Thrust reversing device for jet aircraft engines

Abstract: Thrust reversing device for jet aircraft engines, comprising a pair of semi-shells (5) which can be moved between a retracted position where they define a part of the exhaust nozzle (1) and a deployed position where they define a deflection for the thrust reversion and an end collar (9) installed at the termination of the exhaust nozzle (1) so as to move between an advanced position, where said collar (9) defines the termination of the discharge nozzle (1) forming a discharge nozzle of ideal shape, and a retracted position, which allows the deployment of said semi-shells (5).

Description: The invention relates to thrust reversers for jet aircraft engines. In particular, the invention takes regard for thrust reversers of the so called target type, which is for instance illustrated in U.S. Patent No. 4.966.327 or in FR-A-2 638 783. Thrust reversers of this kind include a pair of half-shells hinged to the wall of the engine exhaust nozzle. The shells are movable from a retracted position in which they form a portion of the exhaust nozzle to a deployed position where they form a wall reversing the jet output by the nozzle. The thrust reverser includes actuators which are in charge of the rotation of the half-shells between their retracted and deployed positions. A thrust reverser of this known type is illustrated in figures 1, 1a and 2 of the drawings. Figures 1 and 2 are schematic side elevations showing the half-shells in their retracted and deployed positions respectively, while figure la shows the device with retracted shells in a perspective view. With reference to these figures, number 1 indicates the exhaust nozzle of an aircraft jet engine which terminates with a substantially round edge 2. Nozzle 1 extends beyond edge 2 with two diametrally opposite lugs, hinged to which in 4 there are two movable half-shells 5 which can be set in a retracted position, shown in figures 1, 1a, where they form the last part of the exhaust nozzle, and a deployed position, shown in figure 2, where they form the wall which deflects forward the jet output by the engine to obtain the thrust inversion. The movement of the shells is actuated by two hydraulic cylinders 6, each held by lug 3, and each inclusive of a piston, not shown in the drawings, connected to two elements 7 which exit the cylinder body through two slits in its sides. Elements 7 are connected through actuating rods 8, hinged to the two shells 5. As shown by figure 2, the curved edge 5a of the two half shells 5 enters into contact in the deployed position of the shells. Due to this, when the shells are retracted, they define an exhaust portion of the exhaust nozzle, with a "fish mouth" cross section. As the edge 5a of each shell has a variable thickness, in particular thicker in the middle and thinner at the edges, such "fish mouth" profile gives way to a pair of steps 5b (see figure 1a) close to the edge of exhaust nozzle 1, which cause a degradation of the aerodynamic characteristics of the exhaust duct of the engine during normal flight, with a consequential loss of performance. The geometry of the exhaust duct of a jet aircraft engine is in fact defined by the manufacturer so as to optimise performance in terms of thrust and of specific fuel consumption at the different operating rates. The geometry selected by the manufacturer corresponds therefore to the the best compromise between the various geometries in the different flight conditions. A modification to the exhaust duct caused by the adoption of a thrust reverser of the type described above, will therefore necessarily cause an overall loss of performance throughout the flight profile of the aircraft except at touch-down and also, in the specified case above, an appreciable loss of trust coefficient CT and of discharge coefficient CD compared to an ideal nozzle, with a consequential reduction of the available thrust and/or increase of specific fuel consumption for equal engine rates. Steps 5b described above also cause a base drag which increases the drag at null aircraft lift. The purpose of this invention is to implement a reverser of the type described above which does not introduce any of the inconveniences above and which can be derived from the known solution above without having to make any modification to the engine discharge nozzle and/or to the cowling of the engine and without requiring a greater complexity of the actuators of the shells. To achieve this result, the invention regards a thrust reverser as specified at the start of this description, with the characteristic of including a collar which is free to move axially on the termination of the discharge nozzle starting from a fore position, where the collar defines a portion of the discharge nozzle termination and a rear position to allow the deployment of the two half-shells. This collar has a front edge which is shaped so as to be complementary to the end edges of the two half-shells when these are retracted and a trailing edge which defines a circular profile contained in a plane perpendicular to the axis of the discharge nozzle. In a preferred actuation form, these actuators are also connected to the end of such collar, so as to determine the movement of the collar between its fore and rear positions simultaneously with the displacement of the two half-shells from their retracted and deployed positions. Further features and advantages of the invention become clear from the description which follows, with reference to the drawings attached, which are provided purely as examples without posing any limitation to the invention, where: figure 3 is a schematic side elevation with cross section of a thrust inverter according to the invention, with the shells retracted, figure 4 shows the device of figure 3 in its active inverting position, with shells deployed, figure 5 is a perspective view partially cross-sectioned, of the device of figure 3, figure 6 is a further perspective view of the device when passing from the retracted to the deployed thrust reversing position, figure 7 is a perspective view with partial cross-section which shows the half-shells in their deployed position, figure 8 is a larger scale view with partial cross-section of a detail of the actuator devices, figure 9 is a perspective view corresponding to that of figure 8 in a different operating condition, figure 10 is a cross section along X-X of figure 8 and figure 11 is a cross section along XI-XI of figure 10. In these figures, parts common to figures 1, la and 2 are shown with the same reference numbers. In the device presented by this invention, a terminal collar 9 is positioned so as to move axially along the discharge nozzle 1 of the jet engine. Collar 9 includes two extended lugs 10, set on diametrally opposite parts of collar 9, which are free to slide along the lengthwise reinforcements 11 of discharge nozzle 1 (figures 6, 7). As clearly shown in the drawings, collar 9 shows a circular trailing edge 12 which corresponds to a circular profile in a plane which is perpendicular to the axis of the nozzle and a leading edge 13 which is complementary to edges 5a of half-shells 5 in their retracted position. In particular, collar 9 can be relocated from a fore position shown in figures 3, 5 and a rear position, shown in figures 4, 6, 7 along the direction of the axis of the discharge nozzle, simultaneously with the relocation of the two shells 5 from their retracted to their deployed positions. In the fore position of collar 9, to which the retraction of the shells 5 corresponds, the leading edge 13 of collar 9 enters into contact with the terminal edges 5a of the shells 5, so that the collar becomes the terminal portion of the discharge nozzle, defining an ideally shaped termination, such as to avoid the inconveniences introduced by the known technique which have been presented above. In the aft position, collar 9 allows that the two shells 5 can be deployed so as to achieve the thrust inversion required. In the preferred form of actuation which is also shown in the drawings attached, the same actuating cylinders 6 used to move the half-shells 5, also simultaneously determine the movement of collar 9 from its fore to its aft position. In this case it is however to be noted that discharge nozzle 1 has a conical shape, so that cylinders 6 are placed along the surface of a cone, while collar 9 and its lugs 10 must shift along a direction which is parallel to the axis of such cone. To take this condition into account, each hydraulic cylinder 6 (see figures 8, 9) carries a support at its end secured by fixed bars 6a to the nozzle structure 1, equipped with fixed lugs 14, 15 which protrude from such support and are rigidly connected to it, to which the opposite ends of two cylindrical guiding rods 16 are fixed, set parallel to the discharge nozzle axis . Guiding rods 16 of each actuator 6 drive a further rod 17 which has a pair of through holes 17b into which guiding rods 16 are inserted. Each rod 17 is connected solidly to the internal surface of a lug 10 of collar 9. In this manner, collar 9 can slide over the discharge nozzle 1 according to a direction which coincides with its axis. Each rod 17 carries a pair of actuating rods 8 hinged by an end in 17a and with the opposite end hinged in 5c to a half-shell 5, so that a displacement of rods 17 along guiding rods 16 causes a rotation of shells 5 around hinges 4 through rods 8. The building details of hydraulic cylinders 6 are not provided, as they are of the known type and because these details do no pertain to the scope of this invention. With reference to figure 10, number 18 is the piston inside hydraulic cylinder 6, which is equipped with two lugs 19 protruding from cylinder 6 through two slits 20 opened lengthwise in it. The lugs 19 serve to slide rod 17 along cylindrical rods 16 in response to a movement of piston 18 within cylinder 6. As such movements take place along different axes, the two appendices 19 are operationally connected to rod 17 through slides which move in two transversal grooves 21 in this rod. In operation, the activation of the two actuating cylinders 6 in one direction, causes the deployment of the two half-shells 5 towards their final thrust reversing position and simultaneously causes collar 9 to be pushed back. The same actuator cylinders 6, activated in the opposite direction, provide for returning the devices back to their flight position, where the two shells 5 are retracted and collar 9, in its for position, defines the terminal part of the discharge nozzle of the jet engine which now has an optimum exhaust profile. Of course, with the principle of this invention still valid, the build details and the forms of actuation may vary substantially compared to what has been described above and illustrated as an example, without leaving the general context of this invention.

Claims: Thrust reversing device for a jet aircraft engine including a discharge nozzle (1), said device comprising: a pair of semi-shells (5) hinged to the wall of the discharge nozzle (1) of the engine, which can be moved between a retracted position where they define a part of the exhaust nozzle (1) and a deployed position where they define a wall which deflects forward the jet output by the nozzle (1), and actuators (6) carried by nozzle (1) to cause the rotation of the two semi-shells (5) between their retracted and deployed positions, characterised by the fact that said thrust reversing device also comprises a collar (9) installed so as to move axially at the termination of the exhaust nozzle (1) between a fore position, where said collar (9) defines the termination of the discharge nozzle (1) and an aft position, which allows the deployment of said semi-shells (5), said collar (9) having a leading edge (13) complementary to the terminal edges (5a) of the two semi-shells (5) in their retracted position and a trailing edge (12) which defines a circular profile contained in a plane which is substantially perpendicular to the axis of the discharge nozzle (1). Thrust reversing device as claimed in claim 1, characterised by the fact that said actuators (6) are also connected to said terminal collar (9) so as to determine the movement of collar (9) between its fore and aft positions simultaneously with the displacement of the two semi-shells (5) between their retracted and deployed positions. Thrust reversing device as claimed in claim 2, characterised by the fact that said collar (9) has two longitudinal lugs (10) which face forward and are free to slide on the discharge nozzle structure (1) parallel to the axis of such discharge nozzle (1). Thrust reversing device as claimed in claim 3, characterised by the fact that said actuators consist of two actuating cylinders (6) installed at opposite sides of the external surface of the discharge nozzle (1) and include a piston (18) operatively connected to said semi-shells (5) and to said lugs (10) of collar (9). Thrust reversing device as claimed in claim 4, characterised by the fact that each lug (10) of collar (9) can slide along guide rods (16) which are parallel to the axis of the discharge nozzle (1) and solidly connected to the body of the actuator cylinder (6). Thrust reversing device as claimed in claim 5, characterised by the fact that each lug (10) of collar (9) is provided with a bracket (17) which can slide on said guide rods (16) and is connected to piston (18) of hydraulic cylinder (6) through a sliding interface of two cylindrical pivots (19) which are solidly connected to piston (18) and emerge from the body of cylinder (6) through lengthwise slits (20) made in it in corresponding transversal grooves (21) made in said bracket (17), said bracket (17) being in turn connected through pivoted rods (8) to the two half shells (5).

Inventors: GATTI ALFREDO, GERBI LUIGI, GATTI, ALFREDO, GERBI, LUIGI
Applicants: FINMECCANICA SPA, FINMECCANICA S.P.A. - RAMO AZIENDALE ALENIA
Application year: 1993
Main classification: F02K1
IPC codes: F02K1