Gas turbine engine airfoil frequency design

A method of repairing an airfoil comprising the steps of:

• providing an airfoil having pressure and suction sides spaced apart from one another in a thickness direction and joined to one another at leading and trailing edges, the airfoil extending in a radial direction of a span that is in a range of 17.2-18.2 inches (436-462 mm), and a chord length extending in a chordwise direction from the leading edge to the trailing edge at 50% of the span is in a range of 10.0-11.0 inches (255-281 mm), wherein the provided airfoil has at least one unrestored mode frequency that is attributable to damage to the airfoil;
• and
• repairing the airfoil to provide at least two of:
• a first mode has a frequency of 51 up to ±10% Hz;
• a second mode has a frequency of 147 up to ±10% Hz;
• a third mode has a frequency of 267 up to ±10% Hz;
• a fourth mode has a frequency of 350 up to ±10% Hz;
• a fifth mode has a frequency of 454 up to ±10% Hz;
• and
• a sixth mode has a frequency of 619 up to ±10% Hz;
• wherein at least one of the first mode frequency, second mode frequency, third mode frequency, fourth mode frequency, fifth mode frequency, and sixth mode frequency corresponds to a restored mode frequency that supersedes the unrestored mode frequency;
• wherein the frequencies are at a zero speed and ambient conditions, and the frequency of any given mode does not exceed the frequency of a higher order mode;
• wherein the first mode is a 1EB mode, the second mode is a 2EB mode, and the third mode is a 1T mode, the 1EB and 2EB modes correspond to deflections substantially parallel to thickness direction, and the 1T mode corresponds to twisting about the radial direction;
• wherein the airfoil is part of a blade;
• wherein the airfoil is a titanium-based alloy, the titanium-based alloy has a density of about 0.16 lb/in3 (4.4 g/cm3), the titanium-based alloy has a modulus of elasticity of about 16-17 Mpsi (110-117 GPa) at room temperature.

A turbofan engine comprising:

• a fan section;
• a compressor section arranged fluidly downstream from the fan section;
• a turbine section arranged fluidly downstream from the compressor section;
• a combustor arranged fluidly between the compressor and turbine sections;
• and
• an airfoil in at least one of the fan, compressor and turbine sections, the airfoil having:
• pressure and suction sides spaced apart from one another in a thickness direction and joined to one another at leading and trailing edges, the airfoil extending in a radial direction of a span that is in a range of 17.2-18.2 inches (436-462 mm);
• a chord length extending in a chordwise direction from the leading edge to the trailing edge at 50% of the span is in a range of 10.0-11.0 inches (255-281 mm);
• and
• at least two of:
• a first mode has a frequency of 51 up to ±10% Hz;
• a second mode has a frequency of 147 up to ±10% Hz;
• a third mode has a frequency of 267 up to ±10% Hz;
• a fourth mode has a frequency of 350 up to ±10% Hz;
• a fifth mode has a frequency of 454 up to ±10% Hz;
• and
• a sixth mode has a frequency of 619 up to ±10% Hz;
• wherein the frequencies are at a zero speed and ambient conditions, and the frequency of any given mode does not exceed the frequency of a higher order mode;
• wherein the first mode is a 1EB mode, the second mode is a 2EB mode, and the third mode is a 1T mode, the 1EB and 2EB modes correspond to deflections substantially parallel to thickness direction, and the 1T mode corresponds to twisting about the radial direction;
• wherein the airfoil is provided in the fan section, the airfoil is part of a blade;
• wherein the airfoil is a titanium-based alloy, the titanium-based alloy has a density of about 0.16 lb/in3 (4.4 g/cm3), the titanium-based alloy has a modulus of elasticity of about 16-17 Mpsi (110-117 GPa) at room temperature.