Agricultural fan blade

Abstract

A fan blade tip for an agricultural fan blade includes a suction surface, a base portion, a transition portion, and a dihedral portion. The base portion includes a first chord length between a first leading edge and a first trailing edge. The transition portion includes a bend towards the suction surface. A hub end of the dihedral portion is connected to the transition portion and extends away from the base portion at a first angle. The dihedral portion has the first chord length between a third leading edge and a third trailing edge at the hub end of the dihedral portion and has a second chord length between the third leading edge and the third trailing edge at a tip end opposite the hub end. The second chord length is smaller than the first chord length.

Description

AGRICULTURAL FAN BLADECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This Application claims priority of U.S. Provisional Patent Application No. 63 / 557,329, filed on February 23, 2024, and is hereby incorporated by reference herein in its entirety.BACKGROUND

[0002] Agricultural frost fans and wind machines are used by farmers to protect crops from cold air damage. During calm and cloudless nights radiation cooling from the ground to the sky creates a thermal gradient near the surface which causes temperatures to drop rapidly over the fields. Horizontal axis fans mounted on towers overlooking the crops are used to mix warmer air above the surface with the colder air nearer to the ground. This helps ventilate the fields to prevent the pooling of cold air. The air movement across the plant surfaces thus prevents the crops from experiencing localized supercooling that can result in frost and can speed up the thawing process if frost has already formed. The fan is often rotated about the vertical axis to maximize the coverage.

[0003] US Patent Application Publication No. 2015 / 0024674, entitled “Agricultural Frost Protection Using Induction Fans” discloses a bladeless induction fan for crop frost protection with improved operational efficiency over propeller-driven wind machines. US Patent Application Publication No. 2015 / 0037164, entitled “Airfoil for Fan Blade” discloses a fan blade airfoil design. Both of these applications are incorporated by reference in their entireties.

[0004] Sound sources that contribute to the noise from the fan include blade-tip vortex interactions, separated boundary layers, and turbulent transition over the blade surface. Most of these mechanisms scale with the local flow velocity to a high power. Due to the rotation of the blade, the flow velocity is strongest at the tips, making this region the greatest contributor to sound. Three performance metrics are typically used to judge the overall performance of the fan system. The first is the acoustic sound level. The second is the aerodynamic performance, often characterized by the net thrust generated by the fan. This results in a flow of air that provides the warming effect. The third is the power required to generate the needed thrust.

[0005] Typical agricultural fans use straight, constant-chord, and unswept blades to simplify manufacturing, for example, enabling manufacture by basic extrusion techniques. Blade twist is typically added after extrusion by mechanically loading the fan blade in a holding fixture while applying a torque to generate a linear- and constant twist profile from root to tip. Increasingly strict sound regulations are limiting agricultural fan performance as current solutions to sound reduction and mitigation have come at the expense of operational (thrust and / or power consumption) performance.BRIEF DISCLOSURE

[0006] A fan blade, and more specifically, a tip for a fan blade is disclosed herein. The fan blade may be used with agricultural fans. Experimentation has identified that the blade disclosed herein reduces operational acoustic level in two-bladed near-horizontal axis agricultural fans of the type used to blow wind over crops for the prevention and mitigation of frost damage. This reduced acoustic level is achieved while maintaining operating fan thrust and approximately the same power draw. The fan blade disclosed herein provides a gradually curved, backward-swept, dihedral geometry at the outer region of the blade.

[0007] A fan blade tip has been designed to reduce the overall sound level generated by straight, unswept rotor designs for horizontal-axis or near-horizontal axis agricultural fans. The new design features a rearward swept and tapered tip with dihedral curvature that generates lower overall sound levels while preserving aerodynamic thrust performance and maintaining similar power requirements compared to the original design. The curved surfaces use gradual contours to eliminate sharp transitions in the profile that are known sources of vorticity and can lead to local separated flow, both of which contribute to sound. The chord length is reduced at the tip due to the taper.

[0008] Existing “straight” blades are made from extruded aluminum with an airfoil- shaped cross section. An axial twist is added by mechanically twisting the extrusion to different angles depending on the model of fan the blade will be used on.

[0009] However, complex blade configurations such as described herein, present additional challenges to manufacture, therefore, methods of blade manufacture are also disclosed herein.

[0010] An example of a fan blade tip for an agricultural fan blade includes a pressure surface and a suction surface. The fan blade tip further includes abase portion, a transition portion, and a dihedral portion. The base portion includes a first chord length between a first leading edge and a first trailing edge. A hub end of the transition portion is connected to the base portion. The transition portion has the first chord length between a second leading edge and a second trailing edge. The transition portion includes a bend towards the suction surface. A hub end of the dihedral portion is connected to the transition portion and extends away from the base portion at a first angle. The dihedral portion has the first chord length between a third leading edge and a third trailing edge at the hub end of the dihedral portion and has a second chord length between the third leading edge and the third trailing edge at a tip end opposite the hub end. The second chord length is smaller than the first chord length.

[0011] In further examples of the fan blade tip, the tip end of the dihedral portion has a cross-sectional shape that is a Yz scaled cross-sectional shape of the cross-sectional shape of the base portion between the first leading edge and the first trailing edge. The third leading edge may may be a convex curve and the third trailing edge may be a concave curve. The bend may include a radius of 12 5 / 8 inches or a radius of 12 5 / 8 inches ±40%, ±30%, ±20%, ±10%, or ±5%, and the bend extends through 10 - 45 degrees of arc. The base portion may have a cross-sectional shape between the first leading edge and the first trailing edge having a cambered pressure surface and a maximum thickness between 7-8% of the chord length. The first angle may be 25° or 30°. The base portion may further twist between a first pitch angle at a hub end and a second pitch angle at the transition portion, wherein the second pitch angle is more shallow than the first pitch angle.

[0012] Examples of an agricultural fan blade includes an airfoil extending in a spanwise dimension between a hub end and a distal end opposite the hub end, the airfoil having a suction surface and a pressure surface opposite the suction surface and a first chord length between an airfoil leading edge and an airfoil trailing edge. A tip is connected to the distal end of the airfoil and continues the suction surface and the pressure surface opposite the suction surface. The fan blade tip includes a base portion, a transition portion, and a dihedral portion. The base portion includes a first chord length between a first leading edge and a first trailing edge. A hub end of the transition portion is connected to the base portion. The transition portion has the first chord length between a second leading edge and a second trailing edge. The transition portion includes a bend towards the suction surface. A hub end of the dihedral portion is connected to the transition portionand extends away from the base portion at a first angle. The dihedral portion has the first chord length between a third leading edge and a third trailing edge at the hub end of the dihedral portion and has a second chord length between the third leading edge and the third trailing edge at a tip end opposite the hub end. The second chord length is smaller than the first chord length.

[0013] In further examples of the agricultural fan blade, the tip end of the dihedral portion has a cross-sectional shape that is al / i scaled cross-sectional shape of the cross-sectional shape of the base portion between the first leading edge and the first trailing edge. The third leading edge may be a convex curve and the third trailing edge is a concave curve. The bend may have a radius of 12 inches or a radius of 12 inches ±40%, ±30%, ±20%, ±10%, or ±5%, and the bend extends through 25 - 45 degrees of arc. The base portion may have a cross-sectional shape between the first leading edge and the first trailing edge has a cambered pressure surface and a maximum thickness between 7-8% of the chord length. The first angle may be 30°. The airfoil and the tip may be a unitary construction. The tip may be a separate component from the airfoil and is secured to the airfoil. The airfoil may be twisted about the spanwise axis. The base portion may further twist between a first pitch angle at a hub end and a second pitch angle at the transition portion, wherein the second pitch angle is more shallow than the first pitch angle. The airfoil may twist from a first pitch angle at the hub end of the airfoil and a second pitch angle at the distal end of the airfoil, wherein the second pitch angle is more shallow than the first pitch angle. The airfoil may twist between 11-14 degrees over the length of the airfoil. The first pitch angle may be between 10°-20°, and optionally be between 13° - 16°. The second pitch angle may be between 3°-6°.

[0014] Examples of an agricultural fan include a tower extending in a vertical dimension, a gearbox at the top of the tower and a hub relatively connected to the gearbox. The bub is configured to rotate about a near-horizontal axis, the horizontal axis generally perpendicular to the vertical dimension. At least two agricultural fan blades each include an airfoil extending in a spanwise dimension between a hub end and a distal end opposite the hub end. The airfoil includes a suction surface and a pressure surface opposite the suction surface and a first chord length between a first leading edge and a first trailing edge. A tip is connected to the distal end of the airfoil and continues the suction surface and the pressure surface opposite the suction surface. The fan blade tip includes a base portion, a transition portion, and a dihedral portion. The base portion includes a first chord length between a first leading edge and a first trailing edge. A hub end of the transition portion is connected to the base portion. The transition portion has the first chord lengthbetween a second leading edge and a second trailing edge. The transition portion includes a bend towards the suction surface. A hub end of the dihedral portion is connected to the transition portion and extends away from the base portion at a first angle. The dihedral portion has the first chord length between a third leading edge and a third trailing edge at the hub end of the dihedral portion and has a second chord length between the third leading edge and the third trailing edge at a tip end opposite the hub end. The second chord length is smaller than the first chord length. In additional examples of the agricultural fan, the tower defines a vertical axis and the gear box is rotatable relative to the tower about the vertical axis.

[0015] A method of constructing an agricultural fan blade includes extruding a fan blade blank having a suction surface, a pressure surface, a first leading edge, and a first trailing edge. The fan blade blank extends between a hub end and a tip end. A second leading edge and a second trailing edge are machined for a dihedral portion of the fan blade blank. A chord length between the first leading edge and the first trailing edge is longer than a chord length between the second leading edge and the second trailing edge at the tip end. A transition portion of the fan blade blank is bent to a curve having a radius and an arc length until the dihedral portion extends away from the rest of the fan blade blank at a first angle. An airfoil portion of the fan blade blank is twisted along a spanwise axis of the fan blade blank.

[0016] Further examples of the method include machining the suction surface of the dihedral portion and / or machining the pressure surface of the dihedral portion. The transition portion may be thermally treated before and / or after bending.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 depicts an example of an agricultural fan.

[0018] Figure 2A is a perspective view of an example of a fan blade of the present disclosure.

[0019] Figure 2B is a front view of the fan blade.

[0020] Figure 2C is a right side view of the fan blade.

[0021] Figure 3 an end view of the fan blade.

[0022] Figure 4 is an isolated end view of the tip.

[0023] Figure 5 is an isolated right side view of the tip.

[0024] Figure 6 is an isolated front view of the tip.

[0025] Figure 7 is an isolated view of the tip depicting the outer edge of the tip.

[0026] Figure 8 is an isolated isometric view of the tip.DETAILED DISCLOSURE

[0027] Figure 1 depicts an example of an agricultural fan 100. The agricultural fan 100 is a wind machine that includes a tower 102. A gear box 104 is at the top of the tower 102 in an elevated position. An engine (not depicted), and which may be located at the bottom of the tower or located remote from the tower provides motive force to the gearbox 104. In examples, the engine may be an electric or combustion engine. The gearbox 104 is connected to a fan 106 with a generally horizontal axis of rotation and which is generally perpendicular to a vertical axis V of the tower 102. The fan 106 includes blades 108. The blades 108 are exemplarily arranged with two blades extending 180° apart from one another about the axis of rotation of the fan 106. As will be discussed in further detail herein, other examples of fans may include more than two blades (e.g. three blades, four blades, or more) as are used in some existing solutions for reducing operational noise. However, such arrangements may typically require more power for the same thrust and are more expensive initially and to maintain.

[0028] The tower 102 elevates the fan 106 above an agricultural crop 110, for example, but not limited to, a citrus grove. In examples, multiple agricultural fans 100 are deployed throughout the agricultural crop 110 to provide the frost prevention and / or frost mitigation to the agricultural crop 110. The gear box 104 is connected to the tower 102 such that the gear box 104, and the fan 106 connected thereto are rotatable about the axis of the tower 102, a generally vertical axis. This rotation extends the effectiveness of the fan 360° about the tower 102, improving the effective acreage coverage of each fan 100 placed within the crop 110. Agricultural fans 100 are effective at mitigating frost risk for crops. Operation of the fans produce noise, which may be a detriment to workers in the fields and / or neighbors of these fields. Specific agricultural fan noise standards and regulations are in development and vary, but in at least one non-limiting example, a sound level of 50 decibels (dB), comparable to about the average interior background noise, is one possible threshold. This sound level of 50 decibels may be sought at 300 meters from the tower or inside the nearest residential building. Thus, the inventors have sought to develop a fan blade with reduced operational noise.

[0029] Table 1 below provides comparative sound data represented as maximum, minimum, average and equivalent continuous sound level (Lcq) at three distances from a test agricultural fan installation fitted with standard fan blades versus fan blades as presently disclosed.Table 1

[0030] As a result of these endeavors, the inventors have developed a new fan blade and blade tip design that reduces the overall operational sound of horizontal-axis or near-horizontal axis agricultural fans. The new design features a rearward swept and tapered tip with dihedral curvature that generates lower overall sound levels while preserving aerodynamic thrust performance and maintaining similar power requirements of existing blade designs. Dihedral is used to reference the tip which is angled relative to the airfoil section of the fan blade. A positive dihedral as shown in the examples herein is exemplarily wherein the tip is angled generally towards the suction surface of the blade when viewed from the leading edge.

[0031] Figures 2A-2C provide length views of an example of the fan blade 108 having an airfoil 112 and a tip 114. Figure 3 is a hub end view of the fan blade 108. Figure 2A is a front perspective view of the fan blade 108. Figure 2B is a front view of the fan blade 108. Figure 2C is a side view of the fan blade 108. The fan blade 108 extends from a hub end 120 to a tip end 130. The airfoil 112 extends for the majority of the length of the fan blade 108 between a hub end 122 of the airfoil and a distal end 124 of the airfoil. The hub end 122 of the airfoil 112 coincides with and provides the hub end 120 of the fan blade 108. A mounting surface 116 is located at the hub end 122 of the airfoil 112. It will be recognized that the mounting surface 116 depicted is merely exemplary and non-limiting as the mounting surface 116 may be shaped or adapted for fitmentwith the hub (not depicted) to which the fan blade 108 is to be secured. Other exemplary mounting surfaces may be of other shapes or configurations and may be manufactured with or without the need for machining. The mounting surface 116 includes a plurality of holes 118 configured to receive fasteners (not depicted), for example threaded fasteners, used in securing the fan blade 108 to the shaft (not depicted) of the gear’ box 104 (Fig. 1), often with the use of one or more intermediate components (not depicted). The airfoil 112 has a twist along the spanwise, or length, dimension between the hub end 122 and the distal end 124 of the airfoil 112. This twist of the airfoil 112 can exemplarily be seen in the end view of Fig. 3. The axial twist is developed entirely over the airfoil section 112 of the blade 108. As will be discussed in further detail herein, in at least one example the tip portion 114 does not include any twist. In an example, the airfoil at the hub end 122 is pitched at a larger angle (e.g. 16°) compared to the airfoil at the distal end 124. It will be recognized that the pitch angle at the hub end 122 may be greater or less than 16° or greater or less than 13°, and for example is between 10° - 20°, 13°-19° or 13°-16°. The twist of the airfoil 112 runs counter to the initial pitch (at the hub end 122) and thus the pitch at the distal end 124 of the airfoil is a shallower pitch (e.g. 4°). When viewed from the hub, the hub end 122 may be rotated clockwise relative to the distal end 124. The pitch at the distal end 124 of the airfoil may be selected based upon the horsepower of the fan, with a 4° pitch exemplarily used for a 145 horsepower fan. In examples, the pitch at the distal end 124 may be greater or less than 4° with examples ranging between 3°-6°, including but not limited to 3°, 3.2°3.8°, 5°, 5.5°, or 6°. Further examples of the pitch angle at the distal end may be between 3.5°-4.5°, 3°-5°, 4°-6°, or similar. In still further examples, the blade twist may continue into the tip 114 as described below to reach the final shallower pitch. As will be discussed herein, in one example, the blade has a span length L of 102 inches (8.5 feet) and a chord length 1 of 10 inches, although other dimensions will be recognized as being within the scope of the present disclosure. Relatedly, thrust, noise, and power consumption may all be different between different fan blade configurations relative to blade span length and chord length.

[0032] The tip 114, as explained in further detail herein may be unitary with the airfoil 112 or the tip 114 may be a separate component secured to the distal end 124 of the airfoil 112. A hub end 126 of the tip 114 is secured to a distal end 124 of the airfoil 112. The tip 114 thus extends away from the hub and the airfoil in the spanwise dimension to the tip end 130. In examples, the tip 114 may be integral with the airfoil 112 as described in further detail herein. In such cases, thedistal end 124 of the airfoil 112 transitions directly into the hub end 126 of the tip 1 14. In other embodiments, the tip 114 may be separately constructed and secured to the airfoil 112 by friction, welding, fasteners, adhesives or other forms of securement as will be recognized by one of skill in the art. In one such example, the tip 114 may be configured as a “glove” to fit over the distal end 124 of an existing airfoil 112. In another example, the airfoil 112 and the tip 114 may be constructed with mating surfaces to facilitate the securement of these components. As described herein, the tip 114 is bent or angled in the direction of the front face of the airfoil 112, for example as seen in Fig. 2C. The tip 114 is further swept backwards as the chord length in the width dimension W of the tip 114 narrows towards the distal end 128 of the tip, as shown in Fig. 2B and 3 and described in further detail herein.

[0033] Figures 4-8 present various isolated views of the tip 114 to better depict the features of the tip 114. Figure 4 is an end view of the tip 114. The tip 114 exemplarily has a cross-section 12 at the hub end 126 of the tip that matches a corresponding cross-section of the distal end 124 of the airfoil 112 (See Fig. 2B). Likewise, the tip 114 at the hub end 126 matches a base chord length 1 of the airfoil 112 at the distal end 124. The tip 114 extends in the width or chord dimension between a leading edge 3 to a trailing edge 2 to define a suction surface 4 and a pressure surface 5. The leading edge 3 and the trailing edge 2 are both rounded and form an aerodynamic crosssection 12 with a camber between the rounded leading edge 3 and the rounded trailing edge 2In an example, the airfoil has a maximum thickness in the aerodynamic cross-section 12 between 7-8% of the chord length. . In non-limiting examples of this, the airfoil has a 7.5% maximum thickness relative to the chord length (e.g. .75 in on a 10 inch chord) or a 7.7% maximum thickness relative to the chord length (e.g. .77 in on a 10 in chord). While configurations of airfoil cross-sections are depicted and described herein, it will be recognized that the present disclosure may be used with other airfoil cross- sections and camber designs as will be recognized by a person of skill in the ait in view of the present disclosure.

[0034] Figure 5 is an isolated right side view of the tip 114, comparable to that as shown in Fig. 2C. The tip 114 extends for a length 6 in the length or spanwise dimension through three portions in order from the hub end 126 to the tip end 128 of the tip 114: a base portion 14, a transition portion 15, and a dihedral portion 16. The base portion 14 generally matches and continues the profile and dimensions of the airfoil 112 in a baseline 2D aerodynamic shape as discussed above. In one example, the base portion 14 maintains the twist angle of the blade 108 asat the distal end 124 of the airfoil 112. For example, if the airfoil 112 had a 6° angle at the airfoil distal end 124 / tip hub end 126, this 6° angle would maintain through the base portion 14. In another example, the blade 108 continues to twist through the base portion 14, such that the angle of the blade 108 at the transition portion 15 is shallower than the angle of the blade at the hub end 126 of the tip 114.

[0035] The transition portion 15 provides the bend or angle of the tip 114 in the direction of the front face of the blade. The transition portion 15 embodies a radius of curvature 8 providing the transition from the base portion 14 to the dihedral portion 16 extending at a dihedral angle 7 relative to the base portion 14. The transition portion 15 starts with the start of the tip 114 bending away from the base portion 14 at the radius of curvature 8. The radius of curvature 8 is exemplarily 125 / 8 inches and as discussed herein may linearly scale with the overall length L of the blade (e.g. 102 inches), exemplarily for a 12 5 / 8:102 ratio. It will be recognized that the radii may be exemplarily ±40%, ±30%, ±20%, ±10%, or ±5% from the example given relative to a blade length. The transition portion 15 exemplarily includes no additional twist as exhibited in the airfoil and in some examples in the base portion 14. Therefore, in examples, the transition portion 15 may maintain the angle of the blade as exhibited by the base portion 14 and / or the airfoil distal end 124. The transition portion 15 continues through the radius of curvature until the tip 114 is angled at the dihedral angle 7.

[0036] When the tip 114 is at the dihedral angle 7 relative to the base portion 14, the dihedral portion 16 extends away at this dihedral angle 7 from the transition portion 15. The dihedral angle 7 is exemplarily 30°, however it will be recognized that in other examples, the dihedral angle may be between 10°-45°, may be between 15°-35°, 10°-25°, 25°-35°, or between 25°-45°. As will be discussed herein, the dihedral angle 7 exemplarily remains consistent between dimensional changes to the fan blade while other feature designs and dimensions are scaled relative to fan blade dimensions, particularly fan blade length. The dihedral portion 16 starts when the transition portion 15 reaches the dihedral angle 7 relative to the base portion. The dihedral portion 16 further tapers in both the chord or width dimension W and a thickness dimension along the length of the dihedral portion 16, as is described in further detail herein.

[0037] Figure 6 is a front view of the tip 114. Figure 7 is a view of the tip end 128 of the tip 114. Figure 8 is an isometric view of the tip 114. In the front view, the chord length 1 of the base portion 14, which exemplarily matches the chord length 1 of the airfoil (not depicted) remainsconsistent through the transition portion 15. Reference 9 denotes the combined length in the spanwisc dimension of the base portion and the transition portion. It will be recognized that due to the curve of the tip 114 in the transition portion, that the overall length of these portions of the tip 114 is longer than the spanwise dimension 9. The length of the dihedral portion 16 in the span wise dimension is denoted with reference 10, similarly due to the dihedral angle 7, the overall length of the dihedral portion 16 is longer than the spanwise dimension length 10. As depicted in Fig. 6, the dihedral portion 16 tapers in the chord dimension from the base portion 14 (and transition portion 15) chord length 1 to the tip chord length 11. The aerodynamic cross-section of the base portion scales to Vi size at the outer end of the dihedral portion 16 The tip chord length 11 is Yi the base chord length 1, and a cross-section 19 at the distal end 128 of the tip has a cross-sectional thickness and thickness profile Fz that of the respective thicknesses in the cross-section 12 of the base portion 14, while the cross-section 19 maintains the thickness to length ratio and the camber shape of the base portion cross-section 12.

[0038] The dihedral portion 16 includes a convex curved leading edge 17 and a concave curved trailing edge 18. As depicted, the trailing edge 18 at the distal end 128 of the tip 114 and the dihedral portion 16 is colinear with the trailing edge 2 of the airfoil 112 and the base portion 14. The concavity of the trailing edge extends interior of the line of the trailing edge 2, but returns to the same line as the trailing edge 2. The convex curved leading edge 17 accounts for the ultimate reduction in chord length from chord length 1 at the interface between the transition portion 15 and the dihedral portion 16 to the chord length 11 at the distal end 128 of the tip 114, as the convex curved leading edge recesses from the line of the leading edge 3. The curved leading edge 17 and the curved trailing edge 18 have radii of curvatures that exemplarily linearly scale with the length of the blade L. In the example described, the blade length L (see Fig. 2B) is 102 inches and the base chord length (1) is 10 inches. The leading edge 17 exemplarily has a curve with a radius of curvature of 22 inches. The trailing edge 18 exemplarily has a radius of curvature of 18 inches. However, it will be recognized that the radii of the leading edge 17 and trailing edge 18 may exemplarily be ±40%, ±30%, ±20%, ±10%, or ±5% from the example given relative to a blade length L. Referring back to Fig. 5, the dihedral portion 16 also tapers in a cross-sectional or thickness dimension along the length of the dihedral portion 16. The taper is also a 1 / 2 scaling of the thickness providing the same scaling as with respect to chord length. In examples, the length10 of the dihedral portion 16 is a length as determined to achieve the 2 scaling of the chord length as discussed above, with the leading and trailing edge curvatures as discussed above.

[0039] Figure 7 is a view of the tip 114 that highlights the aerodynamic shape at the distal end 128 of the tip 114. As previously noted, the chord length 11 at the distal end 128 of the tip is I / 2 the chord length 1 at hub end 126 of the tip. Similarly, the cross-section 19 at the distal end 128 is a Yi scale of the cross section 12 at the hub end 126. In an example, the dimensions of the aerodynamic shape similarly scale by Vi over the length of the dihedral portion 16. However, in additional examples, the scaling may be within a tolerance of, ±10% or a tolerance of ±20%. In one example, the scaling of the round of the leading edge 3 and the round of the trailing edge, and chord length are within a narrower tolerance in the scaling compared to the scaling of the pressure surface 5 or the suction surface 4. In a still further example, a camber of the pressure surface may be within a larger tolerance of the Yi scale for the cross-sectional shape 19 at the distal end 128 of the tip compared to the cross-sectional shape 12 at the hub end 126 of the tip.

[0040] The curved surfaces of the transition portion 15, as well as the curved leading edge and curved trailing edge as the cross-section scales by Yi to eliminate sharp transitions in the profile that are known sources of vorticity and can lead to local separated flow, both of which contribute to sound. The reduced chord length at the outer edge of the tip reduces the strength of tip-vortices which in turn reduces drag and operational noise of the blade. Reduced drag further reduces power needed to drive the fan including the blade.

[0041] The fan blades as described herein may be fabricated in a variety of ways. A separate tip and an extruded airfoil may be manufactured and subsequently secured together. A blade may be created as a one-piece composite (e.g. fiberglass) blade that includes the bent tip. Described in further detail herein is a method of fabrication in which an extruded aluminum blade is machined and bent to form the tip of the blade. This results in a unitary construction which improves blade strength and durability. A one-piece composite blade also provides a unitary construction but requires individualized manufacturing set up for each blade length and twist angle, whereas the one-piece aluminum blade has the option of being twisted to any angle desired after the tip has been formed.

[0042] The geometry of the tip as described above requires more than bending of the aluminum extrusion. The blade blank is extruded to the aerodynamic cross-section 12 of the airfoil 112. The blade blank is cut to a length greater than the intended blade length as bending the tipportion will shorten the linear distance between the hub end 120 and the tip end 130 to the intended blade length L. Prior to bending the tip 114 up to form the transition portion and the dihedral portion, the leading edge and the trailing edge of what will become the dihedral portion is CNC machined to form convex curved leading edge 17 and the concave curved trailing edge 18 to create the scaled chord length. The suction side 4 is CNC machined to form the tapered dihedral portion to the scaled suction side of the cross-section 19. The pressure side 5 is CNC machined to form the scaled cambered pressure side. In another example, only the suction side 4 is machined with the entirety of the taper in the thickness of the cross-section being removed from the suction side 4. Because the extrusion of the blade blank, having the shape of the base portion cross-section already includes a camber, the scaled aerodynamic cross-section at the tip outer end may be achieved within an expanded manufacturing tolerance without machining the pressure side 5. The tip's pre-bend machined geometry is designed so that the correct geometry results after the bending operation is complete. Before and / or after bending the blade, the blade may be heat treated. After bending the blade, the twist in an exemplary amount of 11-14 degrees may be developed along the 102 inch airfoil 112.

[0043] The agricultural fan blade described above provides an advantage over existing agricultural fan blades in reduction of operational sound level while keeping aerodynamic (thrust) performance with minimal impact on operating power as compared to existing designs. One comparative approach is to add additional fan blades to permit slower rotation, reducing flow velocity and operational sound level. However, the slowing of the fan rotation results in reduced thrust and fan effectiveness in preventing and mitigating frost. The tip designs disclosed herein improve aerodynamic effectiveness over existing agricultural fan blade tips, which reduce operational sound levels at the same or less drag.

[0044] In additional uses, the fan blade as described herein may be used for cooling tower fans. Such fans generally rotate about a vertically-oriented axis within a cooling tower. Additionally, such fan blades are typically larger than the 102 inches exemplarily used herein, however, it will be recognized that the scaling as provided within the present disclosure may be used to accommodate the dimensions of these larger-sized fan blades. It will be recognized that similar benefits may be gained in that use case as the examples described herein.

[0045] In a further application, blades, tips, and fan systems as described herein may be used in cooling tower fans. Such cooling tower fan blade may require dimensional changes toaccount for the use, conditions, and operation in a cooling tower fan. This is considered to be within the scope of the present disclosure

[0046] Citations to a number of references are made herein. The cited references are incorporated by reference herein in their entireties. In the event that there is an inconsistency between a definition of a term in the specification as compared to a definition of the term in a cited reference, the term should be interpreted based on the definition in the specification.

[0047] In the above description, certain terms have been used for brevity, clarity, and understanding. No unnecessary limitations are to be inferred therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. The different systems and method steps described herein may be used alone or in combination with other systems and methods. It is to be expected that various equivalents, alternatives and modifications are possible within the scope of the appended claims.

[0048] Methods and operational sequences as described herein are representative of exemplary methodologies for performing novel aspects of the disclosure. While, for purposes of simplicity of explanation, the methodologies included herein may be described as a series of acts, it is to be understood and appreciated that the methodologies are not limited by the order of acts, as some acts may, in accordance therewith, occur in a different order and / or concurrently with other acts from that described herein. For example, those skilled in the art will understand and appreciate that a methodology can alternatively be represented as a series of interrelated states or events, such as in a state diagram. Moreover, not all acts illustrated in a methodology may be required for a novel implementation.

[0049] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims

CLAIMS1. A fan blade tip for an agricultural fan blade, the tip having a pressure surface and a suction surface, the fan blade tip comprising: a base portion, the base portion having a first chord length between a first leading edge and a first trailing edge; a transition portion, a hub end of the transition portion connected to the base portion, the transition portion having the first chord length between a second leading edge and a second trailing edge, the transition portion comprising a bend towards the suction surface; and a dihedral portion, a hub end of the dihedral portion connected to the transition portion and extending away from the base portion at a first angle, the dihedral portion having the first chord length between a third leading edge and a third trailing edge at the hub end of the dihedral portion and having a second chord length between the third leading edge and the third trailing edge at a tip end opposite the hub end, wherein the second chord length is smaller than the first chord length.

2. The fan blade tip of any of claim 1, wherein the tip end of the dihedral portion has a cross-sectional shape is a Vi scaled cross-sectional shape of the cross-sectional shape of the base portion between the first leading edge and the first trailing edge.

3. The fan blade tip of claim 1 or 2, wherein the third leading edge is a convex curve and the third trailing edge is a concave curve.

4. The fan blade tip of claim 1 or 2, wherein the bend comprises a radius of 125 / 8 inches or a radius of 12 5 / 8 inches ±40%, ±30%, ±20%, ±10%, or ±5%, and the bend extends through 10 - 45 degrees of arc.

5. The fan blade tip of claim 1 or 2, wherein the base portion has a cross-sectional shape between the first leading edge and the first trailing edge having a cambered pressure surface and a thickness between 7-8% of the chord length.

6. The fan blade tip of claim 1 or 2, wherein the first angle is 25°.

7. The fan blade tip of any of claim 1 or 2 wherein the base portion further twists between a first pitch angle at a hub end and a second pitch angle at the transition portion, wherein the second pitch angle is more shallow than the first pitch angle.

8. An agricultural fan blade comprising: an airfoil extending in a spanwise dimension between a hub end and a distal end opposite the hub end, the airfoil having a suction surface and a pressure surface opposite the suction surface and a first chord length between an airfoil leading edge and an airfoil trailing edge; a tip connected to the distal end of the airfoil, the tip continuing the suction surface and the pressure surface opposite the suction surface, the tip comprising: a base portion having the first chord length between a first leading edge and a first trailing edge; a transition portion, a hub end of the transition portion connected to the base portion, the transition portion having the first chord length between a second leading edge and a second trailing edge, the transition portion comprising a bend towards the suction surface; and a dihedral portion, a hub end of the dihedral portion connected to the transition portion and extending away from the base portion at a first angle, the dihedral portion having the first chord length between a third leading edge and a third trailing edge at the hub end of the dihedral portion and having a second chord length between the third leading edge and the third trailing edge at a tip end opposite the hub end, wherein the second chord length is smaller than the first chord length.

9. The agricultural fan blade of claim 8, wherein the tip end of the dihedral portion has a cross-sectional shape is a Vi scaled cross-sectional shape of the cross-sectional shape of the base portion between the first leading edge and the first trailing edge.

10. The agricultural fan blade of claim 8 or 9, wherein the third leading edge is a convex curve and the third trailing edge is a concave curve.11 . The agricultural fan blade of claim 8 or 9, wherein the bend comprises a radius of 12 5 / 8 inches or a radius of 12 5 / 8 inches ±40%, ±30%, ±20%, ±10%, or ±5%, and the bend extends through 10 - 45 degrees of arc.

12. The agricultural fan blade of claim 8 or 9, wherein the base portion has a cross- sectional shape between the first leading edge and the first trailing edge having a cambered pressure surface and a maximum thickness between 7-8% of the chord length.

13. The agricultural fan blade of claim 8 or 9, wherein the first angle is 25°.

14. The agricultural fan blade of claim 8 or 9, wherein the airfoil and the tip are a unitary construction.

15. The agricultural fan blade of claim 8 or 9, wherein the tip is a separate component from the airfoil and is secured to the airfoil.

16. The agricultural fan blade of claim 8 or 9, wherein the airfoil is twisted about the span wise axis.

17. The agricultural fan blade of claim 16, wherein the base portion further twists between a first pitch angle at a hub end and a second pitch angle at the transition portion, wherein the second pitch angle is more shallow than the first pitch angle.

18. The agricultural fan blade of claim 16, wherein the airfoil twists from a first pitch angle at the hub end of the airfoil and a second pitch angle at the distal end of the airfoil, wherein the second pitch angle is more shallow than the first pitch angle.

19. The agricultural fan blade of claim 18, wherein the airfoil has a twist between 11- 14 degrees over the length of the airfoil.

20. The agricultural fan blade of claim 18, wherein the first pitch angle is between 10°-20°, optionally between 13° - 16°, and optionally between 11° - 14°.21 . The agricultural fan blade of claim 18, wherein the second pitch angle is between3°-6°.

22. An agricultural fan, comprising; a tower extending in a vertical dimension; a gearbox at the top of the tower; a hub rotatively connected to the gearbox and configured to rotate about a horizontal axis, the horizontal axis generally perpendicular to the vertical dimension; at least two agricultural fan blades, each agricultural fan blade comprising: an airfoil extending in a spanwise dimension between a hub end and a distal end opposite the hub end, the airfoil having a such surface and a pressure surface opposite the suction surface and a first chord length between an airfoil leading edge and an airfoil trailing edge; a tip connected to the distal end of the airfoil, the tip continuing the suction surface and the pressure surface opposite the suction surface, the tip comprising; a base portion having the first chord length between a first leading edge and a first trailing edge; a transition portion, a hub end of the transition portion connected to the base portion, the transition portion having the first chord length between a second leading edge and a second trailing edge, the transition portion comprising a bend towards the suction surface; and a dihedral portion, a hub end of the dihedral portion connected to the transition portion and extending away from the base portion at a first angle, the dihedral portion having the first chord length between a third leading edge and a third trailing edge at the hub end of the dihedral portion and having a second chord length between the third leading edge and the third trailing edge at a tip end opposite the hub end, wherein the second chord length is smaller than the first chord length.

23. The agricultural fan of claim 22, wherein the tower defines a vertical axis and the gear box is rotatable relative to the tower about the vertical axis.

24. The agricultural fan of claim 22, wherein a sound from the fan is less than 50 decibels when measured 300 meters from the fan.

25. The agricultural fan of claim 22, further wherein each agricultural fan blade further comprises any of claims 9-21.

26. A method of constructing an agricultural fan blade, the method comprising: extruding a fan blade blank, the fan blade blank comprising a suction surface, a pressure surface, a first leading edge, and a first trailing edge, the fan blade blank extending between a hub end and a tip end; machining a second leading edge and a second trailing edge for a dihedral portion of the fan blade blank, wherein a chord length between the first leading edge and the first trailing edge is longer than a chord length between the second leading edge and the second trailing edge at the tip end; bending a transition portion of the fan blade blank to a curve having a radius and an arc length until the dihedral portion extends away from the rest of the fan blade blank at a first angle; and twisting an airfoil portion of the fan blade blank along a spanwise axis of the fan blade blank.

27. The method of claim 26, further comprising machining the suction surface of the dihedral portion.

28. The method of claim 27, further comprising machining the pressure surface of the dihedral portion.

29. The method of claim 26, further comprising thermally treating the transition portion before and / or after bending.

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