UAV ducted fan lip shaping

1. A ducted fan air-vehicle comprising:

an air duct comprising a duct lip and defining a circumference, wherein the duct lip comprises an internal duct lip portion and an external duct lip portion,

wherein the internal duct lip portion is substantially curvature continuous around the circumference of the air duct, and the external duct lip portion is substantially curvature continuous around the circumference of the air duct,

wherein the air duct comprises a plurality of cross-sections along the circumference, each of the cross-sections being taken from a plane emanating radially out from a centerline of the air duct,

wherein at least some cross-sections of the plurality of cross-sections have different shapes,

wherein each cross-section of the plurality of cross-sections has an a/b ratio, the “a” in the a/b ratio being defined by a first line that extends axially from a highlight location of the duct lip to a throat location of the air duct, and the “b” in the a/b ratio being defined by a second line that extends radially from the throat location of the air duct to the highlight location of the duct lip, and

wherein the a/b ratio of each cross-section of the plurality of cross-sections is substantially the same.

2. The ducted-fan air-vehicle of claim 1 , wherein the a/b ratio is in a range of 1.9 to 2.5.

3. The ducted fan air-vehicle of claim 1 , wherein each cross-section of the duct has a duct lip highlight location having an axial height and a location of maximum thickness having a radial distance from a center of the duct,

wherein the axial height of the duct lip highlight location is constant in each cross-section around the circumference, and

wherein the radial distance from the center of the duct to the location of maximum thickness varies for a plurality of the cross-sections around the circumference.

4. The ducted fan air-vehicle of claim 3 , wherein the radial distance varies for a plurality of the cross-sections around the circumference such that the duct has a plurality of bulges around the circumference.

5. The ducted fan air-vehicle of claim 4 , wherein the plurality of bulges comprises four bulges that form a substantially square shape around the circumference of the duct.

6. The ducted fan air-vehicle of claim 1 , wherein the internal duct lip portion is elliptically-shaped.

7. The ducted fan air-vehicle of claim 1 , wherein the internal duct lip portion is super-elliptically-shaped.

8. The ducted fan air-vehicle of claim 7 , wherein a super-elliptical shape is defined by the equation



χ

a



n

+



y

b



n

=

1

,

wherein n is within the range of 2 to 4.

9. The ducted fan air-vehicle of claim 1 , wherein the external duct lip portion is elliptically-shaped.

10. The ducted fan air-vehicle of claim 1 , wherein each cross-section of the duct has a duct lip highlight location having an axial height and a location of maximum thickness having a radial distance from a center of the duct,

wherein the duct lip highlight axial height varies for a plurality of cross-sections around the circumference, and

wherein the radial distance from the center of the duct to the location of maximum thickness varies for a plurality of the cross-sections around the circumference.

11. The ducted fan air-vehicle of claim 10 , wherein the axial height varies for a plurality of cross-sections such that there are a plurality of peaks along the circumference of the duct and a plurality of troughs along the circumference of the duct.

12. The ducted fan air-vehicle of claim 11 , wherein the plurality of peaks comprises four peaks separated by substantially 90 degrees along the circumference of the duct.

13. The ducted fan air-vehicle of claim 10 , wherein each cross-section of the plurality of cross-sections has a contraction ratio, and at least two cross-sections of the plurality of cross-sections have different contraction ratios, and wherein the contraction ratios of the plurality of cross-sections are in a range of 1.15 to 2.

14. The ducted fan air-vehicle of claim 10 , wherein when the duct lip highlight location increases in axial height along the circumference, the radial distance around the circumference increases.

15. A ducted fan air-vehicle comprising:

an air duct comprising a duct lip and comprising a circumference,

wherein the air duct comprises a plurality of cross-sections along the circumference, each of the cross-sections being taken from a plane emanating radially out from a centerline of the air duct,

wherein at least some cross-sections of the plurality of cross-sections have different shapes,

wherein each cross-section of the plurality of cross-sections has an a/b ratio, the “a” in the a/b ratio being defined by a first line that extends axially from a highlight location of the duct lip to a throat location of the air duct, and the “b” in the a/b ratio being defined by a second line that extends radially from the throat location of the air duct to the highlight location of the duct lip, and

wherein the a/b ratio of each cross-section of the plurality of cross-sections is substantially the same.

16. A method for shaping an air duct of an air vehicle, the air duct comprising a duct lip and defining a circumference, the method comprising:

shaping the air duct such that the air duct comprises a plurality of cross-sections along the circumference, each of the cross-sections being taken from a plane emanating radially out from a centerline of the air duct, wherein at least some of the cross-sections of the plurality of cross-sections have different shapes; and

shaping the duct lip such that an a/b ratio of each cross-section of the plurality of cross-sections is substantially the same, the “a” in the a/b ratio being defined by a first line that extends axially from a highlight location of the duct lip to a throat location of the air duct, and the “b” in the a/b ratio being defined by a second line that extends radially from the throat location of the air duct to the highlight location of the duct lip.

17. The method of claim 16 , further comprising:

varying the shape of the duct lip around the circumference of the duct such that the shape of the duct lip is substantially curvature continuous around the circumference of the duct lip.

18. The ducted-fan air-vehicle of claim 1 , wherein the a/b ratio of each cross-section of the plurality of cross-sections is within 10% of the a/b ratio of the other cross-sections of the plurality of cross-sections.

19. The ducted-fan air-vehicle of claim 1 , wherein the a/b ratio of each cross-section of the plurality of cross-sections is the same.

20. The ducted-fan air-vehicle of claim 1 , wherein a contraction ratio of each cross-section of the plurality of cross-sections is the same.