Mistuned fan

A compressor rotor for a gas turbine engine, the compressor rotor comprising:

• first blades having a first airfoil thickness distribution defining a first natural vibration frequency;
• at least second blades having a second airfoil thickness distribution different from the first airfoil thickness distribution and defining a second natural vibration frequency different from the first natural vibration frequency;
• the first blades and the at least second blades being mounted to a central hub to form an annular blade array, the annular blade array having the first blades and the at least second blades arranged as generally alternating with one another around a circumference of the compressor rotor;
• the first airfoil thickness distribution including a first frequency modifier on the pressure side of the first blades at a first span distance away from the central hub and the second airfoil thickness distribution defining a second first frequency modifier on the pressure side of the second blades at a second span distance away from the central hub, the second span distance different from the first span distance, both the first span distance and the second span distance being between 60% and 100% of a full span length of the annular blade array, first and second pressure side airfoil thicknesses are respectively defined by the first and second first frequency modifiers, the first pressure side airfoil thickness of the first blades is less than a thickness of the second blades at the first span distance, and the second pressure side airfoil thickness of the second blades is less than a thickness of the first blades at the second span distance, and wherein the first span distance corresponds to a span-wise location of high strain energy and the second span distance corresponds to a span-wise location of low strain energy.