BACKGROUND OF THE INVENTION

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional Patent Application Serial No. 61/712,944, filed October 12, 2012, and U.S. Patent Application No.

13/750346, filed January 25, 2013, both entitled "GAS TURBINE ENGINE TWO DEGREE OF FREEDOM VARIABLE BLEED VALVE FOR ICE EXTRACTION" the disclosure of both are hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to gas turbine engine variable bleed valves and, more particularly, to such valves used to prevent surge and remove ice from duct between booster and core engine compressor.

DESCRIPTION OF RELATED ART

It is well known in the gas turbine engine field to provide variable bleed valves (VBVs), typically, doors that open to provide a bleed path to bleed off compressed air between the booster and core engine compressor of gas turbine engines. The air is often bled from what is referred to as a gooseneck flowpath between the booster and core engine compressor. Aircraft fan jet gas turbine engines and marine and industrial derivatives of such engines have employed various forms of curved flowpaths and VBV bleed doors that are retracted into the flowpath casing so as to form an entrance to a bleed duct that bleeds booster or low pressure compressor discharge airflow to draw particles out of the flowpath in a manner such as that disclosed in U.S. Patent No. 4,463,552 entitled "Combined Surge Bleed and Dust Removal System for a Fan- Jet Engine" by Monhardt et al. Because the bleed flow abruptly curves away from the direction of the compressor flow, it is very difficult to hold larger particles in the bleed flow because of their momentum. This problem is common to aircraft, marine, and ground based gas turbine engines. Turbofan jet engines, such as the General Electric CF6 and GE90 series of engines, have in series relationship a fan, a booster, and a core engine compressor, whereby a portion of the air passing through the fan flows into the booster and then the core engine

compressor. In order to match the inlet airflow of the core engine compressor to its flight operational requirements and to prevent booster stall, a booster variable bleed valve (VBV) is provided in the form of a booster bleed duct having an inlet between the booster and the core engine compressor and an outlet to the fan duct. Opening and closing of the booster bleed duct is conventionally provided by a

circumferentially disposed plurality of pivotal doors that retract into the engine structure or casing and are operated by a single unison ring powered by one or more fuel powered actuators. Bellcrank linkages operably connect the retracting pivotal bleed doors to the unison ring. An example of such a stall prevention system using a retracting pivotal door, as compared to a sliding door or valve in the Monhardt patent, is disclosed in U.S. Patent No. 3,638,428 entitled "Bypass Valve Mechanism" by Shipley et al. and assigned to the same assignee as the present invention and incorporated herein by reference. The operation of the VBV is scheduled by the engine controller, either a mechanical or digital electronic type may be used.

The problem associated with conventional bleed valve ducts and valve doors is that larger particles and amounts of particles such as ice are often not drawn into the bleed duct. It is desirable to have an engine that provides the ability to remove large amounts of ice from the compressor airflow and as well as efficiently bleed air between the booster and the core engine compressor. Thus, it is highly desirable to remove ice from the gooseneck flowpath without removing core airflow or minimizing the amount of core airflow that is removed.

Modern aircraft employ fewer of the higher thrust, fuel efficient,

very-high-bypass engines such as the twin engine Boeing 767 aircraft. Aircraft with fewer engines require more total take-off power and more power per engine in order to satisfy the requirement of being able to fly with one engine out. Therefore, the engines are set to lower power settings resulting in less engine airflow during descent when all engines are operational. This results in high water content for engine airflow since the amount of ice, hail, or water that gets into the engine is the same so long as the aircraft speed remains the same.

On the other hand, higher bypass ratio engines have smaller core flow and larger bullet-nose frontal area. This means more ice, hail, or water gets through the compressor into the combustor resulting in higher water content for the air. These two fundamental phenomena combine to cause substantial increase of water-to-air ratio in the combustor resulting in such aircraft engines being more susceptible to engine flame out problem in rain or hail storms. The higher bypass ratio engines, having the large frontal area, also result in increased ice accretion on the booster inlet and booster stages during idle operation within an icing environment. This results in increased ice shed during the acceleration, including sheds at or near maximum power operation. It also increases the risk of compressor stall due to the ice sheds and more particularly to high speed rotor ice sheds, which historically has been an issue on two- shaft large engines, and will continue to be an issue on future large engines.

Modern high bypass ratio engines incorporate higher pressure core

compressors and lower pressure boosters and, thus, produce less pressure difference between the booster exit and the fan bypass duct. This increases the difficulty of bleeding sufficient amounts of air from downstream of the booster to the fan bypass duct for protecting boosters from stall. The booster stall margin is controlled by opening the VBV doors to dump some of the booster flow overboard so as to control the booster operating line to a point below its stall line.

Thus it is highly desirable to have a variable bleed valve and system for high bypass ratio engines incorporate higher pressure core compressors and lower pressure boosters bleed sufficient amounts of air from downstream of the booster for protecting boosters from stall. It is also highly desirable to have a variable bleed valve and system for such high bypass ratio engines able to prevent ice sheds and more particularly high speed rotor ice sheds from causing compressor stall or flame quenching in the combustor.

SUMMARY OF THE INVENTION

A gas turbine engine variable bleed apparatus (48) includes a variable bleed valve (49) with a variable bleed valve door (50) disposed in a bleed inlet (47) in a transition duct (29). The door (50) is pivotable or rotatable about two or more separate pivot points (160). The variable bleed valve (49) is operable to open and close an aft bleed slot (170) extending generally radially outwardly from the transition duct (29) and extending between an aft lip (52) located at a downstream or aft end also operable to open and close a forward bleed slot (180) extending generally radially inwardly into the transition duct (29) and extending between a forward lip (51) located at an upstream or forward end (53) of the door (50) and the transition duct (29).

The exemplary embodiment of the variable bleed valve (49) operable to transition the door (50) between a first position with the aft bleed slot (170) being open and the forward bleed slot (180) being closed to a second position with the aft bleed slot (170) being closed and the forward bleed slot (180) being open without fully closing the door (50). The door (50) may pivot or rotate about an axis (160) translatable between the two or more separate pivot points.

The transition duct (29) may have a transition duct conical angle (Al) with respect to an engine centerline (12) that is at least about 10 degrees greater than a booster conical angle (A2) of a booster outer shroud (222) upstream and adjacent the transition duct (29).

The gas turbine engine variable bleed apparatus (48) may include a heater (202) in an ice gathering compartment (204) in a radially inner and axially aft section (208) of the fan hub frame (129) for melting ice extracted from the transition duct (29). The door (50) operable to place the aft bleed slot (170) in fluid communication with an opening (210) from the compartment (204) to the aft bleed slot (170) when the aft bleed slot (170) is opened. The door (50) may be operable to place the aft bleed slot (170) in fluid communication with the compartment (204) by uncovering an opening (210) from the aft bleed slot (170) to the compartment (204), and sealing the aft lip (52) of the door (50) against a compartment wall (216) of the compartment (204).

The gas turbine engine variable bleed apparatus (48) may include a bleed valve duct (60) comprising circumferentially spaced apart duct sidewalls (62) extending generally radially outwardly from the door (50). The bleed valve duct (60) includes a generally axially extending duct outer wall (64) spaced radially apart from the door (50) and a flexible tube (230) connecting an exit (232) of the bleed valve duct (60) at an aft end (54) of the door (50) to a hub frame exit (234) on the hub frame (129).

Alternatively, an exhaust duct extension (240) of a bleed exhaust duct (58) may extend forwardly into the hub frame (129) from the bleed exhaust duct (58). The bleed exhaust duct (58) leads away from the hub frame (129). The exhaust duct extension (240) seals against the bleed valve duct (60). Flexible exhaust duct seals (242) on the exhaust duct extension (240) sealingly engage flexible valve duct seals (244) on the bleed valve duct (60).

The gas turbine engine variable bleed apparatus (48) may include

circumferentially spaced apart first and second door hinges (70, 72) near the aft end (54) of the door (50) which rotatably hinge the door (50) to the fan hub frame (129). The axis (160) passes through first and second hinge pins (74, 76) rotatably extending through hinge holes (100) of first and second door hinges (70, 72). The first and second hinge pins (74, 76) rotatably extend through first and second hinge slots (82, 84) in circumferentially spaced apart first and second hinge lugs (86, 88) fixedly attached to the fan hub frame (129). The first and second hinge slots (82, 84) may be linear.

The gas turbine engine variable bleed apparatus (48) may be incorporated in an aircraft gas turbine engine (10) including in downstream serial flow

communication a fan (14), a booster (16), and a high pressure compressor (18) circumscribed about an engine centerline (12), and a bypass duct (36) spaced radially outwardly from the booster (16). An annular fan frame (33) supporting a fan casing (30) surrounding the fan (14) and the bypass duct (36) includes an annular outer frame casing (123), a fan hub frame (129), and a plurality of circumferentially spaced apart duct struts (134) extending therebetween. A transition duct (29) is located at a radially inner end (136) of the fan hub frame (129) and axially disposed between and in fluid communication with the booster (16) and the high pressure compressor (18). Bleed exhaust ducts (58) extend from the fan hub frame (129) to the bypass duct (36) and at least one variable bleed valve (49) including the variable bleed valve door (50) is disposed in a bleed inlet (47) in the transition duct (29).

Radially inner and outer unison rings (102, 104) operably linked to the variable bleed valve (49) may be incorporated for rotating the door (50) and translating the first and second hinge pins (74, 76) through the first and second hinge slots (82, 84) respectively.

The transition duct (29) may be axially disposed between and in fluid communication with relatively low and high pressure compressors.

A method of operating the variable bleed valve (49) includes pivoting or rotating the door (50) about an axis (160) at and translating the axis between two or more separate pivot points (160), opening and closing the aft bleed slot (170) by translating the axis (160) between two or more separate pivot points (160), and opening and closing the forward bleed slot (180) by rotating the door (50) about the axis (160). The method may further include transitioning the door (50) between a first position with the aft bleed slot (170) being open and the forward bleed slot (180) being closed to a second position with the aft bleed slot (170) being closed and the forward bleed slot (180) being open without fully closing the door (50) during the transitioning which may be done by rotating the door (50) about the axis (160) and simultaneously translating the axis (160) during the transitioning.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and other features of the invention are explained in the following description, taken in connection with the accompanying drawings where:

FIG. 1 is a longitudinal part sectional and part diagrammatical view illustration of an exemplary embodiment of an aircraft turbofan gas turbine engine with a two degree of freedom variable bleed valve (VBV).

FIG. 2 is an enlarged part sectional and part diagrammatical view illustration of a door of the valve in a closed position in the engine illustrated in FIG. 1.

FIG. 3 is a perspective view illustration of a hinge and part of a linkage to pivot the door illustrated in FIG. 2.

FIG. 4 is a sectional view illustration of an aft slot formed by the door in an outwardly rotated position with respect to a transition duct in the engine illustrated in FIG. 2.

FIG. 4A is a sectional view illustration of a transition duct conical angle of the transition duct and a booster conical angle of a booster outer shroud in the engine illustrated in FIG. 2.

FIG. 5 is a sectional view illustration of a forward slot formed by the door in an inwardly rotated position with respect to the transition duct in the engine illustrated in FIG. 2.

FIG. 6 is a sectional view illustration of the door in a partially outwardly and a partially inwardly rotated positions in the transition duct in the engine illustrated in FIG. 2. FIG. 7 is a diagrammatical view illustration of a heating system for melting ice extracted by the VBV of the engine illustrated in FIG. 1.

FIG. 8 is a diagrammatical view illustration of a flexible baffled tube connecting an the exit of the VBV bleed valve duct and an inlet of a VBV exhaust duct between a fan frame hub and a bypass duct of the engine illustrated in FIG. 1.

FIG. 9 is a diagrammatical view illustration of an extended VBV exhaust duct extending into the fan frame hub of the engine illustrated in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Illustrated in FIG. 1 is an exemplary aircraft turbofan gas turbine engine 10 circumscribed about an engine centerline 12 and suitably designed to be mounted to a wing or fuselage of an aircraft. The engine 10 includes, in downstream serial flow communication, a fan 14, a booster 16, a high pressure compressor 18, a combustor 20, a high pressure turbine (HPT) 22, and a low pressure turbine (LPT) 24. A core engine 25 includes the HPT or high pressure turbine 22 joined by a high pressure drive shaft 23 to the high pressure compressor 18 and the combustor 20. The LPT or low pressure turbine 24 is joined by a low pressure drive shaft 26 to both the fan 14 and the booster 16.

There are high bypass aircraft gas turbine engines such as some built by Rolls Royce that have more than two compressors and turbines. Rolls Royce, for example has a three spool engine with three compressors each of which is driven by a diferent turbine. Thus, the VBV valve and door disclosed herein may be incorporated between two compressors and is not limited to being only between a low pressure compressor such as the booster illustrated herein and a high prssure compressor.

In typical operation, air 27 is pressurized by the fan 14 and produces an inner or core airflow 15 channeled through the booster 16 which further pressurizes the core airflow 15. The pressurized air is then flowed to the high pressure compressor 18 which further pressurizes the air. The pressurized air is mixed with fuel in the combustor 20 for generating hot combustion gases 28 that flow downstream in turn through the HPT 22 and the LPT 24.

A flow splitter 34 surrounding the booster 16 immediately behind the fan 14 includes a sharp leading edge 32 which splits the fan air 27 pressurized by the fan 14 into a radially inner stream (core airflow 15) channeled through the booster 16 and a radially outer stream or bypass airflow 17 is channeled through a bypass duct 36 spaced radially outwardly from the booster 16. A fan casing 30 surrounding the fan 14 and the bypass duct 36 is supported by an annular fan frame 33 circumscribed about the engine centerline 12. The booster 16 includes alternating annular row of booster blades and vanes 38, 42 extending radially outwardly and inwardly across a booster flowpath 39 in a booster duct 40. The annular row of booster blades 38 are suitably joined to the fan 14. The booster 16 is located forward of the fan frame 33 and radially inboard of the flow splitter 34.

The fan frame 33 includes an annular outer frame casing 123, a fan hub frame 129, and a plurality of circumferentially spaced apart duct struts 134 extending therebetween. The duct struts 134 are airfoil shaped since bypass air passes between the adjacent ones thereof. A transition duct 29 also referred to as a gooseneck is located at a radially inner end 136 of the fan hub frame 129 and is axially disposed between and in fluid communication with the booster 16 and the high pressure compressor 18 of the core engine 25. Bleed exhaust ducts 58 lead away from the hub frame 129 to the bypass duct 36.

Referring to FIGS. 1 and 2, a bleed inlet 47, an opening, is disposed in an outer conical wall 68 of a transition duct 29 between booster 16 and the high pressure compressor 18. A variable bleed apparatus 48 is used to bleed the core airflow 15 between booster 16 and the high pressure compressor 18 to prevent the booster 16 from stalling under certain engine operating conditions. The variable bleed apparatus 48 includes a variable bleed valve 49 (VBV) with a variable bleed valve door 50 disposed in the bleed inlet 47. The VBV door 50 is illustrated in FIG. 2 in a closed position completely closing the bleed inlet 47.

The VBV door 50 includes forward and aft lips 51, 52 located at upstream or forward and downstream or aft ends 53, 54 of the door 50. The VBV door 50 is also used to extract ice from the booster and the transition duct 29 before it reaches the high pressure compressor 18 where it can cause stall conditions, airflow instability conditions, and quench the flame or combustion in the combustor 20. A

circumferentially disposed plurality of booster bleed paths 46 indicated by the arrows and dotted line labeled 46 extend from the VBV door 50 in the fan hub frame 129 through the bleed exhaust ducts 58 to the bypass duct 36.

Illustrated in FIG. 3 is an exemplary embodiment of the variable bleed valve 49 including a scoop or bleed valve duct 60. The bleed valve duct 60 includes circumferentially spaced apart duct sidewalls 62 extending generally radially outwardly from the VBV door 50 and a generally axially extending duct outer wall 64 spaced radially apart from the VBV door 50. Ribs 66 extend generally radially outwardly from the VBV door 50 to the duct outer wall 64 to provide structural support for the bleed valve duct 60.

Referring back to FIG. 2, the VBV door 50 is attached to linkage 55 that provides it with two rotational degrees of freedom allowing the VBV door 50 to be pivoted or rotated about an axis 160 at two or more separate pivot points which is exemplified by a translatable hinge axis 160. The VBV door 50 is actuated by actuators (not shown) that forwardly and aftwardly axially translate and rotate radially inner and outer unison rings 102, 104 with respect to engine centerline 12. It is well known to operate or rotate VBV doors open and close using actuators, unison rings, and bellcranks for positioning the doors. One example of this may be found in United States Patent No. 3,638,428 to Shipley, et al, February 1, 1972, entitled "BYPASS VALVE MECHANISM".

The linkage 55 includes forward and aft inner links 110, 112 linked to forward and aft inner bellcrank arms 120, 122 of an inner bellcrank 1 14. The forward inner link 110 operably links the inner unison ring 102 to the forward inner bellcrank arm 120. The aft inner link 112 operably links the aft inner bellcrank arm 122 to an outer clevis 124 of an outer ball joint 126 on a radially outer end 128 of the variable bleed valve 49. The linkage 55 further includes forward and aft outer links 130, 132 linked to forward and aft outer bellcrank arms 140, 142 of an outer bellcrank 144. The forward outer link 130 operably links the outer unison ring 104 to the forward outer bellcrank arm 140. The inner and outer bellcranks 114, 144 pivot about inner and outer bellcrank axes 116, 118 which are fixed with respect to the fan hub frame 129.

Referring to FIGS. 2 and 3, circumferentially spaced apart first and second bent arm levers 145, 146 are pivotably connected to the fan hub frame 129 of the fan frame 33. Each of the first and second bent arm levers 145, 146 include radially inner and outer bent arms 150, 152. Each of the first and second bent arm levers 145, 146 is pivotably connected at a lever pivot point 147 between the inner and outer bent arms 150, 152 to a hub lug 148 mounted to the fan hub frame 129. The first and second bent arm levers 145, 146 are rotatably connected to each other by a cross bar 154 illustrated herein as being cylindrical and disposed through arm holes 156 in each of the outer bent arm 152 of each of the first and second bent arm levers 145, 146.

The VBV door 50 is hinged to the fan hub frame 129 of the fan frame 33 near the aft end 54 of the VBV door 50. The exemplary embodiment of the variable bleed valve 49 includes circumferentially spaced apart VBV first and second door hinges 70, 72 near the aft end 54 of the VBV door 50. The first and second door hinges 70, 72 rotatably connect or hinge the VBV door 50 to the fan hub frame 129. The first and second door hinges 70, 72 include first and second clevises 90, 92 respectively. Radially inner ends 93 of first and second door links 94, 96 are rotatably connected to clevis lugs 98 of the first and second clevises 90, 92 respectively. Radially outer ends 99 of first and second door links 94, 96 are rotatably connected to the radially inner bent arm 150 of the first and second bent arm levers 145, 146 respectively.

Cylindrical first and second hinge pins 74, 76 are rotatably disposed through linearly aligned coaxial hinge holes 100 in the clevis lugs 98 of the first and second clevises 90, 92 of the first and second door hinges 70, 72 and the inner ends 93 of the first and second door links 94, 96 respectively. The VBV door 50 is rotatably and translatably connected to the fan hub frame 129. The cylindrical first and second hinge pins 74, 76 extend through first and second hinge slots 82, 84 in spaced apart first and second hinge lugs 86, 88 respectively. The first and second hinge lugs 86, 88 are fixedly attached to the fan hub frame 129. Thus, the hinge axis 160 passes through the first and second hinge pins 74, 76 which are translatable about which the VBV door 50 is rotatable. The exemplary embodiment of the first and second hinge slots 82, 84 are linear slots so that the first and second hinge pins 74, 76 can only translate linearly.

The aft outer link 132 operably links the aft outer bellcrank arm 142 to the cross bar 154 so that when the aft outer link 132 is moved forwardly and aftwardly by the outer bellcrank 144, the first and second bent arm levers 145, 146 rotate about the respective lever pivot points 147 which are fixed relative to the fan hub frame 129. This moves or translates the first and second hinge pins 74, 76 through first and second hinge slots 82, 84 respectively, thus, translating and positioning the hinge axis 160 and the VBV door 50. The VBV door 50 is thus operable to rotate into and out of the transition duct 29 about the hinge axis 160 near the aft end 54 of the VBV door 50 and the hinge axis 160 is operable to translate toward and away from the transition duct 29. The exemplary embodiment of the variable bleed valve 49 embodiment includes the hinge axis 160 being operable to translate perpendicularly or along a normal line toward and away from the transition duct 29.

Referring to FIG. 4, the VBV door 50 is translated by actuating or moving the outer unison ring 104 to open an aft bleed slot 170 extending generally radially outwardly from the transition duct 29. The aft bleed slot 170 extends between the aft lip 52 located at the downstream or aft end 54 of the VBV door 50 and the transition duct 29. The VBV door 50 may also be rotated so that the forward lip 51 located at the upstream or forward end 53 of the VBV door 50 remains in sealing engagement with the bleed inlet 47. Thus, the VBV door 50 is rotated into the fan hub frame 129 about the forward lip 51. The aft bleed slot 170 is opened to extract ice from the booster and the transition duct 29 before it reaches the high pressure compressor 18 where it can cause stall conditions, airflow instability conditions, and quench the flame or combustion in the combustor 20.

Referring to FIGS. 1 and 4 A, the aft bleed slot 170 is not very high and is designed to remove ice from the gooseneck or the transition duct 29 and may do so without removing core airflow 15. In order to enhance the ice removal, a booster outer flowpath 220 has a relatively high radius R, as measured from the engine centerline 12, over the last few stages of the booster 16 and the transition duct 29 performs some of the core airflow 15 turning within the transition duct 29. This flow turning is accomplished by the outer conical wall 68 of the transition duct 29 have a transition duct conical angle Al, with respect to the engine centerline 12, at least about 10 degrees greater than a booster conical angle A2 of a booster outer shroud 222. The booster outer shroud 222 surrounds outer ends 224 of booster outlet guide vanes 226 (OGV) at a booster outlet 228 leading to the transition duct 29.

In a more general embodiment of the engine the variable bleed valve 49 may be used in a transition duct 29 between adjacent relatively low and high pressure compressors represented herein by the booster 16 and the high pressure compressor 18 respectively. The booster outer shroud 222, booster outlet guide vanes 226, and booster outlet 228 leading to the transition duct 29 are generally representative of a low pressure compressor outer shroud, outlet guide vanes, and compressor outlet respectively.

Core airflow 15 exiting the booster 16 flows linearly on a path that is tangent to the outer flowpath of the booster outlet 228 which is generally the same as the booster outer shroud 222. In an ice shed, the ice particles follow this same path or trajectory with most of the ice being located in the outer portion of the flowpath. Conventionally, the flow direction set by the outer flowpath of the booster outlet 228 is parallel to the VBV door 50. Having the transition duct conical angle Al greater than the booster conical angle A2 by about 10 degrees or more is more conducive for extracting shed ice at high speed, while minimizing the amount of airflow bleed from the booster discharge and thereby minimizing the exhaust gas temperture (EGT) and other cycle effects.

The core airflow 15 in the booster and transition duct stays attached to the wall, and turns down into the compressor because of its difference in conical angles. However, ice particles have too much mass and inertia to make this turn, and they continue on their straight trajectory out of booster. They then collide with the outer wall of the transition duct and slide along it until the flowpath turns again going into the HPC. When the aft slot is opened up at the aft end of the VBV door, the ice in the outer flowpath either collides with and slides along the bottom of the VBV door into the fan hub frame, or continues on its straight trajectory out of the booster and into the fan hub frame through the aft slot.

Illustrated in FIG. 5, is a forward bleed slot 180 which is opened by rotating the VBV door 50 generally radially inwardly into the transition duct 29. The forward bleed slot 180 is opened by actuating or moving the inner unison ring 102 which, in turn, rotates the VBV door 50 about the hinge axis 160. The inner unison ring 102 rotates the inner bellcrank 114 and its inner bellcrank arm 122 which, in turn, moves the aft inner link 112 operably linked to the radially outer end 128 of the VBV door 50. The forward bleed slot 180 extends between the forward lip 51 located at the upstream or forward end 53 of the VBV door 50 and the transition duct 29. Thus, the VBV door 50 is rotated away from the fan hub frame 129 and radially into the transition duct 29 and is rotated generally about aft lip 52. At low engine speeds such as ground and flight idle, the VBV door 50 is rotated into the core airflow 15 in the transition duct 29 as shown below FIG. 5 thus bleeding bleed air 19 off of the core airflow 15 at these flight conditions. The bled off bleed air 19 flows across the VBV door 50, through the bleed valve duct 60, through the bleed exhaust ducts 58, and to the bypass duct 36. When the engine goes from low to high speed, the VBV door 50 transitions from an ice extraction position illustrated in FIG. 4 in which the aft bleed slot 170 is open and the forward bleed slot 180 is closed to a core bleed position illustrated in FIG. 5 in which the aft bleed slot 170 is closed and the forward bleed slot 180 is open. After the engine reaches a stabilized power condition the VBV door 50 is placed in a fully closed position as illustrated in FIG. 2. When the engine goes from low to high speed, the VBV door 50 transitions to an ice extraction position illustrated in FIG. 4 in which the aft bleed slot 170 is open and the forward bleed slot 180 is closed from a core bleed position illustrated in FIG. 5 in which the aft bleed slot 170 is closed and the forward bleed slot 180 is open.

During this transition, it is desirable to bleed air from the core airflow 15 in the transition duct 29 during the entire time. Therefore, the VBV door 50 does not go to a fully closed position, illustrated in FIG. 2, during transition between the ice extraction and core bleed positions. When in transition, bleed air 19 is bled into the fan hub frame 129 through the forward bleed slot 180 at the forward lip 51, the upstream or forward end 53 of the VBV door 50 and through the aft bleed slot 170 at the aft lip 52 at the downstream or aft end 54 of the VBV door 50. During this transition, the VBV door 50 is rotated about the axis 160 and the axis 160 is simultaneously translated. An example of this transition is illustrated in FIG. 6 with both the aft and forward bleed slots 170, 180 in open positions.

Illustrated in FIG. 7, is an exemplary embodiment of the variable bleed apparatus 48 including a heating system 200 for melting ice extracted from the core airflow 15 in the transition duct 29. The heating system 200 includes a heater 202 illustrated herein as heating pipes or tubes 206 in an ice gathering compartment 204 in a radially inner and axially aft section 208 of the fan hub frame 129. An opening 210 from the compartment 204 to the aft bleed slot 170 is uncovered when the aft bleed slot 170 is opened and the aft lip 52 of the VBV door 50 seals against a compartment wall 216 of the compartment 204. This allows ice 212 to be extracted from the booster and the transition duct 29 into the compartment 204 and very little, if any, of the core airflow 15 to be removed from the transition duct 29. The ice 212 in the compartment 204 is melted and flows through weep holes 214 in the outer conical wall 68 of the transition duct 29 bounding a radially inner end 218 of the

compartment 204 and is exhausted into the core airflow 15 in the transition duct 29. Illustrated in FIG. 8 is a flexible baffled or bellows tube 230 connecting an exit 232 of the bleed valve duct 60 at the aft end 54 of the VBV door 50 to a hub frame exit 234 on the hub frame 129. The bleed exhaust duct 58 extends from the hub frame exit 234 to the bypass duct 36. The bleed air 19 bled off of the core airflow 15 and flowed through the forward bleed slot 180 when it is opened by rotating the VBV door 50 is guided by the baffled tube 230 completely and efficiently to the bleed exhaust duct 58. The baffled tube 230 also isolates ice that has been entrained in the bleed air 19 and extracted from the core airflow 15 through the forward bleed slot 180.

Illustrated in FIG. 9 is a VBV exhaust duct extension 240 of the bleed exhaust duct 58. The exhaust duct extension 240 extends forwardly into the hub frame 129 from the bleed exhaust duct 58 and seals against the bleed valve duct 60 on the VBV door 50. Flexible exhaust duct seals 242 on the exhaust duct extension 240 seal with flexible valve duct seals 244 on the bleed valve duct 60. The bleed air 19 bled off of the core airflow 15 and flowed through the forward bleed slot 180 when it is opened by rotating the VBV door 50 is guided by the exhaust duct extension 240 completely and efficiently to the bleed exhaust duct 58 between the fan hub frame 129 and the bypass duct 36. The exhaust duct extension 240 also isolates ice that has been entrained in the bleed air 19 and extracted from the core airflow 15 through the forward bleed slot 180.

The present invention has been described in an illustrative manner. It is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. While there have been described herein, what are considered to be preferred and exemplary embodiments of the present invention, other modifications of the invention shall be apparent to those skilled in the art from the teachings herein and, it is, therefore, desired to be secured in the appended claims all such modifications as fall within the true spirit and scope of the invention.

Accordingly, what is desired to be secured by Letters Patent of the United States is the invention as defined and differentiated in the following claims: