1. Patent Search
  2. Details

AIRFOIL PROFILE FOR AN AIRCRAFT AND AERODYNAMIC SURFACES USING SAID AIRFOIL PROFILE

20240228073 ยท 2024-07-11

    Inventors

    Cpc classification

    International classification

    Abstract

    An airfoil profile for an aircraft, such as an unmanned aerial system. The airfoil profile includes a leading edge portion and a trailing edge portion that are spaced apart along a chordwise direction, an airfoil centroid; and an upper airfoil surface and a lower airfoil surface. The airfoil surfaces are shaped such that the pressure center of the lifting force is arranged at the same chord location as the airfoil centroid or closer to the trailing edge portion along the chordwise direction than the airfoil centroid. With this, a pitch-down momentum is generated that urges the leading edge portion towards a lower angle of attack.

    Claims

    1. An airfoil profile for an aircraft, the airfoil profile being configured for reducing a noise level, the airfoil profile comprising: a leading edge portion and a trailing edge portion that are spaced apart along a chordwise direction; an airfoil centroid that is arranged from 40% to 60% of a chord length along the chordwise direction; and an upper airfoil surface and a lower airfoil surface that are shaped so as to generate a lifting force in a manner such that a pressure center of the lifting force is arranged at the same chord location as the airfoil centroid or closer to the trailing edge portion along the chordwise direction than the airfoil centroid.

    2. The airfoil profile according to claim 1, wherein the airfoil centroid is arranged from 43% to 55% of the chord length along the chordwise direction.

    3. The airfoil profile according to claim 1, wherein the upper and lower airfoil surface are shaped such that the pressure center of the lifting force is arranged from 40% to 60% of the chord length along the chordwise direction.

    4. The airfoil profile according to claim 1, wherein the upper airfoil surface comprises a first upper curved portion that is arranged between the leading edge portion and the airfoil centroid along the chordwise direction.

    5. The airfoil profile according to claim 4, wherein the first upper curved portion has a maximum modulus of a radius of curvature from 1.8 times to 4.4 times the chord length.

    6. The airfoil profile according to claim 1, wherein the upper airfoil surface comprises a second upper curved portion that is arranged between the airfoil centroid and the trailing edge portion along the chordwise direction.

    7. The airfoil profile according to claim 6, wherein the second upper curved portion has a maximum modulus of a radius of curvature from 1.9 times to 2.1 times the chord length.

    8. The airfoil profile according to claim 1, wherein the upper airfoil surface comprises a third upper curved portion that is arranged between the leading edge portion and the trailing edge portion along the chordwise direction.

    9. The airfoil profile according to claim 1, wherein a third upper curved portion has a minimum modulus of a radius of curvature from 0.5 times to 0.8 times the chord length.

    10. The airfoil profile according to claim 1, wherein the lower airfoil surface comprises a first lower flat portion that is arranged between the leading edge portion and the airfoil centroid along the chordwise direction.

    11. The airfoil profile according to claim 1, wherein the lower airfoil surface comprises a second lower flat portion that is arranged between the leading edge portion and the trailing edge portion along the chordwise direction.

    12. The airfoil profile according to claim 1, wherein the lower airfoil surface comprises a lower curved portion that is arranged between the airfoil centroid and the trailing edge portion along the chordwise direction.

    13. A wing or a propeller blade for an aircraft comprising an airfoil profile according to claim 1.

    14. A propeller for an aircraft comprising a hub and at least one propeller blade according to claim 13 that is supported by the hub.

    15. An aircraft comprising a wing or a propeller blade according to claim 13.

    16. An aircraft, according to claim 15, wherein the aircraft is an unmanned aerial system.

    17. An aircraft, comprising a propeller according to claim 14.

    18. An aircraft, according to claim 17, wherein the aircraft is an unmanned aerial system.

    Description

    BRIEF DESCRIPTION OF THE DRAWINGS

    [0070] Embodiments of the invention are described in more detail with reference to the accompanying schematic drawings that are listed below

    [0071] FIG. 1 depicts an embodiment of a UAS according to the invention;

    [0072] FIG. 2 depicts an embodiment of an airfoil profile according to the invention;

    [0073] FIG. 3 depicts a diagram of the radius of curvature of an upper airfoil surface; and

    [0074] FIG. 4 depicts a diagram of the radius of curvature of a lower airfoil surface.

    DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

    [0075] Referring to FIG. 1 an aircraft 10 is depicted. The aircraft 10 is configured as an unmanned aerial system (UAS) 11. The UAS 11 comprises a UAS body 12 to which a pair of wings 13 is attached. The UAS 11 has a plurality of control surfaces 14 that are arranged in manner known per se. The UAS 11 further comprises a propeller 20 for propulsion.

    [0076] The propeller 20 comprises a hub 21 which supports a plurality of propeller blades 22.

    [0077] Referring to FIG. 2, the propeller blade 22 has an airfoil profile 30. The airfoil profile 30 corresponds to a cross-section through the propeller blade 22 along plane II-II.

    [0078] As depicted, the airfoil profile 30 is viewed along a spanwise direction from the tip of the propeller blade 22 towards the root of the propeller blade 22 that is supported by the hub 21. The spanwise direction therefore corresponds to a direction orthogonal to the drawing plane of FIG. 2.

    [0079] The airfoil profile 30 comprises a leading edge portion 31 and a trailing edge portion 32. The leading edge portion 31 and the trailing edge portion 32 are spaced apart along a chordwise direction. The chordwise direction lies in the drawing plane of FIG. 2. The chordwise direction and the spanwise direction define a vertical direction, that is orthogonal to both the chordwise and the spanwise direction. In other words, the chordwise, spanwise and vertical directions are mutually orthogonal to each other.

    [0080] The airfoil profile 30 comprises an airfoil centroid 33. The airfoil centroid 33 is also called elastic axis. The airfoil centroid 33 extends in the spanwise direction. The airfoil centroid 33 is influenced by the shape of the airfoil profile 30 which is subsequently described in more detail.

    [0081] The airfoil profile 30 comprises an upper airfoil surface 40. The upper airfoil surface 40 extends between the leading edge portion 31 and the trailing edge portion 32. The upper airfoil surface 40 is defined by a 6th-order polynomial of the form:


    y(x)=a.sub.6 x.sup.6+a.sub.5 x.sup.5+a4 x.sup.4+a3 x.sup.3+a2 x.sup.2+a.sub.1 x+a.sub.0; (1)

    where x corresponds to the percentage of the chord length going from 0% to 100%, and the a.sub.n are coefficients that depend on the thickness of the airfoil profile 30. The result of the polynomial is the distance from 0 along the vertical direction in percent of the chord length. In this embodiment, the thickness varies from 8% close to the tip of the propeller blade 22 to 18% close to the root of the propeller blade 22. [0082] a.sub.6 is defined by ?0.0078 t.sup.2?0.043 t?3.4025; [0083] a.sub.5 is defined by 0.0249 t.sup.2+0.0917 t+10.762; [0084] a.sub.4 is defined by ?0.0301 t2?0.0608 t?12.691; [0085] a3 is defined by 0.0165 t2+0.0272 t+6.6256; [0086] a2 is defined by ?0.0041 t2?0.0396 t?1.6238; [0087] a1 is defined by 0.0005 t2+0.0232 t+0.332; and [0088] a0 is defined by 0.0009 t+0.0035;

    [0089] where t is the thickness inserted into the respective equation in percent, e.g., 10% thickness corresponds to t=10.

    [0090] Preferably, the upper airfoil surface 40 lies within a tolerance band of ?5%, preferably ?3%, more preferably ?1%, most preferably ?0.3% from the polynomial of equation (1).

    [0091] The radius of curvature ry of the upper airfoil surface 40 is defined in the conventional manner as:

    [00001] r y = .Math. "\[LeftBracketingBar]" ( 1 + y ( x ) 2 ) 3 / 2 y ( x ) .Math. "\[RightBracketingBar]" ( 2 )

    [0092] where y and y are the first and second derivatives of equation (1) with respect to x. FIG. 3 illustrates ry vs. the normalized chord length for t=8% (continuous line) and t=18% (broken line).

    [0093] The upper airfoil surface 40 comprises a first upper curved portion 41 The first upper curved portion 41 has a maximum modulus of the radius of curvature (see equation (2)) from 1.8 times to 4.4 times of the chord length depending on the thickness. When viewed along the spanwise direction, the maximum modulus of the radius of curvature continuously decreases.

    [0094] The maximum modulus of the radius of curvature for the first upper curved portion 41 is located between the leading edge portion 31 and the airfoil centroid 33 along the chordwise direction. This maximum is preferably located from 21% to 23% of the chord length.

    [0095] The first upper curved portion 41 has a spatial extension along the chordwise direction that is measured as the full-width at half-maximum (FWHM) of the radius of curvature. With the previously selected coefficients, the spatial extension of the first upper curved portion 41 along the chordwise direction is in the range of 15 percentage points to 22 percentage points. When viewed along the spanwise direction, the spatial extension of the first upper curved portion 41 continuously increases.

    [0096] The upper airfoil surface 40 comprises a second upper curved portion 42. The second upper curved portion 42 has a maximum modulus of the radius of curvature (see equation (2)) from 1.9 times to 2.1 times of the chord length depending on the thickness. When viewed along the spanwise direction, the maximum modulus of the radius of curvature continuously increases.

    [0097] The maximum modulus of the radius of curvature for the second upper curved portion 42 is located between the trailing edge portion 32 and the airfoil centroid 33 along the chordwise direction. This maximum is preferably located from 79% to 80% of the chord length.

    [0098] The second upper curved portion 42 has a spatial extension along the chordwise direction that is measured as the full-width at half-maximum (FWHM) of the radius of curvature. With the previously selected coefficients, the spatial extension of the second upper curved portion 42 along the chordwise direction is in the range of 19 percentage points to 26 percentage points. When viewed along the spanwise direction, the spatial extension of the second upper curved portion 42 continuously decreases.

    [0099] The upper airfoil surface 40 comprises a third upper curved portion 43. The third upper curved portion 43 has a minimum modulus of the radius of curvature (see equation (2)) from 0.5 times to 0.8 times of the chord length depending on the thickness. When viewed along the spanwise direction, the minimum modulus of the radius of curvature continuously decreases.

    [0100] The minimum modulus of the radius of curvature for the third upper curved portion 43 is located between the leading edge portion 31 and the trailing edge portion 32 along the chordwise direction. This minimum is preferably located from 50% to 52% of the chord length.

    [0101] The third upper curved portion 43 has a spatial extension along the chordwise direction that is measured as the full-width at double-minimum (FWDM) of the radius of curvature. With the previously selected coefficients, the spatial extension of the third upper curved portion 43 along the chordwise direction is in the range of 36 percentage points to 40 percentage points. When viewed along the spanwise direction, the spatial extension of the third upper curved portion 43 continuously decreases.

    [0102] The airfoil profile 30 comprises a lower airfoil surface 50. The lower airfoil surface 50 extends between the leading edge portion 31 and the trailing edge portion 32. The lower airfoil surface 50 is defined by a 6th-order polynomial of the form:


    z(x)=b6 x6+b5 x5+b4 x4+b3 x3+b2 x2+b 1 x +b0; (3)

    [0103] where x corresponds to the percentage of the chord length going from 0% to 100%, and the bn are coefficients that depend on the thickness of the airfoil profile 30. The result of the polynomial is the distance from 0 along the vertical direction in percent of the chord length. In this embodiment, the thickness varies from 8% close to the tip of the propeller blade 22 to 18% close to the root of the propeller blade 22. [0104] b6 is defined by 0.0021 t2+0.3834 t?2.2564; [0105] b5 is defined by ?0.0068 t2?1.1895 t+7.0593; [0106] b4 is defined by 0.0082 t2+1.4243 t?8.3201; [0107] b3 is defined by ?0.0042 t2?0.8427 t+4.4385; [0108] b2 is defined by 0.0006 t2+0.2768 t?1.2628; [0109] b1 is defined by ?0.0008 t4+0.0439 t3?0.9162 t2+8.3143 t?27.838; and [0110] b0 is defined by ?0.00008 t+0.0017; [0111] where t is the thickness inserted into the respective equation in percent, e.g., 10% thickness corresponds to t=10. Preferably, the lower airfoil surface 50 lies within a tolerance band of ?5%, preferably ?3%, more preferably ?1%, most preferably ?0.3% from the polynomial of equation (3).

    [0112] The radius of curvature rz of the lower airfoil surface 50 is defined in the conventional manner as:

    [00002] r z = .Math. "\[LeftBracketingBar]" ( 1 + z ( x ) 2 ) 3 / 2 z ( x ) .Math. "\[RightBracketingBar]" ( 4 )

    [0113] where z and z are the first and second derivatives of equation (3) with respect to x. FIG. 4 illustrates rz vs. the normalized chord length for t=8% (continuous line) and t=18% (broken line).

    [0114] It should be noted that z has at least one zero at one point along the chord length. For purposes of this disclosure, a portion that has a radius of curvature larger than 10 times the chord length is deemed to be flat.

    [0115] The lower airfoil surface 50 comprises a first lower flat portion 51. The first lower flat portion 51 exceeds modulus of the radius of curvature (see equation (4)) of 10. The first lower flat portion 51 is located between the leading edge portion 31 and the airfoil centroid 33 along the chordwise direction. The location can be defined by the first zero of z from the leading edge portion 31, i.e. the zero closest to the leading edge portion 31. The zero is preferably located from 25% to 30% of the chord length, more preferably from 25% to 29% of the chord length, more preferably from 25.5% to 28.8% of the chord length.

    [0116] The first lower flat portion 51 has a spatial extension along the chordwise direction that is measured as the full-width at a radius of curvature of 10 (FW@R10). With the previously selected coefficients, the spatial extension of the first lower flat portion 51 along the chordwise direction is in the range of 8 percentage points to 30 percentage points. When viewed along the spanwise direction, the spatial extension of the first lower flat portion 51 continuously increases.

    [0117] The lower airfoil surface 50 comprises a second lower flat portion 52. The second lower flat portion 52 exceeds modulus of the radius of curvature (see equation (4)) of 10. The second lower flat portion 52 is located between the leading edge portion 31 and the trailing edge portion 32 along the chordwise direction. The location can be defined by the last zero of z from the leading edge portion 31, i.e. the zero closest to the trailing edge portion 32. The zero is preferably located from 36% to 52% of the chord length.

    [0118] The second lower flat portion 52 has a spatial extension along the chordwise direction that is measured as the full-width at a radius of curvature of 10 (FW@R10). With the previously selected coefficients, the spatial extension of the second lower flat portion 52 along the chordwise direction is in the range of 1 percentage points to 3 percentage points. When viewed along the spanwise direction, the spatial extension of the second lower flat portion 52 continuously decreases.

    [0119] The lower airfoil surface 50 comprises a lower curved portion 53. The lower curved portion 53 has a minimum modulus of the radius of curvature (see equation (4)) from 0.85 times to 1.35 times of the chord length depending on the thickness. When viewed along the spanwise direction, the minimum modulus of the radius of curvature continuously decreases.

    [0120] The minimum modulus of the radius of curvature for the lower curved portion 53 is located between the trailing edge portion 32 and the airfoil centroid 33 along the chordwise direction. This minimum is preferably located from 75% to 79% of the chord length, more preferably from 77% to 78% of the chord length.

    [0121] The lower curved portion 53 has a spatial extension along the chordwise direction that is measured as the full-width at double-minimum (FWDM) of the radius of curvature. With the previously selected coefficients, the spatial extension of the lower curved portion 53 along the chordwise direction is in the range of 23 percentage points to 45 percentage points. When viewed along the spanwise direction, the spatial extension of the lower curved portion 53 continuously decreases.

    [0122] In order to reduce noise, the invention proposes an airfoil profile (30) for an aircraft (10), such as an unmanned aerial system (11). The airfoil profile (30) comprises a leading edge portion (31) and a trailing edge portion (32) that are spaced apart along a chordwise direction, an airfoil centroid (33); and an upper airfoil surface (40) and a lower airfoil surface (50). The airfoil surfaces (40, 50) are shaped such that the pressure center (Cp) of the lifting force is arranged at the same chord location as the airfoil centroid (33) or closer to the trailing edge portion (32) along the chordwise direction than the airfoil centroid (33). With this, a pitch-down momentum is generated that urges the leading edge portion (31) towards a lower angle of attack (AoA).

    [0123] While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms comprise or comprising do not exclude other elements or steps, the terms a or one do not exclude a plural number, and the term or means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.

    LIST OF REFERENCE SIGNS

    [0124] 10 aircraft [0125] 11 unmanned aerial system (UAS) [0126] 12 UAS body [0127] 13 wing [0128] 14 control surface [0129] 20 propeller [0130] 21 hub [0131] 22 propeller blade [0132] 30 airfoil profile [0133] 31 leading edge portion [0134] 32 trailing edge portion [0135] 33 airfoil centroid [0136] 40 upper airfoil surface [0137] 41 first upper curved portion [0138] 42 second upper curved portion [0139] 43 third upper curved portion [0140] 50 lower airfoil surface [0141] 51 first lower flat portion [0142] 52 second lower flat portion [0143] 53 lower curved portion [0144] Cp pressure center