Composite skins having variable hole sizes and shapes formed using photomachining

1. A method of fabricating a face skin for an acoustic panel of a nacelle configured to surround a central longitudinal axis of a gas turbine engine, the method comprising:

locating a masking film over a first surface of a sheet configured to form the face skin for the acoustic panel of the nacelle and thus, configured to surround the central longitudinal axis of the gas turbine engine, the masking film defining a plurality of openings;

forming a plurality of slots in the sheet using abrasive blasting, wherein each slot of the plurality of slots has a length dimension and a width dimension, the length dimension being greater than the width dimension, and wherein each slot is oriented such that the length dimension is substantially perpendicular to an expected direction of airflow through the gas turbine engine and over the slot, the plurality of slots configured to be oriented at an angle relative to the central longitudinal axis of the gas turbine engine, where the central longitudinal axis is different from the expected direction of airflow through the gas turbine engine, wherein the angle is defined by a centerline of each slot of the plurality of slots and the central longitudinal axis, wherein a first end of a first semi-circular wall of at least one first slot in the plurality of slots through the face skin is at least one of axially offset or circumferentially offset from a second end of a second semi-circular wall of the at least one first slot though the face skin based upon a degree of a first angle, wherein a first end of a first semi-circular wall of at least one second slot in the plurality of slots through the face skin is at least one of axially offset or circumferentially offset from a second end of a second semi-circular wall of the at least one second slot though the face skin based upon a degree of a second angle, wherein the first angle is different from the second angle, wherein the plurality of slots in the sheet comprises forming at least three regions with a first region of the sheet having a first percentage of open area and a first number of slots that is greater than a second percentage of open area and a second number of slots in a second region of the sheet and greater than a third percentage of open area and a third number of slots in a third region of the sheet, wherein the second percentage of open area and the second number of slots in the second region of the sheet is greater than the third percentage of open area and the third number of slots in the third region of the sheet, and wherein a percentage of open area and a number of slots in each of the first region, the second region and the third region is selected based on an expected velocity of the airglow over a respective region and acoustic characteristics experienced in the respective region; and wherein the first number of slots is offset from the second number of slots; and

removing the masking film.

2. The method of claim 1 , further comprising determining a pattern of the plurality of openings in the masking film based on an airflow velocity experienced by the face skin.

3. The method of claim 1 , wherein an expected airflow velocity in the first region is different from the airflow velocity in the second region.

4. The method of claim 3 , wherein the sheet comprises a fiber reinforced composite that is at least one of a fiberglass reinforced composite and a carbon fiber reinforced composite, the fiber reinforced composite includes at least one of glass, carbon, ceramic, and a polymer, the fiber reinforced composite includes a matrix with at least one of a thermoset material and a thermoplastic material.

5. The method of claim 4 , further comprising forming each slot of the plurality of slots having:

a first planar wall;

a second planar wall oriented toward the first planar wall;

a first semi-circular wall extending between the first planar wall and the second planar wall; and

a second semi-circular wall opposite the first semi-circular wall and extending between the first planar wall and the second planar wall, wherein a centerline of the slot is substantially perpendicular to the expected flow direction over the slot, the centerline being located midway between the first planar wall and the second planar wall and extending from the first semi-circular wall to the second semi-circular wall.

6. The method of claim 1 , wherein the first slots of the plurality of slots are configured to be oriented at a first angle relative to the central longitudinal axis of the gas turbine engine, wherein second slots of the plurality of slots are configured to be oriented at a second angle relative to the central longitudinal axis of the gas turbine engine, and wherein the first angle is different from the second angle.

7. A method of fabricating an acoustic panel for a gas turbine engine, comprising:

locating a masking film over a face skin of the acoustic panel configured to surround a central longitudinal axis of the gas turbine engine, the masking film defining a plurality of openings;

forming a plurality of slots in the face skin using abrasive blasting, wherein each slot of the plurality of slots has a first dimension and a second dimension, the first dimension being greater than the second dimension, and wherein each slot is oriented such that the first dimension of the slot is substantially perpendicular to an expected direction of airflow through the gas turbine engine and over the slot, the plurality of slots configured to be oriented at an angle relative to the central longitudinal axis of the gas turbine engine, where the central longitudinal axis is different from the expected direction of airflow through the gas turbine engine, wherein the angle is defined by a centerline of each slot of the plurality of slots and the central longitudinal axis, wherein a first end of a first semi-circular wall of at least one first slot in the plurality of slots through the face skin is at least one of axially offset or circumferentially offset from a second end of a second semi-circular wall of the at least one first slot though the face skin based upon a degree of a first angle, wherein a first end of a first semi-circular wall of at least one second slot in the plurality of slots through the face skin is at least one of axially offset of circumferentially offset from a second end of a second semi-circular wall of the at least one second slot though the face skin based upon a degree of a second angle, wherein the first angle is different from the second angle, wherein the plurality of slots in the face skin comprises forming at least three regions with a first region of the face skin having a first percentage of open area and a first number of slots that is greater than a second percentage of open area and a second number of slots in a second region of the face skin and greater than a third percentage of open area and a third number of slots in a third region of the face skin, wherein the second percentage of open area and the second number of slots in the second region of the face skin is greater than the third percentage of open area and the third number of slots in the third region of the face skin, and wherein a percentage of open area and a number of slots in each of the first region, the second region and the third region is selected based on an expected velocity of the airflow over a respective region and acoustic characteristics experienced in the respective region; and wherein the first number of slots is offset from the second number of slots; and

coupling the face skin to a core structure, the core structure defining a plurality of cells, wherein the face skin and the core structure are curved such that the face skin and the core structure surround, at least partially, the central longitudinal axis of the gas turbine engine.

8. The method of claim 7 , further comprising:

removing the masking film; and

coupling a back skin to the core structure opposite the face skin, wherein the back skin is a solid layer.

9. The method of claim 7 , further comprising determining a pattern of the plurality of openings in the masking film based on an airflow velocity experienced by the face skin.

10. The method of claim 7 , wherein the face skin comprises a fiber reinforced composite that is at least one of a fiberglass reinforced composite and a carbon fiber reinforced composite, the fiber reinforced composite includes at least one of glass, carbon, ceramic, and a polymer, the fiber reinforced composite includes a matrix with at least one of a thermoset material and a thermoplastic material.

11. The method of claim 7 , wherein the acoustic panel forms, at least, a portion of a nacelle configured to the surround the gas turbine engine.

12. The method of claim 7 , wherein the acoustic panel forms, at least, a portion of at least one of an inner inlet barrel, an inner fixed structure of a thrust reverser, a translating sleeve of a translating sleeve type thrust reverser, or an exhaust system for the gas turbine engine.

13. The method of claim 7 , wherein the acoustic panel is configured to form, at least, a portion of at least one of an inner inlet barrel, an inner fixed structure of a thrust reverser, a translating sleeve of a translating sleeve type thrust reverser, or an exhaust system for the gas turbine engine.

14. The method of claim 7 , wherein first slots of the plurality of slots are configured to be oriented at a first angle relative to the central longitudinal axis of the gas turbine engine, wherein second slots of the plurality of slots are configured to be oriented at a second angle relative to the central longitudinal axis of the gas turbine engine, and wherein the first angle is different from the second angle.