Cross bar centring mechanism for slave petals in convergent divergent nozzles with variable geometry

Abstract: Divergent petal arrangement for convergent-divergent nozzles with thrust vectoring capability through changes in the divergent section geometry, in which the position of each slave divergent petals 4 is determined by a centring mechanism 31, made up by two centring bars 14 and 27 that sliding across the sled elements 17 and 18 of the master divergent petals 2, fix a centred axial position between divergent master petals 2 and by a hanger element 13 that colliding the stop elements 25 of the master divergent petals limits the displacement on another axial position, avoiding at the same time and in conjunction with the centring mechanism 31 the displacement of the slave divergent petal 4 away from the master petals 2 when the pressure forces act from the air towards the gas side.

Description: The scope of the present invention is a divergent petal arrangement for convergent-divergent nozzles with thrust vectoring capability, as defined in claim 1. Preferred embodiments of the invention are defined in the dependent claims. Many of the existing military aircraft are equipped with convergent-divergent nozzles. These can optimise the thrust for different flying conditions by varying the nozzle throat and exit area. The manoeuvring capability of the aircraft together with the flying envelope can be enhanced by providing the aircraft with the capability of vectoring the thrust by introducing a component perpendicular to the engine axis. Thrust vectoring can be achieved with a change in the geometry of the divergent nozzle section with the convergent section remaining axisymmetric. One of the possible arrangements for the divergent sections consists of a number of master petals positioned circumferentially around a conical section. Slave petals are positioned closing the gaps between each two of the master petals on the internal side of the conical surface. Engine gas pressure pushes the slave petals against the master petals providing adequate sealing. EP-A-0 595 753, EP-A-0 687 810 and US-A-5 484 105 disclose this kind of arrangements. The position of the slave petals between master petals must avoid disengagement or circumstance in which the sides of a master and slave petal cross allowing a gas exit. Slave petals must also be capable to deflect through flexion and/or torsion to adapt their sides to the gas side surfaces of the master petals, guaranteeing proper sealing. The position of the master divergent petals can be determined by an actuation system consisting of hydraulic actuators, an actuation ring and different struts that connect each of the master divergent petals to the actuation ring. For a given position of the actuators and throat area the opening and vectoring degree of the divergent section is determined. The slave petals are positioned radially by the engine gas pressure and the reaction against the master petals. The circumferential and axial position of the each petal is determined by a centring mechanism that can be connected to the convergent section and the adjacent master petals. The mentioned mechanism must guarantee a centred position for both axisymmetric and vectored configurations. The system must also be compatible with the torsion and flexion of the slave petal. Hangers must avoid the displacement of the slave petal away from the master petals when the gas pressure is less than the outer cavity pressure on the air side of the petal. This condition is encountered for large divergence angles at determined points of the flying envelope. The present invention includes a centring mechanism for divergent slave petals which reduces the numbers of parts involved in other known solutions. The mechanism also avoids the need of one of the hangers for withstanding the forces that result from pressure acting on the air side of the petal. The mechanism is also capable of withstanding axial forces and therefore allows the removal of the joint between convergent and divergent slave petals. The present invention further includes a support element joint to the air side of the slave divergent petal to which two centring bars are attached, preferably by spherical joint to accommodate the changes in angle. Each of the centring bars has two grooves that extend from their central position to the sides. The master divergent petals have two pins or sled elements on each side. Two pins or sleds on opposite sides of the petal are forward sleds, characterised by being located closer to the throat area than the rear sleds, which stand nearer to the nozzle exit area. Each of the sled elements slides through a groove on one of the centring bars. The centring bars join the left sleds of the master divergent petal located at the right of the slave divergent petal with the right sleds of the master divergent petal located at the left of the mentioned slave petal. The bars cross each other such that each of the two joins a front sled of one master petal with the rear sled of the other petal. The position of the support of the slave divergent petal is determined by the crossing of the two centring bars. If the pressure difference on the sides of the slave divergent petal results on a net force towards the gas side of the petal, one of the two centring bars contacts the air side of the adjacent master petals limiting the displacement of the slave petal and holding it on an adequate position. In a different axial position to the one of the support of the centring bars and preferably close to the exit area, there is a second support element joint to the slave divergent petal on the air side. A hanger element with two grooves that extend from its centre to the sides, is joint preferably by spherical joint, to the second support element. A stop element, which Is allowed to move freely through the interior of one of the grooves in the hanger, is attached to the master petals, in a similar way to the sleds. The stop elements only contact the sides of the grooves when achieving a limit offset from the centred position. The purpose of the described hanger element is to limit the displacement towards the gas side when the pressure on the air side of the slave divergent petal is higher than the pressure on its gas side and to limit the offset from the centred position at the corresponding axial location, avoiding any disengagement for maximum opening of the nozzle and collision of the slave petals for minimum opening of the nozzle. These main advantages and other features and benefits will be more easily understood in the following description together with the appended drawings, in which the arrangement of the centring mechanism according to the principles of the invention, has been represented over the divergent petals as a non limiting example. In the drawings: Figure 1 represents a partial cut-away perspective of a convergent-divergent nozzle, showing the convergent and the divergent section which includes the centring mechanism/hanger element. Some of the elements have been omitted for clarity. Figures 2-5 represent the positions of the centring mechanism/hanger element for maximum and minimum opening of the nozzle and axisymmetric and vectored arrangements. Figures 6 and 7 represent the elements on the centring mechanism and hanger element together with the preferred joint arrangements. Figure 1 represents an arrangement of a convergent-divergent nozzle showing the master convergent petals 1 and the master divergent petals 2. The slave convergent petals 3 are located between the master convergent petals 1 and the slave divergent petals 4 are located between the master divergent petals 2. The position of the master convergent petals 1 and the slave convergent petals 3 is determined by conventional mechanisms stabilising the nozzle throat area. The position of the master divergent petals 2 is determined by the position of the master convergent petals 1 and actuation mechanism 7, joined to the casing 22. The position of the actuation system 7 determines the position of the actuating ring or semi-ring 8 which can move parallel to the engine axis 33 and rotate around a radial axis 34. The struts 9, which are joined at one side to the actuating ring 8 by a cylindrical joint 10 and on their other side to the gas side of the master divergent petal 2 by a spherical joint 11, determine the position of the master divergent petals 2 for each position of the master convergent petals 1. The master divergent petal 2 consist of a front section 23 joined to the convergent master petal 1 by a cylindrical joint 5, determining the divergence angle of the master divergent petal 2. The front side 23 is joined to the rear side 24by a cylindrical joint 6, determining the yaw angle of the master divergent petal 2. The sleds 17 and 18 and the stop element 25 are joined to the master divergent petal 2 at the air side. The pins or sleds 17 and 18 slide though the grooves 26 of the centring bars 14 and 27 which build up the centring mechanism 31. Each centring bar 14 and 27 has two grooves 26 that join a forward sled 18 of a divergent master petal 2 with a rear sled 17 of the neighbour divergent master petal 2. The centring bars 14 and 27 are joined with the support 12 of the slave divergent petal 4 preferably by a spherical bearing 19 which is held in position by a threaded joint 20. The support 12 is joined to the slave divergent petal 4 from the air side, preferably at an axial position close to the nozzle throat area. The support 12 is positioned at the crossing between the nozzle throat area. The support 12 is positioned at the crossing between bottom 27 and top 14 bars, centring the salve divergent petal 4 between the sides of the divergent master petals 2 and providing the adequate axial position. Figure 2 shows the position of the centring bars 14 and 27 for an axisymmetric nozzle arrangement with maximum opening. The forces that try to move the slave divergent petal 4 away from the centred position are transmitted through the centring bars 14 and 27 to the sleds 17 and 18 on the master divergent petal 2. The lateral force on the master divergent petal 2 is transmitted though the struts 9 to the actuating ring 8 and to the engine casing 22. In the case of failure of one of the centring bars 14 or 27 or of one of the sleds 17 or 18, one of the sleds contacts the centring bar at the end 15 of the groove 26, allowing only small fluctuations around the centred position and avoiding the risk of disengagement or crossing between the sides of the master and slave divergent petals 2 and 4. Figure 3 shows the positions of the centring bars 14 and 27 for an axisymmetric nozzle arrangement with minimum opening. The forces that try to move the slave divergent petal 4 away from the centred position are transmitted to the sleds 17 and 18 through the sides of the groove 26. Figures 4 and 5 show the position for the centring bars 14 and 27 for vectored nozzle arrangements with maximum and minimum openings. If the pressure of the engine gases is larger than the air side pressure, the slave divergent petal 4 is supported against the master divergent petals 2. If the air side pressure is larger than gas pressure, the slave divergent petal 4 moves away from the master divergent petals 2 up to a position in which the lower centring bar 27 contacts the master divergent petal 2 avoiding further movement of the slave divergent petal 4 towards the gas side. A hanger element 13, similar to the centring bars 14 and 27 is joined to a support element 28 located on the air side of the slave divergent petal 4 at an axial position preferably closer to the divergent exit area. The joint between the hanger 13 and the support 28 is done preferably by a spherical joint 21 retained by a threaded bolt 29. The hanger element 13 has two grooves 30 through which the stop elements 25 are allowed to move. The diameter of the stop elements 25 is smaller than the width of the grooves 30 in order to avoid any interference with the axial positioning of the slave divergent petal 4, which is determined by the centring mechanism 31. For vectored positions such as the one shown in figure 5, the offset from the centred position at the axial location of the hanger element 13 is limited by contact between the stop elements 25 and the sides 32 of the groove 30. For maximum area nozzle arrangements, the risk of disengagement between master divergent petals 2 and slave divergent petals 4 , is eliminated by limiting the maximum offset from the centred position with the outer side 35 of the groove 30. For minimum area nozzle arrangements, the risk of collision between slave petals is eliminated by the inner side 16 of the groove 30.

Claims: Divergent petal arrangement for convergent-divergent nozzles with thrust vectoring capability for aircraft engines, which consists of a number of master divergent petals (2) joined to master convergent petals (1) and to an actuation ring (8) through struts (9), and of a number of slave divergent petals (4), each one being mounted between two master divergent petals (2) through a centring mechanism (31), characterised in that the centring mechanism (31) comprises two centring bars (14, 27) joined to a support (12) of the slave divergent petal (4) and in that each centring bar (14, 27) joins, through grooves (26) that extend from the centre to the sides of the centring bars (14, 27), two out of a total of four sleds (17, 18) of the adjacent master divergent petals (2), each of said two sleds (17, 18) being mounted on one of the two master divergent petals (2) adjacent to the slave divergent petal (4), such that the crossing between the centring bars (14, 27) determines the centred position between master divergent petals (2) and the correct axial position of the slave divergent petal (4). Arrangement according to claim 1, wherein the two centring bars (14, 27) are joined to the support (12) of the slave divergent petal (4) by a spherical joint (19). Arrangement according to any of claims 1 and 2, further including a hanger element (13) joined to a support (28) of the slave divergent petal (4), wherein the hanger element (13) joins through two slots (30) that extend from its centre to the sides, two stop elements (25) of the master divergent petals (2) such that the offsets from the centred position of the slave divergent petal (4) on the axial position of the support (28) are limited, avoiding the risk of disengagement between slave divergent petals (4) and master divergent petals (2) and the displacement of the slave divergent petals (4) away from the master divergent petal (2) under pressure forces on the divergent section acting from the air side towards the gas side. Arrangement according to claim 3, wherein the hanger element (13) is joined to the support (28) of the slave divergent petal (4) by a spherical joint (21).

Inventors: ELORRIAGA VICARIO JAVIER, ELORRIAGA VICARIO, JAVIER
Applicants: TURBO PROPULSORES IND, INDUSTRIA DE TURBO PROPULSORES S.A.
Application year: 1997
Main classification: F01K1
IPC codes: F02K1