Composite skins having variable hole sizes and shapes formed using photomachining

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.