GB1567941A

GB1567941A - Nozzles for gas turbine engines

Info

Publication number: GB1567941A
Application number: GB1064076A
Authority: GB
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1976-03-17
Filing date: 1976-03-17
Publication date: 1980-05-21

Description

(54) IMPROVEMENTS IN NOZZLES FOR GAS TURBINE ENGINES (71) We, ROLLS-ROYCE LIMITED a British Company of 65 Buckingham Gate, London, SWIPE 6AT, formerly ROLLS ROYCE (1971) LTD of Norfolk House, St.

James's Square, London, SW1H 4JR, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to nozzles for gas turbine engines and has particular reference to a variable area convergentdivergent discharge nozzle suitable for use with engines capable of propelling aircraft at supersonic speeds.

Variable area convergent-divergent nozzles are known in the art which comprise a circumferential array of axially extending nozzle petals arranged around the circumference of the gas discharge duct of a gas turbine engine. The nozzle petals are alternately master petals, which are directly actuated, inter-digitated with slave petals which follow the movement of the master petals. The petals are connected together either through a slotted or an overlapping arrangement whereby relative movement of the master and slave petals is possible to allow for area variation of the nozzle.

It is a continuing problem in the design of final discharge nozzles, for gas turbine engines, in particular in the design of nozzles which can be changed from a convergent to a convergent-divergent configuration to provide relatively increasingly lighter nozzles of relatively economic construction which require relatively low actuating loads for their operation.In our copending U.K. patent application numbered 18889/75 (Serial No. 1,533,986) and entitled "Improvements in Nozzles for Gas Turbine Engines" there is described and claimed a variable area nozzle for a gas turbine engine comprising a circumferential array of nozzle petals arranged about the discharge opening of a jet pipe, there being in respect of at least some nozzle petals respective curved guide tracks mounted on the jet pipe and respective pairs of axially spaced apart rollers mounted on these nozzle petals wherein the upstream roller of each pair runs on a radially outer surface of one of the curved tracks and the downstream roller runs on a radially inner surface of the curved track and wherein all of said rollers are simultaneously movable along their respective curved tracks thereby to cause movement of the nozzle petals to vary the nozzle outlet area.

Preferably for this nozzle the circumferential array of nozzle petals comprises interdigitated master and slave petals in which only the master petals are provided with said respective pairs of rollers and the movement of the master petals results in a corresponding movement of the slave petals.

In one embodiment of the nozzle the curved tracks are inter-connected by an arrangement of members surrounding the jet pipe whereby radially outward loads exerted on the curved tracks by the downstream rollers are borne at least partially by tension in said members.

In a further embodiment fairing flaps are supported from structure upstream of the discharge opening of the nozzle whereby the downstream ends of the fairing flaps are in sliding contact with the downstream end of the discharge nozzle and the fairing flaps are interdigitated so that a smooth profile is achieved between structure surrounding the jet pipe of the engine and the discharge opening of the nozzle.

This nozzle configuration described as above, and in the previous patent application allows, by suitable curving of the nozzle petals and the curved tracks, both the nozzle throat area and the final divergent flare angle of the nozzle to be simultaneously varied. This arrangement is satisfactory for use with subsonic and supersonic aircraft for operation up to speeds of about Mach 1.2, but for higher speeds of operation significant performance gains are known to be available if the divergent flare angle of the convergent divergent nozzle can be varied independently of the nozzle throat area.

The best aerodynamic performance of the nozzle is achievable when the divergent flate angle of the nozzle can be varied irrespective of the particular nozzle throat area that is chosen. This arrangement however, tends to complicate the nozzle and a satisfactory practical compromise between complexity and nozzle performance is achieved by relating the divergent flare angle to the nozzle throat area at all values up the maximum nozzle throat area and only allowing the divergent flare angle to be further variable when the maximum throat area has been reached.

Certain nozzles have been constructed having this latter capability but have been relatively heavy and complex, have required separate operating linkages for varying the throat area and the divergent flare angle of the nozzle, have incurred relatively large actuating loads and have required considerable space to accommodate the various components of nozzle structure. The increased space necessary to accommodate prior art nozzle structures has resulted in wider engine nozzles than is desirable and this has in turn led to a compromise in the shape of the fairing flaps resulting at certain speeds in breakaway of the flow around the outside of the nozzle with attendant disadvantages.The present invention, which is a modification of the earlier invention seeks to provide a means of allowing the aforesaid variation of the divergent flare angle of a convergent-divergent nozzle and of at least reducing the magnitude of the problems associated with prior art nozzles.

According to the present invention there is provided a variable area nozzle for a gas turbine engine comprising a circumferential array of nozzle petals, including certain master petals, arranged about the discharge opening of a jet pipe, there being in respect of each said master petal an upstream roller and a downstream roller the rollers being axially spaced apart and engaging respective radially outwardly facing and radially inwardly facing guide track surfaces fixed relative to the jet pipe and arranged for changing the inclinations of the petals relative to the jet pipe on operation of means for simultaneously moving the petals axially along the guide track surfaces, the nozzle being further characterised by hinges disposed between upstream and downstream portions of the nozzle petals, the hinges being located downstream of the rollers, and by means for pivoting the downstream nozzle petal portions about the hinges to vary their inclination to the upstream nozzle petal portions thereby to vary the divergent flare angle of the nozzle.

Preferably said means for pivoting the downstream nozzle petal portions and the means operable to move the nozzle petals axially along the guide surfaces are mechanically connected whereby gas loads operative on the downstream petal portions reduce the power required for nozzle throat area variation.

Nozzles constructed in this way allow the attainment of many desirable advantages.

The disposition of the guide track surfaces which allows the inclination of the nozzle petals to change simultaneously with axial movement thereof means that full area variation of the nozzle can take place for relatively short axial movement of the nozzle petals. The disposition of the rollers means that the gas loads operating on the nozzle petals are largely reacted by contact loads on the guide track surfaces, which can then conveniently be borne by tension in a polygonal skin interconnecting at least the radially inwardly facing guide track surfaces.

The relative disposition of the rollers and guide track surfaces necessary to the operation of the nozzle means that the operating mechanism is required to carry only relatively light operating loads. The operating mechanism needed is itself relatively lightly loaded because the light operating loads combined with the short operating movement of the nozzle means that the work supplied in operating the nozzle is significantly relatively reduced.

The interconnection between the operating mechanisms for the upstream and downstream petal portions allows gas pressure operating on the downstream petal portions to be used to counteract the forces necessary to move the upstream petal portions and to counteract the drag forces caused by flow through the nozzle which pull the petals in a downstream direction.

The general disposition of the various elements of the nozzle can conveniently be disposed around the jet pipe of the nozzle so that the width of the nozzle is kept relatively small thus simplifying the problem of fairing the nozzle into other engine or aircraft structure.

The disposition of the nozzle operating elements means they are advantageously shielded from hot exhaust gases which allows them to be made from relatively lightweight materials.

Preferably the means for pivoting the downstream nozzle petal portions comprises a plurality of struts connected by their downstream ends to the downstream petal portions and by their upstream ends to further rollers running on profiled guide tracks and wherein nozzle operating movement applied to the further rollers is also applied to said upstream rollers by further struts connecting the further rollers with the upstream rollers.

The relative movements of the upstream and downstream nozzle portions, which control the overall nozzle configuration, are thus dependent on the profile and orientation of the respective guide tracks.

In one embodiment there is provided a stop capable of limiting axial movement of the upstream rollers and the profiled guide tracks permit further movement of the further rollers to produce only variation in the divergent flare angle of the downstream nozzle portions once the maximum nozzle throat area has been reached.

In a preferred embodiment the means for simultaneously moving the petals axially along the guide track surfaces and the means for pivoting the downstream nozzle petal portions comprise a pair of axially spaced apart axially translatable unison rings each connected by ties to the upstream and downstream nozzle petal portions respectively and means for producing differential axial movement of the two unison rings.

Said means for producing differential axial movement may comprise either a series of screw jacks having two axially spaced apart screw threaded portions of differential pitch. In an alternative form of the invention said differential movement is produced by introducing generally wedge shaped members at intervals around the unison rings and interconnecting the unison rings by a series of pairs of struts, each pair of struts being pivoted to the unison rings by their one ends and pivoted together at a roller by their other ends, the rollers bearing on the wedge shaped members thereby producing differential movement of the rings on operating movement applied to the downstream unison ring.

By the above described embodiments in which only a single operating linkage is used to vary the nozzle geometry it is possible to vary the relationship between the nozzle throat area and the divergent flare angle of the nozzle but only according to a predetermined regime controlled by the detailed mechanical arrangement of the nozzle.

By the addition of a further operating mechanism to the above embodiments it is possible to vary the divergent flare angle irrespective of the nozzle throat area setting.

Thus in a further embodiment the axial positions of the two unison rings are independently controlled by the provision of two sets of screw jacks.

In a modification the wedge shaped members disposed between the unison rings are themselves axially movable by an independent screw jack system.

In a further modification in which the position of the downstream nozzle petal portions is controlled by the said further rollers running on profiled guide tracks the orientation of the further profiled guide tracks with respect to said curved track surfaces is adjustable whereby the divergent flare angle of the nozzle may be altered independently of the setting of the nozzle throat area.

Advantageously the said orientation is adjustable by pivotally supporting the further profiled guide tracks about respective centres lying on a circle concentric with the jet pipe. In this manner the actuating loads for adjusting the orientation of the further profiled guide tracks are kept relatively low.

Embodiments of the invention will now be described by way of example only with reference to the following drawings in which, Figure 1 is a diagrammatic illustration of a gas turbine engine embodying a variable area nozzle of the present invention Figure 2 is a sectional view through a master nozzle petal of the engine of Figure 1 in the convergent position of the nozzle, Figure 3 is a plan view of Figure 2 illustrating details of the operating linkage, Figure 4 is a section on the line IV - IV of Figure 2 to an enlarged scale, Figure 5 is a section on the line V - V of Figure 2 to an enlarged scale, Figure 6 is a section on the line VI - VI of Figure 2 to an enlarged scale, Figure 7 is a sectional view through a slave nozzle petal, Figure 8 is an elevation of the discharge opening of the nozzle taken on the line VIII - VIII of Figure 2, Figure 9 is a sectional view similar to Figure 2 of a modified nozzle construction.

Figure 10 is a longitudinal section through a master petal of an alternative nozzle construction shown in the convergent position, Figures 11, 12 illustrate the nozzle of Figure 10 in intermediate and convergent divergent operating positions respectively, Figure 13 is an isometric view of the nozzle of Figure 10 illustrating an operating mechanism, Figure 14 is an isometric view similar to Figure 13 showing an alternative nozzle operating mechanism, Figure 15 is a further isometric view similar to Figure 13 showing a further alternative nozzle operating mechanism.

Referring now to Figure 1, a gas turbine engine comprises a compressor 1, combus tion equipment 2, a turbine 3 and a jet pipe 4 terminating in a propulsion nozzle 5.

In Figure 2 there is shown a sectional view through one master petal 10 of a circumferential array of petals arranged about the periphery of the jet pipe 4 and forming the propulsion nozzle 5. Attached to each master petal is an upstream roller 13, and a downstream roller 14 which engage respective radially outwardly and inwardly facing guide track surfaces 15, 16 which are formed on opposite sides of a curved beam 17, fixedly mounted on the jet pipe 4 by a flange 18.

The complete nozzle has twelve master petals and twelve interdigitated slave petals.

The nozzle petals and their associated operating mechanism are enclosed by a circumferential array of overlapping fairing flaps 19 which will be later described in further detail. There is provided one curved beam 17 in respect of each master petal, and each beam is of the same radius of curvature and all the centres of curvature of the curved beams lie equally spaced apart on a circle formed about the centre line of the jet pipe.

The master nozzle petals, and similarly the slave nozzle petals are divided by hinges 21 into upstream and downstream nozzle petal portions 22. 23 respectively which allows the divergent flare angle of the nozzle to be varied as required.

In operation the master nozzle petals are moved simultaneously axially along the guide track surfaces by means of operating movement applied to a unison ring 24 from a screw jack 25. Movement of the unison ring 24 is applied to the master nozzle petals, as can be seen in more detail by referring also to Figure 3, via links 26 which pull on further rollers 27 constrained to move in a fixed guide track 28. Movement of the rollers 27 is communicated to the upstream rollers 13 via parallel struts 29.

This causes the nozzle petals to move along the guide tracks between a convergent configuration in which the nozzle throat is formed at the final discharge end 30 of the nozzle and a convergent divergent configuration in which the nozzle throat is formed at the end of the discharge opening 31 of the jet pipe 4.

The precise positioning of the downstream nozzle petal portions 23 is controlled by linkages 32 which operate a series of bellcranks 33 disposed around the downstream petal portions 23 and which interconnect alternate downstream petal portions via links P and Q to synchronise their movement.

The linkages 32 each comprise an upstream strut 34 and a downstream strut 35 pivotally connected together at 36, and the pivot 36 is constrained to move in a parallel sided guide 37 formed in the upstream petal portion 22. The downstream struts 35 are connected to levers 38 for operating the bellcranks 33. In operation gas loads on the downstream petal portions produce compressive forces in the struts 34 and 35 which are communicated to the operating mechanism via the further rollers 27 and which thus reduce the force required from the operating mechanism.

The precise profile and orientation of the guide tracks 28 in relation to the disposition of the guide track surfaces 15, 16 controls the relative movements of the upstream and downstream nozzle petal portions. In particular it will be noted that after a first range of axial movement of the nozzle petals the upstream rollers 13 will abut stops 41. When this occurs the nozzle is at its maximum throat area setting and further operating movement of the unison ring will cause the further rollers 27 to move along the guide tracks 28 thus varying the divergent flare angle of the nozzle.

At the end of the jet pipe 4 there is provided an annular seal 49 which bears on the master and slave petals and substantially prevents leakage of propulsive gases.

A reheat liner 50 is maintained in a concentric position within the jet pipe 4 and in known manner is cooled by a flow of relatively cool air which flows along the annular passage 51 formed between the reheat liner 50 and the jet pipe 4. This flow of cooling air also film cools the master and slave petals.

Turning now to Figures 4, 5 details of the upstream and downstream roller assemblies will be explained. In particular in Figure 4 it will be seen that the upstream roller 13 comprises a pair of roller bearings 43 mounted via an inner race 44 on a cross shaft 45. The shaft 45 is supported in side plates 47, 48 which are part of the master petal and serve also to support the downstream roller 14 as shown in Figure 5. The downstream roller comprises a pair of roller bearings 52 and is constructed in like fashion to the upstream roller 13. Gas pressure within the nozzle acting on the master petals presses the downstream rollers 14 against the radially inwardly face guide track surfaces 16 and the upstream rollers 13 against the radially outwarly facing guide track surfaces 15 of the curved beams 17 and there is a net radially outward load applied to the curved beams. This radially outward load, is borne by tension in a polygonal skin 53 which connects the twelve curved beams together around the periphery of the nozzle.

To either side of the master petal 10 can be seen the interdigitated slave petals 54 whose side edges 55, 56 can slide relative to the master petal 10 to permit variation of the nozzle exit area. The slave petals like the master petals are divided by hinges into upstream and downstream portions and the downstream portions are connected to the outer fairing flaps 19 as can be seen in more detail from Figures 6 and 7.

From Figures 6 and 7 it will be understood that rollers 57 supported by respective yokes 58 attached to the fairing flaps 19 run in respective inclined grooves 59 cut in radial outwardly extending flanges 61 attached one to each slave petal 54. In this manner the slave petals 54 move together with the fairing flaps 19 which themselves move as the master petals 10 are actuated.

The fairing flaps, which can be further seen in Figure 7 and of which there are twenty four in the complete nozzle, are each connected at their upstream ends 62 by hinges 63 to structure 64 which surrounds the jet pipe 4. This structure may be either aircraft or engine structure and the fairing flaps allow the outer surface of the nozzle to blend smoothly with said structure 64 and thus to converge in a conventional boat tail angle for the avoidance of base drag. At their downstream ends the fairing flaps surround and are flush with the outer surface of the master and slave petals in the convergent position of the nozzle but lift and slide over the outer periphery 65 of the petals during operation of the nozzle until in the convergent-divergent configuration the downstream ends of the fairing flaps coincide with the downstream ends of the petals.

The fairing flaps 19 are made from a lightweight honeycomb.

Whilst in this embodiment the slave petals have been shown to be interconnected with the fairing flaps it is equally possible to use other known methods of operating them from the master petals.

In a modification of the above described nozzle shown in Figure 9 two distinct operating mechanisms for the upstream and downstream petal portions are utilised in order to vary the divergent flare angle of the nozzle for any particular nozzle throat area setting whilst retaining the benefits of the compactness and lightness of the basic nozzle configuration.

These benefits are achieved by divorcing the further profiled guide tracks 28 from the curved beams 17 and mounting them, via a plate 71 to respective pivot axes 72 which are disposed on a circle concentric with the jet pipe 4. Providing the pivot axes 72 are not concentric with the centres of curvature of the further profiled guide tracks 27, pivoting of the guide tracks, which is effected by a jack 75 will cause the divergent flare angle of the nozzle to vary.

As the further roller 27 is connected to the upstream roller 13 by struts 29 adjustment of the orientation of the profiled guide track via the jack 75 will lead to simultaneous movement of the roller 13 on the curved guide track 15. This will then result in simultaneous adjustment of the throat area of the nozzle with further repercussions on the divergent flare angle. Should this be unacceptable it is necessary to provide a feedback of the position of nozzle throat which can be used in conjunction with the nozzle throat area and divergent flare angle to trim the nozzle.

The feedback system whilst not specifically illustrated as will be readily appreciated, can conveniently be related to the axial position of the unison ring 24 and the angular orientation of the curved guide tracks, or to some other readily measured parameter representative of the actual nozzle setting.

Turning now to Figures 10, 11, 12 three operating positions of an alternative nozzle construction are illustrated in which like numerals refer to parts common to the earlier embodiments.

In the Figures it will be noted as before that master petals 10 are provided with upstream and downstream rollers 13 and 14 which run respectively on radially outwardly and inwardly facing guide track surfaces.

In distinction to the previous embodiment the upstream rollers are moved directly by ties 81. The linkages 32 for the downstream petal portions 23 are directly connected to a second unison ring 83 and differential axial movement between the unison rings is used to vary the nozzle throat area and the divergent flare angle of the nozzle.

As before slave petals are interdigitated with the master petals and the downstream slave petal portions are connected to the fairing flaps 19 for movement together therewith.

The differential axial movement between the two unison rings may be produced in a variety of ways; in particular in Figure 13 an isometric view of the nozzle illustrates the use of a plurality of ball screw jacks 84 to produce the necessary movement. The ball screw jacks, of which there are six around the nozzle are anchored to fixed structure 85, and have two axially separated screw threaded portions 86, 87 of differing pitch.

With this arrangement rotation of the ball screws produces differential movement of the two unison rings and the difference in pitch regulates the relationship between the nozzle throat area and the final divergent flare angle of the nozzle.

In the modification illustrated in Figure 14 it will be noted that the ball screw jacks 84 operate only on the upstream unison ring 83 and that the downstream unison ring 82 is connected to the upstream unison ring via pairs of struts 88, 89.

The struts 88, 89 are pivoted together by their one ends at rollers 91 and are pivoted by their other ends to the unison rings 83, 82 respectively.

Interposed between adjacent pairs of rollers 91 are fixed wedge shaped members 92 and in operation the loads prevailing on the nozzle cause the rollers to be pressed against the wedge shaped members. Thus as the position of the downstream unison ring is adjusted, the rollers 91 and wedge shaped members 92 co-operate to differentially adjust the position of the upstream unison ring 83. The profile of the wedge controls the relative settings of the nozzle throat area and the divergent flare angle.

By the modification of Figure 15 the positions of the wedge shaped members 92 are adjustable by a separate set of ball screw jacks 93 which enables the divergent flare angle of the nozzle to be varied for any particular nozzle throat area setting.

The positioning of the downstream flap portions can be achieved by various methods other than the bell cranks illustrated in Figures 1 - 9. One particularly useful alternative is illustrated in Figures 13, 14, 15 from which it can be seen that the linkage 32 is modified by replacing struts 35 (Figure 3) with a pair of diverging struts 94, 95. Struts 94, 95 pair with equivalent diverging struts from adjacent linkages 32 and serve to position a circumferential array of wedge cams 96. Rollers 97 supported from arms 98 on the downstream petal portions bear on the profiled sides of the wedge cams and thus axial movement of the wedge cams produce in response to actuating movement of the linkage varies the divergent flare angle of the nozzle.

It will be understood that by profiling the wedge cams the relationship between the nozzle throat area and the divergent flare angle of the nozzle can readily be varied.

It will be apparent that many variations may be made to the nozzle construction and in particular that whilst the radially inwardly and outwardly facing guide track surfaces have been illustrates as being formed on either side of a curved beam they could well be separate constructions and indeed their profiles can be varied to suit the particular requirements of a particular nozzle.

WHAT WE CLAIM IS: 1. A variable area nozzle for a gas turbine engine comprising a circumferential array of nozzle petals, including certain master petals, arranged about the discharge opening of a jet pipe, there being in respect of each said master petal an upstream roller and a downstream roller, the rollers being axially spaced apart and engaging respective radially outwardly facing and radially inwardly facing guide track surfaces fixed relative to the jet pipe and arranged for changing the inclinations of the petals relative to the jet pipe on operation of means for simultaneously moving the petals axially along the guide track surfaces, the nozzle being further characterised by hinges disposed between upstream and downstream portions of the nozzle petals, the hinges being located downstream of the rollers and by means for pivoting the downstream nozzle petal portions about the hinges to vary their inclination to the upstream nozzle petal portions thereby to vary the divergent flare angle of the nozzle.

2. A nozzle according to claim 1 and in which the means for pivoting the downstream nozzle petal portions and the means operable to move the nozzle petals axially along the guide surfaces are mechanically connected whereby gas loads operative of the downstream petal portions reduce the power required for nozzle throat area variation.

3. A nozzle according to either of claims 1 or 2 and in which said means for pivoting the downstream nozzle petal portions comprises a plurality of struts connecting the downstream nozzle petal portions to further rollers running in a profiled guide track and further struts connecting the further rollers to the upstream rollers and wherein said means for moving the nozzle petals along the guide track surfaces comprises a motor arranged to pull the further rollers along the profiled guide tracks.

4. A nozzle according to claim 3 and in which said profiled guide tracks are pivotally connected to fixed structure and in which a further motor is provided for pivotally displacing the profiled guide tracks.

5. A nozzle according to either of claims 1 and 2 and in which the means for pivoting the downstream nozzle petal portions comprises a plurality of struts connected to a first unison ring and in which the means for moving the nozzle petals along the guide track surfaces comprises a second unison ring and a mechanical coupling between the two unison rings for producing differential movement thereof.

6. A nozzle according to claim 5 and in which the mechanical coupling between the two unison rings comprises a series of ball screw jacks having two screw threaded portions of differential pitch each engaging a respective unison ring.

7. A nozzle according to claim 5 and in which the mechanical coupling between the two unison rings comprises a plurality of pairs of struts each strut of each pair of struts being pivotally connected by its one end to a respective unison ring and by its other end to the other strut of the pair and each pair of struts supporting at their common pivotal connection a roller and adjacent pairs of rollers bearing on opposite surfaces of a wedge shaped member.

8. A nozzle according to claim 7 and in which the wedge-shaped members are col

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. respectively. Interposed between adjacent pairs of rollers 91 are fixed wedge shaped members 92 and in operation the loads prevailing on the nozzle cause the rollers to be pressed against the wedge shaped members. Thus as the position of the downstream unison ring is adjusted, the rollers 91 and wedge shaped members 92 co-operate to differentially adjust the position of the upstream unison ring 83. The profile of the wedge controls the relative settings of the nozzle throat area and the divergent flare angle. By the modification of Figure 15 the positions of the wedge shaped members 92 are adjustable by a separate set of ball screw jacks 93 which enables the divergent flare angle of the nozzle to be varied for any particular nozzle throat area setting. The positioning of the downstream flap portions can be achieved by various methods other than the bell cranks illustrated in Figures 1 - 9. One particularly useful alternative is illustrated in Figures 13, 14, 15 from which it can be seen that the linkage 32 is modified by replacing struts 35 (Figure 3) with a pair of diverging struts 94, 95. Struts 94, 95 pair with equivalent diverging struts from adjacent linkages 32 and serve to position a circumferential array of wedge cams 96. Rollers 97 supported from arms 98 on the downstream petal portions bear on the profiled sides of the wedge cams and thus axial movement of the wedge cams produce in response to actuating movement of the linkage varies the divergent flare angle of the nozzle. It will be understood that by profiling the wedge cams the relationship between the nozzle throat area and the divergent flare angle of the nozzle can readily be varied. It will be apparent that many variations may be made to the nozzle construction and in particular that whilst the radially inwardly and outwardly facing guide track surfaces have been illustrates as being formed on either side of a curved beam they could well be separate constructions and indeed their profiles can be varied to suit the particular requirements of a particular nozzle. WHAT WE CLAIM IS:

1. A variable area nozzle for a gas turbine engine comprising a circumferential array of nozzle petals, including certain master petals, arranged about the discharge opening of a jet pipe, there being in respect of each said master petal an upstream roller and a downstream roller, the rollers being axially spaced apart and engaging respective radially outwardly facing and radially inwardly facing guide track surfaces fixed relative to the jet pipe and arranged for changing the inclinations of the petals relative to the jet pipe on operation of means for simultaneously moving the petals axially along the guide track surfaces, the nozzle being further characterised by hinges disposed between upstream and downstream portions of the nozzle petals, the hinges being located downstream of the rollers and by means for pivoting the downstream nozzle petal portions about the hinges to vary their inclination to the upstream nozzle petal portions thereby to vary the divergent flare angle of the nozzle.

8. A nozzle according to claim 7 and in which the wedge-shaped members are col

lectively axially displaceable by separate motor means.

9. A nozzle according to any preceding claim and in which the master petals are interdigitated with slave petals, and the slave petals have downstream portions pivotally connected to upstream portions and are connected to external nozzle fairing flaps for movement together therewith.

10. A nozzle according to any preceding claim and in which the downstream nozzle petal portions of the master petals are mterconnected for simultaneous movement by a series of bell cranks.

11. A nozzle according to any preceding claim and in which said means for pivoting the downstream nozzle petal portions comprises a plurality of struts connected to produce axial movement of a circumferential array of generally wedge-shaped cams and there being one cam for each alternate downstream petal portion and each interdigitated downstream petal portion being provided with a pair of arms each arm straddling a respective adjacent cam and bearing on a cam surface thereof.

12. A nozzle substantially as herein described with reference to and as illustrated in Figures 1,2, 3, 4, 5, 6, 7, and 8, or Figure 9 or Figures 10, 11 and 12, or Figure 13 or Figure 14 or Figure 15.