Fans

[57] ABSTRACT

A fan assembly for attachment to the front of a main gas turbine engine assembly to provide an engine of the ducted-fan by-pass type is constructed as a unitary assembly which can be fitted and removed as such. The assembly comprises a non-ro.tative portion including a main body and a by-pass duct, and a rotative sub-assembly supported in bearings by the non-rotative portion and including a hub structure and fan blading positioned and rotatably supported within the non-rotative by-pass duct.

Claims, 4 Drawing Figures

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PATENTEDMAR131973

SHEET 1 OF 4

3,720,060

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John Al feeoChilman

INVENTORS

BY

ATTORNEY5

PATENTEDKM1 31973

3.720,060

SHEET 2 OF 4

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Stuart Suncan Dflu/es John fiirtEb Ch/lman

INVENTORS

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ATTORNEYS

PATENTEDMAR 131373 3.720,060

SHEET 3 OF 4

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PATENTEDMARl 31073

3,720,060

SHEET OF 4

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r-a

3,720,060

FANS

BACKGROUND OF THE IN VENTION

This invention relates to fans for use in gas turbine engines of the ducted-fan by-pass type, and to gas turbine engines of that type.

SUMMARY OF THE INVENTION

According to one aspect of the invention a fan assembly for attachment to the front of a main gas turbine engine assembly to provide an engine of the ducted-fan by-pass type is constructed as a unitary assembly which can be fitted and removed as such and comprises a non-rotative portion including a by-pass duct, and a rotative sub-assembly supported in bearings by the non-rotative portion and including a hub structure and fan blading positioned and rotatably supported within the non-rotative by-pass duct.

Thus the invention provides a fan assembly, including the non-rotative duct, which is detachable and attachable as a whole thereby facilitating manufacture and maintenance of a by-pass engine. The assembly can also be designed for attachment to an existing engine of non by-pass type, thereby converting the engine to one of the by-pass type.

The fan blading is preferably arranged in a single stage and of variable pitch with the pitch adjustable under the control of a servo-system housed, at least in part, within the hub structure. In preferred constructions the by-pass duct is supported by a main body of the non-rotative portion of the assembly through a ring of stator blading positioned downstream of the fan blading, which main body is adapted for bolting to the front of the main engine assembly and also supports the rotative sub-assembly. Preferably a spinner is provided to enclose the forward part of the hub structure and forms part of the rotative sub-assembly.

The fan may if desired be of tiered form, with an inner tier of blading adapted to charge the engine compressor and an outer tier which charges the by-pass duct. The non-rotative portion of the assembly may include a splitter structure positioned downstream of the fan blading and which separates the air flow from separate tiers. This structure may, when the assembly is fitted, define an entry portion of the engine inlet leading to the engine compressor and a ring of fixed stator blading may be fixed in this entry portion.

When the blading is of variable pitch it is preferably reversible in pitch, and the pitch angle is desirably variable to provide positive pitch, zero or near zero pitch, negative pitch and a feathered position in order to provide complete control of the air flow along the duct. With tiered blading, the pitch of the outer tier may be variable in this manner with the inner tier of blading of fixed pitch. In preferred constructions a pitch-change motor of vane type is employed, having two output members in the form of bevel gears of large diameter which respectively turn in opposite directions about the rotation axis of the fan and which respectively engage opposite sides of small bevel pinions fixed on the root ends of the individual fan blades.

The fan assembly may be adapted for bolting up to the main engine assembly so as to pick up a drive for the fan either from the engine shaft or a reduction gear box embodied in the engine assembly. However, and particularly when the fan assembly is designed for conversion of an existing engine, the non-rotative main body of the fan assembly may house reduction gearing which drives the fan and picks up a drive from the engine. This reduction gearing may also provide a drive for engine auxiliaries.

According to another aspect of the invention a gas turbine engine of the ducted-fan by-pass type has a front-mounted fan assembly which is detachable as a complete assembly and comprises a rotative sub-as¹⁰ sembly, which includes blading and a hub of the fan, and a non-rotative portion by which the assembly as a whole is mounted and which includes a stationary duct portion which surrounds the fan blading.

BRIEF DESCRIPTION OF THE DRAWINGS

Three fan assemblies in accordance with the invention are illustrated in the accompanying drawings and will now be described, by way of example, with 20 reference thereto. The assemblies are shown attached to the forward ends of main gas turbine engine assemblies, whereby in each case to provide a gas turbine engine of the ducted-fan by-pass type also in accordance with the invention. In the drawings:

FIG. 1 is an axial sectional view of one of the assemblies, only the immediately adjacent portion of the engine assembly to which it is attached being shown,

FIG. 2 is a front view of the assembly of FIG. 1, the left-hand half of this figure being shown partly in sec30 tion on the line II — II in FIG. 1,

FIG. 3 is a view similar to that of FIG. 1 but illustrating another of the fan assemblies, and

FIG. 4 is a half view, mainly in axial section, of the third fan assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In each of the illustrated embodiments the fan as₄θ sembly A is attachable to and detachable from the main engine assembly B as a unit. For this purpose of differentiation the fan assemblies are shown in full lines in the drawings and the adjacent portions of the main engine assemblies in broken lines. The fan assembly of 45 each arrangement comprises a non-rotative portion having a main body 10 which defines an interface, identified by the line C in the drawings, at which the assembly A is bolted up to the front end of the main engine assembly B. A rotative sub-assembly including a 50 hub structure 11 and blading 12 of the fan is supported in spaced anti-friction bearings in the non-rotative main body 10. The blading 12 is of variable pitch which is reversible to produce a reverse air flow along a nonrotative by-pass duct 13 within which the fan is ⁵⁵ rotatably supported. The by-pass duct 13, which forms part of the non-rotative portion of the fan assembly A, is supported by the main body 20 through a ring of stator blades 14 disposed downstream of the fan blading 12.

6° The pitch of the fan blading 12 is adjustable under the control of a servo-system including a double-acting multi-vaned vane motor 15 disposed within the hub structure 11. Co-acting vanes 16 and 17 (see FIG. 2) of 6$ the motor 15 are respectively attached to bevel gear output members 18 and 19 which turn in opposite directions about the rotation axis D of the fan. Each of the large multiplicity of adjustable-pitch fan blades 12

3,720,060 has a relatively small bevel pinion 20 fixed to its root end, the bevel teeth 22 and 23 of the members 18 and 19 respectively meshing with each pinion 20 on diametrically opposite front and rear sides of the latter. Thus all the blades 12 are adjustable in unison, with a balanced torque applied to the blade roots from the vane motor 15.

A follow-up servo valve (not shown) controlling the blade pitch is disposed coaxially with and within the pitch change motor 15. This valve is not illustrated as it may be of known type, for example connected to a rearwardly extending pitch control member which passes out of the fan assembly A centrally and which is arranged for external remote control of pitch. Alternatively the valve may be controlled by hydraulic pressure ducted through a control duct disposed centrally of the assembly, a feedback connection from the servo valve extended back rearwardly to the control means providing the hydraulic control pressure. As a further alternative, the blading may be under governor control, in which case the governor hydraulic control pressure is supplied to the control valve within the hub 11.

A spinner 24 which forms part of the rotative sub-assembly encloses the forward end of the hub structure 11, and a guard ring 25 built into the duct 13, shown in FIG. 1, surrounds the tips of the fan blades 12. This protects the duct structure in the event of blade breakage.

In the embodiment of FIGS. 1 and 2 the fan hub structure 11 supports only a single tier of blading 12 which charges both the engine compressor (not shown) and the by-pass duct 13. The non-rotative main body 10 of the assembly A bolts up to the front of the engine casing 26 immediately ahead of the engine compressor inlet 27. A central hollow portion 28 of the hub structure, which extends rearwardly of the fan blading 12 into the main body 10, is supported in said spaced bearings 29 and is driven by a splined quill coupling ₄θ member 30 which is in splined engagement on the one hand with the hub portion 28 and, on the other hand, with a forward female end 31 of the main engine shaft. The hub portion 28 supports the remainder of the rotative sub-assembly and is directly supported in the ₄₅bearings 29 within the main body 10.

In the other two embodiments, shown respectively in FIGS. 3 and 4, two tiers of blading are provided. The outer tier is formed by the variable pitch blading 12 and charges the by-pass duct 13 and the inner tier blading 50 32 charges the engine compressor through the engine inlet 27, a duct 33 formed within the main body 10 leading from the inner tier blading 32 to the engine compressor inlet 27. Only the outer tier blading 12 is of variable pitch, to this end the blading roots of this tier 55 being supported in bearings 34 in a shroud ring 35 which encircles and is attached to the tips of the inner tier blades 32. Thus the shroud ring 35 forms part of the rotative sub-assembly, and the inner tier blades 32 are hollow to allow the roots of the outer blades 12 to project through into the hub structure 11 within which the pinions 20 are disposed for the purpose of pitch adjustment, by the vane motor 15, as already described.

A flared splitter structure 41 which forms part of the stationary main body 10 separates the two air flows, to the compressor inlet 27 and along the by-pass duct 13 respectively, and is in effect an extension of the shroud ring 35 in the aerodynamic sense. The structure 41 provides the outer wall of said duct 33 and not only supports the by-pass stator blading 14, which in turn supports the by-pass duct portion 13 of the fan assembly A, ⁵ but it also in effect extends the engine compressor inlet 27 forwardly to the fixed tier blading 32. Thus the splitter structure 41 defines an entry portion of the compressor inlet, and within this entry portion a further ring of stator blading 36 is fixed within the duct 33.

¹⁰ In the fan assembly A of FIGS. 3 and 4 the non-rotative main body 10 houses reduction gear 37 with coaxial input and output members 38 and 39. The input member 38 picks up a quill drive from the main engine jshaft 40 and the output member 39 is directly coupled to the hollow central portion 42 (FIG. 3) of the fan hub structure. The stationary main body 10 projects forwardly into the fan hub structure 11 in order to provide adequate bearing support for the latter, by way of said

2o spaced bearings 43 (as shown in FIG. 3), forwardly of the reduction gear 37. This necessitates that the vaned motor 15 is mounted forwardly of the fan blading 12 and 32 within the front spinner 24 (as also shown in FIG. 3), the output bevel gears having appropriately 25 cranked webs so that they project rearwardly around the forwardly projecting bearing portion 44 (see FIG. 3) for engagement with the pinions 20 of the outer tier of blading 12.

The embodiments of FIGS. 3 and 4 are generally similar, although in the construction of FIG. 4 the reduction gear 37 also provides an auxiliary drive by way of a vertical drive shaft 45 which projects upwardly through one of the stator blades 36 into the splitter structure 41 where it drives, through right-angle bevel gearing 46, an internally splined hollow drive member 47. When the fan assembly A is fitted to the main engine assembly B the auxiliary drive from the member 47 is provided by a splined auxiliary drive shaft 48 which extends into the front of the main engine casing and is offset from the main engine shaft 40 above the engine compressor inlet 27.

In the drawings the duct portion 13 of the fan assembly A is shown as providing the complete by-pass duct of the ducted-fan engine. However, if a larger overall duct length is required the main engine assembly B may also include a stationary duct portion aligned with and providing a rearward extension of the duct portion 13 of the fan assembly A while leaving the latter still attachable to, and detachable from, the engine assembly B as a complete unit.