GB2303179A - Vertical thrust gas turbine engine - Google Patents

Abstract

In a VTOL aircraft the depth of the fuselage limits the space available for mounting a direct lift engine, that is an engine dedicated to providing vertical thrust and in which the engine is mounted with its axis vertical. The available depth of the airframe is very likely too short to accommodate the overall length of the engine and its exhaust nozzle. The exhaust nozzle 42 is arranged therefore for telescopic movement relative to the engine casing so that it may be retracted within the fuselage 6,8 when the engine is not in use. A door (60)(Fig.2) may be provided to close an exhaust nozzle aperture 12 in the fuselage and linked to deployment of the nozzle.

Description

GAS TURBINE ENGINE The invention relates to a gas turbine engine arrangement. In particular it concerns a lift engine having a retractable nozzle.

A known arrangement for producing vertical lift for a fixed wing aircraft has at least one lift engine or lift fan disposed with its rotational axis in a vertical orientation. Lift is then provided by operating the engine or fan which generates thrust in the axial direction. A drawback with this kind of arrangement can be the overall length of the lift engine. The vertical height of the engine is inevitably limited to the available depth within an aircraft fuselage and any protrusion of the engine assembly outside of the fuselage envelope will create aerodynamic drag during normal forward flight. In the case of vertical lift engine comprising, as it must, an intake duct, compressor, combustor, turbine and a short exhaust duct terminating in a nozzle its overall axial length is often longer than the fuselage depth. The present invention is intended to remedy this drawback.

According to the present invention there is provided a gas turbine engine arrangement comprising a gas turbine engine, an exhaust nozzle mounted for axial translation relative to the engine and actuator means for moving the nozzle.

Preferably the axially translatable exhaust nozzle is arranged to telescope relative to an external casing of the engine, and may be mounted concentrically with the engine casing.

The invention and how it may be carried into practice will hereinafter be described in more detail with particular reference to the accompanying illustrations in which: Figure 1 shows a longitudinal section through a lift engine incorporating an example of a retractable nozzle, Figure 2 shows a single fuselage door for closing the nozzle aperture.

The drawing shows a lift engine, generally indicated at 2, which is installed in a vertical orientation ie with the engine axis in a vertical direction in the fuselage of an ASTOVL aircraft (ASTOVL is an acronym for Advanced Short Take-Off and Vertical Landing). The upper and lower fuselage surfaces of the aircraft are indicated at 6 and 8 respectively. The upper surface 6 is formed with an intake aperture 10 through which the engine 2 receives intake air, and the lower surface 8 is also formed with an exhaust aperture 12 through which the engine exhausts. The apertures 10 and 12 may be closed by hinged or sliding doors (not shown) or some other form of closure means.

The lift engine 2 comprises a two shaft bypass engine.

Immediately within intake 10 is an annular array of fixed inlet guide vanes 14. Underneath these vanes is a fan or LP compressor 16 driven via a first shaft 18 by a LP turbine stage 20. The fan airflow is divided by an annular splitter 22 into a bypass airstream and a core engine flow. The core engine comprises a four stage HP compressor, generally indicated at 24, which is driven via a second shaft 26 by an HP turbine stage 28.

The compressor outlet 30 feeds the core airstream into an annular combustor 32 which exhausts in a vertically downward direction through the two turbine stages 28 and 20. The bypass airstream is carried by an annular bypass duct defined by the engine outer casing 36 and the compressor casing 38 and the combustion chamber outer casing 40. The turbine exhaust from LP turbine 20 and the bypass stream from duct 34 discharge into a convergent nozzle 42. Because of the overall length (or height) of the axial flow lift engine the exit plane of the LP turbine is very close to the plane of the lower fuselage surface 8, therefore leaving insufficient axial length within the fuselage boundaries to accommodate the nozzle 42.

The solution proposed according to the present invention provides that nozzle 42 is telescopically mounted with respect to the engine casing 36, thereby enabling the nozzle to be deployed to its correct operating position shown by solid lines in the drawing, and when the lift engine is inoperative to be retracted to a position shown by dashed lines wherein the nozzle is housed completely within the fuselage boundaries.

The convergent nozzle 42 comprises a parallel sided cylindrical section 44 which transforms towards its lower end into a convergent frusto conical portion 46. The cylindrical section 44 is mounted concentrically with a parallel cylindrical downstream end of the engine outer casing 36 whereby the cylindrical nozzle section 44 may be translated telescopically relative to the engine casing 36. The length of this cylindrical section is chosen such that when the nozzle is fully extended the frusto conical section thereof occupies its preferred design position relative to the turbine exhaust.In this position, as is evident in the drawing, the nozzle 42 extends through the fuselage exhaust aperture 12 and terminates blow the lower fuselage surface 8, but as can be seen from the position of the dashed line in its retracted position the nozzle lies wholly within the boundary of the lower fuselage surface 8.

The cylindrical portion 44 of the nozzle 42 is located within the downstream end of casing 36 by sliding surfaces. The upstream end of section 44 is outwardly flared at 48 to slidably engage the inner face of casing 36. Similarly the downstream end of casing 36 is provided with an inwardly flared lip 50 which slidably engages the outer surface of the cylindrical section 44. These features 48 and 50 maintain reasonable alignment of the nozzle and, when the nozzle is fully extended, engage one with the other to provide an annular limit stop.

Extension of the nozzle 42 is controlled by actuator means comprising, in the illustrated example, four jacks 52 equidistantly spaced around the exterior of the engine casing.

The actuators 52 are mounted on the exterior of the engine casing 36 at fixed mounting points 54 and the movable output actuator rod 56 are connected to four equidistantly spaced mounting brackets on the exterior of the nozzle 42. In one embodiment of the nozzle the four jacks are hydraulically actuated to apply force to a piston carried by the output rods 56 to move those rods axially. The actuator jacks may be synchronised by an interconnecting flexible mechanical drive (not shown). In alternative embodiments the operation of the actuators may be electrically synchronised by means of position potentiometers position signals of which were used by an integrated control system to control individual hydraulic valves in each jack. In yet another embodiment the actuators may comprise electrically driven linear/actuators.

In operation the vertical lift engine is started and run only when vertical lift thrust is required, and in normal flight the engine is inoperative the its intake and exhaust may be concealed behind fuselage doors or other closure means. When lift thrust is required these doors are retracted or opened and the nozzle 42 extended before the lift engine is started, thus actuator loads during nozzle extension are relatively light and engine thrust loads are not a factor. When the engine is running additional nozzle loads are transferred to the engine casing through interengagement of the annular lips 48 and 50.

This also means that hot exhaust gases are ducted clear of the aircraft skin. The inner surface of nozzle 42 is also shielded from hot turbine exhaust gas by the relatively cool bypass air stream as a result of which the nozzle may be constructed of lightweight materials for example carbon/composite material.

In another embodiment of the invention, as an alternative to positive actuation of the nozzle 42, the nozzle is biased, for example by spring loaded bias means replacing the jacks 52, so that the nozzle automatically deploys to its extended position, with retraction being accomplished by closure of the fuselage cover door. The cover door may comprise a single door hinged, for example, along its forward edge or two parts hinged longitudinally along port and starboard sides of the exit aperture 12 so that these half doors meet along the centreline of the fuselage and engine. Each of the doors carries a roller engaged with a track formed on the exterior surface of the nozzle and the doors are positively driven such that in a closing operation the rollers carried by the doors bear against the nozzle tracks against the spring bias force urging the nozzle into its retracted position.

Figure 2 shows a nozzle arrangement including a single closable fuselage door 60 for the fuselage exit aperture 12. The door 60 is hinged towards its forward edge at 62 to a fuselage structural member. The forward edge of the door structure is formed with short upstanding arms 64 at either side. The distal ends of these arms 64 are coupled to door actuating means (not shown) which may comprise linear stroke actuators driven hydraulically or electrically, for example, in synchronism with the nozzle actuation means 52.

In an arrangement in which the nozzle 42 is spring-biased towards its deployed, extended position the fuselage closure door 60 and the nozzle 42 may be interconnected for actuation by the door actuation means.

Claims (10)

1 A gas turbine engine arrangement comprising a gas turbine engine, an exhaust nozzle mounted for axial translation relative to the engine and actuator means for moving the nozzle.

2 A gas turbine engine as claimed in claim 1 wherein the axially translatable exhaust nozzle is arranged to telescopic relative to an external casing of the engine.

3 A gas turbine engine as claimed in claim 1 or claim 2 wherein the axially translatable exhaust nozzle is mounted concentrically with the engine casing.

4 A gas turbine engine as claimed in any preceding claim wherein the axially translatable exhaust nozzle comprises a fixed area convergent nozzle.

5 A gas turbine engine as claimed in any preceding claim wherein the actuator means comprises a plurality of actuators spaced apart around the exterior of the engine casing.

6 A gas turbine engine as claimed in claim 6 wherein the actuator means comprises a plurality of powered actuators.

7 A gas turbine engine as claimed in claim 6 wherein the actuator means comprises means for storing mechanical energy arranged to bias the nozzle to its deployed position.

8 A gas turbine engine as claimed in claim 7 further comprising closure means arranged to cover the nozzle aperture when the nozzle is retracted and the closure means is closed.

9 A gas turbine engine as claimed in any preceding claim wherein the engine comprises a lift engine.

10 A gas turbine engine as claimed in claim 9 wherein the lift engine is a bypass fan lift engine.