FR2664657A1 - Improvements to gas turbine engines - Google Patents

Abstract

The invention relates to turbomotors with two propulsive flows, one of which is variable. Means are provided for displacing the line of thrust of the variable propulsive flow of such an engine, when this flow increases, in order to prevent a substantial change in the position of the line of thrust of the engine. Application to the propulsion of vertical take-off aircraft.

Description

 The invention relates to improvements to gas turbine engines and more particularly to gas turbine engines comprising pivoting nozzles suitable for use on aircraft with short or vertical takeoff.

 Double-flow gas turbine engines with pivoting nozzles are well known in the art of turbine engines and include? in general, a front fan driven by a gas generator and two pairs of nozzles, a first pair of nozzles arranged on each side of the engine and supplied with relatively cold air coming from the fan, and a second pair of nozzles at 1 rear of engine supplied with relatively hot gases from the gas generator turbine.

By rotating each of the nozzles around an axis, the flow of the gas turbine engine can be directed rearward, downward, or forward at will. In order to allow an airplane to take off vertically with a high payload, its gas turbine engine must have a very high thrust / weight ratio. Engine thrust can be easily increased by turning fuel into the relatively cold air flow from the front swivel turbines.

 If, for a vertical take-off, the thrust of the front swivel nozzles is increased compared to that of the swivel nozzles behind the thrust line Along which acts the resultant thrust of the engine is moved forward compared to the case where the thrust of the front nozzles is not increased. The position of the engine thrust line depends on the relative magnitudes of the thrusts of the front and rear swivel nozzles and the position of their respective thrust line.

 The position of the engine thrust line is important because displacements from this line can cause serious problems in the stability of the aircraft. The problem is compounded during a vertical takeoff, since conventional aerodynamic control surfaces are ineffective in controlling the attitude of the aircraft at zero or low forward speeds.

 The present invention aims to overcome or at least reduce the above stability problems by avoiding or reducing the displacement of the engine thrust line during a selective increase in one of the propellant flows of the engine.

 The engine according to the present invention, designed for the jet propulsion of a short or vertical takeoff aircraft, comprises a turboshaft engine capable of producing two propellant flows, at least one respective nozzle capable of varying the direction of exhaust of each of the propellant flow, means for selectively burning fuel in one of the propellant flow so as to increase the thrust provided by this propellant flow, means being provided to vary at least during the downward exhaust of the two propellant flows, the position of the thrust line of said propellant flow, during the increase of this flow in order to avoid significant changes in the position of the thrust line of the engine.

 It is thus provided that, since a variable outlet surface ejection nozzle is necessary to efficiently eject an increased propellant flow, the nozzle can be adapted so that the thrust line has different positions for the increased flow and for the flow not increased.

 In one embodiment of the invention, the engine is provided with a pair of bent pipe-shaped nozzles, arranged on either side of the longitudinal center line of the engine to eject the cold propellant flow, and each nozzle ends in a nozzle of variable surface with petals of variable convergence, having petals longer on one side than on the other so that, in the most convergent position, the nozzle with petals deflects the ejected flow not increased by the axis of flow of the pivoting nozzle.

 It will be understood that the variable petal nozzle mentioned above, in its progressively less convergent configurations adapted to eject progressively increased flows, deflects by a lesser value the flow ejected from the flow axis of the pipe-shaped nozzle bent, until, in a parallel position of the nozzle petals, the flow ejected from the petal nozzle follows the flow axis of the nozzle in the form of> bent pipe.

 By rotating the swivel nozzle in the form of a bent pipe, in its convergent configuration to eject the unincreased flow, to an angular position directed forwards relative to the angular position chosen for a less convergent configuration suitable for ejecting an increased flow , it is possible, due to the deflection caused by the converging petal nozzle, to ensure that both the increased and non-increased flows are ejected vertically downwards but that the thrust line of the nozzle is more incoming for the non-increased flow than for the increased flow. The possibility of displacing the thrust line of the increased flow relative to the position of the thrust line for the non-increased flow practically avoids any displacement of the thrust line of the motor.

 In an alternative embodiment of the invention, there is provided a deflector capable of being placed, at least during vertical takeoff, so as to deflect one of said propellant flows from the engine.

The deflector may be attached to the nozzle, or alternatively, may be attached to the aircraft or to the engine structure. -
Different embodiments of the invention will now be described by way of examples with reference to the accompanying drawings in which:
Figure 1 is a plan view of a partial section of a gas turbine engine according to the invention.

 Figure 2 is a schematic view of the motor shown in Figure 1 seen from the side.

 Figures 3A and 33 are schematic views of another embodiment.

 Figure 4 is a schematic view of another embodiment.

 As shown in FIG. 1, a gas turbine engine 10, intended for the jet propulsion of a plane with takeoff and short or vertical landing, comprises a double-flow engine Il having a front compressor 12 which compresses air supplied from an air inlet 13 and supplies a first part of its outlet via a flow separator 14 to a stilling chamber 15 and the second part to a gas generator.

The gas generator comprises a high pressure compressor 17 to further compress the flow supplied by the flow separator, a combustion chamber 18 in which the flow is mixed with fuel and the mixture is burned, and a turbine 19 driven by the products. combustion and arranged to drive the high pressure compressor 17 via a shaft 20.

 A second turbine 21 is arranged downstream of the first turbine and arranged to drive the front compressor 12 by means of a second shaft 22. The hot gases leaving the second turbine form one of the propellant flows of the engine and are ejected from the engine by through a Y-piece 23 and a pair of pivoting nozzles 24, 25 arranged in lateral planes on either side of the center line 26 of the engine. The nozzles are pivotally mounted in a known manner on respective bearings 27, 28. The relatively cold flow, supplied to the stilling chamber 15, forms a second propellant flow from the engine and is ejected from the engine by a second pair pivoting nozzles 29, 30 arranged in lateral planes on either side of the center line of the engine.

 An auxiliary combustion chamber 31 is provided in the still chamber 15, in which fuel can be burned to increase the thrust of the forward cold flow.

 The front nozzles 29, 30 are pivotally mounted on respective bearings 32, 33 t each nozzle ends at its downstream end with resepctive petal nozzles 34, 35.

 FIG. 2 shows that each petal nozzle has petals 36 longer on one side 37 than on the other side 38. In addition, when the nozzle 30 in the form of a bent pipe is in its position 39 shown in dotted lines and that the petal nozzle 37 is in its most converging position for an unincreased cold flow, the direction of ejection 40 of the petal nozzle is deflected from the flow axis 41 of the pipe-shaped nozzle angled, to discharge vertically downwards. If the flow of the front pivoting nozzles is increased, the petal nozzle is open in its direct parallel configuration, and the pivoting nozzle is moved to its position 42 shown in solid lines. In position 42, the flow is always discharged vertically towards the bottom as shown by arrow 43 but is no longer deflected from the flow axis 4t of the swivel nozzle with bent pipe. The effect of the difference in angular position of the swivel nozzle with bent pipe, combined with the variable deflection of the flow coming from the variable convergence of the nozzle with petals of different lengths, is to move the line of thrust 43 of the increased flow towards the rear relative to the line of thrust 40 of the flow not increased.

 The resulting thrust line of the engine depends on the magnitude of the thrusts of the front and rear pivoting nozzles and the position of the direction of their thrust line. During vertical takeoff, the thrust of the rear pivoting nozzles remains substantially constant and acts along the same line, whatever the increase in the flow ejected by the front pivoting nozzles. The displacement of the thrust line for the flow ejected by the front pivoting nozzles, which depends on the increase in the flow ejected by the front nozzles combined with the fixed thrust line of the rear pivoting nozzles, allows the resulting thrust line engine to be such that it always passes substantially through the center of gravity 45 of the assembly of the aircraft and the engine.

 The pivoting nozzle 30, in the form of a bent pipe, can be moved to its position 44 shown in phantom to discharge backwards, and it will be understood that in this position also, the direction of ejection of the nozzle varies depending on whether the flow is or is not increased.

The problem is not as serious; than when ejected down for the following reasons.

 The center of gravity of the airplane on which the engine is installed is approximately at point 45 so that a change in the direction of ejection of the nozzles 29 and 30, when they are directed towards the rear, only causes a little variation in the plane's pitching moment. It is possible, with the aircraft control surfaces, to balance any weak pitching moment that may be produced. It is also possible to overcome any problem which may arise from a moment of pitching in forward flight by slightly varying the inclination of the rear pivoting nozzles 24 and 25. This will not cause any appreciable loss of thrust since the angular deflection of the rear nozzles need not be significant to produce a significant pitching moment on the aircraft.

 Variations in the direction of ejection of the front pivoting nozzles which occur when the nozzle exit surface is varied during a forward flight, and which are balanced by the aerodynamic control surfaces or by a variation of the 'tilt of the rear swivel nozzles, give rise to a certain induced drag. It is however possible to minimize the drag induced in each particular flight condition. Thus, in the design of an aircraft for supersonic interception missions, the induced drag can be minimized for supersonic flight conditions and the highest induced drag tolerated under subsonic flight conditions.

 When designing a particular aircraft, the choice of the relative orientations of the nozzles and the action of the aerodynamic control surfaces can be modified to take into account the movement of the aircraft's lift center which occurs in supersonic flight.

 The actuation mechanisms of the petal nozzles 34 and 35 have not been described, but those skilled in the art will understand that the known means for controlling the petal nozzles can be applied immediately to the variable petal nozzle described herein. above. In particular, it is possible to use the means described in British patent Si 1,278,801.

 It will also be understood that the actuation mechanisms of the variable section nozzle must operate downstream of the pivot bearing on which the pivoting nozzle is supported.

 Indeed, such mechanisms are necessary to transmit the signal or the actuation force beyond the pivot bearing. A suitable mechanism is described in British Patent No. 1,177,954.

 In an alternative embodiment of the inversion, a pivoting nozzle as shown in FIGS. 3A and 33 has a movable deflector 50 which replaces the nozzle with petals of variable lengths shown in FIGS. 1 and 2.

 The movable deflector 50, which is generally U-shaped, is pivotally mounted around a bearing 5G and is controlled by a mechanism 52 and cooperates with the edge 53 of a pivoting nozzle in the form of a bent pipe to allow variation. both the nozzle outlet surface and the direction of ejection of the propellant flow relative to the flow axis 41 of the nozzle with curved pipe, in a manner analogous to the nozzle with petals of variable lengths.

 According to another embodiment shown diagrammatically in FIG. 4, a deflector screen 60 is supported by the structure of the aircraft 61 and serves to deflect the flow leaving the front pivoting nozzle 61 during vertical takeoff. The front pivoting nozzles 61 are each provided with conventional nozzles 62 of variable section and with petals of equal length and the deflection of the jet from the nozzle flow axis is produced by the screen 60, a screen being provided for each nozzle. The operation of the nozzles for increased or non-increased flows is similar to that of the arrangements of the preceding figures.

 The deflector screens 60 can be retracted or deployed during a flight towards the front of the aircraft by the action of the pneumatic cylinders 63.

The deflector screens 60 can be retracted to positions 54 where they are embedded in depressions 65 which are formed on each side of the fuselage 66, during the forward flight of the aircraft. This latter arrangement has certain advantages, in particular that of avoiding the complications arising from a variable deflection of propellant flow which accompanies variations in the surface of the nozzle during a forward flight. Another advantage comes from the fact that the deflector screen can be used to increase the effective displacement of the point by which the increased thrust of the pivoting nozzles acts without increasing the length of the pivoting nozzles. Such an increase in the length of the pivoting nozzles is disadvantageous since it can create additional drag during forward flight and cause increased operating loads in the nozzle control mechanism. The loads in the nozzle control mechanism will in any case be reduced compared to those of the previous embodiments since the use of a conventional petal nozzle entrains that there are no more lever arms on which the deflected flow can act
Although the deflector screen has been shown to be supported by the structure of the aircraft, it will be understood that it can, in a variant, be supported by the structure of the engine.

 It will further be understood that, although the embodiments described describe swivel nozzles in the form of a bent pipe, other forms of this nozzles can be used. In particular, it is possible to collect the cold propellant flows from the engine in a single nozzle disposed under the fuselage and to provide means for varying the thrust line of this nozzle to compensate for the increase in cold flow.

Claims (6)

REVSoWICADIGYTS  1.- propeller suitable for propulsion by reaction of a plane with short or vertical takeoff, comprising a turbine engine capable of producing two propellant flows, at least one nozzle for each of these flows capable of varying the direction of ejection of each propellant flows, means for selectively burning fuel in one of said propellant flows to increase the available thrust of this propellant flow, characterized in that, at least when the two propellant flows are ejected downward, suitable means are provided moving the thrust league of said propellant flow during the increase of this flow to avoid a significant change in the position of the thrust line of the engine.  2.motor according to claim 1 characterized in that there are provided two pivoting nozzles of a t- n known per se capable of ejecting together said increased propellant flow, each pivoting nozzle having at its downstream end cies. means -to deflect the propellant flow from the axis of flow of the nozzle which, in combination with the variation of the angular position of the pivoting nozzle, makes it possible to vary the position of the line of thrust of the flows ejected from this nozzle .  3. ETototor according to claim 2, characterized in that said means for deflecting the propellant flow from the axis of flow of the nozzle comprises a nozzle with petals of variable surface having longer petals on one side than on another , and which can pass from a first convergent position with a relatively small surface in which the nozzle petals cooperate to deflect the propellant flow from the axis of flow of the pivoting nozzle, to a second relatively increased surface position in which the nozzle petals cooperate to allow substantially non-deflected flow through the pivoting nozzle.  4.- Motor according to claim 2, characterized in that said means for deflecting the propellant flow from the axis of flow of the nozzle comprise a deflector pivotally mounted on the pivoting nozzle, able to be moved between a first surface position relatively reduced, in which it closes the outlet of the pivoting nozzle and deflects the propellant flow of the axis of flow of the nozzle, and a second relatively increased surface position in which the pivoting nozzle is practically not closed by the deflector and in which the flow ejected by the pivoting nozzle is not substantially deflected  5.-Engine according to claim 1, characterized in that there are provided two pivoting nozzles of a type known per se capable of ejecting said increased propellant flow, and at least one deflector screen disposed adjacent to the downstream ends of the pivoting nozzles, to cooperate with the pivoting nozzles in one of its angular positions relative to the engine to modify the thrust line of pivoting nozzles by defleokising the propellant flow ejected from these nozzles.  6. An engine according to claim 5, characterized in that means are provided for retracting the deflector screen in a rest position where it is embedded in the fuselage of an aircraft on which the engine is installed.