Snap fit nose cone

Abstract

A snap fit nose cone comprises a body with a conical nose, and a rim, with a snap fitting lip, configured such that the nose cone can be snapped into place on an inlet housing, and such that the edge of the inlet housing butts up against the inlet housing body edge.

Description

SNAP FIT NOSE CONECROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This application claims the priority and benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application Serial No. 63 / 612,924 filed December 20, 2023, entitled “SNAP FIT NOSE CONE.” U.S. Provisional Patent Application Serial Number 63 / 612,924 is herein incorporated by reference in its entirety.TECHNICAL FIELD

[0002] Embodiments are generally related to turbines. Embodiments are related to engines. Embodiments are further related to manufacturing methods and processes associated with engine turbines. Embodiments are further related to engine turbine parts. Embodiments are directed to snap fit engine turbine nose cones and methods of manufacturing the same.BACKGROUND

[0003] Engine turbines find broad utility in modern society. A turbine can generally be understood to be a machine that converts energy in a fluid flow into some other form of energy to produce work. Common applications for turbines include engines and energy production.

[0004] Turbine engines are often used for aircraft propulsion. In these types of applications, a nose cone is generally provided at the leading interface between the engine and the fluid flow. The nose cone is used to direct airflow and reduce drag. Nose cones also protect internal blade hardware, bushings, fasteners, and other engine parts. To this end, nose cones are generally made of a hard material and are shaped to direct fluid flow around the cone in the desired flow pattern.

[0005] While nose cones are nearly ubiquitous in turbine engine design, there remains aspects of the nose cones which are not ideal. For example, prior art approaches may include bolting the nose cone to a housing. Doing so can interrupt the smooth outer contour of the nose cone, disrupting airflow entering the inlet housing. Likewise, bolting the nose cone adds additional parts and steps to the assembly procedure. Additional parts increase the risk that parts could be missed during assembly or could be misassembled, come loose, and in the worst case, could be ingested into the engine.

[0006] Accordingly, there is a need in the art for improved nose cone assemblies, as disclosed in the embodiments herein.BRIEF SUMMARY

[0007] The following summary is provided to facilitate an understanding of some of the innovative features unique to the embodiments disclosed and is not intended to be a full description. A full appreciation of the various aspects of the embodiments can be gained by taking the entire specification, claims, drawings, and abstract as a whole.

[0008] It is, therefore, one aspect of the disclosed embodiments includes improved nose cone assemblies, and / or parts thereof.

[0009] It is another aspect of the disclosed embodiments to provide methods of manufacturing turbine engine parts.

[0010] It is another aspect of the disclosed embodiments to provide snap fit nose cones for turbine engines.

[0011] For example, in an embodiment, a nose cone comprises a body, a rim formed on the body, and a snap fitting lip formed on the rim of the body. In an embodiment, the rim formed on the body further comprises an axial flange, and a set forward separating a housing body edge and snap fitting lip. In an embodiment, the rim formed on the body further comprises a tip extending beyond the snap fitting lip. In an embodiment, the nose cone further comprises a key formed in the rim. In an embodiment, the nose cone further comprises at least one rim cutout formed in the rim. In an embodiment, the nose cone is configured to snap fit with an inlet. In an embodiment, the snap fitting lip is shaped to match a groove formed in an inlet.

[0012] In an embodiment, a snap fitting nose cone comprises a body, a rim formed on the body, the rim having a smaller diameter than the body, and a snap fitting lip formed on the rim of the body, wherein the snap fitting lip is configured to fit an inlet / casing associated with a turbine. In an embodiment, the rim formed on the body further comprises an axial flange, and a set forward separating a housing body edge and snap fitting lip. In an embodiment, the snap fitting nose cone further comprises a key formed in the rim. In an embodiment, thesnap fitting nose cone further comprises at least one rim cutout formed in the rim. In an embodiment, the snap fitting lip is configured to be permanently engaged to the inlet / casing associated with the turbine.

[0013] In an embodiment, a nose cone comprises a body, a rim formed on the body, and a snap fitting lip formed on the rim of the body, the snap fitting lip comprising: a leading edge slanted surface, a flat top surface, and a trailing edge slanted surface. In an embodiment, the leading edge slanted surface is longer than the trailing edge slanted surface. In an embodiment, the trailing edge slanted surface is steeper than the leading edge slanted surface. In an embodiment, the nose cone is configured to snap fit with an inlet. In an embodiment, the snap fitting lip is shaped to match a groove formed in the inlet. In an embodiment, the groove formed in the inlet comprises a housing trailing edge slanted surface, a back flat surface, and a back engaging slanted surface. In an embodiment, an angle of a housing leading edge slanted surface and an angle of the leading edge slanted surface sum to 180 degrees. In an embodiment, an angle of the trailing edge slanted surface and an angle of a housing trailing edge slanted surface sum to 180 degrees.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying figures, in which like reference numerals refer to identical or functionally similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate the embodiments and, together with the detailed description, serve to explain the embodiments disclosed herein.

[0015] FIG. 1 A depicts a snap fitting nose cone, in accordance with the disclosed embodiments;

[0016] FIG. 1 B depicts another view of a snap fitting nose cone, in accordance with the disclosed embodiments;

[0017] FIG. 2 provides an elevation cross-sectional view of a snap fitting nose cone and inlet housing / case, in accordance with the disclosed embodiments;

[0018] FIG. 3 provides an elevation view of a snap fitting nose cone engaged to an inlet housing / case, in accordance with the disclosed embodiments;

[0019] FIG. 4 provides another elevation view of a snap fitting nose cone and inlet housing / case, in accordance with the disclosed embodiments;

[0020] FIG. 5 illustrates a snap fitting nose cone engaged to an inlet, in accordance with the disclosed embodiments;

[0021] FIG. 6 illustrates steps associated with a method for manufacturing a snap fitting nose cone, in accordance with the disclosed embodiments; and

[0022] FIG. 7 illustrates steps associated with a method for installing a snap fitting nose cone on an inlet, in accordance with the disclosed embodiments.DETAILED DESCRIPTION

[0023] The particular values and configurations discussed in the following non-limiting examples can be varied and are cited merely to illustrate one or more embodiments and are not intended to limit the scope thereof.

[0024] Example embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments are shown. The embodiments disclosed herein can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the embodiments to those skilled in the art. Like numbers refer to like elements throughout.

[0025] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprise" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0026] Throughout the specification and claims, terms may have nuanced meanings suggested or implied in context beyond an explicitly stated meaning. Likewise, the phrase “in one embodiment” as used herein does not necessarily refer to the same embodiment and the phrase “in another embodiment” as used herein does not necessarily refer to a different embodiment. It is intended, for example, that claimed subject matter include combinations of example embodiments in whole or in part.

[0027] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. Itwill be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0028] It is contemplated that any embodiment discussed in this specification can be implemented with respect to any method, kit, reagent, or composition of the invention, and vice versa. Furthermore, compositions of the invention can be used to achieve methods of the invention.

[0029] It will be understood that particular embodiments described herein are shown by way of illustration and not as limitations of the invention. The principal features of this invention can be employed in various embodiments without departing from the scope of the invention. Those skilled in the art will recognize or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific procedures described herein. Such equivalents are considered to be within the scope of this invention and are covered by the claims.

[0030] The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and / or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.” The use of the term “or” in the claims is used to mean “and / or” unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and / or.” Throughout this application, the term “about” is used to indicate that a value includes the inherent variation of error for the device, the method being employed to determine the value, or the variation that exists among the study subjects.

[0031] As used in this specification and claim(s), the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive oropen-ended and do not exclude additional, unrecited elements or method steps.

[0032] The term “or combinations thereof” as used herein refers to all permutations and combinations of the listed items preceding the term. For example, “A, B, C, or combinations thereof” is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.

[0033] All of the compositions and / or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and / or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit, and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.

[0034] The embodiments, disclosed herein are directed to a snap fitting nose cone for an engine, such as a gas turbine engine, that can be assembled to the engine with no fasteners or secondary separate retention features. The snap fitting nose cone features an annular rib across the full 360 degree span located on an axial rib protruding from the aft side of the nose cone. This rib fits into a corresponding groove that can be formed in the inlet housing of the engine. When the nose cone is pressed into the inlet housing, the rib deflects inward radially, before snapping back out into the groove in the inlet housing. Once assembled, the nose cone is securely held in place. This technology reduces assembly time and cost by eliminating any additional fasteners. It also creates a smooth external surface without interruptions for fasteners, improving airflow into the engine.

[0035] The embodiments disclosed herein are directed to a snap fit nose cone 100, as illustrated in FIG. 1 A. The snap fit nose cone 100 generally comprises a body 104 with a conical nose 102. The conical nose 102 can be configured with a rounded or curved profile in certain embodiments.

[0036] The turbine side 106 of the body 104 further includes a rim 108. The diameter of the rim 108 can be smaller than the diameter of the body 104. When the nose cone 100 is snapped into place on an inlet housing, the rim 108 of the body 104 extends inside the inlet housing, and the edge of the inlet housing butts up against the inlet housing body edge 1 16 The rim 108 can further include a snap fitting lip 1 10 as further detailed herein.

[0037] In certain embodiments, a key 1 12 is formed on the body 104, and is configured to match a similar cutout in the inlet housing body. The key 1 12 can be used for alignment purposes, so that the joint between the nose cone 100 body 104 and inlet housing body is flush. In addition, the key 1 12, prevents unwanted rotation between the inlet housing and nose cone 100 after installation.

[0038] The interior 1 14 of the nose cone 100 can be empty, although in other embodiments, additional structural supports can be formed in the nose cone interior 114, to prevent deformation from impacts.

[0039] FIG. 1 B illustrates another embodiment of a nose cone 100. In this embodiment, a series of rim cutouts 120 can be formed in the rim 108 of the body 104. The interruptions from the rim cutouts 120 in the annular rim 108 increase flexibility of the rim. This reduces installation force required to snap the nose cone 100 to an inlet housing, and the removal force required to remove the nose cone 100 from the inlet housing.

[0040] In additional embodiments, a wire channel can be incorporated through the nose cone 100 to allow for a pressure and / or temperature sensor to penetrate through the front of the nose cone.

[0041] FIG. 2 illustrates a perspective cross-sectional view of the top half of a snap fit nose cone 100 in accordance with the disclosed embodiments. As illustrated, the snap fit nosecone 100 generally comprises a body 104 with a conical nose 102. On the turbine side 106 of the body 104, details of the rim 108 are illustrated in this view.

[0042] The rim 108 can comprise an axial flange 202, with the snap fitting lip 110 formed thereon. The snap fitting lip 110 can have a set forward 214 from the housing body edge 1 16. Likewise, the axial flange 202 can include a tip 210, extending slightly beyond the snap fitting lip 110.

[0043] The inlet housing / casing 204 can comprise an annular fitting configured with an annular snap groove 206. The annular shaped snap groove 206 has a profile matching that of the snap fitting lip 110 such that the snap fitting lip 110 fits in the annular snap groove 206. The annular snap groove 206 has a setback 212 from the installation end 208 of the inlet housing / casing 204. The length of the setback 212 can nominally match the length of the set forward 214, so that, when the snap fitting nose cone 100 is engaged to the inlet housing / casing 204, as shown by arrow 218, the installation end 208 of the housing / casing is flush against the housing body edge 116.

[0044] FIG. 3 illustrates a perspective cut away view of the rim 108 of the snap fit nose cone 100 engaged with the inlet housing / casing 204. As illustrated, the annular shaped snap groove 206 is engaged by the snap fitting lip 110 such that the snap fitting lip 1 10 fits in the annular snap groove 206. Similarly, the setback 212 from the installation end 208 of the inlet housing / casing 204. The length of the setback 212 can nominally match the length of the set forward 214, so that, when the snap fitting nose cone 100 is engaged to the inlet housing / casing 204, the installation end 208 of the housing / casing is flush against the housing body edge 116.

[0045] FIG. 4 illustrates aspects of another embodiment of a snap fit nose cone 100. In this view, aspects of the axial flange 202 and snap fitting lip 110 are provided. The snap fitting lip 110 can be configured to have a leading edge slanted surface 402, a flat top surface 404 and a trailing edge slanted surface 406. The leading edge slanted surface 402 can be selected to be longer and less steep than the trailing edge slanted surface 406.

[0046] Likewise, the inlet housing / casing 204 can comprise a vertical front surface 408 and a housing leading edge slanted surface 410, a flat bottom surface 412, and a housing trailing edge slanted surface 414. The inlet housing / casing 204 can further include a back flat surface 420 between the housing trailing edge slanted surface 414 and back engaging slanted surface 418. The housing trailing edge slanted surface 414, back flat surface 420, and back engaging slanted surface 418 create a snap fitting groove 416 in the inlet housing / casing 205.

[0047] It should be noted that the angle of the housing leading edge slanted surface 410 of inlet housing / casing 204 and the angle of the leading edge slanted surface 402 the snap fit nose cone 100 can sum to 180 degrees such that they are parallel and / or at relative angles from the respective flat surface to which they are attached to sum to 180 degrees. The angle of the engaging slanted surface 418 and the angle of the housing leading edge slanted surface 410 can sum to 180 degrees such that they are parallel and / or at relative angles from the respective flat surface to which they are attached to sum to 180 degrees. In addition, the trailing edge slanted surface 406 of the snap fit nose cone 100, and the housing trailing edge slanted surface 414 can sum to 180 degrees such that they are parallel and / or at relative angles from the respective flat surface to which they are attached to sum to 180 degrees.

[0048] In order to install the snap fit nose cone on the inlet housing / casing 204 the leading edge slanted surface 402 can be pushed against the housing leading edge slanted surface 410 of the inlet housing / casing 204. The relative force required to push the snap fitting lip 1 10 past the housing leading edge slanted surface 410 is lower than the force required to remove the snap fitting lip 110 in the annular snap fitting groove 416. This is, in part, because the trailing edge slanted surface 406, and housing trailing edge slanted surface 414 in the snap groove 416 is much steeper. In practice, this makes it much easier to install the snap fit nose cone 100, than to remove it from the inlet housing / casing 204.

[0049] FIG. 5 illustrates an exemplary mating of the snap fit nose cone 100 with the inlet housing / casing 204. This view shows that the snap fit nose cone 100 can mate with the housing / casing 204 such that the respective edges are flush. As further illustrated in FIG. 5, the snap fit nose cone disclosed herein does not require external hardware (e.g. screws,bolts, or rivets) for connecting to the inlet housing / casing 204, which improves airflow, and reduces the number of parts which could fail.

[0050] FIG. 6 illustrates a method 600 of manufacturing a snap fit nose cone, such as snap fit nose cone 100, using an additive manufacturing approach, in accordance with the disclosed embodiments. It should be appreciated that, in other embodiments, other manufacturing methods can be used, and the method provided in FIG. 6 is meant to be exemplary. The method starts at 605.

[0051] At step 610, a snap fitting lip profile can be selected. In certain embodiments, this can include selecting the angle of a leading edge of the snap fitting lip and a trailing edge profile of the snap fitting lip. At step 615, optional cutouts and / or a key can be selected for inclusion in the snap fit cone.

[0052] Next at step 620, the snap fit nose cone can optionally be rendered digitally in cross sections, appropriate for sending to an additive manufacturing device such as a 3D printer. The 3D printer can then render the snap fit nose cone at step 625. It should be appreciated that steps 620 and 625 are exemplary. In other methods, the snap fit nose cone can be machined, injection molded, or produced by other such processes. The method ends at step 630.

[0053] FIG. 7 illustrates a method 700 for installing a snap fit nose cone, such as snap fit nose cone 100 on an inlet housing / case in accordance with the disclosed embodiments. The method starts at step 705.

[0054] At step 710, the rim of snap fit nose cone can be roughly aligned with the profile of the inlet housing / case. If the snap fit nose cone includes a key, the key can be aligned with a matching cutout in the inlet housing at step 715.

[0055] At step 720, the snap fit nose cone rim can be inserted into the inlet housing / case. It should be appreciated that the rim can have a diameter slightly smaller than the inlet housing / case diameter, but can be wide enough to maintain contact with the inlet / housing to provide a tight connection. At step 725, the snap fitting lip can be pushed to engage the snapgroove of the inlet housing / case. The interface creates high friction to prevent nose cone from inadvertently disconnecting from the inlet housing / case. The method ends at 730.

[0056] The snap fit nose cone fit, as disclosed herein, may be dependent on several factors, including but not limited to, the material of the nose cone and the material of the mating case, the thickness of the axial rib on the nose cone and the thickness of the mating case, the height of the annular snap rib, the lead in angle of the snap rib, and the return angle of the snap rib. By adjusting these parameters, the disclosed embodiments of the snap fit nose cone can be configured such that it is easy or difficult to assemble and easy to disassemble; easy or difficult to assemble and difficult to disassemble; or easy or difficult to assemble and impossible to disassemble without destroying the part.

[0057] With that in mind, for the disclosed embodiments, the snap fit nose cone is configured to make it difficult or impossible to remove, since it is critical that the nose cone not come off during engine operation. However, the disclosed embodiments are also configured such that the installation force is not so high that assembly is difficult or impossible. As such, in a preferred embodiments the snap fit nose cone is easy to assemble and difficult to remove. The nose cone can comprise plastic or printed plastic. It should be appreciated that in other embodiments, the nose cone can be other material. However, the mating part (e.g., inlet housing / casing) may often be much stiffer, and can be metal.

[0058] Based on the foregoing, it can be appreciated that a number of embodiments, preferred and alternative, are disclosed herein. In an embodiment, a nose cone comprises a body, a rim formed on the body, and a snap fitting lip formed on the rim of the body. In an embodiment, the rim formed on the body further comprises an axial flange, and a set forward separating a housing body edge and snap fitting lip. In an embodiment, the rim formed on the body further comprises a tip extending beyond the snap fitting lip. In an embodiment, the nose cone further comprises a key formed in the rim. In an embodiment, the nose cone further comprises at least one rim cutout formed in the rim. In an embodiment, the nose cone is configured to snap fit with an inlet. In an embodiment, the snap fitting lip is shaped to match a groove formed in an inlet.

[0059] In an embodiment, a snap fitting nose cone comprises a body, a rim formed on the body, the rim having a smaller diameter than the body, and a snap fitting lip formed on the rim of the body, wherein the snap fitting lip is configured to fit an inlet / casing associated with a turbine. In an embodiment, the rim formed on the body further comprises an axial flange, and a set forward separating a housing body edge and snap fitting lip. In an embodiment, the snap fitting nose cone further comprises a key formed in the rim. In an embodiment, the snap fitting nose cone further comprises at least one rim cutout formed in the rim. In an embodiment, the snap fitting lip is configured to be permanently engaged to the inlet / casing associated with the turbine.

[0060] In an embodiment, a nose cone comprises a body, a rim formed on the body, and a snap fitting lip formed on the rim of the body, the snap fitting lip comprising: a leading edge slanted surface, a flat top surface, and a trailing edge slanted surface. In an embodiment, the leading edge slanted surface is longer than the trailing edge slanted surface. In an embodiment, the trailing edge slanted surface is steeper than the leading edge slanted surface. In an embodiment, the nose cone is configured to snap fit with an inlet. In an embodiment, the snap fitting lip is shaped to match a groove formed in the inlet. In an embodiment, the groove formed in the inlet comprises a housing trailing edge slanted surface, a back flat surface, and a back engaging slanted surface. In an embodiment, an angle of a housing leading edge slanted surface and an angle of the leading edge slanted surface sum to 180 degrees. In an embodiment, an angle of the trailing edge slanted surface and an angle of a housing trailing edge slanted surface sum to 180 degrees.

[0061] It should be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. It should be understood that various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.

Claims

CLAIMSWhat is claimed is:1 . A nose cone comprising: a body; a rim formed on the body; and a snap fitting lip formed on the rim of the body.

2. The nose cone of claim 1 wherein the rim formed on the body further comprises: an axial flange; and a set forward separating a housing body edge and snap fitting lip.

3. The nose cone of claim 1 wherein the rim formed on the body further comprises: a tip extending beyond the snap fitting lip.

4. The nose cone of claim 1 further comprising: a key formed in the rim.

5. The nose cone of claim 1 further comprising: at least one rim cutout formed in the rim.

6. The nose cone of claim 1 wherein the nose cone is configured to snap fit with an inlet.

7. The nose cone of claim 1 wherein the snap fitting lip is shaped to match a groove formed in an inlet.

8. A snap fitting nose cone comprising: a body; a rim formed on the body, the rim having a smaller diameter than the body; and a snap fitting lip formed on the rim of the body, wherein the snap fitting lip is configured to fit an inlet / casing associated with a turbine.

9. The snap fitting nose cone of claim 8 wherein the rim formed on the body further comprises: an axial flange; and a set forward separating a housing body edge and snap fitting lip.

10. The snap fitting nose cone of claim 8 further comprising: a key formed in the rim.1 1 . The snap fitting nose cone of claim 8 further comprising: at least one rim cutout formed in the rim.

12. The snap fitting nose cone of claim 8 wherein the snap fitting lip is configured to be permanently engaged to the inlet / casing associated with the turbine.

13. A nose cone comprising: a body; a rim formed on the body; and a snap fitting lip formed on the rim of the body, the snap fitting lip comprising: a leading edge slanted surface; a flat top surface; and a trailing edge slanted surface.

14. The nose cone of claim 13 wherein the leading edge slanted surface is longer than the trailing edge slanted surface.

15. The nose cone of claim 13 wherein the trailing edge slanted surface is steeper than the leading edge slanted surface.

16. The nose cone of claim 13 wherein the nose cone is configured to snap fit with an inlet.

17. The nose cone of claim 16 wherein the snap fitting lip is shaped to match a groove formed in the inlet.

18. The nose cone of claim 17 wherein the groove formed in the inlet comprises: a housing trailing edge slanted surface; a back flat surface; and a back engaging slanted surface.

19. The nose cone of claim 18, wherein an angle of a housing leading edge slanted surface and an angle of the leading edge slanted surface sum to 180 degrees.

20. The nose cone of claim 18, wherein an angle of the trailing edge slanted surface and an angle of a housing trailing edge slanted surface sum to 180 degrees.

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