Patent Application
20210062661
A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
This invention relates to composite structures, and more particularly to improvements in a structure and a method of constructing a blade retention mechanism and root area of a composite airfoil of a propulsor blade used in aircraft propulsion systems such as, for example, propellers, ducted fans, and the like.
The design disclosed herein provides improvements over a prior invention disclosed in U.S. Pat. No. 6,676,080 B2, issued Jan. 13, 2004, titled “Composite Airfoil Assembly,” by John A. Violette (hereinafter the “'080 patent”), which is incorporated by reference herein in its entirety. The prior, patented invention achieved a significant reduction in the weight of the root attachment joint of composite propulsor blades, while maintaining a high level of strength, safety and durability, which are highly desirable characteristics in aircraft applications. An improvement of the design of the '080 patent is disclosed in U.S. Patent Application Publication No. 2018/0290728 A1, published Oct. 11, 2018, titled “Composite Propulsor Blade Support Structure and System,” by John A. Violette and Eric Stephen Loos, which is also incorporated by reference herein in its entirety. This improvement discloses, inter alia, a preloading component configured to apply a residual compressive force to at least one sleeve and the root portion of the propulsor blade; the residual compressive force being configured to maintain an attachment of the at least one sleeve to the root portion.
As is known, the root portions of propulsor blades typically terminate in a cylindrical shape to accommodate cooperation with a variety of low friction bearing assemblies, generally consisting of ball and/or roller elements. These bearing assemblies interface with individual blade sockets or “arms” of a central hub assembly. In such installations, the bearing assemblies allow the blades to be rotatable, and a pitch control system allows the pitch angle of all blades to be varied simultaneously to maximize thrust for different aircraft operating conditions, resulting in greater aircraft propulsive efficiency.
In addition to the cylindrical shape of the root portion, one or more rings, sleeves or similar components are integrally bonded to inner and outer portions of the cylindrical shaped root portion to accommodate installation of the low friction bearing assemblies. The rings, sleeves or similar components are typically constructed of aluminum, steel or other metals having suitable strength and wear characteristics. For example, and as described in the '080 patent, during construction of a propulsor blade assembly, layers of composite material (e.g., braided glass fiber and graphite) are first dry assembled together with the rings, sleeves or similar components and then inserted into a mold. A suitable resin is then injected into the mold to fill voids and spaces between the composite layers and the rings, sleeves or similar components. The resin is cured at elevated temperature. This process is known to persons skilled in the art as a resin transfer molding (RTM) process. While generally effective for bonding purposes, the composite and metal materials react differently at elevated temperature and thus thermal stresses may be introduced in the composite blade to metal ring/sleeve bond. The inventor has recognized that this thermal stress can introduce misalignment and other undesirable conditions into the method for forming a propulsor blade assembly.
Accordingly, the inventor has discovered that one solution would be to remove at least some of the bonding process currently being done before or in the RTM process, for example, to perform the composite blade to outer sleeve bonding after the RTM process to reduce thermal stresses. In still another improvement, the inventor has discovered that use of a single-row bearing assembly and, for example, a thrust bearing, to retain the blade and reduce ball contact stresses allowing the bearing to carry a greater load without increasing its size. Also, the single-row bearing assembly allows for the removal of other bearings thus reducing an amount of weight and corresponding load on the remaining, single-row bearing assembly.
An embodiment of a blade retention assembly for a blade having a root area at one end of the blade, which includes an inner cavity with a root opening at the one end defined by annular ridge extending radially inward. The blade retention assembly includes an outer sleeve disposed circumferentially around an outer surface of the root area of the blade. The outer sleeve includes a support extending radially inward configured to engage an outer portion of the annular ridge of the root portion of the blade. The support defines a through-bore therein. An inner sleeve includes an inner portion disposed circumferentially around an inner surface of the root area of the blade within the inner cavity and a lower portion disposed circumferentially around an inner portion of the annular ridge of the root area of the blade. A fastener is configured to attach and draw the inner sleeve and outer sleeve together to clamp the annular ridge of the root area of the blade therebetween.
An embodiment of a blade assembly includes a blade having a root area at one end of the blade. The root area includes an inner cavity with a root opening at one end defined by an annular ridge extending radially inward. A blade retention assembly includes an outer sleeve disposed circumferentially around an outer surface of the root area of the blade and includes a support radially extending inward configured to engage an outer portion of the annular ridge of the root area. The support defines a through-bore therein. An inner sleeve includes an upper portion disposed circumferentially around an inner surface of the root area of the blade within the inner cavity and a lower portion disposed circumferentially around an inner portion of the annular ridge of the root area of the blade. A fastener configured to attach and draw the inner sleeve and outer sleeve together to clamp the annular ridge of the root area of the blade therebetween.
An embodiment of a method of attaching a blade to a blade retention assembly includes attaching an inner sleeve of the blade retention assembly within a cavity of a root area of the blade by a resin transfer molding process. The method further includes attaching an outer sleeve of the blade retention assembly to an outer surface of root area of the blade after completion of the resin transfer molding process.
The blade 12 includes a root area 16 (i.e., a base portion), a tip 18, and a leading edge 20 and a trailing edge 22 that extend between the root area 16 and the tip 18. The blade 12, in one embodiment, is cylindrical in shape at the root area 16 and transitions to an airfoil that thins, twists and flattens toward the tip 18 in a well-known manner, depending on the type of propulsor blade to be constructed. A root portion 24 of the blade assembly 10 includes the blade retention assembly 14 configured to receive and securely mount the root area 16 of the blade 12 to the hub 34, such as that shown in
With reference to
The outer portion 40 of the blade 12 is formed adjacent to an inner foam core 42 located in an interior of the blade portion 12. The foam core 42 may be constructed of a lightweight, closed-cell foam material, such as polyurethane foam. As shown, the foam core 40 may stop short of the lower end of the root area 16 to form an internal cavity 44 having an opening 46 at the lower end of the root area. The opening 46 is defined by an annular ridge 48 extending radially inward into the internal cavity 44 of the root area 16. The annular ridge 48 is configured to facilitate connection of the root area 16 of the blade 12 to the blade retention assembly 14, which will be described in greater detail hereinafter. An outer surface 50 of the root area 16, including the annular ridge 48 extending inwardly, provides a generally uniform cylindrical outer wall 52, and thus, provides a root area 16 with a smaller outer diameter than disclosed in prior art embodiments that provide an annular ridge extending radially outward from the outer surface of the root area of the blade as shown in U.S. Pat. No. 6,676,080 B2. The reduced outer diameter of the root area 16 of the blade assembly 14 results in reductions in the diameter and weight of the root portion 24 of the composite blade assembly 10. As can be appreciated, decreasing the outer diameter of the blade root area 16 provides additional weight reduction and aerodynamic performance benefits to the entire aircraft propulsion system of current and “next generation” aircraft, where the trend is to, for example, increase the number of blades to reduce propulsor external noise and vibration transmitted to passengers.
As shown in
In one embodiment, as shown in
The inner sleeve 60 is disposed within the inner cavity 44 of the root area 16 of the blade 12. The outer surface of the inner sleeve 60 at least partially conforms to an inner surface of the root area 16 of the blade 12 and/or the toroidal loop 54. For example, as oriented in
The outer sleeve 62 extends circumferentially around the outer wall of the root area 16 and the toroidal loop 54 of the blade 12. The outer sleeve 62 at least partially conforms to the outer surface of the root area 16. A lower portion of the outer sleeve 62 includes an annular support 76 extending inwardly having an upper curved surface 78 that may conform to the lower portion of the toroidal loop 54 of the root area 16 of the blade 12 and the inner sleeve 60 (intermediate portion 68 and lower portion 70 of the inner sleeve 60.) A through-bore 74 in the lower portion of the outer sleeve 62 is configured to receive the threaded lower portion 70 of the inner sleeve 60 extending through the outer sleeve 62.
The threaded nut 64 is configured to secure onto the lower portion 70 of the inner sleeve 60 extending through the through-bore 74 of the outer sleeve 62 and apply a residual compressive force to the outer sleeve and the root area 16 of the blade 12. The nut 64 threads onto the lower portion 70 of the inner sleeve 60 to force the inner sleeve 62 and outer sleeve 62 together to clamp the toroidal loop 54 therebetween when tightened. The compressive force applied by the nut 64 is supplemental to the compression force provided by centrifugal loads when the blade 12 is rotating with the hub 34. The residual compressive force increases the bending capacity of the blade root 16 when the centrifugal load alone (which is typically low with lightweight composite blades) is insufficient to maintain compressive force all around the bond joint between the outer sleeve 62 and the root portion 16 when bending loads are applied.
The centrifugal pull force produces a compressive load on a substantial portion of the composite between the inner sleeve 60 and outer sleeve 62. This construction is advantageous for at least the following reasons: 1) most of the composite to metal bond joint is in a state of high compression, which maximizes its shear strength by avoiding the weaker peel mode of failure; 2) the required bond area is minimized; and 3) with all composite layers wrapped around the internal ring 56, and with the internal ring 56 being too large to slip past the inner sleeve 60 under the outward centrifugal force, the blade 12 is mechanically locked to the root portion 24. Thus, should there be a bond joint failure, this construction prevents separation of the blade 12 from the root portion 24. Further, if the outer sleeve bond joint were to fail, the threaded nut joint is designed to carry all composite blade loads. Root bending capacity of the composite blade 10 is increased because the composite wrap is all enclosed in metal. The blade retention assembly 14 provides multiple load paths for redundancy, even if the outer sleeve is completely disbanded, the blade is still retained by the inner sleeve 60 and the nut 64. While the nut 64 is described as a means for securing the inner sleeve 60 and blade 20 to the outer sleeve 62, the present invention contemplates any other fastener, e.g. retaining rings and pins, may be used. Furthermore, a bolt may be used as described hereinafter in reference to
The outer sleeve 62 may include various features to facilitate operable connection to the hub 34. The outer sleeve 62 has an annular surface 80 that bears against a retaining surface (not shown) of a rotor hub (not shown) in a well-known manner to prevent separation of the propulsor blade assembly 10 from the rotor hub under high outward centrifugal force during rotation of the hub.
As is known, the root portion 24 of propulsor blades 10 typically terminate in a cylindrical shape to accommodate cooperation with a variety of low friction bearing assemblies, generally consisting of ball and/or roller elements. These bearing assemblies 84 interface with individual blade sockets or arms 32 of a central hub assembly 34. In such installations, the bearing assemblies 84 allow the blades 12 to be rotatable, and a pitch control system allows the pitch angle of all blades to be varied simultaneously to maximize thrust for different aircraft operating conditions, resulting in greater aircraft propulsive efficiency.
For example, as shown in
The blade assembly 10 may also include features to allow the blade pitch to be changed. For example, the blade assembly 10 includes a pitch change pin 36 extending inwardly from the base of the blade 12 and located eccentric to the blade longitudinal axis. The pin 36 interfaces with a blade pitch change mechanism (not shown) for the purpose of adjusting blade angle as desired to improve or optimize propulsor thrust according to aircraft operating condition.
The dry assembly, including the inner core 42, the dry layers of material, the internal ring 56 and the inner sleeve 60, are then inserted into a mold at 104. Suitable resin at 106 is subsequently injected into the mold to fill the spaces between the inner sleeve 60, the foam core 42 and the layers of the materials to form the outer composite layer 40 of the blade 16. At 108 the resin is then cured at an elevated temperature of approximately 120° C. to 180° C., after which the assembly is released from the mold and allowed to cool to room temperature at 110. At 112 once the blade 12 with the inner sleeve 60 bonded thereto are removed from the mold and cooled to room temperature, the outer sleeve 62 also at room temperature may be bonded by an adhesive to the outer surface/wall 52 of the root area 16 of the blade 12 and the lower portion of the toroidal loop 54. Unlike the prior art, the outer sleeve 62 is not bonded to the root area 16 of the blade 12 during the RTM process in order to reduce thermal stresses between the root area 16 of the blade 12 and the outer sleeve 62 during the curing process. At 114 the nut 64 is threaded onto the threaded lower portion 70 of the inner sleeve 60 extending through the opening 46 of the outer sleeve 62. Tightening of the nut 64 draws the inner sleeve 60 and the outer sleeve 62 together thus clamping the toroidal loop 54 of the root area 16 of the blade 12 therebetween. Alternatively, the outer sleeve 62 may be bonded or attached to the root area 16 of the blade 12 simply with the nut 64 without an adhesive.
The advantages of this structure and method of constructing include, but are not limited to, minimizing thermal stresses by integrally bonding the inner sleeve 60 and the internal ring 56 to composite material of the blade 12 when the blade 12 is in the RTM process, and then subsequently bonding or attaching the outer sleeve 62 to the composite material of the blade 12 at room temperature after the blade 12 is molded. Further, the bonding or attachment of the outer sleeve 62 to the root area 16 of the blade 12 after the RTM process not only reduces joint thermal stresses, but also achieves consistent alignment between the airfoil and the blade retention, as some stacking error can be taken up in the bond line between the blade 12 and the outer sleeve 62. Also, the elimination of the outer sleeve 62 from the layup and RTM process when forming the blade 12 makes the holding of the blade easier and simpler without the outer sleeve in place because, for example, wrapping the composite layers around the internal ring 56 without the outer sleeve preserves the composite fiber alignment. As mentioned, the bonding of the outer sleeve 62 after the construction of the blade 12 assures good alignment (stacking) of bearing races to the blade outer airfoil. The assembly or bonding of the outer sleeve 62 to the blade 12 permits the outer sleeve 62 to be designed to be removable and/or replaceable for improved servicing of the blade retention, for example due to wear.
The outer sleeve 62 extends circumferentially around the outer wall of the root area 16, the toroidal loop 54 of the blade 12 and the lower portion 70 of the inner sleeve 60. The outer sleeve 62 at least partially conforms to the outer surface of the root area 16 of the blade 12 and the lower portion 70 of the inner sleeve 60. The lower portion of the outer sleeve 62 includes an annular support 76 extending inwardly having an upper curved surface 78 that may conform to the lower portion of the toroidal loop 54 of the root area 16 of the blade 12 and the bottom portion of the inner sleeve 60 (e.g., at least one of the intermediate portion 68 and the lower portion 70 of the inner sleeve 60.) The annular support 76 extends along at least a portion of a bottom surface 254 of the lower portion 70 of the inner sleeve 60. A lower portion of the funnel-shaped through-bore 72 provides a threaded inner surface 256 for receiving the bolt 252. The support 76 of the outer sleeve 62 includes a through-bore 258 aligned with the lower portion 30 of the funnel-shaped through-bore 72 to enable the bolt 252 to pass through the support 76 of the outer sleeve 62 and thread into the bottom portion of the inner sleeve 60. While a single bolt 252 is shown attaching the inner and outer sleeves 60, 62 together, one will appreciate a plurality of bolts may be used in a similar manner.
Embodiments described herein present a number of improvements and advantages relative to prior art configurations. The blade retention assembly and method for constructing the blade assembly described herein are seen to greatly increase the strength of composite blade designs, and greatly increase the ability to resist high levels of steady and cyclic bending loads experienced by high-power propulsion systems. In addition, the described blade retention assembly and the method for constructing the blade assembly allow for the use of compact and lightweight attachment mechanisms in propulsion systems. Such attachment mechanism interface reliably well in, e.g., central hub assemblies having a bearing and retention system for each blade, which allows for changing blade pitch angles to accommodate changing flight conditions encountered in typical flight profiles of various aircraft.
Embodiments described herein make additional reductions possible in the diameter and weight of the root portion 24 of a composite blade 12, while simultaneously increasing bending capacity. Decreasing the diameter of the blade root 24 provides additional weight reduction and aerodynamic performance benefits to the entire aircraft propulsion system of current and “next generation” aircraft, where the trend is to increase the number of blades to reduce propulsor external noise and vibration transmitted to passengers.
Manufacturers of new aircraft propellers look to increase blade count in new propellers for many reasons. The root diameter of composite blades 12 is typically quite large and heavy to accommodate high-cycle vibratory bending loads. Packaging the large retention bearings of this many blades in a central hub requires a large hub, large pitch change system, and large center body (known as a spinner assembly) to maintain smooth airflow around the root portions of the blades. One benefit of the embodiments described herein is to allow a reduction in the size of each blade root diameter, retention assembly 10 and blade support bearing assemblies, which in turn results in a smaller, more compact hub, pitch change system and spinner size, accompanied by an appreciable reduction in propeller weight, while simultaneously improving propeller efficiency. Furthermore, the reduction in blade root diameter is also seen to decrease blade inboard airfoil thickness, which helps prevent drag arising from choked air flow between blade roots, thus also improves propeller aerodynamic performance.
Although embodiments are described herein in conjunction with aircraft, they are not so limited and can be used in any suitable device or system that utilizes rotor blades. For example, rotor blades can be used in green energy capturing devices such as wind turbines and water turbines.
The terms “first,” “second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. In addition, the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.
Although this invention has been shown and described with respect to the detailed embodiments thereof, it will be understood by those of skill in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed in the above detailed description, but that the invention will include all embodiments falling within the scope of the foregoing description.
This patent application claims the benefit of U.S. Provisional Application No. 62/892,825, filed Aug. 28, 2019, the content of which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62892825 | Aug 2019 | US |
