DUCTED FAN TURBINE ENGINE

Abstract: A ducted fan turbine engine (2) includes an inner discharge nozzle (18) and an outer discharge nozzle (8) surrounding the inner discharge nozzle. The engine (2) is mounted on an aircraft wing by a pylon. The rear part of this pylon supports rollers which run in guide rails (36) which extend rearwardly along the upper portion of the outer discharge nozzle (8). The outer discharge nozzle (8) is secured in its forward operational position adjacent the engine nacelle by bolting support fittings (38) to the pylon. To remove the remainder of the engine, the support fittings (38) are unbolted from the pylon, a locating device (28) is released from the engine thrust reverser structure, and the outer discharge nozzle (8) and a primary nozzle fairing (22) are rolled rearwardly to a park position. The remainder of the engine can then be removed downwardly from the aircraft.

Description: The present invention relates to a ducted fan turbine engine, by which is meant a gas turbine engine in which a portion of the net energy is used to drive a ducted fan. The invention is particularly concerned with the outer discharge nozzle of a ducted fan turbine engine. In the operation of a ducted fan turbine engine air enters the engine core where it is ignited to rotate a turbine at the rear region of the engine. Rotation of the turbine rotates a fan in the forward region of the engine thereby directing by-pass air to flow rearwardly over the outside of the engine core. The main air stream in the engine core leaves the engine through an inner discharge nozzle, and the by-pass air leaves the engine through an outer discharge nozzle surrounding the inner nozzle. The outer discharge nozzle is required to withstand the operational pressure conditions, inertia, acoustic fatigue, and creep or other temperature/strength/time-related forms of degradation. The outer nozzle is also required to be constructed to facilitate engine removal. In order to meet the above-mentioned operational requirements, conventional outer discharge nozzles have been constructed of heat-resistant, high strength/stiffness materials such as titanium, steel and Inconels, and these outer nozzles have either been permanently attached to the engine turbine case, or supported off the aft end of the by-pass duct fixed structure. The above-mentioned materials are considerably more expensive than for example aluminium alloys both to obtain and to work. In addition, these materials are relatively heavy which means that outer discharge nozzles constructed of these materials are correspondingly heavy and require suitably robust mounting supports. In a conventional ducted fan turbine engine, the outer nozzle is supported on the inner or primary nozzle by several struts or vanes extending between the two nozzles. Because of the considerable differences in operational temperature between the inner and outer nozzles, and also because of the internal burst pressure effects, the supporting vanes or struts are subjected to high stresses which cause deformation of both the nozzles. These stresses and deformations have to be allowed for in the design of the engine. When removing from an aircraft a ducted fan turbine engine equipped with a conventional outer nozzle, either the outer nozzle is removed first from the aircraft to be followed by removal of the remainder of the engine, or the engine including the outer nozzle is removed in one operation. With both these removal techniques, the outer nozzle adds considerably to the complexity of the operation because of its weight and size. It will be appreciated that the outer nozzle is also vulnerable to being damaged during or after its removal from the remainder of the engine. A ducted fan turbine engine of the type described in the prior art portion of claim 1 is disclosed in FR-A-291091. This known turbine engine has an inner assembly D including a core engine D2 having an inner discharge nozzle, and an outer assembly having a nacelle comprising a front part B and a rear part C. The rear part C defines an outer discharge nozzle which surrounds the inner discharge nozzle of the core engine D2 and is separate therefrom. The rear part C can be displaced parallel to the longitudinal axis of the engine between the two extreme positions shown in Figures 2a and 2b. In the forward position of Figure 2a, the rear part C is secured to the fan casing D11, and in the rearward position of Figure 2b the rear part C may be separated from the fan casing to allow access for maintenance of the engine. It is clear that the rear part C cannot be moved rearwardly sufficiently to allow removal of the engine. This rear part C can be moved rearwardly only sufficiently to allow maintenance of the engine to be carried out in situ. In consequence, the turbine engine of Fr-A-2291091 suffers from the disadvantages previously described in the specification. It is an aim of the invention to alleviate the above mentioned disadvantages, and according to the invention there is provided a ducted fan turbine engine comprising an inner assembly including an inner discharge nozzle, and an outer assembly having a nacelle and an outer discharge nozzle surrounding the inner discharge nozzle, a mounting assembly extending rearwardly from the forward surface of the outer discharge nozzle along the upper portion of the nozzle, guide rails located in the mounting assembly, rollers mounted on a pylon supporting said engine, and arranged to run on said guide rails,the outer discharge nozzle being moveable between a forward operational position adjacent the nacelle and a rearward park position characterised in that the mounting assembly and guide rails are dimensioned so that when in the rearward park position the outer discharge nozzle clears the inner assembly during removal thereof from the aircraft, support means located at the forward end of the mounting assembly to attach the outer nozzle to the pylon, and locating means at the lower forward face of the outer nozzle to attach the nozzle to a thrust reverser forming part of the engine. The outer discharge nozzle may be made of any suitable light-weight material such as for example a material formed predominantly of aluminium alloys. Two examples of suitable aluminium alloys have the following specifications:- (1) DTD 5070 produced by the Royal Aircraft Establishment, Farnborough, (2) 2219 which is a U.S. specification produced in the U.S.A. by the Aluminium Association Inc. One embodiment of the invention will now be described by way of example with reference to the accompanying illustrative drawings in which:- Fig. 1A is a perspective view of a ducted fan turbine engine mounted on an aircraft wing; Fig. 1B is a perspective view of the inner and outer discharge nozzles of a fan jet engine; Fig. 1C is a diagrammatic view illustrating the mounting of the outer discharge nozzle of Fig. 1B; Fig. 1D is a perspective view of the engine of Fig 1A with the bypass air ducts open. Fig. 2 is a sectional view of the front of Fig. 1B; Fig. 3A is a side sectional view of Fig. 2; Fig. 3B is an enlarged sectional view through the material forming the outer discharge nozzle illustrated in Fig. 3A; Fig. 4 is an enlarged side view of the upper part of Fig 3A; Fig. 5 is a cross-sectional view of part of Fig. 4; and Fig. 6 is a front sectional view of part of the upper part of Fig. 1B. Referring to the drawings, a ducted fan turbine engine 2 is mounted on an aircraft wing 4 by means of a pylon 6. The engine includes at its rear, an outer discharge nozzle 8 which is shaped in the form of a truncated hollow cone open at its forward and rear ends. The forward larger diameter end abuts an engine nacelle 10, and the smaller diameter aft end is open to the atmosphere. The outer discharge nozzle 8 is constructed predominantly of aluminium alloys such as for example the previously mentioned aluminium alloys having the specifications DTD 5070 and 2219. Referring to Fig. 3B, the outer discharge nozzle 8 is constructed of inner and outer sheet members 12 and 14 separated by a honeycomb core 16. The inner and outer sheet members and the honeycomb core are made of an aluminium alloy, and the sheet members are attached to the honeycomb core by means of an adhesive. The inner sheet member 12 is perforated in order to provide sound attenuation. The outer discharge nozzle 8 is mounted coaxially with an inner discharge nozzle 18 through which the hot engine gases are exhausted from the engine core 20. As shown in Fig. 1B, a primary nozzle fairing 22 surrounds the inner discharge nozzle 18 and is coaxial with the inner and outer discharge nozzles 18 and 8. This nozzle fairing 22 smooths the by-pass air in the region of the outer discharge nozzle 8. This nozzle fairing 22 is of hollow truncated conical form open at both ends. Its larger diameter (forward) end lies in a plane approximately parallel to and forward of the plane of the forward edge of the outer discharge nozzle 8. This primary nozzle fairing 22 is attached to the outer discharge nozzle 8, and is not attached to the inner discharge nozzle 18. A bifurcation trailing edge 24 is located between the lower forward part of the inner face of the outer discharge nozzle 8 and the lower forward part of the primary nozzle fairing 22. This trailing edge 24 provides a smooth aerodynamic recombination of the left-hand and right-hand bypass airflows through the engine into a single airflow within the region of the outer discharge nozzle 8. This trailing edge 24 is attached to both the outer discharge nozzle 8 and the primary nozzle fairing 22, and extends a short distance rearwardly of the forward part of the outer discharge nozzle 8 and primary nozzle fairing 22. The primary nozzle fairing 22 consists of a conical outer skin with internal ring stiffening members and is supported by the outer discharge nozzle 8 through its attachment to a fairing 26 and the lower bifurcation trailing edge 24. A locating device 28 is positioned at the forward end of the bifurcation trailing edge 24. Referring particularly to Figs. 1B, 3A and 4, a mounting assembly is located at the upper portion of the outer discharge nozzle 8. This mounting assembly includes a base 30 and two side walls 32 extending rearwardly from the front surface of the outer discharge nozzle 8 to an end wall 34. Two guide rails 36 extend one along each of the side walls 32 and two support fittings 38 are located at the forward ends of these guide rails 36. The mounting assembly is separated from the bypass air flow path by the fairing 26 having its forward end located at the upper part of the primary nozzle fairing 22. This fairing 26 extends rearwardly and outwardly toward the inner surface of the outer discharge nozzle 8 and meets this inner surface closely behind the end wall 34. Referring to Fig. 5, eight rollers 40, which are rotatably mounted on the lower part of the pylon 6, are arranged with four rollers located in each of the guide rails 36 to support the outer discharge nozzle 8. The guide rails 36 and the rollers 40 are dimensioned and arranged so that the outer discharge nozzle 8 can be moved between a forward operational position adjacent the nacelle 10, and a rearward park position. This park position is sufficiently rearward of the nacelle 10 so that the outer discharge nozzle 8 and the primary nozzle fairing 22 clear the aft extremity of the remainder of the engine including the inner discharge nozzle 18 to allow downward vertical movement of the remainder of the engine 2 from the nacelle 10. Fig. 4 illustrates the two extreme forward and rear positions of the outer discharge nozzle 8. When the outer discharge nozzle is in its extreme forward position the two rearmost rollers 40 are located in constricted rear portions of the guide rails 36. An advantage of the invention is that the outer discharge nozzle 8 can be made of aluminium alloys which are considerably lighter and cheaper than the materials required in the conventional construction of outer nozzle assemblies. Aluminium alloys have not previously been used in the construction of conventional outer nozzles because of their poor high-temperature performance. During normal operation of a ducted fan turbine engine the hot gases exhausting from the core are shrouded by the cooler bypass air and therefore do not impinge on the outer discharge nozzle structure. During operation of the thrust reverser, however, the bypass air is diverted forwardly and no longer shrouds the hot exhaust gases from the core. It is envisaged that the outer discharge nozzle 8 will be exposed on its inner surface to an air stream at an elevated temperature for a short period during each flight. By fabricating the outer discharge nozzle 8 so that there is a good thermal pathway between the inner and outer faces of the outer discharge nozzle 8, and by cooling the outer face of the outer discharge nozzle 8 by the external air flow during flight, the heat impinging on the inner face of the outer discharge nozzle 8 is dissipated in and by the outer face. When the engine is assembled, the lower part of the aircraft pylon 6 is located in the outer discharge nozzle mounting assembly between the side walls 32 with the rollers 40 located in the guide rails 36. Referring to Fig. 6, the outer discharge nozzle 8 is retained in its forward operational position by bolting the two support fittings 38 to appropriate parts of the aircraft pylon 6 by means of bolts 42 and nuts 44. In this forward operational position the locating device 28 is engaged by the thrust reverser structure (not shown) which is immediately forward of the outer discharge nozzle assembly. When it is required to remove the remainder of the engine, the support fittings 38 are unbolted from the pylon 6, the locating device 28 is released from the thrust reverser structure, and the outer discharge nozzle 8 and the primary nozzle fairing 22 are rolled rearwardly to the park position illustrated in Fig. 4. The remainder of the engine can then be removed downwardly from the aircraft without contacting the outer discharge nozzle 8 and the primary nozzle fairing 22. The adhesive used in the construction of the outer discharge nozzle 8 must have the following properties:- (1) it must not break the thermal pathway between the inner and outer sheet members 12 and 14, (2) it must be capable of being applied in a manner and form that does not occlude the perforations of the inner sheet member 12, and (3) it must retain its properties throughout the operational life of the outer discharge nozzle 8 and throughout the operational temperature range encountered. It is to be understood that the rollers 40 can be replaced by any suitable slidable members.

Claims: A ducted fan turbine engine comprising an inner assembly including an inner discharge nozzle (18), and an outer assembly having a nacelle (10) and an outer discharge nozzle (8) surrounding the inner discharge nozzle (18), a mounting assembly extending rearwardly from the forward surface of the outer discharge nozzle (8) along the upper portion of the nozzle (8), guide rails (36) located in the mounting assembly, rollers (40) mounted on a pylon (6) supporting said engine, and arranged to run on said guide rails (36) the outer discharge nozzle (8) being moveable between a forward operational position adjacent the nacelle (10), and a rearward park position characterised in that the mounting assembly and guide rails (36) are dimensioned so that when in the rearward park position the outer discharge nozzle (8) clears the inner assembly during removal thereof from the aircraft, support means (38) located at the forward end of the mounting assembly to attach the outer nozzle (8) to the pylon (6), and locating means (28) at the lower forward face of the outer nozzle (8) to attach the nozzle (8) to a thrust reverser forming part of the engine. An engine as claimed in claim 1 including a primary nozzle fairing (22) surrounding the inner discharge nozzle (18) and within the outer discharge nozzle (8) to smooth the by-pass air in the region of the outer discharge nozzle (8). An engine as claimed in claim 2 characterised in that the fairing (22) is of hollow rearwardly tapered truncated conical form. An engine as claimed in claim 3 characterised in that the larger diameter end of the fairing (22) lies in a plane parallel to and forward of the plane of the forward edge of the outer discharge nozzle (8). An engine is claimed in any one of claims 2 to 4 characterised in that the fairing (22) is not attached to the inner nozzle (18). An engine as claimed in any one of claims 2 to 5 further including a bifurcation trailing edge (24) located between the lower forward part of the inner face of the outer discharge nozzle (8) and the lower forward part of the primary nozzle fairing (22). An engine as claimed in claim 6 characterised in that the trailing edge (24) is attached to both the outer discharge nozzle (8) and the primary nozzle fairing (22). An engine as claimed in claims 6 or 7 characterised in that the trailing edge 24 extends a short distance rearwardly of the forward part of the outer discharge nozzle (8) and the primary nozzle fairing (22). An engine as claimed in any preceding claim, characterised in that the outer discharge nozzle (8) is made of a suitable lightweight material. An engine as claimed in claim 9 characterised in that the outer discharge nozzle (8) is made of a material formed predominantly of aluminium alloys. An engine as claimed in claim 10 characterised in that at least one of the aluminium alloys has a specification:- DTD 5070 produced by the Royal Aircraft Establishment, Farnborough. An engine as claimed in claim 10 characterised in that at least one of the aluminium alloys has the specification:- US specification 2219 produced in the USA by the Aluminium Association Inc. An engine as claimed in any preceding claim characterised in that the outer discharge nozzle (8) is constructed of inner and outer sheet members (12) and (14) separated by a honeycomb core (16). An engine as claimed in claim 13 characterised in that the sheet members (12,14) are attached to the honeycomb core (16) by an adhesive. An engine as claimed in claim 13 or 14 characterised in that the inner sheet member (12) is perforated to provide sound attenuation.

Inventors: ARMSTRONG, NORMAN
Applicants: SHORT BROTHERS PLC
Application year: 1989
Main classification: B64D29
IPC codes: B64D29, B64D33