profile-member is produced from a material which is suitable for the high temperatures and resistant to the expansions, for example, from the same material as the floor.

A transverse reinforcement member37reinforces the floor31which is subjected to significant vibration stresses when the turbo engine6operates. A transverse reinforcement member37allows the rigidity of the floor31to be increased in order to better withstand the mechanical stresses. A transverse reinforcement member37follows the expansion of the floor31without bringing about additional thermomechanical stresses with respect to the rear aerodynamic fairing30.

In the Figures which are appended to the above description, each frame32has been illustrated as being a solid panel. It is self-evident that, without departing from the scope of the present invention, a frame32may also have a hollow shape so as to reduce the weight of the rear aerodynamic casing30which is provided with such frames.