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Methods and apparatus to vary reverse thrust of turbofans are disclosed. An example cascade apparatus disclosed herein includes a fixed frame having a plurality of fixed vanes coupled to the frame, where each of the fixed vanes defines a plurality of slots. A plurality of movable vanes intersects th

Methods and apparatus to vary reverse thrust of turbofans are disclosed. An example cascade apparatus disclosed herein includes a fixed frame having a plurality of fixed vanes coupled to the frame, where each of the fixed vanes defines a plurality of slots. A plurality of movable vanes intersects the fixed vanes to form a reverse thrust flow path and slidably coupled to the fixed vanes via the slots. The movable vanes slide relative to the fixed vanes between a first position to provide a first reverse thrust and a second position to provide a second reverse thrust different from the first reverse thrust.

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1. A cascade apparatus for use with a turbofan engine comprising: a frame;a plurality of fixed vanes coupled to the frame, each of the fixed vanes having a plurality of slots formed in the vane; anda plurality of movable vanes slidably coupled to the fixed vanes to form a reverse thrust flow path, t

1. A cascade apparatus for use with a turbofan engine comprising: a frame;a plurality of fixed vanes coupled to the frame, each of the fixed vanes having a plurality of slots formed in the vane; anda plurality of movable vanes slidably coupled to the fixed vanes to form a reverse thrust flow path, the movable vanes being received by the fixed vanes via the slots such that the movable vanes extend across the fixed vanes, the movable vanes to slide relative to the fixed vanes between a first position to provide a first reverse thrust and a second position to provide a second reverse thrust different from the first reverse thrust. 2. The apparatus of claim 1, wherein the movable vanes are to shift relative to the fixed vanes in a radially outward direction relative to a longitudinal axis of the engine when the movable vanes move from the first position to the second position and the movable vanes to shift toward the fixed vanes relative to the longitudinal axis of the engine when the movable vanes move from the second position to the first position. 3. The apparatus of claim 1, wherein the movable vanes and the fixed vanes define a first angle of attack when the movable vanes are in the first position and the movable vanes and the fixed vanes define a second angle of attack when the movable vanes are in the second position, the first angle of attack being different than the second angle of attack. 4. The apparatus of claim 1, wherein the movable vanes comprise a first movable vane and a second movable vane, and wherein the first movable vane moves independently relative to the second movable vane. 5. The apparatus of claim 1, wherein the movable vanes are operatively coupled to a rack-and-pinion assembly. 6. The apparatus of claim 5, wherein the rack-and-pinion assembly comprises a rack operatively coupled to a plurality of pinions, each of the movable vanes being operatively coupled to a corresponding one of the pinions via a link. 7. The apparatus of claim 6, wherein a first end of the link is coupled to a respective one of the movable vanes and a second end of the link is coupled to a respective one of the pinions. 8. The apparatus of claim 7, wherein the second end of the link is coupled to the respective one of the pinions at a position offset relative to a central axis of rotation of the respective one of the pinions such that rotation of the respective one of the pinions about the central axis causes the first end of the link to move relative to the rack in a substantially linear manner. 9. The apparatus of claim 7, wherein the rack is mounted to a translating panel of a thrust reverser blocker door such that operation of the thrust reverser blocker door between a closed position and an open position automatically causes the movable vanes to move between the first and second positions. 10. The apparatus of claim 1, wherein movable vanes vary a reverse thrust provided by the reverse thrust flow path that is proportional to a position of the movable vanes relative to the fixed vanes. 11. The apparatus of claim 1, wherein in the second position, the movable vanes and the fixed vanes provide an angle of attack that enables an aircraft to move in a rearward direction from an initially stationary position. 12. A method to control reverse thrust of a turbofan comprising: varying a position of a plurality of movable vanes relative to a plurality of fixed vanes by sliding the movable vanes in slots formed in the fixed vanes to vary a reverse thrust provided by the movable vanes and the fixed vanes, the reverse thrust being proportional to a position of the movable vanes relative to the fixed vanes, the slots of the fixed vanes to receive at least portions of the movable vanes such that the movable vanes at least partially pass through the fixed vanes. 13. The method of claim 12, wherein varying the position of the movable vanes relative to the fixed vanes includes sliding the movable vanes relative to the fixed vanes along a path defined by the slots formed in the fixed vanes. 14. The method of claim 12, further comprising sliding the movable vanes relative to the fixed vanes simultaneously. 15. The method of claim 12, further comprising moving a first movable vane of the movable vanes relative to the fixed vanes independently from a second movable vane of the movable vanes. 16. The method of claim 12, further comprising moving the movable vanes to a first position relative to the fixed vanes to provide a first reverse thrust and moving the movable vanes to a second position relative to the fixed vanes to provide a second reverse thrust greater than the first reverse thrust. 17. The method of claim 16, further comprising operatively coupling the movable vanes to a drive system of a reverse thrust blocker door such that operation of the reverse thrust blocker door between a first position and a second position causes the movable vanes to slide relative to the fixed vanes between the first and second positions. 18. The method of claim 16, further comprising moving the movable vanes to an intermediate position between the first position and the second position to provide a third reverse thrust different than the first and second reverse thrusts. 19. A cascade apparatus for use with a turbofan comprising: fixed means for directing fluid flow, the fixed means for directing fluid flow having means for sliding; andmovable means for directing fluid flow slidably coupled to the fixed means for directing fluid flow to define a reverse thrust flow path, the movable means being connected to the fixed means via the means for sliding, the means for sliding to cause each of the movable means to be substantially perpendicular relative to the fixed means such that the fixed and movable means intersect, the movable means for directing fluid flow to slidably move relative to the fixed means for directing fluid flow via the means for sliding between a first position and a second position to vary a reverse thrust provided by the reverse thrust flow path, the movable and fixed means for directing fluid flow to produce a first reverse thrust when the movable means for directing fluid flow is in the first position and a second reverse thrust when the movable means for directing fluid flow is in the second position, the first reverse thrust being different than the second reverse thrust. 20. The apparatus of claim 19, further comprising means for actuating operatively coupled to the movable means for directing fluid flow to move the means for directing fluid flow between the first and second positions relative to the fixed means for directing fluid flow. 21. The apparatus of claim 1, wherein each of the fixed vanes has an upper edge and a lower edge opposite the upper edge, the slots to at least partially extend between the upper edges and the lower edges. 22. The apparatus of claim 21, wherein each of the movable vanes has a first end and a second end opposite the first end, the second ends of the movable vanes to be received by the slots of the fixed vanes such that the movable vanes and the fixed vanes define a grid. 23. The apparatus of claim 1, wherein the fixed vanes are to extend in a direction parallel to a longitudinal axis of the engine and the movable vanes are to extend in a direction non-parallel relative to the longitudinal axis when the cascade apparatus is coupled to the engine.