Patent Application
20140271214
1. Field of the Invention
The present application relates generally to rotor blades, and more specifically, to abrasion strips for rotor blades.
2. Description of Related Art
Abrasion strips are well known in the art for effectively protecting the leading edge of a rotor blade during flight, e.g., from water and sand, both known for rapidly destroying the structural integrity of the blades during flight. It is a desired feature to manufacture the abrasion strips having sufficient toughness to prevent the penetration of the water and sufficient durability “hardness” to prevent penetration of the sand, typically at airspeeds approaching Mach 1. To achieve these features, conventional abrasion strips are typically manufactured with metals such as stainless steel, titanium, and/or nickel alloys and generally formed through stretching and electroforming processes.
The aerodynamic performance of the rotor blade is very dependent on maintaining the original manufactured shape of the blade. For this reason, the tolerances on the blade are maintained tightly. The complex contours associated with the blade shapes pose manufacturing challenges for the above-referenced materials.
Abrasion strips composed of stainless steel are typically formed between dies at room temperature from sheet stock material. Common problems with this process are: natural spring back after the forming process; and, limitations in bend radii at the nose of the abrasion strip. The minimum bend radius is also an issue on tapering swept tips where airfoil thickness and nose radius is often below values for forming. It should be noted that stainless steel is relatively dense, which can cause negative weight and balance impacts if used liberally.
Titanium alloys are less dense than stainless steel, but require an advanced manufacturing process and expensive tooling. Conventional manufacturing methods include the process of super-plastic forming (SPF), wherein the titanium requires heating the titanium workpiece and dies in a furnace (typically inert environment) to just below the beta-transus temperature (1600 F-1700 F) of the Titanium alloy and using pressurized inert gas to blow the workpiece into the shape of the forming die. The abrasion strip blank often requires extensive finishing to remove the alpha-case that has formed during the SPF process as well as supplemental chemical milling to smooth material thinning and control thickness variations that have occurred during the SPF process.
Nickel alloy abrasion strips are typically electroformed (forming substrate removed at completion) or are electroplated to a metallic substrate.
Another known process includes stretch forming, as depicted in
It should be understood that the manufacturing processes discussed above adversely affect the structural integrity of the metals. For example, stretching the metal causes work hardening, thereby adversely changing the characteristics of the material. In addition, the processes are time consuming and expensive.
Although the foregoing developments in abrasion strips represent great strides, many shortcomings remain.
The novel features believed characteristic of the embodiments of the present application are set forth in the appended claims. However, the embodiments themselves, as well as a preferred mode of use, and further objectives and advantages thereof, will best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings, wherein:
While the abrasion strip and method of the present application is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular embodiment disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the process of the present application as defined by the appended claims.
Illustrative embodiments of the apparatus and method are provided below. It will of course be appreciated that in the development of any actual embodiment, numerous implementation-specific decisions will be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
The abrasion strip and method of the present application overcome the above-listed problems commonly associated with conventional abrasive strips. Specifically, the abrasion strip of the present application is manufactured with metal having sufficient toughness to prevent water exposure and sufficient hardness to prevent sand and debris exposure to the rotor blade during flight. This feature is achieved by molding an amorphous metallic material so as to have the same contouring of the leading edge of the rotor blade, then thereafter removably attaching the molded amorphous metal to the leading edge. Further detailed description of these features are provided below and illustrated in the accompanying drawings.
The abrasion strip and manufacturing process of the present application will be understood, both as to its structure and operation, from the accompanying drawings, taken in conjunction with the accompanying description. Several embodiments of the system are presented herein. It should be understood that various components, parts, and features of the different embodiments may be combined together and/or interchanged with one another, all of which are within the scope of the present application, even though not all variations and particular embodiments are shown in the drawings. It should also be understood that the mixing and matching of features, elements, and/or functions between various embodiments is expressly contemplated herein so that one of ordinary skill in the art would appreciate from this disclosure that the features, elements, and/or functions of one embodiment may be incorporated into another embodiment as appropriate, unless described otherwise.
Referring now to the drawings wherein like reference characters identify corresponding or similar elements throughout the several views,
Although shown associated with a helicopter, it will be appreciated that the abrasion strips of the present application may also be utilized with different types of rotary aircraft and rotary systems, e.g., windmills and fixed wing aircraft. For example,
Tiltrotor aircraft 311 includes rotor assemblies 313a and 313b that are carried by wings 315a and 315b, and are disposed at end portions 316a and 316b of wings 315a and 315b, respectively. Tilt rotor assemblies 313a and 313b include nacelles 320a and 320b, which carry the engines and transmissions of tilt rotor aircraft 311. Tilt rotor assemblies 313a and 313b move or rotate relative to wing members 315a and 315b between a helicopter mode in which tilt rotor assemblies 313a and 313b are tilted upward, such that tilt rotor aircraft 311 flies like a conventional helicopter; and an airplane mode in which tilt rotor assemblies 313a and 313b are tilted forward, such that tilt rotor aircraft 311 flies like a conventional propeller driven aircraft.
Rotor assemblies 313a and 313b include a plurality of rotor blades 317, commonly known as proprotors, which also utilize the abrasion strips in accordance with the present application.
One unique feature believed characteristic of the present application is manufacturing abrasion strip 501 with an amorphous material that is sufficiently toughness to prevent water from causing damage at the leading edge of the rotor blade, and that is sufficiently durable to prevent damage from sand and debris during flight.
It should be understood that utilizing conventional metals such as stainless steel, nickel, and titanium to form abrasion strips with current manufacturing processes does not provide a good compromise of toughness and strength properties to efficiently prevent water and sand damage during flight. Thus, amorphous metal is preferred in the contemplated embodiment because the metal has sufficient toughness and strength when manufactured through a molding process. The relatively low melting temperature and viscosity of amorphous material is ideal for the contemplated manufacturing process. For example, during the molding manufacturing process, amorphous metals do not crystallize, thereby being formed without undesired grain boundaries that typically cause the metal to fail.
In the preferred embodiment, the amorphous metal is an alloy having atoms of significantly different sizes, leading to low free volume in molten state. The viscosity prevents the atoms moving enough to form an ordered lattice. The material structure also results in low shrinkage during cooling and resistance to plastic deformation. The absence of grain boundaries leads to a better resistance to wear and corrosion. It will be appreciated that the abrasion strip of the present application creates a very smooth surface finish, resulting in reduced finish processing. These features are achieved through pouring mold or pressing at low temperatures. Further, the abrasion strip has a high hardness, which in turn increased durability. Further detailed description of these features is provided below with reference to
It will be appreciated that the process of manufacturing an abrasion having various thicknesses is a complicated and expensive process when utilizing conventional manufacturing methods. For this reason, it is desired to mold abrasion strip 501 such that a desired thickness is achieved while also matching the contouring of the blade. It should be understood that the above conventional metals are not molded due to the limitations of their material properties and manufacturing process.
Although shown as a simplified molding and cold forming process, it is also contemplated using other steps in the manufacturing process. Further, it is also contemplated utilizing different techniques to mold the abrasion strip with the amorphous material without departing from the scope and spirit of the present application.
Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure.
It is apparent that an abrasion strip and method with significant advantages has been described and illustrated. The particular embodiments disclosed above are illustrative only, as the embodiments may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. It is therefore evident that the particular embodiments disclosed above may be altered or modified, and all such variations are considered within the scope and spirit of the application. Accordingly, the protection sought herein is as set forth in the description. Although the present embodiments are shown above, they are not limited to just these embodiments, but are amenable to various changes and modifications without departing from the spirit thereof.
