Toroidal drone propeller

Abstract

A toroidal drone propeller includes a hub supporting a leading blade segment and a lagging blade segment, the leading blade segment and the lagging blade segment each forming a closed loop, the leading blade segment offset from the lagging blade segment, the offset including a separation defined where the leading blade segment starts and the lagging blade segment ends so that they are not in a plane normal to an axis of rotation of the hub.

Description

Attorney Docket No. 410965-501001 WOTOROIDAL DRONE PROPELLERCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit from U.S. Provisional Patent Application Serial No. 63 / 706,730, filed October 13, 2024, which is incorporated by reference its entirety.BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to propellers, and more particularly to a toroidal drone propeller.

[0003] In general, a toroidal drone propeller enables a small multirotor unpiloted aircraft, or drone, to operate more quietly than current drones that use propeller forms unchanged since the beginning of aviation. By enabling a drone that is less of an acoustic annoyance, this propeller may accelerate the acceptance of such aircraft for a wide range of uses — for example, aerial deliveries, cinematography, industrial or infrastructure inspections, agricultural monitoring and environmental monitoring.

[0004] Drones have the potential to completely change the way society functions if their noise output can be reduced.SUMMARY OF THE INVENTION

[0005] The following presents a simplified summary of the innovation in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.

[0006] In an aspect, the invention features a toroidal drone propeller including a hub supporting a leading blade segment and a lagging blade segment, the leading blade segment and the lagging blade segment each forming a closed loop, the leading blade segment offset from the lagging blade segment, the offset including a separation defined where the leading blade segment starts and the lagging blade segment ends so that they are not in a plane normal to an axis of rotation of the hub.

[0007] In another aspect, the invention features a toroidal drone propeller including a hub supporting a leading blade segment and a lagging blade segment, the leading blade segment and the lagging blade segment each forming a closed loop, the leading blade segment offset from the lagging blade segment, the offsetAttorney Docket No. 410965-501001 WOincluding a separation defined where the leading blade segment starts and the lagging blade segment ends so that they are not in a plane normal to an axis of rotation of the hub, wherein a terminal end of the leading blade segment and a terminal end of the lagging blade segment each curve into contact with the hub.

[0008] In another aspect, the invention features a toroidal drone propeller includes a hub supporting a leading blade segment and a lagging blade segment, the leading blade segment and the lagging blade segment each forming a closed loop, the leading blade segment offset from the lagging blade segment, the offset including a separation defined where the midpoint of the chord line of the propeller profile of the leading blade segment at the propeller hub and the midpoint of the chord line of the propeller profile of the lagging blade segment at the propeller hub are not in a plane normal to an axis of rotation of the hub, wherein a terminal end of the leading blade segment and a terminal end of the lagging blade segment each curve into contact with the hub.

[0009] In another aspect, the invention features a method including providing a leading blade segment, providing a lagging blade segment, providing a hub, the hub supporting the leading blade segment and the lagging blade segment, the leading blade segment and the lagging blade segment each forming a closed loop, orienting the leading blade segment to be offset from the lagging blade segment, the offset including a separation defined where the leading blade segment starts and the lagging blade segment ends so that they are not in a plane normal to an axis of rotation of the hub.

[0010] These and other features and advantages will be apparent from a reading of the following detailed description and a review of the associated drawings. It is to be understood that both the foregoing general description and the following detailed description are explanatory only and are not restrictive of aspects as claimed.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 illustrates an isometric view of an exemplary toroidal drone propeller.

[0012] FIG. 2 illustrates isometric view highlighting an exemplary leading blade segment height offset (referred to in shorthand by LBSHO) in a toroidal drone propeller.

[0013] FIG. 3 illustrates a front view of the exemplary toroidal drone propeller.Attorney Docket No. 410965-501001 WO

[0014] FIG. 4 illustrates the characteristics of an exemplary toroidal drone propeller.

[0015] FIG. 5 illustrates analysis of collective pitch angle.

[0016] FIG. 6 illustrates an analysis of tip height taper.

[0017] FIG. 7 illustrates analysis of chord length.

[0018] FIG. 8 illustrates analysis of the best combination of chord taper at the hub with chord length at 1 / 2 R.

[0019] FIG. 9 illustrates analysis of the minor axis length.

[0020] FIG. 10 illustrates analysis of camber.

[0021] FIG. 11 illustrates the effect of applying and varying a leading blade segment height offset on the sound output of the toroidal drone propeller.

[0022] FIG. 12 quantifies the aerodynamic and aero-acoustic advantages of a toroidal drone propeller with a leading blade segment height offset.

[0023] FIG. 13 illustrates the noise reduction of a toroidal drone propeller equipped with a leading blade segment height offset.

[0024] FIG. 14 illustrates an airflow in the toroidal drone propeller with a leading blade segment height offset.

[0025] FIG. 15 illustrates a three-dimensional (3D) model of the toroidal drone propeller with a leading blade segment height offset.

[0026] FIG. 16 illustrates two variations of the leading blade segment height offset.

[0027] FIG. 17 is a flow diagram.DETAILED DESCRIPTION

[0028] The subject innovation is now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It may be evident, however, that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing the present invention.

[0029] A crucial aspect of drone noise production are the propellers, a system of blades that generate thrust. Since the design and organization of the blades can vary greatly, the system can be optimized to meet specific needs, including a lower noiseAttorney Docket No. 410965-501001 WOoutput. The present invention is directed towards a toroidal drone propeller with the greatest aerodynamic efficiency and noise reduction.

[0030] Referring now to FIG. 1 , an exemplary toroidal drone propeller 100 in accordance with the principles of the present invention includes a hub 105. The hub 105 supports a leading blade segment 110 (also referred to as a propeller) and a lagging blade segment 115 (also referred to as a propeller). As shown in FIG. 1 , the leading blade segment 110 and the lagging blade segment 115 each form a closed loop. Although the embodiment illustrated includes two loops comprising of four total blade segments, other embodiments may include additional blade segments and a plurality of loops constructed by additional blade segments.

[0031] As shown in FIG. 2, an exemplary toroidal drone propeller 200 in accordance with the principles of the present invention includes a leading blade segment height offset 205. The leading blade segment height offset 205 represents a separation defined where the leading blade segment 210 starts and the lagging blade segment 215 ends so that they are not in a plane normal to an axis of rotation of the hub 220. A terminal end of the leading blade segment 210 and a terminal end of the lagging blade segment 215 each curve into contact with the hub 220.

[0032] As will be discussed fully below, the leading blade segment height offset 205 is configured to reduce an acoustic signature of the toroidal drone propeller 200 and to increase its efficiency. In one embodiment, the leading blade segment height offset 205 is 0.1 to 0.5 inches. In a preferred embodiment for 8-inch radius drone propellers, the leading blade segment height offset 205 is 0.25 inches.

[0033] It should be noted that as a size of the toroidal drone propeller increases and the specific application of the multirotor unpiloted aircraft, or drone, changes, an optimal leading blade segment height offset will vary.

[0034] FIG. 3 illustrates a front view of the exemplary toroidal drone propeller 300.

[0035] In FIG. 4, characteristics of an exemplary toroidal drone propeller are shown. In addition to the LBSHO, six other toroidal drone propeller features were optimized. Table a) illustrates the seven parameters used to characterize the toroidal drone propeller of the present invention along with their initial values before aerodynamic and aero-acoustic testing. Also illustrated is an isometric view of half of the toroidal drone propeller, where a minor axis is the length from the leading bladeAttorney Docket No. 410965-501001 WOsegment to the lagging blade segment, and the tip taper is the percentage decrease in height at the blade tip.

[0036] Panel i) shows the blade profile at 1 / 2 radius. The cord is the length of the blade cross-section from the leading edge to trailing edge. The camber represents the distance from the cord to the inside edge of the cross section. It is calculated as a fraction of the camber. The pitch angle is the angle that the cross section makes with the horizontal.

[0037] A second panel demonstrates a non-zero leading blade height offset, where the leading blade segment begins at a greater initial height and tapers down to the base of the toroidal drone propeller over the course of the loop.

[0038] As described above, the leading blade segment height offset axially separates where the leading blade segment starts and the lagging blade segment ends.

[0039] To quantitatively analyze the performance of both the conventional control propeller and the variations in the toroidal drone propeller, the following equations were utilized in a scientific study that yielded the present invention.

[0043] The constants in both equations are p, Q, R, and A, which represent air density, angular velocity (RPM), radius, and disk area, respectively. The thrust coefficient (Ct) is calculated with equation (1). This equation non-dimensionalizes the thrust (T) recorded at varying angular velocities, measured in revolutions per minute (RPM), allowing a comparison of Ct at different RPMs. This value represents how much thrust is produced by the propeller. Similarly, the torque coefficient (Cp) is calculated with equation (2) and non-dimensionalizes the calculated torque (Q) at every RPM; it represents the torque required to spin the propeller.

[0044] Since the optimality of a propeller depends on how much thrust it produces while minimizing the torque required by the motor, equation (3) is used to measure the Figure of Merit (FM), which is a measure of how efficient the propeller is.Attorney Docket No. 410965-501001 WOUltimately, FM is used to determine the aerodynamic performance of the propeller, and equations (1) and (2) are used to calculate the FM.

[0045] To analyze the sound output of the drone propellers, this study measures sound pressure level (SPL) in decibels (both raw dB and A-weighted dBA), which are on logarithmic scales. To conduct accurate comparisons in acoustic testing, all propellers are run at the specific angular velocity that produces 2.5N of thrust for each individual propeller. This load condition was chosen to imitate performance on a 1kg wildlife drone. Yet, to calculate overall percentage noise reduction, the SPL must first be converted to pressure is pascals. Equation (4) illustrates the relationship between the sound pressure level (SPL) in dB and the pressure p, where reference sound pressure pref is 20pPa. Equation (5) was then utilized to calculate the percentage difference between the sound pressures created by a toroidal drone propeller without a leading blade segment height offset and a toroidal drone propeller with a leading blade segment height offset.Toroidal Prop w / LBSHO Sound Pressure (Pa)%diff = 1 x 100%Toroidal Prop w / o LBSHO Sound Pressure (Pa)(5)

[0046] In order to arrive upon an optimal design for the toroidal drone propeller of the present invention and before implementing the leading blade segment height offset, a number of parameters were analyzed with their analysis described in the following figures where each plotted data point represents a manufactured toroidal drone propeller.

[0047] As shown in FIG. 5, an analysis of varying the toroidal propeller collective pitch angle was conducted. Increasing the pitch angle both increased the thrust and torque (b-c). While the thrust of toroidal drone propellers of pitch around 25° were very similar to the thrust of the conventional propeller (horizontal line), the torque of all toroidal drone propellers above 20° pitch was greater than the conventional control. For a propeller to be aerodynamically efficient, it must maximize thrust while minimizing torque. Ultimately, the 26° pitch angle propeller had the highest FM (d). Acoustic data was not taken into account since the FM of the toroidal drone propellers were substantially lower than the FM of the conventional design (d, blackAttorney Docket No. 410965-501001 WOhorizontal line). Thus, over subsequent parameters, pitch angle is held constant at 26°.

[0048] As shown in FIG. 6, an analysis of tip height taper was conducted to further increase the FM efficiency of the toroidal propeller of the present invention to a level comparable to that of a conventional drone propeller before sound data was considered. The height at the wing tip of the toroidal drone propeller is defined as a percentage of the height at 1 / 2 R. FIG. 6 depicts the aerodynamic performance of variations in the tip taper of the toroidal drone propeller. In both panels b) and c), it is evident that the presence of a tip taper reduced the torque and reduced the thrust, as both metrics have a downward sloping trend. In fact, the torque coefficient almost reached that of the conventional propeller. In d), the toroidal drone propeller at 0% tip taper represents the best performing propeller of the previous experimental group, before any tip taper was applied. While all toroidal drone propellers with tip taper greater than 50% produced almost 10% higher FM than without any tip taper, the data does not reveal any one tip taper to yield the greatest efficiency. In e), it is evident that the reduction in drag and required torque was greater than the losses of thrust, therefore suggesting that the 90% taper is most optimal efficiency-wise.

[0049] In FIG. 7, analysis of chord length taper at the propeller hub is shown. One key to increasing the efficiency is reducing the required torque. The chord length at the hub of the propeller is defined as a percentage decrease of the chord length at 1 / 2 R. As shown, increasing the chord taper resulted in a decrease in produced thrust, but also resulted in a decrease in produced drag. At a chord taper of 70%, Cp fell to be lower than the conventional propeller (horizontal line in c), but at the same chord taper the thrust produced also decreased dramatically to be lower than the conventional propeller. Plotting both FM and Ct / Cp (d-e) revealed that the chord taper didn’t improve the aerodynamic performance of the toroidal drone propeller.

[0050] Chord lengths of 0.6in, 0.65in, 0.7in, 0.75in, and 0.8in were determined by the computational fluid dynamics model to produce the highest FM efficiency. Three different versions of each of these chord lengths were manufactured, each with a different chord length taper at the propeller hub. FIG. 8 shows the FM of all fifteen propellers. The error bars represent one standard error of the mean FM (since the propeller was tested at seven different RPMs for aerodynamic data, the seven different calculated FM were used to calculate the mean and standard errors). The 0.65in chord with a 20% taper at the hub had the highest FM at 36%.Attorney Docket No. 410965-501001 WO

[0051] The minor axis length of the toroidal drone propeller is the distance between the leading and lagging blade segments. This parameter is expressed as the ratio between the minor axis length (Am) and the radius of the propeller (R).Thus, this ratio can be applied to toroidal drone propellers of any radius. Additionally, the Am / R ratio of 1.3 was the upper bound of the range tested since minor axis lengths greater than this resulted in a self-intersecting geometry at the wing tip.

[0052] FIG. 9 depicts the effect of Am / R on the aerodynamic (a-c) and acoustic (d) performance. For Am / R greater than 0.8, the thrust remained slightly lower than the conventional propeller, while the torque remained slightly greater than the conventional. Over the same interval, the mean FM stayed around the 5% mark. Yet, as Am / R increased, the sound output of the propeller drastically decreased from 85.2 dBA to 7. dBA (9d). The Am / R ratio of 1. was determined to be the optimal since the FM standard error of the mean FM overlapped with other experimental propellers (meaning no one propeller was statistically more efficient) and it was the quietest. It should be noted that at this point in the optimization process, the experimental toroidal propellers were in fact louder than the conventional control; this highlights the importance in optimizing existing toroidal propeller features before testing the novelty of the present invention, which is the leading blade segment height offset.

[0053] Camber is defined as a fraction of the chord length that represents the distance between the chord line and the camber line. This test analyzed the effect of the camber of the toroidal drone propeller on its FM and sound output. As shown in FIG. 10, adding camber to the blades drastically improved the FM. In fact, the toroidal drone propeller with a camber of 6% had the highest mean FM of 46%. The standard error of this experimental propeller overlapped with that of the conventional propeller, suggesting an insignificant difference in the mean FM and a similar performance as that of the control. Additionally, as shown in d), cambered toroidal drone propellers also produced less sound (the camber = 0 propeller was the loudest). The same 6% cambered toroidal drone propeller was only 1.2 dBA louder than the conventional propeller. For this reason, the 6% propeller was determined to be the optimal camber.

[0054] Lastly, before testing the leading blade segment height offset, the trailing edge of the toroidal propeller blade profile was tapered down to model conventional propeller design; this toroidal propeller optimized thus far is referred to as the LBSHOo = 0(in) propeller in subsequent testing of the LBSHO.Attorney Docket No. 410965-501001 WO

[0055] As described above, the key to the toroidal drone propeller of the present invention is the leading blade segment height offset parameter. This parameter is the axial distance between the midpoints of the chord lines of the leading and lagging blade segments.

[0056] FIGs. 11, 12 and 13 compare toroidal drone propellers with and without the leading blade segment height offset to illustrate the advantages of a LBSHO.

[0057] FIG. 11 describes the study conducted on assessing the noise reduction of the LBSHO. Each data point is a manufactured toroidal drone propeller with the LBSHO value described by its x-axis position. The left y-axis constrains the data points and represents the average sound level in dBA. The right y-axis constrains the operating RPM, or the speed at which the given propellers reach 2.5 Newtons of thrust production. As the LBSHO was increased from 0 inches, the sound output of each propeller was reduced as the propellers had the capacity to produce the same thrust at slower speeds. The toroidal drone propeller with LBSHO = 0.25 inches was 1 ,9dBA quieter than the propeller with no LBSHO represented by the leftmost data point. Thus, the LBSHO successfully decreases the sound output of the toroidal drone propeller.

[0058] FIG. 12 demonstrates that the propeller also exhibits a slight efficiency increase when compared to a toroidal drone propeller of identical properties yet with no LBSHO. T-tests were conducted to identify significant results, both the decrease in sound and slight increase in efficiency were observed to be statistically significant.

[0059] As discussed in FIG. 11 , the toroidal drone propeller with the LBSHO exhibits an average sound decrease of 1 ,9dBA when compared to an optimized toroidal drone propeller without LBSHO. FIG. 13 contextualizes this result: a) audiogram data of various terrestrial mammals reveals, generally, the greatest sensitivity to sound lies between 1000 and 10000 hz (VERTICAL LINES). In this same frequency range as in b), the toroidal drone propeller with LBSHO=0.25 inches exhibits a 44.28% noise reduction in this critical frequency range (via equations 4 and 5), resulting in a less intrusive, triggering, and annoying sound to humans and animals.

[0060] In FIG. 14, an illustration of an airflow 100 between a leading blade segment 105 and a trailing blade segment 110 of a toroidal drone propeller is shown, minus a hub for illustration purposes.Attorney Docket No. 410965-501001 WO

[0061] At the conclusion of the described study, FIG. 15 illustrates the final optimized toroidal drone propeller, with previous parameters configured for maximizing efficiency and reducing sound output as well as the implemented novel leading blade segment height offset of 0.25 inches.

[0062] It should be noted that the leading blade segment height offset invention has two variations as illustrated in FIG. 16.

[0063] The first as in a), with a hub 1600 supporting a leading blade segment 1605 and a lagging blade segment 1610, the leading blade segment 1605 and the lagging blade segment 1610 each forming a closed loop, the leading blade segment 1605 offset from the lagging blade segment 1610, the offset including a separation defined where the leading blade segment 1605 starts and the lagging blade segment 1610 ends so that they are not in a plane normal to an axis of rotation of the hub 1600, and the leading blade segment 1605 starting at a higher axial position than where the lagging blade segment 1610 ends. This was the variation tested in the previously described scientific study.

[0064] The second variation is as in b) where a toroidal drone propeller includes a hub 1615 supporting a leading blade segment 1620 and a lagging blade segment 1625, the leading blade segment 1620 and the lagging blade segment 1625 each forming a closed loop, the leading blade segment 1620 offset from the lagging blade segment 1625, the offset including a separation defined where the leading blade segment 1620 starts and the lagging blade segment 1625 ends so that they are not in a plane normal to an axis of rotation of the hub 1615, and the lagging blade segment 1625 starting at a higher axial position than where the leading blade segment 1620 ends.

[0065] As shown in FIG. 17, a method (1700) of manufacturing a toroidal drone propeller includes providing (1705) a leading blade segment.

[0066] The method (1700) includes providing (1710) a lagging blade segment.

[0067] The method (1700) includes providing (1715) a hub, the hub supporting the leading blade segment and the lagging blade segment, the leading blade segment and the lagging blade segment each forming a closed loop.

[0068] The method (1700) includes orienting (1720) the leading blade segment to be offset from the lagging blade segment, the offset including a separation defined where the leading blade segment starts and the lagging blade segment ends so that they are not in a plane normal to an axis of rotation of the hub.Attorney Docket No. 410965-501001 WO

[0069] It would be appreciated by those skilled in the art that various changes and modifications can be made to the illustrated embodiments without departing from the spirit of the present invention. All such modifications and changes are intended to be within the scope of the present invention except as limited by the scope of the appended claims.

Claims

1. Attorney Docket No. 410965-501001 WOWHAT IS CLAIMED IS:

1. A toroidal drone propeller comprising:a hub supporting a leading blade segment and a lagging blade segment, the leading blade segment and the lagging blade segment each forming a closed loop, the leading blade segment offset from the lagging blade segment,the offset comprising a separation defined where the leading blade segment starts and the lagging blade segment ends so that they are not in a plane normal to an axis of rotation of the hub.

2. The toroidal drone propeller of claim 1 wherein the offset is configured to reduce an acoustic signature of the toroidal drone propeller.

3. The toroidal drone propeller of claim 2 wherein the offset is configured to increase efficiency.

4. The toroidal drone propeller of claim 2 wherein the offset is 0.1 to 0.5 inches.

5. The toroidal drone propeller of claim 2 wherein the offset is 0.25 inches.

6. A toroidal drone propeller comprising:a hub supporting a leading blade segment and a lagging blade segment, the leading blade segment and the lagging blade segment each forming a closed loop, the leading blade segment offset from the lagging blade segment,the offset comprising a separation defined where the leading blade segment starts and the lagging blade segment ends so that they are not in a plane normal to an axis of rotation of the hub,wherein a terminal end of the leading blade segment and a terminal end of the lagging blade segment each curve into contact with the hub.

7. The toroidal drone propeller of claim 6 wherein the offset is configured to reduce an acoustic signature of the toroidal drone propeller.Attorney Docket No. 410965-501001 WO8. The toroidal drone propeller of claim 7 wherein the offset is configured to increase efficiency.

9. The toroidal drone propeller of claim 6 wherein the offset is 0.1 to 0.5 inches.

10. The toroidal drone propeller of claim 6 wherein the offset is 0.25 inches.

11. A toroidal drone propeller comprising:a hub supporting a leading blade segment and a lagging blade segment, the leading blade segment and the lagging blade segment each forming a closed loop, the leading blade segment offset from the lagging blade segment,the offset comprising a separation defined where the midpoint of the chord line of the propeller profile of the leading blade segment at the propeller hub and the midpoint of the chord line of the propeller profile of the lagging blade segment at the propeller hub are not in a plane normal to an axis of rotation of the hub, wherein a terminal end of the leading blade segment and a terminal end of the lagging blade segment each curve into contact with the hub.

12. The toroidal drone propeller of claim 11 wherein the offset is configured to reduce an acoustic signature of the toroidal drone propeller.

13. The toroidal drone propeller of claim 11 wherein the offset is configured to increase efficiency.

14. The toroidal drone propeller of claim 11 wherein the offset is 0.1 to 0.5 inches.

15. The toroidal drone propeller of claim 11 wherein the offset is 0.25 inches.

16. A method comprising:providing a leading blade segment;providing a lagging blade segment;providing a hub, the hub supporting the leading blade segment and the lagging blade segment, the leading blade segment and the lagging blade segment each forming a closed loop,Attorney Docket No. 410965-501001 WOorienting the leading blade segment to be offset from the lagging blade segment,the offset comprising a separation defined where the leading blade segment starts and the lagging blade segment ends so that they are not in a plane normal to an axis of rotation of the hub.

17. The method of claim 16 wherein the leading blade segment and the lagging blade segment are propellers.

18. The method of claim 16 wherein the offset is configured to reduce an acoustic signature of the toroidal drone propeller.

19. The method of claim 16 wherein the offset is configured to increase efficiency.

20. The method of claim 16 wherein the offset is 0.1 to 0.5 inches.

21. The method of claim 16 wherein the offset is 0.25 inches.

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