AREA CONTROLLED, THRUST VECTORING VANE CASCADE

Abstract: A plurality of cascade vanes (28, 29, 30) pivot in unison for selectably directing a flow of gas (20) therethrough. A flow regulating vane (36) pivots opposite the cascade vanes (28, 29, 30) for maintaining a constant collective gas flow area.

Description: This invention relates to a method for selectably diverting a flow of gas and concerns a vane cascade having a plurality of variable position, pivoting vanes for directing a flow of gas. The use of a cascade of individually pivotable vanes for selectably diverting a flow of gas passing therethrough is a known method for achieving a desired thrust direction in an aircraft or other similar application. Such systems may be used to provide additional lift during certain flight maneuvers, or to reverse the normal direction of thrust from a gas turbine engine or the like in order to decelerate the aircraft during landing or at other times. A method for selectably diverting a flow of gas passing through a vane cascade as recited in the precharacterizing portion of independent claim 1 and a vane cascade for exhausting a vectorable flow of gas therethrough as recited in the precharacterizing portion of independent claim 4 are disclosed in EP-A-0 180 534. Upper and lower sets of louvers are disposed in an exhaust nozzle assembly and are pivotable to direct the exhaust gases over a wide range of directions including either a forward or a rearward thrust vector. The louvers are closed during forward thrust operation and open during reverse thrust and thrust vectoring operation. Another variable position vane cascade is shown in US-A-3,100,377. The outlet of a gas turbine engine is provided with a plurality of individual movable vanes for directing the engine exhaust either rearwardly along the main axis of the aircraft during normal forward flight, or downwardly, transverse to the major aircraft axis for providing additional upward lift during vertical or short takeoff or landing maneuvers. The vanes traverse a range of motion between these two positions, thus providing a plurality of intermediate thrust vectors for transitioning between these two flight modes. In US-A-3,335,960 there is shown a gas turbine engine outlet equipped with a plurality of movable vanes for providing both thrust vectoring and thrust control by spoiling the gas flow stream in order to reduce thrust. While known in the prior art, such variable position vane cascades typically utilize a plurality of actuators for aligning each vane according to an individual schedule or other control signal to provide the desired collective thrust vector and/or gas outlet flow area. In particular, for vane cascades wherein it is desired to provide thrust vectoring for a flow of exhaust gas from a gas turbine engine or the like, it is desirable that the collective exhaust gas flow area through the cascade be held nearly constant in order to avoid inducing instability in the operation of the gas turbine engine. As will be appreciated by those skilled in the operation of gas turbine engines, a rapid increase or decrease in the area of the engine exhaust nozzle can lead to engine rotor overspeed or compressor blade stalling, respectively. For vane cascades having a plurality of vanes pivoting in unison for vectoring thrust, it will be appreciated that the nozzle outlet area measured normal to the flow of gas from the vectoring cascade will be a function of the sine of the vane angle. Thus, the outlet area of the cascade having vanes positioned at a 45° angle with respect to the general cascade plane will be approximately 70% of the flow area with the vanes oriented normally, i.e. 90°, with respect to the cascade plane. This nearly 30% variation in gas flow area can occur in applications wherein a variable vane cascade is provided for discharging a flow of exhaust gas from a thrust-reversing and/or thrust-maneuvering gas turbine engine exhaust nozzle. In such applications it is desirable to orient the plane of the cascade transversely with respect to the aircraft major axis, pivoting the individual vanes in unison to direct the flow of exhaust gases rearwardly for achieving a forward thrust flight mode, laterally for achieving high transverse and no axial thrust, and forwardly for achieving a rearward or reversing thrust. As will be appreciated by those familiar with such thrust vectoring needs and applications, the time of transition between any two thrust modes may be on the order of 1-2 seconds, especially during landing or high speed evasion maneuvers. As with any aircraft application, the requirement for reduced weight and complexity is a high priority goal for designers in this field. Multiple actuator arrangements, while providing high flexibility in positioning individual vanes, are relatively heavy and complex to operate. What is required is a simple, single actuator, variable position vane cascade which simultaneously vectors the flow of gas therethrough while maintaining a constant collective gas flow area. Accordingly, the object of the present invention is to provide a method and a vane cascade of the type recited for achieving with low constructional complexity a constant collective gas flow area over the range of vane motion corresponding to the thrust vectoring operation of the vane cascade. According to the invention, to achieve this, there is provided a method for selectably diverting a flow of gas passing through a vane cascade having a plurality of adjacent individual vanes each pivotable about a corresponding plurality of parallel pivot axes lying in a plane, said cascade vanes further being pivotable over a thrust vectoring range of motion including a first pitched orientation, a second orientation normal to the plane of the vane cascade, and a third pitched orientation opposite to the first orientation, characterized in that the method comprises the steps of pivoting all of the cascade vanes in unison, providing a flow regulating vane adjacent one end vane of the plurality of cascade vanes, the flow regulating vane being pivotable about an axis parallel to the plurality of cascade vane pivot axes, and pivoting the flow regulating vane oppositely with respect to the pivoting of the cascade vanes over the thrust vectoring range of motion to achieve a constant collective gas flow area over said range of vane motion. In further accordance with the invention there is provided a vane cascade for exhausting a vectorable flow of gas therethrough, comprising a plurality of spanwisely parallel cascade vanes, each vane pivotable about a corresponding parallel pivot axis passing therethrough, and said cascade vanes being pivotable over a thrust vectoring range of motion between a first pitched orientation with respect to the plane of the cascade, a second normal orientation with respect to the plane of the vane cascade, and a third, oppositely pitched orientation with respect to the vane cascade, characterized by means for pivoting said cascade vanes in unison, a flow regulating vane disposed adjacent one end vane of the plurality of cascade vanes and pivotable about an axis parallel to the cascade vane pivot axes, and means responsive to the orientation of the cascade vanes, for pivoting the flow regulating vane in the opposite angular direction from the cascade vanes as the cascade vanes move within the thrust vectoring range of motion. Advantageous features of the method and vanes cascade to achieve a constant collective gas flow area are recited in the dependent claims. Attention is directed to EP-A-0 292 421 and to EP-A-292 422 wherein a method for selectably diverting a flow of gas passing through a vane cascade and a vane cascade for exhausting a vectorable flow of gas therethrough as claimed herein are also described. Both these and other features and advantages of the cascade arrangement will be apparent following a review of the following description and drawing figures, wherein : Figures 1a and 1b show an axial cross section of a gas turbine engine exhaust nozzle including a vectoring vane cascade. Figures 2a, 2b, and 2c show a schematic view of a vane cascade operating over a vectoring range of motion. Figures 3a, 3b, 3c, and 3d show a cross-sectional view of a stowable vectoring vane cascade including a drive linkage therefor. Figures 4a, 4b, and 4c show a stowable vectoring vane cascade with an alternative linkage therefor. Figure 5 shows a cross-sectional view of a vectoring vane cascade having double flow regulating vanes. A third embodiment of the linkage is also disclosed therein. Figure 6 shows a graphical representation of the variation of exhaust gas flow area of a vectoring vane cascade both for a simple unison cascade arrangement and for the flow controlled arrangement according to the present invention. Figure 1a shows a cross-sectional view of an exhaust nozzle 10 taken through the central axis 12 of the gas turbine engine (not shown) and the nozzle 10. The nozzle is of 2D configuration, having a pair of spaced-apart sidewalls 14 and movable upper and lower flap assemblies 16, 18 extending therebetween. Such nozzles typically discharge the exhaust gas 20 from the gas turbine engine rearwardly for providing forward thrust for driving an aircraft or the like. Occasionally it is desired to provide reverse or other direction thrust for the purpose of maneuverability or for arresting velocity during landing of the aircraft. The nozzle as shown in Figures 1a and 1b may provide such alternative thrusting capability as shown in Figure 1b wherein the forward flaps 22, 24 of the flap assemblies 16, 18 pivot into a blocking relationship with respect to the axial exhaust flow path defined as in Figure 1a. Exhaust gases 20 thus are diverted laterally as shown in Figure 1b, passing out of the nozzle 10 through opposed vane cascades 26. As will be described in more detail hereinbelow, the opposed cascades 26 contain a plurality of movable vanes for selectably directing the flow of exhaust gases 20. Such a nozzle as shown in Figures 1a and 1b is disclosed and described in greater detail, although without the vane cascades 26 according to the present invention, in US-A-4,641,782. FIRST EMBODIMENT Figures 2a and 2b show an individual vane cascade 26. Exhaust gases 20, possibly diverted from the axial gas flow path as shown in Figures 1a and 1b, flow into the vane cascade 26 from above as shown. The vane cascade 26 includes a plurality of cascade vanes 28, 29, 30, each pivotable about a corresponding axis 31, 32, 33, extending spanwisely through the respective vane 28, 29, 30. Figure 2a shows the cascade vanes 28, 29, 30 in a first, forward thrust position wherein the vanes 28, 29, 30 are pitched rearwardly for diverting the exhaust gas 20 for producing thrust in the opposite, or forward direction. A static structure 34 surrounds and supports the cascade 26 by any of a number of means, such as bearings at the vane span ends, well known in the art and not discussed further herein. The vane cascade 26 is provided with a flow regulating vane 36 disposed adjacent to one of the cascade end vanes 30 and pivotable about a spanwisely extending axis 37 which is parallel to the axes 31, 32, 33 of the cascade vanes 28, 29, 30. As shown in Figure 2a and in subsequent Figures 2a and 2b, cascade vanes 28, 29, 30 are pivotable in the direction of the allows 38 in unison about their respective pivot axes 31, 32, 33 for selectably directing the exhaust gas 20 laterally as shown in Figure 2b, or forwardly as shown in Figure 2c, as well as a variety of other directions therebetween. For purposes of reference hereinafter the lateral discharge as shown in Figure 2b is termed "a second position" wherein the cascade vanes 28, 29, 30 are oriented generally normal to the plane 40 of the cascade defined by the cascade vane axes 31, 32, 33. Such second position vanes, by directing the exhaust gas laterally with respect to the cascade 26, produce a high lateral thrust without a significant axial component. As discussed hereinabove, the gas flow area defined by a plurality of vanes pivotable in unison is a function of the sine of the angle 42 formed between the chordal lines 44 of the vanes 28, 29, 30 and the plane 40 of the vane cascade. The undesirable variation in area as the cascade vane angle varies over a vectoring range of motion defined by the first, 45° position of Figure 2a, the second 90° position of Figure 2b and the third 135° position of Figure 2c is controlled by the opposite rotation 46 of the first flow regulating vane 36 as shown in Figures 2a-c. Thus, in Figure 2a, the flow regulating vane 36 is oriented chordally parallel to the adjacent end vane 30, for directing the exhaust gases 20 rearwardly in parallel with the cascade vanes 28, 29, 30. As is shown in Figure 2b, the flow regulating vane 36 has rotated so as to be chordally perpendicular with respect to the adjacent end vane 30, blocking off a portion of the cascade 26 thus helping to maintain the gas flow area therethrough. As will further be apparent from examining Figures 2b and 2c, the flow regulating vane 36 has continued to pivot oppositely with respect to the cascade vanes 28, 29, 30, thus again becoming chordally parallel thereto and contributing to directing the exhaust gas 20 in the forward direction for generating rearward or reversing thrust. The flow regulating vane 36, by rotating oppositely with respect to the unison cascade vanes, 28, 29, 30 as they move in the gas thrust vectoring range of motion defined by Figures 2a-2c, maintains a nearly constant collective gas flow area therethrough, avoiding undesirable and possibly destabilizing exhaust area variations. Unlike prior art vane manipulation systems and methods, the counter-rotating flow control vane 36 is a simple, geometrically-determined area regulating means which does not depend on predetermined scheduling of individual vanes to ensure the proper collective gas flow area. A variety of linkages or other actuating means may be used to position the vanes 28, 29, 30, 36 according to the method shown schematically in Figures 2a-2c. Several of such linkages are described hereinbelow. As will be apparent from examining the motion of the vanes 28, 29, 30, 36 over the vectoring range of motion shown in Figures 2a-2c, when the cascade vanes 28, 29, 30 are moved into a stowed, or a flow-blocking relationship wherein each adjacent vane overlaps the next adjacent vane for forming an unbroken barrier against gas flow, the flow regulating vane 36, if it continues to rotate in the opposite direction with respect to the cascade vanes 28, 29, 30 will be oriented perpendicular to the plane 40 of the cascade 26. While such may not be a problem for a cascade 26 which is always passing a flow of gas 20 therethrough and is therefore never stowed, for certain applications, such as the vectoring nozzle 10 shown in Figures 1a and 1b, it is desirable to stow all such vanes in an overlapping, gas blocking relationship. SECOND EMBODIMENT This is accomplished by extending the range of movement of the flow regulating vane 36 to include a nutational rotation, reversing its relative rotation with respect to the cascade vanes 28, 29, 30 as the cascade vanes move from the first position into a stowed position as shown in Figure 3a. The co-rotation of the flow regulating vane 36 in response to movement of the cascade vanes 28, 29, 30 in a stowing range of motion defined between the stowed position as shown in Figure 3a and the first thrust vectoring position as shown in Figure 3b allows the vane cascade 26 to open smoothly between a stowed, blocking mode wherein little or no gas flow 20 may pass therethrough, into the forward thrust mode wherein the gas 20 is diverted rearwardly by the pitched vanes 28, 29, 30, 36 as shown. The reverse pivoting motion of the flow regulating flap 36 over the vectoring range of motion is shown in Figures 3b, 3c, and 3d which parallel Figures 2a, 2b, 2c discussed hereinabove. Such motion provides the same area controlling function as achieved by the simpler, purely counter-rotating vane system described above, but allows the achievement of the overlapping stowed position of Figure 3a for aerodynamic, flow regulating, or other purposes. Figures 3a-3d also disclose a linkage 46 for orienting both the cascade vanes 28, 29, 30 and the first flow regulating vane 36 in response to a single linear motion 48. This is accomplished through an elongated unison link 50 extending across the cascade 26 and being connected at a plurality of spaced-apart locations to each individual cascade vane 28, 29, 30 by a corresponding vane drag link 52. The first flow regulating vane 36 is driven in a reversing, pivoting motion as required in this first embodiment linkage 46 by a first curved cam race 54 secured to the unison link 50 and movable therewith, and a second, static cam race 56 disposed in the surrounding static structure 34. A cam roller 60 rides in both races 54, 56, being driven in a transverse reciprocating motion with respect to the elongated unison link 50. The roller 60 drives a flow regulating vane link 62, drives the first flow regulating vane 36 directly via a pivot connection therewith. As will be appreciated by those skilled in the art, this simple stroking motion of the first embodiment linkage 46 produces both the multi-vane unison motion for the cascade vanes 28, 29, 30, and the nutating movement of the first flow regulating vane 36, including corotation of the first flow regulating vane 36 as the cascade vanes 28, 29, 30 rotate through the stowing range of motion defined between the positions of Figures 3a and 3b, and the counter-rotating motion of the first flow regulating vane 36 as the cascade vanes 28, 29, 30 move through the thrust vectoring range of motion defined between the positions shown in Figures 3b, 3c, 3d. THIRD EMBODIMENT Figure 4a shows a more detailed view of a further embodiment of a variable position vane cascade 26. Cascade vanes 27, 28, 29, 30 pivot in unison about respective pivot axes 35, 31, 32, 33 responsive to the linear movement 48 of a unison link 50. The unison link 50 is driven by a linear actuator 59 secured between a portion of the link 50 and the static structure 34. As in the second embodiment discussed hereinabove, a cam race 54 is secured to the unison link 50 and translates therewith. A cam roller 60 is received within the race 54 and is further pivotally secured to the static structure 34 by an idler link 64 which restrains the roller 60 against axial movement thereby resulting in a reciprocating motion transverse to the movement of the unison link 50 as the link 50 is stroked 48. The transverse motion of the roller 60 imparts nutational motion to the flow regulating vane 36 via a linkage comprising the first flow regulating vane drive link 66 and a corresponding crank 68 pivotally secured to the roller 60 and to each other 70. By using a four bar linkage 64, 66, 68, 34 driven by the roller 60 and cam race 54, the apparatus, and especially the linkage thereof, provides a simple, powerful mechanism for orienting the vanes 27, 28, 29, 30, 36 as the cascade 26 is operated over both stowing and thrust vectoring ranges of motion. In particular, the four bar linkage 64, 66, 68, 34 for driving the first flow regulating vane 36 may be modified by reconfiguring the cam race 54, or resizing the individual links 64, 66, 68, thereof to permit rescheduling or otherwise modifying the motion of the first flow regulating vane 36 in response to the engine nozzle outlet area requirement, thrust vectoring direction, or other parameters which may be influenced by the relative orientation of the first flow regulating vane 36 during operation of the cascade 26. Figures 4a, 4b, and 4c depict the orientation of the individual vanes 27, 28, 29, 30, 36 of the cascade 26 at the first, second, and third positions which define the thrust vectoring range of motion. Figure 4a shows the individual vanes pitched rearwardly for generating forward thrust by the discharged exhaust gas 20. As noted above, the first forward thrust position shown in Figure 4a has been achieved by the corotation of the cascade vanes 27, 28, 29, 30 and the first flow regulating vane 36 in response to linear translation of the unison link 50 and the interaction of the cam roller 60 and the associated linkage 64, 66, 68. Cam roller 60 as shown in Figure 4a has thus reached the top portion of the curved cam race 54 and will therefore begin to reverse the displacement of the cam roller 60 as well as the direction of rotation of the first flow regulating vane 36 upon further movement of the unison link 50 in the rearward or righthand direction. Figure 4b shows the cascade vanes 27-30 in the second or lateral thrust vectoring position, wherein the cascade vanes of Figure 4b have rotated 38 into a substantially normal orientation with respect to the cascade plane 40 and wherein the counter-rotation 46 of the first flow regulating vane 36 as induced by the reverse transverse displacement of the cam roller 60 has caused the first flow regulating vane 36 to move into a blocking orientation thereby reducing the collective cascade gas flow area. Figure 4c shows the vanes 27-30, 36 in the third, reverse thrust position wherein the first flow regulating vane 36 has moved into a chordally parallel orientation with respect to the adjacent cascade vane 30 for directing the exhausted gas 20 in a forward direction. FOURTH EMBODIMENT Figure 5 shows still a further embodiment of the cascade assembly 26, wherein two flow regulating vanes 36, 70 are provided for controlling the gas flow area of the cascade 26 over the vectoring range of motion thereof. As with the previous embodiments, a plurality of cascade vanes 28, 29, 30 rotate in unison under the influence of a unison link 50 driven by a linear actuator 59 shown displaced from its normal position for clarity. A cam race 54 is secured to the unison link 50 and reciprocates therewith for causing reversing transverse movement of the cam roller 60 as in the previous embodiments. In this embodiment, the roller 60 drives a toggle link 72 pivotally secured 74 to the static structure 34 for driving the first flow regulating vane crank 68 via the first flow regulating vane drive link 66. The toggle link and crank arrangement 72, 66, 68 provides a more compact linkage over either the four bar linkage 64, 66, 68, 34 of the third embodiment, or the double cam arrangement of the second embodiment discussed hereinabove. As the movements of the individual vanes 28, 29, 30, 36 have been well discussed hereinabove and are essentially similar in this equivalent, but distinct, embodiment, discussion herein shall be confined to only the additional linkage and movement induced in the second flow regulating vane 70 which extends spanwisely parallel with the other end vane 28 of the plurality of cascade vanes 30, 29, 28 and adjacent thereto. The second flow regulating vane 70 rotates in unison with the first flow regulating vane 36 under the influence of the push rod 76 extending therebetween. First and second push rod cranks 78, 80 are secured to the respective regulating vanes 36, 70 for manipulating the second vane 70 in response to the rotation of the first vane 36. The dual flow regulating vane arrangement of this fourth embodiment provides further flexibility to the cascade designer by permitting a greater portion of the available cascade flow area to be opened or closed as the cascade vanes 30, 29, 28 are positioned for directing the exhaust gas 20 over the vectoring range of motion. Such flexibility is useful in larger cascade arrangements wherein a single regulating vane may not provide adequate blocking or other area control capacity for reducing the undesirable gas flow area variation discussed above. It should be noted that the double vane concept of this embodiment is equally applicable to the preceding embodiments wherein it would be operable to achieve the enhanced flexibility and area control advantages discussed above. Figure 6 provides a graphical representation of the variation of the gas flow area of a cascade arrangement 82 according to the present invention and a prior art cascade arrangement 84 wherein the individual vanes pivot in unison for selectably directing a flow of gas therethrough. Figure 6 shows the variation of the ratio of actual cascade flow area, A F to the maximum achievable cascade flow area A MAX . For the prior art, uncontrolled vane cascade, the curve 84 shows a maximum area ratio occurring at the normal, or 90° orientation of the vanes with respect to the cascade plane 40. As noted, the area is a function of the sine of the vane angle, falling off on each side of the 90° maximum as the vanes pitch to one side or the other. Curve 82 shows the beneficial results of using one or more flow regulating vanes according to the present invention. At the 45 and 135° locations, i.e., the first and third thrust vectoring positions, the area ratios are identical to that of the prior art system 84. As the cascade vanes are rotated into the lateral thrust, 90° orientation, i.e., the second position, the flow regulating vane or vanes have moved to block off a portion of the cascade gas flow area, thus maintaining the collective cascade area approximately constant over the critical range of motion.

Claims: 1. Method for selectably diverting a flow of gas passing through a vane cascade (26) having a plurality of adjacent individual vanes (28,29,30) each pivotable about a corresponding plurality of parallel pivot axes (31,32,33) lying in a plane (40), said cascade vanes (28,29,30) further being pivotable over a thrust vectoring range of motion including a first pitched orientation, a second orientation normal to the plane (40) of the vane cascade (26), and a third pitched orientation opposite to the first orientation, characterized in that the method comprises the steps of: pivoting all of the cascade vanes (28,29,30) in unison, providing a flow regulating vane (36) adjacent one end vane (30) of the plurality of cascade vanes (28,29,30), the flow regulating vane (30) being pivotable about an axis (37) parallel to the plurality of cascade vane pivot axes (31,32,33), and pivoting the flow regulating vane (36) oppositely with respect to the pivoting of the cascade vanes (28,29,30) over the thrust vectoring range of motion to achieve a constant collective gas flow area over said range of vane motion. 2. Method according to claim 1, characterized in that the step of pivoting the flow regulating vane (36) further comprises the steps of: orientating the flow regulating vane (36) chordally parallel with the one end vane (30) when the cascade vanes (28,29,30) are in the first pitched orientation, orienting the flow regulating vane (36) perpendicular to the one end vane (30) when the cascade vanes (28,29,30) are in the second, normal position, and orienting the flow regulating vane (36) chordally parallel to the one end vane (30) when the cascade vanes (28,29,30) are in the third, oppositely pitched orientation. 3. Method according to claim 2, characterized by comprising the steps of: orienting the cascade vanes (28,29,30) in the first pitched position at an angle of 45° with respect to the plane (40) of the vane cascade (26), and orienting the cascade vanes (28,29,30) in the third pitched position at an angle of 135° with respect to the plane (40) of the vane cascade (26). 4. Vane cascade for exhausting a vectorable flow of gas therethrough, comprising: a plurality of spanwisely parallel cascade vanes (28,29,30), each vane pivotable about a corresponding parallel pivot axis (31,32,33) passing therethrough, and said cascade vanes (28,29,30) being pivotable over a thrust vectoring range of motion between a first pitched orientation with respect to the plane (40) of the cascade (26), a second normal orientation with respect to the plane (40) of the vane cascade (26), and a third, oppositely pitched orientation with respect to the vane cascade (26), characterized by means for pivoting said cascade vanes (28,29,30) in unison, a flow regulating vane (36) disposed adjacent one end vane (30) of the plurality of cascade vanes (28,29,30) and pivotable about an axis (37) parallel to the cascade vane pivot axes (31,32,33), and means responsive to the orientation of the cascade vanes (28,29,30), for pivoting the flow regulating vane (36) in the opposite angular direction from the cascade vanes (28,29,30) as the cascade vanes (28,29,30) move within the thrust vectoring range of motion. 5. Vane cascade according to claim 4, characterized in that the means for pivoting the flow regulating vane (36) further comprises: means for aligning the flow regulating vane (36) chordally parallel with the one end vane (30) when the cascade vanes (28,29,30) are in the first pitched position, means for orienting the flow regulating vane (36) perpendicular to the one end vane (30) when the cascade vanes (28,29,30) are in the second, normal position, and means for aligning the flow regulating vane (36) chordally parallel with the one end vane (30) when the cascade vanes (28,29,30) are in the third, pitched orientation.

Inventors: GUERTY, HAROLD GREGORY
Applicants: UNITED TECHNOLOGIES CORPORATION
Application year: 1988
Main classification: F02K1
IPC codes: F02K1, B64D33